US2274463A - Preparation of alkali cellulose - Google Patents

Description

Patented Feb. 24, 1942 UNITED STATES PATENT OFFICE PREPARATION OF ALKALI CELLULOSE Johann Joseph Stoeckly and Richard Bartunek, Teltow-Seeh'of, Germany, assignors to North American Rayon Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application April 9, 1940, Serial 4 Claims.

'I'his invention relates to improvements in lmethods for preparing alkali cellulose.

It is one of the objects of the invention to produce an alkali cellulose adapted for the manufacture of viscose and from which deleterious varieties of cellulose, for example the hemicellulose and principally beta cellulose are substantially eliminated at the outset so as to insure their absence during the viscose producing operations. To this end the invention contemplates the provision of treatment procedures and steps adapted to achieve the aforesaid purpose and also to permit the production of an alkali cellulose which iurthermore can be properly and thoroughly xanthated.

It is a further object of the invention to provide a method for the aforesaid purposes which is capable of application without requiring extensive alteration of existing equipment as used in the present state of the viscose manufacturing art.. I I The usual method for producing viscose. has

. the drawback that the hemicellulose and especially the so-called beta cellulose is eliminated in a far too inadequate manner and'amount. When an ordinary dip lye is used having a caustic soda content of about 18 per cent it is mainly only In Germany March- 31, 1939 the very easily soluble gamma cellulose which is dissolvedout of the cellulosic raw material durart to soak cellulosic raw material in a caustic soda lye of a concentration lower than that'capable of producing mercerization, to drain it with the aid of pressure, and then to mercerize it in aknown manner by a second dipping procedure. This prior art methodhowever also has the drawbacks of, first, requiring a too prolonged dipping time and a very extensive apparatus layout for the dipping and circulation of the lye, and, seccellulose sheets readily fall apart prior to and during the second dipping.

In accordance with the present invention however it has been found that it is possible to start with ordinary cellulosic raw material containing hemicellulose, say, either sulphite cellulose, spruce cellulose, or even alkali-cooked beechwood cellulose, and to separate out the beta cellulose during ,the production per se of the alkali cellulose Without requiring any appreciable alteration of the apparatus customarily used for producing the latter.

In accordance'with the method of the invention, the cellulose raw or starting material is first treated with a caustic soda lye of definite temperature and of such concentration-as is adapted to exert the greatest possible dissolving action on the beta cellulose. Under such conditions, if the reaction time is adequate, substantially all of the beta cellulose is caused to pass into solution in this dilute dip lye and can be separated out by subsequent draining and pressing. When operations are conducted at ordinary room temperatures of to C., it is preferable not to use the same concentration of caustic soda for all varieties of cellulosic raw material because it has been found that the various celluloses require varying concentrations of caustic soda liquor for achieving the most eificient removal of beta cel-- lulose in the individual cases. For example, in the case of ordinary sulphite cellulose derived from spruce wood, a concentration of 10 to 11 7 per cent is usually required, whereas in the case ondly, in the second dipping procedure, the strong into the drained but still lye-laden cellulose mass; moreover, when dipping presses are used, the

dip lye diffuses incompletely andnon-uniformly of an alkali-boiled beechwood cellulose, a 6 to 9 per cent concentration is preferableusing the same temperature of 15 to 20 C. Th proper concentration can readily be ascertained by means of preliminary tests.

Cellulosic raw material, dipped, drained and pressed, and freed from beta cellulose in the manner'aforesaid howeverdoes not yet possess the properties of a serviceable alkali cellulose that can be xanthated in the usual manner and usedfor the preparation of viscose since the required alkali concentration necessary for a mercerized condition is not present. In accordance with the present invention however it is possible to produce a serviceable mercerized condition of the cellulose mass during the course per se of the subsequent comminuting and defibring procedure byinjecting a fine spray ofia more highly concentrated caustic soda liquor (as by means of spray nozzles) into the shredder or the cellulose mass', during the shredding operation, say at the nitiation thereof and-prior to the termination thereof. In this case such an amount of caustic soda liquor and of such concentration should be used as is adapted to produce an alkali cellulose of adequate alkali concentration which can be readily and properly xanthated. In effecting such an increase in the alkali content of the alkali cellulose in the manner described, the usual shredding time of about three hours is amply sufficient. Xanthation of alkali cellulose so produced is accomplished without difiiculty.

In order to avoid the dangers and nuisance caused by the spray of caustic lye, it has been found preferable to effect the spray injection of the caustic soda lye with the aid of spray nozzles in which the liquor is directly subjected to high pressure, that is, with such nozzles as are adapted to operate without the use of air or other propelling gases. The spray injection of the caustic soda lye into the preliminarily alkalinized cellulose raw material'need not necessarily be directly efiected in the shredder but may also be carried out in a separate device, e. g. a container, with the material of course kept in motion by suitable means, and after said material has been preliminarily subjected to a certain amount of caustic soda liquor into the alkali cellulose and the uniform permeation of the entire mass may be facilitated by raising the temperature of the spray injected strong liquor to 30, 40 and even to 50 C., or by allowing the shredder itself to operate at elevated temperatures, or by using both expedients. Wetting agents may also be added to the spray injected liquor to achieve the same purpose. The use of wetting agents serves facilitate the spray injection action, as does also increasing the temperature of the spray iniected strong liquor. Efiecting the defibring at elevated temperatures also has the advantage of permitting the otherwise customary pre-ripening of the alkali cellulose to be largely dispensed with, or, under certain circumstances, to be entirely dispensed with. Several embodimental examples are given herewith to illustrate the method of practising the invention.

Example 1 100 kg. of ordinary air-dry sulphite cellulose having an alpha cellulose content of about 8'7 per cent are immersed in sheet form in a soaking press containing 10.5 per cent caustic soda, at a temperature of C., and after an immersion or soaking period of 1 /2 hours the material is drained and pressed so as to weigh 230 kg. The pressed material is then shredded in a shredder, e. g. of the Weiner-Pfleiderer type, as known in the art, for three hours, and during this period the strength of the alkali content in the alkali cellulose mass is increased to the mercerization point. To effect this, a caustic soda liquor of per cent NaOH content is spray-injected into the shredder while it is in operation and after the material has been preliminarily comminuted as a start, the liquor being run in at such a rate that in 1 hours 80 kg. of a percent caustic soda lye pass into the alkali cellulose mass. The shredding is continued without interruption for a period of 3 hours. The thus obtained, shredded alkali cellulose is then allowed to ripen to the desired extent in the usual manner, and thereupon worked up into viscose.

Example 2 kg. of air-dry sulphite cellulose of ordinary quality and having an alpha cellulose content of 87 per cent are mixed in flake form with a 10.5 per cent caustic soda lye in an iron vessel, the mass being intimately stirred- After one hour the alkali-containing cellulose mass is drained and pressed in a suitable press (e. g. a screw conveyor type press) to a weight of 240 kg., then passed through an attrition or grinding mill (e. g. of the Eirich type, as known in the art) and then placed in a shredder of the Werner-Pileiderer type mentioned above. The shredder is allowed to run for 3 hours and during the first 1 hours, herein referred to as the step in which initiation of the shredding is efiected, 70 kg. of a 45 per cent caustic soda liquor are spray-injected therein by means of spray nozzles of the kind described above. The alkali cellulose is thereupon worked up into viscose in the usual manner.

Example 3 100 kg. of air-dry alkali-cooked beechwood cellulose, in sheet form, are immersed in a dipping press containing a 7 per cent caustic soda liquor and at a temperature of 20 and after 1 hours drained and pressed down to a weight of 220 kg. The pressed material is then placed in a shredder and shredded. After a preliminary shredding of one hour (referred to above as the initiation of the shredding step) 100 kg.'of a 48 per cent caustic soda liquor are spray-injected therein while the shredding procedure is being continued, the spray injectionv being continued for the course of /2 hour and the total shredding step being continued so as to occupy a total of three hours. The alkali cellulose is thereupon worked up further in the usual manner.

Modifications of this invention will readily be recognized by those skilled in the art, and it is desired to cover all variations and modifications coming within the scope of the appended claims.

What is claimed is:

1. In the process of preparing alkali cellulose, the steps in sequence consisting of dipping a hemicellulose-containing cellulose into a dilute caustic soda lye containing approximately 6 to 11 per cent by weight of caustic soda, removing excess lye from said cellulose by pressing, shredding said cellulose and spray-injecting a second caustic soda lye containing approximately 30 to 48 percent by weight of caustic soda to mercerize said cellulose 'while. continuing the shredding thereof to form an alkali cellulose.

2. In the process of preparing alkali cellulose, the steps in sequence consisting of dipping a hemicellulose-containing cellulose into a dilute caustic soda lye containing approximately 6 to 11 percent by weight of caustic soda, removing excess lye from said cellulose by pressing, shredding said cellulose and spray-injecting a second caustic soda lye containing approximately 30 to 48 per cent by weight of caustic soda to mercerize said cellulose while continuing the shredding thereof to form an alkali cellulose, said second lye containing a wetting agent. a

3. In the process of preparing alkali cellulose, the steps consisting of dipping a sulphite cellulose containing about 87% of alpha-cellulose into a lye containing approximately 10.5% by weight of caustic soda, removing excess lye from said cellulose by pressing, preliminarily shredding said cellulose and then spray-injecting a second lye containing approximately 30 to 45% by weight of caustic soda in an amount to mercerize said cellulose while continuing the shredding thereof.

44 In the process of preparing alkali cellulose,

the steps consisting of dipping approximately 100 kgs. of an alkali-cooked beechwood cellulose in' sheet form at a temperature of approximately 20 C. intoa lye containing approximately 7% by weight of caustic soda, removing excess lye after approximately .1 /2 hours by pressing said cellutic soda while continuing said shredding for another period of approximately 90 minutes.

RICHARD BARTUNEK. JOHANN JOSEPH STOECKLY.