Patent GB-675193-A (GB)
Title: Improvements in and relating to the treatment of sodium sulphite
Inventor: MILNER DAVID WILLIAM
IPC: C01D7/02
Filed: 1948-12-06
Abstract: Relates to the conversion, into sodium bicarbonate or carbonate, of sodium sulphite obtained especially in the manufacture of phenols by the fusion of alkali metal salts of sulphonic acids with sodium hydroxide.  The bicarbonate is converted to the carbonate, and causticized to regenerate sodium hydroxide for re-use in the process. In the conversion process, a "residual solution" containing ammonium and sodium sulphites and bicarbonates, and a "residue" consisting of a mixture of sodium sulphite and sodium and ammonium bisulphites are obtained. Some or all of the "residual solution" or "residue" may be used to neutralize the aromatic sulphonic acid, and when ammonium ions are present, the ammonia may be released by heating the solution with a sodium base.  Alternatively, the aromatic sulphonic acid may be neutralized wholly with ammonium bisulphite produced in the process, and the ammonia liberated as above.ALSO:Sodium sulphite, especially as obtained in the manufacture of phenols by the fusion of the alkali metal salts of aromatic sulphonic acids with sodium hydroxide, is reacted in the presence of water with ammonium carbonate, bicarbonate, or carbamate or with ammonia and carbon dioxide under atmospheric or superatmospheric pressure, e.g. 55 p.s.i., absolute and say at 25-40 DEG C to produce sodium carbonate or, preferably, bicarbonate, and ammonium sulphite.  Preferably, ammonium bicarbonate solution is passed through the solid sulphite to yield solid sodium bicarbonate.  The residual solution obtained contains ammonium and sodium sulphites and bicarbonates, and is boiled evolving ammonia, and yielding a "residue" consisting of a mixture of sodium sulphite and sodium and ammonium bisulphites, part or all being in aqueous solution.  When the residual solution contains a large excess of ammonium bisulphite, this can be reduced by adding ammonia, and cooling to crysallize ammonium sulphite.  This may however be avoided by a suitable choice of the reactants; alternatively, sodium sulphite may be added to the residual solution. Ammonia and carbon dioxide are evolved on heating.  The "residue" is treated by the following alternative methods:-(i) anhydrous sodium sulphite is crystallized out above 64 DEG C, leaving a mother liquor containing sodium and ammonium bisulphites; (ii) ammonium disodium hydrogen sulphite is crystallized below 64 DEG C, yielding as mother liquor of sodium bisulphite.  The double salt is fused to separate sodium sulphite leaving a solution of ammonium bisulphites; (iii) the "residue" may be distilled to dryness and the residual material heated at 150-170 DEG C in steam giving a distillate solution of ammonium bisulphite and sulphur dioxide and a residue of sodium sulphite.  Ammonium sulphite and bisulphite produced by the above processes may be heated with ammonium or sodium bisulphate solution, sulphur dioxide being evolved, and on further heating, ammonium or sodium bisulphate as the case may be, being produced.  Alternatively ammonium sulphite may be oxidized with air to produce the sulphate. When some or all of the sulphite in the "residual solution" or "residue" is used to neutralize the aromatic sulphonic acid, and ammonium ions are present, the ammonia may be released by heating the solution with a sodium base.  Alternatively, the aromatic sulphonic acid may be neutralized entirely by the ammonium bisulphite or by the aqueous distillate obtained by heating the "residue" in steam. The ammonia is then recovered as above.