Chemical Engineering Journal 160 (2010) 708–714 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej On the feasibility of in situ steroid biotransformation and product recovery in microchannels M.P.C. Marques a,∗ , P. Fernandes a , J.M.S. Cabral a , P. ˇ Znidarˇ siˇ c-Plazl b , I. Plazl b a IBB-Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aˇ skerˇ ceva 5, SI-1000 Ljubljana, Slovenia article info Article history: Received 9 November 2009 Received in revised form 11 March 2010 Accepted 23 March 2010 Keywords: Steroids Oxidation Microreactor Reaction-diffusion dynamics Modeling Cholesterol oxidase abstract Microchannel reactor technologies are gaining widespread use in a large range of areas, which comprise biotechnology and chemistry. The small volumes involved and the favorable mass and heat transfer inherent to these devices make them particularly useful for the screening of biocatalysts and rapid characterization of bioconversion systems. In the present work, the enzymatic oxidation of cholesterol to 4-cholesten-3-one performed within microchannels by cholesterol oxidase, was studied in a two-phase system, comprising an organic phase as substrate and product pool and an aqueous phase with dissolved enzyme. A mathematical model based on mass balances for cholesterol, 4-cholesten-3-one and dissolved oxygen concentrations, com- prising double-substrate Michaelis–Menten kinetics and the velocity profile of two immiscible fluids, was developed in order to describe and predict the process of cholesterol oxidation. The numerical pro- cedure of solving the non-linear 3D model was based on an implicit finite-difference method improved by non-equidistant differences. In a Y-shape microreactor geometry, roughly up to 70% conversion of cholesterol was achieved at res- idence times below 1 min. The suitable adjustment of the ratio of the fluid flow rates was performed by taking into account the viscosity of the fluids involved. This allowed for phase separation to be reestab- lished at the Y-shaped exit from the microreactor and thereby enabled in situ product separation from the aqueous phase containing the enzyme. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Microchannel reactor technologies have found application in research, development and production processes in several areas, including (bio)chemistry and biotechnology, having already been introduced in industrial-scale applications [1–5]. In contrast with conventional reactors, microchannel reactors offer the option for achieving a more precise control of the process, higher efficiency and safety allied to better selectivity, improved yield and flexible production [5,6]. These reactors can be assembled by microfabrication techniques or by the modification of microcapillaries, using reaction apparatus with small dimensions, typically in the range of micrometers (m) with volumetric capacity in the range of microliters (l) [7]. These systems take advantage of micro- or nano-fluidics, that require low volumes of reactant solutions, offering high-performance effi- ∗ Corresponding author. Tel.: +351 218 419 138. E-mail address: mpc.marques@ist.utl.pt (M.P.C. Marques). ciency and repeatability [8], thus making microchannel reactors an extremely efficient tool for the rapid screening of biocatalysts. The flow patterns in microfluidic systems are mostly laminar, as opposite to macro-scale systems, a feature that favors the strict control of reaction conditions and time [9]. In addition, microchannel reaction systems provide large sur- face to volume ratio, which gives the microreactors superior performance w.r.t. heat and mass transfer compared to conven- tional reactors, e.g. in extractions and multiphase (bio)catalytic reactions [10]. Given their flexibility, microchannel reactors allow furthermore for faster transfer from the development to the production stage, reducing associated cost of scale translation, materials and energy, and manpower. In the particular case of enzymatic microchannel reactors, using either dissolved or immobilized enzymes, these were originally developed mostly in order to improve the routine work in bio- chemical analyses of proteomic and genetic material [8,11]. The use of microreactors has however expanded to other areas, including production processes, as demonstrated by the increased number of 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.03.056