Transitioning the global energy system from finite fossil fuels towards renewable energy resources is probably the most pressing issue of the 21^st century. To mitigate the variability in typical sustainable electricity generation technologies, such as solar and wind power, on-demand generation methods are needed, powered by renewable sources such as biomass. As biomass may be converted into conventional types of fuel, methane (CH₄) for example, it could additionally help minimize the financial investment needed to complete the energy transition.

This thesis designs and analyzes a process for making Liquefied Natural Gas (LNG) from Dutch domestic biomass resources, modeled in Aspen Plus process simulation software. Specifically, the process design combines gasification of biomass pyrolysis oil, desalination and electrolysis of sea water, and Sorption-Enhanced Methanation, as well as cryogenic liquefaction to produce bio-LNG, a renewable liquid fuel. This bio-LNG may then be used to generate electricity, to fuel heavy road traffic, or whatever application might be found for it.

Based on a 6 kg/s intake of wood pyrolysis oil, nearly 12 t/h LNG can be produced, in addition to useful side products such as sea salt and drinking water. Economic evaluation yields a project NPV of nearly €4 billion, and an IRR of 36.7%. Furthermore, the LCOM of this process is lower than several biomass-to-X processes, at €190/MWh.

Traditional carbon capture processes require large amounts of energy to regenerate the solvents used. Recent research has proposed to decrease the energy requirements of this process by integrating the system of carbon capture and electrochemical conversion, removing the need for the traditional regeneration step. The integration of these two steps involves the use of the same medium for both the carbon capture solvent and for the electrolyte for electrochemical conversion of the captured CO2. The proposed methodology takes advantage of the inherent elevated temperatures resulting from ohmic losses in the electrochemical system, especially at an industrial scale and helps optimize the efficiency of the conversion process. This study investigates the use of non-aqueous solutions of 1:4 choline chloride to ethylene glycol coupled with monoethanolamine as the medium for this process, particularly focussing on its use as the catholyte in this system. Specifically, this project targets the production of carbon monoxide using silver cathodes in small laboratory scale compact H-cells, with an anolyte of 0.5 M sulphuric acid and a Nafion-117 cation exchange membrane separating the compartments. Different operating conditions, including pulsed electrolysis, are utilised to attempt to modify the levels of carbon monoxide production and stabilise the system for long term operation.
Initial investigations into this system found that carbon monoxide could successfully be produced at constant reduction potentials vs. Ag/AgCl of -1.5 V and -1.7 V for approximately 10 minutes of operation when operating at 65 °C. Pulsed electrolysis has been proven to be able to increase the stability of carbon monoxide production for up to an hour of operation. The study found that the most promising conditions for the pulsed electrolysis are using positive anodic potentials vs. Ag/AgCl of either + 0.1 V or + 1.5 V for between 5 and 40 seconds in combination with cathodic potentials vs. Ag/AgCl of - 1.5 V. The faradaic efficiency of carbon monoxide production was able reach up to 24 % for one hour of operation with relatively stable production profiles when using pulsed electrolysis.
The results of this project show that this system can produce the desired carbon dioxide reduction reaction and with the use of pulsed electrolysis this can be achieved for at least one hour with faradaic efficiencies of carbon monoxide production greater than 20%. These findings showed a better overview for the next stage of this research. In particular, further work involving longer term operation of the cells is of interest after this research.

This report presents an extensive investigation into the fluidization dynamics within a cold flow nozzle jet air-blown conical fluidized bed, a configuration that remains relatively underexplored in fluidization studies. The primary focus of this research was to understand the behavior of the bed under varying operational conditions, particularly at different bed filling heights and flow rates.

Hydrogen (H2) is an important substance for clean energy storage, but the financial feasibility of large-scale water electrolysis remains a challenge. A promising approach to improve the economics of industrial electrolyzers is the anodic production of hydrogen peroxide (H2O2) during alkaline water electrolysis. This dual production could attract H2O2 producers and increase the value of electrolyzer output. However, achieving high H2O2 selectivity is difficult due to competition with other oxidation products. Recent studies have shown that incorporating polytetrafluoroethylene (PTFE) on carbon fiber paper (CFP) electrodes can enhance H2O2 production. Xia et al. suggest that PTFE's hydrophobicity confines O2, driving the reaction toward H2O2. However, PTFE’s inert characteristic makes complete coverage of the electrode impractical. Vogel et al. further noted that the O2 bubble perimeter, which attracts more OH-, a key reactant for H2O2, could also increase H2O2 yield.

This project explores the effects of varying PTFE applications on carbon electrodes, focusing on three approaches: increasing the PTFE perimeter patterns (P1<P2<P3<P4), increasing the PTFE area patterns (A1>A2>A3>A4), and dip-coating the electrode in PTFE emulsion. The study uses a two-electrode system in a flow cell with a K2CO3 electrolyte, observing performance lifetime via chronopotentiometry and measuring H2O2 yield through permanganate titration. SEM and EDX are also used for electrode observation.

Results show that increasing the PTFE perimeter (P1 to P2) enhances H2O2 yield due to better O2 bubble formation, but further increases (P2 to P4) have little effect. Increasing the PTFE area patterns generally shortens operational lifetime and reduces H2O2 yield, with A2 and A3 showing similar results due to potentially non-optimal spacing. PTFE dip-coating leads to rapid performance degradation, confirming that PTFE’s lack of active sites makes it unsuitable for initiating reactions. Overall, optimizing PTFE surface area is improving H2O2 production in alkaline water electrolysis over than perimeter or dip-coating.

The problem of global warming is becoming every day more and more pressing, leading to the necessity of reducing harmful emissions especially in the shipping sector. Most ships sail with Internal Combustion Engines, reason why it is beneficial to keep using this system, with the prospect of being able, though, to cut down on the emissions. This can be done implementing new fuels, such as PODE and methanol. These two fuels can largely reduce the emissions without the need for major changes to the engine system. Also, they can be produced in an ”eco-friendly” way, reducing the emissions also during the production process. In this study, the working characteristics of a dual fuel engine, considering methanol and PODE are analysed, as well as the production process of PODE from methanol, process that happens on board of the vessel itself. For the dual fuel engine the analysis showed that different ratios of methanol and PODE can be considered for the dual fuel engine and that this system can deliver the required power output. The plant design resulted in a plant consisting of two reactors and a separation system. At last, the necessary fuel can be produced by a plant that is small enough to fit on the ship and not have to reduce the capacity of the vessel significantly.

Driven by the need to reduce the destructive and irreversible effects of global warming caused by greenhouse gas emissions, the world is transitioning away from fossil fuels towards renewable alternatives. This transition brings the growing challenge of intermittency, as the availability of renewable energy from wind and solar fluctuates. This creates a big challenge for the chemical industry, which still relies on a continuous supply of energy and materials. Therefore, the chemical industry must adapt by using flexible processes capable of handling these fluctuations.

One application of flexible chemical processes is blue hydrogen production. Hydrogen is essential for decarbonizing hard-to-abate sectors such as heavy transport, steel, and chemical industries. While green hydrogen, produced from renewable electricity, offers a zero-emission solution, its supply is typically variable due to the intermittency of renewables. Flexible blue hydrogen production, made from natural gas with carbon capture and storage, can provide a reliable back-up supply, ensuring a stable supply of hydrogen for industrial processes with steady demand. By integrating flexibility into blue hydrogen production, the chemical industry can enhance system stability and support the transition to a sustainable hydrogen economy.

The aim of this research is to evaluate the potential of flexible natural gas reforming with carbon capture and storage to stabilize the intermittent supply of green hydrogen, ensuring a stable supply of hydrogen for downstream processes. This is done through a case study where blue hydrogen production compensates for fluctuations in green hydrogen generated from offshore wind energy, with limited hydrogen storage capacity. Using a hypothetical large scale ammonia synthesis plant in the port of Rotterdam as the downstream process. This research identifies process uncertainties, uses strategies to enhance flexibility, and quantifies their effects on process efficiency, costs and emissions.

To evaluate the potential of flexible blue hydrogen production, three case studies were simulated using Aspen Plus V12. The first case modeled a blue hydrogen plant operating continuously at maximum capacity (22.9 tons/h). This was used to clearly define the process steps needed for blue hydrogen production, serving as a benchmark for comparing continuous and flexible operations. In the second case study, an uncertainty is introduced to which the plant needs to adapt to. This uncertainty is modeled using hourly data from the Hollandse Kust Noord offshore wind farm, which supplies electricity to electrolysers with limited hydrogen storage capacity. The fluctuating green hydrogen output (0-11.3 tons/h) and steady hydrogen demand for ammonia synthesis (22.9 tons/h) determined the hourly blue hydrogen production. Multiple steady-state simulations were made in Aspen to model the plant at varying throughputs. In the last case, increased wind power output required the blue hydrogen plant to adapt with higher volume flexibility. An operating envelope of the blue hydrogen plant was developed to find the bottlenecks, and design strategies were applied to increase volume flexibility.

Results show that flexible blue hydrogen, using autothermal reforming with a gas heated pre-reformer, can effectively stabilize fluctuating green hydrogen production. The plants volume flexibility can be increased through design strategies such as selecting inherently flexible equipment, storage for intermediate production and using techniques like inert gas for load regulation. But there is a trade-off between flexibility and cost. The plant produces hydrogen at the lowest cost when operating continuously at maximum capacity, with a levelised cost of hydrogen (LCOH) at 3.19 €/kg. Increasing the volume flexibility of the blue hydrogen plant too much resulted in a LCOH of at least 4.02 €/kg, making alternatives like hydrogen storage a cheaper option for balancing out the intermittent supply of green hydrogen. However, when operating flexibly within its base volume flexibility the LCOH is cost effective compared to some alternatives as it increases only slightly to 3.47-3.57 €/kg. Mainly due to underused CAPEX, but also because of transient state losses and reduced efficiency at lower capacities.

This research shows the potential of flexibility in natural gas reforming processes and how it can play a key role in future energy systems. While there is still much to learn, integrating flexibility into the chemical industry enables it to adapt to the ever growing intermittently available feedstock and energy.

As the global economy continues to expand, the demand for natural gas has surged, leading to a significant increase in LNG consumption. LNG offers a pipeline-free transportation solution, but its integration with standard natural gas systems requires an evaporation process. Currently, LNG evap- oration is commonly achieved through self-consuming processes, seawater, or air evaporators. However, there is growing interest in leveraging the cold exergy of LNG for other processes. With carbon storage gaining prominence due to climate change concerns, integrating LNG evaporation and CO2 liquefaction systems could offer potential cost reductions in the overall process. Singapore could be an optimal location for such an integrated system due to the increasing LNG imports and the desire to become carbon-neutral requiring CO2 exports. The research of this thesis therefore will be: ”How can the LNG evaporation process be integrated with a carbon-dioxide liquefaction process at an LNG terminal in Singapore?” Existing research primarily focuses on self-consuming processes or CO2 purification, leaving a gap in understanding non self-consuming systems for integrating LNG evaporation and CO2 liquefaction at cryogenic temperatures. This study aims to fill this gap by comparing various heat transfer systems and evaluating their technical and economic feasibility. Three systems have been set up to be compared: a Direct heat exchanger system, an intermediate Propane loop and an Organic Rankine cycle. The Organic Rankine cycle has been optimized based on the net power output, first and second law efficiency of the system. Subsequently, the three systems have been compared showing that the Organic Rankine cycle is dominant in technical performance, both being self sustaining and holding a second law efficiency of 82.3%, which is 5% higher than the other designed systems. Additionally, the Organic Rankine cycle has a specific net power output of 7.3 kWh per ton CO2 liquefied, which can be utilized for other processes. After this, a financial assessment is performed on the three systems based on the internal rate of return and net present value of the systems. The Direct heat exchanger showed to be dominant in terms of internal rate of return and net present value ($313M and 534.1%, respectively). The Propane loop would be the second best system in terms of internal rate of return (79.5%). The Organic Rankine cycle could provide a higher net present value than the Propane loop ($285M and $267M, respectively), assuming that constant flows could be guaranteed and no additional evaporator is required. The Direct heat exchanger would be the financial best choice for Vopak but is limited by the high risk of frost formation in the exchangers, making it an unfit choice for this application. While the Organic Rankine cycle could provide an interesting alternative due to it’s higher net present value and power generation, the system complexity, generated electricity value uncertainty and initial investment make it a less attractive choice. Based on the techno-economic analysis in its entirety, the Propane loop was determined to be the best system to combine CO2 liquefaction and LNG evaporation.

Over the coming decades, human society has to transition from being dependent on fossil fuels to renewable energy sources. However, renewable energy sources bring with them several inherent problems that need to be solved to integrate them into our society. The power supply of renewable energy sources is intermittent and does not match the global energy demand, necessitating the need for energy storage to bridge the gap. Additionally, the chemical industry relies heavily upon the usage of fossil fuels as chemical feedstocks that cannot be directly replaced by (electrical) renewable energy. Electrochemical CO2 reduction to these synthetic fuels and chemicals provides a promising approach to both these problems. However, finding a suitable catalyst for this electrochemical reaction has proven difficult. So far, among the monometallic transition metals, only copper has been shown to actively reduce CO2 into the desired synthetic fuels and chemicals. Unfortunately, these reactions take place at high overpotentials and unselectively. Alloying different metals together provides an elegant way to find new promising catalyst materials for the electrochemical reduction of CO2 to synthetic fuels and chemicals. This thesis investigates different aspects of bimetallic electrochemical CO2 reduction to synthetic fuels and chemicals....@en

Ammonia can be used as a global energy carrier to connect the geographically divided landscape of renewable energy sources. Unfortunately, the current ammonia production process of the century old fossil-fuel based Haber-Bosch process is not sustainable and is responsible for approximately 1.2% of the global anthropogenic CO2 emissions. The most polluting part of the process is the hydrogen generation step by either coal gasification or the more common steam methane reforming. The majority of the emissions can be cut down by replacing this step by water electrolysis o en referred to as the electrified Haber- Bosch. An alternative technology for sustainable ammonia production, which is still in its infancy, is ammonia synthesis via the electrochemical reduction of nitrogen (NRR), requiring a proton source and electrons from renewable electricity. The following NRR approaches are prominently reported in the literature: (i) NRR in aqueous based electrolytes at ambient conditions (aqueous NRR), (ii) NRR at elevated temperatures with a solid oxide electrolyte, (iii) Li-mediated NRR in non-aqueous electrolytes at room temperature (Li-NRR). The main aim of this thesis is to identify and understand which of the above-mentioned electrochemical ammonia routes are the most promising for future application...@en

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.

The increasing awareness and urgency of climate change have led to an increase in investments and research into power sources not reliant on fossil fuels. Proton exchange membrane (PEM) fuel cells are a promising technology for automotive, maritime, and auxiliary power applications converting chemical energy into electricity. In order for this upcoming technology to compete with well-established alternatives such as diesel generators and combustion engines, it is of vital importance to improve the power density and durability.

PEM fuel cells produce water and heat during operation. The presence of superfluous liquid water in the fuel cell stack gives rise to flooding of the electrodes, which hampers operation and induces degradation processes. On the other hand, it is of great importance to maintain a high membrane humidification to reduce Ohmic losses over the membranes and avoid the formation of cracks. Therefore, water management plays a vital role both in maintaining the power density and guaranteeing durability.

This thesis is written under the auspices of both TU Delft and PowerCell Group, a manufacturer of PEM fuel cell systems located in Gothenburg, Sweden. Currently, a substantial amount of water condenses in the anode subsystem of PowerCell’s PEM fuel cells in certain operating ranges which subsequently enters the fuel cell stack. This study identifies the influence of certain system operating parameters on responses as the water crossover through the membranes, the relative humidity at the stack inlet, the temperature at the inlet of the stack, the condensation rate in the mixing chamber of the recirculation loop, and the mass flow rates of liquid water and water vapor in and out of the stack. Multiphysics simulation software provided by Gamma technologies is used to simulate 5600 operating points in which the system operating parameters are varied according to the Latin Hypercube sampling method. These simulations give a clear overview of the influence of the operating parameters on the aforementioned responses over the entire operating range of PowerCell’s PS-100 system.

The simulated experiments are subsequently used as a basis to construct metamodels. These metamodels predict the behavior of the system based on the operating parameters varied in the 5600 simulations. The metamodels are constructed both as Krigings and as multilayer perceptrons (MLPs). Kriging is a statistical method which produces an output for a certain response based on known input data where input points which resemble the unknown point are given a greater weight. MLPs are neural networks which recognise patterns in input data and use those to predict an output for a certain response. Finally, the operating parameters are optimized using the metamodels to minimize the liquid water mass flow rate into the stack, to prevent condensation in the mixing chamber of the anode subsystem, and to target a certain inlet relative humidity of the hydrogen feed to the stack. Concluding from these optimizations it would be beneficial to preheat the hydrogen before it reaches the mixing chamber. A number of alternative designs for the anode loop are proposed which require further investigation.

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 transport sector remains one of the largest CO2 emitting sectors globally. Decarbonizing the transport sector is an important aspect in the energy transition. The word transition is key, since it will take several decades or more to transition to a fully sustainable world. During this transition mainly heavy-duty vehicles and probably most vehicles in third world countries will rely on liquid transportation fuels. Affordable and competitive biofuels are the way to fill this need in a sustainable way.

This study will focus on integrating several sustainable units and feedstocks to produce gasoline and diesel, starting with a pyrolysis oil feedstock. The integrated units consist of a gasifier, whose gasifying agent, oxygen, is produced by a SOEC electrolyser, running on renewable electricity. The syngas produced in the gasifier is produced during a low temperature Fischer Tropsch process over a cobalt catalyst. The aim is to choose operating conditions resulting in a large chain growth probability factor to produce heavier hydrocarbons chains, which can be refined to mainly yield diesel. The hydrogen required to upgrade the syngas formed in the gasifier is supplied by the SOEC electrolyser as well. The final upgrading of the produced crude oil is performed by separating the fractions in distillation columns and using a hydrocracker to raise the yield of the desired products. The end products are diesel and gasoline, meant to be blended in with gasoline and diesel from conventional oil refineries. The gasoline and diesel are sulfur free and especially the diesel is of high quality, due to tuning the process to predominantly produce paraffinic hydrocarbons.

The assessment of the process will be a techno-economic analysis based on a model made with Aspen plus. 5000 kg·hr-1 of bio-oil produced by BTG was converted to 990 kg·hr-1 of high-quality diesel and 557 kg·hr-1 of gasoline. The overall carbon conversion of the process to the end products was 57.6 %. By designing a heat exchanger network, optimizing the energy produced and needed by the heat sources and sinks respectively, an overall energy efficiency on LHV base of 57.2 % was reached. The process in the current day and age was found to not be profitable yet, but will definitely be in the future.

Ammonia (NH3) is a bulk commodity chemical known for its large production volumes and application in the global fertiliser industry, and is more recently being explored for its role as a sustainable energy vector. The industry standard ammonia production method is the century-old Haber-Bosch (HB) process, which is power by fossil fuels, and is accompanied with high energy intensity and large carbon-dioxide emissions. In this research, conceptual processes for the electrochemical synthesis of ammonia via the direct electrochemical nitrogen reduction reaction (e-NRR) from air and water were developed to assess their technical and economic viability compared to the HB benchmark. Different scales (91, 544 and 2055 t d-1) and electrolyzer cell configurations (alkaline electrolyzer (AEL), gas-diffusion electrode flow cell (GDE) and solid oxide electrolyzer (SOEL)) were considered. The results showed that small-scale production is more feasible for e-NRR NH3 synthesis due to the economies of scale of the HB benchmark. Among different electrolyzer types, the gas-diffusion electrode flow cell was found to be the most practical and economical for e-NRR NH3 synthesis. A sensitivity analysis showed that the electricity price is the most important parameter for the feasibility of e-NRR, and should ideally be as low as possible. Performance parameters of the electrolyzer, such as stack cost, operational current density, and faradaic efficiency, were optimized for minimal NH3 production cost, but were challenging to estimate due to the early stage of e-NRR technology. An optimized case was presented that demonstrated e-NRR NH3 can reach HB-parity, but the validity of the optimised parameters was difficult. It is advised that reliable laboratory-scale demonstrations are needed for an accurate assessment of the commercial feasibility of electrochemical NH3 synthesis.

The rise of CO2 concentration in the atmosphere is a leading cause of global warming. Utilizing CO2 ob- tained from point sources, such as chemical industries, as a feedstock to produce high energy density fuels and chemicals could mitigate the emission of CO2 as well as provide various economic bene- fits. One promising technology is the electrochemical reduction of CO2, however, the presence of contaminants in the industry-supplied feedstock and the separation of products downstream would be challenging in a continuously operated large-scale plant. To address these challenges and indentify the bottlenecks involved, it is important to study which pre-treatment and post-treatment steps are required and how to integrate these in a large-scale electrochemical CO2 reduction process.

The gas and liquid feed streams to the CO2 electrolyzers are first cleaned to the desired levels. The liquid feed stream is water from the river Rhine that is purified so the specifications of the water meet the requirements for type 1 water (ultrapure water). The gas feed stream is the flue gas stream of an average steel-producing plant in Europe and is cleaned to remove sulfur and nitrogen compounds. A two-step electrolysis process is used where CO2 is first reduced to CO, followed by the reduction of CO to C2+ products. The electrolyzer for the first step is a membrane electrode assembly-based flow cell with a current density of 300 𝑚𝐴 𝑐𝑚2− and a faradaic efficiency (FE) of 96% to CO. In the second step, a gas diffusion electrode-based flow cell with a current density of 300 𝑚𝐴 𝑐𝑚2− and a faradaic efficiency of 9.35%, 15.49%, 45.57%, and 16.38% towards acetic acid, ethanol, ethylene, and propanol, respectively, is used. The anolyte and catholyte in the reactors are recycled 3,500 and 2,000 times, respectively, to reduce the size of purification of the liquid feed stream section and increase the liquid product concentration. In both steps, unreacted CO2 and CO are recycled. The gaseous and liquid products are separated and purified to meet the industry standards using established separation techniques.

The total capital investment for a process with an industrial gas feed of 381.678 tons per hour is 4,053.5 million dollars with a daily operating cost of 7.403 million dollars. The daily income from selling the products is 2.363 million dollars, but this could increase if the FE towards acetic acid is increased since this product has the highest income per electron consumed. The net present value (NPV) for the base case, assuming current technological and market conditions, is -19.4 billion dollars after 15 years. To analyze which parameters have the most influence on the NPV, a sensitivity analysis is also per- formed with a better and optimistic scenario. It was found that the economic feasibility of the currently designed process is not limited by the technological progress, but mainly by the market conditions.

The target of this process is to reduce the emission of CO2, however, the operation of the plant itself contributes to some CO2 emissions. Therefore the process should consume more CO2 than it emits. The units that consume most energy and emit the most CO2 are the CO to C2+ products electrolyzer and the first distillation column in the liquid product separation section to remove acetic acid. It was found that the process is only carbon negative when the consumed energy is generated by nuclear, wind, or solar energy. The net CO2 emission is the lowest when nuclear or wind is used as an energy source. Generating all the required energy from these sustainable sources brings another challenge since the total installed capacity of these sources are currently not sufficient to cater to the needs of such a large-scale continuously operating CO2 electrolysis plant.

Keywords: Electrochemical CO2 reduction, large-scale, pre-treatment, post-treatment, technoeconomical analysis, energy analysis

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.

Embracing the innate human desire to explore and expand our horizons, Mars presents an unparalleled opportunity to secure the future of our species and inspire generations to come. Aiming to facilitate a sustainable human presence on Mars, this master thesis focuses on the design and modeling of an in-situ rocket propellant production plant to fully refuel SpaceX's Starship for the return mission to Earth. The study identifies the best design practices for the in-situ resource utilization (ISRU) rocket propellant production setup and examines its integration with state-of-the-art technologies. The main results include an exergy analysis of the plant to determine its second-law efficiency, and the methodology necessary to conduct an exergy analysis on a different planet with different standard conditions. Furthermore, this work investigates material recycling, sensitivity analyses, exploitation of the Martian environment, and heat recovery opportunities within the plant's modeling. Three essential key performance indicators (KPIs) have been spotlighted to assess the plant’s performance. The first KPI scrutinizes the equipment mass to propellant mass ratio, providing invaluable insights into the economic efficiency of In Situ Propellant Production (ISPP). This ratio reveals that ISPP contributes to an 88.9% reduction in the mass that needs to be transported to Mars, highlighting the economic feasibility of the thesis. The second KPI is the Specific Energy Consumption (SEC) of the plant, standing as a measure of the plant's efficiency. The SEC, calculated by dividing the total power input by the sum of CH4 and O2 mass flows at the outlet, is found to be 6.52 kWh/kg. Furthermore, the plant’s second-law efficiency is examined, revealing how the plant's performance deviates from its theoretical maximum. The second-law efficiency, a significant indicator of the plant's ability to convert high-grade input energy into useful output without substantial degradation, is found to be 62.7%. Lastly, the work addresses the plant's dynamic behavior across Martian seasons, employing data derived from the Curiosity Rover. The focus here is to understand how the plant’s parameters, especially those interacting with the Martian environment, are impacted by diurnal and seasonal cycles. A special operational philosophy is adopted to ensure stable operations amidst these fluctuations. Through these findings, this research offers a thorough understanding of the current best practices and technologies for designing and modeling a propellant production plant on Mars. The output of this work is a model of a full-scale rocket fuel production plant. In conclusion, the insights provided by this work are of great significance for the future exploration and colonization of Mars, as they contribute to the development of a sustainable ISRU rocket propellant production plant, which is a crucial development necessary to guarantee return missions to Earth, thereby making sustained human presence on Mars a closer reality.

According to International Energy Agency (IEA), the demand for high value chemicals (HVC) will increase by 60% to a total of 400 Mt/year by 2050, leading to an increase of 30% in direct CO2 emissions. However, the Paris agreement forces the sector to reduce its emissions by 90-100% in 2050 compared to 1990. This induces the need for a more sustainable character in the petrochemical industry to produce HVC with net-zero emissions by 2050.
Steam cracking is expected to be still the leading production technique for HVC in 2050. Therefore, this research focuses only on petrochemical clusters containing a steam cracker.
Accordingly, the research question to be answered was: How can existing petrochemical clusters containing a steam cracker be transformed to produce
HVC with net-zero emissions in 2050? This thesis aims to look into the potential of alternative feedstocks and combine them with other decarbonisation options for steam cracking to produce HVC with net-zero emissions by 2050 from a cradle-to-gate perspective.
A base model was created of a petrochemical cluster containing a steam cracker capable of serving the global market (3900 kt HVC/year) to answer the research question. The base model was used to develop six models with different decarbonisation options capable of accepting alternative feedstock. Decarbonisation options were based on carbon capture and storage (CCS), both post and pre-combustion, electrification and hydrogen. The alternative feedstock was sourced from the renewable materials: vegetable oils, animal fats, crude tall oil and lignocellulosic biomass. Also, plastic waste (recycled) and synthetic (FT wax and naphtha) feedstock made from captured CO2 and hydrogen were included. The maximum percentage of HVC produced from alternative feedstock was assumed to be 25% due to uncertainties and limitations in the availability of alternative feedstock. The rest of the HVC was yielded from a mixture of fossil feedstock (naphtha, LPG, ethane, gas oil and butene). Different experiments were performed to estimate the emission reduction potential of separate or combined decarbonisation options with HVC yields originating from alternative feedstock ranging from 0% to 25%. The supply chain and associated CO2 emissions of the feedstock were also analysed. Next to determining the emission reduction, the quantitative data from the models were also used to assess the levelized cost of zero emissions HVC and the geographical and infrastructural limitations of decarbonisation options. One problem was the residual fossil fuel gas from the process, possibly leading to unwanted emissions elsewhere if not appropriately handled. In conclusion, the only decarbonisation options capable of dealing with this problem are CCS and auto-thermal reforming combined with CCS. Together with renewable feedstock, from a cradle-to-gate perspective, these options are capable of reaching net-zero emissions or even negative emissions when fossil and renewable feedstock supply chain emissions are drastically reduced. For future research, it is advised to not only focus on producing HVC with steam cracking but also consider other greenfield production method capable of producing HVC with renewable resources. A comparison with the proposed pathways in this research would provide valuable insights.

At the moment, Tata Steel emits 12.6 Mt CO2 per year while producing 7.2 Mt steel per year. To reduce these emissions, Tata Steel has decided to replace the blast furnaces with direct reduced iron (DRI) plants in combination with reducing electrical furnaces. The DRI plants will first operate with a 100% natural gas feed. Whenever green hydrogen becomes available on the market, the natural gas will gradually be substituted with green hydrogen, reducing direct CO2 emissions. Producing steel using 100% green hydrogen as the reducing gas, called green steel, comes along with an awkward problem regarding the carbon content of the DRI. Green steel has a carbon content of 0%, while carbon is essential for multiple aspects of the production process. Furthermore, the metallization of the DRI is a critical parameter in the production process. Thus, the following research question is established: ”What is the influence of the ratio of hydrogen to natural gas inserted in the direct reduced iron plant on the performance of the reactor?”

To answer this research question, an extensive literature review is performed to gain knowledge of the reduction process, reduction technologies, and the existing mathematical models of the DRI plant. Furthermore, a multiscale mathematical model is made of the shaft furnace of the MIDREX plant. This model uses a grain-based pellet model, which incorporates the morphological structure of the pellets during the reduction process. The shaft furnace is modelled as a 1D model with multiple zones, in which the local energy, mass, and momentum equations are solved. However, due to the time restrictions of the thesis period, only the two reduction zones of the shaft furnace are incorporated. Hence, the shaft furnace model lacks the transition and cooling zones.

The shaft furnace model is compared to a real operating MIDREX plant named ”Gilmore”. The simulation results are validated against the simulation results from literature and the real plant data. The average relative error of the simulation results compared to the Gilmore plant is 14.4%. The most significant error can be attributed to the carbon weight fraction in the solid. This is the result of the missing transition and cooling zones, as most of the carburization occurs inside the transition zone. Neglecting the carbon weight fraction, the average relative error is 9.2%.

Increasing the ratio H2 / CH4 in the feed of the MIDREX plant results in an increasing H2 / CO ratio of the reducing gas entering the shaft furnace. Five cases with different H2 / CO ratios are simulated to answer the research question. The metallization of the DRI is affected by two different phenomena. First, increasing the H2 / CO ratio results in a larger gas input mole flow for the same input pressure, which is the effect of a smaller pressure drop over the shaft furnace. Subsequently, a larger gas input mole flow results in better metallization, which is the effect of more heat input and a lower gas oxidation degree in the shaft furnace. Second, as the hydrogen content increases, the temperature decreases as a result of more endothermic reduction. The thermodynamics and kinetics of reduction by hydrogen are favourable at higher temperatures, which results in a slow-down of the reduction. At lower temperatures, the thermodynamics of reduction by carbon monoxide is more favourable, realizing more reduction and increasing the temperature. This second phenomenon is predominant for equal input mole flow, resulting in worse metallization when increasing the H2 / CO ratio, as confirmed by literature. Consequently, to achieve equal metallization for a higher H2 / CO ratio, the process gas compressors of the MIDREX plant will consume more electrical energy. To conclude, substituting natural gas with hydrogen does have its disadvantages, but it is highly necessary to become CO2 neutral in the future.

For further research, the addition of transition and cooling zones to the shaft furnace model is recommended, allowing investigation of the carburization of the DRI. Furthermore, the shaft furnace model is extremely useful for implementation in a complete MIDREX plant model. Such a model could be used to investigate the total CO2, energy, and material balance of the plant for different H2 / CH4 ratios of the feed of the plant.

The olive industries, especially in the Mediterranean countries are known to produce a significant amount of residues such as crude olive pomace (COP) and olive tree pruning waste (OTPW) which can lead to various environmental and societal issues if not treated or further utilized (Garcìa Martìn et al., 2020). Considering the fact that not all olive oil industries make use of these olive residues (COP and OTPW) for further processing, they seem to be a promising candidate to produce renewable energy due to their bioenergy potential and physicochemical properties. These residues could be valorized to produce liquid biofuels which would help creating a circular economy. This work aims to expand the current state-of-art of hydrothermal liquefaction (HTL) of olive residues such as COP and OTPW, which will contribute towards the profitability and sustainability of olive oil industries. This work will also serve as a basis to future studies such as development of a continuous process to support the high commercial demand of the liquid biofuel and carrying out a techno-economic assessment of the HTL process of COP and OTPW at this scale.

Due to the characteristics of the olive residues, especially their high moisture content and organic compounds (Ribeiro et al., 2020), the use of HTL has been proposed for the development of the thermochemical conversion process for bio-oil production. So far, only non-catalytic HTL processes have been investigated in batch scale laboratory setups. Thus, the main novelty of this work is that the effects of catalyst dosage (0 - 10 wt.%) along with reaction temperature (250 - 340 °C) and residence time (5 - 60 min) using a central composite design of experiments has been evaluated. The bio-oil and biochar fractions resulting from HTL were characterized by elemental analysis, bomb calorimetry, X-ray fluorescence (XRF), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy coupled with Energy dispersive spectroscopy (SEM-EDS), and Fourier-transform infrared spectroscopy (FTIR). From the experiments, it was proven that the production of liquid biofuels from olive residue biomass from Spain is possible under both, catalytic and non-catalytic routes. By implementing the central composite design experimental campaign, a set of mathematical models were developed for predicting the mass yields of the bio-oil, biochar, aqueous, and gas phase produced under combinations of the evaluated process variables.

The main finding of this work is that by using a catalyst, significantly higher mass yields of bio-oil were achieved with lower operational conditions when compared with the existing literature. The maximum bio-oil yield was found out to be 56.0% wt. on treating COP at 330°C for 60 minutes and 10 wt. % catalyst whereas for OTPW, the maximum bio-oil yield was found out to be 56.3% wt. at 330 °C for 30 minutes and 7.5 wt. % catalyst. The bio-oil produced under these conditions showed an average energy content of 23.21 MJ/kg. The highest high heating value (HHV) of 32.09 MJ/kg was obtained under non-catalytic HTL route at 340 °C and 15 minutes. The determination of the energy content (HHV) of the bio-oil fractions showed that there is a potential trade-off between the respective mass yield and HHV when using the catalyst.