The organic base which promotes ammonium sulfite oxidation and which should be finely dispersed throughout the aqueous solution during ammonium sulfite oxidation can be any nitrogenous base which is immiscible with aqueous solutions and weaker than ammonia so as not to cause Ammonium or ammonium sulfite to remove ammonia.
Thus, heterocyclic aromatic, aliphatic, cycloalkane and cycloalkene amines, heavy pyridine bases of the type derived from coal tar, xylidine, toluidine, quinoline, dimethylaniline, methylamine, ethanolamine, cyclohexyl Aniline, pyridine, lutidine, diphenylamine, picoline, collidine, methylethylpyridine and bipyridine and other compounds characteristic of pyridine or containing fused pyridine rings, and their nitrogenous basic derivatives Everything can be used.
Preferably, the solution containing ammonium sulfite to be oxidized to ammonium sulfate is a concentrated solution of ammonium sulfate containing about 10% to 15% ammonium sulfite. When practicable, it is desirable to control the uptake of sulfur dioxide from exhaust gases or the like, thereby forming a solution which will be a concentrated solution of ammonium sulphate containing 10% to 15% ammonium sulphite, and the resultant then immediately according to the invention Oxidize the solution.
According to the invention, the oxidation of dissolved ammonium sulfite is carried out by contacting a solution containing ammonium sulfite in the presence of a nitrogenous base with gaseous oxygen which can be introduced in the form of air or pure oxygen or air having the following form. Rich in oxygen. The best results are obtained if the oxidation is carried out at slightly elevated temperatures, for example at temperatures between 40 and 140°C, preferably between 70 and 90°C, and at pressures between 1 and 11 atmospheres absolute. the result of. Operation within the above temperature and pressure ranges is preferred, however, the invention should not be construed as being limited thereto. Generally, slightly higher pressures in combination with slightly lower temperatures are preferred, in other words, the temperature can be the inverse of the pressure used.