Elsevier

Fluid Phase Equilibria

Volume 353, 15 September 2013, Pages 87-92
Fluid Phase Equilibria

Isobaric vapor–liquid equilibrium for systems containing sulfur compounds

https://doi.org/10.1016/j.fluid.2013.05.019Get rights and content

Highlights

  • Isobaric VLE data for four systems was measured in dilute solution.

  • The VLE data in dilute solution were compared with that in the entire concentration.

  • The activity coefficients of trace component varied a lot in its low concentration.

  • The yx of the trace component followed the quadratic polynomial equation.

  • A concept of multi-scale phase equilibrium was proposed.

Abstract

Isobaric vapor–liquid equilibrium (VLE) data for the binary systems of thiophenic compounds with three hydrocarbons in gasoline (2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene and n-heptane) were measured in dilute solutions at 101.33 kPa with a modified Rose–Williams still. General Coulomb meter was used to analyze the compositions of the samples from the vapor–liquid equilibrium systems. The VLE data was compared with the calculated value by the Wilson model with the interaction parameters regressed over the entire concentration range. Results found that neither the activity coefficient model nor the Henry's model could describe the VLE behavior of the trace component in the dilute solution accurately. Thus a concept of multi-scale phase equilibrium was proposed.

Introduction

As a major cause of SOx air pollution and poison for noble metal catalysts in automobiles [1], sulfur in gasoline is compelled to be reduced. Sulfur limits of <150 ppmw (parts per million by weight) have been introduced into China from January 1, 2010 [2], and the European Union has issued regulations that required refineries to reduce the sulfur content of gasoline to <10 ppmw in 2009 [3]. Therefore, deep desulfurization of transportation is receiving increasing attention of the research communities worldwide.

The information of VLE data for the sulfur compounds with other hydrocarbons in gasoline is required for the design and operation of gasoline desulfurization processes [4]. Firstly, the nonideality of reactants and products should be considered in the accurate kinetic equations. Secondly, the description of phase equilibrium is required for the separation processes involved in the desulfurization processes, such as distillation and extraction.

In our previous research [5], [6], the VLE data of thiophenic compounds with the hydrocarbons in gasoline has been determined over the entire concentration range. However, considering that the sulfur content in gasoline is much less than other hydrocarbons, the VLE data determined in the entire concentration range might not be able to describe the phase equilibrium of thiophenic compounds accurately, as the same deviation of the composition would have a greater impact on the equilibrium constant of the dilute component (sulfur) than the conventional component (other hydrocarbons).

Therefore, in this work, isobaric VLE measurements for four binary systems, including thiophene + 2,3-dimethyl-2-butene, thiophene + n-heptane, 3-methylthiophene + 2,3-dimethyl-1-butene and 3-methylthiophene + n-heptane, were performed at 101.33 kPa with a modified Rose–Williams still in dilute solutions with the mole fraction of thiophenic compounds less than 0.0015. Similar measurements studied in this work were not found in the open literature. Besides, the experimental data were compared with the predicted value calculated by the Wilson model with the interaction parameters obtained in our previous research [5], [6].

Section snippets

Materials

Thiophene and n-heptane were supplied by Guangfu Company, 2,3-dimethyl-2-butene and 2,3-dimethyl-1-butenen by Kaifei Company, and 3-methylthiophene by Senbao Chemical Company. The purities of all the substances were checked by a gas chromatograph (GC) equipped with a flame ionization detector. The purity and water content were listed in Table 1.

Apparatus and procedures

The VLE data measurements were carried out in a modified Rose–Williams still (Beiyang Analytical Instrument Company), which was shown in Fig. 1. In a

Reliability test of the instruments

In order to test the reliability of the experimental instrument, the vapor pressure for pure n-heptane was measured in this work and compared with those reported by Weber [8] and Poling et al. [9]. As can be seen from Fig. 2 and Table 2, the measurement in this work is consistent with the open literature [8], and both of the experimental data could be predicted well by the Antoine equation with the parameters in the handbook [9]. Therefore, the experimental instrument used in this work is

Conclusions

The isobaric VLE data for four systems of thiophene + 2,3-dimethyl-2-butene, thiophene + n-heptane, 3-methylthiophene + 2,3-dimethyl-1-butene, and 3-methylthiophene + n-heptane in dilute solution was determined at 101.33 kPa with a modified Rose–Williams still, and was compared with the calculated value using the Wilson model with the interaction parameters regressed by the VLE data determined in the entire concentration range. Results found that the Wilson model with the interaction parameters

Acknowledgements

We acknowledge gratefully the financial support of the Fund of National Basic Research Program of China (973 Program No. 2012CB215000), the Program for Changjiang Scholars and Innovative Research Team in University (IRT0936), and the National Natural Science Foundation of China (No. 20976129).

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