Rheology evolution and CFD modeling of lignocellulose biomass during extremely high solids content pretreatment

Abstract

Design of industrial scale pretreatment reactors requires the accurate physical and rheological parameters of lignocellulose biomass. Rheological properties of raw and pretreated lignocellulose materials had been characterized in previous studies. A large gap of rheological properties between the raw and pretreated lignocellulose raised a difficulty for designing proper pretreatment reactors with maximum efficiency and minimum power consumption. In this study, the dilute acid pretreatment was operated in a 20-L reactor equipped with helical ribbon impeller agitation at high solids content up to 70% (w/w) dry solids. The operation was stopped at different time points, and then the completely or incompletely pretreated lignocellulose materials were released and sent for rheological property measurement. The changing rheological properties of lignocellulose materials were recorded into an evolution profile. The apparent viscosity change was found to be closely related to pretreatment temperature, and then affected the consequent enzymatic hydrolysis yield. The dynamic rheological parameters were fitted into power law model and the CFD model was established for high solids content pretreatment and used for industrial reactor design. Furthermore, the apparent viscosity of the raw and pretreated corn stover and wheat straw increased, instead of decreased, raising an instinct difference with the system of rigid solid particles and water. The study provided the first insight into the evolution of rheological properties during the high solids content pretreatment and the basis for industrial scale pretreatment reactor design.