DESC:FIELD
The present disclosure relates to an integrated synergistic process for producing propylene.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which it is used indicates otherwise.
Chabazite (CHA) zeolite: The term “Chabazite refers to a tectosilicate mineral of the zeolite group, closely related to gmelinite, with formula (Ca, Na2, K2, Mg) Al2Si4O12•6H2O. The different varieties of chabazite include Chabazite-Ca, Chabazite-K, Chabazite-Na, and Chabazite-Sr, depending on the prominence of the indicated cation.
MFI based zeolite: The term “MFI zeolite” refers to zeolite frame type and topology. The designation of the framework type code (FTC) refers to the type material ZSM-FIve (ZSM-5, Zeolite Socony Mobil with sequence number five), having different Si/Al ratio synthesized using TPAOH as a template.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Propane can be converted to propylene through cracking or dehydrogenation. Propane cracking results in many products including propylene in the range of 10% to 20%, and propane dehydrogenation results in products including 95% propylene. Conventionally, nitrogen (N2) or air is used for dehydrogenating propane to propylene in the presence of chromium or platinum based catalyst. Hydrogen (H2) is produced during the reaction along with propylene and some amount of unreacted propane. Hydrogen (H2) is a major by-product of the dehydrogenation. The dehydrogenation reaction is depicted herein below.
CH3CH2CH3 CH3CH = CH2 + H2
Propylene is separated from the products for producing its derivatives, unreacted propane is separated from the products and is recycled to produce propylene, and hydrogen is separated from the products and is used as other industrial usages.
In the dehydrogenation process, the carbon deposition takes place on the catalyst, which leads to reduced activity or life of the catalyst, thereby increasing the capital expenditure (CAPEX) and operational expenditure (OPEX) of the entire process.
There is, therefore, felt a need for an alternative improved process to increase the production of propylene with reduced CAPEX and OPEX.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows.
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide an alternative improved process to increase the production of propylene.
Another object of the present disclosure is to provide an alternative improved process that enhances the life of a catalyst used in dehydrogenation by reducing the deposition of carbon on the catalyst.
Another object of the present disclosure is to provide an alternative improved process to increase the production of propylene with reduced CAPEX and OPEX.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure provides an integrated synergistic process for producing propylene. The first process comprises dehydrogenation of propane in the presence of CO2 and at least one first catalyst, at a temperature in the range of 500ºC to 700ºC and at a pressure in the range of 0.1 kg/cm2 to 1 kg/cm2, to produce a gaseous mixture comprising propylene, unconverted propane, unconverted CO2, and syngas comprising H2 and CO, wherein preferably the ratio of H2 to CO is 1:1. The gaseous mixture is fed to a first separator to obtain a first stream containing syngas and unconverted CO2 and a second stream containing propylene and unconverted propane. The first stream is fed to a second separator to obtain a syngas stream and a CO2 stream. The syngas stream is contacted with at least one second catalyst, at a temperature in the range of 100ºC to 400ºC and at a pressure in the range of 1 kg/cm2 to 60 kg/cm2, to produce an intermediate stream comprising dimethyl ether (DME), unconverted CO2, H2, and CO. The intermediate stream is fed to a third separator for separating the unconverted CO2, and H2 and CO, and DME. The mixture of unconverted CO2 and H2 and CO is fed to the second separator. The separated portion of the unconverted CO2 from the second separator is recycled to the dehydrogenation step and the separated portion of H2 and CO is recycled to the intermediate stream producing step. The intermediate stream after removal of the unconverted CO2, H2, and CO therefrom is contacted with at least one third catalyst, at a temperature in the range of 200ºC to 600ºC and at a pressure in the range of 0.5 kg/cm2 to 10 kg/cm2, to produce a resultant stream comprising propylene, H2O, and unreacted DME. The resultant stream is fed to a fourth separator along with the second stream to obtain a product stream containing propylene and three residual streams, wherein a first residual stream contains separated unconverted propane which is recycled to the dehydrogenation step, a second residual stream contains separated unreacted DME which is recycled to the step of producing resultant stream and a third residual stream contains H2O which is separated from the fourth separator.
The at least one first catalyst can be chromium based catalyst or platinum – tin based catalyst.
The at least one second catalyst can be selected from the group consisting of copper oxide, chromium oxide, zinc oxide, and aluminium oxide.
The at least one third catalyst can be selected from the group consisting of zeolites, alumino-phosphate molecular sieves, silicoalumino phosphate molecular sieves, and substituted forms thereof.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 depicts a flow-path for producing propylene in accordance with the present disclosure.
Reference Numerals
Propane a
CO2 b
Propane dehydrogenation reactor (PDH) + rWGS PR
Gaseous mixture c
First separator SC
Second stream containing propylene and unconverted propane d
First stream containing syngas and unconverted CO2 e1
Second separator SS
DME reactor OD
Intermediate stream i
Third separator SD
Separated portion of CO2 k
Stream containing syngas and unconverted CO2 e2
Separated portion of H2 and CO j
Intermediate stream after removal of the unconverted CO2, H2, and CO therefrom f
DME to propylene reactor DP
Resultant stream g
Propylene h
Separated unconverted propane l
Separated unreacted DME m
Separated H2O n
Fourth separator SP

DETAILED DESCRIPTION
Embodiments, of the present disclosure, will now be described with reference to the accompanying drawing.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed elements.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
As described herein above, Propane can be converted to propylene through cracking or dehydrogenation. Propane cracking results in many products including propylene in the range of 10% to 20%, and Propane dehydrogenation results in products including 95% propylene. Conventionally, nitrogen (N2) or air is used for dehydrogenating propane to propylene in the presence of a chromium based catalyst or a platinum-tin based catalyst. Moreover, in the dehydrogenation process, the carbon deposition takes place on the catalyst, which leads to reduced activity or life of the catalyst, thereby increasing the capital expenditure (CAPEX) and operational expenditure (OPEX) of the entire process.
The present disclosure, therefore, envisages an integrated synergistic process for producing propylene with increased yield and reduced CAPEX and OPEX.
The integrated synergistic process of the present disclosure is described with reference to Figure 1.
Propane (a) and CO2 (b) are introduced into a propane dehydrogenation (PDH) reactor (PR), wherein propane (a) is dehydrogenated in the presence of CO2 (b) and at least one first catalyst, at a temperature in the range of 500ºC to 700ºC and at a pressure in the range of 0.1 kg/cm2 to 1 kg/cm2, to produce a gaseous mixture (c) comprising propylene, unconverted propane, unconverted CO2 (b), and syngas comprising H2, and CO. Particularly, in accordance with Boudouard reaction, the carbon deposited on the catalyst reacts with CO2 to produce carbon monoxide, thereby enhancing the life of the catalyst used in the PDH reactor. Boudouard reaction is depicted herein below.
CO2 + C ? 2CO
The carbon monoxide produced can be used in combination with hydrogen (H2) to produce propylene via dimethyl ether (DME) route.
The at least one first catalyst can be a chromium based catalyst or a platinum-tin based catalyst.
In accordance with the present disclosure, the ratio of H2 and CO in the syngas is preferably 1:1 for the DME process. Either by varying the process conditions of PDH section or by employing reverse water-gas shift reaction or a combination thereof, the ratio of H2 and CO of 1:1 is achieved. The reverse water-gas shift reaction is depicted herein below.
CO2 + H2 CO + H2O
With 1:1 ratio of H2 and CO, one-step dimethyl ether (DME) process can directly use the syngas.
The gaseous mixture (c) is introduced into a first separator (SC) to obtain a first stream (e1) containing syngas and unconverted CO2 and a second stream (d) containing propylene and unconverted propane.
The first stream (e1) is introduced into a second separator (SS) to obtain a syngas stream (j) and a CO2 stream (k). The DME process can accommodate some CO2 in the feed, which can lead to use of less severe separation process for the second separator (SS).
The syngas stream (j) is introduced into a DME reactor (OD), wherein the syngas stream (j) is contacted with at least one second catalyst in the DME reactor (OD), at a temperature in the range of 100ºC to 400ºC and at a pressure in the range of 1 kg/cm2 to 60 kg/cm2, to produce an intermediate stream (i) comprising DME, unconverted CO2, H2, and CO. The at least one second catalyst can be selected from the group consisting of copper oxide, chromium oxide, zinc oxide, and aluminium oxide.
The intermediate stream (i) is introduced into a third separator (SD), wherein at least a portion of the unconverted CO2 and H2, and CO stream (e2) is separated from the intermediate stream (i). The stream (e2) is sent to the second separator (SS) to obtain the syngas stream (j) and the CO2 stream (k). The CO2 stream (k) from the second separator (SS) is recycled to the PDH reactor (PR), and the syngas (H2 and CO) stream (j) from the third separator (SD) is recycled to the DME reactor (OD). In accordance with the present disclosure, the CO2 stream (k) from the second separator (SS) is recycled to the PDH reactor (PR) which is used for producing syngas, producing DME and finally for producing propylene. Due to this, the amount of raw material(s) (propane) required for producing propylene is reduced.
The intermediate stream after the removal of the unconverted CO2, H2, and CO (f) leaving the third separator (SD) is introduced into a reactor (DP), wherein the intermediate stream after the removal of the unconverted CO2, H2, and CO (f) is contacted with at least one third catalyst, at a temperature in the range of 200ºC to 600ºC and at a pressure in the range of 0.5 kg/cm2 to 10 kg/cm2, to produce a resultant stream (g) comprising propylene, H2O (steam), and unreacted DME. The at least one third catalyst can be selected from the group consisting of zeolites, alumino-phosphate molecular sieves, silicoalumino phosphate molecular sieves, and substituted forms thereof.
The resultant stream (g) from the reactor (DP) is introduced into a fourth separator (SP) along with the second stream (d) to obtain a product stream containing propylene (h) and three residual streams, wherein a first residual stream contains separated unconverted propane (l) which is recycled to the PDH reactor (PR), a second residual stream contains separated unreacted DME (m) which is recycled to the reactor (DP) and a third residual stream contains H2O which is separated (separated H2O (n)) from the fourth separator (SP).
The integrated synergistic process of the present disclosure facilitates in producing higher amounts of propylene. The integrated synergistic process of the present disclosure facilitates in enhancing the life of the catalyst used in the PDH reactor. The integrated synergistic process of the present disclosure utilizes propane in presence of CO2 for producing syngas, due to which the amount of raw materials required for producing propylene is reduced. Furthermore, for efficient separation of streams such as CO2, H2O, DME, and propane divided wall columns are used. Particularly, divided wall columns utilize significantly less energy for efficient separation of the streams, thereby reducing CAPEX and OPEX of the entire process.
Typically, olefins can be produced from syngas by converting syngas into methanol and then methanol is converted into olefins. However, for methanol, syngas with H2: CO ratio of 2:1 is required. Additionally, the process conditions required for methanol production are different than that required for the production of syngas or olefins. So, the process with methanol route is also possible; however, the reduction of Capex and Opex would be less than the DME route. This process is also possible with less Capex and Opex advantage compared to only PDH configuration.
Additionally, there are different processes for conversion of DME or methanol. One process only produces propylene and the other process produces ethylene and propylene. When the conversion of DME or methanol to olefins is considered, the separation of products from PDH and DME or methanol to olefins reactors might need different separation units. This process is possible with less Capex and Opex advantage compared to only PDH configuration.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
EXPERIMENTAL DETAILS:
The amounts of propane, CO2, DME etc., taken in PR reactor, OD reactor, and DP reactor are listed in Table 1.
1 mole of propane was dehydrogenated in the presence of 5 mole of CO2 and platinum group noble metal or metal oxide supported catalyst (for dehydrogenation of propane to propylene) (PR reactor), at 600ºC and at a pressure of 1 kg/cm2, to produce a gaseous mixture comprising propylene, unconverted propane, unconverted CO2, and syngas comprising H2 and CO. The gaseous mixture was fed to a first separator (OD reactor) to obtain first stream containing syngas and -unconverted CO2 and second stream containing propylene and unconverted propane. The first stream was fed to a second separator to obtain syngas stream and CO2 stream. The syngas stream was contacted with CuZn/Alumina or Cu based mixed metal oxide supported on various supports like alumina, zeolite (for the conversion of syngas to DME) at a 300 ºC and at a pressure of 50 kg/cm2, to produce the intermediate stream. The intermediate stream was further fed to a third separator for separating the unconverted CO2, and H2 and CO, and DME. The mixture of unconverted CO2, and H2 and CO were fed to the second separator. The separated portion of the unconverted CO2 from the second separator was recycled to the dehydrogenation step and the separated portion of H2 and CO was recycled to the intermediate stream producing step. The intermediate stream after removal of the unconverted CO2, H2, and CO therefrom was contacted with MFI or CHA (Chabazite) based zeolite (for the conversion of DME to propylene) at 500 oC and at a pressure of 5 kg/cm2, to produce a resultant stream comprising propylene, H2O, and unreacted DME. The resultant stream is fed to a fourth separator along with the second stream to obtain a product stream containing 92% propylene.


Table 1:
PR Reactor OD reactor DP reactor SP separator for Propylene
Propane CO2 C J1 I F M G D G1 H N L
In Out In Out In Out IN OUT
PROPANE 1 0 1.304348 0 0 0 0 0 1.304348 0 0 1.304348 0
CO2 0 5 23.64032 0 0.105402 0 0 0 0 0 0 0 0
PROPYLEN 0 0 0.869565 0 0 0 0 0.062615 0.869565 0.056353 0.925919 0 0
CO 0 0 0.347826 0.632411 0.316206 0 0 0 0 0 0 0 0
H2 0 0 0.521739 2.371296 2.05509 0 0 0 0 0 0 0 0
DME 0 0 0 0 0.105402 0.105402 0.103315 0.114794 0 0.103315 0 0 0
WATER 0 0 0.347826 0 0 0 0 0.093922 0 0.08453 0 0 0.08453
Total Flow kmol/hr 1 5 27.03162 3.003707 2.582099 0.105402 0.103315 0.271332 2.173913 0.244198 0.925919 1.304348 0.08453
Total Flow kg/hr 44.09652 220.049 1151.575 22.49433 22.49433 4.855762 4.759608 9.61537 94.10906 8.653833 38.96325 57.5172 1.522835
Temperature deg C 600 300 500
Pressure Kg/cm2 1 50 5

Total Mass balance (kg/hr): D + G1 = H + N + L + M

As per the ASPEN simulation (Aspen plus V8.8) results shown in Table 1, the integrated process in accordance with the present disclosure, it is observed that yield of propylene is enhanced from 40% (conventional PDH Process) to 92% (integrated process) which is 2.3 times higher propylene yield in respect of the conventional process.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of an integrated synergistic process for producing propylene, wherein:
• the life of the catalyst used in the PDH reactor is enhanced;
• propane is dehydrogenated in the presence of CO2 for producing higher amounts of propylene;
• the separated portion of the unconverted CO2 is recycled to the PDH reactor for producing propylene;
• the amount of raw material required for producing propylene is reduced since the separated portion of the unconverted propane is recycled to the PDH reactor for producing propylene;
• divided wall columns are used for efficient separation of the streams such as CO2, H2O, DME, and propane; and
• the CAPEX and OPEX of the entire process are reduced.
The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein.
The foregoing description of the specific embodiments so fully revealed 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 herein 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.
,CLAIMS:WE CLAIM:
1. An integrated synergistic process for producing propylene, said process comprising the following steps:
a) dehydrogenating propane in the presence of CO2 and at least one first catalyst, at a temperature in the range of 500 ºC to 700 ºC and at a pressure in the range of 0.1 kg/cm2 to 1 kg/cm2, to produce a gaseous mixture comprising propylene, unconverted propane, unconverted CO2, and syngas comprising H2 and CO, wherein the ratio of H2 to CO in said syngas is 1:1;
b) feeding said gaseous mixture to a first separator to obtain a first stream containing syngas and unconverted CO2 and a second stream containing propylene and unconverted propane;
c) feeding said first stream to a second separator to obtain a syngas stream and a CO2 stream;
d) contacting said syngas stream with at least one second catalyst, at a temperature in the range of 100 ºC to 400 ºC and at a pressure in the range of 1 kg/cm2 to 60 kg/cm2, to produce an intermediate stream comprising dimethyl ether (DME), unconverted CO2, H2, and CO;
e) feeding said intermediate stream to a third separator for separating at least a portion of unconverted CO2, H2, and CO from said intermediate stream separately and recycling the separated portion of unconverted CO2 to the process step a) and recycling the separated portion of H2 and CO to the process step d);
f) contacting said intermediate stream after removal of the unconverted CO2, H2, and CO therefrom with at least one third catalyst, at a temperature in the range of 200ºC to 600ºC and at a pressure in the range of 0.5 kg/cm2 to 10 kg/cm2, to produce a resultant stream comprising propylene, H2O, and unreacted DME; and
g) feeding said resultant stream to a fourth separator along with said second stream to obtain a product stream containing propylene and three residual streams, wherein a first residual stream contains separated unconverted propane which is recycled to the process step a), a second residual stream contains separated unreacted DME which is recycled to the process step f) and a third residual stream contains H2O which is separated from said fourth separator.
2. The integrated synergistic process as claimed in claim 1, wherein said at least one first catalyst is selected from the group consisting of chromium and platinum - tin.
3. The integrated synergistic process as claimed in claim 1, wherein said at least one second catalyst is selected from the group consisting of copper oxide, chromium oxide, zinc oxide, and aluminium oxide.
4. The integrated synergistic process as claimed in claim 1, wherein said at least one third catalyst is selected from the group consisting of zeolites, alumino-phosphate molecular sieves, silicoalumino phosphate molecular sieves, and substituted forms thereof.