The combination of chemical reaction with distillation in only one unit is called reactive distillation. The performance of reaction with separation in one piece of equipment offers distinct advantages over the conventional, sequential approach. Especially for equilibrium limited reactions such as esterification and ester hydrolysis reactions, conversion can be increased far beyond chemical equilibrium conversion due to the continuous removal of reaction products from the reactive zone. This may lead to an enormous reduction of capital and investment costs and may be important for sustainable development due to a lower consumption of resources.
Figure 1. Typical Reactive Distillation Column
Because of the complex interactions between chemical reaction and separation, the performance of a reactive distillation column is influenced by several parameters, e.g. size and location of reactive and non-reactive column sections, reflux ratio, feed location, or throughput. In order to develop a scale-up procedure and sensitivity analyses, a reliable simulation is required, which should be based upon systematic planned experiments.
Our research focuses on the esterfication and the hydrolysis reaction which are catalyzed by acidic ion exchange resins like Amberlyst 15. Beside reliable information about the VLE of the system a detailed knowledge of the reaction kinetics is required. The reaction kinetic measurement were performed in different type of reactors like stirred tank and trickle-bed reactor. This allows to determine the reaction rate for a wide range of initial compositions and under similar conditions as in the reactive distillation column. The kinetic data are used to evaluate parameters of several kinetic equations and to further improve existing kinetic equations.
Figure 2. Eastman Process of Methyl Acetate Synthesis
In order to guarantee the reliability of the simulation results, numerous experiments over a wide range of operation conditions with a pilot plant reactive distillation column (diameter 50 mm, height app. 10 m) have been performed. The reactive section contains Sulzer-Katapak-S elements filled with Amberlyst 15 whereas the non-reactive section consists of Sulzer-BX packings.
Measurements are conducted with different column setups and different operation conditions. Simulation studies are performed with commercial process simulators (e.g. Aspen Plus, Pro/II). Comparison of the calculated values using an equilibrium stage model with user defined kinetics with the experimental data shows good agreement.
Figure 3 Examples of experimental data compared with simulation results for Methyl Acetate Synthesis in a 1-Feed and 2-Feed Column
One aim is to optimize existing reactive distillation processes like the methyl acetate synthesis and hydrolysis process regarding scale-up and parametric sensitivity. Another goal is to evaluate the possibilities of reactive distillation as a process alternative for other reaction types by experiments and simulation studies.