Glycerol production and its applications as a raw material: A review H.W. Tan, A.R. Abdul Aziz n , M.K. Aroua Chemical Engineering Department, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 13 January 2012 Received in revised form 10 June 2013 Accepted 24 June 2013 Available online 20 July 2013 Keywords: Crude glycerol Tranesterification Saponification Hydrolysis Purification Glycerol abstract Glycerol is a valuable byproduct in biodiesel production by transesterification, soap manufacturing by saponification as well as hydrolysis reaction. The purity of glycerol obtained is low due to the presence of impurities such as remaining catalyst, water, soaps, salts and esters formed during the reaction. Purification of glycerol as well as the conversion of glycerol into valuable products has attained growing interest in recent years due to the dramatic growth of the biodiesel industry. This paper reviews different methods of producing crude glycerol as the major by-product. Purification of glycerol was reported as well as value-added products produced from glycerol. & 2013 Elsevier Ltd. All rights reserved. Contents 1. Introduction ........................................................................................................ 118 2. Physical and chemical properties of glycerol .............................................................................. 119 3. Source of glycerol ................................................................................................... 119 3.1. Transesterification reaction ...................................................................................... 119 3.1.1. Acid catalysed transesterification .......................................................................... 120 3.1.2. Base catalysed transesterification .......................................................................... 120 3.1.3. Enzymatic catalysed transesterification ..................................................................... 121 3.2. Saponification ................................................................................................ 122 3.3. Hydrolysis ................................................................................................... 122 4. Crude glycerol from various production processes ......................................................................... 122 5. Purification of crude glycerol .......................................................................................... 123 6. Glycerol to value-added products ....................................................................................... 123 6.1. 1,3-propanediol ............................................................................................... 123 6.2. Acrolein ..................................................................................................... 124 6.3. Hydrogen .................................................................................................... 124 6.4. Industrial applications .......................................................................................... 124 7. Economic evaluation ................................................................................................. 125 8. Conclusions ........................................................................................................ 125 Acknowledgment ....................................................................................................... 125 References ............................................................................................................. 125 1. Introduction Glycerol, also known as glycerine or propane-1,2,3-triol, is a chemical which has a multitude of uses in pharmaceutical, cosmetic, and food industries. It can be produced as a by-product from saponification and hydrolysis reactions in oleochemical plants as well as transesterification reaction in biodiesel plants [1]. Glycerol produced from oleochemical or biodiesel plant is in crude form that contains Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews 1364-0321/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.rser.2013.06.035 n Corresponding author. Tel.: +60 3 7967 5206; fax: +60 3 7967 5319. E-mail addresses: azizraman@um.edu.my, rshazrin@gmail.com (A.R. Abdul Aziz). Renewable and Sustainable Energy Reviews 27 (2013) 118–127