Adsorption Of Binary Gas Mixtures Research Articles

Kinetic Trapping and Adsorption Equilibration of Binary Mixtures within Nanopores

We investigate the kinetics of competitive adsorption of binary gas mixtures in restrictive nano-porous materials by simulating the uptake dynamics of the mixture inside a longitudinal pore via a K...

Novel Differential Column Method for Measuring Multicomponent Gas Adsorption Isotherms in NaY Zeolite

Separation and purification of gas mixtures using selective adsorbents is widely used in different industries such as gas drying, air separation, and H2 purification. Equilibrium analysis involving adsorption of binary gas mixtures provides important information related to the adsorbent performance in the separation of gases. In this study, a novel technique termed “differential column technique” was developed for binary isotherm measurement employing streams containing carbon dioxide, carbon monoxide, and ethylene at different compositions. This technique is based on measuring the gas desorption by changing equilibrium pressure conditions. The isotherm curve was generated by summing desorption amounts desorbed at each pressure step. Through the application of this technique, the single-component isotherms of CO2, CO, and ethylene on zeolite NaY were measured, and the isotherms were compared to the results obtained by a standard gravimetric technique. (The average relative deviation is less than 6%.) The ...

Pure and Binary Adsorption Equilibria of Methane and Nitrogen on Activated Carbons, Desiccants, and Zeolites at Different Pressures

Several commercially available adsorbents that show promise for the separation of CH4 from N2 including different activated carbons, desiccants, and zeolites were evaluated using single component adsorption isotherms of pure methane and nitrogen that were measured at 303 K for pressures of up to 10 atm using the gravimetric method. Following the screening, the adsorption of binary gas mixtures composed of methane and nitrogen were studied at 303 K and two different pressures on the adsorbents with the highest capacity for CH4 of each of the activated carbons, desiccants, and zeolites. These selected adsorbents included commercial zeolite 13X (Siliporite Nitroxy Pro from CECA Arkema Group), activated carbon (Xtrusorb A754 from Calgon Carbon Corp.), and silica gel (SG-B127 from Grace & Co). A concentration pulse chromatographic method was used to determine the pure component CH4 and N2 Henry’s Law constants, heats of adsorption, and the experimental binary adsorption isotherms for the three selected adsorbe...

Monte Carlo study of adsorption of additive gas mixture

The monolayer adsorption of binary gas mixture on a square lattice has been investigated through grand canonical Monte Carlo method and transfer matrix technique. Repulsive and attractive lateral interactions have been introduced between the adsorbed particles for one component of the gas mixture and for another, respectively, at the same time the particles of different components of the gas mixture have not interacted. The model has been studied in the ground state and at finite temperatures. Interesting features of the phase behavior of the gas mixture adlayer were observed and discussed. The model shows that a simultaneous increasing of the chemical potentials of both gas components can lead to displacing of particles of one component on the surfaces by particles of another component.

Gas Sorption and the Consequent Volumetric and Permeability Change of Coal I: Experimental

Experimental and numerical investigations were conducted to study adsorption and desorption of pure and multicomponent gas on coal, and the sorption-induced volumetric strain and permeability change of the coal. This paper presents the experimental work. Using CO\(_2\), N\(_2\), and CO\(_2\) and N\(_2\) binary mixtures of different composition as injection gases, the measurements were conducted on a cylindrical composite coal core at varying pore pressures and constant effective confining pressure. Sorption was measured using a volumetric method. The initial and equilibrium system pressure and gas phase composition were measured. The total amount of adsorption and the composition of the adsorbed phase (for adsorption of binary gas mixtures) were calculated based on material balance. During the process of sorption, the volume of the core was monitored by recording the volume of the water in the confining pressure vessel. Sorption-induced strain was calculated as the ratio of the sorption-induced volumetric change to the initial volume of the core. After adsorption equilibrium was reached, the permeability of the core was measured based on the Darcy equation for gas flow. Sorption and permeability measurements were conducted for each test gas at first increasing and then decreasing pressures. Volumetric strain was only measured while pore pressure increased. To our knowledge, this is the first study measuring adsorption, volumetric strain, and permeability on the same piece of core with the same apparatus.

Calculation of equilibrium adsorption of binary gas mixtures

A method of calculating partial magnitudes in equilibrium low-temperature adsorption of a neon-helium mixture on a base of the carbon adsorbent AG-2 is proposed and good convergence with experiment is obtained. The method of calculation of partial magnitudes may be applicable to adsorption systems in which an adsorbate forms an ideal adsorption solution.

Adsorption of Binary Gas Mixtures on Strongly Heterogeneous Surfaces

The integral equation (IE) approach coupled with a rectangular adsorption energy distribution and Mean Field Approximation (MFA) is used to describe the adsorption of single gases and their binary mixture on a heterogeneous solid surface. In particular, it is important to stress that all theoretical expressions shown are the exact solution of IE approach. During the analysis of single-gas adsorption isotherms also accompanying calorimetric effects are investigated. The problem of correlations between the best-fit parameters describing energetic heterogeneity and energy of intermolecular interactions is discussed. The predictions of the theory are compared with the experimental literature data. It is shown that the new theoretical adsorption isotherms give the results that are very close to the experimental data.

Adsorption of Binary Gas Mixtures in Heterogeneous Carbon Predicted by Density Functional Theory: On the Formation of Adsorption Azeotropes

Classical density functional theory (DFT) was used to predict the adsorption of nine different binary gas mixtures in a heterogeneous BPL activated carbon with a known pore size distribution (PSD) and in single, homogeneous, slit-shaped carbon pores of different sizes. By comparing the heterogeneous results with those obtained from the ideal adsorbed solution theory and with those obtained in the homogeneous carbon, it was determined that adsorption nonideality and adsorption azeotropes are caused by the coupled effects of differences in the molecular size of the components in a gas mixture and only slight differences in the pore sizes of a heterogeneous adsorbent. For many binary gas mixtures, selectivity was found to be a strong function of pore size. As the width of a homogeneous pore increases slightly, the selectivity for two different sized adsorbates may change from being greater than unity to less than unity. This change in selectivity can be accompanied by the formation of an adsorption azeotrope when this same binary mixture is adsorbed in a heterogeneous adsorbent with a PSD, like in BPL activated carbon. These results also showed that the selectivity exhibited by a heterogeneous adsorbent can be dominated by a small number of pores that are very selective toward one of the components in the gas mixture, leading to adsorption azeotrope formation in extreme cases.

Validation of Simple Equations Describing the Adsorption of Binary Gas Mixtures onto Surfaces with an Asymmetric Distribution of Adsorption Energy

The Monte Carlo simulation method was used to test the accuracy of approximate equations derived for binary gas adsorption onto a heterogeneous surface characterized by a Dubinin-Astakhov adsorption energy distribution (AED) function. In particular, the Condensation Approximation (CA) was applied to obtain simple equations for the partial adsorption isotherms and phase diagrams in the system for which a separate AED was assumed for each component of the mixture. A few cases involving different relationships between the AEDs associated with the adsorbing components were discussed. Additionally, the results of the proposed theory were compared with exact numerical solutions obtained using the Integral Equation method. From both simulations and numerical calculations, it follows that, in general, the CA is not appropriate for the prediction of binary adsorption equilibria when the individual AEDs are of an entirely different shape. On the other hand, when the AEDs were microscopically correlated, i.e. when the adsorption energy of one component on every site was shifted by a constant value compared to that of the other, the phase diagrams obtained were found to be in a very good agreement with their simulated counterparts.

Monte Carlo Simulation of the Adsorption of Binary Gas Mixtures on Heterogeneous Surfaces

The adsorption of a gaseous mixture containing particles A and B was studied via lattice-gas simulations on homogeneous and heterogeneous bivariate surfaces characterized by a chessboard topography of strong and weak adsorbing sites. The effects of lateral interactions among adsorbed particles and of heterogeneity on the adsorption isotherms and differential heats of adsorption were analyzed. The results displayed a rich variety of behaviours and their analysis contributes to the understanding of mixed-gas adsorption at a molecular level.

Adsorption of carbon dioxide, methane and nitrogen: pure and binary mixture adsorption for ZSM-5 with SiO2/Al2O3 ratio of 280

The adsorption of binary gas mixtures of CO2–N2, CO2–CH4 and CH4–N2 were studied by using H-ZSM-5 as the adsorbent with a SiO2/Al2O3 ratio of 280. Pure isotherms for N2 and CH4 at 40 °C and CH4–N2 binary isotherms at 40 °C and 1.0 atm total pressure have been determined using concentration pulse chromatography. For CO2–N2 and CO2–CH4 pure and binary systems, previously published data were used. The applicability of the binary adsorption prediction models, Extended Langmuir (EL), ideal adsorbed solution theory (IAST), and the Flory–Huggins form of the vacancy solution theory (FH-VST) have been studied. The CH4–N2 binary isotherms exhibit behavior similar to the pure component isotherms, with CH4 as the dominant adsorbate. The CH4 binary isotherm did not change from the pure component isotherm. The N2 binary isotherm decreased relative to the pure component N2 isotherm. The theoretical models reasonably predict the binary behavior for the strongly adsorbed component in the binary system, whereas the weakly adsorbed component was not predicted well. The models are able to predict systems where the adsorption capacities of each component are relatively similar. However, none of the models were able to predict the behavior resulting from the initial competing or dominant electrostatic interaction of the adsorbates with the heterogeneous nature of the adsorbent surface.

Adsorption of carbon dioxide, methane, and nitrogen: pure and binary mixture adsorption by ZSM-5 with SiO2/Al2O3 ratio of 30

The adsorption of binary gas mixtures of CO2–N2, CO2–CH4, and CH4–N2 were studied by using H-ZSM-5 as the adsorbent with a SiO2/Al2O3 ratio of 30. Pure isotherms for N2 and CH4 at 40°C and CH4–N2 binary isotherms at 40°C and 1.0 atm total pressure have been determined using concentration pulse chromatography. For CO2–N2 and CO2–CH4 pure and binary systems, previously published data were used. The applicability of the binary adsorption prediction models, Extended Langmuir, Extended Nitta, Ideal Adsorbed Solution Theory, and the Flory–Huggins form of the Vacancy Solution Theory have been studied. The CH4–N2 binary isotherms exhibit behavior similar to the pure component isotherms, with CH4 as the dominant adsorbate. The separation factor steadily declines as the mole fraction of CH4 in the gas phase is increased. All the theoretical models used reasonably predict the binary systems for CH4–N2. The CO2–N2 system was not predicted well. CO2–CH4 behavior was predicted reasonably well by all the models, except by the Extended Nitta. The models appear to be able to predict systems where the adsorption capacities of each component are relatively similar.

Molecular dynamics simulation of gas mixtures in porous media. I. Adsorption

In this paper and its sequel we report the results of Molecular Dynamics simulation of single component and binary gas mixtures in a porous medium with interconnected pores. The porous medium used in the study is a model pillared clay. In the present paper we study adsorption of binary gas mixtures, and investigate in detail the effect of various factors, such as the morphology of the pore space and the adsorbent-adsorbate interactions. A new mean-field statistical mechanical theory of adsorption is developed, and shown to provide very accurate predictions for the simulation results over wide ranges of the pressure, temperature and porosity of the system.

Appearance of Enhancement Effect in Adsorption of Binary Gas Mixtures.

The properties of adsorbents and adsorbates contributing to the enhancement in adsorption of binary gas mixtures were experimentally investigated. It is found that adsorbent is required to maintain the phenolic hydroxyl group and the carbonyl group as acidic surface oxides on the carbon surface, and to have a microporous structure for the main adsorption sites. Each gas component is required to be chemisorbed on the phenolic hydroxyl group or the carbonyl group on the adsorbent, and that both components are adsorbed in the micropores together. From the characterization of absorbents after adsorption-desorption runs, it is demonstrated that the adsorbates in the micropores exist at a higher density than in the bulk state through the promotion of micropore filling when adsorption enhancement appears.

Physical Adsorption of a Multicomponent Mixture in Micropores

This paper presents the theory of vapor−adsorbate equilibrium of a multicomponent mixture on microporous solids. The equilibrium relationships were obtained on the basis of the concept of micropore volume filling and the adsorbed-phase model, in which adsorbate−adsorbent interactions predominate over lateral interaction between adsorbed molecules. The predominant role of micropores is extended to the calculation of adsorbed-phase composition. The only single-gas isotherm parameters are incorporated into equations for calculation of separation factors, adsorption of components, and overall adsorption. It is shown that the separation factor in micropore space is a function of occupied micropore volume, affinity coefficients, adsorbent characteristic energy, temperature, and partial pressures. The theory has been successfully applied to published data for the adsorption of binary gas mixtures on activated carbons.

Model of double associates for sorption of binary gas mixtures on polymers

AbstractA simple model of double associates is used to represent bilayer sorption of binary gas mixtures on a flexible linear chain of a polymer. The isotherm equation derived in terms of this model is a simple product of the isotherm equation describing bilayer adsorption of binary gas mixtures on a homogeneous solid surface and a function reflecting specific features of sorption on polymers.

Thermal equation for the adsorption of a binary gas mixture

An equation proposed previously has been generalized to the case of the adsorption of binary gas mixtures. Based on this equation, the partial thermal equations of adsorption of the components of a mixture have been derived, and the critical parameters of the adsorbed phase have been calculated.

Adsorption of Gas Mixtures of Propene and Propane on Graphitized Carbon Black I. Experimental Method and Results

An apparatus is described for measuring adsorption of binary gas mixtures by particulate solids. Adsorption equilibrium is established by passing a gas mixture of known composition through the adsorption chamber in a thermostat at a controlled pressure (quasi–static method). The gas contained in the adsorption chamber is then transferred to a gas chromatograph by a carrier gas, and the amount of both adsorbates is determined by integration of their elution profiles. The adsorption of binary gas mixtures of propene + propane by graphitized carbon black over the pressure range 10–1000 mbar has been studied at three temperatures (283–313 K) by this method. The consistency of the results was tested by gravimetric measurements of the total adsorbed mass. A weak preferential adsorption of propane from the gas mixture is found, the separation factor α varying between 1·0 and 1·25, depending on pressure, temperature and gas phase composition.

Competitive adsorption of binary gas mixtures on energetically heterogeneous solids

The competitive adsorption model is used to describe the experimental adsorption data for binary gas mixtures on solids. The equation describing this adsorption model involves energetic heterogeneity of the solid surface and difference in molecular size of the two components. This equation gives a good representation of many experimental adsorption data, especially of the data measured at higher surface coverages.

Adsorption of gas mixtures on solids: Analysis of experimental data measured at constant mole fractions of components in the adsorption space

Analytical equations for adsorption of binary gas mixtures on energetically heterogeneous solids have been discussed. These equations are derived by assuming constancy of the mole fractions of components in the adsorption space. The adsorption data of methane-krypton mixture on CaA-zeolite, measured in wide range of temperature, were analyzed by means of these equations.