Low CO2 Partial Pressure Research Articles

CO2Capture from NGCC Power Stations using Electric Swing Adsorption (ESA)

In this work, we have evaluated the technical feasibility of using Electric Swing Adsorption (ESA) to capture carbon dioxide from flue gases. Simulations under different operating conditions were performed to capture CO2 from Natural Gas Combined Cycle power stations where the CO2 concentration is 3.5%. The objective is to determine a proper cyclic operation to achieve a stream with high CO2 purity, running at high unit productivities to reduce the size and energetic consumption of the capture plant. We propose a novel process-scheduling of ESA process to purify the most adsorbed component to very high purities. Using an adsorbent comprising 70% zeolite and 30% of a binder conducting material (with a capacity higher than 1.1 mol of CO2 per kilogram at low CO2 partial pressure), it is not necessary to use a cooling step improving the process productivity. According to our simulations, with the proposed ESA process, it is possible to obtain a concentrated stream with 80% CO2 starting from a stream with 3.5%...

Gas exchange response of barley and pea cultivars to altitude variation in Himalaya

Leaf stomatal density (SD), net photosynthetic rates (PN), and stomatal conductance (gs) of Hordeum vulgare and Pisum sativum cultivars in Himalaya increased with altitude. Higher PN and leaf temperature under low CO2 partial pressure at high altitudes could evoke a higher gs and SD to allow sufficient influx of CO2 as well as more efficient leaf cooling through transpiration.

A Review of the Theories to Explain Arctic and Alpine Treelines Around the World

Forest growth is restricted at high latitudes and high elevations, and the limits of tree growth in these environments are dramatically marked by the treeline transition from vertical, erect tree stems to prostrate, stunted shrub forms. However, after 4 centuries of research, there is still debate over the precise mechanism that causes Arctic and alpine treelines. We review the various theories for treeline, including excessive light, low partial pressure of CO2, snow depth, wind exposure, reproductive failure, frost drought, and temperature. Some of these theories are very old and are no longer held in high esteem; while they may help to explain treeline physiognomy or local variation in treeline position, they generally fail as global explanations. Temperature-based theories appear to be the most reasonable, since cold temperature is really the only trait that is universally characteristic of treelines around the world. Temperature may limit a variety of physiological processes, such as carbon fixation, cuticular ripening, or new tissue development, and theories invoking these mechanisms are discussed. The vertical growth habit of trees is unfavorable to growth in this hostile environment: Low-profile vegetation enjoys a far more favorable microenvironment for growth. Microsite enviroment and ecological facilitation have been shown to be essential for successful regeneration, which is a prerequisite for upward advancement of treeline. Recent evidence supports a theory based on “sink limitation,” i.e., that new tissue development is restricted not by carbon availability but by cold treeline temperatures which limit cell division, and that this situation is exacerbated by arborescent growth (aboveground meristems coupled to cold ambient air temperatures) and self-shading (which keeps soil temperatures cold and restricts belowground activity).

Solubility of CO2 in aqueous solution of newly developed absorbents

The solubility of CO2 in various aqueous amine based solvents was determined at lower CO2 partial pressures. Cyclic capacity of various potential aqueous amine based solvents at 10 kPa CO2 partial pressure was determined by performing CO2 absorption at 30 ∘C, regeneration at 90oC and at 1 atmosphere. 1,7-Diaminoheptane and 1,6-Hexanediamine, N,N’-dimethyl was found to be having high cyclic loading of 0.81 and 0.85 moles CO2/moles amine respectively. Aqueous solution of 1,6-Hexanediamine, N,N’-dimethyl of 0.5 and 2.55 Mole/L concentration was selected for solubility study of CO2 at different partial pressure ranging from 1 up to 40 kPa, 30 ∘C and at 1 atmosphere. The solubilities of CO2 in aqueous 1,6-Hexanediamine, N,N’-dimethyl at 30oC were compared with those in aqueous solution of MEA with similar solution concentrations. The solubility of CO2 in 2.55 Mole/L 1,6-Hexanediamine, N,N’-dimethyl was found to be higher when compared to the 2.5 Mole/L MEA at lower CO2 partial pressure.

Geochemical and isotopic evolution of high-pH groundwater in a carbonate-bearing glacigenic aquifer, SW Finland

The glacigenic Virttaankangas aquifer in SW Finland is characterized by groundwaters with high pH values of up to 9.5. High pH values exceeding 9 are uncommon for shallow groundwaters from unconsolidated glacigenic formations on crystalline bedrock. To evaluate the geochemical evolution of groundwater, water samples were collected from 17 sites. The samples were analysed for the isotopic composition of oxygen, hydrogen, dissolved inorganic carbon (DIC) and strontium, the activities of radiocarbon and tritium, and for the basic chemical composition. Groundwaters in the Virttaankangas aquifer system show a considerable range in water pH from 6.4 to 9.5. The isotopic and chemical characteristics of the groundwater in the aquifer units were observed to vary depending on the aquifer mineralogy, groundwater residence time and the openness of the system to CO2 exchange. The pH values were noted to increase in parallel with the contents of Ca and DIC and δ13CDIC. In higher pH values, the groundwaters had attained saturation with respect to calcite. These chemical changes were interpreted to result from dissolution of calcite, present in trace amounts in the Virttaankangas sediments. Specifically, the highest pH values were attributed to calcite dissolution under closed system conditions at a low partial pressure of CO2.

A new aqueous solvent based on a blend of N-methyldiethanolamine and triethylene tetramine for CO2 recovery in post-combustion: Kinetics study

To struggle against global warming, CO2 emissions should be limited. The improvement in the thermal efficiency of industries and buildings will contribute to reduce the CO2 emissions for each energy unit. But, given the emergency of the situation, it will also be necessary to recover CO2 from more concentrated sources like power plants and store it deep underground. For CO2 recovery in post-combustion, chemical solvents are put forward since they allow a high recovery rate even with a low partial pressure of CO2 in the flue gas. This work focuses on the development of a new solvent based on a blend of N-methyldiethanolamine (MDEA) and triethylene tetramine (TETA), an amine with four amino groups. CO2 absorption has been investigated between 298 and 333 K using a Lewis cell with a constant interfacial area. Several concentrations of MDEA (17.5 and 40 wt.%) and TETA (3 and 6 wt.%) have been assessed. The influence of the CO2 partial pressure on the absorption rate was pointed out. The addition of small amounts of TETA leads to a high increase in the CO2 absorption rates. A numerical model based on the film theory has been used to determine the rate coefficient between CO2 and TETA for each solvent.

Effect of Piperazine on CO2Loading in Aqueous Solutions of MDEA at Low Pressure

Solubilities of CO2 in aqueous solutions of activated methyldiethanolamine (MDEA) has been investigated for temperatures and CO2 partial pressures ranging from 40 to 80°C and 0.1 to 100~kPa, respectively. Piperazine (PZ) is used as activator, with a concentration ranging from 0.01 to 0.1~M, keeping the amine total concentration in the aqueous solution at 2~M. The experimental solubility results were represented by the mole ratio of CO2 per activated amine present in the liquid mixture. The addition of piperazine, as activator for MDEA, increased the solubility of CO2 in the region of low CO2 partial pressure compared to pure MDEA. The CO2 loading increased with decreasing temperature, increasing CO2 partial pressure, and increasing PZ concentration.

Measurement and interpretation of the oxygen isotope composition of carbon dioxide respired by leaves in the dark.

We measured the oxygen isotope composition (delta(18)O) of CO(2) respired by Ricinus communis leaves in the dark. Experiments were conducted at low CO(2) partial pressure and at normal atmospheric CO(2) partial pressure. Across both experiments, the delta(18)O of dark-respired CO(2) (delta(R)) ranged from 44 per thousand to 324 per thousand (Vienna Standard Mean Ocean Water scale). This seemingly implausible range of values reflects the large flux of CO(2) that diffuses into leaves, equilibrates with leaf water via the catalytic activity of carbonic anhydrase, then diffuses out of the leaf, leaving the net CO(2) efflux rate unaltered. The impact of this process on delta(R) is modulated by the delta(18)O difference between CO(2) inside the leaf and in the air, and by variation in the CO(2) partial pressure inside the leaf relative to that in the air. We developed theoretical equations to calculate delta(18)O of CO(2) in leaf chloroplasts (delta(c)), the assumed location of carbonic anhydrase activity, during dark respiration. Their application led to sensible estimates of delta(c), suggesting that the theory adequately accounted for the labeling of CO(2) by leaf water in excess of that expected from the net CO(2) efflux. The delta(c) values were strongly correlated with delta(18)O of water at the evaporative sites within leaves. We estimated that approximately 80% of CO(2) in chloroplasts had completely exchanged oxygen atoms with chloroplast water during dark respiration, whereas approximately 100% had exchanged during photosynthesis. Incorporation of the delta(18)O of leaf dark respiration into ecosystem and global scale models of C(18)OO dynamics could affect model outputs and their interpretation.

Identification of Rhodium−Rhenium Nonacarbonyl RhRe(CO)9. Spectroscopic and Thermodynamic Aspects

The hydrido metal carbonyl HRe(CO)5 reacts rapidly with the cluster Rh4(CO)12 at room temperature in n-hexane solvent under CO and H2 to give the coordinately saturated dinuclear carbonyl complex RhRe(CO)9. At room temperature and low partial pressures of CO and H2 (Pi < 2.2 MPa), an observable equilibrium is established between the reactants: 4HRe(CO)5 + Rh4(CO)12 + 4CO → 4RhRe(CO)9 + 2H2. This observation implies the facile activation of molecular hydrogen on RhRe(CO)9 at mild conditions and in the presence of CO. A pure component spectrum of RhRe(CO)9 was obtained by BTEM analysis from the in situ FTIR spectroscopic measurements of the equilibrated solutions. The new species has absorbance maxima at 1985.6(s), 2012.2(w), 2026.6(vs, br), 2075(s), and 2127.2(w) cm-1, indicative of local trigonal bipyramidal geometry on the −Rh(CO)4 moiety and square bipyramidal geometry on the −Re(CO)5 moiety. Equilibrium measurements on the temperature interval T =289.7−308.2 K and the partial pressure intervals 0.2 MP...

Effect of Temperature and Boron Contents on the Autocausticizing Reactions in Sodium Carbonate/Borate Mixtures

The autocausticizing reactions of sodium carbonate/borate mixtures have been studied by simultaneous TG/DTA. The main reaction occurs in a molten state of the salts, where the carbonate and borate react to form CO2 and more sodium-rich borates. The extent of decarbonation of Na2CO3 is dependent on the amount of added boron, the temperature, and the composition of the surrounding gas atmosphere. At an overall molar ratio of B/Na < 1 and at temperatures of 900−1000 °C, the borate composition of the melt is intermediate to NaBO2 and Na3BO3. The decarbonation reaction is favored by high temperatures and low CO2 contents in the gas phase. The composition of the borate components in the melt shifts toward the Na3BO3 composition at high temperatures, low CO2 partial pressures, and low boron additions. If the surrounding gas contains CO2, the salt melt will be recarbonated as the temperature is lowered and the melt crystallizes.

Stomatal frequency of Betula pubescens and Pinus sylvestris shows no proportional relationship with atmospheric CO2 concentration

We investigated the relationship between stomatal frequency and a range of atmospheric CO2 concentrations ([CO2]atm) in Betula pubescens and Pinus sylvestris, two important boreal trees in Scandinavia. If strong relationships exist, they can be used to reconstruct past [CO2]atm from stomatal frequency of fossil Betula and Pinus leaves. Responses of epidermal characters (stomatal density (SD), epidermal cell density (ED), stomatal index (SI)) to different CO2 concentrations were investigated utilising (1) the lower partial pressure of CO2 at increasing altitudes for B. pubescens, and in herbarium specimens of B. pubescens and P. sylvestris collected during the post‐industrial rise of [CO2]atm from c. 280 ppmv to c. 360 ppmv in 1997 and (2) concentrations (560 ppmv) and temperatures (3° summer) above present day in the CLIMEX greenhouse experiment. All the results show no clear relationship between SD or SI and [CO2] atm for either B. pubescens or P. sylvestris. Most likely there are stronger genetically and environmentally induced factors that affect the development of the leaves. Problems with collecting representative samples from herbarium specimens are discussed. Since the effects of changes in [CO2]atm cannot be statistically modelled, B. pubescens and P. sylvestris are not suitable for reconstructing past atmospheric CO2 concentrations from fossil leaves using stomatal density or stomatal index

Discovery of C4 species at high altitude in Qinghai-Tibetan Plateau

Plant specimens are collected from the areas between latitude 27 ° 42′N and 40 ° 57′N, and longitude 88 ° 93′E and 103 ° 24′E, with an altitudinal range from 2210 to 5050 m above the sea level in Qinghai-Tibetan Plateau. The stable carbon isotope analysis indicates that two of Chenopodiaceae and six of Poaceae in the samples are C4 plants. Four of the C4 plants are found in 11 spots with altitudes above 3800 m, and Pennisetum centrasiaticum, Arundinella yunnanensis and Orinus thoroldii are present in six spots above 4000 m, even up to 4520 m. At low CO2 partial pressure, that sufficient energy of high light improving C4 plant’s tolerance of low temperature and precipitations concentrating in growing season probably are favorable for C4 plants growing at high altitude in Qinghai-Tibetan Plateau.

Differences in the Activation State of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase in Barley, Pea, and Wheat at Two Altitudes

Activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) is an important parameter determining the rate of net photosynthesis (PN) in situ for which no information is available with reference to altitude. We analyzed activation state along with PN in three plant species and their cultivars grown at low (LA, 1 300 m) and high (HA, 4 200 m) altitudes. No significant change in PN and the initial activity of RuBPCO was obtained with reference to altitude. However, activation state of RuBPCO was reduced significantly in the HA plants as compared to the LA ones. Hence low partial pressure of CO2 prevailing at HA might be responsible for the lower activation state of RuBPCO.

Carbon dioxide equilibrium absorption in the multi-component systems of CO2 + TIPA + MEA + H2O, CO2 + TIPA + Pz + H2O and CO2 + TIPA + H2O at low CO2 partial pressures: experimental solubility data, corrosion study and modeling with artificial neural network

Carbon dioxide equilibrium absorption in the multi-component systems of CO2 + TIPA + MEA + H2O, CO2 + TIPA + Pz + H2O and CO2 + TIPA + H2O at low CO2 partial pressures: experimental solubility data, corrosion study and modeling with artificial neural network

Carbon dioxide equilibrium absorption in the multi-component systems of CO2 + TIPA + MEA + H2O, CO2 + TIPA + Pz + H2O and CO2 + TIPA + H2O at low CO2 partial pressures: experimental solubility data, corrosion study and modeling with artificial neural network

Abstract The equilibrium solubility data of CO2 were measured in the various aqueous solutions of TIPA, TIPA+MEA and TIPA+Pz in various concentrations and temperatures ranging from 30 to 70 °C, and CO2 partial pressures below atmospheric pressure. They show that increasing the MEA/TIPA ratio and the addition of some piperazine to the TIPA solution, increases the CO2 loading in the solutions, with MEA being more efficient than piperazine. Furthermore, it is obvious that aqueous TIPA solution has the maximum CO2 absorption capacity at 2 mol/dm3. ANN modeling was carried out to simulate some of experimental data, and proper accommodation between experimental and calculated results was observed. Some immersion corrosion tests were performed on steel-304 and ST-37 alloys and no corrosion was observed. Viscosities of the used solutions were also measured.

Monte Carlo Simulation of Single- and Binary-Component Adsorption of CO2, N2, and H2 in Zeolite Na-4A

We present a molecular model for the adsorption of CO2, N2, H2, and their mixtures in dehydrated zeolite Na-4A. The interatomic potentials for this model were developed by comparing the results of grand canonical Monte Carlo (GCMC) simulations of single-component adsorption at room temperature with experimental measurements. GCMC simulation is also used to assess the adsorption selectivity of CO2/N2 and CO2/H2 mixtures, as a function of temperature and gas-phase composition. At room temperature, Na-4A is strongly selective for CO2 over both N2 and H2, although this selectivity decreases slightly as the gas-phase pressure increases. Ideal adsorbed solution theory is shown to give accurate predictions of the adsorption selectivity at low CO2 partial pressures, provided that a functional form that accurately describes the CO2 single-component isotherm is used. The adsorption properties of CO2/N2 mixtures in Na-4A are compared to the same mixtures in silicalite.

Sickle Hemoglobin Fibers: Mechanisms of Depolymerization

We examined the depolymerization of hemoglobin (Hb) S fibers in the presence of CO by using photolysis of COHbS to create and isolate individual fibers, then removing photolysis to induce depolymerization. Depolymerization occurs at two sites, fiber ends and fiber sides, with different kinetics and by different mechanisms. At low partial pressure of CO (pCO), end-depolymerization is dominant, proceeding at ∼1 μm s −1, whereas at high pCO fibers vanish very rapidly, in much less than one second, by side-depolymerization. Each kind of depolymerization could occur by a ligand-independent path, in which deoxyHb depolymerizes and then is prevented from returning to the polymer by liganding with CO, or by a ligand-dependent path in which CO binds to the polymer inducing dissociation of the newly liganded molecules from it. We find that ligand-independent depolymerization is the dominant path for end-depolymerization and ligand-dependent depolymerization dominates, at least at high pCO, for side-depolymerization. On the basis of our kinetic results and electron micrographs of depolymerizing fibers, we propose a model for side-depolymerization in which a hole is nucleated by cooperative loss of a few molecules from fiber sides, followed by rapid depolymerization from the newly created fiber ends abutting the hole. Potential significance of these results for the pathophysiology of sickle cell disease is discussed.

The effect of growth irradiance on leaf anatomy and photosynthesis in Acer species differing in light demand

AbstractVariation in light demand is a major factor in determining the growth and survival of trees in a forest. There is strong relation between the light‐demand and the effect of growth irradiance on leaf morphology and photosynthesis in three Acer species: A. rufinerve (light‐demanding), A. mono (intermediate) and A. palmatum (shade‐tolerant). The increase in mesophyll thickness and surface area of chloroplasts facing the intercellular airspaces (Sc) with growth irradiance was highest in A. rufinerve. Although the increase in light‐saturated photosynthesis (Amax) was similar among the species, the increase in water use efficiency (WUE) was much higher in A. rufinerve than that in the other species, indicating that the response to water limitation plays an important role in leaf photosynthetic acclimation to high light in A. rufinerve. The low CO2 partial pressure at the carboxylation site (Cc) in A. rufinerve (130 µmol mol−1) at high irradiance was caused by low stomatal and internal conductance to CO2 diffusion, which minimized the increase in Amax in A. rufinerve despite its high Rubisco content. Under shade conditions, interspecific differences in leaf features were relatively small. Thus, difference in light demand related to leaf acclimation to high light rather than that to low light in the Acer species.

Ventilatory sensitivity to changes in inspired and arterial carbon dioxide partial pressures in the chicken

To determine if intrapulmonary chemoreceptors could be the sole peripheral chemoreceptors responsible for ventilatory responses to inhaled CO2, we studied the relationships of minute ventilation, tidal volume, and respiratory frequency to inspired and arterial partial pressure of CO2 (P(I)CO2 and PaCO2) in decerebrate upright chickens when the birds inspired gases containing four low partial pressures of CO2 (0.02, 5.0, 8.2, and 11.4 torr). Because of variability in the measured variables from time to time in the same birds, as well as between birds, and because of the limited precision in measuring PaCO2, a 4 × 4 Latin square design and four statistical methods of data analyses (modified reduced major axis estimator, maximum likelihood estimator, average slope method, and summary slope method) were used. Tidal volume, minute ventilation, and PaCO2 increased, but respiratory frequency remained unchanged, as gases containing increased partial pressures of CO2 were inhaled. The results indicate that intrapulmonary chemoreceptors are not the sole receptors stimulated by inhaling gas containing even low partial pressures of CO2 and that stimulation of arterial and central chemoreceptors also occurs. Stimulation of these latter chemoreceptors may account for the increase in ventilation. Further, the results demonstrate the importance of maintaining a low level of environmental CO2 in poultry houses to minimize its influence on ventilation.

Carbon Dioxide Separation with Novel Solvents as Liquid Membranes

Glycerol carbonate is studied as a new physical solvent for carbon dioxide separation from CO2/N2 mixtures. CO2-selective behavior of glycerol carbonate is explored in an immobilized liquid membrane (ILM) configuration. Pure glycerol carbonate ILMs retained their CO2/N2 selectivity around 80−130 over a large range of CO2 partial pressures. Its CO2 selectivity was not affected by the absence of humidity in feed and sweep streams. When exposed to dry feed gas conditions, the CO2 permeability through pure glycerol carbonate ILMs was about 100 barrer, which increased to about 350 barrer in the presence of humidified feed streams. Addition of small amounts of facilitating carriers such as poly(amidoamine) dendrimer (generation zero) and sodium glycinate appears to significantly help CO2 facilitation at low CO2 partial pressures. However, at high CO2 feed partial pressures, there was a loss of selectivity with the addition of the carriers. The potential for glycerol carbonate based ILMs in CO2 separation from different CO2-containing gas mixtures is discussed and compared with existing solvent/membrane configurations.