Study On The Key Problems Of Bio-ethanol Production From Corn Stalk Biorefining

Our country is a large agricultural country,producing more than 800 million tons of straw-like materials every year.The rational use of straw is directly related to the sustainable development of our economy.Previously,a small amount of corn stover was crushed and returned to the field and livestock feed was made,most of which was used to burn for heat.However,corn stalk contains relatively high glucans and xylan,which can be converted into fermentable sugars for biofuel ethanol production through biological processes.However,due to the physical coating of the glycan component by lignin,corn stover has natural enzymatic hydrolysis resistance,so it needs to be pretreated to improve the enzymatic hydrolysis conversion rate.In this project,the acid sulfite method is used to pretreat corn stalks,which is intended to find a method that can efficiently convert biofuel ethanol,and to study its pretreatment mechanism and the feasibility of corn stalk biorefining.The main research contents and results of this paper are as follows:1. Pretreatment of corn stalk by acid sulfite method、Saccharification and fermentation to produce ethanol and comprehensive utilization of pre-treated waste liquidThe corn stalk was pretreated with acid sulfite method.By comparing the enzymolysis performance of the pre-treated cellulose-rich solids under the condition of low substrate concentration,the optimal pretreatment conditions for the corn stalk pretreatment with acid sulfite method are optimized as follows:7%Na HSO₃,1%H₂SO₄,reaction temperature170℃,reaction time 30 min,solid-liquid ratio 1:4.Under this optimal pretreatment condition,the conversion rate of cellulose and xylan reached 85%or more when the cellulose-rich solid material was hydrolyzed for 48 h after pretreatment.The high-concentration Q-SSF was used to ferment the cellulose-rich solid material to produce biofuel ethanol.It was found that the substrate concentration was 15%for fermentation for 48 h,the ethanol yield reached 36 g/L,the cellulose conversion rate was about 86%,and the ethanol yield was about 0.752 g/L/h.The waste liquid of acid sulfite pretreatment contains a large amount of glycans and lignosulfonate components.Based on the consideration of biological refining,the AB-8macroporous adsorption resin and 95%methanol system were used to effectively separate the glycan and lignosulfonate components in the pretreatment waste liquid.The resulting lignosulfonate has high purity and high sulfur content,indicating that the lignosulfonate can be used as a surfactant or other industrial applications to achieve effective utilization of different components.2. Analysis of composition and structure changes of corn stalk after acid sulfite pretreatmentScanning electron microscope（SEM）,X-ray diffraction（XRD）,specific surface area determination and thermogravimetric-infrared combination were used to analyze and compare the changes in crystallinity,external specific surface area,internal specific surface area,functional groups and pyrolysis properties of corn stalk in cellulose before and after pretreatment with acid sulfite method.The results showed that the acid sulfite pretreatment roughened the surface of the corn stalk,increased the specific surface area and exposed more fine fibers.These changes are accompanied by obvious cracks,severely damaged surfaces and loose structures.The changes caused by pretreatment significantly improved the enzymatic hydrolysis efficiency of corn stalk.From the TG-IR analysis,it was observed that the untreated and pretreated corn stalk showed three thermogravimetric mass loss regions.The thermal decomposition characteristics of corn stalk before and after acid sulfite pretreatment are slightly different,which is related to the proportion of cellulose,hemicellulose and lignin in corn stalk.The volatile gas produced by thermal decomposition is mainly composed of small molecules CO,H₂O,CH₄and CO₂.3. Study on Pyrolysis Properties and Pyrolysis Kinetics of Enzymatic Hydrolysis ResidueAs a waste during the corn stalk biorefining process,residues from enzymatic hydrolysis have not been effectively utilized so far.The thermogravimetric-infrared combined technology（TG-FTIR）was used to study the pyrolysis process and pyrolysis kinetics of the enzymolysis residues after pretreatment by alkaline hydrogen peroxide method and acid sulfite method.The study of the solution mechanism provides a theoretical basis.The results showed that the enzymolysis residues showed three stages of weightlessness,but there was a difference in the rate of weightlessness between the two,which may be caused by different ways and degrees of damage to the lignocellulose structure by different pretreatment methods.The volatiles in the pyrolysis process of enzymatic hydrolysis residues are mainly composed of small molecules CO,H₂O,CH₄ and CO₂,as well as some organic substances such as aldehydes,ketones and phenols.At the same time,using the Coats-Redfern function integration method to study its pyrolysis kinetics.It was further confirmed that the enzymatic residues after different pretreatments can convert lignocellulosic biomass into raw materials with good thermochemical properties.