As global warming proceeds with increasing consequences, new and improved solutions that can mitigate the increasing CO2 emissions are becoming ever more important. Renewable energy technologies are advancing and along with carbon capture technologies, they promise to lower global emissions and help combat climate change. Renewable energy sources can be used to form value-added chemicals from captured CO2 through a method known as CO2 electrolysis. A novel approach to CO2 electrolysis is bicarbonate electrolysis, which uses carbon capture solutions directly to make products. By integrating the capture and conversion process this way, effectively bypassing the energy intensive steps of CO2 recovery required for conventional gas fed operation, CO2 conversion to products can become even more sustainable.

The objective of this thesis is to explore ways to improve the selectivity of carbon monoxide (CO) in a bicarbonate electrolyser. In this experimental study, focus is also placed on the stability of the process, characterising the selectivity over time. Causes of selectivity decline are examined as well as methods of improvement. Furthermore, the effect of pH on CO selectivity and stability is given special consideration. Literature in the field of (bi)carbonate electrolysis was reviewed to gather understanding on the process, to clarify recent advances made and to find areas for improvement. Based on the findings from the literature review the experimental study was designed.

Experiments were conducted in a membrane electrode assembly (MEA) flow-cell in constant current fashion, applying a current of 100 mA/cm2. The membrane chosen was a bipolar membrane (BPM) as it offers the possibility of operating with distinct electrolyte environments, separating the 3M bicarbonate catholyte from the 1M potassium hydroxide anolyte. Gas diffusion electrodes (GDE) were prepared by spray-coating silver nanoparticles on the surface, using Nafion ionomer as binding material. An interdigitated catholyte flow plate was used which ensured the bicarbonate would pass through the GDE due to its discontinuous channels forcing the flow through.

By introducing a catalyst-membrane gap through inserting a hydrophilic porous spacer between the GDE and the BPM, CO selectivity was improved from 50% to 78% in peak production, recording 55%
averaged over 3 hour operation. This enhancement in selectivity can be explained by the defined pH gradient resulting from the gap, permitting a low pH at the BPM for protons to react with the bicarbonate, liberating i-CO2; and a higher pH at the catalyst for CO2 conversion to CO while suppressing the hydrogen evolution reaction (HER). An optimum gap was found to be 135 - 270 μm. These results compare with the previously highest reported CO selectivity values from the literature at ambient conditions and 100 mA/cm2. While improving the selectivity, the stability of CO was not improved by the catalyst-membrane gap. The pH was found to affect both the selectivity and stability of CO, with higher bicarbonate pH leading to reduced selectivity but improved stability. This behaviour is explained by the reduced i-CO2 liberation and increased carbonation reactions taking place at higher pH levels…

Ammonia is essential for global food production as a component of fertiliser, and a potential energy carrier in the energy transition. Electrochemical ammonia synthesis faces numerous challenges as an alternative to the carbon intensive Haber-Bosch process, including competition from hydrogen evolution, and mass transport limitations. An unconventional cell design with a hydrogen permeable electrode could help to address these problems. The reaction mechanism and performance of ammonia synthesis using hydrogen permeable electrodes was investigated at elevated temperatures and pressures of up to 120 °C and 8 bar. Furthermore, a facile method for enhancing the electrochemical surface area of the electrode was developed and tested. Operation at elevated pressure resulted in a moderate increase in cell performance. However, replenishment of the nitrogen vacancies in the nickel nitride catalyst through dinitrogen adsorption is identified as the elementary step that limits activity and stability. The amount of pre-deposited N is found to significantly influence the ammonia production rate and its stability. Dynamics of ammonia desorption could also play a role in nitride regeneration. In future studies, the presence of a decomposition reaction of the nitride should be investigated. Usage of more stable nitride species or a combination of host nitride and dopants is recommended to improve stability and simultaneously promote dinitrogen activation and hydrogenation to ammonia. These findings expand the understanding of the mechanisms underlying the nitrogen reduction reaction, paving the way for the development of a more efficient green ammonia synthesis process.

The rise of CO2 concentration in the atmosphere is a leading cause of global warming. Utilizing CO2 ob- tained from point sources, such as chemical industries, as a feedstock to produce high energy density fuels and chemicals could mitigate the emission of CO2 as well as provide various economic bene- fits. One promising technology is the electrochemical reduction of CO2, however, the presence of contaminants in the industry-supplied feedstock and the separation of products downstream would be challenging in a continuously operated large-scale plant. To address these challenges and indentify the bottlenecks involved, it is important to study which pre-treatment and post-treatment steps are required and how to integrate these in a large-scale electrochemical CO2 reduction process.

The gas and liquid feed streams to the CO2 electrolyzers are first cleaned to the desired levels. The liquid feed stream is water from the river Rhine that is purified so the specifications of the water meet the requirements for type 1 water (ultrapure water). The gas feed stream is the flue gas stream of an average steel-producing plant in Europe and is cleaned to remove sulfur and nitrogen compounds. A two-step electrolysis process is used where CO2 is first reduced to CO, followed by the reduction of CO to C2+ products. The electrolyzer for the first step is a membrane electrode assembly-based flow cell with a current density of 300 𝑚𝐴 𝑐𝑚2− and a faradaic efficiency (FE) of 96% to CO. In the second step, a gas diffusion electrode-based flow cell with a current density of 300 𝑚𝐴 𝑐𝑚2− and a faradaic efficiency of 9.35%, 15.49%, 45.57%, and 16.38% towards acetic acid, ethanol, ethylene, and propanol, respectively, is used. The anolyte and catholyte in the reactors are recycled 3,500 and 2,000 times, respectively, to reduce the size of purification of the liquid feed stream section and increase the liquid product concentration. In both steps, unreacted CO2 and CO are recycled. The gaseous and liquid products are separated and purified to meet the industry standards using established separation techniques.

The total capital investment for a process with an industrial gas feed of 381.678 tons per hour is 4,053.5 million dollars with a daily operating cost of 7.403 million dollars. The daily income from selling the products is 2.363 million dollars, but this could increase if the FE towards acetic acid is increased since this product has the highest income per electron consumed. The net present value (NPV) for the base case, assuming current technological and market conditions, is -19.4 billion dollars after 15 years. To analyze which parameters have the most influence on the NPV, a sensitivity analysis is also per- formed with a better and optimistic scenario. It was found that the economic feasibility of the currently designed process is not limited by the technological progress, but mainly by the market conditions.

The target of this process is to reduce the emission of CO2, however, the operation of the plant itself contributes to some CO2 emissions. Therefore the process should consume more CO2 than it emits. The units that consume most energy and emit the most CO2 are the CO to C2+ products electrolyzer and the first distillation column in the liquid product separation section to remove acetic acid. It was found that the process is only carbon negative when the consumed energy is generated by nuclear, wind, or solar energy. The net CO2 emission is the lowest when nuclear or wind is used as an energy source. Generating all the required energy from these sustainable sources brings another challenge since the total installed capacity of these sources are currently not sufficient to cater to the needs of such a large-scale continuously operating CO2 electrolysis plant.

Keywords: Electrochemical CO2 reduction, large-scale, pre-treatment, post-treatment, technoeconomical analysis, energy analysis

This interdisciplinary thesis gives a simulational approach for the production of basic chemicals in a renewable manner, while simultaneously managing uncertainty inherent in the development of novel and innovative technologies. The simulational approach focuses on the capture of CO2 and subsequent conversion into methanol using Aspen Plus. CO2 is captured by chemical absorption into MEA. The CO2 rich stream is mixed with hydrogen and converted into methanol. The flowsheet is finalized by integrating recycle streams and upgrading of the product. The e-Refinery institute is used as a case study in order to research the managing of uncertainty in the development of these innovative technologies. The concept shared vision is the focus point in the collaboration and a conceptual design of a virtual platform has been developed in order to aid in the development of a shared vision within interdisciplinary research institutes.

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.

Steelmaking process is a highly carbon-intensive process. This is mainly due to the use of coke as a reducing agent in the blast furnaces to produce carbon-rich pig iron, which in turn, is used for the production of low-carbon steel in the basic oxygen furnaces. The exhaust gases from the blast and basic oxygen furnaces, which mainly contain CO and CO₂, are utilised for electricity generation, and thus, these pollutants are released to the atmosphere. One of the possible ways to treat these work’s arising gases (WAGs) is to convert them into syngas, which can then be further converted into syncrude via Fischer-Tropsch synthesis (FTS). The FTS syncrude can then be further refined and processed to produce liquid fuels such as gasoline, kerosene, diesel, etc. These synthetic fuels are sulphur-lean and are essentially capable of replacing the existing fossil-derived liquid fuels, thus contributing to curbing the carbon emissions.

The main objective of this thesis was to develop a detailed model of a multi-tubular fixed-bed reactor (MTFBR) to produce synthetic crude from syngas via Fischer-Tropsch synthesis (FTS). The model was then used to simulate a reactor that utilises the syngas obtained from the processing of work’s arising gases of an integrated steel mill to produce synthetic crude. The FTS product distribution was modelled using the kinetic model based on CO-insertion mechanism, developed by Todic et al. A basic MTFBR model was initially developed using the equations and assumptions from the fixed-bed reactor model of Todic, and the basic MTFBR model was able to produce similar results as that of the Todic’s model, with slight deviations in the temperature and pressures profiles. The basic MTFBR model was then further improved to render it comparable with the commercial FT reactors. The main improvements in the model include the dynamic extraction of thermodynamic and transport properties of the system components using Aspen Properties; calculation of dynamic vapour-liquid equilibrium, liquid holdup and catalyst effectiveness factor; and the use of improved heat transfer and pressure drop equations.

A sensitivity analysis was performed to determine the effect of design and process parameters on the performance of the MTFBR model. The most crucial design parameter was observed to be the tube diameter as it had a considerable effect on the heat management and the pressure drop in the reactor bed. The most important process parameters for the reactor were observed to be the inlet temperature and the feed flow rate. A simplified FTS gas loop process was also modelled in Aspen Plus in order to introduce a recycle stream into the MTFBR. The effect of tail gas recycle for the recovery of unreacted H₂ and CO was also studied, and it was observed that higher recycle ratios resulted in lower conversions per pass; however, overall CO conversions were observed to increase until a maximum, and then decrease thereafter. The optimum conditions for the simplified gas loop process were estimated to be with an inlet temperature of 484.5K and a total recycle of tail gas to the recovery section, for a inlet pressure of 30 bar. Optimised process conditions resulted in a CO conversion per pass of 46%, an overall CO conversion of 89%, a C₅₊ selectivity of 86.6%, a CH₄ selectivity of 6.2%, and a C₅₊ productivity of 252,540 tonnes/y. The optimised model results, in terms of C₅₊ selectivity and overall CO conversion, were also pretty much inline with the available data from the Shell SMDS plant in Bintulu.