The large concentrations of anthropogenic CO2 emissions present in our atmosphere are causing a severe thread on the world as we know it. It is therefore highly necessary to move away from fossil fuels to sustainable alternatives. In order to do so, lots of research has focused already on finding new ways to create renewable energy, through for example solar and wind energy. These renewable energy sources will be able to replace the energy that we need to warm our houses and drive our cars. However, these technologies are not able to replace the chemicals that we use in our daily lives that are made through fossil-based processes. For example, plastic bottles and packing, synthetic fabrics such as polyester and nylon, cosmetics, and detergent are all made from fossil-based chemicals. An sustainable alternative process to make these chemicals is through electrochemical CO2 reduction, where CO2 is converted into chemicals by applying electricity. This involves capturing CO2 from the atmosphere and transforming it into a value-added chemical. In this way, CO2 becomes a resource instead of a waste gas that is vented off into the atmosphere and a so called circular carbon economy can be established.

Typical CO2 capture systems use a thermal step to remove the captured CO2 from the capture solvent and regenerate the solution such that it can be recycled back to the capture step. This thermal process is highly energy intensive and therefore a costly step in the CO2 capture process. However, regeneration of the capture solvent can potentially also be achieved by an electrochemical process. The CO2 rich solvent is sent directly to the electrolyser in which the CO2 is converted into carbon products and simultaneously creates a CO2 lean solvent at the outlet that is suitable for a new CO2 capture cycle. This dissertation studies the feasibility of integrating CO2 capture with electrochemical conversion. This is done by looking at two different pathways using two different solvents. The first pathway investigates the use of an organic solvent and the second pathway uses a (bi)carbonate solvent. This dissertation addresses different challenges related to the effective electrochemical CO2 conversion for these two different solvents and provides a perspective on the feasibility of integrating CO2 with electrochemical conversion.

As global warming proceeds with increasing consequences, new and improved solutions that can mitigate the increasing CO2 emissions are becoming ever more important. Renewable energy technologies are advancing and along with carbon capture technologies, they promise to lower global emissions and help combat climate change. Renewable energy sources can be used to form value-added chemicals from captured CO2 through a method known as CO2 electrolysis. A novel approach to CO2 electrolysis is bicarbonate electrolysis, which uses carbon capture solutions directly to make products. By integrating the capture and conversion process this way, effectively bypassing the energy intensive steps of CO2 recovery required for conventional gas fed operation, CO2 conversion to products can become even more sustainable.

The objective of this thesis is to explore ways to improve the selectivity of carbon monoxide (CO) in a bicarbonate electrolyser. In this experimental study, focus is also placed on the stability of the process, characterising the selectivity over time. Causes of selectivity decline are examined as well as methods of improvement. Furthermore, the effect of pH on CO selectivity and stability is given special consideration. Literature in the field of (bi)carbonate electrolysis was reviewed to gather understanding on the process, to clarify recent advances made and to find areas for improvement. Based on the findings from the literature review the experimental study was designed.

Experiments were conducted in a membrane electrode assembly (MEA) flow-cell in constant current fashion, applying a current of 100 mA/cm2. The membrane chosen was a bipolar membrane (BPM) as it offers the possibility of operating with distinct electrolyte environments, separating the 3M bicarbonate catholyte from the 1M potassium hydroxide anolyte. Gas diffusion electrodes (GDE) were prepared by spray-coating silver nanoparticles on the surface, using Nafion ionomer as binding material. An interdigitated catholyte flow plate was used which ensured the bicarbonate would pass through the GDE due to its discontinuous channels forcing the flow through.

By introducing a catalyst-membrane gap through inserting a hydrophilic porous spacer between the GDE and the BPM, CO selectivity was improved from 50% to 78% in peak production, recording 55%
averaged over 3 hour operation. This enhancement in selectivity can be explained by the defined pH gradient resulting from the gap, permitting a low pH at the BPM for protons to react with the bicarbonate, liberating i-CO2; and a higher pH at the catalyst for CO2 conversion to CO while suppressing the hydrogen evolution reaction (HER). An optimum gap was found to be 135 - 270 μm. These results compare with the previously highest reported CO selectivity values from the literature at ambient conditions and 100 mA/cm2. While improving the selectivity, the stability of CO was not improved by the catalyst-membrane gap. The pH was found to affect both the selectivity and stability of CO, with higher bicarbonate pH leading to reduced selectivity but improved stability. This behaviour is explained by the reduced i-CO2 liberation and increased carbonation reactions taking place at higher pH levels…

Rising global CO2 levels underscore the urgent need for effective carbon capture and utilization (CCU) technologies to support a circular carbon economy. This study evaluates the techno-economic per- formance of a novel integrated CCU system that combines a K2CO3-based capture column with a bicarbonate electrolyser for syngas production, specifically targeting applications in the steel industry. An ASPEN PLUS model of the capture column was developed and integrated with a pH-dependent Faradaic Efficiency (FE) model of the electrolyser in Excel. Five cases were defined: (I) 90 wt% CO2 capture, (II) syngas production with a 2:1 H2/CO ratio for the Fischer-Tropsch process, (III) electrolyser operation with FECO > 50%, (IV) syngas composition suited as feedstock for electric arc furnaces (EAF) in the Energiron III process, and (V) an intermediate pH step. A techno-economic analysis (TEA) was conducted across worst, base, and best-case scenarios for each case.  Key findings reveal a trade-off between achieving high FECO at low pH levels and maximizing CO2 capture efficiency at high pH levels. Systems operating with large pH steps demonstrated a lower Lev- elized Cost of Syngas normalized to the Lower Heating Value (LCOSLHV ), due to increased hydrogen output. In contrast, systems with smaller and narrower pH steps incurred higher LCOSLHV due to their output’s lower LHV. The techno-economic analysis (TEA) indicates that the operational expenditure (OPEX) for the integrated CCU system is currently too high to be cost-competitive with alternative solu- tions. Sensitivity analysis reveals that the integrated CCU system is competitive with other electrolysis methods only under best-case conditions. Electricity costs and a low CO2 utilization ratio are identified as the primary drivers of OPEX. Improvements in these areas result in the most significant reduction in LCOSLHV, making them critical enablers for the integrated CCU system. Additionally, the cost per kilogram of CO2 saved is high compared to EU CO2 Emission Trading System (ETS) prices.  Current bicarbonate electrolysers are more costly than gas-fed CO2RR systems in terms of Unit Capital Cost (UCC) per kilogram of CO produced, largely due to reduced performance at higher current den- sities (>100 mA/cm2). Achieving CAPEX parity with gas-fed CO2RR systems would require increasing current densities while maintaining high FECO and sustaining these efficiencies at alkaline pH levels.  Future work should prioritize reducing both OPEX and CAPEX for the system, with a particular focus on improving the technical performance of the bicarbonate electrolyser. Key objectives include increasing current density while maintaining high FECO at alkaline pH levels, improving the CO2 utilization ratio, and enhancing the stability of the electrolyser.  Keywords: Carbon Capture and Utilization, Bicarbonate Electrolysis, K2CO3-based CO2 Capture, Ben- field Process, Integrated CCU System, Techno-economic Analysis

The objective of this study is to generate insights into the application of the reliability of a W2H system and its impact on the techno-economic performance. This involves examining the case of a single system to analyse on a micro-level the underlying conditions affecting performance, as well as exploring W2H farms to observe performance and the effects of changing conditions on a macro-level. To this end, MATLAB models have been utilised and developed to simulate various components of a system, such as wind turbines and electrolysers, focusing on aspects like hydrogen production and the number of breakdowns per year. The model creates insights into technical and economic parameters.

The petrochemical industry accounts for approximately 20% of global industrial CO2 emissions. Ethylene manufacturing is one of the major components and has a high carbon footprint. This study explores the use of proton-conducting electrochemical cells (PCECs) for ethylene production - the WINNER process. This non-oxidative dehydrogenation (NODH) reaction is still thermochemical, but the hydrogen is electrochemically removed, enhancing the conversion of ethane.
The electrochemically enhanced production of ethylene demonstrates substantial improvements over conventional steam cracking. It decreases Specific Energy Consumption (SEC) by approximately 20%, curtails thermal energy demand by 80% and enables operations at a lower temperature of 550°C. Some parameters are less favourable, but nonetheless, the reduction in SEC indicates a promising potential to decrease carbon emissions attributed to utility consumption.
Economically, the WINNER process outperforms the steam cracking benchmark, with a nearly doubled margin, almost tripled Net Present Value (NPV), and a seven-times higher Internal Rate of Return (IRR). The Minimum Selling Price (MSP) of ethylene reduces by roughly 30% in the WINNER process. Additionally, the WINNER process produces pure, pressurized hydrogen as a high-value byproduct, adding to the economic viability of the process. A sensitivity analysis indicates that the most influential parameters are the prices of ethylene, ethane, and fuel gas.
Under current U.S. grid conditions, the Product Carbon Footprints (PCFs) of the WINNER process and the steam cracking benchmark are approximately equal. An increased contribution from renewable energy sources would enable the WINNER process to lower the utility-based PCF of ethylene production.
In conclusion, the WINNER process exhibits superior techno-economic performance and potential environmental advantages over the steam cracking benchmark, making it a promising alternative for sustainable ethylene production. Therefore, this work lays the groundwork for a sustainable and profitable transition in ethylene production, leveraging advances in electrochemistry.

The primary objective of this study was to address the lack of understanding of the commercial- scale implementation of novel CO2 based carbon nanomaterial (CNM) production and its comparison with status quo CNM production processes using unsustainable fossil resources. To accomplish this objective, first, a literature review was performed on the status quo commercial- scale CNM production, the lab-scale CO2 based processes and the CNM market. In regards to the status quo processes, the literature review yielded mainly chemical vapor deposition (CVD) processes of carbon nanotubes (CNTs) and graphene production. With respect to the lab scale CO2 based processes, the literature review involved categorising the identified processes into four different approaches based on their working principles - CO2 based CVD, molten salt based electrochemical CO2 reduction, liquid metal catalyst aided CO2 reduction and metal reductant enabled CO2 reduction. With regards to the CNM market, CNT materials were found to have the highest market share followed by that of graphene. Startup spinoffs working on the graphene and CNT production from CO2 were identified with origins to university-based research groups.

Following such literature review, a framework was developed to select one process each from the status quo CVD processes and the novel CO2 based processes, which produced comparable CNM. This framework was applied to the processes obtained from the literature review, which led to the selection of a methane-based CVD process and a molten salt-based electrochemical CO2 reduction process for small-diameter multi-walled (MW) CNT production. The methane-based CVD process involved the use of Ni-Mo catalyst on MgO support and high-temperature operating condition of 975°C. The molten salt-based electrochemical CO2 reduction process involved the use of Ni and steel electrodes, pure molten Li2CO3 electrolyte and high-temperature operating condition of 750°C. These selected processes were designed and simulated in Aspen Plus at a commercial-scale production level of 5000 tonnes per operating year. The mass balance, energy balance, and equipment cost data obtained from the simulations were used to assess the technical, economic, and environmental performance of the ex-ante CO2 based production process and the status quo CVD production process.

The technical performance assessment involved the estimation of resource intensity and energy efficiency indicators of the two processes, wherein the CVD process outperformed the electrochemical process in both indicators. The economic performance assessment involved the estimation of total capital investment, operational expenditure, net present value, and payback period. The CVD process performed better than the electrochemical process in all the indicators except total capital investment. Both processes indicated positive net present values and short payback periods, indicating the realisation of commercial scale plants of both processes to be profitable. The environmental performance assessment was carried out using the life cycle assessment methodology in the CMLCA software. The climate change impact indicators at scope 1 and 2 levels along with the net avoided impact from using CO2 were estimated using the CML 2001 impact assessment family. The electrochemical process was shown to perform considerably better than the CVD process in all the climate change impact indicators. Overall, the technical and economic performance of the CVD process was better than that of the electrochemical process. However, the environmental performance of the electrochemical process was shown to outperform that of the CVD process.

The limitations associated with modeling decisions taken in the two processes and with the uncertainty associated with the lack of data were highlighted. Further, the relevance of this study was discussed with respect to the industrial symbiosis potential of using waste CO2 from industries leading to GHG emission reduction and subsequent deceleration of climate change impacts. Finally, future potential studies were highlighted that could build on the research and insights generated in this study. One of these studies involved a case study on the implementation of a commercial-scale electrochemical process for MWCNT production in Port of Rotterdam region. Another study involved a techno-economic and environmental assessment of atmospheric CO2 capture and conversion to carbon nanomaterials for applications that can potentially achieve net negative emissions.

Carbon sequestration involves the conversion of carbon dioxide gas into carbonates through reactions with magnesium or calcium bearing minerals, presenting a potential method to mitigate CO2 emissions and reduce their release into the atmosphere. This process can be classified into two categories: in-situ (subsurface) and ex-situ (surface). CO2 mineralization has demonstrated the ability to permanently store substantial quantities of CO2 without the need for extensive post-monitoring efforts, while also offering potential business model benefits for the generated end products. However, the field of mineralization still faces substantial technical and economic challenges, including high cost projections and slow carbonation kinetics, impeding further technological advancements in the field. Additionally, logistical challenges related to plant design and associated emissions contribute to the complexity of finding solutions to these problems.

In this particular study, the investigation focused on ex-situ carbon dioxide sequestration primarily through direct aqueous mineral carbonation, incorporating a direct air capture element. This approach was chosen due to the flexibility provided by direct air capture in terms of CO2 supply and the desirable characteristics of direct aqueous carbonation. Various models were developed using Aspen Plus software and compared, leading to the selection of the direct aqueous carbonation system as the optimal choice for CO2 carbonation. Further enhancements were implemented in the system, including recycled streams and heat integration, to reduce overall energy consumption. Optimization steps were also undertaken to determine the appropriate sizing of key equipment that make up the majority of the system's overall costs and to improve system efficiency.

An economic analysis was then performed, revealing that plant scales of 50 ktons/year yielded a positive Net Present Value (NPV), indicating profitability. Conversely, smaller-scale plants of 0.5 ktons/year and 5 ktons/year did not generate positive revenue, even with a high carbon credit price. This was followed by a sensitivity analysis that showcased the relevant parameters that holds significant effects on the economic performance of the system.

Moreover, business model cases were also explored, and it was concluded that utilizing the end products in building materials and road construction could potentially generate additional revenue for the mineralization system beyond storage options.

Overall, this investigation highlights the potential of ex-situ carbon sequestration through direct aqueous mineral carbonation, considering direct air capture, and emphasizes the importance of economic viability and revenue diversification in the successful implementation of mineralization systems to mitigate the effects of global warming.

Feasibility improvement of Solid Oxide Electrolysis (SOE) is required to accelerate technology development. The study aims to determine whether and under what conditions reversible operation can improve the techno-economic feasibility of a large-scale open-system SOE. The feasibility of reversibility is assessed under various scenarios and sensitivities for hydrogen and natural gas as secondary feedstock, under hourly fluctuating wind profiles and power prices.
The results demonstrate that reversibility in rSOE mitigates risks associated with SOE, acting as a hedge against high power prices, low hydrogen prices, power profile inconsistency, and price volatility. Moreover, reversibility significantly enhances absolute techno-economic feasibility under specific conditions. The conditions require either a minimum ratio between the average power price and switch-price, choosing natural gas as a secondary feedstock, or meeting balancing market requirements.
This research reveals the feasibility-improvement potential of reversibility in SOE. The corresponding conditions are essential to identify the most suitable applications of the technology.

In the transition towards a renewable energy-powered industrial sector in the Netherlands, hydrogen plays a pivotal role. The anticipated increase in hydrogen demand by 2030 is projected to exceed the anticipated capacity of domestic green hydrogen production, hindered by the high costs and fluctuations of local renewable electricity generation. To address the growing demand, the consideration of importing more cost-effective green hydrogen is regarded as an appealing option. Storing and transporting hydrogen as green ammonia emerges as a compelling choice for hydrogen importation, given high volumetric hydrogen density of ammonia, coupled with its effective storage and well-established infrastructure. An essential element in the importation of hydrogen through green ammonia lies in the decomposition of green ammonia back into hydrogen.

This research evaluates the techno-economic feasibility of hydrogen production using an ammonia cracking process plant in the context of the Netherlands. Two process plant configurations were developed and evaluated on their performance. Both of the plants are set to generate 100 TPD of hydrogen at 50 bar pressure for the Dutch hydrogen grid. The first configuration is designed for the ammonia-to-hydrogen process plant using existing technologies applicable on a large scale by 2030, with a particular focus on the ammonia cracking reactor configuration as the central component. The second configuration is formulated based on the emerging technology of employing the membrane-assisted reactor for ammonia decomposition and is used for comparison with the existing technology configuration in the context of the year 2040.

Economic evaluation of both configurations indicates that the Levelized Cost of Hydrogen (LCOH) derived from green ammonia is primarily driven by the market price of green ammonia. Evaluating the conventional technology at 2030 market predictions, it is established that hydrogen production from imported green ammonia can compete with domestic green hydrogen production and potentially emerge as the most cost-effective option for green hydrogen import if optimistic predictions regarding green ammonia costs materialize. In comparing the conventional and emerging technology configurations for LCOH by 2040, it was determined that the membrane-assisted reactor configuration does not significantly outperform the conventional technology, even when considering the most optimistic scenarios regarding the robustness and scalability of this emerging technology.

The carbon emissions from human activities are causing significant harm to the planet, leading to increased temperatures, melting of polar ice caps, rising sea levels, and other negative impacts on the environment. One promising solution is the use of green hydrogen as a fuel source, which could have a much lower carbon footprint than traditional fossil fuels. The production of hydrogen can be achieved through various methods, including the electrolysis of water, which splits water molecules into hydrogen and oxygen. To mitigate these effects and ensure a sustainable future, countries are taking various measures to reduce their carbon footprint, including increasing the use of clean energy sources and improving energy efficiency. Hydrogen storage and transportation pose major challenges since it is the one of the lightest gases leading to low energy densities.

Ammonia is emerging as a hydrogen carrier due to its high gravimetric storage densities of hydrogen. It is produced through the combination of hydrogen and nitrogen using the Haber-Bosch process. Ammonia can then be used as a clean and efficient fuel for various applications, such as transportation and power generation. Fluctuations in the hydrogen feed flow rate, resulting from variations in renewable energy sources can significantly impact the pressure and operating temperature within the system.

}Morocco holds significant potential for renewable energy development due to its favorable geographic location and natural resources. The geographic location situated close to Europe makes Morocco well positioned for exporting green hydrogen to European markets. The chosen location for the ammonia plant is Boujdour in Morocco due to its excellent wind capacity factor of 67%.

Modern ammonia production plants employ control systems to maintain stable pressure. When there is a reduction in hydrogen feed flow rate, these reductions result in severe pressure reductions which would lead to metal fatigue and damage the entire production unit. Hence, these control systems respond by adjusting parameters to sustain pressure within the system. Aspen Plus Dynamics has been used in the present thesis work to model the dynamics of the ammonia synthesis plant. The varying hydrogen feed flow rate is a consequence of renewable energy fluctuations, which is served as the basis for modeling three distinct scenarios involving a 20%, 50%, and 70% reduction in hydrogen feed flow rate. Three distinct control strategies were developed where each control strategy, based on controlling the cooling duty of the condenser, manipulating the brake power of the recycle compressor, and regulating the nitrogen feed flow rate, demonstrated effective stabilization of the system's pressure, even during dynamically changing input conditions. Both linear and step reduction in hydrogen feed flow rate have been considered to gain understanding of the dynamic the behaviour of the system.

Significant outcomes were found when a reduction in hydrogen feed flow rate is imposed on all three control strategies. For a 20% reduction in hydrogen feed flow rate, the condenser's duty reduced from -1.2 MW to -1.05 MW, while the brake power of recycle compressor reduced from 12.5 kW to 5.5 kW. Furthermore, the stoichiometric ratio of H2:N2 changed from 3 to 2.8. These changes successfully stabilized the pressure in the ammonia synthesis plant under varying hydrogen input flow rate...

Green hydrogen has a pivotal place in the energy transition, addressing carbon emissions in hard-to-abate sectors. As global hydrogen demand rises, decarbonizing green production becomes vital. This study explores the influence of design choices and local weather patterns on the Carbon Footprint (CF) and Levelised Cost of Hydrogen (LCOH) for green hydrogen production.

An optimisation model is developed, simulating the production chain (cradle-to-gate) and optimising it for low CF and LCOH based on location-specific wind and solar data. Three locations (Duqm, Groningen, Dakhla) and three design choices (electrolyser, PV type and wind-solar ratio) are assessed.

Results indicate that local weather patterns significantly affect system performance. Dakhla boasts low production costs due to consistent solar and wind energy. Groningen has a low CF but high LCOH due to ample offshore wind but inconsistent sun. Duqm has a low LCOH but high CF due to abundant sun but inconsistent wind.

Design choices, particularly the solar-wind energy ratio, strongly impact both LCOH and CF. PV technology selection also matters, with CI(G)S performing well overall. Alkaline electrolysis is preferred over PEM.

The research demonstrates that design choices can substantially influence the CF, resulting in serious CF reduction at prices comparable to blue hydrogen.

Future research should include storage, transportation, and off-taker aspects and expand impact categories, including social and critical raw material depletion impact categories.

Methane pyrolysis is a technology that has the potential to greatly reduce the CO2 emissions of hydrogen production on a large scale. The process generates solid carbon instead of gaseous, thereby inhibiting emissions and has a relatively low process energy demand.

A three-step approach was taken to investigate the feasibility of offshore methane pyrolysis for sustainable hydrogen production. Firstly, a model was developed to evaluate the potential for converting methane into hydrogen under various design scenarios. Secondly, the model was utilized as a tool to create an offshore design for the methane pyrolysis reactor, including necessary auxiliary equipment. Finally, a calculation of the levelized cost of hydrogen (LCOH) was conducted to compare it with conventional methane reforming technologies for hydrogen production.

The ultimate results showed a higher LCOH of offshore methane pyrolysis compared to the reforming technologies, however, two main components were identified that have the potential to close this gap. First, the sales of the solid carbon by-product would reduce the LCOH of offshore hydrogen and second the introduction of a CO2 tax would increase the LCOH of reforming technologies where methane pyrolysis is not affected. Thus, it can be inferred that offshore methane pyrolysis can be cost-competitive under the appropriate conditions.

Carbon capture and utilization (CCU) is an emerging technology for reducing the CO2 concentration in the atmosphere and to limit the negative effects on the global warming. Different from carbon capture and storage (CCS), in CCU the carbon captured from point sources or direct from air is processed to valuable carbon containing products. Several studies have been conducted on the technological and economic viability of CCU. However, no detailed process analyses with a system-level approach have been reported. Performance and challenges on pre-treatment and downstream processing of product streams have been ignored or generalized. This work aims to perform a detailed front-end techno-economic and environmental analysis on CCU pathways, focused on thermocatalysis (TC) and low- and high temperature electrolysis (LTE and HTE) of CO2. Identifying the most business critical pathways for valorization and utilization of CO2.

The scope of this study focuses on the identified single-step chemicals, that can directly be produced from CO2 without intermediates. KPI's selected for both conversion technologies are used to determine performance. A parametric analysis is carried out to evaluate the marginal costs of production per unit of weight for the selected chemicals. Based on costs, TRL and phase of product stream a selection of chemicals is made. Products identified as potential viable for industrial scale production and selected for further study are carbon monoxide (LTE, HTE and TC), formic acid (LTE and TC) and oxalic acid (LTE).

Conceptual process designs are made using reported system performance with all required units identified. A model is developed to simulate input- and product streams, scale size of units, calculate required utilities and costs of investment and operation. All processes are modulated according to generic battery limits, use cases and analysis methodology to provide an equal comparative study. It is found that state-of-the-art electrochemical processes are dominated by capital investment costs and are too immature for commercial application. For TC processes, production costs are primarily driven by H2 and CO2 costs. CO shows the most potential in this respect and is competitive with the market price. A sensitivity analysis is performed to gain understanding of the sensitivity of the parameters. Conversion pathways that could gain significant technical improvements are most sensitive to CAPEX varying and are less affected by variance in operating expenses. Main focus for investments on EC technologies should be current density. More mature technologies are most sensitive to varying the costs of feedstock and market parameters.

Opportunities for process improvements are evaluated by a performance analysis for current base-case versus the expected near-term and optimistic future scenarios. The parameters used for modulation vary according to the expected improvements in technical performance, economic performance and electricity price. Opportunities for EC processes lie within extensive R\&D on conversion technology. For TC process, and on the long term for EC, opportunities lie within further development of green H2 production and CO2 capture. EC CCU pathways demonstrate great potential for future performance with potential reduction up to 71\% for near-term future. To quantify the environmental impact of the pathways and their improvements compared to conventional processes, a gate-to-gate life cycle assessment is performed. Switching to a more renewable energy mix offers serious improvements to minimize global warming impact. The most emission reducing pathways are CO TC and OA LTE which utilize more CO2 than is emitted during the process, -0.16 and -0.26 kg CO2-eq per kg of product.

CO2 concentration in the atmosphere has soared since the industrial era owing to the rapid and unabated increase in fossil fuel consumption globally. This has resulted in an increase in global average temperature by ≈ 1.1 C in this period; and has sparked the concern of climate disaster events across the globe. In order to tackle the issue of climate change, research into Carbon dioxide removal (CDR) technology such as Carbon Capture and Storage (CCS) and Carbon Capture and Utilization (CCU) has gained prominence.

Zero Emission Fuels (ZEF) B.V is a technology startup based in Delft, working on the CCU pathway for CDR. ZEF is developing micro plants to capture CO2 and H2O from the atmosphere using Direct Air Capture (DAC) system. The captured CO2 is then compressed to 50bar using compressors while
H2O is split electro-chemically to H2 at 50bar. This high-pressure CO2 and H2 are then used to produce methanol. The energy for the whole process is derived from the sun, making the entire process sustainable and emission-free.

ZEF’s micro-plant will derive its raw materials i.e. CO2 and H2O, from the environment. Thus, variation in the environmental conditions, i.e., humidity, temperature, and solar radiation (external disturbances
for the system), will affect the overall system output. Current work focused on the design of control scheme for the integrated DAC and CO2 compression system, which will be able to meet ZEF’s performance target. The effect of variation in solar radiation was not considered for this work.

At first, the performance parameters for the various sub-systems of the integrated DAC+FM system were identified. With this information, the operating scenarios and the process constraints for the system
were identified. Then, models for the sub-systems of the DAC and compressor system, i.e., Absorber, sump, desorber, flash tank, and compressor system were developed. Parts of the model, the desorber and flash tank, were validated using experimental setup developed by integrating the existing DAC prototype at ZEF with a representative compression system.

The main target of the experimental setup was to develop control scheme to maintain the pressure of the flash tank to the required target levels. Through multiple iterations, the final layout and control system
for the integrated setup was identified which was able to control the pressure of the flash tank at the
target level.

Finally, a control scheme for DAC production control was developed based on the steady-state output from the desorber model. Through this, the feed and power (heat) input to the desorber is varied to control the production of CO2 and H2O.

The system model developed as part of this work can be further used as a tool by ZEF to integrate different sub-systems, test the performance of different sorbents and assess the viability of different control schemes for the integrated system

Using the IEA Ammonia Roadmap aligned with the IMAGE electricity scenarios, an extensive database was produced allowing for prospective LCAs across three storylines from 2020 to 2050 (SSP2-Base, SSP2-RCP26, SSP2-RCP19). The scenarios correspond respectively to 3.9, 2.0, and 1.5°C of global warming in 2100 (vs. pre-industrial levels). Regionally, China produces the largest volume of ammonia as well as the ammonia with the largest climate change impact, due to the dominance of coal gasification technology. To meet 1.5°C of warming (the most sustainable scenario) a global decrease of fossil-based ammonia is needed. For many regions, electrolysis (yellow) ammonia becomes the technology with the lowest global warming potential by around 2045 in the RCP26 storyline and 2035 in RCP19. Until the regional electricity mixes are cleaner, steam reforming, steam reforming with carbon capture and storage, or methane pyrolysis offer lower emission options. However, electrolysis using on-site or designated renewable energy can create emission-free green ammonia, without waiting years for a cleaner regional grid. This means that electrolysis is the best choice for new plants if a producer is not making urea on-site (or has an alternative source of carbon dioxide if they are). Reduction in urea demand will be important for reducing reliance on steam reforming and coal gasification, and a swift uptake of electrolysis with designated renewables must be the focus. However, burden shifting associated with the dominance of renewable electricity systems and bioenergy carbon capture and storage in the RCP19 scenario must be taken into account.

Shipping is, and will continue to be, the most important transportation method around the globe. A vital part of the logistic chain, it is also one of the main contributors to the worldwide CO2 emissions. Current propulsion technologies all rely on the same classic diesel driven technology, as diesel is widely available and has a high energy density.

The goal of this research is to identify greener solutions to propel a vessel sailing for short distances. During a definition study, several fuels and energy converters were studied and benchmarked based on a use case. The results showed that (a combination of) the dual fuel internal combustion, using bio diesel and hydrogen, and the low temperature proton exchange membrane fuel cell, fuelled with hydrogen, is the most feasible setup for the use case. Such a combination in itself is not a new one, but in the literature only an all-electric setup is described. In the proposed solution an internal combustion engine is driving the propellor shaft directly, assisted by an electric motor powered by the fuel cell.

Based on this outcome, the following research question was defined:

How can an internal combustion dual fuel engine and/or LTPEM fuel cell be integrated to form a cost effective solution to propel a short sea ship running on hydrogen?

First, nine designs were created, ranging from a conventional diesel engine setup as a reference case, to a fully electric design powered by fuel cells. All main components in these designs are analyzed regarding part load efficiencies. With these efficiencies, the fuel consumption at different loads are calculated. Based on a use case scenario the total fuel costs are calculated. The CAPEX and the OPEX of the designs are determined to calculate the total costs. As currently no other fuel can compete with diesel, the designs are compared based on the price per tons of CO2 emissions, as the shipping industry is expected to see a CO2 emission penalty in the near future. For each design, what the height of this penalty has to be to reach the breakeven point at the end of the use case was calculated. Based on the lowest CO2 price, an all-electric, fuel cell powered design was identified as the most promising option. Applying additional operational arguments such as redundancy and end user acceptance, it was decided together with Conoship to choose a combination of an internal combustion engine and a fuel cell.
This configuration is worked out in detail to answer the sub questions, covering efficiency improvement and system integration, during which it became apparent that not all information is available to answer all these sub questions. The design needs further research in a multidisciplinary team. A simulation model would be helpful in this further research. A framework and a start to such a model was written together with a list of recommendations.

Due to climate change, the growth in renewable energy is still accelerating and reaching new records each year. Not everything can be electrified, hence, the production of green hydrogen as an energy vector is gaining momentum. However, lowest cost hydrogen will not always be produced at the demand centres, necessitating transport of hydrogen which is nascent. In this, it has been realised that due to its easy liquefaction, proven transport at scales and matured production process, ammonia can be an excellent energy carrier. Currently, ammonia production accounts for more emissions than any other chemical and to achieve net-zero targets these emissions must be reduced ∼ 25-fold. Therefore,
ammonia synthesis with renewable energy will be imperative. Operating with variable hydrogen feed rates will be part of the challenge.

In this work, the dynamics of a small-scale ammonia synthesis plant with a capacity of 60 𝑡𝑜𝑛𝑠/𝑑𝑎𝑦 was studied. The application of chemisorption as replacement for the traditional condensation step for ammonia recovery was adopted in the study. In the system, the hydrogen feed was sourced from an
electrolyser powered by renewable energy. Hence, it was imperative to study the sensitivity and the response of the synthesis loop to the fluctuations in hydrogen feed. For the dynamics model, different scenarios of ramp-up and ramp-down were tested for two control structures to evaluate the response of various system parameters to these deviations. Therefore, the feasibility of these control structures was assessed and some of their potential limitations were identified.

The objective of this work was achieved with three simulation models. A steady-state model was employed to study the equilibrium conditions of the ammonia synthesis loop. A second more extensive model included reaction kinetics, heat integration and a chemisorption operation. The widely applied Temkin-Pyzhev rate equation was modified into LHHW form to fit this application. With the selected ZA-5 iron-based catalyst the operating pressure was established at 130 𝑏𝑎𝑟 to avoid overheating the catalyst. The simulation resulted in the reactor dimensions to attain the maximum possible conversion of 22.1% under these conditions. For the third model, the inputs from the two models were translated
into the a dynamic model. The latter was used to study the behavior of the system parameters when subjected to fluctuations in the hydrogen feed flow.

Three scenarios were tested with respect to the hydrogen variations: a (step and linear) reduction in the hydrogen feed of 10%, 25% and 50% of the initial value. With the default control system, the pressure varied by 16 bar with only a 10% step reduction of the hydrogen feed. This necessitated the development of control strategies to control the pressure deviations in order to eliminate metal
fatigue in the equipment. The first control structure compensated the lack of hydrogen by adding more nitrogen into the system. The second control structure reduced the recycle flow rate to decrease the ammonia production rate in the reactor.

Both control philosophies were successfully applied to control the system pressure for the 10% and 25% H2 ramp-down/up scenarios. The greatest pressure range measured during transient state in a linear 25% H2 reduction scenario for control philosophy 1 and 2 were 3.8% and 4.5%, respectively.
The effects of the variations and the control strategies have also been studied. In this research the nitrogen supply was assumed to be infinite, therefore a nitrogen buffer must be present. In addition, the use of a hydrogen buffer is required for a gradual decrease and dampens rapid changes in the hydrogen supply in order to minimize pressure variations.

The unprecedented rise in CO2 concentration in the atmosphere, and the accompanying rise in global temperature, has created the need for the development of environmentally friendly sources of energy. A very promising line of research focuses in the development of Carbon Capture and Utilisation (CCU) technologies; through which carbon-neutral liquid fuels could be synthesized. A great example of such technologies can be found in Zero Emission Fuels (ZEF), a dutch start-up currently developing a microplant capable of producing methanol from solar energy and ambient air. ZEF’s process involves the capture of CO2 and H2O directly from ambient air, the splitting of the captured H2O into its constituent
elements through electrolysis, and the synthesis of methanol from H2 and CO2. The entire process is powered by solar energy, which makes ZEF’s methanol a carbon-neutral liquid fuel.

This thesis focuses in the capture of CO2 and H2O from ambient air, a process known as Direct Air Capture (DAC). ZEF’s DAC unit differs from industry standards by using a novel continuous chemical absorption process through the flow of an amine based sorbent between its absorption and regeneration systems, instead of using a conventional batch process through a supported sorbent. The work of this thesis pertains the build and experimental characterization of ZEF’s first full scale DAC prototype, referred to as the 10X DAC prototype.

The built prototype, a fully functional DAC unit working in a continuous process, was experimentally characterized in terms of its performance and energy efficiency for the environmental conditions of the Dutch summer (i.e. hot and wet conditions). The absorption process was found to be limited by the capture of CO2 when compared to the H2O capture process, and to be liquid side limited; which aligned with literature sources where CO2 capture is defined as diffusion limited in the liquid side. Overall, the 10X DAC absorption column has the capacity of capturing 0.52 kgCO2/m3·hr; which is higher than the reported capture capacity of a very well established company like Carbon Engineering. In the
regeneration process, residence times in the stripper column as low as six minutes were enough for the sorbent to reach vapour liquid equilibrium (VLE) loadings for a regeneration temperature of 120◦C. The overall 10X DAC process is capable of producing 0.21 kgCO2/hr with an energy demand of up to 33MJ/kgCO2; which is up to 6 times higher than the reported most energy efficient DAC unit in industry. Furthermore, the H2O:CO2 product ratio was found to vary significantly, with a dependence to absolute humidity in the environment.

Through the experimental results of the characterization process, a chemical absorption model was developed which, assuming a liquid side diffusion limited process, considers the effects of the selected sorbent’s characteristics and the environmental conditions in the absorption process. Through this model, and the use of previous developed regeneration models, a DAC cycle is presented through which the effects of varying dynamic conditions (i.e. absolute humidity and ambient air temperature) were determined. Overall, it was noticed that the performance of the absorption process was negatively affected by higher temperatures, while the regeneration process remained unaffected by temperature
changes. Absolute humidity variations affected the H2O loading of the sorbent, which then affected the performance of the regeneration process; lower H2O loadings in the rich sorbent translated to higher CO2 lean loadings after regeneration. Furthermore, it was determined that the current sorbent in ZEF’s process favors cold and humid environments.

Finally, through the learnings and findings from both experiments and the developed absorption model, an optimized 10X DAC design is presented which focuses in meeting the CO2 production and energy demand requirements established by ZEF for its process.

The world is currently in the middle of an energy crisis, with a growing demand for energy playing catch up with an increasing population. The problem stems from the fact that we rely heavily on fossil fuels to meet our energy needs, and the combustion of these fuels are the primary source of greenhouse gas emissions. An accelerated rate of emissions of greenhouse gases has led and continues to lead to an increase in the average temperature of the planet, stated: Global Warming.
Shifting the balance in our favour requires arresting and lowering our emissions. Direct air capture of Carbon dioxide is one solution that has garnered massive traction in the global scientific community. Zero Emission Fuels is a visionary start-up operating out of Delft that aims to build a micro-plant capable of producing methanol using energy derived from the sun and raw material (CO2and H2O)harnessed from the atmosphere. The heart of their concept is liquid amine-based direct air capture. ZEF has pioneered the continuous process that involves the simultaneous absorption and desorption of CO2and water as the amine circulates from the absorber to the desorption column. The raw material and the energy to drive the process is harnessed from the environment. Thus these inputs remain outside the control of the ZEF system and are treated as external disturbances. This research aims to analyse the impact of the varying environmental conditions, i.e. the ambient temperature, absolute humidity and incident solar radiation, on the performance of the desorption column. Following which a control scheme is developed to ensure the system meets the requirements of ZEF, i.e. production of CO2and water in a 3:1 molar ratio and an energy consumption limit of 450 kJ/mole of CO2desorbed.Firstly, a set of experiments with a trayed stripping column were performed to understand the start-up and shut-down behaviour of the column. Based on the observations, a simplistic model of the reboiler was developed to predict the transient behaviour of the column during start-up. A sensitivity analysis was carried out to gain insights into the parameters influencing start-up time and energy demand. Furthermore, different scenarios to start up a column were identified and based on the results, the batch mode is adopted as the efficient way to start up a column. The model predicts that start-up and shut-down account for less than 10% of the total operating time available. Moreover, start-up accounts for a maximum of 6% of the total available energy for production.
Secondly, a set of single-stage kinetic experiments were performed at different temperatures to understand the limitations of the desorption process inside the column. A vapour-liquid equilibrium based stage-by-stage model of a desorption column integrated with a varying space-time yield based absorber model. Design parameters of the integrated DAC model were tweaked, and a base case was developed, to understand the impact of a varying sorbent composition and PV panel output on the performance of the DAC subsystem. It was clear the open model was not capable of meeting the 3:1top ratio specifications of ZEF. Which prompted the implementation of control structures. Single loop mass-flow control, pressure control and cascade mass flow-temperature control schemes were individually tested with the aid of the integrated DAC model. Finally, based on the performance of the individual control schemes, a final parallel control scheme was developed. Wherein the temperature and the pressure of the system adjusts according to the varying power input and the absolute humidity conditions that impact the top ratio of products. The parallel control scheme was found to be adequate in maintaining the top ratio at desired levels.