FORM 2 5
THE PATENTS ACT, 1970
[39 OF 1970]
&
THE PATENTS RULES, 2003
10
COMPLETE SPECIFICATION
[See section 10 and rule 13]
15
“A PROCESS FOR SELECTIVE DIMETHYL CARBONATE (DMC)
SYNTHESIS AND A SYSTEM THEREOF”
20 NAME AND ADDRESS OF THE APPLICANT:
RELIANCE INDUSTRIES LIMITED
3rd Floor, Maker Chamber-IV, 222, Nariman Point,
Mumbai - 400 021, Maharashtra, India
25 NATIONALITY: IN
30
The following specification particularly describes the invention and the manner in which it is
to be performed.
2
5 TECHNICAL FIELD
The present disclosure relates to the field of organic compound synthesis. Particularly, the
present disclosure provides a process for the continuous and selective synthesis of Dimethyl
carbonate (DMC), addressing issues such as choking, reagent consumption and other
downstream issues. Further provided herein is a system for facilitating the said process.
10
BACKGROUND OF THE DISCLOSURE
Dimethyl carbonate (DMC) is an environmentally benign building block chemical with
versatile commercial applications. It replaces toxic/ hazardous reagents such as phosgene,
dimethyl sulphate and can be used as green alternative against existing common solvents. Its
15 excellent fuel additive property extends its perspective on fuel industry to replace methyl
tertiary butyl ether (MTBE). In addition, this is an essential solvent in Li ion battery.
The direct synthesis of DMC from CO2 and methanol is the most eco-friendly and atom
economic process compared to existing industrial process such as oxidative carbonylation of
methanol and transesterification of cyclic carbonate with methanol. However, the process is
20 restricted by low product yield due to thermodynamic and equilibrium limitations.
Existing processes of direct DMC production are also associated with disadvantages such as
low DMC yield, Dimethoxyethane (DME) formation at high temperature, selectivity towards
undesired products such as methyl carbamate (MC) and methyl picolinate (MP), complexity,
reliance on energy intensive steps, choking issues and deactivation of catalysts employed.
25 Importantly, while considering the continuous production of DMC on a large scale, catalyst
activity for prolonged time, regeneration of reactants, low energy requirements and less
complicated regeneration procedures are primary requirements. The present disclosure
provides a process to address the said requirements in the art.
30 SUMMARY OF THE DISCLOSURE
The present disclosure provides a continuous process for selective synthesis of dimethyl
carbonate (DMC) comprising:
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with
an oxide catalyst in a first reactor to obtain a fluid stream;
35 b) contacting the fluid stream with an aromatic solvent to obtain a mixture;
3
c) separating the mixture into a liquid fraction and a gaseous fraction; 5 wherein the
liquid fraction is subjected to further treatment to obtain the DMC;
wherein the process is characterized by recycling of one or more of the CO2, the
alcohol and the nitrile based dehydrating agent back into the first reactor.
10 In some embodiments, the alcohol is selected from a group comprising methanol, ethanol,
propanol, butanol and phenol or any combination thereof; wherein the nitrile based dehydrating
agent is selected from a group comprising 2-cyanopyridine, 3-cyanopyridine, 4-cyanopyridine,
2-Furo nitrile, pyrole-2-carbo nitrile or any combination thereof; the oxide catalyst is selected
from a group comprising CeO2 based catalyst, Zirconia (ZrO2), Praseodymium oxide and
15 Lanthanum oxide (La2O3) or any combination thereof, wherein when the oxide catalyst is a
CeO2 based catalyst, the oxide catalyst is selected from a group comprising CexZr1-xO2, CexPr1-
xO2 and CexLa1-xO2, or any combination thereof, wherein x varies from 0.9 to 0.99; and/or the
aromatic solvent is selected from a group comprising 1,3- dimethoxy benzene, 1,3,5-
trimethoxy benzene, diphenyl oxide, mesitylene, cyclohexyl benzene sulfolane and 3-methyl
20 anisole, or any combination thereof.
In some embodiments, ratio between the carbon dioxide (CO2), the alcohol and the dehydrating
agent ranges from about 1:1:1 to about 6:2:0.5; and/or wherein ratio between the carbon dioxide
(CO2), the alcohol, the dehydrating agent and the oxide catalyst ranges from about 1:1:1:0.2 to
about 6:2:0.5:0.05.
25 In some embodiments, the CO2, the alcohol and the nitrile based dehydrating agent are
contacted with the catalyst at a temperature of about 100°C to about 150°C and pressure of
about 20 bar to about 60 bar; wherein the CO2 is introduced into the first reactor at a space
velocity of about 500 h-1 to about 2500 h-1; and/or wherein the alcohol and the nitrile based
dehydrating agent are introduced into the first reactor at LHSV of about 2 h-1 to about 6 h-1.
30 In some embodiments, the fluid stream in step (a) is maintained at a temperature ranging from
about 120 ºC to about 150ºC in the first reactor; wherein the contacting in step (b) and the
separation in step (c) are performed in a high pressure separator (HPS); wherein the HPS is
maintained at a temperature of about 40°C to about 70°C and at a pressure of about 20 bar to
about 60 bar.
35 In some embodiments, the separated gaseous fraction is subjected to condensation; wherein the
further treatment of the liquid fraction is performed in a flash separator; wherein the flash
4
separator is maintained at a temperature of about 60°C to about 170°C and a 5 pressure of about
0.25 bar to about 10 bar.
In some embodiments, the further treatment comprises separating the liquid fraction into 2
phases comprising:
i) dimethyl carbonate (DMC) in combination with unconverted alcohol and
10 optionally CO2; and
ii) the nitrile based dehydrating agent in combination with its amide derivative and
the aromatic solvent.
In some embodiments, the process of the present disclosure comprises -
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent
15 with an oxide catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture;
c) separating the mixture into a liquid fraction and a gaseous fraction;
d) separating the liquid fraction into 2 phases comprising:
i. dimethyl carbonate (DMC) in combination with unconverted alcohol
20 and optionally CO2; and
ii. the nitrile based dehydrating agent in combination with its amide
derivative and the aromatic solvent.
e) combining phase (i) with the gaseous fraction and subjecting the said
combination to condensation to yield CO2 and a mixture of alcohol and DMC;
25 f) subjecting the mixture of alcohol and DMC to about 1-4 rounds of distillation
to separate the alcohol and the DMC;
g) contacting phase (ii) with a second catalyst in a second reactor; wherein the
second catalyst converts amide derivative of the nitrile based dehydrating agent
in the phase (ii) to the nitrile based dehydrating agent; and yields water and a
30 hydrocarbon product comprising the nitrile based dehydrating agent and the
aromatic solvent;
h) subjecting the hydrocarbon product to about 1-4 rounds of distillation to
separate the nitrile based dehydrating agent, water and the aromatic solvent; and
wherein one or more of the obtained CO2, the nitrile based dehydrating agent
35 and the alcohol are recycled back into the first reactor; and/or wherein the
obtained aromatic solvent is recycled back into the second reactor.
5
The present disclosure further provides a system (100) for continuous selective 5 synthesis of
dimethyl carbonate (DMC), the system comprising:
- a first reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating
agent, the first reactor comprising at least one oxide catalyst to react with the CO2,
the alcohol and the nitrile based dehydrating agent, wherein the first reactor is
10 configured to discharge a first fluid;
- a high pressure separator (HPS) (12) fluidly coupled to the first reactor; wherein the
HPS is configured to a receive an aromatic solvent along with the first fluid, wherein
the solvent is adapted to solubilize the first fluid and the HPS is configured to
discharge a gas fraction away from the liquid in the first fluid;
15 - a condenser (14) configured to receive the gas fraction from the HPS, the condenser
configured to condense vapour products from the gas fraction;
- a flash separator fluidly (15) coupled to the HPS; wherein the flash separator is
configured to receive the liquid discharged from the HPS (12) and separate the said
liquid discharge into
20 a first phase comprising dimethyl carbonate (DMC) in combination with
unconverted alcohol and optionally CO2; and
a second phase comprising the nitrile based dehydrating agent in combination
with its amide derivative and the aromatic solvent;
wherein the first phase is selectively combined with the gas stream from the
25 HPS directed to the condenser;
- a first set of at least one distillation column(s) (16) fluidly connected to the
condenser; wherein the first set of at least one distillation column is configured to
receive condensed products from the condenser comprising alcohol and DMC, and
to separate the alcohol from the DMC, wherein the DMC is collected in a first
30 collection chamber (17);
- a second reactor (300) fluidly connected to the flash separator; wherein the second
reactor is configured to receive the second phase from the flash separator;
- the second reactor comprising at least one second catalyst to react with the second
phase in the presence of nitrogen gas or helium gas; wherein the second reactor is
35 configured to convert amide derivative of the nitrile based dehydrating agent to the
nitrile based dehydrating agent and yield water and a hydrocarbon product
comprising the nitrile based dehydrating agent and the aromatic solvent;
6
- a second set of at least one distillation column(s) (18) fluidly coupled 5 to the second
reactor, to separate the hydrocarbon product into the aromatic solvent, water and
the nitrile based dehydrating agent; and
- a line connecting the second set of at least one distillation column and the second
reactor configured to comprise a molecular sieve (19) and/or the HPS to receive the
10 separated aromatic solvent and reintroduce the aromatic solvent into the second
reactor optionally along with unreacted amide derivative of the nitrile based
dehydrating agent.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
15 In order that the disclosure may be readily understood and put into practical effect, reference
will now be made to exemplary embodiments as illustrated with reference to the accompanying
figures. The figures together with detailed description below, are incorporated in and form part
of the specification, and serve to further illustrate the embodiments and explain various
principles and advantages, in accordance with the present disclosure where:
20 Figure 1 provides a diagrammatic representation of the system of the present disclosure.
Figure 2 provides a diagrammatic representation of the part system that allows regeneration of
the nitrile based dehydrating agent.
DETAILED DESCRIPTION OF THE DISCLOSURE
25 In view of the limitations discussed above, and to remedy the need in the art for energy
efficient, simple and effective processes for DMC preparation, the present disclosure provides
a process for continuous and selective synthesis of DMC.
Particularly, the present disclosure provides a comprehensive continuous process scheme for
the synthesis of DMC from CO2 and alcohol using a nitrile based dehydrating agent.
30 An object of the present disclosure is to restrict the non-catalytic reaction that occurs
downstream of the reactor, to improve the DMC selectivity and prevent DMC loss in gas phase.
This prevents crystallisation possibility of amide derivatives of the nitrile based dehydrating
agent downstream, which resolves general operability issues in a continuous flow reactor, by
maintaining the high selectivity of DMC.
7
Another object of the present disclosure is to develop a continuous DMC synthesis 5 process that
allows regeneration of the nitrile based dehydrating agent from its amide derivative, feasibly
integrating the said regeneration with the main reaction.
Taken together, the present disclosure provides a process for production of DMC characterized
by high activity and selectivity for DMC, avoiding non-catalytic reactions and allowing
10 efficient recycling of the reactants. This process achieves the conversion at a lower energy cost
in order to make the entire process economically viable.
Before delving into the details of the process addressing the above objectives, definitions of
some terms/phrases used throughout the present disclosure are provided below.
15 Definitions
Throughout the present disclosure, the abbreviation “DMC” refers to dimethyl carbonate.
“DMB” refers to 1,3-dimethoxy benzene.
Throughout the present disclosure, the term “reactants” refers to one or more of carbon dioxide
(CO2), alcohol and nitrile based dehydrating agent, which act as starting material to synthesize
20 DMC.
The term “dehydrating agent” in the context of the present disclosure refers to a nitrile based
dehydrating agent which acts as a water trapper in the continuous flow process of the present
disclosure.
The term “zero air” refers to air produced by mixing pure oxygen with pure nitrogen, thereby
25 eliminating all impurities found in ambient air. Particularly, zero air comprises about 19.9-
21.9% oxygen and about 78.1-80.1% nitrogen. Reference to “air/oxygen” in the below
embodiments of the present disclosure envisages the possibility of presence of air comprising
about 19.9-21.9% oxygen, preferably with about 78.1-80.1% nitrogen.
The term “fluid” refers to a product stream comprising liquid and gaseous components.
30 Throughout the present disclosure, the term “selective synthesis” or “selective production” is
intended to convey the ordinary conventional meaning of the term known to a person skilled
in the art and intends to refer to the focussed generation of DMC in the reaction while actively
or passively suppressing the formation of other products that are of low economic significance.
8
Throughout the present disclosure, the term “undesired products” refers to 5 by-products formed
in the process of DMC production, examples of which include but are not limited to methyl
carbamate (MC) and methyl picolinate (MP) and methyl picolinimidate (MPI), which are
referred to in the present disclosure either by their common names or their abbreviations as
captured above.
10 The terms “unconverted” or “unreacted” as used while referring to components of the reaction
such as CO2, alcohol, nitrile based dehydrating agent and its amide derivative envisages said
reactants, that are present in the product stream in a form identical or similar to that used as
reactants in the process, wherein once the said unreacted form is separated from other
components of the product stream, each of the components may be recycled back into the
15 process. The form recycled back into the process or the respective reactors has been
interchangeably referred to as the “regenerated” form of the said reactants.
Reference to “high pressure separator”, “flash separator”, “condenser”, “distillation column”
in the present disclosure merely capture exemplary embodiments of the present disclosure and
envisage in scope the possibility of employment of any alternate gas-liquid separator or liquid20
liquid separator that performs the intended separation of the different phases/fractions as
defined in the respective embodiments.
Throughout this specification, the word “comprise”, or variations such as “comprises” or
“comprising” wherever used, will be understood to imply the inclusion of a stated element,
integer or step, or group of elements, integers or steps, but not the exclusion of any other
25 element, integer or step, or group of elements, integers or steps. The term "about" is used herein
to mean approximately, in the region of, roughly, or around. When the term "about" is used in
conjunction with a numerical value/range, it modifies that value/range by extending the
boundaries above and below the numerical value(s) set forth. In general, the term "about" is
used herein to modify a numerical value(s) above and below the stated value(s) by a variance
30 of 20%.
With respect to the use of any plural and/or singular terms herein, those having skill in the art
can translate from the plural to the singular and/or from the singular to the plural as is
appropriate to the context and/or application. The various singular/plural permutations may be
expressly set forth herein for sake of clarity.
35 As regards the embodiments characterized in this specification, it is intended that each
embodiment be read independently as well as in combination with another embodiment. For
9
example, in case of an embodiment 1 reciting 3 alternatives A, B and 5 C, an embodiment 2
reciting 3 alternatives D, E and F and an embodiment 3 reciting 3 alternatives G, H and I, it is
to be understood that the specification unambiguously discloses embodiments corresponding
to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I;
B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H;
10 C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I, unless specifically mentioned
otherwise.
Disclosure
Addressing the aforesaid objectives, the present disclosure provides a continuous process for
15 selective synthesis of dimethyl carbonate (DMC) comprising:
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with
an oxide catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
20 wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2, alcohol
and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the steps of the process may be performed in any order, sequentially or
simultaneously, in parallel.
25 In some embodiments, the first reactor is of a type that includes but is not limited to a
continuous flow type reactor. However, it will be within the purview of knowledge of the
skilled artisan to suitably replace the said type of reactor with an alternative type of reactor that
yields the same or similar results.
In some embodiments, the first reactor is selected from a group comprising continuous-stirred
30 tank reactor (CSTR), plug-flow reactor (PFR) and packed-bed reactor or fixed bed (PBR). In
some embodiments, the reactors may be subject to suitable modifications taking into
consideration constraints such as but not limited to space, weather, operating conditions, and
capacity.
In an exemplary embodiment, the first reactor is a fixed bed continuous flow type reactor.
10
In some embodiments, the alcohol is selected from a group comprising 5 methanol, ethanol,
propanol, butanol and phenol or any combination thereof.
In an exemplary embodiment, the alcohol is methanol.
Accordingly, in some embodiments, the continuous process for selective synthesis of dimethyl
10 carbonate (DMC) comprises:
a) contacting carbon dioxide (CO2), methanol and a nitrile based dehydrating agent
with an oxide catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
15 wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2,
methanol and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the nitrile based dehydrating agent is a hetero aromatic nitrile.
In some embodiments, the nitrile based dehydrating agent is selected from a group comprising
20 2-cyanopyridine (2-CP), 3-cyanopyridine (3-CP), 4-cyanopyridine (4-CP), 2-Furo nitrile (2-
CF) and pyrole 2- carbo nitrile or any combination thereof.
In an exemplary embodiment, the nitrile based dehydrating agent is 2-cyanopyridine (2-CP).
Accordingly, in some embodiments, the continuous process for selective synthesis of dimethyl
carbonate (DMC) comprises:
25 a) contacting carbon dioxide (CO2), alcohol and 2-cyanopyridine (2-CP) with an oxide
catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
30 wherein the process is characterized by recycling of one or more of the CO2, alcohol
and 2-CP back into the first reactor.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) contacting carbon dioxide (CO2), methanol and 2-cyanopyridine (2-CP) with an
35 oxide catalyst in a first reactor to obtain a fluid stream;
11
b) contacting the fluid stream with an aromatic solvent to obtain 5 a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2,
methanol and 2-CP back into the first reactor.
10 In some embodiments, the oxide catalyst is selected from a group comprising Ceria (CeO2)
based catalyst, Zirconium oxide (ZrO2), Lanthanum oxide (La2O3) and Praseodymium oxide
or any combination thereof.
In an exemplary embodiment, the oxide catalyst is a Ceria (CeO2) based catalyst.
In some embodiments, the Ceria (CeO2) based catalyst is selected from a group comprising
15 CexZr1-xO2, CexPr1-xO2 and CexLa1-xO2, or any combination thereof, wherein x varies from 0.9
to 0.99.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) contacting carbon dioxide (CO2), methanol and a nitrile based dehydrating agent
20 with a Ceria (CeO2) based catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2,
25 methanol and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) contacting carbon dioxide (CO2), methanol and 2-cyanopyridine (2-CP) with a
Ceria (CeO2) based catalyst in a first reactor to obtain a fluid stream;
30 b) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2,
methanol and 2-CP back into the first reactor.
12
In some embodiments, the oxide catalyst is in the form of a powder. In some 5 embodiments, the
said powder catalyst is optionally stabilized and shaped with a binder selected from a group
comprising colloidal silica, ethyl silicate and silica-alumina or any combination thereof.
In some embodiments, weight ratio between the oxide catalyst and the binder ranges from about
3:1 to about 9:1.
10 In some embodiments, the oxide catalyst is a powder catalyst, optionally stabilized and shaped
with a binder selected from a group comprising colloidal silica, ethyl silicate and silica-alumina
or any combination thereof; and/or the ratio between the catalyst and the binder ranges from
about 3:1 to about 9:1.
In an exemplary embodiment, the oxide catalyst is a CeO2 based powder catalyst stabilized and
15 shaped with a binder such as colloidal silica.
In some embodiments, surface area of the oxide catalyst ranges from about 100 m2/g to about
140 m2/g. In some embodiments, surface area of the shaped oxide catalyst ranges from about
100 m2/g to about 140 m2/g.
In some embodiments, the acidity/basicity ratio of the oxide catalyst ranges from about 0.8 to
20 about 3.5.
In some embodiments, surface area of the oxide catalyst ranges from about 100 m2/g to about
140 m2/g; and/or acidity /basicity ratio of the oxide catalyst ranges from about 0.8 to about 3.
In some embodiments, SiC is used as a diluent in the catalyst bed along with oxide catalyst.
Without intending to be limited by theory, the SiC reduces pressure drop during the reaction
25 and improves heat transfer. In a non-limiting embodiment, the SiC is employed as an inert
solid.
In some embodiments, weight ratio between the oxide catalyst and the diluent ranges from
about 1:1 to about 3:1.
In some embodiments, the oxide catalyst is mixed with diluent in the catalyst bed of the reactor;
30 wherein the diluent is silicon carbide (SiC); and/or the ratio between the oxide catalyst and
diluent ranges from about 1:1 to about 3:1.
In some embodiments, ratio between the oxide catalyst, the binder and the diluent ranges from
about 3:1:1 to about 9:1:9.
13
In some embodiments, the oxide catalyst is loaded into the first reactor before 5 introduction of
the carbon dioxide (CO2), the alcohol and the dehydrating agent in the reactor and activated by
heating the first reactor to a temperature of about 250ºC to about 400ºC.
In some embodiments, the said activation is performed in presence of air.
In some embodiments, the air comprises at least about 19.9-21.9% oxygen.
10 In some embodiments, the air is zero air.
In some embodiments, the said activation is performed in presence of pure oxygen.
Accordingly, in some embodiments, the oxide catalyst is loaded into the first reactor before
introduction of the carbon dioxide (CO2), the alcohol and the dehydrating agent in the reactor
and activated by heating the first reactor to a temperature of about 250ºC to about 400ºC, in
15 presence of air/oxygen.
In some embodiments, the oxide catalyst is loaded into the first reactor before introduction of
the carbon dioxide (CO2), the alcohol and the dehydrating agent in the reactor and activated by
heating the first reactor to a temperature of about 250ºC to about 400ºC, in presence of
air/oxygen; wherein the oxygen is pure oxygen or part of air or zero air.
20 In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with
an oxide catalyst in a first reactor to obtain a fluid stream, wherein the oxide catalyst
is activated by heating in presence of air/oxygen prior to contacting with the CO2,
25 alcohol and nitrile based dehydrating agent;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2, alcohol
30 and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
14
a) heating a first reactor comprising an oxide catalyst to a temperature 5 of about 250ºC
to about 400ºC, in presence of air/oxygen in the first reactor for activation of the
oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
the activated oxide catalyst in the first reactor to obtain a fluid stream;
10 c) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
d) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2, alcohol
and nitrile based dehydrating agent back into the first reactor.
15 In some embodiments, temperature of the first reactor is reduced after activation of the oxide
catalyst. In a non-limiting embodiment, post catalyst activation, temperature of the first reactor
is reduced and maintained at about 100ºC to about 150ºC and at a pressure of about 20 bar to
about 60 bar for the reaction to proceed upon introduction of the reactants into the first reactor.
In a non-limiting embodiment, post activation of the oxide catalyst, the first reactor is
20 maintained at a temperature of about 100ºC, about 110ºC, about 120ºC, about 130ºC, about
140ºC or about 150ºC and at a pressure of about 20 bar, about 30 bar, about 40 bar, about 50
bar or about 60 bar for the reaction to proceed upon introduction of the reactants into the first
reactor.
In some embodiments, the carbon dioxide (CO2), the alcohol and the dehydrating agent are
25 contacted with the catalyst at a temperature of about 100ºC to about 150ºC and at a pressure of
about 20 bar to about 60 bar.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
30 to about 400ºC, in presence of air/oxygen, for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
the activated oxide catalyst in the first reactor at a temperature of about 100ºC to
about 150ºC to obtain a fluid stream;
c) contacting the fluid stream with an aromatic solvent to obtain a mixture; and
35 d) separating the mixture into a liquid fraction and a gaseous fraction;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
15
wherein the process is characterized by recycling of one or more of 5 the CO2, alcohol
and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the CO2 is introduced as a gas into the reactor; and the alcohol and the
nitrile based dehydrating agent are introduced as a liquid into the reactor.
The reactants are introduced into the reactor at a suitable flow rate that may be optimized
10 depending upon the size of the reactor and the scale of the reaction.
In some embodiments, the CO2 is introduced into the reactor at a space velocity of about 500
h-1 to about 2500 h-1.
In some embodiments, the alcohol and the nitrile based dehydrating agent are introduced into
the reactor at a Liquid hourly space velocity (LHSV) of about 2 h-1 to about 6 h-1.
15 In some embodiments, the CO2 is introduced into the reactor at a space velocity of about 500
h-1 to about 2500 h-1; and the alcohol and the nitrile based dehydrating agent are introduced
into the reactor at a LHSV of about 2 h-1 to about 6 h-1.
In some embodiments, the CO2, the alcohol and the nitrile based dehydrating agent are
contacted with the catalyst at a temperature of about 100°C to about 150°C and pressure of
20 about 20 bar to about 60 bar; the CO2 is introduced into the first reactor at a space velocity of
about 500 h-1 to about 2500 h-1; and/or the alcohol and the nitrile based dehydrating agent are
introduced into the first reactor at LHSV of about 2 h-1 to about 6 h-1.
In some embodiments, ratio between the alcohol and the dehydrating agent ranges from about
1:1 to about 5:1.
25 In an exemplary embodiment, the ratio between the alcohol and the dehydrating agent is about
2:1.
In some embodiments, the ratio between the alcohol and the CO2 ranges from about 1:4 to
about 4:1.
In an exemplary embodiment, ratio between the alcohol and the CO2 is about 1:1.
30 In some embodiments, ratio between the carbon dioxide (CO2), the alcohol and the dehydrating
agent ranges from about 1:1:1 to about 6:2:0.5.
In an exemplary embodiment, ratio between the carbon dioxide (CO2), the alcohol and the
dehydrating agent is about 2:2:1.
16
In some embodiments, ratio between the carbon dioxide (CO2), the alcohol, 5 the dehydrating
agent and the oxide catalyst ranges from about 1:1:1:0.2 to about 6:2:0.5:0.05.
In some embodiments, the ratio between the carbon dioxide (CO2), the alcohol and the
dehydrating agent ranges from about 1:1:1 to about 6:2:0.5; and/or the ratio between the carbon
dioxide (CO2), the alcohol, the dehydrating agent and the oxide catalyst ranges from about
10 1:1:1:0.2 to about 6:2:0.5:0.05.
Without intending to be limited by theory, the above-defined process yields products in liquid
and gaseous phases, wherein said product emerge as a fluid stream from the reactor.
In some embodiments, the fluid stream or fluid product is maintained at a temperature ranging
from about 120ºC to about 150ºC in the reactor, depending on the scale of the reaction. In other
15 words, in some embodiments, the fluid stream or fluid product obtained after the reaction in
the first reactor is maintained at a temperature ranging from about 120ºC to about 150ºC in the
reactor.
In some embodiments, the fluid stream is contacted with an aromatic solvent in step (b) and
the fluid stream is subjected to separation into liquid and gaseous fractions in the presence of
20 the said aromatic solvent.
Without intending to be limited by theory, in some embodiments, the aromatic solvent is
selected such that it ideally has following characteristics -
a. High boiling point: A high boiling point solvent ensures that regeneration of the
nitrile based dehydrating agent can be performed at higher temperatures well, since
25 the amide derivative of the nitrile based dehydrating agent may remain in solution
phase, further down in the reaction scheme, as well. High temperature of operation
ensures that the rate of regeneration is also large.
b. High solubility with the amide derivative of the nitrile based dehydrating agent: The
solvent should have high solubility with the amide derivative of the nitrile based
30 dehydrating agent, to ensure that less amount of solvent is required to solubilize the
amide derivative, therefore lowering the operating cost.
c. Inertness: The solvent should not react with the amide derivative of the nitrile based
dehydrating agent and the regenerated components. This ensures that the solvent
does not require purification for reuse during the operation and allows easy
35 separation of regenerated components from the stream.
17
d. Stability: Since the solvent is used for multiple cycles with 5 exposure to high
temperature operation, it should remain stable for a long period of operation and
not degrade over time.
e. Hydrophobicity: To ensure that water does not further react with nitrile based
dehydrating agent to form the amide derivative of the dehydrating agent.
10 In some embodiments, the aromatic solvent is preferably hydrophobic, inert and/or stable.
In some embodiments, the aromatic solvent is preferably hydrophobic, inert and stable.
In some embodiments, the aromatic solvent is selected from a group comprising 1,3- dimethoxy
benzene (DMB), 1,3,5- trimethoxy benzene, diphenyl oxide, mesitylene, cyclohexyl benzene
sulfolane and 3-methyl anisole, or any combination thereof.
15 In an exemplary embodiment, the aromatic solvent is 1,3- dimethoxy benzene (DMB).
In some embodiments, the alcohol is selected from a group comprising methanol, ethanol,
propanol, butanol and phenol or any combination thereof; wherein the nitrile based dehydrating
agent is selected from a group comprising 2-cyanopyridine, 3-cyanopyridine, 4-cyanopyridine,
2-Furo nitrile, pyrole-2-carbo nitrile or any combination thereof; wherein the oxide catalyst is
20 selected from a group comprising CeO2 based catalyst, Zirconia (ZrO2), Praseodymium oxide
and Lanthanum oxide (La2O3) or any combination thereof, wherein when the oxide catalyst is
a CeO2 based catalyst, the oxide catalyst is selected from a group comprising CexZr1-xO2,
CexPr1-xO2 and CexLa1-xO2, or any combination thereof, wherein x varies from 0.9 to 0.99;
and/or wherein the aromatic solvent is selected from a group comprising 1,3- dimethoxy
25 benzene, 1,3,5- trimethoxy benzene, diphenyl oxide, mesitylene, cyclohexyl benzene sulfolane
and 3-methyl anisole, or any combination thereof.
In some embodiments, the said separation of the fluid stream into liquid and gaseous fractions
occurs in a high-pressure separator (HPS).
In some embodiments, the fluid stream is first mixed with the fluid stream emerging from the
30 first reactor to obtain a mixture and the said mixture is subjected to separation in an HPS.
In some embodiments, both steps (b) and (c) are performed in an HPS. Accordingly, in some
embodiments, the fluid stream is mixed with an aromatic solvent to obtain a mixture; and the
mixture is separated into a liquid fraction and a gaseous fraction, wherein the said mixing and
separation is conducted in a high-pressure separator (HPS).
18
In some embodiments, the aromatic solvent is introduced into the HPS at about 5 1 to 20 times
molar excess of the nitrile based dehydrating agent.
Amide derivatives of the nitrile based dehydrating agent such as Picolinamide (PA) are solid
at room temperature and have a melting point of about 110ºC. Such amides must be solubilized
in the product mixture to avoid the crystallization over the lines, walls, or BPR which could
10 lead to operational issues for continuous process, especially on an industrial scale. Hence, it
would be straightforward to assume that it is essential to maintain high temperatures in the
downstream lines or the gas-liquid separator (HPS) connected to the first reactor. However,
high temperatures in the range of about 120ºC to about 180ºC result in higher formation of
undesired products such as MC, MP and MPI by non-catalytic/thermal reactions between PA,
15 DMC, unconverted alcohol and 2-CP. Therefore, it was ascertained by the inventors that it is
essential to determine and maintain a suitable temperature, where the PA is completely soluble
in the product mixture.
Accordingly, in some embodiments of the present disclosure, the HPS is maintained at a
temperature of about 40°C to about 70°C.
20 In some embodiments, the HPS is maintained at a temperature of about 40°C, about 41°C,
about 42°C, about 43°C, about 44°C, about 45°C, about 46°C, about 47°C, about 48°C, about
49°C, about 50°C, about 51°C, about 52°C, about 53°C, about 54°C, about 55°C, about 56°C,
about 57°C, about 58°C, about 59°C, about 60°C, about 61°C, about 62°C, about 63°C, about
64°C, about 65°C, about 66°C, about 67°C, about 68°C, about 69°C or about 70°C.
25 In some embodiments, the HPS is maintained at a temperature of about 40°C to about 70°C;
and at a pressure of about 20 bar to about 60 bar.
In some embodiments, the fluid stream in step (a) is maintained at a temperature ranging from
about 120 ºC to about 150ºC in the first reactor; the contacting in step (b) and the separation in
step (c) are performed in a high pressure separator (HPS); and the HPS is maintained at a
30 temperature of about 40°C to about 70°C and at a pressure of about 20 bar to about 60 bar.
In some embodiments, the connection between the first reactor and the HPS is also maintained
at a temperature of about 40°C to about 70°C.
In some embodiments, the connection between the first reactor and the HPS is maintained at a
temperature of about 40°C, about 41°C, about 42°C, about 43°C, about 44°C, about 45°C,
35 about 46°C, about 47°C, about 48°C, about 49°C, about 50°C, about 51°C, about 52°C, about
19
53°C, about 54°C, about 55°C, about 56°C, about 57°C, about 58°C, about 5 59°C, about 60°C,
about 61°C, about 62°C, about 63°C, about 64°C, about 65°C, about 66°C, about 67°C, about
68°C, about 69°C or about 70°C.
Thus, in some embodiments, the connection between the first reactor and the HPS, and the HPS
are maintained at a temperature of about 40°C to about 70°C.
10 In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with
an oxide catalyst in a first reactor at a temperature of about 100ºC to about 150ºC
to obtain a fluid stream;
15 b) contacting the fluid stream with an aromatic solvent at a temperature of about 40°C
to about 70°C to obtain a mixture; and
c) separating the mixture into a liquid fraction and a gaseous fraction at a temperature
of about 40°C to about 70°C;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
20 wherein the process is characterized by recycling of one or more of the CO2,
methanol and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
25 to about 400ºC, in presence of air/oxygen for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
the activated oxide catalyst in the first reactor at a temperature of about 100ºC to
about 150ºC to obtain a fluid stream;
c) contacting the fluid stream with an aromatic solvent at a temperature of about 40°C
30 to about 70°C to obtain a mixture; and
d) separating the mixture into a liquid fraction and a gaseous fraction at a temperature
of about 40°C to about 70°C;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2,
35 methanol and nitrile based dehydrating agent back into the first reactor.
20
In some embodiments, the continuous process for selective synthesis of 5 dimethyl carbonate
(DMC) comprises:
a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
to about 400ºC, in presence of air/oxygen for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
10 the activated oxide catalyst in the first reactor at a temperature of about 100ºC to
about 150ºC to obtain a fluid stream;
c) transferring the fluid stream to an HPS through a temperature controlled line
maintained at a temperature of about 40°C to about 70°C;
d) contacting the fluid stream with an aromatic solvent in the HPS at a temperature of
15 about 40°C to about 70°C to obtain a mixture; and
e) separating the mixture into a liquid fraction and a gaseous fraction in the HPS
maintained at a temperature of about 40°C to about 70°C;
wherein the liquid fraction is subjected to further treatment to obtain the DMC; and
wherein the process is characterized by recycling of one or more of the CO2, alcohol
20 and nitrile based dehydrating agent back into the first reactor.
The HPS separates the fluid stream from the first reactor into solid and liquid fractions.
In some embodiments, the separated gaseous fraction coming out of the HPS is subjected to
condensation. In some embodiments, the condensation is performed in a condenser maintained
at a temperature of about -5°C to about 10°C. In some embodiments, the condenser is
25 maintained at a pressure of about 0.5 bar to about 3 bar.
Post the above-described separation, the liquid fraction that is obtained, comprises the DMC
along with the organic solvent, unreacted alcohol, unreacted nitrile based dehydrating agent
and its amide derivative.
In some embodiments, once obtained, the liquid fraction is subjected to further treatment to
30 obtain the DMC. In some embodiments, said further separation is performed in a flash
separator.
In some embodiments, said further separation is performed in a flash separator; wherein the
flash separator is maintained at a temperature of about 60°C to about 170°C and a pressure of
about 0.25 bar to about 10 bar.
21
In some embodiments, the separated gaseous fraction is subjected to condensation; 5 the further
treatment of the liquid fraction is performed in a flash separator; and the flash separator is
maintained at a temperature of about 60°C to about 170°C and a pressure of about 0.25 bar to
about 10 bar.
In some embodiments, the flash separator separates the liquid fraction to yield two separate
10 phases –
i. dimethyl carbonate (DMC) in combination with unconverted alcohol and optionally CO2;
and
ii. the nitrile based dehydrating agent in combination with its amide derivative and the
aromatic solvent.
15 In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
to about 400ºC for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and 2-cyanopyridine (2-CP) with the
20 activated oxide catalyst in the first reactor at a temperature of about 100ºC to about
150ºC to obtain a fluid stream;
c) transferring the fluid stream to an HPS through a temperature controlled line
maintained at a temperature of about 40°C to about 70°C;
d) contacting the fluid stream with an aromatic solvent in the HPS at a temperature of
25 about 40°C to about 70°C to obtain a mixture;
e) separating the mixture into a liquid fraction and a gaseous fraction in the HPS
maintained at a temperature of about 40°C to about 70°C; and
f) separating the liquid fraction into the following two phases in a flash separator;
i. dimethyl carbonate (DMC) in combination with unconverted alcohol
30 and optionally CO2; and
ii. the nitrile based dehydrating agent in combination with its amide
derivative and the aromatic solvent,
wherein the process is characterized by recycling of one or more of the CO2, alcohol
and nitrile based dehydrating agent back into the first reactor.
35 In some embodiments, the phase (i) is combined with the gaseous fraction emerging from the
HPS and subjected to condensation.
22
In some embodiments, the condensation yields CO2 and a mixture of unconverted 5 alcohol and
DMC. Said CO2, in some embodiments, is circulated back into the first reactor.
In some embodiments, the mixture of unconverted alcohol and DMC as obtained after
condensation is subjected to 1-4 rounds of distillation to separate the DMC and the alcohol.
In an exemplary embodiment, the mixture of unconverted alcohol and DMC as obtained after
10 condensation is subjected to 2 rounds of distillation to separate the DMC and the unconverted
alcohol.
In some embodiments, the phase (i) is combined with the gaseous fraction from the HPS and
subjected to condensation; wherein the condensation yields CO2 and a mixture of the alcohol
and the DMC; and the mixture of the alcohol and the DMC is subjected to about 1-4 rounds of
15 distillation to separate the alcohol and the DMC.
In some embodiments, the aforesaid distillation is performed at a temperature of about 60ºC to
about 95°C and at a pressure of about 0.1 bar to about 0.5 bar
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
20 a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
to about 400ºC for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
the activated oxide catalyst in the first reactor at a temperature of about 100ºC to
about 150ºC to obtain a fluid stream;
25 c) transferring the fluid stream to an HPS through a temperature controlled line
maintained at a temperature of about 40°C to about 70°C;
d) contacting the fluid stream with an aromatic solvent in the HPS at a temperature of
about 40°C to about 70°C to obtain a mixture; and
e) separating the mixture into a liquid fraction and a gaseous fraction in the HPS
30 maintained at a temperature of about 40°C to about 70°C;
f) separating the liquid fraction into the following two phases in a flash separator;
i. dimethyl carbonate (DMC) in combination with unconverted alcohol
and optionally CO2; and
ii. the nitrile based dehydrating agent in combination with its amide
35 derivative and the aromatic solvent; and
23
g) combining the phase (i) with the gaseous fraction emerging 5 from the HPS and
subjecting the said combination to condensation to obtain CO2 and a mixture of
unconverted alcohol and DMC,
wherein the process is characterized by recycling of one or more of the CO2, alcohol
and nitrile based dehydrating agent back into the first reactor.
10 In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
to about 400ºC for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
15 the activated oxide catalyst in the first reactor at a temperature of about 100ºC to
about 150ºC to obtain a fluid stream;
c) transferring the fluid stream to an HPS through a temperature-controlled line
maintained at a temperature of about 40°C to about 70°C;
d) contacting the fluid stream with an aromatic solvent in the HPS at a temperature of
20 about 40°C to about 70°C to obtain a mixture; and
e) separating the mixture into a liquid fraction and a gaseous fraction in the HPS
maintained at a temperature of about 40°C to about 70°C;
f) separating the liquid fraction into the following two phases in a flash separator;
iii. dimethyl carbonate (DMC) in combination with unconverted alcohol
25 and optionally CO2; and
iv. the nitrile based dehydrating agent in combination with its amide
derivative and the aromatic solvent; and
g) combining the phase (i) with the gaseous fraction emerging from the HPS and
subjecting the said combination to condensation to obtain CO2 and a mixture of
30 unconverted alcohol and DMC; and
h) subjecting the mixture of unconverted alcohol and DMC to 1-4 rounds of distillation
to separate the DMC and the unconverted alcohol,
wherein the process is characterized by recycling of one or more of the CO2, alcohol
and nitrile based dehydrating agent back into the first reactor.
35 The present disclosure provides a continuous flow process for the selective regeneration of
hetero-aromatic amides derived from the nitrile based dehydrating agent, to their corresponding
nitriles to yield the nitrile based dehydrating agent under controlled Liquid Hourly Space
24
Velocity (LHSV), gas flow rate and in presence of appropriate solvent(s) and 5 catalyst(s) such
as supported alkali metal or supported alkali metal oxides or alkali metal titanate or alkali metal
containing mixed oxide or metal oxide or mixed metal oxide, mesoporous, moderate basic
catalyst.
In some embodiments, provided herein is a process for regenerating nitrile based dehydrating
10 agent from a mixture of the nitrile based dehydrating agent and its amide derivative, said
process comprising:
contacting the mixture of the nitrile based dehydrating agent and its amide derivative with a
supported alkali metal, or supported alkali metal oxides or alkali metal titanate or alkali metal
containing mixed oxide or metal oxide or mixed metal oxide, mesoporous, moderate basic
15 catalyst in the presence of an aromatic solvent; and
optionally distilling product(s) of the above reaction to obtain the regenerated nitrile based
dehydrating agent.
Accordingly, in the context of the present disclosure, in some embodiments, in order to
facilitate selective regeneration of hetero-aromatic amides derived from the nitrile based
20 dehydrating agent to their corresponding nitriles to yield the nitrile based dehydrating agent,
the phase (ii) arising from the flash separator is contacted with a second catalyst in a second
reactor; wherein the phase (ii) is introduced into the second reactor at an LHSV of about 0.5 h-
1 to about 20 h-1.
In some embodiments, the line connecting the phase (ii) and the second reactor is maintained
25 at a temperature of about 100°C to about 140°C, preferably about 110°C to avoid deposition
the amide derivative of the nitrile based dehydrating agent.
In some embodiments, the second catalyst is loaded into the second reactor before the phase
(ii) and is activated by heating the second reactor to a temperature of about 160 ºC to about 250
ºC in the presence of an inert atmosphere.
30 In some embodiments, the inert atmosphere is achieved by introduction of nitrogen gas or
Helium gas.
In some embodiments, the second catalyst has surface area ranging from about 50 m2/g to about
250 m2 /g, average pore size ranging from about 5 nm to about 30 nm, basicity ranging from
about 0.08 mmol/g to about 0.3 mmol/g; and acidity ranging from about 0.04 mmol/g to about
35 0.35 mmol/g; the second catalyst is loaded into the second reactor before the phase (ii) and
25
activated by heating the second reactor to a temperature of about 160ºC to 5 about 250ºC in the
presence of an inert atmosphere; and the inert atmosphere is achieved by introduction of
nitrogen gas or helium gas.
In some embodiments, the second catalyst is an alkali metal containing catalyst.
In some embodiments, the second catalyst is a supported alkali metal containing catalyst.
10 In some embodiment, the second catalyst is an alkali metal containing catalyst comprises one
or more alkali metals loaded on a silica or metal oxide base.
In some embodiments, the second catalyst comprises one or more alkali metals such as but not
limited to potassium, caesium and sodium loaded on a low acidic base such as such as SiO2,
activated carbon, TiO2 and Nb2O5.
15 In some embodiments, the alkali metal loading in the catalyst is varied in the range of about
0.5 wt% to about 20 wt%.
In some embodiments, the second catalyst is selected from a group comprising Cs/SiO2, K/SiO2,
Cs/CeO2, Cs/activated carbon, K/CeO2, K/activated carbon, Cs/CexZr1-XO2, K/CexZr1-XO2 or
any combination thereof; wherein x varies from 0.9 to 0.99.
20 In some embodiments, the phase (ii) is contacted with a second catalyst in a second reactor;
wherein the phase (ii) is introduced into the second reactor at a flow rate corresponding to
LHSV of about 0.5 h-1 to about 20 h-1; the second catalyst is an alkali metal containing oxide
or mixed oxide catalyst; the alkali metal containing oxide catalyst or mixed oxide catalyst is a
supported alkali metal containing catalyst; and/or the supported alkali metal containing catalyst
25 is selected from a group comprising Cs/SiO2, K/SiO2, Cs/CeO2, Cs/activated Carbon,
K/activated carbon, K/CeO2, Cs/CexZr1-XO2, K/CexZr1-XO2 or any combination thereof;
wherein x varies from 0.9 to 0.99.
In some embodiments, the catalyst has surface area ranging from about 50 m2/g to about 250
m2 /g.
30 In some embodiments, the second catalyst has average pore size ranging from about 5nm to
about 30nm.
In some embodiments, basicity of the second catalyst ranges from about 0.08 mmol/g to 0.3
mmol/g and acidity of the second catalyst ranges from about 0.04 mmol/g to about 0.35
mmol/g.
26
In some embodiments the phase (ii) is introduced into the second reactor 5 at a flow rate
corresponding to LHSV of about 0.5 h-1to about 20 h-1.
In some embodiments, the reaction between the phase (ii) and the second catalyst converts the
amide derivative of the nitrile based dehydrating agent to the nitrile based dehydrating agent;
and yields water and a hydrocarbon product comprising the nitrile based dehydrating agent and
10 the aromatic solvent.
In some embodiments, the hydrocarbon product is subjected to 1-4 rounds of distillation.
In some embodiments, the second catalyst converts amide derivative of the nitrile based
dehydrating agent in the phase (ii) to the nitrile based dehydrating agent and yields water and
a hydrocarbon product comprising the nitrile based dehydrating agent and the aromatic solvent;
15 and the hydrocarbon product is subjected to about 1-4 rounds of distillation to separate the
nitrile based dehydrating agent, water and the aromatic solvent.
In an exemplary embodiment, the hydrocarbon product is subjected to 1 round of distillation.
In some embodiments, the hydrocarbon product is subjected to distillation at a temperature of
about 100°C to about 230°C.
20 In some embodiments, the hydrocarbon product is subjected to 1-4 rounds of distillation at a
temperature of about 100°C to about 230°C to separate the nitrile based dehydrating agent,
water and the aromatic solvent.
In some embodiments, the hydrocarbon product is subjected to a single round of distillation at
a temperature of about 100°C to about 230°C to separate the nitrile based dehydrating agent,
25 water and the aromatic solvent.
In some embodiments, the aromatic solvent obtained is recycled back into the second reactor,
optionally along with unreacted or unconverted amide derivative of the nitrile based
dehydrating agent.
In some embodiments, the aromatic solvent may optionally be recycled back into the HPS.
30 In some embodiments, the obtained CO2, the nitrile based dehydrating agent and the alcohol
are recycled back into the first reactor; and/or the obtained aromatic solvent is recycled back
into the second reactor, optionally along with unconverted amide derivative of the nitrile based
dehydrating agent.
27
In some embodiments, the obtained CO2, the nitrile based dehydrating agent 5 and the alcohol
are recycled back into the first reactor; and/or the obtained aromatic solvent is recycled back
into the second reactor and/or the HPS, optionally along with unconverted amide derivative of
the nitrile based dehydrating agent.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
10 (DMC) comprises:
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent
with an oxide catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture;
c) separating the mixture into a liquid fraction and a gaseous fraction;
15 d) separating the liquid fraction into 2 phases comprising:
i. dimethyl carbonate (DMC) in combination with unconverted alcohol
and optionally CO2; and
ii. the nitrile based dehydrating agent in combination with its amide
derivative and the aromatic solvent.
20 e) combining phase (i) with the gaseous fraction and subjecting the said
combination to condensation to yield CO2 and a mixture of alcohol and DMC;
f) subjecting the mixture of alcohol and DMC to 1-4 rounds of distillation to
separate the alcohol and the DMC;
g) contacting phase (ii) with a second catalyst in a second reactor; wherein the
25 second catalyst converts amide derivative of the nitrile based dehydrating agent
in the phase (ii) to the nitrile based dehydrating agent; and yields water and a
hydrocarbon product comprising the nitrile based dehydrating agent and the
aromatic solvent; and
h) subjecting the hydrocarbon product to 1-4 rounds of distillation to separate the
30 nitrile based dehydrating agent, water and the aromatic solvent;
wherein the process is characterized by recycling of one or more of the CO2,
methanol and nitrile based dehydrating agent back into the first reactor.
In some embodiments, the continuous process for selective synthesis of dimethyl carbonate
(DMC) comprises:
35 a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
to about 400ºC for activation of the oxide catalyst;
28
b) contacting carbon dioxide (CO2), alcohol and 2-cyanopyridine 5 (2-CP) with the
activated oxide catalyst in the first reactor at a temperature of about 100ºC to about
150ºC to obtain a fluid stream;
c) transferring the fluid stream to an HPS through a temperature controlled line
maintained at a temperature of about 40°C to about 70°C;
10 d) contacting the fluid stream with an aromatic solvent in the HPS at a temperature of
about 40°C to about 70°C to obtain a mixture; and
e) separating the mixture into a liquid fraction and a gaseous fraction in the HPS
maintained at a temperature of about 40°C to about 70°C;
f) separating the liquid fraction into the following two phases in a flash separator;
15 v. dimethyl carbonate (DMC) in combination with unconverted alcohol
and optionally CO2; and
vi. the nitrile based dehydrating agent in combination with its amide
derivative and the aromatic solvent; and
g) combining the phase (i) with the gaseous fraction emerging from the HPS and
20 subjecting the said combination to condensation to obtain CO2 and a mixture of
unconverted alcohol and DMC; and
h) subjecting the mixture of unconverted alcohol and DMC to 1-4 rounds of distillation
to separate the DMC and the unconverted alcohol;
i) contacting the phase (ii) arising from the flash separator with an alkali metal
25 containing mixed oxide catalyst in a second reactor to obtain water and a
hydrocarbon product comprising the nitrile based dehydrating agent and the
aromatic solvent; and
j) subjecting the hydrocarbon product to 1-4 rounds of distillation to separate the
nitrile based dehydrating agent, water and the aromatic solvent;
30 wherein the process is characterized by recycling of one or more of the CO2, methanol
and nitrile based dehydrating agent back into the first reactor.
In some embodiments, in the process of the present disclosure, the obtained CO2, the nitrile
based dehydrating agent and the alcohol are recycled back into the first reactor.
In some embodiments, the obtained CO2, the nitrile based dehydrating agent and the alcohol
35 are recycled back into the first reactor and the aromatic solvent obtained is recycled back into
the second reactor and/or the HPS.
29
In some embodiments, the continuous process for selective synthesis of 5 dimethyl carbonate
(DMC) comprises:
a) heating a first reactor comprising an oxide catalyst to a temperature of about 250ºC
to about 400ºC for activation of the oxide catalyst;
b) contacting carbon dioxide (CO2), alcohol and nitrile based dehydrating agent with
10 the activated oxide catalyst in the first reactor at a temperature of about 100ºC to
about 150ºC to obtain a fluid stream;
c) transferring the fluid stream to an HPS through a temperature controlled line
maintained at a temperature of about 40°C to about 70°C;
d) contacting the fluid stream with an aromatic solvent in the HPS at a temperature of
15 about 40°C to about 70°C to obtain a mixture; and
e) separating the mixture into a liquid fraction and a gaseous fraction in the HPS
maintained at a temperature of about 40°C to about 70°C;
f) separating the liquid fraction into the following two phases in a flash separator;
iii. dimethyl carbonate (DMC) in combination with unconverted alcohol
20 and optionally CO2; and
iv. the nitrile based dehydrating agent in combination with its amide
derivative and the aromatic solvent; and
g) combining the phase (i) with the gaseous fraction emerging from the HPS and
subjecting the said combination to condensation to obtain CO2 and a mixture of
25 unconverted alcohol and DMC; and
h) subjecting the mixture of unconverted alcohol and DMC to 1-4 rounds of distillation
to separate the DMC and the unconverted alcohol;
i) contacting the phase (ii) arising from the flash separator with an alkali metal
containing mixed oxide catalyst in a second reactor to obtain water and a
30 hydrocarbon product comprising the nitrile based dehydrating agent and the
aromatic solvent;
j) subjecting the hydrocarbon product is subjected to 1-4 rounds of distillation to
separate the nitrile based dehydrating agent, water and the aromatic solvent;
wherein the process is characterized by
35 recycling of the CO2 obtained in step (g) back into the first reactor;
recycling of the unconverted alcohol obtained in step (i) back into the first reactor;
recycling of the nitrile based dehydrating agent in step (j) back into the first reactor
and/or the HPS; and/or
30
recycling of the aromatic solvent obtained in step (j) back into the second 5 reactor and/or
the HPS, optionally along with unreacted or unconverted amide derivative of the nitrile
based dehydrating agent.
In some embodiments, in the process of the present disclosure, the obtained CO2, the nitrile
based dehydrating agent and the alcohol are recycled back into the first reactor.
10 In a non-limiting embodiment, the process of the present disclosure allows regeneration of
about 20% to about 70% of the employed nitrile based dehydrating agent.
In a non-limiting embodiment, the said yield of the nitrile based dehydrating agent is obtained
without formation of by-products.
In a non-limiting embodiment, yield of the undesired products methyl carbamate (MC), Methyl
15 picolinate (MP) and Methyl picolinimidate (MPI) ranges between about 0.01% to about 0.1%.
In another non-limiting embodiment, the DMC yield arising from the process of the present
disclosure ranges from about 40 mol% to about 80 mol% based on methanol feed.
In some embodiments, selectivity towards DMC formation as observed in the process of the
present disclosure ranges from about 98% to about 99.99%.
20 In some embodiments, about 20% to about 70% of the nitrile based dehydrating agent is
recovered and recycled back into the first reactor; the yield of undesired products methyl
carbamate (MC), methyl picolinate (MP) and methyl picolinimidate (MPI) ranges between
about 0.01% to about 0.1%; and/or the yield of the DMC ranges from about 40% to about 80%;
and/or wherein selectivity towards DMC formation ranges from about 98% to about 99.99%.
25 In order to facilitate the process of the present disclosure, further provided herein is a system
to carry out the said process as defined above. Accordingly, provided herein is a system (100)
for continuous selective synthesis of dimethyl carbonate (DMC), the system comprising:
- a first reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating
agent, the first reactor comprising at least one oxide catalyst to react with the CO2,
30 the alcohol and the nitrile based dehydrating agent, wherein the first reactor is
configured to discharge a first fluid;
- a high pressure separator (HPS) (12) fluidly coupled to the first reactor; wherein the
HPS is configured to a receive an aromatic solvent along with the first fluid, wherein
31
the solvent is adapted to solubilize the first fluid and the HPS 5 is configured to
discharge a gas fraction away from the liquid in the first fluid;
- a condenser (14) configured to receive the gas fraction from the HPS, the condenser
configured to condense vapour products from the gas fraction;
- a flash separator fluidly (15) coupled to the HPS; wherein the flash separator is
10 configured to receive the liquid discharged from the HPS (12) and separate the said
liquid discharge into
a first phase comprising dimethyl carbonate (DMC) in combination with
unconverted alcohol and optionally CO2; and
a second phase comprising the nitrile based dehydrating agent in combination
15 with its amide derivative and the aromatic solvent;
wherein the first phase is selectively combined with the gas stream from the
HPS directed to the condenser;
- a first set of at least one distillation column(s) (16) fluidly connected to the
condenser; wherein the first set of at least one distillation column is configured to
20 receive condensed products from the condenser comprising alcohol and DMC, and
to separate the alcohol from the DMC, wherein the DMC is collected in a first
collection chamber (17);
- a second reactor (300) fluidly connected to the flash separator; wherein the second
reactor is configured to receive the second phase from the flash separator;
25 - the second reactor comprising at least one second catalyst to react with the second
phase in the presence of nitrogen gas or helium gas; wherein the second reactor is
configured to convert amide derivative of the nitrile based dehydrating agent to the
nitrile based dehydrating agent and yield water and a hydrocarbon product
comprising the nitrile based dehydrating agent and the aromatic solvent;
30 - a second set of at least one distillation column(s) (18) fluidly coupled to the second
reactor, to separate the hydrocarbon product into the aromatic solvent, water and
the nitrile based dehydrating agent; and
- a line connecting the second set of at least one distillation column and the second
reactor configured to comprise a molecular sieve (19) to receive the separated
35 aromatic solvent and reintroduce the aromatic solvent into the second reactor,
optionally along with unreacted amide derivative of the nitrile based dehydrating
agent.
32
In some embodiments, the system further comprises a backpressure regulator 5 (BPR) (13)
coupled to the HPS.
Thus, in some embodiments, provided herein is a system (100) for continuous selective
synthesis of dimethyl carbonate (DMC), the system comprising:
- a first reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating
10 agent, the first reactor comprising at least one oxide catalyst to react with the CO2,
the alcohol and the nitrile based dehydrating agent, wherein the first reactor is
configured to discharge a first fluid;
- a high pressure separator (HPS) (12) fluidly coupled to the first reactor; wherein the
HPS is configured to a receive an aromatic solvent along with the first fluid, wherein
15 the solvent is adapted to solubilize the first fluid and the HPS is configured to
discharge a gas fraction away from the liquid in the first fluid;
- a backpressure regulator (BPR) (13) coupled to the HPS, wherein the BPR is
configured to maintain and regulate pressure upstream of its inlet;
- a condenser (14) configured to receive the gas fraction from the BPR, the condenser
20 configured to condense vapour products from the gas fraction;
- a flash separator fluidly (15) coupled to the HPS; wherein the flash separator is
configured to receive the liquid discharged from the HPS (12) and separate the said
liquid discharge into
a first phase comprising dimethyl carbonate (DMC) in combination with
25 unconverted alcohol and optionally CO2; and
a second phase comprising the nitrile based dehydrating agent in combination
with its amide derivative and the aromatic solvent;
wherein the first phase is selectively combined with the gas stream from the
HPS directed to the condenser;
30 - a first set of at least one distillation column(s) (16) fluidly connected to the
condenser; wherein the first set of at least one distillation column is configured to
receive condensed products from the condenser comprising alcohol and DMC, and
to separate the alcohol from the DMC, wherein the DMC is collected in a first
collection chamber (17);
35 - a second reactor (300) fluidly connected to the flash separator; wherein the second
reactor is configured to receive the second phase from the flash separator;
33
- the second reactor comprising at least one second catalyst to react 5 with the second
phase in the presence of nitrogen gas or helium gas; wherein the second reactor is
configured to convert amide derivative of the nitrile based dehydrating agent to the
nitrile based dehydrating agent and yield water and a hydrocarbon product
comprising the nitrile based dehydrating agent and the aromatic solvent;
10 - a second set of at least one distillation column(s) (18) fluidly coupled to the second
reactor, to separate the hydrocarbon product into the aromatic solvent, water and
the nitrile based dehydrating agent; and
- a line connecting the second set of at least one distillation column and the second
reactor configured to comprise a molecular sieve (19) to receive the separated
15 aromatic solvent and reintroduce the aromatic solvent into the second reactor,
optionally along with unreacted amide derivative of the nitrile based dehydrating
agent.
In some embodiments, the first reactor (200) and the second reactor (300) are each selected
from a group comprising continuous-stirred tank reactor (CSTR), plug-flow reactor (PFR) and
20 packed-bed reactor or fixed bed (PBR). In some embodiments, the reactors may be subject to
suitable modifications taking into consideration constraints such as but not limited to space,
weather, operating conditions, capacity.
In an exemplary embodiment, the first reactor (200) and the second reactor (300) are each a
fixed bed continuous flow type reactor.
25 In some embodiments, the first reactor (200) is connected to a separate external supply for each
of the reactants or a single supply for sequential supply of the reactants or simultaneous supply
of a mixture of the reactants. In some embodiments, the supply is metered, wherein the
metering is manual or automated.
In some embodiments, the first reactor (200) comprises inlets for manual supply or input of the
30 reactants.
In some embodiments, the first reactor (200) and the second reactor (300) each comprise a
mechanism for temperature and pressure control.
In some embodiments, the first reactor (200) is heated to a temperature of about 250°C to about
400°C after introduction of catalyst.
34
In some embodiments, the first reactor (200) is maintained at a temperature 5 of about 100°C to
about 150°C after introduction of the CO2, alcohol and nitrile based dehydrating agent.
In some embodiments, the first (200) and the second (300) reactors and the HPS (12) comprise
means for temperature and pressure control; and/or the first reactor (200) is connected to the
HPS (12) by a temperature-controlled channel.
10 In some embodiments, the first reactor (200) is connected to the HPS (12) by a temperaturecontrolled
channel. In some embodiments, the said temperature-controlled channel is
maintained at a temperature of about 40°C to about 70°C.
In some embodiments, the HPS (12) comprises a mechanism for temperature and pressure
control. In some embodiments, the HPS (12) is maintained at a temperature of about 40°C to
15 about 70°C.
In some embodiments, the flash separator (15) is maintained in fluid connection with the line
from the HPS to the condenser, allowing the introduction of the phase (i) in a selective or
regulated manner into the line connecting the HPS to the condenser. In some embodiments, the
regulated connection between the flash separator and the line from the HPS to the condenser
20 allows introduction of the phase (i) at regulated proportions into the line carrying the gas stream
from the HPS to the condenser.
In some embodiments, the condenser is maintained in fluid connection with the first reactor to
allow recycling of the CO2 obtained after condensation back into the first reactor.
In some embodiments, the connection from the BPR (13) to the condenser (14) is maintained
25 at room temperature.
In some embodiments, the system further comprises a backpressure regulator (BPR) (13)
coupled to the HPS, wherein the BPR is configured to maintain and regulate pressure upstream
of its inlet; and the connection from the BPR (13) to the condenser (14) is maintained at room
temperature.
30 In some embodiments, the condenser (14) is maintained between about -5 °C to about 10°C to
condense vaporized components.
In some embodiments, the condenser (14) is fluidly connected to the first set of distillation
columns comprising two distillation columns (16) in succession.
35
In some embodiments, gas emerging from the condenser (14) after the condensation 5 of vapour
products comprises CO2; and wherein the condenser is fluidly connected to the first reactor
(200) for recycling of the said gas.
In some embodiments, the condenser (14) is maintained between -5-10°C to condense
vaporized components; wherein the condenser (14) is fluidly connected to the first set of
10 distillation columns comprising two distillation columns (16) in succession; the gas emerging
from the condenser (16) after the condensation of vapour products comprises CO2; and/or the
condenser is fluidly connected to the first reactor (200) for recycling of the said gas.
In some embodiments, the second reactor (300) is heated to a temperature of about 250°C to
about 400°C after introduction of catalyst.
15 In some embodiments, the second reactor (300) is maintained in fluid connection with the first
reactor (200) or the reactant supply to the first reactor and the HPS for facilitating recycling of
the alcohol and the aromatic solvent, respectively.
In some embodiments, the first set of distillation columns (16) is fluidly connected to the first
reactor for recycling of the obtained alcohol.
20 In some embodiments, the second set of distillation columns (18) is fluidly connected to the
second reactor for recycling of the obtained aromatic solvent, optionally along with
unconverted amide derivative of the nitrile based dehydrating agent.
In some embodiments, the second set of distillation columns (18) is fluidly connected to the
HPS for recycling of the obtained aromatic solvent, optionally along with unconverted amide
25 derivative of the nitrile based dehydrating agent.
In some embodiments, the second set of distillation columns (18) is fluidly connected to the
second reactor and/or the HPS for recycling of the obtained aromatic solvent, optionally along
with unconverted amide derivative of the nitrile based dehydrating agent.
In some embodiments, the connection between the second set of distillation columns (18) and
30 the second reactor comprises a molecular sieve (19).
In some embodiments, the first set of distillation columns (16) is fluidly connected to the first
reactor for recycling of the obtained alcohol; the second set of distillation columns (18) is
fluidly connected to the second reactor for recycling of the obtained aromatic solvent,
optionally along with unconverted amide derivative of the nitrile based dehydrating agent; and
36
the connection between the second set of distillation columns (18) and 5 the second reactor
comprises a molecular sieve (19).
In some embodiments, the first set of distillation columns (16) is fluidly connected to the first
reactor for recycling of the obtained alcohol; the second set of distillation columns (18) is
fluidly connected to the second reactor and/or the HPS for recycling of the obtained aromatic
10 solvent, optionally along with unconverted amide derivative of the nitrile based dehydrating
agent; and the connection between the second set of distillation columns (18) and the second
reactor comprises a molecular sieve (19).
In a non-limiting embodiment, each of the first and the second reactors (200 and 300), the highpressure
separator (12), the flash separator (15) and the condenser (14) may be provided with
15 valves. These control valves being located in immediate vicinity of the respective components
of the system or mid-way between a connection between any two components of the system
(100) as defined above, to control or regulate the supply/withdrawal of reactant, product or
intermediate streams supplied to or emerging from any of the said components of the system.
In an embodiment, the valves may be manually operated or actuator-controlled e.g.,
20 programmable logic controller (PLC).
In an illustrative embodiment as seen in Fig. 1, the system (100) may include a first reactor
(200) configured to receive a gas stream, the said first reactor (200) comprising at least one
activated catalyst to react with CO2, alcohol and nitrile based dehydrating agent. The first
reactor (200) comprises a manual or automated mechanism for temperature and pressure
25 control. The catalyst is pre-loaded into the reactor before introduction of the CO2, alcohol and
nitrile based dehydrating agent and activated by heating the reactor in presence of air/oxygen.
The system further comprises a high-pressure separator (HPS) (12), fluidly coupled to the
reactor by a temperature-controlled channel; wherein the temperature-controlled channel and
the HPS are preferably maintained at a temperature of about 40°C-70°C. The HPS is configured
30 to receive a fluid product stream from the first reactor and an aromatic solvent; and discharge
a liquid to a flash separator (15) and a gas stream away from the liquid. The system may, in an
optional embodiment, additionally comprise a backpressure regulator (BPR) (13) connected to
the gas liquid separator, wherein the BPR is configured to receive the gas stream from the gas
liquid separator and route it to a condenser (15) through a connection maintained at room
35 temperature. The flash separator is configured to receive a liquid comprising a mixture of the
aromatic solvent, the DMC, the nitrile based dehydrating agent and its amide derivative. The
flash separator separates the mixture into two phases - a first phase comprising dimethyl
37
carbonate (DMC) in combination with unconverted alcohol and optionally 5 CO2; and a second
phase comprising the nitrile based dehydrating agent in combination with its amide derivative
and the aromatic solvent. The flash separator is configured to separate the said two phases from
each other. In some embodiments, the flash separator is connected to the line between the HPS
and the condenser such that it selectively delivers the first phase into the said line carrying the
10 gaseous stream from the HPS into the condenser. The system comprises a condenser (14)
configured to receive the gas stream from the HPS in combination with the first phase from the
flash separator, routed through a backpressure regulator (BPR) (13), wherein the condenser is
configured to condense vapour products from the incoming stream. The condenser is connected
to a gas outlet that is in turn connected to the first reactor to facilitate recycling of the gas
15 remaining after the condensation in the condenser. The system further comprises a first set of
at least one distillation column(s) (16) fluidly connected to the condenser; wherein the first set
of at least one distillation column(s) is configured to receive condensed products from the
condenser comprising alcohol and DMC, and to separate the alcohol from the DMC, wherein
the DMC is collected in a first collection chamber (17). The first set of distillation column(s)
20 (16) is fluidly connected to the first reactor for recycling of the obtained alcohol. The flash
separator is fluidly connected to a second reactor (300) configured to comprise an activated
second catalyst and to receive the second phase from the flash separator, for facilitating the
conversation of the amide derivative of the nitrile based dehydrating agent to the nitrile based
dehydrating agent. Line connecting the flash separator and the second reactor is maintained at
25 a temperature of about 100°C to about 140°C, preferably about 110°C to avoid deposition of
the amide derivative of the nitrile based dehydrating agent. Furthermore, the phase (ii) is
introduced into the second reactor at a flow rate corresponding to LHSV of about 0.5 h-1 to
about 15 h-1. The reaction in the second reactor yields water and a hydrocarbon product
comprising the nitrile based dehydrating agent and the aromatic solvent. The system comprises
30 a second set of at least one distillation column(s) (18) fluidly coupled to the second reactor, to
separate the hydrocarbon product into the aromatic solvent, water and the nitrile based
dehydrating agent. The system further comprises line connecting the second set of at least one
distillation column(s) and the second reactor configured to comprise a molecular sieve (19) to
receive the separated aromatic solvent and reintroduce the aromatic solvent into the second
35 reactor, optionally along with unreacted amide derivative of the nitrile based dehydrating agent.
The second set of distillation column(s) (18) is fluidly connected to the second reactor and/or
the HPS for recycling of the obtained aromatic solvent, optionally along with unconverted
amide derivative of the nitrile based dehydrating agent; wherein the said connection optionally
38
comprises a molecular sieve through which the products from the second distillation 5 column
are routed.
Fig. 2 specifically depicts the part system that allows regeneration of the nitrile based
dehydrating agent characterized by the second reactor (300) fluidly connected to the flash
separator configured to comprise an activated second catalyst and to receive the second phase
10 from the flash separator, for facilitating the conversion of the amide derivative of the nitrile
based dehydrating agent to the nitrile based dehydrating agent. The line connecting the flash
separator and the second reactor is maintained at a temperature of about 100°C to about 140°C,
preferably about 110°C to avoid deposition of the amide derivative of the nitrile based
dehydrating agent. Furthermore, the phase (ii) is introduced into the second reactor at a flow
15 rate corresponding to LHSV of about 0.5 h-1 to about 20 h-1. The reaction in the second reactor
yields water and a hydrocarbon product comprising the nitrile based dehydrating agent and the
aromatic solvent. The second reactor is connected to a second set of at least one distillation
column(s) (18) fluidly coupled to the second reactor, to separate the hydrocarbon product into
the aromatic solvent, water and the nitrile based dehydrating agent. In some embodiments, the
20 line connecting the second set of at least one distillation column(s) and the second reactor is
configured to comprise a molecular sieve (19) to receive the separated aromatic solvent and
reintroduce the aromatic solvent into the second reactor, optionally along with unreacted amide
derivative of the nitrile based dehydrating agent. The second set of distillation column(s) (18)
is fluidly connected to the second reactor and/or the HPS for recycling of the obtained aromatic
25 solvent, optionally along with unconverted amide derivative of the nitrile based dehydrating
agent; wherein the said connection optionally comprises a molecular sieve through which the
products from the second distillation column are routed.
Additional embodiments and features of the present disclosure will be apparent to one of
ordinary skill in art based on the description provided herein. The embodiments herein provide
30 various features and advantageous details thereof in the description. Descriptions of wellknown/
conventional processes and techniques are omitted so as to not unnecessarily obscure
the embodiments herein.
Any discussion of documents, acts, materials, devices, articles and the like that has been
included in this specification is solely for the purpose of providing a context for the disclosure.
35 It is not to be taken as an admission that any or all of these matters form a part of the prior art
39
base or were common general knowledge in the field relevant to the disclosure 5 as it existed
anywhere before the priority date of this application.
While the present disclosure is susceptible to various modifications and alternative forms,
specific aspects thereof have been shown by way of examples and drawings and are described
in detail below. However, it should be understood that it is not intended to limit the invention
10 to the particular forms disclosed, but on the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and the scope of the invention as defined
by the appended claims.
EXAMPLES
15 The present disclosure is further described with reference to the following examples, which are
only illustrative in nature and should not be construed to limit the scope of the present
disclosure in any manner.
Examples
20 Example 1: Determination of the suitable temperature of the HPS
The solubility of picolinamide (PA) in product mixture was assessed at different temperatures.
A product mixture of about 1.5 g methanol, about 2.4 g 2-CP, about 2.1 g DMC and about 2.9
g PA was prepared, which yielded 50 % methanol conversion (see Table 1). Similarly, different
product mixtures were prepared to yield different degrees of methanol conversion. The
25 temperature was varied in the range of about 40°C to about 80°C, until PA was found to be
completely soluble in mixture.
Table 1: Solubility of PA in product mixture
Expt.
No.
Methanol
conversion
(%)
PA
concentration
(wt %)
Miscible
temp
(oC)
1 50 32 40
2 60 38 45
3 70 43 50
4 80 48 65
5 90 53 70
40
The temperatures between about 40°C to about 70° were found to be 5 suitable to ensure
miscibility of the picolinamide (PA) in the product mixture. It was also observed that
temperatures below this range led to re-crystallization of PA.
Example 2: Continuous and selective process for conversion of CO2 and methanol to
DMC using 2-cyanopyridine as a dehydrating agent
10 The reaction was carried out in a continuous fixed bed reactor with the catalyst volume of about
12 cc. About 15 g of a Ce based catalyst and about 15 g of SiC were mixed together. The
catalyst bed was fixed to the reactor vertically and subjected to activation by heating the reactor
to a temperature of about 300ºC. The reactor was pressurized up to about 38 bar and the
temperature of the reactor was maintained at about 130ºC. CO2 was introduced into the reactor
15 at a space velocity of about 825 h-1 (methanol: CO2 molar ratio= 1:1). Liquid feed, i.e.,
Methanol& 2-CP mixture, at a about 2: 1 molar ratio, were pumped to the reactor using HPLC
pump at LHSV of about 3 h-1. The product coming out of the reactor was connected to line
heater followed by the high-pressure gas-liquid separator (HPS). The line between the reactor
and the HPS and high-pressure gas-liquid separator temperature was maintained at about 90°C.
20 The gas stream coming out from the top of the HPS was passed through a BPR and maintained
at room temperature.
Table 2: Catalytic activity data
Time on
stream (hrs) MeOH
Conv. (%)
2-CP
Conv. (%)
DMC
Yield (%)
PA yield
(%)
MC
Yield
(%)
MPI
yield
(%)
MP Yield
(%)
12 72.6 79.1 71.1 76.4 1.4 0.2 1.3
24 73.4 75.8 70.8 68.5 1.0 0.2 0.8
36 75.3 76.9 67.9 64.9 0.9 0.2 0.7
48 71.3 73.4 72.7 67.3 0.9 0.2 0.6
60 71.7 72.7 69.9 67.2 0.8 0.2 0.6
65 69.2 70.5 73.8 67.3 0.8 0.2 0.6
As can be seen, the yield of MC, MPI and MP were slightly higher due to the higher
temperature of HPS (90°C). This shows that the temperature of the HPS should be maintained
25 as low as possible, which is preferably between about 40-70°C.
Example 3: Impact of temperature of the first reactor-HPS connector
This reaction was carried out in a continuous fixed bed reactor with the catalyst volume of
about 4 cc. About 4.6 g of Ce based catalyst and about 4.6 g of SiC were mixed together. The
catalyst bed was fixed to the reactor vertically and subjected to activation by heating the reactor
41
to a temperature of about 300ºC. The reactor was pressurized to about 5 38 bar and the
temperature was raised to about 130ºC. CO2 gas flow (methanol: CO2 molar ratio= 1:1) was
maintained at a space velocity of 825 h-1 under about 38 bar pressure. Liquid feed i.e.,
Methanol & 2 CP mixture at a 2: 1 molar ratio was pumped into the reactor using HPLC pump
at liquid hourly velocity (LHSV) of about 3 h-1. The reactor outlet was connected to the down10
stream unit composed of HPS, BPR, condenser and distillation columns for CO2, DMC and
Methanol production/regeneration and flash separator, second reactor and distillation column
for DMB and 2 CP regeneration.
In view of the objective of this experiment, the product coming out of the reactor was connected
to a line heater followed by an HPS. The line heater and the HPS temperature were maintained
15 at about 60°C for one set of experiments and at about 130°C for another set of experiments;
the gas stream coming out from the top of HPS was passed through to a BPR, maintained at
room temperature and routed to the condenser maintained between -5°C to about -10°C to
condense vaporized components.
Table 3: Catalytic activity data observed when HPS-reactor 1 line and HPS temperature was
20 maintained at 60°C
TOS (h) MeOH
Conv.
2-CP
Conv.
DMC
Yield
2-PA
yield
MC
Yield
MPI
yield
MP
Yield
13 75.2 76.9 68.9 66.1 0.8 0.2 0.4
25 61.1 65.9 71.4 64.8 0.5 nil 0.2
37 62.9 66.4 66.9 61.3 0.5 nil 0.2
45 51.8 57.2 55.9 52.0 nil nil 0.2
49 53.2 58.1 59.3 54.1 nil nil 0.1
61 59.3 61.7 62.3 57.4 nil nil 0.2
67 57.6 58.9 55.4 54.4 nil nil 0.1
73 51.7 56.4 57.5 53.4 nil nil 0.1
85 52.9 56.9 56.7 53.1 nil nil 0.1
Table 4: Catalytic activity data observed when HPS-reactor 1 line and HPS temperature was
maintained at 130°C
TOS (h)
MeOH
conv. (%)
2-CP
conv.
(%)
DMC
yield (%)
PA yield
(%)
MC yield
(%)
MP/MPI
yield (%)
2 54.4 52.4 41.1 44.9 4.4 2.5
4 56.0 53.5 40.8 43.1 4.1 2.3
6 50.5 48.0 43.8 47.3 4.1 2.5
42
8 55.1 52.8 39.5 44.1 3.6 2.2
10 52.1 53.9 41.1 43.6 3.4 2.0
12 50.1 50.1 43.1 47.6 4.1 2.4
14 57.4 58.1 36.8 40.5 3.5 2.0
16 47.9 50.7 42.7 46.1 3.6 2.2
18 52.7 52.6 39.8 43.6 3.4 2.1
20 50.2 49.7 41.0 46.6 3.2 2.2
22 49.8 54.3 40.3 41.6 4.2 2.0
24 49.2 48.3 40.6 46.9 4.2 2.2
26 51.0 50.6 39.3 42.8 4.4 2.1
28 49.5 48.6 40.9 43.8 3.8 1.9
30 48.8 52.3 41.3 42.7 3.9 1.9
32 50.1 46.3 41.3 46.6 3.4 2.0
34 49.9 46.7 41.5 45.5 4.2 2.1
36 48.6 47.2 41.6 45.7 3.9 2.0
38 45.8 47.9 42.7 43.2 4.5 2.1
5
The experiment performed while maintaining the temperature of the HPS-reactor 1 line and
HPS at 130°C was terminated at 38 hours in view of the downward trend of the DMC yield
and higher yields of unwanted products such as MC, MP and MPI.
Overall, it was seen that by maintaining the temperature at 60°C, i.e. within the range of about
10 40°C to about 70°C, the MeOH and CO2 conversion and hence DMC yield significantly
improved as compared to when the HPS or HPS/first reactor connection was maintained at
higher temperatures. Similarly, the yield of undesired products MC, MPI and MP was
significantly reduced or completely obviated when the HPS or HPS/first reactor connection
was maintained within the range of about 40°C to about 70°C as opposed to higher
15 temperatures. Thus, overall, better retention of catalytic activity was observed by specifically
maintaining the HPS or HPS/first reactor connection within the range of about 40°C to about
70°C as defined in the present disclosure.
Example 4: Preparation procedure of alkali metal containing mixed oxide catalyst
(second catalyst - cesium/SiO2 mixed oxide catalyst)
20 About 4.1 g of Cs2CO3 and about 44.7 g colloidal Silica were separately weighed and
transferred to a beaker containing about 40 ml water. The mixture was stirred for about half an
hour to ensure complete distribution of solution. The sample was then dried at about 110oC for
about 6 hours and further calcined at about 500 °C for about 3 hours. Acidity of the obtained
43
catalyst was about 0.32 mmol/g and basicity of the obtained catalyst was 5 about 0.16 mmol/g
and basic site density of the obtained catalyst was about 2.9 μmmol/m2.
Example 5: Preparation procedure of SiO2 supported alkali metal catalyst (second
catalyst - cesium/ silica catalyst)
Aqueous solution of Cs2CO3 was impregnated on about 18.60 g of commercial SiO2 support.
10 The sample was subsequently dried at about 110ºC for about 6 hours and calcined at about
500°C for about 3 hours. The corresponding composition of synthesized catalyst was about 6.9
wt% Cs/g catalyst. Acidity of the obtained catalyst was about 0.30 mmol/g, basicity of the
obtained catalyst was about 0.19 mmol/g and basic site density of the obtained catalyst was about
1.1 mol/m2.
15 Example 6: Preparation procedure of SiO2 supported alkali metal catalyst (second
catalyst - Potassium/ silica catalyst)
K supported on SiO2 catalyst was prepared following incipient wetness impregnation process.
About 31 ml aqueous KOH solution of was impregnated on about 46.545 g of commercial SiO2
support (surface area: about 529 m2/g) and then dried at about 110ºC for about 6 hours. The
20 sample was further calcined at about 500°C for about 3 hours, basicity of the obtained catalyst
was about 0.11 mmol/g.
Example 7: Preparation procedure of mixed oxide catalyst (supported WO3/ZrO2
catalyst)
WO3/ZrO2 catalyst was prepared by incipient-wetness impregnation of aqueous solutions of
25 ammonium metatungstate, (NH4)10W12O41·5H2O on the monoclinic ZrO2 support. The samples
were first dried overnight at 110ºC and then calcined in flowing air at about 723 K for about 4
hours.
Example 8: Impact of choice of catalyst (second reactor)
This example illustrates the continuous and selective process for dehydration of picolinamide
30 (PA) to 2-cyanopyridine (2-CP). The reactions were carried out in a continuous fixed bed
reactor with the catalyst volume of about 4 cc. About 2.3 g of catalyst and about 2.3 g of SiC
were mixed together. An inert gas (N2) flow of about 150 ml/min was maintained under
atmospheric pressure. Temperature of the reactor was raised to about 210°C to about 230°C.
A solution of PA in 1,3- dimethoxy benzene (DMB) or sulfolane was prepared for use as feed
35 solution. Then the feed solution was pumped into the reactor by means of an HPLC pump at
44
an LHSV of about 3 h-1. The reactor outlet was directly connected to a product 5 vessel, from
which samples were drawn every hour for analysis.
Table 4. Catalytic activity with different catalysts
Exp.
No.
Feed LHSV at
which the
feed is
pumped (h-
1)
Flow rate of
N2 gas
(ml/min)
Temperature
of Reactor 2
Catalyst
2-CP yield
(mol%)
Pyridine yield
(mol%)
1. 3 % PA in 1,3-
dimethoxy
benzene
3
150
215°C K/SiO2
#
15.1
Nil
2. 3 % PA in 1,3-
dimethoxy
benzene
3
150
215°C Cs/SiO2
#
32.3
Nil
3. 3 % PA in 1,3-
dimethoxy
benzene
1.5 150 210ºC Cs/SiO2#
33.4
Nil
4. 3 % PA in 1,3-
dimethoxy
benzene
1.5 150 210ºC Cs/SiO2*
37.0
Nil
5. 3 % PA in 1,3-
dimethoxy
benzene
0.75
150
215°C Cs/SiO2
*
50
Nil
6. 3% PA in 1,3-
dimethoxy
benzene
15
150
210°C K/SiO2
#
2.1
Nil
45
*Colloidal silica, #Commercial 5 silica support
It was observed that despite variation in process parameters, using the silica supported alkali
metal catalyst/ alkali metal containing mixed oxide catalyst in the second reactor for the
regeneration of 2-CP yield completely suppressed the pyridine yield. Also, as can be observed
from the Table, LHSV, N2 flow rate and the choice of catalyst play a critical role in determining
10 the 2-CP and pyridine yield.
The foregoing description of the specific embodiments fully reveals the general nature of the
embodiments herein that others can, by applying current knowledge, readily modify and/or
adapt for various applications of such specific embodiments without departing from the generic
concept, and, therefore, such adaptations and modifications should and are intended to be
15 comprehended within the meaning and range of equivalents of the disclosed embodiments. It
is to be understood that the phraseology or terminology employed herein is for the purpose of
description and not of limitation. Therefore, while the embodiments in this disclosure have
been described in terms of preferred embodiments, those skilled in the art will recognize that
the embodiments herein can be practiced with modification within the spirit and scope of the
20 embodiments as described herein.
While considerable emphasis has been placed herein on the particular features of this
disclosure, it will be appreciated that various modifications can be made, and that many
changes can be made in the preferred embodiments without departing from the principles of
the disclosure. These and other modifications in the nature of the disclosure or the preferred
25 embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it
is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely
as illustrative of the disclosure and not as a limitation.
7. 3% PA in 1,3-
dimethoxy
benzene
15 150 210°C WOx/ZrO2
1.7
Nil
8. 15 % PA in
sulfolane
3 75 230°C K/SiO2
#
2.9 Nil
9. 15 % PA in
sulfolane
3 75 230°C Nb2O5
1.0
Nil
46
All references, articles, publications, general disclosures etc. cited herein are 5 incorporated by
reference in their entireties for all purposes. However, mention of any reference, article,
publication etc. cited herein is not, and should not be taken as, an acknowledgment or any form
of suggestion that they constitute valid prior art or form part of the common general knowledge
in any country in the world.
We claim:
1. A continuous process for selective synthesis of dimethyl carbonate (DMC) comprising:
a) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a first reactor to obtain a fluid stream;
b) contacting the fluid stream with an aromatic solvent to obtain a mixture;
c) separating the mixture into a liquid fraction and a gaseous fraction; wherein the liquid fraction is subjected to further treatment to obtain the DMC;
wherein the process is characterized by recycling of one or more of the CO2, the alcohol and the nitrile based dehydrating agent back into the first reactor.
2. The process as claimed in claim 1, wherein the alcohol is selected from a group comprising methanol, ethanol, propanol, butanol and phenol or any combination thereof; wherein the nitrile based dehydrating agent is selected from a group comprising 2-cyanopyridine, 3-cyanopyridine, 4-cyanopyridine, 2-Furo nitrile, pyrole-2-carbo nitrile or any combination thereof; wherein the oxide catalyst is selected from a group comprising CeO2 based catalyst, Zirconia (ZrO2), Praseodymium oxide and Lanthanum oxide (La2O3) or any combination thereof, wherein when the oxide catalyst is a CeO2 based catalyst, the oxide catalyst is selected from a group comprising CexZr1-xO2, CexPr1-xO2 and CexLa1-xO2, or any combination thereof, wherein x varies from 0.9 to 0.99; and/or wherein the aromatic solvent is selected from a group comprising 1,3-dimethoxy benzene, 1,3,5- trimethoxy benzene, diphenyl oxide, mesitylene, cyclohexyl benzene sulfolane and 3-methyl anisole, or any combination thereof.
3. The process as claimed in claim 1, wherein the oxide catalyst is a powder catalyst, optionally stabilized and shaped with a binder selected from a group comprising colloidal silica, ethyl silicate and silica-alumina or any combination thereof; and/or wherein ratio between the catalyst and the binder ranges from about 3:1 to about 9:1.
4. The process as claimed in claim 1, wherein the oxide catalyst is mixed with diluent in the catalyst bed of the reactor; wherein the diluent is silicon carbide (SiC); and/or wherein ratio between the oxide catalyst and diluent ranges from about 1:1 to about 3:1.
5. The process as claimed in claim 1, wherein the oxide catalyst is loaded into the first reactor before the carbon dioxide (CO2), the alcohol and the dehydrating agent, and activated by heating the first reactor to a temperature of about 250ºC to about 400ºC, in presence of oxygen; wherein the oxygen is pure oxygen or part of air or zero air.

6. The process as claimed in claim 1, wherein ratio between the carbon dioxide (CO2), the alcohol and the dehydrating agent ranges from about 1:1:1 to about 6:2:0.5; and/or wherein ratio between the carbon dioxide (CO2), the alcohol, the dehydrating agent and the oxide catalyst ranges from about 1:1:1:0.2 to about 6:2:0.5:0.05.
7. The process as claimed in claim 1, wherein the CO2, the alcohol and the nitrile based dehydrating agent are contacted with the catalyst at a temperature of about 100°C to about 150°C and pressure of about 20 bar to about 60 bar; wherein the CO2 is introduced into the first reactor at a space velocity of about 500 h-1 to about 2500 h-1; and/or wherein the alcohol and the nitrile based dehydrating agent are introduced into the first reactor at LHSV of about 2 h-1 to about 6 h-1.
8. The process as claimed in claim 1, wherein the fluid stream in step (a) is maintained at a temperature ranging from about 120 ºC to about 150ºC in the first reactor; wherein the contacting in step (b) and the separation in step (c) are performed in a high pressure separator (HPS); and/or wherein the HPS is maintained at a temperature of about 40°C to about 70°C and at a pressure of about 20 bar to about 60 bar.
9. The process as claimed in claim 1, wherein the separated gaseous fraction is subjected to condensation; wherein the further treatment of the liquid fraction is performed in a flash separator; and/or wherein the flash separator is maintained at a temperature of about 60°C to about 170°C and a pressure of about 0.25 bar to about 10 bar.
10. The process as claimed in claim 9, wherein the further treatment comprises separating the liquid fraction into 2 phases comprising:
i) dimethyl carbonate (DMC) in combination with unconverted alcohol and
optionally CO2; and ii) the nitrile based dehydrating agent in combination with its amide derivative and
the aromatic solvent.
11. The process as claimed in claim 10, wherein the phase (i) is combined with the gaseous fraction from the HPS and subjected to condensation; wherein the condensation yields CO2 and a mixture of the alcohol and the DMC; and/or wherein the mixture of the alcohol and the DMC is subjected to about 1-4 rounds of distillation to separate the alcohol and the DMC.
12. The process as claimed in claim 10, wherein the phase (ii) is contacted with a second catalyst in a second reactor; wherein the phase (ii) is introduced into the second reactor at a flow rate corresponding to LHSV of about 0.5 h-1 to about 20 h-1; wherein the second catalyst is an alkali metal containing oxide or mixed oxide catalyst; wherein the

alkali metal containing oxide catalyst or mixed oxide catalyst is a supported alkali metal containing catalyst; and/or wherein the supported alkali metal containing catalyst is selected from a group comprising Cs/SiO2, K/SiO2, Cs/CeO2, Cs/activated Carbon, K/activated carbon, K/CeO2, Cs/CexZr1-XO2, K/CexZr1-XO2 or any combination thereof; wherein x varies from 0.9 to 0.99.
13. The process as claimed in claim 12, wherein the second catalyst has surface area ranging from about 50 m2/g to about 250 m2 /g, average pore size ranging from about 5 nm to about 30 nm, basicity ranging from about 0.08 mmol/g to about 0.3 mmol/g; and acidity ranging from about 0.04 mmol/g to about 0.35 mmol/g; wherein the second catalyst is loaded into the second reactor before the phase (ii) and activated by heating the second reactor to a temperature of about 160ºC to about 250ºC in the presence of an inert atmosphere; wherein the inert atmosphere is achieved by introduction of nitrogen gas or helium gas.
14. The process as claimed in claim 12, wherein the second catalyst converts amide derivative of the nitrile based dehydrating agent in the phase (ii) to the nitrile based dehydrating agent; and yields water and a hydrocarbon product comprising the nitrile based dehydrating agent and the aromatic solvent; wherein the hydrocarbon product is subjected to about 1-4 rounds of distillation to separate the nitrile based dehydrating agent, water and the aromatic solvent.
15. The process as claimed in claim 11 or 14, wherein the obtained CO2, the nitrile based dehydrating agent and the alcohol are recycled back into the first reactor; and/or wherein the aromatic solvent obtained in claim 14 is recycled back into the second reactor and/or the HPS, optionally along with unconverted amide derivative of the nitrile based dehydrating agent.
16. The process as claimed in claim 1, wherein about 20% to about 70% of the nitrile based dehydrating agent is recovered and recycled back into the first reactor; wherein yield of undesired products methyl carbamate (MC), methyl picolinate (MP) and methyl picolinimidate (MPI) ranges between about 0.01% to about 0.1%; and/or wherein yield of the DMC ranges from about 40% to about 80%; and/or wherein selectivity towards DMC formation ranges from about 98% to about 99.99%.
17. The process as claimed in claim 1, comprising
i) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent
with an oxide catalyst in a first reactor to obtain a fluid stream; j) contacting the fluid stream with an aromatic solvent to obtain a mixture;

k) separating the mixture into a liquid fraction and a gaseous fraction; l) separating the liquid fraction into 2 phases comprising:
iii. dimethyl carbonate (DMC) in combination with unconverted alcohol
and optionally CO2; and iv. the nitrile based dehydrating agent in combination with its amide derivative and the aromatic solvent. m) combining phase (i) with the gaseous fraction and subjecting the said combination to condensation to yield CO2 and a mixture of alcohol and DMC; n) subjecting the mixture of alcohol and DMC to about 1-4 rounds of distillation
to separate the alcohol and the DMC; o) contacting phase (ii) with a second catalyst in a second reactor; wherein the second catalyst converts amide derivative of the nitrile based dehydrating agent in the phase (ii) to the nitrile based dehydrating agent; and yields water and a hydrocarbon product comprising the nitrile based dehydrating agent and the aromatic solvent; p) subjecting the hydrocarbon product to about 1-4 rounds of distillation to separate the nitrile based dehydrating agent, water and the aromatic solvent; and wherein one or more of the obtained CO2, the nitrile based dehydrating agent and the alcohol are recycled back into the first reactor; and/or wherein the obtained aromatic solvent is recycled back into the second reactor and/or the HPS, optionally along with unconverted amide derivative of the nitrile based dehydrating agent. 18. A system (100) for continuous selective synthesis of dimethyl carbonate (DMC), the system comprising:
- a first reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating agent, the first reactor comprising at least one oxide catalyst to react with the CO2, the alcohol and the nitrile based dehydrating agent, wherein the first reactor is configured to discharge a first fluid;
- a high pressure separator (HPS) (12) fluidly coupled to the first reactor; wherein the HPS is configured to a receive an aromatic solvent along with the first fluid, wherein the solvent is adapted to solubilize the first fluid and the HPS is configured to discharge a gas fraction away from the liquid in the first fluid;
- a condenser (14) configured to receive the gas fraction from the HPS, the condenser configured to condense vapour products from the gas fraction;

- a flash separator fluidly (15) coupled to the HPS; wherein the flash separator is
configured to receive the liquid discharged from the HPS (12) and separate the said
liquid discharge into
a first phase comprising dimethyl carbonate (DMC) in combination with
unconverted alcohol and optionally CO2; and
a second phase comprising the nitrile based dehydrating agent in combination
with its amide derivative and the aromatic solvent;
wherein the first phase is selectively combined with the gas stream from the
HPS directed to the condenser;
- a first set of at least one distillation column(s) (16) fluidly connected to the condenser; wherein the first set of at least one distillation column is configured to receive condensed products from the condenser comprising alcohol and DMC, and to separate the alcohol from the DMC, wherein the DMC is collected in a first collection chamber (17);
- a second reactor (300) fluidly connected to the flash separator; wherein the second reactor is configured to receive the second phase from the flash separator;
- the second reactor comprising at least one second catalyst to react with the second phase in the presence of nitrogen gas or helium gas; wherein the second reactor is configured to convert amide derivative of the nitrile based dehydrating agent to the nitrile based dehydrating agent and yield water and a hydrocarbon product comprising the nitrile based dehydrating agent and the aromatic solvent;
- a second set of at least one distillation column(s) (18) fluidly coupled to the second reactor, to separate the hydrocarbon product into the aromatic solvent, water and the nitrile based dehydrating agent; and
- a line connecting the second set of at least one distillation column and the second reactor configured to comprise a molecular sieve (19) and/or the HPS to receive the separated aromatic solvent and reintroduce the aromatic solvent into the second reactor optionally along with unreacted amide derivative of the nitrile based dehydrating agent.

19. The system as claimed in claim 18, wherein the first (200) and the second (300) reactors and the HPS (12) comprise means for temperature and pressure control; and/or wherein the first reactor (200) is connected to the HPS (12) by a temperature-controlled channel.
20. The system as claimed in claim 18, further comprising a backpressure regulator (BPR) (13) coupled to the HPS, wherein the BPR is configured to maintain and regulate

pressure upstream of its inlet; and wherein the connection from the BPR (13) to the condenser (14) is maintained at room temperature.
21. The system as claimed in claim 18, wherein the condenser (14) is maintained between -5-10°C to condense vaporized components; wherein the condenser (14) is fluidly connected to the first set of distillation columns comprising two distillation columns (16) in succession; wherein gas emerging from the condenser (16) after the condensation of vapour products comprises CO2; and/or wherein the condenser is fluidly connected to the first reactor (200) for recycling of the said gas.
22. The system as claimed in claim 18, wherein the first set of distillation columns (16) is fluidly connected to the first reactor for recycling of the obtained alcohol; wherein the second set of distillation columns (18) is fluidly connected to the second reactor and/or the HPS for recycling of the obtained aromatic solvent, optionally along with unconverted amide derivative of the nitrile based dehydrating agent; wherein the connection between the second set of distillation columns (18) and the second reactor comprises a molecular sieve (19).