Conclusions
97
Chapter 7 - Conclusions
This master project is part of the PhD project "Reactive Distillation for Multi-Product Continuous Plants“. In this project, the modelling and conceptual design of reactive distillation operations for multiple polyester products have been carrying out.
Therefore, the objectives of the master thesis are the selection of promising internals, the development of a proper experimental setup and the characterization of hydrodynamics and mass transfer properties for the selected internals with viscous liquids.
Among all possible choices, the structured packings were chosen for the column internal, specifically Flexipac 2X-S, manufactured by Koch-Glitsch, and SuperPak 250Y, manufactured by Rashig Jaeger, appeared promising. Additional experiments on bubble column were performed to evaluate the enhancement due to the packing.
The internship and the experimental activity was performed at the Chemical Engineering and Chemistry Department of Eindhoven University of Technology. The pilot plant used for the experiments was partially available there: after an extensive literature research on the topic and the experimental techniques, it was adapted and completed with measuring instrumentations necessary for the characterization.
Large amount of data are available for the bubble column and the results of the experiments are in agreement with the trends found in the literature, so the set up seems to be adequate for the characterization of column internals.
Conclusions
98 The gas hold up measurements show that the packing increases the gas hold up in the column, the extent of this increase ranges from 10% of the bubble column hold up at low viscosity up to 100% at high viscosity. The comparison between the packings also shows that at the low viscosities the SuperPak provides a higher increase while at the high viscosity the Flexipac does.
The main reason to introduce the packings in the column is the reduction of the axial dispersion: the experiments show that axial dispersion coefficient decreases up to a factor 5 in comparison to the bubble column. This effect is more significant at high gas flow rates and high viscosities.
Despite the good performances in the gas hold up increase and the axial dispersion reduction, the packings do not enhance the mass transfer significantly. Both the SuperPak and the Flexipac produce a volumetric mass transfer coefficient similar to the bubble column, sometimes even lower.
In conclusion, the packing of the column can be a promising alternative for the development of reactive distillation system mainly because of the reduction in the axial dispersion but a further study on the mass transfer is required to enhance the stripping of water in the reactive distillation column and therefore to reduce the residence time of the liquid.
Future development of this work may concern the characterization of different internals and particularly the tray bubble column can be promising. According to the literature this kind of internal can provide much higher gas hold up and mass transfer compared to the bubble column with a low axial dispersion because the sieve trays redistribute and break up the gas bubbles and at the same time they limit the liquid circulation in the column.
Particular attention should be paid to the measuring system. In particular, gas hold up experimental results evidenced the unreliability of the pressure measuring devices used. Probably, the adoption of a differential pressure cell can provide more reliable results.
