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

本次拟进行的研究项目是继申请人之前的研究项目“液相粘度对填料塔蒸馏的影响”之后进行的。对于2-甲基-2-丁醇和2-甲基-1-丙醇二元体系（MB/MP），在粘度为5 mPa s的蒸馏条件下，与参比体系氯苯/乙苯（CB/EB）相比，分离效率降低了50%。使用流体动力学类比方法，可以很好地预测粘度高达5 mPa s的分离效率。然而，对液相粘度>= 10 mPa s的系统的层析研究显示，在这些高粘度下，流动形态发生了变化，并出现了额外的流动类型。预计在粘度大于10 mPa s时发现的不同流动形态对填料塔的流体动力学和分离行为有显著影响。因此，拟议的研究项目将通过在挥发性体系CB/EB和MB/MP中添加非挥发性聚合物，将粘度范围扩大到50 mPa / s。该项目旨在更深入地了解粘度升高对流体动力学和分离效率的影响。将研究三种特性体系：1)CB/EB +聚丁二烯，使其达到与二元MB/MP体系相同的粘度（5 mPa s）；ii) MB/MP +聚乙烯吡咯烷酮，粘度在5mpa - 50mpa之间；iii) CB/EB +聚丁二烯，这样，再次建立与ii)相同的粘度。对于蒸馏实验，开发了一种新的操作程序，可以在精馏塔的分离段建立一个定义良好的恒定聚合物浓度。在这种情况下，塔必须以有限的回流比操作。由于传统的Fenske-Underwood方法已经发展到无限回流比，因此需要建立一种新的数据提取方法。这种新方法将允许在存在非挥发性成分的蒸馏条件下测定分离效率。通过层析研究，将确定高粘度下的流动形态，并量化不同流动模式（薄膜、细流、液滴、接触点液体等）的相对贡献。这为用流体力学类比方法对分离效率进行建模提供了依据。在成功的情况下，将有可能预测流体动力学和高达50 mPa s的粘性蒸馏系统的分离效率，仅基于物理性质，相平衡和独立的层析测量。

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.