Elsevier

Fluid Phase Equilibria

Volume 259, Issue 1, 1 October 2007, Pages 57-65
Fluid Phase Equilibria

Isobaric vapor–liquid equilibria of 1,1-dimethylethoxy-butane + methanol or ethanol + water at 101.32 kPa

https://doi.org/10.1016/j.fluid.2007.01.038Get rights and content

Abstract

Isobaric vapor–liquid equilibrium data (VLE) at 101.325 kPa have been determined in the miscible region for 1,1-dimethylethoxy-butane (BTBE) + methanol + water and 1,1-dimethylethoxy-butane (BTBE) + ethanol + water ternary systems, and for their constituent binary systems, methanol + BTBE and ethanol + BTBE. Both binary systems show an azeotrope at the minimum boiling point. In the ternary system BTBE + methanol + water no azeotrope has been found, however, the system BTBE + ethanol + water might form a ternary azeotrope near the top of the binodal. Thermodynamically consistent VLE data have been satisfactorily correlated using the UNIQUAC, NRTL and Wilson equations for the activity coefficient of the liquid phase. Temperature and vapor phase compositions have been compared with those calculated by the group-contribution methods of prediction ASOG, and the original and modified UNIFAC. Predicted values are not in good agreement with experimental values.

Introduction

The work presented in this paper continues the study on phase equilibria of alcohol and tertiary ether mixtures used as octane-enhancing components in gasoline [1], [2]. The goal of this study is to know the behaviour of these systems when increasing the molecular weight of the ether.

Herein, thermodynamically consistent [3], [4], [5], [6] vapor–liquid equilibrium (VLE) data at 101.325 kPa are presented for the systems 1,1-dimethylethoxy-butane (BTBE) + methanol + water and (BTBE) + ethanol + water and for the two constituent binary systems alcohol + ether. The Wilson [7], NRTL [8] and UNIQUAC [9] equations for the liquid phase activity coefficients are used to correlate experimental data. Group-contribution methods ASOG [10], [11], UNIFAC [3], and modified UNIFAC-Dortmund [12], [13] and UNIFAC-Lyngby [14] are applied to predict VLE data. No VLE data have been found in the open literature for the systems targeted in this work.

Section snippets

Experimental

1,1-Dimethylethoxy-butane (butyl-tert-butyl ether or BTBE) was supplied by Yarsintez (Yaroslav, Russia) with nominal purity >99.9 mass%. Methanol and ethanol were supplied by Merck (Madrid, Spain) and had a nominal purity >99.5 mass%. Water was purified using a Milli-Q Plus system. The water content of BTBE was 0.1 mass%, and for methanol and ethanol were 0.05 and 0.04 mass%, respectively, determined with a Metrohm 737 KF coulometer. Table 1 gathers information about pure components: experimental

Results and discussion

For each binary system studied, Table 2 lists experimental values for x, y, T, γ, and GERT−1. For ternary systems, isobaric VLE data were determined only for the homogeneous zones. Table 3 lists the experimental liquid- and vapor-phase compositions (xi and yi, respectively) and equilibrium temperatures (T), along with the corresponding activity coefficients (γi). Fig. 1 depicts the calculated isotherms of each ternary system. The binodal curves were taken from previous work [19].

At the

Conclusions

Experimental VLE data were determined for the binary systems methanol + BTBE and ethanol + BTBE and for the ternary systems BTBE + methanol + water and BTBE + ethanol + water at the constant pressure of 101.32 kPa. Thermodynamical consistency of the experimental VLE data reported in this work has been checked out by means of the point-to-point Fredenslund's consistency test and the Wisniak's LW test, for the binary systems, and the Wisniak-LW and Wisniak–Tamir's modification of Mac Dermot–Ellis tests, for

Acknowledgment

The authors are grateful to the Ministerio de Ciencia y Tecnología (Spain) for financial support under project PPQ2003-01236.

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