INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1925
It will be noted that the first decided increase in the hydroxyl-ion concentration over that of the immediately preceding silicate took place with the 1: 1.5 ratio silicate, where also, as previously noted, a similar change occurred in the quantity of alkali extracted by the alcohol. It appears, therefore, that as the ratio of KazO to Si02 increases, both the hydroxyl-ion concentration and the alkali extracted by alcohol gradually increase until the Na20:Si02 ratio reaches a value between 1 : Z . O and 1:1.5. when a decided and rather abrupt increase takes place in both and, as far as results have been obtained, this increase becomes disproportionately larger with increasing NazO :Sios ratio. It is significant here to note the work of Kohlrauschj on the conductivity of sodium silicate solutions, in which it was found t h a t as silicic acid was added to a caustic soda solution the conductivity of the latter decreased until the Na20:Si02 ratio reached a value of about 1 :2.0, when no further change in the conductivity took place. This variation in the conductivity 6
2. phystk. Chem
, la, 773 (1893).
197
is in fair agreement with the variation in the hydroxyl-ion concentration herein referred to, although, as pointed out by Bogue, the actual values of the hydroxyl-ion concentration as determined by these two methods are a t variance with each other. Summary
1-The usual free alkali determination in silicated soaps gives results which are due to the extraction of alkali from the sodium silicate by the alcohol. 2-The alkali thus extracted increases with an increase of NaaO in the silicate molecule in a manner somewhat similar to the increase of the hydroxyl-ion concentration of the silicate in water as determined by the hydrogen electrode, and also to the increase of the conductivity of the silicate in water. 3-This extracted alkali should be congidered as a part of the combined alkali of the silicate rather than as a separate constituent.
Laboratory Production of Viscose’ By Foster D. Snell PRATT INSTITUTE,BROOKLYN, hT.1‘.
A
LABORATORY procedure for making viscose which closely parallels the present industrial practice is given here for the information of those who may be confronted with a similar problem. Literature
The viscose process and its literature have been summarized so completely by Worden2 that it will be reviewed only very briefly here. In the literature of the viscose industry are several descriptions of the process, all differing in many ways from the one now used in this country. Cross, Bevan, and Beadle3 patented the method of produc.tion as originally worked out by them and described4the process and the reactions involved. &delh has described a process. Beadle6 described a method of production of viscose for sizing paper. Beltzer7 described a process in considerable detail for both laboratory and plant use. Semenovs gave a laboratory process. Hendersong also described a method of producbion from cotton linters. All of these differ in considerable detail from the procedure used by this laboratory. Manufacture of Viscose
The manufacture of viscose products consists essentially of five steps: mercerizing cellulose, changing alkali cellulose to xanthate, dissolving the xanthate, coagulation (decomposition of xanthate to cellulose in another physical form), purification of the product. Presented before the Division of Cellulose Chemistry a t the 68th Meeting of the American Chemical Society, Ithaca, N. Y . , September 8 t o 13, 1924. 2 “Nitrocellulose Industry,” D. Van hTostrand eo.,1911 ; “Technology of the Cellulose Esters,” D. Van Nostrand Co.,1921. a British Patent 8700 (May 7, 1892). J . Chem. SOC.(London), 69, 837 (1893); J . SOC.Chem. I n d . , 12, 816 (1893); “Cellulose,” Longmans, Green & Co., 1916. 6 Mitt. kgZ. tech. Geraevbemuseums U’ien, 10 (I & 2),35 (1900); Celluloid Supplement, Gummi-Ztg., 22, 13 (1907). 6 Chem. h’ews, 94,127 (1906). r Kunslstofe, 2,41,69,8 5 , 111, 127 (1912). 3 J. Russ. Phys.-Chem. SOL., 44,339 (1912). THISJOURNAL, 16,822(1923).
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The concentration of alkali used for conversion of cellulose to alkali cellulose is variously described as 15 to 30 per cent sodium hydroxide. The use of an oxidizing agent to hasten mercerization has been patented by Glover and Wilson.lo The mercerized product is pressed until the weight is from two to four times the original dry weight and, after mechanical disintegration, is aged, in some cases for A few days’ aging is better practice. After aging combination with carbon bisulfide is effected by treatment with carbon bisulfide vapor in a closed vessel, with carbon bisulfide in various concentrations in an indifferent solvent, or with liquid carbon bisulfide, with or without mechanical mixing. Present practice in this country is Lhe use of liquid carbon bisulfide in a closed vessel with mechanical mixing. The product so obtained is rubbery and has lost the properties of the original cellulose. This product must be carried to the next step at once. The solid cellulose xanthate is dissolved in dilute (4per cent) sodium hydroxide to form a solution, the viscosity of which is seldom specified in the literature. Industrial practice is to reach a viscosity at which a steel ball 3 mm. in diameter will fall 20 mm. in about 30 seconds. The keeping quality of the viscose so prepared depends on the temperature a t which it is kept since, after a time, water separates and leaves a mass of impure regenerated cellulose known as viscoid. At this stage the product is aged so as to give the maximum tensile strength, transparency, and luster when coagulated. The next step is coagulation of the viscose solution to the desired physical form. Although not a step in the production of viscose, it was found necessary in order to judge the quality of viscose produced. It is this stage that has been most prolific of patents. Over fifty patents specify the use of mineral and organic acids, neutral salts and acid salts, and organic agents and their combinations. In general, the coagulant reacts to neutralize the alkali which serves to keep the xanthate in colloidal suspension and at the same time liberates 10
U. S. Patent 1,279,328-9(1918).
INDUSTRIAL A N D ENGINEERING CHEMISTRY sulfur and unknown sulfur compounds, which must later be removed. Agents may be added at this stage which will tend to lower the amounts of these impurities, soften the product, complete the conversion to cellulose, and perform other services. Briefly, the balance of the process consists of removal 01 sulfur and impurities containing sulfur with sodium sulfide souring, bleaching, and drying. Experimental
Thirty-seven grams of surgical cotton were mercerized by immersion in 558 cc. of approximately 17.5 per cent sodium hydroxide (specific gravity 1.2) at 20" C. for 1.5 hours, the process being carried out in a tightly stoppered bottle to prevent absorption of carbon d i o ~ i d e . ~ J lAt the end of the period of mercerization excess soda was drained off and the alkali cellulose pressed to a weight of 160 grams, the minimum obtainable with the method of pressing used. The mass so obtained was picked apart with forks and placed in a tightly stoppered bottle, and kept a t 18" C. for 96 hours. The alkali cellulose or "crumbs" after aging was combined with carbon bisulfide by revolving in a small closed box or churn at about ten revolutions per minute. Excess of carbon bisulfide was added a t intervals, totaling 30 cc. over a 2-hour period. This is a considerable excess over the amount that will react with the alkali cellulose. It was found that fresh alkali cellulose gave only a faint yellow with carbon bisulfide at this stage of the process. After 24,48, and 72 hours at 18" C. the alkali cellulose was not properly matured, but after 96 hours a satisfactory xanthate was formed. The criterion of quality of the xanthate was formation of a deep orange-yellow, rubbery product, showing few fibers under the microscopewhen made into a viscose solution. When the alkali cellulose was allowed to stand in a closed bottle with the same proportion of carbon bisulfide with occasional shaking for 12 hours, the xanthate formed was not uniform in color or composition. The total cellulose xanthate from the previous stage was at once mixed, with mechanical stirring, with a small amount of sodium hydroxide solution and stirring continued with addition of liquid as fast as the mass would take it up until 120 cc. of 4 per cent sodium hydroxide and 25 cc. of 10 per cent sodium sulfite had been added. The viscosity was then taken at intervals and more alkali added until the proper "ball-fall" was obtained. This usually required 40 to 50 cc. of the sodium hydroxide solution. The solution so obtained was brown in color and contained about 10 per cent cellulose by weight.12 Microscopically, it showed a few fibers. The solution was iiltered through light filter cloth, using a pressure of 2.85 kg. per square centimeter (40 pounds per square inch). The color remained unchanged, but the microscope showed an almost complete removal of fibers. It was then placed in a tight bottle at 18" C. and subjected to a vacuum of 20 111111. for 4 hours to remove the many tiny air bubbles present. The bottle was stoppered and left to age at 18" C. until used. The solution used as coagulant was approximately that described in a German patent.lS The composition was glucose 10 per cent, sulfuric acid 10 per cent, zinc sulfate 1 per cent,14anhydrous sodium sulfate 14 per cent, water 65 per cent. This is essentially coagulation by an aqueous solution of sodium acid sulfate with glucose added as softener. After aging, the viscose solution was smeared on glass in as uniform layers as possible and coagulated by flowing the coagulating solution over the viscose layer. The time of treatment was about 2 minutes. When freshly prepared, Eggertz, Kunststofe, 3, 381 (1913). Cross, Bevan, and Sindall, "Wood Pulp and Its Uses," 1911, p. 246. D. Van Nostrand Co. 18 German Patent 260,479(September 16, 1911); C. A., I , 3237 (1913). 14 U.S. Patent 1,085,731(November 26, 1912). 11
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viscose gives a fluffy sheet with little luster. This corresponds to an English patentls on the manufacture of wool-like threads from viscose. No appreciable improvement is shown for 48 hours, but after 72 hours' aging a sheen begins to appear on coagulation, and a t 90 to 150 hours the sheet obtained compares as favorably 3s might be expected with a sheet of commercial cellophane. This sheet is practically as transparent as the commercial product and has few, if any, air bubbles. Early experiments yielded sheets that were nearly opaque with bubbles, but this was largely eliminated by careful protection from absorption of carbon dioxide at every stage of the process. The sheets were then bleached with potassium permanganate followed by sulfurous acid, washed and dried under tension. Comparison with Commercial Product Only two criteria of quality can be given, and of these only one is quantitative. The luster of the sheets was as near %hat of the commercial article as could be expected from the method of coagulation. The transparency approached closely that of the commercial article and when deficient the trouble could be traced to bubbles in the sheet. Because of the unavoidable irregularities in thickness of the sheets, such tests as the bursting test for paper could not be used. The tensile strength of small rolled portions was determined with a dynamometer and compared with data from similar rolls of the commercial product from two different sources. The laboratory samples and commercial specimens were of approximately the same average thickness and irregularities in thickness of the laboratory sample were local. The following data were obtained: SOURCE Commercial Commercial Laboratory Commercial Commercial Laboratory
Weight Grams/meter 0.5709 0.9673 0.9528
1,346 1.441 1.445
Breaking test Kg. 4.1 7.3 6.4 8.2 8.6 8.2
Ereaking test Kg./gram/ meter 7.15 7.50 6.67 6.06 5.98 5.65
The variation in tensile strength is only what is to be expected from the fact that the experimental sheets were not so uniform in thickness as the commercial material. It is believed that if the laboratory samples could be made of as uniform thickness as the commercial product they would have fully as high a tensile strength. Three batches prepared in this manner from cotton gave essentially identical results. The experimental samples are from two of these batches. 16
English Patent 135,205(November 13,1919).
Du Pont Company Enters Synthetic Ammonia Field A plant site for the manufacture of synthetic ammonia has been purchased a t Clinchfield, Va., by Lazote, Inc. (a corporation organized by E. I. du Pont de Nemours & Company). The new corporation, after careful study of the several known processes, has acquired the Claude synthetic ammonia process and will instal it. Field work and construction operations will be started in the early spring and it is expected that the plant will be in operation by the end of the year. Plans provide for a capacity of 25 tons of ammonia a day and they also allow for substantial enlargement. The site is next to coal fields, which will supply the power and raw material, investigations having shown that in the synthetic ammonia process coal or coke can be used more economically than water power in the production of the essential raw materials. Heretofore it has been considered necessary to have cheap hydroelectric power for the operation of synthetic ammonia or fixed nitrogen processes. The special equipment and machinery which will be required are being constructed in the shops of the du Pont Company, and will be ready for installation by the time the buildings are complete.
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