Study On The Effect Of Additives On The Characteristics Of Biochar Prepared By Pyrolysis Of Biogas Residue And The Improvement Of Preparation Process

In recent years,the output of food waste in my country has increased year by year,which has caused serious harm to the urban living environment.At present,anaerobic fermentation technology is one of the effective ways to reduce the quantity and resource disposal of food waste.However,anaerobic fermentation technology produces a large amount of biogas residue while producing clean energy such as biogas.Especially with the rapid development of anaerobic fermentation technology,the output of biogas residue is gradually increasing,which is difficult to absorb and reuse,which seriously hinders the development of anaerobic fermentation technology.High-temperature pyrolysis has the advantages of reducing the volume of biogas residue,killing pathogens and cutting off the source of disease infection,and can produce resource products such as biochar.Currently,biochar has been widely used in environmental soil pollution and water body restoration fields.Therefore,high-temperature pyrolysis is of great significance for the reduction and resource utilization of biogas residue.In this paper,biochar was prepared by slow pyrolysis process using biogas residue after anaerobic fermentation of food waste as raw material,and the biochar was modified by adding additives to biogas residue biomass.The effects of adding additives and not adding additives on the pH,functional group structure,yield of biochar and the pyrolysis characteristics of biomass were compared and analyzed.While realizing the reduction and resource utilization of biogas residue,the addition of additives can increase the yield,pH and functional groups of biochar and improve the preparation process of biochar by pyrolysis.The optimal additives were selected from the actual benefits and economic costs,in order to realize the transition from the research and development stage to the industrial production stage,and finally be applied to industrial production and environmental applications.The main findings are as follows:（1）The pyrolysis temperature has a significant effect on the biochar yield of biogas residue.The higher the pyrolysis temperature,the lower the biochar yield of biogas residue.At 400,500 and 600℃,the yield of the five biochar residues（BC、K-BC、Ca-BC、Mg-BC、Z-BC）from high to low is w _Ca-BC,w _Mg-BC,w _Z-BC,w _K-BC,w _BC.The addition of CaO has the greatest impact on the yield of biochar from biogas residue,and K₂CO₃has the least impact on the biochar yield.With the continuous increase of pyrolysis temperature,the pH of biogas residue biochar gradually increases.At 400℃,the pH of the five biochar residues from high to low is pH_Ca-BC,pH_K-BC,pH_Mg-BC,pH_Z-BC,pH_BC.At 500℃,the pH of the five biochar residues from high to low is pH_Ca-BC,pH_K-BC,pH_BC,pH_Mg-BC,pH_Z-BC.At 600℃,the pH of the five biochar residues from high to low is pH_Ca-BC,pH_K-BC,pH_BC,pH_Mg-BC,pH_Z-BC,adding CaO has the greatest impact on the pH of biochar.（2）Through Fourier Infrared spectroscopy,it can be seen that the surface of biogas residue biochar contains many functional groups,such as-OH,-CH,C=O,C=C,COC,etc..The aliphatic structure on the surface of biochar gradually disappears through pyrolysis,and the absorption vibration peak of the aromatic structure gradually increases.The addition of additives has different degrees of influence on the structure of the functional groups on the surface of the biochar.Compared with no additives,the infrared absorption vibration peaks of-OH,-CH and C=O are gradually weakened,and the infrared absorption peaks of C=C structure gradually increase,indicating that the addition of additives enhances the internal aromatic structure of biochar.（3）The relative content of functional groups on the surface of biochar biochar was studied using the method of split peak fitting and Lamber-Beer law.Additives had an effect on the peak area of main functional groups on the surface of biochar.To a certain extent,compared with without additives,the relative contents of main functional groups on the surface of biochar biogas residue increased to different degrees.（4）The TG-FTIR was used to study the release of volatile gases during the pyrolysis of biogas residue.By adding K₂CO₃,the gas phase distribution spectrum showed two obvious dominant peaks.It shows that the addition of K₂CO₃increases the precipitation of volatile gas compared with other additives.However,the addition of additives inhibited the precipitation of volatile gas from other gas phase distribution spectra.According to the volatile gas released during the pyrolysis of biogas residue,additives have a significant effect on the release of volatile gas,and K₂CO₃ affects the absorption intensity of H₂O infrared spectrum.MgO reduces the precipitation of CO₂and CO.The reduction of CH₄ precipitation is affected by different temperatures and additives.The addition of Ca O has an inhibitory effect on the release of all gases,indicating that additives can reduce the emission of volatile gases.（5）In this study,the process of preparing modified biochar by pyrolysis was improved by adding additives to biomass,and the loss of biochar in the preparation process of modified biochar after pyrolysis was avoided.After screening,CaO is most suitable for the modification of biochar as an additive in terms of actual benefits and economic costs.However,due to the strong corrosiveness of CaO,the corrosion protection of pyrolysis reaction equipment can be realized from three aspects:anticorrosion treatment of pyrolysis reaction equipment,replacement of CaO with MgO,and addition of corrosion inhibitors.