Preparation And Activity Evaluation Of Catalysts For The Conversion Of Fructose

Fructose is an important raw material from biomass.It can be used to selectively synthesize 5-hydroxymethyl furfural（5-HMF）,a biomass platform compound,by dehydration under acid catalyst.2,5-furandicarboxylic acid（FDCA）is a derivative of5-HMF,which can replace terephthalic acid to produce biodegradable polyester.Therefore,the effective utilization of fructose has become a key to the effective utilization of carbohydrate biomass resources.At present,selective catalytic preparation of 5-HMF with fructose as the raw material and the further oxidation of 5-HMF into polyester material FDCA,are the research focus of the fine utilization of biomass resources in recent years.In view of the high efficient transformation of biomass,this paper has achieved the following results on the preparation of two biomass compounds of 5-HMF and FDCA with fructose as the raw material.1.The dehydration of fructose into 5-HMF catalyzed by ethylene tar based solid acidsEthylene tar based solid acids were synthesized by using heavy components of ethylene tar as raw material,divinylbenzene as crosslinking agent,p-toluenesulfonic acid as catalyst and concentrated sulfuric acid as sulfonating agent.The effects of the dosage of catalyst and the dosage of crosslinking agent on the softening point of tar resin were investigated systematically,and the optimum softening point was 150°C.The effects of the dosage of sulfonating agent and sulfonation time on the acid density of the catalyst were discussed,and the optimum acid density was 4.20 mmol/g.The structure and properties of the catalysts were characterized by FT-IR,XRD,BET,Raman,SEM and TGA.It showed that the catalyst was an amorphous structure,and the key active center was the sulfonic functional group.The catalyst has good thermal stability and high acid density.In the system of fructose dehydration with isopropanol as solvent and polyvinylpyrrolidone K-30as additive,96.2%fructose conversion and 52.1%5-HMF yield can be obtained under the optimum conditions.2.The dehydration of fructose into 5-HMF catalyzed by mesoporous ethylene tar based solid acidsIn order to improve the specific surface areas of the catalyst and increase the active sites of the catalyst,pore forming of the catalyst was designed.Two types of ethylene tar based solid acids with different mesoporous structures were prepared by using the heavy components of ethylene tar as raw material and the nano needle-like magnesium hydroxide and anhydrous magnesium acetate as the hard template respectively.The effects of different hard templates on the performance of the catalysts were also investigated.The catalysts were characterized by FT-IR,XRD,BET,Raman,TEM,TGA and acid density tests.The results showed that the performance of the catalyst prepared by anhydrous magnesium acetate as the hard template was better.The catalyst has a large specific surface area（552.4 m²/g）,a high acid density（4.99 mmol/g）and good thermal stability when mass ratio of ET/Mg（CH₃COO）₂ was 1:4 and the carbonization temperature was 550°C.It was used to the dehydration of fructose into 5-HMF,under the optimum conditions,the conversion of fructose was 97.9%,and the yield of 5-HMF was 87.8%.Moreover,the kinetic study of dehydration reaction showed that the reaction conformed to the first-order kinetic equation.The apparent activation energy of the reaction decreased significantly after the addition of the catalyst.3.The oxidation of 5-HMF into FDCA catalyzed by hydrogen peroxide in the strong alkali systemIn order to oxidize 5-HMF into the more practical application value of biobased polyester monomer FDCA,a simple stoichiometric oxidation method was used to oxidize5-HMF into FDCA by dripping hydrogen peroxide in the strong alkali system of potassium hydroxide.Under the optimum conditions,the conversion of 5-HMF was 90.4%and the yield of FDCA was 55.6%.The purity of FDCA was 99.0%.The raw material was amplified by 5 times,the conversion of 5-HMF and the yield of FDCA remain unchanged.This illustrates that the influence of mass transfer and heat transfer process on the reaction rate can be neglected in the amplification process.4.The oxidation of 5-HMF into FDCA catalyzed by Mn-Co-O bimetallic oxides in the weak alkali systemThe use of strong alkali in the stoichiometric oxidation process was not conducive to the green production of FDCA.Therefore,catalytic oxidation of 5-HMF with inexpensive and heterogeneous Mn-Co-O bimetallic oxides in the weak alkali system was designed and realized.A series of Mn-Co-O bimetallic oxides with different Mn/Co molar ratios and different calcination temperature were prepared by hydrothermal and calcination.The catalysts were characterized by XRD,Raman,BET,H₂-TPR,XPS,TEM and TGA.It showed that the catalytic activity of the hexagon Mn1-Co2-O with a hole at the centre was the highest when the Mn/Co molar ratio was 1:2 and the calcination temperature was400°C.Its structure was MnCo₂O₄ spinel,its active center may be Mn³⁺,and the catalyst has high oxygen mobility and reducibility.The catalyst was used for the selective oxidation of 5-HMF,99.5%the conversion of 5-HMF and 70.9%the yield of FDCA can be obtained under KHCO₃ aqueous solution.Moreover,regeneration method of Mn1-Co2-O by first washed and then calcined was adopted,its activity remained stable after 5 cycles.