Low CO2 Partial Pressure Research Articles

Experimental and kinetic study of pressurized CO2 gasification of biomass chars

Pressurized CO2 gasification of biomass represents an effective approach for the utilization of biomass and the reduction of CO2 emissions. The impact of CO2 partial pressure on the gasification kinetics of biomass chars was examined on a pressurized thermogravimetric analyzer at temperatures between 750 and 950 °C and elevated pressures (up to 1MPa). The findings demonstrated that the gasification rates of corn stalk char (CSC), toonasinesis sawdust char (TSC), and rice husk char (RHC) exhibited an increase with rising CO2 partial pressure. The reaction order exhibited variability with respect to CO2 partial pressure, gasification temperature, and biomass type. The reaction order associated with biomass char exhibited a higher value at the elevated CO2 partial pressure range (0.25–1.0MPa) relative to the low CO2 partial pressure range (0.025–0.1MPa). The nth-order model was employed to elucidate the gasification behaviors of biomass chars. The results indicated that the modified random pore model was successfully applied to model the gasification of CSC and TSC. The grain model was effective in predicting the gasification behavior of RHC. The gasification rates of the three biomass chars were accurately predicted by the Langmuir-Hinshelwood model at both low and high CO2 partial pressures. This study presents information on the effect of CO2 partial pressure on biomass char gasification and methods for predicting biomass char gasification under pressurized conditions.

High temperature capture of CO2 on Li4SiO4 sorbents via a simple dry ball-milling coupled with K2CO3 physical addition

The reversible CO2 absorption/desorption of lithium orthosilicate (Li4SiO4) sorbents holds potential for high temperature capture of CO2 from hot flue gases, sorption-enhanced reforming and solar thermochemical energy storage. In this study, we have prepared a series of Li4SiO4 sorbents using a combination of K2CO3 addition and dry ball-milling procedure to improve the relatively slow kinetics under low CO2 partial pressure conditions. The synergistic effects of dry ball-milling and K2CO3 addition on the intrinsic properties of Li4SiO4 sorbents were explored by thermogravimetric analysis and structural characterizations. Thermogravimetric analysis indicate that the highest CO2 uptakes were achieved with dry ball-milling combined with K2CO3 physical addition. The structural characterizations further reveal that this sorbent (P-3K-1.5 M) had the smallest crystallite/particle size, largest surface area, and highest availability of surface alkaline-sites. The kinetics analysis also demonstrates that P-3K-1.5 M exhibited the fastest sorption kinetics during a double process. Additionally, P-3K-1.5 M maintained a high capacity over 10 sorption/desorption cycles. Therefore, this synthesis technique, which is simple, cost-effective, and easily scalable, shows great promise for high-temperature CO2 capture.

Enhancing CO2 solubility for efficient carbon capture via self-assembly deep eutectic solvents on MOF-808

The capture of CO2 from flue gas has emerged as the most effective technology for carbon reduction. The relatively low partial pressure of CO2 in flue gas necessitates the development of CO2-selective adsorbents, which provide a direct pathway to obtaining pure CO2 in one-step, thereby reducing energy consumption. Herein, an amino-rich deep eutectic solution (DES) is dispersed on the surface of formate ligand-removed MOF-808 using a self-assembly approach for post-combustion carbon capture. The high solubility of DES towards CO2 enables the composite to effectively capture CO2, with MOF-808 serving as a porous gas storage tank. Material characterization confirms the loading of DES on the surface of MOF support while retaining its microporous structure. Owing to their unique CO2 solution-diffusion mechanism, DES-modified adsorbents exhibit promising performance on CO2 capacity, kinetics, CO2/N2 selectivity, and isosteric heat. The optimized sample DES-2@MOF-808-FR demonstrates a notable CO2 adsorption capacity of 4.16 mmol/g at 298 K and 1 bar. When tested with simulated flue gas (15 vol% CO2), it maintains a working capacity of 2.86 mmol/g and a CO2/N2 selectivity of 1184, surpassing most of existed materials. DES-2@MOF-808-FR can also retain its capacities after 10 adsorption/desorption cycles in simulated flue gas. This solution-based modification approach circumvents the challenges associated with precise structural control of the adsorbent, thereby facilitating potential industrial applications.

Association of dynamic changes in arterial partial pressure of carbon dioxide with neurological outcomes in aneurysmal subarachnoid hemorrhage

BackgroundCerebral blood flow (CBF) is closely regulated by carbon dioxide (CO2). In patients with aneurysmal subarachnoid hemorrhage (aSAH), abnormal arterial partial pressure of CO2 (PaCO2) might deteriorate brain injuries. Nevertheless, the impact of dynamic PaCO2 fluctuations on neurological outcomes in aSAH patients has not been extensively studied. Our study aimed to investigate the association between dynamic PaCO2 levels and unfavorable neurological outcomes in aSAH patients. MethodsIn this retrospective observational study, we consecutively enrolled 159 aSAH patients from December 2019 to July 2021. Arterial blood gas measurements within 10 days after intensive care unit (ICU) admission for each patient were recorded to calculate the time-weighted average (TWA)-PaCO2, an indicator representing the dynamic changes in PaCO2 levels. For the association between TWA-PaCO2 levels and unfavorable neurological outcomes in aSAH patients, multivariable logistic analysis was used to explore TWA-PaCO2 levels as categorical variables, and restricted cubic spline (RCS) was used to explore TWA-PaCO2 levels as continuous variables. ResultsIn multivariable logistic analysis, after adjusting confounders, when TWA-PaCO2 35–45 mmHg was as a reference, TWA-PaCO2 < 35 mmHg (odds ratio [OR] 2.15, 95 % confidence interval [CI] 0.83–5.55, P = 0.113) and TWA-PaCO2 > 45 mmHg (OR 8.31, 95 % CI 0.72–96.14, P = 0.090) were not independently associated with unfavorable neurological outcomes (modified Rankin score of 3–6). The RCS shows a “U” shape curve between TWA-PaCO2 levels and unfavorable neurological outcomes, with a nonlinear P-value of 0.023. The lowest ORs of unfavorable neurological outcomes were within PaCO2 32.8–38.1 mmHg. ConclusionsBoth lower and higher PaCO2 levels are harmful to aSAH patients. PaCO2 in the range of 32.8–38.1 mmHg is associated with lowest unfavorable neurological outcomes.

Amine-modified SiO2 aerogel for efficient adsorption of low-pressure CO2: Response surface methodology optimization and adsorption mechanism

Amine-modified SiO2 aerogel (AMSA) has shown tremendous potential in CO2 capture due to its unique three-dimensional network structure and excellent stability. However, it still faces many challenges in the preparation optimization, adsorption enhancement at low CO2 partial pressure, and mechanism elucidation. Hence, in this paper, the response surface methodology is employed for the first time and the optimal preparation conditions for AMSA are determined. A regression model is successfully established to accurately predict the CO2 adsorption capacity of AMSA under different synthesis conditions (with a relative error of only 0.98 %). Additionally, the AMSA prepared at optimal conditions exhibits high CO2 adsorption capacity of 2.11 mmol/g and excellent stability (only decreased by 1.44 % after 8 cycles) at 10 % CO2 partial pressure, indicating enormous application potential. Notably, the CO2 adsorption mechanism by AMSA at different temperatures and partial pressures are revealed in detail through fitting with the Freundlich isotherm and the double-exponential model, as well as thermodynamic parameter calculations. Firstly, the CO2 adsorption behavior belongs to the multi-layer adsorption behavior with uneven energy of active sites. Secondly, the CO2 adsorption capacity and rate are jointly controlled by molecular motion and chemical reaction equilibrium, diffusion and chemical reaction steps, respectively. Finally, the adsorption process is exothermic and spontaneous, and the level of disorder decreases at the gas-solid interface. This study not only achieves efficient adsorption of low-pressure CO2, but also deepens the understanding of gas-solid interface adsorption mechanisms, providing scientific basis and technological support for the development of novel efficient AMSA adsorbent materials.

The genomics and physiology of abiotic stressors associated with global elevational gradients in Arabidopsis thaliana.

Phenotypic and genomic diversity in Arabidopsis thaliana may be associated with adaptation along its wide elevational range, but it is unclear whether elevational clines are consistent among different mountain ranges. We took a multi-regional view of selection associated with elevation. In a diverse panel of ecotypes, we measured plant traits under alpine stressors (low CO2 partial pressure, high light, and night freezing) and conducted genome-wide association studies. We found evidence of contrasting locally adaptive regional clines. Western Mediterranean ecotypes showed low water use efficiency (WUE)/early flowering at low elevations to high WUE/late flowering at high elevations. Central Asian ecotypes showed the opposite pattern. We mapped different candidate genes for each region, and some quantitative trait loci (QTL) showed elevational and climatic clines likely maintained by selection. Consistent with regional heterogeneity, trait and QTL clines were evident at regional scales (c. 2000 km) but disappeared globally. Antioxidants and pigmentation rarely showed elevational clines. High elevation east African ecotypes might have higher antioxidant activity under night freezing. Physiological and genomic elevational clines in different regions can be unique, underlining the complexity of local adaptation in widely distributed species, while hindering global trait-environment or genome-environment associations. To tackle the mechanisms of range-wide local adaptation, regional approaches are thus warranted.

PIM-1-assisted structuring of amine-functionalized porous organic copolymer for post-combustion carbon dioxide capture

Capturing CO2 from flue gas of coal-burned power plants has been considered to be a promising technology to mitigate the environmental problems caused by rising level of CO2 at the atmosphere. Amine-functionalized adsorbents, showing impressive CO2 adsorption capability and selectivity even at low CO2 partial pressure, face the challenge of permanent structural changes and performance deterioration due to the irreversibly bonding of SO2, a common impurity of flue gas, particularly under humid condition. Besides, the reported amine-functionalized adsorbents are usually nano-sized powders, impractical for industrial applications. Therefore, the development of efficient, stable, and structured CO2 adsorbents is still an urgent need. Herein, we develop a novel structured mixed-matrix adsorbent (PIM-PP-DETA), using a diethylenediamine-appended porous organic copolymer (PP-DETA, prepared by a copolymerization reaction of dichloro-p-xylene and 4,4′-bis(chloromethyl)biphenyl and a one-step amine grafting process) as main adsorbent and PIM-1 as polymer matrix through a phase inversion process. The as-developed PIM-PP-DETA not only exhibits high CO2 adsorption capacity and outstanding CO2 selectivity over N2, but also shows fast adsorption kinetics and high stability under repeated adsorption-desorption cycling under dynamic flow conditions. Furthermore, PIM-PP-DETA possesses high tolerance towards acidic and moist environments, with CO2 adsorption capacity remained at a relatively high level after SO2 and humid exposure, suggesting its potential usage to post-combustion CO2 capture.

Short communication: Characterizing arterial and venous blood gases over the gas exchange surface, the chorioallantoic membrane, of embryonic American alligators (Alligator mississippiensis) at two points of development

Assessments of arterial and venous blood gases are required to understand the function of respiratory organs in animals at different stages of development. We measured blood gases in the arteries entering and veins leaving the chorioallantoic membrane (CAM) in embryonic alligators (Alligator mississippiensis). The CAM accounts for virtually all gas exchange in these animals, and we hypothesized that the CAM vasculature would be larger in eggs incubated in hypoxia (10% O2 for 50% or 70% of incubation), which would be reflected in a lower partial pressure of CO2 (PCO2). Contrary to this hypothesis, our measurements revealed no effects of hypoxic incubation on PCO2, and seemingly no increase in vascularization of the CAM in response to incubation in 10% O2. PCO2 was lower on the venous side, but only significantly different from arterial blood at 70% of incubation. The calculated blood flow to the CAM increased with development and was lower in both groups of alligators that had been incubated in hypoxia. Future studies should include measurements of blood parameters taken from embryos held in conditions that mirror incubation O2 levels, in combination with direct measurements of CAM artery blood flow.

Synergetic enhancement of CO2 direct air capture with monoethanolamine-impregnated MIL-101(Cr) MOFs

To mitigate the greenhouse effect caused by the increase of CO2 concentration in the atmosphere, research attention has shifted towards CO2 Direct Air Capture (DAC) techniques. Despite that metal organic frameworks (MOFs) functionalized with various amines are promising to serve as suitable CO2 DAC adsorbent, there is few, if any, reports utilizing monoethanolamine (MEA), the most commonly employed in amine scrubbing technologies, as adsorption active sites. Herein, we have successfully impregnated MEA into MIL-101(Cr), resulting in a notably high CO2 adsorption capacity up to 1.20 mmol/g and an impressive amine utilization efficiency of 23% under low CO2 partial pressure (400 ppm). This improved capture efficiency can be attributed to the presence of hydroxyl groups, which alter the reaction dynamics between CO2 and amine groups. DAC simulation studies predominantly utilize synthetic air to replicate the DAC performance of adsorbents, yet precisely emulating air with artificially mixed gases remains an insurmountable challenge. To overcome this, we designed a system capable of testing DAC performance and employed MEA-impregnated MIL-101(Cr) for DAC testing. The adsorbent achieved pseudo-equilibrium DAC capacities of 2.15 and 1.50 mmol/g under humid and dry conditions, respectively, signifying an enhancement in DAC performance under humid condition. Our study offers novel perspectives for DAC adsorbent research, encompassing both material and equipment considerations.

Gasification kinetics of chars from diverse residues under suitable conditions for the Sorption Enhanced Gasification process

Gasification kinetics for six chars from residual origin have been determined in a relatively low temperature range, low CO2 and high H2O partial pressures, typical from Sorption Enhanced Gasification (SEG) processes. In general, models based on the Random Pore Model (RPM) are the best fitting experimental results, but ash composition (in terms of alkali and alkaline earth metals) was crucial for the selection of the reaction model to be applied. Char conversion from biogenic waste with ash content higher than 30 % wt. was modelled with RPM model, but reaction rate for chars with the highest K/Si ratio was better described with modified versions of the RPM capable of predicting maximum reaction rates at high char conversion. For chars with similar ash content and composition, textural properties determined the pre-exponential factor and the activation energy for the gasification reaction (with both CO2 and H2O), while identical fitting parameters for the semi-empirical model were capable of predicting char conversion with time.

Breaking barriers: Unleashing CO2 selectivity with ultrathin poly(1,3-dioxolane) composite membranes produced by continuous assembly of polymers

Carbon dioxide (CO2) emissions have continued to rise with the sustained reliance on fossil fuels. One leading solution to capturing CO2 emissions is ultrathin film composite (UTFC) membranes due to their cost-efficiency and relatively low environmental impact. On-going efforts to overcome the challenges of practical membrane technology have included increased gas selectivity and robustness toward the low partial pressure of CO2 emitted from coal-fired power stations. Poly(1,3-dioxolane) (PDXL) has been discovered to have exceptional CO2/N2 selectivity outperforming similar high-polar polymers including poly(ethylene oxide) (PEO), PolyActive™, and Pebax®. However, designing as a composite membrane with PDXL has never been accomplished due to a vital challenge of poor interlayer adhesion, and this has restricted its further advancements. The surface-confined Continuous Assembly of Polymers (CAP) technology can be used to overcome the issue of poor interlayer adhesion; however this strategy needs to be modified to ensure all layers are covalently linked. In this study, we synthesized crosslinkable poly(1,3-dioxolane) dimethacrylate (PDXLDMA) and fabricated UTFC membranes via a revised CAP process. The resulting PDXL-based UTFC membrane demonstrated the highest CO2/N2 selectivity (71.3) ever achieved under dry conditions, while maintaining a gas permeance of above 1000 GPU. The modified CAP process preserved PDXL's inherent properties in the UTFC membrane and demonstrated excellent chemical and mechanical strength through crosslinked layers and covalent bonding of the multilayer structure.

Calcium-based pellets for continuous hydrogen production by sorption-enhanced steam methane reforming

Sorption-enhanced steam methane reforming (SESMR) can produce high-purity H2 in one step, while removing CO2 to reduce carbon emissions. The sorbents, catalysts or bifunctional composite used in this system typically exist in powder form, which is difficult to use in industrialized fluidized bed reactors. Granulation can effectively avoid reactor clogging, increase practicality and operability of the system. In this work, Al-modified CaO-based sorbents were granulated using the graphite-casting method and test its sorption-enhanced hydrogen production effects during methane steam reforming. The effects of granulation on the microstructure, carbonation reactivity and mechanical properties were characterized. The reaction conditions (temperature and water-gas ratio) and the combination method of catalyst and sorbent (powder mixing, pellets mixing, layered placement and bifunctional materials mixed evenly at the molecular level) on hydrogen yield were investigated. Results showed that CaO-based pellets after granulation had a fluffy and porous structure, exhibited excellent adsorption performance under low CO2 partial pressure. The average crushing load of 75Ca25Al and 15Ni70Ca15Al pellets exceeded 6 N, showing good mechanical strength. The optimal reaction temperature range was found to be 550–600 °C. Increasing the water-gas ratio and reducing the flow rate were effective ways of improving CH4 conversion and H2 purity. The bifunctional 15Ni70Ca15Al powder prepared by sol-gel method had no catalytic effect on CH4–H2O reforming at 600 °C. After granulation, the catalytic performance was improved and the purity of H2 reached 95%, but it declined rapidly during multiple SESMR cycles. In the case of mixed of two pellets (catalyst and sorbent), the outlet H2 reached almost 100% with no decay observed over 15 cycles. When the switching time of feed gas was set to 60 min, high-purity (>96%) hydrogen can be produced continuously for 600 min on the parallel two fixed-bed reactors.

Electrochemical condition optimization and techno-economic analysis on the direct CO2 electroreduction of flue gas

Direct CO2 electroreduction of flue gas is a technology that simplifies CO2 capture and purification process and directly utilizes CO2 in flue gas. Low CO2 reduction reaction selectivity caused by the low CO2 partial pressure and side reactions competition is the challenge. In this study, a direct CO2 electroreduction system for multicomponent flue gases was established. A two-dimensional steady model was developed by considering major electrode reactions of flue gas in CuxO-based catalysts. General influence criteria and optimum operation window for the potential, temperature, and pressure were proposed. In addition, a techno-economic analysis of the flue gas electrolysis system was conducted. The results demonstrated that the CO2 electroreduction reaction performances are weak at atmospheric pressure owing to the side reaction competition and small reactant concentration. A method involving pressurization and catholyte inlet temperature declination is proposed to break the stalemate of tiny reactant concentrations and ensure the dominance of the CO2 electroreduction reaction. The selectivity and current density of the CO2 reduction reaction were 71% and − 148 mA/cm2 at −1.17 V vs. reversible hydrogen electrode potential (RHE), respectively, under the conditions of an inlet electrolyte temperature of 273 K and an operating pressure of 20 atm. C1 products with excellent yields are the dominant products. Furthermore, the techno-economic analysis showed that the flue gas electrolysis system has higher profitability and lower cost than the purified CO2 electrolysis system. The present results can be used to optimize the electrolyzer operating parameters and construct CO2 reduction systems.

Exploitation of pomelo peel developing porous biochar by N, P co-doping and KOH activation for efficient CO2 adsorption

In order to improve the exploitation of biochar-based adsorbents for CO2 capture, novel biochar adsorbents were synthesized with pomelo peel by effective two-step carbonization and activation, (NH4)2HPO4 and KOH were taken as the dopant and activator, then a series of N, P co-doped pomelo peel-based biochar (NPBCs) was prepared, subsequently, the characteristics and adsorption capacity of NPBCs were studied. The results showed that N, P co-doping and KOH activation synergistically promoted the development of meso-, micro-, ultra-micropores and nanocapsules structure in NPBCs, and enabled NPBCs maintaining a certain N, P content. The optimum sample of NPBCs reached the highest CO2 adsorption capacities of 3.41 and 5.74 mmol/g at 298.15 K, 273.15 K and 1 bar. The adsorption kinetics and isotherms of CO2 on biochar were perfectly described by PFO model and Sips model respectively, indicating that the adsorption was a rapid process and dominated by physical effect. Measurements of the thermal range of CO2 adsorption (15.59–26.01 kJ/mol) confirmed strong affinity of the NPBCs to CO2 molecules. CO2/N2 selectivity up to 165 was recorded at ambient temperature and low CO2 partial pressure. The loss of adsorption capacity of NPBCs was only 9.36% after 10 cycles showing good cyclic stability.

Low CO2 partial pressure steers CHO cells into a defective metabolic state.

The accumulation of carbon dioxide during large-scale culture of animal cells brings adverse effects, appropriate aeration strategies alleviate CO2 accumulation while improper reactor operation may lead to the presence of low CO2 partial pressure (pCO2) condition as occurs in many industrial cases. Thus, this study aims to reveal the in-depth influence of low pCO2 on Chinese Hamster Ovary (CHO) cells for providing a reference for design space determination of CO2 control with regard to the Quality by Design (QbD) guidelines. The headspace air over purging caused the ultra-low pCO2 (ULC) where the monoclonal antibody production as well as the aerobic metabolic activity were reduced. Intracellular metabolomics analysis indicated a less efficient aerobic glucose metabolic state under ULC conditions. Based on the increase of intracellular pH and lactate dehydrogenase activity, the shortage of intracellular pyruvate could be the cause of the deficient aerobic metabolism, which could be partially mitigated by pyruvate addition under ULC conditions. Finally, a semi-empirical mathematical model was used to better understand, predict and control the occurrence of extreme pCO2 conditions during the cultures of CHO cells. Low pCO2 steers CHO cells into a defective metabolic state. A predictive relation among pCO2, lactate, and pH control was applied to get new insights into CHO cell culture for better and more robust metabolic behavior and process performance and the determination of QbD design space for CO2 control.

Improved Apparatus for Dynamic Column Breakthrough Measurements Relevant to Direct Air Capture of CO2.

Dynamic column breakthrough (DCB) measurements are valuable for characterizing the adsorption of gaseous species by solid sorbents and are typically used for high concentrations of adsorptives, often at elevated temperatures and pressures. However, adsorbents for the direct capture of carbon dioxide from natural air demand measurement capability at low partial pressures of CO2 at atmospherically relevant temperatures and pressures. We have developed a new apparatus focused on the measurement of DCB curves under typical tropospheric conditions. The new apparatus is described in detail and validated with breakthrough curve measurements. Adsorption capacities are reported at (233.1 to 323.1) K and (351 to 1078) hPa for low carbon dioxide concentrations on 13X zeolite samples on the order of a few hundred milligrams. Measurement uncertainties related to timing, flow, temperature, and concentrations are analyzed and the present results at 273 K, 298 K, and 323 K are compared with static measurements obtained with a manometric adsorption analyzer. In addition, experiments at a typical atmospheric CO2 concentration of 400 μL · L-1 have been performed.

Corrosion Behaviors of N80 and 1Cr Tubing Steels in CO2 Containing Downhole Environment—A Case Study of Underground Gas Storage in LiaoHe Oil Field

In order to evaluate the effect of chromium content in carbon steel on the corrosion resistance of carbon steel materials, the corrosion behavior of 1Cr and N80 steels was investigated in this study by immersion weight loss method under three different CO2 partial pressure and temperature conditions in formation water for 72, 168 and 336 h. Detailed material surface morphological characterization was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser scanning microscopy (CLSM). The results show that the pitting corrosion of N80 carbon steel is serious at medium temperature and low CO2 partial pressure (50 °C, 0.30 MPa), and the corrosion rate is significantly higher than that of 1Cr steel. However, at high-temperature and high CO2 partial pressure (100 °C/0.63 MPa and 114 °C/0.73 MPa), 1Cr steel is more inclined to the mesa corrosion dominated by local corrosion characteristics, and the corrosion rate is seriously higher than that of N80 steel with uniform corrosion. From the experimental results, we can know the corrosion resistance of carbon steel and 1Cr steel is not only affected by the corrosion environment, but also depends on the formation process of the product film, as well as its compactness and integrity characteristics. At low-temperature and low CO2 partial pressure, 1 wt.% chromium content can provide a certain degree of corrosion resistance, while high temperature and high partial pressure can broaden the application window of carbon steel N80 and weaken the corrosion inhibition effect of chromium.

Kinetics of CaCO3 decomposition at low CO2 partial pressure in a vacuum fixed bed

Calcium looping often suffers from sintering during CaCO3 decomposition process, and CaCO3 decomposition in vacuum is a potential solution. Kinetic analysis of CaCO3 decomposition in vacuum is seldom, and most of the kinetics in the literature is obtained from thermogravimetric analyzer in atmospheric pressure. In addition, the reported kinetic data seems scattered, and varies depending on the analyzer employed. This study is focused on the intrinsic kinetics of isothermal CaCO3 decomposition in a vacuum fixed bed from 700 °C to 850 °C. Besides conventional internal/external mass transfer elimination via reducing size/increasing gas velocity, the effect of CO2 partial pressure is specially discussed under vacuum condition. It is found that, this influence could be eliminated only when the relative difference between equilibrium pressure and maximum CO2 partial pressure (Peq -P*CO2)/Peq was higher than 0.98. Tests at atmospheric pressure were also conducted with the same particle size and gas volumetric feeding rate for comparison. The intrinsic reaction rate constants of CaCO3 decomposition in vacuum are 1.05 × 10-3 s−1– 4.76 × 10-3 s−1 between 700 °C and 850 °C, and the activation energy of this reaction is 92.58 kJ/mol.

Current status of CO2 capture with ionic liquids: Development and progress

Global warming triggered by greenhouse gas (GHG) emissions, particularly carbon dioxide (CO2), significantly influences climate change and has become a common environmental issue recently. The current amine-based technologies (ABTs) for CO2 capture (CAPCO2) have high energy demand, low absorption, and desorption rates, and are less environmentally sustainable due to high emissions of volatile solvents. Therefore, the development of environmentally friendly CAPCO2 materials and/or processes is a growing area of research. The utilization of ionic liquids (ILs) for CAPCO2 has recently attracted attention. The unique characteristics of ILs, such as their low vapor pressure and high affinity for CAPCO2 as well as their low volatility make them a viable substitute for the existing processes. This work provides a comprehensive overview of the accomplishments and challenges during the use of ILs for CAPCO2. The Review also outlines the mechanisms of the CAPCO2 with ILs at the molecular level, the properties of ILs, characterization of the CO2/IL systems, and the effect of operating conditions on CO2 uptake (UPCO2) capacity by ILs. It also emphasizes the impact of cations, anions, and functional groups on the solubility of CO2 ((SCO2)) in ILs as well as the biodegradability and toxicity of ILs. Additionally, recent advances in IL membrane technology for the CAPCO2 processes are considered. Lastly, the contribution of molecular simulations to create and assess ILs was reviewed. Protic and aprotic ILs properties have shown outstanding efficiency of UPCO2. The interactions between the anionic part of IL and CO2 enhance the UPCO2 and outperform the efficiency of traditional organic solvents. Functionalized ionic liquids (FUNILs) with tuned functional groups, supported ionic liquids membranes (SILMs) as well as reversible ionic liquids (RILs) have improved the efficiency of ILs as a promising CO2 capturing process from industrial streams even under low CO2 partial pressure. The relative importance of the chemical breakdown of the IL constituents (cation–anion interfacial structuring) during the CAPCO2 process at different operating temperatures is unclear, and more research in this area is required to better inform the design of new ILs. This review provides a proper/systematic guideline to help ILs manufacturers and engineers design high-capacity ILs for appropriate CAPCO2.

Trace level of atomic copper in N-doped graphene quantum dots switching the selectivity from C1 to C2 products in CO electroreduction

To unravel the relationship between trace Cu on the metal-free catalysts toward CO/CO2 reduction reaction (CO/CO2RR), we investigated the effect of trace Cu loading in N-doped graphene quantum dots (NGQDs) on CO/CO2RR. A general trend is that increasing the Cu loading in NGQDs switches the selectivity from C1 (CH4) to C2 products in CORR. When 2.5 μg/cm2 Cu with the atomic size is loaded on NGQDs, the selectivity shifts from 62% Faradaic efficiency (FE) of CH4 to 52% FE of C2 products in CORR. Further increasing the atomic Cu loading to 3.8 μg/cm2 promotes the FE of C2 products to 78%. CO2RR requires one order of magnitude higher Cu loading than CORR to switch the selectivity from C1 to C2 products due to the low partial pressure of CO. This study clarifies the distinct impact of trace (ppm level) Cu on the activity/selectivity between CORR and CO2RR.