2012 - ANTALYA Biodiesel fuel production from waste cooking oil by microwave irradiation Mehdi Zare 1 , Barat Ghobadian 1* , Gholamhasan Najafi 1 , Ahmad Abbaszade 1 , Ebrahim Fayyazi 1 1 Dept. of Mechanics engineering of Agricultural Machinery, Tarbiat Modares University, Iran. Abstract Studies focused around the produce of biodiesel are increasing at a very fast rate. In this study a domestic microwave oven was modified as a biodiesel producing reactor and the effect of microwave irradiation on transesterification of waste cooking oil (WCO) to biodiesel production was investigated. Transesterification of WCO was carried out in the presence of methanol as alcohol, using a molar ratio alcohol/oil of 6:1 and 1.0% w/w of potassium hydroxide (KOH) as catalyst. The reactions were performed at different reaction times (1, 2 and 3 min). The quality of the biodiesel obtained has been confirmed by GC analysis of the isolated product. At the end of all tests biodiesel produced conformed to some ASTM specifications. Compared with conventional heating methods the results show that microwave heating can be applied effectively to obtain high methyl esters of fatty acids (biodiesel) yields, effectively reducing the reaction time and of improving the separation process. However, this emerging technology needs to be further researched for possible scale-up for industrial application. Keywords: Transesterification, microwave, biodiesel, ASTM 1. Introduction One hundred years ago, Rudolf Diesel tested vegetable oil as fuel for his engine. In 1930s and 1940s vegetable oils (VOs) were used as diesel fuels, but only in emergency situations [1, 2]. Alternative fuels for diesel engines are becoming increasingly important due to diminishing petroleum reserves and the environmental consequences of exhaust gases from petroleum fuelled engines [3, 4]. Although the calorific value of VOs is as good as diesel fuel, the low volatility and high viscosity of VOs prohibits its direct application as fuel for diesel engines. However, this technical problem of higher viscosity of VOs has been overcome by transesterification [1]. Transesterification is the process of reacting triglyceride (vegetable oils) with alcohol in presence of catalyst. During the transesterification process, triglycerides are first converted to diglycerides, which in turn are converted to monoglycerides, and then to glycerol. Each step produces a molecule of an ester of a fatty acid [5]. The batch transesterification process is simple but requires large reactor size and takes longer reaction times. This process can convert oil to biodiesel up to 80 to 94% in 30 min to 2 h [6, 7]. The yields were dictated by molar ratio of the oil to alcohol, reaction time, temperature, catalyst type, catalyst concentration, triglyceride properties, and mixing intensity. For conventional heating, heat energy is transferred to the reaction through convection, conduction and radiation from the surfaces of the reactor, which is an inefficient heat transfer. Large amount of energy is used to heat the media. Thus, long reaction time (usually from 30 min to 8h) is required to achieve a satisfactory conversion of oil to biodiesel. Microwave radiation, on the other hand, delivers energy directly to the reactants. Therefore, preheating step is eliminated and heat transfer is more effective than conventional heat. Consequently, transesterification with microwave radiation can be completed in much shorter time [8–10]. Transmethylation of rice bran oil in toluene