Synthesis and kinetics study of trimethylolpropane fatty acid triester from oleic acid methyl ester as potential biolubricant

Abstract

The use of trimethylolpropane triesters as biodegradable lubricant base oil substitute mineral oils could significantly reduce the environmental pollution. In the present work, a commercial oleic acid (72% C18) was utilized as a precursor for the manufacture of trimethylolpropane triesters (TMPTE) through a two-step transesterification process. Oleic acid methyl ester (OME) produced from the first step was subsequently interacted with trimethylolpropane (TMP) using sodium methylate to produce TMPTE. The effect of the operating parameters, temperatures (90 °C, 100 °C, 110 °C, 120 °C, and 130 °C), molar ratio of OME to TMP (3:1, 4:1, 5:1, and 7:1), vacuum pressure (20, 50, 100, and 200 mbar), and catalyst amount (0.5, 0.7, 0.9, and 1.1(w/w)) was investigated. Under the selected reaction conditions (temperature 120 °C, oleic acid methyl ester to trimethylolpropane molar ratio 4:1, catalyst amount 0.9%w/w, vacuum pressure 20 mbar and reaction time 2 h), the final product composition was approximately 85.47% TMPTE, 10.80% TMPDE, 1.40%TMP ME, and 2.33% OME. The kinetics/mathematical model explains the chemical kinetics of transesterification of oleic acid methyl esters (OME) with trimethylolpropane (TMP) to produce biolubricant which has been investigated at temperature 120 °C. To support forward reaction, the excess amount of OME was increased by 10:1 (OME/TMP). The kinetic model suggested for the transesterification process of OME with TMP in this work based on three reversible series-parallel reaction mechanisms. The kinetics equations were solved using LINGO PROGRAM. A harmony between the experimental data and theoretically estimated values was achieved.