Study On Fractional Separation Of Wheat Straw Components By Hydrothermal-Ethanol Method

Lignocellulosic biomass resources have good prospects of replacing fossil resources,under the premise of effective separation of lignocellulose components by pretreatment.However,there is still a lack of a clean and efficient component separation method in the utilization of lignocellulosic resources.The hydrothermal and the organosolv ethanol pretreatment have their unique advantages in the separation of hemicellulose and lignin,which means the combination of these expected to achieve biomass fractionation.Since hydrothermal-ethanol fractionation has low efficiency in lignin separation,we raise the separation efficiency of lignin by hydrothermal-ethanol to separate three major components by introducing catalysts.In addition,the migration mechanism of lignin,the separation mechanism of lignin,and the microstructure variation of solid phase products by hydrothermal and organosolv ethanol treatment were studied.The specific contents are as follows:First of all,the effects of non-catalytic and CH3COOH or HCOOH catalysis on hydrothermal separation of hemicellulose of wheat straw were compared.Then,which were treated with organosolv ethanol.The effects of HCOOH,H2O2 and NaOH on the separation of lignin by organosolv ethanol were discussed,and the microstructure variation of the solid-phase products before and after hydrothermal and organosolv ethanol treatment was revealed.The results showed that HCOOH had a better effect on the separation of hemicellulose by hydrothermal.The removal efficiency hemicellulose reached 91.8%under the condition that the solid-liquid ratio is 1:24 g/mL for 60 min at 170?.After hydrothermal treatment,lignin migrated by the dissolution of hemicellulose to the fiber surface through the pore channels,and deposited in a spherical shape on the surface of the solid phase product.At the same time,the porosity,specific surface and crystallinity of the hydrothermal solid phase products increased.NaOH catalyzed organosolv ethanol has better effect on separating lignin,under the conditions of 3%NaOH,55%ethanol concentration and solid-liquid ratio is 1:16 g/mL for 90 min at 180?,the lignin removal efficiency was 69.3%.After ethanol treatment,there was still a large amount of lignin,which was transformed from glass state to rubber state at high temperature and spread out on the fiber surface to form a dense lignin coating layer.Then,the lignin coating layer was partially dissolved in the ethanol solution,and the rest was adsorbed on the fiber surface in an irregular shape.Secondly,in order to better separate the lignin and cellulose components in the hydrothermal solid-phase product,we compared the separation effect of binary with non-catalyzed ethanol pretreatment on lignin.The results showed under the conditions were as follows:ethanol concentration 55%,temperature 180?,holding time 90 min,and solid-liquid ratio 1:16 g/mL,binary catalysis improves lignin separation by 48.2%compared to non-catalytic,under the conditions of ethanol treatment,the dissolution of S-type lignin was more favorable.Lignin isolate were typical G-S-type lignins,and the degree of lignin condensation during ethanol treatment was higher than that of hydrothermal treatment;binary catalytic ethanol can enhance the degradation and dissolution of lignin,especially for the lignin condensation structures such as ?-?,?-5 and ?-1 damage.The molecular weight and the content of the condensed structure of the binary catalytic lignin,furthermore,the crystallinity and surface lignin content of the binary catalytic crude cellulose were lower than non-catalyzed.Finally,hemicellulose was obtained from hydrothermal filtrate treated by alcohol precipitation,and lignin was obtained from ethanol filtrate treated by dilute precipitation to achieve the fractionation of the three major components.Orthogonal experiments were used to optimize the process parameters of hydrothermal and binary catalytic ethanol treatment.The results showed that the best technological parameters of extracting hemicellulose by hydrothermal were temperature 180?,holding time 40 min,solid-liquid ratio 1:24 g/ml,and the extraction rate of hemicellulose was 38.1%.The optimal technological parameters for lignin extraction by binary catalytic ethanol were ethanol concentration 50%,temperature 190?,holding time 90 min,solid-liquid ratio 1:16 g/mL,the extraction yield of lignin and cellulose was 62.7%and 86.1%,respectively.What's more,the hemicellulose isolated mainly composed of(1,4)-?-D-pyran xylose,and side chain connects the 4-O-methy-?-D-glucuronicacid,?-L-arabinose and acetyl.In summary,the hydrothermal-ethanol method under catalytic conditions can achieve the separation of the three major components of wheat straw,which have a positive significance for the realization of high-value utilization of lignocellulosic biomass after fractional separation.