Experimental Study And Molecular Simulation On Preparation Of High-grade Solid Fuel By Hydrothermal Carbonization Of Corncob And PVC

Rapid urbanization development means higher energy demand and higher ecological environment requirements.PVC waste plastic and lignocellulosic biomass such as corn cob are two typical solid wastes in urban and rural areas.Converting them into high value-added solid fuels to replace non-renewable energy is of great significance for reducing urban and rural environmental pollution and promoting energy transformation.However,the low fuel property caused by the high-water content of waste biomass and the environmental toxicity caused by the high chlorine content of PVC seriously limit the energy utilization of the two solid wastes.In this paper,the co-hydrothermal carbonization method of corncob and PVC was used to prepare compound hydrochar.The influence of operating parameters on the formation characteristics of hydrochar was studied.The synergistic effect of biomass and PVC was explored,and the formation path of hydrochar was studied by density functional theory calculation method.In addition,the influence of process water recycling on co-HTC was explored,and the practical operation of co-HTC was evaluated.(1)The co-HTC characteristics of corncob and PVC were studied.The hydrochar yield and dechlorination efficiency were studied under different HTC temperatures(180-280℃),different residence times(30-90 min)and different raw material ratios.The carbonization degree of raw materials was the deepest at 280℃ and 90 min.The calorific value of hydrochar is between 26.73-36.74 MJ/kg.The hydrothermal dechlorination reaction of PVC satisfies the first order kinetic hypothesis.The corncob can catalyze the dechlorination of PVC,and the activation energy of hydrothermal dechlorination can be reduced from 189.95 kJ/mol to 110.04 kJ/mol.The surface of hydrochar is rich in hydroxyl,carbonyl,ether bond and other oxygencontaining functional groups.The carbon structure is mainly disordered,but partly graphitized.The hydrochar is the best when the blending ratio of the raw material is 1:1.The hydrochar is mainly composed of biomass primary char,secondary char and PVC skeleton carbon.(2)The characteristics of cyclic carbonization of process water were explored.Under the conditions of reaction temperature 280℃,residence time 90 min and raw material ratio 1:1,four cycles of process water were carried out,and the carbon content of hydrochar increased to 78.69%,oxygen content decreased to 13.78%,high calorific value gradually increased to 32.42 MJ/kg.During the cycling process,the hydrochar particles become more uniform,but the porosity is poor.The maximum specific surface area is 1.75 m2/g and the average pore size is between 9.68 nm and 13.51 nm.The recycling of process water does not affect the high thermal stability of hydrochar.And the fuel intense combustion interval is between 400-600℃.Furan organics are consumed in large quantities during the process water recycling and converted into micro carbon spheres.(3)The formation pathways of hydrochar were explored.Based on the transition state theory in molecular simulation,the formation path of β-xylose,β-glucose and guaiacol based on lignocellulosic biomass was proposed.The protonation and aprotonation conversion pathways were compared.It was found that protonation reaction greatly reduced the energy barrier of the reaction,which is the deeper reason that PVC can catalyze the hydrolysis of biomass.Furfural,HMF and guaiacol from the hydrolysis of hemicellulose,cellulose and lignin are the key compounds to form soluble hydrochar precursors.Furan ring type hydrochar,HMFphenyl unit type hydrochar and aromatic hydrochar are all important components of micro carbon spheres.