Mixing Effects in Cellulase-Mediated Hydrolysis of Cellulose for Bio-Ethanol Production

Conversion of cellulose to glucose is the rate-limiting step in converting biomass into fuel. In this paper, we explore the effects of micro- and macro-mixing on the enzymatic hydrolysis of various cellulosic substrates to glucose by using a spatially averaged low-dimensional CSTR model. We quantify the effects of mixing on glucose yield, cellulose depolymerization rate and the synergy between the enzymes. We conclude that micromixing limitations provide an important mechanism to increase yield, reduce the dominance of synergy and guide optimum process design by offsetting inhibitory effects by preventing the inhibitors from coming in contact with the enzymes. On quantifying the effects of inhibition type (competitive vs noncompetitive) and mixing type (macro- vs micro-), we find that noncompetitive inhibition inhibits glucose yield more strongly than competitive inhibition, and that unlike micromixing limitations, macromixing limitations reduce glucose yield. On the basis of our analysis, we recommend 2 tank reactors in series with minimal local mixing in each tank and glucose removal at the exit of the first tank as the optimal reactor configuration for maximizing glucose yield from enzymatic hydrolysis of cellulose.