Abstract:The synthesis of biodiesel has received attention as an alternative source of energy to decrease our dependence on petroleum-based fuels. The catalyzed processes present a series of limitations and drawbacks, among them the high energy required for complex purification and undesirable side reactions. Supercritical fluid (SCF) technology is being proved an efficient approach compared to traditional methods for preparing biodiesel. This review illustrates the advances, advantages, and drawbacks involved in the use of all current biodiesel production technologies.Keywords: biodiesel; catalyst; non-catalytic; supercritical fluid; transesterification. List of abbreviationsBDF, biodiesel fuel; FA, fatty acid; FFA, free fatty acid; FAAE, fatty acid alkyl ester; FAME, fatty acid methyl ester; FAEE, fatty acid ethyl

Abstract:The profitability of biodiesel is nowadays limited by the price of raw materials, which require high purity standards to be employed in conventional production processes. To overcome this problem, the transesterification of triglycerides in alcohol supercritical conditions could be conveniently used: the non-catalytic nature of this process allows the use of recycled raw materials, which are cheaper. To this end, a pilot scale plant for the continuous production of biodiesel in supercritical conditions was designed, manufactured and operated. In this research paper, rapeseed oil and bioethanol were used as raw materials, and the investigated temperatures were between 200 and 340°C, the pressure between 150 and 240 bar, and the alcohol-to-oil ratio ranged between 9 and 100. The best fatty acid ethyl ester (FAEE) yields were obtained at 340°C, 240 bar and a molar ratio of 42, which is line with easier-to-control lab-scale tests in batch conditions found in the literature. This encourages widening of the operating conditions to further improve the maximum achievable yields for the rapeseed oil-ethanol system.

This article presents an environmentally friendly approach for the conversion of rapeseed oil via supercritical ethanol condition, with and without the presence of a solid catalyst, to produce biodiesel. The experiment was conducted in a batch reactor at various temperatures, reaction times, and ethanol to oil molar ratios. The evolution of process was followed by high performance liquid chromatography to determine accurately and quickly the content of final reaction mixture in a single analysis. The results show that the highest biodiesel yields of 93% (with ZnO) and 88% (with CaO) were obtained after the reaction time of 60 min at a temperature of 270°C. This process has high potential in minimizing the production cost of biodiesel due to its simplicity and technical advantage.

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