(Liquid + liquid) equilibria of three ternary systems: (heptane + benzene + N-formylmorpholine), (heptane + toluene + N-formylmorpholine), (heptane + xylene + N-formylmorpholine) from T = (298.15 to 353.15) K

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Abstract

(Liquid + liquid) equilibrium (LLE) data for ternary systems: (heptane + benzene + N-formylmorpholine), (heptane + toluene + N-formylmorpholine), and (heptane + xylene + N-formylmorpholine) have been determined experimentally at temperatures ranging from 298.15 K to 353.15 K. Complete phase diagrams were obtained by determining solubility and tie-line data. Tie-line compositions were correlated by Othmer–Tobias and Bachman methods. The universal quasichemical activity coefficient (UNIQUAC) and the non-random two liquids equation (NRTL) were used to predict the phase equilibrium in the system using the interaction parameters determined from experimental data. It is found that UNIQUAC and NRTL used for LLE could provide a good correlation. Distribution coefficients, separation factors, and selectivity were evaluated for the immiscibility region.

Introduction

In the scope of investigating more efficient solvents as potential replacements for sulfolane [1], [2], [3], [4], [5], N-methylpyrrolidone [6], glycol [7], [8], and as new solvents for separations, N-formylmorpholine has been found to be a excellent solvent for industrial extraction of aromatics from feed stocks, such as hydrogenated pyrolysis gasoline and hydro-refined coke oven oil [9], [10], [11], [12].

The real behaviour of fluid mixtures can be calculated with the help of activity coefficients. The correct description of the dependence on temperature, pressure, and composition in multi-component systems requires reliable thermodynamic models, which allow the calculation of these properties from available experimental data. The UNIQUAC and NRTL activity coefficient models are universal methods in the estimating activity coefficient that has been established to date [13], [14].

To our knowledge, information related to (liquid + liquid) equilibria involving NFM and hydrocarbons are scarce in the literature. These parameters are not entirely available for multi-component systems [11], [12]. Therefore, it is worthwhile to study LLE of ternary mixtures (NFM + aromatics + alkanes), with the aim of contributing to the knowledge of (liquid + liquid) equilibrium with NFM. In the present work, we focus our attention on ternary systems where heptane, aromatic hydrocarbon, and NFM are involved. The LLE measurements for the ternary system (heptane + NFM + aromatic hydrocarbon) (benzene, toluene, and xylene) over the temperature range of (298 to 353) K have been obtained. The results are used to estimate the interaction parameters of the UNIQUAC and NRTL expression.

Section snippets

Chemicals

The purities and refractive indices of all chemicals used in this study are presented in table 1. The purity of the chemicals was determined by gas chromatography, the results confirmed the mass fraction purity was higher than 0.995. All chemicals were used without further purification.

Extraction runs

The experimental apparatus used in the previous study were modified and used in this study [5]. A schematic diagram of the apparatus is shown in figure 1. The apparatus consists of a glass cell with a water

Models and predictions

Our experimental data were correlated with the UNIQUAC model of Abrams and Prausnitz [13] and the NRTL model of Renon and Prausnitz [14]. The excess Gibbs free energy of mixing gE of the NRTL model isgERT=i=1nj=1nτjiGjixjl=1nGlixi,where τji=gji-giiRT, Gji = exp(−α jiτji), aji = 0.3 + bji(T  273.15), (aij = aji), where R is the gas constant, T the absolute temperature. We have set a as temperature dependence function, and aij and aji are the two adjustable parameters in the model for each binary pair

Experimental data

The measured equilibrium mole fractions, distribution coefficient, selectivity, and separation factor are given in TABLE 2, TABLE 3, TABLE 4 for the three ternary systems. The temperature increases the solubility of NFM in the heptane rich phase, while it has little effect upon the solubility of heptane in the NFM rich phase. Parts of the experimental and the predicted tie lines for the ternary systems are shown in FIGURE 2, FIGURE 3, FIGURE 4, FIGURE 5, FIGURE 6, FIGURE 7. The systems studied

Conclusions

An experimental investigation of equilibrium behaviour of (liquid + liquid), {heptane + aromatic hydrocarbon (benzene, toluene, and xylene) + NFM} ternary systems was carried out at temperatures from (298 to 353) K and at an atmospheric pressure. The solubility of NFM in the heptane rich phase increases as the temperature increases, but it has little effect on the solubility of heptane in the NFM rich phase. The mutual NFM-heptane solubility increases as the concentration of aromatic hydrocarbon

Acknowledgements

This work was supported by the Natural Research Fund of Hunan Province, PR China. Project Number: 05JJ40020. The authors thank to the Centre of Laboratory of Central University for GC analysis.

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