Distribution functions of structural heterogeneity of microporous adsorbents

The distribution functions of structural heterogeneity of microporous adsorbents have given. Influences of adsorbents and adsorbates types on this heterogeneity have been studied.

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Verteilungsfunktionen für die Struktur-Heterogenität von mikroporösen Adsorbentien

Zusammenfassung Es werden Verteilungsfunktionen für die strukturelle Heterogenität von mikroporösen Adsorbentien angegeben. Die Einflüsse der Adsorbens- und Adsorbatarten auf diese Heterogenität wurden untersucht.

     

Thermodynamics of vapour adsorption on heterogeneous microporous adsorbents

Fundamental thermodynamic functions have been derived for equations of adsorption isotherms including structural heterogeneity connected with micropore dimensions. Good agreement has been achieved between values of the differential molar enthalpy of adsorption and values of the isosteric adsorption heats obtained experimentally.     

Determination of microporous adsorbents heterogeneity with the condensation approximation method

Using the condensation approximation method the distribution function of adsorption energy for microporous adsorbents has been defined. Due to application of proper equations for the isotherm of global adsorption, the considerations include differencies in the shape of the distribution function of the structural heterogeneity for the microporous adsorbents studied.

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Die Bestimmung der Heterogenität mikroporöser Adsorbentien mit der Kondensationsnäherung

Zusammenfassung Mit Hilfe der Methode der Kondensationsnäherung wurde die Verteilungsfunktion der Adsorptionsenergie für mikroporöse Adsorbentien bestimmt. Die Anwendung entsprechender Gleichungen für die Globalisotherme gestattet die Berücksichtigung von Differenzen in der Gestalt der Verteilungsfunktionen der Strukturheterogenität.

     

A simple isotherm equation for describing gas adsorption on heterogeneous microporous solids

A simple isotherm equation for describing gas adsorption on solids showing heterogeneity of microporous structure is proposed. It is shown that this equation gives a good representation of the experimental data of argon, nitrogen and benzene adsorption on different types of activated carbons. Its parameters may be used to characterize heterogeneity of microporous structure of the solids.

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Eine einfache Isotherme zur Beschreibung der Gas-Adsorption an heterogenen mikroporösen Feststoffen

Zusammenfassung Es wird eine einfache Isotherme zur Beschreibung der Gasadsorption an Feststoffen mit heterogener mikroporöser Struktur vorgeschlagen. Es wird gezeigt, daß diese Gleichung die experimentellen Daten für die Adsorption von Argon, Stickstoff und Benzol an verschiedenen Typen von Aktivkohle gut beschreibt. Die Parameter der Isotherme können zur Charakterisierung der Heterogenität der mikroporösen Struktur von Festkörpern herangezogen werden.

     

Prediction of single component adsorption isotherms on microporous adsorbents

The adsorption of gases on microporous solids is a fundamental physical interaction which occurs in many technical processes, e.g. the heterogeneous catalysis or the purification of gases. In this context the adsorption equilibrium can determine the velocity and/or the capacity of the process. Therefore, it has to be known for designing purposes. The aim of this work has been the a priori prediction of the adsorption equilibria of arbitrary gases on microporous solids like zeolites and active carbon based only on the molecular properties of the adsorptive and the adsorbent. The adsorption isotherm is described completely from the Henry region over the transition zone to the saturation region. The quality of the model permits a first approximation of the planned process without further experimental effort.     

Adsorption of propane andn-butane on polystyrene adsorbents

Summary The adsorption isotherms of propane andn-butane adsorbed on two polystyrene adsorbents with high and low specific surface areas were measured in the concentration range from 500 ppm to 10 800 ppm in a helium carrier gas at 273, 298, 303, and 313K. The isotherms can be represented by either a Freundlich or a Langmuir-Freundlich type equation. The energetic heterogeneities of the two adsorbents were characterized in terms of the dispersion of the adsorption energy. Also, the isosteric heats were calculated from the dimensionless adsorption capacities.

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Adsorption von Propan undn-Butan auf Polystyrol-Adsorbentien

Zusammenfassung Es wurden die Adsorptionsisothermen von Propan undn-Butan an zwei Polystyrol-Adsorbentien mit hohen und niederen spezifischen Oberflächen im Konzentrationsbereich von 500 bis 10 800 ppm in einem Helium-Trägergas bei 273, 298, 303 und 313 K gemessen. Die Isothermen können entweder mittels Gleichungen vom Freundlich- oder Langmuir-Freundlich-Typ dargestellt werden. Die energetische Heterogenität der zwei Adsorbentien wurde in Termen der Dispersion der Adsorptionsenergie charakterisiert. Es wurden auch die isosterischen Adsorptionswärmen aus den dimensionslosen Adsorptionskapazitäten berechnet.

     

Development of nonuniform micropore structure of carbon adsorbents during activation: adsorption and small-angle X-ray scattering studies

The development of the micropore structure of activated carbons during activation was studied by small-angle X-ray scattering and adsorption methods. A new method for the processing of experimental data was used; this method makes it possible to obtain curves of the dimension distribution of micropores from the intensities of small-angle X-ray scattering and the adsorption isotherm. In the initial stage of activation, up to burnouts 0.3, the micropore structure is uniform, micropores with radius of gyration under 0.5–0.6 nm dominate. When activation is more prolonged ( = 0.3÷0.67), a bimodal system withR ₁ ^max 0.6 nm andR ₂ ^max 0.85÷1.0 nm forms, and the volume of large micropores (supermicropores) exceeds that of small ones considerably.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 231–235, February, 1994.     

Effects of micropore size and chemical nature of the surface of carbon adsorbents on the adsorption isotherms of water vapor

Adsorption of benzene and water vapors on activated carbons of various microporous structure was studied. The values of the characteristic energy of adsorption of benzene and water vapors were compared and the affinity coefficients β_H2O for carbons with various degrees of activation were calculated. The values of the β_H2O coefficient for carbons with the same degrees of oxidation remain constant. This makes it possible to use the experimental data on benzene adsorption for prediction of the behavior of microporous activated carbons towards adsorption of water vapor. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2636–2639, December, 2005.     

DTA investigations of n-octadecanol films on complex carbon-silica adsorbents as a method for determination of their surface properties

Summary The properties of n-octadecanol films on complex carbonsilica adsorbents were investigated. It was found that two forms of oriented surface film exist on Carbosil surface. The structure of each form of the film distinctly depends on the nature of the surface patches of Carbosil. It was shown, using differential thermal analysis that it is possible to determine the ratio of carbonized and hydroxylated parts of the Carbosil surface.     

Isotherm equations for adsorption on heterogeneous microporous solids

The overall isotherm equations have been derived for adsorption from gaseous and liquid phases on heterogeneous microporous solids by solvingStoeckli's integral equation. In this integral theDublin-Radushkevich equation is used to describe the local adsorption on micropores having identical shape and dimensions. The above integral has been solved for different types of distribution functions characterizing heterogeneity of microporous structure of the solids.

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Adsorptionsisothermen für heterogene mikroporöse Feststoffe

Zusammenfassung Es wurden Isothermengleichungen für die Adsorption aus Gas- oder Flüssigphasen an heterogenen mikroporösen Feststoffen mittels der Lösung vonStoeckli's Integralgleichung abgeleitet. In diesem Integral wurde dieDubinin-Radushkevich-Gleichung für die Beschreibung der lokalen Adsorption an Mikroporen mit identem Umriß und identer Größe benutzt. Das oben erwähnte Integral wurde für verschiedene Typen von Verteilungsfunktionen, die die Heterogenität der mikroporösen Strukturen von Festkörpern charakterisieren, gelöst.

     

Competitive adsorption from multicomponent non-electrolytic liquid mixtures on heterogeneous solid surfaces

Summary A simple model for competitive adsorption from multicomponent non-electrolytic liquid mixtures on energetically heterogeneous solid surfaces is discussed in terms of statistical thermodynamics. Integral equations are derived for the fundamental thermodynamic quantities that characterize competitive adsorption at the liquid-solid interface. Extensive model studies are presented in order to illustrate the influence of adsorbent heterogeneity on the behaviour of these thermodynamic quantities.on leave from Faculty of Chemistry, M. Curie-Sklodowska University, PL-20031 Lublin, Poland     

High-throughput isotherm determination and thermodynamic modeling of protein adsorption on mixed mode adsorbents

The thermodynamic modeling of protein adsorption on mixed-mode adsorbents functionalized with ligands carrying both hydrophobic and electrostatic groups was undertaken. The developed mixed mode isotherm was fitted with protein adsorption data obtained for five different proteins on four different mixed mode adsorbents by 96-well microtitre plate high throughput batch experiments on a robotic workstation. The developed mixed mode isotherm was capable of describing the adsorption isotherms of all five proteins (having widely different molecular masses and iso-electric points) on the four mixed mode adsorbents and over a wide range of salt concentrations and solution pH, and provided a unique set of physically meaningful parameters for each resin-protein-pH combination. The model could capture the typically observed minimum in mixed mode protein adsorption and predict the precise salt concentration at which this minimum occurs. The possibility of predicting the salt concentration at which minimum protein binding occurs presents new opportunities for designing better elution strategies in mixed mode protein chromatography. Salt-protein interactions were shown to have important consequences on mixed mode protein adsorption when they occur. Finally, the mixed mode isotherm also gave very good fit with literature data of BSA adsorption on a different mixed mode adsorbent not examined in this study. Hence, the mixed mode isotherm formalism presented in this study can be used with any mixed mode adsorbent having the hydrophobic and electrostatic functional groups. It also provides the basis for detailed modeling and optimization of mixed mode chromatographic separation of proteins.     

Exploration of biomass waste as low cost adsorbents for removal of methylene blue dye: A review

Biomass waste, which is abundantly available has been studied as low cost biosorbent for dye sequestration from waste water. The present review reports on recent development for remediation of methylene blue dye by agricultural waste and fruit peel waste material. The aim of this study was to revise latest literature in the field of dye adsorption and discuss the dye adsorption capacity of different types of adsorbents. The activated carbon prepared from several types of biomass waste material enhances the adsorption efficiency after modification. The variety of activating agents, method of activation, characterization of biosorbent material like SEM, EDAX, BET surface area and FTIR analysis has been explored in the present review. The dye adsorption factors such as effect of pH, agitation time, temperature, adsorbate and adsorbent dose were discussed. The detailed investigation on applicability of isotherm model, kinetic model and thermodynamic parameters has also been presented. The adsorption kinetics and adsorption isotherm model focus on selectivity of adsorbent. Adsorption mechanism, Influence of surface area, influence of pH_pzc and comparative study of biomass waste adsorbent with other adsorbents have been carried out. The use of biomass waste adsorbents is economically feasible, environmental healthy and found to have outstanding removal capacity of dyes.     

A model of the two-stage condensation mechanism of water adsorption on nonporous carbon adsorbents

The mechanism of adsorption of water molecules on nonporous carbon adsorbents has been suggested in terms of two different states of adsorbed water; stretched liquid water and water that occupies an intermediate state between the liquid and vapor. Two stages of adsorption were distinguished: condensation and pre-condensation that assumes the formation of molecular associates. The BET model was used to describe the pre-condensation stage. The equations of the adsorption isotherm for water vapor in the region of condensation process and the expression for the determination of the specific hydrophilic surface of adsorbents were found. Examination of the experimental data on adsorption of water vapor on nongraphitized samples of carbon adsorbents shows that in the region of polymolecular adsorption, all isotherms fall into a common curve determined by the equation of the stretched liquid film and can be calculated regardless of the properties of individual liquid water. The equation for adsorption of water vapor on the hydrophobic surface was obtained. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1933–1939, October, 1998.     

Comparative analysis of methods for determination of structural characteristics of carbon adsorbents

Experimental data on the equilibrium adsorption of sulfur hexafluoride, methane, carbon dioxide, and benzene on carbon adsorbents of different porosity obtained in a wide pressure range at 298–408 K were analyzed. The adsorption volumes, surface areas, and sizes of slit-shaped pores of the carbons were determined using several independent methods. A method for determination of the adsorption volume from the experimental isotherm of excessive adsorption of gases and the total content equation was proposed. The resulting values are similar to the adsorption volumes calculated from the data for vapors. A new method for the calculation of the adsorbent surface area is described. The method is based on the dependence of the adsorption volume of adsorbent pores on the effective size of adsorbate molecules. A possibility to determine the average size of narrow slit-shaped carbon pores from the difference of the initial heats of adsorption of the gas under study on the carbon black and porous carbon adsorbent is considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2219–2227, October, 2005.     

Adsorption of water vapor on modified activated carbons

Summary The adsorption isotherms of water vapor on modified activated carbons are measured in order to study the role of various surface groups in the primary adsorption of water molecules on these adsorbents. These adsorption isotherms are analysed by means of the Dubinin-Serpinsky and Jovanovic equations, which take into account the special features of water vapor adsorption on microporous activated carbons. Numerical analysis of the measured adsorption isotherms by means of the above mentioned equations showed their limited applicability for interpreting adsorption mechanism of water molecules on activated carbons.

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Adsorption von Wasserdampf auf modifizierter Aktivkohle

Zusammenfassung Die Adsorptionsisothermen von Wasserdampf auf modifizierter Aktivkohle wurden gemessen, um die Rolle verschiedener Oberflächentypen auf die Primäradsorption von Wassermolekülen auf diesen Adsorbenzien zu untersuchen. Die Adsorptionsisothermen wurden mittels der Dubinin-Serpinsky- und Jovanovic-Gleichungen analysiert, welche die speziellen Eigenheiten von Wasser auf mikroporöser Aktivkohle berücksichtigen. Die numerische Analyse der gemessenen Adsorptionsisothermen mittles der genannten Gleichungen zeigte ihre limitierte Anwendbarkeit zur Interpretation von Adsorptionsmechanismen von Wassermolekülen auf modifizierter Aktivkohle.

     

The heat of adsorption of water on nonporous hydrophilic carbon adsorbents in the model of two-stage adsorption

The behavior of integral and differential heats of adsorption of water in the region of transition from the first stage of adsorption (formation of clusters) to the second stage (formation of a stretched liquid film) was considered. The curve of integral heat of adsorption has an inflection at the transition point, and the differential heat of adsorption changes jumpwise. The values of these effects were estimated by the simplest model of formation of one and two hydrogen bonds between a water molecule and an adsorption center on the surface of the carbon adsorbent. Curves of differential heat of adsorption with transition points for real systems are presented. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1479–1483, August, 1999.     

Consequence of assuming gamma-type distribution for characterizing structural heterogeneity of microporous solids

Extensive model studies were carried out for the gamma-type distribution, which was used to characterize structural heterogeneity of microporous solids. This distribution lead to a simple equation, which gave a good representation of many adsorption isotherms measured on microporous activated carbons. Assuming physically realistic values of the adsorption parameters, the gamma-type distribution curves were calculated together with curves of the adsorption isotherm, micropore distribution, adsorption potential distribution, enthalpy and entropy of adsorption.

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Die Konsequenz der Annahme einer Gamma-Typ-Verteilung bei der Charakterisierung der strukturellen Heterogenität von mikroporösen Feststoffen

Zusammenfassung Es wurden für die Gamma-Typ-Verteilung, die zur Charakterisierung der strukturellen Heterogenität von mikroporösen Feststoffen genutzt wurde, ausgedchnte Modellrechnungen durchgeführt. Diese Verteilung führte zu einer einfachen Gleichung, die eine gute Darstellung vieler Adsorptionsisothermen an mikroporös-aktiviertem Kohlenstoff erlaubt. Unter der Annahme von physikalisch realistischen Werten für die Adsorptionsparameter wurden die Gamma-Typ-Verteilungskurven zusammen mit Kurven für die Adsorptionsisothermen, der Mikroporenverteilung, der Adsorptionspotentialverteilung und der Enthalphie und Entropie der Adsorption berechnet.

     

Application of kinetic investigations for interpretation ofn-hexane and benzene adsorption on active carbon

Differencies between the mechanism ofn-hexane and benzene adsorption on active carbon were investigated on the ground of kinetic measurements. As it has been stated, the kinetic measurements show fundamental differencies between the mechanism of adsorption in spite of analogy existing in the state of adsorption equilibrium. Within the range investigated, only the adsorption ofn-hexane follows the model of volume filling of micropores. Existence of those differencies is also confirmed by measurements of effective diffusion coefficient values as well as changes of activation energy of the diffusion—adsorption process.

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Anwendung kinetischer Untersuchungen zur Interpretation des Adsorptionsverhaltens vonn-Hexan und Benzol an Aktivkohle

Zusammenfassung Mittels kinetischer Messungen untersuchte man die Unterschiede im Mechanismus des Adsorptionsverlaufes vonn-Hexan und Benzol an Aktivkohle. Man stellte fest, daß trotz der Analogie im Adsorptionsgleichgewichtszustand die kinetischen Messungen auf prinzipielle Unterschiede im Adsorptionsmechanismus hinweisen. Im untersuchten Bereich verläuft nur die Adsorption vonn-Hexane nach dem Modell der Mikroporenvolumenausfüllung. Die auftretenden Unterschiede wurden auch durch die Berechnungen der Werte der effektiven Diffusionskoeffizienten sowie Änderungen der Aktivierungsenergie des Diffusions-Adsorptionsprozesses bestätigt.

     

Heat of Adsorption of Pure Sulfur Hexafluoride on Micro-Mesoporous Adsorbents

The isotherms and the isosteric heats of adsorption of pure SF₆ were measured on two microporous zeolites (NaX and Silicalite), one mesoporous alumina, and two activated carbons (BPL and PCB) at 305 K. The adsorption isotherms were Type I by Brunauer classification. The PCB carbon adsorbed SF₆ most strongly and the alumina adsorbed SF₆ most weakly. The adsorption of SF₆ on the other three materials were comparable in the low pressure region despite their drastic differences in the physicochemical properties. The heat of adsorption of SF₆ on the silicalite and the alumina remained practically constant over a large range of coverage. The heat of adsorption of SF₆ increased with increasing adsorbate loading on the NaX zeolite in the high coverage region. The heat of adsorption of SF₆ on the activated carbons decreased with increasing adsorbate loading before leveling off in the high coverage region.