Methanol carbonylation process with rhodium catalyst, an iodide salt and a metallic co-catalyst selected from transition metals, indium, strontium, barium, zinc, tin and heteropoly acids

Abstract

A carbonylation process for making acetic acid uses a metallic co-catalyst composition effective as a rhodium stabilizer and rate promoter at molar ratios of metal/rhodium of from about 0.5 to 30. A preferred process includes: (a) reacting methanol with a carbon monoxide feedstock in a rhodium-based catalytic reaction mixture having: (i) a rhodium catalyst metal, (ii) methyl iodide maintained from about 1 to 20 weight percent, (iii) a lithium iodide co-catalyst, (iv) a metallic co-catalyst composition, (v) water maintained from 0.1 weight percent to less than 8 weight percent, (vi) methyl acetate maintained from about 0.5 to about 30 weight percent, and (vii) acetic acid; (b) flashing crude acetic acid from the reaction mixture; and (c) purifying the crude acetic acid. This process achieves stability and a STY greater than 10 mol/L/hr, with substantially less than a theoretically equivalent inorganic iodide content corresponding to the metallic co-catalyst and lithium iodide.