Patent GB-815797-A (GB)
Title: Concentrated aqueous thiocyanate solutions and method of obtaining same
IPC: C01C3/20
Filed: 1956-05-16
Abstract: A dilute aqueous acid solution of a thiocyanate is rendered neutral or alkaline, and then concentrated.  Sodium, calcium, strontium, barium, zinc, tin and lead thiocyanates are specified. The aqueous solution may also contain methyl or ethyl alcohol, and iron impurities.  The pH may be increased, by the addition of aqueous sodium, potassium, calcium or ammonium hydroxide, or sodium or potassium carbonate, from 4-6.9 to 7.5-9.  The concentration may be increased from 2-10 per cent to 57-58 per cent.  The concentrating may be effected by heating at atmospheric or reduced pressure, by a batch, semi-continuous, or continuous process.  It may be effected in two stages, solution in the first stage being heated by distillate from the second.  The feed may be controlled by indicating liquid-level controllers, while the discharge may be controlled by a recording density controller.  A finely divided decolorizing agent, e.g. activated carbon, bone black, or natural or activated bleaching clay, preferably together with a finely divided filter aid, e.g. diatomaceous earth, may be added in the pH increasing stage, and after the concentration. Alternatively the solution may be passed through a bed of granular decolorizing agent.  The pH of the concentrated solution may be reduced, e.g. to 6.0-6.5, by the addition of acid, or by passing the solution through a bed of cation-exchange resin.  The reduction of the pH may take place before, after, or simultaneously with, the addition of the decolorising agent. Acids specified are acetic, propionic, butyric, sulphuric, phosphoric, and hydrochloric acids.  Methyl or ethyl alcohol may be removed before the pH increasing stage or between filtration and concentration.  The dilute thiocyanate solution may be a spent spinning solution from the production of polyacrylonitrile fibres, and may be reconcentrated for reuse therein.ALSO:A dilute aqueous acid solution of quanidine thiocyanate or a substituted guanidine thiocyanate is rendered neutral or alkaline, and then concentrated.  The aqueous solution may also contain methyl or ethyl alcohol, and iron impurities.  The pH may be increased, by the addition of aqueous sodium, potassium, calcium or ammonium hydroxide, or sodium or potassium carbonate, from 4-6.9 to 7.5-9.  The concentration may be increased from 2-10 per cent to 57-58 per cent. It may be effected by heating at atmospheric or reduced pressure, by a batch, semi-continuous, or continuous process.  Concentration may be effected in two stages, solution in the first stage being heated by distillate from the second.  The feed may be controlled by indicating liquid-level controllers, while the discharge may be controlled by a recording density controller.  A finely divided decolourizing agent, e.g. activated carbon, bone black, or natural or activated bleaching clay, preferably together with a finely divided filter aid, e.g. diatomaceous earth, may be added in the pH increasing stage, and after the concentration.  Alternatively the solution may be passed through a bed of granular decolourizing agent. The pH of the concentrated solution may be reduced, e.g. to 6.0-6.5, by the addition of acid, or by passing the solution through a bed of a cation exchange resin.  The reduction of the pH may take place before, after, or simultaneously with, the addition of the decolourizing agent.  Acids specified are acetic, propionic, butyric, sulphuric, phosphoric, and hydrochloric acids.  Methyl or ethyl alcohol may be removed before the pH increasing stage or between filtration and concentration.