Molecular simulation of swelling and structure for Na-Wyoming montmorillonite in supercritical CO2

Gibbs ensemble Monte Carlo (GEMC) simulations were used to study the swelling stability and interlayer structures of Na-montmorillonite clay in supercritical CO₂ (scCO₂). From the GEMC simulation, it was found that there exist several stable mechanical spacings for Na-Wyoming montmorillonite immersed in scCO₂, which are larger than the stable spacing in vacuum condition. The swelling behaviour of Na-montmorillonite clay in scCO₂ fluid is thermodynamically favourable. However, it was also observed that the clay swelling is inhibited when in contact with CO₂ gas at atmospheric pressure. The interlayer structures were applied to investigate the mechanism of swelling. In the case of stable spacings, the interlayer sodium cations are not only well solvated with the surrounding CO₂ molecules but also show stronger tendency to adhere to the clay surface.     

Hydrophilicity effect on CO2/CH4 separation using carbon nanotube membranes: insights from molecular simulation

Abstract

Molecular simulation methods were applied to study the effect of hydrophilicity on CO₂/CH₄ separation using carbon nanotube (CNT) membranes. CNTs with a diameter of ~1 nm were functionalised by varying amounts of carbonyl groups, in order to achieve various hydrophilicity. The presence of –CO groups inside the CNT allow a significant gain in the diffusion selectivity of CO₂, while in contrast the adsorption selectivity is hardly changed. The corresponding permeation selectivity increases as the hydrophilicity of the CNT-based membrane increases. However, the permeability of CO₂ decreases due to a combination of the intermolecular interactions between the gas and functional groups and the steric effects of the added functional groups. Considering both the permeation selectivity and permeability, it was found that the maximum separation performance is achieved in a certain hydrophilic CNT membrane. Moreover, the separation performance of hydrophilic CNTs for CO₂/CH₄ mixtures breaks the Robeson upper bound.     

Molecular simulation of CO2, N2 and CH4 adsorption and separation in ZIF-78 and ZIF-79

In this study, we investigated the adsorption and separation behaviours of CO₂, N₂ and CH₄ in ZIF-78 and ZIF-79 by means of grand canonical Monte Carlo methods. Our simulations indicate that preferential adsorption sites are mainly located at the regions where guest molecules can maximise interactions with the imidazolate (IM) linkers. The –NO₂ and –CH₃ functional groups are not the major binding sites that directly bind the guest molecules. Instead, they alter the electronic structure and polarity of the adjacent IM linkers to affect the adsorption behaviours. In addition, we found that the selectivity of CO₂ over N₂ or CH₄ is found to be dependent on the component fractions of CO₂/N₂ and CO₂/CH₄ mixtures. Specifically, the selectivity of CO₂ over N₂ increases with CO₂ composition fraction, while the trend for the selectivity of CO₂/CH₄ was opposite.     

Fluxes of CO2, CH4 and N2O from a Welsh peatland following simulation of water table draw-down: Potential feedback to climatic change

A potential effect of climatic change was simulated by manipulating the water table height within intact peat monoliths. The treatment decreased methane flux (maximum –80%) and increased both carbon dioxide flux (maximum 146%) and nitrous oxide flux maximum 936%). Returning the water table height to its original level caused both nitrous oxide and carbon dioxide flux to rapidly return to control levels. However, methane flux remained at its experimentally induced low levels.     

Influence of elevated CO2 and nitrogen nutrition on rice plant growth,soil microbial biomass,dissolved organic carbon and dissolved CH4

Rice (Oryza sativa) was grown in six sunlit, semi-closed growth chambers for two seasons at 350 L L^–1 (ambient) and 650 L L^–1 (elevated) CO₂ and different levels of nitrogen (N) supplement. The objective of this research was to study the influence of CO₂ enrichment and N nutrition on rice plant growth, soil microbial biomass, dissolved organic carbon (DOC) and dissolved CH₄. Elevated CO₂ concentration ([CO₂]) demonstrated a wide range of enhancement to both above- and below-ground plant biomass, in particular to stems and roots (for roots when N was not limiting) in the mid-season (80 days after transplanting) and stems/ears at the final harvest, depending on season and the level of N supplement. Elevated [CO₂] significantly increased microbial biomass carbon in the surface 5 cm soil when N (90 kg ha^–1) was in sufficient supply. Low N supplement (30 kg ha^–1) limited the enhancement of root growth by elevated [CO₂], leading consequently to diminished response of soil microbial biomass carbon to CO₂ enrichment. The concentration of dissolved CH₄ (as well as soil DOC, but to a lesser degree) was observed to be positively related to elevated [CO₂], especially at high rate of N application (120 kg ha^–1) or at 10 cm depth (versus 5 cm depth) in the later half of the growing season (at 80 kg N ha^–1). Root senescence in the late season complicated the assessment of the effect of elevated [CO₂] on root growth and soil organic carbon turnover and thus caution should be taken when interpreting respective high CO₂ results.     

Decomposition of CH4 hydrate: effects of temperature and salt from molecular simulations

We report a molecular simulation study to investigate the decomposition of CH₄ hydrate. The decomposition is revealed to be stepwise from the outer to inner layers. Upon decomposition, the number of 5¹²6² cages drops faster than that of 5¹² cages. CH₄ molecules are released, dissolved in water, then enter gas phase; meanwhile, CH₄ bubbles may form particularly at a high temperature. Based on the variations of potential energy, order parameter, cage number and density profile of CH₄ at different temperatures (300, 330, 345 and 360 K) and NaCl concentrations (0, 0.6 and 1.8 M), the effects of temperature and salt are comprehensively examined. With increasing temperature, the decomposition in pure water is accelerated, whereas two opposite effects are observed in NaCl solution. At 330 K, the decomposition is retarded at a higher NaCl concentration, as attributed to the reduced CH₄ solubility in NaCl solution and the participation of ions in cage formation; at 360 K, however, the decomposition is accelerated when NaCl concentration increases due to bubble formation. This simulation study provides microscopic insights into hydrate decomposition, which might be useful towards the optimisation of operating conditions for CH₄ production from CH₄ hydrate.     

On the Possibility of Finding a Suitable Potential Model For Liquid CO2

Abstract

The behaviour of the lower harmonic coefficients of the liquid state angular correlation function of CO₂ has been studied using theory and simulation.     

Effects of Elevated Atmospheric CO2 Concentrations on CH4 and N2O Emission from Rice Soil: An Experiment in Controlled-environment Chambers

The effects of elevated concentrations of atmospheric CO₂ on CH₄ and N₂O emissions from rice soil were investigated in controlled-environment chambers using rice plants growing in pots. Elevated CO₂ significantly increased CH₄ emission by 58% compared with ambient CO₂. The CH₄ emitted by plant-mediated transport and ebullition–diffusion accounted for 86.7 and 13.3% of total emissions during the flooding period under ambient level, respectively; and for 88.1 and 11.9% of total emissions during the flooding period under elevated CO₂ level, respectively. No CH₄ was emitted from plant-free pots, suggesting that the main source of emitted CH₄ was root exudates or autolysis products. Most N₂O was emitted during the first 3 weeks after flooding and rice transplanting, probably through denitrification of NO₃⁻ contained in the experimental soil, and was not affected by the CO₂ concentration. Pre-harvest drainage suppressed CH₄ emission but did not cause much N₂O emission (< 10 μg N m⁻² h⁻¹) from the rice-plant pots at both CO₂ concentrations.     

Daily and seasonal CO2 exchange in Scots pine grown under elevated O3 and CO2: experiment and simulation

Starting in early spring of 1994, naturally regenerated, 30-year-old Scots pine (Pinus sylvestris L.) trees were grown in open-top chambers and exposed in situ to doubled ambient O₃,doubled ambient CO₂ and a combination of O₃ and CO₂ from 15 April to 15 September. To investigate daily and seasonal responses of CO₂ exchange to elevated O₃ and CO₂, the CO₂ exchange of shoots was measured continuously by an automatic system for measuring gas exchange during the course of one year (from 1 Januray to 31 December 1996). A process-based model of shoot photosynthesis was constructed to quantify modifications in the intrinsic capacity of photosynthesis and stomatal conductance by simulating the daily CO₂ exchange data from the field. Results showed that on most days of the year the model simulated well the daily course of shoot photosynthesis. Elevated O₃ significantly decreased photosynthetic capacity and stomatal conductance during the whole photosynthetic period. Elevated O₃ also led to a delay in onset of photosynthetic recovery in early spring and an increase in the sensitivity of photosynthesis to environmental stress conditions. The combination of elevated O₃ and CO₂ had an effect on photosynthesis and stomatal conductance similar to that of elevated O₃ alone, but significantly reduced the O₃-induced depression of photosynthesis. Elevated CO₂ significantly increased the photosynthetic capacity of Scots pine during the main growing season but slightly decreased it in early spring and late autumn. The model calculation showed that, compared to the control treatment, elevated O₃ alone and the combination of elevated O₃ and CO₂ decreased the annual total of net photosynthesis per unit leaf area by 55% and 38%, respectively. Elevated CO₂ increased the annual total of net photosynthesis by 13%.     

Simulation of separation of C2H6 from CH4 using zeolitic imidazolate frameworks

Separation of important chemical feedstocks, such as C₂H₆ from natural gas, can greatly benefit the petrochemical industry. In this paper, the grand canonical Monte Carlo method has been used to study the adsorption and separation of CH₄ and C₂H₆ in zeolites, isoreticular metal-organic framework-1 (IRMOF-1) and zeolitic imidazolate frameworks (ZIFs) with different topology, including soadlite, gmelinite and RHO topologies. Compared with mordenite zeolite and IRMOF-1, ZIFs and mordenite framework inverted (MFI) zeolite have better separation performance for C₂H₆/CH₄ mixtures at different mole fractions of C₂H₆. From the study of equilibrium snapshots and density distribution profiles, adsorption sites could be grouped as (1) sites with strong interactions with adsorbent and (2) sites with strong interactions with surrounding adsorbates. The gas molecules occupied the first site and then went on to occupy the second site. In CH₄/C₂H₆ mixture adsorption/separation, the adsorption of CH₄ was confined by the existence of C₂H₆. Due to energetic effect, C₂H₆ selectivity was affected by temperature at a low-pressure range, but did not change as much in a high-pressure range because of packing effect in micropore. In binary adsorption, large C₂H₆ molecules favour sites with strong adsorbent interactions. At high pressures, packing effects played an important role and it became easy for small CH₄ molecules to access the sites with strong adsorbate interactions.     

Leaf cavity CO2 concentrations and CO2 exchange in onion,Allium cepa L.

Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO₂ that accumulates within their leaf cavities. Leaf cavity CO₂ concentrations ranged from 2250 L L^–1 near the leaf base to below atmospheric (<350 L L^–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO₂ concentrations with minimum values near midday and maximum values at night. Conductance to CO₂ from the leaf cavity ranged from 24 to 202 mol m^–2 s^–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO₂ was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO₂ concentrations and conductance values or as measured directly by ¹⁴CO₂ labeling experiments. The photosynthetic responses to CO₂ and O₂ were measured to determine whether onion leaves exhibited a typical C₃-type response. A linear increase in CO₂ uptake was observed in intact leaves up to 315 L L^–1 of external CO₂ and, at this external CO₂ concentration, uptake was inhibited 35.4±0.9% by 210 mL L^–1 O₂ compared to 20 mL L^–1 O₂. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO₂ and greatly restrict the refixation of leaf cavity CO₂ by photosynthetic tissue.Abbreviations C_a external CO₂ concentration - C_i intercellular CO₂ concentration - CO₂ compensation concentration - PPFR photosynthetic photon fluence rate     

Quantitative evaluation of atmospheric CO2 sink into forest soils from the tropics to the boreal zone during the past three decades

A model of soil carbon cycling in forest ecosystems was applied to predict the soil carbon balance in nine forest ecosystems from the tropics to the boreal zone during the past three decades (1965–95). The parameters of carbon flows and initial conditions of carbon pools were decided based on data obtained in each forest stand. Assumptions for model calculation were: (i) primary production (i.e. litterfall and root turnover rates) increased with increasing CO₂ concentrations in the atmosphere (10% per 40 p.p.m. CO₂); and (ii) temperature increased by 0.6°C per 100 years, but precipitation changed little. The simulation employed a daily time step and used daily air temperature and precipitation observed near each forest stand over an average year during the last decade. The model calculations suggest that the accumulation of total soil carbon increased 8.5–10.4 tC (ton of carbon) ha^–1 in broad-leaved forests from the tropics to the cool-temperate zone during the past three decades, but the amount of soil carbon (3.0–8.4 tC ha^–1) increased much less in needle forests from the subtropical to boreal zones during the same period. There is a linear relationship between the increasing rate of soil carbon stock during the past three decades (1965–95) in forest stands concerned (R_MS, % per 30 years) and annual mean temperature of their soils (T₀,°C), as: R_MS = 0.34T₀ + 4.1. Based on the data of carbon stock in forest soil in each climate zone reported, the global sink of atmospheric CO₂ into forest soil was roughly estimated to be 42 GtC (billion tons of carbon) per 30 years, which was 1.4 GtC year^–1 on average over the past three decades.     

The C4 pathway: an efficient CO2 pump

The C₄ pathway is a complex combination of both biochemical and morphological specialisation, which provides an elevation of the CO₂ concentration at the site of Rubisco. We review the key parameters necessary to make the C₄ pathway function efficiently, focussing on the diffusion of CO₂ out of the bundle sheath compartment. Measurements of cell wall thickness show that the thickness of bundle sheath cell walls in C₄ species is similar to cell wall thickness of C₃ mesophyll cells. Furthermore, NAD-ME type C₄ species, which do not have suberin in their bundle sheath cell walls, do not appear to compensate for this with thicker bundle sheath cell walls. Uncertainties in the CO₂ diffusion properties of membranes, such as the plasmalemma, choroplast and mitochondrial membranes make it difficult to estimate bundle sheath diffusion resistance from anatomical measurements, but the cytosol itself may account for more than half of the final calculated resistance value for CO₂ leakage. We conclude that the location of the site of decarboxylation, its distance from the mesophyll interface and the physical arrangement of chloroplasts and mitochondria in the bundle sheath cell are as important to the efficiency of the process as the properties of the bundle sheath cell wall. Using a mathemathical model of C₄ photosynthesis, we also examine the relationship between bundle sheath resistance to CO₂ diffusion and the biochemical capacity of the C₄ photosynthetic pathway and conclude that bundle sheath resistance to CO₂ diffusion must vary with biochemical capacity if the efficiency of the C₄ pump is to be maintained. Finally, we construct a mathematical model of single cell C₄ photosynthesis in a C₃ mesophyll cell and examine the theoretical efficiency of such a C₄ photosynthetic CO₂ pump. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plant Molecular and Genomic Responses to Stresses in Projected Future CO2 Environment

The Earth has been undergoing climatic changes for centuries, driven by increasing concentration of atmospheric carbon dioxide (CO₂). The atmospheric CO₂ concentration has been predicted to reach 550–750 μmol mol^?1 by 2050, or twice as high as the current level. Much of the research in the last 20–30 years concerning elevated CO₂ (eCO₂) has been about how plants would respond to the eCO₂ at physiological levels. As eCO₂ can lead to more frequent drought or extreme high or low temperature, increasingly more research has focused on the interactions between eCO₂ and other abiotic stresses. How stresses may affect plant growth and development and productivity, as well as how agricultural practices may be altered to cope with these changes must be determined. These concerns have been the subject of numerous reviews. However, it is only in the last several years that data at the “omics” levels has been available to explore how necessary physiological changes may be brought about in a future complex environment. The systems biology approaches provide us an insight into the mechanism of plant responses to climatic changes at the genomics level. In this review, we present an overview of physiological effects of eCO₂ on plants, but focus on the interactions of eCO₂ with drought, high temperature, O₃, and multiple abiotic stresses, with particular emphasis at the molecular and genomics levels. We also provide perspectives on future research and emphasize the importance of integrated research on eCO₂ and multiple environmental stresses using systems biology approaches.     

Responses of C4 grasses to atmospheric CO2 enrichment

Summary The growth and photosynethetic responses to atmospheric CO₂ enrichment of 4 species of C₄ grasses grown at two levels of irradiance were studied. We sought to determine whether CO₂ enrichment would yield proportionally greater growth enhancement in the C₄ grasses when they were grown at low irradiance than when grown at high irradiance. The species studied were Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica, and Setaria faberi. Plants were grown in controlled environment chambers at 350, 675 and 1,000 l 1^-1 CO₂ and 1,000 or 150 mol m^-2 s^-1 photosynthetic photon flux density (PPFD). An increase in CO₂ concentration and PPFD significantly affected net photosynthesis and total biomass production of all plants. Plants grown at low PPFD had significantly lower rates of photosynthesis, produced less biomass, and had reduced responses to increases in CO₂. Plants grown in CO₂-enriched atmosphere had lower photosynthetic capacity relative to the low CO₂ grown plants when exposed to lower CO₂ concentration at the time of measurement, but had greater rate of photosynthesis when exposed to increasing PPFD. The light level under which the plants were growing did not influence the CO₂ compensation point for photosynthesis.     

不同水生植物对景观水体CO2与CH4排放通量的影响

城市景观水体是大气CO₂与CH₄的排放热源,而水生植物作为景观水体的重要组成要素,对水体温室气体排放动态的影响并不清楚。选择重庆市观音塘国家湿地公园为研究区,利用漂浮箱法与顶空平衡法对观音塘水域7种不同水生植物分布区进行水-气界面CO₂与CH₄排放通量及CO₂、CH₄溶存浓度进行季节性监测,估算了植物传输对气体通量的贡献。结果表明：1)观音塘水体CO₂与CH₄浓度范围分别为8.0—341.8μmol/L和0.23—5.26μmol/L,排放通量分别为26.5—869.1 mmol m^-2 d^-1和0.40—11.15 mmol m^-2 d^-1,是大气净CO₂与CH₄排放源;2)观音塘开敞水区CO₂与CH₄排放通量低于大部分城市湖泊或景观水体...     

Supercritical CO(2): a novel environmentally friendly mutagen

In order to develop mutagenic methods, supercritical CO(2) was evaluated as a new environmentally friendly mutagen. During treatment by supercritical CO(2), the survival rate and the positive mutation rate of Flavobacterium sp. strain YY25 were strongly dependent on pressure, temperature, treatment time and additive (DMSO). 8 MPa, 35 degrees C, 30 min of supercritical CO(2) and 1% of DMSO were believed as the optimum doses. After the seed liquid was treated under these conditions, a mutant strain with about 44.2% increase in lipase yield comparing with the wild strain was acquired, indicating that the novel mutagenic method by supercritical CO(2) was feasible and promising in microbial breeding field.     

CO2 transported in xylem sap affects CO2 efflux from Liquidambar styraciflua and Platanus occidentalis stems, and contributes to observed wound respiration phenomena

The [CO₂] in the xylem of tree stems is typically two to three orders of magnitude greater than atmospheric [CO₂]. In this study, xylem [CO₂] was experimentally manipulated in saplings of sycamore (Platanus occidentalis L.) and sweetgum (Liquidambar styraciflua L.) by allowing shoots severed from their root systems to absorb water containing [CO₂] ranging from 0.04% to 14%. The effect of xylem [CO₂] on CO₂ efflux to the atmosphere from uninjured and mechanically injured, i.e., wounded, stems was examined. In both wounded and unwounded stems, and in both species, CO₂ efflux was directly proportional to xylem [CO₂], and increased 5-fold across the range of xylem [CO₂] produced by the [CO₂] treatment. Xylem [CO₂] explained 76–77% of the variation in pre-wound efflux. After wounding, CO₂ efflux increased substantially but remained directly proportional to internal stem [CO₂]. These experiments substantiated our previous finding that stem CO₂ efflux was directly related to internal xylem [CO₂] and expanded our observations to two new species. We conclude that CO₂ transported in the xylem may confound measurements of respiration based on CO₂ efflux to the atmosphere. This study also provided evidence that the rapid increase in CO₂ efflux observed after tissues are excised or injured is likely the result of the rapid diffusion of CO₂ from the xylem, rather than an actual increase in the rate of respiration of wounded tissues.     

Simulation Study of Sorption of CO2 and N2 with Application to the Characterization of Carbon Adsorbents

Abstract

The Monte Carlo method was used in its grand ensemble variant (GCMC) in combination with CO₂ and N₂ experimental isotherm data at low (77 and 195.5 K) and ambient temperatures (298 and 308 K), in order to characterize microporous carbons and obtain the corresponding pore size distribution (PSD). In particular, the CO₂ and N₂ densities and the isosteric heats of adsorption inside single, slit shaped, graphitic pores of given width were found on the basis of GCMC for pre-defined temperatures and different relative pressures. In a further step, we determined the optimal PSD for which the best match is obtained between computed and measured isotherms. Comparisons were made between the PSDs found for the same carbon sample at low and ambient temperatures for different gases, and conclusions concerning the applicability of the method and the reliability of the resulting micropore size distributions were drawn.     

The Impact of Indigenous Microorganisms on the Mineral Corrosion and Mineral Trapping in the SO2 Co-injected CO2-Saline-Sandstone Interaction

The impact of indigenous microorganisms on the mineral corrosion and mineral trapping in the SO₂ co-injected CO₂-saline-sandstone interaction was investigated in this study by lab experiments under 55?°C, 15?M pa. The results verified that co-injection of SO₂ resulted in a decrease in biomass and shifts in microbial communities within 90?days, but some microorganisms still could adapt to acidic, high-temperature, high-pressure, and high-salinity environments. Firmicutes and Proteobacteria remained dominant phylum, but phylum Proteobacteria showed better tolerance to the co-injection of SO₂ in the initial period. In the SO₂ co-injected CO₂-saline-sandstone interaction under microbial mediation, acid-producing bacteria further promoted the corrosion of K-feldspar, albite, and clay minerals, meanwhile mobilizing more K⁺, Na⁺, Ca²⁺, Mg²⁺ into solution. The acidogenic effect may be linked to the dominant genus of Bacillus, Paenibacillus, Acinetobacter, Pseudomonas and Exiguobacterium. Co-injection of SO₂ inhibited the carbonates capture, while microbial acid production further reduced the pH, further inhibiting carbonates capture. As a result, no secondary carbonate (e.g., calcite) was observed on a short time scale within 90?days. So, microbial acidogenic effect was not conducive to carbonates capture in short term.