Although several physical properties govern the design and performance of distillation columns, the effect of liquid viscosity is critical as it influences both mass transfer and hydrodynamic aspects of distillation columns. While there has been research to analyze the effect of viscosity on distillation, the majority of the research has been conducted with liquid viscosities less than 1.0 cP. There are a few articles in the literature discussing the effect of liquid viscosity greater than 1.0 cP on sieve tray efficiency using glycerol/water mixtures of varying glycerol concentrations
[1]. However, this may not represent a realistic scenario for distillation, as the relative volatility of glycerol/water mixture is well above the typical range of 1.1 to 2.5. Recently, Bradtmöller and Scholl proposed a new test system – isobutanol/tert-amyl alcohol, to study the effect of liquid viscosity on distillation efficiency from 1.0 to 4.0 cP. Although this is a useful system to study the effect of viscosity, additional test systems are necessary for decoupling the effect of viscosity from relative volatility. Therefore, in this study, we propose two new test systems that are relevant to high viscosity distillation conditions. The test systems were identified based on a comprehensive search and the selection criteria included (a) relative volatility in the range of 1.1 to 2.5 (b)boiling temperatures from 25 to 160°C to enable laboratory scale efficiency experiments at atmospheric and vacuum pressures in glass columns (c) viscosities more than 1.0 cP at these boiling temperatures. The newly selected test systems are cyclopentanol/cyclohexanol and tert-butanol/tert-amyl alcohol.
Vapor-liquid equilibrium data for the new systems were experimentally measured using a newly installed vapor-liquid equilibrium apparatus. A validation of the newly installed apparatus was first conducted prior to performing new experiments. The viscosities of these new test systems were also measured to accurately model the non-linear dependence of viscosity with temperature and composition. The new test systems would enable collecting efficiency data at viscosities ranging from 1.0 to 4.5 cP. These data are crucial in order to evaluate the validity of existing efficiency correlations as well as to develop improved efficiency correlations for highly viscous systems.
[1] Mahiout, S. and A. Vogelpohl, Mass Transfer in High Viscosity Media. Chemical Engineering and Processing, 1984. 18: p. 225-232.
