Preparation And Utilization Of Biochar And Biochar Composites

The concern about fossil fuel crisis is spreading worldwide. The heavy use of thetraditional fuel also brings severe negative influence to the environment. Asresearchers, we should devote ourselves into the exploration of fossil energyalternates and the utilization of renewable sources, protecting the living environment,and searching for a way out before the exhaustion of fossil energy.In our earlier researches, the project of the filtrate of dilute acid hydrolyzed ricehusk utilized for furfural preparation has obtained significant progresses. However,the hydrolysis residue has not been fully utilized, which has restricted theindustrialization of the project. As a result, this thesis focuses on the comprehensivelyutilization of silica, lignin and cellulose in the dilute acid hydrolyzed rice husk residue.The series of studies including the preparation of biochar, biochar coated silica,lignin/silica hybrid, carbon/silica composite, silica nano material, porous carbon andso forth.The schematic procedure of this thesis could be included in the following graph. Specifically, the fundamental works are the followings:1. Lignin and silica were liquefied simultaneously from diluted acid hydrolyzedresidue, and then lignin/silica hybrid was prepared via a co-precipitation procedure.The hybrid was then used as the precursor to prepare nano silica and carbon/silicacomposite via high temperature thermal treatment with and without oxygen.Hierarchical porous carbon could be obtained after eliminating silica fromcarbon/silica composite. Precipitation rate and lignin content in the hybrid increase asthe pH value of the co-precipitation procedure decreases. Pore distribution shiftedpositively as the pH value decreases. The sample prepared with the pH of5.5has thehighest micropore ratio, while the sample prepared with the pH of4.5has the bestdeveloped mesopores and so far the best adsorption ability.2. The co-precipitation procedure could also be altered by a two-stepprecipitation process, to obtain silica first, and then lignin. Under inert atmosphere,lignin could be calcined into lignin-carbon material. The calcination temperaturesignificantly affected graphitization degree, capacity and impendency properties of the material. When calcinations temperature was below600℃, the properties of theproduct were mainly affected by benzene ring transformation. Yet when thetemperature is higher than600℃, graphitization degree became the dominant factor.A hydrothermal pretreatment offered the product less compact texture and betterspherical morphology. After pretreatment, there is a44.2%and an8.38%increase ofgraphitization degree and capacitance, respectively, while a53.16%decrease ofresistance.3. The major component of liquification residue was cellulose, which could behydrolyzed by concentrated acid to obtain saccharide solution. The solution could bein situ synthesized into biochar. Hydrolysis effectiveness and product yield could beaffected by liquid to solid ratio, phosphoric acid dosage and other reaction conditions.It is a modest liquid to solid ratio,20mL/g, not too low or too high, that could benefithydrolysis. Hydrolysis degree and saccharide concentration, biochar yield reach peakvalue when phosphoric acid dosages are30%and40%, respectively. The use ofphosphoric acid also contributed to higher graphitization degree and better sphericalmorphology of biochar.4. Biochar coated silica material could be in situ prepared by mixing thesaccharide solution and the precipitated silica. The optimal coating conditions,54%of saccharide solution concentration,100mL/g of liquid to solid ratio,pre-polymerization at62.5℃for2h and carbonization at95℃for4h, wereconfirmed via single-factor experiments using tetraethoxysilane derived silica spheres.The morphology of coated product was regarded as the primary consideration. The higher the concentration of the saccharide solution was, the more completely the silicasphere was coated. The thickness of the coating layer depended on liquid to solid ratio.Pre-polymerization process helped biochar coat on the surface of silica rather thanself-aggregated into spheres. The product had a darker color with a highercarbonization temperature. The functional groups of coated material were similar topure biochar, while some functional groups of silica also existed. Such property couldimprove the surface activity and the ability of the material to mix with polymers.5. The cellulose derived biochar could be turned into active carbon by chemicalactivations. Carbon/manganese composite could be prepared by impregnation orthermal method using biochar and active carbon as matrixes. Manganese acetateimpregnated sample possessed better capacitance property, while manganese sulfateimpregnated sample had lower resistance. Thermal process yielded a composite withthe surface manganese embedded morphology. Active carbon matrix could reduce theentire Mn (IV) to Mn (II), yet biochar matrix could only reduce part of Mn (IV) to Mn(II). The adding of potassium hydroxide is beneficial to the capacitance and resistanceproperties of the composite material.