D-Optimal Design Optimization for Esterification of Palm Fatty Acids Distillate with Polyhydric Alcohols for Biolubricants Production

Plant-based bio-lubricant is crucial to be developed and adopted by many industries. This is due to the presence of toxicity risk, climate change, energy security as well green-environmental approach issues. The utilization of palm oil processing industries’ by-product, palm fatty acid distillate (PFAD-based bio-lubricants is one way of a green environment approach. A synthesis of polyol esters based on PFAD for bio-lubricants was carried out. The esterification of PFAD with high-degree polyhydric alcohols trimethylolpropane (TMP), di-trimethylopropane (di-TMP), pentaerythritol (PE), and di-pentaerythritol (Di-PE) in the presence of sulphuric acid (H2SO4) catalyst have been performed. The optimization of the esterification reaction process was evaluated using a D-optimal design based on three reaction parameters; H2SO4 concentration (%) for the catalyst, esterification time (h), and esterification temperature (°C).  The chemical structure of the synthesized polyol esters was characterized and confirmed by using FT-IR and NMR (1 H and 13 C) spectroscopies. The results showed that PFAD-based polyesters of PFAD-TMP ester successfully produced high yields of 93% compared to others.  The synthesized PFAD-based polyesters showed good lubrication properties with high viscosity indices in the range of 141-187, pour points (-5 to 5 °C), flash points (230-360 °C), and oxidative stability temperature (188-301 °C), respectively. The ester functional group present in the chemical structure of PFAD-based polyesters showed a positive impact on the lubrication properties. The study indicated that PFAD-based polyesters are plausible to be used in industrial bio-lubricant applications.