The Role of Arsine in the Deactivation of Methanol Synthesis Catalysts

The liquid phase methanol (LPMEOH™) process is successfully producing 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. An arsenic-containing species, most reasonably arsine, was found in the feed to the LPMEOH™ commercial demonstration facility located at Eastman Chemical Company’s chemicals-from-coal complex in Kingsport, TN. Laboratory testing showed that arsine is, in fact, a powerful methanol synthesis catalyst poison. At levels as low as 150ppbv, arsine results in a rapid deactivation of the catalyst. Removal of arsine results in a deactivation rate consistent with a clean synthesis gas feed; that is, arsine poisoning stops when it is removed from the feed. We infer that arsine reacts irreversibly with the catalyst under the methanol synthesis conditions. X-ray absorption spectroscopy (XAS) of arsenic-containing used catalyst indicated the presence of zero-valent arsenic in an intermetallic surface phase that is structurally related to Domeykite (Cu3As). Experimental evidence, thermodynamics, and literature relating to other metal–arsine chemistry were consistent with dissociative adsorption of arsine on the copper surface to form gaseous H2 and Cu3As. To deal with arsine poisoning, we have developed adsorption technology that can remove arsine to levels low enough that catalyst performance is unaffected.