Heterogeneous Catalysts in Bio Diesel Production – A Review Shripad Diwakar 1 Rana Pratap Reddy 2 Department of Mechanical Engineering Department of Mechanical Engineering BMSITM, Bengaluru RITM, Bengaluru Abstract: - Bio diesel has attracted in recent years as a renewable fuel with less pollutant emissions as compared to diesel fuel on its combustion. Bio diesel fuel is made from vegetable oils, animal fats and microbial oils. The most common method of Bio diesel production is by means of Trans-esterification process, where, triglycerides present in the oil reacts with monohydric alcohol in the presence of a catalyst. Synthesis of Bio diesel necessarily needs a catalyst to attain the equilibrium in practical manner. Homogeneous acid catalysts are corrosive in nature and take more time for Bio diesel synthesis, alkaline catalysts requires the thorough rinsing with water to remove the leftover catalyst, resulting in waste water generation and consequently results in the loss of production. In order to overcome these constraints, this review article is focused on finding suitable Heterogeneous catalysts that can be easily separated and gives a high yield and conversion. Keywords: Heterogeneous catalyst, Bio diesel, vegetable oils, Trans-esterification 1. INTRODUCTION: In recent years, biodiesel has gained international attention as a source of alternative fuel due to characteristics like high degradability, no toxicity, low emission of carbon monoxide, particulate matter and unburned hydrocarbons [1] Biodiesel is a mixture of alkyl esters and it can be used in conventional compression ignitions engines, which need almost no modification. As well, biodiesel can be used as heating oil and as fuel [2] ,So far,this alternative fuel has been successfully produced by transesterification of vegetable oils and animal fats using homogeneous basic catalysts (mainly sodium or potassium hydroxide dissolved in methanol). Traditional homogeneous catalysts (basic or acid) possess advantages including high activity (complete conversion within 1 h) and mild reaction conditions (from 40 to 65°C and atmospheric pressure). However, the use of homogeneous catalysts leads to soap production. Besides, in the homogeneous process the catalyst is consumed thus reducing the catalytic efficiency. This causes an increase in viscosity and the formation of gels. In addition, the method for the removal of the catalyst after reaction is technically difficult and a large amount of wastewater is produced in order to separate and clean the products, which increases the overall cost of the process. Thus, the total cost of the biodiesel production based on homogeneous catalysis, is not yet sufficiently competitive as compared to the cost of diesel production from petroleum. An alternative is the development of heterogeneous catalysts that could eliminate the additional running costs associated with the above mentioned stages of separation and purification. In addition, the use of heterogeneous catalysts does not produce soap through free fatty acid neutralization and triglyceride saponification. Therefore, development of efficient heterogeneous catalysts is important since opens up the possibility of another pathway for biodiesel production. The efficiency of the heterogeneous process depends, however, on several variables such as type of oil, molar ratio alcohol to oil, temperature and catalyst type. Thus, the objective of this review paper is to present a review of the effect of the variables on important characteristics of biodiesel such as methyl esters content. Some characterization techniques for both, biodiesel and heterogeneous catalysts will also be addressed. 2. TRANS-ESTERIFICATION PROCESS: Nowadays, there are four known methods to reduce the high viscosity of vegetable oils to enable their use in conventional compression ignitions engines: blending with diesel, pyrolysis, emulsification and trans- esterification. The pyrolysis and the emulsification, however, produce heavy carbon deposits, incomplete combustion, an increase of lubricating oil viscosity and undesirable side products such as alkanes, alkenes, alkadienes, aromatic compounds and carboxylic acids. Regarding the direct use of vegetables oils as fuel for combustion engines, this requires the engines to be modified [3] ,Also, the direct use of vegetables oils is not feasible due to their high viscosity and low volatility which affect the atomization and spray pattern of fuel, leading to incomplete combustion, severe carbon deposits, injector choking and piston ring sticking [4] . The alcohol used for trans-esterification is usually methanol. Thus, the most common way to produce biodiesel is by trans-esterification of triglycerides of refined/edible types of oils using alcohol, in presence of an acid or a basic catalyst [5] . The alcohol used for trans-esterification is usually methanol. The general scheme of trans esterification reaction is shown in Fig.1, where R is a mixture of various fatty acid chains [6] International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 Published by, www.ijert.org NCERAME - 2015 Conference Proceedings Volume 3, Issue 17 Special Issue - 2015