High quality biodiesel obtained through membrane technology I.M. Atadashi, M.K. Aroua n , A.R Abdul Aziz, N.M.N Sulaiman Chemical Engineering Department, Faculty of Engineering, University Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 23 April 2012 Received in revised form 3 July 2012 Accepted 4 July 2012 Available online 24 July 2012 Keywords: Ceramic membrane Palm oil Biodiesel Permeate flux Optimization abstract In this study, a ceramic membrane with a pore size of 0.02 mm was used to purify crude biodiesel to achieve biodiesel product that meet both ASTM D6751 and EN 14241 standards specifications. The membrane system was successfully developed and used for the purification process. Process operating parameters such as transmembrane pressure, flow rate and temperature were investigated. Application of central composite design (CCD) coupled with Response Surface Methodology (RSM) was found to provide clear understanding of the interaction between various process parameters. Thus, the process operating parameters were then optimized. The optimum conditions obtained were transmembrane pressure, 2 bar, temperature, 40 1C and flow rate, 150 L/min with corresponding permeate flux of 9.08 (kg/m 2 h). At these optimum conditions, the values of free glycerol (0.007 wt%) and potassium (0.297 mg/L) were all below ASTM standard specifications for biodiesel fuel. In addition the physical properties of biodiesel at the optimum conditions met both ASTM D6751 and EN 14214. This work showed that with ceramic membrane of pore size 0.02 mm, biodiesel with high qualities that meet the stringent standards specifications more than those currently in application can be achieved. & 2012 Elsevier B.V. All rights reserved. 1. Introduction Biodiesel is a clean-burning fuel derived from vegetable oils, animal fats, or grease. The chemical structure of commercial biodiesel is fatty acid alkyl esters (FAAE) [1]. Due to renewability, low gaseous emissions and biodegradability, biodiesel is becom- ing very popular in the European Union (EU) which has set an objective to secure for motor biofuels a market share of 20% of the total motor fuel consumption by 2020 [2]. Because biodiesel is fully prepared from biomass material, it has minimal crude oil residues or metals, aromatic hydrocarbons, and sulfur. Like petro- diesel, biodiesel operates in diesel engines such as those used in private and commercial vehicles and farm equipment. Basically modifications of the engine are not required, and biodiesel maintains the payload capacity and range of petro-diesel. As biodiesel is oxygenated, it is more completely combusted. Besides it has better lubricity than petro-diesel, hence increasing the life times of the diesel engines. Further the higher flash points of biodiesel make it a safer fuel to store, handle and use [1,3]. Also, moderately lower emission profile of esters make them an ideal fuel for application in sensitive environments, such as heavily polluted cities, national parks and forests and marine areas [3]. Biodiesel is most commonly prepared through alkali-catalyzed transesterification. Transesterification is a chemical reaction between triglycerides and alcohol in the presence of catalyst (acid, alkali, or enzyme) as shown in Fig. 1 [2]. This reaction produces biodiesel as a primary product and glycerol as a secondary product. Commercially, biodiesel is produced from refined oils through one-step or two-step alkali-catalyzed transesterification. The schematic diagram of the conventional alkali-catalyzed transesterification is presented in Fig. 2 [3]. After transesterification reaction is completed, removal of glycerol is the first step to be carried out. And because of the difference in polarities and larger density difference between glycerol and esters, separation of glycerol is usually quick. Separation of glycerol from biodiesel mixture is usually achieved through gravita- tional settling or centrifugation. After glycerol is separated, crude biodiesel is subjected to either distillation or rotary evaporation in order to remove the residual alcohol. Conventionally biodiesel is purified via water washing and dry washing methods. Water washing is used to remove the remain- ing glycerol, soap, catalyst, methanol or salts from the alkyl esters [4]. After water washing is completed, the remaining water in biodiesel is removed; vacuum flash process, anhydrous Na 2 SO 4 , magnesol, amberlite, purolite etc., can be used as a final step to dry biodiesel. The process of biodiesel water washing usually provides final biodiesel product that satisfies the stringent bio- diesel standards such as EN 14214 and ASTM D6751. However, separation of hot wash water and the acid from biodiesel in some cases requires application of two centrifuges. Besides, water washing process generates wastewater containing impurities such as free glycerol, residual catalyst and soap which must be carefully handled before being discharged. Otherwise disposal of Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/memsci Journal of Membrane Science 0376-7388/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2012.07.006 n Corresponding author. Tel.: þ603 796 746 15; fax: þ603 796 753 19. E-mail address: mk_aroua@um.edu.my (M.K. Aroua). Journal of Membrane Science 421-422 (2012) 154–164