Selection of Appropriate Plant-Based Oils and Neo-polyols for Transesterification to Produce Polyolesters-Based Bio-transformer Oil

According to rising electrical power consumption, attention to bio-transformer oil (BTO) is increasing due to higher environmental and ecological concerns. Thus, this research aimed to identify the appropriate plant-based oils and polyols to prepare BTO synthesized via two-step transesterification involving the transformation of plant-based oils into fatty acid methyl ester (FAME) with methanol and then reacting with polyols to produce polyolesters (POEs). The plant-based oils—palm kernel oil (PK), refined palm oil (RFP), high olein palm oil (HOP), sunflower oil (SF), and soybean oil (SB)—were reacted with various polyols, neopentyl glycol (NPG), trimethylolpropane (TMP), and di-trimethylolpropane (Di-TMP), to produce BTO in forms of neopentyl glycol diester (NPGDE), trimethylolpropane triester (TMPTE), and di-trimethylolpropane tetraester (Di-TMPTTE), respectively. Among these POEs, BTO with TMPTE structure had appropriate properties in terms of dielectric breakdown voltage, kinematic viscosity at 40 °C, and flash point following IEC 62770 specification. However, the pour point and oxidation stability of BTO derived from each FAME (PK-TMPTE: − 7 °C, 22 h/RFP-TMPTE: 19 °C, 35 h/HOP-TMPTE: 17 °C, 30 h/SF-TMPTE: − 14 °C, 3 h and SB-TMPTE: − 10 °C, 4 h, respectively) failed to meet specified standard requirements (≤ − 10 °C and ≥ 13 h). The balance between steric hindrance and unsaturation level generated from the polyols and plant-based oils was crucial in achieving BTO with the desired properties. A 70/30 (w/w) PK-TMPTE/SF-TMPTE blend ratio was observed as an optimal formulation to provide BTO having a low pour point (− 10 °C) and high oxidation stability (15 h), following the standard specification for transformer oil.

Graphical Abstract