Studies On The Oxidation Of Glyoxal To Glyoxylic Acid By Oxygen Over Vanadium Oxide Catalyst

Glyoxalic acid is an important fine chemical product. Its molecule contains aldehyde group and carboxy group, and it is widely used for synthetic spices, medicine, pesticides, etc. The oxidation of glyoxal is one of the important ways of synthesizing glyoxalic acid. In this paper, vanadium oxide catalysts supported on different carries were prepared by incipient wetness impregnation method, and the precursor was obtained from oxalic acid aqueous solutions of NH4VO3. This catalyst was applied for the liquid phase oxidation of glyoxal to glyoxylic acid. The results showed that Vanadium oxide catalyst exhibited obvious activity for glyoxal oxidation and high selectivity of glyoxylic acid. It proved by ion chromatography that glyoxylic acid could be produced without control of pH value and there was a little oxalic acid from the excessive oxidation of glyoxylic acid. Moreover, vanadium oxide catalysts have the advantages of green chemistry, such as low cost, easily available and no pollution. Therefore, it has the potential for industrial application.Absorbance ratio differential method and ion chromatography were developed for the simultaneous determination of glyoxal and glyoxylic acid: The determinate wavelength of glyoxal is 228.75nm. This method can accurately determinate glyoxal in mixture, but can't accurately determinate glyoxylic acid. Glyoxal does not exist in the form of ion in solution. According to the principle of ion chromatography, it can't be directly examined. But ion chromatography can accurately determinate glyoxylic acid. Both the standard deviation of the detected substances were less than 5%, the linearity are excellent in the certain scope, and the recoveries are ranged between 94% and 107%.Supported vanadium oxide with two different carries have been studied. Under the optimum condition, the conversion of glyoxal was 12.02%, and the yield and selectivity of glyoxylic acid reach to 9.01% and 74.9%, respectively with VOX/SiO2 catalyst applied into the reaction of glyoxal oxidation. In comparison with the VOX/SiO2 catalysts, VOX/SBA-15 catalysts showed higher catalytic performance for glyoxal oxidation to glyoxylic acid. The conversion of glyoxal was 17.28% and the yield of glyoxylic acid was 13.15% after 10h reaction. Furthermore, Catalysts kept favorable stability during its series. Their properties were characterized by XRD, BET and so on. It proved that V2O5 crystalline has been presented for VOX/SiO2 with 3wt% vanadium oxide loading, As for the VOX/SBA-15 catalysts, V2O5 crystalline has not appeared when vanadium oxide content was 10wt%. The XRD and BET pattern shows that the samples have still retained mesoporous structure. From the results of the catalysts characterization and reaction, it is showed that the degree of dispersed VOX species and the number of active component greatly influence the performance of vanadium oxide catalysts. Which also exhibited that SBA-15 have more advantages than other carries, such as larger surface area, the larger pores, and good hydrothermal stability. It is regarded as an excellent catalyst carry.