Catalytic synthesis of methanethiol from CO/H_2/H_2S mixtures using alpha-Al_2O_3

摘要

Sustained synthesis of methanethiol from the reaction of CO/H_2/H_2S mixtures is reported and discussed.Surprisingly,unmodified alpha-Al_22O_3 gives the best results for this reaction and methanethiol selectivities of > 98% at CO conversions of ca.6% can be readily obtained (CO:H_2:H_2S=4:5:1,340 deg C,total pressure=20 bar,200 h~(-1)).Reaction of CO+H_2 (CO:H_2=1:1) in the absence of H_2S using alpha-Al_2O_3 under comparable conditions gives a lower CO conversion (ca.1.3%) with significant selectivities to methane (20%),methanol (28.5%) and ethanol (21.1%).When H_2S is added to the synthesis gas feedstock,the product selectivity switches to sulfur-containing products,almost exclusively methanethiol,but some by-product thiophene is also observed.A range of other catalysts were also investigated (e.g.,gamma-Al_2O_3,Cr_2O_3,Cr_2O_3/Al_2O_3,Cu/Cr_2O_3) but all give inferior catalytic performance when compared with alpha-Al_2O_3.The mechanism of the synthesis of methanethiol is discussed,based on a modification of chain propagation in the Fischer-Tropsch synthesis reaction.