Microwave-promoted synthesis of polyolesters for lubrication oil using a composite catalyst in a solvent-free procedure

Abstract

A rapid, highly efficient and green synthetic approach to polyol esters for lubrication oils is proposed. Using sulfuric acid and p-toluene sulfonic acid as a composite catalyst and C₅–C₉ straight-chain monocarboxylic acids, with pentaerythritol (PE) and dipentaerythritol (di-PE) as starting materials, a series of lubrication oil polyol esters were synthesized in the absence of solvent under microwave irradiation. Compared with the conventional synthetic method, our proposed microwave method exhibits advantages, including higher yields, shorter reaction times and lower reaction temperatures. The viscosity coefficients of the products at 40 °C and their refractive indices at 25 °C were investigated. In addition, the thermal behavior of the starting materials under microwave irradiation was also investigated. The results reveal that the microwave absorbance of n-pentanoic acid is stronger than that of n-hexanoic acid and that of n-heptanoic acid is stronger than that of n-octanoic acid. The microwave absorbance of di-PE is also stronger than that of PE.