Separation And Preliminary Application Of Hemicellulose In Exploded Corn Stalk

After years of development and utilization,the storage reserves of non renewable resources on the earth are decreasing.Transforming the renewable resources through reasonable methods to alleviate the consumption of non renewable resources has become a very important research topic.As a renewable resource,agricultural and forestry biomass is rich in reserves and widely distributed,which can alleviate the consumption of fossil resources.In the north of China,there are a lot of corn plantings,however,corn stalks are burned or abandoned in the fields,which are not fully utilized.Corn stalk contains about 30% of hemicellulose,the separation and extraction of hemicellulose by effective methods can produce a large number of high value-added products to reduce the consumption of fossil resources.In this thesis,the hemicellulose in exploded corn stalk were separated and extracted by hydrothermal method,the hemicellulose dissolved in the extract were adsorbed and purified by activated carbon and continuous fractionation of ethanol.The hemicellulose were analyzed of functional group,sugar component and thermal stability.The green biodegradable hemicellulose / polyvinyl alcohol composite membranes were prepared with the extracted hemicellulose.Firstly,the changes of chemical components in corn stalks before and after exploding treatment were analyzed,and the hemicellulose in the exploded corn stalk was separated and extracted by hydrothermal method and the extraction conditions were optimized.The results showed that cellulose accounted for 39.5%,hemicellulose content was 29.2%,and lignin was 15.6% in puffed corn stalk.After optimization,the optimumal extraction conditions of hydrothermal method for exploded corn stalk hemicellulose was 170?C and 60 min.Under this condition,the highest xylose extraction rate was of 42.0%(based on the hemicellulose in raw materials)was obtained,but under the same conditions,the extraction amount of xylose from unexploded corn stalk was only 34.4%(based on the hemicellulose in raw materials),after the corn stalk was exploded,the extraction rate of xylose increased by 22.1%,The result showed that the exploding treatment was beneficial to the separation and extraction of hemicellulose in corn stalk,which could reduce the extraction temperature and the reaction time,and then reduced the production cost,which was beneficial to saving energy.Activated carbon was used to adsorbed the degradation and dissolution substances in the extract of corn stalk,so as to separate and purify xylose and xylo oligosaccharide from the extract.Activated carbon with high specific surface area was prepared from hydrolytic residues of corncob by hydrothermal carbonization and phosphoric acid activation.The effects of activated carbon content,adsorption time,adsorption temperature,p H value,concentration ratio of extraction liquid on the adsorption effect of activated carbon were discussed.The results showed that the optimum conditions for the adsorption were that activated carbon dosage was 1.5 g/L,40 min,25?C,p H 5,and the concentration of extraction liquid was 5.Under this adsorption condition,the removal rates of lignin,formic acid,acetic acid,5-hydroxymethyl furfural and furfural were 68.8%,43.1%,39.7%,82.6% and 85.7%,respectively.The loss rate of xylose was 25.6% after adsorption.The hemicellulose in the extraction solution of puffed corn stalk extracted by hydrothermal method was separated of ethanol stepwisely,and 64.3% of the total amount of hemicellulose in the exploded corn stalk was separated.Hemicellulose(H1-H7)were separated from the multiple of the concentration of the extract and the multiple of 95% ethanol,among them,the yield of hemicellulose H5 and H7 were 25.7% and 17.1%,respectively.The main sugar components were xylose,and the residue liquid were mainly lignin and some degradation products.The branching degree of hemicelluloses increased with the increase of the volume of ethanol.The main chain of hemicellulose was D-piran xylose connected by 1,4-? glucoside bond,and arabia sugar and glucuronic acid were the side chain.The thermogravimetric analysis showed that the thermal stability of hemicellulose decreased with the increase of the volume of ethanol.Hemicellulose / polyvinyl alcohol composite membranes were prepared from five types of hemicelluloses which was separated of ethanol stepwisely.Based on the mass fraction of 10% polyvinyl alcohol solution,adding 10% montmorillonite solution,5% hemicellulose and 1% glycerin,the mixture was evenly stirred and ultrasonic treated,and then hemicellulose / composite films were prepared by tape casting.The tensile properties,surface morphology,contact angle,functional group,crystallinity,water absorbability and thermal stability of the composite membranes were analyzed and characterized.The results showed that the connection between the hemicellulose,montmorillonite and polyvinyl alcohol in the composite membrane were the hydrogen bond formed on the surface of the hemicellulose and montmorillonite by polyvinyl alcohol and the Al-O-C bond formed by the montmorillonite and the polyvinyl alcohol.These bonds made the mixture more tightly and increased the tensile strength of the composite film.The tensile strength of F5 and F7 increased by 37.1% and 32.3% compared with that of PVA film.The addition of hemicellulose did not notably change the crystal structure of the composite membrane,which is beneficial to the improvement of the mechanical properties of the composite membrane.The addition of hemicellulose and montmorillonite does not significantly increase the roughness of the composite film.The contact angle between F5 and F7 were increased by 73.1% compared with that of the blank film,and the hydrophobicity has been greatly improved.The thermal stability analysis showed that the addition of hemicellulose and montmorillonite could increase the thermal stability of the hemicellulose / polyvinyl alcohol composite membranes,in which the thermal stability of F5 and F7 were higher.