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[1]) 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 the design of a new enzymatic membrane reactor (EMR) with the optimum balance between biocatalytic activity, water permeability, and enzyme loading; where we used co-deposited polyallylamine/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.

Keywords: biocatalytic membrane, polyelectrolyte coating, polydopamine co-deposition, enzyme immobilization, membrane reactor