Higher alcohols from syngas using a K/Ni/MoS2 catalyst: Trace sulfur in the product and effect of H2S-containing feed

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Two types of experiments have been performed related to the higher alcohol synthesis from syngas over a K–Ni–MoS2 catalyst which beforehand has been operated for 1000h on stream in sulfur-free syngas. In the first experimental part, sulfur-free syngas was used as feed and the condensed liquid product was found to contain 67ppmw sulfur, while the sulfur concentration in the gas was 19ppmv. The gas phase was found to contain mainly COS and H2S, while the liquid phase contained methanethiol (13.8ppmwS), ethanethiol (10.6ppmwS), dimethyl sulfide (21.3ppmwS), ethyl methyl sulfide (12.2ppmwS), unidentified sulfur compounds (7.9ppmwS) together with some dissolved COS (0.5ppmwS) and H2S (1.2ppmwS).In the second experimental part, the effect of feeding syngas containing 170ppm H2S compared to a sulfur-free syngas was studied, while all products were carefully monitored online. The presence of H2S in the syngas was found to increase CO conversion, but the largest change was found in product selectivity. The hydrocarbon selectivity greatly increased at the expense of alcohol selectivity, while the alcohol distribution shifted towards longer alcohols (increased C2+OH/MeOH ratio). From product yields it became clear that most of the increased CO conversion with H2S in the feed was due to increased methane formation (and CO2 formation due to the water–gas shift reaction). The presence of H2S in the feed greatly increased the concentration of all sulfur compounds. Together with COS, formation of thiols (methanethiol and ethanethiol) was especially favored by the presence of H2S. The thioether concentration also increased, however, to a much lower extent.