Influence Of Biomass Feedstocks And Pyrolysis Temperatures On Physical And Chemical Properties Of Biochar

Biochars is a solid carbonaceous material that is formed by thermal degradation of biomass feedstocks such as wood,manure or crop straw in an oxygen–limited environment.As a carbon(C)–rich material,biochar can be used to improve the soil fertility and enhancing plant growth.Moreover,as a high porosity and high refractory material,biochar has been used in a wide ranges include pollution treatment,climate change mitigation,etc.Although many researches on the physical and chemical properties of biochar were reported,the sysmatical studies for the physicochemical properties and structural features of biochar that derived from different raw material sources and pyrolysis temperature are very limited.Therefore,biochars produced from various types of biomass under different pyrolysis temperatures were characterized to investigate the influences of biomass feddstocks and pyrolysis temperatures on the forming,carbon fraction distribution,stability,and porosity of biochars in the study.The reasearch results provide important information for the production of biochars from various types of biomass with desired properties for agricultural and environmental applications.Firstly,biochars were produced from agriculture straws such as rice straw,corn straw,and wheat straw under different pyrolysis temperatures and then were comprehensively characterized.The results indicated that the yields of the three biochars all decreased with the pyrolysis temperature increased from 250? to 600?.In addition,the carbon contents of the biochars increased,and the polar acidic functional groups decreased with the increasing pyrolysis temperature.The hemicellulose and cellulose components in the raw crop straw likely decomposed at approximately 300?,and more condensed and ordered aromatic carbon structures were formed in the biochars with the pyrolysis temperature increased.The results also indicated that these three types of biochars showed many similarities in elemental composition and structure.However,some differences were also observed.The type of crop straw materials and pyrolysis temperature both significantly influences the physicochemical and structural characteristics of the biochars,especially pyrolysis temperature.Biochars produced at low pyrolysis temperatures(< 300 ?)have a relatively higher yield and still retain some nutrient fertilizers and various functional groups,such as hydroxyl,carboxyl,carbonyl,etc.,which might have positive effects on soil quality and increase the sorptive capacity of biochar for ionic solutes.When the pyrolysis temperature inceased above 500?,and the liable functional groups tended to be removed completely,leaving the dominated aromatic carbon,which may be preferable for the purpose of amending acid soil or long-term carbon sequestration in soil.Then,the different carbon fractions in biochar fomed from various sources were studied.The results show that the carbon contents of the biochars formed from rice straws and pine wood increased with the increaseing pyrolysis temperature,while the hydrogen and oxygen contents decreased.However,biochars produced from pig manure and sewage sludge present different changes,the carbon,hydrogen,and oxygen contents all showed a decrease trend with the increasing of temperature.Moreover,with the pyrolysis temperature increased,the contents of dissolve organic carbon(DOM)in all types of biochars decreased.The aromaticity of cold water and hot water extracts was stronger than NaOH extracts.The percentage of stable carbon in all types of biochar increased with increasing pyrolysis temperature.The relative contents of stable carbon in four biochars changed as the following trend: pine wood > rice straw > pig manure > sewage sludge.A pyrolysis temperature of 500? should be recommended if the biochar was used in carbon sequestration.The morphology and structural characteristics of biochars were also greatly depend on their feedstock and pyrolysis temperature.Many pores were observed on the biochar obtained from rice straw and pine wood,and the pores size shift towards to large–pore diameters and the pore wall become thinner and even collapsed with the increasing pyrolysis temperature.The surface feature of biochar obtained from pig manure and sewage sludge show greatly different from that rice and pine biochars,but the pores size also increased with the increasing pyrolysis temperature.The results also show that the surface areas calculated from N2 isotherms increased in the range of 3.88-249.6 m2/g,0.22-462.8 m2/g,1.21-74.9 m2/g,and 4.52-14.4 m2/g for biochar derived from rice straw,pine wood,pig manure and sewage sludge,respectively,with the increasing temperature.The pore volumes calculated from N2 and CO2 isotherms both increased against the increasing temperature for all feedstocks,whereas the average pore width decreased.The total pore volume of all types of biochars mainly come from mesoporous and macroporous,while the contribution of microporous were relative small.The surface area of biochars produced from rice straw,pine wood and pig manure are predominantly controlled by pores that less than 10 nm,while for sewage sludge biochar,it mainly was contributed by meso-pores(2-50 nm).The double peak phenomenon were observed in the range of microporous for the four biochar,that was 0.4-0.7 nm and 0.7–0.9 nm.The influence of solvent extraction on micropores properties of biochars that derived from low temperature are higher than that from high temperature.The pores characteristics of pig manure and sewage sludge derived biochars were hardly changed after extracting by dichloromethane.Besides,different types of black carbon(soot and char)produced from different materials were studied by pyrolysis–gas chromatography–mass spectrometry(Py–GC–MS).The results revealed that the pyrolysis products derived from different BC samples were generally similar,including aromatic compounds,N–containing compounds,furan compounds,phenolic compounds and S–containing compounds.They were all dominated by aromatic compounds,indicating these BC materials were characterized by having aromatic nuclei and linear or branched aliphatic chains,and/or oxygen-,nitrogen-containing units.However,some differences were also observed among these BC materials.The pyrolysis products revealed that biomass soots contain more useful information on original biomass materials such as proteins,lignins and polysaccharides,while charcoals contain higher contents of condensed aromatic.