| ELSEVIER Fluid Phase Equilibria 107 (1995) 201-212

I | i

Experimental liquid-liquid miscibility curves for binary systems: ethanenitrile and butanenitrile with n-alkanes

Rosario M. Cuevas, Rafael Eustaquio-Rinc6n, Ascenci6n Romero-Martlnez, Arturo Trejo

Instituto Mexicano del Petr61eo, Subdirecci6n General de lnvestigaci6n y Desarrollo Tecnol6gico en Transformaci6n Industrial, Gerencia de Ciencias B[tsicas e lnvestigaci6n Prospectiva, Eje L6zaro C6rdenas 152,

07730 M~xico, D.F., M~xico

Received 29 September 1994; accepted in final form 26 December 1994

Abstract

Liquid-liquid miscibility temperatures, as a function of composition, have been determined experimentally for the binary systems formed by ethanenitrile (acetonitrile) with octane, nonane, decane, undecane and dodecane and butanenitrile with octane, decane, dodecane, tetradecane and pentadecane. This study was also extended to include binary systems of pentanenitrile with long-chain alkanes, however, no liquid-liquid phase separation was observed from room temperature down to 270 K. All the measured systems present solubility curves characterized by asymmetry with respect to equimolar composition and the presence of an upper critical solution temperature (UCST). The experimental results show that for a given set of binary mixtures with a common nitrile the solubility diminishes with increasing alkane chain length, which is a clear manifestation of increasing non-ideality, and for mixtures with a common alkane the solubility increases with increasing nitrile chain length, which in turn is evidence of the decreasing effective polarity of the nitriles as their chain length increases. The Weimer-Prausnitz modification for polar components of Hildebrand's Regular Solution Theory incorporating a Flory-Huggins entropy of mixing has been used to calculate the UCST for the ten systems measured and these values compare very well with those obtained experimentally considering that no adjustable parameter is included in the theory. The theory was also used to calculate the critical composition and qualitative agreement is observed with experimental data.

Keywords: Experiments; Miscibility data; Liquid-liquid; Upper critical solution temperature; Binary systems; Alkanenitrile; n-Alkane; Regular solution theory; Calculations

1. Introduction

The thermodynamic properties of binary systems are determined by the different molecular interactions that are present in the mixture, thus the experimental investigation of the thermodynamic and phase equilibrium behaviour of fluid mixtures is of the utmost importance in order to progress towards its understanding through the development or improvement of theories or models that relate

* Corresponding author.

0378-3812/95/$09.50 © 1995 Elsevier Science B.V. All fights reserved SSDI 0378-3812(95)02682-7

202 R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212

the macroscopic properties to characteristic molecular parameters. Partial miscibility is a familiar phenomenon in binary liquid systems, and it is well known that there exist systems which form a complete range of homogeneous mixtures above an upper critical solution temperature (UCST), but not below, so that, on cooling certain homogeneous mixtures will separate into two liquid layers in equilibrium (mutually saturated conjugate solutions or phases) and some other systems, below a lower critical solution temperature (LCST), form homogeneous mixtures; that is, they exhibit the extraordi- nary phenomenon of two liquid phases spontaneously mixing on cooling to produce a homogeneous phase. The number of binary systems that exhibit mutual solubility curves with UCST is much larger than that for systems with a LCST; hence, from a qualitative point of view it has been easier to understand the type of unlike molecular interactions that prevail in the former systems by considering the chemical nature of the different components that give rise to this behaviour. Such systems are generally formed by a polar component and a non-polar component, and thus exhibit unlike molecular interactions that are weaker than the mean of the like interactions, which also "explains" large positive molar excess enthalpies and Gibbs free energy, i.e. positive deviations from ideality.

The present work is a continuation of previous studies (Bernabe et al., 1988; Eustaquio-Rinc6n et al., 1991, 1993) on the liquid-liquid miscibility curves of a series of binary systems formed by a common polar component with members of a non-polar homologous series, where the polar component is in turn a member of a homologous series. In this paper experimental data are reported for the miscibility temperature of systems of known overall composition composed of ethanenitrile with octane, nonane, decane, undecane and dodecane and butanenitrile with octane, decane, dodecane, tetradecane and pentadecane. The experimentally derived UCST and critical composition for each binary system have been compared with calculated values from the solubility parameter version of the regular solution theory modified by Weimer and Prausnitz to describe the thermodynamics of polar-non-polar liquid systems.

2. Theory

The solubility parameter version of the regular solution theory (SPRST) in the modified form by Weimer and Prausnitz to include the thermodynamic treatment of mixtures with a polar compound has been discussed for a large number of binary systems (Hildebrand et al., 1970; Weimer and Prausnitz, 1965) including the type of mixtures studied here (McLure et al. 1982), hence, an abridge version will only be given in what follows.

The regular solution theory gives the following expression for the excess Gibbs free energy (Hildebrand et al., 1970):

a E = ( x 1 V 1 .-1- x 2 V 2 ) ( ~ l ( ~ 2 ( C l l -3 t- c22 - 2c12 ) (1 )

where x i is the mole fraction of component i, V/ is the molar volume of pure component i, ~b i is the volume fraction of component i, ci~ is the cohesive energy density of pure component i and c12 is the cohesive energy density corresponding to the interactions between molecules of types 1 and 2.

The solubility parameter of pure component i, 8~, is defined by Hildebrand et al. (1970) in terms of the corresponding cohesive energy density as

6i = Oil-l~2 = (( AHiV - R T ) / V i ) 1/2 (2)

where AHi v is the enthalpy of vaporization of pure component i, generally used at 298.15 K.

R.M. Cuevas et al. / F l u i d Phase Equilibria 107 (1995) 201-212 203

The theory assumes that the unlike molecular interactions are mainly due to dispersion effects thus the geometric mean of the cohesive energy densities or solubility parameters is used to calculate cq as follows:

cij= = (8,2 9) 1/2= (3) Equation (1) can now be expressed in terms of the widely known solubility parameters, so that, by

substituting Eqs. (2) and (3) we have:

G E = ( X l V 1 " -1-x2V2)~l~2(~ 1 - ~2) 2 (4)

which is the well-known result for the solubility parameter version of Hildebrand's regular solution theory (SPRST).

In order to extend the SPRST to polar compounds the model of Weimer and Prausnitz considers that the energy of vaporization of the polar component 1 can be divided in two parts: one includes the dispersion interactions (non-polar part) and the second one results from the dipole-dipole and induction effects (polar part), so that the solubility parameter of the polar component is given as

6 7 = ~,~+ 7, ~ (5)

where )t 2 is the non-polar solubility parameter and 72 is the polar solubility parameter. The solubility parameter 6 i for both the polar and non-polar component, is obtained using Eq. (2),

whereas the evaluation of )t 1 in Eq. (5) involves the homomorph concept proposed by Prausnitz and Anderson (1961), which states that the homomorph of a polar substance is a non-polar substance, usually a hydrocarbon, with the same structure and at the same reduced temperature, using the gas-liquid critical temperature as the reducing parameter, and equally important having the same molar volume as the polar component. Thus, values of /~1 for the alkanenitriles are determined from the well-known energy of vaporization and molar volume of the n-alkane series (Weimer and Prausnitz, 1965).

The cohesive energy density c12 that takes into account the unlike interactions, i.e. between polar and non-polar molecules, in the mixture is obtained with Eq. (3) plus an energy parameter, q~12, that considers the induction energy; hence the final expression for c12 is

C12 = /~1 -1- ~2 "~ ~012 (6)

which substituted in Eq. (1), together with Eq. (5), gives the expression for G E of the Weimer- Prausnitz model:

GE=(x,V, + xzVz)~ba~bz{(A 1 - 62) 2 + 7 2 - 2q~,2 } (7)

It may be observed that Eq. (7) differs from Eq. (4) by the polar contribution, given as 72, and the induction energy term given as -2~o12. Using an analysis of experimental activity coefficients of saturated hydrocarbons at infinite dilution in polar solvents, Weimer and Prausnitz (1965) determined empirically a value of q~12 = 0.39672.

Equation (7) together with the Flory-Huggins entropy of mixing, to take into account the large difference in size or molar volume between the components of the binaries here studied, is differentiated to fulfill the critical point conditions, so that, the UCST and the critical composition x c can be calculated with the following relations:

= + lVjt +

204 R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212

Table 1 Molecular volume V, molar enthalpy of vaporization A H v and solubility parameter 8 for alkanes and alkanenitriles, non-polar A and polar 7 solubility parameters for the alkanenitriles at 298.15 K

Substance V a 10 3 AH v b ~ c A d ~. d

(cm 3 mol-1) (J mol-1) (j1/2 cm-3/2)

Ethanenitrile 52.842 32.93 24.65 16.42 18.37 Butanenitrile 87.889 39.33 20.74 16.28 12.85 Octane 163.530 41.51 15.44 - - Nonane 179.670 46.44 15.64 - - Decane 195.905 51.38 15.79 - - Undecane 212.217 56.36 15.93 - - Dodecane 228.579 61.30 16.04 - - Tridecane 244.924 66.23 16.14 - - Tetradecane 261.312 71.17 16.22 - - Pentadecane 277.698 76.15 16.28 - -

a American Petroleum Institute (1953). b Handbook of Vapour Pressures (1971). c Calculated with Eq. (2). d Weimer and Prausnitz (1965).

and

( x 2 / x l ) c = ( V I / V 2 ) 3/2 (9)

Table 1 contains data for the solubility parameter of alkanes, the non-polar and polar solubility parameters of alkanenitriles, and molar volume and enthalpy of vaporization for both series of

homologues.

3 . E x p e r i m e n t a l

The entire l iquid- l iquid miscibility curve for each of the ten binary systems studied was determined by the wel l -known method of measuring the mixing temperature of a series of mixtures of known overall composit ion in sealed all-glass cells. The heterogeneous or homogeneous liquid binary systems were prepared by weight in an analytical balance to obtain a precision in composit ion of + 0.0001 mole fraction and thoroughly degassed by several f r e e z e - p u m p - t h a w cycles before being sealed under vacuum. A minimum of nine samples with different composit ions were prepared for each binary system to define the miscibility curve. The measurement of temperature was carried out with a Systemteknik AB digital thermometer and a platinum resistance probe. The mixtures were continuously stirred by means of stainless-steel ball bearings inside the glass cells. The reproducibility of the mixing temperatures was _ 0.01 K for the whole temperature range studied. The instrument and technique have been described in greater detail in previous work from this laboratory (Bemabe et

al., 1988; Eustaquio-Rinc6n et al., 1991, 1993). All the samples of the alkanes and alkanenitriles used in this work were obtained from Aldrich,

with a reported purity better than 99 mol%, and were used without further purification other than storing over sodium and a molecular sieve, respectively, to remove any possible traces of moisture.

R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212 205

Chromatographic analysis was carried out on all the samples just before use and only one peak was observed in all cases, indicating that no impurities were revealed.

4. Results and discussion

The experimental values of the liquid-liquid miscibility temperature T as a function of composi- tion x for the binary systems of ethanenitrile and butanenitrile with different alkanes are listed in Tables 2 and 3 and shown graphically in Figs. 1 and 2, respectively. Figure 1 also includes data from the literature (Bemabe et al., 1988) for four other binary systems.

No experimental T - x data were obtained for binary systems of pentanenitrile with long-chain alkanes since their mixtures, in the whole composition range, are completely miscible at room temperature and when cooled down to 270 K the mixtures were observed to display a solid-liquid phase boundary.

The UCST and critical composition of each binary system were evaluated after fitting each set of experimental T - x data with the following relationship:

T(K) = Y',ai{ [ X l / B - x2/(1 - B ) ] / [ X l / B --[.- x2/(1 - B)]} 2i (10)

where T and x i are experimental data, and Ai and B are constants to be determined using a least-squares method.

Table 4 gives the values of the coefficients of Eq. (10) for the ten binary systems studied along with the standard deviations o- for the representation. The full curves through the experimental points, included in Figs. 1 and 2, were calculated from Eq. (10) with these coefficients. The results from Eq. (10) indicate that the coefficient A o is analogous to the UCST and the parameter B corresponds to the critical composition x ¢.

Several interesting features are observed from the results in Tables 2-3 and Figs. 1-2. (i) For a given alkanenitrile the miscibility increases as the alkane chain length decreases, hence the

UCST decreases as the size of the alkane decreases. (ii) For a given alkane the miscibility decreases as the alkanenitrile chain length decreases; hence

the UCST increases as the size of the alkanenitrile decreases. (iii) For a given alkanenitrile the miscibility curves vary from nearly symmetrical, around the

equimolar composition for the systems with alkanes with small chain length, to highly skewed curves, for the systems with long-chain alkanes. Thus the critical composition takes values in the range of about 0.47 up to 0.77 for the systems studied in this work.

The behaviour described above is easier to observe in Figs. 3 and 4 where the UCST and the x c for the two sets of binaries have been plotted as a function of the number of carbon atoms in the alkane molecule, respectively. Figure 3 also includes experimental UCST data from the literature (Eustaquio-Rinc6n et al., 1991) for propanenitrile with several alkanes.

From a qualitative point of view the observed behaviour is mainly due to the reduction of the number of strong dipole-dipole interactions in the pure nitrile when mixed with the non-polar alkane component, that is, overall the mixtures' properties reflect the weaker dipole-induced dipole unlike interactions which give rise to phase separation and large positive H E and G E values (McLure et al., 1982, 1989; Eustaquio-Rinc6n et al., 1994; Kikic et al., 1980; Marongiu and Porcedda, 1990), i.e.

206 R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212

Table 2 Experimental liquid-liquid miscibility temperature as a function of composition for x 1 ethanenitrile+(1-x 1) alkane systems

A l k a n e T(K) X 1 T ( K ) x 1

Octane 358.82 0.3860 364.95 0.6519 360.43 0.4116 364.99 0.6968 362.73 0.4705 364.45 0.7568 363.81 0.5144 359.59 0.8519 364.86 0.5770 349.38 0.9046 364.87 0.6160 330.64 0.9457

Nonane 358.06 0.3105 372.57 0.6469 363.13 0.3678 372.62 0.7065 366.63 0.4200 372.48 0.7475 368.24 0.4498 372.20 0.8001 370.25 0.5063 369.02 0.8685 371.94 0.5580 360.98 0.9032 372.51 0.6028

Decane 370.12 0.4045 379.79 0.6761 370.90 0.4123 379.78 0.6933 373.55 0.4586 379.77 0.7480 375.98 0.4959 379.45 0.7947 376.73 0.5323 378.19 0.8492 377.89 0.5548 372.37 0.8946 378.91 0.6011 367.40 0.9160

Undecane 371.26 0.3846 386.77 0.7511 374.49 0.4277 386.66 0.7996 380.40 0.4895 385.29 0.8507 381.44 0.5084 384.04 0.8971 385.25 0.5989 380.73 0.9100 386.20 0.6510 366.95 0.9451 386.76 0.7013

Dodecane 373.72 0.3684 393.17 0.7700 381.90 0.4513 393.13 0.8093 384.97 0.4930 392.50 0.8517 388.95 0.5565 392.27 0.8669 391.20 0.6076 388.27 0.9015 392.60 0.6540 384.15 0.9224 392.93 0.7397 374.97 0.9484

large posit ive deviations f rom ideality. It is then clear that for a given alkanenitrile the unlike interactions become weaker as the alkane chain length increases. Also, since the permanent dipole

moment s of the two nitriles studied here are similar it is the decreasing surface fraction, or effective polarity, of the CN group in butanenitri le with respect to that of ethanenitrile that determines the decrease of non-ideali ty for binary sys tems with butanenitrile, so that these sys tems present greater mutual solubility (Figs. 1 - 3 ) and lower H E and G E values than those corresponding to ethanenitrile.

Since the solubility parameter is a measure of the total cohesive energy of the molecules in a given compound (Eq. 2), it is to be expected that the strong d ipo le -d ipo le interactions in the nitriles should

R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212 207

Table 3 Experimental liquid-liquid systems

miscibility temperature as a function of composition for x 1 butanenitrile+(1- Xl) alkane

Alkane T(K) x i T(K) x 1

O~ane 255.51 0.2212 260.20 0.5386 257.47 0.2601 259.91 0.5972 258.69 0.3026 259.49 0.6381 259.83 0.3527 257.51 0.7094 260.20 0.3888 253.34 0.7610 260.55 0.4381 247.90 0.8168 260.53 0.4756

Decane 260.28 0.1749 273.28 0.5970 264.17 0.2153 273.10 0.6458 267.88 0.2625 272.36 0.7090 269.98 0.3177 270.98 0.7534 272.30 0.3500 268.92 0.8010 272.81 0.4253 263.19 0.8453 273.15 0.4447 252.32 0.9002 273.36 0.5040 242.23 0.9463 273.33 0.5517

Dodecane 273.00 0.2368 285.22 0.5973 273.42 0.2399 285.12 0.6458 274.75 0.2541 285.00 0.6988 278.92 0.3097 284.35 0.7548 280.99 0.3530 282.84 0.7998 283.02 0.4019 279.06 0.8509 283.95 0.4403 268.12 0.8976 284.89 0.4916 261.97 0.9446 284.99 0.5526

Tetradecane 276.20 0.2585 296.45 0.6487 288.75 0.3615 296.97 0.7008 291.57 0.4099 295.48 0.8044 293.11 0.4512 292.44 0.8524 294.31 0.4997 285.92 0.9018 295.45 0.5447 285.33 0.9057

Pentadecane 292.78 0.3833 300.85 0.8280 299.86 0.5739 299.45 0.8486 300.69 0.6787 298.68 0.8809 301.07 0.7231 278.64 0.9675 300.85 0.7734

lead to greater values o f 8 than those for the pure alkanes, as is observed in Table 1. Furthermore, since the original solubility version of the regular solution theory ascribes the deviations f rom ideality

to the quantity (81 - 82) 2 it is then to be expected that the modificat ion to this theory by Weimer and Prausnitz (Eq. (7)) which considers non-polar, polar and induced interactions, together with the influence of molecular size, should give a quantitative explanation of the experimental miscibil i ty curves and particularly the U C S T values for the sys tems studied here.

208 R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212

I--

0 0.1 0.~ 0.5 0.4 0.5 0.6 0.7 0.8 0.9 I Xl

Fig. 1. Experimental (points) and calculated from Eq. (10) (full curves) values of liquid-liquid solubility for x 1 ethanenitrile +(1- x 1) alkane systems: (d) C8; (e) C9; (f) C1o; (g) Cll; (h) C12. Curves without points: (a) C5; (b) C6; (c) C7; (i) C13 from Bernabe et al. (1988).

A comparison between experimentally derived and theoretical UCST values is presented in Table 5 and Fig. 3 for the two sets of binary mixtures studied. It may be observed not only that the theory successfully predicts the main features of the dependence of the experimental UCST results on changes of molecular size of both nitrile and alkane but that there also exists quantitative agreement within a few degrees for the systems considered. Since the Weimer Prausnitz model does not modify the original equation for the critical composition as given by the SPRST together with the Flory-Huggins entropy of mixing (Hildebrand et al., 1970), the values of x c calculated with Eq. (9) are generally higher than the corresponding experimental values as observed in Fig. 4, although its dependence on the number of carbon atoms in the alkane is qualitatively correct for both sets of binary mixtures.

It must be concluded that the Weimer-Prausnitz modification of Hildebrand's regular solution theory, which considers explicitly a polar contribution, gives an excellent representation of the main

R.M. Cuevas et al. /F lu id Phase Equilibria 107 (1995) 201-212 209

v

I-

25~

0 O.I 0.2 0.3 0.4 0 5 0.6 0.7 0.8 O.e I XI

Fig. 2. Experimental (points) and calculated f rom Eq. (10) (full curves) values of l iquid- l iquid solubility for x 1

butanenitrile + ( 1 - x 1) alkane systems: (a) Cs; (b) C1o; (c) C12; (d) C14; (e) C15.

Table 4

Coefficients and standard deviation ty of Eq. (10)

Alkane B A 0 A 1 A 2 A 3 tr

(K)

Ethanenitrile

C 8 0.6592 365.03 - 9.7 - 39.4 - 45.8 0.11

C 9 0.6938 372.53 2.1 - 106.3 62.0 0.60

C1o 0.7198 379.85 - 9.2 - 50.3 - 25.3 0.33

C 11 0.7577 386.70 - 4.9 - 4.0 - 71.3 0.68

C12 0.7695 393.14 - 1.7 - 98.4 46.5 0.21

Butanenitrile

C 8 0.4785 260.53 - 11.3 1.1 - 97.5 0.14

C lo 0.5412 273.17 2.3 - 74.8 24.0 0.62

C 12 0.6033 284.85 8.6 - 122.2 89.4 0.84

C14 0.6812 296.86 - 20.6 37.0 - 143.3 0.29

C15 0.7385 300.98 - 6.2 - 25.8 - 19.5 0.36

210 R.M. Cuevas et al. // Fluid Phase Equilibria 107 (1995) 201-212

4O@

~ 0 '

~ D 0 ~

. 3 4 0

(n O

3 2 0

3 0 0

2 8 0 ,

2 6 0

I I I I I I I I I

2 4 0 I I I I I I I I I 7 8 9 10 II 12 13 14 15 16 17

N k o n e c a r b o n n u m b e r

Fig. 3. Experimentally derived (points) and calculated with Eq. (8) (full curves) UCST as a function of the number of carbon atoms in the alkane molecule for: (a) ethanenitrile, this work; (b) propanenitrile (Eustaquio-Rinc6n et al., 1991); (c) butanenitrile, this work.

Table 5 Comparison of UCST derived experimentally (coefficient A o in Eq. (10); see Table 4) for the ten binary systems studied in this work with calculated values from the modification of the solubility parameter version of the regular solution theory (Eq. (8)) System Experimental UCST (K) Calculated UCST (K)

Ethanenitrile + C s 365.0 368 C 9 372.5 378 Clo 379.8 389 Cll 386.7 398 C 12 393.1 408

Butanenitrile + C 8 260.5 247 C lO 273.2 262 C12 284.8 277 Ct4 296.9 291 C15 301.0 297

R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212 211

0.9~

0.9

0.85,

o X

0.80

0.75

I I I I

b

o.,o • @

0.65

o ~ •

b 0.55' 0

0~(>

@

0.45 I I I I 6 8 I0 12 14 16

AIImne carbon number

Fig. 4. Experimentally derived (points) and calculated with Eq. (9) (full curves) critical composition as a function of the number of carbon atoms in the alkane molecule for the sets of binary systems studied in this work: (a) ethanenitrile; (b) butanenitrile.

features of the UCST of the systems studied here without using any fitted parameter to describe their behaviour. Nonetheless, and considering the vast amount of experimental information obtained in our laboratory on the liquid-liquid miscibility behaviour of binaries of an alkanenitrile with a hydrocar- bon, at present we are also carrying out calculations using molecular group contribution models in order to establish the strength of the different interactions that are present in these systems and these results will be the object of a future report.

List of symbols

Ai ,B

H E

R

coefficients for polynomial Eq. (10) cohesive energy density associated with interaction of molecules of types i and j molar excess Gibbs function molar excess enthalpy universal gas constant

212 R.M. Cuevas et al. / Fluid Phase Equilibria 107 (1995) 201-212

T Vi X i X c

temperature molar volume mole fraction in liquid phase critical composition

Greek letters

v

~12

Or < g'i

solubility parameter enthalpy of vaporization induction energy density nonpolar contribution to cohesive energy density standard deviation polar contribution to cohesive energy density volume fraction

Acronyms

UCST LCST SPRST WP

upper critical solution temperature lower critical solution temperature solubility parameter version of the regular solution theory Weimer-Prausnitz

5. References

American Petroleum Institute, 1953. Project 44, Table 206 (part 1). Bernabe, D., Romero-Martlnez, A. and Trejo, A., 1988. Liquid-liquid coexistence curves for binary systems. Fluid Phase

Equilibria, 40: 279-288. Eustaquio-Rinc6n, R., Molnar, R. and Trejo, A., 1991. Liquid-liquid miscibility for binary systems: N-methylpyrrolidone +

n-alkane and propanenitrile + n-alkane. Fluid Phase Equilibria, 68: 187-195. Eustaquio-Rinc6n, R., Romero-Martlnez, A. and Trejo, A., 1993. Liquid-liquid miscibility curves for binary systems:

N-methylpyrrolidone with several hydrocarbon isomers. Fluid Phase Equilibria, 91: 187-201. Eustaquio-Rinc6n, R., Garcla, B.E. and Trejo, A., 1994. Vapour-liquid equilibrium of butanenitrile + n-alkanes. J. Chem.

Soc. Faraday Trans., to be submitted for publication. Handbook of Vapour Pressures and Heats of Vaporization of Hydrocarbons and Related Compounds, 1971. American

Petroleum Institute, Project 44, Thermodynamics Research Center, Publications in Science and Engineering No. 101. Hildebrand, J.H., Prausnitz, J.M. and Scott, R.L., 1970. Regular and Related Solutions. Van Nostrand-Reinhold, New York. Kikic, I., Alessi, P., Gozzi, P. Rapasin, R.L. and De Santis, R., 1980. Excess free energy for mixtures containing nitriles. J.

Chem. Eng. Data, 25: 33-36. Marongiu, B. and Porcedda, S., 1990. Thermodynamics of binary mixtures containing alkanenitriles.1. Excess enthalpies of

some n-alkanenitriles + n-alkane or + cyclohexane mixtures. J. Chem. Eng. Data, 35: 172-174. McLure, I.A. and Trejo, A., 1982. Excess functions for (n-alkanenitrile + n-alkane) liquid mixtures.2. Excess enthalpies at

298.15 K for propanenitrile and n-butanenitrile with some C 5 to C14 n-alkanes. J. Chem. Thermodyn., 14: 439-445. McLure, I.A., Trejo, A., Ingham, P.A. and Steele, J.F., 1982. Phase equilibria for binary n-alkanenitrile-n-alkane

mixtures.I. Upper liquid-liquid coexistence temperatures for ethanenitrile, propanenitrile and n-butanenitrile with some Cs-Cls n-alkanes. Fluid Phase Equilibria, 8: 271-284.

McLure, I.A., Trejo A. and Arriaga-Colina, J.-L., 1989. Excess energy at constant volume at 298.15 K for alkanenitrile + alkane liquid mixtures. Rev. Mex. Fis., 35: 357-366.

Prausnitz, J.M. and Anderson, R., 1961. Thermodynamics of solvent selectivity in extractive distillation of hydrocarbons. Am. Inst. Chem. Eng. J., 7: 96-101.

Weimer, R.F. and Prausnitz, J.M., 1965. Screen extraction solvents this way. Hydrocarbon Process., 44: 237-242.