Esterification of levulinic acid with ethanol over sulfated mesoporous zirconosilicates: Influences of the preparation conditions on the structural properties and catalytic performances

Abstract

Levulinic acid is considered one of the most important biomass-derived chemicals owing to its potential as a versatile building block to synthesize valuable fuels and chemicals. Levulinate esters, such as methyl levulinate and ethyl levulinate obtained via esterification of levulinic acid with alcohols, can in particular be used as fuel additives and plasticizers, and thus have a potential to replace a significant amount of petroleum-derived chemical feedstocks. In this article, sulfated zirconosilicates having P6mm hexagonal mesoporous structure were applied as solid acid catalysts to the esterification of levulinic acid with ethanol to produce ethyl levulinate, and the influences of preparation conditions on the structural properties and catalytic performances were investigated. A distinct correlation was observed between the catalytic activity and the density of acid sites, showing that dispersibility of the acid sites and the associated accessibility of the organic reactants play an important role in determining the overall activity. Among the catalysts tested, sulfated Zr–SBA-15 with optimum Zr content (Si/Zr ratio of 10.7) was found to be the best catalyst, the activity of which was far superior to that of conventional sulfated ZrO2. In addition, direct conversion of cellulosic sugars (glucose and fructose) into levulinate esters was also examined.