Conversion Of Hemicellulose And Cellulose To Furfural Catalyzed By Zeolites

Biomass is the only renewable carbon resource.Through catalytic conversion of biomass,important biomass based platform molecules such as furfural and 5-hydroxymethylfurfural can be generated.Zeolites have high thermal stability,unique pore structure,and adjustable acidic sites,which can selectively control the formation of products.They exhibited significant shape selective effects in the conversion of sugars to furan compounds.Currently,zeolites are widely used for the conversion of monosaccharides,while there are few studies on the direct conversion of hemicellulose and cellulose to furfural.This work first established a chromatographic analysis method for the fuan products of lignocellulosic conversion liquid to accurately quantify the experimental products,and then zeolites with different acid properties and pore structure were used to study their catalytic performance for the production of furfural from hemicellulose and cellulose.The role of acid properties and pore structure in the catalytic conversion of hemicellulose and cellulose was studied in detail.The research contents are as follows:（1）Chromatographic analysis of furan products from lignocellulose catalytic conversion.This work has established gas chromatography internal standard methods and high-performance liquid chromatography external standard methods,which could accurately determine furan products.The gas chromatography（GC）with HP-Innowax capillary column and FIDdetector,and the high performance liquid chromatography（HPLC）with Shodexsh-1821 column and refractive index detector were used in this work.In the concentration range of 5.0-5.0 mg/m L,the relative standard deviations of furfural,furfuryl alcohol and 5-hydroxymethylfurfural determined by GC internal method and HPLC external method were ranged from 0.10%to1.7%.,and from 0.14%to 0.71%,respectively.And the recoveries of these two methods were between 95.6%and 102.0%,and between 97.5%and 101.9%,respectively.The correlation coefficients between the signal strength of the detection and the concentration of the compounds were all over 0.999.Both the two methods can all easily and quickly achieve the effective separation and the accurate determination of furan products.（2）Preparation of furfural from xylan catalyzed by zeolites.Conversion of xylan to furfural was investigated over zeolites（Hβ、HY、H-mordenite、HZSM-5 and HZSM-22）.The zeolites were characterized by X-ray diffraction,²⁷Al MAS NMR,IR spectra of pyridine adsorption and NH₃temperature programmed desorption.Hβand HY zeolites with both Br?nsted and Lewis acid sites showed the high yield of furfural.However,H-mordenite and HZSM-5zeolites with fewer Lewis acid sites showed the high yield of xylose.This indicated that Lewis acid sites may played a key role in the catalytic conversion of xylan to furfural.The pore structure of zeolites also had significant impacts on the preparation of furfural from xylan.Hβ、HY and H-mordenite belonged to macroporous zeolites,which was conducive to the diffusion of sugars and furfural.The acid properties of HZSM-5 were similar to those of HM,but the small pore size of HZSM-5 was not conducive to the diffusion of sugar and furfural,so the yield of furfural over H-mordenite is higher than that of HZSM-5.During the reaction process,the Hβzeolite will became inactive due to carbon deposition as the number of cycles increased,and the catalytic performance could be basically restored after regeneration.（3）Preparation of furfural from cellulose catalyzed by zeolites.Conversion of cellulose and starch to furfural was investigated over four zeolites.The zeolites were characterized by X-ray diffraction,²⁷Al MAS NMR,IR spectra of pyridine adsorption and NH₃temperature-programmed desorption.The roles of acidity and pore structure of zeolites in conversion of cellulose and starch were discussed in detail.The results showed that Hβzeolite with appropriate Br?nsted acid sites,Lewis acid sites and pore structure was effective to produce furfural from cellulose and starch.HY zeolite could not catalyze cellulose reaction with high conversion because of its weak acidity.However,HY zeolite was effective to produce 5-hydroxymethylfurfural from starch.H-mordenite and HZSM-5 zeolites with fewer Lewis acid sites could not cause he isomerization reaction from glucose to fructose.So,the further conversion of fructose to furfural or 5-hydroxymethylfurfural was inhibited.The formation of 5-hydroxymethylfurfural only depended on the acid properties of zeolites.The formation of furfural was not only determined by the acidity of zeolites,but also by their appropriate pore structure.