WA-042

J. Chem. Thermodynamics 1996, 28, 3–6

Extraction equilibria of the type 2: ternary liquid

mixture {x1tert-butyl methyl ether+x2water+

(1−x1−x2)1-octanol} at 298.15 K and 308.15 K

Alberto Arce,a Manuel Blanco, Ana Soto, and Isabel Vidal

Department of Chemical Engineering, University of Santiago de Compostela,E-15706 Santiago, Spain

(Received 24 October 1994; in revised form 25 January 1995)

We report liquid–liquid equilibrium data for the ternary system {x1tert-butyl methylether(C5H12O)+x2water+(1−x1−x2)1-octanol} at 298.15 and 308.15 K. The data weresatisfactorily fitted with UNIQUAC and NRTL equations, and were satisfactorily predicted bythe UNIFAC group contribution method. 7 1996 Academic Press Limited

1. Introduction

Little has been published on the thermodynamic behaviour of liquid mixturescontaining the anti-knocking agent tert-butyl methyl ether (C5H12O). In this work thepossibility of using water to separate {xC5H12O + (1−x)C8H18O} mixtureswas investigated by determining liquid–liquid equilibria (LLE) of C5H12O + H2O +C8H18O mixtures at T = 298.15 and T = 308.15 K. {C5H2O + x2H2O +(1 − x1 − x2)C8H18O}. This is a type 2 ternary system, i.e. a mixture of threecomponents with one completely miscible binary pair {xC5H12O + (1−x)C8H18O}and two partially miscible pairs, (C5H12O+H2O) and (H2O+C8H18O).

2. Experimental

C5H12O and C8H18O were supplied by Aldrich with respective nominal puritiesq99.0 mass per cent and q99.5 mass per cent. These purities were verifiedchromatographically, and both compounds were used without further purification.Water was obtained from a Milli-Q Plus system.

Prior to the determination of LLE results, solubility curves at T=298.15 andT=308.15 K were determined by the cloud-point method. The solubility curves soobtained were employed for calibration of the Hewlett-Packard 5890 Series II gaschromatograph subsequently used for analysis of the phases in equilibrium. The

a To whom correspondence should be addressed.

0021–9614/96/010003+04 $12.00/0 7 1996 Academic Press Limited

A. Arce et al.4

experimental apparatus and procedure have been described in detail elsewhere.(3) Inthe LLE experiments, mixtures were shaken for 2 h and then left to settle for 4 hbefore samples of the two phases were withdrawn through hypodermic needles foranalysis. The estimated precision of the measured mole fractions was 20.001. TheLLE data deviated very little from the solubility curve obtained by the cloud-pointmethod, which is accordingly considered redundant and not presented in this paper.

3. Results

Table 1 lists the equilibrium compositions of the aqueous and organic phases at thetwo working temperatures. Temperature had almost no effect on the immiscibleregion. The solubilities of the partially miscible binaries at T=298.15 K, expressedas mole ratios, are 0.3681 for H2O in C8H18O, 0.0001 for C8H18O in H2O, 0.0567 forH2O in C5H12O and 0.0516 for C5H12O in water.

The LLE data were fitted with NRTL(8) and UNIQUAC(1) equations using acomputer program developed by So�rensen(9, 10) as described in previouscommunications.(2, 3) The UNIQUAC structural parameters for the pure components(table 2) were either taken from the literature(7) or calculated by a group contributionmethod.(6) Best NRTL results were obtained setting the non-randomness parametera to 0.1 for T=298.15 K and to 0.2 for the T=308.15 K data.

The optimized binary interaction parameters are listed in table 2. Goodness of fit,as measured by the r.m.s. deviation in mole fraction

F=100Xsk

si

sj

(xijk−x̂ijk )2/6M (1)

and by the r.m.s. relative error in the solute distribution ratio

Db=100Xsk

((bk−b k )/bk )2/M (2)

is indicated in table 2. Here xijk is the experimental mole fraction of the ith componentin the jth phase on the kth tie-line, x̂ijk is the corresponding calculated value, M isthe number of experimental measurements and bk is the solute distribution ratio. Thefit was poor in terms of Db due to the large relative error associated with the verylow concentrations of organic components in the aqueous phase. In terms of F, onthe other hand, the goodness of fit was very satisfactory in comparison withpublished results for other ternary systems. A similar situation has been reported forhydrocarbon–butyronitrile–C8F16O systems.(5)

Predictions of the LLE of the system studied were obtained by the UNIFACmethod(4) using the previously published(6) group interaction parameter to calculatethe activity coefficients of the components in each phase. The predictions were quiteaccurate, with Db values (equation 2) of 1.780 at T=298.15 K (figure 1) and 1.925at T=308.15 K.

LLE of {x1C5H12O+x2H2O+(1−x1−x2)C8H18O} 5

TABLE 1. Liquid–liquid equilibrium data for the system {x1C5H12O+x2H2O+(1−x1−x2)C8H18O} atT=298.15 K and T=308.15 K

Organic phase Aqueous phasex1 x2 (1−x1−x2) x1 x2 (1−x1−x2)

C5H12O H2O C8H18O C5H12O H2O C8H18O

T=298.15 K0.9463 0.0537 0.0000 0.0491 0.9509 0.00000.8516 0.0876 0.0608 0.0448 0.9538 0.00140.7195 0.1299 0.0156 0.0389 0.9580 0.00310.5603 0.1800 0.2587 0.0318 0.9637 0.00450.3818 0.2551 0.3631 0.0232 0.9711 0.00570.2341 0.2597 0.5062 0.0147 0.9795 0.00580.1682 0.2550 0.5768 0.0106 0.9834 0.00600.1135 0.2568 0.6297 0.0073 0.9864 0.00630.0525 0.2673 0.6802 0.0039 0.9898 0.00630.0000 0.2691 0.7309 0.0000 0.9999 0.0001

T=308.15 K0.9206 0.0794 0.0000 0.0066 0.9934 0.00000.7443 0.1203 0.1354 0.0053 0.9947 0.00000.6774 0.1409 0.1817 0.0047 0.9953 0.00000.5400 0.1801 0.2799 0.0035 0.9965 0.00000.4520 0.1831 0.3649 0.0026 0.9974 0.00000.3877 0.1946 0.4177 0.0021 0.9979 0.00000.3094 0.2051 0.4855 0.0015 0.9985 0.00000.2348 0.2190 0.5462 0.0010 0.9990 0.00000.1271 0.2311 0.6418 0.0005 0.9995 0.00000.0000 0.2403 0.7597 0.0000 0.0001 0.9999

TABLE 2. UNIQUAC and NRTL correlation parameters for the system{x1C5H12O+x2H2O+(1−x1−x2)C8H18O}

UNIQUAC NRTLT/K i−j bij bji aij aji

Components

(a=0.1)298.15 1-2 810.12 −73.057 436.39 605.69

1-3 −79.220 174.20 −297.76 469.032-3 −20.707 475.06 2228.5 −599.83

Db=1.6 F=0.382 Db=6.7 F=0.4299

(a=0.2)308.15 1-2 551.53 77.199 310.34 1233.9

1-3 −130.42 88.542 −1584.6 67.5142-3 328.15 190.066 1494.2 −130.82

Db=2.5 F=0.2197 Db=41.0 F=0.2766

UNIQUAC structural parametersComponent r q

C5H12O 4.0678 3.632H2O 0.9200 1.400

C8H18O 6.6219 5.828

A. Arce et al.6

FIGURE 1. Liquid–liquid equilibria of the system {x1C5H12O+x2H2O+(1−x1−x2)C8H18O} at298.15 K. w, Experimental; R, UNIFAC prediction.

4. Conclusions

Because of the almost total insolubility of 1-octanol in water at the workingtemperatures, distribution ratios for the partition of 1-octanol between MTBE andwater are high and the solubility curve for {x1tert-butyl methyl ether+x2water+(1−x1−x2)C8H18O} is almost vestigial for the aqueous phase. Water must thereforebe considered as unsatisfactory for separation of {xC5H12O+(1−x)C8H18O}mixtures. The experimental results are nevertheless fitted well by both UNIQUACand NRTL equations, and satisfactorily predicted by the UNIFAC method.

We are grateful to the Spanish D.G.I.C.Y.T. for financial support under ProjectNumber PB92-0365.

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