The effect of flux and residence time in the production of biodiesel from various feedstocks using a membrane reactor

Biodiesel produced from lipid sources is a clean-burning, biodegradable, nontoxic fuel that is free of aromatic hydrocarbons. Current biodiesel production processes are tedious and involve two to three reaction steps each followed by separation and purification. Process integration of reaction and separation in a single step within a membrane reactor (MR) offers several advantages over conventional reactors. This investigation is aimed at studying the effect of membrane flux and residence time on the performance of a membrane reactor in treating a variety of raw and used feedstocks. A membrane reactor having three selectable reactor volumes was designed to decouple the effect of residence time in the reactor from membrane flux on the performance of the reactor. Low free fatty acid (FFA) oils (FFA < 1%), i.e. canola, corn, sunflower and un-refined soy oils, and high FFA waste cooking oil (FFA = 5%) were base transesterified and the quality of the biodiesel produced was determined in terms of free glycerine, mono-glyceride, di-glyceride and tri-glyceride content. All oils were base transesterified without pretreatment. Based on the composition of the final product, the MR could be operated at the upper limit of the flux tested (70 L/m(2)/h) and a residence time of 60 min. The ASTM D6751 and EN 14214 standards for glycerin and glycerides were reached in the washed biodiesel product for all feedstocks and run conditions. The operating pressure in the reactor was exceeded at 70 L/m(2)/h in treating waste oils and pre-treated corn oil. For these oils, reasonable operating pressures in the reactor were reached at a membrane flux of 30-40 L/m(2)/h. The quality of the washed biodiesel always met ASTM and EN standards. The FAME produced from WCO at intermediate fluxes and high residence times met the ASTM and EN standards without water washing. (C) 2011 Elsevier Ltd. All rights reserved.