Liquidliquid equilibria for the quaternary system perfluoromethylcyclohexane (PFMCH)1-heptenen-heptanen-hexane at 288.15 K and for the ternary systems PFMCH1-heptenen-heptane, PFMCH1-heptenen-hexane and PFMCHn-heptanen-hexane at 279.15 K and 288.15 K are reported.

The experimental results are compared with predicted values calculated using the NRTL and the UNIQUAC models

Bernardo-Gil, M. G.

Soares, Luís Jesus Santos

Fluid Phase Equilibria

M.G. Bernardo-Gil

L.J.S. Soares

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Liquid—liquid equilibria of systems containing perfluoromethylcyclohexane

Universidade do Minho: RepositoriUM

Fluid Phase Equilibria, 61 (1990) 121-130 Elsevier Science Publishers B.V.. Amsterdam 121 LIQUID-LIQUID EQUILIBRIA OF SYSTEMS CONTAINING PERFLUOROMETHYLCYCLOHEXANE M.G. BERNARDO-GIL Dep. Eng. Quimica, I.S. T., 1096 Lisboa Codex (Portugal) L.J.S. SOARES Universidade do Minho, L. PaGo, 4719 Braga Codex (Portugal) (Received July 1, 1988; accepted in final form June 29, 1990) ABSTRACT Bemardo-Gil, M.G. and Soares, L.J.S., 1990. Liquid-liquid equilibria of systems containing perfluoromethylcyclohexane. F&d Phase Equilibria, 61: 121- 130. Liquid-liquid equilibria for the quatemary system perfluoromethylcyclohexane (PFMCH)-l-heptene-n-heptane-n-hexane at 288.15 K and for the ternary systems PFMCH-1-heptene-n-heptane, PFMCH-1-heptene-n-hexane and PFMCH-n-heptane-n- hexane at 279.15 K and 288.15 K are reported. The experimental results are compared with predicted values calculated using the NRTL and the UNIQUAC models. INTRODUCTION Multicomponent mixtures consisting of perfluorocarbons and hydro- carbons change swiftly from type to type pattern over a small temperature range. Following our experimental determination of binary solubility data for some perfluoromethylcyclohexane-hydrocarbon systems (Bernardo-Gil and Soares, 1988), this paper reports the results of measurements on liquid-liquid equilibrium for ternary and quatemary systems containing perfluoromethylcyclohexane (PFMCH), l-heptene, n-heptane and n-hexane. Predictions of equilibrium data for these mixtures were made using NRTL and UNIQUAC perfluoromethylcyclohexane-hydrocarbon parame- ters obtained from binary data. Hydrocarbon-hydrocarbon parameters were calculated by correlating the ternary data. The results are compared with the experimental ones. 0378-3812/90/$03.50 0 1990 - Elsevier Science Publishers B.V. 122 EXPERIMENTAL Materials PFMCH (Fluka, = 98% (GC)), -h n exane, n-heptane (p. a., Merck) and 1-heptene (Fluka, 2: 95%) were used as supplied. Procedure The experimental work was carried out using a thermostatted miniature cell similar to that described by Soares et al. (1974). Temperature was measured within an accuracy of 0.01 K by means of a precision thermom- eter. The mixtures were stirred with a magnetic stirrer for at least 30 n-tin and allowed to settle during a 4 h period. The tie-lines were obtained by analysing the compositions of the two conjugate phases in equilibrium by means of a gas chromatograph (Pye-Unicam) connected to an integrator (Varian CDS 111). Calibration curves were obtained by using at least 10 mixtures of known composition, for which four to six chromatograms were obtained. Four to six samples of both phases were analysed to minimize the experimental error. The observation of the results shows also whether equilibrium has been reached. TABLE 1 Experimental liquid-liquid equilibrium compositions for the ternary system PFMCH (l)-l- heptene (2)-n-heptane (3) Temperature (R) 279.15 Weight fraction Xl, x31 x,2 x32 0.9451 0.0159 0.2469 0.2200 0.9410 0.0239 0.2510 0.2988 0.9448 0.0242 0.2554 0.3320 0.9447 0.0298 0.2556 0.3910 0.9448 0.0362 0.2569 0.4609 0.9432 0.0402 0.2658 0.5362 288.15 0.9188 0.0716 0.3555 0.5567 0.9191 0.0686 0.3546 0.5294 0.9193 0.0601 0.3427 0.4753 0.9216 0.0425 0.3310 0.3586 0.9230 0.0338 0.3233 0.2960 0.9237 0.0266 0.3144 0.2422 0.9260 0.0217 0.3094 0.2069 0.9265 0.0135 0.3000 0.1250 123 TABLE 2 Experimental liquid-liquid equilibrium compositions for the ternary system PFMCH (l)-l- heptene (2)-n-hexane (3) Temperature (R) 279.15 Weight fraction X11 x31 x12 x32 0.9042 0.0750 0.4143 0.4254 0.9179 0.0519 0.3598 0.3602 0.9268 0.0392 0.3348 0.3162 0.9345 0.0280 0.3212 0.2502 0.9390 0.0207 0.2917 0.1973 0.9412 0.0128 0.2691 0.1272 288.15 0.9158 0.0197 0.3399 0.1389 0.9006 0.0330 0.3877 0.2113 0.8969 0.0443 0.3902 0.2363 0.8786 0.0660 0.4506 0.2732 0.8593 0.0870 0.5024 0.2874 0.8195 0.1252 0.6147 0.2579 Tables 1-3 summarize the experimental results obtained for the ternary systems. Quatemary tie-line data are presented in Table 4. ANALYSIS OF RESULTS Prediction of ternary and quaternary liquid-liquid equilibrium data was realized using the well-known NRTL and UNIQUAC models proposed by TABLE 3 Experimental liquid-liquid equilibrium compositions for the ternary system PFMCH (l)-n- heptane (2)-n-hexane (3) Temperature (R) 279.15 288.15 Weight fraction x,1 x31 42 x32 0.8973 0.0812 0.4390 0.4208 0.9094 0.0659 0.4091 0.3812 0.9147 0.0550 0.3873 0.3521 0.9239 0.0357 0.3482 0.2677 0.9272 0.0268 0.3271 0.2199 0.9324 0.0199 0.3136 0.1702 0.9376 0.0098 0.2943 0.0968 0.9083 0.0124 0.3968 0.0750 0.8908 0.0352 0.4501 0.1600 0.8669 0.0627 0.4968 0.2205 0.8455 0.0865 0.5572 0.2350 0.8226 0.1054 0.5942 0.2350 124 TABLE 4 Experimental liquid-liquid equilibrium compositions for the quaternary system PFMCH (1)-l-heptene (2)-n-heptane (3)-n-hexane (4) Temperature (K) Weight fraction X1, XX, &, X1* x32 x42 288.15 0.9148 0.0134 0.0063 0.3201 0.1137 0.0457 0.9095 0.0258 0.0115 0.3485 0.1897 0.0755 0.8782 0.0213 0.0530 0.4485 0.1119 0.2252 0.8421 0.0183 0.0982 0.5228 0.0676 0.2849 0.8355 0.0436 0.0933 0.5360 0.1324 0.2643 0.8848 0.0559 0.0412 0.4396 0.2820 0.1838 0.9002 0.0390 0.0334 0.4014 0.2477 0.1772 0.9048 0.0394 0.0207 0.3880 0.2653 0.1175 0.8865 0.0354 0.0479 0.4484 0.1834 0.2082 0.8627 0.0317 0.0784 0.5245 0.1163 0.2519 0.8309 0.0302 0.1126 0.5925 0.0799 0.2582 0.8677 0.0409 0.0767 0.5320 0.1561 0.2540 0.8787 0.0491 0.0537 0.4751 0.2213 0.2106 0.8892 0.0521 0.0378 0.4270 0.2773 0.1842 0.8981 0.0519 0.0288 0.4162 0.3043 0.1498 0.9063 0.0537 0.0179 0.3869 0.3585 0.1042 0.9081 0.0574 0.0113 0.3748 0.3904 0.0697 .6- yO .2 - / 0 II 0 O- 0 ~ \ 2 .4 Fig. 1. Liquid-liquid equilibrium diagram for PFMCH-n-heptane-n-hexane at (- ) experimental tie-lines; (D) binary data; (0) NRTL equation (ai2 = 0.3. ct 23 = 0.3); (0) UNIQUAC equation. 279.15 K: lx 1s = 0.4, 125 TABLE 5 Recommended values for the NRTL and UNIQUAC parameters at 279.15 K and 288.15 K System NRTL UNIQUAC a12 b 6 Cl2 c21 WI 6) PFMCH-n-hexane 279.15 0.4 392.1 545.1 131.0 3.579 288.15 0.4 347.5 462.8 147.4 - 20.53 PFMCH-n-heptane 279.15 0.3 376.9 568.6 126.7 20.16 288.15 0.3 339.5 538.7 122.0 15.56 PFMCH-1-heptene 279.15 0.3 387.9 602.1 141.1 18.02 288.15 0.3 343.6 600.0 124.4 24.24 Renon and Prausnitz (1968) and by Abrams and Prausnitz (1975) respec- tively. Agreement between calculated and experimental data is expressed in terms of composition root-mean-square deviations (RMSD) : .6 .6 x2 Fig. 2. Liquid-liquid equilibrium diagram for PFMCH-n-heptane-n-hexane at 288.15 K. Symbols as in Fig. 1. 126 TABLE 6 RMSD (X 103) between calculated and experimental values System fK1 Type NRTL UNIQUAC Aa Bb Aa Bb PFMCH-n-heptane- 279.15 II 9.5 9.5 8.9 15.5 n-hexane 288.15 I 4.2 9.9 8.4 10.2 PFMCH-l-heptene- 279.15 II 7.8 8.7 7.8 7.8 n-hexane 288.15 I 12.8 14.3 17.2 17.2 PFMCH-l-heptene- 279.15 II 9.7 10.8 9.6 11.3 n-heptane 288.15 II 4.7 5.2 4.2 4.4 PFMCH-l-heptene- 288.15 II 10.5 12.1 13.2 18.0 n-heptane-n-hexane 1 A: Direct correlation of ternary data, keeping (Y,, constant. B: For the PFMCH-hydrocarbon parameters the linear correlation with temperature was used. The hydrocarbon-hydrocarbon parameters were determined from the ternary data. 6- Fig. 3. Liquid-liquid equilibrium diagram for PFMCH-l-heptene-n-hexane at 279.15 K. Symbols as in Fig. 1. 127 (1) Binary NRTL and UNIQUAC parameters were determined using two alternative approaches. Method A involved direct correlation of ternary data, the number of adjusted parameters varying from 1 to 6, keeping (Y,] constant (0.3 for hydrocarbon-hydrocarbon systems (Renon and Prausnitz, 1968) and the recommended values for PFMCH-hydrocarbon binaries (Bernardo-Gil and Soares, 1988)). In method B, for the PFMCH-hydro- carbon binaries, the linear temperature dependence of parameters obtained from the correlation of binary solubility data was used; hydrocarbon-hydro- carbon parameters were calculated adjusting ternary tie-line data. Fig. 4. Liquid-liquid equilibrium diagram for PFMCH-1-heptene-n-hexane at 288.15 K. Symbols as in Fig. 1. Fig. 5. Liquid-liquid equilibrium diagram for PFMCH-1-heptene-n-heptane at 279.15 K: (- ) experimental tie-lines; (W) binary data; (0) NRTL equation ((xl2 = 0.3, cx13 = 0.3, a23 = 0.3); (0) UNIQUAC equation. Binary parameters from ternary data were calculated using the Nelder- Mead method for the minimization of the following objective functions: (2) MN 2 with 3M > L, M being the available number of tie-lines, N the number of components and L the number of parameters. The NRTL and UNIQUAC parameters recommended for the PFMCH- hydrocarbon binaries are presented in Table 5. Table 6 shows the values of RMSDs between experimental and calculated compositions. Figures 1-6 represent the experimental and calculated tie-lines. 129 CONCLUSIONS The experimental results were correlated in terms of NRTL and UN- IQUAC equations, which represent the binodal curves and the tie-lines correctly either for type I or type II systems. With a slight loss of accuracy (relative to the results obtained from direct correlation of data for individual ternary systems) it is possible to obtain a set of NRTL and UNIQUAC parameters applicable to all multicomponent mixtures of PFMCH and hydrocarbons. The overall results are better for the NRTL equation with use of recom- mended values of aij, although the predicted multicomponent data are strongly dependent on the selected (Y,, for the partially miscible binaries. 6 Fig. 6. Liquid-liquid equilibrium diagram for PFMCH-l-heptene-n-heptane at 288.15 K. Symbols as in Fig. 5. 130 LIST OF SYMBOLS A, B methods of correlation of ternary data (Table 6). b ‘J NRTL parameters, K, where b,, = ( gij - gJj)/R C UNIQUAC parameters, K, where czJ = ( ulJ - ujj)/R g:, uij measures of the interaction energy between molecules i and j xij molar fraction of component i in phase j TJ weight fraction of component i in phase j q, measure of the interaction energy between groups i and j ff 11 non-randomness NRTL parameter ACKNOWLEDGEMENTS The authors express their gratitude to the Instituto National de Investiga@o Cientifica, which through the C.P.Q. (Universidade Tecnica de Lisboa) and C.Q.P.A. (Universidade do Minho) supported this work. The computing facilities offered by Centro de Informatica (I.S.T.) are also gratefully acknowledged. REFERENCES Abrams, D.S. and Prausnitz, J.M., 1975. Statistical thermodynamics of multicomponent liquid mixtures: a new expression for the excess Gibbs energy of partly or completely miscible systems. AIChE J., 21: 116. Bemardo-Gil, G.S. and Soares, L.J.S., 1988. Mutual binary solubilities: perfluoromethyl- cyclohexane/hydrocarbons. Fluid Phase Equilibria, 41: 205 Renon, H. and Prausnitz, J.M., 1968. Local composition in thermodynamic excess functions for liquid mixtures. AIChE J., 14: 135. Soares, L.J.S., Ashton, N.P. and Ellis, S.R.M., 1974. Prediction of multicomponent liquid equilibria data. Proc. Int. Solvent Extr. Conf., Lyon, France, 1974, Vol. 2, p. 1813. 

Liquid-liquid equilibria of systems containing perfluoromethylcyclohexane

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Liquid-liquid equilibria of systems containing perfluoromethylcyclohexane

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