Adsorption of monosaccharides, disaccharides, and maltooligosaccharides on activated carbon for separation of maltopentaose

To study separation of maltopentaose from maltooligosaccharide mixtures, we investigated the adsorption equilibrium and kinetics of monosaccharides (fructose, galactose, and glucose), disaccharides (sucrose, maltose, and lactose), and maltooligosaccharides (maltotriose, maltotetraose, and maltopentaose) on activated carbon. The adsorption amount of maltose consisting of two glucosidic units was the highest among the nine adsorbates studied. It was also found that the different chemical structure of disaccharides with the same molecular weight highly affected the adsorption amount compared to that of monosaccharides. A simple but practical dynamic model was proposed, based on both the ideal adsorbed solution theory (IAST) for multicomponent equilibria and the surface diffusion model for intraparticle mass transport. In spite of its simplicity, the proposed dynamic model successfully simulated the adsorption breakthrough curves up to ternary mixtures.     

Multicomponent adsorption equilibria of highly non-ideal mixtures: The case of chloroaromatic mixtures on zeolite

The adsorption equilibrium behaviour of binary, ternary and quaternary vapour mixtures involving ortho- and para-chlorotoluene, toluene and chlorobenzene on zeolite Ca-X at atmospheric pressure and 230°C has been investigated. Since under these operating conditions the adsorbent surface is saturated and the adsorbed molecules interact strongly with each other, these systems exhibit significant deviations from ideal behaviour. A thermodynamic non-ideal adsorption equilibrium model is presented, which, based only on binary interaction parameters, allows for the prediction of multicomponent equilibrium data. The role of such a model in the simulation of the dynamic behaviour of fixed-bed separation columns is investigated. A surprisingly strong effect of the desorbent on the selectivity of the two isomers is found.     

Adsorption of phenols in a fixed-bed adsorber charged with polymeric sorbents

Adsorption of phenols onto a polymeric sorbent, SP206, was carried out in a fixed-bed adsorber and the saturated bed was regenerated by using 0.05 N sodium hydroxide solution to get information for a cyclic adsorption process as an alternative for the activated carbon process. Furthermore, a simple dynamic model for simulating the dynamic behavior of multicomponent adsorption systems was proposed based on both the ideal adsorbed solution theory (IAST) for multicomponent equilibria and the linear driving force approximation (LDFA) for intraparticle mass transport. In spite of its simplicity, the proposed dynamic model successfully simulated breakthrough curves up to a three-species mixture.     

Single component and competitive adsorption of propane, carbon dioxide and butane on Vycor glass

Equilibrium of gas phase adsorption on Vycor glass has been investigated. Adsorption isotherms for propane, carbon dioxide and butane as pure gases, binary mixtures and ternary mixtures were determined experimentally as a function of temperature using a volumetric method. The single-component isotherms were described with the Langmuir and Freundlich equations. Additionally, a second order isotherm based on statistical thermodynamics and an isotherm equation based on vacancy solution theory taking into account real phase behavior were used for fitting single-component equilibrium data. In order to describe the measured partial isotherms for binary mixtures, at first simple extensions of the single-component isotherm models were used, i.e., the conventional competitive Langmuir model and a multi-Freundlich equation based on the ideal adsorbed solution theory (IAS). Since these two simple isotherm models failed to represent the unusual competitive behavior observed, three model extensions using additional mixture parameters were applied, i.e., two modified multi-Langmuir equations based on: (a) statistical thermodynamics and (b) vacancy solution theory and a modified multi-Freundlich IAS model correcting spreading pressure uncertainties. These three model equations were found to be capable to describe the observed behavior better. Finally, the measured partial adsorption equilibrium data of the ternary system were correlated based on the extended equations using the determined additional binary parameters. The results obtained reveal the difficulty to predict accurately multi-component adsorption equilibria.     

Schnelle Abschätzung des Durchbruchsverhaltens von konkurrierend adsorbierenden Komponenten

Selective adsorption using fixed-bed adsorbers is an important and widely used separation process. Breakthrough curves are an essential factor in the design of adsorbers. The aim of this article in the section “How to: Elegant solutions for practical problems” is to estimate rapidly the position of breakthrough curves in fixed-bed adsorbers. To illustrate the breakthrough behavior of single components and mixtures two literature examples are used and the equilibrium theory of adsorption is explained. The potential of the equilibrium theory for predicting mean retention times and intermediate plateaus generated by competing components is demonstrated.     

Breakthrough behaviour of a binary gas mixture with azeotropic adsorption equilibrium

This contribution reports on the breakthrough behaviour of binary gas mixtures with ideal and non-ideal multicomponent adsorption equilibria. Investigations were carried out on mixtures CO₂/C₂H₄ and C₂H₄/C₂H₆, both adsorbed on molecular sieve 5A (ms5A). The adsorption equilibrium of the system CO₂/C₂H₄/ms5A may exhibit azeotropic behaviour, which subsides with decreasing active pressure (= sum of partial pressures of adsorbable components) or on raising the temperature. In contrast, the system C₂H₄/C₂H₆/ms5A maintains its ideal behaviour also at higher active pressures or lower temperatures. Attempts to calculate the non-ideal adsorption equilibrium from measured single component isotherms have failed when known models were applied. The investigation of the effect of azeotropic equilibrium on the fixed bed adsorption led to intersecting breakthrough curves of the two components. This behaviour is due to a displacement of equilibrium caused by the change in the active pressure and partial pressures, and a superposed temperature effect. This can be shown by calculating the breakthrough curves with the equilibrium model.     

EXPERIMENTAL DETERMINATION AND PREDICTIONS OF BREAKTHROUGH CURVES IN A FIXED BED OF SILICA GEL USING THE TRANSFER UNIT APPROACH

A semi-empirical model was developed to predict the breakthrough curves of moisture adsorption on silica gel under different operating conditions. The model requires only the basic physical and transfer properties of the flowing gas stream. Experimental breakthrough curves were determined in this study for correlating some model parameters. These dynamic experiments were carried out with different values of the gas velocity, the inlet humidity, and the properties of the adsorbent. The breakthrough curves of the modified silica gel with neutron flux in a previous study were used to verify the proposed model. It is feasible to develop a single adsorption model to simulate the fixed-bed breakthrough curves for original and modified silica gels. The results show that the complex breakthrough curves can be predicted and are in very good agreement with the experimental data.     

EXPERIMENTAL DETERMINATION AND PREDICTIONS OF BREAKTHROUGH CURVES IN A FIXED BED OF SILICA GEL USING THE TRANSFER UNIT APPROACH

A semi-empirical model was developed to predict the breakthrough curves of moisture adsorption on silica gel under different operating conditions. The model requires only the basic physical and transfer properties of the flowing gas stream. Experimental breakthrough curves were determined in this study for correlating some model parameters. These dynamic experiments were carried out with different values of the gas velocity, the inlet humidity, and the properties of the adsorbent. The breakthrough curves of the modified silica gel with neutron flux in a previous study were used to verify the proposed model. It is feasible to develop a single adsorption model to simulate the fixed-bed breakthrough curves for original and modified silica gels. The results show that the complex breakthrough curves can be predicted and are in very good agreement with the experimental data.     

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.     

噻吩在Cu+-13X上吸附平衡和动态数据测定

对噻吩在Cu -13X分子筛上的吸附平衡和动态数据进行了测定。对噻吩的吸附平衡数据用Langmuir模型进行拟合,得到了303、323 K下噻吩在Cu -13X上的饱和吸附量分别为232.86、74.78 mg/g;采用固定床测定了不同停留时间及不同初始浓度下的动态透过曲线,结果表明,在透过点以前动态吸附可以实现噻吩的零含量,缩短停留时间和增加初始浓度会影响吸附的透过曲线,实验结果为吸附工艺设计提供了一定的基础数据。     

Surface B-splines fitting for speeding up the simulation of adsorption processes with IAS model

The ideal adsorbed solution theory (IAS) is commonly used in process simulation for predicting multicomponent adsorption equilibrium. However, this model requires a significant computational effort which translates in time consuming simulations.A methodology using surface B-splines fitting was developed for speeding the prediction of the multicomponent equilibrium with IAS theory. As a case study, a breakthrough of an enantiomer bi-component mixture in a fixed bed was simulated and a speed-up of 57.9% was achieved while maintaining the accuracy of IAS multicomponent equilibrium prediction.     

Propane/Propylene Separation by Simulated Moving Bed II. Measurement and Prediction of Binary Adsorption Equilibria of Propane,Propylene, Isobutane,and 1-Butene on 13X Zeolite

Abstract

The design of a simulated moving bed (SMB) process relies on valid thermodynamic predictions of multicomponent adsorption built up from accurate binary adsorption equilibrium data. Experimental adsorption equilibria of binary mixtures constituted by propane, propylene, isobutane and 1-butene on 13X zeolite were determined using breakthrough experiments at 373 K and 150 kPa. In addition, these binary adsorption experiments allow to confirm the choice of isobutane as an interesting desorbent for the separation of propane-propylene by SMB, since it has an intermediate selectivity between the two species to separate. Various prediction models are available in the literature but only a few of them have both physical and thermodynamical consistency. The ideal adsorbed solution theory (IAST), the thermodynamically consistent extended Toth model (TCET), and the physically-consistent extended Toth isotherm (PCET) were used to predict binary adsorption equilibria from pure component adsorption isotherms parameters. The PCET model was found suitable for representing the adsorption equilibrium of the different hydrocarbon mixtures with a reasonably good accuracy.     

MODELLING OF PROTEIN ADSORPTION IN A FIXED-BED: SINGLE AND TWO-SOLUTE BREAKTHROUGH BEHAVIOUR

Single- and two-solute adsorption breakthrough curves of lysozyme and bovine serum albumin on the cation exchanger SP-Sepharose Fast Flow were studied in this paper. A simplified mathematical model was used to model these data. Input parameters of the model such as equilibrium and kinetic parameters were estimated from single-solute batch experiments. For single-component adsorption in a fixed-bed, the breakthrough behaviour of lysozyme was well modelled. In contrast, significant deviations were observed between the measured and theoretical breakthrough curves of albumin. It was shown that the equilibrium parameters measured from batch experiments failed to account for the behaviour of albumin in the fixed-bed. The bisolute system consisting of the simultaneous adsorption of lysozyme and albumin was also modelled using the same set of parameters derived from single-solute batch experiments. Deviations were observed between the measured and theoretical breakthrough curves for both proteins, indicating that the effects of multicomponent equilibria and kinetics must be taken into consideration in parameter estimation.     

Multicomponent Fixed-Bed Ion Exchange: Verification of Equilibrium Coherence Theory

Abstract

The coherence method, a technique for modeling multicomponent fixed-bed adsorption with time dependent feed conditions, has been applied to a fixed-bed ion-exchange system under a variety of operating conditions. Theoretically, the method can handle multicomponent systems with initial and feed conditions of any degree of complexity. This paper will present the results of an experimental study to verify the practical utility of the coherence method. A ternary ion-exchange system of K⁺, Na⁺, Li⁺ on a fixed bed of AG-50WX8 resin has been studied. Breakthrough curves have been obtained for single abrupt, multiple abrupt, and linear influent composition changes. A non-equilibrium model has also been developed and has been used to describe limiting binary exchange cases. The experimental breakthrough curves have been compared with the predictions of both models.     

A generalized procedure for the prediction of multicomponent adsorption equilibria

Prediction of multicomponent adsorption equilibria has been investigated for several decades. While there are theories available to predict the adsorption behavior of ideal mixtures, there are few purely predictive theories to account for nonidealities in real systems. Most models available for dealing with nonidealities contain interaction parameters that must be obtained through correlation with binary‐mixture data. However, as the number of components in a system grows, the number of parameters needed to be obtained increases exponentially. Here, a generalized procedure is proposed, as an extension of the predictive real adsorbed solution theory, for determining the parameters of any activity model, for any number of components, without correlation. This procedure is then combined with the adsorbed solution theory to predict the adsorption behavior of mixtures. As this method can be applied to any isotherm model and any activity model, it is referred to as the generalized predictive adsorbed solution theory. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2600–2610, 2015     

Adsorption of mixed vapors on solids—I Graphon

The adsorption isotherms for ethanol-cyclohexane, ethanol-benzene, and benzene-cyclohexane vapor mixtures on Graphon at 20,30 and 40°C were measured at constant total pressure. The adsorption isotherms for the pure components were also obtained. Isosteric heats of adsorption were calculated for the pure adsorbates on Graphon. The binary vapor adsorption isotherms were compared to the pure component isotherms. The adsorbate-vapor composition diagrams for benzene-cyclohexane mixtures on Graphon all contained adsorption azeotropes. Very little selective adsorption of either component occurred. In general, benzene and cyclohexane were selectively adsorbed from benzene-ethanol and cyclohexane-ethanol mixtures on Graphon. The temperature dependence of the selectivity for the systems studied followed no consistent trend. Comparison of the binary vapor adsorption isotherms with the solution adsorption isotherms indicated that selectivity is generally higher in adsorption from solution. The experimental binary vapor adsorption isotherms compared favorably with those calculated from the pure vapor adsorption isotherms using the ideal adsorbed solution model. It was found that the adsorbed solutions were slightly non-ideal for benzene-cyclohexane mixtures on Graphon. The non-ideal behaviour observed for benzene-ethanol and cyclohexane-ethanol mixtures on Graphon was attributed to the presence of benzene or cyclohexane disrupting the hydrogen-bonded structure of ethanol on the Graphon surface.     

The simultaneous adsorption of carbon dioxide and water vapour by fixed beds of molecular sieves

In an isothermal fixed bed absorption system for constant inlet flowrate of inert gas and concentrations of two adsorbates the more strongly adsorbed component will displace the weaker one and effect its breakthrough characteristics. A small scale technique was used to study this phenomenon for the adsorption of water vapour and carbon dioxide on 4A type synthetic zeolites with helium as the carrier gas. Single adsorbate equilibria and rate data determined with the binary mixtures were then used to calculate the results for the ternary one. Partial differential equations were derived to describe the mass transfer of each adsorbate based on pore diffusion in the adsorbent as a major rate controlling mechanism. With a simplified binary Langmuir equilibrium to describe the effect of water on the adsorption of carbon dioxide, and assuming that the effective pore diffusion coefficient of one adsorbate was not affected by the presence of the other, accurate predictions of the concentration transient were obtained. Four zones are formed in the bed with the ternary mixture resulting from the desorption of carbon dioxide by water, the concentrations of the former rising above the inlet value. An enhanced rate of adsorbed phase transport of water was found, additional to that expected from macropore diffusion, suggesting that surface or capillary flow of the adsorbate occurred.     

Calculation methods for multicomponent adsorption equilibria

The knowledge of multicomponent adsorption equilibria is of great importance for the industrial design and application of adsorptive purification and separation processes. As the experimental determination of the required data is time-consuming and costly, theoretical help is desirable. This contribution presents and assesses the most common theoretical approaches to the calculation of multicomponent adsorption equilibria. The models are based on the assumption of an adsorbed solution, extension of the volume filling of micropores theory or statistical thermodynamics. These models are applied to different adsorptive/adsorbent systems with ideal and non-ideal equilibrium behaviour. It is established that, at low coverages of adsorbent surfaces, all theories provide good estimates of the adsorbed phase composition and total loading while, at high saturations, no model is completely satisfactory.     

CH4, C2H6, and C2H4 Phase Equilibria on SAPO-34 Using the Vacancy Solution Theory

Adsorption data of single, binary, and ternary mixtures of methane, ethane, and ethylene on Silicoalumina-Phosphate molecular Sieve (SAPO-34) were obtained experimentally in the pressure range of 0 to 600 kPa at 303, 313, and 323 K. The adsorbed equilibrium concentration was predicted based on the vacancy solution theory (VST) using excess Gibbs energy (EGE) models of activity coefficients. EGE models were studied comparatively, i.e., the Wilson, Flory Huggins, and NRTL equations. The VSM-model results were compared with the mixture adsorption data. The results revealed higher capability of EGE models against the extended Langmuir equation in predicting adsorption behavior of the so-called gas mixture.     

Multicomponent sorption kinetics of ethane and propane in activated carbon: simultaneous adsorption

Extensive experimental data of binary adsorption kinetics of ethane and propane onto Ajax activated carbon are collected by using a 'differential adsorption bed' over a range of particle sizes and shapes, bulk concentrations and temperatures. A multicomponent model incorporating macropore, surface and micropore diffusion mechanisms recently proposed by Hu and Do (Chem Eng Sci (in press)) is used to predict the binary adsorption dynamic data by using information of single-component isotherms and dynamics. The multicomponent adsorption equilibrium is calculated by using the ideal adsorbed solution theory (IAST), with the single-component isotherm described by a Unilan equation. The model is found to describe the binary adsorption kinetics well and in particular it accurately predicts the degree of the overshoot of the fast-diffusing/less-strongly adsorbed species.