Influence Of Autohydrolysis Intensity On Chemical Reaction And Aggregation Of Poplar And The Regulation Of P-factor

Autohydrolysis is an ideal green bio-refining methods,which uses water as a medium to hydrolyze and transform the chemical composition of wood fibers.Hydrolysis intensity has an important influence on the chemical reaction and aggregation state of poplar autohydrolysis.It is very important for poplar green biorefining to correctly understand its influence rule.The water below the critical point above the boiling point is subcritical water.Its physical and chemical properties are adjustable.With the increase of temperature,the mass transfer performance and ion product of water increase,and there is a tendency to change the characteristics to organic solvents.High temperature liquid water belongs to subcritical water,which has good physicochemical properties and is easy to control.To reveal the chemical reaction and aggregation behavior of lignocellulosic biomass in the process of autohydrolysis,to construct the regulation relationship between P-factor and chemical component removal,and to provide theoretical basis and technical support for green biorefinery of lignocellulosic biomass,which is of great significance to green biorefinery industry.In this study,the autohydrolysis characteristics of poplar wood flour under the conditions of autohydrolysis temperature at 160 ~oC to 180 ~oC and time for 0 min to 120 min were studied.The regularity of chemical composition structure and the behavior of aggregation changes in autohydrolysis residue and autohydrolysate was revealed.The relationship and between P-factor and the removal rates of different chemical components was established.It provides basic theory and process guidance for Poplar green biorefining.The main conclusions of the study are as follows:1.Hydrolysis intensity has a significant effect on the pH value,hydrolysis rate and solid content of the autohydrolysis system.With the change of hydrolysis intensity,the pH values of the system at 160 ~oC,170 ~oC and 180 ~oC showed a rapid decline phase(before 45 minutes)and a slow decline phase(after 45 minutes),with the lowest values falling to 3.9,3.8 and 3.6,respectively.The hydrolysis rate and solid content increased rapidly at 160 ~oC and 170 ~oC and then slowly at48%and 42.5 g/L respectively.Before the reaction of 180 ~oC for 40 minutes,the hydrolysis rate and solid content increased rapidly to 44%and 27.9 g/L respectively.After 40 minutes,the hydrolysis rate continued to rise slowly to 48%,but the solid content decreased rapidly to 17.5 g/L,some of the reaction products were transformed.2.Hydrolysis intensity determines the degree of carbohydrate hydrolysis.When the temperature was 160 ~oC,the reducing sugar concentration in the hydrolysate increased to 5.4 g/L with the prolonging of reaction.After 60 minutes of 170 ~oC reaction,the concentration of reducing sugar increased rapidly from 5.7 g/L to 12.2 g/L at 90 minutes,and then reached equilibrium.After60 minutes of 180 ~oC reaction,the degraded monosaccharides were converted to furfural in large quantities.The concentration of reducing sugar decreased rapidly from 11.8 g/L to 7.1 g/L at 120minutes.At this time,about 40%of monosaccharides were converted and fural concentration was2.7 g/L.The removal of pentose can be divided into slow removal phase,fast removal phase and equilibrium removal phase.Increasing temperature can make the slow removal phase complete in the heating process,and promote the removal of monosaccharides only in two phases when the reaction temperature is higher than 170 ~oC.Arabinose was easier to remove than rhamnose,and almost completely removed in the equilibrium phase.Under the same conditions,the highest xylose removal rate was 91%.The removal rule of hexose is different from that of pentose.Mannose and glucose only show rapid removal phase and slow removal phase at three temperatures.The maximum removal rates were only 58%and 37%respectively.Galactose has a similar rule with pentose,and the maximum removal rate is 95%.The removal of these carbohydrates determines the changes in fiber aggregation.In the early period of autohydrolysis,the removal of hemicellulose increased the crystallinity and degree of polymerization of autohydrolysis residues.When the hemicellulose removal was 20%to 65%before 60 minutes of autohydrolysis,the autohydrolysis mainly occurs in the amorphous region of the fibers,and the crystallinity and hemicellulose removal increased in a proportional manner,while the degree of polymerization remained unchanged.After 60 minutes of autohydrolysis,the hemicellulose content in the autohydrolysis residue decreases,and the crystallinity and degree of polymerization are mainly determined by cellulose.3.Hydrolysis intensity has great influence on lignin.At 160 ~oC,170 ~oC and 180 ~oC,lignin removal can be divided into rapid removal phase(before 60 minutes)and supplementary removal phase(after 60 minutes).The maximum removal rates were 42%,46%and 53%respectively.Acid-soluble lignin is easier to remove than Klason lignin.Lignin is easier to condense and adsorb on the surface of raw materials during the supplementary removal phase of 170 ~oC,and the removal rate of lignin decreases locally.45.9%lignin can be removed by 180 ~oC reaction for 30 minutes,of which acid-soluble lignin mainly undergoes transformation reaction and Klason lignin mainly undergoes condensation reaction.When the system was reduced to 75 ~oC,the autohydrolysis residue and the autohydrolysis solution were separated.Under this condition,only 3.6%lignin was dissolved in the autohydrolysis solution.The dissolved lignin continues to condense with the decrease of temperature and then precipitated.Most of the sediment was lignin-carbohydrate complexes.Autohydrolysis is easier to cut off G-type and H-type lignin in raw materials,and the degree of the lignin is basically the same.Most of the lignin in hydrolysate is condensed lignin.Its molecular weight is 27923 and its polydispersity is 2.67.However,it is closely linked with sugar which leads to a significant decrease in the thermal stability.4.Hydrolysis intensity has a great influence on the benzene-alcohol extractive.The change rate of benzyl-alcohol extractive at 160 ~oC,170 ~oC and 180 ~oC showed two phases.The first phase was before 90 minutes,the change rate of benzyl-alcohol extractive increased to 158%,227%and330%at a constant speed.The second phase was after 90 minutes.When the temperature was 160~oC and 170 ~oC,the change rate of benzyl-alcohol extractive increased slowly,reaching 154%and234%respectively.When the temperature was 180 ~oC,the change rate of benzyl-alcohol extractive began to decrease to 303%.The rule of the significant change of benzene-alcohol extractive in the hydrolysis process needs to be further studied.5.Hydrolysis strength has a great influence on the aggregation of fibers.With the increase of hydrolysis strength,the crystallinity of raw materials increases continuously.When the reaction temperature is 160 ~oC and 170 ~oC,the crystallinity can be increased from 43%(raw material)to64%and 66%by holding in 120 minutes respectively.When the temperature is 180 ~oC,the crystallinity increases rapidly from 60%to 69%before 30 min.From 60 min to 90 min,the degree of crystallinity remains basically unchanged.After 90 min,it decreases slowly from 70%,partial cellulose hydrolysis,which deserves further study.Hydrolysis strength has a great influence on the degree of polymerization of fibers,and there are great differences among different temperatures.The degree of polymerization increased slowly from 568(raw material)to 867 in 160 ~oC reaction for 60 min,and then decreased slowly to 800 after 60 min.The degree of polymerization increased slowly to 842 at 30 minutes of 170 ~oC reaction.After 30 minutes,the degree of polymerization began to decrease,and there was a predictable equilibrium trend after 120 minutes.After heating up to 180 ~oC,the degree of polymerization decreased from 820 to the lowest at 60 min,and then had the same trend to equilibrium as 170 ~oC which is about 410.6.P-factor has good regulation on hydrolysis rate,pH value,holocellulose,pentose and furfural.Among them,hydrolysis rate,pH value,holocellulose and pentacosaccharide can be divided into fast removal phase and slow removal phase.In the rapid phase,the hydrolysis rate(P-factor<1000)and holocellulose(P-factor<500)removal rate reached 42%and 43%,respectively,and the pH value(P-factor<500)reached 3.9.The removal rates of rhamnose,arabinose and xylose(P-factor<700,400 and 1000 respectively)reached 89%,97%and 80%respectively.In the slow phase,hydrolysis rate and holocellulose removal rate reached 47%and 54%,pH value reached 3.6,rhamnose and arabinose could be almost completely removed,xylose removal rate reached 91%.Furfural production can be divided into slow phase with P-factor less than 600(concentration reaching 0.4 g/L),fast phase with P-factor between 600 and 1300(concentration reaching 1.0 g/L)and accelerating phase with P-factor greater than 1300(concentration reaching2.7 g/L).