US2117038A - Process of making cellulose xanthate solutions - Google Patents

Description

' sired solution of cellulose xanthate.

Patented May 10, 1938 airwas PATENT OFFICE PROCESS OF MAKING CELLULOSE XAN- THATE SOLUTIONS George A. Richter, Berlin, N. 11., assignor to Brown Company, Berlin, N. IL, a corporation of Maine No Drawing. Application February 1987, Serial No. 123,850 a 4 Claims.

This invention relates to a process of making cellulose xanthate solutions and more particularly to a process involving the mixture and reaction of cellulose fiber, an aqueous solution-of caustic soda, and liquid carbon bisulphide to produce in a continuous operation in a single vessel cellulose xanthate solutions or viscose syrupssuch as are useful in the'manufacture of artificial silk, films, or kindred ultimate products by the usual practices.

In my application Serial No. 58,539, filed January 10, 1936, I have described a so-called oneatep xanthating operation involving the use as raw material of chips or fragments of sheeted cellulose fiber or pulpboard, the placement of such chips or fragments in a closed mixing and reacting vessel, the mixing of caustic soda solution with the charge of chips or fragments in the vessel until they are successively thoroughly soaked and disintegrated to form a fiber suspension in the solution substantially free from fiber aggregates or clumps, and the mixing of liquid carbon bisulphide with the fiber suspension in the vessel until the fiber is substantially completely xanthated and dissolved to yield the de- In accordance with the present invention, once the mass of sheet fragments or pulpboard chips has been confined in the closed mixing vessel, air is evacuated from the vessel to deaerate to a large extent I the chips or fiber aggregatesand thus to induce more rapid penetration of the subsequently added caustic soda solution into and throughout the chips and, as mixing of the solution with the chips is effected, the defiberizatlon or disintegration of the chips to form a fiber suspension of the desired freedom from clumps or fiber aggregates. The deaeration of the charge .of pulpboard chips or fiber aggregates prior to the addition of the caustic soda solution is of considerable importance in that the rate of penetration of caustic soda solution into the chips otherwise depends upon such factors as the compactness, texture, size of interstices, and moisture content of the sheets or boards from which the chips are de rived. In this connection, it might be observed that the volume of caustic soda solution added to the vessel is calculated to produce a finished viscose solution of .a particular causticity with- "out need of draining excess solution from the vessel. Because such a volume ofsolution is insufllcient to submerge or cover the wood pulp chips completely, there is less tendency to displace or expel air from the chip interstices than when anexcessive volume of solution is employed.

By deaerating the chips and thus doing away with the indeterminate, relatively slow displacement of air from the chips by the caustic soda solution, the efiects of variations in the characteristics of the sheets or boards from which the chips are derivedare minimized and it becomes possible to shorten appreciably the period for the soaking and disintegration of the chips, to foster a more uniform and complete penetration of the chips throughout, and at the same time to produce a fiber suspension in caustic soda solution of the desired smoothness or freedom from fiber aggregates. Thus, by the practice of the present invention, it is possible to save a half an hour or more in the process as a whole when using pulpboard chips as-raw material and thus to realize an increased production of the desired quality of cellulose xanthate solution from a reaction vessel of given size or capacity.

- In practicing the present invention, sheets or boards composed of various kinds of wood pulp or other cellulose fiber may be cut into pieces or chips of the small size desired for introduction into the mixing and reacting vessel, as described in my application Serial No. 58,539. Thus, pulpboard produced from substantially unbeaten wood pulp and having a compactness or density varying from about 50 to and a thickness ranging from 0.030 to 0.060 inch may be cut into chips 01, say, about square to 1" square, and the chips 'added to a mixing and reacting vessel of any suitable type, for instance, that disclosed in application Serial No. 53,689, filed December 10, 1935, by

Orton B. Brown. The sheet compactness values mentioned are obtained by dividing the basis weight of the sheet in pounds by its thickness in inches and multiplying by the factor 10 The basis weight signifies the weight in pounds of 480 sheets whose dimensions are 24 x 36 inches,

that is, the weight of 2880 square feet of sheet material.

After the vessel has been partially filled with a mass .of the pulp chips, it is closed and placed under the evacuating action of a vacuum pump until a comparatively high degree of vacuum or sub-atmospheric pressure is attained in the vessel, for instance, an absolute pressure of 1 to 5 pounds, in consequence of which the chips are very largely deaerated. In the case of a vessel whose mixing blades are constructed to permit a heating medium to be circulated therethrough, as is true of the apparatus of application Serial No. 53,689, it is advantageous to tumble or revolve the vessel while it is being evacuated and whilea 5 heating medium is being circulated through its idle mixing blades so as to raise the temperature of the pulp chips to, say, 50 C. and thus to expel air from the chip interstices as well as residual moisture such as causes dilution of the caustic soda solution subsequently added to the chips. When the desired degree of vacuum has been created in the vessel, communication between the vessel and the vacuum pump is cut off and caustic soda solution in desired volume and concentration is injected into the closed, deaerated vessel. The caustic soda solution is quickly and substantially uniformly absorbed by the mass of deaerated chips and by the fibrous structure of the individual chips so that upon operating the vessel and its mixing blades for a comparatively short period of time, the chips, as they are mixed with the solution, are softened, swollen, and finally disintegrated to yield a thick or quasiplastic suspension of fibers in caustic soda solution of the desired smoothness or freedom from fiber aggregates realized. Liquid carbon bisulphide in the desired volume may then be injected into the vessel and mixing action in the vessel continued until the fibers in suspension have been substantially completely xanthated and dissolved to yield a solution of cellulose xanthate or viscose syrup of the desired character. The entire operation is carried out with the vessel only partially filled, 'that is, with an empty space above the vessel contents.

In some instances, after the deaerated chips or sheet fragments have been thoroughly soaked and softened with the caustic soda solution and finally resolved or disintegrated into the desired suspension substantially devoid of fiber aggregates, a suitable gas may be introduced into the empty space of the vessel above the fiber suspension. Thus, while the smooth or salve-like suspension is being mixed or churned and before the liquid carbon bisulphide is added, oxygen may be introduced into the vessel and mixing or churning of the suspension continued. Such oxygenation of the suspension, particularly under superatmospheric oxygen pressures, causes reduction in the solution viscosity of the cellulose and promotes its subsequent xanthation by the liquid carbon bisulphide. fiber is of sufficiently low viscosity to begin with and there is no need for or advantage in reducing its viscosity by oxygenatiomit may be desirable to introduce into the vessel above the suspension an inert or non-oxidizing gas such as nitrogen under ordinary or superatmospheric pressures more particularly for the purpose of precluding possible ignition of the liquid carbon bisulphide subsequently added to the vessel and avoiding change in the viscosity or other characteristics of the cellulose through leakage of air into the vessel. In other substances, after oxygenation of the suspension has been effected for the desired period of time so as to reduce the viscosity of the fiber, the oxygen may be evacuated or removed from the gas space in the vessel and replaced by .nitrogen so as to provide an inert atmosphere in When the cellulose 10% each is desired, the procedure hereof, so far as concerns proportionality of the various" rcacting ingredients and the temperature conditions under which xanthation is performed, may advantageously accord with the disclosure of my application Serial No. 58,539. It is possible, however, to produce finished viscose solutions by the process hereof of much lower or higher causticity and/or cellulose content. Again, it is possible to carry out the xanthating reaction at temperatures ranging from slightly above the freezing point to room temperature and to perform the treatment of the deaerated pulp chips at distinctly sub-room temperatures down to the freezing point and with caustic soda solutions of varying causticity, depending upon the causticity to be realized in the finished xanthate solution. In other words, the causticity of the solution employed to form the pulp suspension should such as to enable the realization of a xanthate solution which immediately after the xanthating reaction or upon subsequent dilution with water has the desired causticity in combination with the desired cellulose content. It is thus seen that the present invention, although involving the step of deaerating cellulose fiber more particularly in the form of pulpboard chips or sheet fragments preparatory to admixing caustic soda solution therewith to form a smooth pulp suspension, nevertheless lends itself to considerable variation insofar as concerns other aspects, including the temperature, causticity, cellulose content, carbon bisulphide usage, etc., under which xanthation of the pulp suspension is effected. It might be noted that while the step of deaeration is particularly valuable as applied to pulpboard chips, sheet fragments, or other fiber aggregates offering resistance to uniform impregnation and defiberization to form pulp suspensions in caustic soda solution of the desired smoothness or freedom from fiber aggregates, yet such step is also of value in forming such suspensions from cellulose fiber in other conditions, for instance, in shredded condition, as a deaerated mass of shedded cellulose fiber is also more quickly and uniformly wet or soaked with caustic soda solution and resolved into a smooth fiber suspension than when the solution must first displace the air entrained throughout the mass.

I claim: 1. A process of making cellulose xanthate solutions involving the reaction of cellulose fiber, caustic soda solution, and liquid carbon bisulphide, which comprises confining a mass of cellulose fiber in the form of pulpboard chips, sheet fragments, or other fiber aggregates in a closed mixing vessel, evacuating air from the vessel, mixing caustic soda solution with the mass in the evacuated vessel to effect a substantially uniform impregnation and softening of the fiber aggregates with the solution and finally a disintegration of such aggregates into a smooth fiber suspension substantially free from aggregates in the caustic soda solution, and mixing liquid carbon bisulphide with the resulting fiber suspension until the fiber has been substantially completely xanthated and dissolved to yield a solution of cellulose xanthate.

' 2. A process of making cellulose xanthate solutions involving the mixture and reaction of cellulose fiber, caustic soda solution, and liquid carbon bisulphide in a single mixing vessel, which comprises confining in a closed mixing vessel a mass of cellulose fiber in the form of pulpboard chins of an area no greater than about one square inch, of a thickness of about 0.030 to 0.060 inch, and of a compactness of about 50 to 120, evacuating air from the vessel, mixing caustic soda solution with the mass in the evacuated vessel to effect a substantially uniform impregnation and softening of the chips with the solution and finally a disintegration of the chips into a smooth fiber suspension substantially free from aggregates in the caustic soda solution, and mixing liquid carbon bisulphide with the resulting fiber suspension in the vessel until the fiber has been substantially completely xanthated and' dissolved to yield a solution of cellulose xanthate.

3. A process of making cellulose xanthate solutions involving the mixture and reaction of cel-' lulose fiber, caustic soda solution, and liquid carbon bisulphide in a single mixing vessel, which comprises confining in a closed mixing vessel 9. mass of cellulose fiber in the form of pulpboard chips, evacuating air from the vessel, mixing caustic soda solution with the mass in the evacuated vessel to efiect a substantially uniform impregnation and softening of the chips with the solution and finally a disintegration of the chips into a smooth fiber suspension substantially free from aggregates in the caustic soda solution, introducing nitrogen into the vessel above the resulting suspension of fiber, and mixing liquid carbon bisulphide with the resulting fiber suspension in the vessel until the fiberhas been substantially completely xanthated and dissolved to yield a solution of cellulose xanthate.

4. A process of making cellulose xanthate solutions involving the mixture and reaction of cellulose fiber, caustic soda solution, and liquid carbon bisulphide in a single mixing vessel, which comprises confining in a closed mixing vessel 9. mass of cellulose fiber in the form of pulpboard chips, evacuating air from the vessel while heating the mass of chips therein to expel air and residual moisture from the chip interstices, mixing caustic soda solution with the mass in the evacuated vessel to effect a substantially uniform impregnation and softening of the chips with the solution and finally a disintegration of the chips into a smooth fiber suspension substantially free from fiber aggregates in the caustic soda solution, and mixing liquid carbon bisulphide with the resulting fiber suspension in the vessel until the fiber has been completely xanthated and dissolved to yield a solution of cellulose xanthate.

GEORGE A. RICHTER.