SYSTEMS AND METHODS FOR CARBON MONOXIDE PRODUCTION BY REDUCTION OF CARBON DIOXIDE WITH ELEMENTAL SULFUR

Abstract

Thermoneutral systems and methods for producing carbon monoxide (CO) and sulfur dioxide (SO.sub.2) are disclosed. The systems can include a first reaction zone and a second reaction zone, where heat generated in the first reaction zone is sufficient to drive a carbon dioxide gas (CO.sub.2(g)) and elemental sulfur gas (S(g)) reaction to produce a product stream that includes CO(g) and SO.sub.2(g).

Claims

1. A system for producing carbon monoxide (CO) and sulfur dioxide (SO.sub.2), the system comprising: (a) a first reaction zone configured to produce heat from an exothermic reaction of a first reaction mixture and a first product stream; (b) a second reaction zone comprising a gaseous reaction mixture of carbon dioxide (CO.sub.2(g)) and elemental sulfur and configured to receive the produced heat from the first reaction zone in an amount sufficient to heat the gaseous reaction mixture and produce a second product stream comprising CO and SO.sub.2; (c) a first outlet in fluid communication with the first reaction zone and configured to remove the first product stream from the first reaction zone; and (d) a second outlet in fluid communication with the second reaction zone and configured to remove the second product stream comprising CO and SO.sub.2 from the second reaction zone.

2. The system of claim 1, wherein exothermic first reaction mixture comprises carbonyl sulfide (COS) and oxygen source oxygen (O.sub.2) and the first product stream comprises CO.sub.2 and SO.sub.2.

3. The system of claim 1, wherein the second reaction zone encompasses the first reaction zone.

4. The system of claim 3, wherein the first reaction zone and the second reaction zone form a concentric reactor, and wherein the first reaction zone is the annulus of the concentric reactor.

5. The system of claim 1, wherein the first product stream absorbs heat from the exothermic reaction, and the system further comprises a heat exchanging unit in fluid communication with the first outlet and the second reaction zone and configured to exchange heat between the heated first product stream and the second reaction mixture and providing the heated second reaction mixture to the second reaction zone.

6. The system of claim 5, wherein second gaseous reaction mixture further comprises CO.sub.2 and elemental sulfur.

7. The system of claim 1, wherein the produced heat from the first reaction zone is sufficient to drive the CO.sub.2 with the elemental sulfur reaction, a CO and elemental sulfur reaction, or both in the second reaction zone.

8. The system of claim 1, wherein the temperature of the produced heat is at least 250 C.

9. The system of claim 8, wherein the temperature of the produced heat is 250 C. to 2500 C., preferably 900 C. to 2300 C., most preferably 1000 C. to 2200 C.

10. The system of claim 1, wherein the system is thermoneutral.

11. The system of claim 1, wherein the first reaction outlet is configured to provide the produced heat to another system, preferably a power generating system.

12. The system of claim 1, wherein the second reaction zone comprises a catalyst capable of catalyzing the reaction of CO.sub.2 and elemental sulfur to produce the second product stream comprising COS, CO and SO.sub.2.

13. The system of claim 1, wherein the second product stream comprises COS.

14. A method of producing carbon monoxide (CO) and sulfur dioxide (SO.sub.2), the method comprising: (a) providing a first reaction mixture capable of undergoing an exothermic reaction to a first reaction zone; (b) subjecting the first reaction mixture to conditions sufficient to produce a first product stream and heat; (c) providing a second reaction mixture comprising carbon dioxide (CO2) and elemental sulfur gas to a second reaction zone; (d) transferring the produced heat to the second reaction zone; and (e) producing a second product stream comprising CO and SO2 from the second reaction mixture.

15. The method of claim 14, wherein the first reaction mixture comprises carbonyl sulfide (COS) and oxygen gas (O.sub.2) and the first product stream comprises CO.sub.2 and SO.sub.2.

16. The method of claim 14, wherein transferring the heat comprises allowing the heat to transfer from the first reaction zone to the second reaction zone and/or transferring the produced heat from the first product stream to the second product stream.

17. The method of claim 14, wherein the temperature of the second reaction mixture is 250 C. to 3000 C., preferably 900 C. to 2000 C., most preferably 1000 C. to 1600 C., the reaction pressure in the second reaction zone is 1 to 25 bar, or both.

18. The method of claim 14, wherein the transferred heat provides sufficient heat to drive the carbon dioxide (CO.sub.2) and elemental sulfur gas reaction or a carbon monoxide and elemental sulfur reaction, or both in the second reaction zone.

19. The method of claim 14, wherein the temperature in the first reaction zone is at least 1000 C., the reaction temperature in step (b) is 700 C. to 2500 C., preferably 900 C. to 2300 C., most preferably 1000 C. to 2500 C., reaction pressure in the first reaction zone is 0.1 to 50 bar, or combination thereof.

20. The method of claim 14, wherein the second reaction zone comprises a catalyst capable of catalyzing the reaction of CO.sub.2 and elemental sulfur to produce the second product stream comprising COS, CO and SO.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is an illustration of various products that can be produced from syngas.

[0024] FIG. 2 is a schematic of a concentric reactor system of the present invention.

[0025] FIGS. 3 and 4 are cross-sectional views of different types of concentric reactors.

[0026] FIG. 5 is a schematic of two-reactor system of the present invention.

[0027] FIG. 6 is a schematic of a membrane separation system for the separation of SO.sub.2 and CO the present invention.

[0028] FIG. 7 is a schematic of a cryogenic distillation system for the separation of SO.sub.2 and CO of the present invention.

[0029] FIG. 8 is a schematic of a cryogenic distillation system for the separation of SO.sub.2 and CO.sub.2 of the present invention.

[0030] FIG. 9 is a graph of conversion of COS with oxygen versus heat trace across the reactor bed.

[0031] FIG. 10 is a graph of conversion of CO with sulfur versus heat trace across the reactor bed.

[0032] FIG. 11 is a graph of conversion of CO.sub.2 with sulfur versus heat trace across the reactor bed.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention provides a solution to the current energy requirements associated with converting carbon dioxide to carbon monoxide. The solution resides in a system that allows heat to be transferred from a first reaction mixture to a second reaction mixture. Such a system can be thermoneutral and/or energy neutral. The heat can be produced from an exothermic reaction mixture, preferably, from the combustion of COS. The amount of heat produced can be sufficient to drive the reaction of CO.sub.2 and elemental sulfur to form CO, SO.sub.2 and COS and the intermediate CO and elemental sulfur reaction. The resulting product stream can be separated and used in industrial and/or energy applications. For example, The COS can be used to produce herbicides (e.g., thiocarbamate herbicides) and/or recycled to be used as a fuel source in the first reaction zone. 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. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections.

A. Systems

[0034] 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 systems for the reduction of carbon dioxide to carbon monoxide in the presence of sulfur are illustrated with reference to the Figures. FIGS. 2-5 are schematics of reactor systems 200 and 500 of the present invention. In FIG. 2, a system that includes a concentric reactor. FIG. 3 is a cross-sectional view of concentric reactor with a first reaction zone and a second reaction zone with a common wall. FIG. 4 is a cross-sectional view of a concentric reactor have an annulus between the first reaction zone and the second reaction zone. FIG. 5 depicts a system with two reactors in series in combination with a heat exchanging unit. The reactors used in FIG. 5 can be fixed-bed reactors, stacked bed reactors, fluidized bed reactors, slurry or ebullating bed reactors, spray reactors, concentric reactors, or plug flow reactor. The reactors in all the systems can be manufactured from material resistant to corrosion from sulfur and/or carbon dioxide. A non-limiting example of such material is stainless steel.

[0035] 1. Concentric Reactor System

[0036] Referring to FIG. 2A, system 200 includes reaction unit 202 having a first reaction zone 204 and a second reaction zone 206. The reaction unit 202 can be a concentric type reaction vessel, a tube-in-tube type reaction unit, or a multiple tube-in-tube type reaction unit. FIGS. 3 and 4 are cross-sectional views of the concentric reactor. As shown in FIG. 3, first reaction zone 204 is the annulus of the reaction unit that is encompassed by second reaction zone 206 with the first reaction zone 204 and the second reaction zone 206 share a common wall 208. As shown in FIG. 4, annulus 210 can exist between the first reaction zone 204 and the second reaction zone 206. While only one annulus 210 is shown, it should be understood that multiple annuluses can be used and multiple reaction zones 206. The concentric reactor 202 shown in FIGS. 3 and 4 can be designed for maximum heat transfer from the first zone 204 to the second zone 206. A first reaction mixture 212 can enter the first reaction zone 204 via first reaction zone inlet 214. In a non-limiting example the first reaction mixture can include COS and O.sub.2. In some embodiments, the first reaction mixture can include CO.sub.2 as a diluent gas. In some instances, reactants in the first reaction mixture enter the reaction zone 204 via two separate inlets (e.g., a COS inlet and an O.sub.2 inlet). The first reaction zone can be equipped with one or more heat sources (not shown) that provide heat to the first reaction mixture 212 as it enters the reaction zone, or in the reaction zone 204. Heat may be provided to the first reaction mixture in an amount sufficient to combust the first reaction mixture and form a first product stream. When the reaction mixture includes COS and O.sub.2, the first reaction mixture can be heated to a temperature of 700 C. to 2500 C., or 900 C. to 2300 C., 1000 C. to 2500 C., or about 700 C., 750 C., 800 C., 850 C., 900 C., 950 C., 1000 C., 1100 C., 1200 C., 1300 C., 1400 C., 1500 C., 1600 C., 1700 C., 1800 C., 1900 C., 2000 C., 2100 C., 2200 C., 2300 C., 2400 C., or 2500 C. The reaction mixture can react (e.g., combust) and form the second product stream CO.sub.2 and SO.sub.2 and heat. A first product stream 216 can exit the first reaction zone 204 via first product outlet 218. In some instances, the first product stream can include CO.sub.2 and SO.sub.2. The first product stream 216 can be collected, separated, transported, sold or provided to other processing units for further processing.

[0037] The heat from the first reaction zone 204 can transfer from the reaction mixture to the wall 208 or annulus 210 of the reaction unit 202 and then to the second reaction zone 206. The temperature of the produced heat can be at least 250 C. or range from 250 C. to 2500 C., preferably 900 C. to 2400 C., most preferably 1000 C. to 2200 C., or about 250 C., 300 C., 350 C., 400 C., 450 C., 500 C., 550 C., 600 C., 650 C., 700 C., 750 C., 800 C., 850 C., 900 C., 950 C., 1000 C., 1100 C., 1200 C., 1300 C., 1400 C., 1500 C., 1600 C., 1700 C., 1800 C., 1900 C., 2000 C., 2100 C., 2200 C., 2300 C., or 2400 C., or any value or any range there between. In the second reaction zone 206, gaseous elemental sulfur 220 enters the second reaction zone 206 from elemental sulfur storage unit 222 via elemental sulfur inlet 224. In some aspects, solid sulfur is heated in storage vessel 222 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 222, and be pumped to reaction vessel. The components of the sulfur line and the inlet to the section reaction zone can be heated to 250 to 300 C. to inhibit solidification of the molten sulfur in the sulfur line. Flow of the molten sulfur into second reaction zone 206 can be altered using flow switches and/or controllers known in the art.

[0038] Reaction gas (for example, carbon dioxide) 226 can enter the second reaction zone 206 via inlet 228. The gas conduit 120 may include one or more controllers or flow switches to control the flow of gas into the second reaction zone 206. In some embodiments, the gaseous reaction mixture and/or the elemental sulfur are sprayed into the second reaction zone. Second reaction zone 206 can be heated to above the boiling point of sulfur, for example above 415 C., or 250 C. to 3000 C., 900 C. to 2000 C., 1000 C. to 1600 C., or about 300 C., 400 C., 500 C., 600 C., 700 C., 800 C., 900 C., 1000 C., 1100 C., 1200 C., 1300 C., 1400 C., 1500 C., 1600 C., 1700 C., 1800 C., 1900 C., 2000 C., 2100 C., 2200 C., 2300 C., 2400 C., 2500 C., 2600 C., 2700 C., 2800 C., 2900 C., or 3000 C., or any value or range there between, by transfer of heat from the first reaction zone. In some embodiments, the reactant gas is mixed with the hot elemental sulfur prior to entering the second reaction zone 206. As the aerosol mixture of sulfur and/or reaction gas enters the second reaction zone, the sulfur vaporizes or transforms into a gas phase. The gaseous sulfur and reaction gases react in the second reaction zone 206 of reactor 202 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 first reaction zone 204 and the second reaction zone 206 do not include a catalyst. In some aspects of the invention, the first reaction zone 204 does not include a catalyst and the second reaction zone 206 can include one or more catalysts described throughout the Specification positioned in the reaction zone. The gaseous mixture can flow through the second reaction zone 206 and contact the catalyst in the second reaction zone 206. Such contact can produce the gaseous product mixture.

[0039] The gaseous mixture 230 can exit the second reaction zone 206 through reactor outlet 232 and enter separation unit 234. Valves 236 can route a portion of the gaseous mixture 230 to analyzer 238. For example, valves 236 may be three-way valves. Analyzer 238 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 234 can cool the gaseous mixture to a temperature suitable to condense sulfur dioxide, gaseous sulfur, if present, or both from the gaseous mixture. Condenser 234 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.

[0040] 2. Two Reactor and Heat Exchanger System

[0041] Referring to FIG. 5, a schematic of a two reactor system 500 is described. The system 500 can include first reactor 502, heat exchanging unit 504, and second reactor 506. A first reaction mixture 212 can enter the first reactor 502 via first reaction zone inlet 508. In a non-limiting example, the first reaction mixture can include COS and O.sub.2. In some embodiments, the first reaction mixture can include CO.sub.2 as a diluent gas. In some instances, reactants in the first reaction mixture enter the first reactor 502 via two separate inlets (e.g., a COS inlet and an O.sub.2 inlet). The first reactor 502 can be equipped with one or more heat sources (not shown) that provide heat to the first reaction mixture 212 as it enters the reaction zone, or in the reactor 502 (first reaction zone). Heat may be provided to the first reaction mixture 212 in an amount sufficient to combust the first reaction mixture and form a first product stream 216. When the reaction mixture includes COS and O.sub.2, the first reaction mixture can be heated to a temperature of 700 C. to 2500 C., or 900 C. to 2300 C., 1000 C. to 2500 C., or about 700 C., 750 C., 800 C., 850 C., 900 C., 950 C., 1000 C., 1100 C., 1200 C., 1300 C., 1400 C., 1500 C., 1600 C., 1700 C., 1800 C., 1900 C., 2000 C., 2100 C., 2200 C., 2300 C., 2400 C., or 2500 C., or any value or range there between. The reaction mixture can react (e.g., combust) and form the second product stream CO.sub.2 and SO.sub.2 and heat. The first product stream 216 can exit the first reactor 502 via first product outlet 510. In some instances, the first product stream can include CO.sub.2 and SO.sub.2 and absorbed heat.

[0042] The first product stream 216 and second reaction mixture feed stream 512 can enter heat exchanging unit 504. As shown, heat exchanging unit 504 is one heat exchanger, however, the heat exchanger unit can include multiple (e.g., 2, 3, 4 or more) heat exchanging units. Heat exchanging unit can be a shell-in-tube type heat exchanger, a plate heat exchanger, or any other type of heat exchanging unit that is capable of exchanging heat from one gaseous stream to another gaseous stream. While shown as a standalone unit, heat exchanging unit 504 can be a part of the first and/or second reactor. The temperature of the first product stream 216 can be at least 250 C. or range from 250 C. to 2500 C., preferably 900 C. to 2400 C., most preferably 1000 C. to 2200 C., or about 250 C., 300 C., 350 C., 400 C., 450 C., 500 C., 550 C., 600 C., 650 C., 700 C., 750 C., 800 C., 850 C., 900 C., 950 C., 1000 C., 1100 C., 1200 C., 1300 C., 1400 C., 1500 C., 1600 C., 1700 C., 1800 C., 1900 C., 2000 C., 2100 C., 2200 C., 2300 C., or 2400 C., or any value or any range there between. In heat exchanger unit 504, all or a portion of the heat from the first product stream 216 can be exchanged with the second reaction mixture feed stream 512. Heated feed stream 512 can enter second reactor 506 through sprayer 514. The temperature of the heated feed stream 512 can range from above 415 C., or 250 C. to 3000 C., 900 C. to 2000 C., 1000 C. to 1600 C., or 300 C., 400 C., 500 C., 600 C., 700 C., 800 C., 900 C., 1000 C., 1100 C., 1200 C., 1300 C., 1400 C., 1500 C., 1600 C., 1700 C., 1800 C., 1900 C., 2000 C., 2100 C., 2200 C., 2300 C., 2400 C., 2500 C., 2600 C., 2700 C., 2800 C., 2900 C., or 3000 C., or any value or range there between. In some instances, the second reactor 506 is heated using one or more heated source (e.g., electrical heat, jacketed heat) so no heat is lost when the heated feed stream 512 enters the second reactor. In certain aspects, the reaction between CO.sub.2 and elemental sulfur is initiated as the feed stream 512 is being heated in the heat exchanger. In some embodiments, the heat exchanging unit is the second reactor 506. The gaseous sulfur and reaction gases react in the second reactor 506 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 first reactor 502 and the second reactor 506 do not include a catalyst. In some aspects of the invention, the first reactor 502 does not include a catalyst and the second reactor 506 can include one or more catalysts described throughout the specification positioned in the reaction zone. The gaseous mixture can flow through the second reactor 502, through the heat exchanging unit 504, and contact the catalyst in the second reactor 506. Such contact can produce the gaseous product mixture.

[0043] The gaseous second product stream 230 can exit the second reactor 506 through reactor outlet 514 and enter separation unit 234. Valves 236 can route a portion of the gaseous mixture 230 to analyzer 238. For example, valves 236 may be three-way valves. Analyzer 238 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 234 can cool the gaseous mixture to a temperature suitable to condense sulfur dioxide, gaseous sulfur, if present, or both from the gaseous mixture. Condenser 234 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.

[0044] 3. Product Recovery Systems

[0045] 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. 6-8 are schematics of non-limiting examples of recovery or separation systems. FIG. 6 is a schematic of a membrane separation system. FIG. 7 is a schematic of a cryogenic distillation system. FIG. 8 is a schematic of a cryogenic distillation system to separation carbon dioxide from sulfur dioxide.

[0046] 4. Membrane Separation System for Second Product Stream

[0047] Referring to FIG. 6, membrane separation system 600 is in fluid communication with the second product stream from the systems described in FIGS. 2-5. The second product stream 230 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 230 can pass through heat exchangers 602 and 604 in a sequential manner and undergo multiple heat exchanges to reduce the temperature of product stream 230. Cooled gaseous product stream 230 can enter condenser 606, which is at a temperature sufficient to separate liquid SO.sub.2 from gaseous product stream 230 and form liquid sulfur dioxide stream 608 and gaseous product stream 610. In some embodiments, the temperature of the condenser ranges from 150 to 55 C. Liquid sulfur dioxide stream 608 exits condenser 606 and passes through heat exchanger 604 to produce gaseous sulfur dioxide stream 612. In heat exchanger 604, heat transfer between hot gaseous product stream 230 and liquid sulfur dioxide stream 608 can be sufficient to gasify all, or substantially all, of the sulfur dioxide in sulfur dioxide stream 612. Gaseous sulfur dioxide stream 612 can be transported to storage units, transported to other processing units to be converted into other commercial products, and/or sold.

[0048] Gaseous product stream 610 can exit condenser 606, pass through heat exchanger 602, compressor 612, and then enter membrane unit 614. As the gaseous product stream 610 passes through heat exchanger 602, gaseous product stream 610 is heated by exchange of heat with the hot gaseous second product stream 230. Compression of heated gas product stream 610 can further heat the gaseous product stream to a desired temperature for separation in membrane separation unit 614. In some embodiments, compressor 612 is not necessary. Heated gaseous product stream 610 enters membrane separation unit 614 through feed inlet 616. In the membrane separation unit 614, carbonyl sulfide can be separated from gaseous product stream 610 to form carbonyl sulfide stream 618 and gaseous carbon monoxide stream 620. A portion of gaseous carbonyl sulfide stream 332 can be transported to other units or to storage units, or sold through conduit 336. A portion of gaseous carbonyl stream 332 can be provided to first reaction zone 204 and/or first reactor 502. 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 second reaction zone 206 and/or second reactor 504. Gaseous carbon monoxide stream 618 can enter scrubber 622. In scrubber 622, residual amounts of carbonyl sulfide and/or sulfur dioxide can be removed from gaseous carbon monoxide stream 618 to produce purified carbon monoxide stream 624. Scrubber 622 can be any known scrubber system capable of separating COS and SO.sub.2 from CO. For example, scrubber 622 may be an aqueous treatment system. Waste product stream 626 containing carbonyl sulfide, sulfur dioxide, and water can exit scrubber system 622 and be disposed of using known disposal methods. Purified carbon monoxide stream 624 can exit scrubber 622 and be transported to other units for further processing into commercial products, stored, or sold.

[0049] 5. Cryogenic Separation System for Second Product Stream

[0050] Referring to FIG. 7, cryogenic separation system 700 is in fluid communication with the second product stream from the systems described in FIGS. 2-5. System 700 includes heat exchangers 602, 604, and 702, condenser 606, and cryogenic separation unit 704. Gaseous product stream 230 enters condenser 606, which is at a temperature sufficient to separate liquid SO.sub.2 from the gaseous product stream and form liquid sulfur dioxide stream 608 and gaseous product stream 610. In some embodiments, the temperature of condenser 606 ranges from 150 to 55 C. Liquid sulfur dioxide stream 608 exits condenser 606 and can undergo heat exchange in heat exchanger 604 to produce gaseous sulfur dioxide stream 612. In heat exchanger 604, hot gaseous product stream 230 can be used as the working fluid to provide heat to liquid sulfur dioxide stream 608 to sufficiently to gasify all, or substantially gasify all, of the liquid sulfur dioxide in sulfur dioxide stream 612 to gaseous sulfur dioxide. Gaseous sulfur dioxide stream 612 can be transported to storage units, transported to other processing units to be converted into other commercial products, and/or sold.

[0051] Gaseous product stream 610 can exit condenser 606 and pass through heat exchanger 702. Heat exchange in heat exchanger 702 can cool gaseous product stream 610. For example, the temperature of the working fluid in heat exchanger 702 can be about 50 C. Gaseous product stream 610 can enter cryogenic separation unit 704. In some embodiments, heat exchanger 702 is not used, and gaseous product stream 610 enters cryogenic separation unit 704. In cryogenic separation unit 704, carbon monoxide is separated from gaseous product stream 610 to form carbon monoxide stream 706. Cryogenic separation unit 704 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 610. For example, cryogenic distillation can be operated at a temperature of 140 to 55 C. Purified carbon monoxide stream 706 can exit cryogenic separation unit 704 pass through heat exchanger 602 and be transported to storage units, other process facilities or sold as a commercial product. Carbon monoxide stream 706 can have 90 to 100%, or preferably 100% by volume carbon monoxide. While passing through heat exchanger 602, cold carbon monoxide stream 706 may cool hot gaseous second product stream 230 exiting second reactor 506 and/or second reaction zone 206 as described in FIGS. 2-5, and thus, improve the heat efficiency of the system. In some embodiments, carbon monoxide stream 706 does not pass through heat exchanger 602. In cryogenic separation unit 704, 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 liquid carbonyl sulfide stream 708. Liquid carbonyl sulfide stream 708 can exit cryogenic separation unit 704 and pass through heat exchanger 702. In heat exchanger 702, liquid carbonyl sulfide stream 708 is gasified to form gaseous carbonyl sulfide stream 708. Heat in heat exchanger 702 can be provided from gaseous product stream 610, thus maximizing the heat efficiency of cryogenic distillation system 700. Gaseous carbonyl sulfide stream 708 can enter first reaction zone 204 and/or 502 or be mixed with streams entering the first reaction zone.

[0052] 6. Separation System for First Product Stream

[0053] The first product stream can undergo a similar cryogenic distillation as described for FIG. 7. FIG. 8 depicts a schematic for separating carbon monoxide from sulfur dioxide from the first product stream. Referring to FIG. 8, cryogenic separation system 800 is in fluid communication with the first product stream from the systems described in FIGS. 2-5. System 800 includes heat exchangers 802, 804, and condenser 806. Gaseous first product stream 216 enters condenser 806, which is at a temperature sufficient to separate liquid SO.sub.2 from the gaseous product stream and form liquid sulfur dioxide stream 808 and gaseous product stream 810. In some embodiments, the temperature of condenser 806 ranges from 150 to 55 C. Liquid sulfur dioxide stream 808 exits condenser 806 and can undergo heat exchange in heat exchanger 804 to produce gaseous sulfur dioxide stream 812. In heat exchanger 804, hot gaseous product stream 216 can be used as the working fluid to provide heat to liquid sulfur dioxide stream 808 to sufficiently to gasify all, or substantially gasify all, of the liquid sulfur dioxide in sulfur dioxide stream 808 to gaseous sulfur dioxide. Gaseous sulfur dioxide stream 812 can be transported to storage units, transported to other processing units to be converted into other commercial products, and/or sold.

[0054] Gaseous product stream 810 can exit condenser 806 and pass through heat exchanger 802, and be transported to storage units, other process facilities or sold as a commercial product, or recycled to second reaction zone 206 and/or 506. Carbon dioxide stream 810 can have 90 to 100%, or preferably 100% by volume carbon dioxide. While passing through heat exchanger 802, cold carbon dioxide stream 810 may cool hot gaseous first product stream 216 exiting second reactor 506 and/or second reaction zone 206 described in FIGS. 2-5, and thus, improves the heat efficiency of the system. In some embodiments, carbon dioxide stream 810 does not pass through heat exchanger 802.

[0055] With respect FIGS. 2-8, 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.

B. First and Second Reaction Mixtures

[0056] The first reaction mixture can include any mixture that produces heat upon reacting. In one embodiment, the first reaction mixture can include carbonyl sulfide (COS) and an oxidant source. The COS can be obtained from the reaction of carbon dioxide and sulfur as described below. COS can be obtained from various commercial vendors. A non-limiting example of a commercial vendor is Praxair, Inc. (USA). The oxidant source can be oxygen (O.sub.2) gas, air, or oxygen enriched air. The oxidant is available from various commercial vendors. A non-limiting example of a commercial vendors for COS and oxidants is Praxair, Inc. (USA). In the first reaction mixture, a molar ratio of O.sub.2(g) to COS(g) can range from 0.1 to 2 or 1.5 and any range therein. Ratios lower than 0.1:1 and higher than 2:1 are also contemplated in the context of the present invention. Ultimately, the ratio can be varied to produce a desired reaction product profile.

[0057] The second reaction mixture or gaseous reaction mixture 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 all allotropes of sulfur (i.e., S.sub.n where n=1 to infinity). Non-limiting examples of sulfur allotropes include S, S.sub.2, and S.sub.3. Sulfur gas (S.sub.1-3) can be obtained by heating solid or liquid sulfur to its boiling point of about 115 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 Ss 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. 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). In the second reaction 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.

[0058] The first and second reaction mixtures can 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.

C. Reaction Products

[0059] The products made from the reduction of carbon dioxide with elemental 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 equations (6) and (9). Table 1 lists the enthalpy, entropy and Gibbs free energy for reactions (6) through (10). The other products that can be produced by the reaction include CS.sub.2 and COS as shown in equation (11), 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)(11)

TABLE-US-00001 TABLE 1 H, S, H, H, 100 C., 100 C., G, 500 C., S, 500 C., G, 500 C., 1100 C., S, 1100 C., G, 1100 C., Reaction kcal kcal 100 C. kcal cal/K kcal kcal cal/K kcal COS + 1.5O.sub.2 = 131.2 18.9 124.1 131.4 19.5 116.4 131.3 19.4 104.7 CO.sub.2 + SO.sub.2 2CO.sub.2 + S = 2.34 11.4 6.6 2.8 10.6 11.0 4.1 9.4 17.0 CO + SO.sub.2 4CO.sub.2 + S.sub.2 = 98.1 49.3 79.7 98.0 49.4 59.8 96.2 47.7 30.7 4CO + SO.sub.2 CO + S = COS 74.3 32.5 62.2 74.6 33.1 49.0 74.2 32.8 29.2 2CO + S.sub.2 = 45.9 38.6 31.5 45.5 38.1 16.1 44.0 36.6 6.32 2COS

[0060] 1. COS Formation

[0061] Without wishing to be bound by theory, it is believed that, as shown in equation (12), 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 C. 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 or recycled back to the first reaction zone to be used as fuel for heat.

2CO.sub.2(g)+2S(g).fwdarw.2 COS(g)+O.sub.2(g)(12)

[0062] 2. CO and SO.sub.2 Formation

[0063] Without wishing to be bound by theory, it is believed that the carbonyl sulfide and oxygen in equation (12) react with carbon dioxide and sulfur to form SO.sub.2 and CO as shown in equations (13) and (14). 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 SO.sub.2(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 SO.sub.2(g) at 918 C., 1120 C. and 1500 C. and different temperatures are summarized in Table 2.

S(g)+O.sub.2(g).fwdarw.SO.sub.2(g)(13)

COS(g)+2CO.sub.2(g).fwdarw.SO.sub.2(g)+3CO(g)(14)

TABLE-US-00002 TABLE 2 CO.sub.2:S CO:SO.sub.2 ratio CO:SO.sub.2 ratio CO:SO.sub.2 ratio ratio at 918 C. at 1120 C. at 1500 C. 6:1 0.8:1 1.78:1 .sup.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

[0064] 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 3.

TABLE-US-00003 TABLE 3 CO.sub.2:S CO.sub.2/(CO + SO.sub.2) CO.sub.2/(CO + SO.sub.2) CO.sub.2/(CO + SO.sub.2) ratio ratio at 918 C. ratio at 1120 C. ratio at 1500 C. 6:1 6.2:1 .sup.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 .sup.1:1 0.1:1 0.5:1

[0065] 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 (15). 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)(15)

[0066] 3. CS.sub.2 Formation

[0067] 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 (16). 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)(16)

[0068] 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.

D. Catalysts and Reaction Conditions

[0069] 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.

[0070] 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.

E. Further Processing of Products

[0071] 1. CO Processing

[0072] 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 (17). 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(17)

[0073] 2. SO.sub.2 Processing

[0074] 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 (18) through (21).

SO.sub.2+O.sub.2.fwdarw.SO.sub.3(18)

SO.sub.3+H.sub.2SO.sub.4H.sub.2S.sub.2O.sub.7(19)

H.sub.2S.sub.2O.sub.7+H.sub.2O.fwdarw.2H.sub.2SO.sub.4(20)

2NH.sub.3+H.sub.2SO.sub.4.fwdarw.(NH.sub.4).sub.2SO.sub.4(21)

[0075] 3. COS Processing

[0076] 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 thiocyanate and sulfuric acid as shown in equation (22).

KSCN+2H.sub.2SO.sub.4+H.sub.2O.fwdarw.KHSO.sub.4+NH.sub.4HSO.sub.4+COS(22)

[0077] 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

[0078] 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

Exothermic Calculations

[0079] Exothermic calculations were done by using aspenONE Version 8.6 software provided by Aspentech. FIGS. 9-11 are graphs of the calculated exotherms for conversion of COS with oxygen (FIG. 9), CO with sulfur (FIG. 10) and CO.sub.2 with elemental sulfur (FIG. 11) versus heat trace across the bed. Table 4 lists the conversions and corresponding delta % raise for the three different reactions.

TABLE-US-00004 TABLE 4 COS = 1.5O.sub.2 = CO.sub.2 + SO.sub.2 2CO.sub.2 + S = CO + SO.sub.2 CO + S = COS Absolute T, C. Absolute T, C. Absolute T, C. Conversion T, C. raise Conversion T, C. raise Conversion T, C. raise 0 500 0 500 0 500 0.05 756 256 0.05 504 4.3 0.05 784 284.7 0.1 1003 503 0.1 508 8.63 0.1 1062 562.3 0.15 1244 744 0.15 512 13 0.15 1333 833.8 0.2 1481 981 0.2 517 17.4 0.2 1600 1100.6 0.25 1716 1216 0.25 521 21.8 0.25 1863 1363.5 0.3 1949 1449 0.3 526 26.2 0.3 2123 1623.4 0.35 2180 1680 0.35 530 30.6 0.35 2380 1880.5 0.4 2410 1910 0.4 535 35.1 0.4 2635 2187.4 0.45 2639 2139 0.45 539 40 0.45 2887 2387.8 0.5 2867 2367 0.5 544 44.2 0.5 3137 2637.6 0.55 3094 2594 0.55 548 48.7 0.55 3385 2885.8 0.6 3321 2821 0.6 553 53.3 0.6 3631 3132 0.65 3447 3047 0.65 557 58 0.65 3876 3376.3 0.7 3772 3272 0.7 562 62.6 0.7 4118 3618.7 0.75 3997 3497 0.75 567 67.3 0.75 4359 3859.3 0.8 4221 3721 0.8 571 71.7 0.8 4598 4098.2 0.85 4445 3945 0.85 576 76.7 0.85 4835 4335.3 0.9 4669 4169 0.9 581 81.5 0.9 5070 4570.7 0.95 4892 4392 0.95 586 86.2 0.95 5304 4804.3 1 5115 4615 1 591 91 1 5536 5036.3