(372d) Experimental Investigation and Model Validation of a Heterogeneously Catalyzed Reactive Distillation Process to Intensify the Synthesis of n-Butyl Acrylate From Acrylic Acid and n-Butanol

Experimental investigation and model validation of a
heterogeneously catalyzed reactive distillation process to intensify the
synthesis of n-butyl acrylate from acrylic acid and n-butanol

Alexander Niesbach^*, Ron Fuhrmeister, Jan Daniels, Benjamin
Schröter, 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. One of
those is reactive distillation (RD) which exploits the synergy of the combining
reaction and separation at the same place and time. This combination allows to overcome limitations occurring for the reaction and
separation alone such as azeotropes or chemical equilibria. Hence, RD may lead to increased process yields.
The concept of RD has been widely studied for low carbon numbers esterifications.

In this work, the heterogeneously catalyzed
synthesis of n-butyl acrylate (BA) from acrylic acid (AA) and n-butanol (BuOH) in a reactive
distillation column is investigated experimentally and theoretically. The
reaction is catalysed by a strong-acid ion exchange resin. Due to the
limitation of the esterification by the chemical equilibrium, process
intensification using an RD column may increase the yield and lead to a reduced
side-product formation compared to the base case design, see Fig.1.

Additionally, through the use of RD as an integrated process for this
reaction system, the number of apparatuses can be reduced significantly
compared to the conventional process.

Hence, savings in operational and investment costs are expected. Further
savings can be achieved by replacing the conventional homogeneous catalyst by a
heterogeneous catalyst as the separation and recycle of the homogeneous
catalyst is not necessary and the effort for waste water treatment is
reduced significantly.

The main barrier for the application of an RD column is the
polymerisation tendency of both acrylic acid and n-butyl acrylate which
increases rapidly with increasing temperature. To prevent those components from
polymerising, inhibitors need to be added to the process. To ensure a safe
operation of a pilot-scale reactive distillation column during the experimental
investigation, a detailed study was performed during this work to determine the
influence of temperature, inhibitor concentration and the atmosphere on the
resulting inhibition period in lab-scale batch experiments. Based on these
experiments, a concept for adding polymerisation inhibitors to the column was
developed and implemented. Prior to the experimental investigation, the
inhibitor dilution was studied and a concept for the startup
and the shutdown of the column was developed.

Afterwards, pilot plant experiments were conducted in a glass column
with an inner diameter of 50 mm and an effective packing height of 5.7 m. For
this purpose a fractional factorial design of experiments has been developed
and a set of experiments was performed to validate the model in a wide range of
the main operational parameters. Temperature and concentration profiles were
measured along the pilot scale RD column. An online data-reconciliation was
used to monitor the steady-state condition.

The experimental results were compared to a nonequilibrium-stage
model implemented in the simulation environment Aspen Custom Modeler^® (Klöker et
al, 2005). This model considers multicomponent mass and heat transfer rates and
hydrodynamics. Thermodynamic and physical properties are taken into account by
a link to the software Aspen Properties^®. Liquid phase activity coefficients
were calculated using the UNIQUAC model. The Hayden O'Connell equation of state
was used to account for non-idealities in the vapour
phase. A comparison of experimental and simulation results is shown in Figure
2.

This comparison was done for all experimental results to validate the
model in a wide range of the operational parameters. The validated model will
be used for further optimization studies to investigate the optimal process for
the synthesis of n-butyl acrylate from acrylic acid and n-butanol using reactive distillation. 

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