Evaluation of initial material particle size on the hydrothermal pretreatment of poplar powder

Initial material characteristics were one of the decisive factors affecting the hydrothermal pretreatment of woody biomass with a dense structure. In this study, the effect of initial material particle size on poplar hydrothermal pretreatment and enzymatic hydrolysis was evaluated. The enzymatic hydrolysis yield and the accessibility of the enzymatic reaction were significantly increased with an initial material with an average particle size of initial material (D₅₀) < 500 μm, because of the different pretreatment effects of initial material. SEM and compositional analysis indicated that the reduction of the initial particle size facilitated hydrothermal pretreatment with better depolymerization effects. The bulk density of D₅₀ < 500 μm increased by 28.87%, and the SSA increased by 68.51% compared with 2000–2500 μm. In contrast, the water holding capacity decreased by 59.40%. In addition, there was almost no free water in D₅₀ < 500 μm and had weak mechanical properties, which was more conducive to the stirring of the hydrothermal pretreatment. Compared with the particle size of initial material being less than 100 μm, the D₅₀ of initial material between 100 and 2500 μm was more energy saving and economically feasible. The particle size of poplar powder in this study could reduce pretreatment intensity and energy consumption and improve pretreatment energy efficiency significantly. This study was meaningful in identifying the size effects and exploring the optimal properties of initial material for poplar on hydrothermal pretreatment.