Study On Extraction And Functionalization Of Cellulose From Biomass

With the declining reserves of fossil resources and increasing attention on environmental protection,the application of cellulose as a renewable source has become a research hot in recent years.The separation and extraction of cellulose is the basis of cellulose utilization.As a solvent similar to ionic liquid,the deep eutectic solvent(DES)also has low toxicity,biodegradability,low price,and easy preparation in addition to the excellent characteristics of traditional ionic liquids.Therefore,the application of DES is expected to make cellulose extraction effective and green.In this paper,cellulose was extracted from corn cob by DES and was functionalized to prepare carboxymethyl cellulose(CMC).Firstly,three kinds of DES were prepared by mixing hydrogen bond acceptor of choline chloride(ChCl)and three hydrogen donors,including 1,4-butanediol(BDO),ethylene glycol(EG)and glycerol(Gly)to form ChCl-BDO,ChCl-EG,ChCl-Gly.The density and viscosity of ChCl-BDO with different molar ratio were measured.Three kinds of DES with the same molar ratio were analyzed by infrared spectroscopy and thermogravimetry.The results showed that the physical properties of prepared DES were closely related to the nature of the hydrogen bond donor and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor.When the molar ratio of ChCl to BDO was 1:1 or 1:2,DES could not be formed at room temperature.The smaller was the mole fraction of BDO in ChCl-BDO,the greater the density and the viscosity of ChCl-BDO.When the molar ratio was 1:3,ChCl-Gly has the highest thermal stability and ChCl-BDO has the highest freezing point.Secondly,the results of ChCl-BDO,Ch Cl-EG and ChCl-Gly for separating and extracting cellulose were compared,and it was found that ChCl-BDO had the best result.Based on this,the effects of processing temperature,processing time,molar ratio and liquid-solid ratio on the separation and extraction of cellulose by ChCl-BDO were studied,and compared with traditional extraction methods such as high boiling alcohol method,acid method and alkali method.The structures of raw materials and products were characterized using infrared spectroscopy,thermogravimetric,X-ray diffraction and scanning electron microscopy.Under the optimum conditions,the cellulose content in the fiber material by ChCl-BDO was 77.8%,and the removal rate of hemicellulose and lignin were 75% and 95% respectively.The DES with polyols as hydrogen bond donors had good removal effect on hemicellulose and lignin at high temperature.Compared with other methods,DES has a higher removal rate of hemicellulose and lignin with less damage to cellulose,showing a good application prospect in the field of cellulose separation and extraction.Finally,the fiber material obtained by the DES treatment was used as raw material.After purification,CMC with low viscosity and high substitution degree were prepared by three-time alkali addition method and phased etherification process.The process conditions were optimized by the single factor experiment and orthogonal experiment.The obtained CMC was compared with commercial CMC.The raw materials and products were characterized by infrared spectroscopy,thermogravimetry,X-ray diffraction and scanning electron microscopy.The results showed that the substitution degree of CMC prepared under the optimum conditions was 1.52 and the viscosity of its 2% solution was only 15-20mPa·s.The substitution degree and viscosity were better than that of commercial CMC.