Synthesis of complex polyolester as base stock for high-performance lubricant: Optimization, characterization, and evaluation

Abstract

Synthetic esters are expected to have broad application prospects in the high-end lubrication sectors owing to their fascinating custom-tailored properties. Herein, we synthesized a novel complex polyolester (CPE) via a stepwise esterification procedure using stannous oxide as a heterogeneous catalyst. Response surface methodology coupled with the Box–Behnken design (BBD-RSM) was employed to optimize the experimental parameters and elucidate the interactions among the operating variables on the low-temperature fluidity of CPE. The optimization results indicated that the lowest pour point (−42 °C) could be obtained under the catalyst dosage of 1.2 wt%, the first step reaction temperature of 164 °C, the first step reaction time of 100 min, and the second step reaction temperature of 178 °C. Particularly, there is a significant interactive effect between the catalyst dosage and the second step reaction temperature. Followed by the molecular distillation of the crude ester prepared under the optimal conditions, the refining results revealed that the non-ideal components had been effectively removed and the total acid number of the final product was substantially reduced to below 0.1 mg KOH/g. The molecular structures of the as-synthesized esters were confirmed by FT-IR, NMR, GPC, ESI–MS, and TGA characterization and their physicochemical and tribological properties were also evaluated according to standard methods. In view of the unique molecular structural design, the developed CPE displayed plentiful prominent technological specificities, which makes it plausible to be served as a potential high-performance base stock. Therefore, the findings of this study may provide some valuable insights for expanding the application scope of synthetic esters into various special industrial scenarios.