CO2 Pressure Research Articles

Thiophene-Functionalized Cadmium(II)-Based Metal-Organic Frameworks for CO2 Adsorption with Gate-Opening Effect, Separation, and Catalytic Conversion.

Two new porous three-dimensional cadmium(II) metal-organic frameworks (MOFs) containing thiophene-appended carboxylate acid ligands, formulated as [Cd(L1)(4,4'-Bipy)]n.2n(DMF) (1) and [Cd(L2)(4,4'-Bipy)]n.2n(DMF) (2) [where L1 = 5-{(thiophen-2-ylmethyl)amino}isophthalate, L2 = 5-{(thiophen-3-ylmethyl)amino}isophthalate, 4,4'-Bipy = 4,4'-bipyridine, and DMF = N,N'-dimethylformamide] have been synthesized and structurally characterized. The gas adsorption analysis of the activated MOFs shows that they specifically capture CO2 (uptake amount 4.36 mmol/g under 1 bar at 195 K) over N2 and CH4. Moreover, both MOFs show a gate-opening-closing phenomenon, which features the S-shaped isotherms with impressive hysteretic desorption during the CO2 adsorption-desorption process at 195 K. Ideal adsorbed solution theory (IAST) calculations of these MOFs displayed that the obtained selectivity values for CO2/CH4 (50:50) and CO2/N2 (15:85) are approximately 8.6-23 and 93-565, respectively. Configurational bias Monte Carlo simulation was performed to understand the mechanism behind the better CO2 adsorption by these MOFs. Catalytic activity of the MOFs for the CO2 fixation reactions with different epoxides to form cyclic carbonates were tested. These MOFs demonstrated a significantly high conversion (94-99%) of epichlorohydrin to the corresponding cyclic carbonate within 8 h of reaction time at 1 bar of CO2 pressure, at 70 °C, and they can be reused up to five cycles without losing considerably their activity.

Study of CO2 Adsorption Properties on the SrTiO3(001) Surface with Ambient Pressure XPS.

The adsorption properties of CO2 on the SrTiO3(001) surface were investigated using ambient pressure X-ray photoelectron spectroscopy under elevated pressure and temperature conditions. On the Nb-doped TiO2-enriched (1 × 1) SrTiO3 surface, CO2 adsorption, i.e., the formation of CO3 surface species, occurs first at the oxygen lattice site under 10-6 mbar CO2 at room temperature. The interaction of CO2 molecules with oxygen vacancies begins when the CO2 pressure increases to 0.25 mbar. The adsorbed CO3 species on the Nb-doped SrTiO3 surface increases continuously as the pressure increases but starts to leave the surface as the surface temperature increases, which occurs at approximately 373 K on the defect-free surface. On the undoped TiO2-enriched (1 × 1) SrTiO3 surface, CO2 adsorption also occurs first at the lattice oxygen sites. Both the doped and undoped SrTiO3 surfaces exhibit an enhancement of the CO3 species with the presence of oxygen vacancies, thus indicating the important role of oxygen vacancies in CO2 dissociation. When OH species are removed from the undoped SrTiO3 surface, the CO3 species begin to form under 10-6 mbar at 573 K, thus indicating the critical role of OH in preventing CO2 adsorption. The observed CO2 adsorption properties of the various SrTiO3 surfaces provide valuable information for designing SrTiO3-based CO2 catalysts.

Variability of Dissolved Inorganic Carbon in the Most Extensive Karst Estuarine-Lagoon System of the Southern Gulf of Mexico

Coastal ecosystems with karstic geology have a unique characteristic where the dissolution of carbonate rocks can increase total alkalinity (TA) and dissolved inorganic carbon (DIC). This results in higher inorganic carbon budgets in coastal areas. One such ecosystem is the Terminos Lagoon, the most extensive tropical estuarine lagoon system in Mexico, located in the karstic aquifer of the Yucatan Peninsula and connected to the southern Gulf of Mexico (sGoM). We measured TA and DIC to evaluate the variability in Terminos Lagoon’s of the carbonate system. We also estimated pH, partial CO2 pressure (pCO2), and aragonite saturation (ΩAr) along two transects from the main lagoon tributaries (Palizada and Candelaria rivers) to the coastal zone during the dry and rainy seasons. During the dry season, TA and DIC concentrations were significantly higher (3092 ± 452 µmol kg-1 TA, 2943 ± 522 µmol kg-1 DIC) than during the rainy season (2533 ± 228 µmol kg−1 TA, 2492 ± 259 DIC µmol kg−1). Our calculations indicate that the rainy season pCO2 (2532 ± 2371 µatm) seems higher than in the dry season (1534 ± 1192 µatm). This leads to a reduction in pH (7.9 ± 0.3 to 7.8 ± 0.3). These significant changes indicate that rain increases the flow of unsaturated river water into the lagoon. The results of this work contribute toward a dissolved inorganic carbon variability baseline in the sGoM and can be helpful to Terminos Lagoon decision-makers.

Molecular dynamics simulations of shale wettability alteration and implications for CO2 sequestration: A comparative study

Geological CO2 sequestration (GCS) in shale reservoirs is considered an imperative approach to reducing CO2 emissions and mitigating greenhouse gas effects, with the wettability of reservoir rocks playing a critical role in this process. In this study, we comparatively investigated the wetting characteristics of H2O on the organic matter (graphene) and inorganic matter (hydroxylated quartz) surfaces of shale in a CO2 atmosphere utilizing molecular dynamics (MD) simulations and focused on elucidating the effects of CO2 pressure, temperature, and salinity on wettability from the perspectives of the H2O droplet contact angle (CA), gas-water density distributions and interaction energy. The results demonstrate that the H2O droplet is gradually stripped from the graphene surface by CO2 with increasing CO2 pressure, inducing a wetting transition from intermediate-wet to strongly CO2-wet, while the hydroxylated quartz surface consistently exhibits a strongly H2O-wet state. This significant discrepancy in wetting behaviors can be attributed to the differential adsorption capabilities of CO2. The hydrophilicity of graphene and quartz surfaces is enhanced with increasing temperature for the given CO2 pressure condition, and the wettability alteration is more pronounced above the CO2 critical temperature for graphene, while the opposite is observed for quartz. The H2O CA in the CO2-H2O-shale systems only slightly increases with increasing salinity, which is related to the spatial effect of ions in the brine. The results of this work indicate that the CO2-wet feature of shale organic matter during GCS is favorable for the adsorption trapping of CO2 but unfavorable for capillary trapping, while the opposite is true for inorganic matter. This study sheds light on the phenomena and regularity of the wettability alterations of shale organic and inorganic matter by CO2 injection, and the results gained are expected to furnish new insights into CO2 sequestration-enhanced gas recovery (CS-EGR) and gas-water two-phase flow at the nanoscale.

Effect of 2-hexanol and methanol on the <i>one-pot</i> process of dehydration and alkoxycarbonylation for the synthesis of esters

Objectives. To study the possibility of one-pot synthesis (combination of two processes in one reactor) for the following pairs of processes: (1) dehydration of 2-hexanol and isomerizing alkoxycarbonylation of the resulting 2-hexene, in order to obtain 2-hexyl heptanoate, and (2) dehydration of 2-hexanol and isomerizing methoxycarbonylation of the resulting 2-hexene, in order to obtain methyl esters of C7 carboxylic acids. To investigate the effect of the concentrations of 2-hexanol and methanol on the rate of the one-pot synthesis.Methods. One-pot synthesis was studied in a toluene medium in a steel batch reactor designed to operate at elevated pressure and equipped with a glass insert, a magnetic stirrer, a sampler, and gas input and discharge devices. Samples of the reaction mass were taken during the combined process and were analyzed by means of gas–liquid chromatography with a flame ionization detector.Results. The possibility of one-pot combination was demonstrated for 2-hexanol dehydration catalyzed by methanesulfonic acid, as well as for the isomerizing alkoxycarbonylation of the resulting 2-hexene with 2-hexanol and CO, catalyzed by the Pd(PPh3)2Cl2–XANTPHOS–methanesulfonic acid system. The dependencies of the rates of the dehydration of 2-hexanol and the formation of esters of C7 carboxylic acids on the concentration of 2-hexanol were shown to pass through a maximum. The possibility of the one-pot process was proved for the synthesis of esters from 2-hexanol, methanol, and CO with the predominant formation of heptanoic acid esters in the presence of the above catalytic system. The rates of dehydration of 2-hexanol and the formation of 2-hexyl esters of C7 carboxylic acids were found to decrease with increasing the concentration of methanol in the reaction mass. Under mild conditions (temperature 115°C, CO pressure 3 MPa) with the addition of methanol, the total fraction of 2-hexyl and methyl heptanoic acid esters among C7 carboxylic acid esters was determined to be 85.5%.Conclusions. The reactions of intramolecular acid–catalytic dehydration of 2-hexanol and isomerizing alkoxycarbonylation of the resulting 2-hexene, catalyzed by the Pd(PPh3)2Cl2–XANTPHOS–methanesulfonic acid system, can be performed as a one-pot process. Methanesulfonic acid simultaneously functions as a catalyst for the dehydration of 2-hexanol and a cocatalyst for the palladium–phosphine system for the alkoxycarbonylation of hexenes. In the presence of the Pd(PPh3) 2Cl2–XANTPHOS–methanesulfonic acid catalytic system, processes for the synthesis of heptanoic acid esters from 2-hexanol, methanol, and CO can be combined within one reactor. An increase in the methanol concentration negatively affects the rate of the dehydration of 2-hexanol and the formation of 2-hexyl esters of C7 carboxylic acids. A small amount of methanol in the reaction mass leads to an increase in the fraction of heptanoic acid esters among C7 carboxylic acid esters.

Acceleration of chelator on mineralization reaction of cement paste at different CO2 pressures

In order to further improve the mechanical properties of CO2-cured cement paste, effects of chelator on the compressive strength of cement paste cured under different CO2 pressures were investigated, and the mechanism of chelator in accelerating the mineralization reaction was deduced from the analysis of the degree of mineralization reaction, microstructures, and phase compositions, with the contribution of chelator in reducing the net CO2 emissions of cement industry being evaluated. The results showed that the use of chelator could significantly enhance the compressive strength of cement paste cured at different CO2 pressures compared with other methods for improving the compressive strength of CO2-cured cement paste, and the compressive strength of cement paste cured for 48 h at 0.1 MPa and 0.4 MPa CO2 could be enhanced by 23.2 % and 9.4 %, respectively. Chelator could migrate Ca2+ from smaller pores and pore channels to larger pores, decreasing the Ca2+ content and degree of mineralization reaction in smaller pores and pore channels, avoiding the blockage of the stomata by generated CaCO3, and allowing more CO2 to penetrate and diffuse into the cement paste, thereby promoting mineralization reaction and significantly improving compressive strength of cement paste cured at atmospheric pressure. The use of chelator in mineralization curing cement-based materials could further reduce net CO2 emissions from cement production, making significant contribution to the advancement of mineralization curing technology and environmental sustainability.

Experimental comparative analysis of an air-breath direct methanol fuel cell (DMFC) using serpentine and spiral flow fields

In the present study, an experimental comparative analysis of Air Breathe Direct Methanol Fuel Cells (DMFC) was conducted using two different flow field patterns, namely spiral and serpentine. The impact of flow field plates on cell performance, CO2 gas bubble behavior and pressure drop was examined at various mass flow rates and current densities. The experiments were conducted with the same hydraulic diameter and channel length for both flow field patterns, varying mass flow rates from 0.25 to 4 ml/min, and exploring reactant concentrations ranging from 0.25 M to 4 M. From the results it is observed that, for both the flow field patterns, pressure drop increases and CO2 bubble formation decreases with increase in mass flow rate. It is also observed that, under identical operating conditions, the serpentine flow field exhibits higher values for both pressure drop and peak power density compared to the spiral flow configuration. The study reveals that, the serpentine flow appears more efficient in terms of peak power density, while the spiral flow outperforms in terms of minimizing pressure drop under the specified operating condition.

The effect of different breathing conditions on cerebral blood flow in young males during maximal aerobic exercise: A pilot study

BackgroundDuring aerobic exercise, cerebral blood flow (CBF) decreases past 70 % of maximal oxygen uptake (VO2), but transient hypercapnia could mitigate the reduction. AimsTo examine the effect of oral (OB), nasal (NB), and combined (CB) breathing on CBF during a graded maximal exercise test (GXT). MethodsSix young males (age: 21.8 ± 2.3 years) performed three GXTs until volitional fatigue using a randomized breathing condition (OB, NB, or CB) order. Respiratory gases were assessed via a metabolic cart. Ultrasound sonography (7.5 MHz linear transducer) was utilized to assess the peak systolic velocity (PSV), end-diastolic velocity (EDV), and vessel diameter of the internal (ICA) and external (ECA) carotid artery. A one-way ANCOVA, with VO2 as a covariate, followed by a Bonferroni post-hoc analysis, was utilized to examine the differences between the breathing conditions. ResultsThe end-tidal partial pressure of CO2 (PetCO2) was significantly greater (p = 0.006) during NB (33.16 ± 1.37 mmHg) than that of CB (26.63 ± 1.32 mmHg) and OB (26.72 ± 1.37) at 100 % VO2max. There was a trend of a greater PSV in the ICA throughout the entire GXT that was only significantly greater (p = 0.027) during NB (126.12 ± 7.51 cm/s) compared to OB (92.47 ± 7.34 cm/s) but not CB (111.91 ± 7.14 cm/s) at 70 % VO2max. ConclusionsDuring a GXT, NB demonstrated a superior capacity to increase CBF, denoted by a higher PSV in the ICA compared to CB and OB, which might be partly related to an increased PetCO2.

Riverine Influences and Seasonal Dynamics: Exploring Carbonate System Variations and Air‐Sea CO2 Fluxes in the Southern Yellow Sea and East China Sea

AbstractIn this work, the seasonal variations of the carbonate system and air‐sea CO2 fluxes were investigated by two cruises in the southern Yellow Sea (SYS) and the East China Sea (ECS), which were significantly influenced by the Changjiang riverine inputs across seasons. Biological‐mediated change of dissolved inorganic carbon (DIC) was first quantitated through a three end‐member mixing model from winter to spring. Our modeling results suggested that DIC addition through biological remineralization persisted in the SYS during winter and spring, while DIC removal was evident in the Changjiang River Plume and the offshore ECS triggered by river inputs in spring. Horizontal and vertical mixing together constituted the largest contribution to the interseasonal variability of partial pressure of CO2 (pCO2) in the SYS (−69.5%), the river plume (−59.3%), and the ECS offshore (−43.8%), followed by temperature effects in the plume area (29.4%), and biological processes in the ECS offshore (24.1%) and the SYS (−7.7%), with air‐sea CO2 exchange contributing the least in both three subregions. The SYS, the river plume, and the ECS offshore all acted as atmospheric CO2 sinks in both winter and spring. Furthermore, their ability to absorb atmospheric CO2 increased from winter to spring, as reflected in a ∼1.8‐fold increase in the overall spring air‐sea CO2 flux compared to winter estimation.

Study on the influence factors of rock breaking by supercritical CO2 thermal fracturing

At present, there is a growing demand for safe and low-pollution rock-breaking technology. The rock breaking technology of supercritical CO2 thermal fracturing has many advantages, such as no dust noise, no explosion, high efficiency, controllable shock wave and so on. Fully considering the combustion rate of energetic materials, heat and mass transfer, CO2 phase change and transient nonlinear flow process, a multi-field coupled numerical model of rock breaking by supercritical CO2 thermal fracturing was established based on the existing experiments. The influence factors of CO2 thermal fracturing process were studied to provide theoretical guidance for site construction parameters optimization. The numerical simulation results were in good agreement with the experimental observation results. The results showed that the maximum temperature of CO2 and the growth rate of CO2 pressure during the fracturing process would decrease accordingly with the increase of CO2 initial pressure. But the change in CO2 peak pressure wasn't significant. Appropriately increasing the heat source power could improve the heating and pressurization rate of CO2 and accelerate the damage rate of rock. The relevant results were of great importance for promoting the application of rock breaking by supercritical CO2 thermal fracturing technology.

Evaluation of a Sepsis Alert System at a Veterans Affairs Medical Center

Background: Automated sepsis alerts have become a widely implemented screening tool aimed at early detection of clinically unstable patients. Prior research has shown mixed results depending on the type of screening tools used and the patient population studied. This study aimed to evaluate the predictive value of an alert system created for identifying patients with sepsis to determine utility in clinical practice prior to implementation. Additionally, clinical management of those with and without sepsis was compared to measure potential added benefit of this system in clinical decision making. Methods: A TheraDoc® software sepsis alert was generated for non-ICU patients meeting >2 SIRS criteria within a 24-hour time period (temperature >38°C or 90, respiratory rate >20 or partial pressure CO2 12,000 or 10% bands/immature cells) during March 2023. Alerts were excluded if they were duplicates (using identical criteria or a second alert within 24 hours), triggered by labs collected >48 hours prior, or death or discharge occurred before the time of alert. The primary outcome was positive predictive value (PPV) of sepsis identification, confirmed by ICD-10 codes and diagnostic studies (cultures, imaging). Secondary outcomes included clinical management (antibiotic utilization [AU] and choice, infectious disease [ID] consultations and culture collection). Antibiotics were categorized as broad-spectrum using National Healthcare Safety Network (NSHN) criteria. Secondary outcomes were compared between sepsis and SIRS without infection groups (SIRS) by chi-square analysis. Results: After applying exclusion criteria, 116 of 166 alerts were analyzed; 55 of 116 alerts had confirmed sepsis (PPV 47.4%). Patients with sepsis were more likely to have an ID consult (16% [9/55] vs 7% [4/61]) and cultures collected (70.9% [39/55] vs 39.3% [24/61]) compared to SIRS patients, however these differences were not statistically significant. AU was higher with confirmed infections compared to SIRS patients (94.5% [52/55] vs 32.8% [20/61], p < 0 .05) along with use of broad-spectrum antibiotics (73% [38/52] vs 40% [ 8/20] p < 0 .05). Conclusions: While automated alerts may enable early identification of sepsis, use of SIRS criteria alone has poor specificity, which was borne out by the low PPV in this study. Our study found that management of sepsis patients (as measured by AU and culture ordering) was better than expected and combined with the low PPV of this alert system resulted in our team rejecting widespread adoption of SIRS-based sepsis alerts.

Triaxial-mechanical and permeability properties of coal body under varying CO2 pressures

The sequestration of CO2 in coal seams has become an effective way to curb greenhouse-gas emissions. Coal mechanics and permeability properties are key factors affecting the safe sequestration of CO2 in coal seams, and both are significantly affected by the CO2 injection pressure. In this study, triaxial compression-permeability tests were conducted on coal under varying CO2 and limited confining pressures using a measurement system to determine the coupled mechanical properties and adsorption permeability of coal. The effects of CO2 pressure on the mechanical properties and evolution of coal permeability were investigated. A three-dimensional statistical damage constitutive model of coal that considers CO2 adsorption damage was established. The results showed that the stress–strain curve of the coal was divided into four stages. During the first two stages, the amplitudes of the permeability changes were small, whereas at the peak stress point, a permeability “jump” phenomenon occurred, after which an increase in stress resulted in a slower amplitude increase in permeability. The CO2 pressure had an evident damage-deterioration effect on the mechanical properties of the coal samples, and the primary failure characteristic was shearing damage. The higher the CO2 pressure, the higher the degree of internal fragmentation and fracture network complexity of the coal body. During the triaxial compression-permeability experiment, the normalized permeability of the coal samples tended to increase slowly, followed by a rapid increase and back to a slow increase. However, with increasing CO2 pressure, the initial permeability of the coal samples decreased, whereas the normalized permeability increased sharply. The rationality and accuracy of the constitutive model were verified by comparing the established constitutive model and test stress–strain curves of the coal samples. The results of this study can provide theoretical references for CO2 geological storage and facilitate the selection of appropriate CO2 injection pressures.

Decarboxylation cross‐linking of fluorescein‐based copolyimides for gas separations

AbstractA fluorescein‐based diamine, 2‐(3,6‐bis(4‐amino‐3‐hydroxyphenoxy)‐9H‐xanthen‐9‐yl) benzoic acid (CADA), was synthesized and copolymerized with Durene and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) to form a 6FDA‐Durene/CADA (3:2) copolyimide. The copolyimide was thermally cross‐linked at 300–425°C to form a series of decarboxylated cross‐linked polyimides. Compared with the 6FDA‐CADA polyimide, the incorporation of Durene diamine increased gas permeability of the pristine and the thermally cross‐linked polyimides greatly. The copolyimide cross‐linked at 375°C showed separation performance to the O2/N2 gas pair beyond the 1991 Robeson upper limit, while the CO2/CH4 separation property of the copolyimide cross‐linked at 425°C (PI‐425) was close to the 2008 Robeson upper limit. Moreover, the anti‐CO2‐induced plasticization property of the 6FDA‐Durene/CADA(3:2) copolyimides was improved by cross‐linking. The copolyimides cross‐linked at 350°C and above were not plasticized at a CO2 pressure up to 30 atm. This study showed that gas transport property of the decarboxylated cross‐linked polyimides could be improved significantly by the incorporation of bulky diamino moiety. The fluorescein‐based copolyimide had great potentials for gas separation applications.

Fast, accurate and accessible calculations of leaf temperature and its physiological consequences with NicheMapR

Abstract Mechanistic predictions of ecological niches are fundamentally based on energy and mass exchange processes that, to be realistic, must be linked to microclimate and incorporate behaviour and physiology. Estimates of leaf temperature and associated transpiration and net photosynthesis rates are fundamental in ecology, agriculture and global change biology. Equations for calculating leaf energy budgets have been available for over 60 years and complex models of stomatal behaviour have been developed. However, user‐friendly ways of estimating leaf temperature under realistic microclimatic regimes, including soil moisture effects, remain limited. Here we show that the integrated microclimate and ectotherm functions of the NicheMapR package for the R programming environment can be used to make fast and effective estimates of leaf temperature and associated rates of water loss and photosynthesis for a wide range of leaf functional types, root depths and microhabitats. Stomatal conductance may be constant or simulated to change dynamically (a) as a function of vapour pressure deficit and CO2 concentration, (b) as a function of soil water potential and (c) as a thermoregulatory mechanism to avoid heat stress. We tested the approach against hourly leaf temperature observations in summer from an arid shrubland in Australia, a temperate woodland in Montana USA, along an elevational gradient in Colorado USA, and at a botanical garden in Florida, USA. National or global gridded data sets can provide the required forcing data but local observational data or some combination of local and gridded data can be used. The global ERA5 and NCEP datasets allow historical leaf energy budget calculations to be made anywhere in the world and a Shiny app has been developed to facilitate use of the model with these datasets. Situated leaf energy budget calculations can be used to design informative field programs to collect much needed detailed temporal data on leaf temperature under natural settings, enabling better predictions and interpretations of how plants respond to environmental change.

Straw-based biochar prepared from multi-step KOH activation and its structure-effect relationship of CO2 capture under atmospheric/pressurized conditions via experimental analysis and MD/DFT calculations

Porous carbon-based CO2 capture holds great promise. However, the preparation process, pore structure and oxygen/nitrogen functional groups of porous carbon on CO2 adsorption still remain unclear. Herein, we develope straw-based biochar with ultra-high specific surface area(SSA), high micropore ratio and different O/N content by modifying the two-step KOH activation procedure and confirm the KOH activation mechanism, CO2 adsorption characteristics, and the structure-effect relationship of CO2 capture. The KOH activation process is controlled by the activation temperature and is divided into five temperature zones. The pickling treatment enhanced the activation effect of biochar, with a SSA of 3567.33 m2/g and a microporous ratio of 96.05 %. The potassium-containing active components reacts with the defective carbon structure above 800 °C catalyzed by alkali and alkaline earth metals(AAEMs), but reacts with the aliphatic hydrocarbon group after pickling. H-4–9-4-m has a maximum CO2 adsorption capacity of 24.77 mmol/g (25 °C/30 bar), whereas 4–9-2-m has a maximum capacity of 3.46 (25 °C/1 bar) and 5.42 mmol/g (0 °C/1 bar) and outstanding CO2/N2 selectivity (123 at 0.02 bar). The pressurized CO2 adsorption capacity is positively correlated with total pore volume. While under atmospheric pressure, the optimal adsorption site of biochar at 25 °C is ultramicroporous(0.5 nm) and oxygen-containing functional groups, and transforms into ultramicroporous(0.7 nm) and N-5 groups at 0 °C. The simulation results show that 0.5 nm is the pore size of CO2 adsorption from monolayer to bilayer, and both oxygen/nitrogen-containing groups could increase the CO2 adsorption capacity of biochar. This study provides guidance for the preparation of excellent carbon-based CO2 adsorbents according to application scenarios.

Carbon dioxide hydrate crystallization thickening & morphology in a micro-confined environment for carbon capture & sequestration processes

Carbon dioxide capture and sequestration (CCS) are critical processes that are necessary to mitigate the impacts of climate change. In pipelines used for CCS and for ocean sequestration, the formation of CO2 hydrates can occur and be detrimental to the safety and integrity of the CCS equipment and process. Understanding the crystallization thickening behavior of CO2 hydrates is vital for understanding hydrate formation in CO2 pipelines and in other CCS applications, such as sequestration and CO2 capture or storage. In this study, a microfluidic chip reactor was used to crystalize and thicken CO2 hydrates at the channel walls. The morphology of the CO2 hydrates was visually analyzed and quantified using in situ Raman spectroscopy. Two hydrate layers were consistently observed. An annealed, dense layer of hydrate shared an interface with liquid water, while a porous hydrate layer shared an interface with CO2 gas. Capillary-like pore spaces could be observed in the porous layer, which confirms one proposed mechanism for hydrate film thickening. Subcooling (0.5–1.5 K), pressure (2.51, 3.10 MPa), and flow rate of CO2 (0.167, 1.67 mm3/s) were studied for their impact on the overall CO2 hydrate film thickness over time. Over the ranges of these chosen parameters, only CO2 flow rate was found to have a significant impact on the thickening of CO2 hydrates, and a higher flow rate led to thicker crystalline hydrate films. A first principles mass transfer model for hydrate film thickness was developed and applied to the measurement data collected for overall hydrate film thickness.

Optimal Dynamic Regimes for CO Oxidation Discovered by Reinforcement Learning.

Metal nanoparticles are widely used as heterogeneous catalysts to activate adsorbed molecules and reduce the energy barrier of the reaction. Reaction product yield depends on the interplay between elementary processes: adsorption, activation, desorption, and reaction. These processes, in turn, depend on the inlet gas composition, temperature, and pressure. At a steady state, the active surface sites may be inaccessible due to adsorbed reagents. Periodic regime may thus improve the yield, but the appropriate period and waveform are not known in advance. Dynamic control should account for surface and atmospheric modifications and adjust reaction parameters according to the current state of the system and its history. In this work, we applied a reinforcement learning algorithm to control CO oxidation on a palladium catalyst. The policy gradient algorithm was trained in the theoretical environment, parametrized from experimental data. The algorithm learned to maximize the CO2 formation rate based on CO and O2 partial pressures for several successive time steps. Within a unified approach, we found optimal stationary, periodic, and nonperiodic regimes for different problem formulations and gained insight into why the dynamic regime can be preferential. In general, this work contributes to the task of popularizing the reinforcement learning approach in the field of catalytic science.

Evaluation of parameters impacting grey H2 storage in coalbed methane formations

Injecting grey hydrogen into coalbed methane formations has the potential to transform coal into a geologically temporary “H2-Battery” and a permanent “CO2-sink”. This study aims to thoroughly evaluate crucial parameters-sorption, diffusion, and matrix swelling/shrinkage-that impact grey hydrogen injection in CH4-enriched coalbed formations. In terms of sorption capacity, CO2 exhibits the highest, followed by CH4 and then H2. Sorption data affirmed that anthracite coal has a certain degree of adsorption capacity for H2, with H2 demonstrating superior diffusive gas deliverability as indicated by its diffusion coefficient, which is approximately six times higher than that of CO2. These characteristic position coal as a promising candidate for temporary H2 storage and cleaning, optimizing injectivity and depletion efficiency. Interestingly, H2 adsorption induced matrix shrinkage in coal, in contrast to other strong sorption gases such as CH4 and CO2, which resulted in matrix swellings. Matrix deformations induced by H2–CO2 mixture (grey hydrogen) injection were conducted and quantified to evaluate grey hydrogen injection in future field trials. The results reveal that the majority of directional strains indicated that when the partial pressure of CO2 in the H2–CO2 mixture is equivalent to pure CO2 pressure, the latter case induces elevated swelling strains. This finding implicitly supports the hypothesis that H2–CO2 mixture injection causes less matrix swelling than pure CO2 injection at equivalent CO2 pressure. This work provides essential parameters to illustrate an enhanced synergism among hydrogen storage, carbon sequestration, and enhance coalbed methane recovery through grey hydrogen injection in coal formations.

Revisiting Winter Southern Ocean CO2 Uptake Based on CALIPSO Observations

AbstractThe absorption of atmospheric carbon dioxide (CO2) in the Southern Ocean represents a critical component of the global oceanic carbon budget. Previous assessments of air‐sea carbon flux variations and long‐term trends in polar regions during winter have faced limitations due to scarce field data and the lack of ocean color satellite imagery, causing uncertainties in estimating CO2 flux estimation. This study utilized the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite to construct a continuous 16‐year (2006–2021) time series of sea surface partial pressure of CO2 (pCO2) in the Southern Ocean. Our findings revealed that the polar region in South Ocean acts as a carbon sink in winter, with CO2 flux of ∼30 TgC in high‐latitude areas (South of 50°S). This work highlights the efficacy of active remote sensing for monitoring sea surface pCO2 and contributes insights into the dynamic carbonate systems of the Southern Ocean.

Robotic Pediatric Urologic Surgery-Clinical Anesthetic Considerations: A Comprehensive Review.

Minimally invasive robotic approaches have become standard in many institutions over the last decade for various pediatric urological procedures. The anesthetic considerations for common laparoscopic and robotic-assisted surgeries are similar since both require the insufflation of CO2 to adequately visualize the operative area. However, few studies exist regarding anesthesia for robotic procedures in children. We hypothesized that pediatric patients undergoing robotic urologic surgeries would require specific anesthetic strategies, especially given the inherently longer durations of these procedures. This study aimed to evaluate anesthetic considerations, current robotic procedures, optimal patient positioning, and port placement for robotic-assisted surgery in pediatric patients. A comprehensive literature review of all published manuscripts from PubMed, EMBASE database, and Google Scholar was performed, focusing on robotic procedures involving pediatric patients, anesthesia for pediatric urology patients, and related topics from 1996 to 2023. Forty published manuscripts were identified and reviewed in depth. In pediatric cases, insufflation pressures and volumes are lower due to the laxity of the abdominal wall. However, the increase in intra-abdominal pressure and absorption of CO2 may result in disproportionate changes in cardiopulmonary function. Specific patient positioning for robotic approaches may further compound these physiological changes. Correct patient positioning is essential to facilitate surgery optimally and safely. Understanding the physiological changes that can occur during a pediatric patient's robotic urologic surgery allows for safer anesthesia management.