Effects of ball milling on structural changes and hydrolysis of lignocellulosic biomass in liquid hot-water compressed carbon dioxide

Abstract

Mechanical activation is an effective method for destroying the crystalline structure. Biomass, especially its hemicellulose, can be degraded in the green solvent of liquid hot-water compressed carbon dioxide. To improve the degradation of crystalline cellulose in liquid hot-water compressed carbon dioxide, pretreatment of camphorwood sawdust by mechanical activation with a stirring ball mill was studied. Ball milling parameters and their effects on structure were determined by SEM, XRD and FT-IR. The influence of milling parameters on cellulose conversion can be ranked as follows: ball milling speed>activation time>the mass ratio of ball to biomass. The optimum milling condition was obtained at ball milling speed of 450 rpm and mass ratio of 30: 1 of ball to biomass for 2 h. In this condition, cellulose crystallinity of sawdust decreased from 60.93% to 21.40%. The cellulose conversion was 37.8%, which was nearly four times of raw material (10.2%). The glucose yield in the hydrolysate was 1.49 g·L−1, which was nearly three times of that of raw material. It showed mechanical activation can destroy the crystalline structure of cellulose to promote degradation and the damage of lignocellulosic internal structure caused by ball milling is irreversible.