Study On Alkali Fractionation Extraction Of Hemicellulose From Corn Straw And Its Conversion To Xylose

There are many methods for extracting hemicellulose,such as hydrothermal extraction and lye extraction.According to t the different extraction severity required for hemicellulose with different properties and structures,the use of alkaline fractionation can separate a variety of hemicelluloses to meet the diversified applications of hemicelluloses.At the same time,few of the existing studies have explored the influence of the properties of hemicellulose on the preparation of xylose.In order to solve the above problems,the following studies was carried out in this study:Firstly,hemicellulose with different properties and structures was separated with continuous alkali extraction(alkali concentration:1%、1.5%、3%、5%and 7%),which is expected to meet the diversified applications.When the concentration of NaOH was1%、1.5%、3%、5%and 7%,the dissolution rates of hemicellulose were14.45%、29.91%、15.83%、12.54%and 2.03%,the total dissolution ratio of hemicellulose was74.76%.The molecular weight of hemicellulose increased from 36.07 k D to 63.73 k D with the increase of alkali concentration,both the branch degree and color value decreased from 0.39 to 0.2 and 20.59×10~5 to 4.58×10~5.Secondly,batch alkali extraction on hemicellulose was carried out to same alkali concentration.Through a series of characterizations,the differences of batch alkali extracted hemicellulose were compared with that from continuous alkali extraction.After treatment with 7%NaOH,the solid recovery from continuous alkali extraction was 45.21%,while it was 49.44%from batch extraction;the maximum dissolution ratio of batch alkali extracted hemicellulose was 65.09%,while the total dissolution ratio of continuous alkali extracted hemicellulose was 74.76%.Compared with continuous alkali extraction,the weight average molecular weight and color value of hemicellulose obtained from discontinuous alkali extraction presented the different trends.Finally,through single factor experimental design,the optimal reaction conditions for the preparation of xylose by hydrolysis of hemicellulose with maleic acid were determined.The optimal condition obtained was the solid to liquid ratio of 1:10(g/m L)、reaction temperature 130℃、maleic acid concentration 5%and reaction time 60min.Under the optimal conditions,the obtained hemicellulose samples were acid hydrolyzed.Through the experimental data,we can conclude that the hemicellulose samples with high PDI value and low branching degree were conducive to the production of xylose,and the maximum relative yield of xylose was 96.3%for H7sample.