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Biochar is widely regarded as a recalcitrant carbon pool. However, the impact of freeze-thaw cycle events on its storage capacity, particularly on the release of dissolved black carbon (DBC), has remained poorly investigated. This study investigated the release behavior of DBC from biochar pyrolyzed at 300-700 °C during freeze-thaw cycles and their retention capacity in soil. Freeze-thaw cycles dramatically promoted DBC release (33.08-230.74 mg C L -1 ), exhibiting an order of magnitude higher than those without freeze-thaw process. The release kinetics of freeze-thaw-induced DBC varied depending on the pyrolysis temperature of biochar due to the different disintegration mechanisms. Interestingly, the retention capacity of freeze-thaw-induced DBC in soil showed a reduction ranging from 7.7 to 29.5% compared to DBC without the freeze-thaw process. This reduction can be attributed to numerous hydrophilic low-molecular-weight compounds (16.97-75.31%) in freeze-thaw-induced DBC, as evidenced by the results of size exclusion chromatography, fluorescence excitation/emission matrix, Fourier transform infrared spectroscopy, and nuclear magnetic resonance. These compounds tend to concentrate in the aqueous phase rather than being retained in the soil, potentially exacerbating the outflow of dissolved organic carbon. These findings clarify the release behavior of DBC during freeze-thaw cycles and reveal their contribution to the attenuation of carbon pools in cold regions.

Enhanced weathering of (ultra)mafic rocks has been proposed as a promising approach to sequester atmospheric CO 2 and mitigate climate change. However, these silicate rocks contain varying amounts of trace metals, which are essential cofactors of metallaenzymes in methanogens. We found that weathering of crushed peridotite and basalt significantly promoted the growth and methanogenesis of a model methanogen─ Methanosarcina acetivorans C2A under the condition of excess substrate. The released trace metals from peridotite and basalt, especially Fe, Ni, and Co, accounted for the promotion effect. Observation at different spatial scales showed a close association between the rocks and cells. Proteomic analysis revealed that rock amendment significantly enhanced the expression of core metalloenzymes in the methylotrophic methanogenesis pathway. Our study uncovers a previously unrecognized but important negative effect of enhanced rock weathering on methane production, which may counteract the carbon sequestration effort.

Superinsulation aerogels are characterized by low tensile strength and brittleness due to their high porosity. To address these limitations, multiscale architectural design inspired by nacre can be employed. This materials design approach offers a promising strategy for enhancing the mechanical strength of aerogel thermal insulation. In this study, we present nacre-inspired multilayer cellulose-silica aerogel configurations. The cellulose "brick" network imparts structural strength to effectively redistribute energy, while the nanoporous "mortar" silica blocks heat transfer, maintaining insulation and fire retardance. The multilayer composites, with a layering configuration of five cellulose layers with four silica layers (5 + 4) and a cellulose layer thickness of 1.42 mm, exhibit a thermal conductivity of 31.3 mW/(m·K), a flexural modulus of 505 MPa, and an impact strength of 7.33 kJ/m 2 . The hydrophobic composite shows a water contact angle of 127°, enhanced soundproofing with a 27% noise reduction, and a carbon footprint of 0.49 kgCO 2 eq/kg. The multilayer cellulose-silica aerogel design provides a robust, eco-friendly thermal insulation solution for green building applications.

Urban blue-green infrastructure (BGI) offers a multitude of ecological advantages to residents, thereby playing a pivotal role in fortifying urban resilience and fostering the development of climate-resilient cities. Nonetheless, current research falls short of a comprehensive analysis of BGI's overall potential for carbon reduction and its indirect carbon reduction impact. To fill this research gap, we utilized the integrated valuation of ecosystem services and trade-offs model and remote sensing estimation algorithm to quantify the direct carbon sequestration and resultant indirect carbon reduction facilitated by the BGI within the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) (China). To identify the regions that made noteworthy contributions to carbon offsets and outliers, spatial autocorrelation analysis was also employed. The findings of this study reveal that in 2019, the BGI within the study area contributed an overall carbon offset of 1.5 × 10 8 t·C/yr, of which 3.5 × 10 7 and 11.0 × 10 7 t·C/yr were the result of direct carbon sequestration and indirect carbon reduction, respectively. The GBA's total CO 2 emissions were 1.1 × 10 8 t in 2019. While the direct carbon sequestration offset 32.0% of carbon emissions, the indirect carbon reduction mitigated 49.9% of potential carbon emissions. These results highlight the critical importance of evaluating BGI's indirect contribution to carbon reduction. The findings of this study provide a valuable reference for shaping management policies that prioritize the protection and restoration of specific areas, thereby facilitating the harmonized development of carbon offset capabilities within urban agglomerations.

Soil organic carbon (SOC) plays a vital role in global carbon cycling and sequestration, underpinning the need for a comprehensive understanding of its distribution and controls. This study explores the importance of various covariates on SOC spatial distribution at both local (up to 1.25 km) and continental (USA) scales using a deep learning approach. Our findings highlight the significant role of terrain attributes in predicting SOC concentration distribution with terrain, contributing approximately one-third of the overall prediction at the local scale. At the continental scale, climate is only 1.2 times more important than terrain in predicting SOC distribution, whereas at the local scale, the structural pattern of terrain is 14 and 2 times more important than climate and vegetation, respectively. We underscore that terrain attributes, while being integral to the SOC distribution at all scales, are stronger predictors at the local scale with explicit spatial arrangement information. While this observational study does not assess causal mechanisms, our analysis nonetheless presents a nuanced perspective about SOC spatial distribution, which suggests disparate predictors of SOC at local and continental scales. The insights gained from this study have implications for improved SOC mapping, decision support tools, and land management strategies, aiding in the development of effective carbon sequestration initiatives and enhancing climate mitigation efforts.

The preservation of soil organic carbon (OC) is an effective way to decelerate the emission of CO 2 emission. However, the coregulation of pore structure and mineral composition in OC stabilization remains elusive. We employed the in situ nondestructive oxidation of OC by low-temperature ashing (LTA) combined with near edge X-ray absorption fine structure (NEXAFS), high-resolution microtomography (μ-CT), field emission electron probe microanalysis (FE-EPMA) with C-free embedding, and novel Cosine similarity measurement to investigate the C retention in different aggregate fractions of contrasting soils. Pore structure and minerals contributed equally ( ca . 50%) to OC accumulation in macroaggregates, while chemical protection played a leading role in C retention with 53.4%-59.2% of residual C associated with minerals in microaggregates. Phyllosilicates were discovered to be more prominent than Fe (hydr)oxides in C stabilization. The proportion of phyllosilicates-associated C (52.0%-61.9%) was higher than that bound with Fe (hydr)oxides (45.6%-55.3%) in all aggregate fractions tested. This study disentangled quantitatively for the first time a trade-off between physical and chemical protection of OC varying with aggregate size and the different contributions of minerals to OC preservation. Incorporating pore structure and mineral composition into C modeling would optimize the C models and improve the soil C content prediction.

Manure application is a global approach for enhancing soil organic carbon (SOC) sequestration. However, the response of SOC decomposition in manure-applied soil to abrupt warming, often occurring during diurnal temperature fluctuations, remains poorly understood. We examined the effects of long-term (23 years) continuous application of manure on SOC chemical composition, soil respiration, and microbial communities under temperature shifts (15 vs 25 °C) in the presence of plant residues. Compared to soil without fertilizer, manure application reduced SOC recalcitrance indexes (i.e., aliphaticity and aromaticity) by 17.45 and 21.77%, and also reduced temperature sensitivity ( Q 10 ) of native SOC decomposition, plant residue decomposition, and priming effect by 12.98, 15.98, and 52.83%, respectively. The relative abundances of warm-stimulated chemoheterotrophic bacteria and fungi were lower in the manure-applied soil, whereas those of chemoautotrophic Thaumarchaeota were higher. In addition, the microbial network of the manure-applied soil was more interconnected, with more negative connections with the warm-stimulated taxa than soils without fertilizer or with chemical fertilizer applied. In conclusion, our study demonstrated that the reduced loss of SOC to abrupt warming by manure application arises from C chemistry modification, less warm-stimulated microorganisms, a more complex microbial community, and the higher CO 2 intercepting capability by Thaumarchaeota.

Contemporary resource management is doubly burdened by high rates of organic material disposal in landfills, generating potent greenhouse gases (GHG), and globally degraded soils, which threaten future food security. Expansion of composting can provide a resilient alternative, by avoiding landfill GHG emissions, returning valuable nutrients to the soil to ensure continued agricultural production, and sequestering carbon while supporting local communities. Recognizing this opportunity, California has set ambitious organics diversion targets in the Short-Lived Climate Pollutant Law (SB1383) which will require significant increases (5 to 8 million tonnes per year) in organic material processing capacity. This paper develops a spatial optimization model to consider how to handle this flow of additional material while achieving myriad social and ecological benefits through compost production. We consider community-based and on-farm facilities alongside centralized, large-scale infrastructure to explore decentralized and diversified alternative futures of composting infrastructure in the state of California. We find using a diversity of facilities would provide opportunity for cost savings while achieving significant emissions reductions of approximately 3.4 ± 1 MMT CO 2 e and demonstrate that it is possible to incorporate community protection into compost infrastructure planning while meeting economic and environmental objectives.

Plastics are rapidly accumulating in blue carbon ecosystems, i.e., mangrove forests, tidal marshes, and seagrass meadows. Accumulated plastic is diverted from the ocean, but the extent and nature of impacts on blue carbon ecosystem processes, including carbon sequestration, are poorly known. Here, we explore the potential positive and negative consequences of plastic accumulation in blue carbon ecosystems. We highlight the effects of plastic accumulation on organic carbon stocks and sediment biogeochemistry through microbial metabolism. The notion of beneficial plastic accumulation in blue carbon ecosystems is controversial, yet considering the alternative impacts of plastics on oceanic and aboveground environments, this may be the "lesser of evils". Using environmental life cycle impact assessment, we propose a research framework to address the potential positive and negative impacts of plastic accumulation in blue carbon ecosystems. Considering the multifaceted benefits, we prioritize expanding and managing blue carbon ecosystems, which may help with ecosystem conservation, as well as mitigating the negative effects of plastic.

One possible carbon dioxide sequestration strategy is via the carbonation of dissolved Mg 2+ obtained through olivine ((Mg,Fe) 2 SiO 4 ) dissolution. However, silica is also produced during the breakdown of olivine. This component may have a detrimental effect on the yield of Mg-carbonate as Mg 2+ incorporation into complex Mg silicate phases would limit CO 2 uptake by this system. Yet this potential competition is currently not considered. Here, we use crystal growth experiments at temperatures applicable for potential coastal applications to test the effect of silica on the formation of the hydrated Mg-carbonate phase nesquehonite (MgCO 3 ·3H 2 O). Solution chemistry analysis coupled with phase identification demonstrates that the presence of silica in the solution can actually assist the formation of nesquehonite and increase its yield by as much as 60 times. Our findings suggest that the presence of silica changes interfacial stabilities, lowering the energetic barrier for nesquehonite nucleation. In addition, in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) transformation experiments demonstrated that nesquehonite precipitating in a solution containing a high concentration of dissolved silica exhibits enhanced stability against its transformation into hydromagnesite. These findings will help to better constrain what we expect for applications of olivine during carbon remediation strategies as well as assist yields for industrial applications that use Mg-based cement as building materials to facilitate a CO 2 -neutral or negative footprint.

This study presents a geo-spatial and economic framework to localize future bioenergy power plants combined with direct air capture (BEDAC). This framework is applied to two regions in the USA to assess the optimal use of forest biomass and in situ carbon sequestration under three specific short-term sequestration targets. Results show that there are many locations that have both the necessary biomass and geology required for storage. The Southeast has greater potential for forestry biomass due to both the rate of growth and forested areas, but the sequestration potential is mostly limited to a CO 2 solution in saline aquifers. The Pacific Northwest has more sequestration potential than the Southeast given the location of managed forests and storage sites in carbonate mineralization in bedrock. The two combined regions have a total potential sequestration of 9.3 GtCO 2 for the next 20 years that can be achieved under an implicit carbon value of $249/tCO 2 .

Substantial amounts of particulate organic carbon (POC) are released during macroalgal growth; however, the fate of these POCs and their carbon sequestration effects remain unclear. Here, field investigations found that Ulva prolifera caused a significant increase of POC in seawater below the surface during a macroalgal bloom. However, laboratory simulations revealed that 77.6% of these POC was easily degraded by microorganisms in a short period of time, concurrently resulting in the production of dissolved organic carbon (DOC) from POC transformation. Over a period of 3 months, the bioavailable components of macroalgae-released POC and POC-transformed DOC were degraded, leaving 39.6% of the antibiodegradable substances composed of biorecalcitrant POC and biorecalcitrant DOC. However, although the biorecalcitrant POC was rich in humic-like components resisting biodegradation, the biorecalcitrant POC exhibited greater sensitivity to photodegradation than biorecalcitrant DOC. The photodegradation removal rate of biorecalcitrant POC (14.1%) was more than 10 times that of biorecalcitrant DOC (1.2%). Ultimately, a substantial portion (36.3%) of the POC released by growing macroalgae could potentially perform long-term carbon sequestration after conversion to recalcitrant POC and recalcitrant DOC, and these inert carbons derived from macroalgal POC have been previously ignored and should also be included in macroalgal carbon sequestration accounting.

Global climate change significantly increased the duration of droughts in intermittent rivers, impacting benthic microbial-mediated biogeochemical processes. However, the impact of prolonged droughts on the carbon contribution of intermittent rivers remains poorly understood. In this study, we investigated the potential effects of varying drought gradients (ranging from 20 to 130 days) on benthic biofilms community structure (algae, bacteria, and fungi) and their carbon metabolism functions (ecosystem metabolism and carbon dioxide (CO 2 ) emission fluxes) using mesocosm experiments. Our findings indicate that longer drought durations lead to reduced alpha diversity and community heterogeneity, tighter interdomain networks, and an increased role of stochastic processes in community assembly, with a discernible threshold at around 60 days. Concurrently, the biofilm transforms into a carbon sink following a drought period of 60 days, as evidenced by the transformation of CO 2 emission fluxes from 633.25 ± 194.69 to -349.61 ± 277.79 mg m -2 h -1 . Additionally, the partial least-squares path model revealed that the resilience of algal communities and network stability may drive biofilm's transformation into a carbon sink, primarily through the heightened resilience of autotrophic metabolism. This study underscores the significance of the carbon contribution from intermittent rivers, as the shift in carbon metabolism functions with increasing droughts could lead to skewed estimations of current riverine carbon fluxes.

Deep-sea sediments (>1000 m) are often considered to be the ultimate sink for black carbon (BC), and the long-term buried BC in these sediments is believed to potentially provide a negative feedback effect on climate warming. The burial flux of BC in marine sediments is predominantly estimated based on soot BC (SBC) in most studies, frequently ignoring the contribution of char BC (CBC). While this methodology may result in an underestimation of the BC burial flux, the precise extent of this underestimation is yet to be determined. This study used the benzene poly(carboxylic acid) (BPCA) method and chemothermal oxidation (CTO) method to analyze CBC and SBC in four deep-sea sediment cores from the Zhongnan seamount in the South China Sea, respectively. The CBC content increased from 0.026 ± 0.010% at the seamount upper part (1432 m) to 0.039 ± 0.012% at the seamount foot (4278 m), constituting approximately 25 to 42% of the SBC content. The content disparity between CBC and SBC diminishes as depth increases. In deep-sea sediments, biogeochemical factors influence the variation of CBC molecules with depth. In the seamount middle-upper part (1432 and 2465 m), highly condensed CBC gradually accumulated along the core downward profile. In the sediment core profile of the seamount middle-lower part (3497 m), benzenetricarboxylic acid and benzenetetracarboxylic acid content decreased while the BC condensation degree rose, i.e., less condensed CBC was preferentially consumed. Afterward, CBC molecules reached a relatively stable state at the seamount foot. This study reveals that CBC possesses the capacity for long-term carbon sequestration in deep-sea sediments, and its content is not negligible.

In response to climate change, China is making great efforts to increase the green area for carbon sequestration. Road verges, as marginal land with favorable conditions for plant growth and ease of transportation, can be used for biomass production, but the biomass production and carbon sequestration potential have not been assessed. Here, we mapped the biomass production potential of road verges in China by combining a biomass model and Geographic Information System and then evaluated the effect of road runoff and CO 2 fertilization on the production according to the runoff coefficient and vehicle emission inventory. Nationwide, road verges can produce 15.86 Mt C yr -1 of biomass. Road runoff contributes to a biomass production of 1.26 Mt C yr -1 through increasing soil water availability, which mainly occurs in arid regions. The CO 2 fertilization effect by vehicle emission is considerable in Eastern and Southern China, contributing to a production of 0.09 Mt C yr -1 . Life cycle assessment shows that major road verges in China have a carbon sequestration potential of 6.87 Mt C yr -1 currently. Our results revealed that road verges can make a significant contribution to carbon neutrality under proper management.

Organic clathrates formed by combining hydroquinone (HQ) and CO2 could offer very interesting prospects in the near future, particularly in the field of CO2 capture and storage. However, one of the main limitations hindering the large-scale deployment of this type of clathrate-based technology is the slow enclathration kinetics. Our experiments, performed at different pressures (1.5, 3.0, and 4.5 MPa) and temperatures (298, 323, and 348 K), with HQ in different forms (HQ powder, HQ pellets, and HQ-silica composites, each different in nature and in terms of pore size and HQ content) demonstrated that (i) an increase in both pressure and temperature enhances the enclathration rate, (ii) the textural properties of HQ significantly impact kinetics, and composite materials remain the most efficient for improving HQ clathrate formation kinetics. [ABSTRACT FROM AUTHOR]

Carbon capture and sustainable utilization (CCU) is essential to accomplishing the targets of 2015’s Paris Agreement. A promising option consists of algal based CO2 conversion into lipid rich biomass with further processing into polyacrylonitrile (PAN) fiber, the major precursor for carbon fiber production. A first feasibility analysis was carried out under multiple constraints for price, byproduct yield, and consumption of land, CO2, and energy. Several process-route alternatives were composed, modeled, and compared in terms of mass and energy flows, resource needs, and cost. To quantify risks from market and modeling uncertainties, we conducted a primary techno-economic analysis (TEA) with variable process pathways in a dynamic economic model of a related project company (SPV), embedded in a Monte Carlo simulation. First results indicate that process combinations with algal biodiesel-production and biomass-liquefaction (BtL) components come close to meeting the multiple constraints and justify progressing to extended research and development activities. [ABSTRACT FROM AUTHOR]

This work presents an efficient and accurate method for the calculation of the properties of carbon dioxide. This is motivated by the massive employment of this fluid in the industrial domain, especially in the refrigeration industry through supersonic ejector cycles, and in the CO2 capture and storage (CCS) industry. A tabulated equation of state (EoS) is developed in the density-internal energy space, based on the Span-Wagner EoS formulation which is the current international reference for computing CO2 properties. The tabulated EoS is coupled to the Homogeneous Equilibrium Model to calculate properties of the liquid-vapor mixture. To assess the performance of the developed EoS, three configurations are simulated, namely a shock tube, a tube depressurization, and a converging-diverging nozzle. Throughout the comparisons to other EoSs, such as the Peng-Robinson, the Stiffened Gas and the original Span-Wagner EoSs, the high efficiency of the tabulated equation of state is revealed. [ABSTRACT FROM AUTHOR]

CO2 transportation safety is important for the successful implementation of carbon capture and storage (CCS) projects. The formation of solid CO2 is a unique phenomenon in high-pressure CO2 release. The evolution and size distribution of dry ice particles have a significant impact on assessment of the consequences of accidental release of supercritical CO2 from a pipeline. The motivation is to investigate the particle behavior and size distribution and understand how the impact factors affect them. An experiment with various measurement methods was developed to carry out controllable CO2 release from a high-pressure vessel. The macroparameters such as jet configuration, temperature, and velocity were recorded. Meanwhile, motion of the microparticles was also analyzed. In addition, the effects of initial pressure and temperature on the particle size distribution were investigated. The results showed that the agglomeration influenced the size distribution at different positions of the jet. [ABSTRACT FROM AUTHOR]

Chemical absorption is widely regarded as the most commercially ready technology for postcombustion CO2 capture from large industrial emission sources. The benchmark solvent is monoethanolamine (MEA). Alternate solvents to MEA have been developed with improved properties such as solvent loading, regeneration energy, and absorption rate. Improvements in solvent properties can be challenging because of possible adverse interactions between solvent properties. Ideally improving all solvent properties and process designs concurrently is desirable to reduce the total cost of CO2 capture. The changes in cost of CO2 capture for postcombustion CO2 capture from a black-coal power plant using absorption are investigated using Monte Carlo simulations, where key solvent parameters are varied simultaneously. Different classes of solvents are considered covering aqueous and phase-change solvents in conventional and encapsulated solvent systems. The results show that it is not necessary for new solvents to have superior values for all properties. There are combinations of solvent properties where low total capture cost can be achieved because improvements in the more significant parameters offset smaller or negative improvement in other parameters. In particular, low total capture cost can be achieved when solvents have the following properties: good stability toward SOx and NOx, a low heat of reaction, a high absorption rate, a low water vaporization rate, and a low price per unit of the solvent. The results also show that regardless of the solvent type, different solvent systems can potentially achieve almost the same lowest capture cost of approximately U.S. $37-39 per tonne of CO2 avoided. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO2) concentrations in the atmosphere have increased significantly over the past century. Many methods have been devised to reduce CO2 industrial emissions, e.g., CO2 postcombustion absorption by amine-based solvents. Solvent degradation losses are very critical in this process, due to economic and environmental issues. The two main degradation pathways of amine-based aqueous solutions in the presence of CO2 are oxidative and thermal degradation. In this work, a lab-scale pilot plant has been set up to carry out degradation experiments during continuous and dynamic cycles of absorption and stripping with three different amine solvents: MEA (monoethanolamine) used as benchmark solvent for CO2 capture, a blend of 1MPZ (1-methylpiperazine) and PZ (piperazine), and a blend of MDEA (methyldiethanolamine) and MEA. The experimental data have been used to assess the performance of CO2 absorption over time and experimental conditions. The variation of CO2 fraction at the gas outlet of the reactor has been used as an indicator of solvent degradation. To simulate the behavior of the plant at different experimental conditions and with each solvent, a dynamic model has been developed, on the basis of the validation of a fast reaction regime. It reproduces accurately the pilot plant's behavior during the absorption and stripping phases. Among the solvents' physical properties, the effect of viscosity appears to be the most critical for the CO2 absorption efficiency. Kinetics of solvent degradation has finally been optimized to match experimental observations. Of the three solvents studied, 1MPZ/PZ is the most stable, whereas MEA and MDEA/MEA have quite similar degradation rates. [ABSTRACT FROM AUTHOR]

In this work, industrial grade sepiolite (IG-SEP) was premodified with hydrochloric acid, and then premodified sepiolite (SEP) was impregnated with triethylenetetramine (TETA) to create a novel TETA functionalized SEP adsorbent. The effects of TETA loading and adsorption temperature on CO2 adsorption capacity, as well as the CO2 adsorption isotherm and cyclic regenerability were investigated. Results show that, when SEP was optimized at 30 wt % TETA (SEP-TETA-30%), the adsorbent attained a CO2 adsorption capacity as high as 1.93 mmol/g at 50 °C with fast adsorption kinetics and good regenerability. The Freundlich model was best able to fit the experimental adsorption isotherm, and the isosteric heat of adsorption at high CO2 coverage was 28 kJ/mol. The presence of moisture in simulated gas has a positive effect on the adsorption capacity, with less harm to adsorption stability. The adsorbent samples were further characterized by N2 adsorption/desorption, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The increased surface area and pore volume of the SEP allow for effective immobilization of TETA within its channels. A kinetic study demonstrated that the experimental adsorption data for SEP-TETA-30% were well fitted by the pseudo-second-order model. More importantly, an index of cost efficiency was proposed to evaluate the practicability and competitiveness of amine-impregnated adsorbents. The cost efficiency of SEP-TETA-30% adsorbent was estimated as 0.19 mol CO2/$, which was higher than reported adsorbents, suggesting that the TETA functionalized SEP (SEP-TETA-30%) composite is a promising adsorbent for cyclic postcombustion CO2 capture processes. [ABSTRACT FROM AUTHOR]

In this work, the postcombustion CO2 capture performance was explored in 100.000 g of a nonaqueous solution, 30 wt % monoethylethanolamine (EMEA) and 70 wt % diethylethanolamine (DEEA). Porous solids (multiwalled carbon nanotubes (MWCNTs), silica gel (SG), and MCM-41) with mass fractions (0.025, 0.050, 0.100 and 0.200%) were added into the pure nonaqueous solution forming the new absorbents to improve the CO2 capture performance. The CO2 absorption (313 K) and desorption (383 K) of the new absorbents were operated in the absorption-desorption apparatus under atmospheric pressure. The results show that the addition of the porous solids in the nonaqueous solution led to a 2% decrease in the absorption loading, while contributing to a 10 min decrease in the desorption time under the same desorption extent. The maximum desorption rates of the new absorbents peaked about 5 min earlier than that of the nonaqueous solution, with an enhancement order of MWCNTs > MCM-41 > SG. Meanwhile, the new absorbent, nonaqueous solution mixed with 0.050% MWCNTs, had the best enhancement in the desorption process and exhibited a good stability in the absorption-desorption experiment. Analytic methods (XRD, BET, FT-IR, and SEM) were used to characterize MWCNTs before and after the five absorption-desorption cycles, which showed a good stability of MWCNTs with no significant change in the structure and activity. [ABSTRACT FROM AUTHOR]

Functionalization by amine groups has been recognized as an effective route to promote the gas capture and separation performance of MOF materials; however, it remains elusive to date what is the optimal number of functional amine groups and which specific MOFs are suitable to be functionalized. To answer these questions, systemic investigations on the interactions between gas molecules and NH2-functionalized MOFs are necessary. Here a microporous Zn-F-triazolate framework which can be easily decorated by different -NH2 groups is selected (Zn-F-TRZ, Zn-F-ATRZ, and Zn-F-DATRZ; TRZ = 1,2,4-triazole, ATRZ = 3-amino-1,2,4-triazole, DATRZ = 3,5-diamino-1,2,4-triazole) to discuss the effect of amine groups on CO2 and C1/C2 hydrocarbon capture and separation. When the pressure is lower than about 0.15 atm, the CO2 uptakes increase directly with the number of anime groups (Zn-F-TRZ < Zn-F-ATRZ < Zn-F-DATRZ). However, at 1 atm, the decoration of one amine group effectively improves the CO2 adsorption of the Zn-F-triazolate framework, and the addition of a second amine group clearly decreases the CO2 uptakes. A similar uptake trend has been observed for C1/C2 hydrocarbons except for C2H2, which decrease dramatically with the number of amine groups. These results show that the combination of amine functional groups and appropriate pore size is responsible for the low-pressure binding and uptake of CO2 and C1/C2 hydrocarbon molecules in Zn-F-triazolate MOFs. Furthermore, thanks to the functionalization by amine groups, these Zn-F-triazolate frameworks all show excellent gas separation performance. Especially, the initial C2H2/CH4 selectivity (107.0) for Zn-F-ATRZ and initial CO2/CH4 (115.7), C2H4/CH4 (78.9), and CO2/C2H2 (5.9) selectivities for Zn-F-DATRZ at room temperature all surpass those of most of the MOFs reported up to now. [ABSTRACT FROM AUTHOR]

By employing a tricarboxylate ligand 1-(4-carboxybenzyl)-1H-pyrazole-3,5-dicarboxylic acid (H3L), four lanthanide metal-organic frameworks (Ln-MOFs) formulated as {[LnL(H2O)2]·H2O}n (Ln = Eu, 1; Gd, 2; Tb, 3; Dy, 4) have been prepared under hydrothermal conditions. Single-crystal X-ray analyses reveal that compounds 1-4 are isomorphous and exhibit a three-dimensional network structure featuring a one-dimensional rectangular channel with a size of ca. 7.8 Å × 12.1 Å along the b axis. The framework shows strong stabilities toward high temperature, humid air, water, as well as acid/base environments. Efficient ligand-sensitized characteristic luminescence can be observed in the visible region for Eu- and Tb-based compounds. Detailed property investigation shows that TbL is a promising multifunctional material, which can quantitatively detect Fe(III) ions in the solution mixtures of Fe(II)/Fe(III), selectively adsorb CO2 over CH4, and be applied as catalysts in cyclization reaction with epoxides and CO2. [ABSTRACT FROM AUTHOR]

Accurate assessment of the long-term security of geologic carbon sequestration requires knowledge of the mobility of carbon dioxide in brines under pressure and temperature conditions that prevail in subsurface aquifers. Here, we report Raman spectroscopic measurements of the rate of CO2 diffusion in water and brines as a function of pressure, salinity, and concentration of CO2. In pure water at 50 ± 2 °C and 90 ± 2 bar, we find the diffusion coefficient, D, to be (3.08 ± 0.03) × 10-9 m2/s, a value that is consistent with a recent microfluidic study but lower than earlier PVT measurements. Under reservoir conditions, salinity affects the mobility of CO2 significantly and D decreased by 45% for a 4 M solution of NaCl. We find significant differences of diffusivity of CO2 in brines (0-4 M NaCl), in both the absolute values and the trend compared to the Stokes-Einstein prediction under our experimental conditions. We observe that D decreases significantly at the high CO2 concentrations expected in subsurface aquifers (~15% reduction at 0.55 mol/kg of CO2) and provides an empirical correction to the commonly reported D values that assume a tracer concentration dependence on diffusivity. [ABSTRACT FROM AUTHOR]

Carbon capture and storage (CCS) is increasingly being accepted as a necessary component of any effort to mitigate the impact of anthropogenic climate change, as it is both a relatively mature and easily implemented technology. High-temperature CO2 absorption looping is a promising process that offers a much lower energy penalty than the current state of the art amine scrubbing techniques, but more effective materials are required for widespread implementation. This work describes the experimental characterization and CO2 absorption properties of several new ternary transition metal oxides predicted by high-throughput DFT screening. One material reported here, Li5SbO5, displays reversible CO2 sorption, and maintains ~72% of its theoretical capacity out to 25 cycles. The results in this work are used to discuss major influences on CO2 absorption capacity and rate, including the role of the crystal structure, the transition metal, the alkali or alkaline earth metal, and the competing roles of thermodynamics and kinetics. Notably, this work shows the extent and rate to which ternary metal oxides carbonate are driven primarily by the identity of the alkali or alkaline earth ion and the nature of the crystal structure, whereas the identity of the transition ion carries little influence in the systems studied here. [ABSTRACT FROM AUTHOR]

The nitrogen-containing hierarchical porous polymers (NHPPs), which possessed micropores, mesopores, and marcopores simultaneously, were constructed by introducing micropores and mesopores into polystyrene foam by post-cross-linking of the skeleton via Friedel–Crafts reaction. First, polystyrene foams with abundant macropores (voids and windows) were obtained by concentrated emulsion polymerization. Subsequently, micropores and mesopores were generated by post-cross-linking cyanuric chloride into the skeleton of polystyrene foam. Cyanuric chloride was used as external cross-linker because of its rich nitrogen content. Finally, NHPPs with high specific surface areas (up to 1226 m2/g) were obtained. The effects of volume fraction of the dispersed phase of concentrated emulsion, DVB in polystyrene matrix, external cross-linker, and solvent on the textural properties of NHPPs were investigated. Then NHPPs were applied as CO2 absorbent, and the maximum CO2 capacity of 141 mg/g at 273 K, 1 bar and the good reproducibility were achieved. Furthermore, the tentative adsorption mechanism of triazine-ring in NHPPs to CO2 was proposed. Most importantly, the relationship between the structures of NHPPs and their CO2 adsorption capacities was analyzed. The results indicated that the CO2 capacities mostly depended on the microporous volume, and the nitrogen content also had impact on the CO2 capacities. [ABSTRACT FROM AUTHOR]

Solid metal oxides for carbon capture exhibit reduced adsorption capacity following high-temperature exposure, due to surface area reduction by sintering. Furthermore, only low-coordinate corner/edge sites on the thermodynamically stable (100) facet display favorable binding toward CO2, providing inherently low capacity. The (111) facet, however, exhibits a high concentration of low-coordinate sites. In this work, MgO(111) nanosheets displayed high capacity for CO2, as well as a ~65% increase in capacity despite a ~30% reduction in surface area following sintering (0.77 mmol g[sup -1] @ 227 m² g-1 vs 1.28 mmol g-1 @ 154 m² g-1). These results, unique to MgO(111), suggest intrinsic differences in the effects of sintering on basic site retention. Spectroscopic and computational investigations provided a new structure-activity insight: the importance of high-temperature activation to unleash the capacity of the polar (111) facet of MgO. In summary, we present the first example of a faceted sorbent for carbon capture and challenge the assumption that sintering is necessarily a negative process; here we leverage high-temperature conditions for facet-dependent surface activation. [ABSTRACT FROM AUTHOR]

Tetraethylenepentamine (TEPA), consisting mainly of primary and secondary amines, exhibits a high CO2 sorption capacity; however, its poor thermal stability hampers practical utilization in the temperature swing adsorption process for CO2 capture. Here, a facile functionalization of TEPA with 1,2-epoxybutane (EB) substantially enhanced its thermal stability as well as the CO2 adsorption kinetics. Our careful analysis on the liquid-state 13C NMR disclosed the amine state distribution of EB-functionalized TEPA (EB-TEPA). Although the increase in tertiary amine portion induced by EB-functionalization reduced CO2 sorption capacity, the 0.64EB-TEPA (i.e., TEPA functionalized with EB with a TEPA/EB molar ratio of 1:3)/SiO2 showed an excellent long-term stability over the 10 consecutive cycles of adsorption/desorption processes with a CO2 swing capacity of 2.0 mmol CO2 g-1 under dry CO2/N2 (15/85 mol/mol) feed conditions. Also, the first-principles calculation identified the configuration of modified TEPA molecules with XRD measurements, supporting an easy access of CO2 into amine moieties of our modified TEPA molecules. [ABSTRACT FROM AUTHOR]

The performance of an ionic liquid with an aprotic heterocyclic anion (AHA-IL), trihexyl(tetradecyl)phosphonium 2-cyanopyrrolide ([P66614][2-CNPyr]), for CO2 capture has been evaluated considering both the thermodynamics and the kinetics of the phenomena. Absorption gravimetric measurements of the gas-liquid equilibrium isotherms of CO2-AHA-IL systems were carried out from 298 to 333 K and at pressures up to 15 bar, analyzing the role of both chemical and physical absorption phenomena in the overall CO2 solubility in the AHA-IL, as has been done previously. In addition, the kinetics of the CO2 chemical absorption process was evaluated by in situ Fourier transform infrared spectroscopy-attenuated total reflection, following the characteristic vibrational signals of the reactants and products over the reaction time. A chemical absorption model was used to describe the time-dependent concentration of species involved in the reactive absorption, obtaining kinetic parameters (such as chemical reaction kinetic constants and diffusion coefficients) as a function of temperatures and pressures. As expected, the results demonstrate that the CO2 absorption rate is mass-transfer-controlled because of the relatively high viscosity of AHA-IL. The AHA-IL was encapsulated in a porous carbon sphere (Encapsulated Ionic Liquid, ENIL) to improve the kinetic performance of the AHA-IL for CO2 capture. The newly synthesized AHA-ENIL material was evaluated as a CO2 sorbent with gravimetric absorption measurements. AHA-ENIL systems preserve the good CO2 absorption capacity of the AHA-IL but drastically enhance the CO2 absorption rate because of the increased gas-liquid surface contact area achieved by solvent encapsulation. [ABSTRACT FROM AUTHOR]

Carbon capture, storage, and utilization technologies target a reduction in net CO2 emissions to mitigate greenhouse gas effects. The largest such projects worldwide involve storing CO2 through enhanced oil recovery -- a technologically and economically feasible approach that combines both storage and oil recovery. Successful implementation relies on detailed measurements of CO2-oil properties at relevant reservoir conditions (P = 2.0-13.0 MPa and T = 23 and 50 °C). In this paper, we demonstrate a microfluidic method to quantify the comprehensive suite of mutual properties of a CO2 and crude oil mixture including solubility, diffusivity, extraction pressure, minimum miscibility pressure (MMP), and contact angle. The time-lapse oil swelling/extraction in response to CO2 exposure under stepwise increasing pressure was quantified via fluorescence microscopy, using the inherent fluorescence property of the oil. The CO2 solubilities and diffusion coefficients were determined from the swelling process with measurements in strong agreement with previous results. The CO2-oil MMP was determined from the subsequent oil extraction process with measurements within 5% of previous values. In addition, the oil-CO2-silicon contact angle was measured throughout the process, with contact angle increasing with pressure. In contrast with conventional methods, which require days and ~500 mL of fluid sample, the approach here provides a comprehensive suite of measurements, 100-fold faster with less than 1 μL of sample, and an opportunity to better inform large-scale CO2 projects. [ABSTRACT FROM AUTHOR]

This study investigates the speciation of CO2 involving the most common solvents used to capture carbon from flue gas, i.e. ammonia, monoethanolamine (MEA), and diethanolamine (DEA). This requires the knowledge of both the activity coefficients of the species involved and the equilibrium constants of the relevant reactions. In contrast to the equilibrium constants, which can be obtained from the literature, the activity coefficients of the aqueous species are required to be estimated. Normally, semiempirical models are used to estimate these activity coefficients, i.e. equations that contain unknown parameters that are obtained through regression against experimental data. In contrast, in this study the activity coefficients are predicted using equations that require only the knowledge of the ionic radii and charges of the species involved in the equilibrium. As a conclusion, the model developed shows very good agreement with the experimental data obtained, either from spectroscopy or from vapor-liquid equilibrium (VLE), up to a solvent mass fraction of 20%. [ABSTRACT FROM AUTHOR]

Materials composed of high-porosity solid supports, such as SBA-15, containing amine-bearing moieties inside the pores, such as 3-aminopropylsilane (APS), are envisioned for carbon dioxide capture; solid-state 15N NMR can be highly informative for studying chemisorption reactions. Two 15N-enriched samples with different APS loadings were studied to probe the identity of the pendant molecules and structure of the chemisorbed CO2 species. 15N cross-polarization magic-angle spinning NMR provides unique information about the amines, whether they are rigid or dynamic, by measuring contact time curves and rotating frame, T1ρ(15N), relaxation. Both carbamate and carbamic acid are formed; carbamic acid is shown to be less stable than carbamate. After desorption, a steady state for the chemisorbed reaction product is reached, leaving behind carbamate. 15N NMR monitors the evolution of the species over time. During desorption, APS is regenerated, but the ammonium propylsilane intensity does not change, leading us to conclude that carbamic acid desorbs, while carbamate (to which ammonium propylsilane is ion paired) persists. A secondary ditehtered amine present does not react with CO2, and we posit this may be due to its rigidity. These findings demonstrate the versatility of solid-state NMR to provide information about these complex CO2 reactions with solid amine sorbents. [ABSTRACT FROM AUTHOR]

Herein we report an efficient and recyclable system for tandem CO2 capture and hydrogenation to methanol. After capture in an aqueous amine solution, CO2 is hydrogenated in high yield to CH3OH (>90%) in a biphasic 2-MTHF/water system, which also allows for easy separation and recycling of the amine and catalyst for multiple reaction cycles. Between cycles, the produced methanol can be conveniently removed in vacuo. Employing this strategy, catalyst Ru-MACHO-BH and polyamine PEHA were recycled three times with 87% of the methanol producibility of the first cycle retained, along with 95% of catalyst activity after four cycles. CO2 from dilute sources such as air can also be converted to CH3OH using this route. We postulate that the CO2 capture and hydrogenation to methanol system presented here could be an important step toward the implementation of the carbon neutral methanol economy concept. [ABSTRACT FROM AUTHOR]

With advances in porous carbon synthesis techniques, hierarchically porous carbon (HPC) materials are being utilized as relatively new sorbents for CO2 capture applications. These HPC materials were used as a platform to prepare samples with differing textural properties and morphologies to elucidate structure-property relationships. It was found that high microporous content, rather than overall surface area, was of primary importance for predicting good CO2 capture performance. Two HPC materials were analyzed, each with near identical high surface area (~2700 m2/g) and colossally high pore volume (~10 cm3/g), but with different microporous content and pore size distributions, which led to dramatically different CO2 capture performance. Overall, large pore volumes obtained from distinct mesopores were found to significantly impact adsorption performance. From these results, an optimized HPC material was synthesized that achieved a high CO2 capacity of ~3.7 mmol/g at 25 °C and 1 bar. [ABSTRACT FROM AUTHOR]

We report the discovery of novel CO2-based networks stabilized by Li+ cations in solid-state phases. Our exploration of the energy landscape of the Li-CO2 binary phase diagram using ab initio evolutionary structure searches revealed that in addition to the well- characterized C2O42- oxalate in Li2C2O4 viable covalent CO2-based nets emerge upon compression within the 0-100 GPa pressure range. Novel molecular units are described, such as ethene-like C2O44- in C2/m Li2(CO2), finite C4O86- chains in P1 Li3(CO2)2, one-dimensional polymeric forms based on 1,4-dioxane rings in P2/c LiCO2, and the C(O-)2 moieties in Pnma Li2CO2. This investigation shows the oxalate motif is maintained when the concentration of lithium increases from 1 to 2 in LixCO2; this interesting property may have potential in the development of renewable Li-ion batteries. Moreover, a variety of metastable phases were predicted, such as the covalent CO2-based layer in P1 Li(CO2)2. [ABSTRACT FROM AUTHOR]

In recent years, the reduction of CO2 emissions has become a joint effort throughout the world, and carbon capture and sequestration (CCS) is an effective approach to solving the problem of CO2 emissions. In the present study, the effects of adding CH4, Ar, and H2S to CO2 on the interfacial tension (IFT) and wettability (contact angle, CA) of the CO2/water/silica system have been investigated using molecular dynamics simulation methods at 20 MPa and 318 K when the molar concentration of impurity gas was fixed at 20%. For the conditions studied, (1) CH4 has no significant effect; (2) Ar leads to a higher IFT, a larger CA on silica surfaces with a high hydroxyl density, and a smaller CA on silica surfaces with a low hydroxyl density; and (3) H2S causes a decrease of the IFT and an increase of the CA. Capillary pressure and gas storage capacity were predicted using IFT and CA data, and the variation of IFT and CA were explained based on density profiles normal to the gas/water and gas/silica interfaces. These findings might be helpful for better understanding the effects of impurities on CCS. [ABSTRACT FROM AUTHOR]

A series of polyethylenimine (PEI)-linked microporous organic polymers were obtained using glycidyl methacrylate-polyethylenimine monomer (GMA-PEI) and different cross-linking agents. Because of well-defined micropores and CO2-philic plentiful secondary amines, porous organic polymers (POPs) demonstrate high CO2 uptake and excellent selectivity over other permanent gases, such as CH4 and N2. The adsorption capacity of POPs reaches 92 mg g-1 at 273 K and 1 bar, which is higher than that of recently reported polymers supported on various porous materials such as MCM-41 (33 mg g-1), alumina (50 mg g-1), and SBA-15 (60 mg g-1) under the analogous conditions. The high CO2/N2 and CO2/CH4 selectivity is observed and reaches 308 and 39, respectively. It is noteworthy that POPs can be entirely regenerated under mild conditions and no loss in activity is detected after four cycles. Notably, no side product is obtained during the fabrication of POPs. Thus, good adsorption capacity, high selectivity, and energy-saving regeneration of POPs make their use in selective CO2 capture from flue gas and natural gas promising. [ABSTRACT FROM AUTHOR]

Carbon capture and storage (CCS) is regarded as the most efficient approach in handling the global warming crisis. MEA-based CO2 capture is a well-developed chemical absorption method with a long period of industrial application. A novel hydrate-based gas separation (HBGS) method, with a wide range of advantages, has recently received special attention from researchers. In this study, two different CO2 separation processes were simulated utilizing Aspen Plus software. The feasibility of both processes was validated, and the process energy consumption and exergy loss were also compared at the same flue gas condition. Some efforts have also been made to investigate the effects of different operation parameters on the process energy efficiency. Results show that the first law efficiency of the MEA-based CO2 separation system is 88.19% and the second law efficiency of the system is 38.32%, while the corresponding values of the hydrate-based separation system are 74.15% and 38.85%, respectively. Cooling of the lean amine solution and the regeneration process occupy the largest portion of exergy loss in the MEA separation system. In the hydration separation, the flue gas compression and cooling are the major causes for exergy loss. [ABSTRACT FROM AUTHOR]

In the framework of the efforts of the scientific community developed for the reduction of CO2 emissions, the geological storage of CO2 in deep saline aquifers is under focus. An increase of salinity decreases the potential of CO2 solubilization into the water. In salty waters, the salinity is not only due to NaCl but also to others ions and in particular Ca and Mg. Experimental solubility data of CO2 in calcium chloride solution available in the literature at conditions relevant to carbon storage are particularly scarce. In this work, a new analytical method was developed for experimental measurement of CO2 solubility in calcium chloride solutions (1, 3, and 6 mol/kg) at high pressures (5-20 MPa) and temperatures (323.15, 373.15, and 423.15 K). This method is based on conductometric titration coupled with classical pH titration. The conductimetry shows sharper curves than the pH titration allowing a higher precision. Thirty-six new experimental data are reported in this paper. These data presented an experimental average uncertainty of 2.1% with the ANOVA calculation method based on repeatability and reproducibility experiments. The CO2 solubility in CaCl2 solutions is noticeable lower than in NaCl solution increasing the salting out effect. Considering our previous work on NaCl solutions and this paper for CaCl2 solutions, estimations of the real quantity of CO2 that may be dissolved in saline aquifers can be made with a significantly better precision. [ABSTRACT FROM AUTHOR]

The solubilities of carbon dioxide (CO2) in three low-viscous ionic liquids (ILs)-1-ethyl-3-methylimidazolium thiocyanate ([emim][SCN]), 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]), and 1-ethyl-3-methylimidazolium tricyanomethanide ([emim][TCM])-were determined by volumetric method at the temperature range of (298.0 to 373.2) K and pressure range of (0 to 300.0) kPa, which are relevant to the capture of CO2 from flue gas and natural gas. The Henry's law constants and partial molar volume at infinite dilution of CO2 in the three ILs were calculated by fitting the solubility data with the Krichevsky-Kasarnovsky (K-K) model. The absorption enthalpies, Gibbs free energy changes, and absorption entropies of CO2 in the three ILs were also calculated based on the dependence of Henry's constants on temperature. DFT calculations were further performed to better understand the interaction of ILs with CO2 on the molecular level and provide theoretical basis for the different CO2 solubilities in the three ILs. [ABSTRACT FROM AUTHOR]

A pair of homochiral porous supramolecular organic frameworks (JLU-SOF1-R and JLU-SOF1-S) has been assembled from brand-new enantiopure blocks via hydrogen bonding and π-π interactions. The frameworks not only maintain crystallinity well until 250 °C but also exhibit a steep slope N2 adsorption isotherm at 77 K with moderately high surface areas, indicating that the new materials own robust structure and permanent porosity. JLU-SOF1-R shows excellent adsorption capacity for CO2 and C2H6 at ambient conditions. Remarkably, the material takes up a significant amount of CO2, up to 213 cm3 g-1 at 195 K under 1 bar. Furthermore, JLU-SOF1-R exhibits high selectivity toward CO2 over N2 and CH4 as well as C2H6 over CH4. [ABSTRACT FROM AUTHOR]

One critical issue in the development of immobilized amine sorbents for CO2 capture is sorbent degradation, which leads to a significant increase in the overall CO2 capture cost. Here we report a novel approach for enhancing the degradation resistance of a branched polyethylenimine (PEI) by hydroxyl groups (i.e., -OH) of a porous cross-linked poly(vinyl alcohol) (PVA) support. The CO2 capture capacity of a PEI/PVA sorbent showed a 25% decrease and then leveled off. In contrast, the PEI/SiO2 sorbent exhibited more than a 3-fold decrease in CO2 capture capacity after exposure to a cyclic CO2 capture and oxidative degradation environment (15 vol % of CO2 in air at 130 °C). In situ infrared spectroscopic study revealed that the secondary amine is more liable to degrade than the primary amine on PEI/SiO2. On PEI/PVA, the PVA's -OH groups interacted mainly with the secondary amine of branched PEI through a hydrogen bonding, which could contribute to enhancing the resistance of PEI against degradation. This new finding could provide new pathways in the development of low-cost and highly durable amine sorbents by using highly porous polymeric supports with -OH groups. [ABSTRACT FROM AUTHOR]