Environmentally adapted bio-oil compounds-derived polyolesters synthesis: Optimization and properties of base fluids

Highlights: • Green biopolymer alginate derived from brown algae as solid acid catalyst. • High availability of non-edible biomass derived bio oil with high acidity. • Synthesis of polyolester-lubricant via alginate catalyzed esterification of bio oil. • NPG-based polyolester show 76 VI and 2.3 mm² s⁻¹ kinematic viscosity at 40 °C. • Al-Alg catalyst render high reusability with ester yield above 90% after 8 cycle. Non-edible bio-oil derived from lignocellulosic biomass could be used as environmentally friendly lubricant-ester base stock for maritime and road-type transportations. However, the use of crude bio-oil with highly oxygenated compounds required further upgrading to yield ester that mimicked the characteristics of Group V base oil (polyolesters). In this study, bio-oil based polyolesters was produced via esterification using green biopolymer alginate acid catalyst (Al-Alg). The bio-oil compounds used were acetic acid (AcA), propionic acid (PrA) and levulinic acid (LA), while polyols such as neopentyl glycol (NPG), trimethylolpropane (TMP) and pentaerythritol (PE) were used. Optimization studies revealed that NPG-PrA ester gave the best ester purity of 100%, with 95% of diester selectivity under optimum conditions of 15 wt% Al-Alg, 8 h, 6:1 PrA:NPG and 140 °C. The produced polyolesters showed potential lube characteristics with viscosity index of 76, kinematic viscosity of 2.3 mm² s⁻¹ at 40 °C and oxidative induction time of 15 min at 100 °C. Furthermore, a reusability study of the Al-Alg catalyst indicated high NPG-PrA diester selectivity (above 90%) for 8 consecutive cycles. The physico-chemical properties of spent Al-Alg catalyst were also discussed.