Interaction Of Biomass Organic Components In Their Hydrothermal Carbonization And The Prediction Of Solid Product Characteristics

Hydrothermal carbonization(HTC)is a promising thermochemical treatment technique for converting wet biomass into value-added products.But the hydrochar properties of different biomass differ significantly due to the diversity of biomass feedstock and the complexity of HTC reactions.An extensive understanding of hydrochar characteristics and their prediction models is still lacking.Blending lignocellulosic biomass can improve the performance of sewage sludge(protein-rich)hydrochar.Investigating the effects of different lignocellulosic components on the protein HTC reaction pathways and product properties can provide guidance for screening lignocellulosic biomass and improving product quality performance.In this study,the Simplex Lattice Mixture Design method was used and five representative model compounds of biomass components were selected.Prediction models of mass yield(MY),higher heating value(HHV),energy yield,and equilibrium moisture content of the hydrochar,basing on components only,were developed under specific reaction conditions(220°C,2h),and the influence of biomass components on the hydrochar characteristics and the interactions between the components were analyzed.All prediction models had R~2 values above 89%.The results showed that the hydrochar obtained from various individual components exhibited widely different characteristics.MY from high to low was in the order of lignin>cellulose>hemicellulose>protein>lipid.Since the lipid and its hydrolysis products were bound to the hydrochar by chemical bonding and physical adsorption,and itself had a high HHV,it showed a significant synergistic effect when co-HTC with other components.Meanwhile,the lipids attached to the surface of the char hinder the adsorption of water by the hydrochar,and the dehydration performance was better.The set constraint response optimization resulted in the optimal group allocation scheme containing 50.7%hemicellulose,12.4%protein,36.9%lipid and no cellulose and lignin.Verification experiments using additional model biomass showed the relative errors were less than 8%between the prediction and experiment values,and all the experimental results were located within the 95%confidence interval,reflecting a good predictive ability of the proposed mathematical models.For the co-HTC of protein with cellulose,hemicellulose,and lignin in different mass ratios(2:1 and 1:2),respectively,focus was on investigating the effect of the lignocellulosic components on the fuel properties and chemical structure characteristics of protein hydrochar as well as the p H and organic compounds of the liquid phase products.The results showed that the fuel ratio of hydrochar showed different degrees of increase and the fuel grade improved after blending lignocellulosic components.When the protein and hemicellulose co-HTC,the dehydration and decarboxylation reactions were strong,and the resulting hydrochar had the lowest O/C and H/C atomic ratios and the largest synergistic coefficients of mass and energy yields.As the blending ratio of lignocellulosic components increased,the interaction gradually reached saturation,and the synergistic effect decreased,the functional group characteristics of the mixture hydrochar tended to resemble the chemical structures of lignocellulosic components.The Maillard and Mannich reactions between lignocellulosic components and proteins produce solid-phase hydrochar,which results in the re-solidification of N-containing compounds in the liquid-phase products.At the same time,the carbonyl,hydroxyl,and amino functional groups content of the hydrochar was caused to decrease and the aromatic functional groups content increased,improving the aromatization of the hydrochar.The three lignocellulosic components showed different interaction reactions with protein.The degradation products of cellulose and hemicellulose(glucose and furfural)underwent a Maillard reaction with amino acids,etc.(produced by protein degradation),which were further polymerizesd to form N-containing polyaromatic hydrochar.Lignin had a stable phenolic structure,and N-containing compounds in the liquid phase were immobilized onto hydrochar matrix through adsorption or reaction with O-containing functional groups.This study can directly assess the hydrochar characteristics and energy generation potential based on biomass components,provide a theoretical basis for component blending and hydrochar characteristics optimization,and help guide the different types of biomass co-HTC to improve product characteristics and energy efficient utilization.