Production of palm fatty acid distillate based biolubricant

Abstract

Palm fatty acid distillate (PFAD) is a cheap and valuable by-product of edible palm oil processing industries. A synthesis of PFAD esters for biolubricant base oil was carried out through esterification between PFAD based fatty acids (fatty acid mixture, USFA, and SFA) with different types of high degree polyhydric alcohols (TMP, Di- TMP, PE, and Di-PE) in the presence of sulphuric acid as catalyst. The synthesized PFAD esters showed high yield percentages in the range of 78 – 95 %. The chemical structures were characterized and confirmed by using FTIR and NMR (1H and 13C) spectroscopies. The FTIR spectra of PFAD ester products clearly showed the peaks of C=O and C–O of ester group at 1732–1745 cm−1 and at 1166–1251 cm−1, respectively. The peak of the unsaturated aliphatic carbon atoms (C=C) appeared at 3003–3010 cm−1. The 1H NMR analyses confirmed the proton chemical shifts (-CH2-O) of the ester group at 3.83–4.04 ppm, secondary carbons (CH2-C=O) at 2.12–2.25 ppm and unsaturated aliphatic carbons (HC=CH) at 5.31–5.35 ppm. The 13C NMR analyses confirmed the carbon chemical shifts of carbonyl ester signals at 172.4–174.1 ppm, secondary carbons (CH2-C=O) at 34.39–40.33 ppm and (C=C) at 129–130 ppm with different intensities. GC-FID analysis of ester-TMP, USFA ester-TMP and SFA ester- TMP showed the major tri-ester was observed to be 99%. The –OH group of TMP were successfully converted as the formation of tri-ester peaks starts at minute 51.20 and OH groups of di-TMP, and PE were converted as the formation of tetraester peaks starts at minute 60.1 and di-PE converted to hexa-ester peaks starts at minute 70.07. The results for lubrication properties have shown that the PFAD based esters have low-temperature properties with pour points in the range of −15 to 35 °C. Furthermore, the flash point of the esters increased with their molecular weight. SFA ester has the highest flash point in the range of 270 - 310 °C, while USFA ester has the flashpoint in the range of 228 - 250 °C. The oxidative stability in the range of 188 to 322 °C and viscosity indices in the range of 115 to 187 were increased with the molecular weight and carbon chain-saturated of the esters, but decreased for unsaturated and branched chain carbons. In general, the presence of three and more ester functional groups in the structure of PFAD based esters provides a positive impact on the lubrication properties. Overall, the results indicated that the PFAD and USFA based esters could be used as lubricating base oils without any additives, while the SFA based esters can be used as lubricating base oils with pour point depressants.