Acid-base properties, deactivation, and in situ regeneration of condensation catalysts for synthesis of methyl methacrylate

摘要

Condensation reaction of a propionate with formaldehyde is a novel route for synthesis of methyl methacrylate (MMA). The reaction mechanism involves a proton abstraction from the propionate on the basic sites and activation of the aliphatic aldehyde on the acidic sites of the catalyst. The acid-base properties of ternary V-Si-P oxide catalysts and their relation to the NWA yield in the vapor phase condensation of formaldehyde with propionic anhydride has been studied for the first time. Five different V-Si-P catalysts with different atomic ratios of vanadium, silicon, and phosphorous were synthesized, characterized, and tested in a fixed-bed microreactor system. A V-Si-P 1:10:2.8 catalyst gave the maximum condensation yield of 56% based on HCHO fed at 300(degrees)C and 2 atm and at a space velocity of 290 cc/g cat(center dot)h. A parameter called the ''q-ratio'' has been defined to correlate the condensation yields to the acid-base properties. The correlation of q-ratio with the condensation yield shows that higher q-ratios are more desirable. The long-term deactivation studies on the V-Si-P 1: 10:2.8 catalyst at 300(degrees)C and 2 atm and at a space velocity of 290 cc/g cat(center dot)h show that the catalyst activity drops by a factor of nearly 20 over a 180 h period. The activity can be restored to about 78% of the initial activity by a mild oxidative regeneration at 300(degrees)C and 2 atm. The performance of V-Si-P catalyst has been compared to a Ta/SiO(sub 2) catalyst. The Ta- catalyst is more stable and has a higher on-stream catalyst life.