Vitrimer resins have been increasingly considered for circular materials design due to their dynamic covalent networks, yet end-of-life processes remain insufficiently established. In this work, sub-critical hydrothermal liquefaction (HTL) in water was investigated as a chemical recycling pathway for a disulfide-based vitrimer (VR-RD) formulated from EP600 Part A (epoxy), 4-aminophenyl disulfide, and a cardanol-based diluent (LITE 513DF). Batch experiments were performed in Parr autoclave reactor (Model 4560, 300 mL) at a resin-to-water mass ratio of 1:17 under nitrogen. A matrix of conditions was assessed at 310 °C and 340 °C for 35 and 60 minutes, with the 300 mL reactor stirred at 150 rpm. Product streams were separated into gas, aqueous, crude oil, and char; the crude oil was further fractionated by distillation into light, intermediate, and heavy cuts.

Effective depolymerization of the vitrimer network was observed across all runs. Lower temperature and shorter residence time favored liquid formation, whereas higher severity promoted secondary conversion. The most favorable liquid production was obtained at 310 °C for 35 minutes, yielding the highest crude fraction (43.5\% of feed) and a light cut of 11.1\%. At 310 °C for 60 minutes, a reduction in crude oil and an increase in gas were observed, consistent with over-cracking. At 340 °C, liquid yields were diminished and solid/gaseous products increased.

Characterization of products was used to elucidate depolymerization pathways and product quality. Gas chromatography–mass spectrometry (GC–MS) of the light fractions confirmed the presence of aniline, indicating recovery of moieties associated with the epoxy precursor; the 310 °C-60 minutes case exhibited the highest relative aniline abundance (≈44\% within the light fraction). Inductively coupled plasma–optical emission spectroscopy (ICP-OES) of aqueous phases indicated sulfate, consistent with disulfide bond cleavage, and measurable chloride, which displayed contrasting trends with time and temperature. Thermogravimetric analysis (TGA) showed that most chars and heavy fractions possessed reduced thermal stability compared with the parent VR-RD, whereas the char obtained at 310 °C for 60 minutes exhibited a comparable onset temperature, suggesting partial retention or restructuring of thermally stable motifs. The fractionation protocol defined light as <120 °C vapor, intermediate as 120–350 °C vapor (noted as largely lost during handling), and heavy as non-vaporized residue (>350 °C), providing a practical basis for subsequent compositional analysis.

Overall, sub-critical HTL in water was demonstrated as a viable option for chemical recycling of disulfide-based vitrimers. Process severity was shown to govern the balance between depolymerization and secondary conversion, with 310 °C for 35 minutes identified as optimal for maximizing desirable liquids while minimizing over-cracking. These findings provide actionable guidance for scale-up and for coupling HTL with targeted product upgrading.

The growing demand for sustainable construction materials has prompted interest in reusing dredged sediments as an alternative to traditional raw materials in dike construction. Before they can be reused, sediments must undergo the lengthy ripening process, during which they are transformed into stable soil. Accelerating this transformation could significantly improve the feasibility of sediment reuse. This study investigates whether biochar amendment can enhance the biophysicochemical ripening of dredged sediments, focusing on the influence of biochar application rate and particle size.

Dredged material from the port of Hamburg, Germany, that was dewatered and processed at the METHA plant, was mixed with biochar produced by Bio Energy Netherlands from the gasification of wood waste at 800-1000°C for 90-120 minutes. The mixtures contained biochar with varying application rates (2%, 4%, 6%) and particle sizes (<2 mm, 2-5 mm, >5 mm). Over the course of 15 weeks of field ripening, the sediment-biochar mixtures were exposed to natural weather conditions and turned weekly. Biochar amendment introduced additional porosity which increased water holding capacity by 33-72% compared to the control after 15 weeks of ripening, resulting in values of 24-72% DW. The oven-dried COLE, ranged from of 2.2 to 5.4% which represents a decrease of up to 54% relative to the unamended sediments. This improvement can be attributed to the non-plastic behavior of biochar and explains the decreasing shrinkage observed with an increasing application rate. Increasing particle size was correlated to decreasing shrinkage (p <0.05) which could be due to the interrupting effect of coarse biochar particles on tensile load propagation in the rods. A qualitative assessment of the structure development of the experimental variants suggests an acceleration of structure formation with higher biochar application rate and larger particle size when combined with weekly turning. This resulted in a faster breakdown of the dense and platy METHA material into smaller and more aerated aggregates. Overall, the physical ripening of the dredged material was improved with the addition of biochar at increasing application rates and particle size, which promoted a faster stabilization of sediment aggregates and enhanced physical properties beneficial for construction applications.

The occurrence of sulfur oxidation, the main chemical ripening reaction, was evidenced by a loss in the total sulfur content of samples and an increasing electrical conductivity during dry periods. The pH was expected to decrease as a result of the release of protons from this reaction, however this was not observed. Instead, increasing biochar application rates was correlated to a higher pH (p <0.05) and was evidence of the material's buffering capacity which can be attributed to its high functional group and mineral content. The total sulfur content reduced on average by 5% and 22% in the amended samples and the control, and this smaller decrease compared to the control could be explained either by a slower chemical ripening in amended sediments or by measurement limitations. Furthermore, the evolution of electrical conductivity over the 15 weeks of field ripening evidenced the accumulation of chemical reaction products in dry periods.

The influence of biochar on sediment physical and chemical properties, including the increased pore structure, water holding capacity, aeration and buffering capacity, all contributed to creating conditions favorable to microbial activity. A priming effect of biochar application could be observed in the first six weeks of ripening, with high respiration rates, high decomposition rates, and decreasing stabilization of organic matter. In this period, total organic carbon content decreased on average by 30\% in amended samples, compared to only 6% in the control. At the same time, nitrogen content decreased on average by 13% in the samples with biochar, further confirming the high microbial activity. This was followed by a period of decreasing microbial activity until the end of the experiment, which was marked by 14-32% lower respiratory carbon release of the amended samples compared to the control, decreasing decomposition rates and increasing stabilization of organic matter. Thus, biochar application accelerated the decomposition of labile carbon and enhanced the biological stabilization of organic matter in sediments.

These findings suggest that biochar amendment can significantly improve sediment ripening processes and can result in a material with properties desirable for dike construction.

The rapidly growing global demand for heating and cooling is largely met by greenhouse gas-emitting sources and will place increasing strain on future power grids. To meet growing demand and diversify energy sources, novel technologies and sustainable materials are essential. Adsorption heat transformation presents a promising solution for heating, cooling, and heat storage by harnessing sustainable low-temperature or waste heat. This work explores the use of salt hydrates as thermochemical materials and general adsorbents, overcoming their stability challenges by embedding them within porous biochar derived from waste streams. Biochars based on residual wood and chestnut shells were obtained as by-products from two gasification plants and chemically activated with KHCO3 and urea to enhance its pore properties. This treatment significantly increased the specific surface area and pore volume of the chestnut shelland woodbased biochars to 1576 ± 91 m²/g and 0.505 ± 0.01 cm³/g, and 1356 ± 101 m²/g and 0.622 ± 0.05 cm³/g, respectively. The wood-based biochar retained structural features of the original biomass and exhibited pronounced mesoporosity, whereas the chestnut shell-derived biochar predominantly displayed micropores. This structure seems to influence the vacuum impregnation with 80wt.% K2CO3 hydrate, as the structure of wood is still visible and salt is deposited in the nanopores, while chestnut shell biochar appeared coated with a salt layer, determined by SEM/EDS. The resulting composites (subscript ‘ad’) underwent multiple hydration–dehydration cycles to evaluate the stability of the salt hydrates within the carbon support. Initial testing revealed that water uptake and adsorption kinetics improved with cycling, with the wood-based composite showing superior kinetics. This performance is attributed to enhanced vapor transport facilitated by its mesoporous network and large-scale channels inherited from the wood precursor. Long-term cycling of the wood biochar-K2CO3 composite demonstrated stable water uptake of 275 ± 5 kgH2O/kgad over ten cycles, corresponding to a specific water loading of approximately 2.8 molH2O/molK2CO3 . This exceeds the equilibrium uptake of pure K2CO3, indicating altered equilibrium phases due to salt confinement in nanopores. Solution formation was found to significantly influence theoretical power output and energy density of the wood-based composite. Experimental data showed a specific maximum power output exceeding 1 kW/kgK2CO3 for at least ten cycles, and a theoretical energy density of about 1.63 GJ/m³, surpassing that of the pure salt. These findings suggest strong potential for domestic thermochemical energy storage. However, investigation of such systems in residential settings revealed major challenges, including limited efficiency and the availability of more efficient alternatives. In addition to heat storage, the potential for adsorption-based refrigeration was investigated. A composite of wood-based biochar impregnated with 80wt.% CaCl2 hydrate showed enhanced hydration performance, with a maximum water uptake of 1.12 kgH2O/kgad, resulting in a substantial specific cooling effect of up to 2736 kJ/kgad. However, salt solution leakage during hydration was observed, which may limit its use in packed-bed configurations. While the K2CO3 composite delivered a lower overall cooling effect, it demonstrated high specific cooling power, exceeding 550 W/kgad at short cycle times, due to its rapid reaction kinetics. Overall, porous biochar proves to be a promising support matrix for salt hydrates, enabling stable and reversible hydration reactions. The versatility of salt types offers potential not only for novel thermal energy storage systems but also for enhancing existing technologies such as adsorption refrigeration and desalination, particularly by utilizing sustainable low-temperature or waste heat sources

background: To decrease health care’s emissions, the reacquiring of rare earth metals from a complex single use medical device was researched. For a complex single use device (SUD), a cardiac catheter was used, which has electrodes in its tip made of platinum, iridium and palladium. methods: A patent study was done to gain insight into the design and assembly of the catheters, which resulted in the identification of the plastics present. Depending on the electrode type, polyether etherketone (PEEK) or polyamide 12 (PA12) were dominant plastics surrounding the electrode. 5 concepts were developed, all involving a chemical or thermal treatment, which were assessed on their ability to structurally remove these plastics. The treatments used were: nitric acid treatment, sulphuric acid treatment, pyrolysis treatment, toluene treatment and phenol treatment. Treatment removal ability and the purity of the acquired electrodes, were assessed through the use of mass fractions and SEM analyses. Practical aspects, which will be relevant for scale up, such as risk indications, waste created and costs were briefly assessed as well. results: The only treatment that was able to structurally remove all plastics without compromising electrode’s purity, was the sulphuric acid treatment. It is in line with literature that sulphuric acid is the only agent able to structurally remove PEEK at room temperature. Pyrolysis could remove the plastics, but the electrodes were charred. Nitric acid and phenol could only dissolve PA12 but left PEEK structurally present, whereas toluene left all plastics structurally present. conclusion: Reacquiring the electrodes chemically is possible through the use of sulphuric acid. If the spent sulphuric acid can be regenerated, this would be a great benefit since no constant replenishment of acid is required. Pyrolysis could also be investigated further, but a separate cleaning step would be required.

This research investigates the co-liquefaction of Arundo donax and PET plastic to assess their potential as feedstocks for producing bio-oil suitable for bio-pavement applications. The study demonstrates the feasibility of using an invasive species like Arundo donax combined with plastic waste for hydrothermal liquefaction (HTL) to generate bio-oil. The experimental design varied three critical parameters— temperature, residence time, and biomass-to-plastic ratio—to optimize oil yield and gross calorific value (GCV). By employing Response Surface Methodology (RSM) and a Rotatable Central Composite Design (RCCD), the study achieved robust statistical modeling, enabling the identification of optimal conditions across 15 experimental runs and two blank experiments. The results indicated that the char produced from both biomass and PET dominated the product distribution, albeit due to different decomposition mechanisms. PET decomposition primarily yielded solid terephthalic acid (TPA), while biomass char resulted from incomplete lignin and cellulose breakdown. The highest oil yield was obtained under severe conditions, highlighting the significant impact of process parameters on product distribution. Analytical techniques such as FTIR and GC-MS revealed the presence of diverse functional groups and confirmed the decomposition of PET into its monomers. XRD and XRF analyses further characterized the char, identifying key structural components and elemental composition. Statistical analysis showed a significant quadratic relationship between oil yield and GCV, with minimal prediction error, indicating the model’s reliability. The optimized bio-oil exhibited a higher benzene content, suggesting enhanced decarboxylation of PET, which was supported by FTIR data. Rheological testing demonstrated the potential of the bio-oil as a rejuvenator for bio-pavements, with bio-char showing promising properties as a filler. Rheological testing using Dynamic Shear Rheometry (DSR) was conducted to evaluate the bio-oil’s potential as a rejuvenator in bio-pavements. The DSR tests revealed that the bio-rejuvenators effectively reduced the stiffness of aged materials, restoring some of the original flexibility and viscous properties lost due to aging. While the oil derived from pure biomass performed slightly better in this regard, the co-liquefied oil still showed promise, particularly in applications requiring a balance between flexibility and stiffness. Additionally, when bio-char was used as a filler in mastic formulations, it exhibited superior stiffness and rutting resistance compared to conventional fillers, although it was less effective in resisting fatigue cracking. Despite the bio-oil’s lower GCV compared to traditional fuels, the process offers a promising pathway toward sustainable energy production. Continued optimization, particularly of the biomass-to-PET ratio and process conditions, could further enhance the fuel properties of the bio-oil, making it a viable alternative for energy and material applications.

The increasing accumulation of biomass and plastic waste presents significant environmental
challenges, necessitating the development of effective recycling technologies. Hydrothermal
liquefaction (HTL) emerges as a promising solution, converting these wastes into valuable
hydrocarbons, platform chemicals and materials under mild temperature and pressure in the
presence of water. Compared to conventional methods such as pyrolysis and incineration,
HTL offers several advantages, including higher efficiency, reduced emissions, and the ability
to process wet feedstocks without prior drying. Despite its potential, the current state of HTL
technology predominantly involves batch-scale studies, with limited continuous pilot-scale and commercial-scale implementations. Research at TU Delft has significantly contributed to this field, conducting numerous batch experiments with various feedstocks and catalysts. To bridge the gap between laboratory research and industrial application, scaling up to a continuous pilot scale plant is essential. This thesis presents the design of a pilot-scale continuous HTL system for biomass and plastic. This design addresses the major challenges associated with scale-up, providing a blueprint for future advancements in sustainable waste management and resource recovery.
The design process began with identifying three major challenges in continuous HTL: high-pressure solid-liquid slurry pumping, lower heating rates leading to ash formation and reduced yield, and the need for a robust separation system for gas, liquid, and solid phases. The first step involved establishing the basis of design, including selecting the primary feedstock, thermophysical properties, and required solid particle size. A block flow diagram was then developed to define the battery limits. The continuous pilot-scale HTL system was divided into three main sections: feed introduction, reactor, and product separation. All potential options and equipment were evaluated, and the most suitable ones were chosen. Various equipment manufacturers were consulted to understand the suitability and cost implications. Based on the selected equipment, a process flow sheet was generated, followed by detailed sizing of all equipment and finalizing the process and instrumentation diagram. Finally, a cost analysis was conducted to determine the capital expenditure and operational expenditure of the designed plant.
During the design process, it was observed that only one commercially available pump could achieve the required pressure. However, the cost of this pump was extremely high. To address this, a dual piston pump system was developed, effectively pressurizing slurries to the required process pressure (200 bar). This system uses two asynchronously operated hydraulic power pistons and measures the slurry flow rate based on the position of the piston, eliminating the need for flow indicators or control valves. Additionally, a heating system consisting of a tubular preheater and an induction heater was proposed, capable of heating the slurry at a rate of 4°C/s. The separation system was designed with a solid filter, flash tank, and gravity settler to extract bio-crude oil or plastic oil as the final product. Economic analysis showed that operational costs are around 18-21.5% of the capital cost per year, with feed introduction and reactor costs accounting for 85% of the total capital cost. Overall, two design alternatives were developed during the thesis, addressing all identified major challenges. These alternatives provide cost-effective solutions for parametric studies of the HTL process.

As policies and technological advancements accelerate the energy transition, more resources are required to develop sustainable pathways for end-of-life solar modules. Chemical delamination is an attractive option for solar recycling as it has the potential to separate the layers of a module and recover the cell intact. In this work, four primary testing factors were considered to optimize the process: solvent, temperature and residence time with the goal to reduce the reliance on fossil fuel based solvents, improve the reliability of cell material recovery and to attempt to recover cell materials intact. A preliminary solvent screening found three sustainable solvents that could replace current fossil fuel based recommendations. A subsequent optimization under atmospheric conditions found that 60% of the encapsulating EVA could be removed in 3 hours at 160°C. Additionally, this process was observed to be scalable. This research offers a baseline result for chemical delamination that can be built upon to advance the technical and economic viability of this solar recycling method.

In Europe, 20.7 Mt of Polystyrene (PS) was produced in the year 2021, mostly consisting of packaging, insulation, and food utensils. Like many other kinds of plastics, they take hundreds of years to naturally degrade in the environment. To prevent the buildup of plastics in our environment, recycling technology will have to be employed. Current recycling technologies can be divided into three categories: organic, mechanical and chemical recycling. Organic recycling involves the use of biological organisms or enzymes to breakdown plastic into useful materials. Mechanical recycling technologies include processes such as dissolution and conventional mechanical recycling. Among chemical recycling, baseline technology includes
pyrolysis that involves higher temperatures (>500°C) which produces char, gasses, and complex oils. Hydrothermal Liquefaction (HTL) of PS has shown promising results in tackling the problem plastic waste buildup in the environment. This process utilizes water as solvent and subjecting it to mild temperatures and pressures to produce less complex oils that contain building blocks such as monomeric compounds and high value chemicals (HVC). These compounds can then be used as platform chemicals or as source to manufacture new materials, as well as closing the loop on PS waste.
This thesis focuses on the use of catalysis to increase the selectivity for PS conversion through HTL to increase the yields of monomeric compounds and high-value chemicals (HVCs) at lower temperatures (<370°C) than current approaches. In this work, different catalysts were screened and the best performing catalyst was used to optimize the HTL process. The HTL process was optimized using a design-ofexperience (DOE) approach for the following process conditions: temperature (330-350°C), catalyst loading (0-15%) and reaction time (30-60 minutes). The analytical techniques used to characterize the quality of oil as well as determine the amount of chemicals present are: Bomb Calorimetry, Ultimate analysis (CHN-analysis), Gas Chromatography-Mass Spectrometry with Flame Ionization Detection (GCMS-FID)
and Two-Dimensional Gas Chromatography with Flame Ionization Detection (GCxGC-FID).
Results from a screening campaign indicated high yields of oil (90 wt%). Following this, a simple distillation was conducted to separate the lighter fraction from the heavier ones within 90 wt%. Ultimate analysis of the compounds showed high C,H,and N ratios similar to what was found in literature. Bomb calorimetry of the PS-Crude oil product showed of 40 MJ/kg, indicating that oil product is comparable to what is found in literature. GCMS-FID indicated that 17 wt% of styrene was produced from this process,
along with 5.5 wt% of alpha-methyl styrene and other HVCs. The rest of the oil consists of heavy fractions (C-20) which could be go through another upgrading process.
After the screening campaign MgO was chosen as a catalyst to increase the yield of styrene. The yield of oil remain high with 80-90 wt% yield of oil in most cases. Aqueous phase and gas yields remain low (<5 wt%), while char can vary but also remains quite low (<10 wt%). Analysis of Bomb calorimetry showed similar results to screening with an average of 38 MJ/kg. CHNO also showed similar ratios of C,H, and N ratios. When looking at the GCMS-FID and GCxGC-FID, the amount of styrene remained at a maximum of 16-17 wt% with no significant increase. However, results of the research also showed that catalyst does have effect in increasing yield of styrene. Optimization for oil was conducted and optimum point for oil production is at 340°C, 34 minutes and 8% catalyst loading. The research will contribute to the growing body of research into processes for plastic waste valorization and offers more insight into catalytic
hydrothermal liquefaction as well as experimental methodology to separate the oils into its components.

Improving circularity and reducing greenhouse gas emissions can be achieved by utilizing secondary streams like Fischer-Tropsch biosludge, which is typically disposed of in landfills. Biochar, which has accumulated increased interest recently, has significant potential for decreasing carbon emissions and can be created from biosludge. This master thesis was set up as an opportunity-based research project to understand the utilization of Fischer-Tropsch biosludge by the hydrothermal carbonisation process and characterise its product phases; biochar, aqueous phase and gaseous phase. A central composite surface response design was used to conduct experiments to analyse the impact of temperature and time on the characteristics of the phases. Three different levels of the factors have been used. The high ash content and low surface area of the biochar made it difficult to determine a specific use case for the biochar. Yet, the aqueous phase has low ash and possible potential for biogas creation by anaerobic digestion. The gas phase is quantitatively not of significance. Stockpiling the biochar could sequestrate carbon credits and more research can be conducted to find a post- or pre-treatment to improve the biochar for a social-economically benefiting application.