CO2 Removal Research Articles

Removal of Carbon Dioxide and Hydrogen Sulfide from Natural Gas Using a Hybrid Solvent of Monoethanolamine and N-Methyl 2-Pyrrolidone.

The main goal of traditional methods for sweetening natural gas (NG) is to remove hydrogen sulfide (H2S) and significantly lower carbon dioxide (CO2). However, when NG processes are integrated into the carbon capture and storage (CCS) framework, there is potential for synergy between these two technologies. A steady-state model utilizing a hybrid solvent consisting of N-methyl-2-pyrrolidone (NMP) and monoethanolamine (MEA) has been developed to successfully anticipate the CO2 and H2S capture process from NG. The model was tested against important variables affecting process performance. This article specifically explores the impact of operational parameters such as lean amine temperature, absorber pressure, and amine flow rate on the concentrations of CO2 and H2S in the sweet gas and reboiler duty. The result shows that hybrid solvents (MEA + NMP) perform better in removing acid gases and reducing reboiler duty than conventional chemical solvent MEA. The primary purpose is to meet product requirements while consuming the least energy possible, which is in line with any process plant's efficiency goals.

Measuring the Influence of CO2 and Water Vapor on the Dynamics in Polyethylenimine To Understand the Direct Air Capture of CO2 from the Environment

Measuring the Influence of CO₂ and Water Vapor on the Dynamics in Polyethylenimine To Understand the Direct Air Capture of CO₂ from the Environment

Author Correction: Current national proposals are off track to meet carbon dioxide removal needs

Author Correction: Current national proposals are off track to meet carbon dioxide removal needs

Assessment of Potential and Techno-Economic Performance of Solid Sorbent Direct Air Capture with CO2 Storage in Europe.

Direct air capture with CO2 storage (DACCS) is among the carbon dioxide removal (CDR) options, with the largest gap between current deployment and needed upscaling. Here, we present a geospatial analysis of the techno-economic performance of large-scale DACCS deployment in Europe using two performance indicators: CDR costs and potential. Different low-temperature heat DACCS configurations are considered, i.e., coupled to the national power grid, using waste heat and powered by curtailed electricity. Our findings reveal that the CDR potential and costs of DACCS systems are mainly driven by (i) the availability of energy sources, (ii) the location-specific climate conditions, (iii) the price and GHG intensity of electricity, and (iv) the CO2 transport distance to the nearest CO2 storage location. The results further highlight the following key findings: (i) the limited availability of waste heat, with only Sweden potentially compensating nearly 10% of national emissions through CDR, and (ii) the need for considering transport and storage of CO2 in a comprehensive techno-economic assessment of DACCS. Finally, our geospatial analysis reveals substantial differences between regions due to location-specific conditions, i.e., useful information elements and consistent insights that will contribute to assessment and feasibility studies toward effective DACCS implementation.

Magnetic nanoparticle‐induced sorbent regeneration for direct air capture

AbstractDirect air capture (DAC) is a promising technology for decarbonization through the removal of CO2 from the atmosphere. In many DAC processes, the regeneration energy used to restore the capture capacity of sorbents accounts for a significant fraction of the energy required by the whole process. Here we report an effective and scalable sorbent regeneration method for liquid DAC solvents based on magnetic nanoparticles (MNPs) heating with AC magnetic fields. MNPs can be directly heated to provide uniform and rapid volumetric heating, as we demonstrate by promoting the release of captured CO2 from an aqueous solution of potassium sarcosinate. Our results showed that 90% of the solvent can be regenerated within 7.5 min of heating through proposed technique. The MNPs and solvent are found to be stable during the regeneration process and the MNPs showed long‐term stability in the CO2‐saturated solvent. Cyclic experiments showed that the nanoparticles can be reused for multiple cycles without performance deterioration. The process is operated in a noncontact mode through electromagnetic waves, making it an adoptable approach for existing carbon capture systems. The MNPs heating provides an effective regeneration strategy for liquid solvents used in carbon capture processes, in particular for DAC.

High-pressure gas adsorption on activated carbons from pomegranate peels biochar: A promising approach for biogas purification

Biogas is a promising bioenergy source and its composition is based on methane (55–70% vol) but contains impurities such as CO2 (30–45% vol). Various technologies are available to purify biogas and produce biomethane that can be injected into the existing natural gas network. In this work, the effectiveness of activated carbons (ACs) obtained by chemical activation from industrial food waste for CO2 removal by adsorption was investigated. ACs with better textural development were obtained at higher activation temperature and dose of the activating agent (BET surface area and total pore volume up to 1446 m2/g and 0.589 cm3/g, respectively). The adsorbents exhibited a microporous character (micropore volume up to 0.472 cm3/g). The ACs were tested in high-pressure gas adsorption tests (CO2, CH4 and H2 up to 3, 8 and 4 MPa, respectively). All of them showed high, medium and low selectivity against for the adsorption of CO2, CH4 and H2, respectively, although with different efficiencies. The adsorbent obtained under the most aggressive activation conditions (900 °C, 1:1 wt ratio) showed the greatest textural development and the maximum adsorption capacity for CO2 (at 3 MPa) and CH4 (at 8 MPa) (495 mgCO2/g and 126 mgCH4/g). Despite the porosity of the materials, all showed a very low affinity for hydrogen adsorption at 4 MPa (up to 3.71 mgH2/g). Taking the above into account, these activated carbons could be used in the purification of biogas and in the separation of CO2/H2 mixtures to produce pure H2 and obtain hydrogen-free CO2 for capture and storage.

Deployment of carbon removal technologies could reduce the rapid and potentially disruptive pace of decarbonization in South Africa's climate ambitions

As a developing country, South Africa faces the risk of having to undertake disruptive actions to meet its internationally pledged emission reduction targets. It has become necessary to find alternative measures for South Africa to meet its climate targets without such a disruptive and aggressive transformation of its energy sector. To truly reach net-zero CO2 emissions, South Africa must ensure that residual emissions from its recalcitrant sectors are equally compensated by carbon dioxide removal (CDR). Given the potential for CDR technologies to delay the need for rapid emissions cuts, we leverage this characteristic to explore their role in helping South Africa achieve its climate targets on time, but through a less disruptive and overly aggressive pace of energy system decarbonization. Using an integrated assessment model, we show that while reaching its emission reduction targets, the presence of novel CDR (nCDR) approaches could significantly reduce South Africa's mitigation costs to $155-240/tCO2 instead of $190–590/tCO2 by 2050 in the absence of nCDR. Furthermore, the availability of nCDR may allow for a more gradual transition towards renewable and nuclear power generation compared to scenarios without nCDR. Importantly, we reveal that nCDR could help avoid asset stranding of up to 4–6 GW and $15–25 billion in associated costs between 2016 and 2050. However, this comes at the cost of higher residual greenhouse gas emissions due to the continued reliance on fossil fuels under nCDR availability. Overall, South Africa's priority must remain on decarbonization, especially in sectors where fuel switching and energy efficiency are feasible. Nonetheless, the complementary role of nCDR must not be underestimated, and South Africa should begin investing in these emerging technologies to support its ambitious climate goals.

Enhanced weathering for CO2 removal using carbonate-rich crushed returned concrete; a pilot study from SE Ireland

A 1.21-ha pilot study in SE Ireland investigated crushed returned concrete (CRC), applied at a rate of 7.5 tonnes/ha as a soil amendment for carbon dioxide removal (CDR) by enhanced weathering (EW) over a 10-month period. Most, but not all amended sites showed enhanced concentrations of calcium and bicarbonate in shallow soil waters compared with adjacent controls. Soil pH increased rapidly by 0.3 to >1 pH units (5.75 ± 0.25 (n = 8) in controls to 6.5 ± 0.7 (n = 24) at amended sites), with greatest increases in soils that had lowest initial pH (<6.0). Aside from one site where concentrations continued to increase, calcium (1.76–0.39 mM Ca) and bicarbonate (4.06–0.64 mM) values in soil waters declined gradually over the course of the study, consistent with rapid initial dissolution and progressive exhaustion of the fine-grained fraction, as indicated by a shrinking-core model. Most sites exhibited high bicarbonate to cation ratios (1.2–2.2) consistent with CRC dissolution by soil carbonic acid, although two sites adjacent to the field-boundary river that floods periodically showed evidence for strong acid (nitric) dissolution. Enhanced bicarbonate levels in soil waters at amended sites compared with controls, coupled with a downward-flush hydrological model driven by annual effective rainfall to calculate bicarbonate export and a simple stoichiometric correction for nitric acid weathering, indicate gross CDR rates in the range zero to 0.52 tonnes CO2/ha (69 kg CO2/tonne), limited by bicarbonate export rather than weathering rates. Further optimisation of the CDR efficiency of this material should be possible using strategies to avoid or pre-neutralise non-carbonic soil acids and by taking account of sub-aerial carbonation at the post-crushing, pre-amendment stage that arises when the material is crushed in preparation for EW applications. A simplified life-cycle analysis indicates that a discount of about 11% should be applied to account for CO2 emissions from crushing, transport and spreading operations.

Evaluation of carbon capture technologies in the oil and gas industry using a socio-technical systems perspective-based decision support system under interval type-2 trapezoidal fuzzy set

Concerns in relation to consequences of global warming and climate change have activated worldwide attempts for mitigating the concentration of carbon dioxide (CO2) produced by the industrial sector. Decarbonizing the oil and gas refining (OGR) industries is a challenging problem for policy-makers owing to its potential to prevent economic, environmental, and health risks. In this regard, CO2 capture, utilization, and storage (CCUS) technologies are the most encouraging options to decarbonize. The technologies related to the part of CO2 capture can play a vital role in solving the mentioned problem. Various technologies have been employed for CO2 capture, and choosing the appropriate technology is a complex multi-criteria decision-making (MCDM) issue. This work develops a novel and robust decision support system (DSS). The DSS integrates MCDM techniques of the Delphi and Entropy integration method (DAEIM) and complex proportional assessment of alternatives (COPRAS) method with the interval type-2 trapezoidal fuzzy (IT2TF) environment. The proposed DSS is used to evaluate, prioritize, and choose technologies for CO2 capture. A hybrid criteria system, which involves elements of socio-technical systems perspective has been used for evaluating the candidate technologies. For implementing the DSS of this work, five capture technologies of post-combustion (A_cc1), pre-combustion (A_cc2), oxy-fuel combustion (A_cc3), direct air capture (A_cc4), and indirect air capture (A_cc5) have been chosen for evaluation. The final value of each technology is A_cc1 (0. 2907), A_cc2 (0.2602), A_cc3 (0.1005), A_cc4 (0.2304), and A_cc5 (0.1181) and the preferences of the technologies are A_cc1> A_cc2> A_cc4> A_cc5> A_cc3. The evaluation findings reveal that post-combustion technology with the value of 0.2907 is the most suitable scenario for the capture of CO2 emissions from Iran's OGR systems. The computation results demonstrate that the suggested DSS is feasible and applicable and give reliable and robust findings for acquiring the optimal CO2 capture technology.

The role of negative emissions technologies in the UK’s net-zero strategy

The role of negative emissions technologies in the UK’s net-zero strategy

Incidence of heparin resistance and heparin failure in patients receiving extracorporeal membrane oxygenation: an exploratory retrospective analysis

BackgroundUnfractionated heparin (UFH) is used in most centers for extracorporeal membrane oxygenation (ECMO) anticoagulation. When standard doses do not achieve desired target values, heparin resistance is reported, most commonly defined as doses of UFH > 35 000 IU/d. ObjectivesTo study the incidence of heparin resistance and its association with thromboembolic complications in patients requiring ECMO support. MethodsIn this observational cohort study, we included adults who received venovenous, venoarterial ECMO and extracorporeal carbon dioxide removal between January 2010 and May 2022. Main risk factor was heparin resistance (UFH, > 35 000 IU/d or > 20 IU/kg/h); the outcome was thromboembolism. Multivariable Poisson regression was used to estimate the effects of heparin resistance, adjusted for several clinical variables on the thromboembolism rate per 100 ECMO patient-days. ResultsOf the 197 patients included, 33 (16.8%) required UFH > 35 000 IU/d and 14 (7.1%) required UFH > 20 IU/kg/h. Thromboembolic complications occurred at a rate of 5.89/100 ECMO d. Heparin resistance was not associated with thromboembolic events (incidence rate ratio [IRR], 0.93; 95% CI, 0.14-5.82), whereas COVID-19 (IRR, 2.33; 95% CI, 1.4-3.96; P < .001) and ECMO type (venoarterial ECMO: IRR, 2.29; 95% CI, 1.34-3.92; P = .002; extracorporeal carbon dioxide removal: IRR, 2.89; 95% CI, 1.46-5.59; P = .002; reference venovenous ECMO) were significantly associated with the risk of thromboembolic events. ConclusionA significant proportion of patients fulfilled the common definition of heparin resistance. However, this did not influence the occurrence of thromboembolic events.

CO2 capture and H2 production performance of calcium-based sorbent doped with iron and cerium during calcium looping cycle

As the interest in environmentally-friendly energy processes increases, many studies have been focused on producing hydrogen as an alternative energy carrier via catalytic reaction processes. Sorption enhanced water gas shift (SEWGS) that combines WGS and in situ CO2 removal is a promising technology for high-purity H2 production and CO2 capture. In this study, Fe/Ce-modified CaO-Ca12Al14O33 bi-functional porous nanotubes were synthesized in one step by template method and applied for H2 production from SEWGS process. The unique porous nanotube structure fully exposes the catalytic active sites and facilitates the gas-solid transport, resulting in the excellent H2 production and CO2 capture performance in SEWGS/regeneration cycles. The introduction of Ce enhances the basicity of the nanotube material, thereby increasing the affinity for CO2. The interaction of Fe-Ce improves the redox capability of Fe2+ and Fe3+, which is beneficial to the conversion of CO. In addition, the formed Ca2Fe2O5 and Ca2CeO4 both increase the concentration of oxygen vacancies, further enhancing the SEWGS reactivity of the material. The optimal molar ratio of Fe/Ce/Al/Ca is 10/3/10/100, and the CO conversion, H2 concentration, CO2 capture capacity of the Fe/Ce-modified bi-functional material were 76.9 %, 70.1 % and 83.2 % after 20 cycles. The effect of Fe/Ce doping on CaO-based materials was investigated at the molecular level using density functional theory (DFT). The results demonstrate that the addition of Ce can effectively maintain the stable structure of Fe-CaO-based materials. The modification of Fe/Ce is expected to promote efficient H2 generation from CaO-based materials through the SEWGS process.

Fast reduction of Atlantic SST threatens Europe-wide gross primary productivity under positive and negative CO2 emissions

Climate change mitigation through negative CO2 emissions has been recognized as a crucial strategy to combat global warming. However, its potential effects on terrestrial productivity and agricultural activities remain uncertain. In this study, we utilized large ensemble simulations with an Earth system model of full complexity to investigate the response of Gross Primary Production (GPP) to CO2 forcings. Our findings reveal a significant asymmetry in the GPP response to CO2 ramp-up and symmetric ramp-down model experiments, especially in Europe, suggesting that GPP declines rapidly as CO2 levels decrease. Remarkably, during the CO2 removal period, the North Atlantic Sea surface temperature experienced cooling due to a delayed recovery of the Atlantic Meridional Overturning Circulation (AMOC). This cooling led to precipitation and soil moisture deficits, resulting in a rapid reduction in GPP. This asymmetry in GPP response holds consistent across multi-model simulations. These results underscore the potential implications of delayed recovery in ocean circulation, which could unexpectedly accelerate terrestrial GPP reduction. These insights are crucial for policymakers, aiding them in projecting agricultural activity and formulating targeted GPP control policies specific to the European region.

Assessing the future impact of 12 direct air capture technologies

Direct Air Capture (DAC) is regarded as an effective method to decrease the concentration of CO2 in the atmosphere and thus alleviate the greenhouse effect. This article conducts a comparative analysis of the CO2 emissions of 12 state-of-the-art DAC technologies. The evaluations consider regional (EU, USA, and China) and temporal (years 2023, 2030, and 2050) energy supply variations. It is found that the CO2 emissions generally decrease over time for all the different regions considered. The best CO2 emission performance is found in Europe, followed by the United States and China. The evaluation also finds that currently a substantial number of DAC technologies could not achieve net-negative emission, especially for China. In 2050, most of the DAC technologies are found to perform significantly better in terms of their negative emission performance. We also found that the utilization of fossil fuels, especially coal, needed to operate the DAC process, substantially hinders its ability to achieve net-negative emission. Electrochemical-based technologies are found to outperform others in all scenarios, especially when powered with renewable electricity. The DAC technologies relying on steam-based sorbent regeneration can greatly reduce their CO2 emission when low-carbon energy is used for steam generation. Finally, in all the different scenarios, the DAC technologies incorporating high-temperature calcination regenerations exhibit the worst performance due to the lack of low-emission energies for generating fired heat.

Direct air capture using halophilic Cyanobacterium aponinum PCC10605 under illumination of light-emitting diodes in marine environment

Excessive carbon dioxide (CO2) emissions have become a disaster, calling for an effective way to reduce atmospheric CO2 content. Cyanobacteria, also known as blue-green algae, are potent natural carbon sinks with efficient photosynthesis and produce valuable compounds. Herein, we demonstrated the excellent properties of Cyanobacterium aponinum PCC10605 (Capo) in maintaining growth and protein accumulation under salt stress and red light-emitting diodes (LEDs) illumination at 660 nm under direct air capture (DAC) condition. Multi-factor optimization from response surface methodology revealed the best condition of 25 °C, 70 μE light intensity, 17 g/L salt, 16 to 8 h for light to dark period, and 6 mM nitrogen to yield the highest combination of 1.49 g/L biomass and 19.1 % C-phycocyanin (C-PC) content. Capo also thrived in 50 % seawater from Penghu, Taiwan where its DAC capacity was confirmed using an elemental analyzer, showing that 48.2 % carbon content was equivalent to specific capture ratio of 1.75 g-CO2/g-DCW and volumetric efficiency of 2.62 g-CO2/L, respectively. Finally, scaling up cultivation in 2-liter photobioreactor was successfully carried out under red LED illumination. The potential of Capo in reducing atmospheric CO2 level represents an advancement in sustainable biotechnology for climate change mitigation.

Prudent carbon dioxide removal strategies hedge against high climate sensitivity

Uncertainty in climate sensitivity has been shown to warrant early-on mitigation to limit global warming while anticipating future carbon dioxide removal creates mitigation deterrence. Here we use an integrated assessment model to quantify the impacts of under- or overestimating the cost and availability (feasibility) of carbon dioxide removal when limiting warming to 1.5 °C by 2100 under uncertain climate sensitivity. If climate sensitivity uncertainty is disregarded, initial assumptions on the feasibility have only minor effects on mitigation costs. However, the climate sensitivity risk compounds the impact of prior assumptions. Wrong assumptions on carbon dioxide removal feasibility can lead to lower costs under extreme realizations of climate sensitivity. Moreover, scenarios considering uncertainty in climate sensitivity rely less on carbon dioxide removal. A prudential strategy assuming low feasibility for carbon dioxide removal reduces the “double whammy” risk of overestimating carbon dioxide removal in combination with a realization of high climate sensitivity.

Public perception of carbon dioxide removal in three Asian regions

Public perception of carbon dioxide removal in three Asian regions

Biochar in the UK Print News Media: Issue Frames and Their Implications for Opening up Debate About Land-based Greenhouse Gas Removal

ABSTRACT Biochar is a land-based greenhouse gas removal technology with potential to address the climate crisis. This article examines societal debate and discussion around biochar as represented in the UK print news media and reflects on its implications for the democratic governance of novel technologies. Using an “issue frame” analysis approach, the following frames are identified – Innovation, Economics, Security, Governance and Accountability, Risk, Justice, Substitution, Salvation and Tradition – with some more prominent than others. Economics and Innovation frames are particularly pronounced, together with the argument for market-based forms of governance, while Risk and Justice frames are weakly developed. The findings show that some frames and their associated actors dominate debate, while others are absent or side-lined. This might hinder opening up the debate to a wider group of stakeholders and publics and alternative framings, thus constraining effective governance of biochar.

Simultaneous achievement of energy recovery and carbon sequestration through municipal solid waste management: A review

Effective municipal solid waste (MSW) management is a crucial component for sustainable cities, as inefficient waste disposal contributes to the release of about a billion tons of CO2-eq in greenhouse gases (GHG) annually. With escalating global waste generation, there is an untapped opportunity to integrate carbon dioxide removal (CDR) technologies into existing MSW management processes. This review explores current research on utilizing MSW for CDR, emphasizing its potential for both energy generation and carbon sequestration. The investigation covers three waste management practices: landfilling, waste-to-energy (WtE), and biochar production, revealing two paths for carbon sequestration. First, MSW serves as a feedstock in bioenergy with carbon capture and storage (BECCS), acting as a carbon-neutral resource that avoids fossil fuel and energy crop use, reducing GHG emissions and generating value through energy production. Second, direct storage of organic MSW and its derivatives, like biochar, in various carbon sinks allows for extended sequestration, offering a comprehensive approach to address the challenges of waste management and climate change mitigation. Moreover, this review advocates for an extended exploration into several subjects including in-depth analysis of waste, research on MSW-derived biochar recalcitrance across different carbon sinks, and understanding the symbiotic connections with GHG-emitting sectors like agriculture and energy. Finally, this review emphasizes the necessity of conducting life-cycle assessment studies to fully discern the benefits and assess the impacts of any future endeavors exploring the role of MSW in carbon sequestration.

Regional potential of coastal ocean alkalinization with olivine within 100 years

The spreading of crushed olivine-rich rocks in coastal seas to accelerate weathering reactions sequesters atmospheric CO2 and reduces atmospheric CO2 concentrations. Their weathering rates depend on different factors, including temperature and the reaction surface area. Therefore, this study investigates the variations in olivine-based enhanced weathering rates across 13 regional coasts worldwide. In addition, it assesses the CO2 sequestration within 100 years and evaluates the maximum net-sequestration potential based on varying environmental conditions. Simulations were conducted using the geochemical thermodynamic equilibrium modeling software PHREEQC. A sensitivity analysis was performed, exploring various combinations of influencing parameters, including grain size, seawater temperature, and chemistry. The findings reveal significant variation in CO2 sequestration, ranging from 0.13 to 0.94 metric tons (t) of CO2 per ton of distributed olivine-rich rocks over 100 years. Warmer coastal regions exhibit higher CO2 sequestration capacities than temperate regions, with a difference of 0.4 t CO2/t olivine distributed. Sensitivity analysis shows that smaller grain sizes (10 µm) exhibit higher net CO2 sequestration rates (0.87 t/t) in olivine-based enhanced weathering across all conditions, attributed to their larger reactive surface area. However, in warmer seawater temperatures, olivine with slightly larger grain sizes (50 and 100 µm) displays still larger net CO2 sequestration rates (0.97 and 0.92 t/t), optimizing the efficiency of CO2 sequestration while reducing grinding energy requirements. While relying on a simplified sensitivity analysis that does not capture the full complexity of real-world environmental dynamics, this study contributes to understanding the variability and optimization of enhanced weathering for CO2 sequestration, supporting its potential as a sustainable CO2 removal strategy.