Multiphase biotransformations in microstructured reactors: Opportunities for biocatalytic process intensification and smart flow processing

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.