Membrane Separation Technology in Direct Air Capture.

Direct air capture (DAC) technologies are promising but speculative. Their prospect as an affordable negative emissions option that can be deployed in large scale is particularly uncertain. Here, we report the results of an expert elicitation about the evolution of techno-economic factors characterizing DAC over time and across climate scenarios. This is the first study reporting technical experts' judgments on future costs under different scenarios, for two time periods, for two policy options, and for two different DAC technologies. Experts project CO2removal costs to decline significantly over time but to remain expensive (median by mid-century: around 200 USD/tCO2). Nonetheless, the role of direct air capture in a 2°C policy scenario is expected to be significant (by 2050: 1.7 [0.2, 5.9] GtCO2)1. Projections align with scenarios from integrated assessment model (IAM) studies. Agreement across experts regarding which type of DAC technology might prevail is low. Energy usage and policy support are considered the most critical factors driving these technologies' future growth.

To effectively mitigate the global warming problem caused by excessive CO2 emissions, the implementation of direct air capture (DAC) technology has emerged as one of the most promising strategies for capturing CO2 from the atmosphere. The key to DAC technology hinges on the development of high-performance solid sorbent materials that demonstrate high CO2 adsorption capacity and gas separation selectivity, particularly under low CO2 partial pressure conditions. Herein, we have successfully developed a class of MOF@carboxylated wood sponge (MOF@CWS) hybrid sorbents, capable of efficient CO2 capture from low-concentration (less than 10,000 ppm) CO2 sources, achieved by embedding the porous MOF into carboxylated wood sponges (CWS) substrate via an in situ growth route. Within the MOF@CWS series, the CO2 uptake capacity of Mg-MOF-74@CWS is 3.61 and 2.65 mmol/g at 1 bar, 273 and 298 K, respectively, significantly higher than those of CWS and HKUST-1@CWS. Moreover, this material exhibited outstanding DAC performance, with the CO2 sorption capacity at 273 K up to 0.56 mmol/g from ambient air (ca. 400 ppm of CO2), surpassing most other solid sorbents. The obtained Mg-MOF-74@CWS also demonstrated exceptional CO2/CH4 separation performance, primarily due to the unique pore structure and augmented interaction between the CO2 molecules and the hybrid sorbents. The results of this study indicate that Mg-MOF-74@CWS has potential as an efficient solid sorbent for the DAC of CO2.

Direct CO2 capture from the air, so-called direct air capture (DAC), has become inevitable to reduce the concentration of CO2 in the atmosphere. Current DAC technologies consider only sorbent-based systems. Recently, there have been reports that show ultrahigh CO2 permeances in gas separation membranes and thus membrane separation could be a potential new technology for DAC in addition to sorbent-based CO2 capture. The simulation of chemical processes has been well established and is commonly used for the development and performance assessment of industrial chemical processes. These simulations offer a credible assessment of the feasibility of membrane-based DAC (m-DAC). In this paper, we discuss the potential of m-DAC considering the state-of-the-art performance of organic polymer membranes. The multistage membrane separation process was employed in process simulation to estimate the energy requirements for m-DAC. Based on the analysis, we propose the target membrane separation performance required for m-DAC with competitive energy expenses. Finally, we discuss the direction of future membrane development for DAC.

The National Energy Technology Laboratory (NETL) and University of Kentucky (Participant) will collaborate in the development of “Deep Learning Potential-based Molecular Dynamics Simulation Investigation of Chemical Conversion-Absorption Coupling of CO2 at Air-Reactive Deep Eutectic Solvent Interface.” This project is supported by DOE-Office of Science Graduate Student Research (SCGSR) program and managed by Oak Ridge Institute for Science and Education (ORISE). Deep eutectic solvents (DESs) are promising alternative sorbents for direct air capture (DAC) CO2 due to their low vapor pressure, low corrosion, non-toxicity, relatively low cost, and biodegradable nature. Understanding the CO2 reaction-transport mechanisms at the interface can help develop cost-effective DAC by DESs with high capacity and stability. The collaboration will investigate the absorption and chemical conversion of CO2 at the air-DES interface to facilitate the development of novel DAC technology using reactive DESs. The anticipated results will make DAC more efficient, allow more sustainable use of our Nation’s fossil energy resources, and advance NETL’s ongoing CO2 capture efforts.

Current direct air capture (DAC) technology is largely cost-prohibitive for large scale implementation due to the excessive energy required to operate a combined absorption–desorption cycle. As the desorption process consumes much of the supplied energy, there is a demand to find more sustainable sorbent materials that maintain high absorptive capacities yet can be regenerated at lower working temperatures. This work evaluates potassium glycinate (GlyK) as one such alternative absorbent. Through conducting vapor–liquid equilibria and wetted wall column kinetic studies, GlyK is found to have comparable working capacities and liquid mass transfer coefficients to those reported for the industrial standard, monoethanolamine (MEA), yet outperforms it with regards to its distinctly low regeneration temperature. To further understand how GlyK would perform in an industrial scale DAC system, an Aspen Custom Modeler® (ACM) model is developed that integrates the experimentally obtained equilibria and kinetic data with the performance characteristics of a gas-solvent hollow fiber membrane contactor (HFMC). Full-scale simulations show that via implementing a 20°–90 °C absorption–desorption cycle, GlyK can capture up to 83 % of the CO2 in atmospheric air and be 55 % regenerated within a single membrane contactor pass. As these low working temperatures vastly outperform the conventional ∼ 40°–140 °C temperature swing currently implemented in industrial CO2 processing, GlyK is concluded to be a viable and sustainable option for use within energy-efficient DAC technology whereby renewable heat sources can be used.

Proposed is an electrochemical nickel hydroxide based hydroxide exchange membrane carbon capture (HEMCC) device for Direct Air Capture (DAC) of CO2. DAC has been identified as one of the key net negative carbon technologies to achieve net zero carbon emissions. Net negative carbon technologies are required to offset continued emissions from dilute CO2 sources such as agriculture and construction. The majority of current DAC technologies at scale (>1 KT∙yr-1) are adsorbent based technologies with significant energy cost. The traditional DAC energy cost is primarily driven by the temperature swing required to regenerate the sorbent and has been shown to be 1.8 MWh·ton-1 at the system level.Electrochemical pH swing devices are a growing research area for carbon capture devices with the goal of lowering the energy cost required for DAC. A pH gradient is built by generating OH- at the cathode and consuming OH- at the anode. An acid-base equilibrium with CO2 allows for the capture of CO2 at the cathode and release at the anode. This extends from other electrochemical CO2 capture devices based on pKa shifts of an electrochemically active organic species allowing for the capture and release of CO2. Electrochemical CO2 capture is considered promising based on potentially low energy costs to capture CO2 in comparison with current temperature swing adsorption technologies.This work explores Ni(OH)2 electrodes to produce the pH gradient for CO2 capture and release. At the cathode NiOOH is reduced to Ni(OH)2 while at the anode Ni(OH)2 is oxidized to NiOOH. The symmetrical electrodes allow for a low voltage requirement; the thermodynamic potential difference of standard electrochemical reactions is zero. Most of the voltage observed is to produce the pH gradient with the remainder driving the polarization of the electrodes. There is a resistance component as well, but this is small in comparison due to the low current densities used in the device, nominally 2 mA·cm-1.Two similar devices are presented, a traditional MEA (membrane electrode assembly) and a flow-through MEA. The traditional MEA separates the two Ni(OH)2 electrodes with an 80μm Piperion® membrane. While the flow-through membrane separates the electrodes with a three piece membrane consisting of two 80μm Piperion® membranes with a porous membrane between them. In the traditional MEA system air is passed over the cathode for capture, while the flow-through MEA the air is passed through the porous membrane isolated from the electrodes.The traditional MEA has been used to establish a baseline performance of the device and has been shown to capture CO2 at an energy cost of 1 MWh·ton-1 at the device level. An understanding has been built around the components of that energy cost including the relationship of flux to current density, effect of a regeneration process, transient battery behavior, and gas losses coinciding with changing the polarization of the batteries.The flow-through MEA looks to address of transient battery behavior and gas losses. It allows for denser, higher capacity electrodes, which can lean on traditional Ni-MH battery technology used in alkaline batteries used today. The higher capacities, limit the transient battery effect on flux in the device. Gas losses are addressed by having a continuous inlet air stream to the device and continuous outlet product.

The world is increasingly facing the direct effects of climate change triggering warnings of a crisis for the healthy existence of humankind. The dominant driver of the climate emergency is the historical and continued accumulation of atmospheric CO2 altering net radiative forcing on the planet. To address this global issue, understanding the core chemistry of CO2 manipulation in the atmosphere and proximally in the oceans is crucial, to offer a direct partial solution for emissions handling through negative emissions technologies. Many technologies have been proposed to develop a strategic and economic solution for carbon capture, storage, and utilization. In this paper, we review recent advances in technologies proposed for carbon capture and release via electrochemical process for point source/flue gas, direct air capture (DAC), and ocean/seawater capture. Electrochemical approaches to carbon capture are favorable in terms of reaction conditions, their ability to be incorporated into transformation processes, modularity, low relative carbon footprint, and compatibility with the availability of renewable electricity sources. We offer a critical comparative analysis of land- and ocean-based capture technologies to help guide future research and innovation.

A rapid build-out of direct air capture (DAC), deployed in order to mitigate climate change, will require significant amounts of both low-carbon thermal and electrical energy. Firm low-carbon power resources, including nuclear, geothermal, or natural gas with carbon capture, which also will become more highly valued as variable renewable energy penetration increases, would be able to provide both heat and electricity for DAC. In this study, we examined the techno-economic synergy between a hypothetical DAC plant in the year 2030 and a nuclear small modular reactor, and determined two avenues for which this relationship could benefit the nuclear plant. First, we demonstrated that, under certain assumptions, selling a portion of its energy to a DAC facility allows the nuclear plant to take in 21% less revenue from selling electricity to wholesale markets than its projected levelized cost, and still break even. Second, after estimating a potential revenue stream, we showed that an integration with DAC allows for the nuclear plant's capital costs to be up to 35% higher than what would be required if only selling electricity to wholesale markets. This could enable the nuclear plant to operate economically even in the face of variable and decreasing wholesale electricity prices, and also could offer developers more financial certainty when planning a new project. Ultimately, this study shows that the need for low-carbon energy for DAC plants might incentivize the development of advanced nuclear plants and firm low-carbon resources more broadly.

Deploying direct air capture at scale: How close to reality?

Direct air capture (DAC), as a complementary strategy to carbon capture and storage (CCS), offers a scalable and sustainable pathway to remove CO2 directly from the ambient air. This study presents a detailed evaluation of the amine-functionalised metal-organic framework (MOF) sorbent, mmen-Mg2(dobpdc), for DAC using a temperature–vacuum swing adsorption (TVSA) process. While this sorbent has demonstrated promising performance in point-source CO2 capture, this is the first dynamic simulation-based study to rigorously assess its effectiveness for low-concentration atmospheric CO2 removal. A transient one-dimensional TVSA model was developed in Aspen Adsorption and validated against experimental breakthrough data to ensure accuracy in capturing both the sharp and gradual adsorption kinetics. To enhance process efficiency and sustainability, this work provides a comprehensive parametric analysis of key operational factors, including air flow rate, temperature, adsorption/desorption durations, vacuum pressure, and heat exchanger temperature, on process performance, including CO2 purity, recovery, productivity, and specific energy consumption. Under optimal conditions for this sorbent (vacuum pressure lower than 0.15 bar and feed temperature below 15 °C), the TVSA process achieved ~98% CO2 purity, recovery over 70%, and specific energy consumption of about 3.5 MJ/KgCO2. These findings demonstrate that mmen-Mg2(dobpdc) can achieve performance comparable to benchmark DAC sorbents in terms of CO2 purity and recovery, underscoring its potential for scalable DAC applications. This work advances the development of energy-efficient carbon removal technologies and highlights the value of step-shape isotherm adsorbents in supporting global carbon-neutrality goals.

The “Direct Air Capture Recovery of Energy for CCUS Partnership (DAC RECO2UP)” project employs a team approach and supports the U.S. Department of Energy Office of Fossil Energy and Carbon Management’s (DOE-FECM) goal to decrease the cost of capture through the testing of existing direct air capture (DAC) materials in integrated field units that produce a concentrated carbon dioxide (CO2) stream of at least 95% purity. Solid-amine CO2 adsorption-desorption contactor technology, proven in the laboratory, is undergoing high-fidelity design/validation. Recoverable energy is readily available from a large number of commercial locations where DAC can be deployed; therefore, advancing the fidelity of energy recovery to directly reduce the cost of DAC is a key project objective. In addition, many commercial facilities have low-concentration CO2 vents that are uneconomical to treat alone but could provide more efficient mass and thermal transport to DAC systems with integrated energy recovery and flexible CO2 treatment capabilities. Technology scale-up leverages past research and occurs in a commercially relevant environment at the National Carbon Capture Center. Prescreening techno-economic analysis, risk assessments, and life cycle analysis are being performed by experienced team members. Results of the project will address critical technical barriers that, when solved, will improve the capital and operating costs of DAC while validating commercial relevance of cost and product quality/need.

Reduction of greenhouse gas emissions is an important environmental element to actively combat the global warming and climate change. In view of reducing the CO2 concentration from the atmosphere, the Direct Air Capture (DAC) options are promising technologies in delivering negative carbon emissions. The integration of renewable-powered DAC systems with the CO2 utilization technologies can deliver both negative carbon emissions as well as reduced energy and economic penalties of overall decarbonized processes. This work evaluates the innovative energy- and cost-efficient potassium - calcium looping cycle as promising direct air capture technology integrated with various CO2 catalytic transformations into basic chemicals / energy carriers (e.g., synthetic natural gas, methanol etc.). The integrated system will be powered by renewable energy (in terms of both heat and electricity requirements). The investigated DAC concept is set to capture 1 Mt/y CO2 with about 75 % carbon capture rate. Up to 50 % fraction of the captured CO2 stream will be then catalytically converted into the Synthetic Natural Gas (SNG) or methanol using the green hydrogen produced by the water electrolysis (using renewable power), the rest being sent to geological storage. As the results show, the integrated DAC - CO2 utilization system, powered by renewable energy, has promising performances in terms of delivering negative carbon emissions, promoting the utilization of renewables and reducing ancillary plant energy consumptions.

Scenarios for meeting ambitious climate targets rely on large-scale deployment of negative emissions technologies (NETs), including direct air capture (DAC). However, the tradeoffs between food, water and energy created by deploying different NETs are unclear. Here we show that DAC could provide up to 3 GtCO2 yr−1 of negative emissions by 2035—equivalent to 7% of 2019 global CO2 emissions—based on current-day assumptions regarding price and performance. DAC in particular could exacerbate demand for energy and water, yet it would avoid the most severe market-mediated effects of land-use competition from bioenergy with carbon capture and storage and afforestation. This could result in staple food crop prices rising by approximately fivefold relative to 2010 levels in many parts of the Global South, raising equity concerns about the deployment of NETs. These results highlight that delays in aggressive global mitigation action greatly increase the requirement for DAC to meet climate targets, and correspondingly, energy and water impacts. Negative emissions technologies are essential in scenarios for meeting Paris climate targets. Modelling results show that direct air capture could play an important role with less demand for land yet high energy and water use compared with BECCS and afforestation.

Direct air capture (DAC) technology is still facing some challenges that need to be addressed before the technology can be widely deployed. One major challenge is the high overall system energy requirement, and it is the main bottleneck in DAC commercialization. This study aims to unlock the potential of integrating DAC with Heat Ventilation and Air Conditioning (HVAC) systems. A thermodynamic model is used to test the effect of varying the adsorption and desorption conditions on DAC unit performance, and to assess the characteristics of DAC unit positioned in six different locations within air the handling unit (AHU). The results show that by only locating the DAC unit in Position 6 (i.e., positioning the DAC unit after the exhaust fan in AHU) in comparison to a stand-alone unit, the efficiency of the DAC system is improved at varying times through the summer season in Qatar. Specifically locating DAC unit at Position 6 increases DAC efficiency from 5.3% to 27.19% for 8th of June 2022 at 11:00 am in Qatar. Additionally, using the DAC unit with other filters in AHU allows for full air recirculation for 10 h. Based on this scenario and the weather data for 20th of July at 12:00 pm, the hottest day in Qatar in 2022, a reduction of 44% in cooling load is achieved. Locating the DAC unit at a point before the air is supplied from AHU is the best, however, in case of full recirculation of air, positioning the DAC unit after the exhaust fan will achieve better performance.

The rapid development of direct air capture (DAC) technologies has become critical in order to remove CO2 from the atmosphere and limit global warming to a maximum of 1.5°C. In this perspective, we provide a mini review of the current research on the emerging liquid- and solid-based sorbent materials to capture CO2, summarize the existing challenges of DAC technologies, and suggest future research directions to accelerate the development of DAC systems. In particular, the desired properties for a breakthrough sorbent that efficiently captures CO2 from the air and releases it for sequestration are described.