Title Promoter Affiliations Abstract "DynScale: Reactive flow and transport models in complex media with evolving interfaces at the micro scale" "Sorin POP" "Computational mathematics" "This project deals with mathematical models defined in complex, hierarchically organized media. Such models appear in a broad range of real-life applications like geothermal energy, CO2 sequestration, biosystems, or coated nano-materials. The particularity here is in the occurrence of moving interfaces at the micro scale. These are either evolving micro structures, or interfaces separating two different fluids. The movement of such interfaces is not known a-priori and depends on the model unknowns. The goal is to provide a methodology to construct reliable and computable mathematical models for multi scale processes in complex domains, accounting for the micro scale interfaces in evolution. Such issues will be addressed within a generic mathematical and numerical framework, but inspired by the applications mentioned above. Three representative processes are considered, leading to different models: reactive flow where adsorption/desorption affects the micro structure, the flow of two immiscible fluids in complex media, and the elastic deformation of solid materials with complex structure. Besides interfaces in evolution, the focus will be on the interplay between these processes. Two modelling strategies are envisaged at the micro scale: free boundaries and phase fields. For the resulting models, upscaled models are derived to describe the averaged behavior of the solutions, and numerical schemes and strategies based on multi scale techniques are developed." "The impact of re-injection of geothermal fluids on fluid flow properties and mechanical stability in fractured/faulted limestone reservoirs." "Veerle Cnudde" "Department of Geology" "One of the emerging techniques for sustainable energy production is the use of geothermal energy: heat is extracted from the deep subsurface, used for heating or the production of electricity, and then re-injected in the reservoir. The goal is set out to increase the worldwide energy production from geothermal energy from 84.8 TWh in 2017 to 1400 TWh/year in 2050. Therefore, deep and typically less permeable reservoirs are more frequently targeted. Production of deep geothermal energy mostly depends on water circulation in engineered networks of man-made and/or pre-existing fractures and faults. The life expectancy of geothermal systems is typically limited due to decreases in production over time. Also, there is a risk of induced seismicity related to the production of deep geothermal energy. Both the production potential and the mechanical stability can be linked to micro-physical processes at the grain scale within the fractures and faults. We propose an experimental investigation to quantify the long-term changes in fluid flow regime and mechanical stability due to the injection of under- and supersaturated fluids into fractured and faulted analogues of dense limestone reservoirs. We will perform experiments under in-situ reservoir conditions, which can be visualized using X-ray tomography. Based on the observed changes within the fractures and faults, changes in frictional properties, controlling the mechanical stability of the system, will be determined." "Prediction of Turbulent Reactive Flows by means of Numerical Simulations (PRETREF)" "Bart Merci, Sebastian Verhelst" "Department of Structural Engineering and Building Materials, Department of Electromechanical, Systems and Metal Engineering, Department of Data analysis and mathematical modelling, Department of Materials, Textiles and Chemical Engineering, Department of Electronics and information systems, Department of Chemical engineering and technical chemistry, Department of Mathematical Modelling, Statistics and Bio-informatics, Department of Flow, heat and combustion mechanics" "Predicting turbulent flows with chemical reactions accurately is essential for development of technology and fundamental research in a wide range of applications. Biosystems, chemical reactors, internal combustion engines, furnaces and fires are all considered by the multidisciplinary consortium. The common feature in numerical simulations is turbulence with detailed (bio-)chemical kinetics, for which advanced models are applied, exchanged and further developed where necessary." "Multiscale study of reactive gas injection in pyrometallurgical processes." "Bart Blanpain" "Sustainable Metals Processing and Recycling, Department of Materials Engineering" "The goal of this research is to generate fundamental insight into reactive gas-liquid flows for pyrometallurgical gas injection applications through the construction of a multiscale model. The focus will be on the integration of mesoscopic numerical CFD techniques with microscopic thermokinetic models. this will lead to an isothermal mesoscopic model capable of simulating the behavior of one or more gas bubbles, exhibiting the most relevant phenomena in pyrometallurgical processes, namely convection, diffusion, reaction (in the bulk and at the interface) and precipitation. For reasons of feasibility, a model problem is formulated for this research, which contains the most relevant physico-chemical phenomena for a multitude of other pyrometallurgical applications. The process under consideration is the injection of silicon tetraochloride (SiCl4) gas in a batch of liquid zinc (Zn). Both species take part in a reduction raction, leading to the formation of silicon (Si) and gaseous zinc chloride (ZnCl2). This reaction can take place both at he gas-liquid interface and in the bulk of the bubble, since due to its high vapor pressure, zinc will evaporate into the bubble. Solid silicon particles can form through the gas-gas reaction, and silicon can dissolve into the zinc bath at the interface. Additionally, these reaction and diffusion phenomena will be influenced by the convection pattern in and around the rising bubble." "Prediction of Turbulent Reactive Flows by means of Numerical Simulations (PRETREF)" "Sebastian Verhelst" "Department of Electromechanical, Systems and Metal Engineering, Department of Flow, heat and combustion mechanics" "Predicting turbulent flows with chemical reactions accurately is essential for development of technology and fundamental research in a wide range of applications. Biosystems, chemical reactors, internal combustion engines, furnaces and fires are all considered by the multidisciplinary consortium. The common feature in numerical simulations is turbulence with detailed (bio-)chemical kinetics, for which advanced models are applied, exchanged and further developed where necessary." "Solar energy-driven hydrogen production" "Raf Dewil" "Chemical and Biochemical Reactor Engineering and Safety (CREaS)" "Nearly all current hydrogen generating processes use fossil fuels that lead to CO2 and GHG emissions. Towards a de-fossilization of its production, a distinction is now made between non-fossil-based ""green H2"" with very low CO2 emission, ""gray H2"" from hydrocarbons with CO2 emission, and ""blue H2"" where the carbon emission is captured and possibly utilized. The thermal fossil fuel-based hydrogen production technology includes steam reforming, partial oxidation, and ATR processes, respectively. Non-fossil feedstock production methods today mainly include fermentation, gasification or pyrolysis, and electrolysis.Chapter 1 summarizes the different current and potential novel H2 production methods. Although these H2 production methods will be proven technically and economically viable, their moderate to high endothermicity requires the use of a “green” energy supply, where renewable energy appears to be the most indicated option. The application of renewable heat or power will therefore be investigated in the second part of the Ph.D. research, with a special focus on using Concentrated Solar Tower technology, both in a base-load and in a peaker operation mode.Chapter 2 examines four H2 production methods using “gray” or “green” feedstock. Four experimental set-ups were used, including a pilot-scale concentrated solar rig. The reactors contained appropriate quantities of catalyst particles. Experiments were conducted in triplicate under the same operating conditions.A first “gray” feedstock, CH4, was investigated mostly for its Hydrogen-Enriched Natural Gas (HENG) potential. Results demonstrate that the Fe/Al2O3 catalyst (with a 20 wt% loading of Fe) can yield nearly complete methane conversion at a temperature of 700 °C, whereas the Ni/MgO catalyst is less performing at the same temperature and residence time. The carbon formed by the decomposition reaction accumulates within the catalyst with a progressive reduction in H2 yield. A periodic regeneration is required. For both catalyst systems, the reaction rate determines the kinetics at temperatures below ~635 °C whereas external mass transfer becomes increasingly important at higher temperature. The present results confirm that the use of Fe/Al2O3 for CH4 decomposition is recommended.A second “gray” (possibly “green” by future developments in bio-synthesis of methanol) feedstock was CH3OH. Experimental results demonstrate that the catalytic steam reforming of methanol (CSRM) by using Co/α-Al2O3 or MnFe2O4 provides a complete conversion of CH3OH at respectively 300 °C and 400 °C. The H2 yield is about 2.5 mol H2/mol CH3OH (slightly, lower than the stoichiometric yield of 3 mol H2/mol CH3OH). The CH3OH-carbon is transformed into mostly CO and CO2. Coke formation was not detected after long-duration catalyst use. A kinetic analysis demonstrated a high reaction rate, with optimum conversion already achieved within a contact time of 0.3 to 0.5 s. Longer contact times hardly change the product composition, and equilibrium is attained. Using Co/α-Al2O3 for scale-up and fuel cell application is recommended due to the lower CO formation and higher hydrogen yield.Thirdly, the production of H2 from ""green"" or industrial NH3 was studied in the present research using non-noble metal catalysts. “Green” ammonia sources were investigated, such as ammonia produced by stripping from manure and digestate. Three catalysts were tested, wet-impregnated Fe-Al2O3 and dry-milled Fe-Al2O3, and wet-impregnated Ni-Al2O3. The mildly endothermic decomposition of NH3 into H2 and N2 is achieved with a 100% yield at 500 °C using a Fe/γ-Al2O3 catalyst. The alternative and more expensive Ni/γ-Al2O3 catalyst scores significantly lower. The reaction is very fast, with a rate constant of 7.5/s at 500 °C. Full conversion is obtained within 0.4 s. Very pure (> 95%) H2 can be produced and can be stored by several techniques. It is proven that the H2 production from NH3 has a high potential, and merits pilot-scale consideration.Toward the Catalytic steam reforming of bio-ethanol (CSRE), the most promising catalysts were selected from an in-depth literature review and tested in the present research in isothermal electrically heated furnaces, and in a concentrated solar reactor. Over 30 successive hours were assessed, and the H2 production efficiencies were close to the stoichiometric expected values. Approximately 5.5 mol H2/mol ethanol was produced with CO and CO2 as main carbon-bearing reaction products. A kinetic analysis defined the reaction rate expressions and the reaction rate per unit per unit catalyst weight (0.58 mol H2 /gcat h). Moreover, the production system was critically assessed toward a further scale up with maximum heat recovery, H2 upgrading, and H2 use in a SOFC.Chapter 3 focuses upon the thermal conversion of water by appropriate reversible redox reactions. Whereas thermal water splitting to H2 requires high temperatures, thermo-chemical water splitting cycles operate at moderate temperatures. These cycles were previously investigated, mostly by small-scale experiments and mainly to prove their concept without judgment of their practical, economic, environmental and cyclic performance. To facilitate the decision making and to guide future priority research, these multiple aspects were combined in a global screening system that applies the improved Analytic Hierarchy Process (AHP) and gray relational TOPSIS, together with the use of linear and non-linear combination weighing. The assessment is quantitative and comprehensive, emphasizing the complex relationship between energy efficiency, conversion, recyclability, economy and environmental quality. The screening index helps users, system manufacturers, researchers and governments to select the most appropriate future schemes. Twenty-four thermo-chemical water splitting cycles were investigated. After an objective screening, the selected priority redox systems using MnOx/Na2CO3 and MnFe2O4/Na2CO3 were experimentally investigated for short- and long-duration cycling.For the MnOx/Na2CO3 redox water splitting system, tests are carried out both in an electric furnace, and in a concentrated solar furnace at 775 and 825 °C using 10 to 250 gram of redox reactants, respectively. In the solar furnace, the highest conversion (>95%) was obtained with the Mn3O4/ Na2CO3 system at 775 °C. The economic assessments revealed that at least 100 cycles would be needed to achieve competitive H2 prices below 2 €/kg for systems with a cheap energy supply, and provided CO2 could be separated from the reactant gas and reused in the reverse reaction.The MnFe2O4/Na2CO3 cycles were subsequently experimentally investigated at lab- and solar reactor scale. Over 30 successive oxidation/reduction cycles were assessed, and the H2 production efficiencies exceeded 98 % for the coprecipitated reactant after these multiple cycles. Solar reactor experiments confirm the > 95% H2 efficiency. Tentative cost calculations showed a break-even operation for 30 consecutive cycles at H2 prices of 4 €/kg H2. At least 120 cycles before reactant re-activation will reduce the H2 production cost to ~1 €/kg H2. This implies the use of a cheap energy supply, and the complete reuse of CO2 in the reduction reaction. The results certainly foster a further improvement of the system. Coprecipitated MnFe2O4 is purchased at approximately 500 €/ton. The ball-milled reactant can be approximately 30% cheaper.The heating costs are not considered since the system is supposed to use excess photovoltaic or wind turbine electricity, or to operate on concentrated solar heat. Heat recovery will be maximized by good heat management. CO2 should be separated, stored, and used in the reverse reaction. It is also proposed to use membrane modules to produce very pure H2. If the cheaper ball-milled reactant could be improved, the number of required cycles to break even will be reduced. The proposed MnFe2O4/Na2CO3 cycle, if realized at an industrial scale, can be competitive with the electrolysis of water using solar-generated electricity or heat. Further development and large-scale demonstration are needed.Chapter 4 summarizes the contribution of the Ph.D. research into (i) the particle-driven receiver hydrodynamics, where long receiver tubes can now be implemented; and (ii) the determination of the hydrodynamics and thermal design parameters of an appropriate heat exchanger to recover the particle-stored heat. Auxiliary equipment will also be briefly discussed.Since the research will promote hybrid PV-CST solar systems to supply energy to the H2-production reactors, it was deemed necessary to focus on the required improvements of the CST.  Essential results are summarized hereafter for the solar receiver. Introducing Bubble Rupture Promoters largely eliminates slugging. The wall-to-bed heat transfer is further increased from 200 W/m2K to > 600 W/m2K. A deemed key operation of the CST plant, is the storage of hot and cold particles. This was studied at the kWth and MWth scale. Heat losses will occur during storage. The temperature evolution of the hopper is predicted.Particle conveying within the solar loop, is an important operation. The solids heated by the solar receiver are transferred to the power block and stored before their use. In turn, the cooled solids leaving the heat recovery are stored before being transferred back to the solar receiver to be reheated. It should be remembered that the power required to lift the particles by mechanical means (e.g. elevators) is increased by about 220 % because of the weight of chains and buckets and the excessive mechanical friction. It was hence decided to apply a pneumatic particle conveying in dense phase. A similar recommendation to use pneumatic conveying, even for capacities as high as 600 tph and lifting heights of 250 m were proposed in literature. The pneumatic conveying option is hence selected. Rather than applying the air-in-partcle dense phase system using discontinuous blow tanks (with additionlal problems of requiring high T valves), the proposed system will use a continuous particle-in-air dense phase conveying, with lower pressure drop along the conveying pipes. The solution is applicable at large scale only if a heat recovery is integrated to the loop.The release of dust and the associated hot air is to be avoided. High-temperature particle/air separation was introduced. Filters are in service operating at temperatures above 800°C, and the technology is readily applied to the requirements of the solar plant. Filtration (face) velocities can be of the order of 3 m3/m2 min (against 1.2 m3/m2 min for common fabric filters). The blow back flow should achieve 0.15 m/s, and the blow-back pressure is commonly 10 bar. With a 1 μm fibre filter, the de-dusting efficiency will exceed 99 % for 0.1 μm particles. The residual emission will be" "CFD-Assisted Design of an Innovative Multiphase Chemical Reactor for Hydrogen Release." "Patrice Perreault" "Sustainable Energy, Air and Water Technology (DuEL)" "This thesis focuses at designing, optimising, simulating (using computational fluid dynamics, CFD) and testing a multiphase intensified chemical reactors for the fast release of hydrogen from liquid organic hydrogen carrier (LOHC), for its eventual use on-board of ships (with hydrogen-fuelled engines). The reactor will be designed according to the specificity and requirements of the LOHC dehydrogenation chemical reaction, i.e. a slow endothermic heterogeneous catalytic chemical reaction between the LOHC and a catalyst particulate phase, generating high volumes of gas. More specifically, the chemical reaction requires: i) an intimate contact between the liquid phase and the catalyst, ii) an efficient and fast removal of the hydrogen generated without liquid entrainment, iii) an efficient heat transfer for the endothermic catalytic reaction while minimising the thermal stresses on the LOHC, iv) a short contact time between the catalyst and the LOHC, v) processing of high flowrates of LOHC to offset the dehydrogenation slow kinetics, and finally, vi) a compensation for the effect of the ship movements on the gas-liquid interface. Designing this ideal device represents a considerable challenge, and the perfect reactor for this task does not exist yet. However, we will make use of a current trend in chemical reaction engineering that aims at adapting the geometry of chemical reactors so that the elementary steps of a global chemical reaction leading to the desired products are favoured. As part of this thesis, we will establish the building blocks of an automated chemical reactor design procedure: The optimisation of the reactor geometry will be performed using a constrained shape optimisation strategy, from an initial parameterised geometry. The constraints for the optimisation procedure are the mass, energy and momentum balances, evaluated numerically through the use of computational fluid dynamics (CFD), using the open source code OpenFoam. An initial parameterised geometry (chemical reactor configuration to iterate from) is required. The selected doctoral student will first review the potential reactor configurations, but the promotor preliminary proposes a generalisation of the gas-solid vortex reactor (GSVR) concept for multiphase reactor flows (thus defining a Gas Solid Liquid Vortex Reactor, i.e. a GSLVR). This type of centrifugal reactor combines several interesting characteristics. At sufficiently high rotation speed, the effect of gravity can be neglected. The presence of a low pressure zone along it centre axis also allows for a preferred gas outlet. The GSVR is also a centrifugal device, thus combining reaction and separation functions. The parameters to be optimised for this reactor configuration are the number of slots (i.e. entry point for the liquid to the zone where the catalyst is located, the reactive zone), their spacing, the height of the device, the reactive zone chamber diameter, the position of both the LOHC inlet and outlet, as well as the diameter of the exhaust (gas outlet). The ""holy grail"" of numerical experiments, i.e. without experimental validations, is still far from being a realistic objective in the field of CFD. Experimental validation is required, especially in the context of simulations of turbulent reactive flows using the two fluid model (Eulerian-Eulerian approach). A setup allowing for experimental validation and demonstration will be constructed. The Particle Image Velocimetry (PIV) technique will be used to validate both the liquid flow (liquid phase seeded with tracer particles) and catalyst bed (unseeded PIV). Due to the interdisciplinarity of the proposed research, the student will acquire a comprehensive knowledge in numerous complementary fields – chemical (chemistry and catalysis), mechanical (fluid mechanics), programming (C++®, Python®, CFD, etc.) – at both theoretical, computational and experimental levels." "First-principles 3D reactor design: Large Eddy Simulation and Direct Numerical Simulation with detailed chemistry" "Kevin Van Geem" "Department of Materials, Textiles and Chemical Engineering, Department of Chemical engineering and technical chemistry" "The rising computational power makes that new innovations are possible of which 5years ago one could not even dream. This is in particular important for chemicalreactor and reaction engineering where Process Intensification drives researchers tothink outside the box. In the academic as well as the industrial world, innovations aremore and more based on 3D reactor simulations incorporating chemical reactions.Operational optimization and reactor design based on ‘first-principles modeling’ willresult in improved heat and mass transfer, reduced fouling and increased productselectivity. In ‘first-principles modeling’ the basic set of mass, energy and momentumconservation equations is solved accounting for models that calculate physicalproperties and include chemical reaction kinetics.In this project the 3D Computational Fluid Dynamics simulation of chemical reactorswill be performed implementing detailed chemistry. Applying detailed free-radicalmechanisms is essential for processes such as pyrolysis, steam cracking,combustion and partial oxidation. Furthermore the equations describing the reactorbehavior will not be simplified. Large Eddy Simulation, where only small flowturbulence is filtered out, and Direct Numerical Simulation, implying the solution ofnon-simplified or unfiltered equations, will be applied. The simulation results will bevalidated using a detailed set of experimental results obtained in cold flow and hot(reactive) flow pilot setups." "Quantitative testing of conceptual models for hydrothermal carbonate genesis" "Sarah Fowler" "Division of Geology, Geology" "This project focusses on the initial implementation of the new CSMP-GEMSnumerical code, designed for combined fluid flow (CSMP) and reactive transport modelling (GEMS), hence this code can suitable for prediction fluid distributions, temperatures as well as fluid and mineral compositions resulting from water-rock interactions. Although this new code is promising (especially regarding the level of complexity) furthertesting is needed, especially with regard to the combination of hydrologic non-isothermal fluid flow with dynamic permeability and fracture flow. Also the extrapolation of the models with respect to natural system needs to be examined further. Herein lies the innovative aspect of this projects: creating a model that combines a natural complex geometry in combination with realistic porosity and permeabilitychanges in a hydrothermal system and applying this to a natural system.To this end, the Latemar carbonate platform (Italy) was chosen. This region is ideal for testing the codes capacity to model the geometric evolution of the dolomitization (and hence of the dolomitizing fluid) asit contains different lithologies, with each their specific porosity andpermeability, which are cross-cut by fractures and dikes. Furthermore, there is still some debate concerning the nature of the dolomitizing fluid, giving us the opportunity to examine to what extend the code can determine the source of dolomitization.More specifically, this project will be divided into three major parts. The first part will mainly focus on fluid composition and will attempt to determine the source and conditions of dolomitization. The second part will focus more on the geometry of the fluid flow by incorporating the fracture and dike distribution pattern, as well as permeability and porosity changes into the model. The third part will largely depend on the findings of the two previous parts. For now, the idea is to shift the focus towards magmatic intrusion and the resulting effects on the related hydrothermal fluid flow and hence, the effects on the carbonate system" "Design and Evaluation of Translucent Structures for Photocatalytic Reactors" "Tom Van Gerven" "Process Engineering for Sustainable Systems Section, Process Engineering for Sustainable Systems (ProcESS)" "Photocatalysis is a technology which opens up new processing windows for organic synthesis or organic transformation reactions. A common application is the photocatalytic degradation of organic pollutants in water. Degradation reactions are basically oxidation reactions, where the desired end product is usually carbon dioxide. The intermediate products formed during the mineralization process are potentially interesting to valorize meaning that photocatalysis can be used to perform selective oxidation reactions using molecular oxygen. The catalyst used in a photocatalytic process can be present in the same phase as the reacting liquid, which is called homogeneous photocatalysis, or in a different phase than the reacting liquid, which is called heterogeneous photocatalysis. In this work, the focus will be on heterogeneous photocatalysis.Performing a heterogeneous photocatalytic reaction requires a light source, a photocatalyst and a reactor geometry. The reactor needs to be designed in such a way, that it synergizes photon transport and mass transport with a high catalyst loading. Two main types of reactors exist. In the first reactor type, the slurry reactor, catalyst particles are suspended in the reacting liquid resulting in a low controllability over the light distribution and requiring a catalyst separation step after the reaction is completed. A slurry configuration is often used in combination with a batch reactor. In the second category, the catalyst layer is immobilized on a support. This approach is more promising for synergizing photocatalysis with flow chemistry. The catalyst loading can be precisely controlled by the catalyst layer thickness, and there is no need for a catalyst separation step.Despite the interesting possibilities of photocatalysis, no industrial application exists as of yet. One of the reasons can be attributed to the reactor design. The problem regarding reactor design can be made clear using a simple flat-plate reactor as a reference system. In a flat-plate reactor, the reacting fluid is flowing between two plates where both plates can be coated with a photocatalyst which is irradiated perpendicular to the flow direction. The catalyst layer is chosen sufficiently thick to absorb all the incoming light energy. Since photocatalysts are mostly highly absorbing materials, the light transmission is almost equal to 0 after travelling approximately 10 µm in the catalyst layer. In this type of reactor, two problems occur. Firstly, because of the laminar flow profile between the two plates, mass transport from the bulk liquid towards the catalyst layer is dominated by diffusion, which limits the supply of reagents to the catalyst surface. Secondly, when the catalyst layer is too thick, mass transfer limitations inside the layer occur. A potential solution is to decrease the volume of the reactor to microreactor scale in order to decrease the diffusion length and to increase the surface-to-volume area meaning thinner layers can be applied for the same catalyst loading with respect to the liquid volume. However, microreactors are not scalable, not easy to illuminate efficiently due to the small reactor window, and have a low total surface area. As a result, the issue of internal diffusion limitations in the catalyst layer is not solved because the catalyst layer thickness has to be increased to increase the catalyst loading. Also, applying thinner catalyst layers on a microreactor surface leads to light energy losses at the backside of the reactor. The solution to solve all these issues simultaneously is to incorporate multiple microchannels in a larger translucent structure. A translucent structure can be illuminated easily, provides a large surface-to-volume area as well as a large total surface area and has an improved bulk liquid mass transfer. These properties allow for easy light source design and flexibility in choosing the correct catalyst layer thickness avoiding diffusion limitations using the geometry of the structure as a parameter to tweak total catalyst loading and surface area. In this work, the used translucent structure is a packed bed of equally sized borosilicate glass spheres.In a proof-of-concept study, it was proven that the productivity and energy efficiency of the packed bed reactor was higher than the existing designs from the literature. For the photocatalytic degradation of methylene blue, the reactor had a productivity similar to that of a microreactor, but a photocatalytic space-time yield, which is a measure for productivity versus energy efficiency, of 4 to 5 orders of magnitude higher. It was shown that the improved surface-to-volume area leads to high catalyst loadings up to 2.9 g L-1 while maintaining layer thicknesses below 300 nm. In the second part of the work, the effect of the bead size and catalyst layer thickness on external mass transfer and energy absorption was assessed. The bead size of the packed bed reactor can be used to alter the external mass transfer properties of the photocatalytic bed and to tweak the light absorption and surface area in the bed. When in a fixed reactor volume the bead size is decreased while maintaining the same catalyst loading, the number of scattering boundaries increases meaning that less light is being absorbed. In the third part of the work, the optimal catalyst configuration and number of structural layers in a translucent structure were determined. For a light intensity of 200 W m-2 the optimal layer thickness is more or less equal to 1.5 µm in a translucent structure containing a minimum of 5 structural layers. These values vary as a function of the light intensity, since mass transfer limitations are dependent on the catalyst layer reactivity. Finally, translucent packed bed structures were tested for gas-liquid oxidation reactions and it was proven that also for gas-liquid applications translucent structures can improve the productivity of a photocatalytic reaction."