An evaluation of synthesis gas contaminants as methanol synthesis catalyst poisons

The liquid phase methanol (LPMEOH(TM)) process has successfully produced methanol from coal-derived synthesis gas on an industrial scale. This process uses a standard copper, zinc oxide, and alumina catalyst suspended in an inert mineral oil in a slurry bubble column reactor. A series of common synthesis gas contaminants were evaluated to determine their effect on catalyst activity. The following representative species were found to adversely affect the rate of methanol synthesis: phosphine (PH3), carbonyl sulfide (COS), carbon disulfide (CS2), thiophene (C4H4S), methyl thiocyanate (CH3SCN), methyl chloride (CH3Cl), and methyl fluoride (CH3F). The nitrogen-containing contaminants hydrogen cyanide (HCN), acetonitrile (CH3CN), and methylamine (CH3NH2) had no effect on catalyst activity. The surprising inactivity of HCN is likely attributable to its hydrogenation under methanol synthesis conditions. An approximate order of decreasing catalyst poison potency was obtained: C4H4S congruent to AsH3 > CH3Cl > CH3SCN > CS2 > COS > PH3 > CH3F. Based on catalyst surface area and molar effectiveness for each poison, catalyst poisoning cannot be attributed solely to a loss of copper surface area. Although this study involved the liquid phase process, the results should be applicable to methanol synthesis by a gas phase, fixed bed process. A rationalization of contaminant/catalyst reactivity is presented. (C) 2004 Elsevier B.V. All rights reserved.