Light olefins, namely ethylene, propylene, and 1-butene, are essential building blocks of the chemical industry, yet their production remains almost entirely reliant on fossil feedstocks through steam cracking and fluid catalytic cracking. As the chemical sector seeks to reduce its carbon footprint, the direct conversion of captured CO₂ into light olefins via Fischer–Tropsch synthesis (CO₂-FT) has emerged as a promising Power-to-X pathway. Despite its potential, comprehensive process-level assessments integrating reactor modeling, process design, energy integration, and techno-economic analysis remain limited.

This thesis develops and evaluates two process configurations for the production of C₂–C₄ olefins from direct air-captured CO₂ and renewable hydrogen using Aspen Plus. The base configuration consists of a kinetic iron-based CO₂-FT reactor model integrated with a complete product recovery train comprising CO₂ removal and cryogenic separation to produce polymer-grade ethylene and propylene together with chemical-grade 1-butene. A second configuration extends the process by incorporating a downstream steam-cracking unit to convert the C₅–C₁₀ Fischer–Tropsch products into additional light olefins. Both configurations are evaluated within a consistent Power-to-X framework through process simulation, pinch-based heat integration, and techno-economic assessment.

The developed CO₂-FT reactor model operates at an optimal temperature of 350°C, a pressure of 15 bar, a H₂/CO₂ molar ratio of 3, and a chain-growth probability of α = 0.6, achieving a single-pass CO₂ conversion of 39%. The FT-only configuration produces 10.28 t/h of light olefins with a carbon efficiency of 43%, whereas integration of the steam-cracking section increases olefin production to 13.49 t/h and improves carbon efficiency to 56%, while reducing the specific CO₂ consumption from 7.38 to 5.70 tCO₂ per tonne of product. Following heat integration, the FT-only and FT-cracking configurations achieve overall fuel energy efficiencies of 73% and 58%, respectively, corresponding to light-olefin energy efficiencies of 31% and 40%.

The techno-economic assessment indicates that integrating steam cracking decreases the net light olefin production cost from €8.02/kg to €7.03/kg, representing a 12.3% reduction primarily through improved carbon utilization and increased product yield. In both configurations, renewable hydrogen dominates the operating expenditure, and sensitivity analysis identifies hydrogen price as the principal economic driver, substantially outweighing the influence of electricity and CO₂ prices. Although the calculated production costs remain significantly higher than those of conventional fossil-based olefin production, the results demonstrate that economic competitiveness is primarily constrained by hydrogen costs and reactor selectivity.

Overall, this work provides an integrated process design and evaluation of direct CO₂-to-olefins production, combining detailed reactor modelling, process simulation, heat integration, and techno-economic analysis within a unified framework. The results demonstrate that downstream steam-cracking integration significantly enhances carbon utilization and economic performance, while identifying hydrogen cost reduction and improved Fischer–Tropsch catalyst selectivity as the key priorities for the industrial deployment of defossilised olefin production.
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Global plastic production exceeds 460 million tonnes per year, with polyolefins constituting the dominant fraction of post-consumer waste. In Ghana, plastics account for approximately 17 % of municipal solid waste, yet the formal recycling rate remains around 10 %. Clogged waterways, overflowing landfills and open burning are visible consequences of a system overwhelmed by growing consumption and insufficient infrastructure. Polyolefins are particularly challenging to recycle because they resist degradation under the mild conditions of conventional hydrothermal liquefaction, while supercritical water processing requires pressures exceeding 22 MPa, limiting deployment in low-resource contexts. Solvothermal liquefaction (STL) with an organic solvent and a heterogeneous catalyst offers a potentially lower-severity alternative, but its feasibility for polyolefin-rich waste streams remains poorly understood, particularly in low- and middle-income country settings.

This thesis investigates the technical and socio-technical feasibility of catalytic STL for polyolefin plastic waste in Ghana through two complementary studies. The technical study comprised two experimental campaigns on a mixed polyolefin feedstock (50 wt% PP, 30 wt% HDPE, 20 wt% LDPE) sourced from
Accra in Ghana: a subcritical campaign using decanoic acid as solvent with ZSM-5 as catalyst (335–345 °C), and a supercritical campaign using both water and decanoic acid at 455 °C. The socio-technical study conducted 14 stakeholder interviews in Ghana, mapped the plastic waste value chain and identified conditions under which chemical recycling could feasibly be integrated into the existing system.

The subcritical STL campaign with decanoic acid proved technically infeasible in its current form. Visual inspection and analytical characterisation revealed that the original plastic morphology was fully disrupted. No pieces retaining the feedstock structure were recovered from either the solid or the liquid phase,
which both appeared homogeneous, suggesting physical interaction between the polyolefins and the solvent. The nature of this interaction could not be determined from the available evidence. Critically, the solvent could not be separated from the organic phase, making a mass balance impossible and preventing any quantitative assessment of product yields.

The supercritical campaign with water demonstrated effective conversion, achieving an oil yield of 54.01 wt% at 455 °C and 60 min, with o-xylene and mesitylene as the dominant products. The catalyst markedly promoted monomer formation in the gas phase, increasing the combined ethane and ethylene fraction from 19.90 to 29.05 wt% and propylene from 9.80 to 12.76 wt%, opening a pathway toward plastic-to-plastic recycling. In contrast, the supercritical experiments with decanoic acid as solvent showed that at 455 °C, decanoic acid decomposes rather than acting as a stable reaction medium. To confirm this, a decanoic acid blank experiment without plastic was conducted. Ultra-high resolution APCI-FT-Orbitrap MS analysis, evaluated through a heteroatom class histogram, Van Krevelen diagram, DBE versus carbon number plot and KNM versus O/C ratio plot, showed that the decanoic
acid experiment with plastic was virtually indistinguishable from the blank across all four representations, confirming that the oil phase is governed by solvent decomposition products rather than plastic conversion.

The field research identified six structural complexities shaping Ghana’s plastic waste management system and concluded that existing policy frameworks, including the NPAP roadmap, provide a foundation for chemical recycling deployment but require translation into binding legislation, explicit chemical
recycling targets and dedicated financing. A phased Plastic-to-Fuel followed by Plastic-to-Polymer deployment strategy is proposed, leveraging Ghana’s position as a net fuel importer and the growing volumes of otherwise unrecoverable mixed plastic waste. The proposed deployment strategy positions chemical recycling as complementary to, rather than competitive with, mechanical recycling, forming a
cascading system that maximises resource recovery across the full waste stream. ... Read more

The prediction of heat transfer in gas–solid fluidised beds remains non-trivial, particularly once nonisothermal effects and non-standard geometries are introduced. While the hydrodynamic behaviour of these systems is reasonably well established, the coupling between flow structure and thermal transport is less robustly captured in current modelling approaches. This limitation becomes more apparent in conical geometries, where the superficial gas velocity decreases with height, inherently producing spatial variations in fluidisation regime. In the present configuration, the use of a nozzle-based gas inlet further complicates this behaviour by introducing a localised high-velocity jet near the distributor. This
is likely to alter both bubble formation and local heat transfer rates in a way that is not well represented by correlations originally developed for uniformly distributed gas injection.

In this work, heat transfer in a laboratory-scale conical bubbling fluidised bed is investigated numerically using an Euler–Euler two-fluid framework implemented in ANSYS Fluent. The system consists of porous γ-alumina particles fluidised by nitrogen, with gas introduced through a nozzle at the base of the conical section. The model resolves the coupled momentum and energy balances for both phases,
with interphase heat transfer described using the Gunn correlation in the dense regions of the bed and the Ranz–Marshall correlation in more dilute zones. This combination was selected to reflect the strong variation in local void fraction, although the transition between regimes introduces some uncertainty, particularly in intermediate regions where neither correlation is strictly valid.

Three heating strategies were considered: wall heating, gas preheating, and a combined configuration. The simulations indicate that the mode of heat input has a clear impact on both the rate and spatial distribution of temperature rise. In the gas preheating case, the bed approaches a relatively uniform temperature profile more rapidly, which suggests that interphase convection dominates under these
conditions. In contrast, wall heating produces a more gradual thermal response, with temperature gradients persisting over longer times. This behaviour is consistent with a transport mechanism limited by particle–wall heat exchange and conduction through the dense phase. The combined case exhibits the
fastest overall heating, although the improvement appears to be largely additive rather than indicative of a new dominant mechanism.

The conical geometry introduces a noticeable axial dependence in the thermal behaviour. Near the inlet, where gas velocities are highest, heat transfer appears to be convection-driven, likely due to increased slip velocities and more active bubbling. Further up the bed, as the gas velocity decreases, the system transitions towards a denser regime where conductive effects become more significant. This
spatial variation is reflected in the temperature fields, which show a clear delay in heating in the upper sections. The influence of superficial gas velocity is not straightforward: increasing velocity enhances local heat transfer coefficients, but at the same time reduces the solids fraction, which limits the overall heat capacity of the bed. The resulting effect is therefore non-monotonic, suggesting the presence of an optimal operating range rather than a simple scaling with velocity.

Overall, the simulations capture the expected qualitative trends in heat transfer behaviour, but some limitations remain. In particular, the results are sensitive to the choice of interphase heat transfer correlation and to the local prediction of void fraction. Despite these uncertainties, the model provides a useful framework for interpreting the interaction between hydrodynamics and heat transfer in conical fluidised beds. The findings highlight the importance of geometry and inlet configuration in determining thermal performance, and suggest that conventional design correlations may require modification when applied to such systems. ... Read more

The Levelized Cost of Hydrogen (LCOH) is commonly used to evaluate the economic performance of electrolytic hydrogen production. In many studies, electricity costs are represented by static average prices, while assuming simplified operating profiles. This simplification neglects the temporal variability of electricity prices in liberalized power markets and limits the representation of flexible electrolyzer operation.

This thesis develops a techno-economic LCOH framework that incorporates hourly electricity prices, renewable generation profiles, and operational constraints of an alkaline electrolyzer. A bottom-up modeling approach is applied, aggregating hourly operating decisions into discounted lifetime costs. A daily dispatch optimization algorithm is introduced to determine the operation of the electrolyzer based on electricity prices, expected hydrogen revenues, and solar availability, while accounting for start-up penalties, efficiency degradation, and stack replacement.

The framework is applied to a case study of a 1.2 MW alkaline electrolyzer coupled with a large solar field in the Netherlands using historical market data. The results indicate that price-responsive operation can reduce LCOH relative to continuous operation, primarily by avoiding periods of high electricity prices, although this leads to lower overall hydrogen production volumes. Compared with purely solar-following operation, cost reductions are achieved at the expense of higher carbon emissions as a result of increased reliance on grid electricity.

Overall, the study shows that incorporating electricity price dynamics and operational constraints can materially affect LCOH estimates and provides a more transparent basis for evaluating grid-connected electrolytic hydrogen production under volatile electricity markets. ... Read more

The current global average CO2 concentration in the air is 427 ppm, rising at a rate of 2 ppm per year, faster than ever before. This underscores the urgency to capture and either utilise or sequester the carbon. The energy transition is driving a shift from fossil-based generation towards renewable energy sources, with wind and solar energy generation at the forefront. The intermittency of supply from renewable energy generation presents opportunities during peak electricity generation to reduce CO2 electrochemically.
The electrochemical utilisation of captured CO2 offers a sustainable pathway to close the carbon loop by converting waste carbon into value-added chemicals. This thesis explores the electrochemical dicarboxylation of 1,3-butadiene with CO2 to produce 3-hexene-1,6-dioic acid (3HDA), a direct precursor to adipic acid. Adipic acid is a key raw material in Nylon-66 production, and its conventional synthesis from cyclohexane emits significant quantities of N2O, a greenhouse gas with a global warming potential of 298 times that of CO2. In contrast, the pathway studied here aims to decarbonise the process using renewable electricity.
The electrochemical synthesis of 3HDA from 1,3-butadiene and CO2 is employed in an electrolyser cell. Using a sealed, undivided electrochemical cell with acetonitrile and tetraethylammonium chloride as the electrolyte solution, the study systematically investigates the influence of various electrocatalyst morphologies and materials, and process parameters on faradaic efficiency, product selectivity and yield.
Nickel wire was identified as the most effective working electrode, outperforming copper wire and other nickel-based morphologies, employed alongside aluminium coil as a sacrificial anode. Electrochemical characterisation using cyclic voltammetry and chronoamperometry revealed –2.6 V vs Ag/AgCl as the optimal reduction potential for 3HDA formation, with a faradaic efficiency achieved of 14% for 3HDA and 100% selectivity among the carboxylated products. Competing side reactions, such as 3-pentenoic acid (3PA), formate and oxalic acid production, were observed at other reduction potentials. Reduced moisture content in the electrolyte was found to poorly influence the faradaic efficiency. The dry acetonitrile has a similar 3HDA faradaic efficiency when the water content is reduced from 350 ppm to 150 ppm in the electrolyte. Temperature studies indicated that higher temperatures enhance the reaction rate but increase product solubility, reducing solid product formation. Solubility measurements confirmed this behaviour. On calculating the faradaic efficiency of the dissolved 3HDA as well, the efficiency stands at 6.58% for at 40◦C and 3.59% at 60◦C. Further, experimentation with alternative supporting electrolytes like TBABF4 and TBAPF6 was inconclusive due to practical limitations.
Overall, the thesis demonstrates a promising proof-of-concept for the sustainable electrochemical conversion of CO2 and 1,3-butadiene to value-added chemicals of 3HDA. The findings contribute to the broader goals of electrifying chemical synthesis and valorising captured CO2, inspiring future work recommended in improving the process conditions and refining electrolyte and electrode design. ... Read more

Green hydrogen production through electrolysis is increasingly recognized as a critical pathway for decarbonizing the energy sector. However, the integration of electrolyzers with renewable energy systems presents several technical and economic challenges. Renewable energy sources such as wind and solar are inherently variable, leading to fluctuating power inputs that impose dynamic operating conditions on electrolyzers. These fluctuations result in degradation mechanisms, such as start-stop cycles, partial load operation, and power ramping, which reduce efficiency and impact long-term performance and economic viability. While technical challenges related to degradation have been investigated in prior research, the role of hydrogen support mechanisms, such as price premiums, in addressing these challenges remains underexplored.

This thesis extends an existing optimization framework to incorporate degradation effects into the modeling of electrolyzer performance. Degradation is represented asdynamicreductions in efficiency that evolve based on operational conditions, including cycling and variable load profiles. A rolling horizon approach is employed to simulate the cumulative impact of degradation over time, enabling the study of electrolyzer operations under realistic renewable energy inputs. The model evaluates two distinct scenarios: one in which electrolyzers operate without external policy intervention, and another where hydrogen support mechanisms are integrated into the framework. This separation allows for an examination of how these factors independently influence electrolyzer scheduling, efficiency, and the economic viability of green hydrogen production.

The findings indicate that degradation significantly influences electrolyzer performance under variable renewable energy conditions, with dynamic operating profiles leading to efficiency losses over time. The inclusion of hydrogen support mechanisms in the analysis highlights their potential to improve economic feasibility by partially mitigating the financial challenges posed by variability. However, the results are contingent on model assumptions and emphasize the importance of considering operational and market-specific factors when assessing the impact of such mechanisms.

By addressing both technical and economic aspects, this thesis contributes to the understanding of howelectrolyzers performunder variable power inputs and howpolicy mechanisms might influence their operation. The results provide a foundation for further research into optimizing electrolyzer performance and integrating green hydrogen into renewable energy systems. ... Read more

This research investigates the co-liquefaction of Arundo donax and PET plastic to assess their potential as feedstocks for producing bio-oil suitable for bio-pavement applications. The study demonstrates the feasibility of using an invasive species like Arundo donax combined with plastic waste for hydrothermal liquefaction (HTL) to generate bio-oil. The experimental design varied three critical parameters— temperature, residence time, and biomass-to-plastic ratio—to optimize oil yield and gross calorific value (GCV). By employing Response Surface Methodology (RSM) and a Rotatable Central Composite Design (RCCD), the study achieved robust statistical modeling, enabling the identification of optimal conditions across 15 experimental runs and two blank experiments. The results indicated that the char produced from both biomass and PET dominated the product distribution, albeit due to different decomposition mechanisms. PET decomposition primarily yielded solid terephthalic acid (TPA), while biomass char resulted from incomplete lignin and cellulose breakdown. The highest oil yield was obtained under severe conditions, highlighting the significant impact of process parameters on product distribution. Analytical techniques such as FTIR and GC-MS revealed the presence of diverse functional groups and confirmed the decomposition of PET into its monomers. XRD and XRF analyses further characterized the char, identifying key structural components and elemental composition. Statistical analysis showed a significant quadratic relationship between oil yield and GCV, with minimal prediction error, indicating the model’s reliability. The optimized bio-oil exhibited a higher benzene content, suggesting enhanced decarboxylation of PET, which was supported by FTIR data. Rheological testing demonstrated the potential of the bio-oil as a rejuvenator for bio-pavements, with bio-char showing promising properties as a filler. Rheological testing using Dynamic Shear Rheometry (DSR) was conducted to evaluate the bio-oil’s potential as a rejuvenator in bio-pavements. The DSR tests revealed that the bio-rejuvenators effectively reduced the stiffness of aged materials, restoring some of the original flexibility and viscous properties lost due to aging. While the oil derived from pure biomass performed slightly better in this regard, the co-liquefied oil still showed promise, particularly in applications requiring a balance between flexibility and stiffness. Additionally, when bio-char was used as a filler in mastic formulations, it exhibited superior stiffness and rutting resistance compared to conventional fillers, although it was less effective in resisting fatigue cracking. Despite the bio-oil’s lower GCV compared to traditional fuels, the process offers a promising pathway toward sustainable energy production. Continued optimization, particularly of the biomass-to-PET ratio and process conditions, could further enhance the fuel properties of the bio-oil, making it a viable alternative for energy and material applications. ... Read more

Climate change, driven by increased greenhouse gas emissions from fossil fuels, is a critical global challenge. The Netherlands aims for a 55% CO2 reduction by 2030, with the Port of Rotterdam as a significant emitter. Renewable methanol production from biomass offers a promising solution to reduce these emissions significantly. This thesis aims to study the techno-economic trade-offs and synergies of CO2 compared to H2 syngas conditioning for a biomass-based methanol plant. Syngas produced through biomass gasification typically lacks the adequate stoichiometric ratio for methanol production, requiring a conditioning step. The conventional WGS approach, while increasing hydrogen content, also increases CO2 production, leading to higher costs and reduced efficiency. Carbon removal further limits efficiency and methanol production. While H2 syngas conditioning routes and synthesis have been extensively investigated, other approaches like RWGS and CO2 -co-electrolysis require further study. The configurations are assessed employing process simulations from Aspen Plus, which were developed using data from the literature. The gasifier was modelled and validated using the IGT experimental data. OLGA and Rectisol were employed for syngas cleaning. Similarly, four syngas conditioning configurations were modelled: water electrolysis, WGS, RWGS and CO2 co-electrolysis. The conditioned syngas compositions for each configuration were used in a separate isothermal methanol reactor model, including purification. CO2 co-electrolysis and RWGS configurations showed the highest biomass utilisation efficiency, but required significant energy input. Water electrolysis had moderate efficiency and the best environmental performance with nearly zero direct CO2 emissions. WGS was the least efficient and had the highest CO2 emissions. This was primarily due to the separation of CO2. Economically, all options were less competitive than market methanol prices. CO2 coelectrolysis had the lowest levelized methanol (LCOM) cost at €2.39/kg, followed by water electrolysis at €2.42/kg and RWGS at €2.63/kg. WGS performed worst at €3.55/kg. The study reveals that RWGS and water electrolysis configurations demonstrate the lowest CO2 emissions, making them ideal for scenarios where reducing the carbon footprint is a priority, primarily when electricity is sourced from low-cost, renewable energy. CO2 co-electrolysis, while achieving high biomass utilisation efficiency and the lowest LCOM does not have the lowest CO2 emissions due to its reliance on natural gas for heating. Conversely, the WGS configuration, although minimising electricity consumption at 0.60 kWh/kg MeOH, is the least efficient overall, with high CO2 emissions and the highest LCOM. CO2 co-electrolysis and RWGS are more suitable in scenarios where high biomass utilisation and competitive costs are prioritised and where electricity prices are stable or low. The WGS process may be more suitable for high electricity costs, and minimising capital expenditure is crucial. In conclusion, this study presents valuable insights into the techno-economic synergies and trade-offs of syngas upgrading through CO2 conditioning compared to hydrogen conditioning for methanol production from biomass gasification. Addressing the identified challenges and leveraging the synergies can advance towards a more sustainable and economically viable methanol production industry. Future optimisation and validation efforts will be essential for translating these findings into practical, scalable solutions. ... Read more

The CO2 emissions started to peak during the start of this century and the steel manufacturing sector accounts for 25% of the global CO2 emissions. The majority of steel production is based on the route of the basic oxygen furnace (BOF) route, which is energy efficient. This production route results in the emission of BOF gas. So a new method to produce Isopropyl alcohol via BOF gas fermentation was developed for the pilot scale plant and the LCA was performed by Liew et al., (2022). The carbon-negative emissions were calculated and estimated in the pilot scale study. A few inconsistencies were identified in the calculation method, in which the components utilized for the production process contributed less than 5% to the Global Warming Potential value, and the replacements provided to the steel mill for the BOF gas redirection were cut off. The LCA value for the pilot-scale plant was incomplete and inconsistent, and only the GWP was chosen as the prominent midpoint indicator. Based on this pilot-scale plant, an industrial-scale (46 kton/ yr) base case process model was developed for the gas-fermentation process to produce IPA. The fermentation is the major step involved in the production of IPA, which involves the acetogenic bacteria Clostridium Autoethanogenum. The initial process involves the capture of the emission of BOF gas for compression and cooling performed because the temperature of BOF gas is around 1100°C. This compressed gas is fermented using of microbes and filtered out to obtain the filtered broth. Then the IPA is separated from the filtered broth using extractive distillation, using glycerol. The major product of IPA is processed out of the system. This research aims to analyze and estimate the environmental impacts of this process model of BOF gas fermentation to produce Isopropyl alcohol. The assessments were performed for the base case and the 11 process parameters of CO conversion, Volumetric mass transfer rate of CO, Product selectivity, Dilution rate, Extractive distillation glycerol mole fraction, Temperature offgas condenser, Anaerobic waste conversion, Extractive distillation molar reflux ratio, Biomass liq-liq mole fraction and the broth and glycerol purges. The impact assessment results help to identify the potential contributors in the process that affect the environment, so the process model can be optimized to yield lower impact values concerning the environmental perspectives.

The 7 midpoint indicators namely Global Warming Potential (GWP), Stratospheric Ozone Depletion (SOD), Fine Particulate Matter Formation (FPMF), Freshwater Eutrophication (FE), Marine Eutrophication (ME), Human Carcinogenic Toxicity (HCT), and Land Use (LU) were chosen to obtain a detailed view on the ecosystem, human health, and the environmental effects. The replacement calculations estimated for 1 kg of IPA production is 4.324 MJ of heat, and 0.877 kWh of electricity, has to be replaced for the steel mill. The impact assessment for the base case model was performed and compared with the conventional IPA production method (GWP: 2.026 kg CO2 eq.), the global warming potential for the BOF gas fermentation method (GWP: 27.656 kg CO2 eq.) estimated to be a 1265% increase compared with the conventional IPA method. Similarly, all seven impact categories are estimated to have a huge increase in values. An elaborate study compared and identified the most influential process parameters. The process parameter of dilution rate in which the dilution rate is lowered by 30% from the base case value appears to be the process parameter with a lower impact value of 20.464 kg CO2 eq. for the Global Warming Potential (26% lower than base case), 1.72E-05 kg CFC11 eq. for the Stratospheric Ozone Depletion (31% lower than base case), 9.618E-03 kg PM2.5 eq. for the Fine Particulate Matter Formation (38% lower than base case), for the Freshwater Eutrophication the value is 9.853E-04 kg P eq. (53% lower than base case), 5.531E-03 kg N eq. for Marine Eutrophication (33% lower than base case), 1.733E-01 kg 1,4-DCB for the Human Carcinogenic Toxicity (53% lower than base case), and the 3.265 m2a crop eq. (32% lower than base case) for the Land use impact categories. The major contributors are the high-pressure and low-pressure steam utility contributing greater than 56% for the impact category values of the GWP, FPMF, FE, and HCT particularly. The glycerol used for the extractive distillation process contributed greater than 92% for the impact categories of SOD, ME, and LU. The impact assessments across different indicators were interpreted and the major process parameters that are more influential in reducing the impact values are identified. The results indicate that the major contribution to the impact value is reduced by the emission credit ±40% for preventing the BOF gas from flaring. The carbon dioxide emission from the process, glycerol component, and steam utility collectively contribute majorly which account for more than 90% of the total impact values in the impact categories. Lowering the dilution rate, glycerol purge fraction, and glycerol mole fraction by -30%, and increasing the volumetric mass transfer rate by +30% of the process model could result in lower impact values. The CO2 emitted from the process is estimated to be 9.34 kg CO2 eq. This emission is higher than the feedstock (BOF gas) used for the gas-fermentation process. The entertainer glycerol is anaerobically digested and combusted leading to the 10% of the total CO2 emission of the process model. The process model should be updated with the process parameters listed above and a similar life cycle impact assessment has to be performed to compare the impact values. This updated process model might have comparatively better results. The sensitivity study has been performed to estimate the percentage effects of the combined glycerol and steam components on the midpoint indicator impact value. Cutting off the components of glycerol and steam from the process model still yields the GWP value of 6.16 kg CO2 eq. for industrial scale process which is a 204 % increase than the conventional IPA process. This implies that the updated process model with similar process steps cannot obtain impact values lower than the conventional IPA method. To lower the impact value of GWP, the CO2 emission from the process should be sequestrated (carbon capture) to lower the GWP value by 42% from the base case.
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In Europe, 20.7 Mt of Polystyrene (PS) was produced in the year 2021, mostly consisting of packaging, insulation, and food utensils. Like many other kinds of plastics, they take hundreds of years to naturally degrade in the environment. To prevent the buildup of plastics in our environment, recycling technology will have to be employed. Current recycling technologies can be divided into three categories: organic, mechanical and chemical recycling. Organic recycling involves the use of biological organisms or enzymes to breakdown plastic into useful materials. Mechanical recycling technologies include processes such as dissolution and conventional mechanical recycling. Among chemical recycling, baseline technology includes
pyrolysis that involves higher temperatures (>500°C) which produces char, gasses, and complex oils. Hydrothermal Liquefaction (HTL) of PS has shown promising results in tackling the problem plastic waste buildup in the environment. This process utilizes water as solvent and subjecting it to mild temperatures and pressures to produce less complex oils that contain building blocks such as monomeric compounds and high value chemicals (HVC). These compounds can then be used as platform chemicals or as source to manufacture new materials, as well as closing the loop on PS waste.
This thesis focuses on the use of catalysis to increase the selectivity for PS conversion through HTL to increase the yields of monomeric compounds and high-value chemicals (HVCs) at lower temperatures (<370°C) than current approaches. In this work, different catalysts were screened and the best performing catalyst was used to optimize the HTL process. The HTL process was optimized using a design-ofexperience (DOE) approach for the following process conditions: temperature (330-350°C), catalyst loading (0-15%) and reaction time (30-60 minutes). The analytical techniques used to characterize the quality of oil as well as determine the amount of chemicals present are: Bomb Calorimetry, Ultimate analysis (CHN-analysis), Gas Chromatography-Mass Spectrometry with Flame Ionization Detection (GCMS-FID)
and Two-Dimensional Gas Chromatography with Flame Ionization Detection (GCxGC-FID).
Results from a screening campaign indicated high yields of oil (90 wt%). Following this, a simple distillation was conducted to separate the lighter fraction from the heavier ones within 90 wt%. Ultimate analysis of the compounds showed high C,H,and N ratios similar to what was found in literature. Bomb calorimetry of the PS-Crude oil product showed of 40 MJ/kg, indicating that oil product is comparable to what is found in literature. GCMS-FID indicated that 17 wt% of styrene was produced from this process,
along with 5.5 wt% of alpha-methyl styrene and other HVCs. The rest of the oil consists of heavy fractions (C-20) which could be go through another upgrading process.
After the screening campaign MgO was chosen as a catalyst to increase the yield of styrene. The yield of oil remain high with 80-90 wt% yield of oil in most cases. Aqueous phase and gas yields remain low (<5 wt%), while char can vary but also remains quite low (<10 wt%). Analysis of Bomb calorimetry showed similar results to screening with an average of 38 MJ/kg. CHNO also showed similar ratios of C,H, and N ratios. When looking at the GCMS-FID and GCxGC-FID, the amount of styrene remained at a maximum of 16-17 wt% with no significant increase. However, results of the research also showed that catalyst does have effect in increasing yield of styrene. Optimization for oil was conducted and optimum point for oil production is at 340°C, 34 minutes and 8% catalyst loading. The research will contribute to the growing body of research into processes for plastic waste valorization and offers more insight into catalytic
hydrothermal liquefaction as well as experimental methodology to separate the oils into its components. ... Read more

The objective of this study is to generate insights into the application of the reliability of a W2H system and its impact on the techno-economic performance. This involves examining the case of a single system to analyse on a micro-level the underlying conditions affecting performance, as well as exploring W2H farms to observe performance and the effects of changing conditions on a macro-level. To this end, MATLAB models have been utilised and developed to simulate various components of a system, such as wind turbines and electrolysers, focusing on aspects like hydrogen production and the number of breakdowns per year. The model creates insights into technical and economic parameters. ... Read more

The global energy sector is a substantial contributor to greenhouse gas emissions, responsible for approximately 75% of such emissions worldwide. Indonesia, ranking twelfth in energy consumption and ninth in global carbon dioxide (CO2) emissions from fuel combustion, is faced with the challenge of addressing its significant carbon footprint. This challenge is exacerbated by a projected 3.5% annual increase in energy consumption driven by anticipated economic growth. Notably, coal accounts for half of Indonesia's electricity generation capacity, producing 31.5 exajoules (EJ) annually and emitting 3 kilotons of CO2 per kiloton of coal consumed.

Despite its role as a major coal producer, Indonesia has set ambitious targets, aiming to achieve net-zero emissions by 2060, including a 29% reduction in carbon emissions by 2030. A pivotal step towards these goals is exploring alternative energy sources, with a particular focus on the New and Renewable Energy (NRE) sector.

Traditionally used for cooking, biomass energy has expanded within Indonesia's NRE sector, with sustainable biofuel and biogas gaining prominence. Indonesia possesses a substantial biomass potential, estimated at 32.6 gigawatts (GW), offering a sustainable avenue for biomass residue utilization. One promising avenue is co-firing biomass alongside coal in existing Coal-Fired Power Plants (CFPPs). However, initial pilot projects have encountered challenges, with co-firing percentages remaining below 20%, and coal retaining dominance in the energy mix.

This report addresses a critical knowledge gap hindering the progress of biomass co-firing in Indonesia. Its primary objective is to assess the techno-economic potential of retrofitting existing CFPPs in Indonesia for biomass co-firing. The assessment encompasses identifying abundant and suitable biomass residues for co-firing, exploring retrofit scenarios based on technical considerations, conducting an economic feasibility analysis of CFPP retrofitting, and proposing policy recommendations for Indonesia's Ministry of Energy and Mineral Resources.

The study reveals that agricultural by-products account for 70% of available biomass, followed by forestry residues (17%) and Municipal Solid Waste (MSW) (13%). Notable contributors among agricultural residues include rice and palm oil residues, each exhibiting substantial potentials. Forestry residues, such as solid and sawdust residues from pulpwood and sawn wood, also hold promise.

The technical potential for co-firing is estimated at 450 terawatt-hours (TWh), equivalent to the estimated electricity demand in 2030. To achieve practical implementation, proposed CFPP retrofit scenarios consider co-firing percentages, addressing pre-treatment of biomass, boiler efficiency, and equipment modifications.

Using the Levelized Cost of Electricity (LCOE) methodology, the economic assessment yields a range of outcomes, from 2.2 to 10 cents per kilowatt-hour ($c/kWh), based on distinct case studies. The report highlights the economic feasibility of biomass co-firing in Indonesia, even when compared to sub-critical/ultra sub-critical coal plants.

To support biomass co-firing, the report recommends policies such as a significant carbon tax, redirecting coal subsidies, and promoting biomass utilization to support biomass co-firing. Improving the supply chain by identifying biomass sources near coal mines and enhancing transportation infrastructure is also essential for ensuring a stable biomass supply. Despite some limitations in data sources and modeling, the study employs dynamic approaches to present result ranges and diverse scenarios, enhancing the validity of its findings.

In summary, the strategic implementation of recommended measures has the potential to significantly contribute to Indonesia's transition towards sustainable biomass co-firing practices in its energy sector, aligning with its emissions reduction and net-zero goals. ... Read more

The global temperature rise has pushed governments more into finding ways to reduce CO2 emissions, by increasing the use of renewable fuels. Lignocellulosic biomass (wood, forest residues, agricultural residues) is a renewable fuel that has still not been utilized to its full potential. That is because it lacks properties such as homogeneity, high volumetric energy density and low moisture that its main fossil fuel competitor -coal- has. Therefore, a type of pre-treatment is needed for these disadvantages. Torrefaction, a process of heating biomass (200-300 oC) in an inert environment (no combustion), provides a product with improved physicochemical properties: reduced hydrophobicity, easier grindability, homogeneity, reduced microbial activity and increased calorific value. However, it is not enough to torrefy the biomass, as it needs to be densified in order to be utilized. With the process of pelletizing, a type of densification, torrefied biomass becomes compact and can be considered as bio-coal. While pelletizing is influenced by many parameters (moisture content, die pressure, torrefaction temperature etc), herbaceous types of biomass such as wheat straw, hay, reeds and grass, still cannot produce quality pellets without the addition of a binder. Typical organic binders such as starch, lignin and sawdust can either be expensive or biologically degrade in storage conditions. That is why addition of plastic binder should be considered. The aim of this report was to investigate how quality torrefied pellets from herbaceous biomass can be produced with the addition of plastic binder in a commercial capacity. Wheat straw and woodchips were used as feedstock, while polyethylene resin was the plastic binder. The biomasses were torrefied at 240 oC and 270 oC on the Torrgreen facilities, via a pilot-scale packed bed reactor, which recycles the volatiles from torrefaction for inertization and pelletized with a 100 kg/h pellet mill. For the torrefied wheat straw, a design of experiments was formed, to investigate how 4 parameters for pelletizing (torrefaction temperature, moisture content, plastic binder addition and pellet diameter) improved mechanical durability. Results indicated that 5% of plastic improved durability and pellet formation in total, while higher torrefaction temperature weakens the pellets and aggravates pellet formation. The highest durability achieved was 90.3%. Torrefied wood chips were pelletized for reference and showed low durability, mostly due to inability of the pelletizer. Water immersion tests on the straw pellets showed that higher torrefaction temperature increased hydrophobicity a lot, while plastics also had a positive effect. Comparison of the straw pellets produced with conventional wood pellets revealed that the former lack in mechanical durability and are high in ash content, making them incompliant with current standards. Overall, inclusion of plastics in pelletizing of torrefied herbaceous biomass, demonstrated very positive results and improved their quality, while making the operation smoother, but for scaling up and keeping the whole process sustainable a polyethylene (or other plastic) waste stream should be utilized. ... Read more

As part of the Dutch government’s ambitions to realise significant offshore wind energy capacity (70 gigawatts (GW) by 2050), the Port of Rotterdam is to become a hydrogen hub for North-Western Europe. To achieve this, it is expected that around 20 megatonnes (Mt) of hydrogen could be throughput in the Port of Rotterdam, out of which 2 Mt will be produced locally from offshore wind farms. Current offshore wind farms use high voltage electricity cables to transport energy to shore, but could, in the future, also transport energy in the form of hydrogen to shore via a transport infrastructure.
The objective of this thesis is to investigate the techno-economical feasibility of an offshore hydrogen production value chain connected to the Port of Rotterdam. The technical analysis gives insights into the possible technologies that can be used for the offshore value chain. It will also look at the technical feasibility of system integration in the Noth Sea's energy system. The economic analysis gives insights into the economic feasibility of the offshore hydrogen production value chain. The total costs are of importance, as well as the levelised cost of hydrogen.
In this thesis, a qualitative literature study maps the different possibilities per component of the value chain. A decision framework is then used to discuss the best possibility per component and to build three promising designs. These designs are then modelled in MATLAB to size their components. With the model’s output, a cost analysis can be done to determine whether such a value chain would be feasible compared to other ongoing projects. A special focus will be put on the Port of Rotterdam, to which the value chain will be connected.
The offshore decentral configuration is found to be the best-performing design based on assessments through a multi-criteria decision analysis, a technical model and a financial model. It is, therefore, the most promising design.
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Low-carbon hydrogen is expected to have a large role in future energy systems. Recent research shows the short-term financial feasibility of blue hydrogen is often higher than green hydrogen. Ammonia production is particularly carbon-intensive due to its hydrogen production routes. This research focuses on the physics-based modelling of blue hydrogen production for ammonia synthesis, examining the influences of varying input conditions and economic scenarios on process performance and economics. Future energy systems will rely on flexible integrated solutions, emphasizing the importance of understanding how system parameters respond to diverse input conditions.

The ammonia plant consists of a desulphurization unit, a pre-reformer, an ATR, two water gas shift reactors, a physical absorption tower for CCS, a PSA for H2 purification and a Haber-Bosch ammonia synthesis reactor. Auxiliary components consist of heat exchangers, compressors and dehydration units. The modelling efforts focus on medium-fidelity models, reflecting the main thermodynamics and kinetics through first-order differentials assuming reactor simplifications. The plant simulations are based on plant operation in the Netherlands in 2030 under the following price assumptions: C_NH3= 0.472 €/kgNH3, C_elec= 41.77 €/MWh, C_NG= 22.64 €/MWh, C_CO2−tax= 0.135 €/kgCO2(eq), C_CCS= 0.05 €/kgCO2.

Each reactor model was separately validated through industrial data. Then the operational window was selected based on individual reactor limitations and the overall system chain performance: α=0.6, β=2.0, Tin=873.15K, Pin=2.8MPa. α and Tin are the most influential parameters from an economic and environmental perspective, showing the largest influence on levelized costs and emissions. Overall, under the simulated conditions, blue ammonia results in an 85% direct emission reduction compared to grey ammonia. The levelized costs of blue ammonia amount to 0.417€/kg and the NPV is 104 MEUR, the most influential economic parameters are the natural gas price and the ammonia selling price.

Three case studies were conducted in which specific economic and operational conditions were compared. Simulations of three IEA policy scenarios for 2030 show that the overall cost reduction in more sustainable scenarios is mainly driven by the lower natural gas price. Carbon taxes have a limited effect on the price of blue ammonia however do significantly increase the price of grey hydrogen compared to blue (a 0.11-0.17 €/kg difference). This results in a minimum 0.05 €/kgNH3 margin for the capture process costs in the stated scenario (0.09 €/kgCO2(eq) ), the other scenarios give a larger margin. Green ammonia gives a levelized cost of 0.457 €/kg NH3 under the same economic assumptions. The NPV is -480 MEUR, which is most affected by the electricity price and ammonia price. This research yields a 9% LCOA increase for green ammonia when compared to blue. The evolution of electricity prices is paramount in the financial competitiveness of green ammonia, more so than the CAPEX
evolution. The indirect emission intensity of green ammonia is lower than blue ammonia in the simulated conditions. However, this depends on the electricity source. Through carbon taxes blue and green ammonia can become cost-competitive to grey however this comes at a cost for the everyday consumer.
A simulation with dynamic operation yielded that inputting NG feed following seasonal natural gas pricing is not cost-effective when compared to steady-state production at the same seasonal pricing, even for +/-44% price fluctuations. The additional CAPEX costs for storage and larger process units are not sufficiently compensated by the lower variable OPEX costs. Further research should focus on
shorter-term supply and demand matching.

Overall, it can be concluded that this model can sufficiently simulate a blue hydrogen chain and be used for further simulation cases, also with alternative economic and operational assumptions. The technical parameters that affect blue ammonia production most are α and Tin. Economically the ammonia and the natural gas price are most influential. In comparison with grey and green ammonia, under the simulated conditions, blue hydrogen is the most cost-effective. Finally, the economic incentives through the seasonality of natural gas prices do not justify a dynamic operation of the process plant.
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The carbon emissions from human activities are causing significant harm to the planet, leading to increased temperatures, melting of polar ice caps, rising sea levels, and other negative impacts on the environment. One promising solution is the use of green hydrogen as a fuel source, which could have a much lower carbon footprint than traditional fossil fuels. The production of hydrogen can be achieved through various methods, including the electrolysis of water, which splits water molecules into hydrogen and oxygen. To mitigate these effects and ensure a sustainable future, countries are taking various measures to reduce their carbon footprint, including increasing the use of clean energy sources and improving energy efficiency. Hydrogen storage and transportation pose major challenges since it is the one of the lightest gases leading to low energy densities.

Ammonia is emerging as a hydrogen carrier due to its high gravimetric storage densities of hydrogen. It is produced through the combination of hydrogen and nitrogen using the Haber-Bosch process. Ammonia can then be used as a clean and efficient fuel for various applications, such as transportation and power generation. Fluctuations in the hydrogen feed flow rate, resulting from variations in renewable energy sources can significantly impact the pressure and operating temperature within the system.

}Morocco holds significant potential for renewable energy development due to its favorable geographic location and natural resources. The geographic location situated close to Europe makes Morocco well positioned for exporting green hydrogen to European markets. The chosen location for the ammonia plant is Boujdour in Morocco due to its excellent wind capacity factor of 67%.

Modern ammonia production plants employ control systems to maintain stable pressure. When there is a reduction in hydrogen feed flow rate, these reductions result in severe pressure reductions which would lead to metal fatigue and damage the entire production unit. Hence, these control systems respond by adjusting parameters to sustain pressure within the system. Aspen Plus Dynamics has been used in the present thesis work to model the dynamics of the ammonia synthesis plant. The varying hydrogen feed flow rate is a consequence of renewable energy fluctuations, which is served as the basis for modeling three distinct scenarios involving a 20%, 50%, and 70% reduction in hydrogen feed flow rate. Three distinct control strategies were developed where each control strategy, based on controlling the cooling duty of the condenser, manipulating the brake power of the recycle compressor, and regulating the nitrogen feed flow rate, demonstrated effective stabilization of the system's pressure, even during dynamically changing input conditions. Both linear and step reduction in hydrogen feed flow rate have been considered to gain understanding of the dynamic the behaviour of the system.

Significant outcomes were found when a reduction in hydrogen feed flow rate is imposed on all three control strategies. For a 20% reduction in hydrogen feed flow rate, the condenser's duty reduced from -1.2 MW to -1.05 MW, while the brake power of recycle compressor reduced from 12.5 kW to 5.5 kW. Furthermore, the stoichiometric ratio of H2:N2 changed from 3 to 2.8. These changes successfully stabilized the pressure in the ammonia synthesis plant under varying hydrogen input flow rate...

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Green hydrogen has a pivotal place in the energy transition, addressing carbon emissions in hard-to-abate sectors. As global hydrogen demand rises, decarbonizing green production becomes vital. This study explores the influence of design choices and local weather patterns on the Carbon Footprint (CF) and Levelised Cost of Hydrogen (LCOH) for green hydrogen production.

An optimisation model is developed, simulating the production chain (cradle-to-gate) and optimising it for low CF and LCOH based on location-specific wind and solar data. Three locations (Duqm, Groningen, Dakhla) and three design choices (electrolyser, PV type and wind-solar ratio) are assessed.

Results indicate that local weather patterns significantly affect system performance. Dakhla boasts low production costs due to consistent solar and wind energy. Groningen has a low CF but high LCOH due to ample offshore wind but inconsistent sun. Duqm has a low LCOH but high CF due to abundant sun but inconsistent wind.

Design choices, particularly the solar-wind energy ratio, strongly impact both LCOH and CF. PV technology selection also matters, with CI(G)S performing well overall. Alkaline electrolysis is preferred over PEM.

The research demonstrates that design choices can substantially influence the CF, resulting in serious CF reduction at prices comparable to blue hydrogen.

Future research should include storage, transportation, and off-taker aspects and expand impact categories, including social and critical raw material depletion impact categories. ... Read more

Energy demand for heating and cooling makes up 73\% of total energy use of buildings [2]. This figure is expected to increase over the coming decades, as demand for cooling energy may rise in the Netherlands due to climate change. The heating and cooling of buildings are at relatively low temperature compared to the industry and thus allowing for a 5th Generation District Heating and Cooling (5GDHC) network with thermal energy storage. Several guidelines are available for the design of 5GDHC substations \cite{ISSO39}, however they do not integrally consider the control design.
Currently, in literature the performance of the substations is generally based on 1-hour measurements yet the control of the short term dynamics have a significant impact on the performance, thus shorter time steps are required to improve the performance.


This study considers the short term dynamics of substations of large utility buildings connected to a 5GDHC grid, allowing for seasonal thermal energy storage and independent bi-directional consumption for all buildings. A hydro- and thermodynamic model including the controllers are compared with a case study of utility buildings at Utrecht University where high frequency operational data is gathered. This provides a view on the causes of the problems and inefficiencies and new insights into improvements on the hydro- and thermodynamics and control of the substation. A new control method for the heat exchanger and for the Heat Pump (HP) group is proposed to maximise the networks capacity.

The use of Model Predictive Control (MPC) controllers is investigated to determine the performance improvements that can be achieved based on a simple physical system model and the energy demand and temperature setpoint predictions. As the short-term dynamics are discussed, the time steps for the MPC optimisation are relatively small while the many on/off switches that are allowed might make it computationally intensive due to large number of binary variables. The flow in some parts might be reversed, which is modelled using binary variables. Finally, as the system is transporting water at different temperatures and different mass flow rates, it is described by bilinear equations. These equations can be linearised by the McCormick relaxations, however they once again increase the computational burden as new binary variables have to be introduced.

The changed proposal for switching conditions could easily be implemented and reduces the temperature limit violations as well as the proposed control method for the warm Heat Exchanger (HEX) as it stabilises the substation control. The proposed method for the temperature setpoint and capacity control showed an improved regulation of the temperature and energy provided by the heat pumps and could even reduce the consumption of conventional heating sources. Finally, the MPC controller shows an increased performance both for the constant and variable flow conditions, but cannot yet be implemented as the computational burden is too large. ... Read more