Benzotriazoium Bis(2-Ethylhexyl) Phosphate Ionic Liquid as a Catalyst and Multifunctional Lubricant Additive: Synthesis, Optimization, Characterization, and Tribological Evaluation

A new protic ionic liquid (IL) was synthesized by the neutralization reaction of 1H-benzotriazole (BTA) and bis(2-ethylhexyl) phosphoric acid (HDEHP) and evaluated as a catalyst in the esterification reaction of oleic acid and polyethylene glycol (PEG) 400, as well as an anti-wear and anti-corrosion additive in the synthesized ester. The response surface methodology (RSM) was used to design the experiments and optimization of the esterification reaction, which at the optimum conditions (1 wt% of IL, at the molar ratio of acid/alcohol of 1.55, the reaction temperature of 200 °C for 24 h) the maximum conversion of esterification was achieved (more than 99%). Unlike most ILs, [BTAH][DEHP] was fully miscible in synthesized ester and did not separate from the esterification process. [BTAH][DEHP] IL significantly reduced corrosion of copper, aluminum, and steel strips. Also, tribological evaluations illustrated that the 1, 2.5, 5, and 7.5 wt% of [BTAH][DEHP] IL in the PEG400 Oleate reduced the coefficient of friction to 30, 42, 46, and 59%, respectively. Using inexpensive raw materials, a simple synthesis procedure, and preparing green lubricant without catalyst separating, as well as suitable anti-corrosion and anti-wear and friction-reducing properties, could be addressed as advantages of the proposed method.