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Adsorption: Journal of the International Adsorption Society (v.10, #3)
Benzene Adsorption Isotherms on MCM-41 and their Use for Pore Size Analysis by Jerzy Choma; Marcin Kloske; Mietek Jaroniec; Jerzy Klinik (pp. 195-203).
This work is focused on the elaboration of methodology for adsorption characterization of porous silicas by using benzene adsorption isotherms measured on good quality MCM-41 materials. Three MCM-41 samples were synthesized by using tetraethyl orthosilicate (TEOS) as silica source and surfactants, octyltrimethylammonium (C8), decyltrimethylammonium (C10) and cetyltrimethylammonium (C16) bromides as templates. A characteristic feature of this synthesis was relatively long hydrothermal treatment (5 days) at 373 K, which gave well ordered samples as evidenced by powder XRD analysis. Benzene adsorption isotherms measured on these MCM-41 samples were used to evaluate such standard quantities as the BET specific surface area, total pore volume, external surface area and the volume of ordered mesopores, and to obtain the statistical film thickness (t-curve) as well as the Kelvin-type relation, which describes the dependence between pore width and condensation pressure for benzene on silica at 298 K. The latter relations were incorporated into the Barrett-Joyner-Halenda algorithm to extend its applicability to calculate the pore size distributions from benzene adsorption data.
Keywords: adsorption; argon; benzene; MCM-41; pore size analysis
Sorption of Benzene in CoAlPO4-5 Molecular Sieves by J.X. Liu; M. Dong; Z.L. Sun; Z.F. Qin; J.G. Wang (pp. 205-210).
The sorption isotherms of benzene in CoAlPO4-5 at temperatures of 323–399 K were measured by the gravimetric technique. The sorption capacity and isosteric heat were estimated and interpreted on the basis of the pore topologies of the molecular sieves. The isotherms followed the typical Type-I shape, and could be well fitted with Langmuir and Dubinin-Radushkevich equations. The initial heats of sorption at zero coverage could be well explained by the surface curvature model. The isosteric heats of sorption varied with the coverage, which may suggest a shift of molecular packing manner in the sorbed phase.
Keywords: sorption; CoAlPO4-5; benzene; sorption isotherms; heat of sorption
Kinetic and Thermodynamic Study on the Liquid Phase Adsorption by Starchy Materials in the Alcohol-Water System by M.J. Carmo; M.G. Adeodato; A.M. Moreira; E.J.S. Parente Jr.; R.S. Vieira (pp. 211-218).
Improving adsorptive processes demands a constant search for new adsorbents. In the case of alcohol-water separation, zeolites are widely used. The use of new adsorbents as a substitute for zeolites, mainly starch, has been proposed recently. This work is a thermodynamic and kinetic study of liquid phase adsorption of water from methanol, ethanol, propanol and butanol-water mixtures using starch as the adsorbent. The thermodynamic data were obtained by means of the static method at three different temperatures (25, 40 and 50°C), and were correlated by the Langmuir isotherm. The kinetic data were obtained in a finite liquid bath cell. The influence of temperature and molecular chain length of the alcohol on the capacity and adsorption rate were determined.
Keywords: alcohol; starch; adsorption
A Study on the Adsorption of Benzotriazole on Copper in Hydrochloric Acid Using the Inflection Point of the Isotherm by E. Cano; J.L. Polo; A. La Iglesia; J.M. Bastidas (pp. 219-225).
This paper is a contribution to correlate benzotriazole (BTA) adsorption films on copper with BTA concentration in bulk solution with hydrochloric (HCl) acid. Three HCl concentrations were tested, 0.001, 0.005, and 0.01 M. Twelve BTA concentrations, from 1 × 10−5 to 1 × 10−1 M, were added to the HCl acid solution at four temperatures from 298 to 328 K. Commercial copper was used. Gravimetric measurements were performed after 3 h experimentation. The Frumkin isotherm gave the best fit to the experimental results. This result was based on the inflection point approach of the isotherm.
Keywords: copper; hydrochloric acid; benzotriazole; Frumkin and Damaskin-Parsons adsorption isotherms
Thermodynamics of the Exchange Processes between K+, Ca2+ and Cr3+ in Zeolite NaA by M.A.S.D. Barros; P.A. Arroyo; E.F. Sousa-Aguiar; C.R.G. Tavares (pp. 227-235).
In this paper it was analyzed the ion exchange isotherm of K+, Ca2+ and also Cr3+ ions with NaA zeolites at three temperatures: 30, 45 and 60°C. The NaA isotherms were favorable for the metal cations studied. Differences in shape are due to the different influence of temperature in the interaction of the in-going cation with the zeolite framework. As a consequence, sites of different energies were used in the exchange process, which provided non linear Kielland plots. Equilibrium constant, standard free energy, enthalpy and enthopy changes were measured and tabulated. Equilibrium constant is directly proportional to the in-going ion charge. Concerning enthalpy, endothermic and exothermic exchanges were observed due to differences in the cation-framework interaction. The selectivity order based on the standard free energy over the entire temperature range was K+ < Cr3+ < Ca2+, a consequence of different ion exchange mechanisms. It was also noted that the entropy change increases with the polarizibility of the cations.
Keywords: zeolite A; ion exchange; isotherm; thermodynamic data; chromium
Adsorption Behaviour of 134Cs and 22Na Ions on Tin and Titanium Ferrocyanides by E.S. Zakaria; I.M. Ali; H.F. Aly (pp. 237-244).
Tin and titanium ferrocyanides were studied as adsorbents for alkali metal ions, viz., 134Cs and 22Na, which represent radioactive wastes. The ferrocyanides were prepared in granular form. The tin version contained 11.2% water, while the titanium version contained 17.7% water. The exchange capacities for Cs+ and Na+ in the hydrated tin version were about 1.5 and 0.7 meq/g, respectively, while those in the titanium version were 2.2 and 1.2 meq/g, respectively. Drying at 250°C decimated those capacities. The diffusional time constant of Cs+ at 25°C, determined via Fick's second law, was of order of magnitude 1 × 10−3 s−1, though there were minor differences due to particle size and the form of ferrocyanide. Similarly, the effective diffusivity was of order of magnitude 1 × 10−8 cm2/s. The titanium version responded slightly faster than the tin version. Likewise, equilibrium measurements in mixtures with sodium nitrate, potassium nitrate, or uranium oxide, showed that the titanium version exhibited significantly greater selectivity for Cs+ than did the tin version. Unfortunately, tests of complete elution of the Cs+ from the ferrocyanides were mostly disappointing. Work continues on that subject.
Keywords: ion exchange; equilibrium; kinetics; radioactive waste treatment
Boron Removal from Aqueous Solutions by Adsorption on Waste Sepiolite and Activated Waste Sepiolite Using Full Factorial Design by Neşe Öztürk; Duygu Kavak (pp. 245-257).
In the present paper, boron removal from aqueous solution by adsorption was investigated and 23 full factorial design was applied. Non activated waste sepiolite (NAWS) and HCl activated waste sepiolite (AWS) were used as adsorbents. Regression equation formulated for boron adsorption was represented as a function of response variables. The results obtained from the study on parameters showed that as pH increased and temperature decreased boron removal by adsorption increased. Adsorbed boron amount on AWS was higher than that of NAWS. Maximum boron removal was obtained at pH 10 and 20°C for both adsorbents. Adsorption data obtained from batch adsorption experiments carried out with NAWS and AWS fitted to the Langmuir equation. The batch adsorption capacities were found in mg/g: 96.15 and 178.57 for NAWS and AWS, respectively. The capacity value for column study was obtained by graphical integration as 219.01 mg/g for AWS. The Thomas and the Yoon-Nelson models were applied to experimental data to predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design.
Keywords: boron removal; adsorption; waste sepiolite; experimental design; packed bed column