Studies On Full Utilization Of Wheat Straw Based On Magnesium Bisulfite Pretreatment

In this paper,the wheat straw wastes with abundant resources in China are taken as the specific research object,the new technology of magnesium bisulfite is used as the pretreatment agent under milder p H treatment conditions,so as to improve the enzymatic saccharification efficiency of plant fiber raw materials.At the same time,based on the difference of polarity and charged properties,a method for simultaneous separation of xylo-oligosaccharides and lignosufonate was established.The separation and preparation of lignosulfonates and xylo-oligosaccharides from spent liquor were realized,and the integrated technology of neutral sulfite pretreatment for wheat straw full utilization was formed.The probiotic effect of xylo-oligosaccharides and the pesticide dispersibility of lignosulfonate products were further investigated.Specific research is as follows:A magnesium bisulfite pretreatment process（MBSP）for wheat straw waste was established,and the mechanism of the effect of pretreatment on lignin,hemicellulose removal,enzymatic hydrolysis,saccharification and dissolution components was clarified.It was found that magnesium bisulfite pretreatment could effectively remove lignin and hemicellulose components from wheat straw under mild p H conditions,with little damage to cellulose and excellent enzymatic hydrolysis effect of pretreatment residue.In addition to a small amount of lignin degradation products,the pretreatment spent liquor obtained a large amount of xylo-oligosaccharides and lignosulfonates,which had potential application value.The wheat straw was pretreated in 1 L digester with solid-liquid ratio of 1:5,magnesium bisulfite 3.51%（w/v）,p H 5.17 and 170^oC for 40 minutes.The removal yield of hemicellulose and lignin were 85.75%and 78.22%,and the cellulose recovery yield was 97.41%.The wheat straw was pretreated with commercial cellulase（CTec2）with dosage of 15FPU/g cellulose,and the substrate concentration was 10%（w/v）without water washing,after 48 hours of enzymatic hydrolysis,the yield of enzymatic hydrolysis was 88.82%.The pretreatment of wheat straw with magnesium bisulfite can achieve effective enzymatic hydrolysis of 20%substrate concentration,the enzymatic hydrolysis yields at 48 h and 72 h were 82.24%and 90.49%respectively.The concentration of magnesium lignosulfonate and xylo-oligosaccharide in pretreated spent liquor is 86.61 g/L and 10.06 g/L,respectively.The effects of organic solvent precipitation,ultrafiltration and resin separation of xylo-oligosaccharides and lignosulfonates in magnesium bisulfite pretreatment spent liquor were investigated.A simultaneous separation method of xylo-oligosaccharides and lignosulfonates based on polarity and charged property differences was established.Pretreatment with diatomite can effectively remove colored substances,reduce sample viscosity and improve transmittance.The lignosulfonate and xylo-oligosaccharide can be separated simultaneously by macroporous weak alkaline ion exchange resin D354.The separation factor is 111.6.The static adsorption isotherm conforms to Langmuir model,and the maximum static saturated adsorption is 389.61 mg/g at 25 ^oC.The dynamic adsorption is carried out on a 16 mm×12 cm column,and the Yoon-Nelson fitting equation shows that the dynamic adsorption capacity can reach 169.72 mg/g^-1.The resin can be reused for more than five times;and the recovery yield of xylo-oligosaccharides and lignosulfonates from MBSP spent liquor by dynamic fixed bed separation is 93.09%and 98.03%with the purity of 60.09%and 91.92%,respectively.Xylobiose to xylotetrose accounted for 87.13%of the total xylo-oligosaccharides（X2-X6）obtained from the separation of MBSP spent liquor.The magnesium bisulfite pretreatment coupled with downstream separation and purification technology can ultimately achieve the total utilization rate 91.33%,51.56%and 52.17%of cellulose,hemicellulose and lignin,respectively.The probiotic effects of MBSP XOS,IE XOS and CM XOS on typical intestinal probiotics were compared.Bifidobacterium adolescents were proliferated in vitro by 2.91 g/L CM XOS,3.32 g/L MBSP XOS,3.10 g/L IE XOS as carbon sources.The proliferative capacity of the three xylo-oligosaccharides is comparable.The total organic acids produced by the three carbon sources were 2.06 g/L,3.85 g/L,3.30 g/L,respectively,Among them,the organic acids produced by CM XOS were lactic acid,acetic acid and propionic acid in turn;the organic acids produced by IE XOS were acetic acid,lactic acid and propionic acid in turn.Both MBSP XOS and IE XOS can effectively proliferate Bifidobacterium adolescents,and their ability to produce organic acids is higher than CM XOS,showing good probiotic effect.Lactobacillus acidophilus could not metabolize xylose,but xylo-oligosaccharides were consumed by varying degrees.The properties of IE LS and its dispersive application in pesticide imazameth（IMM）were characterized.IE LS owns 3.65 mmol/g sulfonate group,0.69 mmol/g phenolic hydroxyl group and 1.06 mmol/g carboxyl group,its structure is nearly spherical,ranging in size from 0.1 to 0.3μm.The molecular weight is 2842 Da,polydispersity is 1.216,critical micelle concentration is 15 g/L,and surface tension is60.2 m N/M.It can be used as surfactant to reduce the surface tension of aqueous solution.Adding 2.0 g/L UF LS could reduce the Zeta potential on the surface of IMM particles to-30.3 m V,which owns higher impact than that of commercial pesticide dispersants Wigwin-600C and CM LS,and the dispersibility is better.The interface wettability of UF LS on hydrophobic IMM is good,the contact angle of UF LS droplets with concentration of 2.0 g/L on the surface of IMM tablets is 72.38degrees,which is much lower than that of pure water at 116.71 degrees.The interface wettability of UF LS on hydrophobic IMM is better.It is easier to spread on hydrophobic materials,which is conducive to improving the dispersion of IMM particles in water.It has the potential of application in actual spraying operation.In this paper,based on magnesium bisulfite pretreatment technology,combined with downstream separation and purification technology of pretreatment spent liquor,the effective utilization of cellulose,hemicellulose and lignin was realized,it provides a reference for the ultimate full utilization of wheat straw.