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Adsorption: Journal of the International Adsorption Society (v.10, #4)
Pressure-Swing Adsorption Using Layered Adsorbent Beds with Different Adsorption Properties: II—Experimental Investigation by Yaping Lü; Shain-Jer Doong; Martin Bülow (pp. 267-275).
An experimental study was conducted on a layered-bed pressure-vacuum-swing adsorption, PVSA, process with adsorbents that differ in their adsorption properties. An oxygen, O2, PVSA process was employed as an example for investigating how the process performance is affected by bed-layering configuration under different operating conditions for specific purge, product purity, and cycle feature. For two adsorbents with similar nitrogen-to-oxygen, N2/O2, selectivity but different N2 and O2 capacities, placing the high-capacity adsorbent at the product end and the low-capacity adsorbent at the feed end of the adsorption bed results in a better performance than in the case of reversing the layer positions of those adsorbents. The benefit of placing the adsorbent with higher capacity at the product end becomes more significant at high O2 product-purity levels. The experimental data obtained in this investigation agree well with simulation results reported earlier.
Keywords: PVSA processes; performance simulation; layered beds; positioning of adsorbents; adsorption capacity; adsorption selectivity
An Adsorption Isotherm from a Micro-state Model by Bardo Ernst; Josef Bodmann; Deborah Pinheiro Dick; Yeda Pinheiro Dick (pp. 277-286).
The present study is dedicated to the derivation of an alternative adsorption isotherm for liquid-solid interfaces from a micro-state model, where adsorption is predominantly of a chemical nature. We describe adsorption-desorption on a liquid-solid interface starting from a partition function. In the new model the surface site occupation number is controlled by the Pauli principle (monolayer condition) and additional an attractive or repulsive surface potential, which depends on the overall surface coverage (nonlinearity). The effective potential represents adsorbate adsorbent interaction, as well as an influence of adsorbate adsorbate interactions on the surface potential. A Langmuir equivalent isotherm is recovered in the limit of a weak potential. The proposed model and Langmuir’s isotherm are compared using data of humic acid (HA) adsorption on Brazilian Oxisol soil samples. Both models parameterize the experimental data well, but only the new model seems to be self-consistent.
Keywords: adsorption isotherm; liquid-solid interface; micro-state model; humic acid; oxisol
Removal of Phenol by Using Montmorillonite, Clinoptilolite and Hydrotalcite by Saadet Yapar; Meriç Yilmaz (pp. 287-298).
This work is to study the removal of phenol from aqueous solutions by adsorption using three different adsorbents, clinoptilolite, montmorillonite, and hydrotalcite (HT). Except for montmorillonite, the other adsorbents were treated. Clinoptilolite was modified using cetyltrimethylammonium bromide (CTAB) and hydrotalcite was calcined by heating to 550∘C. Adsorption isotherms of phenol on all of the mentioned adsorbents was determined by using the batch equilibration technique and indicated that, the adsorption behavior could be modelled by using the Modified Freundlich equation. The differences observed in the isotherms were explained by the variations in adsorbent-adsorbate interactions under the effects of the different surface structures of adsorbents and the pH dependent ionization behavior of phenol. Calcined hydrotalcite (HTC) was found to be the best among the studied adsorbents since it can adsorb 52% of phenol from a solution containing initially 1 g/L phenol for the 1/100 adsorbent solution ratio while the others can adsorb only 8% of phenol for the same concentration and adsorbent solution ratio.
Keywords: montmorillonite; clinoptilolite; hydrotalcite; organic pollutant; phenol; adsorption
An Analysis of the Interactions of BSA with an Anion-Exchange Surface Under Linear and Non-Linear Conditions by Marvin E. Thrash Jr.; Jessica M. Phillips; Neville G. Pinto (pp. 299-307).
The interactions of BSA with an anion-exchange adsorbent have been studied to aid in the understanding of protein adsorption in ion-exchange chromatography. Linear chromatography, flow microcalorimetry and isotherm measurements were used to analyze adsorption energetics in the linear and overloaded regions of the equilibrium isotherm. The effects of salt type, salt and protein concentration, and temperature are reported. It was observed that under all conditions studied the adsorption process was entropically driven. This was contrary to expectations, since at the pH selected ion exchange is expected to dominate. A major driving force for the adsorption of BSA on the anion exchanger was concluded to be the increase in entropy from the release of water due to interactions between hydrophobic regions on the protein and adsorbent. The data further suggest that the conformational entropy change accompanying protein adsorption on the ion exchanger may also be significant.
Keywords: protein adsorption; BSA; isotherms; ion-exchange; heat of adsorption; zeta potential; water-release
A Highly Efficient Chelating Polymer for the Adsorption of Uranyl and Vanadyl Ions at Low Concentrations by Pinar Akkaş Kavakli; Noriaki Seko; Masao Tamada; Olgun Güven (pp. 309-315).
A new polymer containing double amidoxime groups per repeating unit was synthesized to enhance the metal ion uptake capacity. The adsorption properties of this new polymeric adsorbent, amidoximated poly(N,N′-dipropionitrile acrylamide), for U(VI), V(V), Cu(II), Co(II) and Ni(II) ions were investigated by batch and flow-through processes at very low concentration levels (ppb). The chelating polymer showed high adsorption capacity for uranyl as well as vanadyl ions. In selectivity studies from a mixture of metal ions in aqueous solutions, the adsorbent showed high selectivity for uranyl and vanadyl ions in the following order: U(VI) > V(V) ≫ Co(II) = Cu(II) ≫ Ni(II) as determined by calculating the distribution coefficients D, of corresponding ions. The adsorption of uranyl and vanadyl ions from natural seawater by the new adsorbent was also examined in flow through mode.
Keywords: chelating polymer; poly(dipropionitrile acrylamide); amidoximation; uranyl; vanadyl ion adsorption
The Equilibrium and Kinetic Modelling of the Biosorption of Copper(II) Ions on Cladophora crispata by Ayla ÖZER; Dursun Özer; H. İbrahim Ekİz (pp. 317-326).
The biosorption of Cu(II) ions on Cladophora crispata was investigated as a function of the initial pH, temperature and initial Cu(II) ion concentration. Algal biomass exhibited the highest Cu(II) uptake capacity at 25∘C and at the initial pH of 4.5. Equilibrium data fitted very well to both the Langmuir and Freundlich isotherm models. The pseudo second order kinetic model was applied to describe the kinetic data and the rate constants were evaluated in the studied concentration range of Cu(II) ions at all the temperatures studied. The experimental data fitted well to the pseudo second order kinetic model with a high correlation coefficient (R2 > 0.99), which indicates that the external mass transfer limitations in the system can be neglected and the chemical sorption is the rate-limiting step. The pseudo second order kinetic constants were also used to calculate the activation energy of Cu(II) biosorption.
Keywords: adsorption; equilibrium; pseudo second order kinetics; activation energy
Adsorption of Chromium (VI) on Azadirachta Indica (Neem) Leaf Powder by Arunima Sharma; Krishna G. Bhattacharyya (pp. 327-338).
A novel adsorbent was developed from mature leaves of the Neem tree (Azadirachta Indica) for removing metal ions from water. The adsorbent, in the form of fine powder, was found to be very effective in removing chromium (VI) from aqueous solution. The adsorption was carried out in a batch process taking different concentrations of the metal ion in aqueous solution with variation in adsorbent amount, pH, agitation time and temperature. The suitability of the adsorbent was tested with Langmuir and Freundlich isotherms and with various equilibrium kinetic data. A small amount of the Neem Leaf Powder (NLP) (1.6 g dm−3) could remove as much as 87% of Cr (VI) in 300 min from a solution of concentration 14.1 mg dm−3 at 300 K. The optimum range of pH for the adsorption process was 4.5–7.5 and since the natural pH of the Cr (VI) solution was 5.5, no addition of acid or alkali was necessary for achieving maximum adsorption. The adsorption coefficients indicated a high potentiality for the NLP to be used as an adsorbent for removing Cr (VI) from water.
Keywords: Neem Leaf Powder; Chromium (VI); Metal removal by adsorption
The Adsorption Kinetics of Cethyltrimethylammonium Bromide (CTAB) onto Powdered Active Carbon by Mehmet YalÇin; Ahmet GÜrses; Çetin Doğar; Mustafa SÖZBİLİr (pp. 339-348).
This study investigates the adsorption kinetics of CTAB (cethyltrimethylammonium bromide), a cationic surfactant, onto PAC from aqueous solution with respect to the initial CTAB concentration at 20∘C. The pseudo-first-order, second-order kinetic models and intraparticle diffusion model were used to describe the kinetic data and the rate constants were calculated. The rate parameter, ki, of intraparticle diffusion, the rate parameter, k2, of the pseudo-second-order and k1, the rate parameter for the pseudo-first-order mechanism were compared. It was found that the pseudo-second-order adsorption mechanism is predominant and the overall rate of the CTAB adsorption process appears to be controlled by more than one step, namely both the external mass transfer and intraparticle diffusion mechanisms.
Keywords: adsorption kinetics; CTAB; powdered active carbon; pseudo-first order kinetics; pseudo-second order kinetics; intraparticle diffusion