Conclusion
In this paper, an integrated photo micro-flow adsorption was developed
for product separation, with the option to do that in recycle mode. This
was investigated to produce trans -cyclooctene from itscis -isomer. Here, the thermodynamic equilibrium is shifted by
inserting an in-flow separation in a recycling flow mode, which makes
better use of the given photoenergy (transport intensification).
Further, a full theoretical study of in-flow separation in a recycling
flow mode has been conducted. Moreover, different process design options
to reach an optimum yield of trans -cyclooctene are proposed and
experimentally tested. Radiolabeled trans- cyclooctenes are
valuable in vivo click synthons for PET imaging.
First, the kinetics of the photoisomerisation of cis - totrans -cyclooctene was investigated in a microreactor. Results
confirm that the conversion is limited by equilibrium to nearly 28%.
The comparison of the reaction rate constants, k1 and
k-1, shows that the reaction rate from trans - tocis - is higher than cis - to trans -cyclooctene.
Moreover, an in-depth study of the TCO adsorption on
AgNO3/SiO2 was done. The results
indicate that the adsorption of TCO on AgNO3 follows the
Langmuir isotherm model. The reaction rate is governed by the
equilibrium surface reaction. The analysis of the adsorption kinetic
data demonstrated that the kinetics can be approximated with a
pseudo-second order rate equation. The maximum adsorption capacity of
the trans -isomer adsorbed per gram AgNO3 is equal
to 44.25 mgtrans/gsilvernitrate .
The dynamic behavior of the adsorption column was experimentally studied
and modeled according to the local equilibrium theory. The results of
the model calculations show good agreement with the experimental data.
Based on the model, it is possible to predict the breakthrough curve and
saturation time of the mentioned adsorption column.
Finally, after optimization of each sub process, i.e photoisomerisation
and adsorption, three different integrated process designs for
photoisomerisation of the cis to trans -isomer was
mathematically modeled. According to the calculated model, it is
important to remark that by increasing the flow rate a higher conversion
of cis -isomer was achieved. By increasing the total flow rate,
the time that the flow is passing through connecting parts is reduced
and also, speeding up the feed recycling gives an advantage.
Furthermore, the three different process configurations were tested
experimentally. Comparing three cases, case (c) (Figure 6), shows
improvement of the total conversion of the cis -isomer. 90%
conversion was achieved after 250 min. In case (c) two parallel
photo-microreactors and parallel packed beds in switching mode were
applied. Switching the packed bed as soon as it reaches saturation
results in obtaining higher conversion in less time. Numbering up the
sub processes gives a good promise for scaling up this integrated
process.
It is worth mentioning that in this closed-loop system, solvent can be
added only once at the beginning. In this system solvent is only carrier
medium and is not consumed or converted, thus by recycling, solvent is
also recovered and transferred back to the system. As soon as the amount
of cis -isomer reaches to 0.05 of initial concentration, fixed
amount of cis -isomer can be added to the initial feed vessel
which already contains enough solvent. Therefore, with this closed-loop
design, it is possible to reduce the amount of solvent usage to only
once.