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Microwave energy based chemical synthesis has several merits and is important from both scientific and engineering standpoints. Microwaves have been applied in numerous inorganic and organic chemical syntheses; perhaps, from the time their ability to work as heat source was discovered. Recent laboratory scale microwave applications in biodiesel production proved the potential of the technology to achieve superior results over conventional techniques. Short reaction time, cleaner reaction products, and reduced separation-purification times are the key observations reported by many researchers. Energy utilization and specific energy requirements for microwave based biodiesel synthesis are reportedly better than conventional techniques. Microwaves can be very well utilized in feedstock preparation, extraction and transesterification stages of the biodiesel production process. Although microwave technology has advanced in other food, pharmaceutical and polymer chemistry related research and industry, it has yet to prove its potential in the biodiesel industry at large scale applications. This paper reviews principles and practices of microwave energy technology as applied in biodiesel feedstock preparation and processing. Analysis of laboratory scale studies, potential design and operation challenges for developing large scale biodiesel production systems are discussed in detail.

A comparative study of biodiesel production from waste cooking oil using sulfuric acid (Two-step) and microwave-assisted transesterification (One-step) was carried out. A two-step transesterification process was used to produce biodiesel (alkyl ester) from high free fatty acid (FFA) waste cooking oil. Microwave-assisted catalytic transesterification using BaO and KOH was evaluated for the efficacy of microwave irradiation in biodiesel production from waste cooking oil. On the basis of energy consumptions for waste cooking oil (WCO) transesterification by both conventional heating and microwave-heating methods evaluated in this study, it was estimated that the microwave-heating method consumes less than 10% of the energy to achieve the same yield as the conventional heating method for given experimental conditions. The thermal stability of waste cooking oil and biodiesel was assessed by thermogravimetric analysis (TGA). The analysis of different oil properties, fuel properties and process parametric evaluative studies of waste cooking oil are presented in detail. The fuel properties of biodiesel produced were compared with American Society for Testing and Materials (ASTM) standards for biodiesel and regular diesel

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Process parameter evaluation and catalyst performance study was conducted for biodiesel production using jatropha curcas, waste cooking, and camelina sativa oils. Conversion of triglycerides to methyl esters involves esterification and/or transesterification, depending on the nature of the feedstock. A two-step transesterification process (acid esterification followed by alkali transesterification) was employed to produce biodiesel from high free fatty acids (FFA) in jatropha curcas and waste cooking oils, and a single-step transesterifcation process (alkali transesterifcation) was used for camelina sativa oil conversion. Catalyst selection is vital in transesterification process because it determines biodiesel yield and cost. Transesterification of jatropha curcas and waste cooking oil was optimized by using H 2 SO 4 and ferric sulfate catalysts in the acid esterification step and a KOH catalyst in the alkali transesterification, respectively. Heterogeneous metal oxide catalysts including BaO, SrO, MgO, and CaO were used for the transesterification of camelina sativa oil. Jatropha curcas oil was observed to have yields in the range of 90-95%, with a maximum of 95% obtained at the following process conditions: acid esterification, methanol to oil molar ratio of 6:1, 0.5% of H 2 SO 4 , and 40 ( 5 °C; alkali tranesterification, methanol to oil molar ratio of 9:1, 2% of KOH, and 60 °C. Waste cooking oil yielded biodiesel in the range of 85-96%, with a maximum of 96% observed at the following optimized process conditions: 2 h reaction at 100 °C, methanol to oil molar ratio of 9:1, and 2% of a ferric sulfate catalyst. Comparative experiments on camelina sativa oil conversion showed that the most effective catalyst was BaO that showed >80% yield of camelina to biodiesel. Fuel properties of biodiesel produced from the three different feedstocks were determined and compared with the ASTM standards for biodiesel and petroleum diesel.

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