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

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

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

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

One of the greatest concerns of this century is climate change due to rising greenhouse gas emissions. The ammonia industry is responsible for 1.4% of the global CO2 emissions, thereby having a negative climate impact. However, ammonia is an essential ingredient in nitrogen fertilisers and is also considered as a potential energy carrier. Ammonia is currently produced in the energy intensive Haber-Bosch process, where natural gas, coal or oil are used as the hydrogen and energy source. For these reasons, it is necessary to investigate more sustainable alternatives. One of the alternatives is electrochemical ammonia synthesis, where ammonia is formed out of nitrogen and water, and renewable energy sources fuel the process. The goal of this thesis is to give insight into the required performance metrics of the electrolyser and its production process in order for this technology to become technologically feasible and competitive with a Haber-Bosch process. This is done by investigating different options for the pre-treatment, electrochemical ammonia synthesis and separation steps, and comparing their energy requirements. The final product of this thesis is a process design for an electrochemical ammonia synthesis plant with a production capacity of 1,500 tonnes per day. Cryogenic distillation and pressure swing adsorption are researched and modeled as nitrogen generators. An adsorption column for the pressure swing adsorption unit is modeled in Matlab, while Aspen is used for modeling of the distillation column. Subsequently, an alkaline and a proton exchange membrane electrolyser are considered as ammonia synthesisers. The electrochemical cells are modeled as black boxes, operating at 353 K and 1 bar and 30 bar respectively. Next, a distillation column and a flash drum are modeled in Aspen as ammonia separators. Finally, four different process diagrams are created, two that are based on an alkaline electrolyser and two based on a proton exchange membrane electrolyser. Their overall energy consumptions are analysed and for both types of electrolysers the most optimal route for ammonia production is found. The results of this thesis point out that cryogenic distillation is preferred over adsorption for the generation of nitrogen, with an energy consumption of 0.56 kWh/kg nitrogen for compression, cooling and distillation. Adsorption can be competitive with cryogenic distillation when the nitrogen recovery rate is increased, or at lower production capacities. In a reasonable case for future electrolysers, operating at a cell voltage of 1.77 V and a Faradaic efficiency of 100%, the energy consumption for an alkaline electrolyser amounts to 12.00 kWh/kg ammonia and to 11.95 kWh/kg ammonia for a proton exchange membrane electrolyser. A distillation column was considered as utility for the separation of ammonia from the KOH solute product stream from an alkaline electrolyser. For the cathodic product stream from a proton exchange membrane electrolyser, containing only ammonia, hydrogen and nitrogen, flash separation was determined to be the best separation technology. For both separation options, it was found that an ammonia concentration of at least 10 mol% in the cell’s product stream is required for an efficient separation. Ultimately, with electrolysers operating at 1.77 V and a Faradaic efficiency of 70%, the total energy consumption of an alkaline based process is equal to 17.30 kWh/ kg ammonia and 15.45 kWh/kg ammonia for a proton exchange membrane based process, with overall energy efficiencies of 30% and 33% respectively. Based on the energy consumption of their respective pre¬treatment and separation steps, a proton exchange membrane electrolyser is favoured over an alkaline electrolyser. In order for an alkaline based process to be advantageous, its electrochemical cell should consume at least 1.80 kWh/kg ammonia less than a proton exchange membrane electrolyser. Finally, currently it is not possible for AEL or PEMEL based ammonia synthesis processes to be competitive with the Haber-Bosch production process in terms of energy consumption. However, with Faradaic efficiencies of 100% and minimal overpotentials, a PEMEL based process does come close to reaching this objective.

Within the electricity driven conversion methods, electrocatalysis has been assessed to be the closest to commercialisation. This can only be realised, if the system efficiency is increased in terms of the reaction rate, onset potential and/or selectivity. Current research has shown that, apart from the more widely investigated routes to improve these factors (GDEs, catalyst, etc.), cascade electrode systems and high pressure reactors could prove to be effective for increasing the system efficiency. By splitting the CO2 reduction into two separate steps, CO2 reduction to CO and the sequential reduction to C2+ products, both steps can be optimised in terms of operating conditions. Applying a cascade system has, therefore, shown to increase the selectivity and reaction rates in the system. Additionally, the advantage of the high pressure reactor originates from the fact that increasing the pressure, will result in an increase in the solubility of the reactant. By increasing the solubility, the mass transport to the electrode surface will subsequently be enhanced. The low solubility of reactants is often identified as a main limiting factor in system efficiency, therefore, increasing solubility has proven to increase reactant transport (current density) and selectivity in high pressure systems. Even though both of these advancements have shown promising results, technoeconomic studies indicate that their feasibility is still too low to become commercially attractive at this point. Therefore, this research proposes to combine both technologies to increase the overall system efficiency in terms of: increasing the current density, increasing the Faradaic efficiency and decreasing the overpotential losses for the production of C2+ products. Since this combination has not been investigated before, and both technologies are still rather new, there will be a lot to investigate in order to demonstrate the potential of this new combination. Therefore, in addition to an extensive literature study to uncover the relevant unanswered research questions regarding this field of research, a mathematical model was developed. A model is a valuable resource in determining the potential for a novel system, as it enables instantaneous control over system parameters and, therefore, can provide a lot of insight into its relations and limitations. However, as the accuracy of a model strongly depends on the quality of its input data, this research will also provide a design approach leading to a novel high pressure cascade reactor design. Eventually, the model can, therefore, provide the insight required for extensive experimental research, while the design can simultaneously aid in the improvement of the model. The results evaluated by the model demonstrate both sequential reduction steps are positively affected by increasing the pressure. In addition, the otherwise poor CO solubility, can be dramatically increased by applying the combined system. The reaction rates are also evaluated to increase with the higher reactant concentration of CO and CO2. In addition, since the hydrogen evolution reaction is not affected by the pressure, as it does not present mass transfer limitations, the selectivity has been shown to also increase with increasing the system pressures. Additionally, the presence of the high CO concentration in the reduction towards C2+ products affects the selectivity of the system as well. The CO reduction reactions possess different behaviour from the CO2 reduction reactions. Therefore, by indicating the share of both separate reduction reactions in the generated products, operating conditions for the maximum C2+ selectivity can be identified. This way, the combination of high pressure on a cascade system, has been demonstrated to possess a lot of potential for increasing the system efficiency towards C2+ products.

The steel making industry is highly energy intensive and a great contributor of greenhouse gas (GHG) emissions. It generated between 7% and 9% of direct emissions from the global use of fossil fuels in 2017 [1]. Gas emissions in an integrated steel mill (ISM) arise mainly from three streams: coke oven gas (COG), blast furnace gas (BFG) and basic oxygen furnace gas (BOFG).

This study focuses on the short term solutions to become a carbon neutral steelmaker where blast furnaces (BF) and basic oxygen furnaces (BOF) are still a fundamental part of the steel making process. The Rectisol® process is used to capture CO2 from the works arising gases (WAGs) of an ISM and to generate syngas which can be used as a chemical building block to produce liquid fuels among others.

The Rectisol® wash is a patented process by Air Liquide and Linde which uses chilled MeOH as a solvent. Both processes were first validated against stream data provided by the patents. PC-SAFT EOS was used to simulate the purification plant because of its strong theoretical foundation and its ability to adapt the parameters to predict component behaviour. Various binary interaction parameters proposed in literature were used to simulate the purification plants. From these simulations, it was found that the standard binary interaction parameters with the adjusted parameter for H2S-CH3OH, as proposed by Sun et al. [2], showed the best results.
The configurations of Air Liquide and Linde were used as base configuration to clean the feed stream. From these simulations, it was observed that in both configurations large portions of CO2 are lost in the stripping process of both configurations. Enhanced CCS configurations were investigated to increase the CO2 recovery of both configurations. The desorption of CO2 was altered by introducing multiple intermediate flashes to increase the desorption of CO2. Without optimisation, the downstream constraint for the CO2-rich stream of 95% CO2 content was almost met in the Linde configuration and requires further upgrading in the Air Liquide configuration. The decision was made to use the Linde enhanced CCS configuration as a base configuration since this would solely require a change in operating conditions to meet the downstream CO2 requirement of 95% content in the CO2-rich stream.

HCN and H2O require a seperate wash to avoid accumulation in the main wash. To treat these components together with H2S and COS, two pre-wash configurations combined with the Linde enhanced CCS configuration were looked into. A pre-wash configuration with a separate absorber column and dividing wall column (DWC) and a pre-wash configuration with a separate absorber column and rectifier with purge were examined. Both configurations meet the downstream requirements for the purified gas stream and CO2-rich stream. The main difference between the two configurations is the difference in thermal utility consumption and make-up MeOH. The decision was made to move forward with the pre-wash integrated configuration comprising of a rectifier and purge since additional make-up MeOH would be more cost-effective. The energy recovery method proposed by Linnhoff [3] was used to identify any potential energy saving of the purification plant. A heat exchanger network was designed which reduced the cooling duty by 57% to 54,9 MWth and the reboiler duty by 50,6% to 26,8 MWth. Finally, an economic evaluation was made of the final energy integrated configuration. Equivalent annual cost and operating expenditures of the purification plant were estimated at €12.32m and €51.13m respectively per year. This gives a cost per ton captured CO2 of €37,87.

The so-called “hydrogen economy” became one of the scientific targets among the different renewable energies alternatives, as a result of the efforts to transition from fossil fuels to environmentally-friendly energy sources. In this context, various options to transport and store hydrogen are being explored. Gaztransport & Technigaz (GTT) company, intending to be part of this challenge, is exploring the possibility to transport liquid hydrogen (LH2) in pre-existent ship’s containers initially designed for liquid natural gas (LNG) transportation. This project is about the study of the surface effect of the interaction between hydrogen with iron-based alloys in the case of 304L stainless steel (uncoated and coated with TiO2) and Invar alloy.The methodology consisted of electrochemical induced hydrogen evolution on an iron-based austenitic metal cathode taking advantage of the intermediate adsorbates (atomic hydrogen) generated during the reaction to study the electrochemical adsorption efficiency. Characterisation of the materials, by techniques like XRF, XRD, optical microscopy, and SEM, is conducted before and after hydrogen exposureso that it was possible to evaluate the effect of hydrogen ingress.The results showed that the chemistry of the surfaces is irreversible changed after the electrochemical induced hydrogen sorption/desorption process due to the formation of oxides. The amounts of hydrogen desorbed were quantified after different H2 loading times. In all cases, the amount of hydrogen desorbed showed a maximum after which the hydrogen desorbed decreased significantly. The maximum for uncoated 304L stainless steel was after 24 h, 90 min for the coated 304L, and 2 hfor Invar. The welds are the most vulnerable sections to hydrogen ingress in both cases. XRD results before hydrogen exposure revealed that 304L consists of an austenitic matrix with around 5% of ferrite. An increment of the austenitic volume fraction of 2.2% was observed after the H2 sorption/desorption process. Invar is a purely austenitic phase, and no changes in the phase composition were observed after the H2 sorption/desorption process.

The Dutch government has set out to largely reach reductions in carbon emissions in the electricity sector with the utilization of offshore wind energy. Due to the intermittency of wind energy this poses new problems and challenges for the future electricity system in the Netherlands. The objective of this report is to identify the challenges for the electricity supply of offshore wind farms and to research how energy storage and alternative wind turbine design can aid in these challenges. The problems experienced and possible solutions are first identified by conducting a literature review and data analysis. Subsequently a Matlab model is constructed to simulate an offshore wind farm and energy storage system. This model is used to determine the most cost-efficient storage technique and the impact of this technique on the future electricity system.
Of the challenges for future offshore wind farms do the short-term profile effects have the most influence. These effects negatively affect: 1. the security of supply in the electricity system, 2. the stability of the load on the high voltage grid and 3. the market value of the produced electricity. The impact of these effects is intensified by the strong correlation in power production between the connected (future) onshore and offshore wind farms. To reduce profile effects energy storage is used, the optimal configuration of the storage system has a power capacity between 0.23 and 0.27 times the rated power of the wind farm. For the optimal energy capacity, however, no optimum is found, and the design depends on the desired impact of the system. An analysis on the impact of an optimal design has shown that an offshore wind and energy storage system does not result in an economical feasible system. Short-term profile effect reduction with energy storage, however, is shown to be essential in a future electricity system that is dominated by wind and solar power. The short-term profile effects of wind energy production are correlated too much and will have a too high impact on the system if no energy storage is included in offshore wind electricity production.

Reducing carbon emissions in the power generation sector can be done by generating energy from renewable sources such as wind and sun. However these sources alone cannot provide a reliable electricity system and therefore an energy storage system is needed. Power-to-gas is a concept in which surplus renewable electricity is used for the production a gas fuel. The gas can be stored and is used for electricity production when there is a deficit in renewable electricity. When CO2 exhaust gases form reactants for new production of gas, the system has no net CO2 emissions. The gas functions as an energy carrier for electrical energy. Methane could be an interesting gas for large scale energy storage as there is much knowledge about methane transport, storage and combustion and the gas is easier to store than hydrogen. Power-to-gas-to-power conversions come with great electricity losses. Therefore it is interesting to investigate what waste heat streams can be extracted from the process to use for external purposes. The aim of this thesis is to map the input and output energy streams of a power-to-methane-to-power system operating in 2030 to find the efficiency of the system and to see how efficiency could be maximized by using waste heat streams for external purposes. Also, a power-to-methane-to-power system requires a lot of gas storage capacity. Therefore it is useful to estimate the capacity of the gas storage facility to find if the system is technically feasible and to see what gas storage does with the efficiency of the system. Last, since the aim is to reduce carbon emissions the (small) CO2 emissions of the system are determined and analyzed. The system is scaled up to a scenario in which it provides a fully renewable electricity grid in the year 2050, to explore the feasibility in terms of carbon emissions and required gas storage capacity. The system is also compared to a power-to-hydrogen-to-power system to find the most feasible solution. The round trip energy efficiency of the system in 2030 is 88.0%, which is the sum of an electrical efficiency of 30.0% and a thermal efficiency of 57.1% The total energy efficiency can only be achieved when streams modeled as usable heat output streams can actually be used. This depends highly on the location of the system. The carbons emissions of a system with a 44MW output in 2030 are 56.3kt and the required gas storage capacity is 5.09 x 10^5 m3 of underground salt caverns. When scaling up the system to provide a fully renewable electricity grid, the total gas storage capacity is 9.34 x 10^7 m3, which is 5.5% of the total potential salt cavern volume in the Netherlands. The carbon emissions are 2.78 kt/y, which is 0.0056% of the current annual carbon emissions caused by the Dutch power generation sector. Compared to a hydrogen system the methane system performs worse in term of electrical efficiency, gas storage capacity and carbon emissions.