Study On Hydrothermal Coupling Deep Eutectic Solvent Fractionation Of Lignocellulose And Its Bio-Inks

Lignocellulose is the most abundant renewable resources on the earth,but its utilization efficiency is not high.Due to the inherent complex composition and structure of lignocellulose,it is necessary to pretreat and fraction lignocellulose for comprehensive transformation.Deep eutectic solvent(DES)is a new green solvent,which has similar physicochemical properties with ionic liquid.Its excellent physical and chemical properties,especially its strong ability to disintegrate plant cell wall or lignin,show broad application prospects in biomass pretreatment.At the same time,the hemicellulose is more sensitive to temperature,and the hemicellulose is removed by adding hydrothermal pretreatment(HP)before DES.In view of the difficulty in deconstructing lignocellulose,single pretreatment caused hemicellulose easy degradation,low yield of cellulose and lignin.In this paper,a two-step of fractionation of lignocellulose with hydrothermal coupling deep eutectic solvent is proposed,which can not only obtain water-soluble hemicellulose components,but also obtain highly reactive cellulose and high purity lignin by utilizing the swelling and deconstruction effect of deep eutectic solvent.In this paper,hydrothermal pretreatment coupled with deep eutectic solvent fractional lignocellulose waste was developed.The effects of lignocellulosic type,catalyst content and different DES systems on the process were investigated.At the same time,cellulose acetate and lignin acetate were prepared by acetylation method.The potential of cellulose acetate and lignin acetate after four kinds of lignocellulosic pretreatment was evaluated.The main research contents and conclusions are as follows:(1)The pretreatment effect of hydrothermal coupled DES on poplar(POP),bamboo(MB),corn straw(CS)and wheat straw(WS)was studied.By hydrothermal pretreatment,the removal of hemicellulose can reach 50.8%-65.4%,and the solid recovery was above 60%.Hydrothermal pretreatment can selectively dissolve hemicellulose without damaging cellulose structure.The removal of lignin by DES pretreatment was more than 50%,and the recovery of cellulose was more than 80%.After pretreatment,the crystallinity of cellulose components increased,the reactivity increased,and the polymerization degree of cellulose decreased,which indicates that the strong ionic effect of DES can swelling cellulose,destroy the hydrogen bond between cellulose molecular chains,thus exposing more hydroxyl groups and increasing the accessibility of cellulose.The lignin extracted by DES has a complete lignin skeleton and high thermal stability.These results showed that DES could selectively extract condensed lignin and swollen cellulose at the same time,and obtain cellulose with high reactivity and lignin with more hydroxyl content,which provided structural basis for subsequent acetylation reaction.(2)With hemicellulost removal and solid recovery as the main indexes,ptoluenesulfonic acid was added as catalyst in hydrothermal pretreatment,and the optimal pretreatment conditions were selected.When the concentration of p-toluenesulfonic acid is0.3%,the hemicellulose removal was 100%,and the solid component has a higher solid recovery and polymerization degree.In the process of DES,lactic-choline chloride,citriccholine chloride,glycerol-choline hydroxide,urea-choline hydroxide system were selected.Acidic DES had good cellulose retention effect,but the crystallinity and polymerization degree decreased.Alkaline DES has the ability to dissolve short chain cellulose,therefore,alkaline DES extraction of cellulose cellulose recovery was low,crystallinity and polymerization degree have increased.A large number of β-O-4 bonds were broken in lignin extracted from acidic DES,and electrophilic aromatic substitution occurred in lignin fragments during the condensation process,and the content of C-C bond(β-5)was increased.Alkaline DES extracted lignin retained more β-O-4 bonds,and due to the dissolution of cellulose led to higher molecular weight of lignin and higher lignin extraction yield.(3)Cellulose acetate(POP-CA,MB-CA,CS-CA,WS-CA)and lignin acetate(POP-LA,MB-LA,CS-LA,WS-LA)were prepared by acetylation of the cellulose and lignin obtained from POP,MB,CS and WS after pretreatment,respectively.The substitutions of cellulose acetate were 1.76(POP-CA),2.12(MB-CA),2.17(CS-CA),2.15(WS-CA)and 1.77(MCCCA),respectively.The thermal stability of MB-CA,CS-CA and WS-CA is significantly higher than that of POP-CA and MCC-CA,which is related to their substitution.Because the acetyl groups are successfully inserted into the lignin structure,the thermal stability of lignin is improved.Cellulose acetate and lignin acetate are synthesized by acetylation of the pretreated cellulose and lignin,which can be combined with the resin to become bio-based3 D printing ink,and 3D models can be successfully printed.