GB489302A - Improvements in or relating to processes and apparatus for the extraction of cellulosic fibres from vegetable material - Google Patents

Abstract

<PICT:0489302/IV/1> Semi-pulp suitable for paper-making and cardboard is prepared from fibrous vegetable matter such as straw of wheat, barley, rice, rye and other cereals, stalks of flax, cotton or hemp, canes such as sugar cane, Danube cane, or bamboo, grasses such as esparto, sisal, tambuski, tatching, or elephant grass, wood, bagasse or tow by treating it with alkali, e.g. NaOH of 1 per cent or less, at a temperature between 75 and 100 DEG C. and then with chlorine without application of heat and if desired with cooling, the quantities of reagents employed being not more than sufficient to remove a part only of the non-cellulosic constituents. The chlorine reaction is preferably followed with another treatment with very dilute alkali solution, e.g. caustic soda of ,2 per cent or less. The reagents may be prepared by the electrolysis of common salt solution. The chlorine is preferably moist and diluted with air. Straw or stalks cut to a few inches are loaded into hoppers 10 which deliver it to an apparatus 11 comprising screw conveyers working in a V-shaped chamber 14 to feed the straw mixed therein with the desired quantity of alkali to two towers 12. An adjustable deflector controls the amount of material fed to each tower. 3 Parts of 1 per cent caustic soda solution are used for 1 part of straw. The temperature in the tower is 75-100 DEG C. maintained by steam fed in by pipes 24. The material descends by gravity becoming compacted to form a seal as it descends. The interlaced fibres are removed from the bottom by an extractor 27 the speed of which is adjustable to control the reaction time which may be 1-4 hours. The extractor comprises oppositely rotating parallel shafts fitted with interweaving projecting star-shaped members. Fibres and spent liquor are separated by screens 31 and screw conveyers 32, the fibres being washed in the second part of the screening device. The fibres are then flocculated in an opener 43 having spiked rollers, and raised by air blowers 44 to chamber 46 where a plate 48 deflects it into chlorinating tower 47. Moist chlorine mixed with the desired quantity of air is introduced one third of the way down this tower by pipes 49, the descending material acting as a seal to prevent chlorine leakage. About 4-5 parts by weight of chlorine are used to 100 parts of straw. The chlorine-air mixture passes at 1/10 -\ba1/5 lb. per hour per pound of fibrous material. Chlorination takes 1/2 -3 hours, and is immediately followed by immersion in water in tank 60 with stirrers 61 to minimize the effect of the hydrochloric acid formed on the fibres. Thereupon the material is treated in the cold with 5-20 parts by weight of dilute alkali to 1 part of fibrous material washed and sorted to remove knots. Thermometers and inspection windows are provided in the towers. U.S.A. Specification 1,932,904 is referred to. Reference has been directed by the Comptroller to British Specification 415,224, [Group VIII].