Catalytic synthesis of levulinic acid and formic acid from glucose in choline chloride aqueous solution

Abstract

Levulinic acid (LA) and formic acid (FA) are efficiently synthesized from glucose at moderate temperature (ca. 155 °C) in 90 min by using Lewis/Bronsted acid catalysts in choline chloride (ChCl) aqueous solution. It is found that the reaction time and temperature are two important operation variables to affect the yield and selectivity of LA as well as FA. The yields of LA and FA are around 34.2-38.4 mol% and 39.6-44.2 mol%, respectively, with single Lewis acid catalyst of AlCl3. By combination of AlCl3 with Bronsted acid catalyst of oxalic acid, the yields of LA and FA increase to 51.7 mol% and 56.2 mol%, respectively. The catalytic activity of AlCl3 in this system is considered to be highly promoted by ChCl, a safe and cheap quaternary ammonium chloride, with the assistance of Bronsted acid by accelerating the induction period of LA and FA formation route. A mechanism to explain the reaction route toward LA and FA formation is proposed and a model developed to simulate the compositions of the reaction mixture during reaction with the simulated results in good agreement to the experimental data. Furthermore, the LA can be simply separated from the product by evaporating water and extracting with low boiling point organic solvent such as acetone, and simultaneously the remaining polar liquid phase can be reused.