Chemicals from biomass derived products: synthesis of polyoxyethyleneglycol esters from fatty acid methyl esters with solid basic catalysts

Abstract

In the present work, we have studied the possibility of using heterogeneous base catalysts, of various basic strengths, for performing the transesterification between oleic acid methyl ester (MeO) and various polyethyleneglycols of different molecular weights (PEG-600, -400 and -200) to obtain polyoxyethyleneglycol monoesters. Reactions were performed using Brønsted and Lewis solid bases as catalysts: KF/alumina, Li₂O/alumina (Li–γAl₂O₃), MgO, Al–Mg (HTc–Al/Mg) and Al–Li (HTc–Al/Li) mixed oxides derived from hydrotalcites, CeO₂, a cesium cation exchanged X faujasite (CsX) and Al/Mg calcined–rehydrated hydrotalcites (HTr). The results showed that the order of activity was: Li–γAl₂O₃ > KF/alumina > MgO ≥ HTr > HTc–Al/Li > HTc–Al/Mg > CeO₂ > XCs. This is related to differences in the type and strength of the basic sites in these materials. The influence of the chemical composition of the calcined hydrotalcites, the influence of the hydrocarbon chain length of the fatty acid methyl ester on the activity and selectivity to monoester, and the optimization of reaction variables (such as reaction temperature and PEG/MeO molar ratio) have been studied. By combining a solid Brønsted base catalyst with the optimised reaction conditions it is possible to attain conversions higher than 90% with a selectivity to monoester greater than 98%, this being a real alternative to conventional processes using alkaline hydroxide catalysts.