Dissolution Kinetics And Process Mechanism Analysis Of Corn Stover Polysaccharides

Corn stalk has attracted extensive attention in the fields of preparation of biomass materials,energy and chemicals due to its advantages such as wide distribution of resources,low price,rich available resources and strong regeneration.However,in the corn stalk tissue,cellulose,hemicellulose and lignin together form a complex network structure,which provides mechanical strength for the corn plant,but also limits the difficulty in the separation of the three components of corn stalk.In the previous studies on the extraction of polysaccharide compounds from corn stalk,researchers generally focused on the effect of key process parameters on the behavior of the dissolution process,and few studies focused on the effect on the dissolution efficiency caused by the differences in the chemical composition and organizational structure of the raw materials.Based on this,this paper will mainly from the whole plant of corn stalk chemical composition and tissue structure differences,the dissolution kinetics and mechanical analysis of polysaccharides in corn stalk were analyzed in depth.The details are as follows:Firstly,the corn stalk was divided into three types of raw materials according to the leaf,bark and pith,and its physical structure,chemical composition and cell tissue morphology were analyzed.The results showed that there were significant differences in physical structure and chemical composition from each part.To demonstrate the effect of the above differences on the alkaline dissolution behavior of polysaccharides,the extraction experiments of hemicellulose from the above three raw materials were conducted using the mild alkaline extraction technology,and the dissolution kinetic behavior was monitored and analyzed.The results showed that besides the key process parameters such as alkali concentration,the influence of the structure on the dissolution process of hemicellulose could not be ignored.To evaluate its impact,a kinetic model was established to describe the hemicellulose dissolution behavior of corn stalk leaf,bark and pith,respectively.The mathematical model established indicates that the dissolution process of hemicellulose belongs to the solid-liquid mass transfer process dominated by physical diffusion.Moreover,the activation energies of hemicellulose dissolution in the pith,leaf and bark were gradually increased according to the density of tissue structure,cell volume and thickness,which also confirmed the difficulty of alkali extraction of hemicellulose from the above three parts.The established mathematical model could also be used for accurate control of the alkaline dissolution of corn stalk hemicellulose.Secondly,the degradation and dissolution behaviors of cellulose and hemicellulose-type polysaccharides in the bark and pith of corn stalk during the organic acid pretreatment were also studied.The results showed that compared with acid concentration,it was more reasonable to use the dissociation constant(p Ka)of organic acid to evaluate the dissolution of polysaccharides.After screening more than 10 organic acids,it was found that when oxalic acid with the same acid concentration was hydrolyzed,the polysaccharide in the corn stalk had the most efficient hydrolysis efficiency because the ionized hydrogen ion concentration was the highest.In addition,it was also found that in the acidic hydrothermal environment,the difference in the degradation and dissolution of hemicellulose in the skin and core was small,while the difference in the dissolution behavior of cellulose was more significant.This may be due to the high temperature,high pressure and forced mechanical shearing,the hemicellulose with smaller molecular weight is easier to degrade and dissolve out,and the mass transfer process is less affected.However,cellulose molecules can be dissolved in the form of monosaccharides only through the gradual acid cleavage of the terminal β-glycosidic bonds,so the dissolution process is greatly affected by the compactness of tissue structure.Besides,the organic acid p Ka constant was used as the modification factor of the acid concentration variable to construct the polysaccharide dissolution/degradation kinetic models for the corn husk and core,respectively.The results of external validation showed that the established quantitative mathematical model could also be applied to the hydrolysis of other organic acids with high universality.This study provided theoretical support for organic acid pretreatment of corn stalk or other similar lignocellulosic materials.Finally,the polysaccharides in corn pith were extracted by mild enzymatic hydrolysis.Due to the barrier of the multi-layer spiral structure of various cells in the corn pith and the toxic effect of lignin,the extraction efficiency of polysaccharides during direct hydrolyzed by enzyme is very low.To solve the above problems,we used the long-term research of straw oxy-alkali cooking technology as the pretreatment means to chemically dissociate corn pith and obtained the liquid-phase dissolved and solid-phase residue-type polysaccharide substances.Then,the enzymatic hydrolysis behavior of polysaccharides obtained under different cooking strengths was studied,and the effect of oxy-alkali cooking on the enzymatic hydrolysis efficiency was analyzed.The results showed that non-polysaccharide components in the structure of corn cob could be effectively removed by oxy-alkali cooking.And the micromorphology and the crystal structure of the obtained oxy-alkali fiber are changed.In general,these changes are favorable for the enzymatic saccharification reaction.In addition,with the deepening of the oxy-alkali treatment,the content of hemicellulose and lignin in the black liquor was increased,and the molecular weight of the polysaccharide was gradually decreased,which also promoted the enzymatic hydrolysis efficiency of liquid-phase polysaccharide and the efficient separation of subsequent lignin.