GB514191A - Process and apparatus for extracting cellulose from wood or other cellulosic material - Google Patents

Abstract

514,191. Refining cellulose materials. THURINGISCHE ZELLWOLLE AKT.-GES. Dec. 23, 1938, No. 37475. Convention date, Dec. 27, 1937. [Class 2 (ii)] Cellulose is extracted from wood or other cellulosic material by treating the material in a plurality of successive stages with dilute caustic alkali lye, or following the alkali treatment with water for washing, at a constant but adjustable pressure but at a temperature which is different at each stage. The water and/or lye flows continuously through successive batches of material undergoing different stages of treatment until the lye has acquired a sufficient concentration of salts, and alkali solution preferably in concentrated form is added between each stage so that the amount of alkali consumed in one stage is replaced before the lye passes to the next stage. The spent lye or the washing water containing sodium salts may be strengthened in alkali not by addition of alkali solution but by caustification, e.g. by treatment with calcium hydroxide. The water or lye passes from material in the finished or nearly finished condition, through material in earlier stages of treatment and finally through the raw material. The lye at each stage of treatment may contain about 20-30 grams per litre of NaOH. Cellulose suitable for viscose and artificial silk manufacture, is obtained by the process. Sulphite cellulose pulp may be further refined by subjecting it to the process described. As shown in Fig. 1, the cellulosic material is treated with alkali lye and water in closed boilers K1-9 provided with heaters V1-9 for the alkali or water which may be passed from one boiler to the next by way of ring pipe B. Alkali lye from supply pipe D may be introduced into the boilers through dosage pumps A. Water is supplied from a container E and pipe C under constant but adjustable pressure. Fig. 2 represents one stage of the process at which the material is being treated with alkali in boilers 5-9 and with water in boilers 3, 4. Boilers 3-9 are connected through valves j, o, p, and pre- 'heaters V (Fig. 1). Water for boiler 3 flows from pipe C and preheater V3, and alkali is added at A to each boiler 5-9, the lye, rich in dissolved salts, flowing from the last boiler 9 through valve m, pipe P, and valve N to a regenerating plant. When the material in boiler 2 is completely boiled and washed it is removed by pipe X. Boiler 1 is filled with raw material. When the density of the lye from boiler 9 falls below a determined value it is not sent to the recovery apparatus but is mixed with alkali through cock W and passed through pipe L and valve r to boiler 1 for treating a fresh batch of material. The quantity of lye removed from boiler 9 is replaced by an equal amount of fresh lye at boiler 5. As shown in Fig. 3, the material in boiler 5 is completely treated with alkali, the supply of which is stopped. When boiler 1 is filled with lye, boiler 5 is' supplied with water, and the lye from boiler 1 is passed to the regenerating device.