Low-temperature electrochemical CO₂ conversion has gained growing attention as a potential route towards a more circular and electrified chemical industry, particularly for producing carbon-based chemicals under mild operating conditions. Most progress remains focused on electrochemical reactor performance or lower-order products, while industrial feasibility also depends on process integration, separation, recycle design, purification, and economic performance. It therefore remains unclear whether coupling CO₂ electrolysis with electrocarboxylation can provide feasible pathways to higher-value circular chemicals at industrial scale.

This study assessed the techno-economic feasibility of producing ethylene carbonate (EC) and succinic acid (SA) via direct and tandem low-temperature electrochemical CO₂ conversion pathways in an industrial-scale plant in North-West Europe. A structured screening framework compared CO₂-derived products and pathway concepts using complete CO₂ utilisation, technological readiness, continuous operation, electricity demand, economic attractiveness, strategic fit, and sustainability by design. This led to the selection of EC as the strongest near-term product candidate and SA as a complementary high-value case, with ethylene and carbon monoxide (CO) retained as key intermediates. Four routes were then defined: direct and tandem pathways to EC, and direct and tandem pathways to SA.

The routes were developed as process flow diagrams and implemented as steady-state Aspen Plus models, including electrolysers, electrocarboxylation cells, gas and liquid separation sections, recycle structures, and final purification. The resulting mass and energy balances were used in a techno-economic assessment (TEA), with net present value (NPV) as the main feasibility indicator. Under the base-case assumptions, none of the four routes reached economic feasibility, as expected for early-stage low-temperature CO₂ electrolysis and electrocarboxylation at industrial scale. This result should be interpreted as a current feasibility benchmark rather than as a rejection of the route concepts. Route 1, the direct pathway to EC, showed the strongest process-design and mass-balance performance, while Route 2, the tandem pathway to EC, was the strongest near-term techno-economic option. The SA routes showed higher product-revenue potential and the strongest optimistic-case upside, but were constrained by dry-solvent operation and losses, raw material demand, product purification, and downstream separation uncertainty.

The case analysis showed that technology improvements alone were insufficient, whereas improved economic conditions had a stronger effect and the combined optimistic case made all four routes economically feasible. Overall, the selected routes are technically credible early-stage pathways, but not yet techno-economically feasible under current base-case assumptions in North-West Europe. The main bottlenecks were electrochemical cost, economic exposure, dry-solvent demand, product purification uncertainty, and separation and recycle uncertainty. Future research and development should therefore prioritise integrated electrochemical and separation improvements, focusing on lower stack cost, lower cell voltage, stable high-current operation, dry-solvent recovery, electrolyte-compatible product purification, recycle validation, and realistic North-West European market conditions.

The Netherlands is transitioning towards a fully renewable energy system, aiming to achieve an almost entirely renewable energy supply by 2050. Green hydrogen, produced via water electrolysis powered by renewable energy, offers a key solution for decarbonising energy-intensive sectors. However, high production costs remain a major barrier to widespread adoption. This study investigates the cost-optimal design of a hybrid renewable energy system combining solar PV, onshore wind, and battery storage to supply a 200 MW electrolyser in De Koog, the Netherlands.
A simulation model was developed in Python, incorporating hourly wind and solar generation data, electrolyser operation with on/off stack control, battery charging and discharging, and system degradation over a 20-year lifetime. Multiple system scenarios were evaluated by varying installed capacities, battery sizes, and minimum stack operation rules. Economic performance was assessed using key indicators, including hydrogen sales price, levelised cost of hydrogen (LCOH), net present value (NPV), internal rate of return (IRR), and payback time. Additionally, stack and battery replacement costs were considered. Results show that the cost-optimal system for the chosen location, De Koog, is dominated by wind-only systems, with the electrolyser operating at a capacity factor of 0.659. Inclusion of a small battery provides
minor operational flexibility, increasing annual hydrogen production slightly from 22.98 to 22.99 million kg, but has a negligible effect on hydrogen sales price (7.442–7.444 €/kg), NPV, LCOH, IRR, or payback time. From year 8 onwards, stack replacement costs remain constant, as stacks are replaced annually and battery replacement is scheduled after 13.5 years, leading to only a limited and predictable increase in total system costs. Electrolyser stack granularity affects operational efficiency: smaller stacks reduce curtailment without storage but slightly limit battery utilisation when included.
The findings indicate that the economic performance of green hydrogen production is primarily driven by the balance between renewable generation and electrolyser operation. In particular, the renewable to-electrolyser capacity ratio plays a key role, while battery storage has only a minor influence in the cost-optimal configuration. For the analysed Dutch coastal site, the lowest hydrogen production costs are achieved with a moderately oversized wind capacity, an electrolyser operating at an intermediate capacity factor, and minimal battery integration. However, the optimal capacity ratio and the economic value of battery storage are strongly location-specific and depend on local resource conditions and system design assumptions. This study provides a comprehensive techno-economic assessment of hybrid renewable energy system design, offering practical guidelines for optimising component sizing to achieve cost-efficient green hydrogen production in the Netherlands and supporting the transition to a low-carbon energy system.

The increased emission of carbon dioxide (CO2) derived from the use of fossil fuels has a major in fluence on global warming and climate change. In order to reduce these emissions, carbon dioxide can be capture from the air and converted into useful products. This can be done for example using the Sabatier reaction, in which CO2 and hydrogen (H2) are converted into methane (CH4) and water (H2O). This reaction is reversible and it is therefore desirable to adsorb the water to shift the reaction equilibrium to the product side, applying Le Chatelier’s principle. Water adsorption is achieved using zeolites, which are hydrated minerals with an open crystal structure. There are many zeolite types, both natural and artificial. This study will focus on determining which zeolite type is the most suitable for water adsorption in the Sabatier reaction at relevant process circumstances and which properties account for this superior performance.

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

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

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

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

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

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

This thesis investigates the techno-economic feasibility of an integrated process that captures post-combustion CO₂ and converts it into carbon monoxide (CO) via electrochemical reduction powered by renewable electricity. The approach is intended to reduce the high regeneration energy of conventional amine-based capture while producing a valuable chemical feedstock. A hybrid solvent of 0.5 M MEA in a choline chloride–ethylene glycol deep eutectic mixture was evaluated, showing comparable capture performance to aqueous MEA and a lower heat of absorption (–59.8 kJ/mol), indicating potential energy savings.

Electrolysis was assessed under worst, baseline, and best-case scenarios with current densities between 100 and 300 mA/cm², voltages of 2.5–4 V, and CO faradaic efficiencies of 20–60%. Projected annual CO production ranged from 69.8 to 174.4 kt, with energy efficiencies of 10–48%. A semi-empirical vapor–liquid equilibrium model was applied, achieving high accuracy (R² > 99%, AARD < 3%).

Economic analysis shows that none of the scenarios achieve positive net present value at current market prices (CO: €0.64/kg, H₂: €4/kg). Electricity accounts for about 98% of operating costs, making the system highly sensitive to power price and product value. The best case becomes feasible at €0.06/kWh electricity or €0.96/kg CO, while the baseline requires €1.43/kg CO. The worst case remains unviable under all tested conditions.

In conclusion, the system demonstrates strong technical potential but limited economic feasibility under present conditions. Viability depends on access to low-cost renewable electricity, improved electrolyzer efficiency, and supportive policy or market frameworks. Further research on solvent properties, process integration, and pilot-scale demonstrations is recommended to advance this concept toward industrial application.

As global regulations and International Maritime Organization (IMO) targets intensify, the maritime sector faces increasing pressure for decarbonization, reduction of greenhouse gas emissions and improvement of energy efficiency. Conventional marine auxiliary power systems, typically marine diesel generators, operate at low electrical efficiencies (25–45 %) and produce significant emissions. Bio-methanol, a renewable liquid fuel produced from biomass or renewable electricity, offers an attractive alternative for the yachting sector due to its high energy density, ambient-condition storage, compatibility with existing infrastructure, and ability to yield hydrogen-rich reformate gas for fuel cells. However, integrating methanol steam reforming (MSR) with solid oxide fuel cells (SOFCs) in marine environments remains largely unexplored in the literature.

This thesis investigates the design and modeling of an integrated bio-methanol steam reforming (MSR)–solid oxide fuel cell (SOFC)–Organic Rankine Cycle (ORC) system for a Feadship superyacht, developed in Aspen Plus. The bio-methanol reformer supplies hydrogen-rich gas to the SOFC stack, which subsequently drives both electric generation and heat recovery. Component integration includes thermal coupling between the MSR reactor, the afterburner, preheaters, and the ORC. The system meets auxiliary power demands from 225 kW to 325 kW and is modeled at three representative auxiliary power levels: 225 kW, 275 kW, and 325 kW. Motivated by the need to optimize both system efficiency and heat management, this work addresses a critical research gap in the techno-economic assessment of renewable methanol-based SOFC power systems for maritime applications.

The model incorporates MSR kinetics, SOFC electrochemistry—including activation, ohmic, and concentration losses—and waste heat recovery. Iterative SOFC area sizing and heat integration strategies are developed and validated, while an analysis of the operational expenditure of the system is also included. Sensitivity analyses investigate the influence of SOFC fuel utilization and operating temperature on the system’s performance and consumption of resources. Analyzing key performance indicators, such as electrical generation efficiency and combined heat and power (CHP) efficiency, under different load conditions, has revealed that at the 225 kW partial-load condition, the system achieves a maximum electrical generation efficiency of 57.2% and a CHP efficiency of 79.4%, significantly outperforming conventional marine diesel generators. At the intermediate 275 kW load, the system reaches an electrical generation efficiency of 54.3% and a CHP efficiency of 71.5%. At full load (325 kW), the corresponding efficiencies are equal to 52.0% and 65.9% respectively.

The results confirm the technical feasibility of bio-methanol-fueled SOFC systems for superyacht applications and demonstrate their potential for significant efficiency gains. The developed model provides a foundation for future optimization, hybridization strategies, and onboard integration, supporting sustainable decarbonization in the maritime sector.

As the energy demand is growing rapidly across the globe due to industrialization and higher living standards, along with the depletion of fossil fuel reserves and the effect of climate change more evident than ever [1], there is an urgent need to transition to sustainable methods of energy production. Among various sustainable energy alternatives, bio-energy is expected to play a significant role in the energy transition. Gasification constitutes a thermochemical way of converting carbonaceous feedstock into useful energy. When implemented with biogenic or waste-derived fuels, gasification can provide a promising sustainable energy solution, while it can also simultaneously deal with the landfill waste problem when utilizing feedstocks like Solid Recovered Fuel (SRF). Despite the fact that gasification of coal is often featured in literature, the use of biomass or SRF in gasification practices is still limited. Specific areas like the handling of tars, detailed modeling of the hydrodynamics in the fluidized bed and the freeboard of the reactor, as well as the implementation of chemical kinetics specific to wastederived feedstocks remain underexplored in literature. Furthermore, many studies completely ignore the freeboard region in their models, where critical reactions still occur. Therefore, the aforementioned research gaps are aimed to be answered to in the current thesis project. The purpose of this Master Thesis was to study bubbling fluidized bed gasification and develop a model of its processes using the Python programming language. The open-source software ”Cantera” was used [2], which contains tools for dealing with reaction kinetics, thermodynamics and transport phenomena. To be more exact, the python model includes the chemical reaction kinetics, the mass transfer, and finally the fluid mechanics in the reactor and calculates the composition of the final exiting gas, as well as other physical parameters of the process. The added value of this thesis project lies in the validation of the developed model against experimental results obtained from a series of tests carried out at the TU Darmstadt gasification facility, when experimental gasification campaigns were conducted using Solid Recovered Fuel (SRF) [3]. In addition, this work contributes to the modernization and further development of the model originally presented in Hamel’s PhD thesis [4]. The modeling approach that was followed for the construction of this model was based on a 1-D cell model, where the fluidized bed and the freeboard were discretized in control volumes. Within these control volumes, the local hydrodynamics and the gasification reactions were applied, through mass balance equations. As initial conditions for the gasification model, the outputs of a pyrolysis model were used, applied to the incoming feedstock. The final results of the numerical model show good agreement with the experimental set of data from the TU Darmstadt gasification campaign. More specifically, the model manages to predict with reasonable accuracy the concentrations of four out of the five major syngas species considered. The most notable shortcoming of the model lies in the prediction of the methane content in the final syngas, as this was completely depleted inside the bed, which is an unrealistic behavior given the operating temperature range of the gasification process. This deviation likely lies in the fast kinetics of the steam methane reforming and methane oxidation reactions, pinpointing the need for more accurate reaction kinetics. However, the content of CO, H2, CO2 and H2O were captured reasonably well. In addition, the model predicted a carbon conversion efficiency of 100%, which is unrealistic compared to typical values of around 70-90 % that are observed in real-life applications. This value overestimation lies in the fact that carbon is treated as a pseudo-gaseous species in the model, as well as in the fact that incomplete carbon conversion mechanisms, such as bottom ash removal or particle entrainment with the syngas, are not being considered. Different tests of sensitivity analysis were also conducted to assess the effect of different key parameters on the final product, including the freeboard temperature, the initial gasification conditions, the gaseous distribution through the nozzles and different kinetic parameters. Overall, the model managed to come close to the experimental results, demonstrating its potential in simulating the use of waste-derived fuels in a bubbling fluidized bed gasifier. Therefore, it provides a strong basis for further exploration and development.

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.

In the context of maritime decarbonization, methanol has emerged as a promising alternative fuel due to its favorable storage properties and potential for renewable production. This thesis investigates the techno-economic performance of integrating methanol steam reforming with low-temperature proton exchange membrane fuel cells (LT-PEMFCs) for on-board power generation on a super-yacht. The primary objective is to conduct a comparative analysis of two distinct system architectures: an integrated membrane reactor where reaction and separation occur simultaneously (Configuration A), and a conventional packed-bed reactor followed by a separate membrane purification unit (Configuration B).

To evaluate these systems, two detailed, steady-state process models were developed using the Aspen Plus V12 simulation software. The core unit operations, including the coaxial membrane reformer and the PEM fuel cell, were modelled using custom-developed User2 Fortran subroutines. These subroutines implement detailed, literature-based models for the MSR kinetics (Peppley et al.), hydrogen permeation (Sieverts’ Law), and PEMFC electrochemistry (Correa et al.). The systems were sized to meet a 325 kW net power demand derived from real-world Feadship vessel load data, and comprehensive heat integration strategies were implemented for both.

The simulation results reveal a fundamental trade-off between unit-level conversion efficiency and system-level thermal efficiency across the different power loads. While the membrane reactor (Configuration A) achieved superior methanol conversion due to in-situ hydrogen removal, its fuel-depleted retentate stream necessitated a significant supplementary fuel flow to the burner for heat integration. In contrast, the conventional packed-bed reactor (Configuration B), despite a lower conversion, produced a fuel-rich retentate that greatly improved the effectiveness of its heat recovery loop.

Consequently, Configuration B demonstrated a higher overall system efficiency (59%) and lower specific methanol consumption compared to Configuration A (57%) at the design point. The operational cost analysis further confirmed this advantage, showing lower annual fuel and membrane replacement costs for Configuration B. This study concludes that for an integrated onboard power system where retentate fuel value is critical for thermal self-sufficiency, the conventional reactor with a separate purification unit represents the more efficient and economically viable architecture. Both modelled systems, however, show significant efficiency and emissions advantages over traditional marine diesel engines, validating the promise of methanol-reforming PEMFC technology for sustainable maritime applications.

The present work investigates the valorization of wine industry residues through the production of advanced biofuels, focusing on grape pomace as a representative lignocellulosic feedstock. The study aims to assess the technical and economic feasibility of converting this residue into liquid fuels via hydrothermal liquefaction (HTL)and to compareits performance against the bioethanol basedpathway currently implemented by Destilerías y Biorefinerías Zambrana, S.A. in the Basque Country.

The increasing dependence on fossil fuels for energy and chemicals has caused a significant rise in atmospheric CO2 concentrations, leading to global warming and ecological imbalances. Electrochemical CO2 reduction (CO2R) has emerged as a promising technology to mitigate CO2 emissions while converting it into valuable chemicals and fuels, such as ethylene, ethanol, and acetic acid. With its compatibility with renewable energy sources, moderate operating conditions, and potential for high selectivity, CO2R is positioned as a key player in the transition toward a carbon-neutral economy. However, challenges such as mass transfer limitations, impurities in industrial CO2 feedstocks, and economic feasibility hinder its large-scale implementation. This thesis aims to address these challenges through experimental studies, process design, and techno-economic analysis. The combined findings also reveal key limitations that must be addressed for large-scale deployment.

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.

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...

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....

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.