Patent GB-734304-A (GB)
Title: Improvements in xanthation of cellulose
IPC: D01F2/08
Filed: 1952-12-29
Abstract: <PICT:0734304/IV (a)/1> <PICT:0734304/IV (a)/2> In the production of viscose by a process wherein a continuously moving web of cellulose pulp is treated with caustic liquor to form alkali cellulose, the thus treated web of alkali cellulose is passed into a sealed chamber and uniformly impregnated therein with carbon bisulphide to form cellulose xanthate, and the cellulose xanthate is discharged from the sealed chamber for conversion into viscose.  The web may be a single web or a number of superposed webs of dry cellulose pulp which, after the treatment with caustic liquor to form alkali cellulose, are treated with either gaseous or liquid carbon bisulphide.  As shown in Fig. 1, the continuously moving web of cellulose pulp 3, comprising two superposed sheets 4 and 5, is passed over a rotatable perforated drum 1 having a vacuum section 2.  Caustic liquor is sprayed on to the web from the supply pipes 6 and the liquor flows through the web in the relative volume indicated by the shaded area within the curve 9.  The impregnated web passes between the drum 1 and the press roller 10, which has a vacuum section 8 embracing the area of contact.  The web passes between the soft rubber sealing rollers 12 and 14 and into the sealed chamber B in a substantially unaged state. The bearings which support the roller shafts are enclosed within the chamber, and arcuate plates 16, 17 bear against the rollers and seal them to the wall of the chamber.  The web may optionally be slit into a number of strips by the rotary shears 11 comprising two rollers each having a number of circular shear blades.  The two contacting sheets of the web then pass over the spacing bar 18, which separates them and holds them apart so that liquid carbon bisulphide may be sprayed against their inner opposing faces through the perforated pipe 19.  The web is supported by a number of freely rotatable rollers 22 of non-corrodible material. Shortly after passing the pipe 19 the two sheets of the web come together again and are in contact by the time they pass through the soft rubber sealing rolls 23, 24. The web enters chamber C and passes between the upper and lower vacuum chambers 25 and 26 which have perforated plates on shoes bearing against the upper and lower surfaces of the web, through which the excess carbon bisulphide is removed.  The web then passes between the soft rubber sealing rollers 27, 28, over a guide roller 29 and a number of upper and lower guide rollers 30, 31 (which may be freely rotatable or power driven) in the chamber D, in which the formation of the web into folds delays its passage through the chamber sufficiently to complete the xanthation reaction.  The web finally passes over the guide roller 32 and between the soft rubber sealing rollers 33, 34 into a chamber (not shown) for conversion into viscose.  The web in chamber D may be heated by infra-red heaters 35, or by electrical resistance heaters or steam coils.  The chambers B, C and D may be connected to an exhauster (not shown) by the pipes 37, 38 and maintained at a slightly sub-atmospheric pressure to minimize the escape of carbon bisulphide.  The chambers B and C may be substituted by a single chamber, for example as shown in Fig. 3, in which the two-ply web 3 of alkali cellulose travels through a single chamber B, C provided with sealing rollers 40 ... 43 and is temporarily separated into two sheets and sprayed with carbon bisulphide as in Fig. 1.  In this example, however, the web is supported by the endless travelling belt screen 44 while passing between the vacuum members or suction boxes 46, 47.  The web may then be slit into strips by passing through the rotary shears 45.  In a similar apparatus (Fig. 4, not shown) the two sheets of the web are not separated and the upper surface of the web only is sprayed with carbon bisulphide just in advance of the vacuum member.  In an alternative form of reaction chamber (Fig. 5, not shown) the carbon bisulphide impregnated web passes in a straight path between a series of electronic heating devices, the lower plates of which support the belt.  U.S.A. Specifications 2,542,285 and 2,614,102 are referred to.