Claims:WE CLAIM:
1. A process for producing paraxylene, said process comprising the following steps:
a) reacting carbon dioxide (CO2) with at least one alkane in the presence of a first catalyst at a first pre-determined temperature and a first pre-determined pressure to obtain a first stream comprising syngas and unconverted CO2;
b) separating said unconverted CO2 from said first stream to obtain stream of syngas and recycling said unconverted CO2 to step (a);
c) contacting said stream of syngas with a second catalyst at a second pre-determined temperature and a second pre-determined pressure to obtain a second stream comprising dimethyl ether (DME) and unconverted syngas;
d) separating said unconverted syngas from said second stream to obtain stream of DME and recycling the unconverted syngas to step (c);
e) adding an aromatic stream comprising at least one of toluene and benzene to said stream of DME in the presence of a third catalyst at a third pre-determined temperature and a third pre-determined pressure to obtain a third stream comprising paraxylene and other compounds; and
f) separating paraxylene from said other compounds in said third stream to obtain stream of paraxylene.

2. The process as claimed in claim 1, wherein said syngas contains H2 and CO in 1:1 ratio.

3. The process as claimed in claim 1, wherein said alkane is at least one alkane having carbon atom count varying from 1 to 20.

4. The process as claimed in claim 1, wherein said first pre-determined temperature is in the range of 300ºC to 1000ºC, said second pre-determined temperature is in the range of 100ºC to 400ºC and said third pre-determined temperature is in the range of 200ºC to 600ºC.

5. The process as claimed in claim 1, wherein said first pre-determined pressure is in the range of 1 kg/cm2 to 80 kg/cm2, said second pre-determined pressure is in the range of 1 kg/cm2 to 60 kg/cm2 and said third pre-determined pressure is in the range of 0.5 kg/cm2 to 5 kg/cm2.

6. The process as claimed in claim 1, wherein said first catalyst comprises at least one element selected from a group consisting of nickel, cerium and cobalt, either in elemental or compound form.

7. The process as claimed in claim 1, wherein said second catalyst comprises at least one compound selected from a group consisting of chromium oxide, zinc oxide and aluminium oxide.

8. The process as claimed in claim 1, wherein said third catalyst comprises at least one zeolite modified with one or more of zinc oxides, molybdenum oxide and boron oxide, wherein said zeolite is ZSM-5.

9. The process as claimed in claim 1, wherein said other compounds in said third stream comprise metaxylene, orthoxylene, toluene, benzene, dimethyl ether and water, wherein toluene, benzene, dimethyl ether in said other compounds are separated from metaxylene, orthoxylene, water and recycled to step (e).

10. An apparatus (100) for producing paraxylene, said apparatus (100) comprising:
a) a reformer (104) configured for receiving CO2 and at least one alkane and reacting carbon dioxide (CO2) with said alkane in the presence of a first catalyst to form a first stream comprising syngas and unconverted CO2;
b) a first separating unit (108) for receiving said first stream and separating said unconverted CO2 from said first stream to obtain stream of syngas;
c) a first conduit (106) for leading the first stream from the reformer (104) to the first separating unit (108);
d) a second conduit (130) for recycling said unconverted CO2 to the reformer (104);
e) a first reactor (112) configured for receiving said stream of syngas and contacting said stream of syngas with a second catalyst to obtain a second stream comprising dimethyl ether (DME) and unconverted syngas;
f) a third conduit (110) for leading said stream of syngas from the first separating unit (108) to the first reactor (112);
g) a second separating unit (116) for receiving said second stream, and separating said unconverted syngas from said second stream to obtain stream of DME;
h) a fourth conduit (114) for leading the second stream from the first reactor (112) to the second separating unit (116);
i) a fifth conduit (128) for recycling said unconverted syngas to the first separating unit (108);
j) a second reactor (120) configured for receiving said stream of DME and an aromatic stream (132) comprising at least one of toluene and benzene and reacting the two streams in the presence of a third catalyst to obtain a third stream comprising paraxylene and other compounds;
k) a sixth conduit (118) for leading said stream of DME from the second separating unit (116) to the second reactor (120);
l) a third separating unit (124) configured for receiving said third stream and separating paraxylene from said other compounds in said third stream to yield stream of paraxylene, wherein the other compounds comprise metaxylene, orthoxylene, toluene, benzene, dimethyl ether and water;
m) a seventh conduit (122) for leading said third stream from the second reactor (120) to the third separating unit (124); and
n) an eighth conduit (126) for recycling toluene, benzene and dimethyl ether to the second reactor (120).
, Description:FIELD
The present disclosure relates to a paraxylene production plant.
BACKGROUND
Xylenes are produced by high severity catalytic reforming of naphtha. Xylenes can also be obtained from the pyrolysis of gasoline stream in a naphtha steam cracker and by toluene disproportionation. However, the resultant stream from such processes could lead to a mixture of ortho-, meta-, paraxylenes (PX), and ethyl benzene. The isolation of desirable isomer like paraxylene is based on isomerization of mixed xylenes. Processes such as toluene disproportionation offer an alternative route to produce a paraxylene rich stream and benzene. Other processes involve use of a zeolite catalyst for the alkylation of toluene with methanol to produce paraxylene without the benzene co-product, conversion of propane and butane into paraxylene and benzene. However, there is no process or combination of process which converts carbon dioxide into paraxylene.
Carbon Dioxide (CO2) is a major contributor to industrial emissions, thus contributing to the greenhouse effect. Many technologies in the recent years have focused on capturing CO2 and transforming into useful products. One such transformation is conversion of CO2 to syngas which can be used further for power operations or to produce methanol, olefins, ammonia and urea. However, the use of syngas as fuel could possibly release it back into the atmosphere.
Hence, there is a need for a simple and cost-effective process to obtain paraxylenes from raw materials such as CO2.
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 reduce the consumption of energy by providing an integrated process that combines multiple steps for production of paraxylene from carbon dioxide as a starting material.
Still another object of the present disclosure is to provide an apparatus to obtain paraxylene from carbon dioxide in an integrated process comprising multiple steps.
Yet another object of the present disclosure is to provide a process and an apparatus for effectively separating the products from the by-products in each step of the integrated process.
Yet another object of the present disclosure is to enable recycling of unused feed and by-products for improving the yield of paraxylene production.
Yet another object of the present disclosure is to reduce the CAPEX and OPEX of the overall process.
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
In accordance with the present disclosure, a process is disclosed for producing paraxylene, the process comprising the following steps:
a) reacting carbon dioxide (CO2) with at least one alkane in the presence of a first catalyst at a first pre-determined temperature and a first pre-determined pressure to obtain a first stream comprising syngas and unconverted CO2;
b) separating the unconverted CO2 from the first stream to obtain stream of syngas and recycling the unconverted CO2 to step (a);
c) contacting the stream of syngas with a second catalyst at a second pre-determined temperature and a second pre-determined pressure to obtain a second stream comprising dimethyl ether (DME) and unconverted syngas;
d) separating the unconverted syngas from the second stream to obtain stream of DME and recycling the unconverted syngas to step (c);
e) adding an aromatic stream comprising at least one of toluene and benzene to the stream of DME in the presence of a third catalyst at a third pre-determined temperature and a third pre-determined pressure to obtain a third stream comprising paraxylene and other compounds; and
f) separating paraxylene from the other compounds in the third stream to obtain stream of paraxylene.
In accordance with the present disclosure, the syngas contains H2 and CO in 1:1 ratio.

Typically, in accordance with the present disclosure, wherein the alkane is at least one alkane having carbon atom count varying from 1 to 20.

Typically, in accordance with the present disclosure, the first pre-determined temperature is in the range of 300ºC to 1000ºC, the second pre-determined temperature is in the range of 100ºC to 400ºC and the third pre-determined temperature is in the range of 200ºC to 600ºC.

Typically, in accordance with the present disclosure, the first pre-determined pressure is in the range of 1 kg/cm2 to 80 kg/cm2, the second pre-determined pressure is in the range of 1 kg/cm2 to 60 kg/cm2 and the third pre-determined pressure is in the range of 0.5 kg/cm2 to 5 kg/cm2.

Preferably, in accordance with the present disclosure, the first catalyst comprises at least one element selected from a group consisting of nickel, cerium and cobalt, either in elemental form or compound form.

Preferably, in accordance with the present disclosure, the second catalyst comprises at least one compound selected from a group consisting of chromium oxide, zinc oxide and aluminium oxide.

Preferably, in accordance with the present disclosure, the third catalyst comprises at least one zeolite modified with one or more of zinc oxides, molybdenum oxide and boron oxide, wherein the zeolite is ZSM-5.

Typically, in accordance with the present disclosure, the other compounds in the third stream comprise metaxylene, orthoxylene, toluene, benzene, dimethyl ether and water.
In one embodiment, toluene, benzene, dimethyl ether in the other compounds are separated from metaxylene, orthoxylene, water and recycled to step (e).

In accordance with the present disclosure, an apparatus is disclosed for producing paraxylene, the apparatus comprising:
a) a reformer configured for receiving CO2 and at least one alkane and reacting carbon dioxide (CO2) with the alkane in the presence of a first catalyst to form a first stream comprising syngas and unconverted CO2;
b) a first separating unit for receiving the first stream and separating the unconverted CO2 from the first stream to obtain stream of syngas;
c) a first conduit for leading the first stream from the reformer to the first separating unit;
d) a second conduit for recycling the unconverted CO2 to the reformer;
e) a first reactor configured for receiving the stream of syngas and contacting the stream of syngas with a second catalyst to obtain a second stream comprising dimethyl ether (DME) and unconverted syngas;
f) a third conduit for leading the stream of syngas from the first separating unit to the first reactor;
g) a second separating unit for receiving the second stream, and separating the unconverted syngas from the second stream to obtain stream of DME;
h) a fourth conduit for leading the second stream from the first reactor to the second separating unit;
i) a fifth conduit for recycling the unconverted syngas to the first separating unit;
j) a second reactor configured for receiving the stream of DME and an aromatic stream comprising at least one of toluene and benzene and reacting the two streams in the presence of a third catalyst to obtain a third stream comprising paraxylene and other compounds;
k) a sixth conduit for leading the stream of DME from the second separating unit to the second reactor;
l) a third separating unit configured for receiving the third stream and separating paraxylene from the other compounds in the third stream to yield stream of paraxylene, wherein the other compounds comprise metaxylene, orthoxylene, toluene, benzene, dimethyl ether and water;
m) a seventh conduit for leading the third stream from the second reactor to the third separating unit; and
n) an eighth conduit for recycling toluene, benzene and dimethyl ether to the second reactor.

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 an apparatus 100 to carry out a process of producing paraxylene, in accordance with the present disclosure.

DETAILED DESCRIPTION
Conventional processes to produce xylenes often leads to a mixture comprising all isomers such as ortho-, meta- and paraxylenes. However, amongst various isomers, obtaining paraxylenes is more preferred owing to its applicability in production of several important intermediates and products.
Owing to the environmental concerns, compounds such as carbon-dioxide (CO2) which forms major part of industrial emissions, needs to be transformed into useful products so as to delay its release into the environment. CO2 can be easily transformed into useful compounds such as syngas by reacting CO2 with alkanes. The produced syngas can be then used to obtain other useful intermediates and products.
The present disclosure envisages a multi-step integrated process and an apparatus for producing paraxylene, starting from CO2. The process transforms CO2 into syngas which is further transformed into dimethyl ether. Dimethyl ether then acts as a methylating agent for methylation of aromatic compounds such as benzene, toluene to produce paraxylene. Figure 1 illustrates an apparatus 100 for carrying out the process of producing paraxylene, in accordance with the present disclosure.
The apparatus 100 comprises a reformer 104 configured to receive stream 102 comprising raw material. The raw material comprises carbon dioxide (CO2) and at least one alkane wherein the at least one alkane is selected from a group consisting of methane, ethane and propane. In one embodiment, the alkane is at least one alkane having carbon atom count varying from 1 to 20.Carbon dioxide is reacted with the at least one alkane in presence of a first catalyst in the reformer 104 at a first pre-determined temperature and a first pre-determined pressure to obtain a first stream comprising syngas and unconverted CO2. In accordance with an embodiment of the present disclosure, the syngas in the first stream contains H2 and CO in 1:1 ratio. Although the syngas in the instant embodiment contains 1:1 ratio of H2 and CO as the preferred ratio, however, the syngas in the present disclosure may not be limited to the ratio wherein other combinations are possible. In accordance with the present disclosure, the first pre-determined temperature is in the range of 300 ºC to 1000 ºC and the first pre-determined pressure is in the range of 1 kg/cm2 to 80 kg/cm2. In an embodiment, the first catalyst comprises at least one element selected from a group consisting of nickel, cerium and cobalt, either in elemental form or compound form.
The apparatus 100 further comprises a first separating unit 108 for receiving the first stream and separating the unconverted CO2 from the stream to obtain stream of syngas. In accordance with the present disclosure, a first conduit 106 is configured in the apparatus 100 for leading the first stream from the reformer 104 to the first separating unit 108. In accordance with the present disclosure, a second conduit 130 is configured in the apparatus 100 for recycling the unconverted CO2 to the reformer 104.
The apparatus 100 further comprises a first reactor 112 configured for receiving the stream of syngas and contacting the stream of syngas with a second catalyst at a second pre-determined temperature and a second pre-determined pressure to obtain a second stream comprising dimethyl ether (DME) and unconverted syngas. In the present disclosure, the second stream is formed in a one-step DME process, wherein, the one-step DME process requires H2:CO in the ratio of 1:1 that leads to no water-gas shift reaction and no water consumption. In accordance with the present disclosure, the second pre-determined temperature is in the range of 100ºC to 400ºC and the second pre-determined pressure is in the range of 1 kg/cm2 to 60 kg/cm2. In accordance with an embodiment, the second catalyst comprises at least one compound selected from a group consisting of chromium oxide, zinc oxide and aluminium oxide. In accordance with the present disclosure, a third conduit 110 is configured in the apparatus for leading the stream of syngas from the first separating unit 108 to the first reactor 112.

The apparatus 100 further comprises a second separating unit 116 for receiving the second stream, and separating the unconverted syngas from the second stream to obtain stream of DME. In accordance with the present disclosure, a fourth conduit 114 is configured in the apparatus 100 for leading the second stream from the first reactor 112 to the second separating unit 116. In accordance with the present disclosure, a fifth conduit 128 is configured in the apparatus 100 for recycling the unconverted syngas to the first separating unit 108.

The apparatus 100 further comprises a second reactor 120 configured for receiving the stream of DME and an aromatic stream 132 comprising at least one of toluene and benzene and reacting the two streams in the presence of a third catalyst catalyst at a third pre-determined temperature and a third pre-determined pressure to obtain a third stream comprising paraxylene and other compounds. In an embodiment, the other compounds comprise metaxylene, orthoxylene, toluene, benzene, dimethyl ether and water. In accordance with the present disclosure, the third pre-determined temperature is in the range of 200ºC to 600ºC and the third pre-determined pressure is in the range of 0.5 kg/cm2 to 5 kg/cm2. In one embodiment, the third catalyst comprises at least one zeolite modified with one or more of zinc oxides, molybdenum oxide and boron oxide, wherein the zeolite is ZSM-5.

The apparatus 100 further comprises a third separating unit 124 configured for receiving the third stream and separating paraxylene from the other compounds in the third stream to yield stream of paraxylene. A seventh conduit 122 is configured in the apparatus 100 for leading the third stream from the second reactor 120 to the third separating unit 124. An eighth conduit 126 is configured in the apparatus 100 for recycling toluene, benzene and dimethyl ether to the second reactor 120.
In accordance with an embodiment of the present disclosure, the separating units 108, 116 and 124 may be discrete units, as described above. However, in another embodiment, the separating units 108, 116 and 124 may form sub-units of a single separating unit in the apparatus 100.

The present disclosure also envisages a process for producing paraxylene, wherein the process utilizes carbon dioxide (CO2) in the first step. The formed paraxylene could be transformed into useful chemicals, intermediates or polymers thereby extending the release of carbon dioxide to the atmosphere. The process of the present disclosure comprises multiple steps, wherein the first step comprises reacting CO2 with at least one alkane in the presence of a first catalyst at a first pre-determined temperature and a first pre-determined pressure to obtain a first stream comprising syngas and unconverted CO2, the syngas containing H2 and CO in 1:1 ratio. The second step involves separating the unconverted CO2 from the first stream to obtain stream of syngas and recycling the unconverted CO2 to the first step.
In the third step, the stream of syngas is contacted with a second catalyst at a second pre-determined temperature and a second pre-determined pressure to obtain a second stream comprising dimethyl ether (DME) and unconverted syngas.
The fourth step comprises separating the unconverted syngas from the second stream to obtain stream of DME and recycling the unconverted syngas to the third step. In the fifth step, an aromatic stream comprising at least one of toluene and benzene is added to the stream of DME in the presence of a third catalyst at a third pre-determined temperature and a third pre-determined pressure to obtain a third stream comprising paraxylene and other compounds. The sixth step comprises separating paraxylene from the other compounds in the third stream to obtain stream of paraxylene.
Typically, the other compounds in the third stream comprise metaxylene, orthoxylene, toluene, benzene, dimethyl ether and water. In an embodiment, toluene, benzene, dimethyl ether in the other compounds are separated from metaxylene, orthoxylene, water and recycled to the fifth step of the disclosed process.
Although the first catalyst, the second catalyst and the third catalyst of the present disclosure are preferably selected from the mentioned groups, however, the present disclosure is not limited to the mentioned groups and other suitable catalyst and catalyst systems may be used.
Although the parameters like pre-determined pressure and pre-determined temperature employed in each step of the present disclosure preferably includes the suggested ranges, the pre-determined pressure and pre-determined temperature employed in each step of the process of the present disclosure is not limited to the ranges and several other ranges with permutation and combination are possible.
The process of the present disclosure may be continuous or batchwise. In one embodiment, when the process of the present disclosure is batchwise, then products such as DME may be produced in large quantities and stored.
Again, when the process of the present disclosure is performed in batches, then the reformer 104 may be commonly used for carrying out all the steps of the process sequentially, thereby eliminating the need for the first reactor 112 and the second reactor 120. Alternatively, the first reactor 112 may be commonly used for carrying out the step involving formation of DME and the step of formation of paraxylene, thereby eliminating the need for the second reactor 120.

In an embodiment, when the process of the present disclosure is continuous, the separation of various streams may be done in a single separating unit. In the instant embodiment, a single reactor may be appropriately designed to carry out various steps of the process in the same reactor.
TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process and an apparatus for producing paraxylene, wherein the process:
• enables conversion of CO2 into useful compound such as paraxylene which could be further used for synthesis of important intermediates or chemicals;
• helps in lowering the energy consumption and improves the overall efficiency by integration of three processes with subsequent separation and recycling of the unreacted products/by-products; and
• reduces CAPEX and OPEX of the overall process.

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 as not necessarily 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.