Enhancement of biocatalytic activity in enzymatic membrane reactors: Controlled modification with novel PAH/PDA composites as a tool to optimize reactor performance

Abstract

Enzymatic membrane (EM) is a tool allowing to simultaneously upgrade enzymatic catalysis and membrane separation processes. However, their commercial use is often restricted by a trade-off between catalytic and mass transfer properties of the system. Herein, we report a new approach to the design of enzymatic membrane reactors (EMRs) - aimed to find the optimal balance between biocatalytic activity, water permeability, and enzyme loading; where we used co-deposited polyallylamine hydrochloride/polydopamine (PAH/PDA) membrane coatings as a tool to control the overall reactor performance. First, we demonstrate that tailoring the PAH/PDA coating chemistry can be more effective for promotion of total biocatalytic activity of EM with immobilized alcohol dehydrogenase (ADH) than increasing the amount of immobilized enzyme on a membrane support. Then, we show how the PAH/PDA ratio (0, 1:10, 1:2, 5:2), modification time (0.25, 1, 4, 16 h) and ionic strength (0.1–1.0 M NaCl) affect morphology of the membrane coating and alter the mechanisms of ADH-support interactions. Lastly, we illustrate the versatility of the PAH/PDA-coated membranes for application in other enzymatic systems on the example of glycerol dehydrogenase (GDH) and evaluate the performance of two EMRs as a function of applied pressure (1–3 bar). The final values of biocatalytic activities 25.4 ± 4.0 and 3.5 ± 0.3 mU/cm2 (which correspond to 140 ± 22 and 67 ± 5% immobilization efficiencies) for immobilized ADH and GDH, respectively, demonstrate that PAH/PDA-coated membranes not only can be used for simultaneous reaction and recovery of the biocatalyst, but also for enhancement of enzymatic activity - due to opportunity of reaction rate control in the membrane reactor.