Adsorption Equilibrium Parameters Research Articles

Adsorption separation of N 2, O 2, CO 2 and CH 4 gases by β-zeolite

In the present study, adsorption equilibrium and kinetic separation potential of β-zeolite is investigated for N 2, O 2, CO 2 and CH 4 gases by using concentration pulse chromatography. Adsorption equilibrium and kinetic parameters have been studied. Henry’s Law constants, heat of adsorption values, micro-pore diffusion coefficients and adsorption activation energies are determined experimentally. The three different mass transfer mechanisms, that have to take place for adsorption to occur, are discussed. From the equilibrium and kinetic data, the equilibrium and kinetic selectivities are determined for the separation of the gases studied. With β-zeolite, carbon dioxide has the highest adsorption Henry’s Law constant at all the temperatures studied, followed by methane, nitrogen and oxygen. Carbon dioxide separation from oxygen, nitrogen and methane has good equilibrium separation factors. This factor is not very high for methane/nitrogen and methane/oxygen systems and is the lowest for nitrogen/oxygen system. Micro-pore diffusion is the dominant mass transfer mechanism for all the systems studied, except CH 4, with β-zeolite. The kinetic separation factors are very small at high temperatures for all the systems studied. Nitrogen/carbon dioxide and oxygen/carbon dioxide can be separated in kinetic processes with reasonable separation factors at low temperatures. Both equilibrium and kinetic separation factors decrease as column temperature increases. Considering all the observations from this study, it was concluded that β-zeolite is a good candidate for applications in flue gas separations, as well as natural gas and landfill gas purifications.

Adsorption at liquid interfaces: The generalized Frumkin isotherm and interfacial structure

The thermodynamics of adsorption of amphiphilic surface-active compounds at the interface between two immiscible liquids is considered. At the interface, these molecules are supposed to replace a few of the adsorbed molecules of both solvents. Classical isotherms of adsorption (Frumkin, Frumkin-Damaskin, Langmuir, Henry) were based on the model of non-penetrable interface, where an adsorbate can substitute only molecules of one solvent. At the interface between two immiscible electrolytes, nonpolar oil/water interfaces, and liquid membranes amphiphilic molecules can substitute molecules of both solvent and classic isotherms cannot be used. The generalization of Frumkin isotherm for permeable and non-permeable interfaces, known as the Markin-Volkov isotherm, gives the possibility to analyze adsorption in a general case. The adsorption isotherms of pentafluorobenzoic acid at the octane/water interface at different pHs were measured by the drop-weight method. The thermodynamic parameters of pentafluorobenzoic acid (PFBA) adsorption at octane/water interface were determined. From the measurements of PFBA adsorption, the structure of the octane/water interface was determined. Substitution of one adsorbed octane molecule requires approximately three adsorbed PFBA molecules. This result shows that the orientation of solvent molecules at the interface is different from the bulk. Adsorbed octane molecules have a lateral orientation with respect to the interface. Gibbs free energy of adsorption equilibrium and thermodynamic parameters of PFBA adsorption show that the adsorption of PFBA at the octane/water interface is accompanied by a reduction in the attraction between adsorbed PFBA molecules as the pH decreases to the acidic region.

Adsorption of acetonitrile vapor on sodium and polyhydroxyaluminum montmorillonites

The differential isosteric heats of adsorption of acetonitrile vapor on dehydrated sodium and polyhydroxyaluminum montmorillonites are determined. From the temperature dependence of the parameters of adsorption equilibrium, it is established that the substitution of polyhydroxyaluminum ions for Na+ ions leads to an increase in the volume of micropores and the heat of adsorption.

Analysis of steric mass-action model for protein adsorption equilibrium onto porous anion-exchange adsorbent

The ion-exchange equilibrium of bovine serum albumin (BSA) to an anion exchanger, DEAE Spherodex M, has been studied by batch adsorption experiments at pH values ranging from 5.26 to 7.6 and ionic strengths from 10 to 117.1 mmol/l. Using the unadjustable adsorption equilibrium parameters obtained from batch experiments, the applicability of the steric mass-action (SMA) model was analyzed for describing protein ion-exchange equilibrium in different buffer systems. The parametric sensitivity analysis was performed by perturbing each of the model parameters, while holding the rest constant. The simulation results showed that, at high salt concentrations or low pHs close to the isoelectric point of the protein, the precision of the model prediction decreased. Parametric sensitivity analysis showed that the characteristic charge and protein steric factor had the largest effects on ion-exchange equilibrium, while the effect of equilibrium constant was about 70%–95% smaller than those of characteristic charge and steric factor under all conditions investigated. The SMA model with the relationship between the adjusted characteristic charge and the salt concentration can well predict the protein adsorption isotherms in a wide pH range from 5.84 to 7.6. It is considered that the SMA model could be further improved by taking into account the effect of salt concentration on the intermolecular interactions of proteins.

Adsorption at Liquid Interfaces: The Generalized Langmuir Isotherm and Interfacial Structure

The thermodynamics of adsorption of amphiphilic surface-active compounds at the interface between two immiscible liquids is considered. At the interface, these molecules are supposed to replace a few of the adsorbed molecules of both solvents. Classical isotherms of adsorption (Frumkin, Langmuir, Henry) were based on the model of nonpenetrable interface, where an adsorbate can substitute only molecules of one solvent. However, at the interface between two immiscible electrolytes, like nonpolar oil-water interfaces, or liquid membrane amphiphilic molecules can substitute molecules of both solvents; therefore, classical isotherms are not applicable in these cases. The generalization of Langmuir and Frumkin isotherms for permeable and nonpermeable interfaces, known as the Markin-Volkov (MV) isotherm, gives the possibility to analyze adsorption and the interfacial structure in a general case. In the present paper, the adsorption isotherms of pentafluorobenzoic acid at the octane-water interface at various pH were measured by the drop-weight method. The thermodynamic parameters of pentafluorobenzoic acid (PFBA) adsorption at the octane-water interface were found. From the measurements of PFBA adsorption, the structure of the octane-water interface was determined. Substitution of one adsorbed octane molecule requires approximately three adsorbed PFBA molecules. This result shows that the orientation of solvent molecules at the interface is different from the bulk solution. Adsorbed octane molecules have a lateral orientation with respect to the interface. Gibbs free energy of adsorption equilibrium and thermodynamic parameters of PFBA adsorption show that the adsorption of PFBA at the octane-water interface is accompanied by a reduction in the attraction between adsorbed PFBA molecules as the pH decreases to the acidic region.

Use of stirred batch reactors for the assessment of adsorption constants in porous solid catalysts with simultaneous diffusion and reaction. Theoretical analysis

A simple, pseudo-equilibrium model was derived for a catalytic system with a first order chemical reaction and simultaneous diffusive and adsorptive processes, in order to assess the corresponding kinetics and Henry law's-type adsorption parameters. Solutions from this model were compared to exact solutions from a more detailed, general model. It was shown that under most of the experimental conditions used in stirred batch reactors and the usual model considerations, it is only possible to assess apparent adsorption parameters. Also, we observed that a stable relationship between the concentrations in the gas and solid phases is reached. The error produced in assuming that the apparent adsorption constant is the real one was calculated to be very important. The value of the apparent adsorption constant depends on various system properties and experimental conditions, such as the Thiele modulus, the amount of catalyst and the contact time. The ratio between the apparent and real adsorption constants was shown to be the transient effectiveness factor at any moment. This ratio reaches a maximum value for the pseudo-equilibrium state, that is always larger than the steady-state effectiveness factor, becoming closer as long as the system's adsorption capacity decreases. The analysis determines the operative conditions to reduce the parametric correlation. Also a criterion for the applicability of usual approximations in the assessment of kinetics and equilibrium adsorption parameters in porous solid catalysts by means of pulse injection methods is established.

Adsorption-induced dimensional changes of solids

A new approach based on the thermodynamic theory of vacancy solutions and Hooke's law is developed for the description of the elastic strain of isotropic solid adsorbents during physical adsorption. The equation linking a relative strain with the equilibrium parameters of adsorption is derived. The explicit expression allowing calculation of the contribution from solid strain to heat of adsorption is obtained. Validity of the developed method has been confirmed by comparing the theoretically predicted dimensional changes on adsorption to the experimentally studied system zeolite CaA–krypton where both contraction and expansion occurred.

Modeling and design of vapor‐phase biofiltration for chlorinated volatile organic compounds

AbstractA mathematical model was developed for biofilter design and performance prediction with reference to the purification of contaminated gas streams. The model incorporated important aspects such as mass transfer, biodegradation, and adsorption processes. A systematic modeling protocol incorporated the development of a scale‐up strategy based on dimensional analysis and similitude. Trichloroethylene (TCE) was employed as the model contaminant for biofiltration testing and model verification. The biokinetic and adsorption parameters for the contaminant were determined independently from a series of minibiofilter and miniadsorber column experiments, specifically designed to simulate the actual biofilter operational regimes in a miniature scale. Bench‐scale biofilter experiments employing granular activated carbon columns indicated the good predictive capability of the model for the removal of TCE. Dynamic simulation studies were performed to assess the transient‐ and steady‐state behavior of the model under various operating conditions. Model sensitivity was studied to evaluate the influence of adsorption equilibrium, transport and biological parameters on the biofilter dynamics. The results demonstrated that the biofilter performance was greatly influenced by the Monod coefficients and the biofilm thickness.

Chemical and physical activation of olive-mill waste water to produce activated carbons

Olive-mill waste water is produced in large quantities during the manufacture process of the olive oil in mills. This by-product has been used as raw material to produce activated carbons by both chemical and physical activation methods. In the first case, ZnCl2 and H3PO4 were used as activating agent and in the second case, CO2 at 600 °C for different periods of time. Obtained results indicate that the chemical activation with ZnCl2 and H3PO4 at 600 °C, in an inert atmosphere, yielded activated carbons with the highest area and more developed microporosity, mesoporosity and macroporosity. Adsorption of rate of phenol onto activated olive-mill was studied as a function of several physical-chemical parameters such as temperature, initial concentration in solution and hydrodynamic conditions. Equilibrium parameters of adsorption have been determined using Langmuir constant K.

Adsorption of Fluoride, Phosphate, and Arsenate Ions on a New Type of Ion Exchange Fiber

A new type of ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions has been developed. A batch adsorption technique for investigating adsorption kinetic and equilibrium parameters and determining pH adsorption edges is applied. It is shown that the adsorption properties of the ion exchange fiber for fluoride, phosphate, and arsenate ions depend on the pH value and anion concentration. The adsorption of arsenate on the sorbent reaches a maximum of 97.9% in the pH value range of 3.5 to 7.0. The adsorption percentage of phosphate is more than 99% in the pH range of 3.0 to 5.5. The adsorption of fluoride on the ion exchange fiber is found to be 90.4% at pH 3.0. The Freundlich model can describe the adsorption equilibrium data of fluoride, arsenate, and phosphate anions. The sorption of the three anions on the ion exchange fiber is a rapid process, and the adsorption kinetic data can be simulated very well by the pseudo-second-order rate equation. The column performance is carried out to assess the applicability of the ion exchange fiber for the removal of fluoride, phosphate, and arsenate ions from synthetic wastewaters with satisfactory removal efficiency. The desorption experiment shows that fluoride ion sorbed by the fiber column can be quantitatively desorbed with 5 mL of 0.50 mol/L NaOH at elution rate of 1 mL/min, and 30 mL of NaOH is necessary for the quantitative recovery of phosphate and arsenate ions.

Modeling of copper biosorption by Arthrobacter sp. in a UF/MF membrane reactor.

Copper biosorption by Arthrobacter sp. has been studied in this work. The process has been realized inside of a ultrafiltration/microfiltration (UF/MF) reactor in order to confine cells. A mathematical model has been developed that is able to predict experimental data under different operating conditions. The model takes into account different phenomena, which might occur during the process, such as a dependence of equilibrium parameters on pH, a partial cell disruption, and a change in the membrane retention properties at high biomass concentrations. Experimental tests have been performed under different operating conditions: a full factorial design has been implemented with pH (levels: 4, 5, and 6 units) and biomass concentration (levels: 1 and 5 g/L) as factors. A simple mathematical model based on metal mass balance taking into account the effect of pH on the Langmuir equilibrium adsorption parameters well fitted experimental data at low pH values and biomass concentrations. A more complex mathematical model, which considers a partial cell disruption during the biosorption trial, was proposed to understand and analyze the anomalous system behavior at pH = 6 and biomass concentration equal to 5 g/L. The effect of mechanical stress on biomass performances was also examined by using a discontinuous system (test tube trials) simulating the membrane reactor apparatus. In this alternative system biosorption trials were carried out in test tubes in such a way to avoid or at least minimize the disruption due to mechanical stress. Experimental results obtained by using this system can be modeled up to pH = 5 without considering cell disruption phenomenon, while at pH = 6 possible chemical reactions of biomass constituents could happen.

The Relation between the Efficiency of an Adsorbent in a Refrigeration System and Its Hydration Isotherm

The efficiencies of various types of silica gels, zeolites, and crystalline microporous aluminophosphates in adsorption systems of refrigeration have been determined. On the basis of the results obtained a method is proposed for the determination of the efficiency of an adsorbent from its hydration isotherm without experimental determination of the temperature dependence of the adsorption equilibrium parameters.

Modeling the sorption of toxic metals on chelant‐impregnated adsorbent

AbstractThe application of a microporous adsorbent, such as activated carbon impregnated with 8‐hydroxyquinoline (oxine), a chelating agent, to remove toxic metals from the aqueous phase is studied. A pore and surface diffusion model for predicting the dynamics of fixed‐bed adsorbers using oxine‐impregnated carbon is also discussed. The model incorporates adsorption equilibrium and kinetic parameters determined from independent isotherm tests and rate experiments, as well as adsorber column flow characteristics. Three modeling scenarios were employed with reference to intraparticle transport: (a) combined pore diffusion and surface diffusion; (b) pore diffusion alone, suppressing the effect of surface diffusion; and (c) surface diffusion alone, suppressing the effect of pore diffusion. Surface diffusion alone provided reasonably good predictions of the adsorber dynamics, as reflected by results from adsorber experiments. It is postulated that the sorption mechanism could be a combination of film transport of metal ions, followed by surface diffusion into adsorbent particles, and subsequent chelation of metal ions with the oxine molecules sorbed on carbon. The sorbed metals could be completely recovered under acidic conditions during the carbon regeneration process.

Dynamic analysis of adsorption equilibrium and rate parameters of reactants and products in MTBE, ETBE and TAME production

AbstractAdsorption equilibrium constants of ethanol, methanol, isobutylene, isoamylenes (2M2B, 2M1B), MTBE and TAME on Amberlyst 15 catalyst were evaluated from the packed bed moment technique. Adsorption equilibrium constants of alcohols were found to be two orders of magnitude greater than the adsorption equilibrium constants of i‐olefins and the corresponding tertiary ethers. However, their apparent heat of adsorption values are quite low (‐6,7 kJ/mol and −8.3 kJ/mol for methanol and ethanol, respectively). Among the i‐olefins, isobutylene gave the highest adsorption equilibrium constant and the heat of adsorption (‐54.2 kJ/mol The adsorption equilibrium constant of 2M2B on a catalyst, which was pretreated with ethanol, was about three times greater than the corresponding value obtained on fresh catalyst. Second moment analysis indicated that diffusion resistance in both macropores and microspheres of the catalyst are equally significant.

DYNAMIC ADSORPTION OF S02 ON ZEOLITE MOLECULAR SIEVES†

Sulfur dioxide is one of the major pollutants resulting from fuel combustion. Numerous dry, semi-dry and wet processes have been developed for pollution control of sulfur dioxide. Solid carbonates, natural and synthetic zeolites, ion exchange resins and carbon based sorbents are the most commonly used dry sorbents for sulfur dioxide removal In this study, measurements of the adsorption properties of sulfur dioxide on zeolites were investigated. The adsorbents used in this work are 5A, 4A and AW300 type molecular sieve zeolites. Adsorption equilibrium parameters were determined from the pulse chromatographic response to injections of low concentrations of sulfur dioxide. The method of moments were used to evaluate the adsorption equilibrium parameters from pulse chromatographic experiments. Data, such as adsorption equilibrium constants or reaction rate parameters are essential in the design of adsorption systems or reactors in which sulfur dioxide is removed The experiments were conducted in a temperature range of 523-718 K. The relatively strong adsorption properties of sulfur dioxide on zeolites necessitated the use of high carrier gas flow rates and subsequently non-isobaric operation. Non-isobaric pulse chromatography theory was found to describe accurately the adsorption trends." printpubdate="Adsorption equilibrium constants of S02 were found to decrease considerably with increasing temperature. It was also found out that adsorption of SO2 on the adsorbents investigated were found to decrease in the order of AW300 ⩽ 4A ⩽ 5A. The adsorption equilibrium parameter of S02 on 5A was found as 11.78 at 673 K, whereas it has a value of 157.11 at 523 K. The adsorption equilibrium parameter of S02 on 4A zeolite was determined to be 8.63 at 718 K and 213.78 at 523 K.

Two-step chromatographic procedure for purification of basic fibroblast growth factor from recombinant Escherichia coli and characterization of the equilibrium parameters of adsorption

A two-step chromatographic procedure for purification of basic fibroblast growth factor (bFGF) from high-cell-density cultures of recombinant E. coli is described. Heparin-Sepharose as a material which shows a high affinity to endothelial growth factors was used as sorbent for purification of bFGF from the soluble cell fraction. A one-step affinity chromatographic procedure resulted in very pure bFGF. However, this one-step affinity isolation of bFGF caused the loss of around 60% of the recombinant protein. A combination of ion-exchange chromatography with heparin-Sepharose affinity chromatography was favored for bFGF purification. A first cation-exchange chromatographic step resulted in a solution of bFGF with a purity of around 70%. The weak cation exchanger CM-Sepharose C50 was preferred in comparison to the strong cation exchanger S-Sepharose because of the higher recovery of bFGF. With the ion-exchange chromatographic step prior to the heparin-Sepharose affinity chromatography, the total yield of recovery of bFGF increased to 56% compared to 40% using the one-step purification procedure with heparin-Sepharose. To characterize the equilibrium parameters of adsorption, batch experiments for the calculation of maximum capacities and dissociation constants for CM-Sepharose C50 and heparin-Sepharose were carried out. The equilibrium experiments revealed that adsorption of bFGF to the ion-exchange sorbent followed single-site interaction according to the Langmuir model of adsorption. The adsorption of bFGF to heparin-Sepharose was described by a double Langmuir approach of two independent binding sites with different maximum capacities and dissociation constants. The purified bFGF showed a high biological activity and circular dichroic spectra of a proper folded molecule. The analysis of the N-terminal amino acid sequence revealed a mixture of two fractions of bFGF, which both are characterized by the cleavage of the first amino acid methionine. In addition, half of the bFGF molecules lacked the second amino acid alanine.

Adsorption and Impregnation of Alumina with Molybdenum or Tungsten Solutions

The equilibrium parameters of molybdenum and tungsten adsorption on alumina were compared. Adsorptions were performed from aqueous solutions of monomeric or polymeric ions of these elements. For all solutions tested, molybdenum showed a greater affinity for alumina than tungsten. Assuming a pore-filling impregnation of alumina spheres, a model that interprets this process was used for the calculation of theoretical profiles which showed a smooth decrease in concentration along the sphere radius. In turn, the experimental profiles were similar to those predicted for impregnations with solutions of heptameric molybdate, monomeric molybdate and monomeric tungstate. For polymeric tungstate, however, the experimental tungsten concentration rapidly fell to zero near the sphere surface. Using diffuse reflectance spectroscopy, it was observed that the molybdenum was in tetrahedral and octahedral coordination in spheres impregnated with polymeric or monomeric molybdenum solutions; in addition, the ratio of the concentrations of these species was approximately the same. The species observed in spheres impregnated with tungsten solutions was monomeric tungstate, indicating a distortion in tetrahedral symmetry as a consequence of interaction with the alumina.

Description of the adsorption equilibrium of organic substances absorbed from a flow of moist air by a fixed bed of active carbon moistened to equilibrium

Isotherms of the adsorption of benzene vapor from moist air on active carbon (AC) moistened to equilibrium are obtained from dynamic experiments. The experimental data on the adsorption equilibrium of some organic substances from a flow of moist air by a fixed bed of AC moistened to equilibrium are obtained. The data on the equilibrium adsorption of benzene vapor is analyzed using the Dubinin-Radushkevich equation (the theory of volume filling of micropores). It is revealed that the characteristic adsorption energy of benzene vapor decreases as the filling of the microporous volume with water molecules increases. The characteristic adsorption energy depends on the following factors: polarizability of a substance in the adsorption field created by micropores, the number of carbon atoms in the adsorbate molecules, and parameters of the porous structure. The equation for the calculation of the parameters of equilibrium adsorption of organic substances from moist air on AC moistened to equilibrium are obtained.

Surface tension properties of aqueous solutions of disulfur betaine derivatives

The equilibrium and dynamic surface tensions of aqueous solutions of two newly synthesized surfactants relevant to wool dyeing were studied by means of the Wilhelmy plate and a bubble method. The surfactants ( N α, N α′-bis( N-dodecyl- N, N-dimethylglycine cystine dimethyl ester dihydrochloride) and ( N α, N α′-bis( N-dodecyl- N, N-dimethylglycine) cystamine dihydrochloride), are double-chain and bicationic in character. Their CMCs and Langmuir adsorption equilibrium parameters were determined at 25°C. Both molecules are very efficient surfactants. Their surface tensions equilibrate in time-scales ranging from seconds to hours (concentration c=1000—2 μM). Their dynamic surface tensions under constant and pulsating area conditions indicate that there is a strong barrier to adsorption at the air—water interface. The presence of the micelles accelerates the net rate of adsorption, suggesting fast micellar dissociation.

Dynamic surface tension behavior of aqueous solutions ofN-dodecyl-N,N dimethyl aminobetaine chlorohydrate

The adsorption behavior ofN-dodecyl-N,N dimethyl aminobetaine chlorohydrate (DDAB·HCl) at the air/aqueous interface was studied for solutions in pure water and phosphate buffer (pH=7.4). The equilibrium surface tension versus concentration curves were used to estimate the equilibrium adsorption parameters and CMCs. The buffer solution has a lower CMC and shows higher surface activity below the CMC than the pure water solution. Data and calculations of the dynamic tension behavior at constant-area conditions showed that the adsorption processes of DDAB·HCl solutions are about 10 to 300 times slower than those predicted by a diffusion-controlled model. A mixed kinetics adsorption model with a modified Langmuir-Hinshelwood kinetic equation, which considers an activation energy barrier for adsorption, was applied to find the kinetic adsorption parameters. The dynamic tension behavior at pulsating-area conditions with large amplitude was also examined for frequencies up to 90 cycles/min. The tension amplitude responses depended strongly on the concentration and frequency. Comparisons of diffusion-controlled model predictions and pulsating area tension data confirmed the need to use a mixed kinetics model. The latter model can improve the fit over the diffusion-controlled model, but it does not quantitatively match the observed tensions.