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Adsorption: Journal of the International Adsorption Society (v.15, #4)
Water isotherm models for 4A (NaA) zeolite by Kevin F. Loughlin (pp. 337-353).
The adsorption data of Gorbach et al. (Adsorption 10(1): 29–46, 2004) and Morris (J. Colloid Interface Sci. 28: 149–155, 1968) for the adsorption of water on 4A zeolite pellets is re-analyzed. Model isotherms are derived considering a two site hypothesis, one for the α cage and one for the β cage. Four simple model isotherms are fitted to the data. Both a dual site Toth or dual site Langmuir isotherm model fit the data adequately.The optimized standard enthalpy and entropy of adsorption parameters derived from the data are surprising for the β cage. The optimized standard enthalpy of the β cage is 1/3rd of that observed calorimetrically, and the standard entropy of adsorption is positive, a physical impossibility. Substituting the calorimetric enthalpy of adsorption corrected the standard differential entropy of sorption values resulting in the standard entropy of sorption values varying significantly with temperature. This variation is postulated to be due to either water of hydration formation, or clathrate formation, or the formation of clusters of water such as dimers, trimers, etc.
Keywords: Adsorption; Water; 4A (NaA) zeolite; Langmuir isotherm; Toth isotherm; Ruthven isotherm; Dual site isotherm; Standard enthalpy of adsorption; Standard entropy of adsorption
Applicability of shrinking core model on the adsorption of heavy metals by clarified sludge from aqueous solution by T. K. Naiya; A. K. Bhattacharjee; D. Sarkar; S. K. Das (pp. 354-364).
Shrinking Core model, widely accepted in the solid-fluid non-catalytic reaction system was applied to analyze the adsorption of metal ions like Zn(II), Cr(VI), Cd(II) and Pb(II) from the aqueous solutions onto the clarified sludge (CLS). The diffusivities of different metal ions in clarified sludge were determined by global optimization. The depth of penetration was also estimated for different initial concentrations. The experimental concentration profiles at various initial concentrations for all these four different metal ions matched well with the model predictions.
Keywords: Clarified sludge; Diffusivity; Film mass transfer; Shrinking core; Linear parameter
Adsorptive separation in the enhancement of butene dehydrogenation by Saleh Rawadieh; Vincent G. Gomes (pp. 365-380).
Fixed-bed columns containing solid catalysts and adsorbents were employed for simultaneous reaction and separation. The models developed for butene dehydrogenation reaction were validated with experimental data. The model was then employed for variable bed configurations with and without the effect of pressure and vacuum swing reaction (PSR and VSR). The models for the mass and momentum transfer in the catalyst bed and adsorber were solved using orthogonal collocation within the method of lines. The reactor/separator performances were tested for beds with varying numbers of layers of catalysts and adsorbents arranged sequentially. The reaction columns behaved as reactor/separators in series. As the number of layers increased, a homogeneous distribution of the catalyst and adsorbent was approached in the limit. These configurations with variable catalyst/adsorbent distributions were investigated in terms of product purity, selectivity, conversion, recovery and yield. Improved reactor performance was observed with pressure and vacuum swing separation systems and in particular with close to well-mixed reactor/separator configurations.
Keywords: Adsorption; Separation; Butene dehydrogenation; Pressure swing reaction; Vacuum swing reaction
Adsorption study for removal of Congo red anionic dye using organo-attapulgite by H. Chen; J. Zhao (pp. 381-389).
The organo-attapulgite was prepared using hexadecyltrimethylammonium bromide (HTMAB) with equation equivalent ratio of HTMAB to CEC of attapulgite added and then used as adsorbent for the removal of Congo red (CR) anionic dye from aqueous solution. Adsorbent characterizations were investigated using infrared spectroscopy and X-ray diffraction. The effects of contact time, temperature, pH and initial dye concentration on organo-attapulgite adsorption for CR were investigated. The results show that the amount adsorbed of CR on the organo-attapulgite increase with increasing dye concentration, temperature, and by decreasing pH. The adsorption kinetics was studied with the pseudo-first-order, pseudo-second-order and intraparticle diffusion models, and the rate constants were evaluated. It was found that the adsorption mechanisms in the dye/organo-attapulgite system follow pseudo-second-order kinetics with a significant contribution of film diffusion. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model, and the maximum adsorption capacity was 189.39 mg g−1 for the adsorbent. Kinetic and desorption studies both suggest that chemisorption should be the major mode of CR removal by the organo-attapulgite. The results indicate that HTMAB-modified attapulgite could be employed as low-cost material for the removal of Congo red anionic dye from wastewater.
Keywords: Organo-attapulgite; Congo red; Adsorption; Kinetics; Isotherms; Desorption
Adsorption of crystal violet dye from aqueous solution using mesoporous materials synthesized at room temperature by P. Monash; G. Pugazhenthi (pp. 390-405).
In this work, batch adsorption experiments are carried out for crystal violet dye using mesoporous MCM-41 synthesized at room temperature and sulfate modified MCM-41 prepared by impregnation method using H2SO4 as sulfatising agent. The surface characteristics, pore structure, bonding behavior and thermal degradation of both the MCM-41 samples are characterized by nitrogen adsorption/desorption isotherms, X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy and thermo gravimetric analysis (TGA). The adsorption isotherm, kinetics and thermodynamic parameters are investigated for crystal violet (CV) dye using the calcined and sulfated MCM-41. Results are analysed using Langmuir, Freundlich and Redlich-Peterson isotherm models. It is found that the Freundlich model is an appropriate model to explain the adsorption isotherm. The highest adsorption capacity achieved is found to be 3.4×10−4 mol g−1 for the sulfated MCM-41. The percentage removal of crystal violet dye increases with increase in the pH for both the MCM-41 adsorbents. Kinetics of adsorption is found to follow the second-order rate equation. From the thermodynamic investigation, it is evident that the adsorption is exothermic in nature.
Keywords: Adsorption; Crystal violet; MCM-41; Sulfated; Isotherm
Graphical approach for complex PSA cycle scheduling by Armin D. Ebner; Amal Mehrotra; James A. Ritter (pp. 406-421).
A simple graphical approach for complex pressure swing adsorption (PSA) cycle scheduling has been developed. This new methodology involves a priori specifying the cycle steps, their sequence, and the number of beds, and then following a systematic procedure that requires filling in a 2-D grid based on a few simple rules, some heuristics and some experience. The outcome or solution is a grid comprised of columns that represent the total cycle time, rows that represent the total number of beds, and cells that represent the duration of each cycle step, i.e., the complete cycle schedule. This new approach has been tested successfully against several cycle schedules taken from the literature, including a two-bed four-step Skarstrom cycle, a four-bed nine-step process with two equalization steps, a nine-bed eleven-step process with three pressure equalization steps, and a six-bed thirteen-step process with four pressure equalization steps and four idle steps. This approach also revealed the existence of numerous cycle schedules for each bed and cycle step combination examined. Although it cannot identify the total number of permutations or which one is better, it does provide a very straightforward way to determine some of the possible cycle schedules of virtually any PSA process that can be conceived.
Keywords: Pressure swing adsorption; Cycle scheduling; Cycle sequencing