Progress, prospect and challenges in glycerol purification process: A review M.S. Ardi, M.K. Aroua, N. Awanis Hashim n Department of Chemical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 8 July 2014 Received in revised form 16 October 2014 Accepted 25 October 2014 Available online 18 November 2014 Keywords: Crude glycerol Biodiesel Purification Membrane abstract Glycerol surplus in recent decades due to global increase in biodiesel production has created a new form of challenge in terms of purification for crude glycerol. This review summarizes the progress of crude glycerol purification technologies using various techniques. Critical insights are given regarding the application of suitable techniques for crude glycerol purification which includes chemical pre-treatment, methanol removal, vacuum distillation, ion exchange, activated carbon and membrane separation technology. Extensive discussion is made in relation with stages and processes in the conventional, current and emerging glycerol purification technologies. Lastly, aspects concerning the challenges of glycerol utilization and purification are thoroughly discussed. & 2014 Elsevier Ltd. All rights reserved. Contents 1. Introduction ....................................................................................................... 1164 2. Background ....................................................................................................... 1165 2.1. Effect of impurities on glycerol utilization ......................................................................... 1166 2.2. Grades specification of glycerol.................................................................................. 1166 3. Glycerol purification technology ....................................................................................... 1166 3.1. Neutralization ............................................................................................... 1167 3.2. Methanol removal ............................................................................................ 1167 3.3. Purification and refinery ....................................................................................... 1167 3.3.1. Vacuum distillation .................................................................................... 1167 3.3.2. Ion exchange adsorption ................................................................................ 1167 3.3.3. Adsorption using activated carbon ........................................................................ 1168 4. Membrane separation technology ..................................................................................... 1168 4.1. Application of membrane separation technology in glycerol refining.................................................... 1169 4.2. Prospect of glycerol refining using membrane technology ............................................................ 1169 4.2.1. Hybrid membrane ..................................................................................... 1169 4.2.2. Membrane distillation .................................................................................. 1170 5. Challenges of crude glycerol utilization and purification.................................................................... 1170 6. Conclusion ........................................................................................................ 1170 Acknowledgments ...................................................................................................... 1171 References ............................................................................................................ 1171 1. Introduction As part of a recent renewable energy development interest, biodiesel has attracted numerous researchers worldwide as a viable alternative to rapidly decline fossil fuel consumption. Perhaps the wide interests are largely attributed to biodiesel Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews http://dx.doi.org/10.1016/j.rser.2014.10.091 1364-0321/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. Tel.: þ60 379676892. E-mail address: awanis@um.edu.my (N.A. Hashim). Renewable and Sustainable Energy Reviews 42 (2015) 1164–1173