Aqueous Carbon Dioxide Research Articles

Photoacoustic response in a multivariable dyeing process: Comparison between conventional aqueous and supercritical CO2used for impregnating PET films

Photoacoustic (PA) spectroscopy is used to study impregnation of Poly (ethylene terephthalate) (PET). Films were produced in conventional aqueous bath (CAB) and supercritical carbon dioxide (SC-CO 2 ) and impregnated with disperse dyes Blue 79 (DB 79) and Red 60 (DR 60). It was treated in different temperature, concentration and pressure, and PA intensities used as the response in the multivariate method (Factorial Planning - FP). Results pointed out the SC-CO 2 process with DB 79 dye as more effective.

High‐frequency measurement of partial pressure and total concentration of carbon dioxide in seawater using microporous hydrophobic membrane contactors

To investigate CO2 chemistry in ocean water with greater time‐space resolutions, we developed measurement systems, which have state‐of‐the‐art precision but an order of magnitude or better increase in the frequency of analysis, for carbon dioxide partial pressures (PCO2) and total carbon dioxide concentrations (TCO2) in seawater. The PCO2 system was based on equilibration of a CO2‐free carrier gas stream with aqueous carbon dioxide in a flowing seawater sample stream using a commercially available membrane contactor unit normally employed in industrial applications followed by nondispersive infrared (NDIR) absorbance detection of the CO2 in the exit carrier gas. The TCO2 system was based on injection of a small‐volume seawater sample loop (~1 mL) into an acid (0.1 N HCl) liquid carrier stream to convert all carbonate and bicarbonate ions to aqueous carbon dioxide; this acidified sample was then passed through a custom‐made small‐volume membrane contactor unit where the sample's PCO2 was determined by equilibration of a CO2‐free carrier gas followed by NDIR detection. Results from lab tests and a field experiment in the Ross Sea polynya, Antarctica, are presented. The PCO2 system was determined to have a response time of about 3 s and precision of better than 1 µatm. The TCO2 system had a maximum analysis rate of one sample per 36 s, and reproducibility was determined to be better than 0.2% for a period of hours.

Densities and Solubilities for Binary Systems of Carbon Dioxide + Water and Carbon Dioxide + Brine at 59 °C and Pressures to 29 MPa

Densities and solubilities for binary systems of carbon dioxide + water and carbon dioxide + Weyburn-formation brine were measured at a temperature of 59 °C and pressures up to 29 MPa. Density values were obtained for both the saturated and unsaturated aqueous carbon dioxide solutions at different pressures. A correlation in the literature was used to predict the solubility of carbon dioxide in the aqueous phase, and the results were compared with the measured data. The measured density of aqueous carbon dioxide solutions was correlated as a function of carbon dioxide concentration and pressure. A simple method for determining the density of aqueous carbon dioxide solutions was recommended.

Direct determination of carbon dioxide in aqueous solution using mid-infrared quantum cascade lasers.

A method for the direct determination of carbon dioxide in aqueous solutions using a room-temperature mid-infrared (MIR) quantum cascade laser at 2330 cm(-1) is reported. The absorption values of different carbon dioxide concentrations were measured in a 119 microm CaF2 flow-through cell. An optical system made of parabolic mirrors was used to probe the flow cell and to focus the laser beam on the mercury cadmium telluride (MCT) detector. Aqueous carbon dioxide standards were prepared by feeding different mixtures of gaseous N2 and CO2 through wash bottles at controlled temperature. The concentration of the dissolved CO2 was calculated according to Henry's law, taking into account the temperature and the partial pressure of CO2. The carbon dioxide standards were connected via a selection valve to a peristaltic pump for subsequent, automated measurement in the flow-through cell. A calibration curve was obtained in the range of 0.338 to 1.350 g/L CO2 with a standard deviation of the method sxo equal to 19.4 mg/L CO2. The limit of detection was calculated as three times the baseline noise over time and was determined to be 39 mg/L.

Influence of Turbulent Flow on the Localized Corrosion Process of Mild Steel with Inhibited Aqueous Carbon Dioxide Systems

Abstract Three percent sodium chloride (NaCl) solutions saturated with carbon dioxide (CO2) were used to study the corrosion inhibition of mild steel samples under turbulent flow conditions. The performance of cetyl trimethyl ammonium bromide (CTAB) was tested with three different concentrations (20, 60, and 100 ppm) and three different pH values (3.8, 5, and 6). The rotating cylinder electrode (RCE) was used to test different turbulent flow conditions (1,000 rpm to 5,000 rpm). It was found that the inhibitor performance is a function of concentration and pH. A localized corrosion process was found on the surface samples and further research was carried out to determine its causes. With the use of cyclic anodic polarization curves and surface examinations, it was demonstrated that the localized corrosion process does not occur at a specific rotation speed. Potentiostatic experiments simulated the effect of shear stress and the instantaneous changes in corrosion potential (Ecorr) observed when the rotation...

Euphotic zone variations in bulk and compound‐specific δ13C of suspended organic matter in the Subantarctic Ocean, south of Australia

The carbon isotopic compositions of suspended organic matter δ13CPOC collected from Subantarctic Zone surface waters south of Australia in November 1995 decrease southward from −20 to −26‰ and display strong correlations with aqueous carbon dioxide concentration ([CO2]aq), consistent with previous studies. In contrast, vertical profiles through the euphotic zone (top ∼100 m) of δ13CPOC at six stations display decreases with depth of up to 2.4‰. These decreases in δ13CPOC cannot be fully explained by the small vertical variations in [CO2]aq or its 13C content. Carbon 13 analyses of several individual sterols revealed similar isotopic changes with depth, suggesting that they derive from a fundamental depth control on primary production, rather than from algal community variations or remineralization processes. Growth rate μ appears to be the most likely source of the depth variations. The relationship between μ/[CO2]aq and δ13CPOC derived from surface water samples can explain the vertical variations of δ13CPOC within the mixed layer, provided integrated mixed layer growth rates are used. Below the mixed layer, differences between the observed δ13CPOC and the growth rate model can be explained by recent shallowing in mixed layer depth and the subsequent effect on growth rates. These results suggest that δ13CPOC determinations can be used to provide some information on the recent history of mixed layer processes and that interpretation of sedimentary δ13CPOC records should include consideration of possible growth rate and mixed layer depth variations.

Controls on the molecular distribution and carbon isotopic composition of alkenones in certain haptophyte algae

Although the biochemical functions and biosynthetic pathways of alkenones are still largely unknown, alkenone unsaturation ratios are now used extensively to infer ancient sea surface temperature, and their isotopic compositions have been used to reconstruct ancient atmospheric CO2levels. The inferred relationships between alkenone unsaturation ratios, isotopic compositions, and growth conditions are based on empirical laboratory and field studies and, in the case of isotope fractionation, on simple models of carbon acquisition and fixation. Significant uncertainty still exists concerning the physiological and ecological factors affecting cellular production of alkenones, unsaturation ratios, and isotopic composition. Phytoplankton culture conditions have been shown to affect alkenone unsaturation (U37K′), cellular alkenone content, intracellular isotopic compositions (Δδ), and changes in fractionation (εP) as a function of the quotient of algal growth rate and aqueous carbon dioxide concentration (μ/CO2). Such studies imply that plant physiology can affect the interpretation of environmental signals. The factor(s) controlling cellular alkenone concentrations and unsaturation ratios are reviewed, as well as the carbon isotopic composition of the alkenone‐producing algae. A new technique is presented to determine growth rates of the alkenone‐containing algae in natural settings that will facilitate testing laboratory‐based hypotheses concerning the carbon isotopic fractionation and its relationship to growth rate/growth status of alkenone‐producing algae in the field.

Activity and stability of immobilised soybean lipoxygenase-1 in aqueous and supercritical carbon dioxide media

The activity of immobilised soybean lipoxygenase-1 (LOX-1) was studied in aqueous and supercritical carbon dioxide (SCCO2) media for the production of 13S-hydroperoxyoctadecadenoic acid (13S-HPODE). In SCCO2, it was optimal at 33 °C and 25 MPa. A higher space-time yield of 5.7×10−3 Ms−1 mg−1 LOX-1 for 13S-HPODE was obtained in SCCO2 compared to only 5×10−5 Ms−1 mg−1 LOX-1 in aqueous medium. The stability of immobilised LOX-1 was only significantly affected by the pressurisation and depressurisation steps during reactions in SCCO2.

Sorption–desorption behavior of phenanthrene elucidated by pyrolysis–gas chromatography‐mass spectrometry studies of soil organic matter

AbstractCommonly used partitioning models of hydrophobic organic contaminant sorption in soil, which treat all soil organic matter (SOM) as having identical structure, are unable to explain differences in organic carbon–normalized sorption coefficients (KOC) among sorbents, isotherm nonlinearity, and sorption–desorption hysteresis. This study relates one index of SOM composition, structural fragments quantified by pyrolysis–gas chromatography‐mass spectrometry, to aqueous and supercritical carbon dioxide (SC CO2) sorption–desorption parameters. Results show positive correlations between aqueous KOCs and hydrocarbon fragment peak areas and negative correlation to N‐ and O‐containing peaks, which is consistent with hypotheses attributing sorption of phenanthrene to hydrophobic sorbent domains. Positive correlation between Freundlich n values in SC CO2 and hydrocarbon fragments with negative correlation to N‐ and O‐containing fragments suggests that energetic heterogeneity of polar environments controls nonlinearity in this solvent of limited polarity. Aqueous sorption–desorption hysteresis appears to be surpressed by N‐ and O‐containing moieties and correlates with decreased thermal desorption of phenanthrene at 800°. The SC CO2 extraction efficiency and, to a lesser degree, the desorption response when methanol is added as a cosolvent indicate that polar functional groups play a role in retarding phenanthrene desorption during SC CO2 extraction. Organic matter pyrolysis under varying time and temperature conditions indicates that pyrolysis fragments that do not significantly correlate with functional trends likely evolve by a different pyrolytic mechanism and are generally poorly correlated with sorption–desorption properties. The level of structural detail utilized in structure–function correlations in this work exceeds previous efforts to relate sorption behavior to sorbent structure. However, the work reveals that certain sorption parameters, notably Freundlich n values in aqueous systems, require even more detailed characterization of sorbent structures.

Interactions of calcareous suspended sediment with glacial meltwater: a field test of dissolution behaviour

Abstract Dissolution of calcite and associated interactions of suspended sediment with aqueous solution were investigated in a tributary-free 600 m reach of the main meltstream draining the Tsanfleuron glacier, Switzerland, over a 24-h cycle during which solute concentrations varied inversely with discharge. Downflow, solute calcium, strontium, and alkalinity increased because of calcite dissolution. Using flow-through times from salt-dilution gauging, a consistent small sulphate excess at the downstream site was observed. Given the slowness of sulphate supply by pyrite oxidation, this excess sulphate can be attributed to mixing of around 1% of ion-rich water (seeping from till banks) with the main meltstream. Calcite dissolution is normally directly proportional to exposed surface area of the mineral, yet only a small increase in calcite dissolution was observed when suspended sediment increased by a factor of 25 to 1.3 g/l at peak flow. The suspended sediment displays little variation in size distribution with total suspended load, and contains 30–40% calcite with a minimum specific surface area (S) of 0.25 m2/g sediment. Application of the Plummer–Wigley–Parkhurst (PWP) model predicts dissolution rates broadly similar to those found at lower suspended sediment concentrations given this value of S. At higher suspended sediment loads predicted dissolution rates are too high. This discrepancy is reduced by use of the Buhmann–Dreybrodt (B–D) model which takes explicit account of the slowness of hydration of aqueous carbon dioxide, and the problem of mass transfer of H2CO3 given the surface area of calcite to volume of solutions considered. The remaining discrepancy implies less interaction than expected of suspended sediment particles with turbulent meltwater at high suspended sediment concentrations. The effects of proglacial modification of meltstream geochemistry in this case is a strong decrease in PCO2 accompanied by an increase in total ion load, but decreases in Mg/Ca and Sr/Ca, from the high values characteristic of low water–rock ratio interactions in subglacial environments and till. Nevertheless, the distinctive chemical imprint in meltstream chemistry of non-congruent mineral dissolution in low water–rock ratio glacial weathering environments remain. In contrast, in terrains where calcite is scarce, it will tend to dissolve congruently, contributing significantly to total solutes, and its dissolution will be less limited by CO2 reaction kinetics.

Raman spectra of potassium carbonate and bicarbonate aqueous fluids at elevated temperatures and pressures: comparison with theoretical simulations

One-molal solutions of potassium carbonate and potassium bicarbonate were investigated by Raman spectroscopy from 22° to 550°C and from 1000 to 2000 bar. Experiments were performed in a special hydrothermal pressure vessel fitted with conical diamond windows. Frequencies and half-widths of the vibrational modes were measured for both carbonate and bicarbonate as a function of temperature and pressure. In the case of potassium carbonate solutions, dissolved bicarbonate appeared with its concentration dramatically increasing with increasing temperature and decreasing density. The opposite behavior occurred in the case of potassium bicarbonate: the relative concentration of dissolved carbonate increased relative to total bicarbonate. In addition, at temperatures above 300°C, dissolved aqueous carbon dioxide appeared with its concentration continuing to increase with increasing temperature and decreasing density. Simulations using theoretically-predicted mass action constants were used to compute changes in solution speciation for these solutions as they were subjected to increased temperature and pressure. Results resulting from these predictions matched those discovered in the spectral measurements.

High-Precision Conductometric Detector for the Measurement of Atmospheric Carbon Dioxide

A new, lightweight instrument has been developed for measuring atmospheric mixing ratios of the greenhouse gas carbon dioxide with high precision and accuracy. This modified total organic carbon analyzer uses a bundle of semipermeable hollow fiber membranes to continuously equilibrate CO2 in air with a recirculated stream of deionized water. Aqueous carbon dioxide hydrolyzes and dissociates to form the ions H3O+ and HCO3-, thereby increasing the conductivity. The bipolar pulsed method is used to measure the conductivity of the water before and after contact with air. Potential interferences that may also increase the conductivity, such as acids and bases, are removed at the inlet by bicarbonate and bisulfate scrubbers. The detector has been field tested and exhibits a 1/e response time of ∼30 s and precision (RSD) of 0.1%. Field results for measurements at altitudes in the range of 1700−3600 m MSL exhibited an average deviation of 0.16% from values obtained by flask sampling and laboratory measurement usi...

Azoles. Part 13. Synthesis and bromine ? lithium exchange reactions of some 1-substituted 4,5-dibromo-1H-1,2,3-triazoles and 2-substituted 4,5-dibromo-2H-1,2,3-triazoles

4,5-Dibromo-1H-1,2,3-triazole was synthesised by various routes and reacted with chloromethyl methyl ether (N-1/2), methyl chloroformate (N-1), benzyl chloride (N-1), 4-methoxybenzyl chloride (N-1), 4-nitrobenzyl chloride (N-1/2) or triphenylmethyl chloride (N-2) under various conditions, to give isolable products substituted at the N-atoms shown in parentheses.4,5-Dibromo-l-methoxymethyl-1H- and -2-methoxymethyl-2H 1,2,3-triazole reacted with butyllithium (in diethyl ether or tetrahydrofuran at low temperatures) at position-5 and the resulting lithiated derivatives were quenched with aqueous ammonium chloride, carbon dioxide, methyl chloroformate, benzophenone or dimethyl or diphenyl disulfide to give high yields (71–93%) of the corresponding 5-substituted 1,2,3-triazole. l-Benzyl-4,5-dibromo-1H-1,2,3-triazole was converted similarly into 1-benzyl-4-bromo-5-methylsulfanyl-1H-1,2,3-triazole (91.5%). In a ‘one pot’ sequence and through two successive treatments with butyllithium and the appropriate quenching reagent (Ph2S2 and H2O), 4,5-dibromo-2-methoxymethyl-2H-1,2,3-triazole was converted similarly into 2-methoxymethyl-4-phenylsulfanyl-2H-1,2,3-triazole (47% yield).

Flash calcination of a magnesite ore in a free-fall reactor and leaching of magnesia

Flash calcination of a magnesite ore in a free-fall reactor and leaching of calcined magnesite with aqueous carbon dioxide were investigated. The effect of temperature and particle size on the weight loss were observed in the calcination experiments. The maximum weight loss was obtained as 43.2% for the particles of −100 + 140 mesh at the calcination temperature of 850°C. In leaching experiments; leaching temperature and time, particle size, stirring speed, and solid/liquid ratio were selected as variables. The dissolution fraction of magnesium increases with the increase in the leaching time, temperature and to a lesser degree stirring speed. The dissolution also increases with decreasing solid/liquid ratio and particle size. A thermal gravimetric method was used to measure activation energy, preexponential factor and rate constants for the thermal decompositon of the magnesite ore. The activation energy and preexponential factor were calculated as 39.4 kcal mol −1 and 3.5×10 6 s −1, respectively. The rate constants were found to vary between 1.2×10 4 and 1.3×10 −2 s −1 in the temperature range of 823 to 1023 K.

Origins of calcite in a boiling geothermal system

The formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling, dilution, and condensation. In this paper we show how these processes control the occurrence, distribution, and stable isotope composition of calcite based on a study at Broadlands-Ohaaki. The two principal calcite occurrences in the Broadlands-Ohaaki geothermal system are: (1) as replacement of rock forming minerals and volcanic glass; and (2) as platy crystals infilling voids. Both are stable over a broad temperature range from 160 degrees C to 300 degrees C. Replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino-silicates and sub-boiling liquids that contain 0.3 to 0.75 m CO 2 . Platy calcite, in contrast, forms over a restricted vertical interval of a few hundred meters within the upflow zone. It precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid-rich and vapor-rich fluid inclusions and its formation in the two-phase zone. Fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed. Homogenization temperatures range from 160 degrees C to 310 degrees C and are consistent within the present geothermal regime. Ice melting temperatures range from 0.0 to -1.0 degrees C and indicate the presence of up to 0.5 m dissolved carbon dioxide. Model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling. Most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone, in which the rising fluid (initially containing 0.75 m CO 2 ) begins to boil at approximately 320 degrees C and approximately 2000 m depth; data from well Br-18 instead matches a curve in which the rising fluid (initially containing 0.53 m CO 2 ) begins boiling at approximately 245 degrees C and approximately 900 m depth. The shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water, as it rises and mixes with marginal waters. Calcite precipitates from both shallow formed steam-headed groundwater and deeply derived chloride water, and these waters are isotopically distinct. At Broadlands-Ohaaki, the delta 18 0 values of calcite at 200 degrees C range from 0.5 to 7.5 per mil, whereas delta 18 0 values of calcite at 200 degrees C range from 4 to 10 per mil. Taking appropriate temperature dependent fractionation factors into account, these data indicate equilibration with chloride water (delta 18 0 H2O = -4.5 per mil) and steam-heated groundwater (delta 18 O H2O = -7.0 per mil), respectively. Oxygen isotopes of hydrothermal calcites in the nearby Wairakei and Waiotapu geothermal systems show similar patterns, consistent with the occurrence of both chloride and steam-heated waters there. Calcite formation is explained by a model that describes the distribution of two-phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability. In this ideal situation, platy calcite forms along the inner margin of the two-phase zone, having the shape of an inverted cone, whereas replacement calcite mostly forms in the surrounding one-phase liquid-only zone. The sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the Ohaaki sector at Broadlands-Ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system.

The formation and growth of carbon dioxide gas bubbles from supersaturated aqueous solutions

A simple stopped-flow apparatus has been devised to follow the growth of gas bubbles formed after the rapid establishment of a supersaturated aqueous carbon dioxide solution by the reaction of hydrogen ions with bicarbonate ions. Turbidimetric measurements taken over a period of c.200 ms, supplemented by analysis of photographic and videotape recordings at later times have shown that bubble growth is a diffusion-limited process. Experimental results obtained with a hydrophobised cell led to the conclusion that at supersaturations typical of carbonated beverages the mechanism of bubble formation probably involves pre-existing gas cells trapped on the surface. Adsorption of sodium dodecyl sulphate, β-casein or β-lactoglobulin onto the hydrophobic surface reduced the number of bubbles, but solutions of sodium dodecyl sulphate above the critical micelle concentration produced additional bubbles.

Separation process of ethanol from aqueous solutions usihg supercritical carbon dioxide

Abstract The process of separating ethanol from aqueous solutions using supercritical carbon dioxide is in the development stage and was investigated experimentally using a bench scale test plant. It was operated under conditions based on previous data (Furuta et al. 1990). The results showed that more than 99 mol% of ethanol could be concentrated without any entrainer. A reflux ratio grater than 2 was required for good extraction efficiency. For recycling use, carbon dioxide was easily separated from ethanol using a high pressure distillation column.

5171694 Method for monitoring aqueous carbon dioxide: Dennis J Connolly assigned to The Babcock & Wilcox Company

5171694 Method for monitoring aqueous carbon dioxide: Dennis J Connolly assigned to The Babcock & Wilcox Company

Model of vapor-liquid equilibria for aqueous acid gas-alkanolamine systems. 2. Representation of hydrogen sulfide and carbon dioxide solubility in aqueous MDEA and carbon dioxide solubility in aqueous mixtures of MDEA with MEA or DEA

A physicochemical model developed in earlier work for representing H 2 S and CO 2 solubility in aqueous solutions of monoethanolamine (MEA) and diethanolamine (DEA) was extended to include the mixtures of methyldiethanolamine (MDEA) with MEA or DEA. Activity coefficients are represented with the electrolyte-NRTL equation treating both long(range electrostatic interactions and short-range binary interactions. Adjustable binary interaction parameters of the model were fitted on binary and ternary system MDEA data reported in the literature. The solubility of CO 2 in aqueous mixtures of MDEA with MEA or DEA was measured at 40 and 80 o C over a wide range of CO 2 partial pressures. Representation of the data by the model is good, especially at low to moderate acid gas loadings

Solar energy fixation of carbon dioxide via cadmium sulphide and other semiconductor photocatalysts

Aqueous carbon dioxide is photochemically reduced in the presence of semiconductor suspensions and colloids. Experiments have been performed using CdS, ZnO, SiC, Ba TiO 3, and SrTiO 3, dispersions. Product analysis showed the formation of formic acid formaldehyde, sometimes methanol and in the presence of tetramethylammonium chloride, two-carbon products such as glyoxylic and acetic acids and sometimes acetaldehyde. Product yields and photochemical yields were studied as a function of pH, solution composition, added sacrifical electron donors and catalysts, irradiation intensity and irradiation time. A demonstration experiment with a flat-bed solar collector showed the formation of formic acid and formaldehyde using direct sunlight.