The Research On Preparation Of Levulinic Acid From Lignocellulose Catalyzed By Ionic Liquids

Six acidic ionic liquids were applied to catalyze the straw to levulinic acid(LA)with high selectivity under hydrothermal and microwave conditions,where in ionic liquids could be reused.During the hydrothermal processes,lignocellulose,microcrystalline cellulose and glucose unavoidably produce solid by-products so-called humins,which formation mechanism and applications have been studied herein.Acidic ionic liquid [C3SO3Hmim]HSO4 was applied to catalyze the straw to levulinic acid(LA)with high selectivity under hydrothermal conditions.Through the optimization of reaction conditions,the highest yield of LA is 96.6 mol%(21.6 wt%)based on the amount of C6-sugars in the straw.The relationship between IL structure and LA yield was established,disclosing that acidity and hydrogen bonding ability of anions are crucial to the yield of LA.IL can be reused over 4 cycles without loss of activity.Moreover,the chemical structures and morphologies of the solid residues were investigated by SEM and IR,indicating that the lignin fraction in the straw still has the original skeleton structure without modifications during the reaction.Humins' formation process can be divided into three stages: At the first stage(20~30 min)humins are composed of agglomerated microspheres At the second stage(30 ~ 60 min)microspheres become separated,with humins' quantity fastly increased.At the third stage(60 ~ 120 min)with humins' quantity kept fairly constant,agglomerated micrometer-size particles were observed,in coexistence with microspheres.The intermediates and 5-HMF appeared before the formation of humins,which both disappeared after the conversion of the raw material,so 5-HMF and the intermediates may react to form humins.The IR spectra showed that the oligomers' main absorption peaks were similar to those of humins,so the oligomers assumably polymerize further to form humins Through pyrolysis-GC-MS detection,the functional groups corresponding to three stages were confirmed.With regard to humins formed from 2.2 g of cellulose,at the second phase(1 h)wherein agglomerated nanometer-size particles were generated directly due to the fast reaction speed.With the extension of time humins' degree of polymerization increased.leading to higher C content and lower O content,therefore the heat of combustion.was enhanced.Through extraction by acetone to remove the oligomers,the heat of combustion was increased further.The new microporous and mesoporous structures were formed during humins' formation,so BET surface area was apparently higher than that of the raw material..