Patent GB-646111-A (GB)
Title: Process for producing anhydrous sodium sulphate from glauber's salt
IPC: C01D5/18
Filed: 1948-07-02
Abstract: Anhydrous sodium sulphate is produced from Glauber's salt (Na2SO4.10H2O) by drawing the Glauber's salt through a stream of saturated sodium sulphate solution moving in a direction opposite to that in which the Glauber's salt is drawn, the Glauber's salt being drawn first through a zone of solution of gradually increasing temperature, the maximum temperature of which is the transition temperature of Glauber's salt, i.e. 32.5 DEG  C. and then into a heated zone maintained above 32.5 DEG  C., wherein the Glauber's salt is decomposed into anhy <PICT:0646111/III/1> <PICT:0646111/III/2> <PICT:0646111/III/3> <PICT:0646111/III/4> <PICT:0646111/III/5> drous sodium sulphate and saturated sodium sulphate solution; this saturated sodium sulphate solution moving towards the coolant zone of the solution and thereby forming said stream.  The process is particularly applicable to the recovery and purification of chemicals from viscose rayon spinning baths.  In Fig. 1, Glauber's salt 1 is fed from a hopper 2 into a zone A, B of a jacketted tank 3 and is drawn from left to right by means of scrapers 4 oscillated as shown and finally into a heated zone of solution B, C wherein it is decomposed into anhydrous sodium sulphate 8 which is stirred by a stirrer 16 to effect washing and saturated sodium sulphate solution which flows from right to left and finally through pipe 17 to waste. Zone A, B is cooled by water flowing through an inlet pipe 10, a baffled jacket 9 and an outlet pipe 11 and zone B, C is heated by steam pipes 13, the cooling and heating being such that the temperature at B is 32.5 DEG  C. and at A is 12-14 DEG  C.  In Fig. 3 the zone B, C of the tank is shaped so that the crystals are drained before being introduced into a heated decomposition chamber 20, the crystals in zone B, C being agitated by scrapers 18 oscillated as shown.  The saturated sodium sulphate solution formed in container 20 is fed back into the tank 3 via a channel 23.  In Fig. 4 the tank is formed by a series of intercommunicating tanks 24, the Glauber's salt being propelled by a series of rotating paddles 25.  In Fig. 6 the saturated sodium sulphate flows beyond the point where the Glauber's salt is introduced (which may be where the solution is at 20 DEG C.), whereby Glauber's salt crystals are deposited which are moved by scrapers 29 in the same direction as the solution and deposited in a container 30.  Fig. 7 shows apparatus for the recovery of anhydrous sodium sulphate from viscose rayon spinning baths. Spinning bath liquor at 40-50 DEG  C. is fed via a pipe 33 into a jacketted tank 34, wherein it is cooled so that Glauber's salt (35) is deposited which is drawn up at weir 38, the temperature of which may be 12-14 DEG  C. and which is provided with perforations so that the mother liquor drains away down pipe 44 and may, after adjustment of its composition, be returned to the spinning bath. The crystals are drawn from the top of the weir into a counter-current flow of sodium sulphate solution.  U.S.A. Specification 2,374,004 and Canadian Specification 314,908 is referred to.