Studies on the Physical Adsorption Equilibria of Gases on Porous Solids over a Wide Temperature Range Spanning the Critical Region—Adsorption on Microporous Activated Carbon

Adsorption equilibria of nitrogen and methane on microporous ( < 2 nm) activated carbon were measured for a wide temperature range (103‐298 K) spanning the critical region. Information relating to Henry constants, the isosteric heat of adsorption, and the amount of limiting adsorption were evaluated. All isotherms show type‐I features for both sub‐ and supercritical temperatures. A new isotherm equation and a consideration for the importance of the effect of the adsorbed phase volume allow this kind of isotherms to be modeled satisfactorily. The model parameter of the saturated amount of absolute adsorption (n⁰_t) equals the limiting adsorption amount (n^itm), leaving the physical meaning of the latter clarified, and the exponent parameter (q) proves to be an appropriate index of surface heterogeneity.     

High Pressure Adsorption Data of Methane, Nitrogen, Carbon Dioxide and their Binary and Ternary Mixtures on Activated Carbon

Adsorption equilibria of the gases CH₄, N₂, and CO₂ and their binary and ternary mixtures on activated carbon Norit R1 Extra have been measured in the pressure range 0 P 6 MPa at T = 298 K. Pure gas adsorption equilibria were measured gravimetrically. Coadsorption data of the three binary mixtures CH₄/N₂, CH₄/CO₂, and CO₂/N₂ were obtained by the volume-gravimetric method. Isotherms of five ternary mixtures CH₄/CO₂/N₂ were measured using the volumetric-chromatographic method. First, we present in a short overview the method and procedure of measurement. In a second part, the measured data of pressures, surface excess amounts adsorbed and absolute amounts adsorbed are presented and analyzed. In the last part of the paper the resulting pure gas adsorption data are correlated using a generalized dual-site Langmuir isotherm. Mixture adsorption can be predicted by this model using only pure component parameters with fair accuracy. Results are presented and discussed in several tables and figures.     

Measurement of Gas Mixture Adsorption Equilibria of Natural Gas Compounds on Microporous Sorbents

Physisorption equilibria of multicomponent gases on microporous solids like zeolites or activated carbons are considered. In view of lack of reliable and simple methods to calculate mixture adsorption isotherms from pure component data, experiments are still indispensable. An overview of classical and new methods to measure multicomponent gas adsorption equilibria is given. Some of the basic concepts like the Gibbs excess mass and the absolute mass adsorbed underlying these methods are discussed. Experimental data and a class of new adsorption isotherms for inhomogeneous microporous adsorbents of fractal dimension will be given in another subsequent paper (ADSO 635-98) by the same group of authors.     

在不同复盖度下二组分气体在硅胶上的吸附规律

通过测定不同复盖度下的丙酮－正己烷、苯－正己烷、甲苯－正己烷和正戊烷－正己烷四个二组分气体在硅胶组成吸附等温线，发现它们有着共同的规律，随着复盖度的增加，各体系的组成吸附等温线都逐渐向下靠近它们各自的气液平衡曲线，因此基本上可以反组分吸附相看成二组分液相，其中除了形成最低人沸点的丙酮－正己烷体系以外，其它三个体系的组成吸附等温基本上都可以理想溶液的相对挥发度议程式模拟得到。     

A Thermodynamic Model for Gas Adsorption Isotherms

In this paper based on the principle of solution thermodynamics for gas–solid equilibrium, a relation is developed to express gas adsorption isotherms. An activity coefficient model based on weight fraction of sorbate in the solid phase has been derived that well describes the behavior of various gases on different types of adsorbents. The proposed model has been evaluated and compared with four other models commonly used for gas adsorption isotherms in the literature. For 12 different systems at various isotherms for the temperature range −128 to 100°C and the pressure range 0.02 to 1219 kPa for 689 data points, the proposed model predicts equilibrium pressure with an average deviation of 5.3%, which is about half of the error obtained from other methods. The proposed model clearly outperforms other available methods such as the vacancy solution theory, the ideal adsorption solution model, and other various modified forms of the Langmuir isotherm. Unique features of the proposed model are its simplicity, generality, and accuracy over the entire pressure and temperature ranges.     

阳离子型聚氨酯-脲-胺在二氧化硅水溶胶听吸咐行为

研究了水溶性阳离子聚氨酯-脲-胺乙酸盐在球形、单分散的纳米二氧化硅水分 散注保的吸附行为。PUUA分子链在烯溶液中呈较舒展的构象，分子尺寸小于纳米氧 化硅的粒径。PUUA通过van der Waals作用力和氢键吸附在氧化硅表面。在稳喧吸 附后，等温吸附线呈线性上升，且没有极限值。吸附量随纳米氧化硅粒径的增大、 胶粒表面电荷的减少和电解质乙酸钢加入量的变化均以相同的斜率线性下降。 PUUA分子量增加，吸附量增加，且分子量大的PUUA优先吸附于氧化硅胶粒表面，静 电吸引是PUUA吸附至氧化硅溶胶粒表面的主要作用力。PUUA在氧化硅胶粒上的吸咐 使体系表现粘度下降，敏化作用使体系呈假塑性，而保护作用使体系呈胀流型。     

阴、阳离子表面活性剂混合体系在硅胶/水及硅胶/矿化水界面上的吸附

研究阴、阳离子表面活性剂混合体系(十二烷基氯代吡啶,辛基磺酸钠,辛基三乙基溴化铵/十二烷基苯磺酸钠)在硅胶,纯水和硅胶,矿化水界面上的吸附作用,探讨阴(阳)离子表面活性剂的存在对阳(阴)离子表面活性剂吸附作用的影响．结果表明,阴离子表面活性剂的存在基本不影响阳离子表面活性剂在带负电固体表面的吸附;而阳离子表面活性剂的存在却使本来吸附量就不大的阴离子表面活性剂在带负电的固体表面上不再吸附．在矿化水中阳离子表面活性剂的吸附量比在纯水中明显降低．从硅胶表面吸附机制解释了所得结果．     

Adsorption from Ternary Liquid Mixtures on Partially Dehydroxylated Silica Gel

The formation of mixed adsorbed layers has been tested for ternary mixtures containing a specifically adsorbed component—acetone and binary solvent benzene +n-hepane. The specific excess adsorption isotherms from the liquid phase were measured on silica gel samples partially dehydroxylated. The competition of liquid components for silica surface is discussed on the basis of changes in the mixed solvent composition.     

Characterization of Titania/Silica Gel by Means of Low-Pressure Nitrogen Adsorption

Adsorbents synthesized by grafting of titania onto mesoporous silica gel surfaces at different temperatures were studied by means of nitrogen adsorption–desorption and water desorption. The pore size distribution f(R_p) of titania/silica gel depends on the titania concentration (C_TiO2) and the temperature of titania synthesis. Nonuniformity of TiO₂ phase is maximal at a low C_TiO2 value (3.2 wt.% anatase deposited at 473 K), and two peaks of the fractal dimension distribution f(D) are observed at such a concentration of titania, but at larger C_TiO2 values, only one f(D) peak is seen. More ordered filling of pores and adsorption sites by nitrogen, reflecting in the shape of adsorption energy distributions f(E) at different pressures of adsorbate, is observed for adsorbent with titania (rutile+anatase) grafted on silica gel at a higher temperature (673 K).     

乙二胺硅胶复合材料对Zn2+的吸附特性

以γ-氯丙基三氯硅烷为偶联剂,将乙二胺偶合接枝在硅胶表面,合成对锌离子具有吸附作用的乙二胺硅胶复合材料（EDA/SiO2）,考察了Zn2+溶液pH值、初始浓度、吸附温度和吸附时间等因素对复合材料吸附性能的影响。 结果表明,在研究的溶液浓度及温度范围内,Zn2+溶液pH值对EDA/SiO2的吸附量影响显著,吸附的最佳pH值范围在3.0~5.5;Zn2+的吸附平衡数据符合Langmuir吸附模型,热力学数据显示,EDA/SiO2对Zn2+的吸附行为为一吸热且自发进行的过程,升高温度有利于吸附,并对此吸附行为作了解释;吸附动力学数据可用拟二级吸附动力学方程描述,得到的吸附速率常数与溶液初始浓度有关。     

在不同覆盖度下二组分气体在硅胶上的吸附规律

The composition adsorption isotherms (ya~xg curve) for acetone-n-hexane, benzene-n-hexane, toluene-n-hexane and n-pentance-n-hexane vapor mixtures on silica gel with different surface coverage (θ) at 25℃ were measured. The experimental results indicated that the ya ~ xg curves approached gradually down to corresponding binary liquid-vapor equllibrium curves with increasing of surface coverage. Therefore, the binary adsorbed phases are similarly with the binary liquid phase. Except for acetone-n-hexane system, which had a minimum boiling point, the composition adsorption isotherms of the other three binary systems could be simulated by equation of relative volatility.     

Selective Adsorption of Arsenic Ions on Silica Gel Impregnated with Ferric Hydroxide

Abstract

Selective adsorption of trace arsenite- and arsenate anions in an aqueous solution by ferric hydroxyde supported on silica gel particles was investigated. Silica gel particles were loaded with ferric hydroxide of the range of 1 – 3 wt. % in terms of Fe based on the dry gel, and the extent of adsorption of arsenite or arsenate ion measured by batch- and column processes, being the highest at pH 6 in the presence of diverse foreign ions. With the use of silica gel containing 3.3 wt. % Fe, as much as 0.07 m mol of arsenic per gram of dry gel was adsorbed.     

乙二胺硅胶材料对铜和锌离子的动态吸附

合成了胺基含量为1.35 mmol/g的乙二胺硅胶材料(EDA/SiO2),研究了EDA/SiO2对Cu2+和Zn2+的动态吸附及动态竞争吸附。结果表明,铜溶液流量和初始浓度对材料动态吸附性能有显著影响,随着溶液初始浓度的增大、流速的加快,穿透时间明显缩短。动态吸附实验结果符合Thomas模型,计算结果显示,铜溶液初始浓度由1.99 mmol/L增大至10.00 mmol/L时,模型平衡吸附容量q0从0.272 mmol/g增大至0.476 mmol/g,影响显著;流量对q0影响不显著。溶液流量和初始浓度对吸附速率常数kTh均有影响,随溶液流量增大、初始浓度的降低,速率常数值增大。在单一体系中,EDA/SiO2对Cu2+和Zn2+的工作吸附量分别为0.340和0.127 mmol/g,混合体系的吸附量均小于单一体系中的吸附量,并且对Zn2+的吸附量下降显著,表明EDA/SiO2对Cu2+的吸附能力强于Zn2+。6次循环实验表明,盐酸和氨水可对EDA/SiO2材料实现再生,再生后材料对铜的吸附容量和穿透时间的下降幅度不大,可重复使用。     

有机试剂键合硅胶对牛血清白蛋白的吸附行为

介绍几种偶氮，卟啉，三苯甲烷类有机试剂键合硅胶的合成方法，研究其吸附牛血清白蛋白（ＢＳＡ）的行为，研究结果表明：ＴＰＰ．ＳＧ吸附性能最佳，对ＢＳＡ吸附平衡１ｈ即可达到，最大吸附率为９０％，最大吸附容量为１２．２ｍｇ／ｇ。     

两种形貌的介孔SiO2对纤维素内切酶吸附性能的研究

以EDTA2-、SO42-作为反离子分别合成了具有管状和圆盘状结构的介孔SiO2,并测定了2种介孔SiO2焙烧至不同温度时的表面积、孔体积参数,及其等电点;通过752分光光度计在550nm处测定纤维素内切酶的吸光度,研究了2种形貌的介孔SiO2对纤维素内切酶的吸附性能,同时测定了固定酶的活性。结果表明,管状和圆盘状结构的介孔SiO2对纤维素内切酶的吸附等温线分别为Ⅱ和Ⅰ型;介孔SiO2焙烧至700℃时,两者皆为Ⅱ型;至850℃时,前者转化为Ⅰ型,而后者转化为Ⅴ型。吸附等温线类型与介孔SiO2的结构、等电点以及酶分子尺寸与介孔尺寸的相匹配有关。酶经过介孔SiO2吸附固定后,稳定性明显提高;其中,管状结构的介孔SiO2对酶具有最大的负载量,但固定酶的活性却较低。     

述评超临界温度气体在多孔固体上的物理吸附

本文简要述评超临界温度条件下气体在多孔固体上物理吸附平衡问题提出的背景, 工程应用, 及其理论基础方面存在的问题。     

Correlation and Calculation of Multicomponent Adsorption Equilibria Data Using a Generalized Adsorption Isotherm

Enhanced by the need for reliable and accurate data of multicomponent gas adsorption equilibria on porous solids like activated carbons or zeolites, a new method to measure and correlate coadsorption equilibria has been developed. This method is a combination of gravimetric or volumetric measurements of the total load of pure or multicomponent adsorbates (Staudt, 1994; Gregg and Sing, 1982) and a correlation and calculation procedure using a new adsorption isotherm (AI) (Keller, 1990). This AI is thermodynamically consistent and describes adsorbates with fractal dimension for single- or multicomponent systems and load dependent adsorption energies. This method allows calculation of partial loads of multicomponent coadsorption equilibria from pure component data and the total loads of the mixture adsorption equilibria. This will be demonstrated for binary and ternary adsorption equilibria of CH₄, C₂H₄ and C₂H₆ on activated carbon (Reich et al., 1980).     

Adsorption of SO2 on alumina

The adsorption of SO₂ on alumina used in the aluminium industry, the so-called smelter-grade alumina, was studied in the temperature range 15–120°C. It was found that at temperatures lower than 40°C, sulphur dioxide was bonded to alumina reversibly by physical forces, and the adsorption could be described satisfactorily by the Langmuir adsorption isotherm. The heat of adsorption was estimated to be −33 kJ mol⁻¹. At temperatures ranging from 80°C to 120°C, which prevail in dry scrubbers in the aluminium industry, the heat of adsorption was determined to be −56 kJ mol⁻¹. When SO₂ was adsorbed at temperatures higher than 80°C, about 30 % of the SO₂ could not be desorbed even if the samples were heated up to 250°C. In the presence of SO₂ and oxygen, the formation of sulphate was observed at temperatures above 90°C.     

Measurement and Modeling of Water Vapor Adsorption on Zeolite 4A—Equilibria and Kinetics

The adsorption of water vapor on Zeolite 4A has been analyzed. Both equilibrium and kinetics are examined. The equilibrium is measured with a static-volumetric method in a wide range of partial pressure and temperature and is modeled by several conventional approaches and a new type isotherm model, which fitted the obtained data best. Kinetics are determined by measuring breakthrough curves. The breakthrough curves are matched by a detailed model based on a modified linear driving force (LDF) approximation for the mass exchange. An analytic expression for the corresponding LDF-coefficient is designed in order to describe its dependency on water concentration, temperature and pressure. For the practical range of operating conditions the dependency on concentration can be described by the nonlinearity of the adsorption isotherm. The dependency on temperature and pressure corresponds to that of molecular diffusion. The presented data and models for equilibria and kinetics provide a basis for modeling and optimizing air-drying processes containing Zeolite 4A.An erratum to this article can be found at     

Adsorption of Metallocenes on Silica

The adsorption of the metallocenes ferrocene, doubly deuterated ferrocene, cymantrene and nickelocene, as well as molybdenum hexacarbonyl, proceeds in the absence of a solvent. Large single pieces of silica gel were placed in contact with the solid metallocenes and the adsorption process was visualized on a macroscopic scale and the maximal loadings were determined. ¹H, ²H, and ¹³C solid‐state NMR studies confirmed fast isotropic reorientation of the surface‐adsorbed metallocene molecules within the pores of the silica. All prevalent anisotropic solid‐state interactions were averaged out. The solid diamagnetic and paramagnetic materials were amenable to measurements with a standard solution NMR instrument. All metallocenes adsorbed in a monolayer. In the case of ferrocene and cymantrene, different ¹³C MAS signals were obtained for the cyclopentadienyl ring carbon nuclei and assigned to one ring interacting with the surface and one ring pointing away from it. The relative adsorption strengths of ferrocene on different silica supports, nanotubes, and activated carbon were determined by a novel straightforward method recording the desorption temperature. The reversibility of adsorption has been demonstrated by competition experiments using ferrocene, doubly deuterated ferrocene, and cymantrene. Adsorbed nickelocene could be reduced to small Ni⁰ aggregates on the surface and the catalytic activity of the resulting material for the cyclotrimerization of phenylacetylene was proven.