263705 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: email@example.com)
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.
Figure 1: Comparison of conventional and intensified process for the production of n-butyl acrylate.
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.
Figure 2: Experimental (symbols) and simulation (lines) results of a column profile used for the model validation.
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
1. Klöker, M., E.Y. Kenig, A. Hoffmann, P. Kreis and A. Górak, Chemical Engineering and Processing, 44, 617-629 (2005).