Study On Oxidation And Purification Of Bagasse Alkaline Hemicellulose By Chlorine Dioxide

Pretreatment of alkaline cellulose to extract hemicellulose before pulping is a biological scouring method widely used in chemical pulping of pulping and paper industry.Extract from this method include not only hemicellulose but also a large amount of alkali-solublelignin and lignin-carbohydrate complex components.In order to obtain hemicellulose that can be utilized at a high value,purification ofhemicellulose is required.Weuse chlorine dioxide to remove lignin to obtain purified hemicellulose,analyzes the influencing factors of chlorine dioxide oxidation purification process,and discusses the structural changes of hemicellulose and lignin before and after purification.The conclusions are as follows:Firstly,the main factors of chlorine dioxide purification of hemicellulose were studied using a screening of factors and levels response surface analysis methodwith reference to the influencing factors and process conditions of pulp chlorine dioxide bleaching,the influencing factors of chlorine dioxide purification of hemicellulose were analyzed.The resultsshowed that response value was jointly restricted by p H,temperature and dosage,among with,p H is the main influencing factor,and there is an interaction between p H and the other two factors.The reaction of chlorine dioxide and LCC is different from conventional bleaching.With regard to the change of hemicellulose before and after the purification of chlorine dioxide,Ion chromatography(IC),GPC,FTIR and 2D-HSQC NMR were used to quantitatively measurethe component,content &structure of monosaccharide.The results showed that the form of sugar is mainly xylan.Xylose is the largest proportion of alkali-soluble hemicellulose polysaccharide,about 62%.After purification,the sugar composition was basically unchanged,the lignin structure was largely destroyed,and a carbonyl structure appeared.The retention rate of total sugar maintains around 90%,the molecular weight of hemicelluloseis barely influenced,andits main structural are L-arabino-(4-O-methyl-D-glucurono)-D-xylanafter Chlorinedioxide oxidation.For the analysis of lignin in hemicellulose samples before and after chlorine dioxide purification,by increasingdosage of chlorine dioxide,82.35% lignin content can be removed to the maximum.After lignin reacts with chlorine dioxide,chlorine dioxide reacts with lignin to form a lactone or quinone structure.Meanwhile,β-formaldehyde elimination reaction occurs on the side chain Cγ.There are two ways to connect the lignin-carbohydrate complex(LCC)in the sample,namely hemicellulose-ester-ferulic acid-ether-lignin bridge formed by ferulic acid residues(FA)and phenyl glycosidic bond(Ph Glc)connection.After purification,the ferulic acid residues were largely removed,indicating that the hemicellulose-ester-ferulic acid-ether-lignin bridge was largely destroyed.The reaction rate and degree of reaction of chlorine dioxide on condensed phenolic hydroxyl groups are lower than that of unsubstituted phenolic hydroxyl.