Vv
V. van Steijn
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166Ho is a promising radionuclide for targeted radionuclide therapy, because of its beneficial decay characteristics and the possibility to track its dose delivery in a patient. However, a problem for the use of 166Ho in these treatments is its limited maximally produced specific activity in neutron irradiation of a pure 165Ho target, since the produced 166Ho is chemically inseparable from the 165Ho target. The Szilard-Chalmers method is known to be able to increase the achieved specific activity. It does so by irradiating the target isotope while it is incorporated in a compound. As the target isotope undergoes (n, γ) neutron capture it forms the product isotope and escapes the compound due to recoil from prompt gamma emissions. Then by separating the product isotopes from the compound, which still contains the target isotopes, a high specific activity can be achieved. However, batch irradiations using the Szilard-Chalmers method for production of high specific activity gives low production yields. In order to increase these production yields, a continuous flow Szilard-Chalmers system is proposed. The objective of this research is to investigate the main processes at play in a continuous flow system using the Szilard-Chalmers method on 165HoDOTAfor the production of high specific activity 166Ho. Investigations on the labelling of Ho3+ to DOTA4- have shown that 96±3 % labelling efficiency is achievable. Experiments on relabelling and isotope-exchange have shown that less than 8 % of 166Ho3+ undergoes relabelling with DOTA4- or isotope-exchange with 165HoDOTA-. Also, a cation exchange separation method for separation of Ho3+ from DOTA4- and HoDOTA- was developed. Moreover, investigations on Szilard-Chalmers separation of a dried 165HoDOTAsample have shown that with a 4-minute irradiation it was possible to achieve a specific activity of 2.8±0.2 MBq mg-1 . This corresponds to an enrichment factor of 1.62±0.03 compared to an irradiation without Szilard-Chalmers separation. Decreased radiolysis by shielding and slowed neutrons, and increased initial labelling are expected to be able to increase the achieved enrichment factor even more. The continuous flow Szilard-Chalmers system could in potential prove very useful in high specific activity radionuclide production, but further improvements on its subprocesses are necessary before practical implication is worthwhile.
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166Ho is a promising radionuclide for targeted radionuclide therapy, because of its beneficial decay characteristics and the possibility to track its dose delivery in a patient. However, a problem for the use of 166Ho in these treatments is its limited maximally produced specific activity in neutron irradiation of a pure 165Ho target, since the produced 166Ho is chemically inseparable from the 165Ho target. The Szilard-Chalmers method is known to be able to increase the achieved specific activity. It does so by irradiating the target isotope while it is incorporated in a compound. As the target isotope undergoes (n, γ) neutron capture it forms the product isotope and escapes the compound due to recoil from prompt gamma emissions. Then by separating the product isotopes from the compound, which still contains the target isotopes, a high specific activity can be achieved. However, batch irradiations using the Szilard-Chalmers method for production of high specific activity gives low production yields. In order to increase these production yields, a continuous flow Szilard-Chalmers system is proposed. The objective of this research is to investigate the main processes at play in a continuous flow system using the Szilard-Chalmers method on 165HoDOTAfor the production of high specific activity 166Ho. Investigations on the labelling of Ho3+ to DOTA4- have shown that 96±3 % labelling efficiency is achievable. Experiments on relabelling and isotope-exchange have shown that less than 8 % of 166Ho3+ undergoes relabelling with DOTA4- or isotope-exchange with 165HoDOTA-. Also, a cation exchange separation method for separation of Ho3+ from DOTA4- and HoDOTA- was developed. Moreover, investigations on Szilard-Chalmers separation of a dried 165HoDOTAsample have shown that with a 4-minute irradiation it was possible to achieve a specific activity of 2.8±0.2 MBq mg-1 . This corresponds to an enrichment factor of 1.62±0.03 compared to an irradiation without Szilard-Chalmers separation. Decreased radiolysis by shielding and slowed neutrons, and increased initial labelling are expected to be able to increase the achieved enrichment factor even more. The continuous flow Szilard-Chalmers system could in potential prove very useful in high specific activity radionuclide production, but further improvements on its subprocesses are necessary before practical implication is worthwhile.
Electrochemical reduction of CO2 using renewable energy sources is one of the promising avenues to pursue towards mitigating the emissions of the notorious CO2. However, the CO2 electrolysis in aqueous systems, due to the low solubility of CO2, are severely limited by mass transfer. State of the art review shows that a significant amount of the research is done to improve mass transfer, where a variety of electrolyser designs were studied. Despite the effort, the challenge to enhance mass transfer remains and is the focus of the present work. To improve mass transfer, an innovative concept is proposed - Taylor flow in an electrochemical flow cell. Taylor flow has been extensively studied in the literature, especially in micro channels and monolith reactors. Therefore the characteristics of the Taylor flow are known to a certain extent. But they were never tested in an electrochemical system. For that reason, a numerical investigation is carried out to assess the performance of Taylor flow on the flow cell. A simplified 2D model was formulated using a unit cell strategy and is verified based on experimental data and theoretical concepts. The effect of dissolving bubbles is also modelled using a quasi-steady-state analysis The results of the 2D model show a significant improvement in the performance, i.e. in the current densities of the electrochemical cell compared to a typical flow cell. The maximum calculated current densities increase by an order of magnitude under certain flow conditions. The dissolution studies showed that the current densities deteriorate with time. Nevertheless, the overall performance is still higher than the typical flow cell. Finally, based on the insights from the 2D model, a 1D model is suggested to estimate the current densities and dissolution rates. The present study showed promising results for using Taylor flow in an electrochemical cell. The proposed 2D model can help in aiding future modelling studies while the 1D model can give simple estimates for the experimental work.
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Electrochemical reduction of CO2 using renewable energy sources is one of the promising avenues to pursue towards mitigating the emissions of the notorious CO2. However, the CO2 electrolysis in aqueous systems, due to the low solubility of CO2, are severely limited by mass transfer. State of the art review shows that a significant amount of the research is done to improve mass transfer, where a variety of electrolyser designs were studied. Despite the effort, the challenge to enhance mass transfer remains and is the focus of the present work. To improve mass transfer, an innovative concept is proposed - Taylor flow in an electrochemical flow cell. Taylor flow has been extensively studied in the literature, especially in micro channels and monolith reactors. Therefore the characteristics of the Taylor flow are known to a certain extent. But they were never tested in an electrochemical system. For that reason, a numerical investigation is carried out to assess the performance of Taylor flow on the flow cell. A simplified 2D model was formulated using a unit cell strategy and is verified based on experimental data and theoretical concepts. The effect of dissolving bubbles is also modelled using a quasi-steady-state analysis The results of the 2D model show a significant improvement in the performance, i.e. in the current densities of the electrochemical cell compared to a typical flow cell. The maximum calculated current densities increase by an order of magnitude under certain flow conditions. The dissolution studies showed that the current densities deteriorate with time. Nevertheless, the overall performance is still higher than the typical flow cell. Finally, based on the insights from the 2D model, a 1D model is suggested to estimate the current densities and dissolution rates. The present study showed promising results for using Taylor flow in an electrochemical cell. The proposed 2D model can help in aiding future modelling studies while the 1D model can give simple estimates for the experimental work.