US 2743220 A
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United States Patent 2,743,220 I p METHOD OF RECOVERI'NG: CELLUEOSE Joseph F. Estes,,New York, N. Y.
No Drawing. Applio'ation January lti, 1952, Serial No.. 266,799
4 Claims. (CUM-56).
This invention relates-to a method of. recovering. cellu: lose and the resultant product.
An object of this invention is to providegan, improved method of recovering pure cellulose-from,-cellulose containing materials such as baggasse, hemp or flax hurds, sisal or abaca, waste, or other cellulosic: material.
Another object of this invention is to, providean improved method, of recovering pure cellulose in finely divided form without any cellulose in, fibrous form, the recovered cellulose being free ofi discoloration.
A further object of this; invention is to.provide an improved method of treating material containing beta and gamma cellulose aswellas alpha cellulose, to-recover ahomogeneous product in particulate form, which retains substantially the content of beta and gamma cellulose of the treated material.
Still another object ofthis invention. is. to. provide an improved method of recoveringpurecellulose from waste cellulosic material Where such material is preliminarily treated: in a manner. to avoid: loss. Off beta and gamma cellulose While removing. impurities. therefrom.
Still. a further. object of this inventionv is to-provide a novel form of cellulose which is in finely divided particulate form, comprises the several forms of cellulose found in the cellulosic material from. which the novel cellulose is derived, isaltogether .freeof'cellulose in'fiber form and is particularly adapted to be processed: into filamentary form, plastic,, filrn, gunpowder and the like, without the need for filtering operations. 7
Yet another object ofthisin-vention is to provide an improved method of treating waste cellulosic products to convert the same into a form which may be readily and, economically processed to recover pure cellulose 7 therefrom.
Yet another object ofthis invention is to provide an improved electrolytic method of recovering pure, undiscolored cellulose from cellulosic solutions.
Other objects of this invention will in part be obvious and in part hereinafter pointed out.
The method embodying the invention comprises essentially the use of a novel solution for quickly and readily dissolving various forms of cellulosic material of the waste type such as baggasse, hemp and flax hurds, sisal and abaca waste or the like, as well as other forms of cellulose such as cotton or ramie fiber.
Such a solution comprises essentially the reaction product of a metal salt, ammonium chloride and sodium hydroxide which isdissolved in ammonium hydroxide. The resultant solution dissolves substantial amounts of cellulosic material, which may have been previously treated to effect the removal of lignin and other impurities only and leaving the beta and gamma cellulose content thereof.
The cellulose solution is electrolyzed in a cell having a copper cathode and a copper bearing anode with the pure cellulose depositing as a gelatinous mass on the anode. The anode is periodically removed from the cell, the deposited cellulose being removed therefrom, washed 2,743,220 Patented Apr. 24, 1956 A solution is prepared for dissolving cellulose containingmaterial, in the manner more specifically described. in
application Serial No. 266,800, filed January 16, 1952,"
Such solution may be made by preparing a saturated solution of a metal salt such as copper sulfate, as by dissolving about 2 pounds of the salt in a gallon of water and adding thereto about 0.2 pound of ammonium chloride. A concentrated solution of sodium hydroxide is lso. p p re by g. yd xi e t. h at f. bo 0.5 pound to a quart of water. The sodium hydroxide solution is then added slowly to the copper salt solution with constant stirring to form an apple green precipitate. Such precipitate is washed with water and is dissolved in a concentrated ammonium hydroxide solution, The resultant solution is decanted to separate thesame from any undissolved residue. The ammonium chloride used amounts to not less than 5% by weight of the copper sulfate.
Various cellulose containing materials may be used with the process of the instant invention, including bag gasse, hemp and flax hurds, sisal; and abaca Waste, or thelike. Thus, baggasse is dissolved the solution. in the proportion of about lOparts in about 20 parts solvent, by weight. Solution takes place fairly rapidly.
The prepared cellulose solution is electrolyzed in v a manner more completely described in application Serial No. 267,173 filed January 18, 1952. Essentially, the electrolytic cell used comprises a pair of fixed cathodes of copper with an anode located between the cathodes to receive the cellulose deposit. Such anode when formed of. a copper-bearing irjon having'the following analysis: irjon-.99.874; carbon..0ll; manganese-.017; sulfur- .032; phosphorus-.008; copper-a030, and gases..028, all per cent, produces aproductfree of any discoloration. Direct current is supplied to the electrodes of the .cell ata current density of about 1'0 amp res per square foot of exposed anodesurfacaand at about 6 volts.
Cellulose willbe deposited in the form of a. gelatinous mass, on the anode and when, a layer of suitable thick nessis formed, the anode is adapted to be removed from the cell to permit the removal of, the deposited material, which is then washed with water to remove chemicals and foreign matter. The washed material is dried to form a finely divided, particulate material of a homogeneous nature, which is distinguished by having a content of beta and gamma cellulose substantially in the proportions as the same exists in the baggasse treated. Furthermore, the product is entirely free of cellulose in fiber form.
In order to free the baggasse of a major portion of its lignin content, as well as other non-cellulosic impurities, the baggasse may be pretreated with a weak solution of sodium sulfite, sodium sulfate or ammonium carbonate. Such solution may have a concentration of about 2% and the baggasse may be cooked in such solution for not more than about 1 hour. In this manner while the lignin is at least partially removed, together with other non-cellulosic impurities, beta and gamma cellulose is retained. Any residual lignin left in the baggasse will deposit out in the bottom of the electrolytic cell as a sludge, which is periodically removed from the cell.
. In the case of other cellulose containing materials, such as abaca waste, the pretreatment may include a 5% solution of sodium sulfite or the like, but the treating period does not have to extend over 1 hour. With cotton rags,
the pretreatment is unnecessary since the clean rags may 3 ratio of about 2 parts of rags to 20 parts of solution, by weight.
In electrolyzing the cellulose solution, current densities may range between about 5 amperes to amperes per square foot of exposed anode surface. Voltages may vary between 2 to 12 volts, the voltage being determined by the spacing between the anode and the cathodes. With low amperages, the deposited cellulose will be of a slightly rubbery nature.
While the cellulose dissolving solution may be made up with a copper salt, Zinc or nickel salts, such as the chlorides, sulfates, or the like may also be used, either singly or in combination. The sodium hydroxide used to precipitate the metal salts may have a concentration varying between about 20% and 35%. The ammonium hydroxide solutions used may have a concentration varying between about and It will be apparent that a variety of cellulose containing materials may be readily and quickly dissolved with little or no pretreatment thereof, so that cellulose in pure form may be readily recovered at a minimum cost. Furthermore, beta and gamma cellulose, heretofore lost in the pretreating fiber cooking operation, is retained in the final product. In addition, the electrolytic recovery of the cellulose produces a product which is not only free of discoloration, but is also devoid of cellulose in fiber form. Thus the product may be further processed and chemically modified to convert the same into rayon, gun powder, film, plastic and other forms without the need for filtering equipment to remove undesirable fibrous cellulose.
It has also been found that the homogeneous cellulose product of the instant invention readily and quickly reacts With nitrating, acetylating and other chemical modifying agents so as to further reduce the need for extensive treating installations. The process also allows the more extensive use of waste cellulose products as a source for pure cellulose, inasmuch as the cost of treatment is substantially reduced.
It is to be understood that the foregoing is illustrative of the invention and that different embodiments may be made thereof Without departing from the spirit of the invention and therefore it is not intended to be limited thereby except as indicated in the claims following.
Having thus described my invention, I claim as new and desire to protect by Letters Patent:
1. The method of recovering pure cellulose from cellulose containing material comprising providing an ammonium hydroxide solution of a reaction product of green copper hydroxide and ammonium chloride, dissolving said material in said solution and electrolysing said solution in a cellhaving an iron anode containing about 0.3% copper and a copper cathode.
2. The method of recovering cellulose from cellulose containing material, comprising dissolving the material in a solution containing a copper hydroxide ammonium chloride complex, and electrolyzing said dissolved material in a cell including a copper cathode and an iron anode containing about .03% copper with a current having a density of from about 5 to 20 amperes per square foot of anode surface.
3. The method of forming fiber free cellulose in finely divided particulate form from cellulose containing material comprising mixing a saturated copper sulfate solution containing ammonium chloride with concentrated sodium hydroxide to form a green precipitate, dissolving the said precipitate in ammonium hydroxide to form a solution, dissolving the cellulose containing material in said solution, electrolyzing said cellulose solution in a cell having a copper cathode and an iron anode containing a very small amount of copper at a current density of about 10 amperes per square foot of anode surface, removing the cellulose deposited on the anode and washing and drying the cellulose.
4. The method of recovering cellulose from waste cellulosic material having a content of beta and gamma cellulose comprising mixing a saturated copper sulfate solution containing a small amount of ammonium chloride with a 20% sodium hydroxide solution to form a green precipitate, dissolving the precipitate in ammonium hydroxide, dissolving the Waste cellulosic material in the resultant solution, electrolyzing the cellulose solution in a cell with copper cathodes and an iron anode containing about .03% copper at a current density of from about 5 to about 20 amperes per square foot of anode surface and from about 2 to 12 volts.
References Cited in the file of this patent UNITED STATES PATENTS 908,937 Bayliss et a1 Jan. 5, 1909 1,590,606 Taylor June 29, 1926 1,851,008 Hanson et al Mar. 29, 1932 1,880,045 Richter Sept. 27, 1932 2,045,345 Dreyfus June 23, 1936 2,269,665 Herbst Jan. 13, 1942 2,298,260 Kantorowicz Oct. 6, 1942 2,362,528 Balz et al. Nov. 14, 1944 FOREIGN PATENTS 919,558 France Dec. 9, 1946 OTHER REFERENCES Cellulose and Cellulose Derivatives; by Ott, published in 1943 by Interscience Publishers, Inc., page 750.
Heuser: Cellulose Chemistry; 1944, pp. 3, 8, and 126.