An in situ CIR-FTIR investigation of process effects in the nickel catalyzed carbonylation of methanol

Abstract

The carbonylation of methanol to form methyl acetate and acetic acid was investigated using phosphine modified nickel iodide as the metal catalyst precursor. The course of the reaction was monitored using a high pressure, high temperature in situ Cylindrical Internal Reflectance FTIR reactor (CIR-REACTOR) to acquire data under autogenous conditions. The capabilities of the reactor permit reaction monitoring at temperatures of 190°C and pressures of 13.6 kPa (1500 psig). In this study the reaction kinetics and in situ observations were made at temperatures between ambient and 160°C with an operating pressure of 8.16 kPa (900 psig) for most reactions. This study used methyl acetate as a solvent, and both methyl acetate and acetic acid were products of the catalytic reaction. Conditions were optimized at 160°C using organo-phosphine modified NiI 2 as the catalyst precursor. Under the applied reaction conditions, no anionic carbonyl species such as Ni(CO) x I y − y were detected at high carbonylation rates, in contrast to the anionic carbonyls reported in the rhodium catalyzed acetic acid process. In the rapid kinetic regime, only trace amounts of Ni(CO) 4 were formed in the reactor at steady state. The experimental results suggest a new mechanism involving Ni(PPh 3) 2 as one of the active metal complex intermediates reacting in a slow step with methyl iodide. The in situ reaction monitoring experiments readily enabled the determination of the concentrations of organonickel species as well as the concentration of carbonylation products under fast reaction conditions.