Purification of biodiesel produced by lipase catalysed transesterification by ultrafiltration: Selection of membranes and analysis of membrane blocking mechanisms

Abstract

Abstract The most common reaction for biodiesel production is catalysed by acid, base or enzyme catalysts. When transesterification is completed, the reaction mixture contains various impurities such as soap, catalyst, free glycerol and alcohol that have to be removed to meet the biodiesel international standard specifications. In this work, biodiesel was produced by lipase catalysed transesterification from edible sunflower oil and methanol as substrates. The purification of crude biodiesel was carried out by decantation followed by ultrafiltration membrane technology. Four different membranes, polyethersulfone, polyacrylonitrile, polypropylene and regenerated cellulose were selected and used for biodiesel ultrafiltration. Based on permeate flux and glycerol content in the permeate membrane performance was evaluated. The obtained results showed that two out of four tested membranes have potential for biodiesel purification. Polyacrylonitrile membrane showed the best performance resulting in lowest glycerol content in permeate (0.006% (w/w)). Additionally, polyacrylonitrile membrane was successfully reused six times without significant loss of performance. Furthermore, the membrane blocking mechanisms were analysed for all membranes by Hermina’s model. Consequently, complete cake layer formation was identified as the most dominant blocking effect.