Adipic acid (AA), a critical precursor for nylon-6,6 and other industrial applications, is currently produced at over 3 million tons annually, with projected revenues reaching $6 billion by 2030. However, an alternative to the dominant industrial process, accounting for 95% of global production, has been sought due to inefficiency and significant environmental impact. This conventional route relies on petroleum-derived benzene as a feedstock and involves multiple hydrogenation and oxidation steps, notably utilizing nitric acid, which produces stoichiometric amounts of nitrous oxide (N₂O), a potent greenhouse gas. Furthermore, the high energy feedstocks like benzene, hydrogen, and nitric acid contribute significantly to Scope 3 emissions.

Given these concerns, there is a strong incentive to develop more energy-efficient and environmentally suitable processes. This thesis addresses the gap in comprehensive techno-economic assessments of emerging alternatives, which often overlook practical implementation challenges such as downstream separation, feedstock pretreatment, and overall carbon footprint.

The overarching research question guiding this study is: "How do various electrochemical based alternatives to current AA production compare on an economic and emissions basis from a process systems modeling prospective?". To this end, two promising alternatives were selected for evaluation through the key performance indicators of; profitability in the form of minimum selling price (MSP), emissions based on kg CO₂, and material efficiency based on the excess ratio of theoretical main feedstock to actual main feedstock.

The first modeled process was that of the conventional route. This was done to ensure a consistent feedstock price component in the final adipic acid cost across all assessed production methods, thereby providing valuable validation for modeling assumptions. Furthermore, it serves as a benchmark for comparing the economic and emissions performance of various electrochemical-based alternatives, offering insights into their relative strengths and weaknesses. The results attained were consistent with those of literature, with a minimum selling price of $1.58/kg

The first alternative route employs an electrocatalytic oxidation cell to replace the nitric acid oxidation step of the conventional process. Experimental work of previous researchers was used to create an approximate model of the cell and the electrodialyzer used for the recovery of KOH electrolyte. This was implemented within Apsen Plus along with upstream and downstream processing. The resulting model and subsequent TEA predicted an adipic acid price of $2.33/kg or a 45% increase over the results of the conventional route. However, assuming the use of renewable electricity, the CO₂ equivalent emissions dramatically reduced by half when compared to the conventional process.

The second alternative was the use of biomass based fermentation and subsequent electrochemical oxidation to produce a adipic acid alternative of similar value to industry. Once again, the experimental work of previous researchers was used to predict a final minimum selling price of around $3.97/kg; however, these results are highly susceptible to variations in input parameters. Both alternatives showed lower emissions when compared to the conventional process.

The transition toward renewable energy systems requires flexible energy conversion technologies capable of responding to intermittent power availability. A modular alkaline water electrolysis system offers a promising pathway for such flexibility, as it can dynamically adapt its production capacity to match the fluctuating output of sources like photovoltaics. While alkaline water electrolysis is technically mature, its deployment as a large-scale energy storage solution remains economically unattractive under current market conditions. To improve its viability in this role, targeted optimization of system operation and sizing is essential, particularly in direct coupling scenarios where real-time control is required to ensure both efficiency and safety. Existing literature has largely focused on component-level improvements, whereas system-level behavior under variable conditions remains underexplored.

This thesis presents a physics-based 0-D digital twin of a modular AWE system designed to enable optimal operation under varying power conditions. The model explicitly accounts for electrochemical behavior, heat generation and dissipation, and gas crossover dynamics. To the best of the author's knowledge, this is the first model that integrates these coupled physical phenomena within a modular alkaline electrolysis architecture. The model is validated against experimental data reported by Brauns et al., ensuring accurate representation of steady-state and transient system responses.

Based on the steady-state behavior across a range of voltages, flow rates, and temperatures, a novel voltage tracking strategy is developed that defines a safe and efficient operating voltage window. This approach enables the controller to adjust the number of active stacks and regulate operating conditions in real time, based solely on the measured busbar voltage. The method avoids direct intervention at the stack level, allowing for simple and robust implementation even in systems without power electronics. The digital twin thus serves as the foundation for a low-complexity yet effective control strategy and sizing methodology tailored to directly coupled photovoltaic systems. Its performance is evaluated through dynamic simulations using measured solar irradiance and ambient temperature data from multiple real-world locations. Compared to a conventional system equipped with maximum power point tracking (MPPT), the proposed modular configuration achieves approximately 45% higher power utilization and hydrogen yield over the course of a year, demonstrating a clear performance advantage under real-world solar conditions.

Coffee is a beverage that millions of people around the globe enjoy on a daily basis. Although coffee consumption is becoming increasingly popular, the cultivation of coffee is under threat of: climate change, economic inequality in the coffee value chain, and unsustainable coffee cultivation and processing. Studies predict that all land currently used for the cultivation of Arabica coffee might become unusable by 2080 because of the sensitivity of the crop to changes in temperature, humidity, and the amount of UV irradiation. A shift is needed in the coffee value chain to ensure the livelihood of the current 25 million smallholder coffee farmers responsible for 70 to 80\% of coffee production worldwide. The Climate Smart Coffee Program in the state of Kerala in India focuses on making coffee cultivation and processing more resilient, sustainable, and economical in the future. This is accomplished by conducting research on more sustainable agriculture (such as agroforestry to preserve and nurture valuable land) and reduce carbon emissions and waste generation during the processing of coffee.

The focus of this study is on the use of biomass residues produced during the processing of coffee to meet the energy needs of coffee processing units in the Wayanad district in Kerala. The goal is to make the processing of coffee less carbon-intensive, produce less waste, improve the quality of the coffee, and make coffee processing less energy dependent. This study presents a technoeconomic analysis for a novel approach to the use of these coffee processing mill residues (CPMRs) by using a combination of gasification to produce syngas, a solid-oxide fuel cell (SOFC) to transform the syngas into electricity and heat, and the use of an afterburner to further optimize the energy efficiency of the biomass plant. The biomass plant's goal is to replace the current energy need of the processing units: electricity from the grid and liquefied petroleum gas (LPG).

The results of the technoeconomic model show that the biomass plant produces enough electricity and heat to cover the energy needs of the coffee processing unit that supplies the biomass material. With an hourly feed rate of 1295 kilograms of biomass material the plant produced 2,681 kW of electricity with an electrical efficiency of 41\% and an overall system efficiency of 62\%. The financial analysis of the biomass plant yielded a capital expenditure of \$ 24.1 million, or 8,984 \$ per kWh of electricity generated. The levelized cost of electricity (LCOE) of the plant was 0.45 \$/kWh. A sensitivity analysis revealed that by optimizing the operating conditions of the biomass conversion plant, the LCOE could be decreased to 0.35 \$/kWh. Improving the capacity factor would have the most substantial effect on the costs of the system, increasing the days of operation from 90 in the base model to 300 could result in an LCOE as low as 0.12 \$/kWh.

The percentage of electric vehicles (EVs) in the automotive sector is expected to quadruple by 2040, causing concern regarding the material supply required for the production of lithium-ion batteries. Currently, a substantial part of these materials, such as cobalt and lithium, are subject to non-circular economies, have a substantial environmental impact and are mined in countries with unstable political situations.
Up until now, numerous companies have attempted to resolve these issues through the use of pyro- and hydrometallurgical recycling methods. However, they are yet to meet the mandated recycling goals put in place by the European Commission. This enhances the urgency for the development of a novel, efficient and scalable technology for the recovery of valuable material from spent lithium-ion batteries.
In order to achieve such a development, this study proposes to incorporate Bipolar Membrane Electrodialysis into the standard hydrometallurgical recycling approach. During the course of this research, a prototype of this technology was realized and used to investigate its effectiveness. For practical reasons, the research focused exclusively on the metal and acid recovery from leached LCO cathode material.
Within the subsequent experimental phase of this research a critical issue was identified. Namely, the tendency of divalent cobalt ions to precipitate in non-acidic media. The resolution to this issue required the incorporation of Donnan dialysis into the built BPMED setup, which was used to adjust the acidity of the solutions within the different electrolytic compartments.
Ultimately, this approach led to the respectively recovery of 14 and 22 percent of the lithium and cobalt initially present in the feed solution. Simultaneously, the study recovered a significant amount of the starting leaching agent in the form of 0.6 M nitric acid. Whilst additional optimizations are required to improve the recovery efficiencies, the study successfully demonstrates a proof of concept of the proposed solution.

The intensification of human and industrial activities since the Industrial Revolution has led to a significant increase in global greenhouse gas emissions, posing a threat to life on our planet. As the transportation sector contributes to 23% of global CO2 emissions, it is imperative to reduce its carbon footprint. Developing a worldwide sustainable biofuel production chain is crucial for this purpose. The Biomass4transport project, a collaboration between TU Delft and the Biomass Technology Group, aims to achieve this by focusing on the production of second-generation biofuels in the Dutch context.

In this context, a techno-economic analysis of a Power and Biomass to Liquid (PBtL) plant that incorporates water electrolysis, pyrolysis oil gasification, and synthesis gas upgrading for gasoline production is presented.
The PBtL plant processes 5000 kg/h of pine wood-derived pyrolysis oil, which undergoes gasification in an oxygen-blown entrained flow gasifier. Subsequent purification steps include cyclones, filters, for the removal of particulate matter and solid ZnO sorbents for the removal of H2S. A solid oxide electrolysis cell produces hydrogen and oxygen streams; the former adjusts the H2:COx ratio before syngas upgrading, while the latter serves as an oxidizing agent in the gasifier. The synthesis gas is converted to dimethyl ether (DME) in a one-step direct conversion membrane reactor, enabling in-situ water removal and enhanced conversion performance. In a subsequent reactor, DME is upgraded to a hydrocarbon mixture, which is further processed to obtain gasoline and LPG.

The process has been modelled by integrating Aspen Plus, Matlab - where an isothermal plug flow membrane reactor model has been coded - and Excel. Material recycling and heat integration strategies have been employed to enhance the plant’s performance in terms of product yield and energy efficiency.

Finally, an economic analysis entailing the calculation of the Net Present Value (NPV) of the plant has been conducted, to assess the conditions under which the plant becomes profitable.

The process has an energy efficiency of 51.8% but could potentially rise to 61.8% with an optimized strategy for hydrogen extraction from the sweep gas of the DME membrane reactor. Due to the absence of CO2 extraction along the process, the carbon efficiency of the process is 95.7%. Both values are higher than the ones of PBtL processes based on hydrogen-enhanced methanol-to-gasoline processes found in literature.

Additionally, the economic analysis showed that the plant is not profitable in the current market conditions. However, with a decline in the price of electricity and/or a reduction in the taxation rate for gasoline, the plant could become profitable, as shown by the sensitivity analysis on the NPV.

Many of the high-performance portable electronics and electric vehicles (EVs) on the market depend on lithium-ion batteries (LIBs) as their primary energy source. If millions of EVs are to be manufactured each year, rigorous resource management for EV battery manufacturing, as well as a material- and energy efficient 3R system (reduce, re-use, recycle), will undoubtedly be required to assure the future sustainability of the automotive industry. Since lithium is only
found at a few locations around the world, there is an inherent danger from a geopolitical standpoint when it comes to accessibility. Political turmoil or instability in the nations controlling these lithium stockpiles may have a detrimental impact on world supply. Spent LIBs can be viewed as an alternative source of lithium. Considering that used LIBs contain toxic organic electrolytes and heavy metals, recycling them reduces resource waste and environmental contamination. Due to the difficulty of handling its complex composition and distribution, most recycling efforts and industrial processes focus solely on recycling the cathode and ignore the proper treatment of the aged electrolyte. Recovery of the electrolyte is crucial for achieving the legally mandated recycling efficiency set by the European Commission, as the electrolyte typically comprises of 10-15 wt% of a LIB cell. Therefore, this study explores the feasibility of
using crown ethers (12C4 and 15C5) to extract and recycle the lithium salt (LiPF6) from the electrolyte of spent LIBs. The extraction efficiency of these crown ethers is examined across various extraction conditions to identify the most favorable extraction condition. The results and findings obtained from the conducted experiments reveals that the extraction efficiency correlates with the mole ratio between crown ethers and lithium, up to a certain threshold (6:1 for 12C4 and 12:1 for 15C5) where further increase in mole ratio does not significantly enhance the extraction yield. The extraction yield displays an inverse relationship with temperature, indicating an exothermic extraction process that favors lower temperatures. Remarkably, varying the extraction time within the 5 to 30 min range exhibits negligible influence on extraction yield, suggesting rapid kinetics in the formation of the crown ether-lithium complex. Between the two crown ethers tested, 12C4 emerges as the more suitable option, achieving extraction yields of up to 60%. In contrast, the use of 15C5 necessitates larger quantities compared to 12C4 to achieve equivalent extraction yields. Consequently, using 15C5 not only increases the cost but also diminishes the overall process efficiency. Further research is proposed to conduct experiments for the extraction of the organic solvents in the electrolyte using CO2 and to develop methods for separating the extracted lithium from the crown ether without compromising the integrity of the crown ether, allowing for its reuse in subsequent extraction processes.

Regulations and investments in new technologies for biofuel production as an alternative to fossil fuels have boosted in the last years due to concerns about climate change and anthropogenic CO2 emissions. A valuable supply chain of biomass for biofuel production is one the most significant factors, in order to support the market’s demand. A promising feedstock that is widely available and considered a residue can be Namibia’s encroacher bush (EB). Namibia is facing an environmental crisis with bush encroachment, where EB takes over grasslands, reducing biodiversity and groundwater availability. A thermochemical process that can take advantage of EB can be Hydrothermal Liquefaction (HTL). With HTL, biomass feedstocks are liquefied under hot compressed water, producing bio-oil (BO), biochar (BC), an aqueous phase (AP) and gases. Catalytic HTL is a more attractive pathway, due to the increased BO yield and quality. To this day, there has not been a study investigating the potential of catalytic HTL with EB, thus the present MSc Thesis will attempt to close that knowledge gap and provide state-of-theart insight.

To achieve that, Acacia Mellifera from Namibia was tested in sub-critical HTL conditions. In particular two campaigns were formulated with two different goals. The first one, focused on the selection of a suitable catalyst among 4 different categories of catalysts (zeolites, alkaline earth metals, lanthanides and transition metals). The catalysts performance was evaluated by comparing
the Energy Recovery (ER) under same operational conditions. Then, the catalyst with the highest ER was used in the second experimental campaign using a Desing of Experiments approach. This approach had the goal to optimize HTL reaction conditions -temperature, residence time and catalyst loading- for maximizing BO yield and energy content. Central Composite Design (CCD) of experiments was used, with the parameters ranges being 250-340oC, 5-60mins and 0-10wt%, respectively. Selected BO and BC samples from both campaigns were then characterized using various methods.

The HTL experiments with EB revealed that BO from EB could be produced. The highest ER obtained from the catalyst screening campaign was 41.1% . Main organic compounds found in all the BOs were phenolic derivatives, alicyclic ketones and fatty carboxylic acids. Using the best performing catalyst based one ER, the CCD model indicated that the optimum conditions for maximizing BO yield were 340oC, 60 minutes and 5wt%, which yielded 27.0wt% BO. However, the 330oC - 60 minutes - 7.5wt% point gave both the highest yield and highest ER, 28.5wt% and 46.2% respectively. The CCD also reduced the O content in the BO samples by 54%. Finally, BC samples showed fuel characteristics similar to lignite and low concentration of heavy metals, making them legitimate alternatives for solid fuels or soil amendment.

The global temperature rise has pushed governments more into finding ways to reduce CO2 emissions, by increasing the use of renewable fuels. Lignocellulosic biomass (wood, forest residues, agricultural residues) is a renewable fuel that has still not been utilized to its full potential. That is because it lacks properties such as homogeneity, high volumetric energy density and low moisture that its main fossil fuel competitor -coal- has. Therefore, a type of pre-treatment is needed for these disadvantages. Torrefaction, a process of heating biomass (200-300 oC) in an inert environment (no combustion), provides a product with improved physicochemical properties: reduced hydrophobicity, easier grindability, homogeneity, reduced microbial activity and increased calorific value. However, it is not enough to torrefy the biomass, as it needs to be densified in order to be utilized. With the process of pelletizing, a type of densification, torrefied biomass becomes compact and can be considered as bio-coal. While pelletizing is influenced by many parameters (moisture content, die pressure, torrefaction temperature etc), herbaceous types of biomass such as wheat straw, hay, reeds and grass, still cannot produce quality pellets without the addition of a binder. Typical organic binders such as starch, lignin and sawdust can either be expensive or biologically degrade in storage conditions. That is why addition of plastic binder should be considered. The aim of this report was to investigate how quality torrefied pellets from herbaceous biomass can be produced with the addition of plastic binder in a commercial capacity. Wheat straw and woodchips were used as feedstock, while polyethylene resin was the plastic binder. The biomasses were torrefied at 240 oC and 270 oC on the Torrgreen facilities, via a pilot-scale packed bed reactor, which recycles the volatiles from torrefaction for inertization and pelletized with a 100 kg/h pellet mill. For the torrefied wheat straw, a design of experiments was formed, to investigate how 4 parameters for pelletizing (torrefaction temperature, moisture content, plastic binder addition and pellet diameter) improved mechanical durability. Results indicated that 5% of plastic improved durability and pellet formation in total, while higher torrefaction temperature weakens the pellets and aggravates pellet formation. The highest durability achieved was 90.3%. Torrefied wood chips were pelletized for reference and showed low durability, mostly due to inability of the pelletizer. Water immersion tests on the straw pellets showed that higher torrefaction temperature increased hydrophobicity a lot, while plastics also had a positive effect. Comparison of the straw pellets produced with conventional wood pellets revealed that the former lack in mechanical durability and are high in ash content, making them incompliant with current standards. Overall, inclusion of plastics in pelletizing of torrefied herbaceous biomass, demonstrated very positive results and improved their quality, while making the operation smoother, but for scaling up and keeping the whole process sustainable a polyethylene (or other plastic) waste stream should be utilized.

Transition to renewable and alternative energy sources has become one of the most important subject of the decade. In The Netherlands today, 11.1% of the primary energy demand is obtained from renewable energy and the biomass accounts for 54% [1]. Another promising material for value added chemical synthesis is carbon dioxide. By utilization of CO2, the production of valuable chemical materials such as methanol, formic acid that can be used as a fuel, heat or power source and reducing the greenhouse gas effect by lowering emission levels will provide industrial and environmental advantages at the same time. Formic acid, used in the agriculture, pharmaceuticals and textile, is a key chemical that can also be used in energy conversion processes. In the current industrial practice, formic acid is produced by carbonylation of methanol with carbon monoxide. However, methanol is another value added chemical that is used in energy production, hence expensive for the process. Therefore, researchers started looking into alternative methods. Biomass and carbon dioxide utilization methods are two of them. In this thesis study, 10 kton and 100 kton annual production of 85 wt.% formic acid from wet oxidation of glucose and catalytic reduction of carbon dioxide, have been modeled and a techno-economic analysis is carried out. Additionally, the processes of obtaining glucose from lignocellulosic biomass and carbon dioxide from syngas by pre-combustion capture are also simulated. ASPEN Plus V8.8 process flowsheeting package program has been used for the simulations. From the results, in energy analysis biomass based formic acid synthesis process showed higher efficiency than CO2 based production. When the hydrogen peroxide and oxygen based biomass wet oxidation routes are compared, it is observed that oxygen based operation is more efficient than hydrogen peroxide based conversion because of lower utility requirements. It was determined that biomass based formic acid production can be economically profitable, but only for large scale wet oxidation via oxygen together with the sale of by-products obtained in pre-treatment process. On the contrary, no profit was obtained by the hydrogen peroxide route. In carbon dioxide utilization route, the breakeven selling price (BSP) of the formic acid was computed to be 7% more than the current market price. In order to improve the process, two case studies were created. In the first case, economically the most suitable reactor amount configuration is determined. However, the process was still not profitable. In the second case study, two times more active catalyst, Au=Al2O3, has been utilized. The process took half the residence time of the previous case and BSP value determined to be 2.6% lower than the current market price. Also, slight increase in efficiency is observed. In conclusion, more research should be done and experiments regarding reaction and intermediate substance performances should be conducted, in order to simulate the process more in detail. However, despite the uncertainties, in this era where the transition to greener energy production through the use of biomass and the reduction of carbon dioxide emissions have been made a definite target by the governments, the synthesis methods studied, will gain importance as the purposes of formic acid use increase.

The increase of the average world temperature, as a result of greenhouse gasses, is one of the greatest challenges the world is currently facing and will be facing in the future. One of the many efforts to reduce the increase of carbon dioxide, is to decarbonize the gas network by replacing natural gas with renewable gasses like green gas. Since the current gas network is not always suited for the injection of big green gas volumes, especially during summer periods, the process of decarbonizing the natural gas network requires adjustments of the current functioning of the gas network. Several technical adjustments for obtaining an increased green gas injection capacity exists, although, up to now, the potential green gas injection capacity obtained per solution was not known. Within this study, a dynamic gas network simulation model was developed wherein different gas network function strategies can be explored to obtain the potential green gas injection capacities. With the developed dynamic gas network simulation model one is capable to implement and simulate different gas distribution network configurations, specify green gas suppliers on the location of choice, simulate different gas demand scenarios and consumer profiles, adjust the city gate station pressure used for simulations of static- and dynamic pressure management, and to model the injection of excess green gas into a storage- and from the storage into the network. Within this study, the gas distribution network of Northeast Friesland, The Netherlands was analyzed on its green gas injection capacity after applying static pressure management, dynamic pressure management, and a pressure management strategy combined with storage. The gas network of Northeast Friesland was explicitly chosen since currently, green gas injection problems are experienced within this network. Following the results obtained from the simulations, a city gate station inlet pressure - demand table was defined. Within this table, the total gas demand measured within the network was plotted against the minimum city gate station inlet pressures, while still in compliance with the lower pressure boundary condition. Using this table, the optimal period to statically decrease- and increase the city gate station inlet pressures from 8.3 to 6.5 bar and from 6.5 bar to 8.3 bar, appeared to be respectively 1 May and 1 October. By changing the pressure to 6.5 bar, a safety margin of 1.5 bar was taken into account. For both static- and dynamic pressure management, green gas injection capacities ranging from 400 to 1600 m³/h, divided over three green gas suppliers, were analysed. The results were depicted against the total injectable hours, providing insight in the maximum green gas injection capacity while remaining eligible for the Stimulation of Sustainable Energy Production (SDE+) subsidy. Since with dynamic pressure management the city gate station can inject at lower inlet pressures, dynamic pressure management results in a greater green gas injection capacity. To point out, static pressure management provide 450 m³/h green gas injection capacity, whereas dynamic pressure management provides 650 m³/h green gas injection capacity without experiencing any injection problems.