Dry CO2 Research Articles

Multiphase Modelling of Wormhole Formation in Carbonates by the Injection of CO2

Injection of acids into carbonate formations can lead to the formation of macroscopic flow conduits. These so-called wormholes have the potential to dramatically increase effective permeability, leading to an enhanced well injectivity or productivity. The phenomenon has been studied extensively in the context of acid stimulation of oil production wells in carbonates.In recent years the topic has received widespread interest in the context of CO2 storage. However, the experimental and modelling studies conducted so far have been nearly exclusively limited to carbonated brine injection. This is in contrast to ongoing and planned CO2 injection operations, where nearly-pure (dry) supercritical CO2 is injected, which is not an acid, but an acid-forming agent. This leads to a substantially different scenario, since the acid mobility – and hence the dissolution regime – is limited by two-phase flow effects.This paper addresses two-phase flow effects on dissolution patterns. To this extent Reactive Transport Modelling is applied on a fine scale, allowing for an explicit resolution of wormhole formation and direct comparison to experimental results. This is followed by the development of an effective (upscaled) model for modelling wormholing on the field scale. For this purpose, the so-called Global Wormholing Model, that was developed for acid stimulation, is generalised and adapted for application to two-phase CO2-brine systems. The upscaled model is applied to the near-wellbore scale to predict wormhole lengths and their effect on injectivity.The results show that for dry CO2 injection the potential for (or impact of) wormhole formation is negligible. This is different from the case of carbonated brine injection, which leads to significant wormholing potential over extended injection timescales. A Water-Alternating-Gas (WAG) scenario, which is of interest to CO2 Enhanced Oil Recovery (EOR) operations, exhibits only weak signatures of wormhole formation even after a large number of WAG cycles.

Warm and Humidified Versus Cold and Dry CO2 Pneumoperitoneum in Minimally Invasive Colon Resection: A Randomized Controlled Trial.

Peritoneal insufflation with warm-humidified (WH) CO2 gas during minimally invasive surgical procedures is purported to prevent hypothermia and peritoneal desiccation and is associated with decreased postoperative IL-6 levels. This randomized study's purpose was to determine the clinical impact of WH versus cold-dry (CD) CO2 in minimally invasive colon resection (MICR), and to assess perioperative plasma levels of IL-6, TIMP-1, sVEGF-R1, and HSP-70 after MICR. Operative and short-term clinical data plus perioperative blood samples were collected on MICR patients randomized to receive either WH (36.7°C, 95% humidity) or CD (room temperature, 0% humidity) CO2 perioperatively. Peritoneal biopsies were taken at the start and end of surgery. Outcomes tracked included core temperature, postoperative in-hospital pain levels, analgesia requirements, and standard recovery parameters. Preoperative and postoperative days (PODs) 1 and 3 plasma protein levels were determined via ELISA. A total of 101 patients were randomized to WH CO2 (50) or CD CO2 (51). The WH group contained more diabetics ( P = .03). There were no differences in indication, minimally invasive surgical method used, or core temperature. Pain scores were similar; however, the WH patients required less narcotics on PODs 1 to 3 ( P < .05), and less ketorolac on PODs 1 and 2 ( P < .03). No differences in length of stay, complication rates, or time to flatus/diet tolerance were noted. Plasma levels of the 4 proteins were similar postoperatively. Though insignificant, the WH group had less marked histologic changes on "end-of-case" peritoneal biopsies. This study found significantly lower pain medication requirements for PODs 1 to 3 for the WH group; however, because there were no differences in the pains scores between the groups, firm conclusions regarding WH CO2 cannot be made.

Kinetic analysis of an anion exchange absorbent for CO2 capture from ambient air.

This study reports a preparation method of a new moisture swing sorbent for CO2 capture from air. The new sorbent components include ion exchange resin (IER) and polyvinyl chloride (PVC) as a binder. The IER can absorb CO2 when surrounding is dry and release CO2 when surrounding is wet. The manuscript presents the studies of membrane structure, kinetic model of absorption process, performance of desorption process and the diffusivity of water molecules in the CO2 absorbent. It has been proved that the kinetic performance of CO2 absorption/desorption can be improved by using thin binder and hot water treatment. The fast kinetics of P-100-90C absorbent is due to the thin PVC binder, and high diffusion rate of H2O molecules in the sample. The impressive is this new CO2 absorbent has the fastest CO2 absorption rate among all absorbents which have been reported by other up-to-date literatures.

Prospective, randomized comparison of the use of FloShield Air System® versus the reference technique (water+povidone-iodine solution) during gynecologic endoscopic surgery to evaluate the operative lens vision quality.

The FloShield Air System® is a new device for laparoscopic surgery that utilizes a continuous dry CO2 gas flow over the scope to defog the lens and protect it from condensation, debris and smoke. We set out to compare the performance and efficiency of the device in terms of operative lens vision quality (OLVQ) with the reference technique (water+povidone-iodine (PVI) solution) during gynecologic laparoscopic surgery. We conducted a single-center randomized prospective study between March and June 2016 (Trials Database Registration NCT02702531) including 53 patients undergoing gynecologic laparoscopic surgery with water+PVI solution and 51 patients who underwent surgical procedures with the FloShield Air System. The primary outcomemeasure was the number of laparoscope removals during surgery. Secondary outcome measures were the time to clean, assessment of the quality of vision, the correlation between the laparoscopic surgical complexity and outcomes, and cost effectiveness. Overall, the mean patient age was 43.2years (range 22-86) and body mass index 24.8 (range 16.8-42.7). The mean number of endoscope removals during surgery was 7.0 (range 0-37) in the water+PVI solution arm and 2.8 (range 0-12) in the FloShield Air System® arm. The number of removals was significantly lower in the FloShield arm (p<0.001). No difference in time to clean, quality of vision, level of laparoscopic procedure complexity, or cost was observed between the groups. The FloShield Air System® resulted in fewer laparoscopic lens removals than the water+PVI solution solution, but that there was no difference in quality of vision, cleaning time or cost, especially for the more complex surgery.

Flow measurement of wet CO2 using an averaging pitot tube and coriolis mass flowmeters

The flow measurement of wet-gas is an active field with extensive research background that remains a modern-day challenge. The implication of wet-gas flow conditions is no different in Carbon Capture and Storage (CCS) pipelines. The associated complex flow regime with wet-gas flow makes it difficult to accurately meter the flow rate of the gas phase. Some conventional single-phase flowmeters like the Coriolis, Orifice plate, Ultrasonic, V-Cone, Venturi and Vortex have been tested for this application, usually accompanied with special recommendations. Often, a correlation equation valid within a certain range of specific conditions is required to correct the response of the flowmeter. This paper presents investigations into the suitability and performance of one of the most advanced averaging pitot tubes for the flow measurement of wet CO2 gas. The averaging pitot tube with flow conditioning wing geometry (APT-FCW) was studied and experimentally assessed in earlier work for the flow measurement of pure and dry CO2 within an error of ±1%. Under wet-gas conditions, however, the APT-FCW sensor is found to give an error of up to ±25% and within ±1.5% after appropriate correcting solutions are applied for a liquid fraction of up to 20%.

An in situ near-ambient pressure X-ray photoelectron spectroscopy study of CO2 reduction at Cu in a SOE cell

The cathodic behavior of a model solid oxide electrolysis cell (SOEC) has been studied by means of near-ambient pressure (NAP) X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS), aiming at shedding light on the specific role of the metallic component in a class of cermets used as electrodes. The focus is on the surface chemistry and catalytic role of Cu, the increasingly popular metallic component in electrodes used in CO2 electrolysis and CO2/H2O co-electrolysis. The NAP-XPS and NEXAFS results, obtained in situ and operando conditions and under electrochemical control, have provided important insights about the evolution of the chemical composition of the Cu surface. We have found that in dry CO2 ambient carbon deposits are scavenged at low cathodic potential by the oxidising action of nascent O, while at high cathodic polarisations C grows due to activation of CO reduction. Instead, in CO2/H2O mixtures, surface deposit of C is steady over the whole investigated potential range. The presence of adsorbed CO has also been detected during electrolysis of CO2/H2O mixtures, while no CO is found in pure CO2 ambient.

Effect of water on critical and subcritical fracture properties of Woodford shale

AbstractSubcritical fracture behavior of shales under aqueous conditions is poorly characterized despite increased relevance to oil and gas resource development and seal integrity in waste disposal and subsurface carbon sequestration. We measured subcritical fracture properties of Woodford shale in ambient air, dry CO2 gas, and deionized water by using the double‐torsion method. Compared to tests in ambient air, the presence of water reduces fracture toughness by 50%, subcritical index by 77%, and shear modulus by 27% and increases inelastic deformation. Comparison between test specimens coated with a hydrophobic agent and uncoated specimens demonstrates that the interaction of water with the bulk rock results in the reduction of fracture toughness and enhanced plastic effects, while water‐rock interaction limited to the vicinity of the propagating fracture tip by a hydrophobic specimen coating lowers subcritical index and increases fracture velocity. The observed deviation of a rate‐dependent subcritical index from the power law K‐V relations for coated specimens tested in water is attributed to a time‐dependent weakening process resulting from the interaction between water and clays in the vicinity of the fracture tip.

CO2-Selective Absorbents in Air: Reverse Lipid Bilayer Structure Forming Neutral Carbamic Acid in Water without Hydration.

Emission gas and air contain not only CO2 but also plentiful moisture, making it difficult to achieve selective CO2 absorption without hydration. To generate absorbed CO2 (wet CO2) under heating, the need for external energy to release the absorbed water has been among the most serious problems in the fields of carbon dioxide capture and storage (CCS) and direct air capture (DAC). We found that the introduction of the hydrophobic phenyl group into alkylamines of CO2 absorbents improved the absorption selectivity between CO2 and water. Furthermore, ortho-, meta-, and para-xylylenediamines (OXDA, MXDA, PXDA, respectively) absorbed only CO2 in air without any hydration. Notably, MXDA·CO2 was formed as an anhydrous carbamic acid even in water, presumably because it was covered with hydrophobic phenyl groups, which induces a reverse lipid bilayer structure. Dry CO2 was obtained from heating MXDA·CO2 at 103-120 °C, which was revealed to involve chemically the Grignard reaction to form the resulting carboxylic acids in high yields.

Stability of a Benzyl Amine Based CO2 Capture Adsorbent in View of Regeneration Strategies.

In this work, the chemical and thermal stability of a primary amine-functionalized ion-exchange resin (Lewatit VP OC 1065) is studied in view of the potential options of regenerating this sorbent in a CO2 removal application. The adsorbent was treated continuously in the presence of air, different O2/CO2/N2 mixtures, concentrated CO2, and steam, and then the remaining CO2 adsorption capacity was measured. Elemental analysis, BET/BJH analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis were applied to characterize adsorbent properties. This material was found to be thermally and hydrothermally stable at high temperatures. However, significant oxidative degradation occurred already at moderate temperatures (above 70 °C). Temperatures above 120 °C lead to degradation in concentrated dry CO2. Adding moisture to the concentrated CO2 stream improves the CO2-induced stability. Adsorbent regeneration with nitrogen stripping is studied with various parameters, focusing on minimizing the moles of purge gas required per mole of CO2 desorbed.

Experimental study on CO 2 sorption capacity of the neat and porous silica supported ionic liquids and the effect of water content of flue gas

Abstract In this research, absorption of CO2 in different ionic liquids (ILs) is studied. Thus four ILs were synthesized containing 1-butyl-3-methylimidazolium as the cation and nitrate [NO3]−, thiocyanate [SCN]−, dicyanamide [N(CN)2]− and hydrogen sulfate [HSO4]− as the anions, respectively. The resulting ILs were then immobilized into activated silica support in a 1/1 IL/SiO2 weight ratio via the impregnation-vaporization method. CO2 sorption behavior of both neat and silica supported ILs (ILs-SiO2) were investigated at different temperatures and flow rates under atmospheric pressure, while their desorption process were carried out under 20 mm Hg at 70 °C. In both sorbents, the best results were obtained at 25 °C with a flow rate of 12 mL/min, where [bmim][N(CN)2] with 1.85 (wt%) or 0.42 mmol CO2 per gram of sorbent and [bmim][HSO4]-SiO2 with 2.33 (wt%) or 0.53 mmol CO2 per gram of sorbent showed the highest sorption capacities. The effect of water on CO2 absorption capacity of the neat and silica supported ILs were also studied by transmission of CO2 gas flue containing 400 ppm water. The results indicated that the mass gain was higher when wet CO2 was passed through the sorbents, opposed to passing dry CO2. Because of the existence of a weak coulombic intraction between the sorbents and CO2, desorption occurs rapidly and a readily reuse of the sorbents is therefore provided.

Riparian land uses affect the dry season soil CO2 efflux under dry tropical ecosystems

Riparian ecosystems are amongst the most vulnerable ecosystems of the world. The natural gradients and increasing human perturbations under these ecosystems can be explored for understanding the soil carbon (C) dynamics, especially soil carbon dioxide (CO2) efflux. However, studies on soil CO2 efflux and its governing variables under different land uses of dry tropical riparian ecosystems are limited. Therefore, the present study aimed (1) to assess the impact of riparian land use on soil CO2 efflux, and (2) to identify the key drivers of soil CO2 efflux along the river Ganga, Varanasi, India. The riparian land uses taken in this study were moist sandy flat (MSF), uncultivated sandy land (USL) and cultivated sandy land (CSL) depending upon their slope and distance from river body to upland, respectively. Soil CO2 efflux and other soil biophysical properties were measured at 54 locations distributed in six sites having these land uses, in dry season of 2014–15. Soil biophysical properties considered in this study were soil organic C, soil moisture, bulk density, porosity, fine particles, microbial biomass C and soil pH. Riparian land uses were found to have significant impact over soil CO2 efflux with a respective increase of 222, 424 and 63%, for MSF to USL, MSF to CSL, and USL to CSL land use transitions (P<0.01), respectively. Similarly, the regulators of soil CO2 efflux varied with the land uses. It showed strong positive correlation with soil organic C (r=0.81), fine particles (r=0.64) and porosity (r=0.61), whereas negative correlation with soil moisture (r=0.61) and bulk density (r=0.62) for overall dataset. However, soil organic C, fine particles, microbial biomass C and soil pH at MSF; soil organic C and microbial biomass C at USL; and soil moisture, porosity and microbial biomass C at CSL land uses were observed to regulate soil CO2 efflux. The findings revealed that riparian land uses have significant control over soil CO2 efflux and its biophysical regulators which have relative control over it. Soil organic C, soil moisture, fine particles, porosity and microbial biomass C were identified as prevalent regulators of soil CO2 efflux under dry seasons. Overall, the results indicate that the biophysical variables in addition to human interferences (CSL land use) have pronounced regulation over soil CO2 efflux in dry tropical riparian ecosystems.

Biophysical Regulation of Carbon Flux in Different Rainfall Regime in a Northern Tibetan Alpine Meadow

Abstract: Inter-annual variability in total precipitation can lead to significant changes in carbon flux. In this study, we used the eddy covariance (EC) technique to measure the net CO2 ecosystem exchange (NEE) of an alpine meadow in the northern Tibetan Plateau. In 2005 the meadow had precipitation of 489.9 mm and in 2006 precipitation of 241.1 mm, which, respectively, represent normal and dry years as compared to the mean annual precipitation of 476 mm. The EC measured NEE was 87.70 g C m-2 yr-1 in 2006 and –2.35 g C m-2 yr-1 in 2005. Therefore, the grassland was carbon neutral to the atmosphere in the normal year, while it was a carbon source in the dry year, indicating this ecosystem will become a CO2 source if climate warming results in more drought conditions. The drought conditions in the dry year limited gross ecosystem CO2 exchange (GEE), leaf area index (LAI) and the duration of ecosystem carbon uptake. During the peak of growing season the maximum daily rate of NEE and Pmax and α were approxim...

Effect of Aluminum Addition on the Microstructure, Tensile Properties, and Fractography of Cast Mg-Based Alloys

The present study was performed on Mg-based alloys containing Zn and Mn. The alloys were cast in a permanent metallic mold preheated to 200°C and with a protective atmosphere of dry air, CO2, and SF6. Two main phases are observed in the as-cast condition: Mg-Al-Zn and Mn-Al intermetallics. The size and morphology of the Mg-Al-Zn phase are significantly affected by the concentration of Al. Tensile properties, using standard ASTM B-108 samples, are directly related to the size, morphology, and density of the existing phase particles. The alloy ductility is reduced with increase in the Al concentration, whereas the ultimate tensile strength and the yield strength are more or less stable. The fracture surface of the tested tensile bars is mostly ductile for low Al-containing alloys and tends to be brittle with the increase in Al content as evidenced by an increase in the density of cleavage ruptured areas.

Extension the Shelf-Life of Fresh Golden Rainbow Trout via Ultra-Fast Air or Cryogenic Carbon Dioxide Super Chilling

The objective of this study was to evaluate the possibilities of ultra-fast air or cryogenic super chilling by dry ice (carbon dioxide) for prolongation the shelf life of fresh golden albino of rainbow trout (Oncorhynchus mykiss), and to evaluate its effect on the fish quality comparing with flake ice chilling. The gutted fish 2 h post mortem was packed in transparent plastic polyvinyl dichloride bags with zipper. The first (control) sample was stored chilled at 0°C to 4°C. The second group was cryogenic super chilled by dry ice (CO2) at -78°C with steam flow 0.5 m/s. The third group was ultra-fast super chilled with air at -20°C with air flow 3 m/s and stored at 2°C to 3°C. All samples were examined on 0, 7th, 14th and 21st day of storage. On 21st d of storage comparison between supper chilled samples and flake ice chilled control indicated lower as follows: pH with 18.2%, TVB-N with 24.1%, FFA 9.5 times, POV about 2.5 times, TBARS and FAN approximately 2 times. The 10.40 mg cadaverine/ kg in cryogenic dry CO2 super chilled golden rainbow trout was only determined. Sensory data show a continued acceptability of fish to 14 days for super chilled (to 21st d) than in flake ice chilled (only to 7th d). Microbiological shelf life was determined as 16-18 days and 10-12 days, respectively. The conclusion was made that the ultra-fast air flow super chilling retains better sensory qualities of golden rainbow trout while super chilling with dry carbon dioxide.The objective of this study was to evaluate the possibilities of ultra-fast air or cryogenic super chilling by dry ice (carbon dioxide) for prolongation the shelf life of fresh golden albino of rainbow trout (Oncorhynchus mykiss), and to evaluate its effect on the fish quality comparing with flake ice chilling. The gutted fish 2 h post mortem was packed in transparent plastic polyvinyl dichloride bags with zipper. The first (control) sample was stored chilled at 0°C to 4°C. The second group was cryogenic super chilled by dry ice (CO2) at -78°C with steam flow 0.5 m/s. The third group was ultra-fast super chilled with air at -20°C with air flow 3 m/s and stored at 2°C to 3°C. All samples were examined on 0, 7th, 14th and 21st day of storage. On 21st d of storage comparison between supper chilled samples and flake ice chilled control indicated lower as follows: pH with 18.2%, TVB-N with 24.1%, FFA 9.5 times, POV about 2.5 times, TBARS and FAN approximately 2 times. The 10.40 mg cadaverine/ kg in cryogenic dry CO2 super chilled golden rainbow trout was only determined. Sensory data show a continued acceptability of fish to 14 days for super chilled (to 21st d) than in flake ice chilled (only to 7th d). Microbiological shelf life was determined as 16-18 days and 10-12 days, respectively. The conclusion was made that the ultra-fast air flow super chilling retains better sensory qualities of golden rainbow trout while super chilling with dry carbon dioxide.

Efficient conversion of CO2 in solid oxide electrolytic cells with Pd doped perovskite cathode on ceria nanofilm interlayer

The conversion of CO2 into high energy density fuels and chemicals using electricity generated from renewable sources in High Temperature Solid Oxide Electrolysers is one of the emerging energy storage technologies. By utilising waste heat from industrial processes or solar concentrators or nuclear reactors, HT-SOE devices can reduce the electrical energy input up to 30%. Thus such devices are attractive for utilising CO2 as a renewable energy storage media when coupled with Solar Concentrator Photovoltaic systems. Application of traditional solid oxide fuel cell electrodes such as Ni-YSZ restricts the operation of the electrolyser to using CO2 mixed with reducing gases such as hydrogen or CO to prevent re-oxidation of metallic Ni to NiO in the presence of CO2. Furthermore carbon deposition can occur at high current densities in dry CO2. New redox stable ceramic cathodes (CO2 electrode) are promising alternatives to Ni-YSZ electrodes. In this work, we report electrochemical performance of Palladium (Pd) doped La0.6Sr0.4Co0.2Fe0.8O3−ᵹ (LSCF-Pd) as potential cathode for these devices. Using LSCF-Pd as both anode and cathode, with nanocrystalline thin film doped ceria as an interlayer between the cathode and the electrolyte, current densities in excess of 360mAcm−2 were obtained at 800°C in electrolyte supported tubular cells with high CO2 and steam conversion to syngas. The electrochemical performance of the electrode was found to be stable during the 50h testing of the cell on cyclic load. The cells and reactors used are modular and scalable.

Can Thermally Sprayed Aluminum (TSA) Mitigate Corrosion of Carbon Steel in Carbon Capture and Storage (CCS) Environments?

Transport of CO2 for carbon capture and storage (CCS) uses low-cost carbon steel pipelines owing to their negligible corrosion rates in dry CO2. However, in the presence of liquid water, CO2 forms corrosive carbonic acid. In order to mitigate wet CO2 corrosion, use of expensive corrosion-resistant alloys is recommended; however, the increased cost makes such selection economically unfeasible; hence, new corrosion mitigation methods are sought. One such method is the use of thermally sprayed aluminum (TSA), which has been used to mitigate corrosion of carbon steel in seawater, but there are concerns regarding its suitability in CO2-containing solutions. A 30-day test was carried out during which carbon steel specimens arc-sprayed with aluminum were immersed in deionized water at ambient temperature bubbled with 0.1 MPa CO2. The acidity (pH) and potential were continuously monitored, and the amount of dissolved Al3+ ions was measured after completion of the test. Some dissolution of TSA occurred in the test solution leading to nominal loss in coating thickness. Potential measurements revealed that polarity reversal occurs during the initial stages of exposure which could lead to preferential dissolution of carbon steel in the case of coating damage. Thus, one needs to be careful while using TSA in CCS environments.

Warmed, humidified CO2 insufflation benefits intraoperative core temperature during laparoscopic surgery: A meta-analysis.

BackgroundIntraoperative hypothermia is linked to postoperative adverse events. The use of warmed, humidified CO2 to establish pneumoperitoneum during laparoscopy has been associated with reduced incidence of intraoperative hypothermia. However, the small number and variable quality of published studies have caused uncertainty about the potential benefit of this therapy. This meta‐analysis was conducted to specifically evaluate the effects of warmed, humidified CO2 during laparoscopy.MethodsAn electronic database search identified randomized controlled trials performed on adults who underwent laparoscopic abdominal surgery under general anesthesia with either warmed, humidified CO2 or cold, dry CO2. The main outcome measure of interest was change in intraoperative core body temperature.ResultsThe database search identified 320 studies as potentially relevant, and of these, 13 met the inclusion criteria and were included in the analysis. During laparoscopic surgery, use of warmed, humidified CO2 is associated with a significant increase in intraoperative core temperature (mean temperature change, 0.3°C), when compared with cold, dry CO2 insufflation. ConclusionWarmed, humidified CO2 insufflation during laparoscopic abdominal surgery has been demonstrated to improve intraoperative maintenance of normothermia when compared with cold, dry CO2.

Thermal infrared laser heterodyne spectroradiometry for solar occultation atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; measurements

Abstract. This technology demonstration paper reports on the development, demonstration, performance assessment, and initial data analysis of a benchtop prototype quantum cascade laser heterodyne spectroradiometer, operating within a narrow spectral window of ∼ 1 cm−1 around 953.1 cm−1 in transmission mode and coupled to a passive Sun tracker. The instrument has been specifically designed for accurate dry air total column, and potentially vertical profile, measurements of CO2. Data from over 8 months of operation in 2015 near Didcot, UK, confirm that atmospheric measurements with noise levels down to 4 times the shot noise limit can be achieved with the current instrument. Over the 8-month period, spectra with spectral resolutions of 60 MHz (0.002 cm−1) and 600 MHz (0.02 cm−1) have been acquired with median signal-to-noise ratios of 113 and 257, respectively, and a wavenumber calibration uncertainty of 0.0024 cm−1.Using the optimal estimation method and RFM as the radiative transfer forward model, prior analysis and theoretical benchmark modelling had been performed with an observation system simulator (OSS) to target an optimized spectral region of interest. The selected narrow spectral window includes both CO2 and H2O ro-vibrational transition lines to enable the measurement of dry air CO2 column from a single spectrum. The OSS and preliminary retrieval results yield roughly 8 degrees of freedom for signal (over the entire state vector) for an arbitrarily chosen a priori state with relatively high uncertainty ( ∼ 4 for CO2). Preliminary total column mixing ratios obtained are consistent with GOSAT monthly data. At a spectral resolution of 60 MHz with an acquisition time of 90 s, instrumental noise propagation yields an error of around 1.5 ppm on the dry air total column of CO2, exclusive of biases and geophysical parameters errors at this stage.

Comparison of two closed-path cavity-based spectrometers for measuring air–water CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; fluxes by eddy covariance

Abstract. In recent years several commercialised closed-path cavity-based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO2), methane (CH4), and water vapour (H2O) have become available. Here we compare the performance of two leading models – the Picarro G2311-f and the Los Gatos Research (LGR) Fast Greenhouse Gas Analyzer (FGGA) at a coastal site. Both instruments can compute dry mixing ratios of CO2 and CH4 based on concurrently measured H2O, temperature, and pressure. Additionally, we used a high throughput Nafion dryer to physically remove H2O from the Picarro airstream. Observed air–sea CO2 and CH4 fluxes from these two analysers, averaging about 12 and 0.12 mmol m−2 day−1 respectively, agree within the measurement uncertainties. For the purpose of quantifying dry CO2 and CH4 fluxes downstream of a long inlet, the numerical H2O corrections appear to be reasonably effective and lead to results that are comparable to physical removal of H2O with a Nafion dryer in the mean. We estimate the high-frequency attenuation of fluxes in our closed-path set-up, which was relatively small ( ≤ 10 %) for CO2 and CH4 but very large for the more polar H2O. The Picarro showed significantly lower noise and flux detection limits than the LGR. The hourly flux detection limit for the Picarro was about 2 mmol m−2 day−1 for CO2 and 0.02 mmol m−2 day−1 for CH4. For the LGR these detection limits were about 8 and 0.05 mmol m−2 day−1. Using global maps of monthly mean air–sea CO2 flux as reference, we estimate that the Picarro and LGR can resolve hourly CO2 fluxes from roughly 40 and 4 % of the world's oceans respectively. Averaging over longer timescales would be required in regions with smaller fluxes. Hourly flux detection limits of CH4 from both instruments are generally higher than the expected emissions from the open ocean, though the signal to noise of this measurement may improve closer to the coast.

Oxygen permeation and stability of CaTi0.73Fe0.18Mg0.09O3−δ oxygen-transport membrane

Oxygen permeation membranes consisting of gastight mixed ionic-electronic conductors (MIEC) allow the diffusion of oxygen through the crystal lattice via oxygen vacancies. An extended screening of doped CaTiO3 materials is reported here with the aim of improving the ionic and the electronic conductivity of the material. The dopants were selected taking into account the ionic radii affinity and their aliovalence or multivalence. Moreover, this work presents the oxygen permeability of CaTi1−xFexO3−δ co-doped with Mg. The structural and electrochemical properties of the nominal perovskite CaTi0.73Fe0.18Mg0.09O3−δ (CTFM) are studied. X-ray diffraction demonstrates that the material crystallizes as a single perovskite structure with orthorhombic distorted symmetry, although the MgO segregates as a minor separated phase. The partial addition of Mg2+ to the perovskite results in an increase of oxygen vacancies, and therefore the total conductivity at high temperatures with respect to the non-doped CaTi0.8Fe0.2O3 (CTF). On the contrary, below 800°C the conductivity of CTFM is lower than for CTF, attributed to the lower amount of Fe in the CTFM. Permeation measurements were performed on CTFM gastight membranes of 900 μm thickness, reaching oxygen fluxes of up to 0.95mLmin−1cm−2 at 1000°C. Stability of the membrane to CO2 was evaluated by exposing the membrane to 15% CO2 in Ar atmosphere for 24h at 750°C and O2 fluxes were measured by using this atmosphere as sweep gas. Initial O2 fluxes were maintained after the CO2 treatment. In addition, thermogravimetric (TG) measurements performed on powder CTFM under dry CO2 (5% in Ar) did not show any carbonate formation, confirming the stability of the material in this atmosphere.