V And Nb Oxide For The Selective Oxidation Of Glyoxal Into Glyoxalic Acid

Glyoxylic acid is potentially a using material for the synthetic of many valuablefine chemical, especially in perfumery, cosmetic, food, pharmaceutical andagrochemical industries. At the industrial level, glyxylic acid is currently by nitricacid oxidation of glyoxal. However, this method leads to much oxalic acid andseriously environmental pollution from NOx. In this study, we choose vanadium oxideand niobium oxide to oxidize selectively glyoxal into glyoxylic acid, what canimprove the existing problems in industries.Firstly, the sorts of catalyst, catalyst quantity was investigated on theperformance for the oxidation of glyoxal in peroxide method. The results showed thatV2O5or Nb2O5exhibited high selectivity of glyoxylic acid. And NaNO2was found tobe the highest catalytic performance what may be because homogeneous catalysis isbetter than heterogeneous catalysis. As the catalyst and material ratio was1g NaNO2and1g Nb2O5per100ml glyoxal(30wt.%), after reaction for2h, the conversion ofglyoxal and the selectivity of glyoxylic acid were53%and42%.Then, the effect of catalyst and reaction conditions on the performance for theoxidation of glyoxal in nitric acid method were studied including catalyst category,quantity, mixed-oxide ratio, reaction and temperature and so on. As a result, Nb2O5catalyst exhibited high catalytic activity of glyoxal oxidation. Under optionalconditions of synthesis: m(Nb2O5):V(glyoxal,wt20.%)=1g:100ml, nitric acid(60wt.%)dose20ml reaction temperature318K, reaction time2h, the conversion of glyoxal andselectivity of glyoxylic acid were83%and78%.On that basis, the Nb2O5/SiO2catalysts were prepared by different method andthe influence of preparation and reaction conditions, such as Nb2O5content,calcinations temperature and time, catalyst quantity on the performance for theoxidation of glyoxal has been investigated. The results of BET, XRD, TEM and EDSshowed that the conversion of glyoxal and selectivity of glyoxylic acid increased withthe increase of Nb2O5content(w(Nb2O5)≤18wt.%),meanwhile Nb2O5particles weredispersed on the carrier and most of Nb2O5are attached to the surface of carrier. The conversion of glyoxal and yield of glyoxylic acid decreased when Nb2O5content>18wt%, and the main reason was that Nb2O5particles gathered on thesurface of SiO2and the active surface area of the catalyst decreased. With increasingcalcinations temperature and time, the crystallite of Nb2O5increased with the increaseof calcinations temperature and time. The optimal Nb2O5content was18wt.%,calcinations temperature was993K and calcinations time was2h, the conversion ofglyoxal was85%and the selectivity of glyoxylic acid was87%after2h reaction at318K. The conversion of glyoxal and selectivity of glyoxylic acid were reduced by9%and11%respectively after Nb2O5/SiO2catalyst ran three times. The EDS energyspectrum of fresh and used catalysts showed that Nb2O5losses was responsible fordeactivation of catalyst.In conclusion, Nb2O5/SiO2catalyst is considered appropriate in oxidation ofglyoxal to glyoxylic acid.