New method for the determination of adsorption space volume for sorbents with an arbitrary porous structure from excess gas adsorption isotherm measurements

A new method for the determination of adsorption space volume has been proposed, which is applicable to adsorbents with an arbitrary porous structure, including nonporous adsorbents with open surfaces. The method is based on the use of an experimental excess adsorption isotherm measured over a wide range of pressures in the equilibrium gaseous phase (as a rule up to 100–150 MPa) and the absolute adsorption isotherm equation with unspecified parameters in the most general form, given by statistical physics. The method has been tested for a number of adsorption systems, and it has been found that the result was always unambiguous, correct, and stable in the sense of input data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2381–2385, December, 1995.     

A simplified integral equation for adsorption of gas mixtures on heterogeneous surfaces

Summary The multiple integral representing the overall isotherm for adsorption of gas mixtures on heterogeneous surfaces is transformed to a single integral, which is promising for predicting the mixed-gas adsorption by means of single-gas adsorption parameters. This transformation is possible when the adsorption energies of components for various adsorption sites show a certain type of correlation.

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Eine vereinfachte Integralgleichung für die Adsorption von Gasmischungen auf heterogenen Oberflächen

Zusammenfassung Das multiple Integral, das die Adsorption von Gasmischungen auf heterogenen Oberflächen darstellt, wurde zu einem einfachen Integral transformiert, das zur Voraussage der Adsorption von Gasgemischen mittels der Einzelgas-Adsorptionsparameter geeignet sein sollte. Diese Transformation ist dann möglich, wenn die Adsorptionsenergien der Komponenten einem bestimmten Korrelationstyp angehören.

     

Expressiveness of Adsorption Measurements for Characterization of Zeolitic Materials—A Review

This critical review concerns the author's results and experience in adsorption studies on molecular sieves comprising crystalline microporous aluminosilicates and aluminophosphates as well as amorphous mesoporous aluminosilicates. The discussion is mainly based on three distinctly different standard adsorbates: nitrogen, benzene, and water. The highlights or advantages and the shortcomings or limitations are considered from the points of view of the experimental procedures and expressiveness or concluding. The results are compared to several other zeolitic materials and adsorbates. Adsorption technique is a valuable tool for characterization of the molecular sieves. Since the measurements are very sensitive to modification of the materials, the investigations require sufficiently thorough procedures and the results a careful interpretation. A comparison between the results for larger series of materials yields valuable conclusions that are much more expressive than those from a single measurement or material. Dedicated to the memory of Professor Wolfgang Schirmer.     

超临界氢在活性炭上的吸附等温线研究

通过７７－２９８Ｋ范围内氢在ＡＸ－２１活性炭上的吸附数据，探讨如何用普通Ｉ－型等温线模型处理超临界条件下的吸附等温线，以获取关于超临界吸附系统的正确信息，结果表明，Ｌａｎｇｍｕｉｒ方程虽然可用来表达实验数据，但不能提供关于该吸附系统的任何可靠信息，Ｖｉｒｉａｌ方程虽不是整组数据的最好模型，但却能够可靠地确定Ｈｅｎｒｙ定律常数，然后可从ｖａｎｔＨｏｆｆ标绘决定等量吸附热，通过将实验数据拟合到Ｄｕｂｉ     

Determination of curves characterizing the texture of microporous adsorbents

The possibility of determining the curves characterizing the texture of microporous absorbents on the ground of the Dubinin-Stoeckli (DS) equation has been discussed. The DS equation has been shown not to have any universal character. A more general equation of the adsorption isotherm including all cases of isotherms encountered in adsorption studies has been derived.     

A proposal for the estimation of binary mixture activity coefficients from surface tension measurements throughout the entire concentration range

A method to estimate the concentration dependence of the bulk activity coefficients of both binary mixture components from experimental surface tension data covering the whole concentration range is presented. To this end, high-quality experimental surface tension data as a function of the concentration, paying special attention to the diluted regions, are needed. The method is based on the application of equilibrium conditions to the surface chemical potential arisen from the Volmer equation (the simplest non-ideal surface EOS) and to the bulk chemical potential coming from the three-suffix Margules equation for activity coefficients. It can be applied provided that positive aneotropy is not present and the second derivative of the surface pressure as a function of the mole fraction is not positive in any composition region, which means rather unrestrictive conditions. In order to test the method, a compilation of 25 systems for which surface tension and activity coefficient data are simultaneously available in the literature was performed, turning out that most of them involved water. It was found that surface tension data with enough concentration coverage and good quality are really scarce, which makes the development of this kind of methods difficult.     

On the Correct Use of the Dubinin-Astakhov Equation to Study the Mixed-Gas Adsorption Equilibria

This paper presents the possibilities of Integral Equation (IE) approach to study the mixed-gas adsorption equilibria. As a result, the generalizations of Dubinin-Astakhov equation for the case of mixed-gas adsorption are presented. These new equations are examined using a few adsorption systems recently published in literature.     

二元溶液吸附方程的研究

本文运用统计热力学方法,在分子作用理论基础上应用均一位势模型与理想势阱模型第一次导出了二元溶液吸附量与溶液组成、分子微观参数之间的关系,并采用文献数据给予验证。结果表明本关系式能如实反映有机酸、醇、苯酚、无机碱在炭、硅胶表面的吸附特性,并精确地计算了骨炭、水、醋酸体系中醋酸的吸附量。此公式采取不同数值的参数能描绘出Ⅰ、Ⅱ、Ⅲ三种类型的吸附等温线。本文运用统计热力学方法不但较深入地研究了发生在液－固界面的吸附现象,而且为液相色谱热力学奠定了理论基础。     

Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

Adsorption integral equation via complex approximation with constraints: The Langmuir kernel

The relationship between the measured adsorption isotherm and unknown energy distribution function is described by so‐called adsorption integral equation, a linear Fredholm integral equation of the first kind. We consider the case of the Langmuir kernel when the equation can be reduced to the Stieltjes integral equation. A new method for solving the Stieltjes equation is developed. The method is based on the ideas of complex approximation with constraints. The numerical algorithms constructed on the base of this method allow reduction of the problem under consideration to linear or linear‐quadratic programming problems. The method is compared with the usual regularization methods. The obtained results can be useful for the evaluation of the experimental adsorption energy distribution from experimental data. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 191–200, 2000     

The multi-species surface-micelle model for surfactant adsorption and the BET equations

Based on the multi-species surface micelle model, the adsorption isotherm equations are derived which are identical to the BET equations. Some of the surfactant adsorption phenomena are explained on this basis.     

Monolayer adsorption isotherms and a disordered medium model

A model of disordered medium is proposed to describe the monolayer adsorption isotherm on heterogeneous surfaces. The model is based on the premise that adsorption medium consists of separate regions in each of which there is a permanent local equilibrium constant, the character of the changes of which is determined by the disorder parameter of the medium. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 189–193, May–June, 2006.     

搅拌下吸附富集时不可逆过程峰电流方程式

线性变势吸附伏安法是一种简便的痕量分析方法。本文讨论了此方法中不可逆过程的峰电流方程式,并对其作了验证。仪器与试剂 83-2.5型多阶自动新极谱仪(各档灵敏度已校正),LZ_3-100型函数记录仪,Metrohm E410型悬汞电极,所用试剂同文献[1]。实验方法在含0.1mol/dm~3NH_3/NH_4Cl,1×10~(-4)mol/dm~3丁二肟,pH=9.2的Co(Ⅱ)溶液中用氮气除氧并搅拌。由于配合物的稳定常数很大(β=10~(17)),可以认为Co(Ⅱ)A_2的浓度等于Co(Ⅱ)的浓度。由于电势负于-1.20V时Co(Ⅱ)A_2在电极上不吸附,因此先将电极置于-1.5V,一当从悬汞电极中旋出新的汞滴,立即将电势恒定于-0.8V,富集一定时间,然后关闭搅拌器,30秒后,电势以100mV/s的速度向负方向扫描至-1.3V,同时     

SAPO-34上甲醇及二甲醚吸附等温线及吸附热测量与分析(英文)

在25,60和100°C下分别测定了甲醇及二甲醚在SAPO-34分子筛上的吸附等温线,同时用微量热法测定了微分吸附热与覆盖率的关系曲线(量热线),提出了吸附数据需要利用双吸附位Langmuir方程拟合,并获取了相应的吸附参数.对比测得的吸附等温线与量热线发现,在一定压力下,当甲醇及二甲醚在SAPO-34上达到一定吸附量后,随着吸附质分压增加,量热线快速下降,而吸附等温线显示出吸附量仍然继续增加.由此推断,在SAPO-34分子筛上存在两种吸附位——常规吸附位及弱吸附位,其中弱吸附位在高分压下继续吸附.如缺乏量热数据提供的常规吸附位饱和吸附量数据,对吸附等温线进行单吸附位拟合获取吸附参数极易导致错误结果,尤其是当吸附质分压较高时.建议采用双吸附位Langmuir方程,参照量热线提供的常规吸附位的饱和吸附量,通过拟合可以获得两种吸附位的吸附参数.     

Method for Thermodynamic Description of an Elastically Deformed Electrode, Based on Relating Its Extensive Surface Characteristics to a Strainless Electrode

A theoretical approach to thermodynamic describing elastically deformed electrodes made of isotropic materials is suggested. The approach is based on considering the surface of a strainless electrode as a reference one. A surface analog of the Lame elastic constants is introduced. Dependences of the Shuttleworth equation and the Gibbs adsorption equation on the Lame elastic constants characterizing the surface are found in an explicit form.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 993–996.Original Russian Text Copyright © 2005 by Grafov, Paasch.     

Sorption Mechanism of Cadmium from Aqueous Solution on Iron Sulphide

The characterization and adsorption studies of Cd²⁺ on FeS were performed. Adsorption of Cd²⁺ from aqueous solutions on synthetic iron sulphide (FeS) was investigated as a function of pH (5–7) and temperature (303–323 K). It was found that the iron sulphide (FeS) had adsorptive properties comparable with those of other adsorbents reported in the literature. The sorption of Cd²⁺ was observed to increase with the increase in pH but not strongly sensitive to temperature. The adsorption data fitted both the Kurbatov and Langmuir adsorption models. In addition, ΔG^? values were calculated from the values of the binding constant, which showed that the cadmium adsorption process was spontaneous in nature.     

A Simple Frontal Analysis Equation to Determine the Adsorption Parameters of Solute Molecules on Different Adsorbents

A simple frontal analysis equation to determine the adsorption parameters of solute molecules on different adsorbents was presented. It gives the relationship between the average breakthrough time and the feed solute concentration, and by using its linear form, two important parameters, the thermodynamic equilibrium constant KSL for solute adsorption on the surface of adsorbent and the number nt of total adsorption sites distributed on the surface of adsorbent, can be simultaneously determined. The frontal analyses for some aromatic hydrocarbons on RP-C18 reversed-phase medium, and some protein molecules on RP-C18 reversed-phase, WCX-1 cation-exchange, PEG-400 hydrophobic and Chelating Sepharose Fast-flow separately chelated with Zn^2＋ or Cu^2＋ media, were separately carried out to test this equation and their adsorption parameters KSL and nt were separately obtained. The results show that all these frontal analysis data can be well described by this frontal analysis equation. For all of these frontal analysis systems, their parameters nt can separately approximately keep constant and they are independent of solute molecules used, while their parameters KSL are dependent upon both of the media packed in frontal analysis column and the solute molecules used.     

Thermodynamic issues associated with combined cyclic voltammetry and wafer curvature measurements in electrolytes

A thermodynamic framework has been provided for the interpretation of combined cyclic voltammetry and surface stress measurements, the latter being obtained from wafer curvature or beam deflection measurements of a solid electrode as a function of applied potential (so-called voltstressograms). Firstly, the derivation of electrocapillarity equations for solid electrodes has been critically reviewed by starting from the Gibbs adsorption equation appropriate for solid–electrolyte interfaces. This allowed us to demonstrate the critical importance of elastic surface strain in the thermodynamic boundary conditions of the partial derivatives intervening in the interpretation of voltstressograms. From these considerations, it was shown for the first time that the electrocapillarity equations for solid electrodes are not appropriate for describing the variation of surface stress with potential obtained from wafer curvature measurements, because such measurements are intrinsically incompatible with the constant strain condition implied in the electrocapillarity equations. An alternative explanation is provided for the experimentally observed proportionality between the current density, measured in cyclic voltammograms, and the first derivative of surface stress with respect to potential, obtained from voltstressograms.     

Sulfate adsorption and surface precipitation on a volcanic ash soil (allophanic andisol)

Sulfate strongly adsorbs on metal oxides and soils with variable charges. However, its surface precipitation has not been clearly evaluated and its adsorption mechanism has been in dispute. In the present study, an allophanic andisol, a typical volcanic ash soil having both negative and positive variable charges, was used to identify the adsorption mechanism of sulfate. Sulfate adsorption isotherms were obtained by a batch method at pH values of 4, 5, 6, and 7 in a wide range of concentrations in an Na-H-SO(4)-OH system. Theoretical isotherms were applied to the measured values for the evaluation. The surface precipitation was detected by the measured adsorption isotherms, and the BET isotherm confirmed the presence of multilayer adsorption. Stronger and weaker adsorption sites were suggested by using the Langmuir isotherm for the monolayer adsorption. The adsorption energies obtained from the Langmuir equation and recent spectroscopic analysis suggested that the stronger adsorption corresponded to an inner-sphere surface complex and that the weaker adsorption corresponded to outer-sphere surface complexation. The BET and Langmuir equations showed three types of adsorption mechanisms for the sulfate adsorption on the soil.