Search

Enzymes are gaining increased importance as highly selective catalysts for green chemical synthesis. Multiphase microreaction systems are emerging tools for the development of enzyme-catalysed transformations involving two or more partly immiscible fluids in continuous flow. Mass transfer intensification due to miniaturisation of the flow dimensions and the associated enlargement of the interfacial area presents a powerful approach of effective reaction rate enhancement and thus reactor productivity increase for smart flow bioprocessing. Use of microstructured flow reactors for the study of multiphase (gas-liquid, liquid-liquid) biocatalytic conversions is reviewed. Multiphase flow characterisation based on dimensionless scaling parameters and flow-regime categorisation is presented with emphasis on the different flows applied to experimental studies of enzymatic reactions. Development of instrumented microsystems, flow instabilities, fast inactivation of biocatalysts and low conversion rates are problems often encountered with biotransformation under multiphase flow conditions. Key parameters controlling reaction performance are discussed along with some guidelines for design of scalable multiphase biocatalytic microreactors. Opportunities for biocatalytic process intensification are revealed in examples from fine chemical and materials synthesis.

Featured Application: A natural Tunisian carbonate-rich clay is an active catalyst for the solventless transcarbonatation of glycerol and ethylene carbonate to render valuable glycerol carbonate and ethylene glycol. Biodiesel is nowadays added in 5–10% v/v to diesel, and its production involves the parallel creation of a vast glycerol amount as a by-product. Despite its many applications, there is a surplus of glycerol (Gly) that has boosted the search for new applications of this compound, now transformed into an industrial synthesis intermediate or platform chemical. Its transcarbonation is a type of reaction that occurs under mild conditions, using weak or moderate basic catalysts, and allows the parallel production of glycols of industrial interest with high selectivity, such as ethylene glycol. In this research, we have studied the activity of a Tunisian clay rich in inorganic carbonates that give it a weak basic character. The raw clay (RC) has been fully characterized by XRD, FTIR, SEM-EDS and nitrogen porosimetry. Subsequently, it has been employed as a catalyst to react glycerol (G) with ethylene carbonate (EC) to obtain glycerol carbonate (GC) and ethylene glycol (EG). The main operating variables and their effects on glycerol conversion and initial reaction rate were analyzed: catalyst concentration (2–6% w/w glycerol), reagent molar ratio (EC:G 1.5:1 to 3:1), and temperature (80–110 °C). Then, an appropriate kinetic model was selected from the results obtained under various reaction conditions, including the total deactivation of order 1 of the catalyst. The kinetic constant activation energy in this reaction using Tunisian smectite was found to be around 183.3 kJ·mol−1. In the second phase of the investigation, we explored the reuse of smectite using the kinetic model to appreciate the effect of cycle-to-cycle deactivation. It can be seen that the kinetic constant of the main reaction generally decreases with the number of cycles at low temperature and goes through a maximum at high operating temperature, while the deactivation constant increases with the number of catalytic cycles. The catalyst shows more stability, in general, at higher temperatures. [ABSTRACT FROM AUTHOR]