Net,excess and absolute adsorption and adsorption of helium

The definitions of absolute, excess and net adsorption in microporous materials are used to identify the correct limits at zero and infinite pressure. Absolute adsorption is shown to be the fundamental thermodynamic property and methods to determine the solid density that includes the micropore volume are discussed. A simple means to define when it is necessary to distinguish between the three definitions at low pressure is presented. To highlight the practical implications of the analysis the case of adsorption of helium is considered in detail and a combination of experiments and molecular simulations is used to clarify how to interpret adsorption measurements for weakly adsorbed components.     

Competitive adsorption

A review is presented on the multicomponent competitive adsorption, static equilibrium adsorption, and dynamic nonequilibrium adsorption from gaseous and liquid media onto the surface of porous and disperse solids. The state of the theory of multicomponent adsorption is analyzed. Not only traditional methods were used for investigations in this field but also NMR spectroscopy (difference in the spectra of adsorbed and free compounds), FTIR spectroscopy (difference in the spectra of surface groups and bonds in adsorbates), calorimetry, thermally stimulated depolarization, photon correlation spectroscopy, electrophoresis, and cryoporometry. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 3, pp. 133–169, May–June, 2007.     

Enthalpy of adsorption and adsorption isotherms of polyacrylamide on sea sand

The enthalpy of dilution of polyacrylamide 3530s (HPAM) solution, the enthalpy of adsorption of the polymer on sea sand, and the adsorption isotherms, were determined at 298. 15 K. The effect of NaCl on these properties were also determined. From the experimental results and certain assumptions, it was deduced that, for an adsorbedHPAM molecule, a large number of segments are in contact with the surface of the solid, some of them forming hydrogen-bonds, most of them belonging to Van der Waals interactions, which are much weaker than hydrogenbonds, and theHPAM molecules adsorbed on the surface of the solid are spread out.     

Differential heats of adsorption and adsorption isotherms of alcohols on silicalite

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2117–2120, September, 1989.     

甲烷在活性炭上吸附平衡模型的研究

比较吸附模型分析甲烷在活性炭上吸附平衡的适用性,为吸附式天然气(ANG)的工程应用提供准确的预测模型。基于在温度268.15～338.15 K、压力0～12.5 MPa测试的甲烷在Ajax活性炭上的吸附平衡数据,选择Langmuir、Langmuir-Freundlich和Toth方程,应用非线性回归拟合方程参数后,确定绝对吸附量和甲烷吸附相态,并比较方程在不同压力区域内的预测精度。结果表明,甲烷吸附相密度随平衡温度和压力变化;由绝对吸附量确定的甲烷在Ajax活性炭上的平均等量吸附热为15.72 kJ/mol,小于由过剩吸附量的标绘结果;Langmuir、Langmuir-Freundlich和Toth方程预测结果在0～0.025 MPa的累积相对误差为6.449 8%、7.918 4%和0.910 0%,在1～10 MPa为0.491 1%、0.161 3%和0.369 4%。Toth方程在整个压力范围内的预测结果最为准确,但Langmuir-Freundlich方程在较高压力区域内具有较高的预测精度。     

Equilibrium in an ideal adsorption layer during multiplet adsorption

The equilibrium in an ideal adsorption layer during adsorption of a mixture of substances whose molecules can occupy one or m elementary sites is examined. It is shown that the isotherm for any adsorbate in the mixture can be readily found if the isotherm is known for one of the adsorbed substances whose molecules occupy m elementary surface sites in the absence of other adsorbates. The form of the isotherm for multiplet adsorption depends on the distribution of the elementary sites on the surface.     

Multilayer adsorption equilibrium model for gas adsorption on solids

Adaptation of the ENSIC model to physisorption of nitrogen or argon on a solid surface first led to a 3 parameters model called multilayer adsorption equilibrium model (MAE model). One of these parameters is related to the formation of a multilayer of adsorbate on the solid surface. Exploitation of data from the literature pointed out that this parameter does not depend on the nature of the solid surface and an average value was calculated in the case of N₂ and Ar. As a consequence, the MAE model can be considered as a 2 parameters model. Linearization of the model was established allowing an easy determination of surface areas of macroporous and some mesoporous solids. Fitting of isotherms of meso and macroporous solids has led to promising results compared to the ones obtained with the BET model. Moreover, adaptation of this model to microporous solids can also be used for an uncomplicated determination of porous volume and external surface. Results obtained from data of the literature were close to those obtained with the t-plot model.     

Studies on adsorption indicators : p-ethoxychrysoidine as adsorption indicator

p-Ethoxychrysoidine is studied as adsorption indicator in the direct titration of silver with iodide, bromide, thiocyanate and chloride at pH 4–5. The explanation given by Schulek and Pungor for the colour changes has been modified in the light of compound formation on the surface of the precipitate. The silver compound of p-ethoxychrysoidine has been isolated ; its behaviour provides a suitable explanation for the colour changes as well as the pH changes in the titrations.     

Dynamics of adsorption: A model calculation for HD activated adsorption

We have recently developed a model potential for the interaction of a diatomic molecule with a rigid solid surface. In this note, we report some results of classical trajectory studies designed to simulate the adsorption of a diatomic molecule. Model potentials with different barrier heights are used and a variety of different initial conditions for the incident molecule are studied. In common with gas-phase results, we find that translational energy is most effective in surmounting early barriers and enhancing adsorption.     

Percus-Yevick theory of adsorption

We study adsorption of hard sphere particles on to a plane surface with a delta function adsorption potential. The calculation takes account of exclusion via the Percus-Yevick approximation. At low and intermediate bulk adsorbate densities, both type II and type III BET adsorption isotherms can be found for the surface excess density and for the monolayer surface density. The surface excess isotherm agrees with an expansion of the exact surface excess isotherm to second order in the density. We mention some biochemical ramifications of the results.     

Thermodynamics of adsorption equilibrium

Russian Chemical Bulletin -     

Physical adsorption of gases

Summary Theoretically derived isotherms for monolayer and multilayer adsorption are used to interpret some earlier published experimental data. A satisfactory agreement is found in nearly all cases. To check the validity of the theoretical constant b it is plotted versus l/√T and this results in a straight-line dependence as it is foreseen by the theory. The b values found for the adsorption of n-butane on glass spheres are used to calculate the average settling times τ _L at different temperatures and subsequently τ _0(L) which is estimated to be ∼ 10⁻¹³ sec. It seems that the constant b is quasi-independent of the adsorbent properties which permits to obtain a characteristic plot for nitrogen isotherms.