Methanol reaction with H2S on tungsten-and potassium-promoted alumina was studied in the absence of any diffusional restrictions. We have found that on both W/Al203 and KW/Al203 catalysts methanol reacts with H2S to produce methyl mercaptan, which may convert to dimethyl sulfide through either interaction with the second molecule of methanol or disproportionation.Methanol dehydration yields dimethyl ether. For KW/Al203 catalyst, the generation of methyl mercaptan dominates. Adsorption data permitted us to suggest a mechanism of methanol reaction with H2S. According to this mechanism reaction proceeds via the rapid methoxylation of catalyst surface and further interaction of CH30 groups with the activated H2S, CH3SH, and CH30H. The kinetic equations obtained describe fairly well the reaction on the inhomogeneous catalyst surface.
IntroductionMethanol interaction with H2S on heterogeneous catalysts is of prime interest for the commercial production of methyl mercaptan and dimethyl sulfide. Methyl mercaptan is needed to produce methionine (feed additive, medicine). Dimethyl sulfide is used for the commercial synthesis of dimethyl sulfoxide (medicine, solvent, and extractant). Methyl mercaptan and dimethyl sulfide can be obtained from methanol and H2S on various catalysts. Reaction direction and rate depend on the catalyst nature. Alumina promoted with alkali and transition metal oxides appears to be the most active catalyst for methyl mercaptan production. According to Folkins and Miller (1962a,b), the selectivity toward methyl mercaptan reaches 80-90% at 350-420 "C, H2S:CH30H = 1.5 in the presence of the above catalysts. Mashkina et al. (1988a,b) have shown that support ( A l 2 0 3 , NSi, Si021 promotion with hydroxide, carbonate, or tungstates of potassium or sodium increases the surface basicity, thus increasing the selectivity toward methyl mercaptan generation. Dimethyl sulfide forms in the methanol reaction with H2S on the surface and supported on A l 2 0 3 , AlSi, and oxides and sulfides of transition metals. This fact is proved by Pinegina (1971, 1980) and Miki et al. (1966a-c). Mashkina et al. (1989) have found that acidic additives introduced into the catalyst increase the selectivity toward dimethyl sulfide. Aluminas with acid-base pair sites (strong Lewis acid sites and moderate base sites) are the most efficient catalysts for dimethyl sulfide synthesis. Temperature, rate of reagent feeding, and H2S:CH3-OH ratio affect the parameters of methyl mercaptan and dimethyl sulfide synthesis. Folkins and Miller (1962a,b) proved this fact for a 5% K&o3/f%03 catalyst (2' = 373-427 "C); Pankratova and Pinegina (1971) and Miki et al. (1966b,c) proved it for Al203; Kushelev et al. (1978) proved it for A1203 and a 5% NaOWAl203 catalyst. Miki et al. (1966~) proposed the ways of reaction product formation on Al2O3. They believed that dimethyl ether, the primary reaction product, may convert to methyl mercaptan and dimethyl sulfide and then decompose to carbon oxides and methane under certain conditions. Analyz...
