Description Of Adsorption Equilibrium Research Articles

Cooperative Adsorption and Diffusion of Small Alcohols in Metal-Organic Framework ZIF-8 and Intrinsically Microporous Polymer PTMSP.

Fundamental understanding of molecular interactions and transport within microporous materials displaying cooperative Type V adsorption is challenged by the unique features of this isotherm type. In order to capture a broad understanding of this uncommon, yet industrially relevant, behavior in microporous materials, this investigation examines the adsorption equilibria and kinetics of methanol and ethanol in both a metal-organic framework (MOF) material, ZIF-8, and a high free volume polymer of intrinsic microporosity, poly[1-(trimethylsilyl)-1-propyne] (PTMSP). A novel formulation that can capture the cooperative effects of small alcohols in its description of adsorption equilibria and kinetics is proposed. It is subsequently applied to successfully capture some previously uncharacterized or semiempirically characterized data for equilibria and the loading dependence of the diffusivity in both ZIF-8 and PTMSP, which are materials chosen for their industrial relevance. Finally, it is anticipated that the results of this study can fill the current void that exists in meaningful mechanistic and analytical descriptions of cooperative equilibrium and diffusion phenomena in microporous materials.

Modelling binary non-linear chromatography using discrete equilibrium data

The determination and description of adsorption equilibria is critical for the design of several separation processes. In some instances, the dependence of the solid phase loading on the fluid phase concentration is complex and it is difficult to find a suitable functional form to represent the adsorption equilibria. This difficulty can be overcome by the use of discrete equilibrium data, i.e., using the experimental data of solid phase loadings and the corresponding fluid phase concentrations in its discrete form, without the use of a functional form to describe the adsorption isotherms. In this work we demonstrate how discrete equilibrium data can be used to predict binary competitive equilibria using the ideal adsorbed solution theory. Two approximations to generate data outside the range of measured values are proposed. The effectiveness of these methods in predicting competitive equilibria and elution profile of binary injections is demonstrated using numerical simulations. The application of this framework to estimate the regions of achievable separation for a multi-column simulated moving bed chromatographic separation is also discussed.

The Methanol Adsorption in Microporous Alumina Agglomerates

We have studied theoretical and experimental methods of methanol adsorption in micropores of aluminum oxide agglomerates obtained by gas-dispersion synthesis. It is shown that the necessity to use strict equations based on the theory of volume filling of micropores, which implies a physical and formal analogy between the volume filling of micropores and capillary condensation, for qualitative and quantitative description of adsorption equilibrium in open slit-like micropores. The applicability of the proposed equations for the description of adsorption equilibrium in such systems is demonstrated on the example of experimental methanol adsorption/desorption isotherm on the aluminum oxide, which possesses a microporous structure.

Effect of Salinity and PH on the Industrial Effluent Treatment by Activated Carbon: Modeling of the Kinetic Adsorption and Equilibrium Isotherms

In recent years, interest has been focused on the removal of phenols from contaminated by using a variety of purification techniques. Adsorption of bio-industrial effluent on commercial activated carbon S23 was investigated at ambient conditions. In this wok, phenol and p-hydroxyl benzoic acid (PHBA) was studied as an example of the organic compounds present in the industrial effluent. The effect of temperature, pH, and the presence of inorganic salt NaCl on the pollutants adsorption were studied to give further comprehension of the optimal conditions of the organic compounds adsorption onto activated carbon. It was noted that the increase in temperature resulted in a decrease in phenols adsorption capacity by S23. Lower phenol adsorption was also observed at the solution pH 2 and 10, whereas, favourable adsorption was reached at neutral solution pH, and the coexisting inorganic salt NaCl exerts slightly positive effect on the adsorption process. The isotherms obtained at pH 2.2 and 3.5 (non-buffered solution) are very similar and showed a higher adsorption capacity compared with that obtained at pH 7 and 10 for PHBA which is more adsorbable than phenol. The kinetic of the adsorption processes can be better represented by the pseudo-second order. The results showed also that the total organic carbon (TOC) of the industrial effluent reduced for about 20 %. Freundlich, Langmuir and Jovanovic adsorption models were used for mathematical description of adsorption equilibrium of phenols. The results showed that the experimental data fitted very well to the Freundlich and Jovanovic models.

The Investigation of Phenol Removal from Aqueous Solutions by Water Hyacinth

The potential of water hyacinth ash for phenol adsorption from aqueous solution was studied. Batch kinetic and isotherm studies were carried out under varying experimental conditions of contact time, pH, phenol concentration, and solution temperature. The adsorption of phenol was studied at pH 7. Batch adsorption models, based on the assumption of the pseudo-first-order, pseudo-second-order, and Elovich models, were applied to examine the kinetics of the adsorption. The results showed that kinetic data followed closely to the Elovich kinetic model. The experimental data were further analyzed by the expression of Boyd and the intraparticle diffusion model to determine the actual rate controlling steps. The overall rate of phenol uptake was found to be controlled by external mass transfer at the beginning of adsorption; then it gradually changed to intraparticle diffusion control at a later stage. Various adsorption models were used for the mathematical description of adsorption equilibrium and it was found that the experimental data fitted very well to the Langmuir model. Different thermodynamic parameters such as free energy, enthalpy, and entropy have been calculated and it was concluded that with the increase in temperature adsorption decreases, indicating the exothermic nature of the process.

Adsorption-catalytic removal of fulvic acids on activated carbons in the presence of hydrogen peroxide

We have investigated the impact of the change of the chemistry of the activated carbon surface on the parameters of equilibrium adsorption of fulvic acids from aqueous solutions on carbon in the presence of hydrogen peroxide. The article has considered the possibility of a multicomponent approach to the description of adsorption equilibrium when using, ay least, two hypothetic components in the Freundlich equation. For qualitative assessment of adsorbability from a multicomponent blend of organic matter we proposed to use a notion about “a conditional component”. It is shown that when introducing into the solution of fulvic acids of hydrogen peroxide the adsorption degree of fulvic acids on activated carbon substantially increase due to the catalytic effect of oxidizing organic matter.

Description of adsorption equilibria in liquid chromatography systems with binary mobile phases

Adsorption of some simple compounds from pure and mixed solvents and of some solvents from mixed binary solvent mixtures on columns used in normal-phase, aqueous–organic and non-aqueous liquid chromatography was investigated. The distribution of the compounds between the liquid and the stationary phase is affected by the composition of the solvent mixture. Although preferential sorption of stronger solvents can often be described by the Langmuir isotherm, significant deviations are observed in some systems. A model was suggested accounting for the deviations from Langmuir isotherm by association on already adsorbed molecules. In most systems studied in this work, a simple competitive Langmuir isotherm did not provide a good fit to the experimental distribution data from mixed solvents when competition between the solute and the strong solvent for the adsorption sites was considered. A competitive isotherm taking into account possible association of solute on its own already adsorbed molecules and on the adsorbed molecules of strong solvent improves the fit to the experimental distribution data and enables description of the distribution data in dependence on the concentration of the strong solvent in mixed solvents in normal-phase, aqueous–organic and non-aqueous reversed-phase systems. Even though we need more data to prove the validity of the present model, we observe a good qualitative agreement of the experimental isotherm coefficients with the relative strength of the interactions expected in various chromatographic systems employing mixed solvents.

Application of the DR and DS Equations to Benzene Adsorption from Water Solutions

Equations of the theory of micropore filling have been applied to the description of adsorption equilibria in systems containing microporous carbon and benzene solutions in water. The parameters of these equations have been evaluated from experimental data obtained for two commercial activated carbons. Comparison of the calculated and experimental adsorption isotherms suggest that these activated carbons are characterized by heterogeneous microporosity. The effect of water on the adsorption behaviour of benzene molecules in the micropores has been considered.

Description of adsorption equilibrium on type A zeolites with use of the Polanyi-Dubinin potential theory

A correlation between the adsorption of both water and methanol and the sodium exchange for various cations was studied on type A zeolites, and the adsorption isotherms were plotted. The isotherms were described with both the Dubinin-Astakhov (DA) and the modified Dubinin-Radushkevich-Stoeckli (DRS) equations. The type of adsorbate as well as cation influence the shape of the function of adsorption potential distribution obtained for the zeolites examined.