Valorization of Biodiesel Derived Glycerol to Acetins by Continuous Esterification in Acetic Acid: Focusing on High Selectivity to Diacetin and Triacetin with No Byproducts

This work presents a continuous, easy-to-scale-up esterification system with 100% conversion of glycerol in acetic acid with a high selectivity to DA and TA and no byproducts under industrially applicable reaction conditions. The main emphasis is to obtain TA from glycerol esterification in acetic acid without using any acetic anhydride or harsh conditions. The effects of reaction parameters, including the acetic acid-to-glycerol mole ratio (1–9), temperature (66–134 °C), and pressure (1–199 bar) with a 0.5 mL·min–1 feed flow rate, on the glycerol conversion and selectivities to monoacetin, diacetin, triacetin, and byproducts were investigated. Under the optimum conditions of an acetic acid-to-glycerol mole ratio of 7, a temperature of 100 °C, and a pressure of 1 bar, over 3 g of Amberlyst 36, the glycerol conversion and monoacetin, diacetin, and triacetin selectivities reached 100%, 43%, 44%, and 13%, respectively. The formation of byproducts was not detected under these optimum conditions. Amberlyst 36 remained stable after 25 h on-stream. The recovered catalyst was reused with no significant deactivation after three cycles. This continuous system also can be used for monoacetin synthesis with 85% selectivity and 95% glycerol conversion with an acetic acid-to-glycerol mole ratio of 1, a temperature of 100 °C, and a pressure of 100 bar.