Enhance The Conversion Efficiency Of Corn Straw By Ultrasound-ILs/DES Pretreatment Technology

With the rapid development of the world economy and fossil fuels were about to run out.The search for alternative resources had become a global problem.China is a large agricultural country,and billions of tons of agricultural waste were generated every year.How to effectively add value to agricultural product waste was a research hotspot.However,most agricultural product wastes based on lignocellulose have complex and compact structures.In order to utilize this resource,certain pretreatment methods should be taken to deconstruct lignocellulose.Therefore,the purpose of this research is to construct an ultrasound-ionic liquid/deep eutectic solvent pretreatment system to improve the structure of agricultural waste and increase the efficiency of its conversion to platform compounds.And optimize the parameters in the process of pretreatment and catalytic conversion to achieve the maximum utilization of resources.In this study,corn straw were used as the research object in this study.Firstly,an ultrasound-ionic liquid([Bmim]Cl)/cosolvent(DMSO)system was constructed to study the changes in the structure of corn straw components and the content of hydrolyzed sugar compounds before and after pretreatment;secondly,the effect of this system in catalyzing the conversion of corn stover into platform compounds was studied;thirdly,on the basis of this research,the system was upgraded,using deep eutectic solvents instead of ionic liquids,and studying the changes in the structure of corn straw components and the content of carbohydrates in the hydrolysate under the ultrasound-deep eutectic solvent system;Finally,the effect of the ultrasound-deep eutectic solvent system on catalyzing the conversion of corn straw into platform compounds under high temperature conditions was studied.The main content and results of the research are divided into four parts:(1)First,the ultrasound-[Bmim]Cl/DMSO system was constructed to treat corn straw.First,the corn straw was pretreated with[Bmim]Cl/DMSO as the solvent and ultrasound as the pretreatment method.Secondly,regenerate the pretreated corn straw.Thirdly,the main components of regenerated corn straw were analyzed and hydrolyzed by acid enzyme hydrolysis method to determine the content of carbohydrates in the hydrolysate.Finally,the microstructure of regenerated corn straw was characterized by SEM,XRD and FTIR.The results showed that the recovery rate of regenerated corn straw after ultrasound-[Bmim]Cl/DMSO system treatment was56.27%,and the content of cellulose and hemicellulose in corn straw increased from the original 34.70%and 23.28%to 47.81%and 28.88%,respectively.The lignin content was reduced from the 20.39%to 15.34%.And after ultrasound-[Bmim]Cl/DMSO system pretreatment,the hydrolysis of corn straw was easier,the content of glucose and reducing sugar in the acid hydrolysate was increased by 1.93 and 2.30 times,respectively;the content of glucose and reducing sugar in the enzyme hydrolysate was increased 2.64 and 1.97 times,respectively;In addition,the SEM characterization results showed that the surface of the regenerated corn straw was damaged.XRD showed that the crystallinity of the corn straw was reduced from 39.20%to 24.35%.FTIR showed that the main functional groups of the corn straw did not occur before and after pretreatment.In summary,it is shown that the ultrasound-[Bmim]Cl/DMSO pretreatment system destroyed the apparent structure of corn straw,reduced the crystallinity of cellulose,and made hydrolysis reaction easier.(2)Second,the effect of ultrasound-[Bmim]Cl/DMSO system in catalyzing the conversion of corn straw into platform compounds was studied.Using Cr Cl_3,N,N disulfonic acid butyl triethylene diamine hydrogen sulfate(Bis-SO3H)ionic liquid and acidic macroporous resin D001-cc as catalysts,heating with oil bath,and optimizing the time,temperature,ultrasound,solvent types and catalyst types parameters.The results showed that under 40 k Hz ultrasonic frequency,[Bmim]Cl/DMSO as solvent,Cr Cl₃as catalyst,and oil bath at 140?for 3 h is best.The yield of 5-HMF in the system increased from 6.86%to 32.45%.When the Bis-SO3H ionic liquid was used as the catalyst,the 5-HMF yield was 28.26%,but the Bis-SO3H ionic liquid is green and recyclable,and is a more suitable catalyst for this system.(3)Third,upgrade the pretreatment system to use more environmentally friendly and green deep eutectic solvents as substitute reagents for ionic liquids.Firstly,the ultrasound-deep eutectic solvent system was constructed,and the corn straw was pretreated by microwave heating.Secondly,the main components of regenerated corn straw were analyzed,and the hydrolysis reaction was carried out again by acid enzyme hydrolysis.Finally,through the changes of SEM,XRD,FTIR and other microstructures,the reasons for the changes in the content of corn straw components were inferred.The results showed that the deep eutectic solvent composed of choline chloride,oxalic acid and glycerin could effectively deconstruct corn straw.After pretreatment with ultrasound-deep eutectic solvent system,the cellulose content of corn straw increased from 34.70%to 76.08%,and the content of hemicellulose and lignin decreased from 23.28%and 20.39%to 4.03%and 16.22%,respectively.The content of glucose and reducing sugar in the acid hydrolysis solution was increased by1.72 and 1.80 times,respectively;the content of glucose and reducing sugar in the enzymatic hydrolysis was increased by 4.29 and 4.04 times,respectively.At the same time,the SEM characterization results showed that the regenerated corn straw exposed a large amount of fibrous structure.XRD showed that the crystallinity of the corn straw decreased from 17.24%to 12.82%.FTIR showed that the main functional groups of the corn straw did not occur before and after pretreatment.These research results confirmed the applicability of the ultrasound-deep eutectic solvent system for pretreatment of corn straw.(4)Fourth,the effect of the ultrasound-deep eutectic solvent system in catalyzing the conversion of corn straw into platform compounds was studied.Using deep eutectic solvents(choline chloride and glycerin/choline chloride and oxalic acid/choline chloride,oxalic acid and glycerin)and DMSO as the reaction solvent,Sn Cl₄as the catalyst and oil bath as the heating method.After the reaction was completed,determine the content of furfural,5-HMF,levulinic acid and formic acid in the reaction solution.The time,temperature,ultrasound,solvent parameters and catalyst parameters in the reaction process were studied.The results showed that under 40 k Hz ultrasonic frequency,the corn straw,catalyst(Sn Cl₄),solvent(choline chloride:oxalic acid mass ratio 1:1)and co-solvent(DMSO)according to 2:3:40:40After mixing by mass ratio and heating at 140?for 1 h,the contents of 5-HMF,furfural,levulinic acid and formic acid in the system reached 27.54%,33.64%,20.34%and 36.54%,respectively.The results showed that the ultrasound-deep eutectic solvent system could effectively catalyze the conversion of corn straw into platform compounds.According to the above research results,both ultrasound-[Bmim]Cl/DMSO and ultrasound-deep eutectic solvent systems could achieve the purpose of pretreatment of corn straw,but the ultrasound-deep eutectic solvent system,could increase the cellulose content of corn straw more.Both ultrasound-[Bmim]Cl/DMSO and ultrasound-deep eutectic solvent systems could improve the conversion efficiency of corn straw to platform compounds,but the total output of platform compounds is higher in the ultrasound-deep eutectic solvent system,which is more suitable for catalyzing the conversion of corn straw to platform compounds.