GB707422A - Improvements in or relating to the manufacture of viscose - Google Patents

Abstract

In a continuous process for the manufacture of viscose, an automatically metered stream of continuously produced alkali cellulose is delivered to a churn, carbon disulphide is also delivered to the churn at a rate correctly proportioned to the metered supply of alkali cellulose, and alkali cellulose xanthate is continuously withdrawn and fed to a dissolving and blending unit to which caustic soda or caustic potash solution is supplied at a rate appropriate to the rate of supply of the xanthate. As shown (Fig. 1), cellulose, e.g. wood pulp or cotton linters, is continuously fed to a slurry steeping vessel A to which caustic soda solution is continuously fed from tank 12. The slurry is then passed to a press B, where alkali is expressed, collected in make-up tank 22 and recycled to tank 12. The alkali cellulose crumb is then passed in succession through a disintegrator C, a weighing unit D, and a metering unit E to a churn F to which carbon disulphide is also fed. The xanthate is continuously withdrawn from churn F and pass through a dissolving and blending unit G to which caustic soda solution is added, and the viscose is then passed through ripening and de-aerating units H1, H2 and filters I1, I2. The press B (Fig. 2), is provided with a screw 18 and a pressing outlet comprising a pair of tapered spring-loaded jaws 26, 27, discharge of the alkali cellulose being effected by periodically and automatically opening the pivoted bottom jaw 27 in timed relationship with the rotation of the screw 18 through a cam mechanism (not shown). The weighing unit D (Fig. 3) comprises a counterweighted rotary segmental hopper 34. The metering unit E (Fig. 3) comprises a pair of spaced rotary segmental valves 44, 45, which also serve as a vapour sealing device for the churn F. The alkali cellulose is fed to churn F by a reciprocating ram 43 (Fig. 3), and a pump 54 supplies carbon disulphide to the churn through inlet pipe 42. An electric control system ensures automatic sequential operation of the metering unit, the ram motor and the carbon disulphide pump to supply the alkali cellulose and carbon disulphide to the churn continuously in the desired proportionate amounts. The churn F (Fig. 5) <PICT:0707422/IV(a)/1> <PICT:0707422/IV(a)/2> <PICT:0707422/IV(a)/3> <PICT:0707422/IV(a)/4> <PICT:0707422/IV(a)/5> comprises a rotary jacketed barrel 70 which is canted upwardly and provided with an inlet tube 72, the materials proceeding in the direction of the arrows and being withdrawn through apertures 76 into a fixed shroud 69. The dissolving and blending unit 9 (Fig. 6) comprises a preliminary disintegrator and mixer 78, a grinding pump 79 and a second stage mixer embodying a series of U tubes 80 provided with stirrers 110. Caustic soda solution is fed to the vessel 78 (Fig. 1) through a valve controlled inlet 81, at a rate appropriate to the supply of xanthate to the vessel. To ensure adequate maturing of the alkali cellulose, prematured cellolose may be employed as the starting material or hydrogen peroxide may be added to the steeping unit A. Alternatively, a maturing unit, for example as described in Specification 691,253, may be interposed between the disintegrator C and the weighing unit D. Specification 350,515 also is referred to.