In Belgium, the Boom Clay is currently studied as the reference host formation for the disposal of high-level and long-lived radioactive waste. In case of direct disposal of spent fuel, uranium isotopes are important contributors along with their daughters to the dose rate at very long term. Therefore, it is essential to study the migration of uranium in the host formation. The present work contributes to improve the knowledge of uranium speciation in the Boom Clay, U(IV) versus U(VI), and of the mechanisms controlling the uranium mobility such as solubility, sorption and complexation by organic matter. The information necessary to interpret the migration behaviour is derived from the study of naturally occurring uranium in the rock and from laboratory experiments conducted under conditions representative for the Boom Clay. Uranium naturally present in the Boom Clay is concentrated in detrital heavy minerals and in authigenic iron(II)-bearing minerals such as siderite and glauconite. Despite its reducing capacity, pyrite is surprisingly depleted in uranium relative to the mean content. Furthermore, uranium is also associated with the surfaces of clay minerals. The clayey fraction contains about 4 ppm uranium and is the main contributor to the total uranium content of the Boom Clay since it constitutes up to 60 wt. % of the rock. The correlation observed on the field between uranium and organic matter suggests that uranium is reduced, likely during the early diagenesis process of bacterially-mediated sulphate reduction. If hexavalent oxidation state of uranium predominates as predicted by geochemical calculations based on the most recent thermodynamic data of the Nuclear Energy Agency (NEA), less than 5% of uranium is complexed by humic acids in the Boom Clay pore water. The U(VI) speciation is dominated by the inorganic carbonate complexes, merely UO2(CO3)34-. The conditional constant determined for the complexation of U(VI) by humic acids under in situ Boom Clay conditions is log exp = 12.4. However, experimental studies show that UO2(CO3)34- is reduced by interaction with pyrite, the main reducing mineral present in the rock, and precipitates as a mixed oxide of U(IV)/U(VI), i.e. UO2+x. Moreover, electromigration experiments suggest that U(VI) is not stable in the Boom Clay: U(VI) is reduced and precipitates as U(IV) oxy-hydroxides. The experimentally measured solubility of U(IV) amorphous oxide, UO2(am), in Boom Clay pore water is about 10 8 mol•l 1. This solubility value is not increased by complexation of U(IV) with dissolved organic matter. The dominant effect of organic matter on the dissolution of UO2(am) is the stabilisation of U(IV) real colloids which increase the uranium concentration by three orders of magnitude. However, the mobility of these colloids is expected to be very limited because of the compaction level of the Boom Clay and its ultra-filtrating feature. The diffusive transport of dissolved uranium is furthermore retarded by significant sorption onto clay minerals. In conclusion, the presence of organic matter in the Boom Clay has no negative effect on the uranium retention which is dominated by the solubility and sorption of U(IV) species

In recent years, the use of self-associating block copolymer based drug delivery systems have attracted increasing attention as nanoscopic carriers for the encapsulation and the controlled delivery of water insoluble drugs. Currently, most of the drug formulations proceed by trial and error method with no distinct method to predict the right combination of block copolymers and drugs to give all the desired functional properties. This is simply because such drug delivery systems involve complex intermolecular interactions and geometric fitting of molecules of different shapes. So, in the context of block copolymer design process, quantification and prediction of the interactions between potential block copolymers and the target drug are of great importance. Computer simulations that can predict the level and type of interactions encountered in drug/block copolymer pairs will enable researchers to make educated decisions on choosing a particular polymeric carrier for a given drug, avoiding time consuming and expensive trial and error based formulation experiments. In the present thesis, we reported the use of molecular dynamics (MD) simulation to predict the solubility of sets of hydrophobic drug molecules having different spatial distribution of hydrogen bond forming moieties in a series of micelle-forming PEO-b-PCL block copolymers with and without functionalized PCL blocks. The solubility predictions based on the MD results were then compared with those obtained from the solubility experiments and those obtained by the commonly used group contribution method (GCM). MD analysis techniques like radial distribution functions provided useful atomistic details to understand the molecular origin of miscibility and/or immiscibility observed between drugs and di-block copolymers. Based on the evidence of reported work, intermolecular specific interactions, intra-molecular interactions, local molecular packing, and stereochemistry of the hydrophobic block all play important roles in inducing miscibility between drugs and block copolymers. Additionally, not only the architecture of block copolymers but also the molecular characteristics of drug molecules, e.g., spatial distributions of hydrogen bond donors and acceptors on their molecules can affect the miscibility characteristics of binary mixtures. Depending on the groups present on drugs and block copolymers, any of the above factors can play vital role in the process of favouring encapsulation. The understanding of relative contributions of these interactions can help us to customize the performance of drug carriers by engineering the structure of block copolymers. / Chemical Engineering

The viscous oil-water hydrodynamics in a microchannel and phase equilibria of heavy oil and carbon dioxide gas have been investigated in connection with the enhanced recovery of heavy oil from petroleum reservoirs. The oil-water flow was studied in a circular microchannel made of fused silica with an I.D. of 250 µm. The viscosity of the silicone oil (863 mPa.sec) was close to that of the gas-saturated heavy oil in reservoirs. The channel was always initially filled with the oil. Two different sets of experiments were conducted: continuous oil-water flow and immiscible displacement of oil by water. For the case of continuous water and oil injection, different types of liquid-liquid flow patterns were identified and a flow pattern map was developed based on Reynolds, Capillary and Weber numbers. Also, a simple correlation for pressure drop of the two phase system was developed. In the immiscible displacement experiments, the water initially formed a core-annular flow pattern, i.e. a water core surrounded by a viscous oil film. The initially symmetric flow became asymmetric with time as the water core shifted off centre and also the waves at the oil-water interface became asymmetric. A linear stability analysis for core-annular flow was also performed. A characteristic equation which predicts the growth rate of perturbations as a function of the core radius, Reynolds number, and viscosity and density ratios of the two phases was developed. Also, two micro cells for gas solubility measurements in oils were designed and constructed. The blind cell had an internal volume of less than 2 ml and the micro glass cell had a volume less than 100 µl. By minimizing the cell volume, measurements could be made more quickly. The CO2 solubility was determined in bitumen and ashphaltene-free bitumen samples to show that ashphaltene has a negligible effect on CO2 solubility.

The viscous oil-water hydrodynamics in a microchannel and phase equilibria of heavy oil and carbon dioxide gas have been investigated in connection with the enhanced recovery of heavy oil from petroleum reservoirs. The oil-water flow was studied in a circular microchannel made of fused silica with an I.D. of 250 µm. The viscosity of the silicone oil (863 mPa.sec) was close to that of the gas-saturated heavy oil in reservoirs. The channel was always initially filled with the oil. Two different sets of experiments were conducted: continuous oil-water flow and immiscible displacement of oil by water. For the case of continuous water and oil injection, different types of liquid-liquid flow patterns were identified and a flow pattern map was developed based on Reynolds, Capillary and Weber numbers. Also, a simple correlation for pressure drop of the two phase system was developed. In the immiscible displacement experiments, the water initially formed a core-annular flow pattern, i.e. a water core surrounded by a viscous oil film. The initially symmetric flow became asymmetric with time as the water core shifted off centre and also the waves at the oil-water interface became asymmetric. A linear stability analysis for core-annular flow was also performed. A characteristic equation which predicts the growth rate of perturbations as a function of the core radius, Reynolds number, and viscosity and density ratios of the two phases was developed. Also, two micro cells for gas solubility measurements in oils were designed and constructed. The blind cell had an internal volume of less than 2 ml and the micro glass cell had a volume less than 100 µl. By minimizing the cell volume, measurements could be made more quickly. The CO2 solubility was determined in bitumen and ashphaltene-free bitumen samples to show that ashphaltene has a negligible effect on CO2 solubility.

The effect of fluorine on the solubilities of Mn-columbite (MnNb2O6), Mn-tantalite (MnTa2O6), zircon (ZrSiO4) and hafnon (HfSiO4) were determined in highly fluxed, water-saturated haplogranitic melts at 800 to 1000 °C and 2000 bars. The melt corresponds to the intersection of the granite minimum with the albite-orthoclase tieline (Ab72Or28) in the quartz-albite-orthoclase system (Q-Ab-Or) due to the addition of P2O5 to the melt. The melt content of P2O5 is 1.7 wt. %, and also contains 1.1 and 2.02 wt. % of Li2O and B2O3, respectively. The composition of the starting glass represents the composition of melts from which rare-elements pegmatites crystallized. Up to 6 wt. % fluorine was added as AgF in order to keep the aluminum saturation index (ASI) of the melt constant. In an additional experiment F was added as AlF3 to make the glass peraluminous. The nominal ASI (molar Al/[Na+K]) of the melts is close to 1 and approximately 1.32 in peraluminous glasses, but if Li considered as an alkali, the ASI of the melts are alkaline (0.85) and subaluminous (1.04), respectively. The solubility products [MnO]*[Nb2O5] and [MnO]*[Ta2O5] are nearly independent of the F content of the melt, approximately 18.19 ± 1.2 and 43.65 ± 2.5 x10-4 KSP (mol2/kg2), respectively. By contrast, there is a positive dependence of zircon and hafnon solubilities on the fluorine content, which increases from 2.03 ± 0.03 x10-4 (mol/kg) ZrO2 and 4.04 ± 0.2 x10-4 (mol/kg) HfO2 for melts with 0 wt. % F to 3.81 ± 0.3 x10-4 (mol/kg) ZrO2 and 6.18 ± 0.04 x10-4 (mol/kg) HfO2 for melts with 8 wt. % F. Comparison of the data from this work and previous studies indicates that ASI of the melt seems to have a stronger effect than the contents of fluxing elements in the melt and the overall conclusion is that fluorine is less important (relative to melt compositions) than previously thought for the control on the behavior of high field strength elements in highly evolved granitic melts. Moreover, this study confirms that although Nb, Ta, Zr and Hf are all high field strength elements, Nb-Ta and Zr-Hf are complexed differently.

Solvent selection is an important factor in chemical process efficiency, profitability, and environmental impact. Prediction of solvent phase behavior will allow for the identification of novel solvent systems that could offer some economic or environmental advantage. A modified cohesive energy density model is used to predict the solid-liquid-equilibria for multifunctional solids in pure and mixed solvents for rapid identification of process solvents for design of crystallization processes. Some solubility data at several temperatures are also measured to further test the general applicability of the model. Gas-expanded liquids have potential environmentally advantageous applications as pressure tunable solvents for homogeneous and heterogeneous catalytic reactions and as novel solvent media for anti-solvent crystallizations. The phase behavior of some carbon dioxide/organic binary systems is measured to provide basic process design information. Solvent selection is also an important factor in the anti-solvent precipitation of solid compounds. The influence of organic solvent on the solid-liquid equilibria for two solid pharmaceutical compounds in several carbon dioxide expanded solvents is explored. A novel solvent system is also developed that allows for homogeneous catalytic reaction and subsequent catalyst sequestration by using carbon dioxide as a miscibility switch. The fundamental biphasic solution behavior of some polar organics with water and carbon dioxide are investigated.

The research addressed in this thesis is focused on the solubility and pseudo-polymorphic transition of L-serine in mixed water-methanol systems. Cooling re-crystallizations were carried out that varied both temperature and methanol concentration. Solubilities were measured with high-performance liquid chromatography. It is found that the solubility increased with increase in temperature and decreased drastically with methanol concentration. The effect of temperature at which there is a transition of L-serine crystals from the rod-shaped (anhydrous) form to hexagonal (monohydrate) form was confirmed and that transition temperatures decreased with methanol concentrations in a non-linear manner. The solubility data were correlated and plotted using the vant Hoff equation and the enthalpy and entropy of dissolution were determined. These values increased with increase in methanol concentration. The solid crystals were analyzed by optical microscopy and powder X-ray diffraction. The rod-shaped crystals were identified to be anhydrous L-serine, while the hexagonal crystals were L-serine monohydrate. Dehydration of the monohydrated crystals in their solid-state was examined and the onset of such phenomenon was known to start once the crystals were removed from the solutions.

Ph.D.

The physical stability of guaifenesin in melt-extruded acrylic matrix tablets was investigated. The initial study found that recrystallization was caused by guaifenesin supersaturation in Eudragit[Trademark] L100-55, and that the instability was confined to tablet surfaces. Drug release was not affected by crystal growth as guaifenesin is very water soluble. The addition of a polymer in which guaifenesin showed a higher solubility to the matrix blend decreased recrystallization on storage as supersaturation levels dropped. The second investigation identified heterogeneous nucleation as an additional factor in guaifenesin recrystallization. A quantitative assay showed that talc in matrix tablets accelerated the onset and extent of the recrystallization due to a nucleating effect on guaifenesin. Storage under elevated humidity conditions promoted recrystallization as well, but crystal growth was not correlated with water uptake, which implied a nucleating effect of moisture on guaifenesin. The third study investigated the effect of aqueous film-coating of the matrix tablets to stabilize amorphous guaifenesin using either hypromellose or ethylcellulose as coating polymers. The selection of the coating polymer influenced crystal morphology, and was a major factor in delaying the onset of crystallization, ranging from 1-3 weeks (ethylcellulose film-coatings) to 3-6 months (hypromellose film-coatings). Higher weight gains retarded recrystallization. Factors promoting drug and polymer diffusion, such as long curing times and elevated temperatures during both curing and storage, incomplete film coalescence and high core drug concentrations all resulted in an earlier onset of crystallization. The effects of single-screw extrusion (SSE) and twin-screw extrusion (TSE) of diltiazem hydrochloride and guaifenesin-containing blends in Eudragit[Trademark] L100-55 on drug morphology and dispersion were studied in the fourth project. Guaifenesin solubilized diltiazem hydrochloride, and plasticized Eudragit[Trademark] L100-55. Extrusion temperature influenced the drug morphology in single-screw extrudates, while TSE rendered all formulations amorphous due to higher dispersive mixing capabilities. Drug distribution improved with extrusion temperature and by TSE over SSE. Homogeneous matrices showed the slowest drug release at pH 1.0. Recrystallization was inversely correlated to drug distribution. In conclusion, the physical stability of guaifenesin in hot melt-extruded acrylic matrix tablets was shown to be affected by formulation, processing and post-processing factors. / text

The Electrolyte Nonrandom Two-Liquid Activity Coefficient model in Aspen PlusTM 2006.5 was used to develop a rigorous and consistent thermodynamic representation for the base sub-component systems associated with aqueous combinations of K₂CO₃, KHCO₃, MEA, and piperazine (PZ) in a mixed-solvent electrolyte system for the application of CO₂ absorption/stripping from coal fired power plants. We developed a new vapor-liquid equilibrium apparatus to measure CO₂, amine, and H2O vapor pressures at 40 and 60 oC. We found that the volatility of MEA and PZ can be approximated at 50 and 20 ppmv at 40°C for any solvent composition studied in this work, over the CO₂ partial pressure range from 0.01 to 0.1 kPa. Very few solvent compositions exhibited a greater differential capacity than 7 m MEA at 60°C; specifically 11 m MEA, 3.5 m MEA + 3.6 m PZ, 7 m MEA + 2 m PZ, 7 m MEA + 3.6 m PZ, and 5 m K+ + 7 m MEA + 3.6 m PZ. Piperazine exhibited a possible maximum differential capacity of 2.21 mole CO₂/kg-H₂O at a concentration of 7.3 m. At the Norwegian University of Science and Technology, Inna Kim determined the differential enthalpy of CO₂ absorption for aqueous combinations of K₂CO₃, KHCO₃, MEA, PZ, and CO₂, based on a consistent experimental method developed for MEA, from 40 to 120°C for use in this work. In addition, we developed a consistent method to measure the specific heat capacity for a number of similar solvent combinations. We found that the enthalpy of CO₂ absorption increased with temperature because the apparent partial heat capacity of CO₂ may be considered small. Finally, by using a differential scanning calorimeter, we determined the dissolution temperature for aqueous mixtures of unloaded piperazine, which inferred an effective operating range for solutions of concentrated piperazine, greater than 5 m PZ, over a loading range between 0.25 to 0.45 mole CO₂/2·mol PZ. Through unit cell x-ray diffraction, we were able to identify and characterize the presence of three solid phases (PZ·6H₂O, KHCO₃, and KvPZ(COO)₂) in aqueous mixture combinations of K₂CO₃, KHCO₃, PZ, and CO₂. / text