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

本研究是申请人先前致力于液相粘度对填料塔中蒸馏的影响的研究项目的后续。对于二元体系2-甲基-2-丁醇和2-甲基-1-丙醇（MB/MP），可以表明，与参比体系氯苯/异丙醇（CB/EB）相比，在蒸馏条件下对于5 mPa s的粘度，分离效率已经降低了高达50%。使用流体动力学模拟方法，可以很好地预测粘度高达5 mPa s的分离效率。然而，层析成像的调查与液相粘度>= 10 mPa·s的系统显示在这些升高的粘度的流动形态和外观的变化，额外的流动类型。预计在高于10 mPa·s的粘度值下发现的不同流动形态对填充柱的流体动力学和分离行为具有显著影响。因此，拟议的研究项目应通过向挥发性系统CB/EB和MB/MP中添加非挥发性聚合物，将粘度范围扩大至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。将研究三种特征体系：i）CB/EB +聚丁二烯，使得达到与二元MB/MP体系相同的粘度（5 mPa·s）; ii）MB/MP +聚乙烯吡咯烷酮，以达到5 mPa·s与50 mPa·s之间的粘度; iii）CB/EB +聚丁二烯，使得再次建立与ii）中相同的粘度。对于蒸馏实验，已经开发了一种新的操作程序，其允许在蒸馏塔的分离部分中建立明确定义的和恒定的聚合物浓度。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方法是针对无穷大回流比开发的，因此需要建立一种新的数据提取方法。这种新的方法将允许在蒸馏条件下，在非挥发性组分的存在下的分离效率的测定。使用层析成像研究，将确定粘度升高时的流动形态以及不同流动模式（薄膜、细流、液滴、接触点液体等）的相对贡献量化。这为采用流体动力学模拟方法模拟分离效率提供了基础。在成功的情况下，它将是可能的预测流体动力学和分离效率的粘性蒸馏系统高达50 mPa·s的填充柱的物理性质，相平衡和独立的层析测量的基础上。

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.