With the prevalence of air quality issues in our society, the ability to remove toxic gases from air is a necessity. This work addresses the development of biphasic, nanostructured, ...organoalkoxysilane-grafted, siliceous materials for use in single pass filters of various types for the removal of acidic and basic gases from humid air. Materials exhibit high single pass capacities for sulfur dioxide, a representative acid-forming gas, or ammonia, a representative basic gas. The nanostructured siliceous support provides initial ammonia capacity, and grafted amine and carbonyl groups provide desired functional chemistries for sulfur dioxide and enhanced ammonia capacities. Methacryloxypropyltrimethoxysilane (MAPS)-MCM-41 has the highest ammonia capacity at about 7 mol/kg at 1500 ppmv and 23 °C, and 3-aminopropyltriethoxysilane (APTES)-MCM-41 has the highest sulfur dioxide capacity at 0.85 mol/kg at 500 ppmv and 23 °C. These biphasic materials exhibit high adsorption capacity for two distinct gases and are promising candidates as adsorbents for protection from toxic industrial gases.
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IJS, KILJ, NUK, PNG, UL, UM
High-pressure oxygen is an integral part of fuel cell systems, many NASA in situ resource utilization concepts, and life support systems for extravehicular activity. Due to the limited information ...available for system designs over wide ranges of temperature and pressure, volumetric methods are applied to measure adsorption isotherms of O2 and N2 on NaX and NaY zeolites covering temperatures from 105 to 448 K and pressures up to 150 bar. Experimental data measured using two apparatuses with distinctly different designs show good agreement for overlapping temperatures. Excess adsorption isotherms are modeled using a traditional isotherm model for absolute adsorption with a correction for the gas capacity of the adsorption space. Comparing two models with temperature-dependent coefficients, a virial isotherm model provides a better description than a Toth isotherm model, even with the same number of parameters. With more virial coefficients, such as a cubic form in loading and quadratic form in reciprocal temperature, the virial model can describe all data accurately over wide ranges of temperature and pressure.
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A new equation for describing adsorption equilibria of water on activated carbon is developed based on a mechanism proposed by Dubinin. It is Henry’s law consistent, mathematically simple, and ...explicit in pressure. The model describes the full range of the adsorption isotherm with high accuracy using only a small number of parameters. Adsorption equilibrium data for water on several activated carbons quite different in surface area, surface chemical properties, and pore structure are used to test the model. A two-variable series expansion is used to extend a single adsorption isotherm to an adsorption isotherm family at multiple temperatures. The model description of pure water adsorption isotherms at different temperatures on BPL activated carbon is in good agreement with experimental data.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Experimental data for
n-pentane adsorbed on BPL activated carbon in a nitrogen environment are reported at ultra-low concentrations into the Henry’s law region. We introduce two methods to prepare ...pre-equilibrated samples at known loadings. The samples were analyzed by a purge and trap method. Adsorption data were measured at loadings from 1.0 to 0.0001
mol
kg
−1 and pressures of 6 to 5
×
10
−10
kPa. The transition into the Henry’s law region occurs over a range of loadings near 0.01
mol
kg
−1 for all temperatures. The data are compared with the DR, Langmuir, and Toth equations. We discuss how the three equations transition into the Henry’s law region, and how well they describe the data. Since the DR equation does not have a proper Henry’s law region, we show where this equation no longer applies. The Toth equation describes the data better than the Langmuir equation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The structure of a molecule and its concentration can strongly influence diffusional properties for transport in nanoporous materials. We study mass transfer of alkanes in BPL activated carbon using ...the concentration-swing frequency response method, which can easily discriminate among mass transfer mechanisms. We measure concentration-dependent diffusion rates for n-hexane, n-octane, n-decane, 2,7-dimethyloctane, and cyclodecane, which have different carbon numbers and geometries: straight chain, branched chain, and cyclic. Micropore diffusion is determined to be the controlling mass transfer resistance except at low relative saturation for n-decane, where an external mass transfer resistance also becomes important, showing that the controlling mass transfer mechanism can change with system concentration. Micropore diffusion coefficients are found to be strongly concentration dependent. Adsorption isotherm slopes obtained from measured isotherms, the concentration-swing frequency response method, and a predictive method show reasonably good agreement.
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Adsorption equilibria were measured for binary mixtures of carbon dioxide and water vapor on zeolites 5A and 13X using a volumetric apparatus. The experiments were conducted at (0, 25, and 50) °C ...with water loadings of (1.0, 3.4, and 9.4) mol·kg−1. With an increase in adsorbed water loadings, the loadings of weakly adsorbed CO2 decrease appreciably. Pure component data are described well by a multitemperature Toth isotherm. Binary data show a discrepancy with predictions of the ideal adsorbed solution theory (IAST) but are described well by a virial excess mixing coefficient (VEMC) model, which adds corrective terms to the IAST to account for nonidealities. Data measured at lower CO2 partial pressures and higher water loadings show indications of chemisorption and carbonate formation.
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A mathematical model is developed to examine the sensitivity of the breakthrough of adsorption beds to system parameters. As the process model is integrated a single time, sensitivities are ...simultaneously calculated. The impact of mass and energy transfer effects and adsorbent layer thicknesses are determined by calculating the derivatives of the outlet concentration and outlet temperature. Several examples are considered. To establish a basis, the breakthrough of single beds is considered first. The adsorption of hexane on BPL activated carbon is contrasted with the adsorption of nitrogen on carbon molecular sieve, and combined mass and energy effects are considered by studying the adsorption of nitrogen on BPL activated carbon. The sensitivity data are then applied to determine the optimum bed layering of a two-layer, two-bed PSA system. The solution method presented can be adapted for the sensitivity analysis and subsequent optimization of a large number of adsorption systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A simple formula for water permeability of a Nafion hollow-fiber membrane has been determined. The result shows that water permeability of the membrane is proportional to the 1.5 power of the local ...partial pressure of water vapor in the gas phase. The water permeability was converted to a diffusion coefficient, which was found to attain a maximum value when the number of water molecules per sulfonate in the Nafion membrane is equal to 3.3. This agrees well with some reports in the literature.
An effective mathematical model for a membrane process to remove water vapor from nitrogen gas was developed. Using the obtained permeability expression, the model simulations for the membrane module matched experimental data over a wide range of operating conditions. In most cases, the absolute errors between the predicted product relative humidity and the measured values are within ±2%, and the relative errors are less than 15%. Mass transfer resistances along the membrane module at typical operating conditions were also analyzed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
