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.