GB766359A - Improved process for the regeneration of coagulation baths and/or secondary baths containing sulphuric acid and used for spinning viscose - Google Patents

Abstract

766,359. Sodium bisulphate; regenerating sulphuric acid. NAAMLOOZE VENNOOTSCHAF ONDERZOEKINGSINSTITUUT RESEARCH. May 4, 1954 [June 8, 1953], No. 12999/54. Class 1(2) In the regeneration of coagulation and/or secondary baths having a sulphuric acid content of at least 40 per cent and a sodium sulphate content of maximum 4 per cent; which have been used for the manufacture of high strength products from viscose, such as threads, fibres, films, foils, or bands, wherein the baths are concentrated to obtain a solution containing at least 60 per cent, e.g. 75-80 per cent sulphuric acid and maximum 6 per cent of sodium sulphate, and the concentrated solution is cooled to less than 45‹C., e.g.-10 to 45‹C, preferably less than 20‹C., to precipitate the primary salt mass (Na 2 SO 4 3H 2 - SO 4 TH 2 O), the separated primary salt is treated in such a manner that sodium bisulphate is formed and is separated from the aqueous liquid, which has a composition making it suitable to be used for the preparation and/or correction of coagulation and/or secondary baths. The primary salt may be treated as follows: (1) the primary salt is dissolved at elevated temperature in a limited quantity, usually 35 per cent, of water and the solution is cooled, when NaHSO 4 H 2 O and/or NaHSO 4 crystallizes out, and is separated from the remaining liquid, which, after evaporation, has a low ratio of salt to acid and can be used as coagulation or secondary bath, or as a correction for such baths (2), the primary salt is heated to 90-100 ‹C. and is converted into crystalline NaHS0 4 and a solution containing 70 per cent H 2 SO 4 , which are separated at the heating temperature. The hot liquor can be supplied to the deposition apparatus for primary salt to remove any Na 2 SO 4 still present therein (3), the primary salt is contacted at a maximum 40‹C. with an aqueous liquid containing Na 2 SO 4 and not more than 63 per cent H 2 SO 4 , such as a coagulating or secondary bath, so that the primary salt is converted to crystalline NaHS0 4 , which is separated from the mother liquor. Preferably, the aqueous liquid is passed through the primary salt mass at 15-20‹C.