Direct transesterification of microalgae to biodiesel using ionic liquid catalysts
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Increasing global energy demand coupled with the environmental eﬀects of fossil fuels have, like global warming, reinvigorated the need for the commercialization and development of alternative renewable energy sources such as biodiesel. Microalgae are considered a sustainable feedstock for the commercial production of biofuels because they need not compete with food production, and they can use CO2 and sunlight to produce the lipids needed for biodiesel production. Recently the idea to directly convert unbroken and wet microalgae to biodiesel via in situ transesterification has drawn attention. However, the high moisture content in microalgae biomass is still a main limiting factor for in situ transesterification processes. The overall objective of this work was to develop and optimize the direct conversion of wet microalgae biomass into biodiesel using an ionic liquid catalyst. This process reduces the total operational steps through the simultaneous extraction and transesterification of intracellular lipids from algae biomass and eliminating the need for an energy-intensive drying step. Four types of tetrabutylphosphonium carboxylate ionic liquids ([P4444][CA]) were synthesized and were used to transesterify refined cooking oils (sunflower, canola, and corn oil) into biodiesel and for the direct transesterification of wet microalgae biomass (C. vulgaris) into biodiesel. Phosphonium carboxylate ionic liquids were found to be good catalysts for transesterification in the presence of methanol and capable of both cell disruption and transesterification in a single step. The leading candidate ionic liquid ([P4444][Formate]) was selected for a more in-depth characterization of the effect of process variables on fatty acid methyl ester (FAME) yield. The FAMEs composition and the major properties of synthesized biodiesel from both cooking oils and microalgae were calculated. All synthesized biodiesels fulfilled the biodiesel properties stipulated in the ASTM D6751 and EN 14214 biodiesel standards. The effects of reaction parameters including ionic liquid anion size, reaction time, reaction temperature, the mass ratio of IL to microalgae biomass, and the water content of microalgae on FAME yield were investigated. This process was further optimized using response surface methodology (RSM). The optimal reaction conditions for the FAME yield was found to require a reaction time of 4.6 h, a reaction temperature of 102.4oC, IL:microalgae mass ratio of 8:1, and water content of 40.6%. The FAME yield at these conditions was predicted to be 98.0 ± 2.48%. Finally, the reusability of the ionic liquid was verified. The major properties of the synthesized biodiesel from both cooking oils and microalgae were calculated using the FAME composition of the resulting biodiesel. Finally, the reusability of the ionic liquid was verified which will be necessary to reduce the environmental impact a direct transesterification process.
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Sepandar Malekghasemi (2020). Direct transesterification of microalgae to biodiesel using ionic liquid catalysts. UWSpace. http://hdl.handle.net/10012/16486