Ongoing PhDs Pieter Billen

Integrated sustainability assessment and optimization of mixed plastic waste treatments

Promoter: Pieter Billen, Co-promoter: Steven Van Passel

To prompt plastic packaging from a linear toward a circular economy scheme, the proposed research aims at analyzing the economic and environmental effects of plastic waste recycling technologies across the value chain. To this end, not only will each state-of-the-art recycling technology be assessed for the different waste plastic fractions on the market separately, for the first time decisions regarding the joint selection of pathways will be supported by a holistic multiobjective optimization. The research plan involves a market study, material and energy balance establishment and subsequent life cycle assessment and techno-economic analysis of various technologies, as input for the integrated optimization. The system boundaries will initially be set from waste to recyclate (or energy as reference), and at the Flemish borders, but will be extended to include virgin plastics production and imports and exports at later instance. In this way, we will support Flemish industrial stakeholders, already strongly represented in the plastic packaging sector, in identifying and judging investment opportunities. Additionally, by benchmarking against a profit-for-all model we will develop, techno-economic bottlenecks within the value chain are spotted, and may be relieved by policy incentives to achieve high environmental benefit. The outcomes of this study will prepare the Flemish industry for its role at the forefront of a circular plastics economy.

NADES as new green media for (bio)catalysis

Promoter: Pieter Billen, Co-promoter: Iris Cornet

The proposed research aims at increasing the application potential of natural deep eutectic solvents (NADES) by predicting and understanding how they affect biocatalytic reactions. NADES are mixtures of two or more primary metabolites, whereby charge delocalization by hydrogen bonding between the constituting molecules hinders crystallization at or around room temperature. Their biodegradability, low toxicity, negligible volatility, low price and tailorable properties make them an alternative for common organic solvents as (biocatalytic) reaction media. To date, we posit that industrial application is hindered by a lack of knowledge regarding the effect of NADES on enzymatic (or in general catalytic) reactions. More specifically, an approach to distinguish complex concurring phenomena such as solvation of reagents, enzyme denaturation and mass transfer is currently not available, making even the interpretation of experiments challenging, if not impossible. Therefore, we propose to model and experimentally validate the solubility and solvation energy of reagents in NADES, next to experimental screening and interpreting kinetics of targeted lipase reactions in NADES, benchmarked against classical solvents. Moreover, all predictive and post-experimental modeling will be converted into freely accessible software, aiming at (i) guiding the screening of NADES for application by industrial partners, and (ii) extending the dataset with subsequent further model training.

AirTech'byDesign: Injecting Technology into Urban Design in the battle against Street Canyon Pollution.

Promoter: Maarten Van Acker, Co-promoters: Pieter Billen and Tom Tytgat

The poor air quality in our cities is currently at the centre of public debates on health living conditions and at the pinnacle of innovative urban planning and mobility policies. Especially, so-called 'street canyons' represent the most problematic arteries of our cities: these are narrow inner-city roads that are flanked on both sides by a continuous row of (high) buildings. In these street canyons, the air quality is often below the European standards and those of the World Health Organization. Both urban design and technological solutions, such as photocatalyst, have proven to be a powerful tools for improving the air quality and overall health. However, this research is often restricted to a single domain, sector or discipline (either bioengineering or urban design) and is often limited to the analysis of the impact of a single parameter on air quality. Secondly, the most well-known measures focus on the reduction of emissions of pollutants and are situated on a larger scale planning and policy level. At the local scale level of traffic intensive locations and the so-called street canyons, systematic research on the possible contribution of urban design and technological interventions to improve the air quality is lacking. Moreover, a group of pollutants under less public scrutiny, volatile organic carbon (VOC), are less susceptible to traffic regulations. The treatment of paving, walls and facades with a photocatalyst have proven to contribute to improve the air quality. However, in street canyons the airflow rates are often low for an optimal performance of these photocatalysts. Alterations of the urban design (that improve the air circulation and the integration of UV lightning) can seek VOC abatement in urban street canyons with minimized environmental burden. In conclusion, in terms of air quality on the level of street canyons, there exists a fundamental disciplinary schism between environmental and urban design sciences. 

Dealing with the spatial distribution of air pollution and high threshold to bridge technological innovation with urban planning, this research project aims to combine environmental and design sciences.  Therefore, the Research group for Urban Development (Design Sciences), DuEL and BioGEM (Engineering Sciences) decided to team up to tackle together this pregnant challenge. 
The scientific challenge grasped in this project is threefold: (1) Understand the spatial and molecular distribution of VOC in urban environment, with  focus on street canyons, (2) Maximize the effect of urban design changes to improve the health effects of street canyons by incorporating photocatalytic abatement technologies; (3) Formulate design guidelines for improvement of air quality in street canyons based on LCA metrics, and extrapolate the methodology to future technological improvements. Together these challenges constitute an opportunity to significantly lower the threshold for future developments to improve the health conditions in street canyons. 
Divided over four Work Packages and four years, this multidisciplinary approach of this challenge calls for a combination of methodologies, ranging from literature review, to research by design, over modelling and case study research. The Turnhoutsebaan in Antwerp is selected as case study, being representative for typical Flemish street canyons in terms of structural characteristics (length, height over width ratio), traffic density, demonstrated high air pollution levels and the availability (or lack) of green infrastructure.

CycloPUR – Fundamental insights in reversible polymerization of polyurethanes

Promoters: Pieter Billen, Christophe Vande Velde 

Polyurethanes (PU) are versatile group of polymers, increasingly being used in diverse applications; for instance in mattresses, building foams, automotive and adhesives. PU is a cross-linked polycondensation polymer, in which polyols (polyhydroxyl alcohols) react with highly reactive diisocyanates. As a thermoset (they do not have a melting point), PU is difficult to recycling, and the current state-of-the-art mechanical recycling results in low-value materials. Nonetheless, chemolysis (chemical depolymerization) has been explored since decades as an alternative, yet was only commercially developed for polyol recovery. The absence of a working technology for recovery of diisocyanate derivatives is largely due to the complexity of these molecules, and a lack of knowledge regarding their chemical fate in a chemolysis process. The proposed research aims at understanding how various isocyanate derivatives are formed, and how they react upon alcoholysis, by experiments using model monomers. This knowledge, together with experimental and computational insights in mixing/solubility, will be exploited to create a bottom-up chemolysis process for model polyurethanes. The outcome of the proposed study will be used in subsequent chemolysis of realistic waste polyurethanes, with recovery of both monomers as significant technological novelty. Additionally, the resulting knowledge may be transferred in the future formulation of new polyurethanes with biobased alternative monomers.