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Biodiesel production in micro-reactors: A review
Published in Elsevier B.V.
Volume: 43
Pages: 143 - 161
In recent years, biodiesel, as a renewable and environment-friendly fuel has emerged as one of the most investigated bio-fuel with a goal to decrease our dependence on petroleum fuels and reduce environmental pollution. The current commercial technique of biodiesel production via transesterification is constrained by high operating cost and energy requirements, long residence time and limited conversion due to equilibrium limitations. On the other hand, the process intensification using the micro-reactor technology demonstrated an excellent performance ascribed to short diffusion distance and high surface area-to-volume ratio that can lead to high heat and mass transfer rates and improved mixing compared to the conventional reactors. This review provides an overview of the current status of biodiesel production in micro-reactors. It includes various types of micro-reactors used in the production of biodiesel, factors affecting the biodiesel production (i.e., temperature, residence time, alcohol to oil molar ratio, micro-channel size, inlet mixer type, internal geometries, co-solvent, catalyst type and concentration). This review also includes the factors affecting the liquid-liquid flow patterns and application of micro-reactor technology in the purification of biodiesel. Some of the critical observations from this review are, 1) inlet mixer type, channel size, and internal channel geometry (zig-zag, omega, and tesla shaped channels) have shown a significant effect on mixing in micro-channels. 2) In case of base-catalyzed transesterification, the biodiesel yield was found to increase up to the reaction temperature of 60–65 °C. 3) Homogeneous alkaline catalyst (NaOH, KOH, CH3ONa) was preferred for the feedstock with low free fatty acid content (<1 wt\%). However, an acid catalyst with high concentration, a significant amount of methanol and long reaction time were required for high free fatty acid feedstock (>1 wt\%). Therefore, the current research is more focused on the investigation of heterogeneous catalysts in micro-reactors to develop an ecologically friendly process for the production of biodiesel. 4) Also, the reaction temperature and inlet mixer type had shown a significant effect on liquid-liquid flow patterns. This review also addressed the following literature gaps; a numbering-up technique to increase the throughput; catalyst development for high free fatty acid feedstock; continuous production of biodiesel in micro-reactors with in-line purification step to meet the energy demand and quality standards. © 2018 International Energy Initiative
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Published in Elsevier B.V.
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