Medical oxygen is crucial for effective treatment of patients, yet many low- and middle-income countries (LMICs) without a good healthcare infrastructure have been unable to provide sufficient oxygen therapy for years now. The COVID-19 pandemic highlighted the critical need for more oxygen, leading to supply shortages and rising prices even in developed countries. Currently, most medical oxygen is produced by a few large companies using centralized Cryogenic Air Separation Units (CAS). Pressure Swing Adsorption (PSA) offers a promising alternative, enabling local production of medical oxygen without reliance on suppliers. PSA leverages the pressure dependency of adsorption isotherms to selectively adsorb nitrogen, concentrating the oxygen.

This research has investigated the possibilities of designing a system that not only meets the specific oxygen demands of a Dutch hospital but also complies with the Dutch legal frameworks and forms an economically feasible case. A case study at Reinier de Graaf hospital (RdGG) in Delft used real oxygen consumption data. The applicable regulatory frameworks have been obtained by research in literature and with help of a representative at RdGG. For the technical design and optimisation, a numerical model of the PSA-cycle has been developed. This model is based on the Ideal Adsorption Solution Theory (IAST) and makes use of the Linear Driving Force model for adsorption kinetics. The model behaviour has been validated by experiments within a self-built, small-scale PSA-unit in the Process & Energy (P&E) lab. After this, the setup was scaled to hospital size within the model. A schematic PSA-plant has been designed based on the regulatory frameworks and system requirements which came from the numerical modelling. The economic viability has been addressed based on quotes, consumption data and electricity prices which were provided by RdGG.

Dutch regulations require hospitals to have three oxygen sources, each capable of independently providing the full design flow, with PSA units obligated to produce 93% oxygen concentration (± 3%) and meet strict impurity limits. To achieve the required oxygen purity, a vacuum pressure of 0.05 bar and an adsorption pressure of 6 bar with Oxysiv MDX zeolite are optimal. Depressurization should occur close to atmospheric pressure (1.05 bar) for efficiency. The adsorption column is most effective with a diameter-to-length ratio of 0.1 and a dimensionless time, tc, of 9.56 seconds for maximum oxygen production. The dimensionless time represents the time it takes for the gas to pass through the length of the column based on its inlet velocity.
The PSA unit at RdGG must handle a normal demand of 10 Nm³/h and a peak demand of 80 Nm³/h for three consecutive days. The second source can handle peak demand for three days, while the backup source can manage only 9 hours (tvital). If the PSA-storage has been depleted and the second source fails, tvital is the maximum refill time of the PSA-storage. This requires a production rate of 0.40 mol/s and two packages of storage cylinders (1.6 m³) which store the oxygen at 200 bar. This setup necessitates two 336L columns (3.5m height, 0.35m diameter, 0.36 m/s inlet velocity) and an air inlet flow of 126 m³/hr, supported by a vacuum pump and a compressor. The cycle steps for the adsorption, depressurization and vacuum (tAD = 79 s, tDP = 67 s, tVC = 112.1 s) total 258.7 s, allowing two columns to run in parallel. A 3 m³ air pressure vessel at 10 bar maintains PSA operation for three minutes during compressor disturbances. This setup achieves 93.61% oxygen purity with 41% recovery for 93% oxygen concentration, increasing to 58% recovery for 90% oxygen concentration. Each column requires 127 kg of zeolite, producing 5.75 mol O₂ kg⁻¹h⁻¹ (0.66 m³ O₂ kg⁻¹h⁻¹ at adsorption pressure), with an energy consumption of 29.38 kJ per mole of oxygen, totalling 255 kWh/tO₂.

The total investment for a PSA plant is estimated at 215,190 EUR, with fixed equipment costs of 176,800 EUR. Using straight-line depreciation over 20 years results in annual depreciation of 9,890 EUR. Annual costs also include energy and maintenance.
For an oxygen demand of 234 tons in 2023, the annual cost would be 25,590 EUR using PSA, significantly less than the current 60,840 EUR with the Liquefied Oxygen (LOX) installation. The levelized cost of oxygen over a period of 20 years for PSA is 128.61 EUR/ton, which is 2.1 times lower than the LCOO of LOX which is 270.52 EUR/ton.

The implementation of PSA plants for localized oxygen production in the Netherlands is both technically and economically feasible. A case study at Reinier de Graaf hospital shows significant cost savings compared to current liquid oxygen setups, with potential annual savings of 35,250 EUR. Required equipment is available and the setup size allows it to be installed inside or next to the hospital. Regulatory frameworks are already present and define clear requirements for using a PSA system as primary source. When implementing the right flow and pressure mechanisms the PSA plant can be connected to the current second and backup source, minimizing system adjustments for a smooth integration.

Future research should focus on several key areas to enhance the feasibility of using PSA in Dutch hospitals. Regulatory frameworks need approval or revision by experts in medical oxygen production. Analysing zeolite degradation and validating its performance are crucial for simulating the PSA unit's lifecycle. Improved modelling techniques, considering temperature variations, research on the validity of current assumptions and preventing backflow in the experimental setup will yield more accurate results. Additionally, industry practices should be reviewed to refine the proposed setup and obtaining precise cost estimates from quotes or hospital bills will improve the economic analysis.

Due to greenhouse gas emissions, global warming has severe environmental consequences. To tackle this issue, XINTC produces green hydrogen using alkaline electrolysis to replace fossil fuels. Green hydrogen’s primary challenge is its dependence on intermittent energy sources for electrolysis. Hydrogen storage is necessary for the hydrogen economy to meet production and demand peaks. This work focused on hydrogen storage using double membrane gas holders storing hydrogen at atmospheric pressure, a novel hydrogen storage method. The main goal of the storage is to avoid power cycling the downstream hydrogen compressor. Energy and mass balances are calculated considering molecule permeation through the membranes and water condensation. Weather conditions are also taken into account. To regulate the pressure in the storage, a control system consisting of PID controllers connected to pressure relief valves was designed.
The model shows the behaviour as a response to changing weather conditions. It has been proven that the water in the system will condense and, at certain points, even freeze. A drain is necessary to evacuate the water forming in the system. The control system manages the system accordingly, opening the valves to the desired amounts at the desired moments.
It was also proven that one should not have to worry about forming a combustible hydrogen-oxygen mixture. If the storage is filled at 10% of its maximum value, it takes more than 500 days to reach that value.
The permeation of nitrogen through the membrane is a bigger issue. If the storage is filled to 10% of its maximum value, the maximum concentration of 300 PPM is exceeded within three days at a standstill. Thus, the storage will have to be drained long before safety issues arise.
The model is fully modular, meaning that it can be run for all locations around the world. It can easily compare storage behaviour and performance.
The outcome of this research has led to a better understanding of the behaviour of hydrogen storage in membrane gas holders. The model developed can be used to effectively manage hydrogen storage, reducing any hydrogen losses and maximising storage efficiency

This thesis focused on designing and constructing a deoxygenation reactor through a modular experimental setup for Catalytic Hydrogen Combustion (CHC). The developed system aims to enhance hydrogen purification techniques. The setup enables testing various catalysts and conditions to remove oxygen down to 5 ppm in a hydrogen stream.

The experimental system was designed from the ground up due to the lack of detailed information on existing systems. The design includes gas treatment, the catalytic reactor, and a post-process system, with several iterations for modularity and safety.

The final setup successfully removed oxygen in an initial test and allowed flexible reactor configurations for various catalyst tests. The system operated smoothly, maintaining gas composition and ensuring safe operation. The oxygen sensor performed reliably, providing data that aligned with the 1D model after adjustments.

In summary, this thesis lays a strong basis for further CHC research. The developed experimental setup is a robust and adaptable tool for researchers and engineers aiming to improve hydrogen purity for industrial applications.

Hydrogen's competitiveness as a sustainable energy carrier depends greatly on its transportation and storage costs. Liquefying hydrogen for these purposes offers benefits like purity, versatility, and higher density. However, current industrial hydrogen liquefaction processes face efficiency and cost challenges, with a second-law efficiency below 25% and costs between 2.5-3.0 US$/kg_LH2, and they are mainly limited to small-scale. Scaling up liquefaction plants is a potential solution to reduce costs, but existing models often overlook the economic and technical viability of the conceptual plants.

Most reported liquefaction costs rely on "ballpark" estimation, hindering process economic comparisons between various processes. Industry-sponsored studies often use confidential data, limiting accessibility. Thus, this thesis aims to develop a comprehensive framework for modelling large-scale liquefaction processes and assessing their feasibility, focusing on the large-scale high-pressure hydrogen Claude-cycle liquefier concept.

The technical analysis focuses on the preliminary designs of main equipment, such as compressors, turboexpanders, and heat exchangers, ensuring compatibility with existing technology limitations. Aspen Process Economic Analyzer (APEA) is employed to estimate the capital and operating expenditure. At 0.1 €/kWh electricity price, the techno-economic assessment of the 125 tonnes per day (TPD) Claude-cycle concept yields specific liquefaction costs (SLC) of 1.55 €/kg_LH2. Sensitivity analysis shows electricity price has significant influence. Applying the established design approach, incorporating high-speed centrifugal compressors could reduce the SLC by 5.42% and potentially more.

Scaling up to 250 and 500 TPD shows potential SLC reductions of 7.80% and 9.45%, respectively, at electricity price of 0.1 €/kWh. Future projections suggest a potential 12.6% SLC reduction as the Claude-cycle liquefiers matures. In an ideal scenario, with incentives and low-cost renewable electricity, costs could range from 0.87 to 1.09 €/kg_LH2.

Finally, a cost-scaling curve for hydrogen liquefaction plants are estimated based on the cost results from this study. The curve is comparable to existing cost curves reported by industrial and government joint research projects, validating the methodologies developed in this thesis. Moreover, an experience curve is also predicted using cost data from this study and data found in the literature. The curve indicates a 17% price decrease in hydrogen liquefiers with each doubling of global liquefaction capacity.

The utilization of water electrolysis for hydrogen production is expected to increase significantly in the upcoming decades. Modular system design offers great advantages for emerging markets, whilst providing the necessary flexibility in capacity that intermittent renewable energy sources require. Literature research reveals little information regarding modular water electrolysis systems. However, their availability on the consumer market proves that there is demand for such systems. To facilitate the emerging hydrogen market, a modular engineering design approach is used to develop a containerized alkaline water electrolysis system. This containerized system achieves a high degree of modularity by utilizing multiple modular sections. Each section functions as a stand-alone hydrogen production station, containing all necessary components required for safe hydrogen production. These components include heat exchangers, gas-liquid separators, modular alkaline electrolyzers, and a novel component called flow panels. In conjunction with the Dutch company XINTC, the design of the modular sections and their components is presented. Significant capital expenditure reduction is achieved by operating at atmospheric pressure, allowing for cost-efficient material selection and their corresponding manufacturing methods; both of which are discussed. Thermal, hydrodynamic, and particle dynamic models from literature are presented and evaluated. The proposed hydrogen separator is expected to achieve a separation efficiency of over 99.8%. A thermal system analysis concludes that the system is capable of operating at maximum capacity for ambient temperatures of up to 35 C. Additionally, a hydrodynamic system analysis shows that the pressure drop inside the system is dominated by that of the heat exchanger, and is in conformity with the Pressure Equipment Directive.

Renewable energy resources like wind and solar have the potential to revolutionize our energy infrastructure and enable a decarbonized society. The intermittent nature of renewables poses a challenge to ensuring a consistent and reliable electricity supply. Hydrogen technology is emerging as a promising solution for stabilizing renewable energy systems. There is still significant technological development required to cost-effectively integrate hydrogen with renewable energy assets. Conventional PV solar installations require power electronics for their operation, like charge controllers and inverters. Not only are these power electronic components costly and in high demand, but they also degrade faster than PV solar panels. Removing power electronic components could significantly lower the investment costs associated with a PV solar park.

This work focuses on how PV solar panels can be directly coupled to a modular alkaline electrolyzer, without grid-based buffering or the use of an inverter. Literature research revealed that hydrogen technology has seen little exploration in on-grid Hybrid Renewable Energy Systems (HRES) and no exploration in off-grid HRES. To appropriately investigate whether a directly-coupled HRES would be technically feasible, a megawatt-scale system was modelled and simulated. All elements of the HRES were modelled, duly accounting for physical limits and constraints. Components were sized and configured to complement one another, optimizing for maximum hydrogen production. To experimentally verify the validity of the proposed HRES, a 5 kW pilot system was constructed. To control the HRES, a new algorithm was developed using the Incremental Conductance maximum power point tracking algorithm as a basis. Within the new Maximum Hydrogen Production (MHP) algorithm, the step sizing was discretized and a variable step size was implemented which can be applied to any target slope. This allows for the system to target operational points which optimize hydrogen yield instead of electricity yield. Furthermore, the addition of tracking bias helped adjust for the asymmetric nature of the interaction between electrolyzer stacks and the PV solar park.

Simulation results in The Netherlands demonstrated that the feasibility of the HRES is dependent on the configuration of the PV solar park and on the number of electrolyzer stacks in the system. Compared to industrial and research benchmarks, the proposed HRES increased hydrogen production by 14.9% and 4.2%, respectively. Dynamic 'm-tracking' of the MHP algorithm goal increased hydrogen production by 0.8% in months of high irradiance. Months with a lower average irradiance experienced an artefact in the MHP algorithm, resulting in prolonged periods of zero power output. An experimental setup confirmed the simulation results, showing that it is possible to control a system of PV solar panels directly coupled to a modular alkaline electrolyzer. Experimental results revealed the need for moving average filtering to prevent fluctuations due to changing conditions of the electrolyzer and the weather from causing poor algorithm tracking ability. The low performance of the experimental setup can be attributed to a low iteration and measuring frequency, which increase the likelihood of a tracking error due to rapidly changing operating conditions. Economic analysis of the proposed HRES yielded an LCOH of €3.44 per kg, 20% and 13% lower than industrial and research benchmarks, respectively. Therefore, an HRES featuring PV solar and modular alkaline electrolysis is technologically and economically viable without the use of charge controllers and inverters.

District heating networks (DHN) in the Netherlands have the potential to supply sustainable heat but are currently designed to deliver around 80 \% of the heat from a sustainable source. The peak demand is delivered with a gas boiler because of flexibility and costs. With the share of DHNs increasing in the Netherlands and the goal to be CO$_2$ neutral by 2050, a replacement for gas boilers in DHNs has to be found. This research evaluates the potential of seasonable thermal energy storage to supply the peak load in small-size DHNs in the Netherlands.

The research consists of 3 steps. First, the key performance indicators (KPIs) of the implementation of STES in DHNs are determined and the technologies with the most potential per seasonal thermal energy storage (STES) category (sensible heat storage (SHS), latent heat storage (LHS) and thermo-chemical energy storage (TCES)) are determined. Then a Matlab model is developed to determine the volume, storage losses and total efficiency of the three selected technologies. Multiple scenarios are defined to evaluate the technical and financial potential of STES in different situations and configurations. Lastly, the STES are assessed on their potential to be integrated into a DHN to supply peak demand by analyzing investment costs, operating costs, volume, storage losses, and total efficiency. Throughout the research, a gas boiler is used as the reference scenario.

The models developed in the research are validated and can be used in specific case studies to determine the necessary volume of the STES, temperature profile throughout the year in the STES, mass flows and temperature of the supply HTF to the DHN, and the total losses of the STES, using the heat demand of the DHN, the HTF, the PCM, the reactant, the shape of the tank, the insulation thickness an material and the heat supply of the source.
With the outputs of the developed models, the costs can be calculated. The output of the model and the costs can be used to select the optimal STES to be implemented in the DHN of that specific case study.

This research shows that SHS is most feasible to be integrated into a small-size district heating network to deliver winter peak load in the existing built environment regarding volume, CO2 emissions, and costs.\\
A buried tank with water as the storage medium and heat transfer fluid (HTF) is selected as the technology with the most potential within SHS. For LHS, Paraffin is selected as phase change material (PCM) and water as HTF. For TCES, potassium carbonate is selected as the reactant.

In this thesis, the first part will be a review of the literature that includes as much of the commercially available information on carbon capture and mainly, Direct Air Capture (DAC). What are the difficulties surrounding capturing CO2 from gas mixtures and what are the possible solutions that have been investigated? What type of negative emission technologies have been proposed, what are the important parameters for the design of carbon removal technologies and what are the biggest obstacles that need to be overcome? Gathering sufficient data and comparing the different finding will be of importance, given that DAC technologies are still in developing stages and information is limited. The focus of this thesis will be on chemically amine based solid sorbents, as this can be argued that this is the most promising technology for a viable DAC system.

The modelling part of the thesis will be focused on the design of and development of a DAC model in the open source software ’Python’. The amine based sorbent that is investigated and used for the creation of the model is Lewatit VP OC 1065. Using experimental data gathered from the literature together with feasible assumptions, a model will be built to recreate the the whole DAC process and analyse the system. The main focus will be on acquiring a flexible model for both the adsorption and desorption parts of the DAC process to make further investigation of the system parameters possible. This model will be used after this thesis for further development and, for instance, analysing different possible sorbents.

The heating and cooling sector is one of the biggest sectors at this moment due to drastic fluctuations in climate parameters. Even though this sector helps in making sure everyone gets comfortable temperatures at the home, office, etc., there are environmental consequences attached to them. These consequences are in terms of emissions of greenhouse gases. Almost around 80% of the current greenhouse gas emissions are due to the demand for energy, mostly in the form of electricity and heat. Having looked at these emissions, the demand for heating and cooling in residential and commercial spaces is increasing day by day. The systems which provide the desired effect of cooling and heating use different working mediums i.e. fossil fuels and renewable sources which correspond to 75% and 22% usage in the EU currently. So, to reduce the consumption of fossil fuels, heat pumps came into the picture.
A heat pump uses a refrigerant through which heat transfer is carried out to attain the desired temperature at a particular location. The properties of these refrigerants and other component-based parameters affect the COP (Coefficient of Performance) of the system. For a mobile system, i.e. a portable heating and cooling device used for military camps, agricultural purposes currently use fossil
fuels which lead to enormous emissions, thus, these systems have to be redesigned by using vapor compression technology. One of the constraints is being able to use a refrigerant with GWP (Global Warming Potential i.e. a measure of the amount of heat a greenhouse gas traps in the atmosphere
comparing it with the same amount of CO2) of less than 150. Aspen model was created to assess different refrigerant behavior under some constraints like a cooling capacity of 40 kW, a heating capacity of 60 kW, and an air-air system with an airflow rate of less than 10000 m3/h, these requirements are
obtained from fossil fuel-based mobile systems, as these systems are air-air systems and system is kept outside the desired place, hoses have to be used to provide the air into and out of the system, thus, the specific air flow rate has to be achieved to get the desired temperature inside the desired place, similarly, 40-60 kW is a need for these systems due to high capacity applications. Sensitivity analysis of the aspen model was carried out by changing ambient temperature from 21 to 40 °C for cooling and -5 to 15°C for heating respectively, to quantify the behavior of refrigerants R290, R1234yf, R1234ze, R454C, R455A, R1270, R600a, R717, R516A. Exergy analysis was carried out along with the COP
calculations to examine the second law efficiency for all the refrigerants to see the feasibility of these refrigerants being an alternative option for widely used R410A refrigerant. By varying a few parameters considered for the heat pump systems, optimization and sensitivity analysis resulted in finding the most
suitable refrigerant for this system. For ease of calculations, a few assumptions and constraints were considered while simulating the system.
The maximum COP value obtained for the refrigerants R290, R1270, R1234yf, R1234ze, R454C, R455A, and R516 for cooling effect are 1.75, 1.77, 2.09, 1.91, 2.18, 2.25 and 2.21 respectively and similarly for heating effect are 3.61, 3.26, 2.49, 2.72, 3.56, 3.67 and 3.68 respectively. These COP values are obtained when the pressure drop across the heat exchangers is zero, so, the values with a
pressure drop of 0.5 bar will fluctuate a bit from these values. If not COP, it will surely affect all other component parameters. Apart from COPs, second law efficiency is also a crucial parameter to analyze the system performance compared to a Carnot system i.e. an ideal system. Exergy analysis helped
in quantifying the second law efficiency of the system for each refrigerant, which is calculated by the ratio of the actual COP of the system and Carnot COP of the system (Calculated by taking the source and sink temperature values). The maximum second-law efficiency values obtained for the refrigerants
R290, R1270, R1234yf, R1234ze, R454C, R455A and R516 for cooling effect are 0.32, 0.27, 0.2, 0.16, 0.29, 0.31 and 0.21 respectively and similarly for heating effect are 0.4, 0.41, 0.37, 0.45, 0.405, 0.42 and 0.41 respectively. So, by considering all the COP and second law efficiency values it can be
concluded that a suitable refrigerant for this system with good performance as well as safe to use and handle is R455A, and other potential refrigerants being R454C almost similar performance with respect to R455A, and R290 and R1270 single component refrigerants with the concern of higher flammability
can be used with further optimizations in the model.

The unprecedented increase in mean ambient temperature due to immoderate CO2 emissions has shifted the energy policy towards the replacement of fossil fuels with renewable energy sources. Nevertheless, the intermittency of these technologies renders them unsuitable for reliable energy supply. A prominent solution is the utilization of renewable energy to produce green hydrogen that can be stored for later use.

The most environmental-friendly viable method for green hydrogen production is the electrolysis of water. Between the already existing types, alkaline electrolyser is the one with the highest technological maturity and lowest cost of hydrogen production. Despite that, the low energy efficiency, and the energy losses associated with the materials and the geometrical configuration make it difficult to produce hydrogen at competitive prices compared to fossil fuels. The connection with renewables exposes the electrolyser to variable loads that negatively affect the life of materials and the purity of hydrogen since the operating conditions like temperature and electrical current change constantly. Previous research work has shown that the energy losses owing to the electrode kinetics, diaphragm, and electrolyte resistivity are responsible for higher energy consumption than the thermodynamic minimum. These losses are a strong function of temperature and current density. This research project aims to investigate the performance of the electrolyser under fluctuating working conditions to get an insight into how energy consumption and efficiency are affected.

The research objectives are encountered by building a physical model that accurately predicts the electrochemical behavior of the cell under various circumstances and simulates the thermal response of the electrolyser. The numerous experiments performed at XINTC’s laboratory enabled the improvement of the model’s accuracy and the consideration of effects that are not easily confronted in a purely theoretical investigation. The results showed that the model accurately describes the experimental data of the cell with less than a 2% discrepancy. The model was also used for simulating the cell behavior under different pressures, electrodes, and diaphragm materials. The elevated temperatures and highly electroactive materials such as Nickel significantly reduce the voltage of the cell. Regarding the thermal model of the theoretical electrolysis system, sensitivity analysis of the current density, ambient conditions, and electrolyte flow was performed. The temperature across the system was uniform at an electrolyte volume flow of 5 Lt/min and the cooling load accounted for 20% of the electrolyser power. The thermal modeling of the real experimental setup was successful (<1.5°C deviation) at high current densities indicating the sound assumptions of the model. On the contrary, at low current densities, the discrepancy between the model and the experiments reached 10% due to the additional heat generation induced by the shunt currents. For that reason, a simplified electrical circuit analysis was formulated and included in the model. This led to reducing the deviation to less than 5% and at the same time calculation of the current efficiency in the absence of measuring devices was achieved.

CO2 is the major contributor of green houses gases in the atmosphere. Two notable branches that revolutionized the approach toward reducing the CO2 in the atmosphere are Carbon Capture Storage (CCS) and Carbon Capture Utilization (CCU). CCS has its shortcomings in the long run, a study from MIT shows that the united states have an adequate land area to store CO2 for 100 years [64]. The important question is, what about after 100 years? The need for efficient methods to utilize the stored or captured CO2 is a reasonable solution; therefore successful development of efficient methods in utilizing CO2 is the need for the hour. This work comprises of using reverse water gas shift that utilizes CO2 as raw material and H2 produced via electrolysis using renewable electricity from wind or solar energy to produce syngas replacing gasification of coal or natural gas that produces CO2. Syngas is a major raw material for producing useful chemicals such as methanol, dimethyl ether, acetic acid, hydrocarbons and other valuable chemicals.

On this wide field of syngas production technology, this work aims in determining the optimal operating condition of the reverse water gas shift reactor to produce hydrocarbons. Hydrocarbon heavier than C5+ are used to produce liquid fuels, reverse water gas shift reaction followed by Fischer Tropsch (FT) synthesis is utilized to achieve liquid fuels. FT synthesis requires a particular composition of syngas for effective operation and high selectivity. The challenges faced are side reactions such as Boudouard and CO hydrogenation that produces carbon and methane in the reactor that are undesired. Carbon deactivates the catalyst and carburization causes ineffective conversion of CO2 resulting in high operational costs. Methane is hazardous side product that needs to be minimized in the outlet stream of the reverse water gas shift reactor before feeding the same stream into the Fischer Tropsch reactor.

Less to no literatures are available on reverse water gas shift with respect to carbon formation and methanation. The above mentioned objective is countered by modelling a plug flow tubular reactor. A nickel on calcium alumina catalyst is used in the reactor. The model is used to determine the operating conditions for the reverse water gas shift reactor to minimize carbon formation and methanation in the reactor. The parameters such as inlet conditions, pressure, inlet temperature, heat input to the reactor are all determined for a desired syngas composition, with no carbon formation inside the reactor and minimum methane in the reverse water gas shift reactor outlet.

Climate change due to the extensive use of fossil fuels has led to the deployment of alternative green ones, such as hydrogen. Green hydrogen is produced by renewable electricity and is CO₂-free. This thesis focuses on the production of hydrogen by implementing alkaline water electrolysis as the core technology. 
Due to the intermittency of renewable sources, alkaline water electrolysers are forced to operate in their part-load range. The cathodic hydrogen species that remains dissolved in the liquid electrolyte can end up to the anodic compartment, and hence lower the purity of the produced gaseous oxygen. This phenomenon is prominent in the part-load range and is called gas crossover. When the concentration of hydrogen in oxygen reaches the Lower Explosive Limit which is 4 vol%, spontaneous combustion can occur. Therefore, the electrolyser is forced to shut down for safety reasons.
This thesis focuses on understanding the mass transfer mechanisms of gas crossover in alkaline water electrolysis, in the part-load range. A literature study has been conducted in which the gas crossover mechanisms are thoroughly analyzed. The mitigation of gas crossover can lead the operation to lower current density ranges. From the mitigation strategies, a focus is given on the “dynamic switching of the electrolyte cycles". The dynamic switching of the electrolyte cycles is based on the periodic changeover of the operative electrolyte cycles between the partly-separated and the mixed mode. The anodic hydrogen content acquires a sinusoidal response, where the average value is less than the impurity in traditional operation. 
The gas crossover steady-state and dynamic models are mathematically derived and developed in Python. The models consider the mechanisms of gas crossover through the diaphragm and the electrolyte mixing. Therefore, the anodic hydrogen and cathodic oxygen content are calculated in the steady state and dynamically. The dynamic switching of electrolyte cycles can be simulated with the dynamic model.
The experiments are conducted to define the anodic hydrogen and cathodic oxygen content in a single cell configuration. The first experiment outputs the steady-state impurity as a function of the current density. The steady-state impurities show a descending tendency with an increasing current density. Next, the dynamic switching is performed and the anodic hydrogen content is recorded as a function of time. The average impurity in the dynamic switching is smaller than the result in the steady-state experiment.
The steady-state model sufficiently validates the literature data and verifies the experimental results. The dynamic switching model validates the literature data. Furthermore, it verifies the experimental results, when a correction factor is applied to the total volume of the separator tanks. The correction factor is required because the experimental impurities were measured at the exit of the single cell, resulting in faster system response. Finally, a sensitivity analysis is conducted to test the robustness of the dynamic model. The sensitivity analysis shows that the dynamic model can successfully simulate the operation of an alkaline water electrolyser.

The worlds energy demand is rising as a result of industrial activity and advances in countries around the world. Fossil fuel sources are used to meet this demand for much of the world [1]. The way in which energy is handled causes pollution e.g., CO2 emissions, inducing climate change, therefore a more sustainable industry is desired [2, 3]. Carbon Capture and Utilization (CCU) is a way to use CO2 from the atmosphere or which would end up in the atmosphere, limiting its influence on the climate. Sustainable fuels or chemicals can be produced from the captured CO2, reducing the use of fossil fuels and fossil feedstock [4, 5].
Formic Acid is a favourable product from CO2 electrolysis. Only 2 electrons are required for one molecule Formic Acid, which results in a high normalized price ($/electron) [6]. COVAL Energy works on scaling-up and commercialization of CO2 electrolysis to Formic Acid. Coval has already an operational reactor on lab scale with promising performance, a conversion efficiency up to 90%. Although the reaction kinetics are limited by a poor distribution of reactants on the electrode surface. Previous research by Jos van der Maas showed a highly uneven flow distribution in the cell reactor [7]. Gas bubbles are formed inside the reactor, which likely limit the reaction. Consequences of this poor distribution of reactants and these bubbles are a lower energy efficiency and higher electrical resistance.
The main question of this thesis is: How can the current knowledge of electrolysers be applied to improve the Coval electrolyser design regarding flow distribution and mitigation of the impact of dissolved gas production? Experiments were performed to gain knowledge about the bubble behaviour in the Coval electrolyser. Computational Fluid Dynamics (CFD) was used to screen design ideas on liquid distribution. Promising designs were assessed in a flow and gas bubble visualisation experimental setup, in which also the bubble behaviour was investigated. Finally, prototypes to be tested in the high pressure reactor were produced.

Two auspicious designs were found. The first design has channels in the inter electrode gap. The results showed that with channels the velocity variation over the cell width was reduced. The second design has a manifold like geometry in a calm zone before and after the interelectrode gap. This resulted in an almost constant velocity over the cell width for the entire cell. Additionally, a larger inlet and outlet pipe to and from the cell improves flow homogeneity and reduces pressure dorp in these pipes. The gas fraction in the cell can be kept low by sloping the top part of the cell towards the outlet.
A next step is to assess both designs in the high pressure reactor. Particular attention should be paid to the manufacturing of the design to avoid leakage and mechanical deterioration. It is recommended to measure pressure drop over the cell for better assessment of the designs.

Magnetocaloric heat pumps are those types of heat pumpswhich use a solidMagnetoCaloricMaterial (MCM) in place of a refrigerant to provide the work for the heat pump. MCMs are materials whose temperature changes on the application or removal of a magnetic field. This effect is known as the MagnetoCaloric Effect (MCE). Magnetocaloric heat pumps have the potential in replacing the conventional vapour compression technology for Dutch dwellings, since they have minimum environmental impact due to the absence of the coolant fluids that can harm the environment. A model of the regenerator of the magnetocaloric heat pump is developed in this project having in mind the application of this type of heat pumps to Dutch dwellings. The magnetic field that is used in the development of the model is 0.875 T, with permanent magnets being the source of the magnetic field. A sensitivity analysis is carried out in order to obtain the methods to optimize the regenerator for improving the performance of the heat pump. The performance of the heat pump is measured through its average cooling capacity, average heating capacity, temperature span and Coefficient of Performance (COP) for heating. TheMCM used for the regenerators is Gd with a totalmass of 1.18 kg. The parameter that influences the performance of the heat pump the most is the porosity of the regenerator. The heat losses through the casing have the least impact on the performance of the regenerator. The frequency of the cycle also has a profound impact on the heating capacity and cooling capacity up to temperature spans of around 18 K, but it does not have such an impact on the heating COP. After increasing the frequency, decreasing the particle diameter and decreasing the porosity, the heating capacity and the temperature span are optimized. For a temperature span of 15 K, the heating capacity is 164.2W, and for a temperature span of 20 K, the heating capacity is 99.1W.

The thesis discusses how alternative heat generation for furnaces can be implemented on the Shell Netherlands Refinery to become CO2 neutral by 2050 or sooner. The research analyses the current knowledge, and future alternatives for furnace heat generation and underlines the need for alternative solutions with net-zero emission impact. Furnaces are the equipment that heat process streams before the reactor or distillation column. Hydrogen firing, electrification, biofuel combustion, and heat pumps are the four main topics of alternative technologies that are discussed. The result is a roadmap including all relevant information for the applicability of technologies, developments, value drivers and credible scenarios. Revamping all Pernis’ fired heaters for hydrogen firing is a suitable option and has TRL 6. The ultra-low NOx burners are operational, but hydrogen is not integrated yet as a fuel, and combustion analysers are not field-tested. The blue hydrogen will not be 100% pure, so not all CO2 can be abated. Besides, switching between RFG and hydrogen can cause flame instabilities and a higher thermal NOx emission. The normalised CO2 abatement price against RFG operation, the cost of not emitting a tonne of CO2, is 13 /tCO2. Electrification, such as impedance and immersion heaters, have TRL 7 and are limited to relatively small duties, single-phase, and clean service. Radiant heaters can heat process streams with two-phase and coking services having TRL 2. The concept is proven, but no prototype is tested. Electrical heaters have high efficiencies and might have a yield benefit. However, the showstopper is the plot space availability of the refinery. The normalised CO2 abatement price against RFG operation for electrical heaters is 21 /tCO2. Upgrading biofuel to biomethane allows the gas to be interchangeable with natural gas. Suitable for combustion without any adjustment on the furnace if biomethane is injected into the national natural gas grid. Biomethane combustion, having TRL 7, only impacts the sites emission, and it seems to be an administrative solution, where trading in certificates will be dominating the market. The normalised CO2 abatement price against RFG operation for biomethane is 21 /tCO2. Heat pumps are used in refineries, and they can be used to reduce the furnace load but not to replace the furnace. The potential for replacing fired heaters with TRL 7 heat pumps is low since the maximum operating temperature is 160°C [1]. The development scenarios showing the energy consumption expects that low carbon-intense electricity will expand most, suggesting that electrification is the step forward for SNR. The usage and production of hydrogen tend to increase after 2050, and the amount of biomass is small and will most probably not be an available option for Pernis. Four credible scenarios show that it is possible to abate sufficient CO2. With electrification only, it is impossible to achieve the vision of 2050 due to the plot space constraint. The hydrogen and electrification scenarios are combined in a hybrid scenario, where most CO2 is abated. The net-zero CO2 operation of furnaces requires significant investments and technical developments.

The separation of C8 aromatic hydrocarbons (e.g. xylenes) is one of the most important processes in the petrochemical industry. Current research efforts are focused on materials that can decrease the energy consumption and increase the efficiency of the separation process. Industrial processing of C8 aromatics typically considers adsorption in a zeolite from a vapor or liquid stream of mixed aromatics. Adsorption in porous materials can be used to separate the isomers or to promote catalytic reactions to transform aromatics into high value products. However, little is known about the chemical equilibrium of the adsorbed phase at reaction conditions. Most studies of adsorption of aromatics in zeolites, either experimental or computational, have focused on adsorption of pure components from the vapor phase. Experimentally, it is very difficult to determine adsorption equilibrium at saturation conditions. In molecular simulations, very difficult insertions and deletions of molecules make simulations very inefficient. Nowadays, advanced simulations techniques can be used to overcome this issue. Computer simulations of adsorption of aromatics in zeolites are typically performed using rigid zeolite frameworks. However, it is known that adsorption isotherms for aromatics are very sensitive to small differences in the atomic positions of the zeolite. In this thesis, the following types of questions are addressed: (1) how does framework flexibility influence adsorption and diffusion of C8 aromatics in zeolites?; (2) what is the role of the pore topology? For the separation and catalytic conversion of xylenes; (3) how does the type of framework influence the product distribution of xylene isomers?; (4) are there any possible zeolite structures that may have been overlooked for the processing of aromatics? For this, the different aspects that affect the interactions between aromatic molecules and the aromatics/zeolite systems in the simulations are discussed. The intermolecular interactions between aromatic molecules are studied by computing the vapor-liquid equilibria of pure xylenes and binary mixtures using four different force fields. The densities of pure p-xylene and m xylene can be well estimated using the TraPPE-UA and AUA force fields. The largest differences of computed VLEs with experiments are observed for o-xylene. Binary mixtures of p xylene and o-xylene are simulated, leading to an excellent agreement for the predictions of the composition of the liquid phase compared to experiments. For the vapor phase, the accuracy of the predictions of the composition are linked to the quality of the density predictions of the pure components of the mixture. The phase composition of the binary system of xylenes is very sensitive to small differences in vapor phase density of each xylene isomer, and how well the differences are captured by the force fields. Most of the models commonly used for framework flexibility in zeolites include a combination of Lennard-Jones and electrostatic intra framework interactions. The effect of these models for framework flexibility on the predictions of adsorption of aromatics in zeolites is studied. It is observed that the intra framework interactions in flexible framework models induce small but important changes in the atom positions of the zeolite, and hence in the adsorption isotherms. Framework flexibility is differently ’rigid’: flexible force fields produce a zeolite structure that vibrates around a new equilibrium configuration with limited capacity to accommodate to bulky guest molecules. The simulations show that models for framework flexibility should not be blindly applied to zeolites and a general reconsideration of the parametrisation schemes for such models is needed. The effect of framework flexibility on the adsorption and diffusion of aromatics in MFI-type zeolite is systematically studied. It is found that framework flexibility has a significant effect on the adsorption of aromatics in zeolites, specially at high pressures. For very flexible zeolite frameworks, loadings up to two times larger than in a rigid zeolite framework are obtained at a given pressure. Framework flexibility increases the rate of diffusion of aromatics in the straight channel of MFI-type zeolites by many orders of magnitude compared to a rigid zeolite framework. The simulations show that framework flexibility should not be neglected and that it significantly affects the diffusion and adsorption properties of aromatics in a MFI-type zeolite. The interactions of aromatic molecules inside different zeolite types are studied by computing adsorption isotherms of pure xylenes and a mixture of xylenes at chemical equilibrium. It is observed that for zeolites with one dimensional channels, the selectivity for a xylene isomer is determined by a competition of entropic and enthalpic effects. Each of these effects is related to the diameter of the zeolite channel. For zeolites with two intersecting channels, the selectivity is determined by the orientation of the methyl groups of xylenes. m-Xylene is preferentially adsorbed if xylenes fit tightly in the intersection of the channels. If the intersection is much larger than the adsorbed molecules, p-xylene is preferentially adsorbed. This thesis provides insight on how the zeolite framework can influence the competitive adsorption and selectivity of xylenes at reaction conditions. Different selectivities are observed when molecules are adsorbed from a vapor phase compared to the adsorption from a liquid phase. This suggests that screening studies that consider adsorption only from a vapor phase may have overlooked well-performing candidates for C8 aromatics processing. This insight has a direct impact on the design criteria for future applications of zeolites in industry. It is observed that MRE-type and AFI-type zeolites exclusively adsorb p-xylene and o-xylene from a mixture of xylenes in the liquid phase, respectively. These zeolite types show potential to be used as high-performing molecular sieves for xylene separation and catalysis.

@en

Steam utility systems supply process units with the required heat, rotational power, feed for steam methane reforming et cetera. This work is based on the steam network located at Shell Raffinaderij Nederland in Pernis.
The refinery has grown over the years which has resulted in an extensive and complex steam network which interconnects old and new process units. Operating the network is difficult, especially predicting the effect of changes in the network or finding the optimal operating mode where costs are minimized. The aim of this study is to create a model of the steam network which can predict these effects and able to find the optimal operating point.

The steam network is simulated in two models: one focused on hydraulic calculations and one on operational cost optimization. Both models are created in the software i-Steam from PIL, which is specialized in simulating and optimizing steam utility systems. The hydraulic model incorporates the pipelines and all steam producers and consumers connected to the network. The model is validated for four scenarios which arechosen to include varying ambient conditions and operating modes. The model is applied for testing the
effects of a new unit which must be connected to the existing steam network. The optimization model is focused on steam and electricity production and uses the current market conditions, such as the prices of natural gas, electricity, water and CO2 emission. Another factor in optimizing the system is by comparing the
steam production price with the steam price which can be taken in from the power generation plant 2 (PGP2).
The software uses GAMS as an optimization tool which applies multi integer nonlinear programming to find the operating mode with the minimal operating cost.

The pressure and temperature validation results for the hydraulic model are mostly within the 2.83% accepted uncertainty window. For certain areas the model indicates large steam surpluses over 10 t/h, which are probably due to bad flowmeters on the steam consuming side. The simulations of the new project resulted in the most promising connection to the existing steam network. For 18 barg steam consumption, the new unit should be connected to LS4413 with a backup connection for redundancy to LS980019. For 3 barg steam production,
the economic feasibility of laying 250 meters of pipeline in order to be able to export 4 t/h has to be further researched. The optimization model is validated using monthly timestamps over a two-year period. Optimization of these timestamps resulted in an average operating cost reduction of 1-3 %, with one peak at 6%.

The hydraulic model can simulate the effects of operating scenarios, retrofits and locates the bottlenecks in the steam network. The optimization model reduces the operating costs while providing each process unit with the required steam. Both models can help the employees working at the refinery to study new scenarios and advice in operating the network at its optimal point.

Nitrogen oxides (NOx) are significant sources of air pollution. Nitrogen oxides like Nitric oxide (NO) and Nitrogen dioxide (NO2) are mainly responsible for the acid rain and smog. Nitrous oxide (N2O), also known as the laughing gas, is the major greenhouse gas that is responsible for the ozone layer's damage in the troposphere. According to the Environmental Protection Agency (EPA) report, one pound of N2O is 300 times more potent greenhouse gas than one pound of CO2. The significant emitters of Nitrogen oxides (NOx) are automobiles, agricultural sources, thermal power plants, and chemical processes like Nitric acid production plants, paint manufacturing, etc.   This study mainly focuses on the tail gas emitted from the Nitric acid production facility. The tail gas emitted during the HNO3 production consists of almost 2% of O2, 200-400 ppm of NO2, and NO, whereas 800 ppm of N2O.  As N2O is the most emitted gas from the Nitric acid production facility, it is followed by NO2 and NO, so it is essential to reduce these pollutants from the tail gas. Selective catalytic reduction (SCR) is a well-known technique currently involved in reducing NOx via the adsorption process from the Nitric acid production facility. But the costs involved in these methods are quite high. Nanoporous materials like zeolite exhibit uniform pore size and high thermal stability are said to be the promising adsorbents of NOx. The availability of a large number of zeolites makes it impossible to identify the proper zeolite for NOx adsorption experimentally. In such situations, molecular simulations are a powerful tool that can help identify the perfect zeolite. The time and cost involved in the process of molecular simulations are very low.  In this work, Monte Carlo simulations involving reaction ensemble are implemented to obtain the equilibrium composition of NOx components at desired operating conditions in the Brick molecular simulation package. This is followed by Grand Canonical Monte Carlo simulations (GCMC) and Reactive Grand Canonical Monte Carlo simulations (RXMC-GCMC) for pure and quaternary NOx gas mixture adsorption in five different zeolites (FAU, FER, MOR, MFI, and TON) using simulation package RASPA. The composition results from the reaction ensemble are validated with the composition results obtained using the Gibbs minimization technique in the MATLAB model, and the results are in good agreement. The quaternary gas mixture adsorption results in five different frameworks from RXMC-GCMC simulations are then validated in Ideal adsorbed solution theory in the Python model, and the results are in good agreement at the given operating conditions.

Emissions of greenhouse gases (GHG) are the main cause of climate change, with as effect a rise in global temperature. The culprit in these emissions is carbon dioxide (CO2). Carbon capture and utilization (CCU)Emissions of greenhouse gases (GHG) are the main cause of climate change, with as effect a rise in global temperature. The culprit in these emissions is carbon dioxide (CO2). Carbon capture and utilization (CCU) can mitigate a part of these emissions, by converting carbon species to useful products. The typical route for CCU involves: carbon capture, compression, transportation and utilization. This thesis takes on a slightly different approach. Instead of utilization at a centralized location, the utilization of carbon species will be realized on location. This is beneficial, since no transportation of CO2 is required. Three different high partial pressure carbon sources will be addressed: tail-gas (TG) from steam methane reforming, blast furnace gas (BFG) from the steel industry and biogas from the bacterial degeneration of biomass. Each of these gas streams are composed of up to 50-60 mol % CO2 and or CO. By capturing the carbon species in these gases or removing some of the inert components, different ratios of CO2, CO, H2 and inerts can be obtained. Electrolysis technologies will be used to upgrade the captured gases, with the addition of hydrogen or by adjusting the CO/CO2 ratio. The electrolysis technologies considered are PEM and SOEC. The advantage of electrolysis is the potential for integration with renewable energy sources such as, wind, solar and hydro power. Depending on the electrolysis technology and carbon source, syngas with CO/CO2 ratios varying between 0-4 can be obtained. Five different cases were defined with CO/CO2 ratios equal to 0, 0.25, 1, 3 and 4. The upgraded syngas can then be used in the conversion towards several liquid fuels, such as methanol and Fischer-Tropsch (FT) liquids. Both methanol and FT liquids require a stoichiometric ratio of at least 2. For these two product routes a techno-economic analysis was performed. As a first production route, methanol synthesis was discussed. The feasibility for each of the five cases was assessed, by comparing the cost price of the methanol with the respective market price. A reference methanol plant from literature was implemented in Aspen Plus to obtain the energy and mass balances for each case. The mass balances showed the amounts of hydrogen and carbon species required to produce one ton of methanol. The total cost price of the methanol consists of the operational expenses (OPEX) and capital expenses (CAPEX). The OPEX reflects the costs required to run the process. This includes the prices for the feedstock and labour costs for example. The CAPEX consists of the capital investments. Based on the CO/CO2, Case 3 with CO/CO2 = 4, should be the cheapest case as less hydrogen has to be added to produce one ton of methanol. However, Case 4 with a CO/CO2 = 0.25 is the cheapest option. Case 4 originated from the TG stream, which already had a high fraction of H2 present in the TG. Therefore, Case 4 requires less addition of hydrogen. Capture costs were also lower in Case 4, compared to the other cases. At a market price for methanol of €400 per ton, a maximum electricity price of €30 per MWh was allowable. FT liquids were overall found to be an unfeasible product, when considering renewable production of hydrogen and CO from CO2 electrolysis. In FT liquids, waxes (C20+) are a requirement in the product fraction as these can be sold at the highest price. When considering the production of gasoline and diesel, the renewable FT route proved to be unfeasible. In general it was found that for each case, irrespective of product, more than 50 % of the product cost price, was included in the costs for electrolysis. And as the electrolysis technologies require electricity to operate, it can be concluded that electricity is the determining factor.
can mitigate a part of these emissions, by converting carbon species to useful products. The typical route for
CCU involves: carbon capture, compression, transportation and utilization.
This thesis takes on a slightly different approach. Instead of utilization at a centralized location, the utilization of carbon species will be realized on location. This is beneficial, since no transportation of CO2 is
required. Three different high partial pressure carbon sources will be addressed: tail-gas (TG) from steam
methane reforming, blast furnace gas (BFG) from the steel industry and biogas from the bacterial degeneration of biomass. Each of these gas streams are composed of up to 50-60 mol % CO2 and or CO. By capturing
the carbon species in these gases or removing some of the inert components, different ratios of CO2, CO, H2
and inerts can be obtained. Electrolysis technologies will be used to upgrade the captured gases, with the
addition of hydrogen or by adjusting the CO/CO2 ratio. The electrolysis technologies considered are PEM
and SOEC. The advantage of electrolysis is the potential for integration with renewable energy sources such
as, wind, solar and hydro power. Depending on the electrolysis technology and carbon source, syngas with
CO/CO2 ratios varying between 0-4 can be obtained. Five different cases were defined with CO/CO2 ratios
equal to 0, 0.25, 1, 3 and 4. The upgraded syngas can then be used in the conversion towards several liquid
fuels, such as methanol and Fischer-Tropsch (FT) liquids. Both methanol and FT liquids require a stoichiometric ratio of at least 2. For these two product routes a techno-economic analysis was performed.
As a first production route, methanol synthesis was discussed. The feasibility for each of the five cases was
assessed, by comparing the cost price of the methanol with the respective market price. A reference methanol
plant from literature was implemented in Aspen Plus to obtain the energy and mass balances for each case.
The mass balances showed the amounts of hydrogen and carbon species required to produce one ton of
methanol. The total cost price of the methanol consists of the operational expenses (OPEX) and capital expenses (CAPEX). The OPEX reflects the costs required to run the process. This includes the prices for the feedstock and labour costs for example. The CAPEX consists of the capital investments. Based on the CO/CO2,
Case 3 with CO/CO2 = 4, should be the cheapest case as less hydrogen has to be added to produce one ton
of methanol. However, Case 4 with a CO/CO2 = 0.25 is the cheapest option. Case 4 originated from the TG
stream, which already had a high fraction of H2 present in the TG. Therefore, Case 4 requires less addition
of hydrogen. Capture costs were also lower in Case 4, compared to the other cases. At a market price for
methanol of €400 per ton, a maximum electricity price of €30 per MWh was allowable.
FT liquids were overall found to be an unfeasible product, when considering renewable production of hydrogen and CO from CO2 electrolysis. In FT liquids, waxes (C20+) are a requirement in the product fraction as
these can be sold at the highest price. When considering the production of gasoline and diesel, the renewable
FT route proved to be unfeasible. In general it was found that for each case, irrespective of product, more than
50 % of the product cost price, was included in the costs for electrolysis. And as the electrolysis technologies
require electricity to operate, it can be concluded that electricity is the determining factor.

Rising CO2 levels in the atmosphere are becoming increasingly problematic, due to the effect of CO2 on climate change. CO2 capture and utilization has high potential as strategy to close the carbon cycle. An example of utilization of CO2 is the electrochemical reduction of CO2 to more valuable compounds. This thesis discusses the electrochemical reduction of CO2 to oxalic acid. Until now, oxalic acid as target product of the electrochemical CO2 reduction has not been studied in great depth, mainly because it only forms in non-aqueous solutions. The influence on several parameters, namely cathode material, applied potential,
anolyte, catholyte, membrane, supporting electrolyte, and temperature, on the electrochemical conversion of CO2 to oxalic acid has been studied. The first step in scaling-up has been taken, from a batch reactor (H-cell reactor) to a semi-continuous system (flow-cell reactor). In order to investigate the feasibility and its implementation in the industry, several options for the downstream processing of oxalic acid are discussed and a techno-economic analysis is performed on the proposed process design.

From the parametric study that was carried out, the parameters that had a considerable effect on the performance of the electrochemical reduction of CO2 to oxalic acid were cathode and anode material, catholyte and anolyte, membrane, applied potential and temperature. With the batch reactor optimal results in terms of faradaic efficiency and current density have been found, using lead as cathode, platinumas anode, propylene carbonate+0.7M tetraethylammonium chloride as catholyte and 0.5M H2SO4 as anolyte in which the cathodic and anodic compartment are separated by a Nafion 117 membrane. At higher temperatures, higher current densities were induced by reduction of mass transfer limitations. Within the range of -2.2V to -2.7V vs Ag/AgCl, increasing current densities and decreasing faradaic efficiencies were found with increasing applied potential. Semi-continuous flow-cell was investigated as a strategy to increase the mass transfer in the system. Although higher reduction currents were measured during CO2 reduction in a flow-cell compared
to the batch reactor, the faradaic efficiency towards oxalic acid was lower. The oxalic acid produced during CO2 reduction in the electrochemical reactor is dissolved in the liquid electrolyte. A further separation step of the oxalic acid from the liquid needs to be present to recover the product in a solid state. In order to assess the feasibility of the separation of oxalic acid, several technologies were addressed. Liquid-liquid extraction followed by crystallization is experimentally proved to be a suitable method for the separation and recovery
of oxalic acid from the electrolyte. Based on this separation method, a process design is proposed and a techno-economic analysis has been performed. The techno-economic analysis showed a favorable economic potential for this technology if certain key performance indicators can be achieved. However, the maturity level of this process is still in early stages. Some of those key performance indicators still need to be experimentally improved, further research should focus on increasing the obtained current densities and obtaining
stable faradaic efficiencies.