Transesterification of palm kernel oil with ethanol catalyzed by a combination of immobilized lipases with different specificities in continuous two-stage packed-bed reactor

Abstract Technically and economically viable production processes are frequently reported, but products often fail to meet EN 14214 specifications. This study aimed to investigate the transesterification of palm kernel oil catalyzed by a combination of lipases from different sources and produce biodiesel in accordance with current quality standards. Transesterification reactions were first carried out in a stirred batch reactor at 45 °C using an oil:alcohol molar ratio of 1:8. In batch runs, a 50:50 mixture of Burkholderia cepacia lipase and Thermomyces lanuginosus lipase immobilized onto a silica hydroxyethylcellulose matrix resulted in the highest fatty acid ethyl ester yield (98%) and a decrease in kinematic viscosity from 30.35 to 4.00 mm2 s−1. The product had undetectable levels of DAG and low content of MAG (1.68 wt%). The enzymes were then packed separately in a continuous two-stage reactor operating at different space times (16 and 14 h) and oil/alcohol molar ratios (1:12, 1:10, and 1:8). The highest volumetric productivity (415.3 μmol gcat−1 h−1) was achieved using an oil/alcohol molar ratio of 1:8 and space–time of 16 h. The biodiesel had an alkyl ester content above 98%, a MAG content of less than 0.7 wt%, undetectable DAG content, and kinematic viscosity of 4.22 ± 0.25 mm2 s−1, thereby complying with EN 14214.