INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 17, No. 2
Free Alkali in Silicated Soaps' By A. Edeler THEPROCTER & GAMBLE^ Co.,IVORYDALE, OHIO
T
HE determination of free alkali and of sodium silicate
are among the most common operations in the analysis of commercial soaps. The interrelation of these two analytical operations does not appear to have been considered in the literature, although it is well known that caustic alkali reacts readily with ordinary sodium silicate to form a silicate containing a lower percentage of silica and a higher percentage of combined alkali. T.he object of the present investigation has been to study the effect of sodium silicates of varying NazO:SiOz ratios on the free alkali determination as it is usually made in soap analysis-i. e., by dissolving the soap in alcohol, filtering, washing the residue, and titrating the alcoholic filtrate with standard acid.2 Experimental
For this purpose concentrated silicate solutions of varying composition were prepared by adding strong caustic soda to portions of a commercially made silicate solution, and after 3 days3 a free alkali determination was made on each silicate solution in the absence of soap. Five grams of each solution were treated with 200 cc. neutral alcohol (No. 30 denatured) and heated on a steam bath with occasional stirring by means of a glass rod for about 30 minutes. After filtering and washing several times with alcohol, the filtrate with washings was titrated with normal sulfuric acid, using phenolphthalein as indicator. Also, each silicate solution was treated with a neutralized solution of 10 grams of soap (purest commercial grade, containing about 26 per cent water) in 200 cc. alcohol (KO.30 denatured) and the determination of free alkali carried out in the same manner as indicated above. The composition of the silicate solutions and the titrations of the alcoholic filtrates from these silicates, with use of both alcohol alone and alcohol containing 10 grams of soap, are shown in Table I. Each analysis was made in duplicate on separate samples and the results of each individual titration are shown. Table I-Titrations
NazO Per cent 9.18 11.37 13.48 17.72 23.97
of Alcoholic Filtrates from Sodium Silicates of
Varying Composition C C N ~. HiSOi r o Ratio NEUTRALIZE A L C O I X O ~ IFILTRATE C Si02 Naz0:SiOa Soap absent Soap present Per cent (Molecular). (1) ( 2 ) (1) (2) . 0.10 tr. tr. 0.10 29.71 133.33 0.05 0.05 0.25 0.25 28.18 1:2.55 0.60 0.30 0.35 0.55 26.13 1:1.99 2.20 1.40 1.45 2.20 1:1.54 26.50 8.05 8.35 9.40 9.60 1:1.01 23.48
The first strong silicate solution described in Table I is typical oi the sodium silicate used in soap manufacture and all except the first two samples lie entirely outside the range of sodium silicates commonly used. If the titration of the alcoholic filtrate from the silicate solution of 1:2.55 ratio is translated into terms of free alkali indicated to be present in the silicate, this silicate solution appears, by the method in question, to contain only 0.2 per cent free NaOH. With neutral soap dissolved in the alcohol, an almost negligible percentage of free alkali appears to be present in this silicate and even less in the silicate of 1:3.33 ratio. In the next series of experiments, similar free alkali determinations were made on soaps into which had been Received September 27, 1924. THISJOURNAL, 14, 1160 (1922). 3 This time of standing was much longer than was found necessary to insure reproducible results. 1
2
crutched concentrated sodium hydroxide and sodium silicate solutions in the order named. The silicate contained 37 per cent solids and was of 1:3.22 ratio. Each soapalkali mixture was stirred about 5 minutes at 65' to 75" C. with half its weight of the strong silicate solution and the resulting product allowed to stand several hours. Fifteen grams of the crutched soap were taken for each determination, so that the results may be compared directly with those in Table I. Table I1 shows the SasO:SiOz ratio of the sodium silicate in these mixtures, calculated on the assumption that all the free sodium hydroxide reacts with the original sodium silicate, and also shows the titrations of the alcoholic filtrates obtained in the free alkali determination. Table 11-Titrations of Alcoholic Filtrates from Silicated Soaps Free NazO in soap Resulting Apparent free before adding ratio C C . N HZSO4 NazO in sili. silicate NazO :SiOa t o neutralize cated soap Per cent (Molecular) alcoholic filtrate Per cent 0.05 0.0 1:3.22 0.05 0.01 1.21 1:2.52 0.30 0.40 0.07 0.30 2.32 1:2.12 0.50 0.10 5.02 1:1.52 2.40 2.60 0.52
The last two samples described in Table I1 were allowed to stand about 16 hours longer, a t the end of which time the free alkali determination was repeated but showed no material change. It seems probable that equilibrium had been established a t the time original determinations were made. It will be noted that in Table I1 the titrations of the aicoholic filtrates from the silicated soaps agree fairly closely with the corresponding titrations in Table I. It appears that free alkali in soap reacts readily with sodium silicate-an observation which, of pourse, is not new. It further appears that the determination of free alkali in silicated soap by the usual method is a purely arbitrary procedure which determines in reality the free alkali extracted from the silicate itself. The amount of free alkali so extracted is dependent upon the composition of the silicate. In Table I it will be noted that the first decided increase in the extracted alkali over that of the immediately proceeding mix was obtained in the case of the silicate of 1:1.54 ratio. Comparison with Results of Other Investigators
It is interesting to compare the results in Table I with some of those obtained by Bogue4 in his work on the hydrolysis of sodium silicate. He examined electrometrically solutions of sodium silicates of varying iYaQO:SiO:! ratios and in various dilutions with water and calculated the pH values, hydroxylion concentrations, the degree of hydrolysis, the hydrolytic dissociation constants, and the ionization constants. For the purpose of this comparison only the results of the hydroxylion concentrations will be noted here, and those only in one dilution (1 gram-molecule in 100 liters of water), as the values on all the dilutions given are on the whole fairly similar. Table 111-Apparent Hydroxyl-Ion Concentrations of Solutions of Sodium Silicate of Varying Composition (Bogue) NazO: Si03 ratio Hydroxyl-ion concentration . 1:4 3.00 1:3.5 3.36 1:3.0 3.72 1:2.5 4.94 1:2.0 6.00 1:1.5 17.6 1:l.O 54.0 4
J . A m . Chem. Soc., 42, 2575 (1920).
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).
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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 A few days’ disintegration, is aged, in some cases for 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).
