Ionic Liquid-Catalyzed Conversion Of Cellulose To HMF And LA

The demand for energy in modern society is increasing,but most of the energy used by humans today is non-renewable fossil energy,and fossil energy is facing depletion.Cellulose is the most abundant biomass and renewable resource in nature,so its conversion into other useful chemicals has received a lot of attentions from researchers.5-hydroxymethylfurfural（HMF）and levulinic acid（LA）are important platform compounds that can be prepared from petroleum and biomass,which have several active functional groups,can synthesize a series of important chemicals.HMF can be prepared from monosaccharides such as glucose and fructose.However,the cost of raw materials is high,and if a large amount of HMF can be made at one time from cellulose.Ionic liquids are green solvent that can dissolve cellulose and achieve homogeneous catalysis of the reaction.The double-liquid phase system is to add organic solvent to the aqueous phase,and the organic solvent can extract the HMF and LA to separate the target product and the reaction system.Therefore,the degradation of cellulose by ionic liquids and double-liquid phase systems has been widely studied.In this paper,the conversion of cellulose to HMF and LA in[BMIM]Cl with Cr Cl₃and WCl₆as synergistic catalysts have been investigated.Temperature-responsive ionic liquids and two-liquid-phase systems has been used in one-pot method for the conversion of cellulose to HMF and LA.In the first chapter,conversion of cellulose to HMF catalyzed by Cr Cl₃and WCl₆in[BMIM]Cl have been investigated.The effects of reaction temperature,reaction time,the ratio of two metal chlorides,and the amount of cellulose on the yield of HMF have been studied.The experimental results showed that Cr Cl₃and WCl₆had a synergistic catalytic effect,which was better than that of Cr Cl₃or WCl₆alone.The optimal dosage ratio of the two metal chlorides was 3:1.The optimal reaction conditions were 6 h at 120℃with the addition of 0.03 g Cr Cl₃and 0.01 g WCl₆.The HMF yield and TRS yield were up to 43.4%and nearly 100%,respectively.The mechanism of the reaction was investigated.Cr³⁺and W⁶⁺played a role in weakening the glycosidic bond during the hydrolysis of cellulose.Cr³⁺could catalyze the isomerization of glucose,and W⁶⁺played a catalytic role in the dehydration stage of fructose.Due to the difficulty of ionic liquids to separate the products,a kind of temperature-responsive ionic liquids was synthesized as a catalyst in this chapter.A water-methylisobutyl ketone（MIBK）two-liquid-phase system was used for the separation of the target products and as the reaction medium.The temperature-responsive ionic liquid was synthesized by phosphotungstic acid to provide acidity and alkyl chains of quaternary ammonium salts to provide hydrophobicity.The effects of reaction temperature,time,catalyst amount and quaternary ammonium salt type on the yields of HMF and LA were also investigated.The experimental results showed that the temperature-responsive ionic liquid catalysts using phosphotungstic acid and tetrabutylammonium bromide gave the highest HMF and LA yields of 45.26%and 64%,respectively.The optimal reaction conditions for the highest HMF yield were 180℃,1 h reaction and 1:2 mass ratio of catalyst to cellulose,the optimal catalyst dosage for the highest LA yield was different from that of HMF,with the optimal catalyst ratio of 1:1.The reaction mechanism was explored and cycling experiments were conducted.It was found that the catalytic activity of the catalyst only slightly decreased after three cycles.Temperature-responsive catalysts prepared by quaternary ammonium salts and phosphotungstic acid have Br?nsted acid but low Lewis acidity.To solve this problem,imidazole-type ionic liquids and pyridine-type ionic liquids were synthesized and Cr³⁺was added to provide Lewis acid in this chapter.The factors affecting the yields of HMF and LA were investigated.The results showed that the catalyst prepared by pyridine and phosphotungstic acid according to 3:1（pyridine-1HPW）had the highest HMF yield of 48.56%at 165℃for 1 h.When the mass ratio of catalyst to cellulose was 1:2;the catalyst prepared by pyridine and phosphotungstic acid according to 1:1（pyridine-3HPW）had the highest LA yield of 46.55%at 165℃for 3 h.When the mass ratio of catalyst to cellulose was 1:1,the highest LA yield was 46.55%at 165℃for 3h.When the mass ratio of catalyst to cellulose was 1:1 at this time.Recovery experiments were conducted afterwards.The mechanism of the reaction was investigated.It was concluded that the sulfonic acid group plays a role in breaking the glycosidic bond,glucose isomerizes and dehydrates in the presence of Cr³⁺to produce HMF.LA is generated by the hydration of HMF in the presence of H⁺.In the recycle experimental group,it was found that the yields of HMF and LA did not decrease significantly after four cycles of the catalyst after supplementation with 0.005 g Cr Cl₃.