Population ensemble modeling of biomass dissolution

Abstract

A major barrier to the efficient utilization of biomass is the recalcitrance to dissolution of semicrystalline cellulose. The present study addresses the kinetics of swelling and dissolution of cellulose particles at conditions emulating large-scale biomass processing where the particles exhibit a broad distribution of size. To this end, we have developed a model in which the behavior of a population of particles is obtained from an ensemble of individual particle dissolution models. The dissolution of an individual semicrystalline polymer particle involves decrystallization and disentanglement as two important and potentially rate-determining steps in the process. Using this population ensemble model, novel results on the evolution of cellulose particle size distribution and polydispersity over the dissolution time have been obtained, and the impact on dissolution of the particle size distribution width and mean particle size has been examined at different conditions. The high number of smaller particles determines initially the dissolution behavior of a polydisperse system, however, at long dissolution times, relatively small numbers of larger particles dictate the overall dissolution behavior. Reducing the mean particle size increases the dissolved fraction more at disentanglement control conditions than at decrystallization control conditions. Having a wider particle size distribution would always increase the cellulosic biomass solubility at disentanglement control conditions. At decrystallization control conditions, a wider size distribution is beneficial initially, however, at long times a system with narrower particle distribution dissolves more. Findings from this study would benefit the rational design and optimization of pretreatment processes to reduce the particle size for enhanced biomass utilization. The developed model can be applied to the dissolution of polydisperse particles for various polymers of interest to drug delivery and plastics recycling.