Study On The Catalytic Conversion Of Mannose And Its Ketose Isomer Into 5-Hydroxymethylfurfural

In the background of global shortage of fossil fuels,converting renewable biomass into fine chemicals and fuels is significant to support the sustainable development.5-Hydroxymethylfurfural?5-HMF?is a bio-based platform compound with a broad of application prospects in many fields such as fine chemicals,transportation fuels,pharmaceuticals and polymer materials.The production of 5-HMF from biomass has received much attention.The main component of biomass is lignocellulose,which is mainly composed of cellulose,hemicellulose and lignin.At present,although many advances have been made in the conversion of fructose,glucose and their corresponding polysaccharides into 5-HMF,there are only limited reports on the conversion of hemicellulose into 5-HMF.The development of conversion technology for hexoses of hemicellulose will be of great importance to the application of hemicellulose and even natural lignocellulose.Mannose is a major hexose unit in hemicellulose,but less reports have been reported on the conversion of mannose into 5-HMF.In this paper,metal chloride,inorganic acid,metal chloride-mineral acid and supported metal MCM-41 were used as catalysts,and some reaction parameters such as catalyst type,catalyst dosage,water content in the system,feedstock dosage,reaction temperature and reaction time was investigated in detail.The mechanism on the conversion of mannose and its ketose isomer into5-HMF was investigated,which provided important information for the efficient conversion and utilization of mannose.The main research contents are as follows:The dehydration of mannose into 5-HMF was investigated by using a series of metal salts and inorganic acids as catalysts and DMSO as the solvent.It was found that AlCl₃·6H₂O exhibited a superior catalytic activity among the tested catalysts.Mannose could be effectively converted into 5-HMF with a yield of 52%and 84%mannose conversion at 130°C for 30 min.Information on the reaction mechanism was elucidated by using the model compound for comparative control experiments.The dehydration of fructose to 5-HMF was investigated in DMSO by using a series of metal salts as the catalyst and P₂O₅ as the co-catalyst.It was found that the mixture of P₂O₅/metal salt could effectively catalyze fructose into5-HMF at lower temperature?80°C?.For example,taking P₂O₅ and NiCl₂·6H₂O as catalysts,a fructose conversion of 88%was achieved with a 5-HMF yield and selectivity of 75%and 85%at 80°C for 30 min.In this paper,the catalytic conversion of sugar into 5-HMF was also investigated with heterogeneous catalysts in detail.Firstly,a mesoporous molecular sieve,MCM-41,was synthesized by hydrothermal reaction.The MCM-41 catalysts supported Cr,Al,and Sn were prepared by the impregnation method.The structures and physicochemical properties of the as-synthesized catalyst were characterized by X-ray diffraction?XRD?,Fourier Transform Infrared Spectrometer?FT—IR?,Transmission electron microscope—Energy dispersive X-ray spectroscopy?TEM—EDX?,N₂ adsorption and desorption,Ammonia temperature-programmed desorption?NH₃—TPD?,Pyridine adsorption Transform Infrared Spectrometer?Py—FTIR?,X-ray photoelectron spectroscopy?XPS?and X-ray fluorescence?XRF?spectrometer.The above MCM-41 supported metal materials were used as the catalyst for the conversion of mannose into 5-HMF.It was found that the tin-supported catalyst Sn/MCM-41 exhibited a superior catalytic activity to Cr/MCM-41 and Al/MCM-41.When using Sn/MCM-41 as the catalyst,mannose could be effectively converted into 5-HMF with a yield of 45%and 88%conversion in DMSO solvent at 150°C for 60 min.The Sn/MCM-41 catalyst could still maintain a good catalytic activity after 8 times reuse test.