Pyrolysis Characteristics And Product Distribution Of Biomass Pretreated With H₂O₂ In A Nitrogen-Enriched Atmosphere

The preparation of high quality liquid fuels,high performance carbon materials and high value-added chemicals by rapid pyrolysis of biomass is an effective way to achieve efficient and high value conversion of biomass,and plays an important role in building a clean,low-carbon and efficient modern energy and chemical system.To address the problems of strong acidity,complex components,low content of single organic component and poor stability of bio-oil obtained by conventional pyrolysis technology,we propose a technical pathway to improve the pyrolysis characteristics of raw materials by H₂O₂ pretreatment and prepare high-quality bio-oil and nitrogen-containing chemicals by nitrogen-rich pyrolysis,and systematically study the effects of different pretreatment concentrations,pretreatment times,pyrolysis temperatures and acid-base conditions on the characteristics of biomass raw materials and pyrolysis products.The effects of different pretreatment concentrations,pretreatment times,pyrolysis temperatures and acid-base conditions on the characteristics of biomass feedstock and the distribution pattern of pyrolysis products were systematically investigated to clarify the regulatory mechanisms between pretreatment-pyrolysis conditions and product distribution,and to grasp the competition between the production of major nitrogen-containing compounds and other components in bio-oil,in order to explore the establishment of a highly selective H₂O₂ pretreatment biomass nitrogen-rich catalytic pyrolysis reaction system.The main methods and conclusions adopted are as follows.Corn stover was used as raw material,and the pretreated raw material was characterized using FT-IR,SEM,GC-MS,ICP-OES,and TG/DTG.The effects of different H2O2concentrations,pretreatment times,and pyrolysis temperatures on the distribution of corn stover pyrolysis products were investigated.It was found that H2O2 pretreatment could effectively remove alkali and alkaline earth metals（AAEMs）from corn stover,and the concentration of 5%H2O2 had the most significant effect on the removal of AAEMs from corn stover,in which potassium and calcium elements decreased to 1.89%and 9.95%of untreated corn stover,respectively,effectively degrading lignin and hemicellulose and producing pore structure.When the H2O2 concentration was 5%,the pretreatment time was 2 h,and the pyrolysis temperature was 500°C,the yield of levoglucan generated from the pyrolysis of corn stover was 15.42%,and the yield of levoglucan increased more than 9 times.The effect of H₂O₂ pretreatment on the distribution of corn stover pyrolysis products under acidic and alkaline conditions was investigated by using corn stover as raw material and characterizing the pretreated raw material using FT-IR,SEM,GC-MS,ICP-OES,and TG/DTG.It was found that the H₂O₂ pretreatment under alkaline environment was more effective in removing Na and Mg,causing severe damage to the microstructure of corn stover,which not only destroyed its fiber bundle structure,but also the resulting pore-like structure.H₂O₂ in acidic environment was more effective in removing K and Ca.With the increase of p H,the yield of bio-oil and biochar of pretreated corn stover decreased and the yield of biogas increased.And the production of levoglucan was inhibited.Pretreatment of corn stover with H₂O₂ under alkaline environment promoted the production of furans.The effects of different concentrations of H₂O₂ pretreatment on the nitrogen-rich pyrolysis of corn stover were investigated using corn stover as raw material.It was found that H₂O₂pretreatment could promote the co-pyrolysis of corn stover and urea,increase the relative content of bio-oil and inhibit the generation of biochar and biogas.When the ratio of corn stover and urea was 3:2,the highest relative content of nitrogenous substances was found in the bio-oil obtained from the pyrolysis of 5%H₂O₂ pretreated corn stover,with a relative content of43.16%.Compared with pyrolysis alone,the relative content of ketones in the bio-oil obtained by nitrogen-rich pyrolysis was significantly reduced,and the species of ketones was also significantly reduced,and no signal of furfural was detected in the bio-oil to promote the production of acetamide.