Experimental Study On The Production Of Furfural From Microwave-assisted Catalytic Pyrolysis Of Cellulose

As a resource with negative carbon potential,the utilization of biomass is of great signif-icance to achieve carbon peak and carbon neutralization in China.Furfural（FF）is one of the high-value chemicals produced by biomass rapid pyrolysis,which can be used as extractant,preservative and chemical raw materials.At present,sulfuric acid hydrolysis is commonly used to prepare FF in industry.This process has some disadvantages,such as long reaction time,difficult solvent recovery,and can only convert hemicellulose.Cellulose generally has a large proportion in biomass,and its structure is simple and easy to study.However,the fast pyrolysis of cellulose has low FF selectivity and poor economy.Acid catalyst can promote the dehydration of cellulose to FF,and microwave heating technology can reduce the secondary reaction and avoid further conversion of FF.Therefore,this paper mainly studies the charac-teristics of FF preparation from cellulose catalyzed by metal chlorides,compares the formation characteristics of FF from microwave pyrolysis and conventional pyrolysis,and explores the influence of solid acid catalysis on the preparation of FF from cellulose under microwave conditions,so as to provide a theoretical basis for the realization of FF enrichment.Firstly,cellulose was pretreated with seven metal chlorides（Fe Cl₂,Fe Cl₃,KCl,Mg Cl₂,Ca Cl₂,Zn Cl₂,Ni Cl₂）by impregnation,and then pyrolyzed in a fixed bed.The results showed that the highest FF selectivity of cellulose impregnated with Fe Cl₂ was 40.31%,which was13.5 times higher than that of pure cellulose.In order to explore the mechanism of Fe Cl₂ pro-moting the formation of FF,the pyrolysis characteristics of Fe Cl₂/cellulose and Fe Cl₃/cellulose at different temperatures and different impregnation ratios were further studied.The results show that Fe Cl₂ and Fe Cl₃ can significantly promote the decomposition of cellulose.Fe Cl₂mainly promotes the conversion of pyrolysis volatile to non-condensable gas,while Fe Cl₃mainly promotes to carbon deposition.Fe Cl₂ can significantly improve the selectivity of FF,which is related to the existence of ionic state after Fe Cl₂ impregnation,which provides a good active site for the dehydration of cellulose.After Fe Cl₂ treatment,the selectivity of FF in-creased continuously with the increase of temperature,and reached the highest value（48.28%）at 600℃,and the best impregnation amount was 1 mmol/g.Then,in order to ensure the accuracy of the microwave reaction temperature,the heating characteristics of the Si C and the temperature distribution of the microwave field were tested first,and then the pyrolysis characteristics of cellulose,Fe Cl₂/cellulose and Fe Cl₃/cellulose were investigated under three heating methods（electric heating,microwave indirect heating and microwave direct heating）.The results show that microwave heating can significantly re-duce the yield of carbon,and the decrease of solid products is most obvious due to the hot spot effect of bio-char and Si C.Low temperature microwave（<400℃）is helpful for the conver-sion of pyrolysis volatile to bio-oil,while high temperature microwave（>500℃）is helpful for the conversion to non condensable gas.Fe Cl₃/cellulose makes the gas product richer in H₂due to the hot spot effect of Fe₂O₃ produced during the pyrolysis process.Microwave heating,due to its unique thermal and non thermal effects,promotes the further conversion of dehy-drated sugars to furans,and reduces the optimal temperature of furfural formation by 200℃.For Fe Cl₂/cellulose,the FF selectivity of direct microwave heating is the highest（51.88%）,which is 14.02%higher than indirect microwave heating and 17.16%higher than electric heat-ing.Finally,a new type of solid acid catalyst was prepared by modifying the selected Al₂O₃with Fe Cl₂ and Fe Cl₃ as active components.The performance,stability and microwave effect of the catalyst were investigated by combining microwave with solid acid catalysis.The results show that Fe Cl₃ modification can improve the catalytic performance of Al₂O₃ acid,thus im-proving the selectivity of FF.With the increase of reaction temperature,the selectivity of FF increased obviously at first and then decreased continuously,reaching the maximum of 30.66%at 400℃.With the increase of C/B,the FF selectivity first increased and then decreased,and reached the highest when the C/B was 4:1.With the increase of the loading,the FF selectivity decreased slightly at first and then sharply.The optimum loading was 0.25 mmol/g.The se-lectivity of FF was about 10%when the catalyst was used for the first four cycles.The micro-wave effect of direct contact with Si C can significantly increase the FF selectivity from 30.66%to 33.74%,an increase of 10.05%.