Study On Separation And Utilization Of Corn Straw Based On Classification Conversion

The full research and utilization of lignocellulosic biomass is expected to alleviate the environmental and energy crisis faced by mankind,and provide guidance for the production of high value-added chemicals.Achieving clean and efficient separation and classification conversion of cellulose,hemicellulose and lignin in biomass resources has become a research hotspot.Based on the guiding principles of process cleanliness,high-efficiency separation and conversion,corn straw was used as raw materials.This paper developed and expanded the subcritical CO₂-assisted autohydrolysis technology,organic acid and deep eutectic solvents synergism treatment technology and the"one-step"solvent thermo conversion technology,as well as developed novel separation and extraction method of lignin.Three-component separation and hierarchical utilization technology was constructed,and the purification method of lignin and other products was proposed,which is of great significance to promote the utilization efficiency of lignocellulosic biomass.The research and development of subcritical CO₂-assisted autohydrolysis technology can synchronously separate and convert hemicellulose into oligosaccharides,cellulose into fermentable sugar,and better preserve the lignin in raw materials of corn straw.The prehydrolysate was rich in xylose,and among the xylose,about 90.2%existed in the form of xylo-oligosaccharides(XOS),as well as the functional XOS took up about 40%.Structural analysis shown that the degree of polymerization of functional XOS is mainly concentrated in2-4,and the monomers were mainly linked by?-(1?4)glycosidic bonds.Few inhibitors were formed during the pretreatment and there was almost no effect on subsequent fermentation.Combined with enzymatic hydrolysis,the highest glucose yield was 90.6%(32.8 g/100 g corn straw)in enzyme hydrolysate and 89.4%(21.2 g/100 g corn straw)of lignin was recovered in the enzymatic hydrolysis residue.The characterization data were also obtained through the analysis of optimally pretreated solids(pretreatment conditions:170?,5 Mpa CO₂ and 40min residence time)by using HSQC,XRD,FTIR,SEM and TG,which revealed that the technology can realize the full-scale conversion and utilization of cellulose and hemicellulose with little lignin degradation.The development of organic acid and deep eutectic solvents synergism treatment technology can realize the simultaneous production of functional oligosaccharides and fermentable sugars as well as the efficient separation of lignin.It was found that synergism treatment,especially for the lactic acid(Lac)treatment combined with choline chloride/Lac system,could not only selectively convert the hemicellulose to xylo-oligosaccharides(XOS),which account for 89.7%of total xylose in prehydrolysate(the functional XOS(DP<5)took up about 35%),but also significantly promote the glucose/xylose release(33.2g and 16.9g/100g corn straw)with enzymatic hydrolysis and well lignin separation(representing 40.9%in whole process).XRD,FTIR,SEM,TG and other technologies showed that synergism treatment can separate hemicellulose and lignin step by step and realize efficient conversion of cellulose.Compared with the single organic pretreatment at higher modified severity index(SI),the synergistic technology had the advantages of simple operation,mild treatment conditions,low equipment cost and high lignin recovery,which was a good choice for the separation and conversion of lignocellulosic biomass.Developed"one-step"rapid thermo conversion technology to achieve promptly conversion of lignocellulosic glucose and xylose to oligosaccharides of biomass.The results showed that fermentable glucose and xylose could be converted to oligosaccharides by adjusting the reaction temperature and time under nitrogen atmosphere within a certain temperature range(300-700?)and a short time(5-180s).The highest Cello-oligosaccharides(COS)yield(44.62%)with higher COS selectivity(65.84%)and glucose conversion(67.89%)were obtained at 500?in 38 s.The highest xylo-oligosaccharides(XOS)yield and selectivity were 47.09%and 75.25%,respectively,and xylose conversion was 62.63%at 500?in 30 s.The air was considered to be the appropriate quenching method for low temperature(<500?)preparation process.The conversion procedure was similarly under varied reaction temperatures,and it can be summarized into three stages,i.e.initial stage,formation of oligosaccharide stage and active reaction stage.Oligosaccharides were mainly formed from monosaccharides through intermolecular dehydration,and were accompanied by condensation reactions during thermochemical conversion.The degree of polymerization of oligosaccharides was mainly concentrated in 2-6,and the monomers were mainly linked by?-(1?4)glycosidic bonds.As the reaction progresses,major by-products such as formic acid,acetic acid,furfural,hydroxymethyl furfural,and a small amount of soluble sugar polycondensation products were produced.The molten yellow product produced during the reaction was an oligosaccharide precursor,which was an important intermediate for the thermal conversion of monosaccharides to prepare other functional products.The conversion process was"clean and efficient"without introducing harmful chemicals,further expanding the field of high-value utilization of lignocellulosic biomass.Based on novel green process of step separation and classification of whole components of corn straw,a variety of new enzymatic hydrolysis/extraction lignin has been developed and prepared.The results showed that the enzymatic lignin after acid treatment had a higher yield,and the subcritical CO₂-assisted autohydrolysis enzymatic lignin had the highest yield of89.68%.The deep eutectic solvents extraction lignin has higher purity,of which the lignin extracted by choline chloride/lactic acid system had the highest purity of 89.15%.Both the enzymatic hydrolysis lignin and the deep eutectic solvents extraction lignin had the characteristic signal peaks of typical herbal lignin and the overall molecular weight is small,which is beneficial to high value-added utilization and the conversion of high-quality fuel.subcritical CO₂-assisted autohydrolysis and choline chloride/lactic acid treatment processes were more likely to lead to the dehydration,oxidation or modification of the hydroxyl groups of the lignin side chain,and the content of condensed phenolic hydroxyl groups was higher.With the synergistic effect,more dehydration and acylation reactions happened and more?-O-4 ether bonds could be broken.Both acid treatment and choline chloride/lactic acid treatment system could enhance the thermal stability of enzymatic/extraction lignin.The enzymatic hydrolysis lignin showed a higher high calorific value than the extracted lignin,and it could be increased after acid treatment.The deep eutectic solvents extraction lignin had higher char residue content than enzymatic lignin,which would more likely carbonization at high temperature.