Research On High Valued Utilization Technology And Mechanism Of Wheat Straw Based On Difference In Aggregated Structure Of Cellulose

The major resources for microcrystalline cellulose products are cotton andwood. Cellulose fibers are isolated from the biomass through the pulping process.After purification, refined cellulose is obtained in the form of cotton pulp andwood pulp. Microcrystalline cellulose is produced after acid hydrolysis, drying,grinding, and other process. Due to the shortage of cotton and wood resources inour country, the production scale of microcrystalline cellulose is limitedextremely, and the cost is very high. Besides, the degradation products of theamorphous regions of hemicellulose and cellulose generated in producing processare emitted as litters currently, which are a pollution of environment and a wasteof resources. Wheat straw is a plentiful and cheap resource, is employed as theraw material in this dissertation study. Considered the differences on chemicalproperties of cellulose and lignin of wheat straw, the crude cellulose is firstseparated from lignin using recyclable organic solvent system. The organicsolvent thermally decompose the wheat straw and lignin is dissolved. The highpurity cellulose is obtained using low-pollution TCF refining technology toseparate residual lignin and hemi cellulose. The amorphous regions of high puritycellulose are separated from crystal regions by degradation by considering t thedifferences on the natural aggregation structures of crystal and amorphousregions. The crystal regions from high purity cellulose are used in producesynthetic leather, microcrystalline cellulose, which is a high value-added product.The amorphous regions from high purity cellulose are converted into glucose,which can be used in producing cellulose ethanol by fermentation. The wholeprocess employed in this study fulfills the use of cellulose as and in energy fields.This can be achieved by avoiding current technical barriers of biomass utilization,including low accessibility to crystalline regions and difficulty in enzymatichydrolysis. Lignin separated by dissolving is used in preparation of modifiedcement water reducer. This study helps utilization agricultural wheat straw,including multi-component, multi-structure, and multi-product cogeneration. By this not only the problem of cotton shortage is solved, but the wheat straw, whichis a kind of agriculture waste, is made to full use. Therefore, the process in thestudy has great potential in both economic value and social benefits.This study take advantage of ethanol-acetic solvent system, which is arecyclable binary organic solvent, to have wheat straw thermally decomposed andlignin is dissolved to get crude cellulose. The optimum process conditions ofethanol-acetic solvent thermal decomposition of wheat straw is that ethanolaqueous concentration is55%(v/v), acetic acid dosage is2%v/v of ethanol,liquid ratio is1:8, the highest temperature is195°C，holing time is60min. Thecrude cellulose yield and α-cellulose content are49.84%and83.77%, and theKappa number is20.3after the treatment.In order to increase the purity of cellulose, this study uses the Chlorine-freeand non-polluting process, which is a combination of ozone, hydrogen peroxide,and xylanase treatment, to obtain high purity cellulose. The results show that theprocessing of wheat straw to refine crude cellulose is excellent by following thistechnology. O3treatment is helpful in removing of residual lignin. H2O2refiningis useful in enhancement of whiteness. The xylanase treatment reduces thecontents of hemi cellulose efficiently. The final result of refining meets therequirement. The optimum process conditions of O3treatment are that pulpconcentration is45%, pH is2, and O3dosage is1.2%. The optimum processconditions of H2O2treatment are that pulp concentration is12%, tri-sodiumcitrate dosage is1.0%, H2O2dosage is3%, NaOH dosage is1.8%, refiningtemperature is70°C, and treatment time is120min. The optimum xylanasedosage is1.5IU·g-1. The parameter of refined cellulose are that α-cellulosecontent is94.67%, Pentosan content is4.29%，whiteness is86.1%ISO, degree ofpolymerization is628, crystallinity is27.36%, ash content is2.07%. The yield ofrefined cellulose is87.31%.The study on separation and refining of cellulose amorphous region usinghydrochloric acid hydrolysis technology is carried out based on the differences onthe natural structures of crystal and amorphous regions of cellulose. The optimumprocess conditions of hydrochloric acid hydrolysis are that HCl concentration of2mol/L, solid and liquid ratio is1:15, hydrolysis temperature is70°C, and hydrolysis time is90min. The cellulose yield after hydrolysis is79.68%. In orderto enhance the selectivity of acid hydrolysis to cellulose amorphous regions, thisstudy explore the technology and mechanism of transition metal ion assistedcatalytic acid hydrolysis with the purpose of getting hydrolyzed cellulose withhigher crystallinity. The results show that Fe3+has higher selectivity of acidhydrolysis than Cu2+. The optimum process conditions are that Fe3+concentrationis0.4mol/L, HCl concentration is2.5mol/L，reaction temperature is80°C,reaction time is55min, solid and liquid ratio is1:15. In this condition, thecrystallinity of hydrolyzed cellulose can reach81.94%, which is31.04%higherthan acid hydrolysis without the co catalysis of metal ions. The yield is86.89%.The mechanism is that metal ion catalysts increase the rate of acid hydrolysis,and promote the hydrolysis of amorphous regions. It results in most of the acid inthe system is consumed by degradation of the amorphous regions rather than onthe crystal regions, which protect the crystal regions to some extent.In consideration that wheat straw has high ash content, especially high SiO2content, this study try to reduce ash content using base treatment of silicon, anddoes some research on subsequent grinding process. The results show that ashcontent of microcrystalline cellulose is reduced from2.05%to0.32%, which is areduction of84.39%using this process. The optimum process conditions of basetreatment are that base dosage is15%, temperature is80°C, microcrystalcellulose is10%, and the treatment time is30min. The study of grinding processshows that the granularity of microcrystalline cellulose can be controlledefficiently by using a planetary ball mill. The optimum grinding time is100minin condition that the pellet ratio is1:1. The average particle size obtainedmicrocrystalline cellulose is23.33μm.The characterizations of wheat straw microcrystalline cellulose are carriedout using IR, XRD, SEM-EDS, TGA, and laser particle size analyzer. The resultsare in agreement with certain national standard accurately. After the appraisalfrom analysis testing center of No.203Nuclear Industry Research Institute, allthe parameters met the requirements of Chinese forestry industry standards ofsynthetic leather microcrystalline cellulose (LY/T1333-1999). The obtainedwheat straw microcrystalline cellulose undergoes application test. The results show that the permeability, tensile strength, and shear strength of homemadewheat straw microcrystalline cellulose as shift membrane packing of PUsynthetic leather is better than other synthetic leather microcrystalline cellulosemade in China. After the test from Huafu synthetic leather Co., Ltd. in Kunshan,expansion ratio, the tensile load (transverse), and fracture elongation (transverse)of homemade synthetic leather of microcrystalline cellulose are slightly lowerthan lignin microcrystalline cellulose from imports. However, the othercharacteristics are better than the lignin microcrystalline cellulose from Germany.The homemade synthetic leather of microcrystalline cellulose has better qualityand can be used in different applications than the domestic synthetic leather ofmiddle and top grade.The analysis of the microstructure of PU synthetic leather product showsthat sectional structure of synthetic leather, which is added with domesticmicrocrystalline cellulose, has a large number of coarse pores on the surface,especially for the domestic lignin microcrystalline cellulose II. But the middlepart of the coacervate contains a small amount of the pores, and has a densestructure. PU synthetic leathers added with microcrystalline cellulose fromGermany and wheat straw microcrystalline cellulose have smaller pores on thesurface, but more micropores in the middle part of the coacervate. Therefore,microcrystalline cellulose from Germany and homemade wheat strawmicrocrystalline cellulose are helpful with the improvement of the coacervatemicrostructure of PU synthetic leather, which results in the enhancement ofstrength and permeability.The liquid waste solution of wheat straw thermal decomposition is distilledto collect ethanol. The precipitated lignin from the liquid waste undergoeshydroxymethyl activation and sulfonation. The structures and properties ofobtained modified ethanol lignin cement water reducer are characterized andstudied. The results show that ethanol lignin cement water reducer has goodresults. Cement paste fluidity reaches208mm when5%of cement water reduceris added. The water reduction rate is14.9%in this situation, which is30.7%higher than sodium lignosulphonate water reducer that has been used currently.The compressive strength of mortar mixed with modified ethanol lignin decreases with the growth age. The3-day and7-day compressive strength ratio of mortar is13.8%and9.9%higher than mortar mixed with sodium ligninsulfonate separately.The optimum sulfonation conditions are that weight ratio of sulfonation agent andlignin is1:3, the temperature is95°C, pH is11, and the time is3h.At last, this study explores the conversion of glucose into biobased ethanolby using mixed-neutralizing fermentation technology from the waste liquid fromacid hydrolysis and alkaline treatment. The pH of the mixture of acid and alkalinewaste liquids reaches5.0(the most suitable pH for Saccharomyces cerevisiae),when the volume ratio of waste acid and alkaline is2.83:1. In this condition,reducing sugar content in the mixed waste liquid is around20.60g/L. It showsthat the higher the concentration of reducing sugar, the higher the ethanolproduction. The optimum process condition of ethanol producing fromfermentation of mixed waste liquid and the amount of yeast inoculation is10%,fermentation temperature is34°C, fermentation time is72h, and the pH is5.0.