Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Adsorption: Journal of the International Adsorption Society (v.15, #1)
Behavior of ethylene and ethane within single-walled carbon nanotubes. 1-Adsorption and equilibrium properties by Fernando J. A. L. Cruz; Erich A. Müller (pp. 1-12).
Endohedral adsorption properties of ethylene and ethane onto single-walled carbon nanotubes were investigated using a united atom (2CLJQ) and a fully atomistic (AA-OPLS) force fields, by Grand Canonical Monte Carlo and Molecular Dynamics techniques. Pure fluids were studied at room temperature, T=300 K, and in the pressure ranges 4×10−4<p<47.1 bar (C2H4) and 4×10−4<p<37.9 bar (C2H6). In the low pressure region, isotherms differ quantitatively depending on the intermolecular potential used, but show the same qualitative features. Both potentials predict that ethane is preferentially adsorbed at low pressures, and the opposite behavior was observed at high loadings. Isosteric heats of adsorption and estimates of low pressure Henry’s constants, confirmed that ethane adsorption is the thermodynamically favored process at low pressures. Binary mixtures of C2H4/C2H6 were studied under several (p,T) conditions and the corresponding selectivities towards ethane, S, were evaluated. Small values of S<4 were found in all cases studied. Nanotube geometry plays a minor role on the adsorption properties, which seem to be driven at lower pressures primarily by the larger affinity of the alkane towards the carbon surface and at higher pressures by molecular volume and packing effects. The fact that the selectivity towards ethane is similar to that found earlier on carbon slit pores and larger diameter nanotubes points to the fact that the peculiar 1-D geometry of the nanotubes provides no particular incentive for the adsorption of either species.
Keywords: Adsorption; Molecular simulation; Carbon nanotubes; Ethylene; Ethane; Grand canonical Monte Carlo; Molecular dynamics
Behavior of ethylene and ethane within single-walled carbon nanotubes, 2: dynamical properties by Fernando J. A. L. Cruz; Erich A. Müller (pp. 13-22).
The dynamical behavior of ethylene and ethane confined inside single-walled carbon nanotubes has been studied using Molecular Dynamics and a fully atomistic force field. Simulations were conducted at 300 K in a broad range of molecular densities, 0.026 mol⋅L−1<ρ<15.751 mol⋅L−1(C2H4) and 0.011 mol⋅L−1<ρ<14.055 mol⋅L−1(C2H6), and were oriented towards the determination of bulk and confined phase self-diffusion coefficients. In the infinite time limit, Fickian self-diffusion is the dominant mode of transport for the bulk fluids. Upon confinement, there is a density threshold (ρ=5.5 mol⋅L−1) below which we observe a mixed mode of transport, with contributions from Fickian and ballistic diffusion. Nanotube topology seems to have only a small influence on the confined fluids’ dynamical properties; instead density (loading capacity) assumes the dominant role. In all cases studied and at a given density, the diffusivities of ethylene are larger than those of ethane, although the difference is relatively minor. We note the collapse of self-diffusivities obtained from the bulk fluids and confined phases into a unique single trend. These results suggest that it might be possible to infer dynamical properties of confined fluids from the knowledge of their bulk phase densities.
Keywords: Diffusion; Carbon nanotubes; Ethylene; Ethane; Molecular dynamics
Studying the uptake of aniline vapor by active alumina through in-line monitoring a differential adsorption bed with near-infrared diffuse reflectance spectroscopy by Chen-Bo Cai; Qing-Juan Han; Li-Juan Tang; Lu Xu; Jian-Hui Jiang; Hai-Long Wu; Ru-Qin Yu (pp. 23-29).
Through non-invasive monitoring the uptake of aniline vapor by active alumina in a differential adsorption bed (DAB) with near-infrared diffuse reflectance spectroscopy (NIR-DRS), we have studied several features of the adsorption, including isotherm, kinetics and the chemical state of aniline molecules in aniline-alumina system. What is perhaps more important, since the information above is obtained synchronously, the proposed methodology could provide information about the type of adsorption (chemical or physical adsorption), the change of chemical state of aniline in the system during the adsorption process, whether the chemical adsorption and physical adsorption took place simultaneously, the rate of the chemical and physical adsorption, and so on.
Keywords: Adsorption; Differential adsorption bed; Near-infrared spectroscopy; In-line process analytical chemistry; Partial least squares model; Isotherm; Kinetics; Aniline; Alumina
Interpretation of integrated gas sorption and mercury porosimetry studies of adsorption in disordered networks using mean-field DFT by Sean P. Rigby; Peter I. Chigada (pp. 31-41).
The presence of co-operative adsorption behaviour, operating between neighbouring pores within a disordered, void-space network, such as advanced adsorption effects, can significantly complicate the interpretation of gas adsorption data for complex porous solids, such as coked heterogeneous catalysts. The novel integrated gas sorption and mercury porosimetry method can be used to abstract the specific adsorption and desorption behaviour for particular, small sub-sets of similarly-sized pores contained within the complex network of a disordered porous solid. It will be shown in this work how, for ink-bottle geometries, the integrated experiments also allow the deconvolution of the gas sorption behaviour in pore necks, as well as pore bodies, and therefore enable the mechanism of desorption from the pore bodies to be determined. However, proper interpretation of the adsorption data from integrated experiments can be problematic using classical adsorption theories. In this work, it has been demonstrated that the experimental observations can be better understood in the light of mean-field DFT simulations of adsorption in representative pore models. Hence, a better description of the particular physical mechanisms underlying adsorption isotherms in disordered porous solids has been obtained. In addition, the new method allows more detail of the void space geometry to be obtained, such as the ratio of pore neck length relative to pore body length.
Keywords: Adsorption; MFDFT; Mercury porosimetry; Hysteresis
Gas adsorption process in activated carbon over a wide temperature range above the critical point. Part 1: modified Dubinin-Astakhov model by M.-A. Richard; P. Bénard; R. Chahine (pp. 43-51).
Simulations of the thermal effects during adsorption cycles are valuable tools for the design of efficient adsorption-based systems such as gas storage, gas separation and adsorption-based heat pumps. An analytical representation of the measured adsorption data over the wide operating pressure and temperature swing of the system is necessary for the calculation of complete mass and energy conservation equations. In Part 1, the Dubinin-Astakhov (D-A) model is adapted to model hydrogen, nitrogen, and methane adsorption isotherms on activated carbon at high pressures and supercritical temperatures assuming a constant microporous adsorption volume. The five parameter D-A type adsorption model is shown to fit the experimental data for hydrogen (30 to 293 K, up to 6 MPa), nitrogen (93 to 298 K, up to 6 MPa), and for methane (243 to 333 K, up to 9 MPa). The quality of the fit of the multiple experimental adsorption isotherms is excellent over the large temperature and pressure ranges involved. The model’s parameters could be determined as well from only the 77 K and 298 K hydrogen isotherms without much reducing the quality of the fit.
Keywords: Adsorption; Activated carbon; Dubinin-Astakhov; Supercritical; Hydrogen; Nitrogen; Methane; Modeling
Gas adsorption process in activated carbon over a wide temperature range above the critical point. Part 2: conservation of mass and energy by M.-A. Richard; P. Bénard; R. Chahine (pp. 53-63).
Simulations of the thermal effects during adsorption cycles are a valuable tool for the design of efficient adsorption-based systems such as gas storage, gas separation and adsorption-based heat pumps. In this paper, we present simulations of the thermal phenomena associated with hydrogen, nitrogen and methane adsorption on activated carbon for supercritical temperatures and high pressures. The analytical expressions of adsorption and of the internal energy of the adsorbed phase are calculated from a Dubinin-Astakhov adsorption model using solution thermodynamics. A constant adsorption volume is assumed. The isosteric heat is also calculated and discussed. Finally, the mass and energy rate balance equations for an adsorbate/adsorbent pair are presented and are shown to be in agreement with desorption experiments.
Keywords: Gas adsorption; Activated carbon; Dubinin-Astakhov; Supercritical; Hydrogen; Nitrogen; Methane; Internal energy; Isosteric heat; Modeling
What is the correct form of BET isotherm for modeling liquid phase adsorption? by Amanollah Ebadi; Jafar S. Soltan Mohammadzadeh; Anvar Khudiev (pp. 65-73).
In this work subtleties of application of BET isotherm for liquid phase adsorption is presented. It has been shown that direct use of the classical BET equation (which was developed for gas phase adsorption) to liquid phase adsorption leads to ambiguous and erroneous results. Some cases of misuse of BET equation for liquid phase adsorption have been revisited. By close examination of the development of the classical equation, the causes of misunderstandings were elucidated and the suitable form of the BET equation for liquid phase adsorption was developed. As case studies, the classical form of the BET equation along with the correct form of the equation for liquid phase have been applied for modeling liquid phase adsorption of methyl tert-butyl ether (MTBE) on perfluorooctyl alumina, phenol on activated carbon and pentachlorophenol on carbonized bark. It has been shown that direct application of the classical BET isotherm to liquid phase adsorption results in poor and erroneous estimation of the equation parameters. For example, in aqueous phase adsorption of MTBE on perfluorooctyl alumina, the monolayer adsorption capacity of the adsorbent was calculated as 9.7 mg/g instead of 3.3 mg/g or the saturation concentration of MTBE in water was calculated as 1212 mg/L instead of 42000 mg/L.
Keywords: BET isotherm; Liquid phase adsorption; Multilayer adsorption
Bioadsorption and ion exchange of Cr3+ and Pb2+ solutions with algae by Maria das Graças Nunes Matos; Vivian Gouveia Diniz; Cesar Augusto Moraes de Abreu; Augusto Knoechelmann; Valdinete Lins da Silva (pp. 75-80).
Heavy metals can be removed from effluents and recovered using physico-chemical mechanisms as biosorption processes. In this work “Arribada” seaweed biomass was employed to assess its biosorptive capacity for the chromium (Cr3+) and lead (Pb2+) cations that usually are present in waste waters of plating industries. Equilibrium and kinetic experiments were conducted in a mixed reactor on a batch basis. Biosorption equilibrium and fluid-solid mass transfer constants data were analyzed through the concept of ion exchange sorption isotherm. The respective equilibrium exchange constants (K eqCr=173.42, K eqPb=58.86) and volumetric mass transfer coefficients ((k mCr a)′=1.13×10−3 s−1, (k mPb a)′=0.89×10−3 s−1) were employed for the dynamic analysis of Cr and Pb sorption in a fixed-bed flow-through sorption column. The breakthrough curves obtained for both metals were compared with the predicted values by the heterogeneous model (K eqCr=171.29, K eqPb=60.14; k mCr a=7.81×10−2 s−1, k mPb a=2.43×10−2 s−1), taking into account the mass transfer process. The results suggest that these algae may be employed in a metal removal/recovery process at low cost.
Keywords: Ion exchange; Algae; Chromium; Lead
Bioadsorption and ion exchange of Cr3+ and Pb2+ solutions with algae by Maria das Graças Nunes Matos; Vivian Gouveia Diniz; Cesar Augusto Moraes de Abreu; Augusto Knoechelmann; Valdinete Lins da Silva (pp. 75-80).
Heavy metals can be removed from effluents and recovered using physico-chemical mechanisms as biosorption processes. In this work “Arribada” seaweed biomass was employed to assess its biosorptive capacity for the chromium (Cr3+) and lead (Pb2+) cations that usually are present in waste waters of plating industries. Equilibrium and kinetic experiments were conducted in a mixed reactor on a batch basis. Biosorption equilibrium and fluid-solid mass transfer constants data were analyzed through the concept of ion exchange sorption isotherm. The respective equilibrium exchange constants (K eqCr=173.42, K eqPb=58.86) and volumetric mass transfer coefficients ((k mCr a)′=1.13×10−3 s−1, (k mPb a)′=0.89×10−3 s−1) were employed for the dynamic analysis of Cr and Pb sorption in a fixed-bed flow-through sorption column. The breakthrough curves obtained for both metals were compared with the predicted values by the heterogeneous model (K eqCr=171.29, K eqPb=60.14; k mCr a=7.81×10−2 s−1, k mPb a=2.43×10−2 s−1), taking into account the mass transfer process. The results suggest that these algae may be employed in a metal removal/recovery process at low cost.
Keywords: Ion exchange; Algae; Chromium; Lead
Effect of synthesis time and treatment on porosity of mesoporous silica materials by Asli Ertan; Pradeep Kodumuri; Orhan Talu; Surendra N. Tewari (pp. 81-86).
Nitrogen adsorption at 77 K on mesoporous silica materials (MPS) with varying synthesis time and treatment conditions was investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were also used to characterize the mesoporous materials. This study was performed at 6, 24 and 72-h synthesis times. It is shown that 6-h is not enough for complete formation of the MPS material and at least 24-h is necessary. The pore structure starts decaying for the 72-h synthesis time. The three-after-synthesis treatment conditions used were 1) washed, 2) washed and calcined and 3) directly calcined after synthesis. Ethanol/HCl mixtures were used for washing and calcinations were performed at 550°C. Among these samples, directly washed sample yields the lowest adsorption capacity while washed and calcined sample yields the highest adsorption capacity. Hence, it is concluded that washing stabilizes the structure before high temperature treatment.
Keywords: Mesoporous silica synthesis; Nitrogen adsorption; Treatment; Synthesis time