Direct electrolytic dissolution of silicate minerals for air CO2 mitigation and carbon-negative H2 production

We experimentally demonstrate the direct coupling of silicate mineral dissolution with saline water electrolysis and H₂ production to effect significant air CO₂ absorption, chemical conversion, and storage in solution. In particular, we observed as much as a 10⁵-fold increase in OH⁻ concentration (pH increase of up to 5.3 units) relative to experimental controls following the electrolysis of 0.25 M Na₂SO₄ solutions when the anode was encased in powdered silicate mineral, either wollastonite or an ultramafic mineral. After electrolysis, full equilibration of the alkalized solution with air led to a significant pH reduction and as much as a 45-fold increase in dissolved inorganic carbon concentration. This demonstrated significant spontaneous air CO₂ capture, chemical conversion, and storage as a bicarbonate, predominantly as NaHCO₃. The excess OH⁻ initially formed in these experiments apparently resulted via neutralization of the anolyte acid, H₂SO₄, by reaction with the base mineral silicate at the anode, producing mineral sulfate and silica. This allowed the NaOH, normally generated at the cathode, to go unneutralized and to accumulate in the bulk electrolyte, ultimately reacting with atmospheric CO₂ to form dissolved bicarbonate. Using nongrid or nonpeak renewable electricity, optimized systems at large scale might allow relatively high-capacity, energy-efficient (<300 kJ/mol of CO₂ captured), and inexpensive (<$100 per tonne of CO₂ mitigated) removal of excess air CO₂ with production of carbon-negative H₂. Furthermore, when added to the ocean, the produced hydroxide and/or (bi)carbonate could be useful in reducing sea-to-air CO₂ emissions and in neutralizing or offsetting the effects of ongoing ocean acidification.     

Template-Mediated Synthesis of Hierarchically Porous Metal–Organic Frameworks for Efficient CO2/N2 Separation

Carbon dioxide (CO₂) is generally unavoidable during the production of fuel gases such as hydrogen (H₂) from steam reformation and syngas composed of carbon monoxide (CO) and hydrogen (H₂). Efficient separation of CO₂ from these gases is highly important to improve the energetic utilization efficiency and prevent poisoning during specific applications. Metal–organic frameworks (MOFs), featuring ordered porous frameworks, high surface areas and tunable pore structures, are emerging porous materials utilized as solid adsorbents for efficient CO₂ capture and separation. Furthermore, the construction of hierarchical MOFs with micropores and mesopores could further promote the dynamic separation processes, accelerating the diffusion of gas flow and exposing more adsorptive pore surface. Herein, we report a simple, efficient, one-pot template-mediated strategy to fabricate a hierarchically porous CuBTC (CuBTC-Water, BTC = 1,3,5-benzenetricarboxylate) for CO₂ separation, which demonstrates abundant mesopores and the superb dynamic separation ability of CO₂/N₂. Therefore, CuBTC-Water demonstrated a CO₂ uptake of 180.529 cm³ g⁻¹ at 273 K and 1 bar, and 94.147 cm³ g⁻¹ at 298 K and 1 bar, with selectivity for CO₂/N₂ mixtures as high as 56.547 at 273 K, much higher than microporous CuBTC. This work opens up a novel avenue to facilely fabricate hierarchically porous MOFs through one-pot synthesis for efficient dynamic CO₂ separation.     

Alternative Materials for the Enrichment of Biogas with Methane

Carbonaceous adsorbents have been pointed out as promising adsorbents for the recovery of methane from its mixture with carbon dioxide, including biogas. This is because of the fact that CO₂ is more strongly adsorbed and also diffuses faster compared to methane in these materials. Therefore, the present study aimed to test alternative carbonaceous materials for the gas separation process with the purpose of enriching biogas in biomethane and to compare them with the commercial one. Among them was coconut shell activated carbon (AC) as the adsorbent derived from bio-waste, rubber tire pyrolysis char (RPC) as a by-product of waste utilization technology, and carbon molecular sieve (CMS) as the commercial material. The breakthrough experiments were conducted using two mixtures, a methane-rich mixture (consisting of 75% CH₄ and 25% CO₂) and a carbon dioxide-rich mixture (containing 25% CH₄ and 75% CO₂). This investigation showed that the AC sample would be a better candidate material for the CH₄/CO₂ separation using a fixed-bed adsorption column than the commercial CMS sample. It is worth mentioning that due to its poorly developed micropore structure, the RPC sample exhibited limited adsorption capacity for both compounds, particularly for CO₂. However, it was observed that for the methane-rich mixture, it was possible to obtain an instantaneous concentration of around 93% CH₄. This indicates that there is still much potential for the use of the RPC, but this raw material needs further treatment. The Yoon–Nelson model was used to predict breakthrough curves for the experimental data. The results show that the data for the AC were best fitted with this model.     

From the Cover: Setting cumulative emissions targets to reduce the risk of dangerous climate change

Avoiding “dangerous anthropogenic interference with the climate system” requires stabilization of atmospheric greenhouse gas concentrations and substantial reductions in anthropogenic emissions. Here, we present an inverse approach to coupled climate-carbon cycle modeling, which allows us to estimate the probability that any given level of carbon dioxide (CO₂) emissions will exceed specified long-term global mean temperature targets for “dangerous anthropogenic interference,” taking into consideration uncertainties in climate sensitivity and the carbon cycle response to climate change. We show that to stabilize global mean temperature increase at 2 °C above preindustrial levels with a probability of at least 0.66, cumulative CO₂ emissions from 2000 to 2500 must not exceed a median estimate of 590 petagrams of carbon (PgC) (range, 200 to 950 PgC). If the 2 °C temperature stabilization target is to be met with a probability of at least 0.9, median total allowable CO₂ emissions are 170 PgC (range, −220 to 700 PgC). Furthermore, these estimates of cumulative CO₂ emissions, compatible with a specified temperature stabilization target, are independent of the path taken to stabilization. Our analysis therefore supports an international policy framework aimed at avoiding dangerous anthropogenic interference formulated on the basis of total allowable greenhouse gas emissions.     

Comparison of CO2 Separation Efficiency from Flue Gases Based on Commonly Used Methods and Materials

The comparison study of CO₂ removal efficiency from flue gases at low pressures and temperatures is presented, based on commonly used methods and materials. Our own experimental results were compared and analyzed for different methods of CO₂ removal from flue gases: absorption in a packed column, adsorption in a packed column and membrane separation on polymeric and ceramic membranes, as well as on the developed supported ionic liquid membranes (SILMs). The efficiency and competitiveness comparison of the investigated methods showed that SILMs obtained by coating of the polydimethylsiloxane (PDMS) membrane with 1-ethyl-3-methylimidazolium acetate ([Emim][Ac]) exhibit a high ideal CO₂/N₂ selectivity of 152, permeability of 2400 barrer and long term stability. Inexpensive and selective SILMs were prepared applying commercial membranes. Under similar experimental conditions, the absorption in aqueous Monoethanolamine (MEA) solutions is much faster than in ionic liquids (ILs), but gas and liquid flow rates in packed column sprayed with IL are limited due to the much higher viscosity and lower diffusion coefficient of IL. For CO₂ adsorption on activated carbons impregnated with amine or IL, only a small improvement in the adsorption properties was achieved. The experimental research was compared with the literature data to find a feasible solution based on commercially available methods and materials.     

Multiscale observations of CO2, 13CO2, and pollutants at Four Corners for emission verification and attribution

There is a pressing need to verify air pollutant and greenhouse gas emissions from anthropogenic fossil energy sources to enforce current and future regulations. We demonstrate the feasibility of using simultaneous remote sensing observations of column abundances of CO₂, CO, and NO₂ to inform and verify emission inventories. We report, to our knowledge, the first ever simultaneous column enhancements in CO₂ (3–10 ppm) and NO₂ (1–3 Dobson Units), and evidence of δ¹³CO₂ depletion in an urban region with two large coal-fired power plants with distinct scrubbing technologies that have resulted in ∆NO_x/∆CO₂ emission ratios that differ by a factor of two. Ground-based total atmospheric column trace gas abundances change synchronously and correlate well with simultaneous in situ point measurements during plume interceptions. Emission ratios of ∆NO_x/∆CO₂ and ∆SO₂/∆CO₂ derived from in situ atmospheric observations agree with those reported by in-stack monitors. Forward simulations using in-stack emissions agree with remote column CO₂ and NO₂ plume observations after fine scale adjustments. Both observed and simulated column ∆NO₂/∆CO₂ ratios indicate that a large fraction (70–75%) of the region is polluted. We demonstrate that the column emission ratios of ∆NO₂/∆CO₂ can resolve changes from day-to-day variation in sources with distinct emission factors (clean and dirty power plants, urban, and fires). We apportion these sources by using NO₂, SO₂, and CO as signatures. Our high-frequency remote sensing observations of CO₂ and coemitted pollutants offer promise for the verification of power plant emission factors and abatement technologies from ground and space.Trace gas [nitrogen oxides (NO_x), sulfur dioxide (SO₂), and carbon monoxide (CO)] and carbon dioxide (CO₂) emissions from anthropogenic fossil energy production are major contributors to air pollution and global warming. Under the Clean Air Act, in the United States these emissions are considered a threat to public health and welfare and are regulated by the Environmental Protection Agency (EPA). Although reporting requirements for air pollutants are well established, they are still under development for CO₂. Reported inventories of CO₂ and pollutant gases are calculated for specific activities using emission factors that depend on fuel composition, combustion efficiency, and scrubbing methods. These bottom–up inventories are subject to significant uncertainties and manipulations (1). Alternatively, atmospheric observations offer an independent top–down method to verify emissions of pollutant trace gases that have low atmospheric background levels and exhibit large and distinct increases near various combustion sources. For example, satellite observations of NO₂ have been used to evaluate regional and local emissions (2), but they are only useful for trend analysis, because their large observational footprint can underestimate NO₂. In contrast, background levels of CO₂ are high with significant variability, making source attribution and verification by direct CO₂ measurements elusive (3), limiting our ability to develop an effective global climate treaty or carbon-trading scheme (4). We postulate that measurements of coemitted trace gases and isotopic composition can be used to isolate anthropogenic CO₂ emissions and identify contributions from specific sectors with distinct composition (trace gas-to-CO₂ emission ratios, ER_X = X/CO₂, or isotopic ratio ¹³CO₂/¹²CO₂). We hypothesize that remote column trace gas measurements over large scales, which are less sensitive to small-scale variability from meteorology than in situ point surface measurements, can provide a more precise method for identifying trends in emissions and emission factors (5). We evaluate this method by using extensive ground-based in situ and remote observations, and forward modeling using reported in-stack emissions at a site with large power plant emissions of CO₂ and pollutants.     

Thin Film Mixed Matrix Hollow Fiber Membrane Fabricated by Incorporation of Amine Functionalized Metal-Organic Framework for CO2/N2 Separation

Membrane separation technology can used to capture carbon dioxide from flue gas. However, plenty of research has been focused on the flat sheet mixed matrix membrane rather than the mixed matrix thin film hollow fiber membranes. In this work, mixed matrix thin film hollow fiber membranes were fabricated by incorporating amine functionalized UiO-66 nanoparticles into the Pebax^® 2533 thin selective layer on the polypropylene (PP) hollow fiber supports via dip-coating process. The attenuated total reflection-Fourier transform infrared (ATR-FTIR), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) mapping analysis, and thermal analysis (TGA-DTA) were used to characterize the synthesized UiO-66-NH₂ nanoparticles. The morphology, surface chemistry, and the gas separation performance of the fabricated Pebax^® 2533-UiO-66-NH₂/PP mixed matrix thin film hollow fiber membranes were characterized by using SEM, ATR-FTIR, and gas permeance measurements, respectively. It was found that the surface morphology of the prepared membranes was influenced by the incorporation of UiO-66 nanoparticles. The CO₂ permeance increased along with an increase of UiO-66 nanoparticles content in the prepared membranes, while the CO₂/N₂ ideal gas selectively firstly increased then decreased due to the aggregation of UiO-66 nanoparticles. The Pebax^® 2533-UiO-66-NH₂/PP mixed matrix thin film hollow fiber membranes containing 10 wt% UiO-66 nanoparticles exhibited the CO₂ permeance of 26 GPU and CO₂/N₂ selectivity of 37.     

Supercritical CO2 Curing of Resource-Recycling Secondary Cement Products Containing Concrete Sludge Waste as Main Materials

This study aims to develop highly durable, mineral carbonation-based, resource-recycling, secondary cement products based on supercritical carbon dioxide (CO₂) curing as part of carbon capture utilization technology that permanently fixes captured CO₂. To investigate the basic characteristics of secondary cement products containing concrete sludge waste (CSW) as the main materials after supercritical CO₂ curing, the compressive strengths of the paste and mortar (fabricated by using CSW as the main binder), ordinary Portland cement, blast furnace slag powder, and fly ash as admixtures were evaluated to derive the optimal mixture for secondary products. The carbonation curing method that can promote the surface densification (intensive CaCO₃ formation) of the hardened body within a short period of time using supercritical CO₂ curing was defined as “Lean Carbonation”. The optimal curing conditions were derived by evaluating the compressive strength and durability improvement effects of applying Lean Carbonation to secondary product specimens. As a result of the experiment, for specimens subjected to Lean Carbonation, compressive strength increased by up to 12%, and the carbonation penetration resistance also increased by more than 50%. The optimal conditions for Lean Carbonation used to improve compressive strength and durability were found to be 35 °C, 80 bar, and 1 min.     

From the Cover: Highly efficient separation of carbon dioxide by a metal-organic framework replete with open metal sites

Selective capture of CO₂, which is essential for natural gas purification and CO₂ sequestration, has been reported in zeolites, porous membranes, and amine solutions. However, all such systems require substantial energy input for release of captured CO₂, leading to low energy efficiency and high cost. A new class of materials named metal-organic frameworks (MOFs) has also been demonstrated to take up voluminous amounts of CO₂. However, these studies have been largely limited to equilibrium uptake measurements, which are a poor predictor of separation ability, rather than the more industrially relevant kinetic (dynamic) capacity. Here, we report that a known MOF, Mg-MOF-74, with open magnesium sites, rivals competitive materials in CO₂ capture, with 8.9 wt. % dynamic capacity, and undergoes facile CO₂ release at significantly lower temperature, 80 °C. Mg-MOF-74 offers an excellent balance between dynamic capacity and regeneration. These results demonstrate the potential of MOFs with open metal sites as efficient CO₂ capture media.     

Splitting CO2 into CO and O2 by a single catalyst

The metal complex [(tpy)(Mebim-py)Ru^II(S)]²⁺ (tpy = 2,2^′ : 6^′,2^′′-terpyridine; Mebim-py = 3-methyl-1-pyridylbenzimidazol-2-ylidene; S = solvent) is a robust, reactive electrocatalyst toward both water oxidation to oxygen and carbon dioxide reduction to carbon monoxide. Here we describe its use as a single electrocatalyst for CO₂ splitting, CO₂ → CO + 1/2 O₂, in a two-compartment electrochemical cell.     

Comparison between air and carbon dioxide insufflation in the endoscopic submucosal excavation of gastrointestinal stromal tumors

AIM:To evaluate the safety and efficacy of CO2 insufflation compared with air insufflation in the endoscopic submucosal excavation(ESE) of gastrointestinal stromal tumors.METHODS:Sixty patients were randomized to undergo endoscopic submucosal excavation,with the CO2 group(n = 30) and the air group(n = 30) undergoingCO2 insufflation and air insufflation in the ESE,respectively.The end-tidal CO2 level(pETCO2) was observed at 4 time points:at the beginning of ESE,at total removal of the tumors,at completed wound management,and 10 min after ESE.Additionally,the patients' experience of pain at 1,3,6 and 24 h after the examination was registered using a visual analog scale(VAS).RESULTS:Both the CO2 group and air group were similar in mean age,sex,body mass index(all P 0.05).There were no significant differences in PetCO2 values before and after the procedure(P 0.05).However,the pain scores after the ESE at different time points in the CO2 group decreased significantly compared with the air group(1 h:21.2 ± 3.4 vs 61.5 ± 1.7;3 h:8.5 ± 0.7 vs 42.9 ± 1.3;6 h:4.4 ± 1.6 vs 27.6 ± 1.2;24 h:2.3 ± 0.4 vs 21.4 ± 0.7,P 0.05).Meanwhile,the percentage of VAS scores of 0 in the CO2 group after 1,3,6 and 24 h was significantly higher than that in the air group(60.7 ± 1.4 vs 18.9 ± 1.5,81.5 ± 2.3 vs 20.6 ± 1.2,89.2 ± 0.7 vs 36.8 ± 0.9,91.3 ± 0.8 vs 63.8 ± 1.3,respectively,P 0.05).Moreover,the condition of the CO2 group was better than that of the air group with respect to anal exsufflation.CONCLUSION:Insufflation of CO2 in the ESE of gastrointestinal stromal tumors will not cause CO2 retention and it may significantly reduce the level of pain,thus it is safe and effective.     

Greater focus needed on methane leakage from natural gas infrastructure

Natural gas is seen by many as the future of American energy: a fuel that can provide energy independence and reduce greenhouse gas emissions in the process. However, there has also been confusion about the climate implications of increased use of natural gas for electric power and transportation. We propose and illustrate the use of technology warming potentials as a robust and transparent way to compare the cumulative radiative forcing created by alternative technologies fueled by natural gas and oil or coal by using the best available estimates of greenhouse gas emissions from each fuel cycle (i.e., production, transportation and use). We find that a shift to compressed natural gas vehicles from gasoline or diesel vehicles leads to greater radiative forcing of the climate for 80 or 280 yr, respectively, before beginning to produce benefits. Compressed natural gas vehicles could produce climate benefits on all time frames if the well-to-wheels CH₄ leakage were capped at a level 45–70% below current estimates. By contrast, using natural gas instead of coal for electric power plants can reduce radiative forcing immediately, and reducing CH₄ losses from the production and transportation of natural gas would produce even greater benefits. There is a need for the natural gas industry and science community to help obtain better emissions data and for increased efforts to reduce methane leakage in order to minimize the climate footprint of natural gas.With growing pressure to produce more domestic energy and to reduce greenhouse gas (GHG) emissions, natural gas is increasingly seen as the fossil fuel of choice for the United States as it transitions to renewable sources. Recent reports in the scientific literature and popular press have produced confusion about the climate implications of natural gas (1–5). On the one hand, a shift to natural gas is promoted as climate mitigation because it has lower carbon per unit energy than coal or oil (6). On the other hand, methane (CH₄), the prime constituent of natural gas, is itself a more potent GHG than carbon dioxide (CO₂); CH₄ leakage from the production, transportation and use of natural gas can offset benefits from fuel-switching.The climatic effect of replacing other fossil fuels with natural gas varies widely by sector (e.g., electricity generation or transportation) and by the fuel being replaced (e.g., coal, gasoline, or diesel fuel), distinctions that have been largely lacking in the policy debate. Estimates of the net climate implications of fuel-switching strategies should be based on complete fuel cycles (e.g., “well-to-wheels”) and account for changes in emissions of relevant radiative forcing agents. Unfortunately, such analyses are weakened by the paucity of empirical data addressing CH₄ emissions through the natural gas supply network, hereafter referred to as CH₄ leakage.^* The U.S. Environmental Protection Agency (EPA) recently doubled its previous estimate of CH₄ leakage from natural gas systems (6).In this paper, we illustrate the importance of accounting for fuel-cycle CH₄ leakage when considering the climate impacts of fuel-technology combinations. Using EPA’s estimated CH₄ emissions from the natural gas supply, we evaluated the radiative forcing implications of three U.S.-specific fuel-switching scenarios: from gasoline, diesel fuel, and coal to natural gas.A shift to natural gas and away from other fossil fuels is increasingly plausible because advances in horizontal drilling and hydraulic fracturing technologies have greatly expanded the country’s extractable natural gas resources particularly by accessing gas stored in shale deep underground (7). Contrary to previous estimates of CH₄ losses from the “upstream” portions of the natural gas fuel cycle (8, 9), a recent paper by Howarth et al. calculated upstream leakage rates for shale gas to be so large as to imply higher lifecycle GHG emissions from natural gas than from coal (1). (SI Text, discusses differences between our paper and Howarth et al.) Howarth et al. estimated CH₄ emissions as a percentage of CH₄ produced over the lifecycle of a well to be 3.6–7.9% for shale gas and 1.7–6.0% for conventional gas. The EPA’s latest estimate of the amount of CH₄ released because of leaks and venting in the natural gas network between production wells and the local distribution network is about 570 billion cubic feet for 2009, which corresponds to 2.4% of gross U.S. natural gas production (1.9–3.1% at a 95% confidence level) (6).^† EPA’s reported uncertainty appears small considering that its current value is double the prior estimate, which was itself twice as high as the previously accepted amount (9).Comparing the climate implications of CH₄ and CO₂ emissions is complicated because of the much shorter atmospheric lifetime of CH₄ relative to CO₂. On a molar basis, CH₄ produces 37 times more radiative forcing than CO₂.^‡ However, because CH₄ is oxidized to CO₂ with an effective lifetime of 12 yr, the integrated, or cumulative, radiative forcings from equi-molar releases of CO₂ and CH₄ eventually converge toward the same value. Determining whether a unit emission of CH₄ is worse for the climate than a unit of CO₂ depends on the time frame considered. Because accelerated rates of warming mean ecosystems and humans have less time to adapt, increased CH₄ emissions due to substitution of natural gas for coal and oil may produce undesirable climate outcomes in the near-term.The concept of global warming potential (GWP) is commonly used to compare the radiative forcing of different gases relative to CO₂ and represents the ratio of the cumulative radiative forcing t years after emission of a GHG to the cumulative radiative forcing from emission of an equivalent quantity of CO₂ (10). The Intergovernmental Panel on Climate Change (IPCC) typically uses 100 yr for the calculation of GWP. Howarth et al. (1) emphasized the 20-year GWP, which accentuates the large forcing in early years from CH₄ emissions, whereas Venkatesh et al. (2) adopted a 100-yr GWP and Burnham et al. (4) utilized both 20- and 100-yr GWPs.GWPs were established to allow for comparisons among GHGs at one point in time after emission but only add confusion when evaluating environmental benefits or policy tradeoffs over time. Policy tradeoffs like the ones examined here often involve two or more GHGs with distinct atmospheric lifetimes. A second limitation of GWP-based comparisons is that they only consider the radiative forcing of single emission pulses, which do not capture the climatic consequences of real-world investment and policy decisions that are better simulated as emission streams.To avoid confusion and enable straightforward comparisons of fuel-technology options, we suggest that plotting as a function of time the relative radiative forcing of the options being considered would be more useful for policy deliberations than GWPs. These technology warming potentials (TWP) require exactly the same inputs and radiative forcing formulas used for GWP but reveal time-dependent tradeoffs inherent in a choice between alternative technologies. We illustrate the value of our approach by applying it to emissions of CO₂ and CH₄ from vehicles fueled with CNG compared with gasoline or diesel vehicles and from power plants fueled with natural gas instead of coal.Wigley also analyzed changes in the relative benefits over time of switching from coal to natural gas, but that was done in the context of additional complexities including specific assumptions about the global pace of technological substitution, emissions of sulfur dioxide and black carbon, and a specific model of global warming due to radiative forcing (5). We compare our results with Wigley’s in the next section.     

Inhibitory effects of carbon dioxide insufflation on pneumoperitoneum and bowel distension after percutaneous endoscopic gastrostomy

AIM: To evaluate the inhibitory effects of carbon dioxide (CO₂) insufflation on pneumoperitoneum and bowel distension after percutaneous endoscopic gastrostomy (PEG).METHODS: A total of 73 consecutive patients who were undergoing PEG were enrolled in our study. After eliminating 13 patients who fitted our exclusion criteria, 60 patients were randomly assigned to either CO₂ (30 patients) or air insufflation (30 patients) groups. PEG was performed by pull-through technique after three-point fixation of the gastric wall to the abdominal wall using a gastropexy device. Arterial blood gas analysis was performed immediately before and after the procedure. Abdominal X-ray was performed at 10 min and at 24 h after PEG to assess the extent of bowel distension. Abdominal computed tomography was performed at 24 h after the procedure to detect the presence of pneumoperitoneum. The outcomes of PEG for 7 d post-procedure were also investigated.RESULTS: Among 30 patients each for the air and the CO₂ groups, PEG could not be conducted in 2 patients of the CO₂ group, thus they were excluded. Analyses of the remaining 58 patients showed that the patients’ backgrounds were not significantly different between the two groups. The elevation values of arterial partial pressure of CO₂ in the air group and the CO₂ group were 2.67 mmHg and 3.32 mmHg, respectively (P = 0.408). The evaluation of bowel distension on abdominal X ray revealed a significant decrease of small bowel distension in the CO₂ group compared to the air group (P < 0.001) at 10 min and 24 h after PEG, whereas there was no significant difference in large bowel distension between the two groups. Pneumoperitoneum was observed only in the air group but not in the CO₂ group (P = 0.003). There were no obvious differences in the laboratory data and clinical outcomes after PEG between the two groups.CONCLUSION: There was no adverse event associated with CO₂ insufflation. CO₂ insufflation is considered to be safer and more comfortable for PEG patients because of the lower incidence of pneumoperitoneum and less distension of the small bowel.     

Carbon dioxide insufflation for colonoscopy: evaluation of gas volume, abdominal pain, examination time and transcutaneous partial CO2 pressure

Background  

Insufflation with carbon dioxide (CO₂) in colonoscopy has not been widely adopted and, consequently, limited data are available on insufflated gas volume and blood pCO₂. The aim of this study was to compare CO₂ and air as an insufflation agent in patients undergoing colonoscopy without sedation in terms of insufflated gas volume, pCO₂, pain and examination time.     

Influence of Method of Alveolar Air Collection on Results of Breath Tests

The influence of the method alveolar aircollection on measurements of trace gas concentrationhas received little attention. We measured theconcentrations of H₂, CH₄, CO, andCO₂ in sequential fractions of alveolar air collected with and withoutbreath-holding. Without breath-holding, theconcentration of these gases increased appreciably asincreasing quantities of alveolar air were expelled.Twenty seconds of breath-holding markedly reduced thisnonhomogeneity of alveolar air. Prediction of theexcretion rate of trace gases from measurements of theirconcentration relative to CO and literature values for resting CO₂ excretion underestimatedthe true excretion rate. We conclude that breath-holdingprior to sample collection enhances the reproducibilityof trace gas measurements. When calculating the rate of excretion of trace gases, the use ofliterature values for resting ventilation orCO₂ excretion may result in appreciableunderestimations of the true rate.     

Effect of pH-Regulation on the Capture of Lipopolysaccharides from E. coli EH100 by Four-Antennary Oligoglycines in Aqueous Medium

Bacterial lipopolysaccharides (LPS) are designated as endotoxins, because they cause fever and a wide range of pathologies in humans. It is important to develop effective methodologies to detect trace quantities of LPS in aqueous systems. The present study develops a fine-tuning procedure for the entrapment of trace quantities of LPS from E. coli EH100. The capture agents are self-assemblies (tectomers) formed by synthetic four-antennary oligoglycine (C-(CH₂-NH-Gly₇)₄, T4). Based on previously performed investigations of bulk and adsorption-layer properties of aqueous solutions containing T4 and LPS, the optimal conditions for the entrapment interactions are further fine-tuned by the pH regulation of aqueous systems. A combined investigation protocol is developed, including dynamic light scattering, profile analysis tensiometry, microscopic thin-liquid-film techniques, and transmission electron microscopy. The key results are: (1) two types of complexes between T4 and LPS are generated—amphiphilic species and “sandwich-like” hydrophilic entities; the complexes are smaller at lower pH, and larger at higher pH; (2) an optimum range of pH values is established within which the whole quantity of the LPS is entrapped by the tectomers, namely pH = 5.04–6.30. The obtained data substantiate the notion that T4 may be used for an effective capture and the removal of traces of endotoxins in aqueous systems.     

A Low-Cost Porous Polymer Membrane for Gas Permeation

In this work, an efficient technique was used to produce porous membranes for different applications. Polyethylene (PE) was selected for the matrix, while corn starch (CS) was used to create the porous structure via leaching. The membranes were produced by continuous extrusion (blending)–calendering (forming) followed by CS leaching in a 20% aqueous acetic acid solution at 80 °C. A complete characterization of the resulting membranes was performed including morphological and mechanical properties. After process optimization, the gas transport properties through the membranes were determined on the basis of pure gas permeation including CH₄, CO₂, O₂, and N₂ for two specific applications: biogas sweetening (CH₄/CO₂) and oxygen-enriched air (O₂/N₂). The gas separation results for ideal permeability and selectivity at 25 °C and 1.17 bar (17 psi) show that these membranes are a good starting point for industrial applications since they are low-cost, easy to produce, and can be further optimized.     

Safety and efficacy of carbon dioxide insufflation during gastric endoscopic submucosal dissection

AIM: To compare the safety and efficacy of carbon dioxide (CO₂) and air insufflation during gastric endoscopic submucosal dissection (ESD).METHODS: This study involved 116 patients who underwent gastric ESD between January and December 2009. After eliminating 29 patients who fit the exclusion criteria, 87 patients, without known pulmonary dysfunction, were randomized into the CO₂ insufflation (n = 36) or air insufflation (n = 51) groups. Standard ESD was performed with a CO₂ regulation unit (constant rate of 1.4 L/min) used for patients undergoing CO₂ insufflation. Patients received diazepam for conscious sedation and pentazocine for analgesia. Transcutaneous CO₂ tension (PtcCO₂) was recorded 15 min before, during, and after ESD with insufflation. PtcCO₂, the correlation between PtcCO₂ and procedure time, and ESD-related complications were compared between the two groups. Arterial blood gases were analyzed after ESD in the first 30 patients (12 with CO₂ and 18 with air insufflation) to assess the correlation between arterial blood CO₂ partial pressure (PaCO₂) and PtcCO₂.RESULTS: There were no differences in respiratory functions, median sedative doses, or median procedure times between the groups. Similarly, there was no significant difference in post-ESD blood gas parameters, including PaCO₂, between the CO₂ and air groups (44.6 mmHg vs 45 mmHg). Both groups demonstrated median pH values of 7.36, and none of the patients exhibited acidemia. No significant differences were observed between the CO₂ and air groups with respect to baseline PtcCO₂ (39 mmHg vs 40 mmHg), peak PtcCO₂ during ESD (52 mmHg vs 51 mmHg), or median PtcCO₂ after ESD (50 mmHg vs 50 mmHg). There was a strong correlation between PaCO₂ and PtcCO₂ (r = 0.66; P < 0.001). The incidence of Mallory-Weiss tears was significantly lower with CO₂ insufflation than with air insufflation (0% vs 15.6%, P = 0.013). CO₂ insufflation did not cause any adverse events, such as CO₂ narcosis or gas embolisms.CONCLUSION: CO₂ insufflation during gastric ESD results in similar blood gas levels as air insufflation, and also reduces the incidence of Mallory-Weiss tears.     

Respiratory disorders during sleep in chronic obstructive pulmonary disease

Patients with COPD may show slow, progressive deteriorations in arterial blood gases during the night, particularly during rapid eye movement (REM) sleep. This is mainly due to hypoventilation, while a deterioration of ventilation/perfusion mismatch plays a minor role. The severity of gas exchanges alterations is proportional to the degree of impairment of diurnal pulmonary function tests, particularly of partial pressure of oxygen (PaO₂) and of carbon dioxide (PaCO₂) in arterial blood, but correlations between diurnal and nocturnal blood gas levels are rather loose. Subjects with diurnal PaO₂ of 60–70 mmHg are distinguished in “desaturators” and “nondesaturators” according to nocturnal oxyhemoglobin saturation behavior. The role of nocturnal hypoxemia as a determinant of alterations in sleep structure observed in COPD is dubious. Effects of the “desaturator” condition on pulmonary hemodynamics, evolution of diurnal blood gases, and life expectancy are also controversial. Conversely, it is generally accepted that occurrence of sleep apneas in COPD is associated with a worse evolution of the disease. Nocturnal polysomnographic monitoring in COPD is usually performed when coexistence of sleep apnea (“overlap syndrome”) is suspected, while in most other cases nocturnal oximetry may be enough. Nocturnal oxygen attenuates sleep desaturations among stable patients, without increases in PaCO₂ of clinical concern. Nocturnal treatment with positive pressure ventilators may give benefit to some stable hypercapnic subjects and patients with the overlap syndrome.     

Tropical mid-tropospheric CO2 variability driven by the Madden-Julian oscillation

Carbon dioxide (CO₂) is the most important anthropogenic greenhouse gas in the present-day climate. Most of the community focuses on its long-term (decadal to centennial) behaviors that are relevant to climate change, but there are relatively few discussions of its higher-frequency forms of variability, and none regarding its subseasonal distribution. In this work, we report a large-scale intraseasonal variation in the Atmospheric Infrared Sounder CO₂ data in the global tropical region associated with the Madden–Julian oscillation (MJO). The peak-to-peak amplitude of the composite MJO modulation is ∼1 ppmv, with a standard error of the composite mean < 0.1 ppmv. The correlation structure between CO₂ and rainfall and vertical velocity indicate positive (negative) anomalies in CO₂ arise due to upward (downward) large-scale vertical motions in the lower troposphere associated with the MJO. These findings can help elucidate how faster processes can organize, transport, and mix CO₂ and provide a robustness test for coupled carbon–climate models.