Photodimerization of Maleic Anhydride in a Microreactor Without Clogging

Photodimerization of maleic anhydride (MA) gives insoluble precipitated products that can be a trigger to clog a conventional microreactor. To avoid this problem, we devised a microreactor that uses liquid/gas slug flow and ultrasonication. Inert N-2 gas introduced into the reaction solution swept through the reactor tube and transported precipitated products in the liquid segnients. Ultrasound vibrations inhibited the adhesion and sedimentation of precipitate in the reactor tube. The combination of gas and ultrasound prevented the tube from clogging. Fluorinated ethylene propylene (FEP) tubes of various sizes were investigated to use as a tube reactor. The tubes were wound around a high-pressure Hg lamp with a Pyrex immersion well which has been using generally as a light source of photoreaction, and the reaction solution was then passed through the tube and irradiated through the tube wall. The slug flow microreactor could be operated for more than 16 h continuously without clogging. Compared to using a batch reactor, this method achieves better product quality, improved conversion, and reduced waste.