Catalytic Process for the Conversion of Synthesis gas to Ethanol for Use as an Alternative Fuel

Abstract

Higher alcohols are increasing as a proportion of the transportation fuel market, and can be used as neat fuels, or as blends with conventional fuels. For a number of reasons, these C2+-alcohols will be of interest in the foreseeable future. Large-scale production of higher alcohols will likely be carried out via syngas, which can be produced from a number of feedstocks, including coal, natural gas and biomass. Rhodium-based catalysts have been found to be the most active/selective for higher alcohols. However, the literature shows that the yields of C2+-alcohols that can be achieved with current catalysts, even the most active/selective, are not practical, typically less than 10%. Also, due to the high cost of rhodium, the production of ethanol from Rh-based catalysts is not economically feasible at industrial scale. This research is based on development of non-rhodium based catalysts for conversion of synthesis gas to C2+-alcohols, with focus on ethanol. The work reported here aims to identify active catalysts, synthesize them using advanced methods that allow atomic-level control of the surface, and characterize them using state-of-the-art facilities, such as LSU’s synchrotron beam line and in-situ FTIR. Studies on cobalt-rhenium catalysts showed that precursors have a significant effect on the catalyst characteristics. Cobalt acetate precursor catalyst was found to be highly dispersed compared to the nitrate precursor catalyst. The nitrate precursor catalyst was found to be more active for CO hydrogenation compared to the acetate precursor catalyst, but selectivity towards oxygenates was lower. In-situ FTIR results showed that CO adsorption takes place relatively weakly on the acetate precursor catalyst, owing to its high dispersion, as compared to the nitrate precursor catalyst. The weakly adsorbed CO on the acetate precursor catalyst is believed to be responsible for higher oxygenates selectivity. Studies on cobalt-palladium catalysts showed that they are active for CO hydrogenation. A 2 wt% cobalt catalyst was found to be more selective towards oxygenates formation as compared to 10 wt% cobalt catalyst, both having same loading of 2 wt% palladium. In-situ DRIFTS results showed that the active sites for CO hydrogenation were terminal (for 10%Co) and bridge-type (for 2%Co).