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Distillation Science (Coleman)

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    This is a ten-part series of technical articles on Distillation Science, as is currently practiced on an industrial level. It is organized as it would be used for the process design of large-scale distillation columns, which may differ from the way topics are introduced to students academically. As a part of distillation column design, these articles also involve the vapor-liquid equilibria (VLE) of binary systems, with potential extension to multi-component systems. For application or other questions, the author can be contacted at

    • 1: Overview
      While chlorosilanes and their electronic impurities are used as recurring examples, the technology developed here has great application in other mildly polar and hydrogenated compounds, which are normally excluded from theoretical treatment in many texts. The emphasis is on industrial level applications.
    • 2: Vapor Pressure
      This article deals with the pure component VP relationships commonly found in textbooks, as well as their limitations. This article lays the basis for subsequent articles on improving VP equations and tying in Equations of State.
    • 3: Critical Properties and Acentric Factor
      This article deals with the tabulation of these properties for selected fluids based on globally collected data. Data analysis and validation are discussed, as well as estimation techniques for those fluids for which data is either poor or non-existent. Critical properties are used to convert temperature, pressure, and specific volume from conventional units used in both chemistry and chemical engineering, to the reduced form.
    • 4: New Vapor Pressure Equation
      This article shows how a new vapor pressure equation form allows practice of distillation applications at the elevated pressures more common to industry. The culmination of this article is a thermodynamically consistent equation form that is valid between the atmospheric boiling point and the critical point, and which allows evaluation of other required distillation properties such as saturated phase densities and latent heat of vaporization.
    • 5: Equation of State
      This article deals with the recommendations for Equation Of State (EOS), as well as the mathematical techniques for solving such non-intrinsic EOS equation forms. The module explains why an EOS is needed to evaluate the pure-component physical properties that are used in distillation science, reviews the various options and makes a recommendation. Also included are techniques for solving the EOS cubic equations and some work-arounds near the critical point.
    • 6: Fugacity
      This article deals with the one of the two possible departures from ideal pure-component vapor pressure in binary mixtures, as is commonly found in practical application of distillation science.
    • 7: Liquid Activity Coefficients
      This article deals with Liquid Activity Coefficients,  the second type of departure from pure-component vapor pressure.  It describes the application and estimation of Liquid Activity Coefficients, as commonly found in practical application of distillation science. Various activity coefficient models are reviewed along with some limited data and a recommended estimation technique given where data is lacking.
    • 8: VLE Analysis Methods
      This article discusses the recommended methodology used when data-collecting binary systems, in order to assure that systemic errors are minimized. This topic also deals with validation whenever data collection is done on reactive fluids, which can disproportionate or dimerize during study.
    • 9: Putting It All Together
      This article shows how to combine the components of the above Distillation Science topics in a practical application, as well as illustrating why it is necessary to include departures from ideal behavior in real binary systems, as commonly encountered in industrial practice.
    • 10: Convergence Strategy
      This last article shows how VP equation solutions are best obtained for additional fluids in non-intrinsic or nested-loop equation forms, such as the recommended vapor pressure equations. While this topic is more mathematical or computer-science oriented than chemistry, it is a necessary technique to understand when dealing with modern technology.

    Thumbnail: A double effect distillation plant. (CC BY-SA 3.0 Unported; Luigi Chiesa via Wikipedia)

    This page titled Distillation Science (Coleman) is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Larry Coleman.

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