Synergistic effects in competitive adsorption of carbohydrates on an ion-exchange resin

Adsorption of the three carbohydrates sucrose, glucose and fructose from aqueous solutions was investigated on an ion-exchange resin. The adsorption equilibrium of single components, binary and ternary mixtures was quantified by frontal analysis and the adsorption-desorption method. The experiments covered a concentration range up to 600 g/L at 60 degrees C and 80 degrees C. Within this range the adsorption isotherms of carbohydrates exhibited anti-Langmuirian behavior. Data of mixture adsorption revealed reversed competitive (synergistic or cooperative) effects, i.e., an increase of the concentration of one component of the mixture enhanced the adsorption of others. To model such an adsorption behavior the anti-Langmuir model has been used. The isotherm parameters determined for single components were used to simulate the competitive adsorption equilibria through the IAS (ideal adsorbed solution) theory. Finally, dynamic concentration profiles of multicomponent mixtures have been recorded. The shapes of adsorption and desorption curves confirmed the observed competitive effects found in the equilibrium studies. The breakthrough curves measured were simulated using the equilibrium theory as well as a numerical solution of the equilibrium dispersive model.     

A thermodynamically consistent explicit competitive adsorption isotherm model based on second-order single component behaviour

A competitive adsorption isotherm model is derived for binary mixtures of components characterized by single component isotherms which are second-order truncations of higher order equilibrium models suggested by multi-layer theory and statistical thermodynamics. The competitive isotherms are determined using the ideal adsorbed solution (IAS) theory which, in case of complex single component isotherms, does not generate explicit expressions to calculated equilibrium loadings and causes time consuming iterations in simulations of adsorption processes. The explicit model derived in this work is based on an analysis of the roots of a cubic polynomial resulting from the set of IAS equations. The suggested thermodynamically consistent and widely applicable competitive isotherm model can be recommended as a flexible tool for efficient simulations of fixed-bed adsorber dynamics.     

Adsorption equilibria of binary gas mixtures on graphitized carbon black

Adsorption equilibria for binary gas mixtures (methane-carbon dioxide, methane-ethane, and carbon dioxide-ethane) on the graphitized carbon black STH-2 were measured by the open flow method at 293.2 K. The experimental pressure range was (0 to 1.6) MPa. The extended Langmuir (EL) model and the ideal adsorption solution theory (IAST) have been adopted to predict the equilibria of binary gas mixtures. The results indicate that gas mixtures adsorbed on the homogeneous surface of STH-2 exhibit the nonideal behavior, which is mainly induced by adsorbate-adsorbate interactions. The real adsorption solution theory (RAST) has been used to analyze the property of the adsorbed mixtures. The activity coefficients have been correlated with the Wilson equation. The investigation demonstrates that the nonideality of adsorbed phase is completely dissimilar with the bulk liquid phase. The adsorption of the heavier component would benefit the adsorption of the lighter component.     

Determination of competitive adsorption isotherms applying the nonlinear frequency response method: Part I. Theoretical analysis

In this work adsorption equilibria of binary mixtures are quantified analyzing the nonlinear frequency response of a chromatographic column. Local partial derivatives of an isotherm model can be estimated for certain steady-states from the low frequency asymptotes of the corresponding frequency response functions (FRFs). The required FRFs correspond to two different compounds and the type of the imposed inlet concentration changes, e.g. periodical inlet concentration changes of only one compound or of both of them. For an accurate determination of isotherm parameters, it is necessary to approach as close as possible the low frequency asymptotic behaviour of these functions. Based on principles valid for the FRFs corresponding to the adsorption of a single solute, frequencies needed to reach the low frequency asymptotes of the functions of interest for estimating competitive isotherms are defined in this paper. The relation between the accuracy of the isotherm parameters determined and numbers and types of periodical inlet concentration changes and steady-states analyzed is also evaluated.     

Adsorbed solution model for prediction of normal-phase chromatography process with varying composition of the mobile phase

The adsorbed solution model has been used to predict competitive adsorption equilibria of the solute and the active component of mobile phase in a normal-phase liquid chromatography system. The inputs to the calculations were the single adsorption isotherms accounting for energetic heterogeneity of the adsorbent surface and non-ideality of the mobile phase solution. The competitive adsorption model has been coupled with a model of the column dynamics and used for simulating of chromatography process at different mobile phase composition. The predictions have been verified by comparing the simulated and experimental chromatograms. The model allowed quantitative prediction of chromatography process on the basis of the pure-species adsorption isotherms.     

Dependence of the adsorption of polymer mixtures from solution on the amount of an adsorbent

Simultaneous competitive adsorption from solutions of mixtures of poly(butyl methacrylate) and polystyrene and adsorption of each component from binary solutions have been studied for three ratios of the adsorbent mass to the solution volume, A/V. It was found that adsorption from both binary and ternary solutions strongly depends on the amount of an adsorbent, adsorption of poly(butyl methacrylate) being preferential. The characteristic adsorption isotherms of both polymers were constructed under conditions of equal equilibrium concentration of each component to estimate the parameters of preferential adsorption and their dependence on the A/V ratio. It was found that the A/V effect plays an important role in adsorption from polymer mixtures and determines the peculiarities of adsorption from polymer mixtures as well as from solution of single polymers. Changing the A/V ratio may be one way to regulate the composition of an adsorption layer consisting of two chemically different polymers. The reasons for the A/V effect are considered in the framework of the concept of the plurality of adsorption equilibria between two chemically different components and between fractions of different molecular mass of each component having various absorbability.     

Competitive adsorption of aqueous metal ions on an oxidized nanoporous activated carbon

Competitive adsorption is the usual situation in real applications, and it is of critical importance in determining the overall performance of an adsorbent. In this study, the competitive adsorption characteristics of all the combinations of binary mixtures of aqueous metal ion species Ca2+(aq), Cd2+(aq), Pb2+(aq), and Hg2+(aq) on a functionalized activated carbon were investigated. The porous structure of the functionalized active carbon was characterized using N2 (77 K) and CO2 (273 K) adsorption. The surface group characteristics were examined by temperature-programmed desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, acid/base titrations, and measurement of the point of zero charge (pHpzc). The adsorption of aqueous metal ion species, M2+(aq), on acidic oxygen functional group sites mainly involves an ion exchange mechanism. The ratios of protons displaced to the amount of M2+(aq) metal species adsorbed have a linear relationship for both single-ion and binary mixtures of these species. Hydrolysis of metal species in solution may affect the adsorption, and this is the case for adsorption of Hg2+(aq) and Pb2+(aq). Competitive adsorption decreases the amounts of individual metal ions adsorbed, but the maximum amounts adsorbed still follow the order Hg2+(aq) > Pb2+(aq) > Cd2+(aq) > Ca2+(aq) obtained for single metal ion adsorption. The adsorption isotherms for single metal ion species were used to develop a model for competitive adsorption in binary mixtures, involving exchange of ions in solution with surface proton sites and adsorbed metal ions, with the species having different accessibilities to the porous structure. The model was validated against the experimental data.     

Sorption equilibrium prediction of competitive adsorption of herbicides 2,4-D and MCPA from aqueous solution on activated carbon using ANN

The simultaneous adsorption of two herbicides—2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA)—from their aqueous binary mixtures onto granular activated carbon was studied. The quantities adsorbed were determined by HPLC with UV detection. The experimental data were analysed using the Freundlich adsorption isotherm. The high correlation coefficients indicated that the adsorption equilibrium fitted the Freundlich isotherm well. A multilayer perceptron (MLP) (an artificial neural network model—ANN) was applied to describe the adsorption equilibrium in multicomponent systems. This enabled sorption isotherms to be predicted for all possible combinations of the two herbicides. The experimental results and the calculated data obtained from MLP for the solutions of the individual components and their mixtures suggest that MCPA is better adsorbed onto activated carbon than 2,4-D.     

Study of the competitive isotherm model and the mass transfer kinetics for a BET binary system

The competitive adsorption behavior of the binary mixture of phenetole (ethoxy-benzene) and propyl benzoate in a reversed-phase system was investigated. The adsorption equilibrium data of the single-component systems were acquired by frontal analysis. The same data for binary mixtures were acquired by the perturbation method. For both compounds, the single-component isotherm data fit best to the multilayer BET model. The experimental overloaded band profiles are in excellent agreement with the profiles calculated with either the general rate model or the modified transport-dispersive models. The competitive adsorption data were modeled using the ideal adsorbed solution (IAS) theory. The numerical values of the coefficients were derived by fitting the retention times of the perturbation pulses to those calculated using the IAS theory compiled with the coherence conditions. Finally, the elution profiles of binary mixtures were recorded. They compared very well with those calculated. As a characteristic feature of this case, an unusual retainment effect of the chromatographic band of the more retained component by the less retained one was observed. The combination of the General Rate Model and the adsorption isotherm model allowed an accurate prediction of the band profiles.     

Influence of preferential adsorption of mobile phase on retention behavior of amino acids on the teicoplanin chiral selector

The adsorption behavior of two amino acids, i.e., l,d-threonine and l,d-methionine has been investigated on the chiral stationary phase (CSP)column packed with teicoplanin bonded to a silica support. The study has been performed under non-linear conditions of adsorption isotherm for various types of organic modifiers (methanol, ethanol, propan-2-ol and acetonitrile) in the reversed-phase mode. A heterogeneous adsorption mechanism of amino acids has been identified that was strongly affected by the nature of organic modifier. Generally, isotherm non-linearity and retention decreased with decrease of the modifier content in the mobile phase exhibiting a minimum at water-rich mobile phases. These trends were suggested to result from a combined effect of the mobile as well as the adsorbed phase composition. To determine the composition of the adsorbed phase the excess adsorption of modifiers in aqueous solutions has been measured and their binary adsorption equilibria have been quantified and compared. Strongly non-ideal behavior of solvents in the mobile phase and the adsorbed phase has been accounted for by activity coefficients. The fraction of the modifiers in the adsorbed phase decreased in the sequence: methanol, ethanol, propan-2-ol and acetonitrile.     

Binary Adsorption of Phenol and m-Cresol Mixtures onto a Polymeric Adsorbent

Adsorption processes are gaining interest as methods of purifying industrial effluents. Most industries discharge effluents containing several components. The adsorption of phenol and m-cresol mixtures from aqueous solutions onto a macroporous polymeric adsorbent, Duolite ES-861, was investigated experimentally in a fixed-bed adsorber for different flowrates, feed concentrations and bed initial conditions (clean or pre-saturated).The experimental results are presented in this work, where the major objective is placed on the modelling of these fixed bed adsorption experiments using an extended Langmuir isotherm equation for two components, based on single component equilibrium data obtained for phenol and m-cresol.The model presented in this paper takes into account axial dispersion of the liquid phase, film diffusion and intraparticle mass transfer and successfully simulates the adsorption behaviour of the phenol and m-cresol mixtures.     

Heats of immersion of titanium dioxide pigments in aqueous solutions: Part II. The immersion of dried rutile pigment in solutions of varying solute concentration

The heats of immersion of a partially-dried coated ruffle pigment in water and aqueous solutions of several surfactants were measured by a differential calorimetric method. The variations in heats of immersion with solute concentration are interpreted in terms of a theoretical model involving the heats of adsorption of water and solute. The heats of immersion were more exothermie in the solutions than in water itself although it is not certain whether the solute is adsorbed on top of a fully adsorbed water complement or whether competitive adsorption between water and the solute occurs.     

Estimation of the Activity Coefficients in Liquid Mixtures by Using Volumetric Data

We present an equation that relates the partial molar volume of binary liquid mixtures with the natural logarithms of the activity coefficients of solute and solvent. This equation, in combination with one of the activity coefficient models such as those of Margules, Wilson, Van Laar or NRTL, can be used to estimate the activity coefficients of binary liquid mixtures, knowing only the densities of the mixtures over the full range of concentration. In addition, we show a comparison of the estimated activities and activity coefficients at infinite dilution with experimental values for aqueous solutions of 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, and 1,4-butanediol at 298.15?K. This method for the estimation of activity coefficients can be applied to aqueous binary mixtures, because the equation presented is deduced from physicochemical principles.     

Band splitting in overloaded isocratic elution chromatography II. New competitive adsorption isotherms

The equations of two new binary competitive isotherms models are derived. The first of these models assumes that the isotherms of the two pure, single compounds have distinct monolayer capacities. Its derivation is based on kinetic arguments. The ideal adsorbed solution (IAS) framework was applied to derive the second model that is a thermodynamically consistent competitive isotherm. This second model predicts the competitive adsorption isotherm behavior of a mixture of two compounds that have single-component adsorption behavior following a BET and/or a Langmuir isotherms. Both models apply well to the binary adsorption of ethylbenzoate and 4-tert.-butylphenol on a Kromasil-C18 column (with methanol-water, 62:38, v/v, as the mobile phase). The best single-solute adsorption isotherms of these two compounds are the liquid-solid extended multilayer BET and the Langmuir isotherms, respectively. The kinetic and thermodynamic new competitive models were compared, regarding the accuracy of their prediction of the elution band profiles of mixtures of these two compounds. A better agreement between experimental and calculated profiles was observed with the kinetic model. The IAS model failed because the behavior of the ethylbenzoate/4-tert.-butylphenol adsorbed phase mixture is probably non-ideal. The most striking result is the qualitative prediction by these models of the peak splitting of 4-tert.-butylphenol during its elution in presence of ethylbenzoate.     

On the thermodynamics of alcohol solutions. Phase equilibria of binary and ternary mixtures containing any number of alcohols

Nagata, I., 1985. On the thermodynamics of alcohol solutions. Phase equilibria of binary and ternary mixtures containing any number of alcohols. Fluid Phase Equilibria, 19: 153–174.Binary vapor—liquid and liquid—liquid equilibrium data for alcohol solutions includin one or two alcohols are correlated with the UNIQUAC associated solution theory (Nagata and Kawamura). The theory uses pure liquid association constants determined by the method of Brandani and a single value of the enthalpy of the hydrogen bond equal to ?23.2 kJ mol ^?1 for pure alcohols. For alcohol-active nonassociating component mixtures and alcohol—alcohol mixtures the theory involves additional solvation constants. The theory is extended to contain ternary mixtures with any number of alcohols. Ternary predictions of vapor—liquid and liquid—liquid equilibria are performed using only binary parameters. Good agreement is obtained between calculated and experimental results for many representative mixtures.     

Adsorption of Phenolic Compounds from Water on Activated Carbon: Prediction of Multicomponent Equilibrium Isotherms using Single-Component Data

Batch-type experiments were carried out to obtain equilibrium isotherms for the adsorption of phenol and m-cresol in aqueous solutions on activated carbon. Single solute systems, at 20 and 40^∘C, were tested for Langmuir, Freundlich and Sips adsorption isotherms in the range of concentrations up to 200 mg/L. Equilibrium data were more closely followed by the Freundlich and Sips equations for all cases. Adsorption isotherms for bisolute systems at 20^∘C, with two different initial concentrations of phenol and m-cresol, were predicted solely on the basis of single solute equilibrium parameters by using the equations of Butler and Ockrent and the IAS theory. The best agreement with the experimental loading values was afforded with the IAS theory based on Sips isotherm for pure compounds. However, this theory is found to be not able to predict with success the binary isotherms in this work where significant displacement of one solute by the other is observed. Chemical interactions in the adsorbed phase, estimated by a modified Butler–Ockrent model, can be responsible for this lack of success of the conventional IAS theory. The predictions based on the IAS theory are compared with the results of some empirical models.     

The significance of a second adsorption phase with weakly adsorbed species for the calculation of the surface concentrations of a mixture: methanol–DME and methanol–ethene adsorption in SAPO-34

With the calorimetric (adsorption heat versus coverage) curve also measured together with the adsorption isotherm, the simultaneous use of both curves showed that there were two phases of adsorption in the adsorption of methanol, dimethyl ether, ethene and propane in SAPO-34. The dual-site Langmuir equation gave good fits to the adsorption data to support the interpretation that a second (type 2) adsorption phase occurred in the high-pressure region in addition to a first (type 1) adsorption phase on the acid sites at lower pressures. Adsorption experiments and calculations using binary gas mixtures showed that due to the existence of two types of adsorption, the multicomponent Langmuir isotherm equation (Langmuir competitive adsorption model) calculated incorrect surface concentrations when the concentrations were high. In contrast, the ideal adsorbed solution theory (IAST) calculated correct surface concentrations in the adsorption of mixtures.     

Carbon dioxide-methane mixture adsorption on activated carbon

In this work, we report new experimental data of pure and binary adsorption equilibria of carbon dioxide and methane on the activated carbon RB2 at 273 and 298 K. The pressure range studied were 0–3.5 MPa for pure gases and 0–0.1 MPa for mixtures. The combination of the generalized Dubinin model to describe the pure CO₂ and CH₄ isotherms with the IAST (Ideal Adsorbed Solution Theory) for the mixtures provide a method for the calculation of the binary adsorption equilibria. This formulation predicts with acceptable accuracy the binary adsorption data and can easily be integrated in general dynamic simulation of PSA (pressure swing adsorption process) adsorption columns. It involves only three parameters, independent of the temperature, and directly determined with only one adsorption isotherm of CO₂.     

Effect of controlled deactivation on the thermochemical characteristics of hydrogen adsorption on skeletal nickel from sodium hydroxide-water solutions

Differential heats of adsorption in a wide range of surface coverage and maximum amounts of adsorbed hydrogen are determined by adsorption calorimetry on partially deactivated skeletal nickel from aqueous solutions of sodium hydroxide. The effect of the composition of solutions on the values of limiting adsorption and adsorption equilibria of individual forms of hydrogen is shown.