(399a) Process Intensification by Membrane-Assisted Reactive Separation Processes: A Design Tool Based On Process Analysis and Optimization

Process Intensification by Membrane-Assisted Reactive
Separation Processes: A Design Tool based on Process Analysis and Optimization

Johannes Holtbruegge^a), Deenesh K. Babi^b), Philip Lutze^a), Rafiqul Gani^b),
Andrzej Górak^a)

a) TU Dortmund University, Laboratory of Fluid
Separations

Emil-Figge-Strasse
70, D-44227 Dortmund, Germany

Phone: +40 (0) 231 755-2342, E-Mail: johannes.holtbruegge@bci.tu-dortmund.de

b) Technical University of Denmark, Computer Aided
Process Engineering Center

Soltofts
Plads 229, DK-2800 Kongens Lyngby, Denmark

Due to decreasing fossil fuel reserves, sustainability is an important
factor in the chemical industry that has to be considered when new processes
are developed. One opportunity to reach higher efficiencies in the production
of bulk chemicals is the use of intensified processes. Two promising examples
from the field of process intensification are (1) reactive distillation (RD)
combining reaction and distillation within one apparatus and (2) hybrid
separation processes, for instance the external integration of distillation
with membrane separation. In both cases, synergetic effects lead to an
increased sustainability in means of economics and ecologics. The use of a
multifunctional reactor such as reactive distillation within a hybrid separation
process promises even higher benefits. Despite all advantages, the potential of
those and other intensified processes is hardly exploited in industry. The main
reasons are a lack of process know-how and missing process synthesis tools.

Here, a combined methodology for process intensification is proposed
consisting of four integrated blocks which are starting with the general design
problem as input followed by ?system identification & analysis?, a
?synthesis/design? and finally a ?model-based validation/verification? to
identify a near optimal intensified process¹⁾. Whenever and wherever
necessary, knowledge from experiments are generated and transferred by the
block ?experimental validation/verification?.

In the ?system identification & analysis?, the process under
investigation is analysed to identify limitations and/or identify critical
phenomena which need to be intensified for the targeted performance
improvement. Based on these results, criteria are used to identify which workflow(s)
is/are followed for ?synthesis/design? of the intensified process. The
synthesis/design workflows are a knowledge based approach (KBS), a
unit-operation based workflow (UBS) and/or phenomena based approach (PBS).
While the complexity and the time spent to obtain a solution arises from KBS to
PBS, also the novelty and potentially the achieved process improvement
increases. The results of the ?synthesis/design? which are a small number of
potentially promising (intensified) process options are verified in the ?model-based
validation/verification? to identify the best process option.

Figure 1: Simplified flowsheet of
the developed membrane-assisted reactive separation process

In this contribution, the whole combined methodology will be presented
and highlighted through the application to a case study which is the chemical
equilibrium-limited transesterification of propylene carbonate with two
molecules of methanol to produce the target product dimethyl carbonate and the
byproduct 1,2-propanediol. The objective is to minimize the production costs
per ton of dimethyl carbonate. Two synthesis/design workflows will be highlighted
which are KBS and UBS. It will be shown that the use of the UBS workflow lead
to the development of a membrane-assisted reactive separation processes that
consists of an RD column, a vapor permeation membrane and a conventional
distillation column (see Figure 1). Finally, in the ?model-based validation/verification?
an evolutionary algorithm based on the ?modified differential evolution? approach
is used to solve the reduced optimization problem of the remaining process
options from the UBS and KBS workflow by determining apparatus dimensions and
operating conditions for the minimal objective function. The results for the
membrane-assisted reactive separation process compared to the base-case process
obtained from KBS for the production of dimethyl carbonate comprises high savings
in capital and energy use leading to lower production costs.

References:

¹⁾:
Lutze, P. et al.: Phenomena-based Process Synthesis and Design to achieve
Process Intensification; Proc. 21^st European Symposium on Computer
Aided Process Engineering ? ESCAPE 21, 2011, Greece

Acknowledgements:

The financial support of the German Federal Ministry
of Education and Research for the project ?Energy Efficiency Management and
Benchmarking in the Process Industry? is gratefully acknowledged.