Evaluation for the distillation of viscous mixtures in packed colomns - A theoretical and experimental approach

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The proposed research project follows up the previous project of the applicants dedicated to the influence of liquid-phase viscosity on the distillation in packed columns. For the binary system 2-methyl-2-butanol and 2-methyl-1-propanol (MB/MP), it could be shown that already for viscosities of 5 mPa s at distillation conditions, separation efficiency is reduced by up to 50 % as compared to the reference system chlorobenzene/ethylbenzene (CB/EB). Using the Hydrodynamic Analogy approach, the separation efficiency could be well predicted for viscosities up to 5 mPa s. However, tomographic investigations for systems with liquid-phase viscosities >= 10 mPa s revealed changes in the flow morphology and the appearance of additional flow types at these elevated viscosities. It is expected that the different flow morphology discovered at viscosity values higher than 10 mPa s has a significant impact on the fluid dynamics and separation behavior of packed columns. The proposed research project shall, therefore, extend the range of viscosities up to 50 mPa s by adding non-volatile polymers to the volatile systems CB/EB and MB/MP. The project aims at a deeper understanding of the influence of elevated viscosity on fluid dynamics and separation efficiency. Three characteristic systems will be investigated: i) CB/EB + polybutadiene, such that the same viscosity (5 mPa s) is reached as for the binary MB/MP system; ii) MB/MP + polyvinylpyrrolidone, to reach viscosities between 5 mPa s and 50 mPa s; iii) CB/EB + polybutadiene, such that, again, the same viscosities are established as in ii). For the distillation experiments, a new operating procedure has been developed that permits a well-defined and constant polymer concentration in the separation section of the distillation column to be established. In this case, the column has to be operated with a finite reflux ratio. Since the conventional Fenske-Underwood method has been developed for an infinity reflux ratio, the establishment of a new data extraction method is required. This new method will allow the determination of the separation efficiency under distillation conditions in presence of a non-volatile component. Using tomographic investigations, the flow morphology at elevated viscosity will be determined and the relative contributions of the different flow patterns (films, rivulets, droplets, contact-point liquid, etc.) quantified. This provides the basis for the modeling of separation efficiency with the Hydrodynamic Analogy approach. In case of success, it will be possible to predict fluid dynamics and separation efficiency of viscous distillation systems up to 50 mPa s in packed columns solely on the basis of physical properties, phase equilibria and independent tomographic measurements.