Effects of non-ideal adsorption equilibria of gas mixtures on column dynamics

A theoretical study has been made for simulating the dynamic behavior of non-ideal gas mixtures in an isothermal fixed-bed adsorber. A mathematical model was developed which takes into account the non-ideality of adsorbable species on the adsorbed phase under equilibrium. The model is based on both the real adsorbed solution theory (RAST), which incorporates the activity coefficients in the multicomponent isotherm equations to account for the deviations from ideality, and the linear driving force (LDF) model for representing diffusion resistance inside the adsorbent particles. To describe the effect of non-ideal adsorption equilibrium of gas mixtures on the breakthrough curves, we considered several model mixtures of binary and ternary components which exhibit non-ideal behavior with azeotropic crossovers in the composition domains at equilibrium. Sample calculations of a fixed-bed adsorption were done with various inlet gas compositions of binary and ternary mixtures, respectively, at a fixed total concentration. From the calculation results, it was shown that the order of breakthrough curves could be changed at a certain value of inlet gas composition ratio. This result implies that the dynamic behaviors of fixed-bed adsorption are greatly influenced by multicomponent equilibrium models. Furthermore, the reversal phenomenon of breakthrough curves could not be simulated by the ideal adsorbed solution theory (IAST).     

Multicomponent adsorption equilibria of phenols on activated carbon

Multicomponent adsorption equilibria of phenols on activated carbon were predicted by the ideal adsorbed solution (IAS) theory and results were compared with those calculated from two different Freundlich-type isotherms. Although some deviations between measured and calculated results are observed, the IAS theory permits rapid and relatively accurate predictions of adsorption equilibria for two-and three-component systems comparing with other isotherms. The results obtained show that the IAS theory is quite suitable for the extended application to multicomponent adsorption systems.     

Enhanced separation of highly non-ideal mixtures with extractive heterogeneous-azeotropic distillation

The distillation based separation can be extremely complex if highly non-ideal mixtures are to be separated. In spite of different successfully applied unit operations there is still a possible way to improve the distillation technique and widen its toolbar. A new improvement in this area is the development of the extractive heterogeneous-azeotropic distillation (EHAD). This unit operation includes the merits of extractive- and heterogeneous-azeotropic distillations in one unit without extra material addition. Our work supports EHAD features with successful experiments compared with modelling and comparison with other separation structures proving that the application of EHAD makes the separation of extremely non-ideal mixtures possible on an easy, powerful, energy saving, and cost efficient way.     

Multicomponent adsorption equilibrium of ethylene,propane, propylene and CO2 on 13X zeolite

Experimental adsorption isotherms of binary, ternary and quaternary mixtures of ethylene, propane, propylene and CO₂ on 13X zeolite have been obtained at 293 K. Experimental data of mixtures were fitted to three theoretical models, the ideal adsorbed solution (IAS), real adsorbed solution (RAS) and spreading pressure dependence (SPD) models to reproduce and predict equilibrium data. With the SPD model, two other temperatures were also studied, 279 and 308 K, in order to calculate the model parameters. The best models for binary and multicomponent mixtures showing the highest deviation from ideality were RAS and SPD, with RAS better than SPD for ternary mixtures.     

Prediction of adsorption and separation of water–alcohol mixtures with zeolite NaA

A new effective pair potential was parameterized for the prediction of the adsorption of mixtures of water and methanol or ethanol in zeolite NaA. The pressure dependence of the adsorption properties such as equilibrium amount of adsorption and isosteric heat of adsorption were calculated at 378 K by molecular simulations. Significantly higher adsorption selectivities were found for water in a wide range of pressure as compared with previous simulation results. The verification of the new model was made by calculating also some structural characteristics of the system.     

沸石分子筛吸附性能的测定方法

介绍了沸石分子筛吸附性能常用的测定方法,综述了近年来沸石分子筛吸附性能的研究进展。认为在众多方法中,气相色谱法、智能重量分析技术、频率响应法、分子模拟技术等以其方便有效的优点,是测定沸石分子筛吸附性能的重要手段。     

The adsorption of methane-ethane mixtures on activated carbon

The single component adsorption of methane and ethane and also the adsorption of binary mixtures of methane and ethane have been studied in a small fixed isothermal bed containing activated carbon. Results indicate that an empirical Langmuir isotherm fits the experimental data for single components. An extended form of the empirical Langmuir isotherm, in which the parameters are obtained from single component data, satisfactorily describes the adsorption of binary mixtures. The potential theory of Polanyi is also helpful in extending the experimental data. Breakthrough curves of both components from a diluted feed of methane and ethane could be predicted with good precision for the two activated carbons studied. Furthermore, the concentration waves of the components were sufficiently spaced to suggest that these carbons may be of use as a separating agent for methane-ethane mixtures.     

沸石改性及其吸附性能研究

对沸石进行降低硅铝比改性，改性沸石对H2O，H2S，NH3的饱和吸附量分别为16.8％，18．2mg/g，71．1mg/g，而只进行过焙烧的沸石为9．3％，11．7mg/g,38.4mg/g，表明沸石经降低硅铝比改性后，对H2O，H2S，NH3的吸附量大大提高。     

Multicomponent adsorption calculations based on adsorbed solution theory

A new calculation method for multicomponent adsorption equilibria was proposed based on the real adsorbed solution theory (RAST) and the concept of arbitrary isotherm. According to the latter, we assigned a respective isotherm, which gave the best fit to single-component equlibrium data, to each component, instead of using a specific type of isotherm for all adsorbates as in most previous works. This enabled us to evaluate the spreading pressure for pure components more accurately, which will be used in multicomponent adsorption calculations later. The usefulness of the proposed method is verified by carrying out sample calculations for ternary data reported in literature.     

Thermodynamics of hydrogen adsorption on the zeolite Ca-Y

Variable-temperature infrared spectroscopy was used for a thermodynamic study on hydrogen adsorption on the zeolite Ca-Y. Adsorption renders the H–H stretching mode infrared active, at 4078 cm⁻¹; and simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, over a range of temperature, allowed standard adsorption enthalpy and entropy to be determined. They resulted to be ΔH°= −15.0(±1.0) kJ mol⁻¹ and ΔS° = −127(±10) J mol⁻¹ K⁻¹, respectively. These relatively high values of adsorption enthalpy and entropy are discussed in the broader context of corresponding data for other hydrogen adsorbents.     

Multicomponent phase equilibria of thin liquid films and their vapour

Subject of the paper are multicomponent phase equilibria between extremely thin liquid films and their vapour phase on curved or planar solid surfaces. The solid surface is either heated or cooled, so that the liquid films are evaporating or the vapour is condensing.The curvature of the film surface and long range molecular forces due to the van der Waals attraction acting over distances of about 0.2- between solid and liquid film can lead to a composition shift in liquid and vapour phase compared to the composition that would be observed at planar and not extremely thin liquid films in equilibrium with their vapour phase.The Kelvin equation for the interfacial pressure is derived, as well as the equations for the composition shift. As a numerical example shows the van der Waals forces considerably influence the pressures at the liquid-vapour interface. Responsible for the composition shift is a dimensionless thermodynamic quantity . For small values D_i→0, liquid-vapour phase equilibria become identical with those of planar surfaces. For D_i?0 the vapour phase contains less and for D_i?0 more of the lighter volatiles than planar interfaces.     

Prediction of mixed-gas adsorption equilibria from pure component adsorption isotherms

Using only a single binary interaction parameter per adsorbate-adsorbate pair, the adsorption nonrandom two-liquid theory successfully correlates binary gas adsorption experimental data and predicts multicomponent gas adsorption equilibria. This work estimates the binary adsorbate–adsorbate interaction parameters from pure component isotherms and shows very promising agreement with the binary interaction parameters identified from regression of binary gas adsorption data. The results support the feasibility to predict binary and multicomponent gas adsorption equilibria from pure component isotherms for various adsorbents including silica gel, activated carbon, zeolites, and metal–organic frameworks.     

Calculation of multicomponent distillation of non-ideal mixtures by a short-cut method

The Smith-Brinkley method has been modified for use in computing non-ideal multicomponent distillations. The procedure proposed is of particular advantage for rapid calculating hydrocarbon fractionators.     

沸石的改性处理及吸附性能研究

介绍了沸石改性的方法,讨论了影响沸石吸附性能的因素.实验表明,在废水温度为25℃,pH为6,Cd2 的初始质量浓度为50 mg/L,吸附剂的用量为20g/L,吸附时间为120 min的条件下,改性沸石对镉离子的去除率达到99.12%.     

疏水硅沸石吸附1,3-丙二醇的研究

FX-Ⅱ型沸石对1,3-丙二醇单组分溶液中1,3-丙二醇的静态饱和吸附量达到121.1 mg/g;在1,3-丙二醇和甘油的混合溶液中,研究了甘油质量浓度、吸附时间、吸附温度和盐离子质量浓度对1,3-丙二醇吸附的影响,实验结果表明高的甘油质量浓度对1,3-丙二醇吸附影响较大,吸附时间为14 h时1,3-丙二醇吸附达到平衡,低温及低盐离子质量浓度有利于1,3-丙二醇吸附;对实际发酵液的静态吸附结果表明,增大发酵液pH值可以减少有机酸对1,3-丙二醇的竞争吸附;pH值为7时,1,3-丙二醇吸附量达到102.5 mg/g;筛选了与吸附剂相关的脱附剂,用体积分数50%的乙醇解吸,解吸率达到86%。在此基础上初步研究了沸石对发酵液中1,3-丙二醇的动态吸附,1,3-丙二醇解吸率为82%。与传统的蒸馏法相比,沸石吸附法工艺简单,具有较大的研究和应用前景。     

Ignition temperature of coal 3. Multicomponent coal mixtures

The ignition temperature of three-component mixtures is determined. The mixtures contain coal of different metamorphic development, in various proportions. It is found that the actual ignition temperature differs from the values calculated on the basis of the sum rule; the actual ignition temperature is lower. A formula is derived for predicting the ignition temperature of three-component and multicomponent mixtures.     

Correlation of adsorption equilibria of CO2 on activated carbon

Adsorption isotherms of CO₂ on three types of activated carbon were measured over wide temperature range, from 298‡K to 194.5‡K. The adsorption equilibria were correlated according to the Dubinin-Radushkevich equation. The correlations for the carbons in temperature indifferent characteristic curve were yielded by the use of pressure variable density of adsorbed phase in deriving adsorption volume. The pressure variable density, which is the density of saturated liquid CO₂ under given equilibrium adsorption pressure, was determined from reduced density correlation and empirical vapor pressure function of CO₂. Density and vapor pressure of quasi-liquid state CO₂ at below the triple point were evaluated by extrapolation of the correlations.     

Gas-liquid equilibria in mixtures of hydrogen and thianaphthene

Gas-liquid equilibrium conditions in binary mixtures of hydrogen and thianaphthene were experimentally determined at temperatures of 190 to 430°C and pressures to 250 atm in a flow apparatus. The same apparatus was also employed to measure the vapor pressure of thianaphthene. Comparisons of the new mixture data with Chao-Seader and Grayson-Streed correlations show that both correlations predict the thianaphthene equilibrium ratios well but are in error by up to about 45 and 35% respectively for K-values of hydrogen.     

改性沸石对气态汞吸附的实验研究

为了获得消耗量小、性能高效的燃煤烟气脱汞吸附剂,采用活性MnO2浸渍、FeCl3浸渍和不同温度下渗硫等方法,对沸石进行了改性,制得一系列改性沸石吸附剂。采用固定床吸附的方式,对吸附剂在不同条件下的吸附效果进行了测试,筛选出一种高效、廉价的MnO2浸渍沸石吸附剂,和原沸石吸附剂相比,改性沸石吸附剂对汞蒸气的吸附能力有较大提高,有效吸附时间大大增加,在有效吸附时间内,穿透率大大降低。改性后的沸石吸附能力大大提高的原因在于其吸附过程中,除了物理吸附,还发生了化学吸附。     

甲烷在石墨化炭黑上吸附平衡的分子模拟

采用GCMC法对不同温度和压力下纯CH4在石墨化炭黑上的吸附平衡进行了分子模拟研究,选用Lennard-Jones 12—6势能函数和联合原子力场参数（TraPPE）对体系进行势能计算,并将吸附平衡预测结果与实验数据进行了比较分析。结果表明,在所研究的温度范围内,除了在低压的一定区间外,GCMC模拟结果在中压和高压条件下与实验数据基本吻合,表明采用GCMC方法模拟甲烷分子在石墨化炭黑上的吸附平衡数据是可以进行准确预测的。在此基础上,利用模拟的吸附平衡数据计算不同温度下CH4的Henry常数进而到得极限吸附热,计算结果与实验数据接近。