| Energy shortage and environmental problem are two major problems that human beings are facing at present.There are abundant biomass resources,and the production of chemicals and fuels from biomass resources is the development trend of the future chemical industry.Sugars include cellulose and hemicellulose from lignocellulose,as well as derived polysaccharide and monosaccharide.Furfuralcohol(furfuryl alcohol and 2,5-furandimethanol)can be prepared from sugar,Furfuryl alcohol can be used to produce various resins with excellent properties,and 2,5-furandimethanol has a wide range of applications in the synthesis of drugs,resins,crown ethers and so on.However,the studies of furfuralcohol production are concentrated on the transformation of sugar step-by-step now,and the reduction step involves the use of molecular hydrogen,which brings about issues such as complex process,long process route,large energy consumption and high cost.In order to solve these problems,this paper puts forward a new idea of furfuralcohol production from catalytic transfer hydrogenation of sugar in one pot with formic acid as hydrogen donor,and builds the green and efficient preparation system of biomass based furfuralcohol,including the screening and characterization of catalyst,the optimization of process conditions,and the exploration of reaction mechanism.The work will promote the efficient utilization of sugar and the green preparation of furfuralcohol.The work of this paper is summarized as follows:Firstly,because the acidity of formic acid will destroy the active site of the bare catalyst and make it inactive,it is necessary to prepare heterogeneous catalysts with stable structure and high activity in the environment of formic acid.Co-N-C-1 catalyst was prepared by using 1,10-phenanthroline monohydrate as N and C precursor,cobalt acetate tetrahydrate as metal precursor and nano MgO as template,and Co-N-C-1 catalyst had good stability in the environment of formic acid.A catalytic system for Co-N-C-1 catalyzed transfer hydrogenation of furfural to furfuryl alcohol with formic acid as hydrogen donor was established.The results showed that Co-N-C-1-700(calcined at 700?)had the highest catalytic activity.It was speculated that the structure of Co-N-C-1 was the cobalt encapsulated by nitrogen-doped carbon layers through characterization.Combined with the reaction results,the encapsulated structure could not only inhibit the generation of by-products,but also prevent the loss of cobalt effectively under acidic conditions.The optimization experiment showed that the full furfural conversion and>99%furfuryl alcohol yield could be obtained at 150? for 6h.Secondly,although a high yield of furfuryl alcohol can be obtained from furfural,direct preparation of furfuryl alcohol from sugar is more attractive.Considering that formic acid can be used as both an acid catalyst for the dehydration of sugar and hydrogen donor for the transfer hydrogenation,the method of preparing furfuryl alcohol from xylose in one pot with formic acid as hydrogen donor was studied on the basis of the catalytic system of furfuryl alcohol preparation from furfural above.The results showed that the activity of Co-N-C-1 catalyst was superior to other Ni,Fe,Cu-N-C-1 and commercial Pd,Pt and Ru based catalysts,and could effectively catalyze the one-pot synthesis of furfuryl alcohol from xylose.The optimization experiment showed that when the water content of the solvent was 22%and the amount of formic acid was 20 times of xylose,the yield of furfuryl alcohol was 70.8%at 160? for 4 h.Combined with process optimization and reaction kinetics,it was speculated that coupling xylose dehydration and furfural transfer hydrogenation could promote the transformation of xylose and the generation of furfuryl alcohol.The feasibility of preparing furfuryl alcohol from xylan was studied,and the yield of furfuryl alcohol and furfural were 44.8%and 11.7%,respectively.Thirdly,the ordered mesoporous nitrogen-doped carbon Co catalyst(Co-N-C-2)was prepared by changing the template agent on the basis of Co-N-C-1 catalyst,and the method and mechanism for transfer hydrogenation of 5-hydroxymethylfurfural to 2,5-furandimethanol catalyzed by Co-N-C-2 with formic acid as hydrogen donor were studied.The results showed,that the catalytic activity of Co-N-C-1-A was better than that of other common Co based catalysts and commercial precious metals such as Pd,Pt and Ru based catalysts,and Co-N-C-1-A can effectively catalyze the transfer hydrogenation of 5-hydroxymethylfurfural to 2,5-furandimethanol.Combined with the characterization of the catalyst and reaction results,it was clarified that the active site of Co-N-C-2-A catalyst was Co-Nx rather than bare Co.A series of controlled experiments,including deuterium labelling experiment,NMR analysis,in situ Drifts and substrate adsorption over the catalyst,were employed for proposing a possible reaction mechanism:formic acid dehydrogenation could be rate-limiting for catalytic transfer hydrogenation of 5-hydroxymethylfurfural,in which hydrogen was transferred directionally from formate to the a-carbon of carbonyl group.Co-N-C-2-A catalyst had a good stability and could be reused in this system.Fourthly,although 2,5-furandimethanol can be prepared from 5-hydroxymethylfurfural,the chemical properties of 5-hydroxymethylfurfural are active and the storage conditions are strict and the price is high.And direct preparation of 2,5-furandimethanol from sugar can simplify the process and reduce the cost.Therefore,a one-pot process for the preparation of 2,5-furandimethanol from fructose with formic acid as hydrogen donor was studied on the basis of the above catalytic system for the preparation of 2,5-furandimethanol from 5-hydroxymethylfurfural.The results showed that the catalytic activity of Co-N-C-2 was better than that of other single metal or bimetal Ni,Fe,Cu-N-C-2 catalysts.The optimization experiment showed that when the water content of the solvent was 30%and the amount of formic acid was 15 times of fructose,the yield of 2,5-furandimethanol was 60.2%at 170? for 3 h.Co-N-C-2-A catalyst had a good stability and could be reused in this system.Finally,considering the high price of fructose,the industrial application of the above methods is limited to a certain extent.Compared with fructose,glucose is abundant and cheap,but now,there is rarely report about the direct preparation of 2,5-furandimethanol from glucose in one pot.Based on the above synthesis of 2,5-furandimethanol from fructose,a method of synthesis of 2,5-furandimethanol from glucose in one pot with formic acid as hydrogen donor and metal chloride and Co-N-C-2 as catalysts was proposed.The results showed that different metal chlorides have different catalytic activities for the preparation of 5-hydroxymethylfurfural from glucose,and NiCl2 was selected for further study.The optimization experiment showed that when the amount of formic acid was 20 times of glucose,the yield of 2,5-furandimethanol was 59.9%at 160? for 4 h.The high fructose corn syrup can also be directly converted into 2,5-furandimethanol,and the yield of 2,5-furandimethanol can reach around 50%-60%.Using disaccharide and glucan as raw materials,2,5-furandimethanol can also be prepared directly. |
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