Elsevier

Fluid Phase Equilibria

Volume 227, Issue 1, 1 January 2005, Pages 19-25
Fluid Phase Equilibria

Isobaric vapor–liquid equilibria for the binary systems isobutyl alcohol + isobutyl acetate and tert-butyl alcohol + tert-butyl acetate at 20 and 101.3 kPa

https://doi.org/10.1016/j.fluid.2004.10.022Get rights and content

Abstract

New consistent vapor–liquid equilibrium data for the binary systems isobutyl alcohol (IBA) + isobutyl acetate (IBAc) and tert-butyl alcohol (TBA) + tert-butyl acetate (TBAc) are reported at 20 and 101.3 kPa. The IBA + IBAc system, which deviates positively from ideal behavior, can be described as symmetric solution and presents azeotrope at both pressures. The TBA + TBAc system shows positive deviations from ideal behavior and presents azeotrope only at 20 kPa. The activity coefficients and boiling points of the solutions were correlated with their composition by the Wilson, UNIQUAC, NRTL and Wisniak–Tamir equations.

Introduction

Isobutyl acetate (IBAc) and tert-butyl acetate (TBAc) are solvents widely used in chemical industry. They are used alone or in solvent blends in applications including coatings, inks, adhesives, industrial cleaners and degreasers. Both acetates are produced by esterification of acetic acid with the corresponding alcohol. Final purification of acetates in traditional technologies is a relative complex procedure due to the existence of a minimum boiling point azeotrope in the isobutyl alcohol (IBA) + IBAc mixture and a low relative volatility region in the tert-butyl alcohol (TBA) + TBAc system at atmospheric pressure.

The separation can be improved by adding an agent that alters the relative volatility of the components (extractive distillation) or making a simple change in pressure, provided that the azeotropic composition is sensitive to pressure (pressure swing distillation).

Unfortunately, azeotropic data frequently are not available at different pressures. The present work was undertaken to measure the phase equilibrium properties (VLE data) of the two systems mentioned at 20 and 101.3 kPa. Further, we can use these properties to simulate the pure components recovery without adding a separating agent and to find a feasible sequence in which the columns operate at different pressures. Some VLE data are available in literature for these related mixtures [1], [2], but only at atmospheric pressure.

The VLE data were found to be thermodynamically consistent at all pressures and were correlated with their composition by Wilson, UNIQUAC and NRTL equations.

Section snippets

Chemicals

IBA (99.5 mass%, HPLC grade), IBAc (>99 mass%, analytical grade), TBA (>99.5 mass%, HPLC grade) and TBAc (>99 mass%, analytical grade) were purchased from Aldrich Ltd. The reagents were used without further purification after chromatography failed to show any significant impurities. The water content was small in all chemicals (<0.05 mass%). Before measurements, the liquids were dried over molecular sieves (Union Carbide, type 4 Å, 1/16 in. pellets). The densities and refractive indexes of pure

Results and discussion

The pure component vapor pressure Pi0 for isobutyl alcohol was taken from Ref. [6]. For isobutyl acetate, tert-butyl alcohol and tert-butyl acetate, pure component vapor pressures were determined experimentally as a function of the temperature, using the same equipment as that for obtaining the VLE data. The pertinent results appear in Table 2. The measured vapor pressures were correlated using the Antoine equation:ln(Pi0)(kPa)=AiBiT(K)+Ciwhose parameters Ai, Bi and Ci are reported in Table 3

Acknowledgment

Financial support from the Ministerio de Ciencia y Tecnología of Spain, through project No. PPQ 2000-1335 and the Conselleria de Cultura, Educació i Esport (Generalitat Valenciana) of Valencia (Spain) is gratefully acknowledged.

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