FORM 2
THE PATENTS ACT, 1970
[39 OF 1970]
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10 and rule 13]
“A PROCESS FOR SELECTIVE DIMETHYL CARBONATE (DMC) SYNTHESIS AND A SYSTEM THEREOF”
NAME AND ADDRESS OF THE APPLICANT: RELIANCE INDUSTRIES LIMITED 3rd Floor, Maker Chamber-IV, 222, Nariman Point, Mumbai - 400 021, Maharashtra, India
NATIONALITY: IN
The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD
The present disclosure relates to the field of organic compound synthesis. Particularly, the present disclosure provides a process for the selective synthesis of dimethyl carbonate (DMC). More particularly, the present disclosure provides a process for inhibiting catalyst deactivation in a process for selective DMC synthesis. Further provided herein is a system for facilitating the said process.
BACKGROUND OF THE DISCLOSURE
Dimethyl carbonate (DMC) is the most useful organic carbonate and benign substitute for phosgene and dimethyl sulfate which are highly toxic and corrosive carbonylating and methylating agents. DMC is used as electrolyte in Li-ion batteries and as starting material for polycarbonate resins. A promising future large volume use is as additive to gasoline and diesel fuels. IDMC represents a viable alternative to acetate esters and ketones in most applications, from paints to adhesives, due to its good solvency power.
Existing processes of commercial DMC production such as liquid phase oxidative carbonylation of CH3OH with CO and O2, vapour phase oxidative carbonylation of methyl nitrite and transesterification of ethylene carbonate use toxic and corrosive chemicals. Direct synthesis of DMC by carboxylation of methanol in presence of efficient dehydrating agent like aromatic nitriles technologically is attractive for full-scale development. However, catalyst deactivation is a major challenge for its upgradation and scale-up.
Other challenges with currently known processes include carbon monoxide generation, low reaction rate and yield or productivity, reliance on energy intensive steps, operation complexities, difficulties in large-scale production and catalyst regeneration.
Importantly, while considering the continuous production of DMC on a large scale, catalyst activity for prolonged time, 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.
SUMMARY OF THE DISCLOSURE
Addressing the aforesaid need in the art, the present disclosure provides a process for selective
synthesis of dimethyl carbonate (DMC) comprising:

contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
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 and pyrole-2-carbo nitrile, or any combination thereof; and/or wherein the oxide catalyst is selected from a group comprising Ceria (CeO2) based catalyst, Zirconia (ZrO2) and Praseodymium oxide (Pr2O3), Lanthanum oxide (La2O3), CexZr1-xO2, CexPr1-xO2, CexLa1-xO2 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 about 0.9 to about 0.99.
In some embodiments, the oxide catalyst is loaded into the reactor before the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent; and the oxide catalyst is activated by heating the reactor to a temperature of about 250°C to about 400°C in the presence of air.
In some embodiments, the air in the reactor is zero air or pure oxygen; wherein the zero air or the pure oxygen is continuously circulated in the reactor; the air is introduced at a space velocity of about 15 h-1 to about 225 h-1; the air and the carbon dioxide (CO2) are introduced into the reactor as a gas stream; wherein the oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol %; and/or CO2 to O2 volume ratio in the reactor ratio ranges from about 18 to about 300.
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 150°C and pressure of about 30 bar to about 50 bar; the CO2 is introduced into the reactor at a space velocity of about 600 h-1 to about 2000 h-1; and/or the alcohol and the nitrile based dehydrating agent are introduced into the reactor at LHSV of about 2 h-1 to about 5 h-1.
In some embodiments, the fluid stream is subjected to separation at a temperature of about 40°C to about 60°C to obtain a liquid stream and a gaseous stream; the liquid stream is the DMC; and the gaseous stream is subjected to secondary condensation.

In some embodiments, the secondary condensation condenses vapourized DMC and unconverted methanol in the gaseous stream; wherein the secondary condensation yields DMC and methanol and a remainder gas; wherein the remainder gas comprises a mixture of CO2 and zero air; wherein the remainder gas is recycled into the process without further purification.
In some embodiments, yield of the DMC ranges from about 40 mol% to about 80 mol%; wherein yield of undesired products methyl carbamate (MC), methyl picolinate (MP) and methyl picolinimidate (MPI) ranges from about 0.01% to about 1%; and/or yield of the DMC is at least 20 % higher after about 100 hours of run than a process conducted in the absence of air.
Further provided herein is a process for inhibiting catalyst deactivation in a process for selective dimethyl carbonate synthesis from carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent comprising providing controlled delivery of air to a reactor facilitating continuous and selective dimethyl carbonate synthesis from the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent.
The present disclosure also provides system (100) for selective synthesis of dimethyl carbonate (DMC), the system comprising:
- a reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating agent, the reactor comprising at least one catalyst to react with the CO2, alcohol and dehydrating agent, the reactor fluidly connected to a continuous supply of air;
- an air dispenser (12) fluidly coupled to the reactor to facilitate continuous supply of air into the reactor (200);
- a gas liquid separator (13) fluidly coupled to the reactor by a temperature controlled channel; the gas liquid separator configured to receive a fluid stream from the reactor; the gas liquid separator configured to discharge a liquid to a first collection chamber and a gas stream away from the liquid;
- a backpressure regulator (BPR) (14) connected to the gas liquid separator, the BPR configured to maintain and regulate pressure of the gas stream upstream of its inlet;
- a secondary condenser (15) configured to receive the gas stream from the BPR to condense vapour products from the gas stream; wherein the secondary condenser is connected to a gas outlet (16) and a second collection chamber (17).

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES 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:
Figure 1 provides a diagrammatic representation of the system of the present disclosure.
Figure 2 depicts results of the selectivity and conversion efficiency of the catalyst that is achieved using the process of the present disclosure up to about 500 hours of operation.
Figure 3 depicts results of the selectivity and conversion efficiency of the catalyst that is achieved in the absence of introduction of air in the reactor as per the process of the present disclosure up to about 250 hours of operation.
DETAILED DESCRIPTION OF THE DISCLOSURE
In view of the limitations discussed above, and to remedy the need in the art for a process facilitating the continuous production of DMC on a large scale where catalyst activity is retained for a prolonged period of time, the present disclosure provides a simple process for DMC synthesis from alcohol, carbon dioxide (CO2), in the presence of a nitrile based dehydrating agent and a small quantity of air.
However, before delving into the details of the said process, definitions of some terms/phrases used throughout the present disclosure are provided below.
Definitions
Throughout the present disclosure, the abbreviation “DMC” refers to dimethyl carbonate.
Throughout the present disclosure, the term “reactants” refers to one or more of carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent, which act as starting material to synthesize 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 terms “continuous supply” and “circulating” or equivalent terms have been used in the context of air that is present in the reactor to indicate consistent presence of a trivial amount of air in the reactor, throughout the reaction.
The term “zero air” refers to air produced by mixing pure oxygen with pure nitrogen, thereby eliminating all impurities found in ambient air. Particularly, zero air comprises about 19.9-21.9% oxygen and about 78.1-80.1% nitrogen.
The term “fluid” refers to a stream comprising liquid and gaseous components.
The term “remnant gas” or “remainder gas” refers to the remaining gas obtained after the secondary condensation of the vapourized components in the secondary condenser.
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 a reaction while actively or passively suppressing the formation of other products that are of low economic significance.
Throughout the present disclosure, the term “undesired products” refers to 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.
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 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 envisages extended boundaries above and below the numerical value(s) defined. In general, the term "about" is used herein to modify a numerical value(s) above and below the stated value(s) by a variance of up to 5-10%.
With respect to the use of any plural and/or singular terms herein, those having skill in the art can extrapolate from plural to singular form and/or from singular to plural form without exceeding the scope of the present disclosure. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

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 example, in case of an embodiment 1 reciting 3 alternatives A, B and 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;
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
In order to address the issues pertaining to deactivation of oxide catalysts in the selective synthesis of dimethyl carbonate (DMC), the present disclosure provides a process for the continuous synthesis of DMC from carbon dioxide (CO2) and alcohol using a nitrile based dehydrating agent characterized by a continuous supply of trivial amount of air during the reaction.
Particularly, the present disclosure provides a process for selective synthesis of dimethyl
carbonate (DMC) comprising:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the alcohol is selected from a group comprising methanol, ethanol, propanol, butanol and phenol, or any combination thereof.
In an exemplary embodiment, the alcohol is methanol.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), methanol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
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 2-cyanopyridine (2-CP), 3-cyanopyridine (3-CP), 4- cyano pyridine (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).
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and 2-cyanopyridine (2-CP) with an oxide catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), methanol and 2-cyanopyridine (2-CP) with an oxide catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
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 (Pr2O3), or any combination thereof.
In an exemplary embodiment, the oxide catalyst is a Ceria (CeO2) based catalyst.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with a Ceria (CeO2) based catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), methanol and a nitrile based dehydrating agent with a Ceria (CeO2) based catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:

contacting carbon dioxide (CO2), methanol and 2-cyanopyridine (2-CP) with a Ceria (CeO2) based catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the CeO2 based 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.
In an exemplary embodiment, the CeO2 based catalyst is CexZr1-xO2, wherein x varies from 0.9 to 0.99.
In some embodiments, the alcohol is selected from a group comprising methanol, ethanol, propanol, butanol and phenol, or any combination thereof; the nitrile based dehydrating agent is selected from a group comprising 2-cyanopyridine, 3-cyanopyridine, 4-cyanopyridine, 2-Furo nitrile and pyrole-2-carbo nitrile, or any combination thereof; and/or the oxide catalyst is selected from a group comprising Ceria (CeO2) based catalyst, Zirconia (ZrO2) and Praseodymium oxide (Pr2O3), Lanthanum oxide (La2O3), CexZr1-xO2, CexPr1-xO2, CexLa1-xO2 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 about 0.9 to about 0.99
Without intending to be limited by theory, when the catalyst is a Ceria (CeO2) based catalyst, the presence of air in the reactor obviates the formation of heteroaromatic amide anion interaction with CeO2 surface sites, thereby retarding catalyst deactivation.
Further, when the process is characterized by the use of the CeO2 based catalyst, one of the objects of the present disclosure is to maintain a ratio between Ce4+ and Ce3+ that promotes alcohol conversion and/or DMC selectivity. Optimum Ce4+/Ce3+ ratio, with higher amount of Ce4+ is associated with optimum defects as well as acid-base sites, which in turn results in high DMC yield. On the other hand, high concentration of Ce3+ leads to poisoning by large amounts of carbonaceous contamination.
In some embodiments, the oxide catalyst is in the form of a powder. In some embodiments, the said powder catalyst is optionally stabilized and shaped with a binder selected from a group comprising silica, preferably colloidal silica, silica-alumina and ethyl silicate, or any combination thereof.
In some embodiments, ratio between the oxide catalyst and the binder ranges from about 3 :1 to about 9:1.

In some embodiments, the oxide catalyst is a CeO2 based powder catalyst stabilized and shaped with a binder such as colloidal silica.
In a non-limiting embodiment, the mixing and shaping is performed prior to introduction of the catalyst into the reactor.
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 a non-limiting embodiment, surface area of the shaped oxide catalyst is about 100 m2/g to about 110 m2/g, about 110 m2/g to about 120 m2/g, about 120 m2/g to about 130 m2/g, about 130 m2/g to about 140 m2/g, about 100 m2/g, about 105 m2/g, about 110 m2/g, about 115 m2/g, about 120 m2/g, about 125 m2/g, about 130 m2/g, about 135 m2/g or about 140 m2/g.
In some embodiments, the acidity /basicity ratio of the oxide catalyst ranges from about 0.8 to about 3.5.
In a non-limiting embodiment, the acidity /basicity ratio of the oxide catalyst is about 0.8 to about 1, about 1 to about 1.5, about 1.5 to about 2, about 2 to about 2.5, about 2.5 to about 3, about 3 to about 3.5, about 0.8, about 1, about 1.5, about 2, about 2.5, about 3 or 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, the oxide catalyst is a powder catalyst, optionally stabilized and shaped with a binder selected from a group comprising colloidal silica, silica-alumina and ethyl silicate, or any combination thereof; 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 3.5.
In some embodiments, the oxide catalyst is used in combination with a diluent such as but not limited to Silicon Carbide (SiC).
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 the tendency for pressure drop during the reaction and improves heat transfer.

In some embodiments, weight ratio between the oxide catalyst and the diluent ranges from about 1:1 to about 3:1.
In a non-limiting embodiment, weight ratio between the oxide catalyst and the diluent is about 1:1, about 2:1 or about 3:1.
In some embodiments, the oxide catalyst is mixed with a diluent in the catalyst bed of the reactor; the diluent is silicon carbide (SiC); and the ratio between the oxide catalyst and the diluent ranges from about 1:1 to about 3:1.
In some embodiments, the oxide catalyst is loaded into the reactor before introduction of the carbon dioxide (CO2), the alcohol and the dehydrating agent in the reactor and activated by heating the reactor to a temperature of about 250ºC to about 400ºC.
In a non-limiting embodiment, the oxide catalyst is loaded into the reactor before introduction of the carbon dioxide (CO2), the alcohol and the dehydrating agent in the reactor and activated by heating the reactor to a temperature of about 250ºC to about 300ºC, about 300ºC to about 350ºC, about 350ºC to about 400ºC, about 250ºC, about 300ºC, about 350ºC or about 400ºC.
In some embodiments, the activation of the oxide catalyst is performed in the presence of air.
In some embodiments, the catalyst is loaded into the reactor before the carbon dioxide (CO2), the alcohol and the dehydrating agent, and activated by heating the reactor to a temperature of about 250ºC to about 400ºC in the presence of air.
In some embodiments, the temperature of the reactor may be reduced prior to introduction of the reactants i.e. the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- heating a reactor comprising an oxide catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:

- mixing an oxide catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
- heating a reactor comprising the stabilized catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing an oxide catalyst with a diluent such as but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
- heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing an oxide catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
- mixing the stabilized catalyst with a diluent such as but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
- heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing an oxide powder catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
- subjecting the stabilized catalyst to shaping to obtain a shaped catalyst;

- introducing the shaped catalyst in combination with a diluent such as but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
- heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing a ceria-based powder catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
- introducing the stabilized catalyst into a reactor and heating the reactor to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing a ceria-based powder catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
- subjecting the stabilized catalyst to shaping to obtain a shaped catalyst;
- introducing the shaped catalyst into a reactor;
- heating the reactor comprising the shaped catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing a ceria-based powder catalyst with a diluent such as but not limited to
Silicon Carbide (SiC) in the catalyst bed of a reactor;

- heating the reactor to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- mixing a ceria-based powder catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
- subjecting the stabilized catalyst to shaping to obtain a shaped catalyst;
- introducing the shaped catalyst in combination with a diluent such as but not limited to Silicon Carbide (SiC) in the catalyst bed;
- heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, both, the activation of the oxide catalyst and the reaction between the reactants in the reactor takes place in presence of air.
Accordingly, in some embodiments, the process of the present disclosure is characterized by continuous supply of a trivial amount of air.
In some embodiments, the air supplied is supplied to the reactor at a rate ranging from about 1 ml/minute to about 15 ml/minute.
In some embodiments, the air is introduced into the reactor at a space velocity of about 15 h-1 to about 225 h-1.
In a non-limiting embodiment, the air is introduced at a space velocity of about 15 h-1 to about 50 h-1, about 50 h-1 to about 100 h-1, about 100 h-1 to about 150 h-1, about 150 h-1 to about 200 h-1, about 200 h-1 to about 225 h-1, about 15 h-1, about 50 h-1, about 100 h-1, about 150 h-1, about 200 h-1 or about 225 h-1.
In some embodiments, the air is zero air or pure oxygen.

In some embodiments, the zero air comprises about 19.9% to about 21.9% O2 and the balance is about 78.1% to about 80.1% of N2.
In a non-limiting embodiment, the zero air comprises about 19.9%, about 20% or about 21.9% O2 and the balance is about 78.1%, about 80% or about 80.1% of N2.
In some embodiments, the process of the present disclosure is characterized by continuous supply of a trivial amount of zero air or pure oxygen in the reactor.
In some embodiments, the air and the carbon dioxide (CO2) are introduced into the reactor as a gas stream that facilitates controlled delivery of air along with the CO2. In some embodiments, the said gas stream may be introduced into the reactor after catalyst activation as described above.
Accordingly, in some embodiments, envisaged herein is a process for selective synthesis of dimethyl carbonate (DMC) comprising:
contacting CO2, alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in the presence of a gas stream facilitating controlled delivery of air along with the CO2, to obtain a fluid stream comprising the DMC.
In some embodiments, oxygen (O2) content in the air circulated in the reactor is maintained at about 0.5 vol% to about 15 vol % of the total gas stream.
In some embodiments, the CO2 to O2 volume ratio in the reactor ranges from about 18 to about 300. In a non-limiting embodiment, the CO2 and air are supplied to the reactor from separate sources and mixed to one line prior to entering the reactor as a gas stream.
In some embodiments, the air in the reactor is zero air or pure oxygen; wherein the zero air or the pure oxygen is continuously circulated in the reactor; wherein the air is introduced at a space velocity of about 15 h-1 to about 225 h-1; wherein the air and the carbon dioxide (CO2) are introduced into the reactor as a gas stream; wherein the oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol %; and/or wherein CO2 to O2 volume ratio in the reactor ratio ranges from about 18 to about 300.
In some embodiments, oxygen (O2) content in the gas stream is maintained at about 0.5 vol%, about 1 vol%, about 1.5 vol%, about 2 vol%, about 2.5 vol%, about 3 vol%, about 3.5 vol%, about 4 vol%, about 4.5 vol%, about 5 vol%, about 5.5 vol%, about 6 vol%, about 6.5 vol%, about 7 vol%, about 7.5 vol%, about 8 vol%, about 8.5 vol%, about 9 vol%, about 9.5 vol%,

about 10 vol%, about 10.5 vol%, about 11 vol%, about 11.5 vol%, about 12 vol%, about 12.5 vol%, about 13 vol%, about 13.5 vol%, about 14 vol%, about 14.5 vol%, or about 15 vol %.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of a continuous supply of air supplied at about 1 ml/minute to about 15 ml/minute into the reactor to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of zero air or pure oxygen to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of continuous supply of zero air or pure oxygen supplied at about 1 ml/minute to about 15 ml/minute into the reactor to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and 2-CP with an oxide catalyst in a reactor in
presence of continuous supply of zero air or pure oxygen supplied at about 1 ml/minute to
about 15 ml/minute into the reactor to obtain a fluid stream comprising the DMC.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), methanol and 2-CP with a ceria-based catalyst in a reactor in
presence of continuous supply of zero air or pure oxygen supplied at about 1 ml/minute to
about 15 ml/minute into the reactor to obtain a fluid stream comprising the DMC.

In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide
catalyst in a reactor in presence of a gas stream facilitating controlled delivery of air along with
the CO2 obtain a fluid stream comprising the DMC;
wherein oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol
%.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide
catalyst in a reactor in presence of a gas stream facilitating controlled delivery of air along with
the CO2 to obtain a fluid stream comprising the DMC;
wherein oxygen (O2) content in the gas stream is maintained at about 0.5 vol%, about 1 vol%,
about 1.5 vol%, about 2 vol%, about 2.5 vol%, about 3 vol%, about 3.5 vol%, about 4 vol%,
about 4.5 vol%, about 5 vol%, about 5.5 vol%, about 6 vol%, about 6.5 vol%, about 7 vol%,
about 7.5 vol%, about 8 vol%, about 8.5 vol%, about 9 vol%, about 9.5 vol%, about 10 vol% ,
about 10.5 vol% , about 11 vol% , about 11.5 vol% , about 12 vol% , about 12.5 vol% , about
13 vol% , about 13.5 vol% , about 14 vol% , about 14.5 vol% , or about 15 vol %.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), alcohol and 2-CP with an oxide catalyst in a reactor in
presence of a gas stream facilitating controlled delivery of air along with the CO2 to obtain a
fluid stream comprising the DMC;
wherein oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol
%.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC)
comprises:
contacting carbon dioxide (CO2), methanol and 2-CP with a ceria-based catalyst in a reactor in
presence of a gas stream facilitating controlled delivery of air along with the CO2 to obtain a
fluid stream comprising the DMC;
wherein oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol
%.

In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
a) heating a reactor comprising an oxide catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the oxide catalyst; and
b) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor to obtain a fluid stream comprising the DMC; wherein step (b) is performed in presence of a continuous supply of air supplied at a rate of about 1 ml/minute to about 15 ml/minute to the reactor.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
a) mixing an oxide catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst and/or mixing the oxide catalyst with diluent including but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
b) heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
c) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor to obtain a fluid stream comprising the DMC; wherein step (c) is performed in presence of a continuous supply of air at a rate ranging from about 1 ml/minute to about 15 ml/minute in the reactor.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
a) mixing an oxide catalyst with diluent including but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
b) heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC to activate the catalyst; and
c) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor to obtain a fluid stream comprising the DMC; wherein step (b) is performed in presence of a continuous supply of air at a rate ranging up to about 100 ml/minute into the reactor; and/or
wherein step (c) is performed in presence of a continuous supply of air at a rate of about 1 ml/minute to about 15 ml/minute into the reactor.

In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
a) mixing an oxide catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
b) mixing the stabilized catalyst with a diluent such as but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
c) heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
d) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor to obtain a fluid stream comprising the DMC; wherein step (c) is performed in presence of a continuous supply of air at a rate of up to about 100 ml/minute in the reactor; and
wherein step (d) is performed in presence of a continuous supply of air at a rate of about 1 ml/minute to about 15 ml/minute into the reactor.
In some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
a) mixing an oxide catalyst with a binder such as but not limited to colloidal silica to obtain a stabilized catalyst;
b) mixing the stabilized catalyst with a diluent such as but not limited to Silicon Carbide (SiC) in the catalyst bed of a reactor;
c) heating the reactor comprising the catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst; and
d) contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor to obtain a fluid stream comprising the DMC; wherein step (c) is performed in presence of a continuous supply of air ranging up to about 100 ml/minute in the reactor; and
wherein step (c) is performed in presence of a continuous supply of air at a rate of up to about 100 ml/minute into the reactor; and/or
wherein step (d) is performed in presence of a continuous supply of air at a rate of about 1 ml/minute to about 15 ml/minute into the reactor.
In some embodiments, the reactor 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 reactor is selected from a group comprising continuous-stirred 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 reactor is a fixed bed continuous flow type reactor.
The temperature of the reactor is reduced after activation of the catalyst.
In some embodiments, as briefly mentioned in one of the previous paragraphs, post catalyst activation, temperature of the reactor is reduced and maintained at about 100ºC to about 150ºC, preferably at a pressure of about 30 bar to about 50 bar for the reaction to proceed upon introduction of the reactants into the reactor.
In a non-limiting embodiment, post catalyst activation, the reactor is maintained at a temperature of about 100ºC, about 110ºC, about 120ºC, about 130ºC, about 140ºC or about 150ºC, preferably at a pressure of about 30 bar, about 40 bar or about 50 bar for the reaction to proceed upon introduction of the reactants into the reactor.
Thus, in some embodiments, the carbon dioxide (CO2), the alcohol and the dehydrating agent are contacted with the catalyst at a temperature of about 100ºC to about 150ºC and at a pressure of about 30 bar to about 50 bar. The said feature may be applicable to each of the above defined embodiments of the present disclosure and are not repeated for the sake of brevity.
Thus, in some embodiments, the process for selective synthesis of dimethyl carbonate (DMC) comprises:
- heating a reactor comprising an oxide catalyst to a temperature of about 250ºC to about 400ºC in presence of air to activate the catalyst;
- reducing the temperature of the reactor to about 100ºC to about 150ºC; and
- contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with the activated catalyst in the reactor in presence of air to obtain a fluid stream comprising the DMC.
In some embodiments, the CO2 is introduced as a gas into the reactor; and the alcohol and the dehydrating agent are introduced as a liquid into the reactor.

In some embodiments, the CO2 is introduced as a gas into the reactor, independent of the air supplied into the reactor. In some embodiments, the CO2 is introduced into the reactor as a separate stream, different from the air supplied into the reactor.
In some embodiments, as mentioned above, the CO2 is introduced into the reactor admixed with the air supplied into the reactor.
In some embodiments, the CO2 supply into the reactor is started only post catalyst activation. Similarly, the alcohol and the dehydrating agent are introduced into the reactor only post catalyst activation.
The reactants are introduced into the reactor at a suitable flow rate that may be optimized 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 600 h-1 to about 2000 h-1.
In a non-limiting embodiment, the CO2 is introduced into the reactor at a space velocity of about 600 h-1 to about 1000 h-1, about 1000 h-1 to about 1500 h-1, about 1500 h-1 to about 2000 h-1, about 600 h-1, about 800 h-1, about 1000 h-1, about 1200 h-1, about 1400 h-1, about 1600 h-1, about 1800 h-1 or about 2000 h-1.
In some embodiments, the alcohol and the dehydrating agent are introduced into the reactor at Liquid hourly space velocity (LHSV) of about 2 h-1 to about 5 h-1.
In a non-limiting embodiment, the alcohol and the dehydrating agent are introduced into the reactor at Liquid hourly space velocity (LHSV) of about 2 h-1, about 3 h-1, about 4 h-1, about 5 h-1.
In some embodiments, the CO2 is introduced into the reactor at a space velocity of about 600 h-1 to about 2000 h-1 ml/min; and the alcohol and the dehydrating agent are introduced into the reactor at a rate of about 0.1 ml/min to about 0.3 ml/min; and an LHSV of about 2 h-1 to about 5 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 150°C and pressure of about 30
bar to about 50 bar; the CO2 is introduced into the reactor at a space velocity of about 600 h-1 to about 2000 h-1; and/or the alcohol and the nitrile based dehydrating agent are introduced into the reactor at LHSV of about 2 h-1 to about 5 h-1.

In some embodiments, the ratio between the alcohol and the dehydrating agent ranges from about 1:2 to about 2:1.
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 1:3 to about 1:0.5.
In an exemplary embodiment, the ratio between the alcohol and the CO2 is about 1:1.
In some embodiments, the ratio between the carbon dioxide (CO2), the alcohol and the dehydrating agent ranges from about 1:1:1 to about 2:2:1.
In an exemplary embodiment, the ratio between the carbon dioxide (CO2), the alcohol and the dehydrating agent is about 2:2:1.
Without intending to be limited by theory, the above defined process yields products in liquid and gaseous phases, wherein said products emerge as a fluid stream from the reactor.
In some embodiments, the fluid stream is subjected to separation at a temperature of about 40°C to about 60°C to obtain a liquid stream and a gaseous stream.
In some embodiments, the fluid stream is subjected to separation at a temperature of about 40°C, about 45°C, about 50°C, about 55°C or about 60°C to obtain a liquid stream and a gaseous stream.
In some embodiments, the liquid stream comprises DMC and unconverted MeOH and is collected after separation of the liquid and the gaseous streams.
In some embodiments, the said separation of the fluid stream into the liquid stream and the gaseous stream is performed in a gas-liquid separator.
In some embodiments, the gas-liquid separator is a primary condenser.
In some embodiments, the separation of the fluid stream into the liquid stream and the gaseous stream is performed in a primary condenser maintained at a temperature of about 40°C to about 60°C.
In a non-limiting embodiment, the separation of the fluid stream into the liquid stream and the gaseous stream is performed in a primary condenser maintained at a temperature of about 40°C, about 45°C, about 50°C, about 55°C or about 60°C.

In some embodiments, the connection between the reactor and the gas-liquid separator/primary condenser is also maintained at a temperature of about 40°C to about 60°C.
In a non-limiting embodiment, the connection between the reactor and the gas-liquid separator/primary condenser is also maintained at a temperature of about 40°C, about 45°C, about 50°C, about 55°C or about 60°C.
In some embodiments, the gaseous stream from the gas-liquid separator/primary condenser is subjected to further condensation.
In some embodiments, the fluid stream is subjected to separation at a temperature of about 40°C to about 60°C to obtain a liquid stream and a gaseous stream; wherein the liquid stream is the DMC; and wherein the gaseous stream is subjected to secondary condensation.
In a non-limiting embodiment, the gaseous stream is subjected to a secondary condensation at a temperature of about 5°C to about 10°C.
In some embodiments, the gaseous stream is subjected to condensation at a temperature of about 5°C, about 6°C, about 7°C, about 8°C, about 9°C or about 10°C.
In some embodiments, the secondary condensation of the gaseous stream is performed in a secondary condenser. In a non-limiting embodiment, the gaseous stream may be routed to the secondary condenser through a backpressure regulator (BPR).
In some embodiments, the secondary condensation condenses vapourized DMC and unconverted methanol in the gaseous stream; wherein the secondary condensation yields DMC, methanol and a remainder gas.
In some embodiments, the DMC obtained after secondary condensation is collected.
In some embodiments, the DMC collected after secondary condensation is optionally mixed with the DMC obtained after the separation of the liquid and gas streams in the primary condenser.
In some embodiments, the remainder gas comprises a mixture of CO2 and zero air.
In some embodiments, the secondary condensation condenses vapourized DMC and unconverted methanol in the gaseous stream; wherein the secondary condensation yields DMC, methanol and a remainder gas; and wherein the remainder gas comprises a mixture of CO2 and zero air.

In some embodiments, the remainder gas is recycled into the process without further purification. Accordingly, in some embodiments, the outlet of the remainder gas from the secondary condenser is connected to the reactor.
In some embodiments, the secondary condensation condenses vapourized DMC and unconverted methanol in the gaseous stream; the secondary condensation yields DMC and methanol and a remainder gas; and the remainder gas comprises a mixture of CO2 and zero air; the remainder gas is recycled into the process without further purification.
In some embodiments, the remainder gas arising from the secondary condensation, or a part thereof may be subjected to gas chromatography. Without intending to be limited by theory, the gas chromatography rules out complete or partial oxidation of alcohol.
In a non-limiting embodiment, the process of the present disclosure facilitates selective formation of DMC from alcohol without formation of formaldehyde via alcohol oxidation or CO2/H2 via alcohol decomposition.
In a non-limiting embodiment, yield of the DMC ranges from about 40 mol% to about 80 mol%.
In a non-limiting embodiment, yield of the DMC is about 40 mol%, about 45 mol%, about 50 mol%, about 55 mol%, about 60 mol%, about 65 mol%, about 70 mol%, about 75 mol% or about 80 mol%.
Accordingly, out of the total products arising from the process, about 40 mol% to about 80 mol% is DMC. The remaining 20 mol % comprises of unconverted methanol and methyl carbamate.
In some embodiments, yield of undesired products methyl carbamate (MC), Methyl picolinate (MP) and methyl picolinimidate (MPI) ranges from about 0.01% to about 1%.
In a non-limiting embodiment, yield of undesired products methyl carbamate (MC), Methyl picolinate (MP) and methyl picolinimidate (MPI) is about 0.01%, about 0.25%, about 0.5%, about 0.75% or about 1%.
In some embodiments, yield of the DMC is at least about 20 % higher after about 100 hours of run than a process conducted in the absence of air.
In some embodiments, the yield of the DMC ranges from about 40 mol% to about 80 mol%; the yield of undesired products methyl carbamate (MC), methyl picolinate (MP) and methyl

picolinimidate (MPI) ranges from about 0.01% to about 1%; and/or the yield of the DMC is at least 20 % higher after about 100 hours of run than a process conducted in the absence of air.
Therefore, the process of the present disclosure provides a significantly high yield of DMC while restricting the formation of undesired products, without or with marginal loss in selectivity of the catalyst.
In accordance with the objective of the present disclosure, in another embodiment, provided herein is a process for inhibiting catalyst deactivation in a process for selective dimethyl carbonate synthesis from carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent comprising providing controlled delivery of air along with the CO2 in a gas stream to a reactor facilitating continuous and selective dimethyl carbonate synthesis from the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent.
As mentioned above, in some embodiments, the air is zero air or pure oxygen.
In some embodiments, the zero air comprises about 19.9% to about 21.9% O2 and the balance is about 78.1% to about 80.1% of N2.
In some embodiments, the process is a continuous process, suitable for industrial scale application.
Each of the embodiments provided while characterizing the process of selective dimethyl carbonate synthesis as defined in the earlier paragraphs of the present disclosure are equally applicable to the process for inhibiting catalyst deactivation in the process for DMC synthesis and are not repeated for reasons of brevity.
In some embodiments, the above process(s) of the present disclosure enhances the long-term stability of the catalyst employed in the above process.
In some embodiments, in view of the above process(s) of the present disclosure, the activity-selectivity of the catalyst employed in the continuous process as described above remains the same after about 500 hours of operation/run or more.
Further provided in the present disclosure is a system (100) for selective synthesis of dimethyl carbonate (DMC), the system comprising:
- a reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating agent, the reactor comprising at least one catalyst to react with the CO2, the alcohol

and the dehydrating agent, the reactor fluidly connected to a continuous supply of air;
- an air dispenser (12) fluidly coupled to the reactor to facilitate continuous supply of air into the reactor (200);
- a gas liquid separator/primary condenser (13) fluidly coupled to the reactor by a temperature-controlled channel; the gas liquid separator/primary condenser configured to receive a fluid stream from the reactor; the gas liquid separator/primary condenser configured to discharge a liquid to a first collection chamber and a gas stream away from the liquid;
- a backpressure regulator (BPR) (14) connected to the gas liquid separator/primary condenser, the BPR configured to maintain and regulate pressure of the gas stream upstream of its inlet; and
- a secondary condenser (15) configured to receive the gas stream from the BPR to condense vapour products from the gas stream; wherein the secondary condenser is connected to a gas outlet (16) and a second collection chamber (17).
In some embodiments, the reactor (200) is selected from a group comprising continuous-stirred 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 reactor (200) is a fixed bed continuous flow type reactor.
In some embodiments, the reactor (200) is characterized by a continuous supply of air from the air dispenser (12).
In some embodiments, the amount of air continuously supplied to the reactor (200) is metered. Accordingly, the connection from the air dispenser (12) to the reactor to facilitate continuous supply of air into the reactor is metered, wherein the metering is manual or automated.
In some embodiments, the CO2 is supplied into the reactor through the same line as the air.
In some embodiments, the CO2 is supplied through a line different from that used for the air supply.
In a non-limiting embodiment, the CO2 and air are supplied to the reactor from separate sources and mixed to one line prior to entering the reactor.

In some embodiments, the reactor comprises a mechanism for temperature and pressure control.
In some embodiments, the reactor is heated to a temperature of about 250°C to about 400°C after introduction of catalyst.
In some embodiments, the oxide catalyst is loaded into the reactor before the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent; and the oxide catalyst is activated by heating the reactor to a temperature of about 250°C to about 400°C in the presence of air.
In some embodiments, the reactor is maintained at a temperature of about 100°C to about 150°C after introduction of the CO2, alcohol and nitrile based dehydrating agent.
In some embodiments, the gas-liquid separator/primary condenser comprises a mechanism for temperature and pressure control. In some embodiments, the gas-liquid separator/primary condenser is maintained at a temperature of about 40°C to about 60°C.
In some embodiments, the connection between the reactor and the gas-liquid separator is temperature regulated and maintained at a temperature of about 40°C to about 60°C.
In some embodiments, the connection from the BPR to the secondary condenser is maintained at room temperature.
In some embodiments, the secondary condenser is maintained at a temperature of about 5°C to about 10°C to condense vaporized components.
In some embodiments, the connection between the reactor (200) and the gas-liquid separator
(13) is maintained at a temperature of about 40°C to about 60°C; the connection from the BPR
(14) to the secondary condenser (13) is maintained at room temperature; and/or the secondary condenser (15) is maintained at a temperature of about 5°C to about 10°C to condense vaporized components.
In some embodiments, the secondary condenser comprises a gas outlet connected to a gas chromatography column configured to detect oxidation of the alcohol.
In some embodiments, the gas outlet is from the secondary condenser is connected to the reactor to facilitate recycling of the remainder gas into the reactor.
In a non-limiting embodiment, each of the air dispenser (12), the reactor (200), the gas liquid separator/primary condenser (13) and the secondary condenser (15) may be provided with valves. These control valves being located in immediate vicinity of the air dispenser (12), the

reactor (200), the gas liquid separator/primary condenser (13) and the secondary condenser (15) 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 air dispenser (12), the reactor (200), the gas liquid separator (13) and the secondary condenser (15). In an embodiment the valves may be manually operated or actuator-controlled e.g., programmable logic controller (PLC).
In an illustrative embodiment as seen in Fig. 1, the system (100) may include a reactor (200) configured to receive a gas stream, the said reactor comprising at least one catalyst to react with CO2, alcohol and dehydrating agent in presence of a controlled supply of air facilitated by fluid connection of the reactor with an air dispenser (12), and wherein the reactor comprises a manual or automated mechanism for temperature and pressure control. The system further comprises a gas liquid separator/primary condenser (13) fluidly coupled to the reactor by a temperature-controlled channel; wherein the gas liquid separator/primary condenser is preferably maintained at a temperature of about 40°C-60°C and is configured to receive a fluid product stream and discharge a liquid to a first collection chamber and a gas stream away from the liquid. The system may comprise a backpressure regulator (BPR) (14) connected to the gas liquid separator, wherein the BPR is configured to maintain and regulate pressure of the gas stream upstream of its inlet. The system comprises a secondary condenser (15) configured to receive the gas stream from the BPR, wherein the secondary condenser is configured to condense vapour products from the gas stream arising from the gas liquid separator. The secondary condenser is connected to a gas outlet (16) and a second collection chamber (17) for collection of the products, such that the DMC and methanol are collected in the second collection chamber (17) and a remainder gas is sent to the gas outlet. The gas outlet of the secondary condenser is optionally connected to a gas chromatography column connected to configured to detect possible oxidation of alcohol. In some embodiments, the gas outlet is connected to the reactor to facilitate recycling of the remainder gas.
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 various features and advantageous details thereof in the description. Descriptions of well-known/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. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure 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 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
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.
Example 1: Catalyst preparation
About 180 gm of Ce0.95Zr0.50O2, about 60 ml of colloidal silica and about 70 ml of water were mixed at room temperature and further dried at about 110 °C overnight. The dried sample was subsequently calcined at about 550 °C for about 4 hours to obtain a shaped catalyst. Acidity of the final catalyst was about 0.21 mmol/g and basicity of the final catalyst was about 0.08 mmol/g.
Subsequently, the catalyst was activated in the reactor in presence of equal proportion of Silicon Carbide at about 300 °C in presence of zero air comprising about 78.9-80.9% N2 and about 19.1-21.1% O2 at a flow rate of about 100 ml/minute prior to all reaction runs. The reactor was a continuous fixed bed reactor down-flow reactor of height about 62 cm and Inner Diameter (ID) about 1.57 cm with a catalyst bed length of 3-4 cm. The reactor was equipped with a thermowell of diameter about 3 mm and length about 40 mm for the estimation of catalyst bed temperature.

Example 2: DMC synthesis as per the present disclosure
After the catalyst loading at a volume of about 4cc and its activation as per example 1, the reactor was pressurized up to 38 bar and the temperature was raised to 130ºC. CO2 gas flow of 55 ml/min (methanol: CO2 molar ratio = 1:1) was maintained under 38 bar pressure. Subsequently zero air comprising about 78.9-80.9% N2 and about 19.1-21.1% O2 was introduced in the reactor in the same line as CO2 at a flow rate of about 15 mL/min using Mass flow controller (MFC). Liquid feed, Methanol & 2 CP mixture, 2:1 molar ratio, were pumped into the reactor using HPLC pump at LHSV 3 h-1. The reactor outlet was connected to the gas-liquid separator/primary condenser followed by back pressure regulator (BPR) and then the secondary condenser was maintained at about 5°C to about 10°C, where the temperature of post reactor line and gas-liquid separator was maintained at about 40-60°C. About 4.5 g/hr of DMC was collected from the gas-liquid separator in the first product collection chamber. Thereafter, post condensation, the vaporized fraction of DMC was obtained in liquid form and collected in the second product collection chamber.
The product analysis was performed through gas chromatography. It was seen that selectivity and activity of the catalyst was consistently maintained for at least about 500 hours of operation (Figure 2).
Example 3: Comparative example - Effect of absence of air
After the catalyst loading and its activation as described in example 1, the reactor was pressurized to about 38 bar and the temperature was adjusted to about 130ºC. CO2 gas flow was initiated at a flow rate of about 55 ml/min, the reactor was maintained under 38 bar pressure. Liquid feed comprising a mixture of 38 wt% methanol & 62 wt % 2 CP at a molar ratio of about 2:1, was pumped into the reactor comprising the activated catalyst using HPLC pump at a Liquid Hourly Space Velocity (LHSV) of about 3 h-1. The reactor outlet was connected to the gas-liquid separator/primary condenser followed by back pressure regulator (BPR) and then the secondary condenser maintained at about 5°C to about 10°C, where the temperature of post reactor line and gas-liquid separator/primary condenser was maintained at about 40-60°C. About 3.5g/h DMC was collected from the gas-liquid separator in the first product collection chamber. Thereafter, post-secondary condensation, the vaporized fraction of DMC was obtained in liquid form and collected in the second product collection chamber.
The products arising from the gas-liquid separator/primary condenser and the secondary condenser were subjected to analysis using gas chromatographic technique (Figure 3).

Comparing the efficiency of conversion between Examples 2 and 3, it can be seen that contrary to Example 2 where air was continuously supplied during the course of the reaction and selectivity and activity of the catalyst was maintained, in Example 3, the activity of the catalyst started declining with the progress of the reaction, right after commencement of the reaction.
The above, therefore, shows that the process of the present disclosure, particularly characterized by introduction of a small quantity of air during the reaction indeed had surprising effect in terms of prolonged retention of catalyst activity and selectivity in view of in-situ regeneration of the catalyst.
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 such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be 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 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 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.
All references, articles, publications, general disclosures etc. cited herein are 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 process for selective synthesis of dimethyl carbonate (DMC) comprising: contacting carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent with an oxide catalyst in a reactor in presence of air to obtain a fluid stream comprising the DMC.
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 and pyrole-2-carbo nitrile, or any combination thereof; and/or wherein the oxide catalyst is selected from a group comprising Ceria (CeO2) based catalyst, Zirconia (ZrO2) and Praseodymium oxide (Pr2O3), Lanthanum oxide (La2O3), CexZr1-xO2, CexPr1-xO2, CexLa1-xO2 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 about 0.9 to about 0.99.
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, silica-alumina and ethyl silicate, or any combination thereof; wherein surface area of the oxide catalyst ranges from about 100 m2/g to about 140 m2/g; and/or wherein acidity/basicity ratio of the oxide catalyst ranges from about 0.8 to about 3.5.
4. The process as claimed in claim 1, wherein the oxide catalyst is mixed with a diluent in the catalyst bed of the reactor; wherein the diluent is silicon carbide (SiC); and wherein the ratio between the oxide catalyst and the 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 reactor before the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent; and wherein the oxide catalyst is activated by heating the reactor to a temperature of about 250°C to about 400°C in the presence of air.
6. The process as claimed in claim 1, wherein the ratio between the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent ranges from about 1:1:1 to about 2:2:1.
7. The process as claimed in claim 1, wherein the air in the reactor is zero air or pure oxygen; wherein the zero air or the pure oxygen is continuously circulated in the reactor; wherein the air is introduced at a space velocity of about 15 h-1 to about 225 h-

1; wherein the air and the carbon dioxide (CO2) are introduced into the reactor as a gas stream; wherein the oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol %; and/or wherein CO2 to O2 volume ratio in the reactor ratio ranges from about 18 to about 300.
8. 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
150°C and pressure of about 30 bar to about 50 bar; wherein the CO2 is introduced into the reactor at a space velocity of about 600 h-1 to about 2000 h-1; and/or wherein the alcohol and the nitrile based dehydrating agent are introduced into the reactor at LHSV of about 2 h-1 to about 5 h-1.
9. The process as claimed in claim 1, wherein the fluid stream is subjected to separation at a temperature of about 40°C to about 60°C to obtain a liquid stream and a gaseous stream; wherein the liquid stream is the DMC; and wherein the gaseous stream is subjected to secondary condensation.
10. The process as claimed in claim 9, wherein the secondary condensation condenses vapourized DMC and unconverted methanol in the gaseous stream; wherein the secondary condensation yields DMC and methanol and a remainder gas; wherein the remainder gas comprises a mixture of CO2 and zero air; wherein the remainder gas is recycled into the process without further purification.
11. The process as claimed in claim 1, wherein yield of the DMC ranges from about 40 mol% to about 80 mol%; wherein yield of undesired products methyl carbamate (MC), methyl picolinate (MP) and methyl picolinimidate (MPI) ranges from about 0.01% to about 1%; and/or wherein yield of the DMC is at least 20 % higher after about 100 hours of run than a process conducted in the absence of air.
12. A process for inhibiting catalyst deactivation in a process for selective dimethyl carbonate synthesis from carbon dioxide (CO2), alcohol and a nitrile based dehydrating agent comprising providing controlled delivery of air to a reactor facilitating continuous and selective dimethyl carbonate synthesis from the carbon dioxide (CO2), the alcohol and the nitrile based dehydrating agent.
13. The process as claimed in claim 12, wherein the air is zero air or pure oxygen; wherein the zero air or pure oxygen is continuously circulated in the reactor; wherein the air and the carbon dioxide (CO2) are introduced into the reactor as a gas stream; wherein the oxygen (O2) content in the gas stream is maintained at about 0.5 vol% to about 15 vol

%; wherein the CO2, the alcohol and the nitrile based dehydrating agent are contacted with the catalyst at a temperature of about 100°C to 150°C and pressure of about 30 bar
to about 50 bar; wherein the CO2 is introduced into the reactor at a space velocity of about 600 h-1to about 2000 h-1; wherein the alcohol and the nitrile based dehydrating agent are introduced into the reactor at LHSV of about 2 h-1 to about 5h-1; and/or wherein CO2 to O2 volume ratio in the reactor ratio ranges from about 18 to about 300.
14. A system (100) for selective synthesis of dimethyl carbonate (DMC), the system
comprising:
- a reactor (200) configured to receive CO2, alcohol and nitrile based dehydrating agent, the reactor comprising at least one catalyst to react with the CO2, alcohol and dehydrating agent, the reactor fluidly connected to a continuous supply of air;
- an air dispenser (12) fluidly coupled to the reactor to facilitate continuous supply of air into the reactor (200);
- a gas liquid separator (13) fluidly coupled to the reactor by a temperature controlled channel; the gas liquid separator configured to receive a fluid stream from the reactor; the gas liquid separator configured to discharge a liquid to a first collection chamber and a gas stream away from the liquid;
- a backpressure regulator (BPR) (14) connected to the gas liquid separator, the BPR configured to maintain and regulate pressure of the gas stream upstream of its inlet;
- a secondary condenser (15) configured to receive the gas stream from the BPR to condense vapour products from the gas stream; wherein the secondary condenser is connected to a gas outlet (16) and a second collection chamber (17).

15. The system as claimed in claim 14, wherein the reactor (200) is a fixed bed continuous flow reactor; wherein the reactor (200) comprises a mechanism for temperature and pressure control.
16. The system as claimed in claim 14, wherein the connection between the reactor (200) and the gas-liquid separator (13) is maintained at a temperature of about 40°C to about 60°C; wherein the connection from the BPR (14) to the secondary condenser (13) is maintained at room temperature; and/or wherein the secondary condenser (15) is maintained at a temperature of about 5°C to about 10°C to condense vaporized components.

17. The system as claimed in claim 14, wherein the secondary condenser (15) comprises a gas outlet connected to a gas chromatography column configured to detect oxidation of the alcohol.