(516f) Process Analysis and Generic Optimization of the Synthesis of n-Butyl Acrylate in an Industrial Scale Reactive Distillation Column

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).

 

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).