Selective synthesis of PEG-monoester using cesium heteropoly acid as heterogeneous catalyst

Abstract

Esterification of oleic acid with polyethylene glycol 600 (PEG-600) to produce polyethylene glycol monooleate (PEG-monooleate) and polyethylene glycol dioleate (PEG-dioleate) as by-product has been studied in the presence of heterogeneous acid catalysts, i.e. cesium heteropoly acid (Cs HPA). The results are compared with those obtained from a classical homogeneous acid catalyst; p-toluene sulphonic acid (p-TSA). The reaction was conducted under nitrogen flow with vigorous stirring at 130 °C and 150 °C. The catalyst loading kept at 4% and the reaction was monitored at 1, 3, 7 and 24 hours. Reaction samples were analyzed using high performance liquid chromatography (HPLC) equipped with evaporative light scattering detector (ELSD). The results obtained showed that Cs HPAs exhibit 100% selectivity of PEG-monooleate from the first hour until 24 hours. However, this does not happen with homogeneous p-TSA, where formation of by-product; PEG-dioleate is observed in the initial stage. It is also showed that the mole ratio is the most important parameter not only to produce high yield of monoester but also to maintain it along the reaction. Chemical and physical properties of catalysts were characterized using Thermal Gravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Tranmittance Infra-Red (FTIR), ammonia temperature programmed desorption (NH 3 -TPD) and X-ray Diffraction (XRD).