Vapor-phase Carbonylation of Dimethyl Ether on Supported Nickel Catalyst -Vapor Phase Carbonylation of Organic Compound over Supported Transition Metal Catalysts. V.-

Abstract

Vapor-phase carbonylation of dimethyl ether(DME) to methyl acetate with nickel/active carbon catalyst was carried out in the presence of methyl iodide (Mel) promoter. The reaction was studied using a continuous-flow reactor with a fixed catalyst bed under the conditions of 200-300°C and 10-40 atm.
Methyl acetate was form ed with a selectivity more than 90% along with small amounts of acetic acid, acetic anhydride and methane. The catalyst with 2.5 wt% nickel gave the best yield of methyl acetate (Fig.1). Figure 2 and 3 show that the primary product of carbonylation is methyl acetate while acetic acid and acetic anhydride and formed succeedingly. The increase of reaction temperature and pressure resulted in an increase of the yield of methyl acetate and a decrease of the selectivity. However, with increasing of the MeI/DME ratio, both the yield and selectivity were increased (Fig.7).
The experimental rate equation was determined in a differential type reactor as follows (Fig.8):_??_
The dependency of the rate of DME carbonylation on the p artial pressure of methyl iodide was higher than that of methanol carbonylation and the rate of DME carbonylation was slower than methanol carbonylation. The important difference between the reactions of DME and MeOH is that the former reaction proceeds in a water-free system.
These observations suggest that the step of MeI adsorption is slow in DME carbonylation and water accelerates the step of MeI adsorption. In fact, introduction of water to DME carbonylation increased the reaction rate (Fig.9) and the selectivity of acetic acid (Fig.3). It is also presumed that water decomposes the methyl acetate which retards the carbonylation due to its strong adsorption.