There is an increase in the amount of CO2 emissions in the past few decades and the process of capturing it back is at a much lower rate. The need of the hour is to reduce the emission rate or even avoid producing them in certain aspects. There is a transition towards renewable energy sources
that could help us maintain the balance required. Hydrogen is one of the energy sources that are at the forefront of this transition in the manufacturing and automotive industry, but without sustainable methods for producing hydrogen, it would not be a great alternative to existing energy sources like
fossil fuels. Presently the most used method for hydrogen production is steam methane reforming from natural gas, which produces a significant amount of CO2 during the process and needs to be captured which reduces the efficiency and thus higher energy requirements. To tackle the existing
problems of CO2 emissions and help in the transition towards sustainable hydrogen is the main goal of this study. The project focuses on producing low-emission CO2 hydrogen from natural gas and biomethane by using a process called methane pyrolysis, an innovative process that does not produce
any GHG emissions during the process, the produced hydrogen is called Turquoise Hydrogen. Here the study focuses on different types of hydrogen production methods and different methods within methane pyrolysis. This research helped in understanding and choosing the right type of methane
pyrolysis method for further study and analyzing its process and economic advantages over traditional methods like the steam methane reforming process.

To produce an alternative fuel like Methanol from scratch, on a miniature scale- the reactants CO2 and H2O are sourced locally. Zero Emission Fuels B.V. (ZEF) does this by collecting carbon dioxide from the air, via carbon capture techniques and compressing it to high pressure of 55bars. As a consequence of humidity inside the captured CO2, condensation is observed which is detrimental to the life of the compressor. To avoid this, a packed-bed drying system is designed as an auxiliary to the rolling piston compressor. This study aims to understand and model these two systems and subsequently integrate them to examine the effects of their dynamic operation. The purpose of this model is to provide a design tool, with the ability to predict the reaction of the system when sized differently, in various environments.

At first, the physics and governing principles of the two subsystems are studied and a layered modelling approach was devised. The systems were modelled individually and then integrated using Simulink- a tool that allows this layering up of the models. To build a dynamic model of such a setup, a characteristic time scale analysis was performed to identify the relevant phenomena inside each subsystem. Significant internal factors to be modelled were variations in relative humidity and temperature caused by the drying system, the changes in thermo-physical properties of the gas due to a change in temperature and the pressure fluctuations caused by the compressor. The external factors to be modelled were the changes in ambient temperature over operation time, caused by a variation in solar irradiation. The main finding was that the compressor's characteristic time scale (300s) was considerably smaller than that of the drying system (4-8hours/day). This meant an almost instantaneous operation of the compressor, rendering it uninteresting in the dynamic model of the integrated system.

A mechanistic dynamic model of the drying system, based on literature, was made with inherent controls to flip it between adsorption and desorption modes. It is responsive to the changes in the ambient and allows optimisation by changing the duty cycles of energy inputs. The model was then validated using experimental data from two working prototypes at ZEF. Some heat and mass transfer properties were then fitted to conform to these setups. A methodology to obtain these parameters while sizing a new design is discussed. The key performance indicators, which are cycle time and cycle capacity are given by the model and are crucial in deciding the energy consumption of the system.

On the other hand, an empirical model is built to replicate the rolling-piston compressor. The compressor is treated like a grey box and is described by a polytropic coefficient. A novel approach to create a compressor map for a positive displacement compressor, that is not mass-produced, is chosen. This compressor map is then used to predict the mass flow and output temperature of the system. Since the compressor map is empirical, the model was also validated using data from the literature.

Finally, the drying system and the compressor were integrated, in the model and experiments, by means of a capillary tube. A model was made for this as well to obtain the `interacting parameters'- which were the mass flow into the compressor, mass flow out of the capillary tube and the temperature and pressure of this re-loop flow. The effects of integration and the consequences to other systems upstream and downstream of this setup were scrutinised.

To conclude, a validated model is built to size new iterations of the setup. Multiple cycle models of a packed bed drying system and compressor maps of positive displacement compressors- that are not found commonly in literature are explored in this study and recommendations to further develop them are given towards the end.

To anticipate for future demand of sustainable liquid fuels, Zero Emission Fuels B.V. develops a solar powered micro plant which produces methanol from water and carbon dioxide captured from outside air. An intermediate step in this process is the electrolysis of water to create hydrogen which reacts with carbon dioxide to methanol. This study encompasses an integration of the pressurised alkaline electrolysis system, in which problems observed in previous generations of the electrolyser have been solved and functionalities have been added. In addition to that, electrolyte samples are taken after different periods
of operation to investigate electrolyte deterioration over time.

A new Balance of Plant (BoP) has been designed, realised and tested. Eight new features to the system can be distinguished, two of which are included to add functionality: the degasser to decontaminate the carbon dioxide-rich
feed water and the pressure booster to replenish the consumed water at system
pressure. The other features are integrated to enlarge the operational envelope, the determination of which was central to the experiments conducted in this research.
Experiments are conducted to find and characterise the four limitations to the operational envelope: the relative valve opening duty (RVOD), flow stagnation, temperature control and crossover.

The RVOD experiments showed deviations from the modelled valve opening cycles, attributed to additional pressure drops, valve opening interference and smaller discharge volumes. Subsequently a corrected model is presented to improve valve cycle time predictions.
Flow stagnation was investigated at various current densities, pressures and temperatures using camera images and a characteristic temperature response to establish flow stagnation. The results showed a minimum volume flow rate decrease in comparison to the previous system, expressed in parameter 𝑋 which decreased from 3.4 to 0.74 A K bar^-1 cm^-2. The minimum volume flow rate decrease is attributed to the larger number of cells and the increase of the height difference between the stack and buffer tanks.
In the temperature control experiments, steady state temperatures were monitored at different current densities, with and without crossflow fan operation. This resulted in a temperature control map, in which the reachable temperatures for different current density are depicted. Furthermore, electrolyte mass flows are determined and pressure dependency of temperature control was investigated at low current densities, concluding that steady state temperatures are independent from pressures in the 10 bar to 50 bar regime. 
Hydrogen crossover was tested by taking gas samples at different operating conditions and subsequent gas composition analysis in a gas chromatograph; oxygen crossover was determined by an oxygen sensor implemented downstream the hydrogen exhaust. All steady state crossovers values were found to be below the safety limits, concluding that crossover is not limiting in the acquired system on all possible operating points. Overnight diffusion crossover experiments showed that maintaining the system under pressure overnight, keeps crossover values below the safety limit.
In addition to the operational envelope, complementary general characteristics such as power consumption and efficiency are presented and compared to industry and literature. On top of that, unexpected findings, design deficits and other relevant phenomena are described to complete the perspective on system performance and behaviour of the electrolysis system. Due to the electrolyte mist purged into the degasser and pressure booster, the electrolyte deterioration experiments are deemed inconclusive. Moreover, a demister is found to be an essential system feature to include in the next generation electrolyser, because both degasser and pressure booster were damaged by the electrolyte spill.

In the effort against climate change the company ZEF has as its target to make methanol (CH3OH) out of atmospheric CO2; a process which can be seen as power-to-fuel and/or power-to-x. In light of the developmental cycle within ZEF a new reactor with an increased size and enhanced mass manufacturability is required. The reactor contains three main components: reactor bed, condenser and heat exchanger. The heat exchanger design has been shown to be highly efficient as well as the underlying design philosophy [1]. However, an exact in depth evaluation of the condenser performance has not been performed yet. Furthermore, in light of reactor optimisation, an investigation on the reactor bed design for the use case of ZEF is seen as necessary. The condenser plays a dual role in the reactor: it acts as the separation mechanism of products from the recycle stream and as vital factor in generating mass flow. Due to the current modelling architecture/philosophy of ZEF computationally simple descriptions of condensation phenomena are desired. A method based on linear relations for the latent heat release is developed. In combination with a PT-flash plug-in for MatLab this allows for modelling of heat effects and liquid-gas separation due to condensation. According to literature local heat transfer of condensation is significantly hampered com- pared to ideal Nusselt Film Condensation theory. The reason for this degradation is the presence of Non-Condensable Gasses which will limit the heat flux of the condensing species to the condenser surface. A sub model is used to evaluate whether this effect is significant. A combined model and experimental approach is used for evaluation of these models. The reactor bed is the generation site of the methanol and in previous work it has been found there might be limiting effects in this bed [1]. Evaluation of literature on the causes indicates that mass transfer and temperature limitations are likely the cause. Furthermore literature suggests that the reactor bed might be able to attain a higher Space Time Yield. A set of models are made to describe the mass and heat transport of the reactor bed. These are based on 1-D heat transfer correlations, a linearized Thiele modulus, and the Bussche & Froment kinetic model. Furthermore, the reactor bed and condensation models are integrated into an existing overall model. This enables the simulation of synergy between these processes. A new reactor bed design is made based on these models which should increase the Space Time Yield, and is subject to experimental validation. For the experimental validation a new reactor was designed and build based upon the new models developed. Characterisation experiments indicate satisfactory qualitative behaviour of the condensation modelling. Quantitatively deviations are observed which are expected to be due the over prediction of methanol formation by the reactor bed models. The reactor bed model deviations are mainly attributed to a lower than predicted mass flow rate, and adverse flow fields in the reactor bed. A new reactor bed design is proposed which should significantly reduce the adverse flow field effects while increasing thermal performance. The reactor bed design used allows for a decrease in catalyst size without causing a significant decrease in mass flow rate. An increase of a factor 1.25 for the Space Time Yield compared to the previous design has been observed during experiments. Insulation performance is satisfactory with the insulation performing within 20 W as modelled. Thermal efficiency has decreased by a factor 1.8 and is attributed to the under performance of the reactor bed. Furthermore, the control of the reactor has been evaluated in terms of mass flow rate measurements, the prevention of the stalling of flow, and control. A new mass flow rate measurements device based on differential pressure, a new feed injection design, and further development of control have been experimentally validated. Designs for each of these subjects have been found to be satisfactory. Furthermore, it was found that reactor bed geometry also has an effect on the control of the reactor.   

Zero Emission Fuels B.V. (ZEF) is developing a microplant, which ultimately provides a pathway to produce a hydrocarbon in a sustainable manner. This microplant consists of several subsystems. One of which is an alkaline water electrolyser, in which water is split into oxygen and hydrogen under specific operating conditions.
As a mixture of the product gasses can be highly explosive, gas crossover in alkaline water electrolysis (AEC) systems is a point of concern in terms of safety. This explorative study aims to identify the main routes for crossover in AEC systems, as well as characterizing the ZEF AEC system. This characterization has been accomplished by studying the effect of process conditions and system geometry on gas crossover.

Based on a literature study, gas crossover is found to be the result of diffusion as well as convection. Both of these phenomena occur at the interconnects between the sides of the system, which is over the diaphragms and over the pressure equalization tube (PET) in case of the ZEF AEC system.

Gas measurements where conducted during over 194 hours of experiments. From this it was concluded that hydrogen crossover is the main point of concern in terms of safety. Operating pressure and temperature both very clearly affect hydrogen crossover. The effect of current density is also significant but obscured by the fact that temperature is an uncontrollable variable in the ZEF AEC system. From the steady-state data a window for safe operations has been framed.
Upon start-up of the system a spike in oxygen-side hydrogen concentration is consistently measured, which is a result of crossover by diffusion during system off-time. This spike in concentration also poses a threat in terms of safety.
Three different pressure equalization tubes have been tested to investigate the influence of interconnect geometry on gas crossover.

In order to identify the main route for hydrogen crossover a CSTR model of the oxygen side gas phase was developed, in which temperature and pressure effects were taken into account. The model showed that hydrogen crossover by diffusion could be held accountable for ~8% of the total amount of crossed-over hydrogen, which is in line with reports in literature for a mixed electrolyte cycle AEC system. The model also showed that crossover by solely diffusion through the PET is negligible compared to through the diaphragm.

From this, it was concluded that the ZEF AEC system behaves more like a system with mixed electrolyte cycles with respect to gas crossover levels. Recommendations are made in order to reduce hydrogen crossover, and enlarge the window for safe operation as a result.

When experimenting with the compression of a gas similar to the output of a CO2 Direct Air Captureunit using an off-the-shelf lubricated compressor, Zero Emission Fuels B.V.(ZEF) encountered severecondensation, damaging the compressor. This explorative study aims to identify the cause of thisproblem, create a concept solution, and test this concept based on model-supported experimentation.Based on a literature study all theoretical concepts are divided into three solution classes. Twoconcepts are then created and theoretically compared. A concept is selected that is based on theadsorption of water into a solid desiccant.As the concept solution is to operate in a closed system, regeneration of the desiccant needs to befaster than its utilization. For this, an experiment is made where a controlled quantity of inert gas ismoisturized, dried, and used to regenerate a second column. From this it can be concluded that thegas can be dried adequately, and that regeneration can be done thoroughly.A model is made to verify the experiment’s workings, based on models from literature. This modelis then validated using literature, and then fitted to experimental data. Combining experiment andliterature data, three key performance indicators are calculated: Cyclic capacity, energy usage, anddesorption rate. The design tools and models developed throughout this thesis are used to size thenext iteration of the concept according to the needs of ZEF.From this, it is concluded that the presented concept is indeed viable to prevent, rather than solve,the problem stated at the start of this thesis. Recommendations are done concerning further develop-ment of the prototype, experiments, model, and overall system

The last decade has seen an increase in the world wide energy demand, it was recorded as the highest spike encountered in the energy demand over a decade. On analyzing the main sources which were able to satisfy this overwhelming demand it was found that the majority was still from non-renewable sources or fossil fuels such as coal, oil and natural gas. The aftermath of the continued use of these fossil fuels are already well known, one can argue that there has still not been a serious attempt to phase out these non-renewable sources even though the concerns regarding the harmful emissions being released with their continued use are subject of numerous discussions and studies. It is paramount that the share of renewable energy technologies in the overall energy mix needs to be increased,various options must be explored such that it is possible to substitute these renewable energy sources in place of fossil fuels particularly in energy and emission intensive industries without a comprise in meeting their energy demand. Refuse derived fuel (RDF), which is the combustible fraction that has been separated from municipal solid waste (MSW) has gained attention due to it being seen as an alternative to convectional fossil fuels as well as a method of sustainable waste management and disposal. The reason for their use as an alternative fuel is mainly attributed to their physical and chemical characteristic such as their low moisture content, high grindability and calorific value. However, the challenges faced in their application as a substitute fuel or feedstock is attributed mainly to the high variability in the properties of the RDF material that is being supplied to the relevant industries. Therefore a standardization in its properties needs to be carried out particularly with regards to their moisture content and calorific value in order to promote their application. Torrefaction, also referred to as mild pyrolysis is a thermal treatment method that usually is carried out in temperature ranges of 200-300°C and residence times of 30-60 min in the absence of oxygen. The material that is being subject to this treatment method partly decomposes to release volatiles,and the left over solid product has been reported to undergone a modification its physical and chemical characteristics when compared to the initial solid material. From a chemical point of view the final solid product is reported to have an increase in the carbon content and decrease in the hydrogen and oxygen content which leads to a higher calorific value than the original material. Several experimental studies have been conducted for the torrefaction of RDF with aim of improving and standardizing the calorific value and have yielded promising results. However there has not yet been a work that has focused on the torrefaction of RDF on large scale, that takes into account the process design and economics associated with their production. The aim of this thesis was to carry out a techno-economic evaluation into the torrefaction of refuse derived fuel. An initial composition of raw RDF was selected from literature which has a high moisture content and low calorific value. The raw material is then subject to several process such as drying, torrefaction, grinding and pellitization with the aim producing torrefied RDF pellets. These process were simulated and optimized through Aspen Plus in order to obtain a better understanding of the influence of process parameters such as moisture content, drying temperature, torrefaction temperature and residence time on the final product as well as to select the optimum route for their production. Economic evaluation was also carried out to determine if the implementation of such a project is feasible. This was done on the basis of certain economic or profitability indicators. Results from simulations show that the optimum torrefaction conditions were 250°C and residence time of 30 min, which resulted in the final torrefied RDF having an increased calorific value. The economic analysis provides positive results particularly when moving towards a higher processing capacity of initial raw RDF. Finally, the effect of substitution of the torrefied RDF in a cement plant was also evaluated and has shown that significant savings can be achieved through the reduction in fossil fuel consumption and carbon dioxide emissions.

Capturing CO2 directly from the atmosphere and subsequently using it to produce hydrocarbon fuels could help decrease mankind's reliance on fossil fuels and mitigate the risks of climate change. Zero Emission Fuels (ZEF) is developing a small-scale methanol plant, which utilizes atmospheric CO­2 and H2O vapor as feedstocks for renewable methanol synthesis. In this study, the vapor liquid equilibrium (VLE) of CO2 and aqueous solutions of tetraethylenepentamine (TEPA) was measured and correlated using thermodynamic models. The equilibrium pressure of aqueous solutions of 30, 70 and 80 wt% TEPA was measured from 313.15 to 393.15 K using a mechanically stirred and temperature controlled autoclave. The binary VLE data was correlated using Wilson's activity coefficient model. Using the same experimental set-up, the equilibrium solubility of CO2 in aqueous solutions of 30 and 70 wt% TEPA was measured at 313.15, 353.15 and 393.15 K. A simple chemical model, incorporating the extended Debye-Hückel law for activity coefficients of ionic species, was regressed to the ternary VLE data. Additionally, a theory was proposed that the polyamine can be modelled as a multiple of smaller amines, using the ratio of the amine groups as a scaling factor. Both models were applied in a simple process simulation of the absorption and stripping column of the direct air capture unit of ZEF to provide an estimation of the energy demand of the process under different conditions. The lowest regeneration energy demand was 533 kJ/mol CO2 absorbed, which is approximately 3 times higher than that of monoethanolamine, the current benchmark solvent for amine-based CO2 capture. However, through the addition of a rich-lean heat exchanger and process optimization to minimize the required reflux stream, this value could potentially be decreased.

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.

The dwindling of natural resources, mainly fossil fuels, and the alarming increase in the global average temperatures, are the biggest concerns of the engineering and scientific community of 21st century. Studies have found that known reserves of oil and natural gas will last another 50 years. Coal will last another 110 years, which points towards dire consequences. The experience will not be that of a car slowly running out of gas, but rather like driving off a cliff, since we innately depend on these resources. The realization of these concerns has lead to a rise in the investments all over the globe for Sustainability. The right questions are now being asked. How can we fulfill our demands without compromising the demands of our future generations? One of the keen areas of interest is the conversion of power into fuel. Synthesis of hydrocarbons from sequestrated carbon can produce carbon-neutral fuels that can replace some of the conventional fossil fuels. Methanol has been actively wiping the floor with the research community due to its simplicity of production and less toxic nature. While there are quite a lot of ways of producing methanol, very few of them are carbon neutral. Zero Emission Fuels B.V. has embarked on a venture to produce methanol by a totally carbon neutral process. They begin by capturing carbon dioxide and water from air and splitting the water into hydrogen and oxygen using solar power. Carbon dioxide and hydrogen are then combined in a reactor to form methanol, making a truly carbon-neutral process. They aim to make fuel consumption, a completely circular process while keeping it economic. An experimental characterization of ZEF’s methanol reactor under varying pressures and H2/CO2compositions was done. The new reactor design focuses on heating the feed gases before catalyst bed, more heat integration, reliable sensor data, and the ability to mix gases in desired compositions. Methanol yield, quality, energy efficiency, reactor inlet and outlet temperatures, power requirements were experimentally determined in a transient analysis. It was seen that the reactor produces 4.84 mmol/gcat /hr of methanol at 50 Bar and reactor wall temperature of 250◦C with H2 : CO2 = 3:1 mol% feed gas. The catalyst exhibited partial deactivation during night after shutdown. Contrary to expectation, the reactor produced more methanol at lower pressure. The production was reported at 5.96 mmol/gcat /hr at 35 Bar. Although, only 4.36 mmol/gcat /hr at 25 Bar. Moreover, the pressure reduction caused the natural circulation to slow down, and increase the inlet temperature from 208◦C at 50 Bar to 234◦C at 35 Bar, which is the reason for the observed increase in yield. It can be concluded that the reactor yield under these conditions is limited by kinetics and not thermodynamics. The reduced mass flow rate allowed the reactor to consume less power and show higher energy efficiency. It increased from 34.7% at 50 Bar to 43.2% at 35 Bar. The rate of pressure decline in the reactor was correlated with the methanol yield using gas law by accounting for non-ideality with the compressibility factor. The predicted yield was seen to be in good agreement with experimentally determined. The methanol yield of the reactor with variable feed gas composition was obtained for 50 Bar and 250◦C reactor wall temperature and seen to decrease on either side of the ideal composition. It was concluded that the yield becomes both stoichiometrically and kinetically limited.
It is recommended that similar experiments be done at increasing temperatures and equilibrium yield be determined experimentally. Additionally, the reactor needs to be operated with varying compositions and higher reactor wall temperatures at constant pressure, to obtain the operating line for maximum production of reactor.

The extensive use of fossil fuels and the emission of greenhouse gases has resulted in severe issues such as global warming and climate change. The energy and transport sector generate a major share of greenhouse gases globally. Though renewable energy can supply some of the energy demands, fossil fuels are still considered as a primary source to balance the world energy requirements. CO2 is the major constituent of the greenhouse gases, carbon capture process (from the source of emission and from the air) has been proposed as a promising technology to alleviate the effects of global warming in the near future. Alongside, technologies have been developed to produce fuels or other useful chemicals from the captured CO2. This process is called carbon re-utilization. Zero Emission Fuels (ZEF B.V.) is a company in the Netherlands that is working towards developing a system that produces Methanol from CO2 and water captured from ambient air viz. Direct air capture (DAC).
In the ZEF DAC process, polyethylenimine (PEI) and tetraethylenepentamine (TEPA) are used as CO2 absorbents. These amines capture CO2 and water at ambient conditions (absorption phase). The CO2 and water is then stripped from the amine at elevated temperature (desorption phase) and the gases are used for methanol production. During the process of absorption and desorption, the amines undergo losses such as evaporation and degradation. This leads to a decrease in the efficiency of the DAC system over time. This thesis is focused
on determining the evaporation and CO2 induced degradation losses that might occur of PEI and TEPA during the direct air capture process. To determine the losses in PEI and TEPA, it is necessary to understand the behavior of amines in a cyclic absorption-desorption. PEI and TEPA were subjected to 30 cycles of alternative absorption and desorption processes. Regarding evaporation losses, both PEI and TEPA showed significant loss of mass during the desorption process (80 ∘C, 120 ∘C were the selected desorption temperatures). Theoretically, the partial pressure of CO2 and water absorbed by the amine reduces the evaporation rate of the mixture (amine+water+CO2). But, during the desorption process, as the CO2 and water are stripped out of the amine, the evaporation rate of the mixture increases. To, determine the maximum evaporation that could take place under a negligible partial pressure of CO2 and water, pure samples of PEI and TEPA were heated at 80 ∘C, 100 ∘C, 120 ∘C. Results showed that, in a long term operation, both PEI and TEPA might undergo evaporation losses (relatively, TEPA evaporates faster than PEI) and replacing the amine frequently would increase the cost of DAC process. Another important observation was that a significant mass of CO2 remained in the sample after every desorption cycle. PEI accumulated more CO2 than TEPA. This suggested that the process of desorption carried out during the experiment was inefficient. A hypothesis was proposed to explain the accumulation taking place in both the amines. Furthermore, Fourier Transform Infrared Spectroscopy (FTIR) was carried out on the samples subjected to cyclic experiments to identify the formation of degradation products. Results showed that during the cyclic absoprtion-desorption process, TEPA might have degraded when desorbed at 120∘C. PEI samples did not show any indications of degradation. Finally, future experiments are proposed to understand the degradation losses which might help in deciding the suitable amine for the DAC process.

Dredging is an energy-intensive operation and, due to the nature of the process, there are large and rapid fluctuations in the power requirement. With the signing of the Paris Agreement, implementation of IMO 2020 and expansion of ECAs, the external pressures for the reduction of different emissions(CO2, SO_x, PM, and/or NO_x) in dredging are rising. Additional motivating factors are the rise in the fuel expenses which form a major component of dredging project costs and the incentives from regulatory authorities to reduce the carbon intensity in dredging operations. Often, the achievement of one objective leads to deterioration of another, for example, the use of IMO-compliant fuel can increase the overall carbon emissions. In recent years, alternative fuels like LNG and biofuels have been explored. However, they suffer from their own set of issues and with the predicted trends, the usage of these alternative fuels would imply lower production and earnings, especially in large dredging projects. In this work, a marine power plant concept that has been rarely discussed in the context of dredging is explored and forwarded: a nuclear-based system. Fundamentally, such a power plant addresses the issues related to the emissions and essentially eliminates bunkering stops. This was the first study focused on nuclear-powered Trailing Suction Hopper Dredgers (TSHD), the most common type of dredging vessel. In this work, a system-level study was carried out to ascertain the retrofittability of a nuclear-based system on four existing TSHDs. The feasibility of retrofitting the nuclear-based system has been studied by comparison of mass and volume requirements of the nuclear power plant, with the mass and volume of the engine and fuel storage system of current dredging vessels. No re-design of the vessel was considered here.The ”inherently safe” High Temperature Gas-cooled Reactor (HTGR) with Nuclear Air-Brayton Cycle (NABC) was determined as the nuclear power system of choice. It appeared that for such a system,the TSHD sizes that are interesting for the deployment starts around 12000 m³ hopper capacities.The bigger the hopper capacities than this baseline, the better the nuclear system performed. It was found that despite the satisfaction of the mass and volume constraints, a redesign of the TSHD is required for the placement of the reactor and for the compliance with the nuclear related regulations.In addition to the nuclear power plant, the retrofitting of the TSHDs with Proton Exchange Membrane Fuel Cell (PEMFC) in combination with solid, compressed and liquid H₂ storage and batteries was considered. With the current commercially available offerings, PEMFC with liquid or 500 bar compressed H₂ storage were found to be suitable for maintenance dredging or capital dredging for a short duration(couple of days). However, it was established that the realisation of endurance level of current dredgers is not possible without a reduction of hopper capacities or factorial increase in energy density of storage. Further, the smaller TSHDs were found to be better suited to use PEMFC or battery-based systems.A part of this work also tried to answer the pertinent question of the third party liability insurance premiums for a nuclear-powered vessel and the regulations such a ship would be subjected to. Further, a preliminary business case was developed and the sustainability of the concept was evaluated. It was realised that the technological forces and trends like the development of Small Modular Reactors, deep-sea mining and autonomous ships, could favour the development of a fleet of nuclear-powered dredging vessels in the future. However, the regulations and the support for these vessels would be highly dependent on the flag country and operational location.

The growing population is accompanied by an increase in the global energy and resource demand. Biorefining can be considered a means to help meet these growing demands through a range of bio-based materials. A biorefinery approach for developing an upstream process for the production of valuable products from macroalgae would be essential to realize a feasible valorisation chain downstream, wherein these products can be tailored to various applications. On a global scale, the biorefinery concept incorporates mainly, terrestrial first and second-generation biomass which compete with food and other energy applications, as well as involving sustainability issues such as land use change. Third generation macroalgae or seaweed thus has tremendous scope within the biorefinery concept. Seaweed has rapid reproduction rates and can be cultivated with minimal resource inputs thereby offering the attractiveness of high biomass yields. This study deals with the sustainable fractionation of two seaweeds, namely, Ulva lactuca (green seaweed) and Palmaria palmata (red seaweed) for the extraction of rhamnose and xylose, respectively. These sugars are of interest as they can be used to produce 5-methylfurfural and furfural serving as platform chemicals for various applications, including fuel production. Focus is laid on alternative hydrolysis methods of low severity for the extraction of the targeted sugars including enzymatic hydrolysis, hot water treatment and hydrolysis with organic acids and chelating salts. The characterization of the seaweeds and determination of their biochemical compositions are performed by acid hydrolysis, after the application of pre-treatment steps like washing with water and soxhlet extractions in order to maximize the sugars recovered. These compositions then form a basis for the study of low severity and more sustainable hydrolysis methods.A series of low temperature enzymatic hydrolysis experiments are conducted in order to screen a number of potential enzymes for the two seaweed types, which led to enzyme selection for further investigation. It is followed by a study of the effect of operating conditions and parameters namely, the reaction temperature, the pH and enzyme dosage. Hydrolysis treatments with hot water, organic acids (acetic, formic, oxalic, citric) and chelating salts (sodium acetate, sodium citrate) are also conducted at different temperatures and for a selected range of reaction times. These are carried out in a multiclave, enabling the running of a large number of screening tests to determine the best combination of the hydrolysing agent, temperature and reaction time. The results from these low severity treatments and enzymatic hydrolysis tests are applied onto a larger reaction scale in order to implement a cascade biorefinery approach for the extraction of rhamnose and xylose. Hot water treatments at 120℃ and 140℃for the Ulva lactuca and Palmaria palmata, respectively are chosen as the feasible routes. As for the enzymatic hydrolysis studies, hydrolysis with ‘X’ enzyme cocktail and ‘Y’ at 50℃ are selected. Enzyme dosages of ‘a’ % and ‘b’%, respectively are deemed suitable for the release of the targeted sugars after 72 hours of hydrolysis.Ultimately, the cascading approach is applied to a larger amount of seaweed (1.5 kg) where the biomass is washed followed by subsequent centrifugation in a decanter-centrifuge to separate the washed seaweed. The washing liquid fraction is further fractionated through membrane filtration to recover MW fractions of >100kDa, 100-1kDa and <1kDa. The separated solids are thereafter subjected to enzymatic hydrolysis in the bioreactor as well as autoclave treatments at a 2-3L scale, in accordance with the conclusions from the screening treatments in order to further evaluate the scalability of the process. In this cascading approach, a complete mass balance of the seaweed biomass components of interest (sugars, inorganics, protein) is carried out in order to evaluate the efficiency of the cascade approach and maximize the same by realizing the potential of the by-product and residual streams.

In recent years, the energy transition has led to increasingly higher installed capacities of intermittent renewable energy sources. This has sparked the interest in power-to-fuel technology to store excess renewable energy in the chemical bonds of synthetic fuels. As a highly reactive, turn-key process, plasma-chemical conversion offers a promising approach to power-to-fuel technology. However, recent studies have shown limitations in either energy efficiency, conversion or flow rate. The novel Spinning Arc Plasma Reactor (SAPR) developed by J. van Kranendonk stabilises the plasma by mechanical rotation with the potential to contain a liquid film for in-situ product removal. The aim of this thesis is to characterise this reactor by studying the effect of rotational confinement on the reactor performance. To this end, the prototype initially built by J. van Kranendonk was further developed. A wealth of recent studies on the plasma-chemical conversion of CO2 as a step in the formation of synthetic fuels serves as a benchmark to compare reactor performance of the SAPR concept against. A series of experiments with argon were performed to establish the relationship between the system variables (pressure, power, flow rate and rotational speed) and the plasma parameters (electron temperature and electron density). Based on this knowledge, a series of experiments with CO2 were performed to establish the relationship between the reactor performance measured by the conversion and energy efficiency and the system variables: pressure, power and flow rate. The maximum conversion of about 30% to 55% was obtained at an energy efficiency of approximately 0.25% and the maximum energy efficiency of about 3% was achieved at a conversion of approximately 8.5% conversion. Similarly to other studies, improvements to either one came at the expense of the other. The performance of the SAPR proved comparable to dielectric barrier and other glow discharges but was outperformed by microwave and gliding arc discharges. Especially energy efficiency was inferior to these configurations. Further analysis of the discharge emission spectra suggested that CO2 dissociation mainly occurred through electron impact excitation. This explains the large difference in energy efficiency as microwave and gliding arc configurations are able to exploit more energy efficient dissociation channels. Nonetheless, this study was able to further develop the concept and has laid the ground work to explore the potential effect of a liquid film and in-situ product removal on the reactor performance.

Increasing renewable electricity production calls for innovative methods to store electricity as well as a desire for electrification of processes that currently rely on fossil fuels. Zero Emission Fuels is a company that is developing a system to convert carbon dioxide and water from the air into methanol, a liquid hydrocarbon fuel, using photovoltaic energy. The scale of the system is fit for a single solar PV panel. The desired methanol output is 25 grams per hour.
In this work, a new design for the methanol synthesis reactor of the system is developed, built and experimentally characterized. Knowledge from work by Basarkar and Gutierrez on a previous prototype is used as the starting point. The focus of the new design is placed on the heat integration network, the natural circulation effects, and tilting of the reactor. The heat exchanger makes use of heat pipes to transfer heat. Natural circulation is increased by increasing the channel dimensions of the system. This led to an increase in mass flow rate of over 3000%, making the mass flow rate the limiting factor for reactor performance. The mass flow rate is roughly 800% higher than assumed in the design phase; the resulting energy flows are too high for the heat exchanger to work effectively. Nevertheless, the heat exchanger heating duty relative to total heating is 230% higher than Basarkar. Tilting the reactor 20 degrees reduced the mass flow rate by 46% to 0.41 g/s, improving almost all aspects of reactor performance. Productivity increased by 58% to 15.7 g/h; 182% higher than Basarkar, though the space time yield is lower (4.1 vs 6.8 mmol/gcat/h). The energy efficiency of the system is close to Basarkar at 36.5% (vs. 37.5%). It is clear from experimental correlations that reducing mass flow rate will increase productivity, energy efficiency and heat exchanger performance.
By simulating the requirements for an autothermal reactor it is found that the catalyst bed dimensions should be increased in terms of diameter and length to increase to residence time in the catalyst bed. The results agree with the experimental conclusion that the mass flow rate should be reduced. Furthermore, it is recommended to heat the fluid by convection instead of conduction to ensure a more homogeneous temperature profile in the catalyst bed. Also, the heat exchanger should be expanded by adding more heat pipes and increasing the heat transfer surface area.

The present-day industrialized nations reached high standards of living using cheap fossil fuel energy. The high CO₂ emissions as a result of burning these fuels over the years have started outpacing the natural carbon cycle, resulting in climate changes around the globe. We have reached a point in our history where merely reducing our carbon emissions would not solve the problem, rather carbon has to be captured from the atmosphere and either stored or converted to fuels. Converting the captured CO₂ into methanol has been gaining traction in recent years as it is not only an excellent fuel but also serves as the building block to manufacture other important chemicals like dimethyl ether (DME), paraffin, olefins, plastics and polymers.

This thesis focusses on the complete experimental characterization of a small scale, energy efficient methanol synthesis reactor modelled on the concept developed by Wim Brilman of the University of Twente, with respect to feed flow rates, methanol production and overall efficiency. The problem of comparative energy inefficiency of the Brilman reactor was solved by carrying out the reactions in a novel, natural circulation loop (NCL) fixed packed bed reactor with internal heat recovery using Cu/ZnO/Al₂O₃ as the catalyst. A mixture of H₂ and CO₂ in the molar ratio of 3:1-the optimum ratio for methanol production was fed into the reactor. A sensitivity analysis was carried out with regards to the sampling time of the liquids at the outlet and the reaction temperature. Maximum methanol productivity of 6.8 mmole (millimoles) CH₃OH/g_cat/h was obtained at 228 °C reactor wall temperature and 62 °C condenser wall temperature using 5 mm diameter pellets compared to 4.3 mmole CH₃OH/g_cat/h obtained by Brilman at 210 °C reaction temperature and 85 °C condenser temperature. Also, a high carbon conversion of 99.2% and methanol selectivity of 99.0% was achieved. The energy demand (in MJ/kg_CH3OH) was reduced from 75 in the Brilman reactor to 24 using the current design. From these results, it was established that methanol could be synthesized using a small, lab-scale reactor in an energy efficient manner.
It was further observed that reduced size of the catalyst did not contribute much to methanol yield due to the high-pressure drop. Finally, a brief analysis of the heat losses in the system led to the conclusion that an additional 14.6 W of heat would have enabled autothermal operation.