Improvements in and relating to a process for the production of alkali cellulose

In the manufacture of alkali cellulose by forming a slurry of cellulose in caustic alkali solution, separating the solution from the alkali cellulose so produced, and withdrawing a part of the separated solution, for treatment for the removal of hemi-cellulose, before returning it to the slurry-forming stage, all as described in the parent Specification, the removal of suspended fibres from the withdrawn portion of the solution is facilitated by adding cellulosic fibres to the solution and allowing it to flow through a perforated screen so that a filter bed of fibres is maintained on the screen. The fibres to be added to the solution are preferably also of alkali cellulose. As shown, a container 1 and drum 2, which consists of a wire mesh cylinder, comprise the filtration unit. The solution passes into the container 1 through pipe 12 and thence into the drum 2, which rotates slowly about solid shaft 6 and hollow shaft 7, the fibres being thus deposited as a mat. A doctor blade 13 is placed close to the periphery of the drum and so removes most of the mat as the drum rotates. Between the blade 13 and the shoot 14, by means of which the fibres are removed, there is a slot 15, which may be varied in width by means of an adjustable plate 16. Thus a proportion of the fibres removed by the blade is returned to the container by way of the aperture 15 to be eventually redeposited on the drum. The solution inside the drum, which is substantially free from fibres, passes through the weir 7 to pipe 11 to be treated by dialysis to remove hemi-cellulose before re-use or to be used directly as a xanthate dissolving liquor.