Non catalytic synthesis of biodiesel and solubilities of mixtures of lipid derivatives in supercritical fluids

Abstract

The fossil fuels are depleting rapidly as the demand for energy and its allied chemicals is continuously increasing in the modern world. In addition, the concerns over climate change due to the greenhouse gases emitting from the usage of these fossil fuels necessitates the need for alternative fuels. Biodiesel is one such alternative fuel that can replace the conventional diesel existing in the market. Biodiesel is a mixture of fatty acid alkyl esters produced from vegetable oils, animal fats, waste cooking oils and microalgae oils. Conventionally, biodiesel is obtained from the transesterification reaction in the presence of acid or base catalyst. This process has several disadvantages such as longer reaction times, soap formation and separation of catalyst from the final product. To avoid these issues, supercritical fluid technology can be used for the synthesis of biodiesel. Supercritical fluids are fluids that cannot be distinguished as either gases or liquids above their critical point. These fluids have liquid like densities and gas like diffusivities. The major advantage of using these fluids is that the solvating power can be tuned by changing temperature and pressure. Therefore, supercritical fluid technology can be used for reaction media as well as extraction/separation of high boiling point chemicals obtained from various processes. Hence, Chapter 1 of the thesis introduces about supercritical fluids and their properties. Further, it includes an overview of transesterification reaction of microalgae to biodiesel and the solubilities of pure and mixtures of low volatile liquid solutes in SCCO2 useful in downstream processing of lipids/lipid derivatives. Chapter 2 deals with the synthesis of fatty acid methyl esters from Schizochitrium limacinum microalgae using three different supercritical fluids namely, methanol, dimethyl carbonate and methyl acetate. The effect of important parameters such as ratio of methylating agent to algae (vol./wt.), pressure, temperature and time were discussed. In additio...