Microfluidic devices or microdevices refer to systems with a characteristic length in the micrometer range. Systems in this size allow handling small quantities of reagents and samples, with reduced residence time, better control of chemical species concentration, high heat and mass transfers, and high surface/volume ratio. These characteristics led to the application of these microdevices in several areas, such as biological systems, energy, liquid-liquid extraction, food, agricultural sectors, pharmaceuticals, flow chemistry, microreactors, and biodiesel synthesis. Microreactors are devices that have interconnected microchannels, in which small amounts of reagents are manipulated and react for a certain period of time. The traditional characteristics of microreactors are less quantities of reagents and samples, high surface area in relation to volume (10000 m2 m-3), reduction of resistance to heat and mass transfer, reduced reaction times, and narrower residence time distributions. In recent years, several studies have been carried out on biodiesel production in microreactors that explore the influence of operating conditions, mixing and reaction yield, numbering, and especially the microdevices design. Despite all the advantages of microreactors, the literature shows that there are only a few applications on an industrial scale. Two main reasons that hinder the adoption of this technology are the scale-up to a large enough volume to deliver the necessary production capacity and the costs related to industrial manufacturing microreactors. It is often stated that large-scale production of microreactors can be easily achieved by numbering-up. However, researches show that an incredibly high number of microdevices would be needed, which results in a technical unfeasibility and a strong impact on the construction costs of the industrial system. The present review aims to show whether microreactors can replace conventional biodiesel production processes and how this replacement technology could be carried out. The current chapter was divided into the following sections: Introduction, Synthesis and Purification of Biodiesel in Microreactors, Fundamentals of CFD, and Fundamentals of Scale-up. Finally, conclusions and future perspectives are exposed.

Methyl oleate, an example of a FAME (fatty acid methyl ester), was produced by oleic acid (OA) photoesterification with TiO2 and UVA light. Different parameters were evaluated and optimised: catalyst pretreatment, temperature (25–65 °C), catalyst loading (1–30 % w/wOA) and oleic acid : alcohol molar ratio (1 : 3–1 : 55). Response surface quadratic methodology obtained by central composite rotational design (RSM‐CCRD) was used to evaluate the main operational conditions of the photoesterification process. A high conversion of 98 % (±0.8) at 55 °C, 20 % TiO2 (w/wOA), and 1(OA) : 55(methanol) molar ratio was achieved. The photoesterification mechanism is furthermore proposed. The Langmuir‐Hinshelwood kinetic model considered the forward and backward reaction as first‐order fits with the best accuracy (R2 of 0.997). The thermodynamic results (ΔG338.15K=−20.75 kJ/mol, ΔH=13.75 kJ/mol, and ΔS=0.47 kJ/mol.K) indicate that the operating conditions are important, both to supply the energy requirement of the reaction, but also to increase the miscibility of the reactants.

Biopolymer alginate is capable of triggering interchain interactions in the presence of divalent and trivalent cations. Calcium alginate particles obtained by the emulsification method have been used in ion-exchange packed bed tests to remove synthetic copper effluents. Adsorption equilibrium data were obtained from single and binary component systems, which were subsequently subject to mathematical modeling. In the case of the modeling system with binary components, where the calcium was considered as a second ion, there was no significant improvement for the models analyzed, in counterpoise to the isotherm models applied to the single component system. The ideal law of mass action and the law of mass action which presupposed that both phases were non-ideal showed similar results. This process was found to be effective and feasible for industrial applications used to in heavy metal removal processes.

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