Enhancing Carbonization of Microcrystalline Cellulose through Ball Milling under Decoupled Temperature and Pressure Hydrothermal Conditions

Hydrothermal treatment of cellulose is a promising green route for bioenergy and biochemical production, yet requiring investigations of the mechanisms. In this study, the effects of cellulose crystallinity and decoupled temperature and pressure conditions on cellulose conversion and product distribution were investigated. Microcrystalline cellulose was ball-milled for varying durations, leading to a reduction in crystallinity, with 4 h of milling sufficient to achieve near-complete amorphization. Unlike concurrent recrystallization and hydrolysis observed under autogenous pressure, decoupled conditions significantly accelerated hydrolysis of cellulose. Notably, lower crystallinity cellulose exhibited significant improvements in glucose and 5-HMF yields, with 4-hour ball milling showing optimal performance among all samples. Furthermore, carbon sub-micron spheres were largely produced, which were confirmed via PTFE encapsulation experiments to primarily consist of secondary char deriving from re- polymerization and condensation reactions of the liquid phase. Overall, this study demonstrates that lower crystallinity not only facilitates hydrolysis but also accelerates the carbonization processes under decoupled pressure conditions, highlighting its potential for efficient biomass conversion into valuable products.