Process of preparation of glyoxylic acid aqueous solution
The invention relates to a method for preparing an aqueous solution of glyoxylic acid by oxidation of an aqueous solution of glyoxal with oxygen or a gas containing oxygen, in the presence of a catalytic quantity of nitric acid and/or at least one nitrogen oxide, a strong acid not oxidizing glyoxal, and by maintaining conditions satisfying the equation K L a/Q>10, where K L a is the total volumetric mass transfer coefficient and Q is the heat load liberated by the reaction per mole of glyoxal.
1. A process for preparing an aqueous solution of glyoxylic acid by oxidation of an aqueous solution of glyoxal with oxygen or a gas containing oxygen, wherein the oxidation is carried out
in the presence of a catalytic quantity of nitric acid and/or at least one nitrogen oxide, of between 0.005 and 0.1 mole per mole of glyoxal,
in the presence of a strong acid not oxidizing glyoxal, selected from the group consisting of hydrochloric acid, hydrobromic acid, sulfuric acid, sulfonic acids, ion exchange resins of the sulfonic type, perfluorinated resins bearing sulfonic groups or mixtures thereof, and
by maintaining conditions satisfying the equation K L a/Q>10, where K L a is the total volumetric mass transfer coefficient (h −1 ) and Q is the heat load liberated by the reaction (watts/mole of glyoxal).
2. The process according to claim 1 , wherein the catalytic quantity of nitric acid and/or nitrogen oxide is between 0.01 and 0.07 mole per mole of glyoxal.
3. The process according to claim 1 , wherein the catalytic quantity of nitric acid and/or nitrogen oxide is between 0.005 and 0.06 mole per mole of glyoxal.
4. The process according to claim 1 , wherein the nitrogen oxide is selected from the group consisting of the following gases: nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrogen tetroxide (N 2 O 4 ), nitrogen trioxide (N 2 O 3 ) and mixtures thereof.
5. The process according to claim 1 , wherein the nitrogen oxide is selected from the group consisting of metal salts of nitric acid, metal salts of nitrous acid and mixtures thereof.
6. The process according to claim 1 , wherein the quantity of strong acid not oxidizing glyoxal is between 0.05 and 1 mole per mole of glyoxal.
7. The process according to claim 1 , wherein the quantity of strong acid not oxidizing glyoxal is between 0.2 and 0.7 mole per mole of glyoxal.
8. The process according to claim 1 , wherein the strong acid not oxidizing glyoxal is selected from the group consisting of hydrochloric acid, hydrobromic acid, sulphuric acid, p-toluenesulphonic acid and mixtures thereof.
9. The process according to claim 8 , wherein the strong acid not oxidizing glyoxal is hydrochloric acid.
10. The process according to claim 1 , wherein a compound generating a strong acid not oxidizing glyoxal, is used.
11. The process according to claim 1 , wherein K L a is between 100 h −1 and 1000 h −1 .
12. The process according to claim 1 , wherein the oxidation is carried out in an apparatus comprising a reactor with a suction jet mixing nozzle placed internally or externally.
13. The process according to claim 1 , wherein the oxidation is carried out in an apparatus comprising a reactor in a closed circuit with a built-in suction jet mixing nozzle, an external liquid phase flow duct connected to the ejector and a pump.
14. The process according to claim 1 , wherein the oxidation is carried out in an apparatus comprising stirred gas liquid reactors or bubble columns comprising packings.
15. The process according to claim 1 , wherein Q is between 5 and 150 watts/mole of glyoxal.
16. The process according to claim 1 , wherein the ratio of the total volumetric mass transfer coefficient K L a (h −1 ) to the heat load liberated by the reaction Q (watts/mole of glyoxal) is such that 10<K L a/Q≦100.
17. The process according to claim 1 , wherein the oxygen or a gas containing oxygen is introduced under a pressure of between 200 and 3000 kPa.
18. The process according to claim 1 , wherein oxygen is used.
19. The process according to claim 18 , wherein the oxygen consumption is between 0.5 and 1 mole per mole of glyoxal.
20. The process according to claim 1 , that it is carried out at a temperature between ambient temperature and 85° C.
21. The process according to claim 20 , that it is carried out at a temperature between 35° C. and 75° C.
22. The process according to claim 1 , wherein the reaction is carried out for 1 hour to 20 hours.
23. The process according to claim 1 , wherein the reaction is carried out in the presence of nitric acid and a metal salt selected from sodium nitrite, potassium nitrite, sodium nitrate, potassium nitrate, silver nitrate, copper nitrate or mixtures thereof.
24. The process according to claim 1 , wherein the reaction is carried out in the presence of nitric acid and the amount of nitric acid consumed is less than 0.01 mole per mole of glyoxal.