Patent GB-758366-A (GB)
Title: A method and an apparatus for the continuous preparation of nitrocellulose
IPC: C08B17/04
Filed: 1953-10-05
Abstract: Nitrocellulose is produced continuously by charging cellulose material and nitrating acid continuously to a single large enclosed nitrating vessel, continuously conveying and overflowing nitrocellulose and spent nitrating acid into a receptacle, continuously separating from the nitrocellulose the bulk of the spent acid by passing the nitrocellulose and spent acid through a perforated cylinder, continuously and rapidly cooling the separated nitrocellulose and the remaining spent acid by mixing it with a cooled spent acid which has been recovered in the course of the process, separating the acid from the cooled nitrocellulose by means of a continuous centrifugal separator, and subse <PICT:0758366/IV(a)/1> quently quickly drenching the separated nitrocellulose in water. As shown, nitrating acid at 30 DEG  C. and dry tissue paper cut into small pieces are simultaneously and continuously charged through the pipe 5 and hopper 6 into the oval nitrating tank 1.  The end of the pipe 5 encircles the hopper 6 and is provided with an elongated narrow slit so located that the acid falls from the pipe in the form of a thin cylindrical film in such a manner that the stream of paper leaving the hopper is always surrounded by the film of acid falling from the ring-shaped end of the pipe 5 and is immediately submerged in the acid in the nitrating tank 1.  This tank is provided with two vertical agitators comprising shafts 2, 3 provided with a number of blades 4 inclined at an angle of about 30-50 degrees to the horizontal so as to impart a slow downward motion to the contents of the tank.  The cover of the tank is provided with a valved gas outlet pipe 7 and a valved compressed air inlet pipe 8.  The walls of the tank are provided with jackets 10 for the circulation of a temperature-control liquid.  The tank 1 is filled initially with spent nitrating acid recovered during the production of a previous batch of nitrocellulose, and this acid is maintained in the tank at a temperature of about 30 DEG  C. The paper charged into the tank is disintegrated and distributed uniformly in the upper portion of the acid in the tank by the rotation of the agitators and reaches the bottom of the tank in about 30-35 minutes, during which the nitration is almost completed.  The nitrated cellulose and spent nitrating acid are then passed through the tubular structure 11 which, with the tank 1, forms a U-shaped chamber and which consists of three communicating tubes 12, 13, 14 provided with worms 15, 16, 17 throughout their length.  The pitch of each worm is about the same as the diameter of the tube in which it is located, and the diameter of each worm is about 10 mm. smaller than its tube.  The tube 14 is provided with temperature control jackets 18.  The upper portion of the shaft of the worm 17 is surrounded by the concentric hollow shaft 20 which is driven independently of the worm and is provided with blades 21 to assist in pushing the mixture of nitrated cellulose and spent acid from the top of the tube 14 into the inclined acid-separating tube 27, the lower end of which communicates with the upper end of the tube 14.  The upper portion of the tube 14 is provided with a cylindrical screen 22 through which a portion of the spent acid passes and may be returned to the tank 1 through a pipe 23 provided with a control valve 24, by means of which a suitable difference in height between the levels 25 and 26 of the liquid in the tube 14 and tank 1 may be maintained.  The mixture overflows through the aperture 19 at the top of the tube 14 into the lower end of the acid-separating worm conveyor 27 provided with a coaxial cylindrical screen 28, and is passed through the conveyer by means of the worm 29.  About 90-95 per cent of the spent acid passes through the screen 28 and is discharged through the pipe 30. Nitrated cellulose moist with the remaining spent acid is discharged from the upper end of the conveyer 27 into the vertical tube 33, into which there is passed continuously through pipe 31 spent acid cooled to about 10 DEG  C.  The tube 33 is provided with a sight glass 34 and communicates with the larger end of the conical cooling worm conveyer 35.  The cooled acid supplied through the pipe 31 is chiefly the cold spent nitrating acid which has been separated in the conical worm conveyer 35 and cooled by means of refrigerated brine.  The cooler 35 is provided with a worm 36 and a conical screen 37 through which about half the acid present in the mixture passes and is discharged from the cooler through the pipe 38.  The mixture is rapidly cooled to about 20-25 DEG  C. during its passage through the tube 33 and the worm conveyer 35 and it is then passed into the upper end of the vertical worm conveyer 41 provided with a worm 40.  The mixture is continuously discharged by means of this conveyer into a distributor 43 at the top of the bell-shaped or truncated-cone shaped rotor 49 of a continuous centrifugal separator 48.  As soon as the mixture enters the distributer 43 it is discharged therefrom by centrifugal force on to the outer perforated wall 50 of the conical centrifuge basket 65, which is rotated at a speed of about 800 r.p.m.  The spent acid in the mixture is forced through the perforated basket 50 into the casing 39 and runs down into the peripheral gutter 51 from which it is discharged through the pipe 52.  The nitrocellulose layer deposited on the inner surface of the perforated basket 50 is scraped off the surface downwardly by the screw or worm 44 on the rotor 49, which is coaxial with and in closely spaced relationship to the basket 50 and is driven at a speed about 1 per cent higher than that of the basket.  The nitrocellulose falls into the drenching tank 58 half-filled with water and is removed therefrom by means of the worm conveyer 62 provided with a worm 63.  The joint between the casing 39 and the rotating portions of the centrifuge 48 is rendered air-tight by means of a running gland.  On the completion of a run, all the valves of the nitrating tank are closed and dry compressed air is introduced into the nitrator 1 through the pipe 8 while continuing to rotate all the shafts of the apparatus.  By this means all the acid is discharged from the nitrator 1 and the worm conveyer 12 while the nitro-cellulose is removed by the worm conveyer 14.