Carbon monoxide production from carbon dioxide reduction by elemental sulfur

Abstract

Disclosed is a method of producing carbon monoxide (CO) and sulfur dioxide (SO.sub.2), the method comprising obtaining a reaction mixture comprising carbon dioxide gas (CO.sub.2(g)) and elemental sulfur gas (S(g)), and subjecting the reaction mixture to conditions sufficient to produce a product stream comprising CO(g) and SO.sub.2(g).

Claims

1. A method of producing carbon monoxide (CO) and sulfur dioxide (SO.sub.2), the method comprising: (a) obtaining a reaction mixture comprising carbon dioxide gas (CO.sub.2(g)) and elemental sulfur gas (S(g)); and (b) contacting the reaction mixture with a catalyst under conditions sufficient to produce a product stream comprising CO(g), COS(g), and SO.sub.2(g), wherein the catalyst comprises a metal, a metal oxide, a metal sulfide from Groups IIA, IB, IIB, IIIB, IVB, VIB, VIII, a lanthanide, lanthanide oxide, or any combination thereof, wherein the conditions comprise a temperature of at least 445 C., a pressure of 1 to 25 bar and a gas hourly space velocity (GHSV) of 1,000 to 100,000 h.sup.1.

2. The method of claim 1, wherein the product stream further comprises CO.sub.2(g).

3. The method of claim 1, wherein the product stream further comprises carbon disulfide (CS.sub.2(g)).

4. The method of claim 1, wherein the product stream further comprises CO.sub.2(g) and S(g).

5. The method of claim 4, wherein the product stream consists essentially of CO(g), SO.sub.2(g), COS(g), CO.sub.2(g), and S(g) or CO(g), SO.sub.2(g), COS(g), CS.sub.2(g), CO.sub.2(g), and S(g).

6. The method of claim 1, wherein the reaction mixture comprises a CO.sub.2(g):S(g) molar ratio of 1:1 to 6:1.

7. The method of claim 6, wherein the reaction mixture comprises a CO.sub.2(g):S(g) molar ratio of 4:1.

8. The method of claim 7, wherein the product stream does not include CS.sub.2(g).

9. The method of claim 6, wherein the reaction mixture comprises a CO.sub.2(g):S(g) molar ratio of 6:1.

10. The method of claim 9, wherein the product stream does not include CS.sub.2(g).

11. The method of claim 1, wherein the metal sulfide comprises molybdenum or zinc.

12. The method of claim 1, wherein the lanthanide, or lanthanide oxide includes La, Ce, Dy, Tm, Yb, Lu, CeO.sub.2, Dy.sub.2O.sub.3, Tm.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, or La.sub.2O.sub.3, or any combination thereof.

13. The method of claim 1, wherein the catalyst is a bulk metal catalyst.

14. The method of claim 1, wherein the catalyst is a supported catalyst.

15. The method of claim 14, wherein the supported catalyst comprises a metal sulfide, a metal carbide, a metal nitride, or a metal phosphate, and any combination thereof.

16. The method of claim 1, wherein hydrogen gas, oxygen gas, methane gas, and water are not included in the reaction mixture.

17. The method of claim 1, wherein the product stream comprises CO(g), SO.sub.2(g) and COS(g), and the COS (g) is recycled to step (b) at a reaction temperature of 900 C. or more.

18. The method of claim 17, wherein recycling the COS (g) inhibits formation of additional COS (g).

19. The method of claim 1, wherein the conditions comprise a temperature of at least 900 C.

20. The method of claim 1, wherein obtaining a reaction mixture comprising carbon dioxide gas (CO.sub.2(g)) and elemental sulfur gas (S(g)) comprises: heating molten sulfur to produce a S(g) stream, and combing the elemental sulfur gas stream with the CO.sub.2(g) to form the reaction mixture.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an illustration of various products that can be produced from syngas.

(2) FIG. 2 is a schematic of a plug-flow reactor system of the present invention.

(3) FIG. 3 is a schematic of fluidized bed reactor system of the present invention.

(4) FIG. 4 is a schematic of a membrane separation system of the present invention.

(5) FIG. 5 is a schematic of a cryogenic distillation system of the present invention.

(6) FIG. 6 are plots of the equilibrium composition of different gaseous products of the present invention with a feed composition of 1 kmol CO.sub.2 (g) and 1 kmol S(g).

(7) FIG. 7 are plots of the equilibrium composition of different gaseous products of the present invention with a feed composition of 2 kmol CO.sub.2 (g) and 1 kmol S(g).

(8) FIG. 8 are plots of the equilibrium composition of different gaseous products of the present invention with a feed composition of 4 kmol CO.sub.2 (g) and 1 kmol S(g).

(9) FIG. 9 are plots of the equilibrium composition of different gaseous products of the present invention with a feed composition of 6 kmol CO.sub.2 (g) and 1 kmol S(g).

(10) FIG. 10 are bar graphs of equilibrium composition of product gases of the present invention at 918 C. and 1 bar with four different feed gas compositions.

(11) FIG. 11 are bar graphs of equilibrium composition of product gases of the present invention at 1220 C. and 1 bar with four different feed gas compositions.

(12) FIG. 12 are bar graphs of equilibrium composition of product gases of the present invention at 1500 C. and 1 bar with four different feed gas compositions.

(13) FIG. 13 are bar graphs of the ratio of CO/SO.sub.2 in equilibrium mixture of the present invention at three different temperatures and four different feed compositions.

(14) FIG. 14 are bar graphs of the ratio of CO/COS in the equilibrium reaction mixture of the present invention at three different temperatures and four different feed compositions.

(15) FIG. 15 are bar graphs of the ratio of CO.sub.2/(CO+SO.sub.2) in equilibrium mixture of the present invention at three different temperatures and four different feed compositions.

(16) FIG. 16 shows graphs of the effect of COS recycling the presence of a Mo.sub.2S catalyst at two different temperatures in a system of the present invention.

(17) FIG. 17 shows graphs of the effect of COS recycling in the presence of a Mo.sub.2S catalyst at two different temperatures in the present invention in a system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(18) The present invention provides a solution to the current problems associated with converting carbon dioxide to carbon monoxide. The solution resides in reacting gaseous sulfur with carbon dioxide to produce carbon monoxide and sulfur dioxide, which is represented by equation (6) shown above. The reaction can be tuned via the reaction temperature and amounts of reactants used to obtain a particular product stream profile. For instance, other reaction products that can be produced during the reaction include COS(g), S(g), and CS(g). Each of the reaction products can be further processed into desired chemicals. By way of example, the produced carbon monoxide can be converted to syngas by converting part of the carbon monoxide to into hydrogen gas by the water gas shift reaction (see equation (5)). Syngas can be used in a variety of processes to produce desired chemicals, examples of which are provided in FIG. 1. The produced SO.sub.2 can be converted into SO.sub.3 and then sulfuric acid and ultimately ammonium sulfate fertilizers. Similarly, COS(g) and S(g) can be converted into valuable commercial products or used as reactants to produce more carbon monoxide. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

(19) A. Reaction Feed

(20) The reactant mixture or feed in the context of the present invention can include a gaseous mixture that includes, but is not limited to, sulfur gas (S(g)), and carbon dioxide gas (CO.sub.2(g)). Alternatively, the S(g) and CO.sub.2(g) feeds can be introduced separately and mixed in a reactor. Sulfur gas (S(g)) in the context of the present invention can be referred to as elemental sulfur and can include, but is not limited to, all allotropes of sulfur (i.e., S.sub.n where n=1 to ). Non-limiting examples of sulfur allotropes include S, S.sub.2, S.sub.4, S.sub.6, and S.sub.8, with the most common allotrope being S.sub.8. Sulfur gas can be obtained by heating solid or liquid sulfur to their boiling points of about 445 C. Solid sulfur can contain either (a) sulfur rings, which may have 6, 8, 10 or 12 sulfur atoms, with the most common form being S.sub.8, or (b) chains of sulfur atoms, referred to as catenasulfur having the formula S.sub.. Liquid sulfur is typically made up of S.sub.8 molecules and other cyclic molecules containing a range of six to twenty atoms. Solid sulfur is generally produced by extraction from the earth using the Frasch process, or the Claus process. The Frasch process extracts sulfur from underground deposits. The Claus process produces sulfur through the oxidation of hydrogen sulfide (H.sub.2S). Hydrogen sulfide can be obtained from waste or recycle stream (for example, from a plant on the same site, or as a product from hydrodesulfurization of petroleum products) or recovery the hydrogen sulfide from a gas stream (for example, separation for a gas stream produced during production of petroleum oil, natural gas, or both). A benefit of using sulfur as a starting material is that it is abundant and relatively inexpensive to obtain as compared to hydrogen gas.

(21) Carbon dioxide used in the present invention can be obtained from various sources. In one non-limiting instance, the carbon dioxide can be obtained from a waste or recycle gas stream (e.g. from a plant on the same site, like for example from ammonia synthesis) or after recovering the carbon dioxide from a gas stream. A benefit of recycling such carbon dioxide as a starting material in the process of the invention is that it can reduce the amount of carbon dioxide emitted to the atmosphere (e.g., from a chemical production site).

(22) The reactant mixture may further contain other gases, provided that these do not negatively affect the reaction. Examples of such other gases include nitrogen or argon. In some aspects of the invention, the reactant gas stream is substantially devoid of other reactant gas such as hydrocarbon gases, oxygen gas, hydrogen gas, water or any combination thereof. Hydrocarbon gases include, but are not limited to, C.sub.1 to C.sub.5 hydrocarbon gases, such as methane, ethylene, ethane, propane, propylene, butane, butylene, isobutene, pentane and pentene. In a particular aspect of the invention the gaseous feed contains 0.1 wt. % or less, or 0.0001 wt. % to 0.1 wt. % of combined other reactant gas. In the reactant mixture, a molar ratio of CO.sub.2(g) to S(g) can range from 1:1 to 6:1 and any range therein. Ratios lower than 1:1 and higher than 6:1 are also contemplated in the context of the present invention. Ultimately, the ratio can be varied to produce a desired reaction product profile.

(23) B. Reaction Products

(24) The products made from the reduction of carbon dioxide with sulfur in the gas phase can be varied by adjusting the molar ratio of CO.sub.2(g) to S(g), the reaction conditions, or both. The major products produced from the reaction of carbon dioxide and sulfur is carbon monoxide and sulfur dioxide as shown in reaction equation (6). The other products that can be produced by the reaction include CS.sub.2 and COS as shown in equation (7), with 10% or less of the reaction product being CS.sub.2 at any ratio of CO.sub.2 to S. In some aspects of the invention, the distribution of products in the product stream (for example, COS(g), SO.sub.2, CS.sub.2, CO.sub.2, CO and SO.sub.2) can be controlled by adjusting the ratio of carbon dioxide to sulfur from 1:1 to 2:1 and up to 6:1 and the temperature of the reaction.
CO.sub.2(g)+S(g).fwdarw.COS(g)+SO.sub.2(g)+CS.sub.2(g)+CO(g)(7)

(25) 1. COS Formation

(26) Without wishing to be bound by theory, it is believed that, as shown in equation (8), carbon dioxide initially reacts with sulfur to form carbonyl sulfide and oxygen. In some aspect of the invention, the amount of COS(g) produced can be adjusted by varying the temperature of the reaction. At a temperature 400 and 700 C., the product stream contains COS and SO.sub.2 with a minimal amount of CO. At these temperatures, the ratio of COS:SO.sub.2 can be 2:1 or 1:1. In some aspects of the invention, the COS can be separated from the SO.sub.2 and CO.sub.2 as described throughout this Specification and sold or further processed into other chemical products.
2CO.sub.2(g)+2S(g).fwdarw.2COS(g)+O.sub.2(g)(8)

(27) 2. CO and SO.sub.2 Formation

(28) Without wishing to be bound by theory, it is believed that the carbonyl sulfide and oxygen in equation (8) react with carbon dioxide and sulfur to form SO.sub.2 and CO as shown in equations (9) and (10). In some aspects of the invention, CO and SO.sub.2 are produced at temperatures between 700 and 3000 C., 900 to 2000 C., or 1500 to 1700 C., with a preferred temperature of between 1000 and 1600 C. and CO.sub.2 to S ratios of 1:1 to 2:1, and up to 6:1. In other instances, however, lower temperatures are also contemplated (e.g., 250 C. or more or certain temperature and pressure conditions can be used to ensure sulfur is in the gaseous phasee.g., conditions at which substantial vapor pressure of S exists, e.g., vapor pressure of S is 510.sup.4 atm at 119 C. and 1 atm at 444.6 C.). The ratio of CO(g) to SO2(g) in the product mixture can range from 0.1:1, 1:2, 1:1, 2:1. The temperature of the reaction and/or CO.sub.2/S ratio can be adjusted to produce a desired CO/SO.sub.2 ratio. For example, if a high CO/SO.sub.2 is desired, a temperature of 1200 C. can be used instead of 1500 C. On the other hand, if a high CO/COS ratio is desired, a CO.sub.2/S ratio of 6:1 and temperature of 1500 C. or 1200 C. can be used. The of equilibrium ratios of CO(g) to SO2(g) at 918 C., 1120 C. and 1500 C. and different temperatures are summarized in Table 1.
S(g)+O.sub.2(g).fwdarw.SO.sub.2(g)(9)
COS(g)+2CO.sub.2(g).fwdarw.SO.sub.2(g)+3CO(g)(10)

(29) TABLE-US-00001 TABLE 1 CO.sub.2:S CO:SO.sub.2 ratio at CO:SO.sub.2 ratio at CO:SO.sub.2 ratio at ratio 918 C. 1120 C. 1500 C. 6:1 0.8:1 1.78:1 2:1 4:1 0.55:1 1.55:1 1.9:1 2:1 0.3:1 1.1:1 1.6:1 1:1 0.1:1 0.9:1 0.5:1

(30) A ratio of CO/COS at about 900 C. is about 120:1 with a starting CO.sub.2 to S ratio of 6:1. Equilibrium ratio of CO.sub.2 to the combined CO and SO.sub.2 is summarized in Table 2.

(31) TABLE-US-00002 TABLE 2 CO.sub.2/(CO + SO.sub.2) CO.sub.2/(CO + SO.sub.2) CO.sub.2/(CO + SO.sub.2) CO.sub.2:S ratio at ratio at ratio ratio 918 C. 1120 C. at 1500 C. 6:1 6.2:1 2:1 1.2:1 4:1 4.9:1 1.5:1 0.8:1 2:1 2.8:1 0.8:1 0.3:1 1:1 1:1 0.1:1 0.5:1

(32) Without wishing to be bound by theory, it is believed that at temperatures above 1500 C., additional CO(g) is formed through the decomposition of any remaining COS to CO(g) and S(g) as shown in equation (11). In embodiments when the CO.sub.2 to S ratio is greater than 2:1, the COS(g) decomposition can be suppressed.
COS(g).fwdarw.CO(g)+S(g)(11)

(33) 3. CS.sub.2 Formation

(34) In certain aspects of the invention when the ratio of CO.sub.2 to S is 1:1 or 2:1, and the temperature of the reaction is from about 445 to about 700 C., the amount of CS.sub.2 formed as shown in equation (12). The amount of carbon disulfide produced can be about 10% or less on a molar basis. The oxygen produced can react with sulfur to form sulfur dioxide.
CO.sub.2(g)+2S(g).fwdarw.CS.sub.2(g)+O.sub.2(g)(12)

(35) In some aspects of the invention, to inhibit or reduce the amount of carbon disulfide formation, the amount of CO.sub.2 can be increased in the reaction mixture. Without wishing to be bound by theory, it is believed that the increased CO.sub.2 reacts with the CS.sub.2 to give CO and SO.sub.2 at higher concentrations of CO.sub.2. In some aspects of the invention, at a CO.sub.2:S ratio of 4:1, no, or undetectable amounts of, CS.sub.2 is formed at temperatures between 400 to 3000 C. It is believed that at temperatures greater than 1000 C., any carbon disulfide that is generated decomposes to carbon monosulfide CS(g) and S(g). The generated sulfur can react with excess carbon dioxide to continue production of COS, CO and SO.sub.2. Without wishing to be bound by theory, it is believed that the carbon monosulfide can polymerize at reaction temperatures above 1000 C.

(36) C. Process

(37) The reaction of carbon dioxide and sulfur can be performed at conditions to produce a product stream that includes carbonyl sulfide, carbon monoxide and sulfur dioxide. Non-limiting examples of process for the reduction of carbon dioxide to carbon monoxide in the presence of sulfur are illustrated with reference to the Figures.

(38) 1. Reactor Systems

(39) FIGS. 2 and 3 are schematics of reactor systems 100 and 200 of the present invention. The reactors used for the present invention can be fixed-bed reactors, stacked bed reactors, fluidized bed reactors, slurry or ebullating bed reactors, spray reactors, or plug flow reactor. The reactors can be manufactured from material resistant to corrosion from sulfur and/or carbon dioxide. A non-limiting example of such material is stainless steel. In FIG. 2 a plug flow type reactor 102 is depicted and in FIG. 3, a fluidized bed reactor 202 is depicted. Referring to FIG. 2, sulfur is provided to storage vessel 104 as molten sulfur. In some aspects, solid sulfur is heated in storage vessel 104 to about 250 C. to liquefy the molten sulfur. Storage vessel may be to 250 to 300 C. to maintain the sulfur in a liquid phase. Molten sulfur can exit storage vessel 104 through outlet 106, and be pumped through conduit 108 to reaction vessel inlet 110 at the top of the reactor 102 using pump 112. The outlet 106, the conduit 108, and the reaction vessel inlet 110 can be heated to 250 to 300 C. to inhibit solidification of the molten sulfur in the outlet, conduit, or inlet. Flow of the molten sulfur into reaction vessel inlet 110 can be altered using flow switch 114. As shown in FIG. 2, the flow switch 114 is in a disabled or unconnected position which inhibits the molten sulfur from flowing into reaction vessel inlet 110. When flow switch 114 is engaged or connected, the molten sulfur flows from conduit 108 to reaction vessel inlet 110. Reaction gases can be stored in a gas storage unit 116. Reaction gas (for example, carbon dioxide or a mixture of carbon dioxide or carbonyl sulfide can exit the gas storage unit 116 through a gas outlet 118, flow through a gas conduit 120, and enter the reaction vessel inlet 110. The gas conduit 120 may include a flow switch 122. As shown in FIG. 2, the flow switch 122 is in a disabled or unconnected position which inhibits the reaction gases from flowing into reaction vessel inlet 110. When the flow switch 122 is engaged or connected, the reaction gases flow from the conduit 108 to the reaction vessel inlet 110. The reaction vessel inlet 110 can couple to a nozzle 124 positioned inside the reactor 104. The nozzle 124 can be any known nozzle suitable for providing an aerosol or mist to the inside of the reactor 104. The reaction vessel inlet 110 and the spray nozzle 124 can be heated to 250 to 400 C. As the molten sulfur and reaction gas enter the spray nozzle 114, the compounds are mixed and sprayed as an aerosol into a reaction zone of the reactor 104. Reactor 104 can be heated to above the boiling point of sulfur, for example above 415 C. As the aerosol mixture of sulfur and reaction gas enters the reactor 104, the sulfur vaporizes or transforms into a gas phase. The gaseous sulfur and reaction gases react in the reaction zone of reactor 104 to form the reaction products described throughout the Specification. For example, gaseous sulfur reacts with carbon dioxide in the reaction zone to form a gaseous mixture. The gaseous mixture can include CO(g), SO.sub.2(g), COS(g), or any combination thereof. In some instances, gaseous sulfur is also in the produced gaseous mixture. As shown, the reactor 102 does not include a catalyst. In some aspects of the invention, the reactor 102 may include one or more catalysts throughout the Specification positioned in the reaction zone described. The gaseous mixture can flow through the reactor 102 and contacts the catalyst in the reaction zone. Such contact can produce the gaseous mixture.

(40) The gaseous mixture can exit the reactor 104 through reactor outlet 126 through gas conduit 128 to condenser 130. Conduit 128 can include one or more valve 132. Valves 132 may be capable to route a portion of the gaseous mixture to analyzer 134. For example, valves 132 may be three-way valves. Analyzer may be any suitable instrument capable of analyzing a gaseous mixture. A non-limiting example of an analyzer is a gas chromatograph in combination with a mass spectrometer (GC/MS). The condenser 130 may cool the gaseous mixture to a temperature suitable to condense sulfur dioxide, gaseous sulfur, if present, or both from the gaseous mixture. Condenser 130 may be part of a recovery unit that separates the components of the gaseous mixture. Such a recovery unit is described in more detail in the following sections.

(41) Referring to FIG. 3, a schematic of fluidized bed reactor system 200 is depicted. The system 200 includes reactor 202, catalyst treatment unit 204, and sublimation unit 206. In the reactor system 200, solid sulfur may be provided to a sublimation unit 206 through sublimation inlet 208. In sublimation unit 206, the sulfur is heated to about 100 C. to allow the sulfur to sublime into catalyst treatment unit 204 through sublimator 210. In the catalyst treatment unit 204, the sublimated sulfur contacts the catalyst and adsorbs onto the catalysts. Contact of the sulfur with the metals in the catalysts activates the metals in the catalyst. The activated catalyst exits the catalyst treatment unit 204 through catalyst treatment unit outlet 212 of the reactor 202 through reactor catalyst inlet 214. Reactant gas (carbon dioxide) enters reactor 202 through reactor gas inlet 216 under pressure. The pressure of the reaction gas is sufficient to move the catalysts in an upwardly direction in the reactor 202 and mix the catalyst with the reaction gas. As the mixture of reaction gas and catalysts enters a reaction zone 218, the sulfur reacts with the reactant gas to form a gaseous product mixture that includes CO.sub.2, SO.sub.2, COS, or combinations thereof. The reaction zone 218 can be heated to 500 to 1500 C., which can accelerate the reaction between the absorb sulfur and the reaction case. The gaseous mixture can exit the reactor 202 through reactor gas outlet 220 and be transported to one or more recovery systems. Spent catalyst may exit the reactor 202 through reactor catalyst outlet 222 and enter catalyst treatment unit 204 through catalyst treatment inlet 224. In catalyst treatment unit 204, the catalyst is contacted with fresh sublimated sulfur and the cycle is repeated.

(42) 2. Product Recovery Systems

(43) In some aspects of the process, the components of the gaseous product mixture can be separated into sulfur, sulfur dioxide, carbonyl sulfide, carbon monoxide or combinations thereof using known separation technology methods. In some embodiments, thermal-based separation systems (e.g. condensation, distillation) can be used to remove each component and produce a pure stream of CO. Other forms of separation, such as chemi- and physi-sorption systems can also be used to remove particular components. For example, carbon dioxide (CO.sub.2) can be removed using amine based chemi-sorption. Carbonyl sulfide (COS) can be removed using an aqueous treatment system. In some embodiments, the products can be separated using a membrane system or a cryogenic distillation system. FIGS. 4 and 5 are schematics of non-limiting examples of recovery or separation systems. FIG. 4 is a schematic of a membrane separation system. FIG. 5 is a schematic of a cryogenic distillation system. As shown, in FIGS. 4 and 5 the flow of gas is upwardly through the reactor, however, it should be understood that a linear flow reactor or a reactor with downwardly flow can be used.

(44) 3. Membrane Separation System

(45) Referring to FIG. 4, membrane separation system 300 includes a reactor 302, heat exchangers 304 and 306, condenser 308, membrane separation unit 310, and scrubber 312. Gaseous reactant stream 314 that includes S(g) and CO.sub.2(g) enters reactor 302 through reactor inlet 316. Flow of the gaseous reactant stream can be regulated using valve 318. Valve 318 can be a mixing valve or 3-way valve that allows other streams to mix with the gaseous reactant stream 314 as they enter the reactor 302. In some embodiments, a gaseous sulfur stream and a gaseous carbon dioxide stream enter valve 318 or reactor 302 through separate inlets. In reactor 302, the gaseous reactant stream 314 is heated at temperatures and pressures described throughout this Specification to produce the gaseous product stream 320. In some embodiments, the gaseous reactant stream 314 is contacted in a reaction zone with a catalyst described throughout this Specification under sufficient conditions to produce the gaseous product stream 320. The gaseous product stream 320 can include gaseous carbon monoxide, gaseous carbonyl sulfide, and gaseous sulfur dioxide. In some embodiments, the gaseous product stream includes gaseous carbon disulfide and gaseous sulfur. The gaseous product stream 320 can pass through heat exchangers 304 and 306 in a sequential manner and undergo multiple heat exchanges to reduce the temperature of product stream 320. The cooled gaseous product stream 320 can enter the condenser 308, which is at a temperature sufficient to separate liquid SO.sub.2 from the gaseous product stream 320 and form liquid sulfur dioxide stream 322 and gaseous product stream 324. In some embodiments, the temperature of the condenser ranges from 150 to 55 C. The liquid sulfur dioxide stream 322 exits condenser 308 and passes through heat exchanger 306 to produce a gaseous sulfur dioxide stream 326. In heat exchanger 306, heat transfer between hot gaseous product stream 320 and liquid sulfur dioxide stream 322 can be sufficient to gasify all, or substantially all, of the sulfur dioxide in the sulfur dioxide stream 326. The gaseous sulfur dioxide stream 326 can be transported to storage units, transported to other processing units to be converted into other commercial products, and/or sold.

(46) The gaseous product stream 324 can exit condenser 308, pass through the heat exchanger 304, the compressor 328, and then enter membrane unit 310. As the gaseous product stream 324 passes through heat exchanger 304, the gaseous product stream 324 is heated by exchange of heat with the hot gaseous product stream 320. Compression of the heated gas product stream 324 can further heat the gaseous product stream 324 to a desired temperature for separation in membrane separation unit 310. In some embodiments, the compressor 328 is not necessary. The heated gaseous product stream 324 enters the membrane separation unit 310 through a feed inlet 330. In the membrane separation unit 310, carbonyl sulfide can be separated from the gaseous product stream 324 to form a carbonyl sulfide stream 332 and a gaseous carbon monoxide stream 334. A portion of the gaseous carbonyl sulfide stream 332 can be transported to other units or to storage units, or sold through conduit 336. A portion of the gaseous carbonyl stream 332 can be provided to the valve 318, mixed with the gaseous reactant stream 314 and feed to reactor 316. In some embodiments, a gaseous sulfur stream, a gaseous carbon dioxide stream and a gaseous carbonyl sulfide stream, or combinations thereof are provided directly as single streams or mixtures of streams to the reactor 302. The gaseous carbon monoxide stream 334 can enter the scrubber 312. In the scrubber 312, residual amounts of carbonyl sulfide and/or sulfur dioxide can be removed from the gaseous carbon monoxide stream 334 to produce purified a carbon monoxide stream 338. The scrubber 312 can be any known scrubber system capable of separating COS and SO.sub.2 from CO. For example, the scrubber 312 may be an aqueous treatment system. Waste product stream containing carbonyl sulfide, sulfur dioxide, and water can exit the scrubber system 312 through the waste outlet 336 and disposed of using known disposal methods. The purified carbon monoxide stream 338 can exit scrubber 312 through scrubber outlet 340 and be transported to other units for further processing into commercial products, stored, or sold.

(47) 4. Cryogenic Separation System

(48) Referring to FIG. 5, cryogenic separation system 400 includes the reactor 302, heat exchangers 304, 306, and 402, the condenser 308, and the cryogenic separation unit 404. The gaseous reactant stream 314 that includes S(g) and CO.sub.2(g) enters the reactor 302 through the reactor inlet 316. Flow of the gaseous reactant stream can be regulated using the valve 318 as described above. In the reactor 302, the gaseous reactant stream 314 is heated at temperatures and pressures described throughout this Specification to produce a product stream 320. The gaseous product stream 320 can pass through the heat exchangers 304 and 306 to undergo multiple heat exchanges to reduce the temperature of the product stream 320. The gaseous product stream 320 can enter the condenser 308, which is at a temperature sufficient to separate liquid SO.sub.2 from the gaseous product stream 320 and form the liquid sulfur dioxide stream 322 and the gaseous product stream 324. In some embodiments, the temperature of the condenser ranges from 150 to 55 C. The liquid sulfur dioxide stream 322 exits the condenser 308 and can undergo heat exchange in the heat exchanger 306 to produce the gaseous sulfur dioxide stream 326. In heat exchanger 306, the hot gaseous product stream 320 can be used as the working fluid to provide heat to the liquid sulfur dioxide stream 322 to sufficiently to gasify all, or substantially gasify all, of the liquid sulfur dioxide in the sulfur dioxide stream 326 to gaseous sulfur dioxide. The gaseous sulfur dioxide stream 326 can be transported to storage units, transported to other processing units to be converted into other commercial products, and/or sold.

(49) The gaseous product stream 324 can exit condenser 308 and pass through the heat exchanger 402. Heat exchange in the heat exchanger 402 can cool the gaseous product stream 324. For example, the temperature of the working fluid in the heat exchanger 308 can be about 50 C. The gaseous product stream 324 can enter cryogenic separation unit 404 through cryogenic separation inlet 406. In some embodiments, heat exchanger 402 is not used, and gaseous product stream 324 enter cryogenic separation inlet 410. In cryogenic separation unit 404, carbon monoxide is separated from gaseous product stream 324 to form a carbon monoxide stream 408. The cryogenic separation unit 404 may have 2 to 100, 20 to 50, or 30 to 40 distillation plates and be operated at temperatures and pressures sufficient to separate carbon monoxide from gaseous product stream 324. For example, cryogenic distillation can be operated as a temperature of 140 to 55 C. The purified carbon monoxide stream 408 can exit the cryogenic separation unit 404 through a gas outlet 410, pass through heat exchanger 304 and be transported to storage units, other process facilities or sold as a commercial product. Carbon monoxide stream 408 can have 90 to 100%, or preferably 100% by volume carbon monoxide. While passing through heat exchanger 304, the cold carbon monoxide stream 408 may cool the hot gaseous product stream 320 exiting reactor 302 and, thus improve the heat efficiency of the system. In some embodiments, the carbon monoxide stream 408 does not pass through heat exchanger 304. In cryogenic separation unit 404, the conditions are sufficient to liquefy or partially liquefy carbonyl sulfide (i.e., at temperatures below the boiling point of carbonyl sulfide (about 50 C.) and form a liquid carbonyl sulfide stream 412. The liquid carbonyl sulfide stream 412 can exit the cryogenic separation unit 404 through liquid outlet 414 and pass through heat exchanger 402. In the heat exchanger 402, the liquid carbonyl sulfide stream 412 is gasified to form gaseous carbonyl sulfide stream 416. The heat in heat exchanger 402 can be provided from the gaseous product stream 324, thus maximizing the heat efficiency of the cryogenic distillation system 400. The gaseous carbonyl stream 416 can enter valve 318 and be mixed with a gaseous reactant stream 314 to continue the process cycle. In some embodiments, the gaseous carbonyl stream 416 directly enters the reactor 302.

(50) With respect FIGS. 2-5, not all conduits and vessel inlets and outlets are described as it should be understood that the units described in the figures have inlets, outlets and conduits that in fluid communication. It should also be understood that the arrangement of the components in the systems can be combined and/or used in a different order.

(51) D. Catalysts and Reaction Conditions

(52) Catalytic material used in the context of this invention may be the same catalysts, different catalysts, or a mixture of catalysts. The catalysts may be supported or unsupported catalysts. The support may be active or inactive. The catalyst support can include refractory oxides, alumina oxides, aluminosilicates, silicon dioxide, metal carbides, metal nitrides, sulfides, or any combination thereof. Non-limiting examples of such compounds includes MgO, Al.sub.2O.sub.3, SiO.sub.2, Mo.sub.2C, TiC, CrC, WC, OsC VC, Mo.sub.2N, TiN, VN, WN, CrN, Mo.sub.2S, ZnS, and any combination thereof. All of the support materials can be purchased or be made by processes known to those of ordinary skill in the art (e.g., precipitation/co-precipitation, sol-gel, templates/surface derivatized metal oxides synthesis, solid-state synthesis, of mixed metal oxides, microemulsion technique, solvothermal, sonochemical, combustion synthesis, etc.). One or more of the catalysts can include one or more metals or metal compounds thereof. The metals that can be used in the context of the present invention to create bulk metal oxides, bulk metal sulfides, or supported catalysts include a metal from Group IIA or compound thereof, a metal from Group IB or compound thereof, a metal from Group IIIB or compound thereof, a metal from Group IVB or compound thereof, a metal from Group VIB or compound thereof, a metal from Group VIII or compound thereof, at least one lanthanide or compound thereof, or any combination thereof. The metals or metal compounds can be purchased from any chemical supplier such as Sigma-Aldrich (USA), Alfa-Aeaser (USA), Strem Chemicals (USA), etc. Group IIA metals (alkaline-earth metals) and Group IIA metal compounds include, but are not limited to, Mg, MgO, Ca, CaO, Ba, BaO, or any combinations thereof. Group IB metals and Group IB metal compounds include, but are not limited to, Cu and CuO. Group IIB metals include zinc or zinc sulfide. Group IIIB metals and Group IIIB metal compounds include, but are not limited to, Sc, Sc.sub.2O.sub.3, the lanthanides or lanthanide compounds, or any combination thereof. Lanthanides that can be used in the context of the present invention to create lanthanide oxides include La, Ce, Dy, Tm, Yb, Lu, or combinations of such lanthanides. Non-limiting examples of lanthanide oxides include CeO.sub.2, Dy.sub.2O.sub.3, Tm.sub.2O.sub.3, Yb.sub.2O.sub.3, Lu.sub.2O.sub.3, or La.sub.2O.sub.3, or any combination thereof. Lanthanide oxides can be produced by methods known in the art such as by high temperature (e.g., >500 C.) decomposition of lanthanide salts or by precipitation of salts into respective hydroxides followed by calcination to the oxide form. Group IVB metals and Group IV metal compounds include, but are not limited to, Zr and ZrO.sub.2. Group VIB metals and Group VI metal compounds include, but are not limited to, Cr, Cr.sub.2O.sub.3, Mo, MoO, Mo.sub.2O.sub.3, or any combination thereof. Group VIII metals and metal compounds include, but are not limited to, Ru, RuO.sub.2, Os, OsO.sub.2, Co, Co.sub.2O.sub.3, Rh, Rh.sub.2O.sub.3, Ir, Ir.sub.2O.sub.3, Ni, Ni.sub.2O.sub.3, Pd, Pd.sub.2O.sub.3, Pt, Pt.sub.2O.sub.3, or combinations thereof. The catalytic material can be subjected to conditions that results in sulfurization of the metal in the catalytic material. Non-limiting examples of metal that can be sulfided prior to use are Co, Mo, Ni and W. The catalyst material can, in some instances include a promoter compound. A non-limiting example of promoter compound is phosphorus. A non-limiting example of a catalyst that includes a promoter compound is catalyst material that includes MoNiP. In some instances, the metal oxides described herein can be of spinel (general formula: M.sub.3O.sub.4), olivine (general formula: M.sub.2SiO.sub.4) or perovskite (general formula: M.sup.1M.sup.2O.sub.3) classification.

(53) The catalyst used in the present invention is sinter and coke resistant at elevated temperatures, (e.g., 445 C. to 3000 C., 900 to 2000 C., or 1000 to 1600 C.). Further, the produced catalysts can be used effectively in reaction of sulfur with carbon dioxide at a pressure of 1 to 25 bar, and/or at a gas hourly space velocity (GHSV) range from 1000 to 100,000 h.sup.1.

(54) E. Further Processing of Products

(55) 1. CO Processing

(56) The carbon monoxide produced using the method of the invention can be partially converted into H.sub.2 through water gas shift reaction for the production of syngas of desired H.sub.2/CO ratio as shown in equation (13). The produced CO.sub.2 can be used in the current process to produce more carbon monoxide. This provides an efficient, economic, and novel method to convert a greenhouse gas (CO.sub.2) into value added and useful products.
CO+H.sub.2O.fwdarw.H.sub.2+CO.sub.2(13)

(57) 2. SO.sub.2 Processing

(58) The sulfur dioxide produced using the method of the invention can be converted to SO.sub.3, which can be further processed into sulfuric acid and ammonium sulfate as shown in the equations (14) through (17).
SO.sub.2+O.sub.2.fwdarw.SO.sub.3(14)
SO.sub.3+H.sub.2SO.sub.4.fwdarw.H.sub.2S.sub.2O.sub.7(15)
H.sub.2S.sub.2O.sub.7+H.sub.2O.fwdarw.2H.sub.2SO.sub.4(16)
2NH.sub.3+H.sub.2SO.sub.4.fwdarw.(NH.sub.4).sub.2SO.sub.4(17)

(59) 3. COS Processing

(60) The carbonyl sulfide produced using the method of the invention can be used in the production of thiocarbamates. Thiocarbamates can be used in commercial herbicide formulations. The method of the invention provides an advantage over commercially prepared COS, which is synthesized by treatment of potassium thiocyanide and sulfuric acid as shown in equation (18).
KSCN+2H.sub.2SO.sub.4+H.sub.2O.fwdarw.KHSO.sub.4+NH.sub.4HSO.sub.4+COS(18)

(61) The conventional treatment produces potassium bisulfate and ammonium bisulfate which needs to be separated, which is a difficult and time consuming process. The method of the invention provides an efficient and economic method solution to the production of COS.

EXAMPLES

(62) The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Equilibrium Calculations of Reactions

(63) Multiphase equilibrium composition calculation was done by using HSC Chemistry 7.1 software (Outotec Oyi, Espoo, Finland). The parameters used in the calculations were ratios of gaseous carbon dioxide to gaseous sulfur ranging from 6:1 to 1:1 at temperatures between 0-3000 C. FIGS. 6-9 are graphs of the calculated equilibrium composition obtained by treating different ratios of CO.sub.2 with gaseous S at temperatures from 0 and 3000 C. FIGS. 10-12 are graphs of the amount of different gaseous species at equilibrium conditions between four different feed ratios of CO.sub.2/S were compared at three different temperatures. FIGS. 13-15 are bar graphs of various product ratios in the equilibrium reaction mixture at three different temperatures and four different feed compositions. FIG. 5 are plots of the equilibrium composition of different gaseous species with a feed composition of 1 kmol CO.sub.2 (g) and 1 kmol S(g). FIG. 7 are plots of the equilibrium composition of different gaseous species with a feed composition of 2 kmol CO.sub.2 (g) and 1 kmol S(g). FIG. 8 are plots of the equilibrium composition of different gaseous species with a feed composition of 4 kmol CO.sub.2 (g) and 1 kmol S(g). FIG. 9 are plots of the equilibrium composition of different gaseous species with a feed composition of 6 kmol CO.sub.2 (g) and 1 kmol S(g). The calculated results demonstrate that gaseous S reacts with CO.sub.2 to form equilibrium mixture of SO.sub.2, CO, CS.sub.2 and COS in different amounts at different temperature. Referring to FIGS. 6 and 7, it was found that when the CO.sub.2/S ratio was 1 and 2, small amount of CS.sub.2 forms. Referring to FIGS. 8 and 9, it was found that when the CO.sub.2/S ratio was 4 to 6, CS.sub.2 did not form at any temperature. It was also found that SO.sub.2 formed between 0-3000 C. in considerable quantity between 0-3000 C. when the CO.sub.2/S ratio is 1, but as the ratio increased from 2-6, the amount of SO.sub.2 below 1000 C. became nearly of that of at high temperature of above 1500 C.

(64) The amount of different gaseous species at equilibrium conditions between four different feed ratios of CO.sub.2/S were compared and plotted in FIGS. 10-15. FIG. 10 are bar graphs of equilibrium composition of product gases at 918 C. and 1 bar with four different feed gas compositions. FIG. 11 are bar graphs of equilibrium composition of product gases at 1220 C. and 1 bar with four different feed gas compositions. FIG. 12 are bar graphs of equilibrium composition of product gases at 1500 C. and 1 bar with four different feed gas compositions. FIG. 13 are bar graphs of the ratio of CO/SO.sub.2 in equilibrium mixture at three different temperatures and four different feed compositions. FIG. 14 are bar graphs of the ratio of CO/COS in the equilibrium reaction mixture at three different temperatures and four different feed compositions. FIG. 15 are bar graphs of the ratio of CO.sub.2/(CO+SO.sub.2) in equilibrium mixture at three different temperatures and four different feed compositions. From the obtained data, reaction temperatures and the CO.sub.2/S ratio can be determined to produce the desired products. Referring to FIG. 13, it was determined that to obtain high CO/SO.sub.2 at a CO.sub.2/S ratio of 1:1, reaction temperatures of 1200 C. are preferred. Referring to FIG. 14, it was determined that to obtain high CO/COS ratio, it is preferable to have a CO.sub.2/S ratio of 6 and temperature of 1500 C. or 1200 C. Referring to FIG. 15, the CO.sub.2/(CO+SO.sub.2) ratio can be altered depending upon the final application this can be applied.

(65) The equilibrium calculations and the obtained results demonstrate that the method and systems of the present invention reaction of gaseous carbon dioxide and gaseous sulfur provides carbon monoxide and sulfur dioxide in an efficient manner and converts a greenhouse product into useful commercial products.

Example 2

Production of CO and SO2 with Recycle of COS

(66) General Procedure.

(67) Experiments were conducted at 800 C. and 900 C. in a saturator reactor using MoS.sub.2 and ZnS catalysts to produce CO and SO.sub.2 with recycle COS to limit the further production of COS. A gaseous mixture of CO.sub.2 (25 ml/min) Ar (25 ml/min) was passed through the saturator reactor containing molten sulfur held at 180 C. The sulfur saturated gaseous CO.sub.2 and Ar mixture was passed over the MoS.sub.2 or ZnS catalyst (500 mg) held at 800 C. and 900 C. Both ZnS and MoS.sub.2 were procured from Sigma-Aldrich, USA. Table 3 lists the physical and kinetic parameters of the catalysts and the reactions.

(68) TABLE-US-00003 TABLE 3 Parameters ZnS MoS.sub.2 Surface area (BET) 20.7 m.sup.2/g 3.6 m.sup.2/g Pore volume (BJH) 0.082 cm.sup.3/g 0.026 cm.sup.3/g Pore diameter(4V/A) (BJH) 14.0 nm 30.4 nm Ea, kJ/mol 27.5 30 R.sub.CO2, mol/g.s (900 C.) 5.63 10.sup.7 5.43 10.sup.7 Ea = activation energy and Rco.sub.2 = rate of CO.sub.2 decomposition

(69) MoS.sub.2 Catalyst.

(70) In the saturation reactor, the temperature was raised to 900 C. in presence of CO.sub.2 and S mixture and held at that temperature for about 1.5 hrs to produce COS (4000 ppm), CO (7000 ppm) and SO.sub.2 (5000 ppm). The produced COS (4000 ppm) was recycled through the saturation reactor. Results from the production of CO and SO.sub.2 from a MoS.sub.2 catalyst with recycle of COS at two different temperatures is shown in FIG. 16. The top line is CO production and the bottom line is COS production. The product stream was further monitored for 45 minutes and it was determined (See, FIG. 16, time frame between 2 and 3 hours) that the addition of COS in feed steam did not result in an increase in the COS concentration in the product stream. Thus, recycling COS at 900 C. over the MoS.sub.2 catalyst inhibited formation of more COS due to reaction between CO and S.

(71) To determine the effect of the catalyst on the COS production at lower temperatures, the addition of 4000 ppm COS to the CO.sub.2 and S feed stream was stopped, the reactor temperature was reduced to 800 C., and product gas stream was monitored for about 60 min. At this condition, nearly COS (1800 ppm) was produced. The produced COS (1800 ppm) was fed through the reactor and outlet gas stream was monitored for 50 minutes. It was observed that the COS concentration in the outlet stream gradually increases over time. (See, FIG. 16, time frame between 4 and 5 hours). Thus, recycling COS at 800 C. did not inhibit formation of COS due to the reaction between CO and S.

(72) ZnS Catalyst.

(73) In the saturation reactor, the temperature was raised to 900 C. in presence of CO.sub.2 and S mixture and held at that temperature for about 1.1 hrs to produce COS (3600 ppm), CO (7200 ppm) and SO.sub.2 (5140 ppm). The produced COS (3600 ppm) was recycled through the saturation reactor for Results from the production of CO and SO.sub.2 from a ZnS catalyst with recycle of COS at two different temperatures is shown in FIG. 17. The top line is CO production and the bottom line is COS production. The product stream was further monitored for 20 minutes and it was determined (See, FIG. 16, time frame between 2 and 3 hours) that the addition of COS in feed steam did not result in an increase in the COS concentration in the product stream. Thus, recycling COS at 900 C. over the ZnS catalyst inhibited formation of more COS due to reaction between CO and S. After 20 minutes, the COS concentration was doubled to 7200 ppm instead of 3600 ppm and outlet gas stream was monitored for 60 minutes. At these conditions, the COS concentration increased and CO concentration decreased with time. These results proved that having equilibrium amount of COS in the feed stream overcomes further formation of COS due to the reaction between CO and S, and having more than an equilibrium amount hinders formation of CO as well.

(74) To determine the effect of the catalyst on the COS production at lower temperatures, the addition of COS (7500 ppm) to the CO.sub.2 and S feed stream was stopped, the reactor temperature was reduced to 800 C., and product gas stream was monitored for about 60 min. At this condition, nearly COS (2600 ppm) was produced. The produced COS (2600 ppm) was fed through the reactor and outlet gas stream was monitored for 30 minutes. It was observed that the COS concentration in the outlet stream gradually increases over time. (See, FIG. 17, time frame between 4 and 3 hours). Thus, recycling COS at 800 C. did not inhibit formation of COS due to the reaction between CO and S.

(75) In summary, ZnS and MoS.sub.2 were found to catalytically dissociate CO.sub.2 at temperature above 600 C. in presence of metallic sulphur. COS was a major byproduct and its production was controlled by separation and recycling. Recycling the COS over ZnS or MoS.sub.2 at 900 C. overcame further formation of COS due to the reaction between CO and S.