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Adsorption: Journal of the International Adsorption Society (v.4, #1)
Adsorption of BSA and Hemoglobin on Hydroxyapatite Support: Equilibria and Multicomponent Dynamic Adsorption by Claire Fargues; Michel Bailly; Georges Grevillot (pp. 5-16).
Interactions of Bovin Serum Albumin and Hemoglobin with an hydroxyapatite gel (HA-Ultrogel, Sepracor), have been studied separately in batch experiments. The adsorption isotherms are of the Langmuir type and can be used directly to scale column operations.For adsorption of hemoglobin alone, in column at pH 6.8 (equal to its isoelectric point) we notice that a classical intraparticle transfer model, based on a constant effective diffusion coefficient represents perfectly the symmetrical breakthrough curve. For acid pH values (pH 5.8), Langmuir isotherms of BSA and hemoglobin adsorptions showed a strong curvature, sign of a quite irreversible adsorption and breakthrough curves obtained under these conditions, exhibit a high dissymmetrical shape for both proteins. In that case, a model of diffusion based on the adsorption on two types of independent sites, with two intraparticle transfer coefficients, gives a good representation of the breakthrough for adsorption of both proteins separately.Binary mixtures of these components were prepared and injected in columns packed with the same support. Competitive Langmuir equation, based on the results obtained in monocomponent batch experiments, give a very good fit to our system. The intraparticle transfer in that case seems to be facilitated, and one effective coefficient alone is enough to predict the breakthrough curves obtained. This behaviour may be the result of an increase of the solution ionic strength, and of the smaller irreversibility feature of the adsorption when proteins are in competition.
Keywords: chromatography; multicomponent; intraparticle diffusion; experimental data; proteins
Analysis of the Piezometric Method for the Study of Diffusion in Microporous Solids: Isothermal Case by Stefano Brandani (pp. 17-24).
The piezometric method used for the measurement of diffusion coefficients in microporous solids is examined in an attempt to establish the limits of applicability. In the present study isothermal conditions are assumed. The theoretical model for the description of the transient behaviour is linearized and solved to yield analytical solutions. The effect of the physical parameters governing the system response is described. It appears that severe limitations must be considered for strongly adsorbed and fast diffusing species.Based on the results it is possible to suggest improvements to the experimental technique and an alternative approach to analyze the experimental response curves, in which the only unknown parameter is the diffusional time constant.
Keywords: measurement method; mathematical model; intraparticle diffusion; zeolite
Adsorption of SO2 from Wet Mixtures on Hydrophobic Zeolites by Sabina A. Rouf; Mladen Eić (pp. 25-33).
Breakthrough curve measurements of SO2 and water vapor were carried out on a number of selected mordenite and pentasil zeolites from their binary and ternary mixtures with CO2 at 50 and 100°C. SO2 capacities of these samples were found to be significantly reduced by the presence of water. Competitive adsorption led to unusually high overshoot peaks of SO2 breakthrough curves. On the other hand, SO2 was found to displace water on the samples with very high silica to alumina ratio. A linear driving force, isothermal model was used to predict the breakthrough curves. Langmuir and extended Langmuir equilibrium models were used to describe the equilibrium properties of water and SO2, respectively. The overall mass transfer resistance obtained from the model was compared to the values calculated from a simplified biporous adsorbent model to shed some light on the adsorption kinetics.
Keywords: hydrophobic zeolites; breakthrough curves; adsorption; binary mixtures; modeling; overall mass transfer; roll-up
Adsorption of the Ternary Liquid Mixture Ethanol/n-Octane/n-Hexadecane onto Activated Carbon: I. The Adsorption Excess of the Ternary Mixture and of Its Binary Combinations by G. Kalies; U. Messow; P. Bräuer; K. Quitzsch (pp. 35-56).
The adsorption isotherms of the binary mixtures of ethanol/n-Octane, ethanol/n-hexadecane and n-octane/n-hexadecane onto the activated carbon TA 95 were measured at 278 K, 288 K, 298 K and 308 K and described with mathematical functions. About 300 experimental values of the adsorption excess of the ternary mixture ethanol/n-octane/n-hexadecane onto activated carbon TA 95 at 298 K were measured by gas chromatography inside the ternary triangle. The ternary miscibility gap was determined at three temperatures. A good representation of the ternary data and the calculated activity coefficients (using the UNIFAC model) in three-dimensional space was possible with the help of transformation of coordinates. It was possible, too, by utilization of the conception of the quasi two-component representation of the mole fractions with and without miscibility gap. Several influencing factors on ternary adsorption isotherms were discussed for the system ethanol/n-octane/n-hexadecane/TA 95.
Keywords: liquid phase adsorption; binary and ternary mixtures; excess isotherms; miscibility gap; mathematical description
Correlation and Calculation of Multicomponent Adsorption Equilibria Data Using a Generalized Adsorption Isotherm by R. Staudt; F. Dreisbach; J.U. Keller (pp. 57-62).
Enhanced by the need for reliable and accurate data of multicomponent gas adsorption equilibria on porous solids like activated carbons or zeolites, a new method to measure and correlate coadsorption equilibria has been developed. This method is a combination of gravimetric or volumetric measurements of the total load of pure or multicomponent adsorbates (Staudt, 1994; Gregg and Sing, 1982) and a correlation and calculation procedure using a new adsorption isotherm (AI) (Keller, 1990). This AI is thermodynamically consistent and describes adsorbates with fractal dimension for single- or multicomponent systems and load dependent adsorption energies. This method allows calculation of partial loads of multicomponent coadsorption equilibria from pure component data and the total loads of the mixture adsorption equilibria. This will be demonstrated for binary and ternary adsorption equilibria of CH4, C2H4 and C2H6 on activated carbon (Reich et al., 1980).
Keywords: multicomponent adsorption; coadsorption; fractal dimension; adsorption isotherm; heat of adsorption
A Study of Adsorption of Water Vapour on Wool under Static and Dynamic Conditions by Semra Ülkü; Devrim Balköse; Tayfun Çağa; Fehime Özkan; Sevgi Ulutan (pp. 63-73).
Adsorption of water vapour on wool provides not only textile comfort, but also convenience in transportation due to increase in its bulk density. The adsorption and desorption isotherms of water vapour for wool were determined by both volumetric technique using a Coulter Omnisorp 100CX instrument and gravimetric method employing a Cahn 2000 electronic microbalance. Adsorption isotherm fitting to B.E.T. model and hysteresis on desorption was observed. The average effective diffusion coefficient of water in wool was found to be 8.4 × 10-14 m2s-1 at 25°C from gravimetric data. The effects of packing height and air velocity on the breakthrough curves were also investigated in the wool packed columns. For pseudo first order model, k values changing between 0.33 × 10-6 − 69 × 10-6 s-1 was obtained for 2.2–6.4 cm s-1 air velocity and 0.05–0.20 m packing height ranges.
Keywords: wool; water vapour; adsorption; diffusion; column dynamics