The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Modelling and Measuring Vapour-Liquid Equilibria for the Removal of Sulphur Compounds

Erlin Sapei

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Chemical Technology for public examination and debate in Auditorium KE2 at Helsinki University of Technology (Espoo, Finland) on the 9th of November, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-22-8999-8)   [1073 KB]
Dissertation is also available in print (ISBN 978-951-22-8998-1)

Abstract

Increasing concern about air pollution has led many countries to adopt more stringent regulations, which impose an ultra-low concentration of sulphur in gasoline. These regulations place many challenges for the refining industry. Lower sulphur levels are being recommended for gasoline and diesel for environmental reasons.

New methods and innovations are required to further reduce the sulphur level in liquid fuels. Separation process design to accomplish the removal of sulphur compounds requires knowledge of the vapour-liquid equilibrium (VLE) of sulphur compounds with hydrocarbons, particularly their activity coefficients at infinite dilution. However, the investigations concerning the systems containing sulphur compounds are very limited.

This thesis deals with the VLE measurements of selected sulphur compounds (1-propanethiol, diethyl sulphide, and thiophene) with various hydrocarbons (C6 to C8) and 2-ethoxy-2-methylpropane (ETBE) under isobaric and isothermal conditions, using a circulation still and the infinite dilutions activity coefficients measurements of 1-propanethiol, ethyl methyl sulphide, and thiophene in toluene, n-heptane, and 2,2,4-trimethylpentane at 90 kPa using comparative ebulliometer techniques.

The gamma-phi approach was used in the calculation of VLE. The activity coefficients of the liquid phase (γ) were correlated with the Wilson model. The Wilson model gave a good correlation for all systems. The activity coefficients at infinite dilution (γ∞) were extrapolated from the VLE measurements with the Wilson model.

The γ∞ values of sulphur compounds for the systems thiophene + toluene and thiophene + 2,2,4-trimethylpentane obtained from the recirculation still measurements are compared with the γ∞ values of sulphur compounds obtained from the comparative ebulliometer measurements. The agreement between the measurements is good.

All the measured γ∞ of sulphur compounds in hydrocarbons are less than two. 1-Propanethiol, thiophene, and diethyl sulphide in toluene show nearly ideal behaviour, and thus the γ∞ of sulphur compounds for these systems are one. The activity coefficients of sulphur compounds in hydrocarbons show the typical behaviour of positive deviations from Raoult's law, which become smaller with increasing temperature and with an increase in the number of C-atoms of the alkanes.

The systems 1-propanethiol, thiophene, and diethyl sulphide in toluene show nearly ideal behaviour. No azeotrope formation was observed for the systems thiophene + 1-hexene and diethyl sulphide + 1-hexene. The reaction between 1-propanethiol and 1-hexene was observed. The systems thiophene + n-hexane and thiophene + 2,2,4-trimethylpentane, as well as the systems diethyl sulphide + n-heptane and diethyl sulphide + 2,2,4-trimethylpentane, show positive deviations from Raoult's law. These systems exhibit maximum pressure azeotropy. The systems thiophene + 1-hexene and thiophene + 2-ethoxy-2-methylpropane, as well as the systems diethyl sulphide with n-hexane, 1-hexene, cyclohexane, and 2-ethoxy-2-methylpropane, show positive deviation and strong nonideality. No azeotropes formed in these systems.

The original UNIFAC predictive model is adequate to describe the behaviour of sulphur in hydrocarbons, even though its application is limited to the availability of the functional group interaction parameters. COSMO-RS gives poor prediction for all the systems studied, and thus it is not currently a suitable model for predicting the behaviour of systems containing sulphur compounds.

These new consistent measurements can be used to improve and develop thermodynamic models in dilute systems, and thus the behaviour of organic sulphur compounds in the distillation of hydrocarbons can be simulated.

This thesis consists of an overview and of the following 8 publications:

  1. Kim, Y., Sapei, E., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary systems of 2-propanol + 1,1-diethoxyethane at 353 K, ethyl ethanoate + 1,1-diethoxyethane at 348 K, and 2-propanone + 1,1-diethoxyethane at 328 K, Journal of Chemical and Engineering Data, 50 (2005) 364-368.
  2. Sapei, E., Zaytseva, A., Uusi-Kyyny, P., Kim, Y., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary system of 1-propanethiol, thiophene, and diethyl sulfide with toluene at 90.03 kPa, Journal of Chemical and Engineering Data, 51 (2006) 1372-1376.
  3. Sapei, E., Zaytseva, A., Uusi-Kyyny, P., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary system of thiophene + n-hexane at (338.15 and 323.15) K and thiophene + 1-hexene at (333.15 and 323.15) K, Journal of Chemical and Engineering Data, 51 (2006) 2203-2208.
  4. Sapei, E., Zaytseva, A., Uusi-Kyyny, P., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary system of diethyl sulfide + n-heptane and diethyl sulfide + 2,2,4-trimethylpentane at (363.15 and 353.15) K, Journal of Chemical and Engineering Data, 52 (2007) 192-198.
  5. Sapei, E., Zaytseva, A., Uusi-Kyyny, P., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary system of diethyl sulfide + n-hexane at (338.15 and 323.15) K and diethyl sulfide + 1-hexene at (333.15 and 323.15) K, Journal of Chemical and Engineering Data, 52 (2007) 571-576.
  6. Sapei, E., Zaytseva, A., Uusi-Kyyny, P., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary system of diethyl sulfide + cyclohexane at 353.15 and 343.15 K and diethyl sulfide + 2-ethoxy-2-methylpropane at 343.15 and 333.15 K, Fluid Phase Equilibria, 252 (2007) 130-136.
  7. Sapei, E., Zaytseva, A., Uusi-Kyyny, P., Keskinen, K. I., Aittamaa, J., Vapor–liquid equilibrium for binary system of thiophene + 2,2,4-trimethylpentane at 343.15 and 353.15 K and thiophene + 2-ethoxy-2-methylpropane at 333.15 and 343.15 K, Fluid Phase Equilibria, accepted for publication on 15.06.2007.
  8. Sapei, E., Uusi-Kyyny, P., Keskinen, K. I., Aittamaa, J., Infinite dilution activity coefficients of organic sulphur compounds in hydrocarbons by comparative ebulliometry, Proceedings of the 7th World Congress of Chemical Engineering, Glasgow, United Kingdom, 2005, 83582/1-83582/6.

Keywords: vapour-liquid equilibrium, VLE, sulphur compounds, hydrocarbons, 2-ethoxy-2-methylpropane, ETBE, 1-propanethiol, diethyl sulphide, thiophene, fuels, gasoline

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2007 Helsinki University of Technology

Last update 2011-05-26