Abstract
Oxidative O2‐dependent biotransformations are promising for chemical synthesis, but their development to an efficiency required in fine chemical manufacturing has proven difficult. General problem for process engineering of these systems is that thermodynamic and kinetic limitations on supplying O2 to the enzymatic reaction combine to create a complex bottleneck on conversion efficiency. We show here that continuous‐flow microreactor technology offers a comprehensive solution. It does so by expanding the process window to the medium pressure range (here, ≤34 bar) and thus enables biotransformations to be conducted in a single liquid phase at boosted concentrations of the dissolved O2 (here, up to 43 mM). We take reactions of glucose oxidase and d‐amino acid oxidase as exemplary cases to demonstrate that the pressurized microreactor presents a powerful engineering tool uniquely apt to overcome restrictions inherent to the individual O2‐dependent transformation considered. Using soluble enzymes in liquid flow, we show reaction rate enhancement (up to six‐fold) due to the effect of elevated O2 concentrations on the oxidase kinetics. When additional catalase was used to recycle dissolved O2 from the H2O2 released in the oxidase reaction, product formation was doubled compared to the O2 supplied, in the absence of transfer from a gas phase. A packed‐bed reactor containing oxidase and catalase coimmobilized on porous beads was implemented to demonstrate catalyst recyclability and operational stability during continuous high‐pressure conversion. Product concentrations of up to 80 mM were obtained at low residence times (1–4 min). Up to 360 reactor cycles were performed at constant product release and near‐theoretical utilization of the O2 supplied. Therefore, we show that the pressurized microreactor is practical embodiment of a general reaction‐engineering concept for process intensification in enzymatic conversions requiring O2 as the cosubstrate.
Highlights
Advanced process technologies for chemical production are increasingly built on process intensification and continuous processing as the central pillars of their development (Adamo et al, 2016; Clomburg, Crumbley, & Gonzalez, 2017; Hessel, Kralisch, Kockmann, Noël, & Wang, 2013; Wiles & Watts, 2014)
Operating the flow reactor in the experiments described below involved a lower‐limit STY of ∼1 mM/min. This STY was chosen as reference point for an analysis of reaction intensification based on literature (Chapman et al, 2018; Jones et al, 2012; Karande et al, 2016; Toftgaard Pedersen et al, 2017; Tomaszewski, Schmid, et al, 2014; Tomaszewski, Lloyd, et al, 2014; van Schie et al, 2018), as further discussed later
We considered that the glucose oxidase (GOX) might become inactivated by the H2O2 formed in the reaction
Summary
Advanced process technologies for chemical production are increasingly built on process intensification and continuous processing as the central pillars of their development (Adamo et al, 2016; Clomburg, Crumbley, & Gonzalez, 2017; Hessel, Kralisch, Kockmann, Noël, & Wang, 2013; Wiles & Watts, 2014). The main parameters of reaction efficiency (product concentration, space–time yield (STY), and catalyst turnover) all depend on, and are often severely limited by, how effectively O2 is made available within the liquid phase (Gemoets et al, 2016; Pedersen, Rehn, & Woodley, 2015). A falling‐film microreactor operated in continuous countercurrent gas–liquid flow showed a kLa of 450 min−1 (Bolivar, Krämer, Ungerböck, Mayr, & Nidetzky, 2016) These developments notwithstanding, important engineering problems remain. Requirement for optimum use of the enzyme activity is a steady‐state concentration of O2 ([O2]opt) surpassing the enzyme Km by roughly one magnitude order This implies the clear need for new process windows to be exploited for biocatalytic oxidations by O2. We developed an instrumented pressurized flow reactor for continuous enzymatic transformations in a single liquid phase at substantially enhanced O2 concentration. We demonstrate that the pressurized flow reactor is a powerful engineering tool for process intensification in O2‐dependent biochemical conversions
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