Phase equilibria properties of binary and ternary systems containing isopropyl ether + isobutanol + benzene at 313.15 K. R.M. Villamañán 1, M.C. Martín 2, C.R. Chamorro 2, M.A. Villamañán 2, J.J. Segovia 2 1 Dpto. de Didáctica de las Ciencias Sociales y Eperimentales, Escuela Universitaria de Educación, Campus Universitario de Palencia. E-34004 Palencia, Spain. 2 Laboratorio de Termodinámica y Calibración TERMOCAL, E.T.S. de Ingenieros Industriales Universidad de Valladolid, E-47071 Valladolid, Spain, osseg@eis.uva.es. Abstract Isothermal vapour-liquid equilibrium data have been measured for the ternary system (isopropyl ether + isobutanol + benzene) and two of the binary systems involved (isopropyl ether + isobutanol) and (isobutanol + benzene) at 313.15 K. A static technique consisting of an isothermal total pressure cell was used for the measurements. Data reduction by Barker's method provides correlations for G E using the Margules equation for the binary systems and the Wohl epansion for the ternary system. Wilson, NRTL and UNIQUAC models have been applied successfully to both the binary and the ternary systems. Keywords:VLE data, ternary mitures, isopropyl ether (DIPE), isobutanol, benzene 1. Introduction. Ethers and alcohols have been traditionally used as blending agents in the formulation of new gasolines for enhancing the octane number. To better understand and model these unleaded gasolines we started many years ago a research program on the thermodynamic characterization of ternary mitures, as the simplest multicomponent system, containing oygenated additives (ethers and alcohols) and different type of hydrocarbons (paraffins, cycloparaffins, aromatics, oleffins). Methyl tert-butyl ether (MTBE), tert-amylmethyl ether (TAME) and isopropyl ether (DIPE) were chosen as representative ethers; methanol, isopropanol, 1-propanol, and tert-amyl alcohol as alcohol additives. Now, we continued studying ternary mitures containing DIPE, benzene and different butanol isomers. Here, we report vapour-liquid equilibrium data concerning the ternary miture DIPE + isobutanol + benzene at 313.15 K. The eperimental technique used is a static type of high accuracy. These highest quality of vapour-liquid equilibrium data are required to improve the interaction parameters of the predictive models which are used in process simulation packages. The accuracy of a process simulation depends strongly on the thermodynamic models used to describe the physical behaviour of the involved components. Both purposes are carried out with these measurements. 2. Eperimental. All the chemicals used were purchased from Fluka Chemie AG and were of the highest purity available, chromatography quality reagents (of the series puriss. p.a.) with a purity >99.5 (G.C.). All liquids degassed prior to measurements using a modified distillation method based on the technique of Van Ness and Abbott [1], under vacuum. The purities of the chemicals were checked by gas chromatography and were found to be >99.5 for all the
compounds. In Table 1, the vapour pressures of the pure constituents measured in this work are compared with those reported in the literature as a check for complete degassing. Table 1 Average values of eperimental vapor pressures (P s i ) for the pure compounds measured in this work, and literature values (P s i ) (lit.) at T =313.15 K. DIPE (i=1) Iso-butanol (i=2) Benzene (i=3) s p i /(kpa) 37.108 4.008 24.386 p s i (lit.) /(kpa) 37.128 a 3.988 c 24.398 a,e 37.090 b 4.026 d 24.367 f a Reported by Chamorro et al. [4] b Reported by Ambrose et al. [11] c Reported by Ambrose et al. [12] d Reported by Garriga et al. [13] e Reported by Garriga et al. [14] f Reported by Oracz [15] An isothermal total pressure cell has been employed for measuring the vapour-liquid equilibrium of binary and ternary mitures. The apparatus and static measuring technique are based on that by Van Ness and has been described in detail in the literature [2,3]. The equilibrium properties measured directly and their uncertainties are: inected volume ±0.03 ml, temperature ±10 mk and total pressure ±5 Pa. Eperimental values of total vapour pressure for the binary mitures are obtained in two overlapping runs starting from opposite ends of the composition range; for the ternary miture they are obtained by adding a third component up to a mole fraction of = 0.5, to a binary miture with a mole fraction of one component close to = (0.3, or 0.7), si dilution lines were carried out. 3. Results and discussion. In this work, they are reported eperimental isothermal P--y data for the ternary system di-isopropyl ether (DIPE) + isobutanol + benzene and two of the binary systems involved DIPE +isobutanol and benzene + isobutanol at 313.15 K. The other binary system has been measured and published before.[4] Data reduction for the binary and ternary mitures was done by Barker s method according to well established procedures [5,6]. The non-ideality of the vapour phase was taken into account with the virial equation of state, truncated after the second term. Data for the ternary system is adequately correlated by the three-parameter Wohl equation [7]: E Gm g = = g + g + g + ( C + C + C (1) 123 12 13 23 0 1 1 2 2 ) RT which also includes the parameters of the corresponding binaries g i, according to equation (2). The adustable parameters C 0, C 1 and C 2 are found by regression of the ternary data. Correlations for g i are given by a five-parameter Margules equation of the following form: g i = RT G E m 2 2 = { Ai i Ai ( λ i i + λi ) i + η i } i 1 2 3 + (2) The binary and ternary systems have also been correlated using Wilson [8], NRTL [9] and UNIQUAC [10] models. The data correlation results for the binary systems reported here are
summarized in table 2, including, for convenience, those of (DIPE + Benzene), which have been reported previously [4]. Table 2 Determined parameters of the models used for the binary subsystems of ternary system Di-isopropyl ether (1) + isobutanol (2) + benzene(3) at T=313.15 K, together with the root mean square deviation of pressure ( r.m.s.d. p) and the maimum value of the deviation (ma p ). The p term is defined as the difference between the eperimental and calculated pressure. Margules Wilson NRTL UNIQUAC Di-isopropyl ether (1) + iso-butanol (2) A 12 0.7426 0.8125 0.8103 0.4799 A 21 1.0429 0.4075 1.0792 1.3749 λ 12-0.1483 λ 21-0.0589 η -0.3775 α 12 0.1217 r.m.s.d. p/kpa 0.009 0.051 0.017 0.017 ma p /kpa 0.016 0.120 0.048 0.050 Benzene (1) + iso-butanol (2) A 12 1.2579 0.6505 0.4014 0.5683 A 21 2.1115 0.1768 0.6924 1.0065 λ 12 0.6985 λ 21 1.8268 η 1.2086 α 12 0.5694 r.m.s.d. p/kpa 0.012 0.044 0.053 0.173 ma p /kpa 0.018 0.092 0.098 0.310 Di-isopropyl ether (1) + Benzene (2) a A 12 0.2134 0.5515-0.4967 0.9014 A 21 0.1277 1.3762 0.7905 1.0698 λ 12 =λ 21 0.0282 α 12 0.3 r.m.s.d. p/kpa 0.005 0.006 0.005 0.006 ma p /kpa 0.009 0.013 0.008 0.013 a Data published in ref.[4] All the models fit quite good both binary systems however slight better results are obtained for the five-parameter Margules equation. The root mean square deviation between eperimental and calculated pressure is 9 Pa with a maimum deviation of 16 Pa for (DIPE + isobutanol) and they are 12 Pa and 18 Pa, respectively, for (benzene + isobutanol). Both binary systems present a large positive deviation from the ideality with a maimum value of the ecess molar Gibbs energy of 950 Jmol -1 for (benzene + isobutanol) and 585 Jmol -1 for (DIPE + isobutanol), which are located near isobutanol liquid mole fraction of 0.45. Eperimental P- data for the binary systems are shown on figure 1 (a), the vapour compositions have been calculated by Margules equation. As an eample of the fits of models to the data, figure 1 (b), shows a plot of the pressure residuals versus liquid composition for both binary systems using five-parameters Margules equation. It shows how the model fits the data and also, the good agreement of eperimental pressure measured twice for compositions 0.4 1 0.6.
40 0.03 35 0.02 30 P/kPa 25 20 15 10 5 (Pcalc-Pep)/kPa 0.01 0-0.01-0.02 0 0 0.2 0.4 0.6 0.8 1 1, y1 (a) -0.03 0 0.2 0.4 0.6 0.8 1 1 (b) Figure 1: (a) Total vapour pressure for binary systems as a function of the liquid, 1, and vapour compositions, y 1 : ( ) di-isopropyl ether (1) + isobutanol (2); ( ) benzene (1) + isobutanol (2); and ( ) di-isopropyl ether (1) + benzene (2). (b) Pressure residuals as a function of the liquid composition, 1 : ( ) di-isopropyl ether (1) + isobutanol (2); ( ) benzene (1) + isobutanol (2). For the ternary system correlation results are summarized in table 3 which contains the correlations parameters, the root mean square pressure deviation and the maimum value of this deviation. The good results of the fits from all the models are shown in the table, the root mean square pressure deviation varies between 23 Pa for Wohl epansion to 51 Pa for Wilson equation and the maimum value of the deviation is 174 Pa for Wilson equation. Table 3 Summary of the data reduction results obtained for the ternary system (DIPE (1) + isobutanol (2) + Benzene (3)) at 313.15 K. Wilson NRTL UNIQUAC Wohl A 12 0.8279 1.8293 0.4662 C 0 = 2.1822 A 21 0.3996-0.6995 1.3989 C 1 = 0.6538 A 13 0.3788-0.6234 1.2626 C 2 = -0.4358 A 31 1.6794 0.9980 0.7328 A 23 0.1966 0.6878 1.1095 A 32 0.6249 1.5279 0.4950 α 12 0.1217 α 13 0.3000 α 23 0.5694 r.m.s.d. p/kpa 0.051 0.036 0.042 0.023 ma p /kpa 0.174 0.109 0.146 0.040 Results for the ternary system are also shown graphically in figure 2. They are plotted lines of constant total pressure and lines of constant ecess molar Gibbs energy for the ternary system calculated with Wohl epansion; eperimental data are also drawn in the figure. Total pressure of the ternary system varies from the lowest vapour pressure pure component (isobutanol) to the highest vapour pressure pure component (DIPE). On the other hand the maimum value of ecess molar Gibbs energy corresponds to the least ideal binary system.
(a) (b) Figure 3. Plots for the ternary system di-isopropyl ether (1) + isobutanol (2) + benzene (3) at 313.15 K as a function of liquid composition, i,. (a) Isobar lines in kpa (b) Iso-G E lines in Jmol -1. List of symbols A i, A i adustable parameters of the correlation models C 0, C 1, C 2 parameters in Eq. (1) G E molar ecess Gibbs energy (Jmol -1 ) i, constituent identification: 1, 2 or 3 P total pressure (kpa) s P i vapour pressure of pure constituent i (kpa) rmsd root mean square pressure deviation mole fraction, liquid phase y mole fraction, vapour phase Greek letters α i λ i η signifies difference parameter for NRTL model parameter for Margules equation parameter for Margules equation Acknowledgements Support for this work came from the Spanish Ministry of Science and Technology, proect PPQ2002-04414-C02-02. References [1] H.C. Van Ness, M.M. Abbott, Ind. Eng. Chem. Fundam. 17 (1978) 66-67. [2] L M Lozano, E A Montero, M C Martín, M A Villamañán, Fluid Phase Equilib. 110 (1995) 219-230. [3] J J Segovia, M C Martín, C R Chamorro, M A Villamañán, Fluid Phase Equilib. 133 (1997) 163-172 [4] C R Chamorro, J J Segovia, M C Martín, M A Villamañán, Entropie 224/225 (1999) 67-73. [5] M.M. Abbott, H.C. Van Ness, AIChE Journal 21 (1975) 62-71. [6] M.M. Abbott, J.K. Floess, G.E. Walsh Jr. and H.C. Van Ness, AIChE Journal 21 (1975), 72-76. [7] K. Wohl, Chem. Eng. Prog. 49 (1953) 218. [8] G.M. Wilson, J. Amer. Chem. Soc. 86 (1964) 127-130. [9] H. Renon, J.M. Prausnitz, AIChE Journal 14 (1968) 135-144. [10] D.S. Abrams, J.M. Prausnitz, AIChE Journal 21 (1975) 116-128.
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