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

The carbonylation of methanol to form methyl acetate and acetic acid was in vestigated using phosphine modified nickel iodide as the metal catalyst pre cursor. The course of the reaction was monitored using a high pressure, hig h temperature in situ Cylindrical Internal Reflectance FTIR reactor (CIR-RE ACTOR) to acquire data under autogenous conditions. The capabilities of the reactor permit reaction monitoring at temperatures of 190 degrees C and pr essures of 13.6 kPa (1500 psig). In this study the reaction kinetics and in situ observations were made at temperatures between ambient and 160 degree s C with an operating pressure of 8.16 kPa (900 psig) for most reactions. T his study used methyl acetate as a solvent, and both methyl acetate and ace tic acid were products of the catalytic reaction. Conditions were optimized at 160 degrees C using organo-phosphine modified NiI2 as the catalyst prec ursor. Under the applied reaction conditions, no anionic carbonyl species s uch as Ni(CO)(x)I-y(-y) were detected at high carbonylation rates, in contr ast 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 n ew mechanism involving Ni(PPh3)(2) as one of the active metal complex inter mediates reacting in a slow step with methyl iodide. The in situ reaction m onitoring experiments readily enabled the determination of the concentratio ns of organonickel species as well as the concentration of carbonylation pr oducts under fast reaction conditions. (C) 1999 Elsevier Science B.V. All r ights reserved.