Synthesis and evaluation of polyol based biolubricants from vegetable oils
Abstract
Vegetable oil is over 95% triacylglyceride (TAG) making it a potential low-cost feedstock for biolubricant production. The objective of this project was to develop a polyol-based biolubricant from vegetable oils with excellent oxidative stability and low temperature flow properties.
In the first study, a strong positive correlation was observed between saturated fat content and melting point while the content of polyunsaturated fatty acids (PUFA) was negatively correlated with oxidative stability. Brassica rapa cultivars, with less than 3.5% saturated fat and less than 20% polyunsaturated fat, can be an excellent feedstock with improved cold fluidity and oxidative stability.
In the second study, B. rapa TAG molecules were modified to produce fatty acid methyl ester (FAME) and then the acyl moieties were linked to trimethylolpropane (TMP) a branched neopentyl polyol by a two-step base-catalyzed transesterification reaction. The addition of FAME to TMP was explored and optimized by altering reaction protocols and catalysts. An efficient conversion (100%) of FAME and TMP to TMP triesters (TE) was successfully achieved under the optimum condition of 1wt% potassium carbonate as the catalyst, 130 ºC reaction temperature, 18 h reaction time and a mole ratio of FAME to TMP of 3.9.
In the third study, the oxidative stability index (OSI) of the original vegetable oil, FAME and product TMP esters were all measured. The highest stability was observed in vegetable oil while the processed products were less stable. It is likely that natural antioxidants removed during purification of FAME and TMP esters contributed to the superior OSI value of the vegetable oil. The low temperature flow behaviour of TMP based biolubricants was determined between 298 K and 238 K using T2 relaxation. The results showed that the singlet attributed to TMP protons broadened until it disappeared as temperature decreased. The results indicated that the log of the spin-spin relaxation time is linearly correlated with rising temperature.