In spite of the fact that there are many advantages of alkali activated materials (also called geopolymers) over the cement-based materials, geopolymer concrete has been used in the past for construction purposes on a very limited level. Among the many advantages of geopolymers compared with the cement-based materials is less CO2 emission, it uses byproducts as a binder, less energy consumption during its production, more durable as a material, fast setting time and high strength development. This work is an attempt to exert some light on the usability and applicability of geopolymers in the field of construction with concentration on its use in the 3D printing. The main aim of this study is to propose a design methodology for geopolymer paste mixture to be used in 3D printing process. For achieving this goal, one paste mixture design was selected among six ones on the bases of longer workability/flowability, suitable extrudability and specific setting time. These six designs have different binder ratios. The selected mixture design, named S20, was tested further to find out its suitability for 3D printing process. This S20 mixture was tested on compressive strength, setting time, rheological properties, open time, buildability and 28 days tensile bonding strength of two layers. To find the best suitable design, modifications were done on the S20 mixture by changing the ratios between the used alkaline solutions Na2SiO3 and NaOH (0.25 was selected). These alkaline solutions played a major role in delaying the initial setting time for rheological tests (90 minutes were selected) and the extrudability for the 3D printing process. Another factor for the best design is the Acti-gel as an additive. This additive has a direct link with the buildability, extrudability and viscosity when added with different percentages. The best selected percentage of the Acti-gel was 0.75% for this mixture design. The open time and the 28 days tensile bonding strength tests were selected to be 33 minutes and 1.32 MPa respectively. Comparing the measured plastic viscosity to the open time test, the extrudability of the mixture is not anymore valid beyond 8.8 Pa.s plastic viscosity. This short open time of 33 minutes for such geopolymer mixture design needs a fast-performing 3D printer. This might help in achieving construction projects within short time.

To obtain radionuclides for medical use from an isotope generator, mother and daughter nuclides need to be separated. In contrast to adsorption-based generators where the mother nuclide is retained on a static column, in liquid generators both mother and daughter nuclides are in solution and need to be separated via extraction. Microfluidic techniques are promising for the extraction process because mass transfer is very efficient and in theory the laminar two-phase flow in the microchannel can be easily separated at the end.

The generator of interest in this thesis is the W-188/Re-188 generator. However, some work also concerns the chemical similar Mo-99/Tc-99m generator and the Lu-177m/Lu-177 generator.

The start objective was to find a less water miscible replacement for the commonly applied organic phase methyl ethyl ketone (MEK) in the W-188/Re-188 generator, since with this system precipitation was observed previously in the microchannel. Several organic phases have been tested for precipitation, but also for their extraction efficiencies and abilities to separate rhenium from tungsten. The best results were observed for 0.2 M Aliquat 336 in 1,3-diisopropylbenzene, an organic phase that shows no precipitation, has suitable wetting behaviour in the microchannel and an even higher extraction efficiency than MEK.

Another issue addressed in this thesis is the incomplete phase separation at the Y-splitter (end) of the channel. Either some aqueous phase leaves through the organic outlet or some organic phase leaves through the aqueous outlet. One possible reason for the leakage is the uniform surface of both outlets, and therefore the preferred wetting of the hydrophilic glass wall of the microchannel with one phase. Coating one side of the microchannel hydrophobically showed that the leakage can be stopped. The effects of radiation on the coating have been investigated using an external gamma source and a threshold of 5 kGy before deterioration was found.

An even easier method to achieve complete phase separation is the use of a membrane separator.
Here, two phases are combined in simple 0.5 mm tubing in droplet fashion before being separated by a membrane. With the above mentioned organic phase, an extraction efficiency of 95% was reached within 5.3 minutes contact time. This is considerably longer than the typical contact time in the microchannel (in the order of seconds), but the total handling time was reduced from over 3 hours (with a microchannel) to 16 minutes by using a membrane separator. For lutetium, an extraction efficiency of 99% was reached after 2 minutes contact time, reducing the total handling time by a factor of 2.5 compared to the conventional method.

Supercritical water gasification is a process in which wet biomass is converted to bio-syngas. In this process the temperature and pressure are raised above the critical point of water (374 C, 221 bar), creating a supercritical medium in which a high conversion and energetic efficiency of biomass to bio-syngas is realized. Due to these high efficiencies supercritical water gasification has received much attention as a potential treatment technique for sewage sludge from wastewater treatment plants.
To design a supercritical water gasification process kinetic models are used. They provide predictions on the decomposition products of the organic components of the biomass during treatment. However, kinetic data on lipids, which can make up to 25% of the organic matter in sewage sludge, are not available yet. This study aims to identify main reaction pathways and corresponding kinetic parameters that describe the decomposition of lipids in supercritical water.

Experiments were performed to provide data of decomposition products yields and find the dominant reaction pathways. Oleic acid was used as a model compound for lipids from sewage sludge. Experiments were conducted in a stainless steel batch reactor which was heated by immersion in a fluidized hot sand bath. Investigated temperatures and residence times were 400, 420, 460 and 520 C and 15, 35 and 65 min, respectively. Oleic acid feed concentration was 10 wt% and a pressure of 25 MPa was applied.

From experimental results the decomposition of oleic acid into aliphatic hydrocarbons and shorter chain fatty acids was identified. With increasing time and temperature these products would either gasify or the aliphatic hydrocarbons would dehydrogenate to cyclic and (poly)-aromatic compounds. A remarkably high selectivity towards the light hydrocarbon gases (C2H6, C2H4, C3H8, C3H6) compared to an earlier study into the decomposition of oleic acid in supercritical water was observed for all temperatures and residence times.

Parameters for a kinetic model, build up from the identified reaction paths, were fitted to the experimental data using Matlab. The Arrhenius equation was used to describe the reaction constants as function of temperature. For the oleic acid decomposition an activation energy of 151 kJ/mol was fitted first with a percentage output variation of 82% between 420 C and 520 C. Parameters for the other reactions were fitted using this activation energy as constraint.
Qualitative trends on the gas and liquid decomposition products distribution over time and temperature were predicted well by the model, but predictions on the quantitative yield of them were concluded to be inaccurate. Largest differences between experimental and model yields were observed for CH4 and the light hydrocarbon gases.

One reason for these model errors is the scarcity of data points in the 0-15 min time-scale, where the process was highest in reactivity. Also some of the reaction pathways in the model might have been oversimplified, neglecting certain dominant decomposition reactions.