Liquid–liquid equilibria for n-alkanes (C12, C14, C17) + propylbenzene + NMP mixtures at temperatures between 298 and 328 K
Introduction
Ternary phase equilibrium data are essential to the proper understanding of the solvent extraction processes. The separation of aromatic and aliphatic compounds from their mixtures is an important goal in chemical operations that produce both types of compounds. On the other hand smoke point of kerosene, cetane index of diesel, and viscosity index of lubricating oil can be improved by removing aromatic hydrocarbons. N-methyl-2-pyrrolidone (NMP) is a dipolar aprotic solvent used in the well-established Arosolvan process [1] for separating aromatic hydrocarbons from petroleum fractions. A few experimental liquid–liquid equilibrium data have been published for NMP + aromatic + n-alkanes (C5–C9) and hardly any for systems containing carbon number greater than nine for the alkanes and/or aromatics [2], [3], [4], [5], [6], [7], [8], [9].
This paper is considered as a part of our project to study the liquid–liquid phase equilibria for dearomatisation of Kuwait middle distilled fraction. The purpose of this work is to study LLE of three ternary systems: system-I {dodecane (1) + propylbenzene (2) + NMP (3)}, system-II {tetradecane (1) + propylbenzene (2) + NMP (3)}, and system-III {heptadecane (1) + propylbenzene (2) + NMP (3)}. The LLE data for the studied ternary systems were measured at 298, 308, 318, and 328 K and correlated by the UNIQUAC model of Abrams and Prausnitz [10] and the NRTL model of Renon and Prausnitz [11].
Section snippets
Chemicals
The purities and refractive indices of all chemicals used in this study are presented in Table 1. The NMP and aromatic hydrocarbons were stored under 4 Å molecular sieve. The purity of the chemicals was determined by gas chromatography. All chemicals were used without further purification.
Determination of critical solution temperature (Tc)
In order to find the operating extraction temperatures, the miscibilities and critical solution temperature Tc, of the systems studied were measured. The miscibilities of binary mixtures were measured by adding
Models and predictions
Our experimental data were correlated with the UNIQUAC model of Abrams and Prausnitz [10] and the NRTL model of Renon and Prausnitz [11]. The excess Gibbs free energy of mixing gE of the NRTL model iswhere R is the gas constant, T the absolute temperature, we have set α equal to 0.2 and aij and aji are the two adjustable parameters in the model for each binary pair that we find
Experimental data
Fig. 1 presents the measured critical solution temperatures of binary mixtures: NMP + dodecane, or tetradecane, or heptadecane at different phase ratio. The equilibrium coexistence curves have a rather horizontal top and become asymmetric with increasing CH2 group of the n-alkanes. Our experimental result is in agreement with that obtained by Bittrich et al. [14].
Fig. 2 presents the measured critical solution temperature of ternary mixtures: dodecane, or tetradecane, or heptadecane + propylbenzene +
Conclusions
An experimental investigation of equilibrium behavior of liquid–liquid, NMP + propylbenzene + dodecane, or tetradecane, or heptadecane ternary systems were carried out at temperatures of 298–328 K and at atmospheric pressure. The solubility of NMP in n-alkanes rich phase increases as the temperature increases, but it has little effect on the solubility of n-alkanes in NMP rich phase. The mutual NMP-alkanes solubility increased as the concentration of propylbenzene increases. Both the UNIQUAC and the
Acknowledgement
The authors thank the Public Authority for Applied Education and Training (PAAET-TS-01-001) for the financial support of this work.
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