The solubility of water in mixtures of dimethyl ether and carbon dioxide

This paper reports measurements of the solubility of water in liquid and supercritical fluid mixtures of dimethyl ether and carbon dioxide. The measurements were made by extracting water under saturation conditions using premixed liquid dimethyl ether–carbon dioxide mixtures. Results are reported for temperatures of 313.8 K and 333.3 K at 9.0 MPa and 15.0 MPa. Results are fitted to the Peng–Robinson cubic equation of state with mixing rules according to Wong and Sandler, using binary interaction parameters fitted to the literature data for the respective binary systems: dimethyl ether–water; dimethyl ether–carbon dioxide; and carbon dioxide–water. Liquid densities for dimethyl ether–carbon dioxide mixtures, measured using a coriolis flow instrument, are also reported.     

Thermodynamic and transport properties of argon/carbon and helium/carbon mixtures in fullerene synthesis

The equilibrium composition and thermodynamic and transport properties of argon; carbon and helium/carbon mixtures are calculated in the temperature range 300–20,000 K. The curves for the composition of mixtures of 50%, carbon in argon or helium are shown fir a pressure of 1.33 × 10⁴ Pa. The calculations for the heat capacity at constant pressure (C_p) and transport coefficients are validated with other studies, for the cases or pure argon and pure helium at a pressure of 10⁵ Pa. The properties of mixtures with various proportions of carbon in argon and helium are calculated. Results are presented at pressures of 105 and 1.33 × 10⁴ Pa, typical of reactors for the synthesis of fullerenes and nanotubes. It is observed that the properties of carbon and mixtures of carbon with a buffer gas (argon or helium) are very different from those of the buffer gas, thus the need to consider this effect in simulations. In general, the mixtures follow trends intermediate to those of the pure gases from which they are composed except for the thermal conductivity which shows a deviation from this tendency in the region between 11,500 and 19,000 K for argon/carbon mixtures and between 8,000 and 12,000 K for helium/carbon mixtures. Also, the electrical conductivity of mixtures of low carbon concentration is very close to that ofpure carbon. A datafile containing the transport properties of mixtures for pressures between 10⁴ and 10⁵ Pa is available free of charge from the authors.     

Determination of carbon dioxide in gaseous samples by gas diffusion-flow injection

A gas diffusion-flow injection system was developed for the determination of carbon dioxide in gaseous samples. The calibration was based on the use of either gaseous carbon dioxide or aqueous sodium carbonate standards. Gaseous carbon dioxide samples and gaseous or aqueous standards were injected directly into a donor stream of 1.0×10⁻⁴ M H₂SO₄. In the gas diffusion unit, carbon dioxide diffused through a PTFE membrane into an acceptor stream containing a mixed acid/base indicator. The absorbance of the acceptor stream was monitored spectrophotometrically at 554 nm. The calibration plot was linear over the range of 5.00×10² to 1.27×10⁴ μl l⁻¹ with a sample throughput of 28 h⁻¹ and 3.2% R.S.D. ([CO₂]=2.37×10³ μl l⁻¹, n=12). The detection limit was determined as 2.50×10² μl l⁻¹. The flow system was successfully applied to the analysis of several natural gaseous samples and the headspace of milk containers during storage. The flow injection results were found to be statistically indistinguishable at the 95% confidence level from those obtained by gas chromatography using thermal conductivity detection.     

Temperature programmed decomposition studies: high-sensitivity determination of carbon monoxide,carbon dioxide and methane by gas chromatography

Carbon monoxide, carbon dioxide and methane, evolved in very low amount during temperature programmed decomposition of transition metal cluster catalysts, can be determined quickly (<3 min) by gas chromatography on a Porapak S column. Catalytic conversion of the CO and CO₂ to methane makes it possible to use a hydrogen fiame ionization detector. The advantages are that the limit of detection is about 1 ppm (ca. 4.4 × 10^?11 mol cm^?3, STP) and that the procedure is applicable to decompositions studied in helium/oxygen or other reactive gas mixtures.     

Fixed-bed adsorption of carbon dioxide/methane mixtures on silicalite pellets

The adsorption of carbon dioxide and methane on silicalite pellets packed on a fixed bed has been studied. Equilibrium and kinetic measurements of the adsorption of carbon dioxide and methane have been performed, and a binary adsorption isotherm for carbon dioxide/methane mixtures has been obtained. A model based on the LDF approximation for the mass transfer has been used to describe the breakthrough curves obtained experimentally. A PSA cycle has been proposed for obtaining methane with purity higher than 98% from carbon dioxide/methane mixtures containing 38% and 50% methane, and its performance has been simulated using the proposed model. The simulation results show that silicalite can be a suitable adsorbent for employment in a PSA separation process for carbon dioxide removal from coalseam and landfill gases.     

Solubility of carbon dioxide in aqueous solutions of diisopropanolamine and methyldiethanolamine

The solubility of carbon dioxide in aqueous solutions of alkanolamines was measured by means of two experimental methods. The solubility of carbon dioxide was measured at 298 K with a static total pressure apparatus in solutions of water + diisopropanolamine (DIPA) having mass fraction of DIPA equal to 10.1%, 11.0% and 33.9%. The density of the water + DIPA solution was measured continuously during the experiments to investigate the changes in density introduced by the absorption of carbon dioxide. A correlation for the density of CO₂-loaded aqueous solutions of DIPA is presented.     

Effect of variation in argon content of calibration gases on determination of atmospheric carbon dioxide

Carbon dioxide (CO₂) is a greenhouse gas that makes by far the largest contribution to the global warming of the Earth's atmosphere. For the measurements of atmospheric CO₂ a non-dispersive infrared analyzer (NDIR) and gas chromatography are conventionally being used. We explored whether and to what degree argon content can influence the determination of atmospheric CO₂ using the comparison of CO₂ concentrations between the sample gas mixtures with varying Ar amounts at 0 and 18.6 mmol mol⁻¹ and the calibration gas mixtures with Ar at 8.4, 9.1, and 9.3 mmol mol⁻¹. We newly discovered that variation of Ar content in calibration gas mixtures could undermine accuracy for precise and accurate determination of atmospheric CO₂ in background air. The differences in CO₂ concentration due to the variation of Ar content in the calibration gas mixtures were negligible (<±0.03 μmol mol⁻¹) for NDIR systems whereas they noticeably increased (<±1.09 μmol mol⁻¹) especially for the modified GC systems to enhance instrumental sensitivity. We found that the thermal mass flow controller is the main source of the differences although such differences appeared only in the presence of a flow restrictor in GC systems. For reliable monitoring of real atmospheric CO₂ samples, one should use calibration gas mixtures that contain Ar content close to the level (9.332 mmol mol⁻¹) in the ambient air as possible. Practical guidelines were highlighted relating to selection of appropriate analytical approaches for the accurate and precise measurements of atmospheric CO₂. In addition, theoretical implications from the findings were addressed.     

Methane and carbon dioxide solubility in 1,2-propylene glycol at temperatures ranging from 303 to 423 K and pressures up to 12 MPa

This work reports solubility data of methane and carbon dioxide in 1,2-propylene glycol and the Henry's law constant of each solute in the studied solvent at saturation pressure. The measurements were performed at 303, 323, 373, 398 and 423.15 K and pressures up to 4.5 MPa for carbon dioxide solubility and pressures up to 12.1 MPa for methane solubility. The experiments were performed in an autoclave type phase equilibrium apparatus using the total pressure method (synthetic method). All investigated systems show an increase of gas-solubility with the increase of pressure. A decrease of carbon dioxide solubility with the increase of temperature and an increase of methane solubility with the increase of temperature was observed. From the variation of solubility with temperature, partial molar enthalpy and entropy change of the solute for each mixture were calculated.     

Reaction between carbon dioxide and elementary fluorine

Reactions between carbon dioxide and fluorine were examined at temperatures of 303-523 K under various pressure and mixture ratios of both gases. Reactions were carried out similarly under the existence of NaF, CsF and EuF₃.After the reaction, fluorine was removed and the reaction products were analyzed using FT-IR, GC/FT-IR and GC/MS. The major products were CF₃OF, COF₂, CF₄ and CF₂(OF)₂.The best yield of COF₂ was 11.1% under the reaction condition of CO₂/F₂ = 76 kPa/76 kPa with temperature of 498 K for 72 h in a direct reaction. The formation rate of COF₂ in the direct reaction was estimated as 0.232 dm³ mol⁻¹ h⁻¹ under the reaction conditions of CO₂/F₂ = 76 kPa/76 kPa, at 498 K. In the presence of CsF, it was estimated as 1.88 dm³ mol⁻¹ h⁻¹ at CO₂/F₂ = 76 kPa/76 kPa at 498 K.The activation energy of the COF₂ formation in the direct reaction was estimated as 45.7 kJ mol⁻¹ at CO₂/F₂ = 76 kPa/76 kPa at 498 K. In addition, 24.2 and 38.9 kJ mol⁻¹ were evaluated at CO₂/F₂ = 76 kPa/76 kPa at 498 K, respectively, in the presence of CsF and EuF₃.     

Separation of carbon dioxide/methane mixtures by adsorption on a basic resin

In this work, the separation of carbon dioxide/methane mixtures by PSA using a basic resin (Amberlite IRA-900) has been studied. Adsorption equilibrium and kinetics of carbon dioxide and methane on a fixed-bed of this adsorbent have been measured, and a binary adsorption equilibrium isotherm has been obtained. The adsorbent deactivation with the number of adsorption-desorption cycles, and its regeneration, have also been analysed. A model based on the LDF approximation has been used to describe the experimental breakthrough curves. The applicability of the basic resin to the separation of carbon dioxide/methane mixtures has been studied in an experimental PSA setup using a single bed. The validity of the model used in the fixed-bed study for simulating a PSA system has been checked by comparing the simulated and the experimental performance of the proposed PSA cycle.     

Density measurements on binary mixtures (nitrogen + carbon dioxide and argon + carbon dioxide) at temperatures from (298.15 to 423.15) K with pressures from (11 to 31) MPa using a single-sinker densimeter

A single-sinker densimeter was built to specifically investigate the (p, ρ, T, x) behavior of fluid mixtures relevant for carbon capture and storage (CCS). Due to the use of a magnetic-suspension coupling, the densimeter enables measurements over the temperature range from (273.15 to 423.15) K with pressures up to 35 MPa. A comprehensive analysis of the experimental uncertainties was undertaken. The expanded uncertainties (k = 2) are 35 mK for temperature, 3.39 kPa for pressure, and 0.033% for density determination. The apparatus was used for measurements on the binary systems (nitrogen + carbon dioxide) and (argon + carbon dioxide). The compositions for both systems were (0.05 and 0.01) mole fraction carbon dioxide. Density measurements were carried out at temperatures from (298.15 to 423.15) K with pressures from (11 to 31) MPa. The relative combined expanded uncertainty (k = 2) in density was 0.15% for the (nitrogen + carbon dioxide) mixtures and 0.12% for the (argon + carbon dioxide) mixtures. A major contribution to this uncertainty emerged from the uncertainty in the gas mixture composition. The new experimental data were compared to the GERG-2008 equation of state (EOS) for natural-gas mixtures as implemented in the NIST REFPROP database and to the EOS-CG, another new Helmholtz energy model for CCS mixtures as implemented in the TREND software package of Ruhr-University Bochum. Relative deviations were mostly within 0.5%. The agreement of the new density values with the only available literature data closest to the composition range under study was better than 0.1%.     

Phase equilibria of clathrate hydrates of methane + carbon dioxide: New experimental data and predictions

In this communication, we report experimental dissociation conditions for region clathrate hydrates of methane + carbon dioxide in gas–liquid water–hydrate (G–Lw–H) equilibrium. The temperature and pressure conditions are in the range of (279.1–289.9) K and (2.96–13.06) MPa, respectively. Concentrations of carbon dioxide in the feed gas are also varied. An isochoric pressure-search method was used to perform the measurements. The dissociation data generated in this work along with the literature data are compared with the predictions of a thermodynamic model and a previously reported empirical equation. A discussion is made on the deviations between the experimental and predicted data.     

Experimental study on equilibrium solubility (at low partial pressures), density, viscosity and corrosion rate of carbon dioxide in aqueous solutions of ascorbic acid

In this paper, ascorbic acid as a new carbon dioxide (CO₂) absorbent was investigated. The equilibrium solubility of CO₂ into 0.5, 1 and 1.5 mol dm⁻³ (M) aqueous ascorbic acid solutions were measured experimentally with a stirred batch reactor at total atmospheric pressure over the CO₂ partial pressure ranging from 0 to 45 kPa and temperatures between 298 and 313 K. The results of the gas solubility are presented as loading capacity (mol CO₂/mol ascorbic acid) as function of partial pressure of CO₂ for all experimental runs. Experimental results showed that solubility of CO₂ increases with increase in molar concentration of ascorbic acid solution at a given temperature and decreases with increase in temperature at a given concentration. The densities and viscosities of the ascorbic acid solutions were measured at the same conditions of the solubility measurement. Some corrosion rate tests were also performed on carbon steel at temperature of 308 K. It was observed that viscosity and corrosion rate increase when the molar concentration of ascorbic acid solution increases.     

Poly(ethylene-2,6-naphthalate) microfiber prepared by carbon dioxide laser-thinning method

Poly(ethylene-2,6-naphthalate) (PEN) microfiber was continuously obtained by using a carbon dioxide (CO₂) laser-thinning method. As a winding speed increased, the fiber diameter decreased, and its birefringence increased. When the PEN microfiber, obtained by irradiating the laser operated at a power density of 9.15 W cm⁻² to the original fiber supplied at 0.33 m min⁻¹, was wound up at 1594 m min⁻¹, the obtained microfiber had a diameter of 2.8 μm, a birefringence of 0.174, tensile modulus of 5.4 GPa, and a tensile strength of 0.36 GPa.     

Adsorption and selectivity of carbon dioxide with methane and nitrogen in slit-shaped carbonaceous micropores: Simulation and experiment

We have used the grand canonical Monte Carlo method to study the adsorption and selectivity of mixtures of carbon dioxide with methane and nitrogen at high (i.e., ambient) temperatures in model slit pores with graphitic surfaces. Experimental data, including new high pressure measurements for carbon dioxide and methane on a non-porous graphitic standard, were used to test the potential models. The mixture simulations predict that carbon dioxide is preferentially adsorbed in both systems. The results are discussed in terms of competing energetic and entropic effects and the underlying molecular mechanisms.     

Solubility of oxygen, carbon dioxide and water in semifluorinated alkanes and in perfluorooctylbromide by molecular simulation

Solubilities of oxygen, carbon dioxide and water in substituted fluorocarbons perfluoroctylethane (PFOE), perfluorohexylethane (PFHE), perfluorohexylhexane (PFHH) and perfluoroalkylbromide (PFOB) were studied by computer simulation, between 293 and 313 K at 1 bar. The solubilities do not show a marked temperature dependence, are similar in all solvents and have values of the order of 4×10⁻³ for oxygen, 2×10⁻² for carbon dioxide and 3×10⁻⁶ for water, in mole fraction. The gases are slightly less soluble in PFHE when compared with the other solvents, whereas water is slightly more soluble in this liquid. The solubilities were obtained from Henry’s law coefficients, in turn derived from residual chemical potentials of the solutes at infinite dilution obtained by molecular simulation techniques using full atomistic force fields.     

Isothermal phase equilibria and structural phase transition in the carbon dioxide + cyclopropane mixed-gas hydrate system

The isothermal phase equilibria of the carbon dioxide + cyclopropane mixed-gas hydrate system were investigated by means of static temperature measurement and Raman spectroscopic analysis. Raman spectra indicated that the crystal structure of the carbon dioxide + cyclopropane mixed-gas hydrate changes from structure-I to structure-II and back to structure-I with an increase of the equilibrium carbon dioxide composition at 279.15 K, while each simple gas hydrate belongs to structure-I at the temperature. Whereas, unlike 279.15 K, no structural phase transition occurs along the isothermal stability boundary at 284.15 K.     

A miniature chemiresistor sensor for carbon dioxide

A carpet-like nanostructure of polyaniline (PANI) nanothin film functionalized with poly(ethyleneimine), PEI, was used as a miniature chemiresistor sensor for detection of CO₂ at room temperature. Good sensing performance was observed upon exposing the PEI–PANI device to 50–5000 ppm CO₂ in presence of humidity with negligible interference from ammonia, carbon monoxide, methane and nitrogen dioxide. The sensing mechanism relied on acid–base reaction, CO₂ dissolution and amine-catalyzed hydration that yielded carbamates and carbonic acid for a subsequent pH detection. The sensing device showed reliable results in detecting an unknown concentration of CO₂ in air.     

Vapor–liquid equilibria of the carbon dioxide (CO2) + 2,2-dichloro-1,1,1-trifluoroethane (R123) system and carbon dioxide (CO2) + 1-chloro-1,2,2,2-tetrafluoroethane (R124) system

Binary vapor–liquid equilibrium data were measured for the carbon dioxide (CO₂) + 2,2-dichloro-1,1,1-trifluoroethane (R123) system and the carbon dioxide (CO₂) + 1-chloro-1,2,2,2-tetrafluoroethane (R124) system at temperature from 313.15 to 333.15 K. These experiments were carried out with a circulating-type apparatus with on-line gas chromatography. The experimental data were correlated well by Peng–Robinson equation of state using the Wong–Sandler mixing rules.     

Solubility of carbon dioxide in 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate

Experimental results for the solubility of carbon dioxide in the ionic liquid 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate are not reported in the literature. To this end, we present in this work new solubility data for carbon dioxide in 1-ethyl-3-methylimidazolium 2-(2-methoxyethoxy) ethylsulfate for temperatures ranging from (303.2 to 343.2) K and pressures up to 6.7 MPa using a thermogravimetric microbalance. The carbon dioxide solubility was determined from absorption saturation (equilibrium) data at each fixed temperature and pressure. The buoyancy effect was accounted in the evaluation of the carbon dioxide solubility. Highly accurate equations of states for carbon dioxide and for ionic liquids were employed to determine the effect of buoyancy on carbon dioxide solubility. The solubility measurements are presented as a function of temperature and pressure. The present experimental solubility results have been successfully correlated using an extended Henry’s law equation.