Isobaric (vapour + liquid) equilibria for the (1-propanol + 1-butanol) binary mixture at (53.3 and 91.3) kPa

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Abstract

In this work, isobaric (vapour + liquid) equilibrium data have been determined at (53.3 and 91.3) kPa for the binary mixtures of (1-propanol + 1-butanol). The thermodynamic consistency of the experimental values was checked by means the traditional area test and the direct test methods. According to the criteria for the test methods, the (vapour + liquid) equilibrium results were found to be thermodynamically consistent. The experimental values obtained were correlated by using the van Laar, Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The binary interaction parameters of the activity-coefficient models have been determined and reported. They have been compared with those calculated by the activity-coefficient models. The average absolute deviation in boiling point and vapour-phase composition were determined. The calculated maximum average absolute deviations were 0.86 K and 0.0151 for the boiling point and vapour-phase composition, respectively. Therefore, it was shown that the activity-coefficient models used satisfactorily correlate the (vapour + liquid) equilibrium results of the mixture studied. However, the performance of the UNIQUAC model was superior to all other models mentioned.

Introduction

The aliphatic alcohols such as 1-propanol and 1-butanol are of interest as fuels because they can be synthesized biologically. The 1-propanol and 1-butanol are considerably less toxic and less volatile than methanol, which is a benefit for fire and explosion safety [1]. They are used as a solvent in the pharmaceutical, paint, and cosmetic industries. Also, they may be used as an extraction solvent for natural products and as a chemical intermediate in the manufacture of other chemicals [2], [3]. Large streams of mixed aliphatic alcohols (consisting mostly of 1-butanol) are produced from various sources and the feasibility of their separation was undertaken by distillation [4]. The measurements of the (vapour + liquid) equilibrium (VLE) have an important role in the correct design and optimized operations of distillation processes as the most economical and utilized globally separation method to obtain improved purity products [5]. There are various theoretical and empirical models to estimate VLE of non-ideal systems but especially in the final design step the necessary VLE data need to be determined experimentally [6], [7].

In this work, isobaric VLE results for the binary mixture of (1-propanol + 1-butanol) were obtained at (53.3 and 91.3) kPa. The VLE results obtained for the binary mixture and the activity coefficients were found to be thermodynamically consistent. The experimental values were correlated with using the simple empirical models such as van Laar [8] and Margules [9] and three local composition models such as Wilson [10], NRTL [11], and UNIQUAC [12] for the liquid phase activity coefficients. The measured values have been compared with those correlated by the activity-coefficient models. The correlated parameters of the models as well as the average absolute deviation in boiling points and vapour-phase compositions were determined and reported.

Section snippets

Chemicals

Pure grade compounds, 1-propanol and 1-butanol were supplied by Merck Co. Inc., Germany. The purity of the chemicals was checked on the basis of its refractive index at T = 293.15 K. The refractive index was measured using a thermostatically controlled Abbe Refractometer (Atago 1T/4T) equipped with a digital thermometer with an uncertainty of ±0.05 °C with an accuracy of ±0.0001nD. The measured physical properties of 1-propanol and 1-butanol are listed in table 1 along with values from the

Vapour pressure

The experimental vapour pressure measured in this work is given in table 3. Those data were compared with the values obtained via the Antoine equation, which is expressed in the following forms:lgPvp/100kPa=A-B(T/K)+C-273.15,where A, B, and C are constants. Table 4 shows the Antoine constant parameters of the chemicals from the literature [9]. The measured 1-propanol and 1-butanol vapour pressure and the predicted value via the Antoine equation are presented in figure 1. According to this

Conclusion

Isobaric VLE values were determined experimentally for the {1-propanol (1) + 1-butanol (2)} binary mixture at 53.3 and 91.3 kPa. The results revealed no major deviations from ideal mixture-like behaviour. The VLE results obtained data were examined by the thermodynamic consistency tests. By the analysis of the consistency test methods, the VLE results were of acceptable quality. The VLE values were correlated by the five activity-coefficient models, namely, van Laar, Margules, Wilson, NRTL, and

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