(507a) Optimal Reactor Design for the Hydroformylation of Long Chain Olefins in Thermomorphic Solvent Systems

Optimal
Reactor Design for the Hydroformylation of Long Chain Olefins in
Thermomorphic Solvent Systems

Benjamin
Hentschel¹, Andreas Peschel², Hannsjörg
Freund³, Kai Sundmacher^1,2

¹Process
Systems Engineering, University of Magdeburg, Magdeburg/DE

²Max
Planck Institute for Dynamics of Complex Technical Systems,
Magdeburg/DE

³Chemical
Reaction Engineering, University of Erlangen-Nürnberg,
Erlangen/DE

The
use of thermomorphic solvent
(TMS) systems is a promising approach that is currently investigated
regarding its applicability for the rhodium catalyzed
hydroformylation of long chain olefins. By taking advantage of a
temperature dependant miscibility gap, homogeneous reaction and
efficient liquid-liquid phase (and thus catalyst) separation can be
performed with a single solvent system by using the temperature as
“switch” to tune the phase behavior.

On
the example of the hydroformylation of 1-dodecene in a TMS it is
demonstrated how the optimal reactor for such innovative systems can
be derived. The demanding interplay of the thermodynamics of the TMS,
complex reaction network, and solvent recycles requires a model based
reactor design approach which considers the dynamics of the whole
process rather than an isolated reactor design. For this purpose a
reference process flow sheet (Fig. 1) was developed in order to allow
for the derivation of a process-wide optimal reactor.

Fig. 1: Flow sheet of the
hydroformylation process.

Due
to
the numerous process constraints and the complexity of the reaction
system a heuristic reactor design approach is unlikely to be able to
yield the optimal reactor. Hence, to account for the full potential
of this innovative reaction and solvent system a reactor design based
on the optimal reaction route is pursued. Considering a fluid element
of the system which is traveling through the reactor, optimal
profiles of energy and material fluxes over reaction time can be
calculated as solution of an optimal control problem. This problem is
constrained by the dynamic equations of the fluid element,
constitutive equations describing phase properties, reaction
kinetics, gas solubilities, and the balance equations of the
remaining process units. For each unit appropriate cost models are
implemented enabling the minimization of the total production costs
of the desired linear aldehyde product.

As
a result of this optimization it
could be shown that the solvent recycle leads to an increase in the
selectivity that can be achieved in the reactor. Thus, a separate
optimization of the reactor without considering the recycles would
lead to a falsified lower reactor performance prediction.
Furthermore, the cost optimal solution, considering all recycles,
turns out to be a combination of necessary separation efficiency and
optimal reaction route. Assuming an annual production of 10.000 tons
of product, the advanced reaction route leads to a reduction of the
total production costs of 5% compared to an optimized reference case.
This corresponds to an annual saving of about 2.2 Mio. US$.

In
summary it could be demonstrated that reactor
and process have to be optimized as an integrated system in order to
find the process-wide optimal solution, rather than focusing on local
objectives of the reactor, such as product selectivity. Exemplified
on the hydroformylation of long chain olefins in TMS it could be
shown that the presented reactor design method can yield a
process-wide optimal reactor design based on the cost optimal
solution, in which optimal reactant dosing and heat removal is
realized along the reactor.