CO2 Removal Research Articles

The implementation of indirect calorimetry for patients with acute respiratory failure: Invited commentary on techniques and procedure.

Respiratory failure is a life-threatening condition that occurs when the lungs are unable to deliver adequate oxygen to the blood or remove carbon dioxide from the body. Patients with respiratory failure often have difficulty maintaining oral nutrition intake because of associated breathlessness and are at increased risk of malnutrition, given both their metabolic response to stress and their dependence on nutrition support. Predictive equations assist clinicians in determining specific energy (caloric) needs for patients with respiratory failure; however, they are inaccurate, complex, and difficult to calculate. Recent technological advances have allowed for commercially available bedside measurement of energy needs using indirect calorimetry. The purpose of this review is to describe how indirect calorimetry (IC) can be used to influence clinical decision-making and nutrition care for patients with respiratory failure who are mechanically ventilated. We provide examples of how IC is utilized in a large tertiary care hospital as well as a small community hospital and strategies for successful adoption of IC.

Optimizing the Synthesis of CO2-Responsive Polymers: A Kinetic Model Approach for Scaling Up

The kinetic model is a crucial tool for optimizing polymer synthesis protocols and facilitating the scaled-up production processes of the CO2-responsive polymer poly(N-[3-(dimethylamino)propyl]-acrylamide)-b-poly(methyl methacrylate)(PDMAPAm-b-PMMA), which is supposed to be implemented in direct air capture (DAC) technology. This study presents a simulation of the kinetic model developed for the Reversible Addition−Fragmentation Chain-Transfer (RAFT) polymerization of N-[3-(dimethylamino)propyl]-acrylamide (DMAPAm), alongside an investigation into the kinetics of this polymerization using the simulation as an analytical tool, as well as the application of the simulation for the upscaling of RAFT polymerization. Ultimately, the kinetic model was validated through two kinetic experiments, confirming its reliability. It was subsequently employed to optimize the synthesis recipe and to predict the properties of PDMAPAm homopolymers, thereby supporting the upscaling of PDMAPAm-b-PMMA diblock copolymer synthesis. In the end, the preliminary results of the CO2-responsiveness of the diblock copolymer were determined with a simple experiment.

Ocean alkalinity enhancement (OAE) does not cause cellular stress in a phytoplankton community of the subtropical Atlantic Ocean

Abstract. A natural plankton community from oligotrophic subtropical waters of the Atlantic near Gran Canaria, Spain, was subjected to varying degrees of ocean alkalinity enhancement (OAE) to assess the potential physiological effects in the context of the application of ocean carbon dioxide removal (CDR) techniques. We employed nine mesocosms with sediment traps attached to the bottom, each enclosing a volume of 8.3 m3, to create a gradient in total alkalinity (TA). OAE was based on the addition of carbonates (NaHCO3 and Na2CO3). The lowest point on this gradient was 2400 µmol L−1, which corresponded to the natural alkalinity of the environment, and the highest point was 4800 µmol L−1. Over the course of the 33 d experiment, the plankton community exhibited two distinct phases. In phase I (days 5–20), a notable decline in the photosynthetic efficiency (Fv/Fm) was observed. This change was accompanied by substantial reductions in the abundances of picoeukaryotes, small-size nanoeukaryotes (nanoeukaryotes-1), and microplankton. The cell viability of picoeukaryotes, as indicated by fluorescein diacetate hydrolysis by cellular esterases (FDA green fluorescence), slightly increased by the end of phase I, whilst the viability of nanoeukaryotes-1 and Synechococcus spp. did not change. Reactive oxygen species levels (ROS green fluorescence) showed no significant changes for any of the functional groups. In contrast, in phase II (days 21–33), a pronounced community response was observed. Increases in Fv/Fm in the intermediate OAE treatments of Δ900 to Δ1800 µmol L−1 and in chlorophyll a (Chl a), chlorophyll c2 (Chl c2), fucoxanthin, and divinyl Chl a were attributed to the emergence of blooms of large-size nanoeukaryotes (nanoeukaryotes-2) from the genera Chrysochromulina, as well as picoeukaryotes. Synechococcus spp. also flourished towards the end of this phase. In parallel, we observed a significant change of 20 % in the overall metaproteome of the phytoplankton community. This is considered a significant alteration in protein expression, having a substantial impact on cellular functions and the physiology of the organisms. Medium levels of ΔTA showed more upregulated and less-downregulated proteins than higher ΔTA treatments. Under these conditions, cell viability significantly increased in pico- and nanoeukaryotes-1 at intermediate alkalinity levels, while in Synechococcus spp., nanoeukaryotes-2 and microplankton remained stable. ROS levels did not significantly change in any functional group. The pigment ratios DD+DT : FUCO and DD+DT : Chl a increased in medium ΔTA treatments, supporting the idea of nutrient deficiency alleviation and the absence of physiological stress. When all data are taken together, this study shows that OAE did not cause cellular stress in the phytoplankton community studied, and physiological fitness was not impaired. The drawdown in phytoplankton cell numbers that was observed at times seemed to have been most likely caused by nutrient limitation.

PERFORMANCE EVALUATION OF A GAS ENGINE OPERATING ON HIGH-CO₂ NATURAL GAS AT LATE INJECTION TIMING

The increasing energy demand in the transportation sector and the depletion of conventional fossil fuel reserves necessitate the exploration of alternative fuel sources. Malaysia holds significant untapped natural gas reserves with high carbon dioxide (CO₂) content, which has historically been considered unsuitable for commercial use due to economic and technical challenges associated with CO₂ removal. This study investigates the feasibility of utilizing highCO₂ natural gas directly in internal combustion (IC) engines and its effects on engine performance. A single-cylinder, four-stroke, direct-injection compressed natural gas (DI-CNG) engine was used to evaluate the impact of CO₂ addition on key performance parameters, including brake torque, brake power, brake specific fuel consumption (BSFC), and brake thermal efficiency (BTE). Experiments were conducted at a late injection timing of 120° crank angle before top dead center (BTDC) and an engine speed of 2100 rpm, with CO₂ proportions ranging from 0% to 40% by volume. The results demonstrated that moderate CO₂ additions (up to 20%) improved BTE and reduced BSFC due to enhanced combustion control and lean-burn stability. However, higher CO₂ proportions (>20%) led to significant reductions in brake torque and brake power, attributed to dilution effects and reduced calorific value. The findings suggest that controlled CO₂ inclusion in CNG can optimize combustion and emissions, offering a potential pathway for utilizing Malaysia’s undeveloped natural gas reserves.

Sorbent Regeneration via Radiofrequency-Assisted Dielectric Heating for Direct Air Capture of CO2

Sorbent Regeneration via Radiofrequency-Assisted Dielectric Heating for Direct Air Capture of CO₂

Simultaneous Capture of N2O and CO2 from a N2O/N2/CO2/O2 Mixture with a Ni(II)-Pyrazolecarboxylate Framework.

Nitrous oxide (N2O) is a potent greenhouse gas and a major contributor to ozone depletion. Its primary industrial emission source is tail gas from adipic acid production, which typically comprises a mixture of N2O, CO2, N2, and O2. Current technologies for the removal of N2O and CO2 from tail gas are energy-intensive and operationally complex. Herein, for the first time, simultaneous capture of N2O and CO2 from the quaternary mixture is achieved using a Ni(II)-pyrazolecarboxylate framework, BUT-167. This material demonstrated an exceptional adsorption capacity (135.8 cm3 cm-3 at 40 kPa) and a high packing density (790 mg cm-3) for N2O, outperforming reported sorbents. Moreover, BUT-167 also exhibits a remarkable CO2 adsorption capacity (101.5 cm3 cm-3 at 4 kPa), achieving simultaneously high selectivity values of 257.6 for CO2/N2 (4:96, v/v) and 135.7 for N2O/N2 (40/60). Importantly, BUT-167 exhibits robust and outstanding dual-gas removal performance across multiple adsorption-desorption breakthrough cycles under both dry and humid conditions. The strong affinity toward CO2 and N2O could be attributed to multiple hydrogen bonding interactions facilitated by its highly confined channel structure, as confirmed through single-crystal X-ray diffraction analysis.

Isolated and Paired Metal Sites in Zeolites using Solid-State Ion Exchange.

Isolated and paired extraframework transition metal cations in zeolites are emerging as top candidates for numerous applications not limited to selective methane oxidation to methanol, selective catalytic reduction of nitrogen oxides, propane dehydrogenation, propylene epoxidation, and direct air capture of carbon dioxide. Importantly, these well-defined heterogeneous catalysts offer parallels with molecular and metalloenzyme catalytic active sites. Aqueous-phase ion exchange (APIE) is the most common synthesis technique to obtain these catalysts. Solid-state ion exchange (SSIE) is an often-overlooked technique that offers synthetic advantages compared to APIE. Thus, recent advances in solid-state synthesis strategies merit contemporary contextualization. In this minireview we describe the basic principles, methods, mechanisms, challenges, and advances insolid-state ion exchange in the context ofwell-defined transition metal cationactive sites located in extraframework positions of the zeolite.

Isolated and Paired Metal Sites in Zeolites using Solid‐State Ion Exchange

Isolated and paired extraframework transition metal cations in zeolites are emerging as top candidates for numerous applications not limited to selective methane oxidation to methanol, selective catalytic reduction of nitrogen oxides, propane dehydrogenation, propylene epoxidation, and direct air capture of carbon dioxide. Importantly, these well‐defined heterogeneous catalysts offer parallels with molecular and metalloenzyme catalytic active sites. Aqueous‐phase ion exchange (APIE) is the most common synthesis technique to obtain these catalysts. Solid‐state ion exchange (SSIE) is an often‐overlooked technique that offers synthetic advantages compared to APIE. Thus, recent advances in solid‐state synthesis strategies merit contemporary contextualization. In this minireview we describe the basic principles, methods, mechanisms, challenges, and advances in solid‐state ion exchange in the context of well‐defined transition metal cation active sites located in extraframework positions of the zeolite.

Forestation in CMIP6: wide model spread in tree cover and land carbon uptake

Abstract Forestation is expected to play an significant role as a terrestrial carbon dioxide removal technology in low-emission scenarios by storing carbon in the biosphere, thereby changing the physical properties of the land surface. To represent land use change, including afforestation and reforestation (AR), Earth system models (ESM) that contribute to the Coupled Model Intercomparison Project Phase 6 (CMIP6) draw on common projected land use data from Integrated Assessment Models. The extent and spatial distribution of AR differ substantially between the CMIP6 models ranging from −197 to 363 Mha of tree cover change by 2100 in the low-emission scenario SSP1-2.6 that has the highest AR among all future scenarios. The variability in simulated tree cover distributions, in combination with different representations of the carbon cycle, causes a high uncertainty in future land carbon uptake. Here, we disentangle the input information used to represent AR by CMIP6 models and differences in the carbon uptake process to explain the variable simulated potential of carbon sequestration due to AR. We provide recommendations on how AR might be implemented more consistently in future model intercomparison studies, especially regarding more consistent tree cover input (e.g. aligning present-day tree cover, consistent transition between land use and land cover types), and carbon-cycle-related processes (e.g. nitrogen cycle and disturbances). Adoption of these recommendations would increase the relevance of ESMs in terms of providing more accurate estimates of future land carbon uptake through AR.

Comparative analysis of industrialization potentials of direct air capture technologies

This study deals with the question which direct air capture technologies currently have the biggest potential for reaching a gigaton scale of capture capacity. Technologies that were examined are alkaline gas washing, temperature-vacuum swing adsorption, electro-swing adsorption, and accelerated weathering carbon capture. A multi-criteria decision-making model (PROMETHEE II) and cost predictions based on learning by doing were used to determine which technology has the highest potential. The results show that electro-swing adsorption has the highest potential but comes with a lot of uncertainties that need to be cleared in the future, such as costs and supply for adsorbents. In addition, it was not tested under ambient conditions, and therefore, it is unclear how this technology will perform at atmospheric CO2 levels. Next best would be accelerated weathering carbon capture, which needs no fresh water and has lower energy demand compared to temperature-vacuum swing adsorption. A major disadvantage might be the land requirements and the high temperatures to regenerate the carbonates. Temperature-vacuum swing adsorption follows shortly after, mainly profiting from a great cost reduction potential from learning by doing and a comparably small land footprint. Alkaline gas washing showed the lowest potential, but through improving the process, it will also have the possibility to be applied at gigaton scale.

H2 and CO2 network strategies for the European energy system

Abstract Hydrogen and carbon dioxide transport can play an essential role in climate-neutral energy systems. Hydrogen networks serve regions with high energy demand, whereas emissions are transported away in carbon dioxide networks. For the synthesis of carbonaceous fuels, it is less clear which input should be transported: hydrogen to carbon point sources or carbon to low-cost hydrogen. Here we explore both networks’ potential synergies and competition in cost-optimal carbon-neutral European energy systems. In direct comparison, a hydrogen network is more cost effective than a carbon network, as it serves to transport hydrogen to demand and to point sources of carbon for utilization. However, in hybrid scenarios where both networks are present, the carbon network effectively complements the hydrogen network, promoting carbon capture from distributed biomass and reducing reliance on direct air capture. The layouts of the hydrogen and carbon dioxide networks are robust if the climate target is tightened to be net negative.

Motivations and challenges for carbon dioxide removal development: empirical evidence from market practitioners

Abstract Carbon dioxide removal (CDR) is critical in mitigating climate change. Currently, its deployment is largely driven by voluntary actions from private organizations rather than by policy mandates. In this formative phase of the CDR sector, the important role these organizations play is acknowledged, yet there are scarce empirical insights into their perspectives. This study explores the role of private companies in shaping the early CDR innovation ecosystem by conducting 79 interviews with senior practitioners (suppliers, purchasers / marketplaces, investors) actively involved in CDR markets. Examining their motivations, I find themes that range from personal upbringing and caring for the following generations, to being catalytic in the creation of a new industry. All motivations are grounded in the recognition of CDR as an important component of global climate change mitigation. Identified challenges stretch across the categories of technology, organizations, policy and regulation, ecosystem, finances, and the public eye. This presents a complex picture, as all actors seek to solve a multi-faceted, concurrent coordination and scaling problem while dealing with a challenging set of uncertainties. For suppliers, the main challenge is to coordinate with other actors while proving their technology and not losing track of their long-term strategies. Investors and purchasers currently struggle with formulating a case that is suitable for their organizations, in the absence of regulation. Theanalysis underscores the underexplored yet significant role of private organizations in CDR governance and market development, thus addressing a gap in the existing literature. Concluding, I offer directions for measures that support a timely, efficient, and responsible scale-up of CDR.

Frameworks to assess climate change responses - A systematic analysis to enhance frameworks for Carbon Dioxide Removal

Abstract Achieving ambitious climate targets, such as greenhouse gas neutrality, will require a diverse range of Carbon Dioxide Removal (CDR) measures on different scales and timeframes. The planning and implementation of these measures necessitate holistic assessment frameworks that transparently and consistently evaluate what is feasible and desirable in both the short and long term to achieve these targets. While the development and refinement of such frameworks is increasingly discussed in the context of CDR, a need for a systematic analysis of existing frameworks against prevailing requirements remains. This study addresses this gap by conducting a systematic literature review of assessment frameworks used for climate change responses, analyzing how they address what we identified as key requirements. By expanding the scope beyond CDR-specific assessment frameworks, we identify and derive valuable insights and approaches that can inform their refinement. Following a three-step approach, we first conducted a preceding scoping review to determine key requirements for holistic assessments. Second, a systematic literature review was conducted to identify a broad range of assessment frameworks for climate responses. Third, based on a qualitative content analysis we examined how these frameworks address the key requirements identified earlier. The results reveal that existing assessment frameworks often lack consistent and transparent conceptual and operational structure, leading to misinterpretations and misunderstandings. Policy-relevant aspects such as the integration of temporal dynamics and portfolio assessments, including the investigation of synergies and trade-offs, are rarely addressed, although promising approaches are emerging. Following the current discussion to adjust assessment frameworks for CDR, future research should incorporate both short- and long-term temporal dynamics while strengthening the inclusion of ethical and social science perspectives. By synthesizing existing approaches and identifying critical gaps, this review provides guidance towards more robust and transparent assessment frameworks, supporting well-informed decision-making in the context of CDR.

Removing atmospheric CO2 through mass scaleup of crops with enhanced root systems

Abstract The Intergovernmental Panel on Climate Change estimates that societies may need to remove 5–16 GtCO2 from the atmosphere annually to reach global net-zero CO2 emissions within this century. Yet there has been little analysis of how quickly carbon dioxide removal (CDR) strategies could scale to meet this expected need. We develop a new integrated modeling approach for assessing scalability that combines insights from the history of analogous technological revolutions with information about the efficacy and specific constraints of CDR strategies. We illustrate our approach with genetically enhanced crops that grow larger roots and, in turn, increase soil carbon. Unlike many CDR technologies whose deployment will be slowed by the need for novel and costly infrastructures, history suggests that crop innovations can scale rapidly in countries that admit them. Within 13 years of first deployment, diffusion of enhanced crops could peak and remove 0.9–1.2 GtCO2 yr–1—about 7 times larger than all CO2 offsets supplied today to the global voluntary offsets market. Upscaling depends on policy and politics, as they affect the total land area on which carbon-absorbing crops are allowed. Early scaling could allow crop engineering to play an outsized role in a portfolio of CDR strategies that, overall, scales to IPCC-like levels of carbon removal, even though carbon storage in soils is less permanent than geological storage.

Deep uncertainty in carbon dioxide removal portfolios

Abstract Deep uncertainty about the costs and resource limits of carbon dioxide removal (CDR) options challenges the design of robust portfolios. To address this, we here introduce the CDR sustainable portfolios with endogenous cost model, a mixed-integer linear optimization model for cost-optimal and time-dependent CDR portfolios including endogenous treatment of technology cost dynamics. We explore future uncertainty in three key dimensions: realisable mitigation potentials, cost dynamics, and resource constraints. Our results demonstrate that afforestation and reforestation, and soil carbon sequestration appear as robust options, deployed regardless of the removals required. Direct air carbon capture and storage emerges as the most deployed technology in 2100 at median value (6.7 GtCO2 yr−1), but with the widest range of possible outcomes (interquartile range from 4 to 8.7 GtCO2 yr−1) depending largely on future renewable energy capacity and annual geological storage injection rates. Bioenergy with CCS deployment remains severely constrained by available land, as the median falls from 1.8 to 0.3 GtCO2 yr−1 in land-constrained scenarios, but gains portfolio share when future energy availability is bounded. Our simulations also reveal that ocean alkalinisation could become a dominant solution in high removal scenarios. Evaluating the performance of portfolios beyond economic costs, we also provide a framework to explore trade-offs across different aspects relevant to planetary boundaries.

Formation mechanism of the (2 × 1) reconstruction of calcite (104)

Calcite has recently attracted extensive research interest in fields ranging from geoscience to carbon dioxide removal. Although much effort has been made to study the (2 × 1) reconstruction of the most stable (104) surface, the origin of this reconstruction remains unclear. Here, we carefully investigated the atomic and electronic structures of calcite (104) via density functional theory methods with van der Waals corrections. The results unambiguously show that the driving force for this reconstruction is the intrinsic demands of surface atoms to increase the coordination numbers. Upon reconstruction, calcite (104) forms four additional Ca‒O bonds per (2 × 1) unit cell. In addition, the phonon spectra indicate that both the unreconstructed and reconstructed surfaces are dynamically stable. Finally, by applying the climbing image nudged elastic band method, an energy barrier is predicted during the reconstruction. This work provides a full picture of the formation of calcite (104)-(2 × 1) reconstruction and can greatly advance the understanding of surface science for calcite.

CO2–switchable surfactant with amino–terminated polypropylene oxide

AbstractCO2–responsive surfactants are one of the research hotspots in colloid chemistry, and identifying suitable CO2–responsive surfactants is of significant importance. This study investigates the CO2–responsive properties of the amino–terminated polyether ZFL–1001 and its potential as a switchable surfactant. The research demonstrates that ZFL–1001 exhibits reversible changes in conductivity, surface tension, viscosity, and emulsion stability when exposed to alternating CO2 and N2 conditions. The protonation of secondary amine groups triggered by the introduction of CO2 enhances hydrophilicity, leading to increased conductivity, reduced surface tension, and the formation of stable micelle networks. These networks significantly influence viscosity and emulsion behavior. Conversely, the removal of CO2 reverses these effects, returning the system to its initial state. ZFL–1001 also facilitates reversible phase transitions in crude oil emulsions, offering a novel method for emulsion regulation in oil reservoirs. These findings highlight the potential of ZFL–1001 to serve as an environmentally friendly and efficient CO2–switchable surfactant for applications in smart materials, crude oil extraction, and emulsion control systems.

Peak Shaving with Solar Radiation Modification Would Shorten Global Temperature Overshoot

Abstract Projected rates of emissions reductions are unlikely to keep global temperatures from crossing the Paris Agreement temperature targets. Large-scale carbon dioxide removal (CDR) could help recover a target temperature after it has been exceeded, producing an overshoot scenario. Solar radiation modification (SRM) is the idea to cool the planet by increasing the reflection of incoming solar radiation. SRM could be used in an overshoot scenario for ‘peak shaving’, where SRM is deployed to maintain a temperature target during the overshoot. Here, we quantify the effect of SRM peak shaving on the duration of the overshoot using an adapted extension of the SSP2-4.5 scenario and an ensemble of variants of the FaIR simple climate model. We find a substantial reduction in overshoot duration, which ranges from approximately 5% for multi-decade overshoots up to approximately 20% for multi-century overshoots. The shortening is predominantly driven by the ocean response to peak shaving. Peak shaving results in lower ocean temperatures relative to the overshoot scenario, inducing a stronger surface temperature response to decreasing and negative emissions, driving overshoot shortening. Thus, SRM, when deployed as a complement to emissions reductions and CDR, could end overshoot decades earlier than otherwise.

ESG and the Greenhouse Gas Neutralization Plan in the State of Espírito Santo: an Analysis of Project Hierarchization

Objective: to identify the degree of convergence between the order of priorities for the execution of projects included in the Espírito Santo Greenhouse Gas Decarbonization and Neutralization Plan and the Social, Environmental and Governance criteria. Methodology: to present the aforementioned classification, the AHP model was used because it is the best known and most widely used multicriteria model. The 22 projects in the plan, which are subdivided into four thematic areas (Energy & Industries, Waste, Transportation and Agriculture, Forestry and Land Use), were classified within their respective thematic areas according to the economic, regulatory, technological and social criteria. Originality/relevance: to use the concepts of sustainable finance and Environmental, Social and Governance together with the Hierarchical Process Analysis methodology to prioritize the projects included in the Espírito Santo Government's Greenhouse Gas Mitigation Plan. Results: low-carbon industry, urban mobility, CO2 removal from the atmosphere and energy efficiency projects were predominant within their thematic areas, which shows that the plan is in line with the environmental improvement initiative, but that the effects of its implementation need to take into account economic and social aspects. Contributions: the work contributes by presenting the hierarchical organization of projects based on scientific and theoretical criteria that can facilitate the process of choosing the priority and most impactful projects for reducing air pollution more efficiently and with greater impact in the medium and long term.

Effects of ocean alkalinity enhancement on plankton in the Equatorial Pacific

Ocean alkalinity enhancement is a potential strategy for gigatonne-scale atmospheric carbon dioxide removal. It uses alkaline substances to convert seawater carbon dioxide into (bi)carbonate, enabling uptake of additional carbon dioxide from the atmosphere. A critical knowledge gap is how ocean alkalinity enhancement could influence marine plankton communities. Here we conducted 19 ship-based experiments in the Equatorial Pacific, examining three prevalent alkaline substances (sodium hydroxide, olivine, and steel slag) and their effects on natural phytoplankton populations under realistic and moderate alkalinity enhancements (16–29 μmol kg−1). Results demonstrate that sodium hydroxide had a negligible effect on phytoplankton while providing predictable alkalinity. Conversely, olivine disrupted plankton, especially cyanobacteria, heterotrophic bacteria, and picoeukaryotes while only providing 0.06 mmol alkalinity g−1 olivine. Steel slag moderately changed phytoplankton communities and fertilized growth while delivering 8 mmol alkalinity g−1 slag. Our study helps to determine which alkaline substance could be suitable for application in the Equatorial Pacific.