New Double-Column Systems for Batch Heteroazeotropic Distillation

Abstract

Distillation is the method the most frequently applied for the separation of liquid mixtures, e.g. for the recovery of the components of the waste solvent mixtures. Because of the high energy demand of these processes the optimal design and operation of the distillation equipments are important from economic and also environmental points of view. The separation of the azeotropic mixtures needs special distillation methods like heteroazeotropic distillation. In the pharmaceutical and fine chemical industries it is often applied in batch mode. The aims of the thesis are to study the feasibility of a new Double-Column System (DCS) for batch heteroazeotropic distillation and to compare it with the traditional Batch Rectifier (BR) equipped with a decanter to study the above configurations by rigorous simulation to extend the DCS (Generalised Double-Column System, GDCS) and to study this new configuration by the above methods to do laboratory experiments for both configurations in order to prove the feasibility of the separation and validate the calculations, respectively. Two new double-column configurations for batch heteroazeotropic distillation were studied. These configurations are designed to produce simultaneously the components of binary heteroazeotropic and homoazeotropic mixtures (by using an entrainer). They are operated in closed system (without continuous product withdrawal). First the feasibility of the separation of a heteroazeotropic mixture (1-butanol – water) and that of a homoazeotropic one by using an entrainer (isopropanol – water + benzene or cyclohexane) in the DCS were investigated by a simplified model. Then the operation of this configuration was modelled by rigorous simulation by using the dynamic simulator of the professional flowsheet simulator ChemCAD (CC-DColumn). On the basis of the results obtained by both methods the new configuration was compared with the BR. The DCS proved to be feasible and competitive with the BR: during the same or shorter time the recoveries of the components were higher. Then the DCS was extended to a more flexible version (Generalised Double-Column System, GDCS), which is suitable for the separation of binary homoazeotropic mixtures (by using an entrainer, in this work: cyclohexane or n- exane). The feasibility method was extended for the study of this configuration, as well. The GDCS proved to be feasible. Then the effects of its additional operational parameters on the duration were studied by rigorous simulation. The GDCS was compared with the DCS by rigorous simulation, as well. The GDCS proved to be more advantageous than the DCS: the duration was shorter and the specific energy demands of the products were lower. The DCS and GDCS were also investigated by laboratory and pilot plant experiments. First laboratory experiments were done for the separation of the binary heteroazeotropic mixture in a simple small size glass equipment operated as BR and DCS. The DCS proved to be feasible and competitive with the BR also on the basis of the results of these experiments: during the same time the recovery of both components were higher. Then a pilot plant was used for the same separation as a DCS. After this experiment the separation of the binary homoazeotropic mixture by using n-hexane as entrainer was studied in the equipment operated as BR and GDCS. The experiment showed that the simultaneous production of two components is feasible also in the GDCS