Study On Preparation Of Rice Husk-based Solid Acid And Catalytic Hydrolysis Of Corn Cob To Promote Sugar And Volatile Fatty Acid Production

The shortage of fossil energy and the environmental pollution problems caused by its utilization make human beings show unprecedented enthusiasm for the utilization of renewable clean energy.Lignocellulosic biomass is a kind of clean and renewable energy,which has the characteristics of wide source,low price,strong reproducibility and clean.The development and utilization of biomass energy is of great significance to alleviate the energy crisis,reduce environmental pollution,and slow down the greenhouse effect.Lignocellulose has a complex cellulose-hemicellulose-lignin cross-linked structure,which has tensile strength,mechanical strength,and biodegradation resistance.Hydrolysis is the rate-limiting stage in its utilization process.In this study,biomass was used as char base to prepare solid acid,and corncob was used as the object of hydrolysis.Solid acid pretreatment was used instead of traditional liquid acid pretreatment to catalyze the hydrolysis of corncob.The characteristics of solid acid pretreatment of corncob anaerobic fermentation to produce volatile fatty acids?VFAs?was studied.The purpose of this study is to open up a new way for biomass pretreatment and improve the efficiency of converting agricultural and forestry wastes into energy chemicals in a clean and environmentally friendly way.Solid acid is a new type of catalyst,which has the advantages of easy separation,easy recovery,low corrosion and reusability.Biomass char-based solid acid has the advantages of stable structure,wide source of raw materials,renewable and green.Three solid acid catalysts?RH-SO₃H,AC-SO₃H,MC-SO₃H?were prepared by one-step carbonization-sulfonation method using rice husk,activated carbon,microcrystalline cellulose as raw materials and concentrated sulfuric acid as sulfonating agent.The solid acid RH-SO₃H showed the highest catalytic activity.The suitable preparation temperature of RH-SO₃H is 160?,at this temperature the yield of solid acid is 64%.FT-IR,XRD,SEM,elemental analysis,energy spectrum analysis and other characterization results showed that the rice husk-based solid acid contains active groups such as-SO₃H,-COOH,and-OH,and presents an amorphous aromatic carbon sheet structure.The solid acid RH-SO₃H still retains more than 80%catalytic activity after four uses of corncob hydrolysis.Rice husk-based solid acid RH-SO₃H shows excellent catalytic hydrolysis activity for lignocellulosic biomass represented by corn cob in a hydrothermal reaction system.By optimizing the hydrolysis conditions,the maximum reducing sugar yield is 486.53 mg/g and the xylose yield is 253.03 mg/g at a reaction temperature of 160?,reaction time of 3 h,and catalyst to substrate ratio of 1:2.The high catalytic activity of rice husk-based solid acid RH-SO₃H is attributed to the carbon-based solid acid containing three functional groups-OH,-COOH and-SO₃H.Functional group-OH and-COOH can adsorb the?-1,4-glucan chemical bond in biomass,which can promote the contact between-SO₃H and the substrate,and then break the?-1,4-glycosidic bond.The three functional groups work synergistically.At the same time,due to the characteristics of high energy density,high content of cellulose and hemicellulose,and low lignin content,corncobs have obvious advantages in producing reducing sugar.VFAs are new energy chemicals with great potential.VFAs can be used as carbon substrate,fuel additive,coating,plasticizer,etc.After solid acid pretreatment,dilute sulfuric acid pretreatment,hydrothermal pretreatment and unpretreated,corncobs were fermented by anaerobic fermentation to produce VFAs.Results showed that solid acid pretreatment effectively increased the yield of VFAs,and the yield of VFAs was as high as 6684.67 mg/L.Corncob anaerobic fermentation is dominated by acetic acid type fermentation.Acetic acid accounted for the largest proportion?70.4%?in the fermentation products,with a concentration of 4820.25 mg/L.High-throughput sequencing was used to analyze the characteristics of microbial community structure.The test found that Firmicutes is the dominant bacterial species at the phylum level.Ruminiclostridium,Clostridium and Bacteroides are the dominant bacterial species at the genus level.This study provides a new idea for the preparation of solid acids with high catalytic activity using rice husk,and provides a new efficient,green and environmentally friendly way for solid acids to be used in the hydrolysis of lignocellulosic biomass to produce sugar and the pretreatment of biomass to produce VFAs.