Patent GB-700693-A (GB)
Title: Method and apparatus for producing viscose
IPC: D01F2/08
Filed: 1951-01-03
Abstract: <PICT:0700693/IV(a)/1> <PICT:0700693/IV(a)/2> <PICT:0700693/IV(a)/3> A process for the continuous production of viscose comprises the steps of steeping and shredding cellulose in an aqueous alkaline solution, pressing the steeped cellulose to form a cake thereof having a pre-determined ratio of alkali cellulose to original dry cellulose, ageing the alkali cellulose cake by passing it through a path in intermittent steps, disintegrating the cake, mixing the disintegrated cake with carbon disulphide and reacting it therewith to form cellulose xanthate, mixing the xanthate with an aqueous alkaline solution to form a slurry, and homogenizing the slurry. Preferably, succeeding portions of the steeped cellulose are pressed and the disintegrated cakes are successively reacted and mixed to provide a continuous stream of viscose.  The cakes may be advanced through a housing during the ageing operation. Conveyers, inclined sideways, or interconnecting conduits may be provided for transferring the cellulosic material from one treatment stage to the next.  As shown in Fig. 1, wood or cotton pulp sheets 2 are removed from table 3 <PICT:0700693/IV(a)/4> <PICT:0700693/IV(a)/5> and placed in tank 4 or 4a.  The required amount of caustic soda solution is supplied from tank 1.  The steeping tank is provided with a wire beater driven by motor 7, and is pivotally mounted to facilitate discharge of the slurry into hopper 11.  Tanks 4 and 4a are operated alternately at predetermined time intervals.  The slurry passes from hopper 11 to the hydraulic press 15.  Conduit 17 is lowered by means of cylinder 18 to form a continuous conduit extending into the top of the press to prevent splashing.  As conduit 17 descends, the cover plate 21 is automatically moved aside but it is replaced in position when conduit 17 is retracted. The slurry is pressed into a cake containing the predetermined ratio of alkali cellulose to dry pulp. The cover plate is then removed and the cake is raised just out of the press cylinder. The plate 21 then moves back and pushes the cake on to a conveyer belt 40 which takes the cake to the base of one of the ageing towers 41, 42, successive cakes being conveyed to alternate towers.  A ram in cylinder 43 pushes the cake from belt 40 on to the platen of the tower charger which is operated by air cylinder 45.  Similarly the following cake is placed at the base of tower 42.  The starting and stopping of the motor 7a which drives the belt 40 is controlled by the cake which closes first a starter switch and then a limit switch, stopping at the alternate positions being determined by a time controller.  As shown in Fig. 5, the top surface of platen 44 is grooved for the reception of the forked gate 49, whereby the cake may be transferred to the gate after being pushed into the tower by platen 44.  As new cakes are pushed into the tower, the cakes already in the tower are gradually advanced towards the top.  As shown in Fig. 6, each tower is provided with a top section 52 which is automatically adjustable in length to compensate for differences in cake thickness or slight changes in ageing times.  The section is moved by rack 53 and pinion 54 on the shaft 55 of a reversible slow speed brake-controlled motor 56.  The direction of rotation of the motor is determined by switch 57 which is actuated by the position of a cake 58.  As a new cake is pushed into the bottom of the tower, an aged cake is pushed out of the top into a position from which it is pushed by the piston of cylinder 60 to the shoot 61. If a thin cake is pushed into the bottom of the tower, the top cake will not come competely out of the top.  The metal bar 65 then rests in contact with the lower contacts 63 and the motor is operated to move section 52 downwardly until the top cake is completely uncovered.  If an abnormally thick cake is pushed into the bottom of the tower, the bar 65 contacts the upper contacts 66 and the motor is operated to move section 52 upwardly to increase the effective length of the tower.  The cakes are conveyed by shoot 61 to a belt 67 (Fig. 1) which discharges each cake on to a scale 70 which records the weight of the cake so that either manually or automatically, the correct charge of carbon disulphide may be added at the xanthation stage.  The cake is then pushed down shoot 72 (Fig. 2) into cake breaker 73.  The broken alkali cellulose falls into hopper 79 and is formed into soft fluffy crumbs in blower 80.  The crumbs pass into air separator 82 and then drop into the top compartment of the CS2 vapour-seal chamber 87.  This chamber is divided into several compartments by dampers 92-95 which may be opened or shut by rack and pinion mechanism.  The alkali cellulose passes from one compartment to the next in succession until it reaches chamber 108, the slide gate 109 being opened to receive it, and then closed.  A following charge of alkali cellulose is then received in chamber 91 to await the next xanthation.  Carbon disulphide is forced through nozzles 113 into chamber 108 and mixed with the alkali cellulose with the aid of the rotary agitator 112.  The mixture is passed into the xanthation tower 184 and when the cellulose xanthate reaches the bottom of the tower, it comes to rest on the belt 185 which is driven intermittently.  The belt has transverse blades to discharge the xanthate evenly across the bottom of the tower.  The xanthate is carried into a weighing hopper 195 (Fig. 11) which has hinged gates 204,205.  Solenoids 212, 213, are energised at predetermined intervals to open the gates and to discharge the xanthate into the mixer 229.  The weight of xanthate in the hopper is indicated on scale 196, the pointer 230a being reset before each weighing to a position corresponding to the desired average weight of the batch. The scale rotor 216 controls a selsyn generator 215 which rotates one way or the other according to the swing of the pointer from the set position to that of a light or heavy batch of xanthate.  Selsyn rotor 217 is similarly rotated to cause up or down movement of probe 218 within the solvent liquid i.e. caustic soda solution in tank 219.  A fixed probe 225 is also situated in tank 219.  The probes are electrically connected to control the supply and discharge valves 224, 227a.  The position of probe 218 thus controls the volume of solvent liquid supplied to each batch of xanthate.  From the mixer 229, the slurry flows through valve 230 and a magnetic separator 234, for removal of ferrous particles, to a roll disintegrator 233 where it is homogenized.  The viscose leaves the disintegrator in a continuous stream.