Nick Van Oosterwyck

• Friday 17 November 2023
• 5 p.m.
• Campus Groenenborger - room g.Z.126
• Promotors: prof. dr. Stijn Derammelaere & prof. dr. Annie Cuyt​
• Faculty of Applied Engineering

Abstract

Rising energy costs and the pressing climate crisis emphasize the need for energy-efficient industrial machines. Consider a robot transferring an object: often, it just needs to get the object to its destination on time. By adjusting when and where the machine speeds up and slows down, energy can be saved. Our method, presented in this thesis, identifies the best motions faster and more effectively than previous methods, cutting energy use by up to 63% without altering the machine or affecting production rates.

Kevin Van Daele

• Monday 23 oktober 2023
• 5 p.m.
• Campus Drie Eiken - room d.O.1
• Promotors prof. dr. Tom Breugelmans & dr. Deepak Pant
• Faculty of Applied Engineering

Abstract

Since the start of the second industrial revolution in the late 19th century, a rapid increase in anthropogenic CO₂ emissions and land-use changes have been supercharging the natural greenhouse effect, making CO₂ Earth’s most harmful and prevalent greenhouse gas, bringing about global warming, disrupted weather patterns and an acidification of the oceans.The electrochemical CO₂ reduction (eCO2R) into industrially valuable products has become one of the most promising technologies to valorise anthropogenic CO₂ emission, while simultaneously providing a means of energy storage for intermittent renewable sources, such as wind-, solar- and hydro energy. According to most eCO₂R literature and techno-economic assessments, the eCO₂R towards formate/formic acid (FA) has the potential to generate the highest revenue per mole of consumed electrons. However, for this process to become industrially feasible, a low cost catalyst with excellent activity, selectivity and stability is required. While state-of-the-art literature reports a wide variety highly selective and active Sn-based electrocatalysts, their stability is currently inadequate for industrial application of the eCO₂R towards formate/formic acid.Throughout this dissertation, several important insights were gained concerning the stability of Sn-based electrocatalysts. Moreover, several major morphological degradation pathways were diminished, utilising a particle confinement strategy, and the possibilities to further enhance Sn-based electrocatalyst stability, by decreasing in situ SnO₂ reduction via pulsed-eCO₂R, were explored, paving the way for future research.

Veerle Akkermans

• Monday 11 September 2023
• 4 p.m. 
• Campus Drie Eiken - room  d.Q.002
• Promotors: prof. dr. Jan Dries 
• Faculty of Applied Engineering

Abstract

Surfactants are used in various industrial applications, as well as many aspects of our daily lives, such as in home and personal care. Historically these compounds are produced from fossil fuel, but these have largely been replaced with biobased products. More recently, microbially produced biosurfactants have gained interest due to their excellent interfacial properties and mild production conditions. Mannosylerythritol lipids (MEL), a biosurfactant produced by the yeast Moesziomyces aphidis, are currently produced from vegetable oil, thereby competing with food security due to the fertile land use. In this research, waste and side streams were used to produce MEL, as proof of concept. Furthermore, the used substrate has a major impact on the produced MEL structure. The use of an unconventional substrate resulted in a new-to-nature MEL-like compound.

Yon Vanommeslaeghe

• Friday 8 September 2023
• 4 p.m. 
• Campus Middelheim - room  m.G.010
• Promotors: prof. dr. Paul de Meulenaere & prof. dr. Joachim Denil 
• Faculty of Applied Engineering

Abstract

A cyber-physical system is a system that integrates software (cyber) and physical parts. Such systems are all around us. They play an important role in areas such as industrial automation, aviation, defence, etc. Even in our daily lives, we interact with cyber-physical systems of varying levels of complexity. For example, our cars, home appliances, heating and air conditioning systems, etc., all include software to control or monitor them.

This combination of the 'cyber' and the 'physical', means that engineers from different fields need to work together when designing and developing these systems. These systems are becoming ever more complex, driven by the demand for ever better performing, safer, and more intelligent systems. This also makes their design and development more complex. Engineers not only have to consider more and more design variables and objectives within their own field; the different fields also become increasingly intertwined. This introduces new challenges throughout the design and development process.

In this thesis, we propose methods to alleviate some of these challenges. We show how we can explicitly capture the dependencies between the different engineering fields and how this can be used to better design and optimize our cyber-physical systems. We also present techniques to make the impact of certain dependencies visible to the engineers early on in the development process, allowing us to identify and address potential problems sooner. Lastly, we investigate how to properly validate the design of these systems.

Nikolett Wittner

• Tuesday 27 June 2023
• 4 p.m.
• Campus Drie Eiken - room d.Q.002
• Promotors: prof. dr. Iris Cornet & prof. dr. Siegfried Vlaeminck 
• Faculty of Applied Engineering

Abstract

Did you know that it is possible to produce biochemicals and biofuels such as bioethanol from wood without using harmful chemicals, large amounts of energy and water? Solid-state fungal pretreatment is one such environmentally friendly technique. It makes the carbohydrates in recalcitrant wood more available by using fungi to remove the unwanted lignin compound. However, these fungi also consume some of the desired carbohydrate components. In this thesis, the influence of additives such as metal ions, different inoculation techniques and fermentation strategies on the fungal fermentation process was investigated. The knowledge gained has made it possible to improve the selectivity and efficiency of this technique. The large amount of experimental data obtained from this study was used to develop near-infrared and ATR-FTIR spectroscopy-based lignin determination methods as rapid process monitoring tools. They are valuable alternatives to the conventional laborious wet chemistry-based methods. Finally, the feasibility of producing fermentable sugars from poplar wood using fungal fermentation was evaluated in a techno-economic analysis. The results obtained increase the understanding of solid fungal pretreatment and may facilitate the transition to a wood-based bioeconomy.

Jonathan Schalck

• Thursday 8 June 2023
• 4 p.m.
• Campus Drie Eiken - room d.O.002 en O.004
• Promotors: prof. dr. Tom Breugelmans, prof. dr. Jonas Hereijgers & ir. Wim Guffens 
• Faculty of Applied Engineering

Abstract

Ethylene oxide is a key commodity chemical, representing an indispensable link in the C2 valorization chain of the organochemical industry, enabling the synthesis of a wide variety of high(er) value chemicals through for example polycondensation or via alkoxylation reactions. The current industrial standard for a large-scale ethylene oxide production proceeds via a catalytically driven, partial oxidation of ethylene. Whilst this process is efficient, the direct greenhouse gas (GHG) emissions of partial oxidation reactors correspond to an estimated 7 Mton of CO₂ worldwide per year. To mitigate a worst case scenario in global warming, carbon heavy processes, such as the partial oxidation reaction, should transition into a carbon lean alternative. In this light, this PhD investigates the bromine mediated, indirect electrosynthesis of ethylene oxide in a bespoke continuous production setup. The electrosynthesis approach utilizes electrochemical reactions to supply the necessary reagents to tigger the synthesis of ethylene oxide at room temperature, thereby completely omitting combustion reactions thus CO₂ emissions. At its core, this PhD answers the question whether this novel electrosynthesis pathway can replace the partial oxidation process as green and economically viable alternative.

Bert Van Acker

• Tuesday 2 May 2023
• 2 p.m.
• Campus Middelheim - lecture room m.G.010
• Promotors: prof. dr. Joachim Denil & prof. dr. Paul De Meulenaere 
• Faculty of Applied Engineering

Abstract

Engineering Cyber-Physical Systems has become increasingly complex, e.g. due to the vastly increasing performance and safety demands. This makes it harder to correctly develop such systems. One way to tackle this development complexity, is adhering to Model-Based Systems Engineering (MBSE) approaches, which enable the use of (system) models throughout almost the complete engineering process. Within MBSE, physics-based models, models representing the physical behavior of the system, are commonly used. The value of such models is tightly coupled to how well the model reflects the system’s physical behavior and the correct model use, within it’s known valid range. If models are used outside this validity range, the produced model behavior is untrustworthy, as we do not know if it’s correct, slightly off or even completely wrong. By ignoring a model’s validity, we cannot reason about the trustworthiness off the produced model behavior, making them unusable for further engineering activities such as preliminary system analysis. Within this dissertation, we point the importance of the model validity and propose the Validity Frame concept as enabler for explicit model validity reasoning and usage. This theoretical Validity Frame concept is practically elaborated and the use is demonstrated on different academic applications.

Atilla Kovács

• Thursday 23 March 2023
• 2 p.m.
• Campus Groenenborger- lecture room g.V.009
• Promotors: prof. dr. Pieter Billen, prof. dr. Iris Cornet & prof. dr. Erik Neyts. 
• Faculty of Applied Engineering

Abstract

​Natural deep eutectic solvents (NADES) represent a green alternative to common organic solvents in the biochemical industry due to their benign behavior and tailorable properties, in particular as media for enzymatic reactions. This study aimed to build a structured, holistic understanding of the effect of NADES media on enzymatic reactions, whereby effects on solubility, solvation, viscosity, inhibition and denaturation are distinguished.Experimental and computational chemistry methods were combined to separately study the interactions between enzyme, substrate and NADES as reaction media. The initial enzyme activity and final conversion of vinyl laurate transesterification by immobilized Candida antarctica lipase were studied experimentally. The direct effect of NADES on the same enzyme was modeled by molecular dynamics simulation, which results were also validated with Raman optical activity spectroscopy.The effect of solubility was studied by both experimental and computational methods. To predict the solubility and viscosity of NADES, data-driven models were developed by the combination of group contribution and machine learning methods, based on the accumulated experimental knowledge on NADES found in literature. Finally, the composed relations and prediction models were applied in the practical example of mannosylerythritol lipids (MELs) deacetylation.The experimental findings show that the chosen NADES system has significant effect on both the apparent initial activity and the final conversion. However, in the simulations the enzyme retains its original structure; moreover, NADES has extra stabilizing effect on the enzyme. Additionally, the changes in the molar ratio of the compounds in NADES do not show significant effect on enzyme stability. These results indicate that the main effect of the NADES on the reaction relates primarily to the substrate-solvent interactions (solvation energy) and to the viscosity of the system. On the other hand, the experimental results only confirmed the significance of solvation, the viscosity did not show clear correlation with the studied reaction parameters.The machine learning models built on solubility and viscosity gave quantitative prediction on these properties. The accumulated knowledge was used to optimize the yield in the deacetylation reaction of MELs.The combination of these methods ensures fundamental knowledge on biocatalysis, but the findings are also transferable to other uses of NADES.

Daniel Choukroun

• Tuesday 14 March 2023
• 5 p.m.
• ​Campus Drie Eiken - room d.Q.002
• Promotor: prof. dr. Tom Breugelmans​
• Faculty of Applied Engineering

Abstract

Carbon dioxide (CO₂) is a molecule composed of a central carbon atom bonded to two oxygen atoms. It is a gas phase molecule under ambient conditions of pressure and temperature (1 atm, 25°C). Importantly, it is the final product of many chemical reactions between organic matter - such as wood or oil for example - and the oxygen molecules in air. Once initiated, these so-called combustion reactions supply the energy that enables modern life as we know it: to heat up water for comfort, hygiene and disinfection, to boil water and make steam for the sake of electricity production and to drive engines and vehicles. CO₂ is not harmful at low concentrations; humans and animals exhale it constantly and at large volumes. One of CO₂’s unique molecular properties, however, is that it absorbs sunlight as the latter reflects back from the surface of the Earth into the atmosphere. The energy of the light is then dissipated as heat in a process known as the greenhouse effect. The problem lies not so much with the phenomenon itself, but rather with the fact that CO₂ emissions have increased too much over the past decades due to industrial human activity, thus overshooting the natural capability of our planet to accommodate them and average global temperatures.Most of the aforementioned emissions come from stationary sources. It is therefore relatively straightforward (and urgent!) to capture CO₂ and purify it on-site for the sake of future storage or recycling/utilization. Namely, CO₂ can be used as a “building block” to make other molecules using a variety of previously established, large-scale industrial chemical processes. However, some of these processes still require natural-oil derivatives as reagents or high-temperatures to operate (which requires additional energy input if residual heat cannot be recovered for that purpose). In order to reduce our dependency on natural-oil and fossil fuels and advance a sustainable global energy transition, this thesis deals with the prospect of employing electrochemical reactors and catalysts to achieve similar transformations. Electrochemical reactors are in fact energy conversion devices; they take electricity as energy input in order to break the chemical bonds between the atoms in CO₂. In the simplest sense, the reactor is a closed electrical circuit composed of a voltage/current source and two conductive metal plates facing each other, with an aqueous salt solution - which acts as a kind of resistor - in between. One of the metal plates, or electrode, acts as a catalyst for the conversion of CO₂. Its nature dictates what product or molecules are formed from CO₂, and to which extent water is converted to hydrogen. Perhaps absurdly nowadays, hydrogen is the major and unwanted side-product of CO₂ conversion.In this thesis electrodes based on metallic copper (Cu) were investigated. In contrast to other metals, Cu is capable of converting CO₂ to products having more than one carbon atom, notably ethylene and ethanol, two of the largest-volume chemicals produced globally. Cu does so by first converting CO₂ to carbon monoxide (CO), which “sticks” to the surface, allowing the latter to react further. How to direct the conversion of CO₂, and hence CO, to just one particular product was one of the major research questions of this work. Instead of using a plate as an electrode, it was opted to prepare Cu nanoparticles (NPs) and disperse them onto the surface of a different conductive surface. That surface can either be inert – which means, without any affinity for CO₂ or water - or active, allowing conversion of CO2 to CO as final product and further conversion of CO to products on Cu. Significant emphasis was put on controlling the activity of the support material, the properties of the Cu NPs - their size, distribution and method of deposition - and on the interface configuration. It is concluded that the combination of two active, segregated catalytic components in close vicinity (so-called tandem catalysts), of which one is Cu, favors CO/CO₂ conversion under conditions where the pure metal loses its activity. That strategy helps suppress the undesired hydrogen evolution reaction, with additional products other than ethylene being formed in the process, at the cost of single-product efficiency. Electrodes made by bottom-up fabrication and stacking of Cu NPs into three-dimensional porous films, without aid of an active support or component, were found to suppress the formation of another by-product and greenhouse gas, methane, almost entirely. Taken together, these findings improve our understanding of the process and what it takes to render it more controllable and efficient. It is nevertheless argued that the energy consumption of CO₂ conversion to ethylene and ethanol is intrinsically high, so that from a sustainability standpoint it is paramount to take into account not only the energy efficiency but also the carbon efficiency and the energy source of the process. Clearly, the latter should have preferably little to zero carbon footprint.

Thomas Janssen

• Tuesday 17 January 2023
  
• 5 p.m.
• Stadscampus - Klooster van de Grauwzusters (Lange St-Annastraat 7, 2000 Antwerp)
• Promotors: prof. dr. Maarten Weyn & dr. Rafael Berkvens​
• Faculty of Applied Engineering

Abstract

Location data is required for a plethora of Internet of Things (IoT) applications running on billions of mobile devices worldwide. A few example applications include asset tracking, search-and-rescue operations and the scientific monitoring of air or water quality.

Global Navigation Satellite Systems (GNSSs), such as Global Positioning System (GPS) or Galileo, have been established as the standard for worldwide localization. However, the rapidly increasing need to locate IoT devices in recent years has exposed several shortcomings of traditional GNSS approaches. These limitations include the weak signal propagation in indoor and dense environments, a high energy consumption and the inability to communicate a location to a remote end user. Therefore, several industries have shown an increasing demand for alternative, innovative, and energy-efficient positioning solutions that are more suited in an IoT context.

In contrast to GNSS, Low Power Wide Area Networks (LPWANs) were designed for energyefficient communication of small sensor readings in a metropolitan area. In this type of terrestrial networks, thousands of IoT devices can send a message to nearby gateways, which in turn deliver the message to a central server. Interestingly, the uplink communication signals can be exploited to locate the mobile transmitter. Such a localization approach benefits from the low-power and low-cost LPWAN communication, as well as from the coverage in indoor environments.

Another very promising alternative to GNSS is the use of satellites in Low Earth Orbit (LEO) for Positioning, Navigation and Timing (PNT). Driven by the recent ‘New Space’ movement, the commercialization of the space market has opened the door to a myriad of opportunities. The thousands of LEO satellite launches of Iridium, SpaceX, Amazon, OneWeb and many others enable applications such as high-quality satellite telephony, worldwide Internet access and smart agriculture through Earth Observation. Providing PNT services through LEO satellites in an energy-efficient way will only improve the value of these applications in the emerging market of satellite IoT.

The objective of this thesis is to investigate innovative, large-scale, and energy-efficient positioning technologies and techniques in the context of IoT. I examine how wireless networks, either terrestrial or space-based, can be leveraged for locating IoT devices, and how I can improve their positioning performance.

The performance analysis and optimization of localization using LPWAN technologies constitute a significant part of the work in this thesis. To this end, three major LPWAN technologies are investigated: Sigfox, LoRaWAN and Narrowband IoT (NB-IoT). Localization experiments are carried out using real-world measurement data collected in Antwerp, Belgium. Within these experiments, I analyze the performance of Received Signal Strength (RSS)-based positioning algorithms. More specifically, I evaluate different path loss models in range-based algorithms and apply Machine Learning to optimize the performance of RSSbased fingerprinting methods. Furthermore, I discuss how the positioning performance can be further improved through changes in network infrastructure and User Equipment (UE).

In the final part of this work, I conduct a survey for the European Space Agency (ESA) with the goal to explore innovative space-based PNT solutions, again with a focus on low energy consumption. I analyze the state-of-the-art performance of novel GNSS approaches, such as Assisted GNSS (A-GNSS) and snapshot processing techniques (S-GNSS). When compared to conventional pseudoranging, these techniques significantly reduce the overall energy consumption of the UE. Moreover, my survey covers the potential of Doppler positioning techniques leveraging LEO satellite Signals of Opportunity (SOOP), as well as the promising dedicated LEO-PNT systems under development.

IoT-enabled devices have different constraints and application requirements. Therefore, the important trade-off between positioning accuracy and energy consumption is discussed throughout this work. There exists no one-size-fits-all technology that performs excellent in any use case in terms of these two parameters. Thus,  interoperability between technologies is key to enable global energy-efficient communication and positioning applications.