Synthesis of methyl methacrylate by vapor phase condensation of formaldehyde with propionate derivatives

Abstract

The gas phase condensation of formaldehyde with propionic acid, propionic anhydride, and methyl propionate was studied over a series of V-Si-P catalysts of varying atomic ratios. Propionic anhydride gave the maximum yield of methacrylic acid (56%, based on formaldehyde fed to the reactor) at 300°C, 2 atm, 290 cc g −1 h −1 and a stoichiometric anhydride/ formaldehyde ratio of 2:1. This yield was obtained for the optimum V-Si-P catalyst, which had an atomic ratio of 1:10:2.8. This is the highest yield reported to date for the heterogeneous catalytic condensation of propionic anhydride with formaldehyde. A parameter called the q-ratio has been defined to correlate condensation yields to catalyst acid-base properties. Higher q-ratios (0<q<1) correspond to a higher proportion of strong acid sites and are directly related to higher condensation yields. The long-term deactivation studies on the V-Si-P 1:10:2.8 catalyst at 300°C, 2 atm and 290 cc g −1 h −1 show that catalyst activity drops by nearly a factor of 20 over a 180-h period, and that 78% of the activity can be restored by a mild oxidative regeneration. The performance of a V-Si-P catalyst has been compared to a Ta/SiO 2 catalyst; Ta catalyst is more stable and has a higher on-stream life.