CO2 Point Sources Research Articles

Elucidating flow-directed 98% CO2 absorption using millimeter-sized coiled flow inverters: Nanocellulose-aided sustainable scope

The Sustainable Development Goals (SDGs) adopted by the United Nations drive the global efforts to discover a sustainable carbon capture method for the reduction of anthropogenic CO2 emissions. Concentrated alkanolamine solutions are being used as CO2 capture mediums for batch processes amid several disadvantages, such as energy intensiveness and poor efficiency. In this work, millimeter-sized coiled flow inverters (CFI) have been explored as a point-source CO2 capture tool for highly efficient, continuous operations. Solvent and CO2 gas flow rates are found to dictate the slug flow regime and, more specfically, slug lengths. High interfacial area and residence time remain the driving factors for enhanced CO2 capture using CFI. About 98% CO2 absorption efficiency has been achieved for 3% aqueous diethanolamine solution in CFI . The efficacy of nanocellulose, a sustainable nanomaterial has been unearthed for CO2 capture at low flow rate.

Process Development and Techno-Economic Analysis for Combined and Separated CO2 Capture-Electrochemical Utilization

Combining CO2 capture and utilization into a single unit operation offers a feasible solution for converting a sustainable feedstock into marketable commodity chemicals, while reducing energy requirements from separated processes. In this research, we developed a process model and performed a techno-economic analysis (TEA) for point-source CO2 capture and electrochemical-based utilization in light olefins production under both separated and integrated scenarios. CO2 containing flue gas from a 500 MW power plant was utilized as a feed while CO2 utilization involved electrochemical reduction reactions to produce light olefins directly from CO2. A meticulous analysis was conducted, probing into the multifaceted impacts of various operating parameters, material properties, and downstream treatment units. Factors such as pressure, temperature, H2O/CO2 molar ratio, catalyst and adsorbent activities, deactivation rate, and heat integration were optimized to achieve 95 % CO2 recovery and > 90 % conversion, and > 85 % ethylene yield. Through a comprehensive TEA, our findings unveiled that the combined process utilizing bifunctional adsorbent/catalyst materials (BFMs) incurs costs of approximately $284/ton CO2, whereas the separated process reported expenses of ∼$516/ton CO2. This study, pivotal in its contributions, evaluated economic feasibility of combined capture-conversion method based on BFMs for CO2 removal and subsequent utilization via a promising advanced process model for sustainable feedstocks conversion to commodity chemicals.

CO2 trapping dynamics in tight sandstone: Insights into trapping mechanisms in Mae Moh's reservoir

The reliance on fossil fuels is a major contributor to increased anthropogenic CO2 emissions, driving global challenges such as climate change through the greenhouse effect. Carbon capture and storage (CCS) is a promising interdisciplinary technology aimed at mitigating these emissions by securely sequestering gigatons of CO2. This study focuses on the feasibility of storing point-source CO2 emissions in saline formations, with a particular emphasis on the Mae Moh coal-fired power plant in Lampang, Thailand, which is located near its associated coal mine. The region presents challenges due to tight sandstone reservoirs buried over 2000 m deep. With reservoir simulation, this study evaluates the impact of various factors on CO2 containment and trapping in these geological settings. Results show that elevated temperatures decrease structural trapping of 43.0%–28.9% and increase solubility trapping of 28.55%–46.5%, at 40 °C and 80 °C respectively. Hysteresis is found to enhance residual trapping by immobilizing up to 31.1% of CO2 within pore spaces at 0.5. Permeability heterogeneity has a minimal impact on overall trapping efficiency due to the less heterogeneity of the tight sandstone. However, the kV/kH ratio significantly influences vertical CO2 migration which resulted in residual trapping at its highest at the ratio of 0.1, while lower ratios support lateral dispersion. Moderate rock compressibility values are identified as optimal for structural and residual trapping, while extreme compressibility enhances solubility trapping by up to 30%. These findings emphasize the complexity of CO2 trapping mechanisms in tight sandstone formations, emphasizing the need for careful consideration of key factors in CCS projects.

The Role of Surface Roughening in Improving the Selectivity of Copper for CO2 Electroreduction

Electroreduction of CO2 (eCO2RR) has emerged as a promising alternative for production of renewable fuels and important commodity chemicals such as ethylene and ethanol. Simultaneously, it opens an economically attractive path to mitigate point sources of CO2, a potent greenhouse gas. Despite decades of research efforts, Cu remains the only catalyst capable of producing significant amounts of desirable C2+ products, containing more than one carbon atom. However, further improvement is needed for industrial applications. It is known that roughened copper-based electrocatalysts surfaces exhibit enhanced selectivity towards C2+ products during electroreduction of CO2. This poses a challenge for modeling efforts aiming to find a rationale for the enhanced selectivity. In this work, we use an innovative modeling approach to investigate roughened copper surfaces derived from cuprous oxide on structures of 100x100 nm2 size with atomic resolution and accuracy compared to density functional theory (DFT). We combine semilocal DFT (RPBE) in VASP, effective medium theory (EMT), and linear scaling relationships via the recently proposed alpha parameter scheme to investigate the site-resolved catalytic selectivity of copper sites. Electrode potential-dependence is included via the use of the VASPsol implicit solvation and a grand canonical potential approach. The approach allows us to investigate the effect of varied macroscopic roughness on the intrinsic catalytic activity of copper by comparing surfaces exposed to simulated sputtering and electropolishing, respectively. The study highlights i) the challenge for designing improved copper catalysts for CO2RR with monodisperse active site selectivity, ii) the need for careful experimentation when comparing to theory, and iii) the limitations of macroscopic roughness in controlling atomic scale activity.

Understanding Limitations in Electrochemical Conversion to CO at Low CO2 Concentrations.

Low-temperature electrochemical CO2 reduction has demonstrated high selectivity for CO when devices are operated with pure CO2 streams. However, there is currently a dearth of knowledge for systems operating below 30% CO2, a regime interesting for coupling electrochemical devices with CO2 point sources. Here we examine the influence of ionomer chemistry and cell operating conditions on the CO selectivity at low CO2 concentrations. Utilizing advanced electrochemical diagnostics, values for cathode catalyst layer ionic resistance and electrocatalyst capacitance as a function of relative humidity (RH) were extracted and correlated with selectivity and catalyst utilization. Staying above 20% CO2 concentration with at least a 50% cathode RH resulted in >95% CO/H2 selectivity regardless of the ionomer chemistry. At 10% CO2, however, >95% CO/H2 selectivity was only obtained at 95% RH under scenarios where the resulting electrode morphology enabled high catalyst utilization.

A methodology for the determination of future Carbon Management Strategies: A case study of Austria

The achievement of global climate targets outlined in the Paris Agreement represents a critical challenge in the coming decades. Certain industry sectors cannot completely avoid all emissions from their processes. In this context, the term unavoidable or Hard-to-abate emissions is used. Carbon Capture and Utilization (CCU) and Carbon Capture and Storage (CCS) are recognized as essential components for addressing those emissions to achieve Net Zero Emissions. To identify effective Carbon Management Strategies, balancing future CO2 sources and possible sinks for achieving long-term climate targets is essential. Especially in Austria hardly any comprehensive studies have been carried out. This work presents a comprehensive analysis of Austria’s CO2 point sources as well as their projected development until 2050 based on technology-based scenarios. Geological CO2 storage in Austria is primarily feasible in former hydrocarbon reservoirs and saline aquifers. Future demands for CO2 as CCU feedstock will arise in the chemical industry. By 2050, industry will emit approximately 4 Mt of unavoidable CO2 annually. These emissions must be stored in the long term and correspond to the minimum demand for CCS. Fugitive emissions from agriculture, for example, cannot be captured. Thus, they are not subject of CCU/S measures. Negative emissions are therefore necessary to achieve the climate targets. These negative emissions and the possible use of CO2 as feedstock are covered by biogenic CO2.

Revisiting the quantification of power plant CO2 emissions in the United States and China from satellite: A comparative study using three top-down approaches

Top-down constraints of CO2 emissions from coal-fired power plants are critical to improving the accuracy of CO2 emission inventory and designing carbon reduction strategies. Different top-down models based on satellite observation have been proposed in previous studies, but discrepancies between these models and the underlying drivers are rarely explored, limiting the confidence of their application for monitoring point-source CO2 emissions from satellite. Here, we apply three top-down models to estimate CO2 emissions from individual coal-fired power plants in the United States (US) and China in 2014–2021 from Orbiting Carbon Observatory 2 (OCO-2) satellite observations. The first one applies the Gaussian plume model to optimize emissions by fitting modeled CO2 enhancement to the observation. The second and third methods apply the same inversion framework using the maximum likelihood estimation, but with WRF-Chem and WRF-FLEXPART as forward models, respectively. We evaluate consistency between the three methods in estimating emissions of 10 power plants in the US, using daily reported values from the US Environmental Protection Agency (EPA) as a benchmark, and then apply the three methods to quantify emissions of 13 power plants in China. Results show that the WRF-Chem and WRF-FLEXPART based inversion results are consistent with the EPA reported emission rates, with correlation coefficients (r) of 0.76 and 0.85 and mean biases (MB) of 4.06 and 3.97 ktCO2/d relative to EPA reports at all 10 power plants, respectively. The Gaussian plume model driven by wind fields from WRF-Chem model without the wind rotation shows comparable ability in reproducing the EPA reported emission rates at 7 power plants (r = 0.82, MB = 6.17), but is not applicable for the other three cases. We find that application of the high-resolution three-dimensional wind fields can better capture the shape of observed plumes, especially under complex wind conditions, compared to the Gaussian plume model which relies on wind field at a single point, and thus the Gaussian plume model has difficulty to optimize emissions under inhomogeneous wind fields or when observations are far away from the power plant. In general, using the WRF-FLEXPART model as the forward model in the inverse analysis shows advanced capability to simulate narrow-shape plumes in the absence of numerical diffusion which is inherent in Eulerian model such as WRF-Chem. Emissions estimated by the three top-town methods show a moderate consistency at 13 coal-fired power plant cases in China, with 8 of 13 cases showing differences of <30% between at least two methods. However, large differences emerge when wind fields are inhomogeneous and number of available observations is limited. Using different meteorological wind fields and OCO-2 data versions can also bring substantial differences to the posterior emissions for all three approaches. We find that the posterior CO2 emissions, though only reflecting instantaneous emission rates at satellite overpass time, are not proportional to the reported capacities of these power plants, indicating that attributing CO2 emissions simply based on the capacity of power plants in some bottom-up approaches may have significant discrepancies. Our study exposes the capability and limitation of different top-down approaches in quantifying point-source CO2 emissions, advancing their application for better serving increasing constellations of point-source imagers in the future.

A general Energy-Efficient strategy for optimizing CO2 Capture: Designing and harnessing the rapid adsorption kinetics of Amine-Impregnated adsorbents

This study aims to optimize the performance of amine-impregnated CO2 adsorbents for both direct air capture (DAC) and point source CO2 capture (PSC) applications. The main objective of this study is to investigate the relationship between the weight fraction of amine loading and the efficiency of CO2 uptake on the designated support, aiming to find a straightforward method to design effective amine support materials. To this end, a composite material denoted as PEI/CNT@ZIF-8 has been developed. This composite is comprised of polyethylenimine (PEI), multi-walled carbon nanotubes (CNTs), and zeolitic imidazolate frameworks (ZIF-8). CNTs offer several advantages for enhancing CO2 uptake, including rearranging the ZIF-8 particles to facilitate PEI loading, creating strong electrostatic interaction for amine anchoring, and establishing CO2 diffusion channels to improve CO2 capture kinetics. In DAC scenarios, with a CO2 concentration of 400 ppm balanced with N2, the 25.0 wt% PEI/CNT(1)@ZIF-8(5) demonstrates superior CO2 uptake, achieving 4.08 mmol g−1 within a one-hour interval by harnessing the rapid kinetic region and exhibiting a low desorption energy of 55.8 kJ mol−1 for releasing CO2. In PSC scenarios, with a CO2 concentration of 15 vol% under both dry and wet conditions, the 37.5 wt% PEI/CNT(1)@ZIF-8(5) exhibits excellent CO2 uptake of 2.21 and 2.58 mmol g−1, respectively, at 50 ℃. The findings suggest that adjusting the balance between CO2 uptake and adsorption kinetics by considering the amine weight fraction can optimize the performance of solid amine CO2 adsorbents across diverse operational conditions. Furthermore, rather than relying on a single support material, this study reveals the potential of combining CNTs with materials such as SiO2 nanoparticles, Al2O3, or metal–organic frameworks (MOFs) to enhance CO2 capture performance. This approach holds promise as an effective and straightforward strategy.

A portable low-cost device to quantify advective gas fluxes from mofettes into the lower atmosphere: First application to Starzach mofettes (Germany)

In this study, we introduce a portable low-cost device for in situ gas emission measurement from focused point sources of CO2, such as mofettes. We assess the individual sensors’ precision with calibration experiments and perform an independent verification of the system’s ability to measure gas flow rates in the range of liters per second. The results from one week of continuous CO2 flow observation from a wet mofette at the Starzach site is presented and correlated with the ambient meteorological dynamics. In the observed period, the gas flow rate of the examined mofette exhibits a dominant cycle of around four seconds that is linked to the gas rising upwards through a water column. We find the examined mofette to have a daily emission of 465 kg ±16 %. Furthermore, two events were observed that increased the flow rate abruptly by around 25 % within only a few minutes and a decaying period of 24 hours. These types of events were previously observed by others at the same site but dismissed as measurement errors. We discuss these events as a hydrogeological phenomenon similar to cold-water geyser eruptions. For meteorological events like the passages of high pressure fronts with steep changes in atmospheric pressure, we do not see a significant correlation between atmospheric parameters and the rate of gas exhalation in our one-week time frame, suggesting that on short timescales the atmospheric pumping effect plays a minor role for wet mofettes at the Starzach site.

CO2 concentration retrieval and emission rate estimation over Indian thermal power plants using radiative transfer approach and AVIRIS-NG data

Carbon dioxide (CO2) emissions from thermal power plants (TPPs) are regarded as the primary source of CO2 at the boundary-level atmosphere. The first step toward mitigating these emissions is to improve emission estimation methods at the facility level and establish a reliable emission reporting system. This study aims to establish a transparent and reliable methodology for detecting point source CO2 emissions from TPP and estimating the emission rate released from the stakes of TPP. A remote sensing method continuum interpolated band ratio (CIBR) has been utilized to detect and estimate CO2 emissions over Indian TPPs using Airborne Visible/InfraRed Imaging Spectrometer - Next Generation (AVIRIS-NG) data acquired by the ISRO-NASA joint campaign over India in 2015 and 2018. MODerate resolution atmospheric TRANsmission (MODTRAN) 5.3 radiative transfer (RT) model simulations were carried out for TPP sites to develop a CIBR algorithm for CO2 retrieval. Two AVIRIS-NG short-wave infrared (SWIR) bands were utilized for CO2 concentration retrieval, and the results from each band were compared based on their emission detection capabilities. Comparatively, SWIR-2 (1960–2120 nm) bands show higher sensitivity of CO2 than SWIR-1 (1560–1640 nm). Therefore, we utilize SWIR-2 results for the CO2 retrieval and emission rate estimation. Maximum CO2 emissions of 53.10, 46.36, 96.84, and 53.49 ppmv were detected at Maithon, Dhariwal, Udupi, and Parangipettai TPPs. The study includes one USA-based TPP to compare emission results for validation and test the method in diverse atmospheric conditions. In addition, we compared CO2 estimation results with AVIRIS-NG benchmark data. The simple band ratio method uses only three SWIR bands and operates with minimal computational facility, making it suitable for CO2 retrieval in hyperspectral data. Further, the integrated mass enhancement (IME) method has been used for emission rate estimation using CO2 concentration values from SWIR-2 retrieval results and wind speed at the sites. Yearly 5.96, 6.82, 2.29, and 3.52 Mt emissions were estimated for Maithon, Dhariwal, Udupi, and Parangipettai TPPs, respectively. The emission results have been validated by establishing a relationship between TPP's coal consumption and CO2 emissions. Further, estimated emission rates have been validated with former investigations and the CO2 baseline emission database of India's Central Electricity Authority (CEA) reports. Not having in-situ measurements and uncertainty in wind data may limit the study.

Wood biochar as a point source CO2 adsorbent-impact of humidity on performance

Adsorption of carbon using biobased materials is a sustainable approach to point source carbon capture and storage, particularly if the biomass is a “waste” and the adsorbent can then be re-used in soils. In this work, biochar derived from fast pyrolysis of softwood residues (sawdust) was investigated as a CO2 adsorbent under humid conditions to determine the effect of water on biochar adsorption performance. Dry and wet adsorption experiments were run at concentrations of CO2 between 20–80 vol.% (balanced with N2) at 20 °C. Water concentrations were set by saturating the N2 stream and resulted in 0.5–1.8 vol.% (relative humidity of 20%–80%). For the dry gas experiments, the adsorption capacities doubled (0.83–1.98 mmol/g) as the CO2 concentration increased from 20% to 80%. The capacity did not change between wet and dry experiments for 20, 40, and 60 vol.% CO2; however, at 80 vol.% CO2, the adsorption capacity increased by 38% for the “wet” gas from the dry gas. This is potentially due to carbonates formed due to CO2 dissolution/reaction in water. The adsorption time was not impacted by the range of water concentrations studied. The Avrami kinetic model best represented the rate of adsorption in both dry and wet conditions. The fact that neither the biochar adsorption capacity nor its adsorption rate was negatively impacted by water shows that biochar can be a promising option for stack gases, which contain water vapor. However, more experiments at higher temperatures are required.

A Two-Dimensional Transport Model of Bipolar Membrane Electrodialysis for the Electro-Regeneration of Carbon Capture Solvents

Bipolar membrane electrodialysis (BPMED) is a promising technology that uses an electric field to split water into H+ and OH- ions. A repeating stack of cation selective, anion selective, and bipolar membranes are placed between two electrodes, creating a repeating pattern of acid, base, and diluting flow chambers. A major application of BPMED is the electrochemical solvent regeneration of capture solutions used in CO2 point source (PS) or direct air capture (DAC). Protons generated using BPMED can be used to shift the acid-base equilibria back to CO2, providing a more sustainable alternative to traditional thermal regeneration methods when integrated with renewable electricity sources. This method combines electrosynthesis and separation, producing a pure stream of CO2 for sequestration and a concentrated base stream.Despite its potential, current limitations to BPMED implementation for this application stem from a large power consumption and high membrane costs. In addition, gas bubbles in solution can cause high electrical resistances, and experimental studies of this phenomenon are challenging due to the small scale on which it occurs. To address these challenges, we present a two-dimensional model of BPMED for CO2 capture solvent recovery. This model depicts a single repeating cell triplet and was constructed using COMSOL Multiphysics version 6.1. The Navier-Stokes equations were implemented to compute a convection field, and the ionic species concentration was found by solving the Nernst-Planck equation. A source term in the concentration partial differential equations was implemented to account for ionic speciation and water splitting reactions, captured through kinetic rate expressions.Experimental validation was conducted on a PC Cell BED 1-4 recirculating batch system with a stack of seven cell pairs of PC acid 60 (anion selective), PC SK (cation selective), and PC Bip (bipolar) membranes. Good agreement between the model and experimental results across a range of conditions and variables demonstrates accuracy and robustness. The calculated pH and concentration profiles revealed that the majority of the speciation reaction takes place inside, or directly adjacent to, the bipolar membrane, including bubble nucleation. Bubbles form inside membrane pores and displace the electrolyte, greatly increasing the electrical resistance of the membrane, particularly when membrane porosity is low. However, the reaction plane location where bubbles are generated can be manipulated by increasing the channel width or reducing the applied voltage.Future research will focus on expanding to multiphase CFD simulations to investigate the effect on flow. Our two-dimensional model provides valuable insights into the complex and multifaceted nature of BPMED, offering a powerful tool for investigating small-scale processes and advancing the use of BPMED for CO2 capture solvent recovery. Figure 1

Two years of satellite-based carbon dioxide emission quantification at the world's largest coal-fired power plants

Abstract. Carbon dioxide (CO2) emissions from combustion sources are uncertain in many places across the globe. Satellites have the ability to detect and quantify emissions from large CO2 point sources, including coal-fired power plants. In this study, we routinely made observations with the PRecursore IperSpettrale della Missione Applicativa (PRISMA) satellite imaging spectrometer and the Orbiting Carbon Observatory-3 (OCO-3) instrument aboard the International Space Station at over 30 coal-fired power plants between 2021 and 2022. CO2 plumes were detected in 50 % of the acquired PRISMA scenes, which is consistent with the combined influence of viewing parameters on detection (solar illumination and surface reflectance) and unknown factors (e.g., daily operational status). We compare satellite-derived emission rates to in situ stack emission observations and find average agreement to within 27 % for PRISMA and 30 % for OCO-3, although more observations are needed to robustly characterize the error. We highlight two examples of fusing PRISMA with OCO-2 and OCO-3 observations in South Africa and India. For India, we acquired PRISMA and OCO-3 observations on the same day and used the high-spatial-resolution capability of PRISMA (30 m spatial/pixel resolution) to partition relative contributions of two distinct emitting power plants to the net emission. Although an encouraging start, 2 years of observations from these satellites did not produce sufficient observations to estimate annual average emission rates within low (&lt;15 %) uncertainties. However, as the constellation of CO2-observing satellites is poised to significantly improve in the coming decade, this study offers an approach to leverage multiple observation platforms to better quantify and characterize uncertainty for large anthropogenic emission sources.

Performance of Na-Ru/Al2O3 dual function material for integrated CO2 capture and methanation with the presence of coal ashes

Integrated Capture and Methanation of CO2 (ICCM) with H2 produced from renewable energy is a novel Power-to-Gas technology. The combination of ICCM with CO2 point source, such as coal-fired power plant, is anticipated, which greatly motivates the investigations into the influences of coal ash on the key performance of dual function material (DFM) used in ICCM process. Via the experimental study on the coal ash impacts, this work explored the adaptability of DFM and ICCM to coal-fired power plant. Na-Ru/Al2O3 DFM and two ashes collected from the electrical precipitators of supercritical coal-fired power plants were used for experiments. It showed that fly ashes contaminated CO2 adsorbents and active sites of DFMs, and caused successive drops in carbonates conversion and CH4 selectivity upon cyclic ICCM reactions. The CO2-TPD and H2-TPSR tests revealed that the declined supplycapability of hydrogen atoms by Ru sites, and the increased rate gap between CO formation and the following CO hydrogenation were responsible for the declined methanation ability of ash-contaminated DFMs. The roles of SiO2 and Fe2O3 phases in ashes were identified, indicating that SiO2 reacted with adsorbent components and masked Ru sites, and then induced DFM deactivation by affecting the transport processes of key reactants; Fe2O3 successively invaded both Ru sites and Na2CO3/γ-Al2O3 interface, leading to successive losses in methanation ability and CO2 desorption capacity with cyclic ICCM reactions.

Evaluation of Simulated CO2 Point Source Plumes from High-Resolution Atmospheric Transport Model

Coal-fired power plants, as major anthropogenic CO2 emission sources, constitute one of the largest contributors to global greenhouse gas emissions. Accurately calculating the dispersion process of CO2 emissions from these point sources is crucial, as it will aid in quantifying CO2 emissions using remote sensing measurements. Employing the Lagrangian Particle Dispersion Theory Model (LPDTM), our study involves modeling CO2 diffusion from point sources. Firstly, we incorporated high-resolution DEM (Digital Elevation Model) and artificial building elements obtained through the Adaptive Deep Learning Location Matching Method, which is involved in CO2 simulation. The accuracy of the results was verified using meteorological stations and aircraft measurements. Additionally, we quantitatively analyzed the influence of terrain and artificial building characteristics on high spatial resolution atmospheric CO2 diffusion simulations, revealing the significance of surface characteristics in dispersion modeling. To validate the accuracy of the LPDTM in high-resolution CO2 diffusion simulation, a comparative experiment was conducted at a power plant in Yangzhou, Jiangsu Province, China. The simulated result was compared with observation from aerial flights, yielding the R2 (Correlation Coefficient) of 0.76, the RMSE (Root Mean Square Error) of 0.267 ppm, and the MAE (Mean Absolute Error) of 0.2315 ppm for the comparison of 73 pixels where the plume intersected with flight trajectories. The findings demonstrate a high level of consistency between the modeled CO2 point source plume morphology and concentration quantification and the actual observed outcomes. This study carried out a quantitative assessment of the influence of surface features on high-resolution atmospheric CO2 point source diffusion simulations, resulting in an enhanced accuracy of the simulated CO2 concentration field. It offers essential technological and theoretical foundations for the accurate quantification of anthropogenic CO2 emissions using top-down approaches.

Ink Formulation, Binder, Catalyst & Metal Loading - How Can the Properties of Gas Diffusion Electrodes be Influenced to Control CO2 Reduction?

Exceptionally hot summers, floods and other extreme weather events of recent years underline the importance of combating climate change. Electrochemical CO2 reduction (CO2RR), which can be applied directly at CO2 point sources such as cement plants is a promising way to convert the harmful greenhouse gas into valuable compounds (e.g., alcohols). The integration of a selective catalyst into a gas diffusion electrode (GDE) allows CO2 reduction at industrially relevant current densities above 200 mA cm-2.[1] Combinations of copper and zinc, or copper and silver, are especially suitable for CO2 reduction to multi-carbon products. Whilst copper is the only metal capable of catalyzing C-C bond formation, zinc and silver are known for their CO selectivity in CO2RR. The selectivity of the reaction is shifted towards the formation of multi-carbon products such as ethylene or alcohols by the enrichment of the important intermediate CO at the catalyst surface due to the activity of Zn or Ag.[2] Here we present the preparation of bimetallic catalysts by impregnating carbon black with copper and zinc, followed by the incorporation of the catalysts into GDEs and testing of their electrocatalytic activity in CO2RR. The ink formulation for preparing a catalyst layer by spray-coating was optimized using, among other compounds, the pore-forming agent methylcellulose, the non-ionic surfactant Triton, and PTFE as binding material, to provide a stable CO2RR with the highest possible yield of C2+ products. In addition, the impact of the post-treatment steps pressing and sintering on the CO2RR performance of the electrodes was assessed.[3] Using the optimized formulation and post-treatment to produce the GDE, the influence on the product distribution was evaluated by varying (1) the PTFE powder (2) the metal loading of the catalyst (Cu and Zn in relation to the carbon black content), (3) the catalyst loading of the GDE, and (4) the current densities during CO2RR.PTFE acts as both a binder and a hydrophobizing agent of the electrode to ensure stable electrolysis on the produced GDE in a flow cell. The variation of PTFE powders shows that mechanical and electrochemical stability of the electrodes as well as the product distribution during CO2RR depend on the PTFE powder used. Although hydrophobicity and surface morphology are similar prior to CO2RR, shifts within the product distributions and differences in stability are evident during electrolysis depending on the PTFE powder chosen. Catalyst loading affects the supply and removal of reactants and products and therefore significantly influences the product distribution, which also showed a strong dependence on metal loading. In general, a trend toward increased formic acid formation was observed with increasing metal loading and film thickness. An optimum for C2+ product formation was found at 17.5% metal loading with Faraday efficiencies of 17% for ethanol and 31% for ethylene at current densities of 200 mA cm-2. SEM-EDX images show increased carbonate formation within the electrode with increasing metal loading as well as with increasing current densities. The increase in metal loading was found to be accompanied by metal agglomeration in the catalyst and is further enhanced by the GDE fabrication process.The work provides insight into the interaction of catalyst, electrode composition, and CO2RR parameters and reveals key tuning screws for a selective and stable reaction in liquid electrolysis cells. [1] Gawel, A.; Jaster, T.; Siegmund, D.; Holzmann, J.; Lohmann, H.; Klemm, E.; Apfel, U.-P. Electrochemical CO2 reduction - The macroscopic world of electrode design, reactor concepts & economic aspects. iScience 2022, 25, 104011. [2] Jaster, T.; Gawel, A.; Siegmund, D.; Holzmann, J.; Lohmann, H.; Klemm, E.; Apfel, U.-P. Electrochemical CO2 reduction toward multicarbon alcohols - The microscopic world of catalysts & process conditions. iScience 2022, 25, 104010. [3] Jaster, T.; Albers, S.; Leonhard, A.; Kräenbring, M.-A.; Lohmann, H.; Zeidler-Fandrich, B.; Özcan, F.; Segets, D.; Apfel, U.-P. Enhancement of CO2RR product formation on Cu-ZnO-based electrodes by varying ink formulation and post treatment methods. J. Phys. Energy. 2023, 5.

Optimisation of carbon dioxide pressurisation pathways for pipeline offshore delivery

To maximise economies of scale of future CO2 transport infrastructure, new CO2 pipelines within the carbon capture utilisation and storage (CCUS) value chain, should ideally have excess capacity to satisfy future transportation demand. However, in scenarios where booster compressors cannot be employed along the pipeline, the rise in pipeline mass flow rate over time culminates in higher energy consumption of upstream compression/liquefaction. This work explores the optimisation of various CO2 pressurisation pathways and assesses their flexibility in handling a variability in pipeline mass flow rates whilst delivering a captured CO2 stream at a fixed final pressure of 100 barg. The study is based on the Dunkirk 3D Project, which has a planned nameplate capture capacity of 1 MtCO2/y, with other CO2 point sources taking up additional pipeline utilisation capacity. Two categories of CO2 pressurisation pathways are considered, gas compression and subcritical liquefaction and pumping. These pathways are optimised to enable a fair comparison, considering the number of compression stages, compression ratio, and cooling/liquefaction system. Modelling results indicate that the temperature of the cooling utility has the greatest influence in reducing the overall work duty and sensitivity to a variability in pipeline mass flow rate. Furthermore, the utilisation of 5 °C seawater as a cooling and liquefaction utility reduces the work duty of the conditioning process by 25.4% and requires fewer compression stages relative to conventional gas compression utilising cooling water at 30 °C.

Point-source CO₂ capture gets $2.5 billion in US funds

Point-source CO₂ capture gets $2.5 billion in US funds

Development of CCUS clusters in Croatia

Carbon Capture and Storage is a concept that is not yet fully implemented largely because of the high costs. Clustering of industrial stakeholders is imposed as a measure for cost reduction. All relevant emitters, possible transport routes, including existing gas pipeline corridors, and their geographic location in relation to potential storage locations are assessed in this paper. Site availability and CO2 storage capacity are examined, summarizing all study results gathered under the Strategy CCUS project. The CO2 enhanced oil recovery is being studied for CO2 storage rather than extra oil recovery. As logical choices, three clusters were recognized. Only less expensive, onshore injection was taken in consideration for assessment of early (economic) feasibility in the Adriatic, Central, and Eastern clusters. Because of the shorter distance between CO2 emitters and injection sites, the Eastern and Central clusters are being investigated in more detail, despite the fact that the largest point source emitter is in the Adriatic region. Because of small number of point source CO2 emitters and huge theoretical storage capacity, further research is needed to better assess the storage capacities as well as possibilities for development of cross-border projects. Based on previous research (particularly regarding the emitters), the number of facilities (fewer facilities, with more concentrated emissions), and the availability of storage objects, the Eastern cluster is recommended to be further studied as the next stage of Carbon Capture, Utilization and Storage cluster research and development in Croatia and nearby cross-border regions.

Potential of renewable surplus electricity for power-to-gas and geo-methanation in Switzerland

Energy systems are increasingly exposed to variable surplus electricity from renewable sources, particularly photovoltaics. This study estimates the potential to use surplus electricity for power-to-gas with geo-methanation for Switzerland by integrated energy system and power-to-gas modelling. Various CO2 point sources are assessed concerning exploitable emissions for power-to-gas, which were found to be abundantly available such that 60 TWh surplus electricity could be converted to methane, which is the equivalent of the current annual Swiss natural gas demand. However, the maximum available surplus electricity is only 19 TWh even in a scenario with high photovoltaic expansion. Moreover, making this surplus electricity available for power-to-gas requires an ideal load shifting capacity of up to 10 times the currently installed pumped-hydro capacity. Considering also geological and economic boundary conditions for geo-methanation at run-of-river and municipal waste incinerator sites with nearby CO2 sources reduces the exploitable surplus electricity from 19 to 2 TWh.