Abstract
Triglycerides are the main constituents of lipids, which are the fatty acids of glycerol. Natural organic triglycerides (viz. virgin vegetable oils, recycled cooking oils, and animal fats) are the main sources for biodiesel production. Biodiesel (mono alkyl esters) is the most attractive alternative fuel to diesel, with numerous environmental advantages over petroleum-based fuel. The most practicable method for converting triglycerides to biodiesel with viscosities comparable to diesel fuel is transesterification. Previous research has proven that biodiesel–diesel blends can operate the compression ignition engine without the need for significant modifications. However, the commercialization of biodiesel is still limited due to the high cost of production. In this sense, the transesterification route is a crucial factor in determining the total cost of biodiesel production. Homogenous base-catalyzed transesterification, industrially, is the conventional method to produce biodiesel. However, this method suffers from limitations both environmentally and economically. Although there are review articles on transesterification, most of them focus on a specific type of transesterification process and hence do not provide a comprehensive picture. This paper reviews the latest progress in research on all facets of transesterification technology from reports published by highly-rated scientific journals in the last two decades. The review focuses on the suggested modifications to the conventional method and the most promising innovative technologies. The potentiality of each technology to produce biodiesel from low-quality feedstock is also discussed.
Highlights
The conversion of renewable energy sources to alternative fuels has been at the forefront of sustainable energy research due to the increased environmental awareness and worries from the expected depletion of fossil fuel resources [1,2,3]
Fatty acid methyl ester (FAME), known as biodiesel, is a fuel generated from renewable sources used in traditional compression ignition engines
Special attention needs to be given to developing new routes of transesterification that render the utilization of low-quality feedstock feasible for biodiesel production, with fewer downstream processes
Summary
The conversion of renewable energy sources to alternative fuels has been at the forefront of sustainable energy research due to the increased environmental awareness and worries from the expected depletion of fossil fuel resources [1,2,3]. Biodiesel is an alternative fuel with the high potentiality to compete with petroleum fuel from environmental and economic points of view [7,13,14,15]. The main problem regarding vegetable oil as fuel is its greater viscosity besides its low volatility and bad cold flow properties, which affect the proper operation of the diesel engine [18,19]. Transesterification is the most practicable process, among these four ways, for reducing the viscosities of vegetable oils and producing alkyl esters with characteristics comparable to diesel. This is the reason why transesterified vegetable oils are popularized as “biodiesel” [24,25].
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