Elsevier

Fluid Phase Equilibria

Volume 377, 15 September 2014, Pages 56-75
Fluid Phase Equilibria

III. Study of critical and maximum temperatures of coexistence of liquid and gas phase in hydrocarbons binary mixtures of aromatic hydrocarbons with alkanes and cycloalkanes

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Abstract

Form of the phase diagrams in the coordinates “temperature-density”, critical and maximum temperature of liquid and vapor phases coexistence for binary mixtures (n-C5, n-C6, n-C8, n-C11) + benzene, n-C5 + toluene and н-C5 + 2-methylbiphenyl were determined by isochoric method. Their interrelation with the difference of the critical temperatures of components forming the mixture was determined. The prediction method was developed and tested using own experimental and literature data on critical and maximum temperatures of binary mixtures of aromatic hydrocarbons with alkanes and cycloalkanes.

Introduction

Information on critical properties and maximum temperatures of liquid and vapor phase coexistence (maximum temperature or Tmax,m) for industrially important mixtures is essential for development of supercritical technologies. In near critical and supercritical regions it is possible to attain a unique and very effective hydrodynamic condition. Alkylation technologies are based on mixtures of aromatic hydrocarbons and alkanes. However, the available data for these mixtures are limited. The analysis of literary data shows that at present empirical information has been obtained only for 25 binary mixtures, of which 18 are of benzene with (C3–C16) alkanes [1], [2], [3], [4], [5] or (C5–C8) cyclical alkanes [2], [3], [5], 3 are of toluene with n-pentane, n-hexane, and cyclohexane [2], [5], and 4 are of ethylbenzene with (C5–C8) linear alkanes [5] (Table 1).

It is important to note that empirical information is available only for the critical properties of the mixtures. In addition, for 24 mixtures the difference between the critical temperatures of the components ΔTc(i,j) does not exceed 160 K [2], [3], [4], [5], and is 193 [1] and 256 K [5] for the remaining two. Maximum temperatures of phase coexistence were not determined.

This article supplements the structural succession of aromatic hydrocarbons with a study of mixtures containing isopropylbenzene and 2-methylbiphenyl, provides more reliable data across the 0–160 K range of critical temperature differences, widens the ΔTc(i,j) range up to 290 K, and provides the grounds for efficient application of the data on the critical conditions of the substance to the technologies involving mixtures of aromatic hydrocarbons with alkanes and cycloalkanes.

Section snippets

Materials

The experiment was carried out using commercially available samples with purity level declared by the maker. The quality of the compositions was verified by GC.

The degree of purity of the samples was determined using a Kristall-2000M chromatograph equipped with a flame ionization detector and a quartz capillary column with bonded stationary phase SE-30 of 50 m length, inside diameter 0.25 mm, carrier gas–helium, inlet pressure – 1.5 atm, evaporator temperature – 623 K, detector – 523 K.

Content of

Results of experiment

For every pure substance which was used as a component of the mixtures, critical temperatures were measured (Table 2). The critical temperatures we obtained are in good agreement with the published data within the declared margin of error of the experiment ±0.5 K (Table 2).

The following mixtures were studied in the present research: n-pentane + benzene, n-hexane + benzene, n-octane + benzene, n-undecane + benzene, n-pentane + toluene, n-pentane + isopropylbenzene, n-hexane + isopropylbenzene, n-pentane + 

Database

Systemized experimental and published data on critical temperatures of mixtures of cyclical hydrocarbons with alkanes and cycloalkanes are represented in Table 4.

Critical temperatures of mixtures

The data represented in Table 4 are used for the development of Tc,m predictions methods.

For development of prediction methods and testing their applicability the Tc,m, which demonstrated good mutual consistency across each system when processed by Redlich–Kister equation [13] were used:Tc,m=xiTci+xjTcj+xixj(A1+A2(xixj)+A3(xixj)2)where, xi, xj – mole fractions of mixture components; Tci, Tcj – critical temperature of the mixture components, K; A1, A2, A3 – coefficients obtained from the

Critical temperatures of mixtures

Most published data is well represented by Redlich–Kister equation (3), with median absolute deviations of predicted values from the experimental not exceeding 0.5 K (see Table 4). This is the evidence that the mutual comparability of the data across each system is good.

During the development of prediction methods the difference of the critical temperatures of the components of the mixtures was calculated by equation:ΔTArAl=TcArTcAlwhere TcAr is the critical temperature of the aromatic

Conclusions

Critical and maximum temperatures for eight aromatic hydrocarbons with n-alkanes mixtures were obtained by experimental research across the full range of components. Important aspects of obtaining maximum and critical temperatures of binary mixtures by the isochronous method are discussed.

On the basis of experimental research and systemized literary data, an estimation of the potential for predicting critical and maximum temperatures of aromatic hydrocarbons and linear and cyclical alkanes

Acknowledgments

This work was financially supported by The Ministry of Education and Science of Russian Federation within the framework of the basic part of governmental tasks of Samara State Technical University (project code 1708).

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