Study On The Characteristics Of Catalytic Fast Pyrolysis Of Biomass Over Biochar Catalysts

Biochar,a by-product of biomass pyrolysis,is widely used as a catalyst in catalytic fast pyrolysis（CFP）to improve the quality of biooil.However,its catalytic process for CFP has become complicated due to the various characteristics of biochar.And the current research has not specifically revealed the effect of various characteristics of biochar on CFP.In this study,pretreatment of biochar was used to highlight the unique characteristics of biochar.The role of specific surface area,active functional groups and alkali and alkaline earth metals in catalytic pyrolysis were studied in depth.The research content is as follows:The bamboo wastes were pyrolyzed under different ammonia atmospheres（0vol.%,5vol.%,10vol.%And 30vol.%）to obtained N-doped biochar with different content of N-and O-containing functional groups.These N-doped biochar were used as catalysts in biomass in-situ catalytic pyrolysis to investigate the effects of N-and O-containing functional groups on CFP.The results had shown that the N-and O-containing functional groups made biochar have higher catalytic activity,which could promote the production of phenols（-82%）in biooil,especially 4-ethyl phenol（31%）and 4-vinyl phenol（16%）.They could also promote the production of aromatics,while inhibit the production of acid and O-species.The N-containing functional groups played the role of adsorption,catalysis and reaction.The alkaline N-containing functional groups adsorbed pyrolytic intermediates firstly on the surface of N-doped biochar,then active N-and O-containing functional groups catalyzed conversion of them or reacted with them to form phenols and aromatics.Activated biochar with different specific surface areas(S_BET)and O-containing functional groups were produced by using potassium salts（CH₃COOH,KOH,KHCO₃ and K₂CO₃）to active biochar and were used in biomass ex-situ catalytic pyrolysis to study the effects of S_BET and O-containing functional groups.Results had shown that-OH,O-C=O and C-O in activated biochar had higher catalytic activity,and the content was significantly reduced after being used.The S_BET could promote the decomposition of pyrolysis intermediates,so that the yield of biomass oil decreased as S_BET increased.The S_BET of biochar also promoted the enrichment of phenols,and the content of phenols was proportional to the S_BET,up to 67%(S_BET=1286.44m²/g).Alkali and alkaline earth metals（AAEM:KCl,Na Cl,Ca Cl₂,and Mg Cl₂）were blended into AC-KOH,and these biochar were used to study the influences of AAEM in CFP.The results had shown that the addition of AAEM improved the reactivity of carbon in biochar and promoted the decomposition of biomass into small molecule gases during pyrolysis of biomass（K>Ca>Mg>Na）.AAEM will further promoted the deoxygenation of pyrolysis intermediates,resulting in an increase in the oxygen content of the biomass gas,and promoted the dehydroxylation of phenols to generate aromatics.