Acid Hydrotropic Fractionation Mechanism Of Lignocellulose And Its Application

Lignocellulosic is the most important renewable carbon resource on earth.The efficient and comprehensive utilization of lignocellulosic is of great significance to solve the problems of resource shortage and environmental pollution.Lignocellulosic is composed of lignin,cellulose and hemicellulose,which are closely connected and structurally stable.Effective separation of each component is the premise of effective utilization of lignocellulosic.At present,most of the commonly used component separation methods have the problems of high temperature and high-pressure reaction conditions or high production cost.Acid hydrotropic fractionation conditions are relatively mild,the process is relatively simple and the energy consumption is low,and the reagent can be recycled for many times.In recent years,the application of hydrotropes in the field of efficient lignin removal has attracted people’s attention.Acid hydrotropic fractionation mechanism of lignocellulose is a complex and comprehensive problem,and the mechanism of dissolving and aggregating lignin needs to be studied systematically.p-Toluenesulfonic acid(TSA)and maleic acid(MA)are important acid hydrotropes for lignocellulose fractionation.The delignification mechanism of TSA and MA fractionation of eucalyptus wood chips was studied.The results are as follows:1.Molecular thermodynamics and wettability of acid hydrotropes in water.The Minimum Hydrotrope Concentration(MHC)of TSA and MA solutions was determined by the conductance,which were 11.5% and 25.0% respectively at 25℃.The MHC increased with the increase of temperature.The accumulation of acid hydrotropes in aqueous solution is a spontaneous,exothermic and entropy-increasing process,and the contribution of entropy is larger than that of enthalpy,which is a mainly entropy-driven process.The activation energy of TSA solution is greater than that of MA.The wettability analysis of TSA and MA on the hydrophobic surface showed that the contact angle of acid hydrotropes decreased with the increasing of the concentration on the different surface of hydrophobic materials.The contact angle of TSA on the hydrophobic surface is less than that of MA,and the wettability is higher than that of MA,and the delignification rate was also higher,the mean particle size of lignin aggregate in acid hydrotropes measured by dynamic light scattering changed dramatically around the MHC of acid hydrotropes.2.Reaction kinetics of acid hydrotropic fractionation.By using orthogonal analysis method,determined the temperature is the main parameter to effect efficiency in MA fractionation,while time is the main parameter to effect efficiency in TSA fractionation.Both acid hydrotropes have high delignification efficiency,the maximum delignification rate of TSA was 67.94%,MA was65.14% in the scope of experiments.The delignification rate of TSA was higher than MA at the same hydrotrope concentration.The combined delignification factor(CDF)and combined hydrolysis factor(CHF)curves showed that acid hydrotropes could be divided into fast reaction stage and slow reaction stage,and the reaction conditions at the turning point between the two stages of CDF and CHF curves are the same with the same acid hydrotrope concentration.The hydrotropic delignification rate is relevant to its hemicellulose degradation.3.Chemical structure changes of lignin of acid hydrotropes fractionation.2D-HSQC and FTIR analysis showed that the β-aryl ether linkage of lignin was broken under severe condition of acid hydrotropes fractionation.The reaction intensity is severe at high CDF,the delignification rate increased with the β-aryl ether bond breakage increasing at high CDF.Condensation became substantial at the most severe conditions,which decreased the delignification rate,and the molecular weight of lignin increased.The β-aryl ether bond content of TSA hydrotropic lignin was higher than that of MA under mild conditions.MA lignin aromatic ether bond content decreased faster than TSA at the rapid reaction stage.4.Pretreatment improved of acid hydrotrope fractionation efficiency.Mechanical grinding increased the specific surface area of material,the chip delignification rate of P40T70t60 increased from 28.3% to 45.42% after ball milling.And the P40T70t60 extracted lignin rate from ball milled eucalyptus powder was 35.33%,which was 19% higher than that of dioxane extraction.2D-HSQC revealed that the function groups of the two lignin were same,the β-aryl ether bond content were similar.The GPC showed that the molecular weight distribution of the two lignin was similar too.TG and DSC showed that thermal stability of two lignin hadn’t much difference.So,the standard lignin can be obtained by acid hydrotrope under mild conditions.Chemical pretreatment can also improve delignification rate.Delignification rate of P40T80t90 and M55T120t180 could be increased by about 10% after two hours of pretreatment at 80℃ with4% Na OH.Alkali pretreatment can also increase the specific surface area of the material,so improve the delignification rate and fiber quality.No new functional groups were formed after hydrotrope fractionation both in fiber fraction and lignin fraction,and the chemical structure also did not change after pretreatment.5.Study on enzymatic hydrolysis of solid fraction by acid hydrotropes.Enzymic hydrolysis experiments were performed on solid fraction treated by acid hydrotropes near the turning point of CDF curve.The glucose yield of TSA solid fraction was 90.63%,and that of MA was 52.42%.The enzymatic hydrolysis efficiency of fiber fraction by TSA was significantly higher than that treated by MA.Na OH pretreatment can improve the enzymatic hydrolysis efficiency.When the enzyme dosage is 20 FPU,the enzymatic hydrolysis efficiency of N4T80T120 increases by 4.6%and 15.71% compared with P40T80t90 and M55T120t180.