K. Claessens and F. Fontyn
Rijkshoger Technisch lnstituut voor de Kernenergiebedrijven Brussels I, Belgium
Testing Distillation Columns with
Cis-Trans Decalin
M i x t u r e s for testing distillation columns a t pressures lower than 10 mm H g are rare (1). Fenske, et al. proposed the syst,em cis-trans-decalin (9) for this purpose. Since most commercial decalins are mixtures of the cis and trans isomers in varying proportions according t o their origin, we had our students undertake the separation of decalin mixtures from various sources using several distillatiou columns under reduced pressure. They also determined the equilibrium diagram for mixtures of decalins.
pure cis-decalin remained a t the bottom of the distillation apparatus. Testing Distillotion Columns with Cis-Trons-Decalin
The Procedure
The course of the distillations and the purity of all fractions was followed by glc. Smaller amounts of pure cis- and trans-decalin were obtained by preparative glc on an Aerograph 700 apparatus. Separation of 6 ml samples was performed on a 21-m column filled with 10yo Carbowax 201'1 on Chromosorb A 20/30 mesh. Temperature was 150°C and carrier gas flow 600 ml/ min hydrogen.
Preporotion of the Pure Isomers
Anolysis of Decolin Mixtures
We needed the pure isomers t o make up mixtures of known compositio~i. Pure tvans-dccalin was prepared by the method of Chiurdoglu and Jaminet (S), first. proposed by Zelinsky and Turova-Pollak (4). Starting with a commercial mixture of cis- and tvansdecalin, the cis isomer was isomerized t o trans under the influence of AlC1,. Pure trans-decalin was then distilled from the reactiou mixture through a 14-plate column a t 6 mm Hg, some cracking products (substituted cyelohexanes, etc.) coming over first. The boiling point was 53°C. Pure cis-decalin was obtained by slow distillatiou of a commercial mixture through our 14-plate column a t 7 mm Hg. With this column we could not obtain pure trans-decalin; even the first fractions still contained considerable amounts of cis-deealin. At the end of the distillation, however,
Samples coming from the equilibrium still, and those from the distillation of the commercial decalins, were analyzed by refractive index and by glc. As a first indication, analysis was made with the use of the refraetive index of the mixtures. For mixtures of cis- and trans-decalins, n? as a function of the % trans-decalin is given in the literature (5). This method failed t o determine the composition of a sample with EastmanKodak material because this contained considerable amounts of tetraliu. Quantitative analysis by glc was more accurate, so that the trapezoidal construction of Condal-Bosch ( 6 ) was applied. We used a PerkinElmer (Ueberlingen) 116 E Fraktometer, with a 2-m column filled with Apiezou "M" grease (lOyc on Chromosorb R 60/SO mesh) a t 17S°C. Carrier gas flow was 70 m/miu helium.
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I n order to have the detector linear, we injected S p1 samples of 20 vol. yc solutions of the decalin mixture in isooctane. The detector was calibrated with the pure cis- and trans-decalin coming from the preparative glc.
Table 2. Number of
Eauilibrium Data for the Svstem
% Tvona-deoalin with -Relraetlon Indexnottom Tor,
Deteymingtmn
% T~ona-deoalinwith -Quantitative G L C nottom Tor,
Composition o f Commercial Decalins
Some decalins of different origin were analyzed by quantitative glc. The results are given in Table 1. Table 1.
Composition of Some Commercial Decolins
Oricin British Drug Houses Carlo-Erba Dehydag Eastman-Kodak
Noary-Baker Merok IIopkin and Williamr Hopkin and Williams ia6n
Catalogue Number 269850 441201
%
Table 3. Testing Distillation Columns with Cis-Trons Decolin
',rrana-
decalin
Sample P 1905
30.3 36.6 40.6 36.8
7023 3101 3598 3600
38.0 34.4 46.8 46.1
24219
62 1
Remarks
Contained tetrhlin
Equilibrium Apparatus ond Data
Starting from synthetic mixtures, made up with the pure cis- and trans-decalins, the equilibrium diagram was determincd with a simplified Othmer still, as described in a current manual of practical physical chemistry (7). However, an asbestos insulation was wrapped around the apparatus, which was heated with an infraredlamp of 300 w, controlled by means of a rheostat. The pressure of 7 mm Hg was held constant by glass manostat. After about 30 min the equilibrium was reached; then samples were taken from bottom and top product and analyzed using the methods described in a previous section. The equilibrium data are given in Table 2. Compositions are indicated in % trans-decalin. Testing Some Fractionating Columns
Once the equilibrium diagram was obtained, we used it to determine the number of theoretical plates of two types of fractionating columns, under conditions of t,otal reflux. The first column was of the Vigreux type, with 65-cm length and 2.5-cm diamet,er, of Quickfitt origin. The second column was of the sieve-plate type and was composed of three elements with five real sieve-plates each. This column was manufactured by Schott und Gen., Mains, Germany, and is known under the name of Sigwart column.
Compoaition of Testing Mixture (% trans1
Columns Vigreux Sigwart Si~~vart
40 13 25
Number
Preasore (mm H d
Throughput
Wminl
of Theoretical Plates
7
2.2 4.3 4.1
4 14 14
9 10
The throughput was determined principally from the temperature rise and the debit of the cooling water a t the top of the columns. The heats of condensation of the decalins were calculated with the Clapeyron equation. The results of this testing can be seen in Table 3. Both determinations at the Sigwart column were made a t slightly higher pressures than 7 mm Hg. However, as the relative volatility only slowly rises with lowering pressure, small pressure differences will not be harmful. Acknowledgment
Our thanks are due t o Professor M. Verzele of the University of Ghent, Ghent, Belgium, for the separation of decalin samples into the cis and trans isomers by preparative glc. Literature Cited
(1) KRELL,E., "Hendbuch der Laboratoriamsdestillation," (1st ed.), Deutscher Verlag der Wissenschaften, Berlin, 1958, p. 124. -...
(2) FEN~KE, M. R.,MEYERS,H. 8., AND QUIGGLE, D., ha.Eng. Chem., 42,649 (1950). G., AND JAMINET, J. J., Bull. Sac. Chim. Belges, (3) CHIURDOGLU, 62,448 (1953). N. D.. AND TUROVA- POLL^. M. B.. Rer.., 65.1173. (4) . . ZELINSKY. . 1299 (1932). ( 5 ) SEYER,W. F.,AND WALKER, R . D., J . Am. Chem. Soc., 60, 2125 (1938). (6) CONDAL-Boscn, L., J. CAEM.EDUC.,41, A242 (1964). (7) DAYIDSON, A . W., VANKIOOSTER, H. S., BAUER,W. M., AND JANZ,G . J.. "Laboratory Manual of Physical Chemistry" (4th ed.), John Wiley & Sons Inc., New York, 1956, p. 98.
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Volume 45, Number 10, Ocfober 1968
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