Study On Physicochemical Properties Of Choline Chloride Based Deep Eutectic Solvents And Its Application In The Pretreation Of Cellulose And Extraction Flavonoids

As an effective substitute for ionic liquids(ILS),Deep eutectic solvent(DESs)has been called a new generation of green solvents.In addition,DESs is considered to be the best solvent to replace traditional organic solvents and ILs due to its advantages of economy,simple preparation and biodegradability,and it needs to further break through the technical bottleneck in the field of biomass pretreatment and biological extraction.Based on this,this study synthesized a series of choline chloride DESs,and applied it to the pretreatment of microcrystalline cellulose and ultrasound-assisted extraction of flavonoids from chrysanthemum.Specific research contents are as follows:(1)In this paper,25 kinds of choline chloride base DESs were synthesized by the molar ratio of 1:2.First,the molecular structure was analyzed by FT-IR,and the mechanism of DES formation among components was discussed.Then the effects of water content and temperature on the physical properties of the solvent system were investigated.The results show that the influence of water content and temperature on the viscosity and conductivity of DESs is very significant.Therefore,the effect of solvent application can be improved by controlling the temperature and water content.(2)In this experiment,the synthetic choline chloride DESs was used to pretreat the microcrystalline cellulose without dissolution,in order to achieve the purpose of improving the saccharification effect.Three better pretreatment solvent systems were selected: DES-9(Ch Cl/hydroquinone),DES-12(Ch Cl/acetamide)and DES-16(Ch Cl/acetic acid),and the optimal pretreatment conditions were optimized.Among them,the optimum conditions of DES-9 and DES-12 were the same as 110 °C,4 h,and the optimum conditions of DES-16 were 90 °C,4 h.In addition,the saccharification effect of microcrystalline cellulose treated with DES-16 as the optimal solvent was the best,and the saccharification rate was increased by 20.5%.Finally,the structure and morphology changes of microcrystalline cellulose before and after treatment were investigated in detail through tests such as degree of polymerization,degree of crystallinity,SEM and enzyme adsorption.The results showed that DESs pretreatment made the surface of microcrystalline cellulose become rough,and improved the accessibility of cellulose and enzymes,thus improving the saccharification effect.(3)In this study,the synthetic choline chloride DESs and ultrasonic-assisted extraction of flavonoids(total flavonoids,total quercetin,quercetin)from wild chrysanthemum were selected.The optimal extraction conditions were optimized as follows: water content of 30%,extraction time of 45 min,solid-liquid ratio of 1:50 g/m L,extraction temperature of 60 °C.And it was determined that DES-3(Ch Cl/propylene glycol)had the best extraction effect on total flavonoids and quercitrin,with the highest extraction rates of 74.48 and 10.97 mg/g,respectively.DES-10(Ch Cl/urea)had the best extraction effect on total quercitrin,with the highest extraction rate of 12.97 mg/g.Finally,the mechanism of extracting flavonoids by DESs was analyzed by SEM and XRD,which indicated that DESs could destroy the structure of wild chrysanthemum and was beneficial to the dissolution of flavonoids.