SEPARATION OF BINARY SYSTEMS B Y STEAM DISTILLATION FROM
AQUEOUS SOLUTIONS Biased Steam Distillation K I M - H O K K O H Bureau of Comniodztj Inspection and Quarantine, T a i p i . Taire'an
Following a study of the separation of linalool and camphor b y steam distillation from an aqueous solution of sodium salicylate, phthalate, or benzoate, mixtures of ethyl salicylate-safrole and methyl benzoatelinalool were steam-distilled from aqueous solutions of sodium salicylate and benzoate, respectively. The orders of distillates were reversed compared with steam distillation from water alone. The postulate that similarity of chemical structure i s impprtant for the intermolecular attractive energy was supported by steam distillation of a mixture of ethyl benzoate and 1 -menthol from an aqueous solution of sodium benzoate.
THE separatiqn of the binary system linalool (b.p. 198.3'
( M - .V)
C.
at 760 rnm.)-camphor (b.p. 204' C. a t 760 mm.) by distillation from a n aqueous solution of sodium salicylate ( 7 ) led the author to extend the previous investigation. T h e mechanism of this separation may be explained in the following way. When the molecules of sodium salicylate come in contact with molecules of camphor and linalool: the intermolecular attractive energy of each may be taken as M and S,respectively. .M and .V are not largc enough to cause reaction to take place. The equilibrium of the binary system with the sodium salicylate solution is modified when heated, and vapors of linalool and camphor distill out. LVhen the binary system linalool-camphor is distilled from water alone, the intermolecular attractiveenergy of water with camphor and linalool is taken as 1l.m and T17n,and it is proposed that
kY
> (Jt7m- I I n )
Therefore the molecules of camphor are held back and the vapor pressure of the camphor is changed. Thus the mixture of linalool and camphor is separated efficiently. I n this paper the distillation of a binary mixture from aqueous salt solutions is referred to as "biased steam distillation." This implies that the intermolecular attraction between the components of the binary system and the solute is of comparable magnitude. T h e solute in the aqueous solution is called a "biasing agent." Biased steam disrillation can be applied not only in the separation of t\vo compounds the vapor pressures of which approach equality and of the azeotropic mixtures, but also in reversing the order of distillates of the components of a binary system. This report discusses the effect of the sodium salts of aromatic
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I
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1
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SODIUM SALICYLATE SOLUTION
1
+ 90.0
$ 0
FROM SODIUM SALICYLATE SPLUTION +FROM SODIUM PHTHALATE
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OFROM SODIUM BENZOATE a
80Pl
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W
FROM WATER ALONE I
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VOLUME
Figure 1.
SOLUTlON SOLUTION
4 0.0
30
(ML.)
Distillation of mixture of linalool and camphor
l&EC PROCESS DESIGN A N D DEVELOPMENT
IO
20 VOLUME
30
40
50
( M L.)
Figure 2 . Distillation of mixture of ethyl salicylate and safrole
carboxylic acids (sodium benzoate and phthalate) and a phenolic aromatic carboxylic acid (salicylate). Experimental
Materials. Chemicals used as biasing agents were all chemically pure. Linalool was purified by the butyl borate process from Ho oil (oil of camphor containing more than 75% of linalool). Safrole was purified from oil of camphor by freezing followed by distillation. Camphor and menthol were the refined pro'ducts of Taiwan. Methyl benzoate, ethyl benzoate. and ethyl salicylate were prepared by the general esterification method. The volatile materials were all rectified and fractions boiling within 0.1' C. were collected. Vapor phase chromatography of volatile materials showed them to be at least 99%;.pure. Procedure. A given quantity of the binary system was steam-distilled from an aqueous solution of the biasing agent. All aqueous solutions of biasing agents were neutralized by a n excess of the corresponding acids. The oily layer of the distillate was \vashed wii:h 5% sodium carbonate solution and ivater until neutral. As the base of comparison, the same san;ple was distilled from water alone. For each fraction the quantitative determinations were carried out and the results were compared graphically by plotting. Separation of Binary System, Linalool-Camphor. To compare the separation effect of the sodium salts of benzoic, phthalic. and salicylic acids as biasing agents, the mixture (.V,)*S 1,4599) of linaloB1 and camphor (linalool 90y,, camphor was selected, since the vapor pressures are closely similar (linalool b.p. 198.3' C. at ?60 mm.; camphor b.p. 204' C. a t 760 mm.). For each batch, 30 ml. of the mixture of linalool and camphor were steam-distilled in 150 grams of water Iiith 1 iO grams of the biasing agent. Thirty milliliters of the same sample liere also distilled from 300 grams of \vater alone.
1OY6)
'The results of the det.erminaGon of linalool content by vapor phase chromatography are shown in Figure 1. which indicates that sodium salts of benzoic acid and phthalic acid may be used as biasing agents in this case. and sodium salicylate is most effective. Similarity of Chemical Structure. An effective separation of the binary system linalool-camphor by steam distillation in an aqueous solution of sodium salicylate led the author to attempt the separation of a mixture of ethyl salicylate and safrole by biased steam clistillation. Fifty milliliters of a mixture of equal quantities ( v . ; ~ . ) of ethyl salicylate (b.p. 233.75' C. a t 760 mm.) and safrole (t1.p. 234.5' C. at 760 mm.) were distilled from approximately 500 grams of 50% sodium salicylate solution. For each solution the ester content was determined.
Figure 2 shows the superiority of sodium salicylate as a biasing agent-i.e., the attractive energy between sodium salicylate and ethyl salicylate changed the vapor pressure of ethyl salicylate, causing it to distill out after safrole. This suggests that the intermolecular attraction may be caused by the similarity of chemical structure. T o obtain further evidence, 30 ml. of a mixture of equal quantities (v./v.) of methyl benzoate (b.p. 198.13'C. a t 760 mm.) and linalool (b.p. 198.3' C. a t 760 mm.) were distilled from 150 grams of water with 150 grams of sodium benzoate. For each fraction the ester content was determined. The result is shown in Figure 3, which indicates that the evaporation of the methyl benzoate molecules was retarded because the intermolecular attractive energy between methyl benzoate and sodium benzoate was larger than that between linalool and sodium benzoate. Thus the order of distilling out was reversed as compared to distillation from water alone. Then a mixture of two parts of ethyl benzoate (w.) (b.p. 212.08' C. a t 760 mm.) and one part of 1-menthol (w.) (b.p. 216' C. at 760 mm.) was separated under the conditions described above. Figure 4 indicates that the attractive energy between sodium benzoate and ethyl benzoate is larger than that between the same salt and 1-menthol; therefore the separation was less effective by biased steam distillation than by steam distillation from water alone. This result of the "biased steam distillation" provided additional support for the conjecture that intermolecular attraction may be increased by the similarity of chemical structure.
Conclusions
In distillation of a mixture of linalool and camphor from the sodium salt solutions of benzoic, phthalic, and salicylic acids, linalool was most effectively separated from camphor by the sodium salicylate solution. Sodium salts of benzoic and phthalic acids were found that might be used as biasing agents in this case. The difference of the intermolecular energy may be increased by the similarity of chemical structure. Support of this was afforded when a mixture of ethyl salicylate and safrole \vas biased-steam-distilled, for the structure of ethyl salicylate is more like that of sodium salicylate than is the structure of safrole. Further evidence was given by biased
8 0 * o r A F R O M WATER A L O N E W
*FROM SODllJM BENZOATE SOLUTION
t I< 0
w
m A F R O M WATER ALONE I I-
k W
I
5 0.0L VOLUME
Figure 3. linalool
(ML3
Distillation of mixture of methyl benzoate and
I
1
20
IO
VOLUME
30
( M U
Figure 4. Distillation of mixture of ethyl benzoate and 1 -menthol VOL. 4
NO. 1
JANUARY 1 9 6 5
27
steam distillation of mixtures of methyl benzoate-linalool and ethyl benzoate-1-menthol from a n aqueous solution of sodium benzoate, for the Structures of methyl benzoate and ethyl benzoate are obviously more closely similar to that of sodium benzoate than are the structures of linalool and 1-menthol. T h e mechanism of the biased steam distillation, however, has not been completely established. Further studies in this field are in progress.
Acknowledgment
T h e author thanks M. D. Sutherland and the late Sinichiro Fujise for giving much advice in the latter part of this work. literature Cited K.-H., Ind. Research) Tatzcan ' (l)
9 35 (1958). RECEIVED for review May 22. 1962 RESUBMITTED August 13, 1964 ACCEPTED September 17, 1964
PRECIPITATION OF PLUTONIUM TRIFLUORIDE G L E N N A.
B U R N E Y A N D
F R A N K W . TOBER
Savannah River Laboratorv, E. I . du Pont de S r m o u r s t 3 Co.. Aiken, S. C.
A process was developed to precipitate plutonium trifluoride from plutonium nitrate solution.
Large crystals are precipitated b y controlling the ratio of nitric acid to hydrofluoric acid to maintain the required plutonium trifluoride solubility during addition of the plutonium nitrate solution to the precipitant. The solubility of the trifluoride i s decreased prior to filtration b y lowering the ratio of nitric acid to hydrofluoric acid. The soluLosses of plutonium to the filtrate are minimized b y adding bility product of PuF3 i s 2.4 + 0.4 X ascorbic acid to the feed immediately before precipitation to reduce Pu(IV) and adding sulfamic acid to decrease the rate of oxidation of Pu(ll1). The plutonium trifluoride is easily filtered and dried to the anhydrous salt and is pure enough for subsequent reduction to plutonium metal.
THE o,bjFcti,ve of this work was to develop a plant process for precipitation of plutonium trifluoride. an intermediate in the production of plutonium metal ( 2 ) . Although plutonium trifluoride had been prepared in the laboratory, no study had defined conditions for effectively maintaining plutonium in the trivalent state in a nitrate system or for precipitating the trifluoride under conditions which would yield the large, easily filtered crystals required for a production process. In the development of the process, the effects of the important variables were studied, including reductants for Pu(IV), composition of the precipitant. the ratio of nitric acid to hydrofluoric acid during formation and digestion of the precipitate. the degree of agitation, and the method of combining the plutonium solution with the precipitant. Also, the separation of plutonium from cationic impurities present in the feed solution was measured. This precipitation process has been used successfully in a production plant for several years. T h e plant process and the conversion of plutonium trifluoride to plutonium metal have been described by Orth (2).
trifluoride florved continuously from the first vessel into the second-stage vessel, where more fluoride was added. .4lthough the one-stage process was found to perform adequately for the laboratory studies. the two-stage process was selecteti for plant operation because it was quicker and offered more favorable nuclear safety. Most of the laboratory tests were made with 5-gram batches of plutonium. T h e precipitator was a 500-ml. polyethylene vessel 5.5 cm. in diameter. T h e contents were stirred by a paddle having two sets of four blades that measured 4.8 cm. from tip to tip. T t e paddle was rotated at approximately 600 r.p.m. The solutions were added to the precipitator through capillary polyethylene tubing. The precipitate \cas filtered through a disk of fritted Teflon (Du Pont) with a diameter of 1.8 cm. and a mean pore size of less than 10 microns. The fritted material was not uniform; to compensate for the difference in porosity of different filters, the filtration time ivas measured relative to the time required to transfer a n equal volume of \+ater through the filter under identical conditions. T h e plutonium(II1) nitrate feed solution was prepared by cation exchange. T h e hydrofluoric acid and nitric acid were reagent grade.
Experimental
Discussion
Two methods were studied for precipitating plutonium trifluoride. T h e first utilized a single-stage precipitator, the second utilized a two-stage unit. I n the one-stage precipitation, all of the plutonium nitrate feed solution and some of the fluoride precipitant were added simultaneously and at controlled rates to a nitric acid-hydrofluoric acid diluent solution in the precipitator. After feed addition was complete, more hydrofluoric acid was added to depress the solubility of plutonium trifluoride. In the two-stage precipitation. the plutonium feed and a fraction of the fluoride precipitant lvere added simultaneously a n d a t controlled rates to a nitric acid-hydrofluoric acid diluent solution in the first-stage vessel. A slurry of plutonium
A number of variables influence the physical properties and solubility of plutonium trifluoride : the plutonium valence, nitric acid and hydrofluoric acid concentrations in the precipitation media. the degree of agitation of the precipitate. and the manner in which the reactants are combined. The effects of these variables were studied in the laboratory. and conditions were defined for a plant precipitation process. Feed Composition and Valence Adjustment. T h e precipitation of essentially pure plutonium trifluoride is required for a practical plant process. The presence of plutonium tetrafluoride leads to high losses to the filtrate and to a precipitate with undesirable physical properties. In contrast to the tetrafluoride, the trifluoride is crystalline and contains no
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l&EC PROCESS DESIGN A N D DEVELOPMENT
