A pervaporation-assisted bioreactor to enhance efficiency in the synthesis of a novel biolubricant based on the enzymatic transesterification of a castor oil based biodiesel

The use of biolubricants is being considered an alternative to reduce problems derived from the actual mineral lubricants, such as pollution of soil, water and other ecosystems. Originated from vegetable raw materials, the main advantage of biolubricants lies in their biodegradability. A promising novel biolubricant can be produced from the transesterification of castor oil biodiesel with trimethylolpropane (TMP) using a lipase from Candida rugosa as biocatalyst. However, the catalyst cost added to energy and purification costs are yet to be optimized to allow an economically viable large-scale process. For this reason, considerable effort has been devoted to improve the technology and membrane separations fit well in this quest for efficiency and low energy consumption. As transesterification is a reversible reaction, a pervaporation-assisted bioreactor was proposed in this work, in order to promote the shift of the reaction equilibrium by removing one byproduct, methanol, aiming at increasing efficiency (higher conversion with less lipase). The pervaporation device consisted of a submerged pack of polydimethylsiloxane hollow fibers. The effect of the membrane area/reaction volume ratio on the conversion was evaluated for several initial reacting conditions. A necessary balance of removal rates of initially added water and produced methanol revealed to be critical for a successful operation. A periodic feed of water to maintain relatively constant a low concentration of water needed to activate the lipase biocatalyst also resulted as an alternative. The improvement brought by the pervaporation-assisted reaction is well illustrated when a biodiesel conversion corresponding to 88% of the stoichiometric maximum is obtained, in comparison to the 41% of the original equilibrium conversion in the same conditions, corresponding to an enhancement of 115% in the biolubricant production. (C) 2017 Elsevier Ltd. All rights reserved.