Study On The Solubility And Dissolution Mechanism Of Bamboo Hemicellulose In 1-Butyl-3-Methylimidazolium Ionic Liquids

So far,the uncontrolled exploitation of fossil resources including coal,oil and natural gas has led to the serious crisis of energy resources.Because of large output and renewable,the conversion of lignocellulosic biomass to fuels,chemicals and materials has attracted worldwide attention.Hemicellulose,one of the three main components of lignocellulosic biomass,accounts for 30⁴0%.Therefore,the efficient development and utilization of hemicellulose form lignocellulosic biomass have siginficent value in practice and economic.Ionic liquids?ILs?exhibit excellent performance in the separation and extraction of lignocellulosic biomass components due to their high thermal stability,designability and non-toxicity.However,there have been few reports on the dissolution of hemicellulose in ILs,and also lacked of systematic understanding of the corresponding dissolution mechanism.Deeply understanding the dissolution behavior of biomass hemicellulose in ILs is significant for designing ILs with high efficiency for pretreatment and separation of lignocellulosic biomass.Therefore,this study uses bamboo hemicellulose as a model and its solubility and dissolution mechanism of it in 15 kinds of midazolium ionic liquids with the same cationic structure but different anionic structure were measured.The main research contents and conclusions are given:1.The solubility of hemicellulose in 15 kinds of midazolium ionic liquids with the same cationic structure but different anionic structure was determined in the temperature range from 30 to 150?.The effects of temperature and anionic structure of ionic liquids on the solubility of hemicellulose were investigated.The maximum solubility of hemicellulose in BmimCl,BmimBr,Bmim[H₂NCH₂COO]and Bmim[CH₂=CHCOO]at 120?,100?,110? and 130?,respectively,corresponding to 18.84 g/100 g IL,10.00.g/100 g IL,3.17 g/100 g IL and 4.02 g/100g IL,respectively.Sometimes high temperature was not benefitial for dissolution of hemicellulose in ILs.To obtain the higest solubility of hemicellulose,a suitable temperature was necessary.When the temperature was higher than 90?,BmimCl and Bmim[CH₃COO]showed excellent solvents for dissolving hemicellulose.2.The physicochemical properties of hemicellulose before and after dissolution by ILs were analysed using CPC,GC-MS,FT-IR and TGA techniques.Also,the difference of physicochemical characteritics between the original hemicellulose abd preteated hemicellulose by ILs was compared.The results showed that ILs acted as solvents for dissolving hemicellulose.ILs were not destroied the skeleton structure of hemicellulose and only slight degradation of the hemicellulose took palce.The thermal stability of original hemicellulose was higher than that of the original regenerated hemicelluloses.3.The dissolution mechanism of hemicellulose in ionic liquids was analyzed by¹H NMR and ¹³C NMR techniques.The results show that the dissolution mechanisms of hemicellulose in imidazolium halide-based ILs and imidazolium carboxylate-based ILs were not the same.In the dissolving process of hemicellulose in imidazolium halide-based ILs,only the halogen anion interacted with the hydroxyl proton of the pyranose unit in the hemicellulose molecule,resulting in efficient dissolution of the hemicellulose.At the same time,the hydrogen bond between the halogen anion and the hydroxyl proton at C2 position of pyranose unit in hemicellulose preferentially form.However,there was no hydrogen bond between the imidazolium cation and hemicellulose.Duringthe process of dissolving hemicellulose in imidazolium carboxylate-based ILs,both the imidazolium cation and the carboxylic acid anion promoted the dissolution of hemicellulose,but the anion played a leading role.The carboxylate anion preferentially interacted with the hydroxyl proton at the C2 position on the pyranose structural unit in the hemicellulose molecule to form hydrogen bond.The C2-H proton on the imidazole cation in the imidazolium carboxylate type ILs also formed a hydrogen bond with the hydroxyl oxygen atom in the hemicellulose molecule.