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 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.

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

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

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

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

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

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

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

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

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

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

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