Combination of fatty acids extraction and enzymatic esterification for biodiesel production using sludge palm oil as a low-cost substrate

The alternative approach to the production of biodiesel from sludge palm oil (SPO) via two steps of extraction and enzymatic esterification was performed. Free fatty acids (FFAs) from SPO were obtained through saponification reaction and subsequent extraction. The FFAs were further converted to biodiesel (fatty acids methyl esters) via esterification reaction catalysed by immobilised Rhizopus oryzae lipase on alginate-polyvinyl alcohol (PVA) beads. The esterification reaction was investigated by variations of temperature (30-50 degrees C), molar ratio of methanol to FFAs (1:1 to 5:1), agitation rate (100-300 rpm) and for 4 h. The results were revealed that optimal condition for biodiesel production reached at reaction temperature of 40 degrees C, methanol to FFAs molar ratio of 3:1 and agitation rate of 200 rpm. Under the optimum condition, the highest biodiesel yield of 91.30% was achieved. Successfully, biodiesel production from SPO gave high conversion rate. In addition, the biocatalyst also showed in high catalytic efficiency and stability up to 15 cycles. The process cost could be reduced cost effectively for biodiesel production when a low cost substrate of SPO as well as the capable biocatalyst were used. (C) 2019 Elsevier Ltd. All rights reserved.