Patent GB-581366-A (GB)
Title: Method for the recovery of reagents in the cuprammonium process used in the manufacture of fibres and filaments
IPC: C01G3/14
Filed: 1943-05-22
Abstract: <PICT:0581366/IV/1> In the cuprammonium process for the production of regenerated cellulose fibres, films &c., wherein the materials are formed from a cuprammonium cellulose solution containing sodium sulphate in a sodium hydroxide setting bath, and successively washed with water, the reagents employed are recovered by mixing the initial water wash liquor with spent setting bath, heating the mixture to dispel ammonia and to form copper oxide, separating the copper oxide from the solution of sodium hydroxide and using the latter solution for the preparation of fresh setting bath, and mixing the separated copper oxide with the sulphuric acid wash liquor in order to convert the oxide to copper sulphate without leaving an appreciable excess of sulphuric acid in the solution, the copper sulphate being recovered as such or converted to copper tetramminosulphate.  The cuprammonium cellulose spinning solution is extruded from a spinnerette 1 into a setting bath 2 containing a solution of sodium hydroxide.  The setting bath is constantly replenished from constant-level tank 3 whilst spent spinning bath constantly overflows into tank 5.  The regenerated cellulose product passes over rollers 6 and between press-rolls 7 where a considerable part of the adhering liquid is removed and collected in tank 5.  It is then given a warm or hot water wash on drum 8, the wash water being collected in tray 9 and mixed with the spent setting bath in tank 5.  Ammonia escaping from the spinning and water-wash areas is removed and collected by exhaust system 4. The mixed spent setting bath and waste water wash liquor containing copper hydroxide, copper ammino complex, dissolved ammonia, sodium sulphate, sodium hydroxide and hemicelluloses, is passed through heat exchangers 10 and 16 to the multiple effect evaporator 12, where ammonia and water vapour are driven-off, condensed in 13 and concentrated, if desired, in still 14 and ammonia-tower 15.  Copper hydroxide is converted to copper oxide which leaves the evaporator along with sodium hydroxide, sodium sulphate, and copper-cellulose complex in the concentrated liquor. The liquor passes through heat-exchanger 16 to settling tank 17 where the copper oxide sludge containing copper-hemi-cellulose complex is separated and subsequently dehydrated in centrifuge or filter 19. The liquor removed in the filter 19 is mixed in tank 18 with the sodium hydroxide effluent from the settling tank 17. From the tank 18 the liquor is conveyed through heat-exchanger 21 to a chiller 22 and dehydrator 23 where sodium sulphate crystallizes out and is removed. The solution leaving the dehydrator 23 containing sodium sulphate and sodium hydroxide is passed through heat-exchanger 21 to make-up tank 25 where fresh sodium hydroxide is added and the revivified solution is then supplied to the constant-level tank 3.  The prewashed cellulose fibres are treated with dilute sulphuric acid on reel 26, or in the case of cellulose films, on a series of rollers immersed in adjacent troughs.  The amount of sulphuric acid employed should be sufficient to convert all the sodium hydroxide carried over by the cellulose material to sodium sulphate, any ammonia to ammonium sulphate, and copper to copper sulphate, and sufficient to convert the amount of copper removed from the fibres or films prior to the acid-wash to copper sulphate.  Water is also applied to the material on reel 26, and the wash liquor containing sulphuric acid, sodium sulphate, copper sulphate and ammonium sulphate is collected in tray 27 and passed to mixing tank 28. The dehydrated copper oxide containing copper hemicellulose complex obtained in filter 19 is added to tank 28, and hemicellulose is precipitated and removed on filter 29.  Any free acid in the solution leaving tank 28 is neutralized by the addition of sodium hydroxide.  The filtered solution is passed through heat-exchanger 31 to a single or multiple effect evaporator 32, and through a heat exchanger 33.  The concentrated solution containing copper sulphate is then reacted with ammonia and air in tower 37 to produce basic copper sulphate.  The solution is subsequently passed through heat exchanger 33 and down a tower 36 containing metallic copper in the presence of an ascending stream of ammonia and air.  Copper tetrammino-sulphate is formed and may be employed in the preparation of fresh spinning solutions. Alternatively, the copper may be recovered as copper sulphate by omitting the treatment in towers 36 and 37. The cellulose material is given a second water wash on drum 34, the waste wash liquor being passed through heat exchanger 33 and used for the hot water wash on the drum 8.