Acetic Acid Production via Low-Pressure, Nickel-Catalyzed Methanol Carbonylation

Nickel-catalyzed methanol carbonylation under high pressure and temperature has been known for decades. The parameters that bring the catalytic activity of the nickel catalyst to the same level of the rhodium process have been examined. Promoters stabilize the nickel catalyst and enhance the reaction rate under mild reaction conditions. The most efficient promoters are phosphines, alkali metals and tin. Combining two different promoters gives maximum reaction rate. Hydrogen and metals of group VIB promote reaction rate and catalyst stability. The reaction is first order with respect to iodine and nickel and is retarded by the presence of high water or methanol concentrations and high CO partial pressure. A mechanism is proposed to explain the function of the different promoters and reaction parameters.