Dioxide CO2 Research Articles

Kinetics of the reactive absorption of carbon dioxide in high CO 2-loaded, concentrated aqueous monoethanolamine solutions

The kinetics of the reaction between carbon dioxide and high CO 2-loaded, concentrated aqueous solutions of monoethanolamine (MEA) were investigated over the temperature range from 293 to 333 K , MEA concentration range from 3 to 9M, and CO 2 loading from ∼0.1 to 0.49 mol/mol. The experimental kinetic data were obtained in a laminar jet absorber at various contact-times between gas and liquid. The obtained experimental data were interpreted with the aid of a numerically solved absorption-rate/kinetic model. The results showed that only the termolecular mechanism of Crooks and Donnellan could be used to explain all observed kinetic phenomena. These results allowed us to develop a new termolecular-kinetics model for CO 2 reaction with MEA solutions, which proved to be better than previously published kinetic models. The model was comprehensive enough to describe for the first time the absorption of CO 2 in highly concentrated and high CO 2-loaded aqueous MEA solutions for a wide temperature range.

Continuous observations of carbon dioxide at Mace Head, Ireland from 1995 to 1999 and its net European ecosystem exchange

A 5-yr record of continuous high-frequency carbon dioxide CO 2 observations over the 1995–1999 period for the Mace Head Atmospheric Research Station has been examined to reveal a complex interplay between local- and regional-scale sources and sinks. During the winter months, an additional CO 2 source, over and above fossil fuel combustion, is required to support the observed concentrations of CO 2 in European regionally polluted air masses. During the summer months, an additional CO 2 sink is required. Over the entire study period, the additional net European ecosystem exchange source–sink required is –0.36±0.4 Gtonne C yr −1.

Filters for tin dioxide CO gas sensors to pass the UL2034 standard

CO gas sensors have to fulfil the requirements of standards like the UL2034 or BS7860. Unfortunately, tin oxide gas sensors are also highly sensitive to volatile organic compounds (VOCs) like long chain hydrocarbons, alcohols or ethyl acetate. These standards require negligible interference in cross-sensitivity tests of CO sensors. To fulfil the standards, charcoal filters were used combined with a micromachined SnO 2 sensor. The latter was operated in a pulsed mode. Sensors with optimized size and material parameters of the charcoal filters are shown to fulfil the UL2034. The sensors are characterized by electrical measurements as required by these standards. The filters are characterized by SEM, EDX, BET and TG/DSC.

The Effect of Carbon Dioxide Pneumoperitoneum on the Portal Hemodynamics in a Portal-Hypertensive Rat Model

As use of laparoscopic surgery grows, various complications with pneumoperitoneum have been reported. However, there are no reports on the relation between the carbon dioxide (Co2) pneumoperitoneum and portal hemodynamics. The purpose of this study was to determine how the pneumoperitoneum affects the portal hypertensive state. Portal-hypertensive rats, control rats, and sham operation rats were studied. The mean arterial pressure, portal venous pressure, central venous pressure, red blood flow volume of the viscera, and liver and renal function were investigated. The findings of this study suggest that Co2 pneumoperitoneum at less than 10 mm Hg does not present any undue risk to the portal hemodynamics in portal-hypertensive rats; however, more attention should be paid to the IAP in PHT patients undergoing surgery.

Kinetic studies on the carboxylation of 6-amino-penicillanic acid to 8-hydroxy-penillic acid

The carboxylation in aqueous solution of 6-amino-penicillanic acid (6-APA) to 8-hydroxy-penillic acid (8-HPA) was studied at 25°C and pH 6·5. During sparging with either a citrate buffer or a chemically defined cultivation medium containing 6-APA with mixtures of carbon dioxide and air (2·7–41% (v/v) CO 2), the kinetics for conversion of 6-APA was followed by HPLC. In the citrate buffer 6-APA was converted by two competitive reactions each following first order kinetics with respect to the concentration of 6-APA: 1. carboxylation into 8-HPA; and 2. slow conversion into an unknown compound. Formation of the unknown compound was not observed in the cultivation medium. The carboxylation of 6-APA was also found to be first order with respect to the concentration of dissolved carbon dioxide. The rate constant for formation of 8-HPA did not differ significantly in the cultivation medium compared to the citrate buffer. The kinetic was found to be the same at pH 5·0 and 6·5, and it is therefore concluded that it is dissolved carbon dioxide and not bicarbonate (or carbonate) that is involved in the carboxylation of 6-APA. Attempts to identify the unknown compound in an incubation mixture of citrate and 6-APA by both NMR spectroscopy and HPLC revealed the presence of three new citrate-containing penicillins substituted at the amino position. Upon treatment with β-lactamase one of the citrate-containing penicillins coeluted with the unknown compound. The unknown compound is most likely formed by hydrolysis of the β-lactam ring and eventually further chemical modifications of a citrate-containing penicillin.

Penetrant-plasticized permeation in polymethylmethacrylate

Pure and mixed gas permeation of CO 2 and C 2H 4 in PMMA have been measured. Carbon dioxide permeability and CO 2/C 2H 4 selectivity for the mixture is significantly lower than estimates based on pure gas permeabilities. At 15 atm, CO 2 permeability is reduced from 0.71 barrer to 0.41 barrer. CO 2/C 2H 4 selectivity calculated from pure gas values yields a value of 185 while the actual selectivity in the mixture is 80. Analysis of these data reveal that competitive sorption effects are responsible for the large depression in CO 2 permeability. Available information indicates that specific interactions between CO 2 and the ester moiety in PMMA are responsible for large increases in the diffusivity of C 2H 4 in PMMA. The increase in C 2H 4 diffusivity causes a two-fold increase in permeability further accentuating the selectivity drop caused by the reduction in CO 2 permeability. This study indicates that specific interactions play an important role in penetrant-induced plasticization.

Photosynthate Supply and Utilization in Alfalfa

Long-term carbon dioxide enrichment, (14)CO(2) feeding, and partial defoliation were employed as probes to investigate source/sink limitations of photosynthesis during the development of symbiotically grown alfalfa. In the mature crop, long-term CO(2) enrichment does not affect the rates of net photosynthesis, relative growth, (14)C export to nonphotosynthetic organs, or the rates of (14)C label incorporation into leaf sucrose, starch, or malate. The rate of glycolate labeling is, however, substantially reduced under these conditions. When the mature crop was partially defoliated, a considerable increase in net photosynthesis occurred in the remaining leaves. In the seedling crop, long-term CO(2) enrichment increased dry matter accumulation, primarily as a result of increases in leaf starch content. Although the higher rates of starch synthesis are not maintained, the growth enhancement of the enriched plants persisted throughout the experimental period. These results imply a source limitation of seedling photosynthesis and a sink limitation of photosynthesis in more mature plants. Consequently, both the supply and the utilization of photosynthate may limit seasonal photosynthesis in alfalfa.

Measurement of CO2 Dissolved in Aqueous Solutions Using a Modified Infrared Gas Analyzer System

Total dissolved inorganic carbon (SigmaCO(2)) and aqueous carbon dioxide (H(2)CO(3) (*)) in nutrient solutions may be measured by the injection of small gas or liquid samples (1 microliter to 8 milliliters) into a gas stripping column connected in-line with an infrared gas analyzer. The measurement of SigmaCO(2) in solution requires sample acidification, while H(2)CO(3) (*) and gaseous CO(2) are measured without the addition of lactic acid. The standard curve for SigmaCO(2) was linear up to 300 nanomoles CO(2). Maximum sensitivity was approximately 300 picomoles. Measurements of H(2)CO(3) (*) were independent of pH. Consequently, SigmaCO(2) and H(2)CO(3) (*) could be used to calculate the pH, HCO(3) (-), and CO(3) (2-) values of nutrient solutions. Injection and complete analyses required from 0.8 to 2 minutes.

Control of breathing during methadone addiction

Chemical control of breathing was studied before and after the administration of the daily dose of methadone in 14 former heroin addicts who were enrolled in a methadone maintenance program and taking 60 to 100 mg/day. Two major groups were identified: group 1 in which subjects (n = 6) had taken the drug for less than two months, and group 2 in which the subjects (n = 6) had taken the drug from eight to 43 months. Prior to the daily dose of methadone, the levels of arterial carbon dioxide tension were significantly higher and ventilatory responses to hypoxia significantly lower in group 1 than in group 2. Ventilatory responses to carbon dioxide (CO 2) were also lower in group 1, but the difference was not statistically significant. Following the daily dose of methadone, the subjects in group 1 manifested significant reductions of ventilation and arterial oxygen tension, significant increases in arterial carbon dioxide tension and significant depressions of ventilatory responses to both CO 2 and hypoxia in comparison to values before the administration of methadone. In contrast, subjects in group 2 manifested only a significant decrease in ventilatory responsiveness to hypoxia with no change in ventilation, arterial blood gas tensions or ventilatory responsiveness to CO 2 following the dally dose. Two intermediate subjects (five and seven months) behaved as long-term subjects with regard to arterial carbon dioxide tension and CO 2 responses but as short-term subjects with regard to responsiveness to hypoxia. Thus, during the first two months of methadone maintenance, there is continual alveolar hypoventilation due to depression of both central (CO 2) and peripheral (hypoxia) chemoreception. After five months, alveolar hypoventilation is abolished as the CO 2-sensitive chemoreflex acquires full tolerance to methadone at the maintenance dose level. In contrast, tolerance of the hypoxia-sensitive chemoreflex is developed more slowly and is never complete.