Synthesis and oxidative stability of trimethylolpropane fatty acid triester as a biolubricant base oil from waste cooking oil

Abstract Trimethylolpropane fatty acid triester (TFATE), which was used as a biolubricant base oil, was synthesized by transesterification of fatty acid methyl esters from waste cooking oil with trimethylolpropane. The reaction parameters and the oxidative stability of TFATE have been studied. Under the selected conditions (potassium hydroxide as the catalyst, molar ratio of catalyst to trimethylolpropane of 1:4, molar ratio of fatty acid methyl esters to trimethylolpropane of 4:1, reaction temperature of 128 °C, and vacuum pressure at 200 Pa), TFATE with a yield of 85.7% was obtained. After being purified by molecular distillation at 120 °C, the content of TFATE in the product reached 99.6%. The addition of alpha -tocopherol, butylated hydroxyanisole, and tert -butylhydroquinone enhanced the oxidative stability of TFATE, while 2,5-di-tertbutyl-hydroquinone and rosemary extract R40 did not improve TFATE's oxidative stability. When being used with alpha -tocopherol, butylated hydroxyanisole had a positive synergistic effect on the oxidative stability of TFATE. In addition, the TFATE's chem–physical properties met the requirements of ISO VG32.