Continuous biodiesel production from acidic oil using a combination of acidic and alkaline composite catalytic membranes in flow-through membrane reactors

A continuous integrated process, which combines esterification using acidic catalytic composite membranes (ACCMs), online separation, and transesterification by polymer-based alkaline composite catalytic membranes (PACCMs), was developed to produce biodiesel from acidic oil (soybean oil and oleic acid) in flow-through mode. Free fatty acids (FFAs) in the oleic acid were first converted to methyl esters by esterification using methanol under optimal reaction conditions. After the reaction, the mixture was online separated into two layers. The methanol-water-oleic acid mixture at the top layer was reclaimed. The bottom layer, mainly containing soybean oil and methyl ester, was transesterified through PACCMs under optimal reaction conditions. The ACCMs and PACCMs presented good stability during the continuous running process. The conversions of FFAs (above 98%) and soybean oil (95.43%) were achieved and the yield of biodiesel in this integration process reached <= 97.52% under the optimal conditions. The main parameters of the biodiesel product obtained meet the GB/T 20828 Chinese standard.