Study Of In-situ Catalytic Pyrolysis Of Biomass Volatile Over Char And Volatile-char Interactions

As the"zero-carbon energy"resource,biomass utilization is of great significance to the sustainable development of our country’s energy economy and the realization of the long-term goal of"carbon peak and carbon neutrality".Through fast pyrolysis,biomass can be converted into bio-oil,bio-char and other products.However,the primary products of biomass fast pyrolysis are complex and low in quality,which greatly limits the development of biomass pyrolysis technology.In addition,as one of the products of pyrolysis,biochar also has a certain catalytic effect.In view of this,this paper used biomass pyrolysis to perform in-situ catalytic upgrading of pyrolysis volatiles.Focusing on the interaction between biochar and pyrolysis volatiles and product characteristics,starting from the fast pyrolysis characteristic of large particles of biomass,the influence characteristics of char and potassium on biomass pyrolysis products were studied.The reaction mechanism and product conversion process of biochar and nitrogen-doped biochar in situ catalyzed by biomass pyrolysis volatiles were revealed.The catalysis of char during the fast pyrolysis of biomass and the possibility of preparing biomass char as a functional catalytic material through N-doped were described.It provided theoretical support for the subsequent optimization of biomass pyrolysis process and in-situ modification of bio-oil.（1）The infrared heating reactor was used to study the fast pyrolysis characteristic of pine sawdust at different heating rates（5℃/s,20℃/s,100℃/s）and temperatures（350℃,425℃,500℃）.The effects of char and potassium-loaded char on biomass pyrolysis products were discussed.The results showed that high temperature promoted the formation of phenol compounds in biomass pyrolysis volatiles.The high heating rate promoted the decomposition of small molecular compounds such as ketones in bio-oil into gaseous products such as CO,at the same time,which contributed to the release of O1s and the accumulation of C1s in biochar.The presence of char helped to enhance the secondary cracking reaction of volatiles,especially to promote the decomposition of small molecule acids,ketones and other compounds into CO₂,CO and other gases.And through demethoxy and demethylation reactions,the guaiacol compounds were transformed into simple phenolic compounds.Potassium improved the pyrolysis reactivity of biomass,so that the secondary reaction temperature of biomass pyrolysis and volatilization was reduced,and promoted the conversion of small-molecule acid compounds into CO₂.（2）Nitrogen-rich biochar was prepared by an exogenous nitrogen-doped method,and the effects of different preparation temperatures and different nitrogen source precursors on the configuration of N-containing groups in nitrogen-doped biochar（NBC）were studied.The characteristics of biochar and different NBC in-situ catalytic pyrolysis biomass volatiles were discussed.The interaction between NBC and biomass volatiles was studied by changing the reaction conditions,and the catalytic stability of NBC was also analyzed.The results showed that the high preparation temperature was easy to lead to a decrease in the doping amount of N atoms in the biochar structure,and an increase in the content of graphite N and N oxide groups.Biochar promoted the secondary cracking reaction of small molecule compounds such as esters and ketones to generate CO and H₂,and it also promoted guaiacol to generate monophenol and bisphenol through demethoxy and demethylation reactions at the same time.Urea doped carbon helped to increase the content of esters and furans in the bio-oil and reduced the yield of phenolic compounds.Melamine doped char and ammonium chloride doped char further promoted the demethylation reaction of guaiacol to generate bisphenol compounds,and the former had a stronger effect.Under the catalysis of NBC,high temperature promoted the conversion of small molecule compounds such as alcohol,acid,aldehyde in biomass pyrolysis oil to gas,and increased the yield of furans.The NBC cycle catalysis results showed that the surface N atoms of the catalyzed NBC were reduced,and pyridine N was converted to graphite N.In addition,after repeated catalysis,NBC contributed to the accumulation of ester compounds and dehydrated sugars in the bio-oil,and the H₂ yield gradually decreases.（3）In order to further explore the in-situ catalytic effect of biochar and nitrogen-doped biochar on biomass pyrolysis volatiles,four typical lignocellulose model compounds of cellulose,D-xylose,lignin and guaiacol were selected as the research object for catalytic pyrolysis reaction.The results showed that biochar catalyzed the secondary reaction of the conversion of small-molecule aliphatic compounds such as esters and ketones in cellulose and D-xylose pyrolysis oil into gas products such as CO₂ and H₂.NBC inhibited the further decomposition of anhydrosugars,resulting in a decrease in the content of derivative compounds.For lignin and guaiacol,the catalytic effect of biochar was mainly to promote the demethoxy reaction of guaiacol to form more simple phenolic compounds such as phenol and 2-methylphenol,while the addition of nitrogen in biochar weakened the catalytic effect.