A study using classical or membrane separation in the biodiesel process

Biodiesel is a clean burning biofuel produced from renewable resources (straight vegetable oil, animal oil/fats, tallow and waste cooking oil), which can be blended at any level with petroleum diesel to create a blend of biodiesel. The EU has adopted a series of directives to promote and to represent some of the most important renewable energy sources out of biofuels also covering biodiesel as well. The main processing stages currently applied for biodiesel technology are represented by transesterification, neutralization of mixture, phase separation, biodiesel and glycerine purifications. The reaction, generally occurring in a two-stage mixer-settler unit, arises some difficulties for clear cut separations. A new alternative technology, using hydrophobic porous membranes, can be used to prevent bulk mixing of the two phases and facilitate contact and mass transfer of species between the two phases. The glycerine side stream (roughly representing 10% of biodiesel) typically contains a mixture of many components, which are generally difficult to separate. Current methods for glycerine purification are complicated and conducted with higher costs. In this case, the new technology provides an economical solution for the purification of crude glycerine stream combining the high efficiency of electro-dialysis and nano-filtration processes. A comparative cost approach based on available information is sketched. Also, some examples sustain the aim of the study. (C) 2009 Elsevier B.V. All rights reserved.