TERNARY LIQUID-LIQUID AND MISCIBLE BINARY VAPOR-LIQUID EQUILIBRIUM DATA FOR THE TWO AND WATER ACETONITRILE-ETHYL ACETATE

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1 TERNARY LIQUID-LIQUID AND MISCIBLE BINARY VAPOR-LIQUID EQUILIBRIUM DATA FOR THE TWO SYSTEMS n-hexane ETHANOL ACETONITRILE AND WATER ACETONITRILE-ETHYL ACETATE Hiroshi SUGI and Takashi KATAYAMA Department of Chemical Engineering, Faculty oj Engineering Science, Osaka University, Toyonaka 560 Liquid-liquid equilibrium data are obtained for the two ternary systems «-hexane-ethanolacetonitrile at 40 C and water-acetonitrile-ethyl acetate at 60 C. Vapor-liquid equilibria for the two miscible binaries of each ternary system are also determined. The measured ternary liquid-liquid equilibria are compared with those predicted from the constituent binary data alone by use of various activity coefficient equations. Introduction Good prediction of ternary liquid-liquid equilibria from constituent binary data alone is a difficult problem, but is required in design calculations of separating operations. Several attempts based on thermodynamic relations and activity coefficient equations6'7)9'13'15'16) have been made for predicting and correlating ternary liquid-liquid equilibria. In prediction, generally, the parameters in an activity coefficient equation for a completely miscible binary are evaluated from vapor-liquid equilibrium data, while mutual solubility data are used for a partially miscible binary. However, the three binary data which constitute a ternary system are rarely available at the same temperature, and this fact limits progress in predicting ternary liquid-liquid equilibria. In this work, liquid-liquid equilibria were measured for the two ternary systems w-hexane-ethanol-acetonitrile at 40 C and water-acetonitrile-ethyl acetate at 60 C. For the former system, vapor-liquid equilibrium data at 40 C were also determined for the two miscible binaries n-hexane-ethanol and acetonitrileethanol. For the immiscible binary system 72-hexaneacetonitrile, mutual solubilities were determined at the sametemperature. For the latter system, vaporliquid equilibria at 60 C were measured for the two miscible binaries acetonitrile-water and ethyl acetateacetonitrile. Mutual solubilities were determined for the water-ethyl acetate system at the sametemperature. Various activity coefficient equations1>8'12>18) were Received December2, Correspondence concerning this article should be addressed to T. Katayama. VOL ll NO utilized to predict the two ternary liquid-liquid equilibria from the constituent binary data, and the predicted equilibria were compared with the experimental data. 1. Experimental 1. 1 Vapor-liquid equilibria The experimental apparatus used for the measurement of vapor-liquid equilibria was a Brownstill3\ The volume of the boiling flask is 250 cc. The diameter of the Cottrell pumpis 10 mm.to facilitate measurement at lower pressures. At pressures lower than 120 mmhg, it was difficult to operate the still steadily. This was the main reason why the equilibria for the two ternaries were measured at different temperatures. The equilibrium temperature was measured by a calibrated thermister in a thermometer well and a Wheatstone bridge of Yokogawa Electric Co., Ltd. Adjustment in pressure by a two-liquid manostat was made so as to maintain the temperature. After steady-state conditions were attained, the equilibrium pressure was measured by a calibrated AMPGauge of Tokyo Aircraft Instrument Co., Ltd. (limit of error±0.3 mmhg), and liquid and liquefied vapor samples were withdrawn from liquid and vapor samplers, respectively. The samples were analyzed by a gas chromatograph connected to a digital computer HITAC-10II of Hitachi Seisakusho Co. A stainless steel column, 160cm long, separating packed the three with P.E.G. 20M was used for components for the system 77-hexane-ethanol-acetonitrile. A similar column packed with Porapak-g was used for the system water- 167

2 Material Acetonitrile Ethanol Ethyl acetate w-hexane Water Table 1 Physical properties of materials used Density at 25 C [g/cc] Vaporpressure [mmhg] Lit.14) Exptl. Lit. Exptl ** estimated by the method of Tsonopoulos1T). Water contamination of 0.22% was found by the Karl Fischer test. Table 2 Vapor-liquid equilibrium data for the two systems w-hexane (l)-ethanol (2) and acetonitrile (l)-ethanol (2) at 40 C xi yi P [- I [-] [mmhg] «-Hexane (l)-ethanol (2) system ( 12= -870* cc/mol) ** 0.708** 374.5** Acetonitrile (l)-ethanol (2) system (512= -510* cc/mol) ** 0.586** 210.9** estimated by the method of Tsonopoulos17) estimated value of azeotrope acetonitrile-ethyl acetate Liquid-liquid equilibria [-] r2 [-] (40 C) (60 C) (40 C) (60 C) (40 C) (60 C) (40 C)n) (60 C)4) (40 C)2) 418.ll (60 C)14) (40 C)2) (60 C)2) Second coefficient yirial * [cc/mol] (40 C) (60 C) (40 C) (60 C) (40 C) (60 C) CB12= -2250* cc/mol) Mutual solubilities of the two binary systems and the solubility curves of the two ternary systems were determined by a cloud-point method reported previously1^. Mutual solubilities were measured for the Table 3 Vapor-liquid equilibrium data for the two systems acetonitrile (l)-water (2) and ethyl acetate (l)-acetonitrile (2) at 60 C xi yi P [-] [-] [mmhg] [-] Acetonitrile (l)-water (2) system 0.728** 0.728** 421.7** Ethyl acetate (l)-acetonitrile (2) system ( 12 = -2430* cc/mol) ** 0.653** ** estimated by the method of Tsonopoulos17) estimated value of azeotrope system rc-hexane-acetonitrile at 40 C and for the system water-ethyl acetate at 60 C. Solubility curves were determined for the ternary systems ra-hexaneethanol-acetonitrile at 40 C and water-acetonitrileethyl acetate at 60 C. Tie-lines were determined by gas chromatographic analysis of liquid samples drawn from the two liquid phases at equilibrium. The two-phase liquid mixture 168 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN

3 Fig. 3 Activity coefficient-composition curves of acetonitrile (l)-water (2) system at 60 C Fig. 1 Activity coefficient-composition curves of w-hexane (l)-ethanol (2) system at 40 C Fig. 4 Activity coefficient-composition curves of ethyl acetate (l)-acetonitrile (2) system at 60 C Fig. 2 Activity coefficient-composition curves of acetonitrile (l)-ethanol (2) system at 40 C of 20cc was shaken vigorously in a 30cc test tube immersed in a water bath. The water bath was regulated withinzbo.ofc with a Takara Thermostat model C-113. After the phases were separated completely, 2 cc samples were withdrawn from each layer with a preheated syringe and hypodermic needle and were immediately transferred to 5 cc tablet tubes. For the /2-hexane-ethanol-acetonitrile system, they were kept in an air bath at a temperature a little above the equilibrium temperature in order to avoid phasesplitting due to cooling. For the water-acetonitrileethyl acetate system, ethanol was added for the same reason. The homogeneous liquid mixture obtained was analyzed by gas chromatography, using the same method as for vapor-liquid equilibrium measurements Materials Acetonitrile, ethyl acetate, and /z-hexane were VOL ll NO MerckUvasol spectrograde chemicals of minimum purities 99.7 % 99.7 % and 99 %, respectively. Ethanol was spectrograde of minimum purity 99.5 % obtained from Nakarai Chemicals, Ltd. All organic materials were used without further purification. The water used in the experiment was deionized water distilled in an all-glass distillation flask. Physical properties of the materials used in this work are summarized in Table Experimental results 1) Vapor-liquid equilibria: The vapor-liquid equilibrium data at 40 C for the two binary systems ft-hexane-ethanol and acetonitrile-ethanol are presented in Table 2, and the data at 60 C for the two binary systems acetonitrile-water and ethyl acetateacetonitrile are in Table 3. For each of the four systems, a minimum boiling azeotrope was found. Estimated values at each azeotrope are also given in Tables 2 and 3. Columns 4 and 5 of Tables 2 and 3 show the liquid-phase activity coefficients, and Figs. 1 to 4 show the relationships of activity coefficients vs. liquid mole fraction. From the experimental P-x-y data, the activity coefficients were calculated by 169

4 Table 4 Solubility data for the two ternary systems n- hexane (A)-ethanol (B)-acetonitrile (A)-acetonitrile (B)-ethyl acetate (C) at 40 C and (C) at 60 C water XA XB XA XB XA XB [-] [-] [-] [-] [-] [-] /z-hexane (A)-ethanol (B)-acetonitrile (C) system Water (A)-acetonitrile (B)-ethyl acetate (C) system Table 5 Tie-line data for the two systems w-hexane (A)- ethanol (B)-acetonitrile (C) at 40 C and water (A)- acetonitrile (B)-ethyl acetate (C) at 60 C ComponentA-rich v 1 phase r1 ComponentC-rich rll phase rll XA XB XA XB _JH M DH [-] w-hexane(a)-ethanol (B)-acetonitrile (C) system Fig. 5 Liquid-liquid equilibria of «-hexane (A)- ethanol (B)-acetonitrile (C) system at 40 C and the predicted results of the various activity coefficient equations Water (A)-acetonitrile (B)-ethyl acetate (C) system The vapor-phase from the virial fugacity coefficients equation truncated were calculated after the second term. The second virial coefficients for pure components and the cross-coefficients calculated by the Tsonopoulos correlation17} are listed in Tables 1, 2 and3. For the activity coefficients obtained, the conventional thermodynamic consistency test was applied. It is the dynamic well-known consistency area test, by which the thermo- of the data was confirmed for each system within the limit of a practical guide10}. 2) Liquid-liquid equilibria: The solubility data for the two ternary systems n-hexane-ethanol-acetonitrile at 40 C and water-acetonitrile-ethyl acetate at 60 C are listed in Table 4. In the table, mutual solubility data for the two binary systems rc-hexane- Fig. 6 Liquid-liquid equilibria of water (A)- acetonitrile (B)-ethyl acetate and the predicted results of (C) system the various at 60 C activity coefficient equations acetonitrile at 40 C and water-ethyl acetate at 60 C are also included. The tie-line data of the two ternary systems are listed in Table 5. Figures 5 and 6 showthe experimental data of the two ternary systems. In the figures, circles are tie-line data and solid binodal curves are the smoothed ones of the solubility data in Table4. 2. Correlation and Prediction of Equilibria The correlation of the measured vapor-liquid equilibrium data were made by use of various activity coefficient equations. These are the Wilson equation193, the modified Wilson equation185, the two- 170 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN

5 *" System Component1 Component 2 «-Hexane ethanol Acetonitrile ethanol «-Hexane acetonitrile Acet onitrile water Ethyl acetate acetonitrile Water ethyl acetate Table 6 Parameters in various activity coefficient equations Wilson Modified 2-parameter Temp. eq. Wilson NRTL eq. [ C] eq. A12 A12 T12 An A21 t ^ ^12 *"21 3 -parameter NRTL eq. LEMF eq. r12 UNIQUAC eq ^12 Wilson equation19) : GE/RT= -x± In (xl+a12x2)-x2 In Cx2+Ai*i) Modified Wilson equation18) : GE/RT= -x± In (xt+azlx2)-x2 In {A12xx+x2)+x± In {x±+p2ix2)+x2 In (p12xx+x2) NRTL equation12) : GE/RT=x1x2 r-21exp(-av21), z-12exp(-(xt12) x1+x2qxp(-az21) ' x2+x1exp(-at12) LEMF equation8) : GE/RT=x1x2 r21 exp z-2i r12 exp r12 Xi+^exp rsi Xs+Xi exp z-12 UNIQUAC equation1) : GE/RT=x1ln-^ +x2ln-2 ' Z In JL±- -\rq2x2 In Xi X' -q1x1 In (01 +02*21) -q2*2 In (#ir12+#2) 9 parameter NRTL equation12}, the three-parameter NRTL equation12), the LEMF equation8), and the UNIQUAC equation1]. The parameters of these equations, listed in Table 6, were determined so as to minimize the value of ZtCri/^expti.-Cri/^caic.]2. In Figs. 1 to 4, the activity coefficients calculated by the Wilson parameters in Table 6 are compared with the experimental ones. Applicability of the UNIFACmodel of Fredenslund et al.b) was examined for these binary systems and it was found that the model gives satisfactory results, as shown in Figs. 1 to 3. In the ethyl acetate-acetonitrile system, the prediction of activity coefficients could not be made by the UNIFAC model since the group-interaction parameters between ester and nitrile groups are not available. From the mutual solubility data for the two systems ft-hexane (A) - acetonitrile (C) and water (A) - ethyl acetate (C), the parameters of the modified Wilson equation, the two-parameter NRTL equation, the LEMFequation and the UNIQUACequation were determined by solving the following simultaneous equations : (xara)i=(-^ara)ll (xcrcy = (xcrc)u The parameters of these equations obtained are also listed in Table 6. In the table, the parameters of the UNIQUAC equation for the ^z-hexane-acetonitrile system are not given, as the computer technique failed to converge. The mutual solubilities (x\-x") of the rc-hexane (A)-acetonitrile (C) system predicted by use of the UNIFAC model are ( ), (2) which give a slightly narrower solubility range than the experimental one. The UNIFAC model was not applicable to the water-ethyl acetate system since the group-interaction parameters between water and ester groups are not available. The ternary liquid-liquid equilibria for the two systems w-hexane-ethanol-acetonitrile and wateracetonitrile-ethyl acetate were predicted by the various activity coefficient equations with the constituent binary parameters. The calculation was performed by solving the following simultaneous equations. (xtr(y=(xirt)u For the ternary liquid-liquid equilibria of the system /2-hexane-ethanol-acetonitrile, the experimental results are compared in Fig. 5 with the results predicted by the two-parameter NRTL equation, the LEMF equation, and the UNIFACmodel. The predicted result (not shown) by the modified Wilson equation was almost the same as that by the two-parameter NRTL equation. The predicted result (not shown) by the NRTLequation with the three parameters for the constituent miscible binary systems gives an immiscible region as large as that of the UNIFACmodel. This shows that in predicting a multicomponent system the three-parameter NRTL equation is not always superior to the two-parameter one. In the system, each predicted set of ternary liquid-liquid equilibria shows a larger immiscible region than the experimental set, except for that of the LEMF equation. For the system water-acetonitrile-ethyl acetate, the ternary liquid-liquid equilibria predicted by the (3) VOL. ll NO

6 UNIQUAC equation, the LEMF equation, and the modified Wilson equation are shown in Fig. 6 with the experimental values. The predicted result (not shown) by the two-parameter NRTLequation or the threeparameter NRTLequation lies in the region between those of the UNIQUACequation and the modified Wilson equation. In the system, all predicted results give larger immiscible regions than the experimental one. Conclusion Experimental data were obtained for liquid-liquid equilibria for ft-hexane-ethanol-acetonitrile at 40 C and water-acetonitrile-ethyl acetate at 60 C. Vaporliquid equilibrium data were also obtained for the two miscible binary systems of each ternary system. In comparison with the experimental data, applicabilities of the various activity coefficient equations were tested in predicting the ternary liquid-liquid equilibria from the constituent binary data alone. However,no satisfactory results were obtained for these ternary systems. The data presented in this work will be used to examinehowclosely an activity coefficient equation can predict ternary liquid-liquid equilibria from the constituent binary data alone. Acknowledgments The authors thank the Computer Center, Osaka University, for the use of its facilities and Mr. Takashi Murayamafor his assistance in the experimental measurements. Nomenclature total pressure gas constant absolute temperature liquid molar volume liquid-phase mole fraction vapor-phase mole fraction [mmhg] [cal/mol - K] [K] [cc/mol ] = liquid-phase activity coefficient [-] [-] r j (j> = vapor-phase fugacity coefficient [-] <Subscripts> calc. exptl. = calculated value = experimental value i = componenti <Superscripts> L = liquid phase II =saturation component A-rich phase = component C-rich phase Literature Cited 1) Abrams, D. S. and J. M. Prausnitz: AIChEJ., 21, 116 (1975). 2) American Petroleum Institute Research Project 44, "Selected Values of Properties of Hydrocarbonsand Related Compounds", Thermodynamic Research Center, Texas A & M Univ., Texas (1969). 3) Brown, I. : Austr. J. Sci. Res. Ser. A-Phys. Sci., 5, 530 (1952). 4) Brown, I. and F. Smith: Austr. J. Chem., 8, 62 (1955). 5) Fredenslund, A., R. L. Jones and J. M. Prausnitz: AIChE J., 21, 1086 (1975). 6) Guffey, C. G. and A. H. Wehe: ibid., 18, 913 (1972). 7) Hiranuma, M. : Ind. Eng. Chem., Fundam., 13, 219 (1974). 8) Marina, J. M. and D. P. Tassios: Ind. Eng. Chem., Process Des. Dev., 12, 167 (1973). 9) Marina, J. M. and D. P. Tassios: ibid., 12, 271 (1973). 10) Prausnitz, J. M.: "Molecular Thermodynamics of Fluid Phase Equilibria", Prentice-Hall, Englewood Cliffs, N. J. (1969). ll) Prausnitz, J. M., C. A. Eckert, R. V. Orye and J. P. O'Connell : "Computer Calculations for Multicomponent Vapor- Liquid Equilibria", Prentice-Hall, Englewood Cliffs, N. J. (1967). 12) Renon, H. and J. M. Prausnitz: AIChEJ., 14, 135 (1968). 13) Renon, Des. Dev., H. and J. M. Prausnitz: 1, 220 (1968). Ind. Eng. Chem., Process 14) Riddick, J. A. and W. B. Bunger: "Organic Solvents", John Wiley & Sons, Inc., New York (1970). 15) Rod, V.: Chem. Eng. J., ll, 105 (1976). 16) Sugi, H., T. Nitta and T. Katayama: /. Chem. Eng. Japan, 9, 12 (1976). 17) Tsonopoulos, C : AIChEJ., 20, 263 (1974). 18) Tsuboka, T. and T. Katayama: /. Chem. Eng. Japan, 8, 181 (1975). 19) Wilson, G. M.: /. Amer. Chem. Soc.t 86, 127 (1964). 172 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN