D-optimal design optimization of unsaturated palm fatty acid distillate and trimethylolpropane esterification for biolubricant production

Abstract

An edible palm oil processing industries produces an economical by-product or waste of palm fatty acid distillate (PFAD). Many researchers have put an effort to utilize uneconomical PFAD to produce valuable, versatile and high-end products. In this work, polyol ester of green biolubricant base oil was synthesized through the esterification of unsaturated palm fatty acid distillate (USFA PFAD) with polyhydric alcohol, trimethylolpropane (TMP) in the occurrence of sulphuric acid catalyst. The optimization process was conducted by using D-optimal design of the response surface methodology (RSM). The results showed that the highest yield percentage of resultant polyol ester, USFA-TMP ester was obtained at $96.0 \pm 0.5\%$ with $99.9 \pm 0.9\%$ of tri-ester selectivity. These were obtained at the esterification optimal condition at reaction temperature of 150 °C for 6 h with 5% $\text{H}_2\text{SO}_4$. The polyol ester chemical structure was characterized by using spectroscopy analysis techniques of infrared (FTIR), proton (${}^1\text{H}$) and carbon (${}^{13}\text{C}$) nuclear magnetic resonance (NMR). The resultant USFA-TMP ester recorded viscosity index of 163, pour points at $-45~\text{{°}C}$, flash points at 298 °C, and thermal oxidative stability temperatures at 215 °C. I was found that the ester product as a Newtonian fluid with viscosity grade lubricant ISO VG 46. In overall, the resultant polyol ester has shown good lubrication properties that make it conceivable to be used for many industrial green biolubricant applications.

Keywords

• Unsaturated palm fatty acid distillate
• D-optimal design
• Esterification
• Green biolubricant
• Trimethylolpropane
• Unsaturated palm fatty acid distillate