264287 Process Analysis and Generic Optimization of the Synthesis of n-Butyl Acrylate in an Industrial Scale Reactive Distillation Column

Wednesday, October 31, 2012: 2:35 PM
323 (Convention Center )
Alexander Niesbach1, Hanns Kuhlmann1, Philip Lutze2 and Andrzej Górak1, (1)TU Dortmund University, Department of Biochemical and Chemical Engineering, Laboratory of Fluid Separations, D-44227 Dortmund, Germany, (2)Department of Biochemical and Chemical Engineering, Laboratory of Fluid Separations, TU Dortmund University, Dortmund, Germany

Process analysis and generic optimization of the synthesis of n-butyl acrylate in an industrial scale reactive distillation column

 

Alexander Niesbach*, Hanns Kuhlmann, Philip Lutze, Andrzej Górak

  Laboratory of Fluid Separations, TU Dortmund University, Germany (*Corresponding Author's E-mail: alexander.niesbach@bci.tu-dortmund.de)

 

ABSTRACT

 

The development of innovative apparatuses and techniques has led to process intensification and achieving ecologic and economic improvements, such as decreasing energy consumption and increasing process efficiency.

Reactive distillation (RD) has already emerged as an excellent technology for process intensification exploiting the synergy effects of the combination of reaction and distillation phenomena at the same place and time. This combination allows overcoming limitations regarding thermodynamic and chemical equilibria which leads to an increased process yield. RD has been successfully studied mostly for esterifications with low carbon reactants.

Some of the reasons for this limited application to higher carbon numbers are the more complex chemistry as well as the risk for polymerization of some of the chemical compounds in the system. Besides, the identification of a near optimal set of operational as well as decisive variables for a complex RD system is difficult.

Therefore, within this project, the results of the experimental as well as model-based development of an RD process for a high carbon number esterification which is the heterogeneously catalyzed synthesis of n-butyl acrylate (BA) from acrylic acid (AA) and n-butanol (BuOH) is presented. The near optimal design is identified by a three step approach: 1) An indicator based feasibility analysis for identification if RD may be promising; 2) Experiments for rigorous rate-based model validation; 3) Optimization for identification of the near-optimal design. Furthermore, in step three, different solvers such as commercial solvers from ASPEN as well as an evolutionary algorithm have been checked for best performance.

For the design of the RD column, a theoretical and experimental feasibility analysis based on the properties of the system was done. At first the technical feasibility of the application of an RD column for the synthesis of n-butyl acrylate was proven by a theoretical study at the institute that was presented before (Keller et al, 2010).

In the second step, an experimental study was performed and the experimental results were used to validate a rate-based reactive distillation model implemented in the simulation environment Aspen Custom Modeler™, which was developed in a previous work (Klöker et al., 2005) and adapted to the present system.

Within this presentation, the third step will be presented, where the complex mixed-integer non-linear design problem needs to be solved. For this system, it turned out that an evolutionary algorithm showed best performance. Hence, the validated rate-based RD model was used and implemented into an evolutionary optimisation method to design an optimal RD column for the production of n-butyl acrylate. The production costs for n-butyl acrylate are used as objective function. For the column design several structural parameters (e.g. number of stages, feed position) as well as operational parameters (e.g. reflux ratio, distillate-to-feed ratio) have to be considered. Optimised variables have been found minimising the production cost of n-butyl acrylate for a chosen annual production of 20.000 t n-butyl acrylate in consideration of the required product purity. Several boundary conditions, like product purity and maximum temperature in the catalytic section, were taken into account. Hereby, a process design based on a heterogeneously catalysed reactive distillation has been developed and the overall production cost of n-butyl acrylate is reduced compared to the conventional process (Figure 1).

Figure 1: Comparison of conventional and intensified process for the production of n-butyl acrylate.

  Acknowledgement: The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 228867, F3-Factory

 

References

  1.      Keller, T., T. Tretjak, S. Lacroix, A. Hoffmann and A. Górak,  Presentation at CHISA 2010., (2010), Prag, Czech Republic.

2.      Klöker, M., E.Y. Kenig, A. Hoffmann, P. Kreis and A. Górak, Chemical Engineering and Processing, 44, 617-629 (2005).


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