CO2 Removal Research Articles

Carbon neutral energy systems: Optimal integration of energy systems with CO2 abatement pathways

AbstractReducing emissions requires transitioning towards decarbonized systems through avoiding, processing, or offsetting. Decisions on system design are associated with high costs which can be reduced at the planning stage through optimization. The temporal variations in power demand and renewable energy supply significantly impact the design of a low‐emissions energy system. Effective decision‐making must consider such impact in a comprehensive framework that accounts for the potential synergies between different options. This work presents a mixed integer linear programming model that considers the impacts of energy supply and demand dynamics to optimize the design and operation of an integrated energy system while adhering to a set emissions limit. The model integrates renewable power with CO2 capture, utilization, and sequestration by considering H2 production and storage. The case study showed including negative emissions technologies and CO2 capture and processing with renewable energy allows achieving net zero emissions power.

Sustainable tourism in the Tremiti Islands (South Italy)

An analysis of the pressure factors that influence the sustainable tourism in the Tremiti Islands (TI) has been performed. Tourist’s fluxes have been investigated in terms of monthly arrival and presences showing a high value of the territorial exploitation index with high number of arrivals, particularly in August, and low occupancy rate. Effects of climatic change has been analyzed in TI with reference to the increase of average air and sea temperature in the islands. Some measures of contrast to climate change and to favour sustainable tourism have been discussed also. The CO2 emissions by ferries transport, solid waste and wastewater treatment have been calculated. Environmental taxation for sustainable tourism aimed tat CO2 content reduction is also assessed identifying the value in 1.47 €/capita on the basis of the tourist arrivals and presences considering the environmental cost for CO2 removal and showing that tourism taxation should be well accepted if funds are destined to environmental purposes.

A facilitated transport membrane composed of amine-containing ionic liquid confined in a GO/CNT network for highly efficient carbon capture

Carbon capture is a key approach to manage carbon dioxide (CO2) emissions and promote net removal of CO2 from the atmosphere. Post combustion flue gas emissions from power plants contribute a significant fraction of CO2 released into the atmosphere. Membrane-based separation strategies offer environmentally sustainable and economically viable solutions for efficient CO2 capture from power plants. Facilitated transport membranes, although showing strong capability for CO2 capture at low concentrations and under humid conditions, suffer from the loss of facilitators, such as amines, leading to decline in performance over long-term operation. Ionic liquids (ILs) are chemically and thermally stable and have low vapor pressure, which is ideal to prevent aforementioned losses. However, making a thin network for effective IL confinement is still a challenge. In this work, we developed a stable high performing IL based CO2 selective membrane that can operate at temperatures as high as 80 °C under humid conditions. An amino acid-based IL (containing facilitated carriers), 1-ethyl-3-methylimidazolium glycinate, [EMIM][GLY], was used as the separating agent. In order to selectively load and confine the IL in a thin selective layer, we designed and fabricated a network composed of stacked graphene oxide (GO) nanosheets intercalated by carbon nanotubes (CNT). While CNT acts as a nanowedge that helps in increasing the nanochannels to facilitate low-resistance gas transport, GO nanosheets act as anchoring sites due to presence of various functional groups resulting in electrostatic interaction between GO and cation of IL. Due to the aforementioned reason, distribution of GO in the network plays a critical role in forming a thin, uniform selective IL layer. The GO distribution was optimized by adjusting the pH of the coating solution; after optimizing IL coating, this results in a thin, defect free selective layer, providing a membrane with high CO2 permeance of ∼1600 GPU and CO2/N2 selectivity of 400, superior to most of the reported IL membranes. This network composed of GO/CNT network not only facilitates fabrication of a stable, ultrathin, high permeance and high selectivity supported IL membrane but also provides a platform for preparation of other IL-based membranes for desired separations.

Can coastal and marine carbon dioxide removal help to close the emissions gap? Scientific, legal, economic, and governance considerations

In this Policy Bridge, we present the key issues regarding the safety, efficacy, funding, and governance of coastal and marine systems in support of climate change mitigation. Novel insights into the likely potential of these systems for use in mitigating excess carbon dioxide emissions are presented. There may be potential for coastal blue carbon and marine carbon dioxide removal (mCDR) actions to impact climate change mitigation significantly over the rest of the 21st century, particularly post 2050. However, governance frameworks are needed urgently to ensure that the potential contribution from coastal and ocean systems to climate change mitigation can be evaluated properly and implemented safely. Ongoing research and monitoring efforts are essential to ensure that unforeseen side effects are identified and corrective action is taken. The co-creation of governance frameworks between academia, the private sector, and policymakers will be fundamental to the safe implementation of mCDR in the future. Furthermore, a radical acceleration in the pace of development of mCDR governance is needed immediately if it is to contribute significantly to the removal of excess carbon dioxide emissions by the latter half of this century. To what extent large-scale climate interventions should be pursued is a decision for policymakers and wider society, but adaptive legal, economic, policy, research, and monitoring frameworks are needed urgently to facilitate informed decision-making around any implementation of mCDR in the coming decades. Coastal and ocean systems cannot be relied upon to deliver significant carbon dioxide removal until further knowledge of specific management options is acquired and evaluated.

Production of high calorific value hydrogen-rich combustible gas by supercritical water gasification of straw assisted by machine learning

This article reveals the basic laws of straw supercritical water gasification (SCWG) and provides basic experimental data for the effective utilization of straw. The paper studied the impact of three operational conditions on the production of high-calorific value hydrogen-rich combustible gases through SCWG of straw within a quartz tube reactor. The findings reveal that elevated reaction temperatures, extended residence times, and reduced feedstock concentrations favor the SCWG of straw. When combustible gas contains carbon dioxide, the maximum low heating value (LHV) of the gas is 21 MJ/Nm3. Upon removing carbon dioxide, the LHV of the gas reached 38 MJ/Nm3. Subsequently, a machine learning (ML) model was developed to forecast gas yield and LHV during the SCWG process. The results demonstrate that the model exhibits robust generalization capabilities. ML can be extensively applied to forecast biomass SCWG processes across various operational conditions.

The impact of design and operational parameters on the optimal performance of direct air capture units using solid sorbents

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Visible Light-Driven CO2 Capture and Release Using Photoactive Pyranine in Water in Continuous Flow.

The urgent need to address climate change and its environmental consequences demands innovative carbon capture technologies, given the relationship between rising global temperatures and increased atmospheric CO2 levels. Here, we present a reversible photochemical carbon capture and release strategy and system utilizing photoactive pyranine in an aqueous bicarbonate buffer system. Control experiments suggested that the photoacid effect occurs at the surface which contributes to CO2 release, complemented by the photothermal effect at the surface and in the bulk. A continuous flow setup employing a tube-in-tube configuration with a hollow fiber membrane demonstrates the efficiency and reliability of the visible light-driven carbon capture system, with the release of CO2 captured from a 15% CO2 feed in the dark, at a rate of 0.48 mmol CO2 per hour to a nitrogen sweep stream under light irradiation at 200 W/m2, a level comparable to solar intensity of visible light (150 W/m2 of blue light -250 W/m2 of blue and green light). The robustness and scalability of the system has been demonstrated, with long-term operation over 7 days yielding 60 mmol (1.34 L CO2 at STP) of cumulated CO2 separation. Additionally, we explored the potential for direct air capture, yielding 3 μmol of CO2 separation over 2 h of operation from a bicarbonate buffer solution saturated with ambient air (420 ppm). This work introduces the prospect of photoswing of carbon capture systems, which can avoid external energy input beyond solar irradiation, offering promising avenues for addressing the challenges associated with climate change.

(Invited) Energy-Efficient and Impurity-Tolerant Electrochemical Co-Generation of Acid and Base Solutions

The sequential application of acid and base solutions can be used to perform chemical transformations that are of interest for carbon management and sustainable resource utilization, including CO2 capture, CO2 removal, production of slaked lime, and recovery of critical minerals. Electrochemical co-generation of acid and base from salt solutions enables their use in closed-loop processes that could be powered by renewable electricity, wherein acid and base are regenerated from the salt byproduct of their application. To be viable at scale, acid-base co-generating systems need to be energy-efficient and tolerant to impurities that are inevitably released into recycle loops. Conventional electrochemical methods for co-generating acid and base, such as bipolar membrane electrodialysis (BPMED), rely on the use of ion exchange membranes (IEMs) to inhibit H+ and OH– recombination, but IEMs cause large resistive losses that severely limit the energy efficiency and current density of these systems. In addition, cation exchange membranes (CEMs) do not tolerate polyvalent cations (e.g., Ca2+, Mg2+) in the presence of base, yet polyvalent cations are intrinsic to all high-impact applications. In this talk, I will describe our development of acid-base co-generating systems in which H+ and OH– recombination is inhibited by competitive transport of supporting electrolyte and H+ masking, which enables the use of a simple porous diaphragm separator instead of IEMs. We developed an ion transport model to predict the current efficiency for acid-base co-generation as a function of the electrolyte composition and operating parameters. Instead of a bipolar membrane, our systems use the H2 oxidation reaction (HOR) and H2 evolution reaction for H+ and OH– generation, respectively. We demonstrate IEM-free production of acid and base at useful concentrations in the presence of polyvalent cations with much higher energy efficiency and current density than state of the art BPMED systems. Individual cells can be stacked by combining HOR and HER electrodes into bipolar gas diffusion electrodes that recirculate H2 with near-unity efficiency. To demonstrate the utility of the acid and base solutions generated by this system, I will describe their use to extract Mg(OH)2 from ultramafic rocks for application in CO2 removal.

Life cycle assessment of carbon dioxide removal and utilisation strategies: Comparative analysis across Europe

Anthropogenic climate change necessitates urgent implementation of carbon dioxide (CO2) removal and utilisation strategies. While the CO2 removal efficiency of such strategies is commonly evaluated, their environmental impacts beyond CO2 emissions needs consideration to avoid burden shifting. This study performs a life cycle assessment of CO2 removal and utilisation strategies in ten specific European locations. The study considers strategies such as direct air carbon capture, permanent storage, the production of fuels and polymers. The energy source, CO2 transport distances, transport mode (pipeline and ship) and the CO2 storage medium vary between the locations. Results indicate that seven of the ten considered locations have a CO2 removal efficiency greater than 95%. In addition, the hotspot analysis indicates CO2 capture and its transport contribute to between 0.3% and 13.1% of global warming impacts of polymer production and between 0.4% and 16.5% for fuel production (varies based on the polymer and fuel type).

Hysteresis of Northern Hemisphere permafrost to carbon dioxide emissions

Abstract Carbon dioxide removal (CDR) is proposed to limit the level of global warming and minimize the impacts of climate crises. However, how permafrost may respond to negative carbon emissions remains unknown. Here, the response of near-surface permafrost in the Northern Hemisphere is investigated based on idealized carbon dioxide (CO2) ramp-up (284.7–1138.8 ppm) and symmetric ramp-down model experiments. The results demonstrate that the timing of the minimum permafrost area lags the maximum CO2 concentration for decades, which is also observed in soil temperatures at different depths and active layer thicknesses. When the CO2 concentration is reversed to the preindustrial level, the permafrost area decreases by ~12% relative to the initial conditions, together with additional warming in the ground temperature at the top of the permafrost, indicating the hysteresis of permafrost to CO2 removal. The most profound hysteretic responses occur at high latitudes for soil temperatures owing to Arctic amplification, while at the southern margins of the permafrost zones for permafrost and active layer thickness that largely linked to the climate state. Moreover, the sensitivity of permafrost and the associated thermodynamic factors to CO2 change is generally lower during the CO2 ramp-down phase than during the ramp-up phase, likely due to the release of stored heat on land. The results reveal the behaviour of permafrost in response to negative carbon emissions, which is informative for the projections of permafrost towards carbon neutral targets. In addition, the results may provide a reference for permafrost-related tipping points (e.g., releasing long-term stored greenhouse gases and destabilising recalcitrant soil carbon) and risk management in the future.

(Invited) Electrochemical Marine Carbon Dioxide Removal (mCDR)

Ebb Carbon is developing an electrochemical system to safely remove carbon dioxide from the atmosphere and store it in the ocean as dissolved inorganic carbon. The core process uses bipolar electrodialysis (BPED) to process incoming seawater into aqueous acid and alkaline seawater. The acid is kept on land and used for beneficial purposes that result in its neutralization. The alkaline seawater is returned to the ocean, shifting the carbonate buffer system toward carbonate, resulting in the removal of CO2 from the air into oceanic bicarbonate as air-sea equilibration is restored.For the mCDR system to be impactful on a global level, it must reach gigaton scale while being energy efficient and cost effective.The BPED stack dominates the energy demand of the system and is a prime design task for Ebb Carbon. The stack and system are undergoing development and testing in Ebb Carbon’s labs as well as at the labs of institutional partners. Combining all of these system elements requires a multitude of scientific and engineering disciplines to work together. In this talk, I will discuss the potential for improving the energy and Faradaic efficiencies of these systems, including the opportunity for collaboration with the electrochemical research community.

Continuous Direct Air Capture and Electrochemical Conversion of CO2 and H2O into Ethylene and Oxygen in Solid Electrolyte Reactor

Chemelectronics LLC has developed economical approach to use solar energy to convert CO2 directly captured from air using carbon dioxide capture conductive sorbent materials coated on carbon foam electrodes into chemical products (ethylene) and oxygen from nick foam electrodes separated with solid polyelectrolytes. We take advantage of commercial off-the-shelf solar panels as electricity to supply the electrochemical reduction of CO2 directly captured from air into chemical products with zero carbon emission.Based on the life cycle analysis, there is no CO2 emission from CO2 capture and conversion. The energy will be produced from solar panels.

Design and Implementation of Iron-Based Electrochemical System for Simultaneous Carbon Capture and Hydrogen Gas Recovery

The catastrophic results of climate change and energy crisis, such as the rise in wildfires, floods, and ecosystem disruptions highlight the critical need of urgent and innovative global-scale solutions for carbon dioxide (CO2) removal (CDR). Ocean-based CDR methods, leveraging the ocean's capacity as a large sink to sequester up to 30% of emissions, offer a great promise. Yet, implementing and testing marine CO2 removal (mCDR) techniques such as ocean iron fertilization (OIF) or ocean alkalinity enhancement (OAE) face significant challenges. To overcome these challenges, a novel self-operating electrochemical technology is designed and presented in this work. The proposed technology, namely electrochemical OIF (EOIF), does not only combine OIF and OAE, but also recovers hydrogen gas (H2) from seawater, offering a promising solution for achieving quantifiable and transparent large-scale mCDR. The EOIF design s focused on employing Fe/Fe-producing anodes to eliminate the production of acids at the anode in traditional electrochemical OAE systems and replace it with Fe release, where the cathode can be made from naturally abundant cost-effective materials, such as carbon. The obtained results show that the EOIF system can be implemented to increase both the concentration of ferrous iron (Fe+2) by 0-0.5 mg/L, and the seawater pH by 8% (i.e., 25% decrease in the hydrogen ions concentration). It also offers the flexibility to optimize the release of iron (Fe+2/Fe+3) by adjusting the magnitude of the electric current in the systems, as well as by optimizing the electrode material and geometry. In certain ocean regions, enhanced iron concentrations stimulate the naturally occurring biological carbon pump (BCP), leading to increased phytoplankton growth, CO2 uptake, and subsequent export of carbon to the deep ocean. Simultaneously, the system increases seawater alkalinity and the buffer capacity, enhancing CO2 solubility and storage in the shallow ocean through the solubility pump. The techno-economic assessment shows that the combined advantages of the EOIF system can lower the mCDR cost by more than 95% compared to the traditional methods. The obtained measurements demonstrate the scalability of EOIF and its ability to operate using solar energy at a lower cost. Overall, the proposed EOIF technology offers a practical, effective, and sustainable solution for addressing climate change and energy recovery on a large-scale.

CO2 Uptake and Stability Enhancement in Vinyltrimethoxysilane-Treated SBA-15 Solid Amine-Based Sorbents.

Silica-supported amine absorbents, including materials produced by tethering aminosilanes or infusion of poly(ethyleneimine), represent a promising class of materials for CO2 capture applications, including direct air and point source capture. Various silica surface treatments and functionalization strategies are explored to enhance stability and CO2 uptake in amine-based solid sorbent systems. Here, the synthesis and characterization of novel vinyltrimethoxysilane-treated Santa Barbara Amorphous-15 (SBA-15) supports and the corresponding enhancement in CO2 uptake compared to various SBA-15-based control supports are presented. The relationship between CO2 diffusion and amine efficiency in these systems is explored using a previously reported kinetic model. The synthesized materials are characterized with CO2 and H2O isotherms, diffuse reflectance infrared Fourier transform spectroscopy, 1H T1-T2 relaxation correlation NMR, and rapid thermal cycling experiments. The novel support materials are shown to enable high amine efficiencies, approaching a fourfold improvement over standard SBA-15-supported amines, while simultaneously exhibiting excellent stability when cycled rapidly under humid conditions. As the poly(ethyleneimine) loadings are held constant across the various samples, enhancements in CO2 uptake are attributed to differences in the way the poly(ethyleneimine) interacts with the support surface.

Observing Electrochemical Performance Trends with the Physical Scaling of Bipolar Membrane Electrodialysis for the Capture and Concentration of Atmospheric CO2

Bipolar membrane electrodialysis (BPMED) is a proven technology for separating ionic species driven by electrochemical potential through ion conductive membrane separators. When using a bipolar membrane (BPM) as the separator, a pH gradient is created by the generation of acid and base via water dissociation at the internal interface of an anion conductive and a cation conductive membrane. BPMED can been used for the capture and concentration of atmospheric CO2, for example when using a liquid alkaline capture sorbent, where the acidification of the capture stream can be used to regenerate pure CO2 while further basification of the remaining effluent regenerates the alkaline capture sorbent to be re-used in the direct air capture process. Current commercial BPMs require high overpotentials to drive water dissociation and can only operate at low to moderate current densities. While considerable work has gone into the development of efficient, electrochemically active BPMs through improved membrane polymer chemistries and high-activity water dissociation catalysts, little work has been done to physically scale up these materials and use them in electrodialysis-driven carbon capture and concentration systems beyond lab scale (i.e., >1 cm2).In this presentation, we will report a scalable BPMED cell that can sense the resistive contributions of the individual membrane components (i.e., the anion exchange and cation exchange membranes, and the water dissociation at the internal BPM interface) with increasing membrane active area from 1 cm2 to 25 cm2. With this BPMED cell, changes in the BPM and water dissociation catalyst compositions and structures are related to electrochemical performance metrics (overpotential and CO2 recovery efficiency) at increasing physical scales. Electrochemical impedance spectroscopy (EIS) was used to reveal resistive contributions to the cell at increasing active area, while the inlet and outlet pH were measured to confirm the overall acidification and basification of the dialysis cell to promote carbon capture and conversion, as well as sorbent regeneration. This study aims to build a bridge between the necessary improvements in the membrane and water dissociation catalyst compositions with industrially relevant energy efficiency and conversion performance, accelerating the development of high performance BPMs.

(Invited) EDAC Labs: Carbon Removal via Acid-Base Electrochemistry

EDAC Labs(https://edaclabs.com/) uses the electrochemical production of acid and base to decarbonize the world through conventional direct air capture, enabling carbon-negative mining, and by providing technology for other applications such as direct ocean capture, ocean alkalinity enhancement, and enhanced weathering. EDAC Labs’ electrosynthesizer device creates acid and base at reduced energy cost of conventional processes. For conventional direct air capture developers, EDAC Labs provides technology that is low cost and operates at ambient temperature and pressure. For direct ocean capture and ocean alkalinity enhancement developers, EDAC Labs supplies electrochemistry solutions to developers that lower project costs. For metal mines, EDAC Labs provides technology that extracts valuable metals while sequestering carbon to achieve carbon-negative mining. The acid is used to start the recovery of valuable metals from mine tailings, and the base is used to capture CO2 from air. The acid and base streams are then combined to extract metals that can be sold for applications such as batteries, and to create solid carbonates, which permanently store CO2. Figure 1

Minimize Energy Consumption of CO2 Release in a Flow Electrolyzer By Optimizing Direct Air Capture Solvents

Under the 2015 Paris Agreement, almost 200 nations have committed to the global goal of limiting the rise in average temperatures to 2.0 °C above preindustrial levels, with an even more ambitious aim of striving for 1.5 °C. Achieving the 1.5 °C objective requires a 45% reduction in global greenhouse gas emissions by 2030, ultimately reaching net-zero emissions by 2050. Numerous industries are increasingly making commitments to combat climate change by minimizing their CO2 emissions. However, certain sectors face challenges due to the current high costs associated with emissions reduction through available technologies, though these costs are expected to decrease over time. Moreover, in specific industries like cement production, there are emissions sources that cannot be entirely eliminated, such as those arising from the inherent calcination process. Given these constraints, realizing the emissions reduction pathway to the 1.5 °C target requires the adoption of negative emissions processes, including technologies like direct air capture (DAC), to actively remove CO2 from the atmosphere.The operational concept of the DAC process explored in this study is based on the utilization of both the solvent-based method and alkaline water electrolysis. This involves regenerating the solvent through pH fluctuations generated by a carbonate electrolyzer. As depicted in Figure 1, the consumption of OH- ions during O2 evolution leads to a decrease in pH at the anolyte loop, while the production of OH- ions through water splitting causes an increase in pH at the catholyte loop. Consequently, the lowered pH environment facilitates the release of CO2 gas from dissolved carbon species such as CO32-, while the heightened pH environment promotes the formation of alkaline hydroxides for carbon capture in an air absorber.In this work, we will aim to analyze the energy consumption per mole of CO2 released from the anolyte loop of a flow electrolyzer. Utilizing a combination of theoretical predictions and experimental validations, significant insights were obtained for optimizing the DAC solvent. This optimization involves minimizing energy consumption by adjusting alkalinity levels and incorporating supporting electrolytes. Figure 1

Carbonate Electrolysis for Energy Efficient Direct Air Capture of CO2

Yearly global energy related CO2 emissions continue to increase, reaching a record breaking 37 billion metric tons in 2022. As a major greenhouse gas, CO2 levels need to be reduced by 10s of gigatons to prevent the worst of climate change, something that is no longer feasible with net-zero emissions alone. Removing atmospheric CO2 is therefore of critical importance for the future of our planet. While major improvements have been made in CO2 capture from large point sources, a significant portion of CO2 emitted each year from the United States comes from distributed sources such as cars and smaller factories. Due to the dilute concentrations of CO2 in ambient air, Direct Air Capture (DAC) needs to be highly selective to preferentially absorb CO2 to collect useable amounts. These challenges have made current DAC systems quite costly, both energetically and economically, and require vastly different strategies than carbon capture from concentrated sources.At Giner, we are developing a novel process for the capture and regeneration of CO2 from air into a purified, concentrated CO2 stream that can be redirected as a feedstock for a wide range of applications, including chemical manufacturing and syngas formation. This process involves the capture of CO2 in a concentrated KOH solution using a high-surface area air contactor to form potassium carbonate. The potassium carbonate is then efficiently electrolyzed in a hydrogen-assisted process to regenerate the CO2 at a low operating potential, increasing the electrical efficiency of the process while producing concentrated and purified CO2. In addition, water, hydrogen, and KOH are also regenerated as byproducts that can be recycled back into the CO2 capture and electrolysis processes, reducing both overall energy and chemical consumption.Giner has developed a unique 3-compartment carbonate electrolysis flow cell. Using our electrolyzer, we have seen operating voltage as low as 1.2 V at 100 mA/cm2 in a 5 cm2 cell for potassium carbonate conversion to CO2 with H2 assisted electrolysis. Significant improvements in operating voltage have come from optimization of gas-diffusion layers (GDLs), cell geometry, and membrane selection. Furthermore, we have achieved >97% pure CO2 formation in the internal flow-through compartment. Currently, scale-up is in progress to apply these developments to approach comparable conditions in a 50 cm2 multi-cell stack. Further developments will enable pairing with an in-house, carbonate based, air contactor allowing for capture and regeneration of over 1 ton CO2 per year. Acknowledgement: The project is financially supported by the Department of Energy's ARPA-E Office under the Grant DE-AR0001495

Understanding Electrochemical and Mechanical Durability of Bipolar Membranes Used in Electrodialysis

Using renewable energy to drive direct carbon capture systems is a powerful way to contribute to net negative emissions. When using liquid alkaline sorbents for CO2 direct air capture, it is critical to reduce the energy demand for CO2 concentration and sorbent regeneration. Electrodialysis is an ideal candidate technology to integrate renewable energy into this process, however, to enable this ion-exchange membrane separators that can operate at high ion flux and low voltage are needed. Bipolar membranes (BPMs), that generate protons and hydroxide ions from the dissociation of water when operated in reverse bias, are the enabling component to generate acid and base in electrodialysis systems. Bipolar membrane electrodialysis (BPMED) uses a BPM to create acidifying and basifying chambers which are well suited to concentrate and release CO2 and concentrate the remaining alkaline effluent to cycle back to the capture process. Current BPM durability, however, sufferers at high current density (ion flux) and physical scale. BPMs have several known degradation mechanisms including chemical breakdown of ion exchange polymers, loss of junction adhesion, or physical breakdown due to shearing force and pressure swings in an electrodialysis cell.To assess the electrochemical and mechanical durability of BPMs under operational conditions, we investigated how fabrication conditions (including preconditioning, hot pressing, and catalyst loading) impact the adhesion of custom made BPMs. T-peel studies were performed ex-situ to quantify adhesive forces of BPMs made of different compositions and prepared under different conditions, and BPMED experiments were performed to assess the electrochemical performance of the corresponding BPMs. The BPMED results show that, while adhesion is necessary to physically maintain the BPM junction, mechanical adhesion alone cannot overcome poor ion and water transport management at the water dissociation junction. The results of this systematic comparison indicate that in order for BPMs to operate at high current densities, high adhesion forces made during fabrication of BPMs will need to be balanced with water dissociation kinetics and ion/water transport through the individual membrane layers.

Optimizing Air Contactor Design for Efficient Carbon Capture in Direct Air Capture Systems: A Multi-Disciplinary Approach

As carbon dioxide (CO2) emissions continue to rise, direct air capture (DAC) has emerged as an important technology for removing CO2 from ambient air to combat climate change. The air contactor design is a critical factor impacting DAC system performance and costs. This research describes a strategy for improving the design of a single air contactor unit to increase CO2 capture flux while minimizing costs using optimization techniques grounded in experimental data .The research focuses on a 100 m2 slab air contactor modeled utilizing cooling tower and scrubber principles. The system includes the chemical, mechanical, and structural engineering disciplines. The mass transfer coefficient, air velocity, packing depth, and capital cost per frontal area are four major design characteristics that were maximized.The model integrated requirements for low air velocity, pressure drop, and energy consumption, as well as adequate gas-liquid interaction via structured packing selection and depth.The design space was explored using a multi-objective optimization strategy based on gradient-based and heuristic methods. Initial sampling via a design of experiments methodology demonstrated response surface trends in the objective function across the design space. The response surfaces mapped the optimization objective as a function of the design variables. Using gradient information, sequential quadratic programming efficiently located an optimal design vector that met all constraints on the design variables and feasibility requirements. The constraints included bounds on mass transfer coefficient, air velocity, packing depth, and capital cost per frontal area. The optimized air contactor design achieved a CO2 capture flux of 10,440 kg/m2-yr at a cost of $ 0.068 per kg CO2 captured. The developed optimization framework maximizes contactor performance while decreasing operational costs. A multi-objective genetic algorithm approach was used to identify the trade-offs between the two competing objectives of maximized CO2 capture and minimized cost by expanding the formulation. The Pareto-optimal front of the optimization results offered numerous optimized solutions with specific DAC system setups. This methodology, as well as the optimum configurations identified, serve as the foundation for constructing larger-scale DAC systems, in future. Ongoing research aims to improve solution approaches by including advanced optimization software packages such as DAKOTA, which offers global optimization algorithms, as well as to boost model accuracy via integrating additional choice variables. Future optimization and modeling studies will include contactor interactions and the modeling of a full DAC facility to boost confidence that a globally optimal design has been established.Overall, this study illustrated an efficient optimization strategy for air contactor design and contributes to the improvement of sustainable carbon capture technology, which is crucial to controlling rising global CO2 levels. Contactor configuration optimization enables superior DAC system designs at lower costs, hence promoting the urgent deployment of negative emissions solutions.