GB691756A - Improvements in and relating to continuous xanthation of alkali cellulose - Google Patents

Abstract

<PICT:0691756/IV (a)/1> In a continuous process for xanthating alkali cellulose, an alkali p cellulose crumb is passed continuously through a vacuum zone in which the crumb is de-aerated and then through a xanthation zone in which the crumb is forwarded and agitated in the presence of carbon bisulphide vapour, vapour seals being provided to prevent transfer of gas or vapour into and out of both zones with the crumb. As shown, alkali cellulose crumb is fed continuously by screw-conveyer 11 into a vacuum chamber 21 wherein air is removed, and then into an inclined rotating drum 29 along which the crumb is tumbled and into which carbon bisulphide is fed from tank 31 at a rate controlled by valve 35. Pairs of rotating bell valves 14, 15 and 23, 24 constitute vapour-sealing means. Drum 29, which is heated by fluid jacket 40, is previously evacuated so that liquid carbon bisulphide is immediately vaporized on entry. The length and speed of the drum and the rate of feed of the crumb and carbon bisulphide are so controlled that when the crumb reaches the drum outlet 66 it is completely xanthated and no excess of carbon bisulphide remains. The xanthate is withdrawn at 66 and compacted in 67 by piston 68, the hard compacted mass forming a vapour seal for the drum outlet. The following modifications are mentioned: the countercurrent flow of carbon bisulphide vapour; a more positive control of the rate of flow of the crumb through the drum by the provision of an internal screw-feed device or of helical vanes on the drum wall; automatic means to control valve 35 when the crumb feed is interrupted; and the provision of a scraper blade to prevent adhesion of material to the drum.