US1842649A

US1842649A - Process of treating cellulose material

Info

Publication number: US1842649A
Application number: US356308A
Authority: US
Inventors: Harry P Bassett
Original assignee: Individual
Current assignee: Individual
Priority date: 1929-04-18
Filing date: 1929-04-18
Publication date: 1932-01-26
Anticipated expiration: 1949-01-26

Description

Patented Jan. 26, 1932 UNITED STATES HARRY P. BASSETT, 01 GYNTIHIANA, KENTUCKY PROCESS OF TREATING CELLULOSE MATERIAL No Drawing. Application filed April 18,

This invention relates to a process of treating cellulose material and more particularly to a process of purifying natural cellulosecontaining fibers, such as cotton linters, wood t; or the like, prior to the preparation of cellulose products therefrom.

This application is a continuation in part of my application Serial No. 269,878, filed April 13th, 1928.

The principal object of this invention is to provide a process of removing impurities from and improving cellulose-containing material without substantial injury to the material being treated.

A. further object of this invention is to provide a digestion process of removing impurities, such as coloring matter, ligneous material, gums, resins and like impurities from fibrous material, such as wood, cotton linters or the like, without substantial injury to the cellulose fibers thereof.

Uther objects and advantages of this invention will become apparent during the course of the following description.

in the preliminary treatment of wood pulp and other cellulose material for use in certain branches of the so-called cellulose industry such, for example, as the artificial silk industry, it is common practice to treat raw cellulose-containing material, such as wood, Wood pulp, jute, straw, cotton linters or the like, with a digesting liquor of high concentration under pressure and at a high temperature, for a relatively prolonged period and thereafter r removing the digesting liquor from the treated material, for the purpose of removing impurities present in the cellulose-containing material in order to substantially isolate the cellulose present. Ordinarily, Wood, wood pulp, jute, straw and the like are treated in a single operation with a relatively strong solution of an alkali or a hot.sulphite solution. 'lhis treatment is generally drastic due to the high temperatures, pressures and concentrations of digestants employed and it not invariably happens that the cellulose itself is attacked and detrimentally altered in character during the treatment. Moreover, it frequently is the case that this treatment causes coloring matter and other impurities lit) 1929. Serial No. 356,308.

to be fixed or set in or on the cellulose fibers so that the removal of such impurities is substantially impossible.

The primary purpose of this invention is p to eliminate the disadvantages of the digesting processes heretofore employed and to provide a process of treating cellulosecon taining materials to remove impurities therefrom in an efficient manner and Without substantial injury to the cellulose. I have discovered that this purpose can be realized by subjecting the cellulose material to aplurality of digestions under controlled conditions of temperature, pressure and concentration of digestants, as hereinafter specifically described. By this process, the impurities present in the cellulose material, such as gums, hulls, resins, low celluloses and the like can be satisfactorily removed Without any substantial penetration of the digestant or impurities into the cellulose fibers, and the cellulose material simultaneously whitened to a marked degree.

In its broad aspects, my process comprises subjecting the cellulose material to be treated to a plurality of boiling operations or boilouts the initial boil-out or boil-outs being conducted at such temperature and pressure and with such a degree of concentration of the digesting liquor that the impurities present are partially removed without injury to the cellulose present and the coloring matter or other impurities is not substantially fixed or set n or on the cellulose fibers. Such preliminary treatment is followed by one or more boil-outs preferably at an increased temperature and pressure and with substantially the same or a lower degree of concentration of the digesting liquor. Between the several boil-outs; the cellulose material is preferably washed Without access to air althou h in some instances I have found that satisfactory results are obtained by omitting the washing and merely drawing off the digesting liquor which is replaced with fresh li uor.

n preparing the digesting liquor I may employ numerous compounds or mixtures of compounds. For example, I may employ sodium hydroxide, sodium acid sulfite or the fit) other digestant may be used in this and/or subsequent boil-outs, as suggested above. If the material treat-ed appears to contain an excessive amount of impurities the boil-out may be advantageously carried on under the same temperature and pressure conditions as the first boil-out. However, under ordinary conditions I have found it advantageus to conduct the second boil-out at a temperature sufficient to create a pressure of from 50 to 125 pounds per square inch. A large portion of the impurities having been removed in the first boil-out, a more complete purification is obtained and the digesting accelerated by employing a higher pressure in this stage of the process. The preferred pressure is approximately 80 or 90 pounds per square inch. The time of heating the material will vary according to the amount and type thereof, but treatment for from approximately 2 to 4% hours is generally satisfactory.

A certain measure of success is obtained by practicing only two boil-outs but the preferred practice is to employ another boil-out and in some exceptional cases a fourth boilout. Obviously, the number of such treatments may be further increased but actual practice has demonstrated that three, or at most four boil-outs is sufficient for wholly satisfactory results.

After the second boil-out is completed, the cellulose material is either washed with hot water or the digesting liquor removed in the manner suggested above. Thereafter, if further purification is desired, the material is subjected to a further boil-out, the conditions of temperature, pressure and concentration preferably remaining the same as in the second boil-out except in the case where the second boil-cut consisted of a second prelimi nary treatment wherein the pressure did not exceed 50 pounds per square inch. In-other words, the third boil-out should be conducted at a pressure offrom approximately 50 to 125 pounds per square inch. In this connection, it is to be noted that various sequences of pressures in the various boil-outs may be employed. For example, the boilouts may be conducted at pressures respectively of 50,80 and 90 pounds per square inch, or 50, 50 and 80 pounds per square inch, or 30, 80 and 100 pounds per square inch, the particular sequence employed being optional and depending upon the material and condition of material being treated.

The foregoing illustrative example of the invention will be found to givesatisfactory results under ordinary conditions. However, the process may be refined in various ways. i For example, the digesting liquors used in the various boil-outs may be modified in order to particularly adapt the process to the material being treated. As stated above, when ligneous material such as spruce is used, the first boil-out should be conducted with a digesting liquor which is a particular solvent for the ligneous material. the material contains a substantial amount of resins, a digesting liquor which is a solvent for such resins is preferably used. These modifications will be apparent to one skilled in the art.

As suggested above, the preliminary boilout or boil-outs should be conducted at comparatively low pressures in order to avoid the setting of impurities in or on the cellulose fibers and to prevent substantial deterioration of the cellulose by the penetration of the fibers thereof by the digestant employed. However, higher pressures may be used in the final boil-out or boil-outs since, as I have discovered, the preliminary boiling treatment described not only removes the major proportion of impurities but apparently favorably affects the cellulose fibers so that the subsequent higher pressurcs, and attendant higher temperatures, are not substantially injurious thereto. Such higher pressures are advantageous not only for the acceleration of the digesting 'action resulting therefrom but also for the reason that, as I have discovered, the viscosity of the material may be regulated, particularly in the production of a product of low viscosity, by the control of the pressures in the final boiling treatment. For example, I have found that the degree of viscosity of the product will vary according to the pressure employed in the final boiling treatment, the higher the pressure the lower the viscosity, other factors remaining constant. This feature is of great importance when the process is employed for the treatment of cellulose material to be used in the manufacture of artificial silk.

During the final boiling operation or operations at relatively elevated pressures I have found it highly advantageous to add to the digesting liquor a small amount of a bufier compound in order to preserve a high alpha cellulose content in the final product. Ordinarily 1 or 2 pounds of the buffer compound to approximately 100 pounds of the original cellulose material to be treated will be found to be satsifactory although a greater or smaller amount may be successfully em ployed. As a buffer compound I prefer to employ a salt of a base-forming metal such. for example, as sodium carbonate, sodium phosphate, potassium carbonate, sodium acetate, or the like. Sulfates should not be employed as buffers since their use does not produce the desired results.

The following process of treating cotton linters to remove impurities therefrom may be taken as illustrative of a specific example of the invention. While in this process only two boil-outs are described, since this number of boil-outs has been found in commercial practice to be sufficient for purifying cotton inters, it is obvious that one or more Similarly when additional boil-outs may be used, as is advisable when purifying certain types of wood pulp. Accordingly, in the preferred practice of my process in treating cotton linters, bales or bundles of this raw material are first broken up by picking them apart in any suitable manner. A suitable quantity, for example, 100 pounds of the cotton linters are then placed in a digester into which is introduced an aqueous solution of a digestant of the character referred to above, preferably caustic such as caustic soda or caustic potash. The strength of the caustic solution will vary according to the grade of linters being treated but I have found that from 3 to 10 pounds of caustic, dissolved in water in the proportions of from 10 to 20 pounds of water to 1 pound of caustic, provides a solution suitable for satisfactorily treating 100 pounds of linters. In the case of average second cut linters I prefer to treat 100 pounds of such linters with approximately 6 pounds of caustic dis solved in approximately 16 times its weight of water.

The thus prepared caustic solution having the linters suspended therein is then boiled under a pressure ranging from atmospheric pressure to approximately 50 pounds per square inch for a period of from 1 to 6 hours, the actual length of treatment depending upon the pressure and the grade of stock being treated. I have 'found'that boiling for a period of approximately 3 hours under a pressure of preferably from 25 to 50 pounds per square inch produces wholly satisfactory results. In this preliminary boil-out I find it disadvantageous to employ a pressure materially in excess of 50 pounds per square inch since such excessive pressure causes the digestant, in this case caustic soda, and impurities present to penetrate the fibers, thereby materially lowering the grade of the product.

After continuing the boiling for the desired period of time the liquid and the dissolved impurities contained therein are drawn or blown off from the digester and the remaining mass of cellulose material is washed several times, preferably with water and preferably out of contact with the air. To the washed material in the digester are then added from approximately 5 to 16 pounds, preferably 8 pounds, of caustic dissolved in from 10 to 20 times its weight in water. The resulting mass is then boiled under a pressure of from 50 to 125 pounds er square inch for from 3 to 10 hours, and preferably 5 hours. As indicated above the actual pressure employed Wlll depend upon the degree of viscosity of the final product desired. During the second boil-out I prefer to dissolve in the digesting liquor approximately 1 or 2 pounds of a buffer compound, preferably sodium acetate.

After the mass has been treated in the manner described above for a desired period of time the. treating solution is drawn or blown ofi' from the digester and the remaining mass washed several times, preferably with water and preferably out of contact with the air. The cellulose material is then ready for use in preparing cellulose solutions or the likeand may be treated according to any of 'the usual methods for preparing such products.

The foregoing example is typical of the invention when a cellulose material having a relatively small content of impurities is to be treated. If, however, a third and/or fourth boil-out is desired it is obvious that such a procedure may be followed. In this event, the concentrations of the digesting liquors in the first and second boil-outs are somewhat reduced, the total amount of the digestant being apportioned according to the number of boil-outs. Moreover, as suggested above, should the material to be treated contain a relatively high content of impurities, it is often advisable to subject the material to two preliminary boil-outs insteadof one initial boil-out described in the specific example of the process set forth above. In this event it is preferable to conduct the two pre liminary boil-outs under conditions of relatively low temperature, pressure and concentration of the digesting liquor. As will be obvious, various other modifications of the process will be apparent to those skilled in the art.

While I have described in detail the preferred practice of my invention it is to be understood that various changes in the details of procedure may be resorted to without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

1. The herein described process of treating such material with a solution of caustic at a pressure not in excess of 50 pounds per square inch, removing the liquid from said material, and thereafter treating the material with a solution of caustic and a buffer com pound to regulate the degree of viscosity thereof, said caustic solutions being of such concentrations as to be capable of dissolving impurities in said cellulose material but substantially incapable of materially deteriorating the cellulose.

2. The herein described process of treat ing cellulose material which comprises boiling such material with a solution of caustic at a pressure not in excess of 50 pounds per mg cellulose material which comprises boilsquare inch, removing the liquid from said as to be capable of dissolving impurities in said cellulose material but substantially incapable of materially deteriorating the cellulose.

3. The herein described process of treating cellulose material which comprises boiling such material with a solution of caustic at a pressure not in excess of pounds per square inch, treating such material to remove the impurities therefrom, and thereafter treating said material with a boiling aqueous solution of caustic and a buffer compound at a pressure of from approximately 50 to 120 pounds per square inch for a period of approximately from 3 to 10 hours, said caustic solutions being of such concentrations as to be capable of dissolving impurities in said cellulose material but substantially incapable of materially deteriorating the cellulose.

4. The herein described process which comprises treating cotton linters with an aqueous solution of caustic at the boiling temperature thereof at a pressure of from approximately atmospheric pressure to 50 pounds per square inch for a period of from 1 to 6 hours, the caustic being present in approximately the proportions of from 3 to 10 pounds of caustic to 100 pounds or linters and being dissolved in water in the proportion of one part of caustic to from 10 to 20 parts by weight of water, removing the caustic solution from the linters, washing said linters, and thereafter treating said linters with a solution of caustic at the boiling temperature thereof at a pressure of from 50 to 120 pounds per square inch for from 3 to 10 hours, approximately from 6 to 15 pounds of caustic being present and dissolved in water in approximately the proportions of one part of caustic to from 10 to 20 parts by weight of water.

5. The herein described process which comprises treating cotton linters with an aqueous solution of caustic at the boiling temperature thereof at a pressure of from approximately atmospheric pressure to 50 pounds per square inch for a period of from 1 to 6 hours, the caustic being present in approximately the proportions of from-3 to 10 pounds of caustic to 100 pounds of linters and being dissolved in water in the proportion of one part of caustic to from 10 to 20 parts by weight of water, removing the caustic solution from the linters, washing said linters, and thereafter treating said linters with a solution of caustic and a buffer compound at the boiling temperature thereof at a pressure of from 50 to 120 pounds per square inch for from 3 to 10 hours, approximately from 6 to 15 pounds of caustic being present and dissolved in water in approximately the proportions of one part of caustic to from 10 to 20 parts by weight of water removing the solution from the treated linters, and washing said linters.

6. The herein described process of refining cellulose material to remove impurities including coloring matter therefrom which comprises successively digesting cellulose material in a closed container under pressure with boiling solvent solutions capable of dissolving impurities therein and substantially incapable of materially deteriorating the cellulose material, the initial boiling operation being conducted at a temperature sufficient to cause the solvent solution to boil but not sufficient to create a pressure in said container substantially in excess of 50 pounds per square inch, and a subsequent boiling operation being conducted at a temperature sufficient to create a pressure in said container in excess of 50 pounds per square inch but not in excess of 125 pounds per square inch.

7. The herein described process of refining cellulose material to remove impurities including coloring matter therefrom which comprises successively digesting cellulose material in a closed container under pressure with boiling solvent solutions capable of dissolving impurities therein and substantially incapable of materially deteriorating the cellulose material, the initial boiling opereration being conducted at a temperature sufficient to cause the solvent solution to boil but not sufficient to create a pressure in said container substantially in excess of 50 pounds per square inch, and the final boiling operation being conducted under controlled conditions of temperature and pressure to regulate the degree of viscosity of the cellulose material.

8. The herein described process of refining cellulose material to remove impurities including coloring matter therefrom which comprises boiling such material with a solution of caustic in a closed container at a vapor pressure not in excess of 50 pounds per square inch, and thereafter boiling the resulting material with a solution of caustic in a closed container at a vapor pressure. in excess of 50 pounds per square inch, said caustic solutions being of such concentrations as to be capable of dissolving impurities in said cellulose material but substantially incapable of materially deteriorating the cellulose.

9. The herein described process of refining cellulose material to remove impurities including coloring matter therefrom which comprises boiling such material with a solution of caustic in a closed container at a vapor pressure not in excess of 50 pounds per square inch, removing the liquid from said material and thereafter treating the material to regulate the degree of viscosity thereof, said caustic solution being of such concentration as to be capable of dissolving impurities in said cellulose material but substantially incapable of materially deteriorating the cellulose. Y

10. The herein described process of refining cellulose material to remove impurities including coloring matter therefrom which comprises boiling such material with a solution of caustic in a closed container at a vapor pressure not in excess of pounds per square inch, removing the liquid from said material, washing said material, and thereafter heating said material with a solution of caustic in a closed container to a temperature sufficient to create a pressure in said container in excess of 50' pounds per square inch to regulate the degree of viscosity thereof, .said caustic solutions being of such concentrations as to be capable of dissolving impurities in said cellulose material but substantially incapable of materially deteriorating the cellulose.

In testimony whereof I aflix m si HARRY P. B S

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