Cobalt-molybdenum sulfide catalyst materials and methods for stable alcohol production from syngas
The present invention provides methods and compositions for the chemical conversion of syngas to alcohols. The invention includes catalyst compositions, methods of making the catalysts, and methods of using the catalysts including techniques to maintain catalyst stability. Certain embodiments teach compositions for catalyzing the conversion of syngas into products comprising at least one C 1 -C 4 alcohol, such as ethanol. These compositions generally include cobalt, molybdenum, and sulfur, and avoid metal carbides both initially and during reactor operation.
1. A method of producing at least one C 1 -C 4 alcohol from syngas, the method comprising:
(a) providing a reactor including a catalyst composition comprising cobalt, molybdenum, and sulfur, wherein at least some of said cobalt and some of said sulfur are present as a cobalt-sulfur association having a molar ratio of sulfur to cobalt (S:Co), calculated by assuming all molybdenum is present as MoS 2 ;
(b) flowing syngas into said reactor at conditions effective to produce at least one C 1 -C 4 alcohol; and
(c) injecting additional sulfur, or a compound containing sulfur, into said reactor, in an amount that is sufficient to maintain at least some of said cobalt in a sulfided state, and is further sufficient to maintain said molybdenum in a completely sulfided state wherein said additional sulfur injected in step (c) is contained in one or more compounds selected from the group consisting of elemental sulfur, hydrogen sulfide, dimethyl sulfide, diethyl sulfide, dimethyl disulfide, dibutyl polysulfide, dioctyl polysulfide, diphenyl polysulfide, dicyclohexyl polysulfide, methylthiol, ethylthiol, cysteine, cystine, methionine, potassium disulfide, cesium disulfide, sodium disulfide, and any isomers thereof.
2. The method of claim 1 , wherein said molar ratio S:Co is controlled to between about 0.1 and about 4.
3. The method of claim 2 , wherein said molar ratio S:Co is controlled to a ratio of at least 1.
4. A method for maintaining catalyst stability while producing at least one C 1 -C 4 alcohol from syngas, said method comprising:
(a) providing a reactor including a catalyst composition comprising cobalt, molybdenum, and sulfur;
(b) flowing syngas into said reactor at conditions effective to produce at least one C 1 -C 4 alcohol; and
(c) injecting additional sulfur, or a compound containing sulfur, into said reactor, in an amount that is sufficient to inhibit the formation of cobalt carbides or molybdenum carbides under said conditions effective to produce at least one C 1 -C 4 alcohol.
5. The method of claim 4 , wherein said step (c) inhibits the formation of cobalt carbides.
6. The method of claim 5 , wherein said cobalt carbides include crystalline Co 2 C.
7. The method of claim 4 , wherein said step (c) inhibits the formation of molybdenum carbides.
8. The method of claim 4 , wherein said step (c) prevents the formation of cobalt carbides or molybdenum carbides.
9. The method of claim 4 , wherein said additional sulfur maintains at least some of said cobalt in a sulfided state.
10. The method of claim 9 , wherein said additional sulfur maintains said cobalt in a sulfided state.
11. The method of claim 4 , wherein said additional sulfur maintains said molybdenum in a sulfided state.
12. The method of claim 4 , wherein said additional sulfur injected in step (c) is contained in one or more compounds selected from the group consisting of elemental sulfur, hydrogen sulfide, dimethyl sulfide, diethyl sulfide, dimethyl disulfide, dibutyl polysulfide, dioctyl polysulfide, diphenyl polysulfide, dicyclohexyl polysulfide, methylthiol, ethylthiol, cysteine, cystine, methionine, potassium disulfide, cesium disulfide, sodium disulfide, and any isomers thereof.
13. The method of claim 4 , comprising maintaining, for at least 1000 hours on-stream, one or more parameters selected from the group consisting of CO conversion, ethanol selectivity, total alcohol selectivity, total alcohol productivity, and methane selectivity.
14. The method of claim 4 , further comprising recovering sulfur downstream of said reactor and recycling at least a portion of said sulfur into said reactor.