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

A continuous process for the production of acetic acid comprising:

• (a) reacting a compound, selected from the group consisting of methanol and reactive derivatives thereof, with carbon monoxide to produce acetic acid in an aqueous reaction mixture, the reaction being carried out while maintaining a concentration of water in the reaction mixture of from 0.1 wt % up to about 8 wt %, the reaction also being carried out in the presence of a homogeneous rhodium-based catalyst system comprising:
• (i) a rhodium catalyst metal;
• (ii) an iodide promoter;
• (iii) an inorganic iodide-providing co-catalyst at a molar ratio of inorganic iodide-providing co-catalyst:Rh of less than 76:1;
• and
• (iv) a metallic co-stabilizing or rate-promoting composition including a metal selected from the group consisting of transition metals, indium, strontium, barium, zinc, tin, HPA, and mixtures thereof;
• and
• (b) recovering acetic acid from the reaction mixture;
• wherein the inorganic iodide-providing co-catalyst and the metal of the metallic co-stabilizing or rate-promoting composition are present in a molar ratio of 15:1 to 0.6:1 and wherein further the reaction mixture contains less than 70% of a theoretical amount of inorganic iodide equivalent to the presence of both the metal of the metallic co-stabilizing or rate-promoting composition and the inorganic iodide-providing co-catalyst.