Studies On Metal Salts/Ionic Liquids Catalyzed Sugars To 5-Hydroxymethylfurfural And The Product Separation

With the decrease of the reserves of fossil resources, the prices ofpetrochemical downstream products have become higher and higher, and seekingalternatives for sustainable development has become increasingly important. Inrecent years, biomass which was expected as a renewable alternative to fossil energyresources in the future attracted more and more attentions. Preparing5-hydroxymethylfurfural (5-HMF) from biomass is one of the research hot pointsfor comprehensive utilization of biomass. As an important component of biomass,sugar (carbohydrate) converting to 5-HMF deserves more and more attentions.5-HMF is an important organic intermediate, which is traditionally obtained fromsugars catalyzed by inorganic acids or solid acids or other acid catalysts. However,inorganic acids are very corrosive, and the yield of 5-HMF is not good whilecatalyzed by other catalysts. Therefore, this project used ionic liquids, which areknown as "green solvents", as solvent and catalyst and metal salts as co-catalyst toconvert the sugars to 5-HMF. The separation of 5-HMF were studied usingextraction method and vacuum distillation method respectively. Besides, theeconomic analysis of fructose dehydration to 5-HMF reaction was preliminarystudied.In this thesis, two ionic liquids [BMIM]C1 and [Et₃NH][HSO₄] were mainlysynthesized and used as both solvent and catalyst in the preparation of 5-HMF fromsugars. In addition, two novel metal chlorides IrCl₃ and AuCl₃·HCl as well as othergeneral metal salts Cu(NO₃)₂,FeCl₃,PbCl₂,Ce(NH₄)₂(NO₃)₆ and Zr(NO₃)₄ were usedas co-catalysts to catalyze the degradation of sugars.It was found that the degradation of fructose was easier than that of other sugars.While [BMIM]Cl was used as catalyst and solvent, the yield of 5-HMF increased firstand decreased later with the increase of temperature, which reached maximum of61.7% at 110℃. 5-HMF yield was greatly improved while IrCl₃ and AuCl₃·HCl wereadded as co-catalyst respectively. By studying the reaction factors of fructosedegradation catalyzed by IrCl₃/[BMIM]Cl, it was found that 5-HMF conversion rate increased with the decreasing of water content in reaction system and the inceasing ofIrCl₃ used. Under the optimal reaction conditions (120℃, 20 min), 5-HMF yield wasup to 89.0%. The catalytic activity of metal salts increased according to thenucleophilic ability of the anion. The order of the catalyst according to the yield of5-HMF was as follows: Ce(NH₄)₂(NO₃)₆＞Cu(NO₃)₂·3H₂O＞FeCl₃＞Cr(NO₃)₃＞CrCl₃＞PbCl₂＞Cu(CH₃COO)₂. Besides [BMIM]Cl, another ionic liquid[Et₃NH][HSO₄] was also studied for comparison. But because of its strong Bronstedacidity, the selectivity of 5-HMF was not very good. Addition of dimethylsulfoxide(DMSO) could improve the yield of 5-HMF to a certain extent. At the mass ratio ofm([Et₃NH][HSO₄]) : m(DMSO)=1 g : 1 g, the conversion of fructose was 88.6% andthe yield of 5-HMF was 47.0% at 100℃for 1 h reaction.Compared with the degradation of fructose, the degradation of glucose, sucroseand maltose was more difficult, among which the sucrose was relatively easier todegradation and the yield of 5-HMF was up to about 35%. However, the degradationof glucose and maltose was much more difficult: the maximum 5-HMF yield wasonly about 7%. When metal salts catalyzed the dehydration of glucose in [BMIM]Cl,the stronger the electrophilic activity of the cation and the nucleophilic of anion, thestronger the catalytic activity of metal salts. The order of the catalyst according tothe yield of 5-HMF was as follows: Cr(NO₃)₃≈CrCl₃＞Zr(NO₃)₄＞Ce(NH₄)₂(NO₃)₆≈IrCl₃.When ethyl acetate was used as extractant to extract the substrate after fructosedehydration, extraction condition was as follows: m([BMIM]Cl) : m(H₂O) : m(ethylacetate)= 1 g : 2.5 g : 3.5 g, the distribution coefficient of 5-HMF was 0.86. Whenvacuum distillation method was used to separate 5-HMF, the percentage of 5-HMFin the substrate decreased with the time. And 5-HMF only remained 4.0% in thesubstrate after 24 hours. We made a simple budget of preparation of 5-HMF fromfructose. The results showed that the cost of 5-HMF was 1190 yuan/kg withoutconsidering the labour cost and equipment cost. Comparing to market price 9000yuan/kg, the profit space is very large. All in all, fructose is a promising substitutefor petrochemical oils to prepare 5-HMF.