Screening of solid acid catalysts for etherification of glycerol with isobutene under identical conditions

Abstract

We compared the performance of more than 70 solid acid catalysts with Bronsted acid function for the etherification of glycerol with isobutene under identical reaction conditions of 75 degrees C, 10 bar, 6 h and with an isobutene/glycerol molar ratio of 3/1. The catalysts were selected from a wide range of solid acid catalysts including ion exchange resins, zeolites, silica, and heteropolyacids, and their counterparts modified by simple treatments, with more than half of them being investigated for the first time for this reaction. For the modified commercial acid catalysts, the desired glycerol tertiary butyl ether (DTBGE and TTBGE) selectivity improved from 75 to 87 wt% upon partial cation exchange of the sulfonic acid protons in AmberlystT type ion exchange resins with Na+ cations; from 66 to 85 wt% by hydrothermal steam treatment of zeolite H-Y (SiO2/Al2O3 = 80); and from 75 to 80 wt% with partial La+-exchange of zeolite H-Beta (SiO2/Al2O3 = 300), all at high (90-100%) glycerol conversion. Impregnation of the heteropolyacids, tungstosilicic acid (TSA) and tungstophosphoric acid (TPA), on silica at a loading of 50 wt% provided a glycerol conversion of higher than 65 wt% and with a desired ether selectivity in the range of 62 to 76 wt%. In general, total ether selectivity increased with decreasing acid capacity for ion exchange resins, while the desired ether selectivity was enhanced with increasing acid strength for zeolites and supported heteropolyacids on mesoporous silica. Data present a detailed guideline for the selection of solid acid catalysts for the etherification of glycerol with isobutene.