Process for preparing unsaturated esters proceeding from aldehydes by direct oxidative esterification

摘要

The present invention relates to a process for preparing methyl methacrylate by a direct oxidative esterification of methacrolein with oxygen and methanol, which is conducted in the liquid phase at a pressure of 2 to 100 bar with a gold catalyst. According to the invention, the liquid phase is withdrawn continuously from the reactor and optionally enriched with oxygenous gas, the pH, after the withdrawal, is adjusted to a pH between 5 and 9 by means of addition of a basic solution and this liquid phase is conducted back into the reactor again to an extent of at least 50%.

主权项

1. A process for preparing methyl methacrylate, comprising:
reacting methacrolein in a continuous oxidative esterification with oxygen and methanol which is conducted in a liquid phase in a reactor at a pressure of 2 to 100 bar in the presence of a heterogeneous catalyst comprising gold-containing nanoparticles having a particle size less than 20 nm; withdrawing continuously the liquid phase from the reactor and adjusting the pH after the withdrawal to a pH between 5 and 9 by addition of a basic solution outside of the reactor; and conducting at least 50% of the withdrawn liquid phase having a pH between 5 and 9back into the reactor, wherein the methacrolein is dewatered by distillation in the presence of methanol before being fed into the reactor.