Gas Adsorption Model Research Articles

Adsorption Modeling with the ESD Equation of State

The simplified local density approach (SLD) is extended to the Elliott−Suresh−Donohue (ESD) equation of state for the modeling of gas adsorption on activated carbon, providing significant improvement in quantitative modeling compared to the SLD approach using the Peng−Robinson equation of state or the van der Waals equation. Compared to the Peng−Robinson and van der Waals equations, the ESD equation more accurately represents the temperature dependence of adsorption.

Thermodynamic Consistency for Binary Gas Adsorption Equilibria

An integral and a differential thermodynamic consistency test between pure and binary gas adsorption data and three differential thermodynamic consistency tests for binary gas adsorption data alone can be formulated using the Gibbsian surface excess model of gas adsorption. These relationships originate from the Gibbs adsorption equation. It is necessary to measure the surface excess of the components of the binary gas mixture as functions of pressure at constant gas phase composition and temperature, as functions of gas phase compositions at constant pressure and temperature, and as functions of temperature at constant gas phase compositions and pressures, to apply these tests practically. The tests are very useful to check the quality of the data before they can be extrapolated for adsorptive process design using multicomponent equilibrium adsorption models. A set of pure and binary gas data for adsorption of CH4 and N2 on a 5A zeolite was used to demonstrate the applicability of these consistency tests...

Doping effects and reversibility studies on gas-exposed α-sexithiophene thin films

The electronic effects produced by controlled gas exposures on α-sexithiophene thin films have been investigated using x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Incremental exposures of α6T films to NO2, O2, NH3 in N2, and water vapor in N2 were performed in ultrahigh vacuum, while repeated doses of O2, H2 in N2, and methanol vapor in N2 were performed ex situ at ambient pressure. In both conditions XPS spectra of gas-exposed films showed no evidence of chemical changes. However, the features in both XPS and UPS spectra were observed to shift as a function of gas dosage, with the magnitude dependent on each particular gas. These effects could be reversed by heating the films to temperatures around 100 K. This behavior is interpreted in terms of doping by weakly bonded gas species within the near-surface region of the α6T films. Greater doping effects were observed for films dosed at ambient pressure. We discuss possible gas adsorption models that may explain the differing gas sensitivities and their dependences on pressure, temperature, and exposure time. Finally, temperature programmed desorption was used to study the reversibility and resistance to reaction of α6T films during this gas adsorption/desorption process. The films were found to be chemically stable to gas exposure and subsequent thermal desorption in the dosage ranges explored.

Model of gas adsorption on magnetic surfaces

The semi-empirical self-consistent tight-binding model of gas (C, N, O) chemisorption is suggested to study its influence on surface magnetism. For the strongly ferromagnetic Fe(001), we find that the adsorbates are not effective in magnetism reduction. For the hypothetical magnetic V(001) surface, the magnetization is very sensitive to the vanadium d-band occupation used in the calculation. Supposing that the magnetization is weak, it can be essentially suppressed by the gas contamination. The effect is explained by the Stoner criterion.

Stochastic Properties of the Solution Vector of Parameters for the Model of the Partially Mobile Adsorption of a Single Gas on an Energetically Heterogeneous Microporous Adsorbent

For the previously formulated model of single gas adsorption on energetically heterogeneous microporous solids, two adsorption isotherms were generated — one for each distribution function of the localization energy dividing two neighbouring adsorption sites. Using numeric methods, a mass measurement error was ascribed to each point generated for both adsorption isotherms and an analysis of the influence of the normal distribution of this error on the type of distribution of the optimized parameter values was undertaken. The hypothesis regarding the agreement of the distributions of the parameter values for both energy distribution functions was verified. The work described was carried out for three arbitrary assumed values of the variation coefficients of the adsorbate mass measurement error.

An Engineering Model for Adsorption of Gases onto Flat Surfaces and Clustering in Supercritical Fluids

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAn Engineering Model for Adsorption of Gases onto Flat Surfaces and Clustering in Supercritical FluidsRamkumar Subramanian, Hena Pyada, and Carl T. LiraCite this: Ind. Eng. Chem. Res. 1995, 34, 11, 3830–3837Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/ie00038a021RIGHTS & PERMISSIONSArticle Views232Altmetric-Citations46LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (908 KB) Get e-Alerts Get e-Alerts

Analysis of a MOS integrated gas sensor using a surface chemistry based model

To facilitate gas sensor design with the associated signal-conditioning circuitry, a previously developed gas adsorption model is implemented in the popular circuit simulation program SPICE. The model is based on the gas adsorption theory. With the adsorption model implemented in SPICE, the performance of a MOSFET gas sensor integrated with the associated circuitry can be studied. The analysis was applied to three sensors, namely, the H 2 sensor, the NH 3 sensor and the CO sensor. A noise analysis of the sensors was also performed and their lower bounds of detectivity determined. A chopper-stabilized circuit was applied to the sensing circuitry. Simulation results show that noise in gas sensors can be reduced.

Pore size distribution of BPL activated carbon determined by different methods

Current methods of obtaining pore size distributions (PSDs) of microporous carbons are based on the interpretation of gas adsorption measurements through adsorption equilibrium models. We examine the consistency of five such models by constructing PSDs of a single adsorbent, BPL activated carbon, from an N 2 adsorption isotherm at 77 K and from water desorption isotherms at various temperatures. For each method the adsorbent is modeled as a collection of independent, parallel-sided, slit-shaped pores. The distributions confirm that BPL carbon is a predominantly microporous material, but the maxima in the differential volume distributions vary from pore widths of 5.9 to 18 Å. The variation among the distributions indicates a lack of consistency among the five gas adsorption models.

The use of solution theories for predicting water vapor absorption by amorphous pharmaceutical solids: a test of the Flory-Huggins and Vrentas models.

The limitations of traditional gas adsorption models for describing water vapor sorption by amorphous pharmaceutical solids are described and an alternative approach based on polymer solution theories is proposed. The approach is tested by comparing a priori predicted isotherms with literature data for the poly(vinylpyrrolidone)(PVP)-water system. The well-known Flory-Huggins model is able to describe the water vapor sorption isotherm only when the PVP-water mixture is in the rubbery state (i.e., above its glass transition temperature). However, a newer model developed by Vrentas and coworkers, which takes into account the plasticizing effect of water on the polymer, is able to describe the entire form of the isotherm. Consideration of the parameters in this model allows a number of critical variables to be identified and also enables the characteristic shape of the water vapor sorption isotherm to be explained.

Effects of concentration dependence of surface diffusivity on the transport and adsorption of gases in a solid sphere with bidisperse pores

A model for transport and adsorption of gases in a biporous solid sphere was presented assuming a linear adsorption isotherm and linear concentration dependence of surface diffusivity. When put into dimensionless form this model is characterized by four dimensionless parameters. To help assessing the error involved in using constant effective diffusivities, numerical results were presented for the uptake of pure gases into a biporous solid sphere with concentration dependent diffusivity and compared with those for effective diffusivity model. The error in transient uptake was found to be as large as ten percent.

An isotherm model for adsorption of gases and vapours on heterogeneous adsorbents

The adsorption of gases and vapours on heterogeneous adsorbents is generally described by assuming that the surface of an adsorbent consists of several energetic sites or patches. The adsorption on a site or a patch can be described by a local isotherm, such as the Langmuir, BET or Jovanovich equations, whereas the heterogeneity or the energy distribution on the adsorbent is expressed by a probability density function such as normal distribution, gamma distribution and exponential distribution. The overall adsorption isotherm is then derived by summing the contributions of all sites. Although the parameters of the energy distribution are generally related to the heat of adsorption, the overall adsorption isotherm is often insensitive to the parameters of the probability density functions, which are assumed on statistical grounds. In the present work, a new isotherm model is derived for the adsorption of gases and vapours on heterogeneous adsorbents, which combines the Jovanovich local isotherm and an exponential-six type energy potential function. The new model can correlate both Type I and Type II isotherms and has been tested successfully with the literature data for the adsorption of various gases and vapours on several different heterogeneous adsorbents. The absolute average error for most of the systems is below 3%. A comparison of the present model with other models for heterogeneous surfaces is presented.

Application of time-power series to nonequilibrium critical phenomena

We treat the kinetics of a one-dimensional lattice gas adsorption model with a critical point. We use a matrix method to construct an exact time-power series to describe the dynamics. Inverting the series gives the time as a function of the density in terms of a well-behaved density series from which one can derive a set of finite polynomials that give successively improving estimates of the critical parameter. From the ratios of successive coefficients in the density series one can estimate the critical exponent for the time dependence of the critical process.

Mechanoluminescence in Centrosymmetric Crystals

AbstractThe paper reports that the mechanoluminescence (ML) is not an inherent property of only the non‐centrosymmetric crystals. The ML may appear in number of centrosymmetric crystals due to variety of processes. The ML of 82 centrosymmetric crystals are reported and different models are proposed for the ML excitation. The models proposed are: space charge electrification model, triboelectrification model, phase transformation model, gas adsorption model, chemical reaction model, thermal population model, molecular deformation model, cleavage electrification model, defective piezoelectric phase model, dislocation defect stripping model, dislocation unpinning model, dislocation annihilation model, charged dislocation model and incandecent light emission model. It is shown that on the basis of the proposed model, intense mechanoluminescent materials with desired nature and characteristics may be prepared.

A statistical mechanical model for adsorption and flow of pure and mixed gases in porous media with homogeneous surfaces. Part I: Theoretical development

AbstractA unified statistical mechanical treatment is developed for adsorption and surface diffusion on homogeneous surfaces. Using molecular parameters, the model accounts for all physical effects of adsorbent‐adsorbate, adsorbate‐adsorbate, and adsorbate‐gas interactions at submonolayer coverages.

A statistical mechanical model for adsorption and flow of pure and mixed gases in porous media with homogeneous surfaces. Part II: Applications

AbstractApplication of the model of Part I is made to several systems with various graphitized carbon blacks over wide ranges of temperatures and submonolayer coverage. Agreement with all data for equilibrium and transport is probably within experimental error.

FATIGUE CRACK GROWTH RATE BEHAVIOUR OF STAINLESS STEEL CLADDINGS IN AIR AND UNDER VACUUM AT 300°C

AbstractCT type specimens containing two layers of 309L and 308L cladding stainless steels welded to A508 carbon steel and 316 stainless steel were specially devised to test the influence of R ratio and environment on the crack propagation rate behaviour of cladding materials at 300°C. Large effects are shown. The crack growth rate under vacuum can be smaller by more than one order of magnitude as compared to air. Large differences are also shown on the fracture surfaces, where it is observed than vacuum promotes the formation of large crystallographic {111} facets. The effect of environment is briefly discussed on the basis of existing gas adsorption models.

Interaction between Water and Thin Copper Films Model of Immobile Gas Adsorption

Interaction between Water and Thin Copper Films Model of Immobile Gas Adsorption

The effect of the nonlinear adsorptions of benzene and water vapors on molecular transport distribution functions

We give an asymptotic solution of the general dispersion equation for molecular transport through porous adsorbing solids, taking into account the nonlinearity of the adsorption isotherm. The solution indicates that the nonlinearity causes retardation or advancement of the adsorption front depending on the curvature of the isotherm. This effect is shown quantitatively for nonlinear adsorptions of benzene vapor on silica gel and water vapor on styrene–divinylbenzene copolymer. The model shows that the parameters that characterize the adsorption isotherm can be deduced from the experimentally measurable molecular transport distribution functions. Application of the model for adsorption of gases and vapors at low temperatures is suggested.

Chopper circuit put on op-amp chip : L. Altman. Electronics August 16 (1973). p. 125

To facilitate gas sensor design with the associated signal-conditioning circuitry, a previously developed gas adsorption model is implemented in the popular circuit simulation program SPICE. The model is based on the gas adsorption theory. With the adsorption model implemented in SPICE, the performance of a MOSFET gas sensor integrated with the associated circuitry can be studied. The analysis was applied to three sensors, namely, the H2 sensor, the NH3 sensor and the CO sensor. A noise analysis of the sensors was also performed and their lower bounds of detectivity determined. A chopper-stabilized circuit was applied to the sensing circuitry. Simulation results show that noise in gas sensors can be reduced.

Tests of a Simplified General Model for Adsorption of Rare Gases on Solids.

Tests of a Simplified General Model for Adsorption of Rare Gases on Solids.