CO2 In Geological Formations Research Articles

Toxicity and environmental aspects of surfactants

Abstract As the single largest class of specialty chemicals, surfactants are consumed in huge quantities in our daily life and in many industrial areas. In the past, the attention was focused entirely on technical performance. However, starting from the 1970s and 80s, surfactant related environmental concerns have become the main driving force to upgrade surfactant production technology to make more benign or “greener” products. For this reason, environmental issues, dermatological effects, and oral toxicity are the main priorities when surfactants are considered for a specific purpose. In this paper, we present five cases to demonstrate how the surfactant industry tackles these challenges to mitigate the environmental and health effects associated with surfactant consumption. We also discuss the important role played by surfactants in a current carbon capture and storage (CCS) strategy to reduce the CO2 level in the atmosphere. Surfactant-based stable CO2 foam flooding is a well-established enhanced oil recovery technique. It has been considered to be an economically realistic procedure to sequester large amounts of CO2 in geological formations.

Geochemistry in Geological CO2 Sequestration: A Comprehensive Review

The increasing level of anthropogenic CO2 in the atmosphere has made it imperative to investigate an efficient method for carbon sequestration. Geological carbon sequestration presents a viable path to mitigate greenhouse gas emissions by sequestering the captured CO2 deep underground in rock formations to store it permanently. Geochemistry, as the cornerstone of geological CO2 sequestration (GCS), plays an indispensable role. Therefore, it is not just timely but also urgent to undertake a comprehensive review of studies conducted in this area, articulate gaps and findings, and give directions for future research areas. This paper reviews geochemistry in terms of the sequestration of CO2 in geological formations, addressing mechanisms of trapping, challenges, and ways of mitigating challenges in trapping mechanisms; mineralization and methods of accelerating mineralization; and the interaction between rock, brine, and CO2 for the long-term containment and storage of CO2. Mixing CO2 with brine before or during injection, using microbes, selecting sedimentary reservoirs with reactive minerals, co-injection of carbonate anhydrase, and enhancing the surface area of reactive minerals are some of the mechanisms used to enhance mineral trapping in GCS applications. This review also addresses the potential challenges and opportunities associated with geological CO2 storage. Challenges include caprock integrity, understanding the lasting effects of storing CO2 on geological formations, developing reliable models for monitoring CO2–brine–rock interactions, CO2 impurities, and addressing public concerns about safety and environmental impacts. Conversely, opportunities in the sequestration of CO2 lie in the vast potential for storing CO2 in geological formations like depleted oil and gas reservoirs, saline aquifers, coal seams, and enhanced oil recovery (EOR) sites. Opportunities include improved geochemical trapping of CO2, optimized storage capacity, improved sealing integrity, managed wellbore leakage risk, and use of sealant materials to reduce leakage risk. Furthermore, the potential impact of advancements in geochemical research, understanding geochemical reactions, addressing the challenges, and leveraging the opportunities in GCS are crucial for achieving sustainable carbon mitigation and combating global warming effectively.

CO2-brine mass transfer patterns and interface dynamics under geological storage conditions

CO2 geological storage is a promising carbon negative technology with important application prospects. Dissolution trapping is a reliable method throughout the life cycle of a storage project, because it plays a significant role in minimizing risks. A comprehensive understanding of its mechanism is challenging due to the complex mass transfer process controlled by numerous physical and chemical factors, which needs to be clarified at different scales but still significantly limited in current research. Investigating CO2-brine interfacial mass transfer in real rock cores during imbibition provides valuable insights into the behavior of CO2 in geological formations. This study conducted a series of pore-scale CO2-brine interfacial mass transfer experiments during imbibition in three rock cores using an X-ray micro-computed tomography machine. The dissolution patterns and interface dynamics during the dissolving processes were discussed systematically. The results indicate that the overall slice-averaged and per-cluster mass transfer coefficient between CO2 and brine is in the order of 10−8 m/s, but its specific value depends on the dissolution patterns and bubble sizes. Various dissolution patterns were found in different rock cores. A core-length dissolution finger was formed in the Berea core, causing higher per-cluster mass transfer coefficients around the finger, while lower coefficients elsewhere in the dissolution experiments. The interfacial mass transfer process, coupled with gravity instability, induced remobilization of isolated CO2 bubbles at a much lower capillary number than the critical capillary number. The remobilization of CO2 bubbles can even occur at single-pore scale. CO2 remobilization also created a phenomenon similar to intermittent pathway flow. Interface dynamics of CO2 dissolving processes were revealed for the first time, giving rise to non-uniform dissolutions in CO2 singlets, ganglia, and clusters, respectively.

Climate performance of liquefied biomethane with carbon dioxide utilization or storage

In the process of upgrading biogas to biomethane for gas grid injection or use as a vehicle fuel, biogenic carbon dioxide (CO₂) is separated and normally emitted to the atmosphere. Meanwhile, there are a number of ways of utilizing CO₂ to reduce the dependency on fossil carbon sources. This article assesses the climate performance of liquefied biomethane for road transport with different options for utilization or storage of CO₂. The analysis is done from a life cycle perspective, covering the required and avoided processes from biogas production to the end use of biomethane and CO₂. The results show that all of the studied options for CO₂ utilization can improve the climate performance of biomethane, in some cases contributing to negative CO₂ emissions. One of the best options, from a climate impact perspective, is to use the CO₂ internally to produce more methane, although continuous supply of hydrogen from renewable sources can be a challenge. Another option that stands out is concrete curing, where CO₂ can both replace conventional steam curing and be stored for a long time in mineral form. Storing CO₂ in geological formations can also lead to negative CO₂ emissions. However, with such long-term storage solutions, opportunities to recycle biogenic CO₂ are lost, together with the possibility of de-fossilizing processes that require carbon, such as chemical production and horticulture.

Effect of temperature on convective-reactive transport of CO2 in geological formations

Geological CO2 sequestration (GCS) remains the main promising solution to mitigate global warming. Understating the fate of CO2 behavior is crucial for securing its containment in the reservoir and predicting the impact of dissolved CO2 on the host formation. Most modeling-based studies in the literature investigated the convective-reactive transport of CO2 by assuming isothermal conditions. The effect of temperature on the convective-reactive transport of CO2 is still poorly understood, particularly at the field scale. The objective of this study is to provide an in-depth understanding of CO2-related reactive thermohaline convection (RTHC) processes at field scale. Thus, a new numerical model based on advanced finite element formulations is developed. The new model incorporates an accurate time integration scheme with error control. Numerical experiments confirm high accuracy and efficiency of the newly developed model. The effect of temperature on CO2 transport is investigated for a field case in the Viking reservoir in the North Sea. Results show that including the temperature effect intensifies the fingering processes and, consequently, CO2 dissolution. Neglecting the thermal convection processes and the impact of temperature on the dissolution rate can significantly impact the model predictions. A sensitivity analysis is developed to understand the effect of parameters governing the dissolution rate on the fingering phenomenon and the total CO2 flux.

Carbon capture and storage – a safe and reliable monitoring and verification plan developed using oil and gas industry core skill sets

Carbon capture and storage (CCS) is a necessary technology essential for meeting global emissions targets and limiting the impact of climate change – all identified pathways to global net-zero 2050 emissions targets require significant scale-up and deployment of CCS. The Moomba CCS project is an example of the type of projects that will reduce emissions and enable decarbonisation technology such as Direct Air Capture (DAC). The first phase of the project will utilise depleted hydrocarbon fields in the Cooper Basin, South Australia, to safely capture and permanently store 1.7 Mtpa CO2 that is currently vented. This paper will highlight the oil and gas industry’s unique skill sets that make it ideally placed to measure, monitor and verify the permanent storage of CO2 in geological formations. A monitoring and verification plan (M&V plan) has been developed based on SEO and ISO standards that encompasses four key elements: injection telemetry, reservoir surveillance, well integrity and environmental assurance. The plan was developed using a methodical approach to identify key risks, evaluate consequences, take preventative actions and put mitigating controls in place. Core oil and gas industry skill sets were utilised for the evaluation such as geomechanical and geochemical analysis, seal analysis, fault interpretation and reservoir modelling of CO2 migration. A program of surveillance activities will be undertaken to monitor and verify CO2 containment within the storage complex on an ongoing basis for the life of the project, and the M&V plan sets out a response plan and actions that will be taken in the case of deviation from expected performance.

Continuous conditional generative adversarial networks for data-driven modelling of geologic CO[formula omitted] storage and plume evolution

Storing CO2 in geological formations requires accurate monitoring of the plume evolution for safe long-term operations, and traditionally, carbon storage practices rely on the numerical simulation of the multiphase flow and plume movement. Such simulations may be impractical for rapid, real-time monitoring, in which the risks involved are dynamically anticipated and/or mitigated, as they require the numerical solution of large non-linear systems of equations that also change over time. In this work, we investigate the application of continuous conditional generative adversarial networks (CCGAN) for predicting the CO2 plume evolution in cases in which limited data is available. We adapt the CCGAN for mapping the sparsely available input data from three wells to the spatially distributed CO2 saturation over the whole domain. Our main focus in this work is the accuracy and performance of the CCGAN when only sparse data is available. As such, we limit our investigation to the 2-D conceptual model of an aquifer and employ a simple immiscible and isothermal two-phase flow model. Our results show that the CCGAN can predict the CO2 plume from sparse data with at least 90% of accuracy while allowing a substantial reduction in the computational cost when compared to traditional methods based on numerical simulations, with a speed-up of no less than 700-folds. Future works may include the extension to 3-D reservoir models with irregular geometry.

Influence of impurities on reactive transport of CO2 during geo-sequestration in saline aquifers

Carbon capture and storage (CCS) is a promising technology to reduce greenhouse gas emissions by storing CO2 in geological formations. Storing less pure CO2, which has low percentages of impurities, can reduce the cost of the process. However, impurities can affect the dynamics of CO2 propagation and its trapping mechanisms in porous media, potentially impacting the overall effectiveness of the storage process. Therefore, this study investigates the effect of impurities on the reactive transport of CO2 during geo-sequestration in a saline aquifer using a reliable reactive transport model. The effect of co-injected H2S and CH4 in the CO2 stream on CO2 plume migration, CO2 trapping mechanisms, minerals dissolution and precipitation, and cap rock integrity, was studied here. To do so, reactive transport modeling was performed using a compositional simulator based on actual data from Sleipner storage site. The model was run for pure CO2 and mixtures (CO2 with 5 wt% H2S and CO2 with 5 wt% CH4). The results showed that the impurities co-injected with CO2 affect the CO2 plume migration in the aquifer. For instance, injecting the CO2-CH4 mixture increased the CO2 horizontal migration below the cap rock compared to the pure CO2 injection case. However, the buoyancy effect of the injected gas was slightly reduced by adding H2S to the CO2 stream. The impurities influenced the pH of the system, and hence minerals dissolution and precipitation, and cap rock porosity changes. The impurities (CH4 and H2S) injected with CO2 were found to suppress an anticipated increase in the cap rock porosity and accelerated the mineral trapping of CO2 compared to pure CO2 storage. While, among the studied cases, the CO2-CH4 mixture case had the highest structural trapping and the lowest solubility trapping of CO2. Thus, this study suggests that storage of impure CO2 can enhance mineral trapping, maintain cap rock sealing, and change CO2 distribution in porous media while reducing separation costs.

Investigation of solubility trapping mechanism during geologic CO2 sequestration in Deccan Volcanic Provinces, Saurashtra, Gujarat, India

Solubility of CO2 in connate water plays a crucial role in facilitating the safe disposal of CO2 in geological formations, and this phenomenon in CO2 geological sequestration is termed solubility trapping. A multiphase-reactive transport code that solely considers CO2 dissolution and its accompanying pH fluctuation are used to investigate the influence of the geological and sequestration parameters on a solubility trapping mechanism. A 3-dimensional synthetic geological domain is modelled based on the geological data of Deccan volcanic provinces in Saurashtra, Gujarat, India. The stairsteps kind of morphology of geological formation obtained from literature was considered. Simulation results have shown that parameters such as caprock morphology, petrophysical properties, and injection location significantly affect solubility trapping. Solubility trapping can be observed by examining the pH variation, pressure distribution, and CO2 migration patterns. Analysis of such domains can give foresight about the possible implementation of CO2 sequestration and its influence on the solubility trapping mechanism.

Real-Time Monitoring of Gas-Phase and Dissolved CO2 Using a Mixed-Matrix Composite Integrated Fiber Optic Sensor for Carbon Storage Application.

Novel chemical sensors that improve detection and quantification of CO2 are critical to ensuring safe and cost-effective monitoring of carbon storage sites. Fiber optic (FO)-based chemical sensor systems are promising field-deployable systems for real-time monitoring of CO2 in geological formations for long-range distributed sensing. In this work, a mixed-matrix composite integrated FO sensor system was developed with a purely optical readout that reliably operates as a detector for gas-phase and dissolved CO2. A mixed-matrix composite sensor coating consisting of plasmonic nanocrystals and hydrophobic zeolite embedded in a polymer matrix was integrated on the FO sensor. The mixed-matrix composite FO sensor showed excellent reversibility/stability in a high humidity environment and sensitivity to gas-phase CO2 over a large concentration range. This remarkable sensing performance was enabled by using plasmonic nanocrystals to significantly enhance the sensitivity and a hydrophobic zeolite to effectively mitigate interference from water vapor. The sensor exhibited the ability to sense CO2 in the presence of other geologically relevant gases, which is of importance for applications in geological formations. A prototype FO sensor configuration, which possesses a robust sensing capability for monitoring dissolved CO2 in natural water, was demonstrated. Reproducibility was confirmed over many cycles, both in a laboratory setting and in the field. More importantly, we demonstrated on-line monitoring capabilities with a wireless telemetry system, which transferred the data from the field to a website. The combination of outstanding CO2 sensing properties and facile coating processability makes this mixed-matrix composite FO sensor a good candidate for practical carbon storage applications.

Experimental investigation for the impact of chlorite dissolution on CO2 mineral trapping in a sandstone‐brine‐CO2 system

AbstractThe mineral trapping of CO2 in geological formation is the most promising and safe mechanism for permanent carbon storage. The chlorite shows a great influence on the form and capacity of carbon storage in sandstone reservoirs due to its wide distribution and strong chemical activity. In this paper, to better understand the dissolution process of chlorite after the injection of CO2 and its potential impacts on carbon mineral trapping patterns, two sets of hydrothermal batch reactions toward chlorite and CO2 fluid are conducted at elevated temperature‐pressure conditions (120 °C/180 °C, 18 MPa), considering the effects of extra calcite addition and the initial concentration of Ca2+ in solution. During reactions, the changes in water chemistry and mineral surface morphology are monitored through effluent sampling and scanning electron microscope (SEM) observation, respectively and they are further analyzed in PHREEQC by the method of mineral saturation index. It is found that the simultaneous dissolution of chlorite and calcite in CO2 saturated solutions will lead to a competition for H+, and the formation of massive surface complex CaHCO3– by Ca2+ in the initial solutions will lead to the consumption of H+. These inhibit the proton‐promoted dissolution of chlorite. But when the concentration of Ca2+ is increased to meet the requirements for ankerite precipitation, the demand of ankerite precipitation for elements Fe and Mg will conversely promote the chlorite dissolution. Besides, the concentration of Ca2+ required for the precipitation of ankerite is relatively low, which implies that the injected CO2 can be mineralized and trapped by the chlorite dissolution process easily. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Carbon Capture and Storage Potential in Ireland — Returning Carbon Whence It Came

Summary Carbon capture and storage (CCS) involves the capture of CO2 emissions produced from industrial and electricity generation sources, followed by transport to permanent underground geological storage. Hence, CCS is one mitigation option available to achieve the targets set out in the Paris Agreement. Here we discuss CCS potential with particular reference to Ireland’s emission targets, policy positions and geological storage options. In Ireland, CCS could be utilised (1) with gas-powered electricity to provide secure and reliable low-emissions electricity, (2) to reduce emissions in hard-to-abate industries such as cement manufacturing, and (3) to facilitate the future deployment of negative emissions technologies. Ireland has significant potential to store CO2 in geological formations in depleted gas fields and deep saline aquifers in its offshore sedimentary basins. Two high-graded options are the offshore Kinsale Head and Corrib gas fields. Provisional estimates for the CO2 storage capacity of these two fields are 321 Mt and 44 Mt respectively. The depleted Kinsale Head gas field alone could have sufficient storage capacity to take the equivalent of up to 40 years of CO2 emissions from the top 10 point-source emitters in Ireland. Further work is needed to fully characterise and mature the potential for CCS in Ireland.

Periodic CO2 Injection for Improved Storage Capacity and Pressure Management under Intermittent CO2 Supply

Storing CO2 in geological formations is an important component of reducing greenhouse gases emissions. The Carbon Capture and Storage (CCS) industry is now in its establishing phase, and if successful, massive storage volumes would be needed. It will hence be important to utilize each storage site to its maximum, without challenging the formation integrity. For different reasons, supply of CO2 to the injection sites may be periodical or unstable, often considered as a risk element reducing the overall efficiency and economics of CCS projects. In this paper we present outcomes of investigations focusing on a variety of positive aspects of periodic CO2 injection, including pressure management and storage capacity, also highlighting reservoir monitoring opportunities. A feasibility study of periodic injection into an infinite saline aquifer using a mechanistic reservoir model has indicated significant improvement in storage capacity compared to continuous injection. The reservoir pressure and CO2 plume behavior were further studied revealing a ‘CO2 expansion squeeze’ effect that governs the improved storage capacity observed in the feasibility study. Finally, the improved pressure measurement and storage capacity by periodic injection was confirmed by field-scale simulations based on a real geological set-up. The field-scale simulations have confirmed that ‘CO2 expansion squeeze’ governs the positive effect, which is also influenced by well location in the geological structure and aquifer size, while CO2 dissolution in water showed minor influence. Additional reservoir effects and risks not covered in this paper are then highlighted as a scope for further studies. The value of the periodic injection with intermittent CO2 supply is finally discussed in the context of deployment and integration of this technology in the establishing CCS industry.

The development of UK CCUS strategy and current plans for large-scale deployment of this technology

For over 20 years, carbon capture utilisation and storage (CCUS) has been recognised as a useful tool to help reduce UK national emissions. Over this period the target reduction in greenhouse gas emission rates for 2050 has increased, from 60% to 100%, i.e. net zero. This has led to change in the role envisaged for CCUS, from initially just cutting emissions on coal power plants by around 50%, to the point where capture and secure sequestration of all fossil CO2 emissions is required, either directly at source or indirectly via carbon dioxide removal from the air (CDR). Additional CDR, either through the use of biomass energy with carbon capture and storage (BECCS) or direct air carbon capture and storage (DACCS), will also be required to compensate for other UK greenhouse gas emissions. Potentially over 100 MtCO2/yr of CCUS is needed by 2050. Current UK plans are to establish four CCUS clusters by 2030, capturing and storing a minimum of 10 MtCO2/yr from industry, power, hydrogen production and, potentially, CDR. The UK has a large amount of secure storage capacity for CO2 in geological formations a kilometre or more below the sea bed in the North Sea and the Irish Sea.

The need for a portfolio of solutions rooted in common messaging to facilitate negative emissions science

The need for a portfolio of solutions rooted in common messaging to facilitate negative emissions science

Overview of the Adsorption and Transport Properties of Water, Ions, Carbon Dioxide, and Methane in Swelling Clays

It is quite challenging to understand the details of the complex mechanisms involved in the swelling processes of clays such as montmorillonite as a function of relative humidity (RH), and the adsorption and transport processes of CO2 and CH4 in swelling clays. Here we present a review of the molecular simulation results for the swelling clay systems which not only compare well with the experimental data but also provide deep insights into the details of these mechanisms. The presence of CO2 and CH4 hardly affects the distribution and mobility of the interlayer water and ions in these systems. Under all conditions, the stable basal d-spacing was mainly determined by the type of counterion present in the interlayer region and the amount of water in each hydration state was almost independent of the RH and the layer charge. The uptake of CH4 in the 1W state of the Na-clay was much smaller compared to that of CO2. The adsorbate mobility generally increased with increasing hydration/RH because of the associated swelling of the interlayer region. Interestingly, the uptake of CO2 in the high-charge clay was dramatically decreased, and the mobility of CO2 in each hydration state was almost independent of the type of cation. The preferential adsorption of CO2 over CH4 plays an important role in the diffusion processes. Such an understanding is important for the successful mitigation of climate change via storage of anthropogenic CO2 in geological formations.

Understanding initial opportunities and key challenges for CCUS deployment in India at scale

India's CO2 emissions have risen at a compounded annual growth rate of 3.1% over the last three decades, primarily from an increase in consumption of fossil fuels . Carbon capture, utilization, and storage (CCUS) is considered one of the most effective strategies to counter these trends by reducing the carbon footprint of existing and upcoming infrastructure. Utilization of captured CO2 (CCU) to produce valuable green chemicals is an economically viable proposition. On the other hand, storage of CO2 (CCS) reduces the carbon footprint by sequestering the captured CO2 in geological formations, which in some cases, facilitates hydrocarbon recovery. This paper showcases how a multifaceted approach of combining CCU and CCS in an economically viable manner is a key factor in the maintaining of sustainable development. We discuss at a systems level, the benefits of the implementation of CCUS for India's energy security, positive path dependency, and resiliency. This is followed by a bottom-up review of the symbiotic relationship between the capture and utilization/storage. We provide an assessment of sustainable CCUS implementation by pairing state-of-the-art technologies in the field of carbon storage/utilization with possible future directions in India. We also suggest pathways for the potential and the impact of India's carbon-intensive sources in different CCUS chains such as markets for large-scale utilization of CO2 in emerging methanol economy. Finally, we provide research and policy recommendations that would facilitate a sustainable collaborative effort across sectors in mitigating the increasing carbon dioxide in the atmosphere.

The Role of Surface Hydrophobicity on the Structure and Dynamics of CO2 and CH4 Confined in Silica Nanopores

Advancing a portfolio of technologies that range from the storage of excess renewable natural gas for distributed use to the capture and storage of CO2 in geological formation are essential for meeting our energy needs while responding to challenges associated with climate change. Delineating the surface interactions and the organization of these gases in nanoporous environments is one of the less explored approaches to ground advances in novel materials for gas storage or predict the fate of stored gases in subsurface environments. To this end, the molecular scale interactions underlying the organization and transport behavior of CO2 and CH4 molecules in silica nanopores need to be investigated. To probe the influence of hydrophobic surfaces, a series of classical molecular dynamics (MD) simulations are performed to investigate the structure and dynamics of CO2 and CH4 confined in OH-terminated and CH3-terminated silica pores with diameters of 2, 4, 6, 8, and 10 nm at 298 K and 10 MPa. Higher adsorption extents of CO2 compared to CH4 are noted on OH-terminated and CH3-terminated pores. The adsorbed extents increase with the pore diameter. Further, the interfacial CO2 and CH4 molecules reside closer to the surface of OH-terminated pores compared to CH3-terminated pores. The lower adsorption extents of CH4 on OH-terminated and CH3-terminated pores result in higher diffusion coefficients compared to CO2 molecules. The diffusivities of both gases in OH-terminated and CH3-terminated pores increase systematically with the pore diameter. The higher adsorption extents of CO2 on OH-terminated and CH3-terminated pores are driven by higher van der Waals and electrostatic interactions with the pore surfaces, while CH4 adsorption is mainly due to van der Waals interactions with the pore walls. These findings provide the interfacial chemical basis underlying the organization and transport behavior of pressurized CO2 and CH4 gases in confinement.

Convective-reactive transport of dissolved CO2 in fractured-geological formations

Carbon dioxide (CO2) storage in geologic formations is an attractive means of reducing greenhouse gas emissions. The main processes controlling the migration of CO2 in geological formations are related to convective mixing and geochemical reactions. The effects of heterogeneity on these coupled processes have been widely discussed in the literature. Recently, special attention has been devoted to fractured geological formations that can be found in several storage reservoirs. However, existing studies on the effect of fractures on the fate of CO2 neglect the key processes of geochemical reactions. This work aims at addressing this gap. Based on numerical simulations of a hypothetical reservoir, we explore the effect of fracture properties and topology on the domain's storage capacity at different rates of CO2 mineral dissolution. It is found that the fractures not only can help the mixing convection and reaction process in the domain but also may play a restrictive role in entering dissolved CO2 and hinder the plume fingers from growing. The hypothetical case is relevant in providing preliminary understanding but can show varying degrees of geological realism. For more representative geology, we investigate the migration-dissolution of buoyant CO2 on a large-scale outcrop of a volcanic basalt rock formation. The results show that neglecting thin fractures can significantly affect the predicted amount of trapped CO2. The storage capacity is more sensitive to heterogeneity at low dissolution rates. The findings are useful for the management of CO2 sequestration in fractured domains.

Geological storage of CO2–N2–O2 mixtures produced by membrane‐based direct air capture (DAC)

AbstractCarbon capture and storage has been considered as a realistic approach to reducing atmospheric CO2 concentrations. However, the cost of capturing high‐purity CO2 typically used for geological storage (e.g., 98%) is high. Direct air capture (DAC), a technology that extracts CO2 of relatively low‐purity from the ambient atmosphere, has been recently proposed as a means to achieve negative CO2 emissions when the product is sequestered underground. Although the CO2 produced by DAC is of low‐purity, the other gaseous components (mainly nitrogen and oxygen) are not hazardous materials like NOx and SOx that must be typically dealt with by conventional projects in coal‐burning plants. Here, we evaluate geological storage of the low‐purity CO2 captured via advanced membrane‐based DAC technology. The ubiquity of ambient air is important in reducing transport costs and ensuring social acceptance as the CO2 product can be both produced and stored at sites in remote areas, such as deserts and offshore platforms. We calculated the density of CO2–N2–O2 mixtures via molecular dynamics simulation and evaluated the cost of the low‐purity CO2 storage. Our evaluation suggests that the storage of low‐purity CO2 in geological formations is environmentally acceptable and economically viable. © 2021 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.