An environmentally friendly production ofester‐biolubricantfrom oleic acid

Abstract

The production of oleic‐based trimethylolpropane (TMP) esters via the esterification reaction between oleic acid (OA) and TMP in a reactive distillation system, employing the environmentally friendly catalyst methanesulfonic acid, was explored. The homogeneous acid catalyst, the OA/TMP molar ratio within 1.0–3.0, the esterification reaction enhancement and a new purification technique, using choline hydroxide (ChOH), for obtaining choline carboxylate as a subproduct, were studied. It was found that using an OA/TMP molar ratio of 3.0, only unreacted OA remained as an impurity. The deleterious or beneficial effect of intermediate products, unreacted OA and temperature on the kinematic viscosity were unraveled. The kinematic viscosity behavior for the products was practically independent of temperature but an abrupt enlargement of the kinematic viscosity was observed in the presence of functional groups in the intermediate esters, even greater than the Mark–Houwink counterpart effect. On contrary, the presence of OA in the final product decreased the kinematic viscosity attending to its lower molecular weight with respect to the trimethylolpropane trioleate one. It was found that trimethylolpropane monooleate is undesirable for the viscosity index, whereas the presence of trimethylolpropane dioleate could also increase the viscosity index to a small extent, requiring a complex purification process. Finally, it is possible to affirm that the optimal TMP‐based lubricant obtained using an OA/TMP molar ratio of 3.0, after OA neutralization presented good marginal benefit and a viscosity index of 208.7, which is applicable for gear lubricants. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.