Study On Formation Mechanism And Moisture Absorption Properties Of Biochar During Pyrolysis

Biochar used to solve the ecological security and sustainable development problems of agriculture.environment and energy,has caused extensive concern by international and domestic scholars.Biochar has porous structure,strong ability of adsorption,oxidation resistance and the ability to resist biological decomposition characteristics,which determines the application direction and value of biochar,and the physicochemical properties of biochar are affected by pyrolysis conditions and raw material.At present,the researches on the physicochemical properties of biochar are relatively few and not comprehensive.Moisture absorption property characterizes the physicochemical properties of biochar,and also reflects its application properties in soil.The preliminary study on the moisture absorption property of biochar and its impact on soil moisture have been done,while the influence factors and mechanism are not clear.Therefore,the in-depth and systematic research on the physicochemical properties and moisture absorption property of biochar have important guidance and reference on its production and utilization.Hence,the influence factors and mechanism of the pyrolysis parameters and biomass raw materials on the physicochemical properties of biochar are studied,and the differences between physicochemical properties of biochar are explored by the cluster analysis funded under the national natural science foundation of china "Migration and immobilization mechanism of heavy metal in multiphase system mixed with biochar and soir".The moisture absorption process,the variation and the influence factors mechanism of equilibrium moisture content are carried out.Finally,the effects of biochar on the physicochemical properties and moisture absorption property of soil are explored.The development mechanism on the physicochemical properties of rice husk and wheat straw biochar were studied by using the fixed bed reactor of tube furnace and the infrared analyzer,and influence mechanism of pyrolysis temperature on the physicochemical properties of biochar were analyzed.Results showed that with the increase of pyrolysis temperature,the yield of rice husk and wheat straw biochar reduced,surface functional groups with hydrogen and oxygen gradually decomposed,while the bulk density,true density and porosity increased.The surface area and volume of rice husk and wheat straw biochar increased firstly and then decreased,with the maximum value at 550 ?.Biochar products made at different temperature were alkaline.Total soluble substances of rice husk and wheat straw biochar increased firstly and then decreased,with the maximum value at 750 ? and 550 ?.The influence of raw material on the physicochemical properties of biochar were then contrastively studied,and the classification analysis based on the physicochemical properties of biochar was carried out by the cluster analysis.Results showed that the physicochemical properties of biomass played an important role on biochar properties,and wheat straw biochar had higher soluble matter content and pore structure properties.The influence of pyrolysis temperature on the physicochemical properties of biochar can be divided into three temperature sections:350-450 ?,about 550?,650-850 ? by the cluster analysis.The moisture absorption process properties of biochar were studied in the constant temperature and humidity incubator device by the on-linecontrol system of the quality,and the dynamical mechanism analysis of moisture absorption process were analysed to explore the moisture absorption mechanism.Results showed that the equilibrium moisture content of biochar increased with the increase of humidity and temperature.The modified Halsey model can accurately predict the equilibrium moisture content of biochar.Humidity had the greatest impact on equilibrium moisture content of biochar,followed by temperature and sample mass.Porosity had the greatest impact on had the greatest impact on equilibrium moisture content of biochar equilibrium moisture content,followed by bulk density,pH,and volatile.The pseudo-second order model could well describe the moisture absorption process,and the three-stage intraparticle diffusion equation can further clarify the moisture adsorption mechanism of biochar.The high volatile matter,oxygen,O/C,pH,total soluble matter content and porosity might be conducive to the increase of the moisture content of might be conducive to the increase of the equilibrium moisture content.The moisture absorption property of biochar was affected by physicochemical characteristics and humidity,and the effects of physicochemical characteristics under different humidity were different.The influence rules and mechanisms of wheat straw biochar addition on the physicochemical properties and moisture absorption property of hubei paddy soil were finally studied.Results showed that wheat straw biochar made the soil moisture absorption property increase,and the equilibrium moisture content of soil increased with the increase of biochar amount.The high pH,total soluble matter content and porosity might be conducive to the increase of the equilibrium moisture content and water-retention content of biochar-added soil under different humidity conditions.