Chemical Synthesis of Xylonic Acid and Its Applications

Author:Ma Ji Liang

Supervisor:sun run cang


Degree Year:2019





As an important renewable biomass resource,lignocellulose can be not only converted into small molecular compounds such as ethanol,ethylene glycol and furfural by chemical or biological methods but also converted into high-value fuels such as gasoline,diesel oil and aviation fuel,which is of great significance to the sustainable development of human society.Xylose is the second most abundant saccharide after glucose in nature,which accounts for a large proportion in lignocellulose.The efficient utilization of xylose is the critical element and prerequisite in achieving the high-value use of lignocellulose.Xylonic acid,an important product which can derive from the selecvtive oxidation of xylose,is widely used in the realms of food,agriculture,medicine and construction,etc.In recent years,the new application of xylonic acid is found unceasingly and the needs of xylonic acid are increasing,resulting in a more and more favorable and expansive marketing prospect of xylonic acid.To date,the methods for the synthesis of xylonic acid include biological and chemical technologies.Compared with the biological method,synthesis of sugar acid by chemical method has attracted much interest for the advantages of easy-controllable reaction,high selectivity of products,low cost and less environmental pollution,etc.In this work,the new application of xylonic acid as well as design and preparation of mild and efficient catalyst for the synthesis of xylonic acid by chemical methods were studied.The obtained results were as follows:1.Nitrogen-doped mesoporous carbon materials(N-MC)derived from xylose and ethylenediamine were prepared by hydrothermal-solvothermal-calcination-etching four-step method.The IrO2@N-MC nanocatalyst was synthesized via impregnation method with N-MC and IrO2,which could catalyze the synthesis of xylonic acid by selective oxidation of xylose.With this approach,the valuable xylonic acid was produced in excellent yields(88.0%)under base-free conditions,and the conversion of xylose reached 99.0%.The catalyst has good stability and recyclability.After 10 cycles of recycling,the morphology and catalytic activity of the catalyst have not changed significantly.Furthermore,the synergistic effect of IrO2 and N-MC on the synthesis of xylonic acid catalyzed by IrO2@N-MC was confirmed by comparative experiments.2.An efficient catalyst system,Au nanoparticles anchored on the inner walls of hollow Al2O3 nanospheres(Au@h-Al2O3),was obtained via a template method,which could catalyze the selective oxidation of xylose into xylonic acid.It was found that Au@h-Al2O3 could efficiently synthesis of xylonic acid from xylose under base-free conditions.The Au@h-Al2O3catalyst could be reused for 10 times and the xylonic acid yield and xylose conversion retained nearly 96.6%and 98.9%of its original values.At the same time,the composition and morphology of the catalyst did not change significantly,indicating that Au@h-Al2O3 had good stability and recyclability.In addition,the DFT theoretical calculation and experimental results confirm that the Al2O3 shell is the preferred adsorption site for xylose,the interface between Au nanoparticles and Al2O3 shell is the dissociation site of O2,and the exposed surface of Au nanoparticles in Au@h-Al2O3 is the active site during the process of Au@h-Al2O3 for the synthesis of xylonic acid from xylose.3.The TiO2@MXene photocatalyst was synthesized with MXene as the Ti source by hydrothermal synthesis method and was used in the synthesis of xylonic acid by photocatalysis.The results showed that the TiO2 obtained by hydrothermal treatment for 8 h was anatase phase.The optimum reaction conditions of photocatalytic oxidation of xylose to xylonic acid over TiO2@MXene catalyst were as follows:the dosage of TiO2@MXene catalyst was 20 mg,the concentration of KOH solution was 80 mmol/L,the reaction temperature was 70 oC,and the reaction time was 1.0 h.Under these conditions,the yield of xylonic acid was 69.9%,and the conversion of xylose was 95.0%.In addition,the conversion of xylose and the yield of xylonic acid can retain nearly 98.4%and 94.2%of its original values after 10 cycles of recycling,indicating that the catalyst has good recyclability.4.The CuO NB@CN composite with multilayer structure was obtained by thermal polymerization between the self-made CuO nanobelts(CuO NB)and melamine.After simple calcination and acid treatment,two-dimensional ultra-thin oxygen-doped CN nanosheets(2D CN)were obtained from CuO NB@CN composite,and was used in the synthesis of xylonic acid by photocatalysis.The results showed that the thickness of 2D CN is about 1.5 nm,and the spatial distribution of HOMO and LUMO orbits of 2D CN is obviously different.The 2D CN photocatalyst can efficiently catalyze for the synthesis of xylonic acid from xylose under alkaline conditions.Meantime,the yield of xylonic acid in the 500-fold magnification experiment was 62.2%.Combining with the advantages of simple preparation process,economic and environmental protection,good stability,low energy consumption and reusability of the catalyst used in the process,the results laid a basis for large-scale industrial production of xylonic acid.5.The novel g-C3Nx photocatalyst(selectively introducing cyano group into the g-C3N4framework)was synthesized from nitrogen-containing compounds(urea,thiourea,melamine,dicyandiamide,etc.)and low melting point chloride salts or chloride salts(aluminium chloride hydrate,ferric chloride,ammonium chloride,magnesium chloride and zinc chloride,etc.),and was used in the synthesis of xylonic acid by photocatalysis.The results showed that the bandgap of the prepared g-C3Nx photocatalyst decreases gradually with the increase of the dosage of low melting point chloride salt or chloride hydrate,which enhances the absorption range of visible light by g-C3Nx.At the same time,the mobility of photogenerated carriers on the surface of g-C3Nx is higher,improving the photocatalytic activity of g-C3Nx.The highest yield of xylonic acid catalyzed by g-C3Nx under alkaline conditions was 64.3%.After 10cycles,the catalytic activity of g-C3Nx did not decrease significantly.In addition,the yield of xylonic acid in 500-fold magnification experiment reached 64.0%,which was very close to the milligram-level production level.Considering the overall economy and environmental protection of the reaction system,this process has the potential of magnifying applications.6.Based on the good acidity and cohesiveness of xylonic acid,it was used in the catalytic synthesis of three-component reaction.The results showed that Biginelli reaction was catalyzed by xylonic acid and carried out under mild conditions.Under optimum conditions,xylonic acid can efficiently catalyze the Biginelli reaction between aldehydes,α,β-carbonyl compounds and urea or thiourea,and the yields could be up to 23.0-93.0%.In this reaction system,xylonic acid also plays the role of“green”solvent.Furthermore,xylonic acid was also used in the synthesis of 5-phenyl-1(4-methoxyphenyl)-3[(4-methoxyphenyl)-amino]-1H-pyrrol-2(5H)-one and 12-phenyl-9,9-dimethyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one with excellent yields of78.0%and 89.0%,respectively,indicating that xylonic acid has general applicability in the synthesis of three-component reaction.