I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1222
water, although reducing the extraction temperature, does not lower the extraction pressure correspondingly because of the high vapor pressure of ammonia. It may be concluded that the water solutions of ethylene glycol are the more desirable solvent combinations investigated because of the lower extraction temperatures and pressures required to accomplish toluene recovery.
TABLE V. RECOVERY OF TOLUENE FROM THE TOLUENE CONCENTRATE FROM HYDROFORMED NAPHTHA (Assuming 95% recovery of toluene from concentrate containing 50% toluene as 98.0 volume % toluene extraot) EstiSolvent mated Dosage, Oqerat Yol. 1ng Solvent/ Theoretical stagPressure, Vol. of Extraotion Lb./Sq. Temp., Recycle Charge StfipEnInoh So1vent ' C. Ratioa Stock pine riching Total Abs,b Water 274 0 71 14.6 8.5 2.5 11 1160 Water sojution of 20% ammonia 232 1.14 14.4 7.7 3.3 11 1440 Water solution of 25% ethylene glycol 274 2.10 14.0 7.5 3.5 11 1140 Water 302 2.86 13.4 6.8 6.2 11 1695 Water solution of 25% ethylene glycol 302 3.85 11.2 6.0 5.0 11 1670 Water solution of 20% ammonia 274 Inoperable (I
Reoyole ratio
=
LITERATURE CITED
(1) Arnold, G. B., and Coghlan, C. A,, IND. ENO.CHEM., 42, 177 (1960). (2) Franklin, E. C., and Kraus, C. A., J . Am. Chom. SOC.,20, 820 (1898). (3) Hill, L. R., Vincent, G. A,, and Everett, E. F., Natl. Petroleum Newa, 38, R-456 (1946).
Of
volume of extract oil'
b Estimated from extrapolated vapor pressure curves of solvent and of toluene.
ethylene glycol to the solvent water. However, substantially the same solvent dosage is required because of the increased recycle ratio. Addition of ammonia to the solvent
Vol. 42, No. 6
(4) Maloney, J. O.,and Schubertt A. E., *ram. Am. Engrs., 36, 741 (1940). Smith, A. s., and J, E,, IM., 40, 211 (1944). RECEIVBD January 7, 1960.
Solvent Extraction of Thiodiacetic Acid from Water Solutions J. W. CLEGG AND A. E. BEARSE Battelle Memorial Institute, Columbus 1, Ohio
To produce thiodiacetic acid economically by
the reaction of sodium chloroacetate and sodium sulfide, it is necessary to separate the acid from the salts formed, which accompanj it in water solution. The most feasiblc means of making this separation is by solvent extraction. A successful solvent for this purpose is 2-butanone. Although the acid is more soluble in water than in this solvent, the salting-out effect of the accompanyingsalts makes the extraction possible. This paper presents phase equilibrium data for this system, and describes a few experimental runs made in a 4-inch diameter column packed with Raschig rings. The development of methods of analysis for the acid and solvent in the presence of the other components and excess mineral acid is also described.
T
H E classical method for the preparation of thiodiacetic (thiodiglycolic)acid (6) is by the reaction of sodium sulfide and sodium chloroacetate in water solution, and "springing" the organic acid with sulfuric acid, according to the equations below: NalS
+ 2NaOzCCHzCl+ NaOzCCH2-S-CHtC02Na
NaO&CH2SCHzCOzNa
+ HzS04 --+
+ 2NaC1
(1)
+
HOZCCHZSCHZCOZH NaZS04 (2)
One mole of the free acid is accompanied by 2 moles of sodium chloride and 1mole of sodium sulfate. The acid is quite soluble in water (40.05% by weight a t 20" C.), and its separation from the accompanying inorganic salts has customarily been accomplished by fractional crystallization. However, only a portion of the acid
present could be obtained in a salt-free condition by this procedure. Because of the difficulty of recovering the acid, it had never achieved commercial significance, despite the fact that i t is a potentially valuable dibasic acid manufactured from inexpensive raw materials. In the Battelle laboratories, it was found that this acid could be extracted from the aqueous solution obtained in the reactions outlined above with 2-butanone (methyl ethyl ketone) ( 1 ) . This was despite the fact that the acid is more soluble in water than in 2-butanone. The problem of obtaining a quantitative understanding of this extraction to permit scaling up the laboratory process acd making i t a continuous procedure, thus, presented itself. The purpose of this paper is to present phase equilibrium data for this system, and to describe a few experimental runs made in a 4-inch diameter column packed with Raschig rings. SOLUBILITY DATA
The first step in the quantitative analysis of the extraction operation was the collectionof phase equilibrium data. Except for one reference (6)citing the solubilityof thiodiaceticacid in water at 18" C. as 29.7% by weight, no data on the solubility of this compound were available. The mutual solubilities of 2-butanone and water had been reported by Langedijk (6),Evans ($), and Ginnings et al. (S),but these three sources of information were not entirely in agreement, as shown in Table I. It was apparent that the desired extraction could be effected only by virtue of the salts dissolved in the original process solu-
INDUSTRIAL AND ENGINEERING CHEMISTRY
lune 1950
TABLE I. REPORTEDSOLUBILITIES AND SPECIFIC GRAVITIESOF %BUTANONE AND WATER
Sourae of Information
Solubility of 2-Butanone in Water, Wt. %
8p. Gr. of Water Phase P/40
c.
.
S Gr.of Solubility of Water in 2-f;utanone 2-Butanone, Wt. % top/%.
Solubilities
At 25’ C. Langedijk (6) Ginninga et al. (9) his paper At 20° C. Langedijk (6) Ginnin et al. (8) Evans
G)
21.6’ 25.57 29.32
0.9611 0.9622
10.10 11.72 10.76
0.8322 0.8312
22.6 27.33 26.7
0.9620 0.962
9.9 11.59 12.1
0,8353 0.836
Specific Gravity of %Butanone Sp. Gr., Sp Gr 20°/4” C. 26°)4Q 6. Langedijk (6) 0.805 0.7997, Ginnings, et al. (8) ... 0.8007 This paper 0.7994 Interpolated between vsluse for 20° and 40° C. b Interpolated between values for 20° and 30° C.
...
1223
tion, since the acid is more soluble in pure water than in 2-butsnone. In other words, the salting-out effect of the sodium chloride and sulfate present in the solution was essential. Some device was required, therefore, to represent a six-component system (water, sodium chloride, sodium sulfate, sulfuric acid, thiodiacetic acid, and 2-butanone) on a triangular graph of phaseequilibrium data. It was decided (and later shown to be feasible) to treat the water and other inorganic materials which generally remained in the water phase as a single component. For convenience, then, the apexes of the proposed triangular plot would be designated as ( a ) thiodiacetic acid, ( b ) 2-butanone, and (e) “salt solution.” This method of treatment meant that solubility data would be required for Zbutanone in “salt solution” anH thiodiacetic acid in “salt solution.” It also proposed the problem of analyzing in a convenient manner for 2-butanone in a solution cohtaining inorganic acid and salts and for thiodiacetic acid in the presence of excess inorganic acid. The first of these analyses was accomplished by distilling the Zbutanonc out of solution, and the second, by extraction of the acid. Both empirical methods proved reliable, and are described under Analytical Procedures. In solutions containing only 2-butanone and water, the specific gravity would furnish a ready index of composition. Since these data could not be obtained from the literature, they were determined in the laboratory, and are given in Tables I1 and I11 and Figures 1and 2.
PER CENT 2-BUTANONE IN WATER
Figure 1. Specific Gravity of Solutions of 2-Butanone in Water us. Concentration
TABLE 11. SPECIFICGRAVITY OF SOI~UTIONS OF %BUTANONE IN WATER,25’/4’ C. Volume % 2-Butanone
Weight % .8p Gr 2-Butanone 250j40 2. 0 0 1.00 0.80 2.00 1.61 3.00 2.42 4.00 3.23 5.00 4.06 7.85 9.00 10.00 8.18 12.00 9.86 16.00 13.25 14.97 18.00 20.00 16.70 18.46 22.00 24.00 20.21 21.98 26.00 27.00 22.88 23.78 28.00 29.00 24.68 26.58 30.00 27.40 32.00 (29.33) 8atd. (34.10)‘ Solubility value for saturated solution obtained by extrapolation of opeoifia gravity aurve.
TABLE 111.
GRAVITYO F SOLUTIONS %BUTANONE, 25 ‘/4 C.
SPECIFIC
Volume % Water 0 1.33 2.00 4.00 6.00 8.00
Weight % Water 0 1.65 2.48 4.91 7.31 9.68 12.04 (12.90)
OF
WATER
IN
Sp. Gr.,
25’/4” C. 0.7994 0,8028 0.8056 0.8124 0.8183 0.8240 0.8291 0.8312
10.00 Satd. (10.75)O 11.00 12.00 0.8312 13.00 Solubility value for saturated solution obtained by extrapolation of speci6a gravity aurve.
... ...
...
0 7 4
1
I
b
I
ib 1 I
4 8 PER CENT WATER IN 2-BUTANONE
Figure 2. Specific Gravity of Solutions of Water in 2-Butanone us. Concentration Commercial technical anhydrous methyl ethyl ketone, obtained from the Shell Petroleum Company in 55-gallon drums, was used in the determinations of water solubility, and the measurements of specific gravity were performed with a Westphal balance. A constant temperature bath controlled to 25‘ * 0.05’ C. was used to bring the samples to temperature. Room temperature was controlled to 25’ * 1’ C. while the specific gravity determinations were made. All determinations were made in volume %, and later calculated to weight yo. Standard calibrated volumetric flasks and burets were used for measuring the volumesof solutions. ANALYTICAL PROCEDURES
%BUTANONE I N SALT-CONTAINING AQUEOUS SOLUTIONS. It was necessary to analyze aqueoua solutions containing salt and small quantities of sulfuric acid for 2-butanone. These additional materials interfered with the direct use of the specific gravity as an index of concentration. Therefore, the 2-butanone content was determined by distilling a 150-ml. sample from exactly 500 ml. of solution, and relating empirically the specific gravity of the distillate to the quantity of 2-butanone in the original solution. The s‘ample was placed in a particular assembly of flask (1000-ml.) and condenser, and heated with a hemispherical Glas-Col heating mantle with 115 volts alternating current applied. The relationship between the specific gravity of the distillate and the 2butanone content of the original solution is shown in Figure 3.
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1224
TABLE Iv.
PERFORMANCE
DATAON
EXTRACTION OF
Vol. 42, No. 6
THIODIACETIC ACIDFROM WATER SOLUTIONS WITH %RUTANONE
Diameter of column: 4.0 inches Packing: 0.5-inch Raschip rings Packed height: 8.08 feet Run
NO. 1 2
a
Concn. of Acid in Feed, Wt. % 13.07 13.52 13,52
Concn. of Aoid in Extract, Wt. % 12.55 13.89 18.08
Conon. of Aoid in Raffinate, Wt. % 1.54 0.42 0.97
Solvent Compn., Wt. % 2-Butanone 88.0 88.0 88.7
Rate of Feed CII.Ft./Hour 0,890 2.675 a. 545
Rate of Solvent Go. Ft./Hhur 1.147 3.103 2.078
Acid Recovered in Extract, % 89.3 97.2 93.2
Rate of Extract,ion Lb. Acid/H/ur 7.94 24.78 22.18
mutual solubilities at 25' C. of the three apex compositions in pairs were determined as follows: Component Pair Thiodiacetic acid in salt solution Thiodiscetic acid in 2-butanone %Butanone in aalt solution Salt solution in 2-butanone (actually only water dissolved in the 2-buta: none) Thiodiaoetic acid in water
ORIGINAL MLUTION CONCENTRATION , PER CENT 2 - B U T A N O N E
Figure 3. Curve for Empirical Distillation Analysis for 2-Butanone
The maximum concentration this method would handle was 8% 2-butanone. Solutions containing up to 100%butanone could be analyzed, however, by appropriate dilution. The specific gravity of the original solution was also determined to permit weight % figures to be computed. THIODIACETIC ACID IN AQUEOUSSOLUTIONS CONTAINING INORGANIC SALTS AND MINERAL ACID. Samples of 100 ml. of the unknown solution were pipetted into a 250-ml. separatory funnel and extracted with four 50-ml. portions of 2-butsnone saturated with water. The extract was collected in a tared 2 5 0 4 . beaker (containing tared stirring rod), and evaporated in a 130' C. vapor bath for 3 hours. (If the thiodiacetic acid content wasless than 2 grams per 100 ml., 2 hours were sufficient.) The samples were then dried in a vacuum oven at 75' C. and 29 inches of mercury vacuum for 4 hours. After cooling in a desiccator, the net weight waa recorded as thiodiacetic acid. This method proved reliable and reproducible, as shown by four analyses on a known solution containing 12.040 grams of thiodiacetic acid per 100 ml.: 12.060, 12.085, 12.000, 12.060.
Weight % 17.87 13.20 2.10 10.40 40.05
For these and subsequent solubility determinations, thiodiacetic acid, recrystallized twice from water and dried in a vacuum oven, WM used. To determine the maximum solubility, an excess of the acid was agitated for 1hour with the liquid of interest in the constant temperature bath. Samples were analyzed for their acid content by titration with standard base, and the specific gravity of the solution was determined with a Westphal balance. THlOOlACLTlC ACID
o.&O
I.PHPSE RfGiON
0I WEIQHT PER CENT Z.BUTPNONE
Figure 4, Ternary Equilibrium Diagram for the System 2-Butanone, Salt Solution, and Thiodiacetic Acid
CONSTRUCTION OF PEASE DIAGRAM
The process solution to be extracted was of the following composition : Weight % Thiodiacetic acid Sodium ohloride Sodium sulfate Water Total Free sulfuric acid (excess)
12.95 84.31 100.00 1 to 5% of the thiodiscntio acid
To construct a phase equilibrium diagram, therefore, s eelt solution of the same composition aa above, except for omission of the thiodiacetic acid (and ignoring the small exces8 of sulfuric aoid), waa prepared aa follows: Sodium ohloride Sodium sulfate Water
Total
Weight % 11.43 14.84 73.73
100.00
For points on the boundary of the triangular solubility plot,
Next, three d8erent mixtures of all three components were equilibrated, and the aqueous and organic phases were each analyzed for 2-butanone and thiodiacetic acid by methods already described. The phase equilibrium data are plotted on a triangular diagram in Figure 4. The exact location of the lines shown as dotted lines on the diagram was not determined. ESTIMATES OF COLUMN REQUIREMENTS
The concentration of the feed to a continuous extraction column was fixed by the conditions of the process at 12.8% acid by weight. A solvent composition corresponding to the Zbutanonewater azeotrope (11.0% water by weight) (6)was selected as the most feasible for initial calculations; higher concentrations would necesaitate an additional dehydration step in the solvent-recovery operation, and lower concentrations would require a larger column. In the laboratory, i t had been shown that a five-stage extraction with fresh portions of the 2-butanone-water azeotrope, each por
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1950
L
.
tion equal to 20% of the volume of the process solution, quantitatively removed thiodiacetic acid (greater than 99.6% recovery). Therefore, an extraction efficiency of 99% waa set as a tentative requirement for a continuous extraction apparatus. By the method of Hunter and Nash ( 4 ) ,the number of theoretical stages required was calculated as a function of the ratio of solvent-to-solution and also as a function of the Concentration of acid in the extract. These data are given for the range one to five stages in Figure 5. Thus, by increasing the number of stages from one to five, the acid concentration in the extract could theoretically be increased from 5% to 30%, and the solvent requirement decreased from 325 to 23 pounds per 100 pounds of solution treated. 9
40
LE. OF KXVENT PER 100 LS FEED SOWTION 87 120 160 2p 2“ 280
320
90
1225
OPERATION OF COLUMN
Only limited experimental data were obtained. These are re. ported as three runs in Table IV. Previously, a short preliminary run had been made to ascertain that the column worked. Best operation seemed to be obtained with the butanone as the continuous phase, and all subsequent runs were made with this the caw. It was also found necessary to introduce some supplementary water with the 2-butanone azeotrope (solvent), reducing the %butanone concentration to 86 to 88%, to prevent precipitation of salt in the column. The runs in Table IV are representative of sections of a production campaign during which about 40 pounds of thiodiacetic acid were made, Unfortunately, the opportunity to return to this work and oompletely evaluate the operating variables has not been presented. RESULTS AND CONCLUSIONS
PER CENT THlDDlACETlC ACID IN EXTRACT
Figure 5. Plot of Solvent-Feed Ratio and Acid Concentration in Extract V.S. Theoretical Stages No data were available on the height of a theoretical stage or transfer unit for this system. Since it was desired to set up equipment to produce about 100 pounds of thiodiacetic acid, i t was decided to build a 4inch column in the laboratory to obtain quantitative design data. COLUMN CONSTRUCTION
An extraction column was constructed of &inch standard glass pipe, The column was 8.0 feet high, with a packed height of 6.08 feet, a top disengaging section of 0.92 foot, and a bottom disengaging section of 1.0 foot, The packing support was large-mesh stainless steel screen supported at a flanged joint in the column, and the packing was 0.5-inch ceramic Raschig rings. The free volume in the packed section was measured as 59.1% by water displacement. The liquids were supplied to the column by two small centrifugal pumps through appropriately sired rotameters, previously calibrated with the fluids to be metered. The distributors were peripherally drilled stainless steel pipe caps. The lower liquid exit was through a movable leg to permit adjusting the interface level. v, ? .
‘Lm
The &inch column proved effective for the extraction of thiodiacetic acid with an over-all recovery better than 95%. No difficulties were experienced, other than early ones with salt de osition in the column. !‘he number of theoretical stages obtained in the experimental! runs were estimated a hically as between one and three in all three cases, making g e t e i g h t , equivalent to a theoretical stage fall between 2 and 6 feet. More extended treatment of the limited performance data wah not believed warranted. Se arate material balances were made for acid, 2-butanone, end salt L r each run. These were within 4% of balance in all cases exce t one, where the unbalance figure rose to 10% (thiodiacetic acidialance in run 3). This brief description indicates that the combination of solveu1 extraction and the ealtin out effect may be useful in other a plications, particularly in t f e isolation of organic compounds t?orri a ueous solution. This, incidentally, is an example of a process wlere solvent extraction is the only feasible means of product separation. ACKNOWLEDGMENT
The authors wish to express their appreciation to the C. P. Hell Company of Akron, Ohio, who sponsored this work a t Battelle for permission to publish the results of the investigation. Grateful acknowledgment is also made to Francis A. Warren, now of the Naval Ordnance Testing Station, Inyokern, Calif., for his assistance in carrying out much of the experimental work while n member of the Battellestaff. LITERATURE CITED (1)
Bearse. A. E. (to C. P. Hall Company). U. S. Patent 2,426,224 (Aug. 6,1947).
(2) Evans, T. W., IND.END.CREM.,ANAL.ED.,8, 206 (1936). (3) Ginninns. P. M., Plonk, D., and Carter, E., J. Am. Chem. Svc.. (4)
62,1823 (1940). Hunter. T. G., and Nash, A. W., J . SOC.Chem. Ind. (Lundon).51. 96T (1934).
(5) (6)
Langedijk, S. L.,Ibid., 1938,p. 891R. Prager and Jacobson, “Beilstein’s Handbuch der organisnbeu Chemie,” 4th ed., Vol. 3. p. 263, Berlin, Springer, 1921.
RECEIVEDJanuary 18, 1980.
* * * * *
The July issue (Jf I.&E.C. will conteiii B group of papers which were a part of the Symposium oti Adsorption conducted a t the Atlantic City A.C.S. Meeting last September by the Division of Petroleum Chemistry with the Divisions of Anctlytical and Micro, Industrial and Engineering] and Physical and Inorganic Chemistry, This sympofiiumwaa presented in four sessions to consider (1) the general nature of the subject and ita application in (2) research, (3) analysis, and (4)industry. The papers to be published in July are representative of these four categories: Fundamentals of the subject are covered in papers on the adsorption of light hydrocarbons by activated charcoal and adsorption equilibrium data for hydrocarbon gas mixtures; applications in research by surface area measurements of alumina and calcined alumina hydrates; analytical techniques by the distribution of chloroplast pigments in an adsorption column and a theoretical analysis of the adsorptive process; and industrial developments by discussions of a new method for separating linear aliphatic from branched and cyclic hydrocarbons, the separation and desulfurization of cracked naphthas, the separation of iso- and n-paraffina, and liquid-phase adsorption equilibria and kinetics.
