(317g) Potassium Promoted CoMo Sulfide as a Catalyst for the Synthesis of Higher Alcohols From Syngas

Cellulosic biofuels (e.g., ethanol) are receiving tremendous academic and industrial attention due to potential economic rewards associated with an almost exponential increase in renewable biofuels demand for the next decade, as mandated by the Energy Independence and Security Act of 2007. Catalytic conversion of biomass derived syngas to higher alcohols is one attractive alternative for production of biofuels; however, active and selective catalysts such as promoted metal sulfides and rhodium based catalysts still lack appropriate performance (CO conversion, alcohols STY, etc.) for a commercial process. Better understanding of reaction mechanism and of the influence of process variables should assist in the design of improved catalysts. In this work, unsupported K-CoMoS_x was investigated as a catalyst for the synthesis of ethanol and higher alcohols from syngas. The catalyst was prepared by coprecipitation methods and tested in a fixed bed reactor with online analysis of products which mainly consisted of C₁-C₅ hydrocarbons and linear alcohols. Carbon balances closed to 100 ± 5%. Under typical reaction conditions 330 ^oC, 82 bar, 4000 scc g_cat^-1 h^-1, and H₂/CO=1 alcohols space time yield was about 200 g kg_cat^-1 h^-1. The major byproduct is CO₂ which is mainly formed via water gas shift reaction (CO + H₂O = CO₂ + H₂). Results suggest that water gas shift reaction is quasi-equilibrated under the studied reaction conditions and acts as an internal chemical control for oxygen rejection as CO₂. We have also observed the presence of oscillations in the rates of formation of the products which appears to be directly linked to an oscillatory behavior of the water gas shift reaction on the K-CoMoS_x catalyst.