Toward Continuous Lignin Extraction from Corn Stover via Low-Temperature Dilute Alkaline Pretreatment in a Packed-Bed Reactor

Abstract Lignin and cellulose from lignocellulosic biomass are two of the most abundant naturally occurring polymers. These materials have great potential for cost-effective conversion into energy, chemicals, and materials. Isolating lignin from lignocellulose using a low-concentration alkaline solution at low temperatures has been shown to minimize the degradation of both lignin and cellulose structures. To enable continuous lignin extraction from corn stover while producing cellulosic substrates for downstream saccharification, we propose to use a flow-through packed-bed reactor to perform low-concentration alkaline pretreatment at low temperature and atmospheric pressure conditions. The results showed that, at 90 °C, lignin yield reached 58.26% with NaOH loading of 86.7 g/kg biomass. Compared with previously reported result from pretreatment in batch type paddle reactors, lignin yield from a packed-bed reactor pretreatment under similar conditions does not decrease despite the lack of active agitation. We developed a reaction kinetics model and bulk permeability model to predict the impact of lignin extraction on the operation of a packed-bed reactor to guide further experiment design and scale-up. Compared with conventional maximum likelihood estimation, the Bayesian inference approach provides parameter distributions for better predicting experimental observations with credible intervals. Our kinetic model predicts the yield of lignin extraction from previously reported results with varying particle sizes. Experimental results show that the lignin extraction process is limited by the chemical reaction rate in the particle size range studied in this work.