Direct production of propylene glycol from propylene using bifunctional Al-TS-1

Abstract

Propylene glycol (PG) is an important industrial chemical used in pharmaceuticals, cosmetics, and antifreeze. The conventional industrial process for producing PG involves a two-step procedure: the epoxidation of propylene (PP), followed by the hydrolysis of propylene oxide (PO) into PG. However, this process involves multiple separation and purification steps that are economically and energetically inefficient. Herein, we present a bifunctional Al-TS-1 catalyst for the direct synthesis of PG from PP using H2O2 as an oxidant under mild conditions. The catalyst features two active centers of isomorphic substituted monomeric titanium in a zeolite framework for PP epoxidation as well as Br & Oslash;nsted acidic aluminum sites for PO hydrolysis. Al-TS-1 efficiently facilitates epoxidation and hydrolysis with over 95 % PG selectivity from PP, higher than that of physically mixed TS-1 and ZSM-5 catalysts. However, its activity is relatively low owing to pore blocking by the produced PG. To overcome this low activity, we optimized the reaction media to acetone/H2O, which enhanced PG dissolution from zeolite pores and increased the accessibility of propylene to the active centers in the zeolite pores. As a result, over 99 % catalytic overall activity and over 98 % PG selectivity was achieved using Al-TS-1. The direct PG production from the PP system using a bifunctional Al-TS-1 catalyst successfully demonstrates high PG selectivity and broadens its potential for efficient PG production.