Thermodynamic modeling of freeze pretreatment in the destruction of rice straw structure combined with alkaline-hydrothermal method for enzymatic hydrolysis

Freeze pretreatment combined with alkaline-hydrothermal method of rice straw for enzymatic hydrolysis was studied. Crystallization stress in the rice stem pores caused by water freezing at −20– −40 °C was modeled to illustrate the destruction mechanism. The stress was calculated as 22.5–38.3 MPa that were higher than the tensile yield stress of untreated stems (3.0 MPa), indicating ice formation damaging pore structure. After freeze at −20 °C, rice straw was further hydrothermally treated at 190 °C with 0.4  M Na 2 CO 3 , achieving 72.0 % lignin removal and 97.2 % cellulose recovery. Glucose yield rose to 91.1 % by 4.3 times after 24 h hydrolysis at 10 FPU loading of Cellic®CTec2 cellulase. The specific surface area of rice straw was 2.6 m 2 /g increased by 1.2 times after freeze. Freeze combined with alkaline-hydrothermal treatment is a green and energy-efficient method for improving enzymatic hydrolysis.