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Adsorption: Journal of the International Adsorption Society (v.14, #6)

Amine functionalised metal organic frameworks (MOFs) as adsorbents for carbon dioxide by Bjørnar Arstad; Helmer Fjellvåg; Kjell Ove Kongshaug; Ole Swang; Richard Blom (pp. 755-762).

Three different porous metal organic framework (MOF) materials have been prepared with and without uncoordinated amine functionalities inside the pores. The materials have been characterized and tested as adsorbents for carbon dioxide. At 298 K the materials adsorb significant amount of carbon dioxide, the amine functionalised adsorbents having the highest CO₂ adsorption capacities, the best adsorbing around 14 wt% CO₂ at 1.0 atm CO₂ pressure. At 25 atm CO₂ pressure, up to 60 wt% CO₂ can be adsorbed. At high pressures the CO₂ uptake is mostly dependent on the available surface area and pore volume of the material in question. For one of the iso-structural MOF pairs the introduction of amine functionality increases the differential adsorption enthalpy (from isosteric method) from 30 to around 50 kJ/mole at low CO₂ pressures, while the adsorption enthalpies reach the same level at increase pressures. The high pressure experimental results indicate that MOF based solid adsorbents can have a potential for use in pressure swing adsorption of carbon dioxide at elevated pressures.

Keywords: Metal organic frameworks; Amine functionality; Carbon dioxide; Adsorption

Study on hexane adsorption in zeolite ITQ-29 by molecular simulation by Miguel A. Granato; Thijs J. H. Vlugt; Alírio E. Rodrigues (pp. 763-770).

Adsorption isotherms and isosteric heat of adsorption of n-hexane in zeolite ITQ-29 were simulated using the Configurational Bias Monte Carlo (CBMC) technique in the grand-canonical (μ VT) ensemble and compared with experimental results published by Gribov et al. and obtained by IR spectroscopy where the fractional loadings of n-hexane in ITQ-29 are presented in units from integral intensities of the absorption bands [u.a.]. In this work we present the simulation loadings of n-hexane in ITQ-29 converted to fractional coverages and compared to the experimental results. The simulations were performed using a united atom force field. In addition, we calculated equilibrium adsorption isotherms of ethane and propane in ITQ-29 in excellent agreement with published experiments. This force field successfully reproduces adsorption properties of linear alkanes in cation-free LTA zeolite and is suitable for fast and accurate adsorption data predictions.

Keywords: Molecular simulation; Adsorption; Monte Carlo; Zeolite ITQ-29; Hexane

Adsorption of chlorobenzene vapor on V₂O₅/Al₂O₃ catalyst under dynamic conditions by Leonid Asnin; Anatoly Fedorov; Dina Yakusheva (pp. 771-779).

Adsorption dynamics of chlorobenzene vapors on a 5% V₂O₅/Al₂O₃ catalyst has been investigated using the frontal chromatography technique. The uptakes of chlorobenzene have been measured as a function of vapor concentration and adsorption equilibrium has been found to follow formally the Langmuir isotherm. The breakthrough time proved to be a linear function of the column length as expected. Breakthrough profiles have been reported for different experimental conditions and quantitatively fitted by a reduced lumped diffusion model. This model provides an analytical solution that facilitates engineering calculations. Model parameters show complex behavior as functions of stream characteristics and depend on column length. When empirical expressions relating model mass transfer coefficients with influencing variables are found the model demonstrates good accuracy in predicting column performance.

Keywords: Adsorbents; Diffusion and kinetics

High temperature adsorption of CO₂ on various hydrotalcite-like compounds by Nick D. Hutson; Brian C. Attwood (pp. 781-789).

A study was conducted to describe and quantify how substitution of the divalent cation and interlayer charge compensating anions affect the CO₂ adsorptive capacity of various hydrotalcite-like compounds (HTlcs). Physical and chemical properties of the HTlcs were evaluated using a number of methods and the CO₂ adsorption rate and capacity were measured at elevated temperature (603 K). The results showed that the synthetic analogue of the naturally occurring hydrotalcite mineral, [Mg_0.73Al_0.27(OH)₂](CO₃)_0.13⋅xH₂O, had the best overall adsorption capacity and kinetics. The stability of the adsorption capacity was tested by subjecting the model HTlc to 10 equilibrium adsorption and desorption cycles. At the end of the cycle, the HTlc had maintained approximately sixty-five percent of its initial capacity. Temperature programmed desorption of CO₂ was used to quantify the surface basicity of the various HTlcs. The results showed that the reversible physisorption portion of the CO₂ isotherm was correlated to the number of surface basic sites on the HTlcs.

Keywords: Layered double hydroxides; LDH; Hydrotalcite; HTlc; CO₂ adsorption; Carbon capture

Comparison of sorption of Pb²⁺ and Cd²⁺ on Kaolinite clay and polyvinyl alcohol-modified Kaolinite clay by E. I. Unuabonah; K. O. Adebowale; B. I. Olu-Owolabi; L. Z. Yang (pp. 791-803).

Kaolinite clay obtained from Ubulu-Ukwu, Delta state in Nigeria was modified with polyvinyl alcohol (PVA) reagent to obtain PVA-modified Kaolinite clay adsorbent. Scanning Electron Microscopy (SEM) of the PVA-modified adsorbent suggests that Kaolinite clay particles were made more compact in nature with no definite structure. Modification of Kaolinite clay with PVA increased its adsorption capacity for 300 mg/L Pb²⁺ and Cd²⁺ by a factor of at least 6, i.e., from 4.5 mg/g to 36.23 mg/g and from 4.38 mg/g to 29.85 mg/g, respectively, at 298 K. Binary mixtures of Pb²⁺ and Cd²⁺ decreased the adsorption capacity of Unmodified Kaolinite clay for Pb²⁺ by 26.3% and for Cd²⁺ by 0.07%, respectively. In contrast, for PVA-modified Kaolinite clay, the reductions were up to 50.9% and 58.5% for Pb²⁺ and Cd²⁺, respectively.The adsorption data of Pb²⁺ and Cd²⁺ onto both Unmodified and PVA-modified Kaolinite clay adsorbents were found to fit the Pseudo-Second Order Kinetic model (PSOM), indicating that adsorption on both surfaces was mainly by chemisorption and is concentration dependent. However, kinetic adsorption data from both adsorbent generally failed the Pseudo-First order Kinetic model (PFOM) test.Extents of desorption of 91% Pb²⁺ and 94% Cd²⁺ were obtained, using 0.1 M HCl, for the Unmodified Kaolinite clay adsorbent. It was found that 99% Pb²⁺ and 97% Cd²⁺, were desorbed, for PVA-modified Kaolinite clay adsorbents within 3 min for 60 mg/L of the metal ions adsorbed by the adsorbents.

Keywords: Adsorption; Desorption; Kaolinite; Kinetic; Model; Modified adsorbent

Adsorbents for acetone in cyclohexane effuent employed in Ziegler-Natta catalyst process by Maria A. C. Gollmann; Larissa B. Capeletti; Adriano G. Fisch; João Henrique Z. dos Santos; Márcia S. L. Miranda (pp. 805-813).

Adsorption of acetone from cyclohexane on silica, alumina, coal, natural and leached chrysotile was investigated. Adsorption phenomenon was investigated by non-linear fitting, considering the Langmuir or Freundlich models. According to non-linear regression, coal present the highest K L (12.07) and K F (9.115) parameters. Silica and leached chrysotile exhibited similar behavior in terms of both K L and K F parameters. Alumina presented the highest adsorption capacity according to both Langmuir (q m=58.689) and Freundlich (1/n=0.844) models. Non-supported Ziegler-Natta catalyst systems were shown to be more sensitive to acetone contamination. For the polymerization reactions carried on with contaminated solvent after the percolation through the adsorbents, good results were observed in the case of silica and alumina. Coal was not suitable for use in this catalyst system, probably due to leaching of organic components by the solvent (cyclohexane).

Keywords: Adsorption; Acetone; Ziegler-Natta catalyst; Poison; Polymerization

Adsorption of reactive dye on chitosan in air-lift reactor by Urszula Filipkowska; Karolina Waraksa (pp. 815-821).

This study was undertaken to identify factors exerting the strongest influence on the adsorption of dye. The maximum adsorption capacity (at the adopted operating conditions) was the main parameter used to evaluate the process. In addition, the feasible adsorption capacity of chitosan was evaluated. Breakthrough experiments were carried out in a circulating air-lift reactor at a constant concentration of reactive dye Black 8 (100 mg/dm³). The tests studied different chitosan concentrations in the reactor and a range of flow intensities. The results of the breakthrough tests were compared by means of apparent mass transfer coefficients, determined by slopes at C/C ₀=1/2. The adsorption capacity of chitosan was affected to the greatest extent by the flow rate of the medium to the reactor. In turn, the utilization of the maximum adsorption capacity of chitosan, at the assumed efficiency of dye removal, was determined by chitosan concentration in the reactor.

Keywords: Adsorption; Chitosan; Air-lift reactor; Black 8

Removal of Cr (VI) from aqueous solutions by the nonliving biomass of Alligator weed: kinetics and equilibrium by Xue Song Wang; Ye Ping Tang; Sheng Rong Tao (pp. 823-830).

The removal of Cr (VI) from aqueous solutions using Alligator weed, a freshwater macrophyte, was investigated in batch studies. Various factors including solution pH, Cr (VI) concentrations, agitation time, and temperature were taken into account and promising results obtained. An initial solution pH of 1.0 was most favorable for Cr (VI) removal. The kinetic data were analyzed using several models, including the pseudo-second-order equation, external diffusion model, and intraparticle diffusion model. The comparison gave insight about the mechanism of adsorption and potential rate controlling step. The results suggested that the Cr (VI) adsorption at all temperatures was best represented by the pseudo-second-order equation. The external film diffusion played an important role in the adsorption mechanism. The Freundlich, Langmuir and Langmuir-Freundlich isotherms for the present system were analyzed. The best interpretation for the equilibrium data at different temperatures was given by the Langmuir-Freundlich isotherm. The Alligator weed could serve as low-cost adsorbent to remove Cr (VI) from aqueous solutions.

Keywords: Batch adsorption; Cr (VI); Alligator weed; Isotherm; Separation

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Adsorption: Journal of the International Adsorption Society (v.14, #6)

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Adsorption: Journal of the International Adsorption Society (v.14, #6)