New Insights in the Formation Mechanism of Cellulose-Based Biochar

In the process of hydrothermal carbonization of cellulose to produce biochar, the promotion or inhibition roles of the main hydrolysates of cellulose such as 5-hydroxymethylfurfural (5-HMF), furfural (F), formic acid (FA), and levulinic acid (LA) on biochar formation are still unknown, limiting the development of controllable preparation of biochar. Here, the 5-HMF itself, the mixtures of 5-HMF and F, 5-HMF and FA, as well as 5-HMF and LA are, respectively, used as precursor for the preparation of biochar to elucidate their interactions on biochar formation. Combining the consumption rate of reactants and the physicochemical properties of the resulting biochar, the results have been found that 5-HMF and FA promote the formation of biochar, but F and LA inhibit the formation of biochar. The promoting effect of FA is reflected in its ability to reduce critical aggregation concentration of colloidal particles and improving biochar precipitation. Additionally, FA can react with ─OH on the surface of biochar to form furan─FA compounds and increase the particle size of biochar and oxygen-containing content (O/C = 0.39). This work is first to elucidate a new pathway of FA effecting biochar formation and provides a new insight for the formation of cellulose-based biochar.