Study On Synthesis Of Glyoxylic Acid By Extraction Oxidation Of Gyloxal With H₂O₂

Glyoxylic acid?GA?is the simplest ketonic acid and is an important organic synthesis intermediate.Method for industrial production of glyoxylic acid are oxidation glyoxal by nitric acid,electrolytic reduction of oxalic acid and the ozone oxidation of maleic anhydride,these above methods have bad production security,environmental pollution and other issues.The synthesis of glyoxylic acid by oxidation extraction of glyoxal with H2O2 is proposed in this study in order to solve the problems in the industrial production of glyoxalic acid.First of all,the reaction properties of synthesis of glyoxylic acid by oxidation of glyoxal with H2O2 were studied,the effects of glyoxal concentration,oxidation atmosphere and reaction time on the conversion rate of glyoxal and the selectivity of glyoxylic acid were investigated.The results showed that in the absence of N₂,the conversion rate of glyoxal was slightly higher,but the selectivity of glyoxylic acid was significantly improved under N2 protection conditions.With the increase of reaction time,the conversion rate of glyoxal increased,but the selectivity of glyoxylic acid first decreased and then increased.The influence of the glyoxal concentration showed that there presence a suitable concentration.That is,when glyoxal concentration is 30%,the selectivity of glyoxylic acid is the highest,and the conversion rate of glyoxal is high too.Second,by adding trioctylamine extractant to the reaction system,the effect of extraction conditions on the reaction was studied,and the effects of extraction agent,extractant concentration,and diluent on the extraction reaction were examined.The results showed that the partition coefficient of glyoxylic acid in trioctylamine extractant with n-octanol as diluent was higher than that of raw materials glyoxal and by-products oxalic acid,formic acid and glycollic acid.When the reaction time is 180 minutes,the conversion and selectivity of the reaction were increased from 75.37%and 56.07%to79.61%and 67.52%,respectively.When the concentration of extractant was increased,the conversion of glyoxal and the selectivity of glyoxylic acid first increased and then decreased.When the volume ratio of trioctylamine to n-octanol was 1:1.5,the conversion of glyoxal and the selectivity of glyoxylic acid reached the highest which was 87.05%and 71.21%,respectively.Different diluents have different effects on the extraction reaction.The effect of the diluent on the conversion and selectivity is from high to low:n-octanol>methyl isobutyl ketone>carbon tetrachloride>n-hexane.Finally,the glyoxylic acid in the extraction phase was washed,stripped and purified,and the appropriate conditions for reverse extraction and purification were:The reaction solution obtained by the experiment was washed with 25wt%glyoxylic acid solution and then stripped with water,and the stripped solution was concentrated to obtain 75wt%glyoxylic acid concentrate.Then add it to the crystallizer,add 0.01wt%seed crystal at5°C,under the stirring speed of 100r/min,the cooling rate is 5°C/h,the end temperature of cooling is-5°C,heat preservation for 2h,filtration with nitrogen,and vacuum drying at 20°C for 10h,solid glyoxylic acid with a purity of 98 wt%or more can be obtained.From this,it was concluded that by adding extraction agent to oxidation of glyoxal with H₂O₂ to glyoxylic acid reaction system,the glyoxylic acid produced by the reaction rapidly enters into the organic phase,it not only can improve the conversion rate of glyoxal,but also can increase the selectivity of glyoxalic acid,and has important significance for improving traditional method of glyoxylic acid by means of oxidation glyoxal with nitric acid.