Recent developments for biodiesel production by ultrasonic assist transesterification using different heterogeneous catalyst: A review K. Ramachandran, T. Suganya, N. Nagendra Gandhi, S. Renganathan n Department of Chemical Engineering, Anna University, Chennai-600 025, Tamil Nadu, India article info Article history: Received 3 September 2012 Received in revised form 28 January 2013 Accepted 31 January 2013 Keywords: Biodiesel Ultrasonic Heterogeneous catalyst Transesterification Process intensification abstract Biodiesel is mainly produced by transesterification reaction between lipid feedstock such as vegetable oil or algal oil and alcohol. Considering the depletion of conventional fossil fuel, biodiesel is gaining more attention as a renewable, sustainable and environmental friendly fuel. Heterogeneous catalysts are mostly applied in transesterification reaction due to many advantages such as easy catalyst separation and reusability, improved selectivity, reducing process stages and cost effective. Biodiesel process faces various problems related to immiscible nature of oil and alcohol leads to poor mass transfer rate. This requires long reaction time, higher catalyst consumption, higher methanol-oil molar ratio, high temperature and high stirring rate. This review discusses that the latest advances in ultrasonic assist transesterification reaction with the use of heterogeneous catalysts to produce biodiesel with cost effective. Ultrasonic energy can emulsify the reactants to reduce the catalyst requirement, methanol-oil ratio, reaction time and reaction temperature. & 2013 Elsevier Ltd. All rights reserved. Contents 1. Introduction ........................................................................................................ 1 2. Raw materials used for biodiesel production .............................................................................. 2 3. Transesterification reaction for biodiesel production ........................................................................ 4 4. Heterogeneous catalytic transesterification ............................................................................... 4 5. Ultrasonic assisted transesterification using heterogeneous catalyst............................................................ 5 6. Conclusion ......................................................................................................... 7 7. References ......................................................................................................... 8 1. Introduction Due to the limited conventional fossil fuels, it has become necessary to find alternative clean and renewable energy resources. Biodiesel is a liquid fuel consisting of mono alkyl esters (methyl or ethyl) of long chain fatty acids derived from vegetable oils or animal fats or micro and macro algal oil. It is a kind of bio- energy as a substitute for conventional petro diesel fuel [1]. Biodiesel is known as an alternate to conventional petro diesel due to its renewability and better combustion performance properties [2]. It is an environmental friendly biodegradable fuel. Besides being a non toxic, it is free from sulfur and aromatics components and becoming a cleaner burning fuel than petroleum diesel. Biodiesel can be mixed with petroleum fossil fuel at any weight ratio or percentage, and it can be used without blending with fossil fuel (B100) as a successful fuel [3]. It has similar properties (physical and chemical) of petroleum diesel fuel. However, biodiesel properties have been found to be superior when compared to conventional fossil fuel. It has higher flash point, better cetane number and specific gravity, ultra-low sul- phur concentration and better lubricating efficiency [4]. The standards (ASTM and EN) for biodiesel and petroleum based diesel are represented in Table 1 for the comparison. Biodiesel is normally produced by the transesterification of the waste vegetable oil, algal oil or animal fat as a feedstock. The most commonly used alcohol is methanol or ethanol to produce methyl esters or ethyl esters. It is generally referred as fatty acid methyl esters (FAME) or fatty acid ethyl esters (FAEE) [5]. Nowadays, there are four different methods are available to reduce the viscosity of vegetable or algal oil such as Blending of oil with petroleum diesel, pyrolysis (Thermal Cracking), emulsification and transesterification [6]. The diesel combustion engines to be Contents lists available at SciVerse 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.2013.01.057 n Corresponding author. Tel.: þ91 442 235 9145, Mob.: 99 4161 3532. E-mail address: rengsah@rediffmail.com (S. Renganathan). Renewable and Sustainable Energy Reviews 22 (2013) 410–418