Biodiesel Production from Waste Cooking Oil using Microwave Irradiation
IIIrd year B.E.(Hons.) Chemical Engineering, BITS-Pilani.
Abstract - The paper outlines production of biodiesel from vegetable oil or animal fat using induction through microwaves (2.45 - 915 MHz). Transesterification is carried in a reaction cavity coupled with microwave generator. The process occurs by dissipating the microwaves’ energy using polarization mechanisms and electric conductivity generated in the reaction medium due to the high dielectric permittivity, propitiated by the catalyst. Once the reaction is complete, glycerin and biodiesel are gravity separated. Unreacted alcohol in biodiesel is flash vaporized and recycled back. Biodiesel is produced at ambient conditions. Keywords ' microwaves, transesterification, biodiesel fuel.
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. A number of studies have shown that triglycerides hold promise as alternative diesel engine fuels. However, the direct use of vegetable oils and/or oil blends is generally considered to be unsatisfactory and impractical for both direct-injection and indirect type diesel engines. Biodiesel is one viable non-petroleum-based product that can be implemented on a large scale. Biodiesel consists of long chain alkyl esters, made by transesterification of vegetable oil or animal fat, which can be used (alone, or blended with conventional petrodiesel) in unmodified diesel-engine vehicles. Biodiesel can be used in pure form (B100) or may be blended with petroleum diesel at any concentration (BX) in most modern diesel engines. Transesterification, also called alcoholysis, is the displacement of alcohol from an ester by another alcohol in a process similar to hydrolysis, except that an alcohol is employed instead of water. Suitable alcohols include methanol, ethanol, propanol, butanol, and amyl alcohol. Methanol and ethanol are utilized most frequently, especially methanol because of its low cost and its physical and chemical advantages. This process has been widely used to reduce the viscosity of triglycerides, thereby enhancing the physical properties of renewable fuels to improve engine performance. Thus, fatty acid methyl esters (known as biodiesel fuel) obtained by transesterification can be used as an alternative fuel for diesel engines. The paper outlines a method of making a compact biodiesel generator that produces biodiesel from vegetable oil or animal fat using induction through microwaves (2.45 - 915 MHz) in a batch process. The microwaves provide intense localized heating that may be higher than the recorded temperature of the reaction vessel. Once the reaction is complete, two major products exist: glycerin and biodiesel. The glycerin phase is much denser than biodiesel phase and the two can be gravity separated with glycerin simply drawn off the bottom of the settling vessel. Once the glycerin and biodiesel phases have been separated, the excess alcohol in each phase is removed with a flash evaporation process.
The transesterification reaction with alcohol represented by the general equation shown below consists of a number of consecutive, reversible reactions. The first step is the conversion of triglycerides to diglycerides, which is followed by the conversion of diglycerides to monoglycerides and of monoglycerides to glycerol (1), yielding one methyl ester molecule from each glyceride at each step. Normally, the reaction is performed in an alkaline medium, since it is usually faster, easier to control than in acid medium. Although it is also possible to carry out the reaction in acid medium, using the heating apparatus, this process is avoided since it requires longer reaction time as well as the use of higher temperatures. The reaction can also be...
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