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Adsorption: Journal of the International Adsorption Society (v.9, #2)

Activated Carbon Adsorption of Some Phenolic Compounds Present in Agroindustrial Wastewater by J.F. García-Araya; F.J. Beltrán; P. Álvarez; F.J. Masa (pp. 107-115).

Single solute and simultaneous experimental adsorption isotherms of three phenolic compounds: gallic acid, p-hydroxybenzoic acid and syringic acid, have been investigated at 20, 30 and 40°C, using a bituminous coal based activated carbon. Regardless of temperature, the capacity of the activated carbon used to adsorb these compounds presented the following order: syringic acid > p-hydroxybenzoic acid > gallic acid. The increase of temperature slightly favored the adsorption capacity of the phenolic compounds. In binary and ternary component adsorption, experimental data suggest that interactions between adsorbates improve the adsorption capacity of some of the phenolic acid compounds. On the contrary, at high organic concentrations, adsorbed gallic acid was partially removed from the activated carbon surface because of the presence of the other components.

Keywords: activated carbon; adsorption equilibrium; phenolic acid compounds; gallic acid; p-hydroxybenzoic acid; syringic acid

Focusing in Liquid Thermal Adsorption Systems by Jeung Kun Kim; Gopalan Natarajan; Phillip C. Wankat (pp. 117-123).

Focusing can be obtained in liquid thermal cycling zone adsorption by significantly increasing the temperature of the hot feed. To prevent boiling column pressure is raised. This method for concentrating dilute fluids was studied using the simulation package ADSIM. The systems studied were ethanol-water on silicalite and toluene-n-heptane on silica gel. Substantial concentration of dilute feeds while producing a pure solvent product were obtained. This research highlights the need for equilibrium data for liquid adsorption systems at elevated temperatures and pressures.

Keywords: adsorption; cycling zone adsorption; focusing

Equilibrium and Kinetic Modelling of Adsorption of Phosphorus on Calcined Alunite by Mahmut Özacar (pp. 125-132).

The adsorption of phosphorus onto calcined alunite has been studied. Its equilibrium isotherm has been measured. The isotherm was determined by shaking 1.0 g calcined alunite, particle size range 90–150 μm, with 100 mL phosphorus solution of initial concentrations from 0.5 to 2.5 mmol/L. The water bath shaking a constant rate of 200-rpm was used and the temperature maintained at 298 ± 2 K. A contact time of 120 min was required to achieve equilibrium. The experimental isotherm data were analyzed using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich equations. The monolayer adsorption capacity is 1.355 mmol P per g calcined alunite. Three simplified kinetic models including a pseudo first-order equation, pseudo second-order equation and intraparticle diffusion equation were selected to follow the adsorption process. Kinetic parameters, rate constants, equilibrium sorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the adsorption of phosphorus could be described by the pseudo second-order equation.

Keywords: alunite; adsorption isotherms and kinetics; phosphorus; pseudo second-order; intraparticle diffusion

Use of Nonlinear Frequency Response for Discriminating Adsorption Kinetics Mechanisms Resulting with Bimodal Characteristic Functions by Menka Petkovska; Ljubica T. Petkovska (pp. 133-142).

One of the characteristic examples of the inability of the classical linear frequency response (FR) method to identify the correct kinetic mechanism is adsorption of some substances (p-xylene, 2-butane, propane or n-hexane) on silicalite-1. The linear FR resulted with bimodal FR characteristic functions, which fitted equally well to three different kinetic models: nonisothermal micropore diffusion, two independent isothermal diffusion processes, and an isothermal diffusion-rearrangement process. We show that the second order frequency response functions (FRFs), obtained from the nonlinear FR, can be used for discrimination among these three mechanisms. Starting from the nonlinear models, we derive the theoretical expressions for the first and second order FRFs corresponding to these three mechanisms and show that different shapes of the second order FRFs are obtained for each mechanism. This would enable identification of the real mechanism from nonlinear FR data.

Keywords: nonlinear mathematical models; nonlinear frequency response method; bimodal characteristic functions; isothermal and nonisothermal models

A Kinetic Investigation of Chromium by Sevgi Kocaoba; Göksel Akcin (pp. 143-151).

A kinetic investigation was performed with an ion exchange resin for chromium. A chelating cation exchange resin (Amberlite IRC 718) was used for removal and recovery of chromium. The effect of concentration, resin amount, particle size and stirring speed on kinetics were investigated. The metal concentration range studied was between 5 to 160 mg L⁻¹, the resin amount range was between 5 to 20 mg, the particle size range was between 0.35 to 1.8 mm and the stirring speed range was between 1000 to 3500 rpm.Kinetic studies were done using a Kressman-Kitchener stirrer reactor system and the results were compared with existing kinetic models. Two models; Nernst-Plank film diffusion control model (fdc) and solid phase diffusion control model (pdc) were identified and the dependence of the rate on parameters, such as solution concentration, particle size, resin amount, stirring speed, etc., was examined for each of them. As a result, interpretation of these data showed that the system is probably controlled both film and particle diffusion.

Keywords: kinetics; chelating weakly acidic exchange resin; chromium; Kressman-Kitchener stirrer reactor

The Adsorption of CHF₃ on NaY5.6 Zeolite and Microdynamic Behaviors in Small Pores by Mitsuhiro Yoshikawa Murata; Mitsumasa Ishiwata; Toshihisa Yoshida (pp. 153-164).

Adsorption of CHF₃ on a NaY5.6 zeolite has been studied by the measurement of H and F NMR of the CHF₃ molecule, focusing in particular on the measurements of a chemical shift and a longitudinal relaxation time, together with the adsorption isotherm measurements. A coordination structure of the adsorbed CHF₃ is determined from the relationship between a chemical shift and an adsorption amount. Relaxation times of H and F were measured at respective two resonance frequencies for various adsorption amounts and temperatures. These relaxation data have been analyzed by use of the thermally activated diffusion model proposed by Torrey. From these analyses, various microdynamic variables such as a mean life time of the trapped state and a mean jump distance in the diffusion were determined as functions of an adsorption amount and temperature.

Keywords: adsorption; zeolite; trifluoromethane; H and F NMR; chemical shift; adsorption structure; translational diffusion; microdynamics in the pores

Investigations for Modification of Polyacrylamide-Bentonite by Phytic Acid and its Usability in Fe³⁺, Zn²⁺ and UO₂ ²⁺ Adsorption by Ulvi Ulusoy; Selçuk Şimşek; Özlem Ceyhan (pp. 165-175).

Composite of polyacrylamide-bentonite (PAA-B) was prepared by direct polymerisation of PAA in a suspension of bentonite (B). Adsorption and thermodynamic features of phytic acid (Phy) adsorption onto B, PAA and PAA-B, and those of Fe³⁺, Zn²⁺, UO₂ ²⁺ adsorption onto PAA-B and its modification by Phy (PAA-B-Phy) have been investigated. The reusability, storagability, ion selectivity and recoverability of sorbed ions with 1 M HCl have also been considered.The chemical and physical structure of adsorbents has been characterised by means of FT-IR and XRD. All adsorption isotherms for Phy and the ions were L-type of the Giles classification except, the one which is S type for adsorption of Phy onto PAA. The maximum adsorption capacities for the ions adsorbed were in order of UO₂ ²⁺ > Fe³⁺ > Zn²⁺ for PAA-B and Zn²⁺ > Fe³⁺ > UO₂ ²⁺ for PAA-B-Phy. Langmuir equilibrium constants for the adsorption of ions onto PAA-B-Phy were significantly higher than those found for PAA-B; the magnitude of increase for UO₂ ²⁺ was about 100. The thermodynamic parameters indicated that adsorption reactions are spontaneous in terms of adsorption free enthalpy.The chemical structure of PAA-B-Phy was not changed at the end of the studies of reusability and storagability. The composite was selective for UO₂ ²⁺ of the ions of interest.The composite of PAA-B and its modification by Phy have been used for the first time in this investigation. It is proposed that the composites can be practically used in the investigations and applications of adsorption.

Keywords: metal adsorption; uranium; composite; bentonite; polyacrylamide; phytic acid

Determination of Absolute Gas Adsorption Isotherms by Combined Calorimetric and Dielectric Measurements by J.U. Keller; W. Zimmermann; E. Schein (pp. 177-188).

A new method to determine absolute masses of gas adsorbed on the external and internal surfaces of a porous solid is proposed. It consists on a combination of calorimetric and dielectric measurements. These lead to the enthalpy and the dielectric polarization of the adsorbed phase from which by purely thermodynamic calculations the absolute mass adsorbed can be determined without using the so-called helium volume hypothesis nor any other equivalent assumption.As example adsorption of subcritical carbon dioxide (CO₂) on zeolite (Degussa DAY) at 298 K and pressures up to 0,4 MPa is considered. As expected data of absolute masses adsorbed are always somewhat larger than the corresponding Gibbs excess masses calculated from both volumetric and gravimetric measurements via the helium volume of the zeolite.

Keywords: absolute mass adsorbed; Gibbs excess mass; helium volume hypothesis; permittivity of adsorbates; enthalpy of adsorption

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Adsorption: Journal of the International Adsorption Society (v.9, #2)

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Adsorption: Journal of the International Adsorption Society (v.9, #2)