Preparation And Characterization Of Kenaf Core-based Biochar Microspheres By Benign Hydrothermal Method

Hydrochar microspheres,which have a variety of oxygen-containing functional groups,are excellent soft template materials.In this paper,we focus on preparation of the kenaf core-based carbon spheres from abandoned kenaf by benign hydrothermal method.In order to seek a simple green way to obtain a high yield of carbon microspheres with a regular spherical structure,size and good monodispersity,the relationship between different catalyst and carbon microspheres was investigated.Research results enrich the content of preparation of carbon microspheres from biomass by hydrothermal carbonization at low temperature.It has great theoretical reference value for the abandoned kenaf core to realize maximum utilization.First,preparation of kenaf core-based carbon spheres by sulfuric acid and formic acid(FA)as catalyst were studied,respectively.The influence factors of preparation like pretreatment,hydrolysis conditions,carbonization conditions and catalyst concentration were discussed.The particle size,morphology and surface chemical properties and chemical composition of products were characterized by field emission scanning electron microscope(FE-SEM),fourier transform infrared spectroscopy(FT-IR),photoelectron spectroscopy(XPS)and elemental analyzer(EA).The results show that the efficiency of hydrolysis and hydrothermal carbonization were ideal by liquid acid as catalyst.Taking sulfuric acid as catalyst,carbon microsphere with 150-500 nm were obtained under 95? for 6h.Adding formic acid as catalyst,carbon microspheres with a higher yield and regular structure were obtained after holding temperature at 180? for 4h.In addition,formic acid catalyst can use many times after recovery.It would be highly advantageous to realize the green,low cost to prepare carbon microspheres.The efficiency of hydrolysis and carbonization under phosphotungstic acid and sulfonated chloromethyl polystyrene resin(CP-SO3H)as catalyst were studied as well,respectively.The results showed that low concentrations of phosphorous acid(5wt%-10wt%)as catalysis,kenaf core-based carbon spheres by the second step hydrothermal carbonization have a smooth surface,particle size and spherical structure.Furthermore,with phosphotungstic acid concentration increasing,the average particle size of carbon microspheres increases gradually as well,and has a tendency to gradually aggregated into clusters.Even if being reused four times,phosphotungstic acid catalyst recovered by ethyl ether extraction didn't cause obviously decreased catalytic effect on the hydrothermal carbon microspheres yield.The kenaf core-based carbon spheres,which prepared by synthesized CP-SO3 as catalyst through two-step hydrothermal carbonization method have a smooth surface,even particle size and spherical structure.The concentration of CP-SO3 had slight effect on morphology.But those carbon microspheres had poor monodispersity by this method.Carbon microspheres,which prepared by sulfuric acid as a catalyst,is a good carbon-based solid acid catalyst.Hydrolysis of microcrystalline cellulose using the carbon microspheres as catalyst was investigated.The relationship between the amount of sulfonated carbon microspheres,hydrolysis temperature and other factors was investigated based on reducing sugar yield as an index.The results showed that sulfonated carbon microspheres can degrade cellulose to reducing sugar effectively.Moreover,the catalyst can keep high catalytic activity though a simple and easy activation method.