Mixing effects on the kinetics and the dynamics of two-phase enzymatic hydrolysis of hemicellulose for biofuel production

Abstract

This work uses a coupled experimental and modeling approach to explore the effects of macro- and micro-mixing on the kinetics and the dynamics of two-phase enzymatic hydrolysis of hemicellulose. Reactor mixing does not alter the non-competitive nature of product inhibition in hemicellulose hydrolysis by endoxylanase, but produces stronger inhibition that reduces the soluble sugar yield by 8–14.5%, as the mixing speed increases from 0 to 200 rpm. The kinetic constants (Km, Vmax, Kx) assume mass-transfer disguised values at 0–200 rpm. An optimal mixing strategy, comprising of 55–70 min of initial rapid convective macromixing followed by diffusive micromixing (without any macromixing) for the rest of the hydrolysis, increases xylose and reducing sugar yields by 6.3–8% and 13–20%, respectively, over continuous mixing at 200 rpm, for 1–5 mg/ml substrate loading at an optimum enzyme to substrate ratio of 1:20, with an energy saving of 94–96% over 24 h.