Development of a membrane-based separation process for the continuous enzymatic saccharification of lignocellulosic biomass

We are currently evaluating the feasibility of performing continuous enzymatic hydrolysis of lignocellulosic biomass to product sugars using a membrane-assisted reaction/separation process. The overarching technical goals are to continuously remove the sugars—this lowers product feedback inhibition—retain and recycle active enzyme, and continuously recover the co-product of lignin.  Experimental data is being collected to support preliminary technoeconomic analysis of the speculative process designs versus the current state-of-the-art batch enzymatic hydrolysis. Prospective savings are anticipated due to higher time-averaged productivity from capital equipment investments, and lower enzyme usage.

Our initial studies included characterizing cake-layer resistances for varying slurry solids loadings during crossflow filtration. These results highlighted the fact that the membrane's nominal permselective properties are less important than its module configuration and ease-of-cleaning because the cake formation controls the flux and fine tunes the selectivity. Thus, our current studies include two aspects. Firstly, we are coupling tubular ultrafiltration membranes to a continuous stirred-tank reactor and continuously removing the sugars and recycling the bulk of the water back to the reactor after concentrating them. Overall reaction kinetics and yield are being assessed and compared with classical batch hydrolysis results. Secondly, the membrane processing is being studied using computational fluid dynamics (CFD) in order to improve membrane module design for these particle laden slurries. Different parameters such as mass fraction of insolubles in slurry, shear rate provided to slurry, and membrane/cake permeance characteristics are varied to study energy consumption and uncover scenarios that may be especially problematic.