| dc.description.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 addition, the reaction kinetics has been studied. In Chapter 3, synthesis of fatty acid ethyl esters from Schizochitrium limacinum microalgae using supercritical ethanol and ethyl acetate have been studied. The effect of important parameters on the conversion of fatty acid ethyl esters have been studied. Further, kinetics of a process was studied by pseudo first order kinetic model. Chapter 4 deals with the experimental determination of solubilities of castor oil derivatives, namely ricinoleic acid, methyl ricinoleate and methyl 10-undecenoate in supercritical carbon dioxide (SCCO2). A new model based on solution theory coupled with regular solution theory for activity coefficients was developed to correlate the pure component solubilities in SCCO2. In Chapters 5 and 6, experimental determination of solubilities of mixture of 10-undecenoic acid + methyl 10-undecenoate, 10-undecenoic acid + methyl ricinoleate and methyl 10-undecenoate + methyl ricinoleate in SCCO2 have been done. Two new models based on association and solution theories coupled with regular solution theory for activity coefficients have been derived to correlate the mixture solubilities of lipid derivatives in SCCO2. Chapter 7 outlines the important conclusions from the above mentioned works and provide the scope for future works.
The transesterification reaction and the solubilities of lipid derivatives in supercritical fluids reported in the current work have been studied for the first time. The work on the production of biodiesel from Schizochitrium limacinum microalgae highlights the importance of supercritical fluid technology by overcoming the problems associated with the conventional process and improving the value of overall process by using alternative alkylating agents. Further, the work on the solubilities of mixtures of castor oil lipid derivatives in SCCO2 highlights the importance of CO2 as a green solvent in developing and designing of the separation and purification processes | en_US |
