WO2017077420A1

WO2017077420A1 - Process for syngas production from co2 and h2

Info

Publication number: WO2017077420A1
Application number: PCT/IB2016/056415
Authority: WO
Inventors: Mubarik Ali BASHIR; Awais Ahmed
Original assignee: Sabic Global Technologies B.V.
Priority date: 2015-11-03
Filing date: 2016-10-25
Publication date: 2017-05-11

Abstract

Methods and systems for preparing syngas are provided. An exemplary method can include hydrogenation of carbon dioxide (CO2) via a reverse water gas shift (RWGS) reaction. A system can include a feed-effluent exchanger, a fired heater, an adiabatic reverse water gas shift reactor, a product cooler, and a CO2 removal system.

Description

PROCESS FOR SYNGAS PRODUCTION FROM C0₂ AND H₂ CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 62/250,334, filed November 3, 2015. The contents of the referenced application are incorporated into the present application by reference.

FIELD

[0002] The presently disclosed subject matter relates to methods and systems for conversion of carbon dioxide (C0₂) into synthesis gas (syngas) via hydrogenation of C0₂.

BACKGROUND

[0003] Light olefins (e.g., C₂-C₄ olefins) are important industrial chemicals. Light olefins such as ethylene, propylene, and butene isomers (1-butene, czs-2-butene, trans-2-butene, and isobutylene) are widely used as feedstocks for polymerization.

[0004] There is interest in preparing light olefins and other chemical feedstocks from carbon dioxide (C0₂). C0₂ is an abundant, non-toxic and economical starting material. Use of C0₂ as a feedstock in chemical processes can reduce emissions of C0₂ and improve overall sustainability.

[0005] Synthesis gas (also known as syngas) is a mixture of carbon monoxide (CO) and hydrogen (H₂). Syngas can be prepared by reaction of C0₂ with H₂. This process can be described as hydrogenation of C0₂. C0₂ and H₂ can react to form carbon monoxide (CO) and water (H₂0) through a reverse water gas shift (RWGS) reaction. The RWGS reaction is endothermic and can be described by Equation 1 :

(1) C0₂ + H₂→ CO + H₂0

The RWGS reaction is reversible; the reverse reaction (from CO and H₂0 to C0₂ and H₂) is known as the water gas shift reaction. The RWGS reaction can be conducted under conditions that provide partial conversion of C0₂ and H₂, thereby creating an overall product mixture that includes C0₂, H₂, CO, and H₂0. C0₂ and H₂0 can optionally be removed from such a product mixture, thereby providing a purified syngas mixture containing primarily CO and H₂. Syngas can then be utilized in the production of chemicals such as methanol, oxo alcohol, Fischer Tropsh synthesis, olefins, dimethyethylene (DME), and monoethylene glycol (MEG).

[0006] However, preparation of syngas by this method can result in poor conversion of C0₂. As noted above, the RWGS reaction is reversible and endothermic. Increasing reaction temperature can increase conversion, but increasing the temperature of RWGS reactions is also known to increase side reactions. For example, U.S. Patent Application Pub. No. 2013/0150466 notes that conducting a RWGS reaction at too high of a reaction temperature can induce unwanted reactions.

[0007] Thus, there remains a need in the art for new methods for improving conversion of C0₂ into syngas with H₂:CO ratios appropriate for downstream chemical production.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

[0008] The presently disclosed subject matter relates to methods and systems for conversion of C0₂ into synthesis gas.

[0009] In certain embodiments, a method for preparing syngas can include heating a first stream comprising pressurized C0₂ and H₂ to produce a second stream at a first temperature. In certain embodiments, the method can further include heating the second stream to produce a third stream at a second, higher temperature. In certain embodiments, the method can further include contacting the third stream with one or more catalysts to form a fourth stream comprising shift reaction products. In certain embodiments, the method can further include cooling the fourth stream to form a fifth stream at a third, lower temperature. In certain embodiments, the method can further include recovering unreacted C0₂ from the fifth stream. In certain embodiments, the method can further include pressurizing and recycling the unreacted C0₂ back into the first stream. In certain embodiments, the method can further include recovering reaction product mixture H₂ and CO from the fifth stream in a ratio of from about 1 : 1 to at least about 3 : 1.

[0010] In certain embodiments, the product mixture comprises H₂ and CO in a molar ratio (H₂:CO) of about 1 : 1 to about 3 : 1, about 1.5: 1 to about 3 : 1, about 2: 1 to about 3 : 1, or about 2.5: 1.

[0011] In certain embodiments, the product mixture further comprises H₂0.

[0012] In certain embodiments, the first stream is pressurized at from about 10 to about 40 bar.

[0013] In certain embodiments, the third stream is at a temperature of about 600 to about 700°C. In certain embodiments, the fifth stream is at a temperature of less than about 45°C.

[0014] In certain embodiments, pressurizing and recycling the unreacted C0₂ is performed by a combination of cryogenic C0₂ recovery and an acid gas removal process.

[0015] The presently disclosed subject matter provides a system for preparing syngas that includes a feed-effluent exchanger configured to heat a stream of C0₂ and H₂. In certain embodiments, the system can further include a fired heater, coupled to the feed-effluent exchanger, configured to further heat a stream of C0₂ and H₂. In certain embodiments, the system can further include an adiabatic reverse water gas shift reactor, coupled to the fired heater, configured to react the stream of C0₂ and H₂ in the presence of catalyst to produce CO, and coupled to the feed-effluent exchanger to reduce the product temperature. In certain embodiments, the system can further include a product cooler, coupled to the feed-effluent exchanger, for cooling CO. In certain embodiments, the system can further include C0₂ removal system, coupled to the product cooler, for separation of CO to produce a purified CO product. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a schematic diagram presenting an exemplary system for preparation of syngas from C0₂ in accordance with one non-limiting embodiment of the disclosed subject matter. FIG. 1 depicts the integration of a RWGS reactor with product coolers.

[0017] FIG. 2 is a schematic diagram depicting an exemplary method for a hybrid propylene and absorption chiller refrigeration cycle in accordance with one non-limiting embodiment of the disclosed subject matter.

DETAILED DESCRIPTION

[0018] There remains a need in the art for new methods of preparing syngas from C0₂. The presently disclosed subject matter provides methods of converting C0₂ and H₂ into syngas with improved H₂:CO ratios appropriate for downstream chemical production.

[0019] As used herein, the term "about" or "approximately" means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can mean a range of up to 20%, up to 10%, up to 5%), and or up to 1% of a given value.

Reactors and Reaction Chambers

[0020] For the purpose of illustration and not limitation, FIG. 1 is a schematic representation of an exemplary system according to the disclosed subject matter. The system 100 can comprise a feed-effluent exchanger 104, a fired heater 106, a shift reactor 108, a product cooler 111 and/or a C02 removal system 113.

[0021] The system of the present disclosure can involve feed-effluent exchangers for preheating gaseous reagents, e.g., streams of C0₂ and H₂. A mixture of H₂ and C0₂ can be termed a "reaction mixture." The mixture of H₂ and C0₂ can alternatively be termed a "feed mixture" or "feed gas." [0022] The feed-effluent exchanger 104 can be constructed of any suitable materials capable of holding high temperature, for example up to about 600°C. In certain non-limiting embodiments, the feed-effluent exchanger also recycles hot effluent 109 produced by a reverse water gas shift reaction to provide energy required to preheat the gaseous reagents. In certain embodiments, the gaseous reagent feeds, e.g., C0₂ and H₂, are individually pressurized before mixing. In certain embodiments the gaseous reagent feeds can be pressurized to about 10 to about 40 bar.

[0023] In certain non-limiting embodiments, a feed-effluent exchanger is coupled to a fired heater 106.

[0024] The system of the present disclosure can involve fired heaters suitable for reactions of preheating gaseous reagents, e.g., streams of C0₂ and H₂. The heater 106 can be constructed of any suitable materials capable of preheating gaseous reagents to a high temperature, for example to produce a reagent stream 107 at a temperature of about 600°C to about 700°C. In certain non-limiting embodiments, a feed-effluent exchanger is coupled to a shift reactor.

[0025] The system of the present disclosure can involve fixed bed isothermal or adiabatic reactors 108 suitable for reactions of gaseous reactants and reagents, e.g., streams of C0₂ and H₂, catalyzed by solid catalysts, i.e., a reverse water gas shift reaction. The reactor can be constructed of any suitable materials capable of holding high temperatures, for example from about 600°C to about 780°C. Non-limiting examples of such materials can include metals, alloys (including steel), glasses, ceramics or glass lined metals, and coated metals. The reactor can also include a reaction vessel enclosing a reaction chamber.

[0026] The dimensions of the reaction vessel and reaction chamber are variable and can depend on the production capacity, feed volume, and catalyst. The geometries of the reactor can be adjustable in various ways known to one of ordinary skill in the art. [0027] In certain embodiments, reaction conditions within the reaction chamber can be isothermal. That is, hydrogenation of C0₂ can be conducted under isothermal conditions. In certain alternative embodiments, a temperature gradient can be established within the reaction chamber. For example, hydrogenation of C0₂ can be conducted across a temperature gradient using an adiabatic reactor.

[0028] The pressure within the reaction chamber can be varied, as is known in the art. In certain embodiments, the pressure within the reaction chamber can be atmospheric pressure, i.e., about 1 bar.

[0029] In certain non-limiting embodiments, the reactor is coupled by a transfer line 109 to a feed-effluent exchanger 104 as discussed above.

[0030] In certain non-limiting embodiments, feed-effluent exchanger 104 as discussed above is coupled to a product cooler 111. The product cooler can contain one or more heat exchangers in series which reduce the temperature of the product feed, e.g., CO and H₂, from the feed-effluent exchanger. In certain embodiments, the temperature of the product feed 112 is reduced to less than 45 °C. In certain embodiments, the product cooler is coupled to a C0₂ removal system.

[0031] The system of the present disclosure can involve a C0₂ removal system 113 for separating a product stream 114 and unreacted reactants, e.g., unreacted C0₂, 116. In certain embodiments, the C0₂ removal system can be a combination of cryogenic C0₂ recovery and a commercial available acid gas removal process. In certain embodiments, the acid gas removal process can be, but is not limited to, one of the following: acid gas removal with methyl diethanolamine (MDEA), the Benfield Process, and the Recitsol® process.

Methods of Preparing Syngas

[0032] The methods of the presently disclosed subject matter include methods of preparing syngas. [0033] For the purpose of illustration and not limitation, FIG. 2 is a schematic representation of methods according to non-limiting embodiments of the disclosed subject matter. In one embodiment, an exemplary method 200 can include providing a system 100, as described above for converting mixtures of H₂ and C0₂ into syngas via the reverse water gas shift (RWGS) reaction.

[0034] The method 200 can include heating, e.g. , within a feed-effluent exchanger, a first stream comprising pressurized C0₂ and H₂ to produce a second stream at a first temperature. The method can further comprise heating the second stream, e.g., within a fired heater, to produce a third stream at a second, higher temperature. The method can further include contacting the third stream with one or more catalysts to form a fourth stream comprising shift reaction products, e.g., within a shift reaction chamber. The method can include cooling the fourth stream, e.g., by a product cooler, to form a fifth stream at a third, lower temperature and recovering unreacted C0₂, e.g., within a C0₂ recovery system, from the fifth stream. The method can further include pressurizing and recycling the unreacted C0₂ back into the first stream and recovering reaction product mixture H₂ and CO from the fifth stream in a ratio of from about 1 : 1 to at least about 3 : 1.

[0035] In certain embodiments, the methods of the presently disclosed subject matter can include separating at least a portion of C0₂ and/or H₂0 from the fifth stream, to provide purified syngas. C0₂ and/or H₂0 can be separated by various techniques known in the art. In certain embodiments, C0₂ can be removed from the product mixture and contributed to the reaction mixture, thereby recycling C0₂ through the RWGS reaction and improving overall economy of the process. In certain embodiments, C0₂ can be removed from the product mixture by acid gas removal, as described above.

[0036] In certain embodiments, the method can include contacting the third stream with the catalyst at a reaction temperature greater than 600 °C, thereby inducing a RWGS reaction to provide a fourth stream, e.g., a product mixture that includes H₂ and CO. The product mixture can further include H₂0 (a product of the RWGS reaction, as shown in Equation 1) and unreacted C0₂.

[0037] The C0₂ in the reaction mixture can be derived from various sources. In certain embodiments, the C0₂ can be a waste product from an industrial process. In certain embodiments, C0₂ that remains unreacted in the RWGS reaction can be recovered and recycled back into the RWGS reaction. The H₂ in the reaction mixture can also be derived from various sources. In certain embodiments, the H₂ can be obtained from gas streams from many of the process plants, for example methanol, ammonia, and/or steam cracking plants. In certain embodiments, H₂ can also be sourced through water splitting using renewable energy.

[0038] Reaction mixtures suitable for use with the presently disclosed methods can include various proportions of H₂ and C0₂. In certain embodiments, the reaction mixture can include H₂ and C0₂ in a molar ratio (H₂:C0₂) between about 5:1 and about 1:2, e.g., about 5:1, 4:1, 3:1, 2.8:1, 2.6:1, 2.5:1, 2.4:1, 2.3:1, 2.2:1, 2.1:1, 2:1, 1.9:1, 1.8:1, 1.7:1, 1.6:1, 1.5:1, 1.4:1, 1.3:1, 1.2:1, 1.1:1, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2. The reaction mixture can include H₂ and C0₂ in a molar ratio (H₂:C0₂) of about 2:1 to about 1:1. In certain embodiments, the reaction mixture can include H₂ and C0₂ in a molar ratio (H₂:C0₂) of about 1.6:1.

[0039] The reaction mixture can be fed into the reaction chamber at various flow rates. The flow rate and gas hourly space velocity (GHSV) can be varied, as is known in the art.

[0040] The reaction temperature can be understood to be the temperature within the reaction chamber. The reaction temperature can influence the RWGS reaction, including conversion of C0₂ and H₂, the ratio of H₂:CO in the product mixture, and the overall yield. In certain embodiments, the reaction temperature can be greater than 600 °C, e.g., greater than about 610 °C, 620 °C, 630 °C, 640 °C, 650 °C, 660 °C, 670 °C, 680 °C, 690 °C, or 700 °C. In certain embodiments, the reaction temperature can be between about 600 °C and about 700 °C.

[0041] In certain embodiments, the product mixture can include H₂ and CO in a molar ratio (H₂:CO) of about 0.5: 1 to about 5: 1. In certain embodiments, the product mixture can include H₂ and CO in a molar ratio (H₂:CO) of about 1 : 1 to about 3 : 1, e.g., about 1 : 1, 1.1 : 1, 1.2: 1, 1.3 : 1, 1.4: 1, 1.5: 1, 1.6: 1, 1.7: 1, 1.8: 1, 1.9: 1, 2: 1, 2.1 : 1, 2.2: 1, 2.3 : 1, 2.4: 1, 2.5: 1, 2.6: 1, 2.7: 1, 2.8: 1, 2.9: 1, or 3 : 1. In certain embodiments, the product mixture can include H₂ and CO in a molar ratio (H₂:CO) of about 1.5: 1 to about 3 : 1, about 2: 1 to about 3 : 1, or about 2.5: 1. As noted above, the molar ratio (H₂:CO) of the product mixture can be influenced by the molar ratio (H₂:C0₂) of the reaction mixture.

[0042] In certain embodiments, the RWGS can be performed to relatively high conversion. That is, the amount of C0₂ present in the product mixture can be relatively low. In certain embodiments, the product mixture can include less than about 25% C0₂, by mole or less than about 20% C0₂, by mole. For example, the product mixture can include about 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8% by mole.

[0043] In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

[0044] It will be apparent to those skilled in the art that various modifications and variations can be made in the compositions and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents. Various patents and patent applications are cited herein, the contents of which are hereby incorporated by reference herein in their entireties.

Claims

A method of preparing syngas, the method comprising:

a. heating a first stream comprising pressurized C0₂ and H₂ to produce a second stream at a first temperature;

b. heating the second stream to produce a third stream at a second, higher temperature;

c. contacting the third stream with one or more catalysts to form a fourth stream comprising shift reaction products;

d. cooling the fourth stream to form a fifth stream at a third, lower temperature; e. recovering unreacted C0₂ from the fifth stream;

f. pressurizing and recycling the unreacted C0₂ back into the first stream; and g. recovering reaction product mixture H₂ and CO from the fifth stream in a ratio of from about 1 : 1 to at least about 3 : 1.

The method of claim 1, wherein the product mixture comprises H₂ and CO in a molar ratio (H₂:CO) of about 1 : 1 to about 3 : 1.

The method of claim 2, wherein the product mixture comprises H₂ and CO in a molar ratio (H₂:CO) of about 1.5: 1 to about 3 : 1.

The method of claim 2, wherein the product mixture comprises H₂ and CO in a molar ratio (H₂:CO) of about 2: 1 to about 3 : 1.

The method of claim 2, wherein the product mixture comprises H₂ and CO in a molar ratio (H₂:CO) of about 2.5: 1.

The method of claim 1, wherein the product mixture further comprises H₂0.

The method of claim 1, wherein the first stream is pressurized at from about 10 to about 40 bar.

The method of claim 1, wherein the third stream is at a temperature of about 600 to about 700°C.

9. The method of claim 1, wherein the fifth stream is at a temperature of less than about 45°C.

10. The method of claim 1, wherein step f) is performed by a combination of cryogenic C0₂ recovery and an acid gas removal process.

11. A system for preparing syngas comprising:

a. a feed-effluent exchanger configured to heat a stream of C0₂ and H₂;

b. a fired heater, coupled to the feed-effluent exchanger, configured to further heat a stream of C0₂ and H₂;

c. an adiabatic reverse water gas shift reactor, coupled to the fired heater, configured to react the stream of C0₂ and H₂ in the presence of catalyst to produce CO, and coupled to the feed-effluent exchanger to reduce the product temperature;

d. a product cooler, coupled to the feed-effluent exchanger, for cooling CO; and e. a C0₂ removal system, coupled to the product cooler, for separation of CO to produce a purified CO product.