Study Of Catalytic Conversion Carbohydrate Into Hydroxymethylfurfural And Levulinic Acid

Due to the extensively exploitation and use of non-renewable fossil energy,environmental pollution and ecological damage have been highlighted.Therefore,it is imperative to develop new and renewable energy sources.Biomass has the advantages of wide source,low price,friendly environment,and renewable energy,so the efficient transformation and utilization of the biomass is regarded as an effective way to solve the above problems.This work mainly focus on conversion the carbohydrate such as fructose,glucose,and cellulose into various high value-added chemicals including hydroxymethylfurfural?HMF?,and levulinic acid?LA?.The detailed research results are achieved as follows:1:A sulfonic acid-functionalized magnetically separable solid acid catalyst?Fe₃O₄@SiO₂-SO₃H?was prepared by co-precipitating and well characterized by various technologies including XRD,FT-IR,BET,NH₃-TPD,TEM and VSM.The results showed that the synthesized Fe₃O₄@SiO₂-SO₃H catalyst has a high acid density and thermal stability,and the surface of the catalyst contains a large number of-SO₃H group.The catalytic performance of the prepared catalyst was investigated for the dehydration of fructose to HMF under different reaction conditions.The results showed that the Fe₃O₄@SiO₂-SO₃H catalyst has a high catalytic activity for fructose dehydration to HMF,which afford a highest HMF yield of 96.1 mol%with 100 mol%fructose conversion at 120?for 90 min,even increasing the concentration of the fructose to 10 wt.%,the yield of the HMF still above 82 mol%.It was found that there was a synergistic effect between the-SO₃H group on the surface of the catalyst and the DMSO in the reaction medium,and the above two together promoted the rapid and efficient dehydration of fructose to HMF.2:Heterogeneous catalyst,Fe-MMT,was prepared by ion-exchanged and characterized by various technologies such as XRD,BET,NH₃-TPD,ICP and Py-FT-IR.The result showed that the prepared Fe-MMT catalyst having large specific surface area and high acid loading,containing both Lewis and Br?nsted acid sites on the surface of the catalyst.The catalytic performance of the prepared catalyst was investigated for the dehydration of glucose to HMF in 2-Butanol/H₂O-NaCl biphasic system,and the results showed that the highest HMF yield of 70.2 mol%with 93.5mol%glucose conversion were obtained at 170?for 90 min.In addition,some black insoluble-solid known as humin was also produced during the reaction,and mainly formed from the condensation of glucose and HMF.It was found that the Lewis acid site was beneficial for the isomerization of glucose to fructose,while the Br?nsted acid site was helpful to the dehydration of fructose to HMF.3:Conversion the glucose to LA over three Br?nsted acids?H₂SO₄,HCl,H₃PO₄?or/and four Lewis acids?AlCl₃,CrCl₃,FeCl₃,CuCl₂?has been investigated.The results showed that coupling of CrCl₃ and H₃PO₄ as a mixed catalyst has a positive synergistic catalytic effect on glucose conversion to LA compared with single CrCl₃or H₃PO₄,and the synergy factor of the above mixed H₃PO₄-CrCl₃ reach up to 2.09.Furthermore,a kinetic analysis showed that the glucose decomposition rate constant in the H₃PO₄-CrCl₃ catalyst system is obviously larger than that in the pure H₃PO₄catalyst system,implying that CrCl₃ catalyst has the advantage of accelerating the decomposition of glucose through glucose-fructose isomerization.On the other hand,the formation rate constants of HMF and LA in the mixed H₃PO₄-CrCl₃ catalyst system were much larger than that of relevant humins formation rate constants,respectively,which implied that H₃PO₄ has the function to enhance the LA selectivity during the conversion of glucose.4:A series of Cr modified HZSM-5 catalysts were synthesized by impregnation method and characterized by XRD,BET,TEM,NH₃-TPD and Py-FT-IR.The results showed that the prepared Cr/HZSM-5 catalyst had a larger specific surface area?308.9m²/g?and a higher acid density?6.64?mol/m²?,containing both Lewis and Br?nsted acid sites on the surface of the catalyst.Besides,the catalyst also showed excellent activity for the dehydration of glucose to LA,in which the maximum yield of LA was 60 mol%and obtained from 100 mol%glucose conversion at 180?for180 min.It was found that the yield of LA is not only related to the reaction conditions,but also has some relationships with the intrinsic properties of the catalyst.The conversion of glucose to LA can be divided into two stages,i.e.,glucose dehydration to HMF,and HMF rehydration to LA;the impregnation of Cr into HZSM-5 enhancing the catalyst Lewis acid sites,and thus finally accelerated the glucose conversion to LA through glucose-fructose isomerization.5:The SO₄^2-/TiO₂ catalyst was prepared by the impregnation method,and was coupled with the ZnCl₂·RH₂O hydrate to depolymerize the cellulose to various high-value chemicals.The results showed that the introduction of sulfate into the TiO₂significantly enhanced the catalyst acid amount,especially for Br?nsted acid site?from 68.1?mol/g to 728.3?mol/g?,which is beneficial for subsequent cellulose depolymerization.ZnCl₂·RH₂O hydrate,only a narrow composition range of water,specifically 3.0?R?4.0,can dissolve cellulose,which finally resulted the cellulose with low crystallinity and weak intrachain and interchain hydrogen bond network.Coupling of ZnCl₂·RH₂O hydrate and SO₄^2-/TiO₂ catalyst as a mixed reaction system promoted cellulose depolymerization,and the products can be adjusted by the control of reaction conditions,the low temperature?80-100??seemed beneficial for glucose formation?maximal yield 50.5%?,and the high temperature?120-140??favored to produce levulinic acid?maximal yield 43.1%?.Besides,the addition of organic co-solvent making HMF as the main product?maximal yield 38.3%?.