High CO2 Partial Pressure Research Articles

Geochemical evolution and seasonality of groundwater recharge at water-scarce southeast margin of the Chihuahuan Desert in Mexico

Climate models for the 21st century project further reduction in the warm season precipitation and more frequent droughts across Mexico. In the possible scenario of enhanced aridity from global warming, the δ18O (−10.6 to −6.3 ‰) and δ2H (−71.1 to −57.1 ‰) compositions and deuterium-excess (0.2–14.6‰) of shallow groundwater from two different basins (Sandia and El Potosi) with similar geological and geomorphological settings were considered to evaluate the influences of early summer rainfall and later summer tropical storms on aquifers at water-scarce southeast margin of the Chihuahuan Desert. Groundwater of the Sandia Basin was recharged mainly from tropical storms. Higher CO2 partial pressure (log pCO2: −2.70 to −1.61) caused more gypsum dissolution (Ca–Mg–SO4 facies) and the effect of irrigation return flow (Ca–Mg–Cl facies) was minor. Even though the El Potosi Basin is in proximity, its groundwater was recharged from both the early and late summer precipitations. The multivariate factor analysis helped to separate the process of rock-water interactions from the recharge seasonality. Gypsum dissolution was less as the partial pressure of CO2 was comparatively lower (log pCO2: −3.01 to −2.15), and the ion exchange along with carbonate mineral dissolutions led to Ca–Mg–HCO3 facies. Over-exploitation under the condition of reduced warm season rainfall would continue to enhance the salinity of groundwater in this region. Hence, the drought mitigation policies should prioritize sustainability of the depleted aquifers and cultivation of salinity resistant crops.

Shaping a reactor microbiome generating stable n-caproate productivity through Design-Build-Test-Learn approach

n-Caproate production by reactor microbiomes is receiving more attention due to its high economic and environmental benefits. However, the ecological complexity within the bioreactor obstructs the development of functional microbiome shaping technology, which is expected to further unlock the potential of microbiomes. This study adopted the “Design-Build-Test-Learn approach” to develop a fast and reliable microbiome shaping technology. In the first step, 10 mM n-butyrate was a better electron acceptor than 10 mM acetate when 50 mM L-lactate was used as an electron donor, but the n-caproate selectivity was only 33.9%. This was ascribed to the high H2 and CO2 partial pressure causing a high homoacetogenic activity of the microbiome, hindering n-caproate production. The second step was conducted by continuously removing headspace CO2, and as a result n-caproate selectivity increased to 68.6%. This process was repeated five times to apply selection pressures, and a stable n-caproate specificity (i.e., 57.3–62.6%) was achieved using 50 mM L-lactate and 10 mM n-butyrate. Finally, a n-caproate-producing microbiome with a high productivity (10.0 gCOD/L/day, 0.19 g/L/h) was shaped in a substantially shorter start-up period (84 h) than other studies had achieved. An 16S rRNA sequencing analysis of the shaped microbiome identified the abundance of C. carboxidivorans, which is a chain-elongating bacterial species.

Controls on Physical and Chemical Denudation in a Mixed Carbonate‐Siliciclastic Orogen

AbstractMixed siliciclastic‐carbonate active orogens are common on Earth's surface, yet most studies have focused on erosion and weathering in silicate‐rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed‐lithology regions. However, our knowledge of weathering and erosion in mixed carbonate‐silicate lithologies is limited and, thus, so is our understanding of the mechanistic coupling between uplift, weathering, and the carbon cycle. Here, we partition denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennines—a mixed carbonate‐siliciclastic active orogen—using dissolved solutes, the carbonate sand fraction, and existing 10Be denudation rates. Erosion generally dominates total denudation fluxes relative to weathering by an order of magnitude. Carbonate and silicate contributions to erosion vary between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be kinetically limited, whereas carbonate weathering may be limited by acid supply. Carbonate re‐precipitation estimated by comparing ion ratios (Sr, Ca, Na) from rivers and bedrock suggests that up to 90% of dissolved Ca2+ is lost from carbonate‐rich catchments. Corresponding [Ca2+] estimates for the weathering zone are high, likely driven by high soil CO2 partial pressures (pCO2); however, re‐equilibration with atmospheric pCO2 in rivers converts solutes back into grains that become part of the physical denudation flux. Weathering limits in this landscape therefore differ between the subsurface weathering zone and riverine exports, and our findings suggest that carbon cycle models may overestimate the sensitivity to erosion of solute exports (Ca2+ and HCO3−) derived from carbonate weathering.

Exploring the Role of the Central Carbide of the Nitrogenase Active-Site FeMo-cofactor through Targeted 13C Labeling and ENDOR Spectroscopy.

Mo-dependent nitrogenase is a major contributor to global biological N2 reduction, which sustains life on Earth. Its multi-metallic active-site FeMo-cofactor (Fe7MoS9C-homocitrate) contains a carbide (C4-) centered within a trigonal prismatic CFe6 core resembling the structural motif of the iron carbide, cementite. The role of the carbide in FeMo-cofactor binding and activation of substrates and inhibitors is unknown. To explore this role, the carbide has been in effect selectively enriched with 13C, which enables its detailed examination by ENDOR/ESEEM spectroscopies. 13C-carbide ENDOR of the S = 3/2 resting state (E0) is remarkable, with an extremely small isotropic hyperfine coupling constant, Ca = +0.86 MHz. Turnover under high CO partial pressure generates the S = 1/2 hi-CO state, with two CO molecules bound to FeMo-cofactor. This conversion surprisingly leaves the small magnitude of the 13C carbide isotropic hyperfine-coupling constant essentially unchanged, Ca = -1.30 MHz. This indicates that both the E0 and hi-CO states exhibit an exchange-coupling scheme with nearly cancelling contributions to Ca from three spin-up and three spin-down carbide-bound Fe ions. In contrast, the anisotropic hyperfine coupling constant undergoes a symmetry change upon conversion of E0 to hi-CO that may be associated with bonding and coordination changes at Fe ions. In combination with the negligible difference between CFe6 core structures of E0 and hi-CO, these results suggest that in CO-inhibited hi-CO the dominant role of the FeMo-cofactor carbide is to maintain the core structure, rather than to facilitate inhibitor binding through changes in Fe-carbide covalency or stretching/breaking of carbide-Fe bonds.

Evolution of a Deep Fluid in a Surficial Environment Using Stable Carbon and Sulfur Isotopes: Case of the Transitional Zone of the Edwards Aquifer in South Central Texas

The Edwards Aquifer in south central Texas (USA) features a distinct fault line defining the freshwater and saline water zones. We aim to elucidate the evolutionary behavior of carbon and sulfur emanating from deep environments and flowing in surficial environment so as to better understand the cycling of these metals in water environments. To characterize the evolution of carbon and sulfur species in surficial environment as the fluid emanates from a deep saline aquifer, we monitored the chemical and isotopic (δ13CDIC and δ34SSO4) parameters over a 700-m stretch on a stream-pond system situated on the saline-freshwater line of the Edwards Aquifer’s artesian zone. A three-tier evolution process associated with the interaction of a deep saline fluid with a fresh-ponded water was observed, namely: A deep fluid control zone characterized by decreasing pH values and relatively high total dissolved solids (TDS) concentrations along the stream path; a mixing zone of the deep fluid and fresh-ponded water where the TDS concentrations showed a sharp decline and a continual decrease in pH values; and a fresh-ponded water-controlled zone with a stable pH value and low TDS concentrations. The decreasing pH values were a result of CO2 outgassing due to the relatively high CO2 partial pressures (10–2.53 atm) relative to atmospheric (10–3.50 atm) in the aqueous system, and the high TDS concentrations were attributed to the deep saline fluid emanating at the well-head. The enrichment in the δ13CDIC and δ34SSO4 for the initial stream path reflects the kinetic isotopic fractionations associated with CO2 outgassing and with the microbial conversion. The zonation of the evolutionary process indicates that (i) solutes play a critical role in the evolution of carbon and sulfur in surficial environment, (ii) kinetic and chemical fractionation are the dominant processes controlling carbon evolution, and (iii) microbial metabolism primarily controls sulfate fractionation and evolution through the conversion of sulfate to thiosulfate.

Controlling factors of seasonal and spatial variation of riverine CO2 partial pressure and its implication for riverine carbon flux

Global carbon cycle is closely related to the earth's energy budget, because CO2 plays an active role in the global climate change. The higher CO2 partial pressure (pCO2) in inland water in comparison with atmosphere, causing a CO2 evasion from water to the air. However, the relationship between CO2 evasion, riverine carbon export, and hydrochemistry in watershed has remained largely unknown. This study collected 84 river water samples in Jiulongjiang River, to further address this subject on a small watershed scale. Water temperature fluctuation, riverine photosynthesis, and acidic matter input could not account for the seasonal variation of pCO2 in Jiulongjiang River. The spatial shifts of pCO2 were derived from the mixing process between headwater and soil influx. The soil influx with high pCO2 compensated the CO2 lost from evasion and caused pCO2 in Jiulongjiang River higher than the atmospheric level. The seasonal variation of pCO2 was caused by the precipitation difference between the wet season and dry season. The addition of rainwater significantly decreased the riverine pCO2 and HCO3− concentration in the wet season. The CO2 evasion rate in Jiulongjiang River was clearly higher than that in most worldwide large rivers. The annual CO2 evasion flux in Jiulongjiang River Basin was estimated about 2.48 × 105 T C/year, which was higher than the riverine total carbon export. The CO2 evasion rate exhibited significantly positive relationship with water surface area, indicating that the global CO2 evasion flux may be roughly estimated based on the observed regression relationship. Overall, our study indicated that it still requires collaborative effects to investigate the carbon dynamics in river water, more estimations of CO2 outgassing flux from river water under different hydrologic and geologic conditions are necessary.

Techno-economic assessment and comparison of absorption and membrane CO2 capture processes for iron and steel industry

An economic assessment of the post-combustion CO2 capture process for the iron and steel industry is presented herein. Absorption- and membrane-based CO2 capture processes were modeled and simulated using Unisim® and MATLAB®, and an economic assessment based on the multiparameter scaling methodology was used to evaluate the economics of the CO2 capture processes. Flue gases with CO2 concentrations in the range of 4.8–27.3 mol% were selected from a typical steel plant, and their techno-economic impact on process design and CO2 capture cost was systematically analyzed. As the flue gas CO2 concentration increased from 4.8 to 27.3 mol%, the CO2 capture cost of the absorption-based process without CO2 compression decreased from 73.5 USD2019/tCO2 to 55.3 USD2019/tCO2, and that of the membrane-based process decreased from 271.7 USD2019/tCO2 to 41.7 USD2019/tCO2. The economics of the CO2 compression process integrated case were also evaluated. This dramatic change in the capture cost for membrane systems is related to the high partial pressure of CO2 being favored for membranes, compared to absorption-based processes. The case study confirms that the membrane-based CO2 capture process becomes more cost-effective and energy-efficient than the absorption-based process as the CO2 concentration of flue gas increases.

Emission of species of environmental and process concern during simulated oxy-fuel gasification

The release of species of environmental concern during simulated oxy-fuel gasification in a laboratory scale fluidised bed have been investigated. Fluidising gases containing a high partial pressure of CO2 and in some tests, steam, were used. The species considered are tars, H2S and NH3 and the aim has been to gain an understanding of the impact of the gasifer operating conditions on their release. This is part of a programme of work on the potential of oxy-fuel gasification as a means of enabling the use of coal to continue as a source of energy, whilst capturing the CO2 for sequestration to minimise the impact on climate change.It has been shown that the tars released during pyrolysis are efficiently destroyed during their passage through the hot, char containing bed. The measured emission of tar was very low, particularly when compared to a conventional fixed bed gasifier. The extent of S release as H2S depends on the fuel-S and ash-Ca contents, and on the operating conditions. Increasing the partial pressure of CO2, steam and raising the temperature increased the proportion of S released. Adding dolomite, to retain S, decreased the emission level at atmospheric pressure, provided the temperature was above 950 °C. The use of this method to reduce S emissions at elevated pressure would require careful consideration, as the high partial pressure of CO2 in the fluidising gas can prevent the calcination of the dolomite and therefore reduce its effectiveness. Steam was found to increase the proportion of fuel-N converted to NH3 and the concentration also depended on the bed temperature. A peak in the concentration was noted at 850 °C, due to the opposing impacts on increased release as the temperature was raised and increasing equilibration of NH3 to N2 and H2.

High CO2 levels drive the TCA cycle backwards towards autotrophy.

It has recently been shown that in anaerobic microorganisms the tricarboxylic acid (TCA) cycle, including the seemingly irreversible citrate synthase reaction, can be reversed and used for autotrophic fixation of carbon1,2. This reversed oxidative TCA cycle requires ferredoxin-dependent 2-oxoglutarate synthase instead of the NAD-dependent dehydrogenase as well as extremely high levels of citrate synthase (more than 7% of the proteins in the cell). In this pathway, citrate synthase replaces ATP-citrate lyase of the reductive TCA cycle, which leads to the spending of one ATP-equivalent less per one turn of the cycle. Here we show, using the thermophilic sulfur-reducing deltaproteobacterium Hippea maritima, that this route is driven by high partial pressures of CO2. These high partial pressures are especially important for the removal of the product acetyl coenzyme A (acetyl-CoA) through reductive carboxylation to pyruvate, which is catalysed by pyruvate synthase. The reversed oxidative TCA cycle may have been functioning in autotrophic CO2 fixation in a primordial atmosphere that is assumed to have been rich in CO2.

Steel Corrosion in Aqueous Piperazine at Water Wash Conditions

Corrosion of a carbon steel (C1010) and three stainless steels (430, 304L, and 316L) was measured at water wash conditions in the low-gas flow reactor. Due to the low piperazine (PZ) concentration in the water wash (WW), dissolved CO2 in the WW solution can be acidic and cause C1010 corrosion. The presence of PZ increases the solution pH and reduces the corrosion rate, and the correlation between C1010 corrosion rate and PZ concentration is presented. Solutions saturated with CO2 in N2 mixtures showed lower carbon steel corrosion than those with a CO2 in air mixture. Higher CO2 partial pressure in the gas phase results in a more acidic solution, which requires more PZ to lower the corrosivity. Stainless steels have great resistance to corrosion in the WW.

Hydrochemical state of the Uglovoy Bight (Amur Bay) in different seasons

Hydrological and chemical surveys were conducted in the Uglovoy Bight in October, 2019, February, May and June, 2020 (in total 120 stations) and chemical analyses of water from 13 small rivers running into the bight were done on October 21-22, 2020. Extremely high concentration of nutrients was detected in the Peschanka, Saperka and Gryaznukha Rivers that was obviously caused by waste waters discharge. These rivers were the main source of the bight eutrophication. Within the bight, the highest anomalies of chemical parameters, as low oxygen content, low pH, high concentrations of nutrients (N, P, Si), high turbidity, and high CO2 partial pressure were observed close to these rivers mouths, in particular under the ice in winter, when wind mixing was absent. The hypoxia disappeared in the warm period of year because of wind mixing. High concentrations of total nitrogen (10.0-40.0 μmol/L), total phosphorus (1.5-2.0 gmol/L), dissolved organic carbon (3-5 mgC/L), and chlorophyll a (0.5-2.0 μg/L) in all seasons were the results of active production-destruction processes, obviously with prevalence of organic matter destruction, since the water in the bight was undersaturated with oxygen and supersaturated with carbon dioxide — the bight accumulates and mineralizes organic matter from terrestrial and riverine discharge. Underwater photographs did not detect Zostera meadows at the bottom, which were observed in the northwestern Uglovoy bight in the past. Comparison of historical data on episodic studies in the bight with results of the surveys indicates degradation of its ecosystem, with such signs as disappearance of seagrass, hypoxia in winter, and CO2 flux into the atmosphere. Reduce in water exchange between the bight and the Amur Bay caused by construction of the underwater pipeline in 1982 and the bridge in 2012 is suggested as a reason of the degradation.

Carbonate‐Phyllosilicate Parageneses and Environments of Aqueous Alteration in Nili Fossae and Mars

AbstractThe equilibrium thermodynamics of Fe/Mg‐phyllosilicates and carbonates have been investigated using numerical modeling, with emphasis on the effects of evaporation and temperature (hydrothermalism) under conditions related to present‐day and primitive Mars, that is, low or high CO2partial pressure, under oxidizing or reducing environments. Findings are discussed in relation to alteration and weathering of minerals found in the Nili Fossae region. Results show that nontronite precipitates at very high water‐to‐precipitate ratio and low temperature, in association with ferrihydrite. During evaporation, this assemblage leads to carbonates: calcite and magnesite, and to low temperature iron‐rich serpentine phyllosilicates such as cronstedtite or berthierine under reducing conditions. At high temperature, the initial paragenesis dominated by nontronite leads to hematite and berthierine at low CO2partial pressure, and to talc, magnesite and antigorite at high CO2partial pressure. Thus, the Fe/Mg‐smectites, Mg‐carbonate, and Mg‐serpentine found near Nili Fossae may result from several alteration events. Weathering of primitive bedrock formed nontronite, with subsequent or concurrent hydrothermalism leading to Mg‐serpentine. Further carbonation due to CO2‐rich fluids led to talc, magnesite and to hydrogen/carbon monoxide/methane in the presence of iron, but at relatively low partial pressures (up to 10−4 bar). Unless the serpentinization process acted for extended periods of time and over a large portion of the martian surface, it is unlikely it significantly contributed to the atmospheric composition, except maybe for H2. However, such water‐rich active environments with the presence of redox reactions could have been suitable for the potential emergence of biological activity.

Response of soybean genotypes to iron limiting stress in calcareous vertisol under ambient and elevated CO2 and temperature conditions

Aim: To compare the relative performance of two contrasting genotypes of soybean to iron limiting conditions under ambient and elevated CO2 and temperature conditions. Methodology: A pot culture experiment was performed using calcareous vertisol soil. The environmental factors viz. CO2 and temperature were combined and applied as a single factor with two levels: a-[CO2+T] (400±10 µmol mol-1, day/night temperature 30oC/22oC) and e-[CO2+T] (610±10 µmol mol-1, day/night temperature 34oC/26oC). Soybean genotype that differed in iron use efficiency was used as another factor and two contrasting genotypes were used as two levels viz. iron efficient and responsive (FeER) and iron inefficient and responsive (FeIR). Results: The higher partial pressure of CO2 under elevated carbon dioxide and temperature condition (Pco2 = 61.8 Pa) dissolved the native CaCO3 from calcareous vertisol soil and thereby resulted in higher HCO3- ion concentration. The antagonistic interaction between Fe2+ with HCO3- ion resulted in greater iron stress. As compared to ambient condition, seed yield was significantly reduced under more stressed e-[CO2+T] condition and resulted in ~1.4 and ~1.9 times drop in FeER and FeIR genotypes, respectively. Iron efficient and responsive (FeER) genotype recorded an impressive performance, as compared to the iron inefficient and responsive (FeIR) genotype, in counteracting iron deficiency stress, both under ambient and elevated conditions. Interpretation: The intra-specific variability between soybean genotypes and their response to elevated CO2 and temperature can be exploited to remediate the emerging iron deficiency stress in soybean plants and suggest ways to structure the future breeding programmes to adapt to the climate change. Key words: Calcareous vertisol, Chlorosis, Climate change, CO2, Soybean

Selective Conversion of Carbon Dioxide to Formate with High Current Densities

Selective conversion of CO2 to formate with high current densities is highly desirable but still challenging. Copper hollow fibers with interconnected pore structures were fabricated via a facile method and used as a stand-alone cathode for highly efficient electrochemical reduction of CO2 to formate. Our studies revealed that delivering the reactant CO2 gas to the inner space of the hollow fiber could build up a higher CO2 partial pressure in the pores and presumably reduce the concentration of H[Formula: see text] from the electrolyte to effectively suppress the major competing reaction, hydrogen evolution reaction (HER), from 46.9% faradaic efficiency (FE) to 15.0%. A high selectivity for CO2 reduction to formate with a maximum FE of 77.1% was achieved with a high current density of 34.7[Formula: see text]mA cm[Formula: see text], which is one of the highest FEs on Cu-based materials. Mechanistic studies suggest that the abundant active sites along with the unique crystal facets induced by the high pressure of CO2 at the pore surface in the “gas in” mode are attributed to the superior electroactivity and selectivity for the CO2 reduction to formate. The Cu hollow fiber electrodes exhibit an outstanding long-term stability at high current density, showing great potential for large-scale practical applications.

Investigation of ZIF‐78 Morphology and Feed Composition on the Mixed Gas CO2/N2 Separation Performance in Mixed Matrix Membranes

AbstractIn this work, the influence of the zeolitic imidazolate framework 78 (ZIF‑78) morphology, with 1D pores, on the mixed matrix membrane (MMM) CO2/N2 mixed gas separation performance is investigated as well as the influence of the feed composition and pressure. Low aspect ratio and a high aspect ratio ZIF‑78 particles are synthesized and incorporated in Matrimid with 10 and 20 wt% additive content. High pressure CO2 and N2 sorption measurements show that both the low and high aspect ratio ZIF‑78 metal–organic frameworks (MOFs) exhibit similar sorption behavior. The incorporation of ZIF‑78 into Matrimid results in improved CO2 permeabilities up to 39%, without compromising the selectivity, relative to native Matrimid membranes. Both at low and high CO2 partial pressures, the MMMs containing the different ZIF‑78 morphologies show equal CO2 permeabilities, indicating that the ZIF‑78 morphology and consequently the aspect ratio are insignificant for these particular MMMs, contradicting previous observations in literature. Thus, depending on the MOF/polymer system, the MOF morphology and aspect ratio can be considered as a design aspect. Finally, a clear influence of feed composition and pressure on the MMM solubility coefficient and diffusivity is observed, emphasizing the importance of the mixed gas composition and measurement conditions.

Impact of controlled atmosphere storage on physiological quality of soybean seed

Soybean seed tends to lose its quality property if kept in inappropriate storage conditions. The aim of this work was to evaluate the effect of different oxygen (O2) and carbon dioxide (CO2) partial pressures, combined with different temperatures on the soybean seed physiological potential maintenance. In 2017, seed of the cultivars 8473 RSF and TECIRGA 6070RR were stored for 7 months under: [1] ambient air; controlled atmosphere (CA) with [2] 1 kPa O2 + 0.04 kPa CO2; [3] 2 kPa O2 + 0.04 kPa CO2; [4] 2 kPa O2 + 30 kPa CO2; and [5] 2 kPa O2 + 80 kPa CO2. In 2018, seed of NA 5909 RG and FEPAGRO 37RR were stored for 7 months under the following conditions: [1] ambient air; and CA with [2] 1 kPa O2 + 0.04 kPa CO2; [3] 1 kPa O2 + 15 kPa CO2; [4] 1 kPa O2 + 30 kPa CO2; [5] 2 kPa O2 + 0.04 kPa CO2. In both years the storage conditions were conducted at three temperatures (20, 25 and 30 °C). The seed were stored with moisture content between 11 and 11.5. The reduction of the O2 until 1.0 kPa maintained higher germination, however, storage above 25 °C is not recommended. High CO2 partial pressure did not have additional effects on physiological quality conservation compared to solely low O2. Seed of 8473 RSF stored at 25 and 30 °C resulted in low germination, regardless of the CA condition. NA 5909 RG reached 80% of germination, when CA was used, regardless of temperature. The ambient air did not maintain the seed physiological quality when stored at 25 and 30 °C and CA may efficiently maintain the physiological quality of soybean seed after 7 months, even in the higher temperature for NA5909 RG, but not for the other cultivars.

A comparative evaluation of recarbonated CaCO3 derived from limestone under oxy-fuel circulating fluidized bed conditions

SO2 emissions from coal-fired boilers are air pollutants and a source of acid rain, causing extensive environmental pollution. Limestone (CaCO3) is a Ca-based sorbent which is injected into circulating fluidized bed (CFB) boilers, where it combines with SO2 to produce calcium sulfate (CaSO4). As a result, SO2 emissions from a power plant are reduced. In this study, CaCO3 addition was proposed and the desulfurization efficiency improved. The direct desulfurization reaction is dominant in a commercial CFB boiler due to the high CO2 partial pressure, but CaO is formed at a fast reaction rate by calcination in the high temperature or in the low CO2 partial pressure region. When CaO remains in the loop seal, it is exposed to a high CO2 partial pressure condition moving through the recirculation section for an extended period and re-injected into the furnace as recarbonated CaCO3. To analyze the direct desulfurization reaction kinetics, a shrink core model in which the reaction proceeds inside the particle was adopted. Surface observations through FE-SEM of CaSO4 produced by the 180 minute long desulfurization experiment using TGA suggest that the CaSO4 crystal growth rate increased after the pre-treatment (recarbonation) of limestone. Recarbonation lowered the limestone crystallinity, causing a faster reaction. The CaCO3 recarbonation increased the Ca utilization by more than 20% when the direct desulfurization reaction occurred. The TGA experiments show that recarbonation contributes to CaSO4 conversion. Increasing the desulfurization efficiency using recarbonation can reduce the fixed investment and operating costs of oxy-fuel CFB plants because only desulfurization in the furnace is able to meet SO2 emission regulations or lower the flue gas desulfurization (FGD) dependence. Accordingly, the desulfurization conversions of recarbonated CaCO3 and limestone were compared in this study. Morphological changes in the limestone were also evaluated using XRD, FE-SEM, and other analysis methods.

High selectivity of CO2 conversion to formate by porous copper hollow fiber: Microstructure and pressure effects

Electrochemical reduction of CO2 by Cu hollow fibers to CO with high selectivity has previously been reported but selective conversion of CO2 to formic acid at high current densities, although highly desirable, is still challenging. Herein, a Cu hollow fiber with an interconnected pore structure is fabricated via a facile method and used as a stand-alone cathode for highly efficient electrochemical reduction of CO2 to formate. We obtain a high selectivity for CO2 reduction to formate with a maximum FE of 77.1% at a high current density of 34.7 mA cm−2, one of the highest FE on Cu-based materials. Our results suggest that delivering the CO2 gas into the inner space of the hollow fiber leads to a higher CO2 partial pressure in the pores due to the pressure drop across the wall of the Cu hollow fiber. As both the CO2 and H+ ions (from the electrolyte) compete for adsorption on the Cu hollow fiber active sites, the higher CO2 partial pressure makes CO2 adsorption more favorable, thereby reducing the concentration of the H+ on the active sites. This effectively suppresses the major competing reaction, hydrogen evolution reaction (HER), from 46.9% Faradaic efficiency (FE) to 15.0%. Furthermore, our studies reveals the impotency of the co-existence of Cu(100) and Cu(110) active site facets towards excellent selectivity of formate formation under high CO2 partial pressure. Additionally, the designed catalyst also exhibits out-standing long-term stability at high current density, demonstrating potential for large-scale practical applications.

A new concept for pore-scale precipitation-dissolution modelling in a lattice Boltzmann framework – Application to portlandite carbonation

Modelling of combined dissolution-precipitation at the pore scale requires the conceptualization of mineral precipitation and crystal growth, the formation of a protective diffusive layer by precipitants and slow reaction kinetics that are all coupled with alterations of the microstructure. In this work, we propose an improved approach for handling these challenges in a pore-scale coupled reactive transport model and apply it to portlandite carbonation. The model combines mineral geometry update as a consequence of dissolution-precipitation reactions during diffusive transport through a saturated porous medium, thermodynamic equilibrium chemistry and dissolution kinetics. Transport of ions is calculated by the lattice Boltzmann transport solver YANTRA. Transport and reaction processes are incorporated at different spatial length scales with the multilevel approach, i.e. mixed liquid-solid nodes in a pore-scale model, which accounts for processes at scales below the model spatial resolution. Instead of defining arbitrary values such as threshold or residual porosities to initiate or halt precipitation, information on crystal shapes, packing and solubility in nano-pores based on interfacial surface energy is used to control precipitation. Additionally, the sensitivity study has been performed on model parameters such as portlandite dissolution kinetics, interfacial surface energy, calcite crystal size, CO2 partial pressure on the rate of carbonation and on the calcite layer properties such as residual porosity and thickness. From the comparison between the modelled calcite growth and the experimental data it has been found that low diffusivity of calcite layer decreases the effect of portlandite dissolution kinetics rate in case of carbonation and diminishes the effect of CO2 partial pressure. Also differences in the structure of the calcite layer were observed for carbonation of portlandite at low and high CO2 partial pressures.

Paramètres dérivés du CO2 pour évaluer l’état hémodynamique chez le malade de réanimation

Le dioxyde de carbone (CO2) constitue le produit de dégradation final du métabolisme cellulaire. Plusieurs gradients de CO2, obtenus grâce à la mesure de la pression partielle de CO2 (PCO2) dans différents compartiments, sont utilisés afin d’évaluer l’état circulatoire des patients de réanimation. Au cours d’un état de choc, l’augmentation de la PCO2 veineuse et tissulaire est principalement la conséquence d’une hypoperfusion tissulaire et non d’une hypoxémie, reflétant ainsi une anomalie macro et/ou microcirculatoire. Un gradient veino-artériel de PCO2 (Pv-aCO2) ≥ 6 mmHg peut suggérer une inadéquation du débit cardiaque. À l’échelle locale, un gradient tissu-artériel en PCO2 (Pt-aCO2) élevé malgré un Pv-aCO2 normal (< 6 mmHg) peut faire évoquer une atteinte de la microcirculation locale. Enfin, un indice combiné des paramètres dérivés du CO2 et de l’O2, comme le rapport entre le Pv-aCO2 et la différence des contenus artériel et veineux en oxygène (Pv-aCO2 / CaO2 – CvO2), suggère une hypoxie tissulaire lorsqu’il dépasse 1,4. Chez les patients de réanimation en insuffisance circulatoire, les paramètres dérivés du CO2 doivent toutefois s’intégrer dans une approche multiparamétrique (examen clinique, marqueurs biologiques, échocardiographie et autres outils hémodynamiques).