Removing a Trace Isomer in Propylene Glycol Methyl Ether via Reactive Separation

Removing the minor isomer in propylene glycol methyl ether (PGME) is essential for the production of electronic grade PGME that is widely used in the semiconductor industry. However, conventional approaches based on multistage distillation are energy-intensive and time-consuming and require expensive equipment. Herein, we report a multistage distillation-free approach that removes the trace amount of the minor isomer in PGME by preferentially adding a tag to the minor isomer covalently, thus allowing efficient removal of these tagged isomers. We used the nucleophilic substitution reaction between alcohol and triphenylchloromethane in the presence of organobase for chemoselective tagging and systematically investigated the effect of the feed ratio, PGME purity, water content, organobase, and scale of the reaction. Our strategy could reduce the percentage of the minor isomer from 0.56% to below 0.1% at a 200 g scale and decrease the water content from over 340 to below 70 ppm. We also developed a chemical recycling protocol to reduce the chemical wastes as well as the overall cost of our chemoselective tagging strategy and conducted theoretical calculations to provide a rational guide for further optimization. Our strategy represents a promising alternative to conventional multistage distillation in the purification of PGME.