Extraction of Technetium-99 m Using a Two-Phase Flow in a Microchannel

This thesis describes the research done on a microfluidic extractor used for the extraction of technetium99m. The extractor is based on a two-phase parallel flow with a stable liquid-liquid interface. Within this system a molybdenum solution containing the technetium compound pertechnetate (TcO4 ) is used as one of the phases. The technetium compound is extracted to 2-butanone in the other phase. To establish a successful and efficient extraction, multiple features have to be taken into account. First of all, the geometrical properties of the extractor influence the stability of the interface and the extraction efficiency. Stability of the interface means that the interface is located in the middle of the channel and is not disrupted. The efficiency of the extractor is taken as the the amount of pertechentate that is extracted from the molybdenum solution compared to the amount of pertechentate left in the molybdenum solution. Furthermore, the chemical properties of the substances present in the system, such as the viscosity of the solutions, the interfacial tension, the diffusion coefficients and the distribution coefficient, have an effect on the operation and efficiency of the extractor. It is a challenge to find the right combination of all these parameters resulting in an efficient extraction of the desired chemical entity. The goal of this research is to obtain an accurate simulation model for the extraction process of technetium-99m and find the optimized parameters for the geometrical design of the microfluidic platform to establish the highest possible extraction efficiency. For this reason, a numerical model for the diffusion process is created. Beside this, the forces acting on the flow in the channel are studied. The force balance determines the stability of the interface. The force balance exists of the hydrodynamic pressure difference and the Laplace pressure. The hydrodynamic pressure difference accounts for the viscosity and flow rates of the fluids. The Laplace pressure is initiated by the surface tensions of the phases. From the force balance an expression for the maximum extraction length (Lext ) for the channel is derived. An analytically obtained result for an optimized extraction length has been reported by Goyal and Desai in 2013 [1]. Their expression was adjusted to account for a two-phase flow instead of a one-phase flow. Furthermore, a miscalculation was detected in their derivation. A new expression for the maximized extraction length is used for further calculations. For all analysis, calculations were performed for a channel width ranging from 10-100μm, a channel height ranging from 10-100μm and flow rates ranging from 10-100μL/min. From the calculations on the force balance it could be concluded that a larger channel width and height results in a longer maximal extraction length. Furthermore, the extraction length is longer for lower flow rates. The diffusion model was used for the optimization process. First, the optimal extraction lengths were calculated for the widths, heights and flow rates whitin the given ranges. Next, the contact time was derived from the optimal extraction length and flow rate. The contact time and width were used to calculate the amount of diffused pertechentate through the interface. Finally, the extraction efficiency is calculated. The optimization is conducted for four test cases, namely: 1. To obtain the highest extraction efficiency possible, what are the corresponding geometrical parameters and flow rate? 2. If the extraction length is limited by the chips dimensions, take Lext < 0.01m. What is the maximum extraction efficiency that can be reached? 3. What is the extraction efficiency under the conditions Lext < 0.01m and the lower limit of the flow rate range is increased to 20μL/min? 4. What efficiency can be reached when our system is limited to a channel height of 50μm. For this test case the conditions proposed before still apply. The first test case resulted in an extraction efficiency of 99% and an extraction length of 12.0 cm. For the second test case an extraction efficiency of 64% and extraction length of 8.09 mm was obtained. The third test case resulted in an extraction efficiency of 44% and an extraction length of 9.41 mm. Finally, the fourth test case resulted in an extraction efficiency of 27% and an extraction length of 8.68 mm.