Adsorption Equilibrium Parameters Research Articles

The burnt solid in adsorption treatment of water from heavy metal ions

The process of adsorption of ions of heavy metals Cu2+, Pb2+, Zn2+, Cd2+ from aqueous solutions with the mineral adsorbent burnt solid was investigated. Kinetic data on the adsorption process were obtained. Parameters of adsorption equilibrium using the Langmuir and Dubinin–Radushkevich equations have been calculated. The efficiency of extracting heavy metal ions upon modification of the adsorbent and in the area of low concentrations is shown.

Simple Methods for the Determination of Adsorption Rate and Equilibrium Parameters in the Recovery of Acetic Acid Using GAC and Synthetic Resins

Industrial acetic acid production based on anaerobic fermentation technology is not economically viable at present due to the high cost of product recovery by adsorption or extraction at neutral pH conditions. In this study, kinetics and equilibria of acetic acid sorption onto granular activated carbon and weak base resins were examined at pH < pKa of the acid. Comparative data on equilibrium sorption from a fermentation broth are also reported. It is observed that the weak base resins have higher adsorption capacities and selectivities for the uptake of organic acids from complex mixtures compared to activated carbon. A simple method to estimate intraparticle diffusivities from batch kinetic data using approximations to analytical solutions is developed. Methods for the accurate estimation of isotherm constants and external mass transfer coefficients are discussed and implemented. The estimated coefficients are shown to predict batch kinetic data well. This study will help in the screening of sorbents fo...

Removal of gentian violet in aqueous solution by activated carbon equilibrium, kinetics, and thermodynamic study

The quantitative kinetic and equilibrium adsorption parameters for chlorure de méthylrosaniline (gentian violet, crystal violet) removed by commercial activated carbon were studied by UV–visible spectroscopy.Activated carbon with a high specific surface area 1250 m2/g was characterized by the Brunauer, Emmett et Teller (BET) method and the zero charge point pH (pzc). The adsorption properties of both activated carbon with gentian violet were conducted at variable stirring speed 100–700 trs/min, adsorbent dose 1–8 g/l, solution pH 1–14, initial gentian violet concentration 5–15 mg/l, contact time 0–50 min, and temperature 299–323 K using batch mode operation to find the optimal conditions for a maximum adsorption. The adsorption mechanism of gentian violet was studied using the pseudo-first-order, pseudo-second-order, and Elovich kinetic models. The adsorption kinetics was found to follow a pseudo-second-order kinetic model with a determination coefficient (R2) of 0.999. The Weber–Morris diffusion model was applied for the adsorption mechanism. The equilibrium adsorption data of gentian violet were analyzed by the Langmuir, Freundlich, Elovich, and Temkin models. The results indicate that the Langmuir model provides the best correlation ( qmax = 22.727, 32.258 mg/g at 26 and 40°C, respectively). The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters, i.e. free energy (Δ G° = − 2.30 to −5.34 kJ/mol), enthalpy (Δ H° = 36.966 kJ/mol), entropy (Δ S° = 0.131 kJ/mol K), and activation energy ( Ea) 40.208 kJ/mol of gentian violet adsorption. The negative Δ G° and positive Δ H° indicate that the overall adsorption is spontaneous and endothermic in nature.

Ampicillin removal by adsorption onto activated carbon: kinetics, equilibrium and thermodynamics.

Pharmaceutical compounds are essential to preserve human and animal welfare, as well as to prevent illnesses. However, the elevated consumption of drugs, followed by incorrect disposal and inefficient wastewater treatment, may increase their environmental risk. In the case of antibiotics, such as ampicillin, some of the already known consequences are bacterial resistance and some toxic interactions with aquatic organisms. The scope of the present work is to investigate the removal of ampicillin through batch adsorption experiments onto granular activated carbon (GAC). The influence of pH and phase contact time were evaluated. Pseudo-first order, pseudo-second order and intraparticle diffusion models were adjusted to experimental data to determine process kinetics. In order to study adsorption equilibrium and thermodynamics parameters, isotherms at 298 K, 298 K and 308 K were constructed. The models of Langmuir, Freundlich and Sips fitted to experimental data. The best results (73% of removal, residual concentration 5.2 mg L-1) were reached at pH 6 and 120 minutes of contact time. Pseudo-first order model better represented the adsorption kinetics (R2 = 0.99), while the Langmuir equation suited well the experimental isotherms at 288 K and 298 K (R2 = 0.998 and R2 = 0.991) and the Sips equation better represented the system at 308 K (R2 = 0.990). Thermodynamic parameters were estimated as ΔG° = -6,000 J mol-1; -6,700 J mol-1; -7,500 J mol-1 at 288 K, 298 K and 308 K respectively, ΔH° = 14,500 J mol-1 and ΔS° = 71.0 J mol-1 K-1. The results indicate that this process is spontaneous, efficient and potentially applicable in the removal of ampicillin from water.

Decontamination of cadmium from aqueous solutions using zeolite decorated by Fe3O4 nanoparticles: adsorption modeling and thermodynamic studies

Release and dispersion of toxic substances like heavy metals in environment have adverse effects on human health and other living organisms. Therefore, contaminant removal prior to discharging them into environmental is so crucial. This study aimed to investigate the efficiency of magnetic Fe3O4 nanoparticles coated with natural clinoptilolite zeolite (Fe3O4@Z) for cadmium removal from aqueous solution. In this study, the effect of operational parameters such as pH, contact time, nanocomposite dosages, initial cadmium concentration, and temperature on cadmium adsorption was investigated. In addition, adsorption equilibrium, kinetics, modeling, and thermodynamic parameters were analyzed. Maximum cadmium adsorption was observed at pH = 6 and the contact time of 60 min. By increasing the adsorbent dosage from 0.2 to 1 g/L, removal efficiency increased from 24.4.1 to 68.9% for 20 mg/L Cd concentration. Also, Cd removal followed Freundlich isotherm with R2 = 0.997 and pseudo-second-order kinetic model with R2 = 0.992. Modeling showed that reciprocal quadratic (R2 = 0.9594), rational function (R2 = 0.9996), and polynomial fit (R2 = 0.9990) models represented the best fitness for changes of cadmium removal efficiency with changes of pH, adsorbent dose, and concentration, respectively. Based on the obtained results, Fe3O4@Z nanocomposite could be applied as an efficient adsorbent for cadmium removal from aquatic environments.

Adsorption of 2–nitrophenol using rice straw and rice husks hydrolyzed by subcritical water

The potential of rice husks and straw as adsorbents after being processed by subcritical water hydrolysis (SWH) was investigated. The influences of temperature (453, 493 and 533 K) and liquid/solid ratio (7.5 and 15 g water/g biomass) on the rice straw and rice husks characteristics and on the adsorption capacity of 2-nitrophenol were evaluated at pH 4 and 7. Adsorption kinetics, equilibrium and thermodynamic parameters were also studied. The adsorption capacity was favored at pH 7. Pseudo-first-order model was suitable to predict the kinetic curves for 2-nitrophenol concentrations of 25, 50, 75 and 100 mg/L and the isotherm data obeyed the Freundlich model. Overall, the thermodynamic results revealed a spontaneous and exothermic process. The maximum adsorption capacity (92.97 ± 1.31 mg/g) was obtained for rice straw that has undergone an SWH at 453 K and 7.5 g water/g straw. The integration of processes to valorize co-products can make the production of cellulosic bioethanol more feasible.

Study on transport phenomena and intrinsic kinetics for CO2 adsorption in solid amine sorbent

A study on the intrinsic kinetics of CO2 adsorption on solid amine sorbent is performed. For this, a new experimental method is developed to exclude heat and mass transfer limitations during the kinetic adsorption experiments. Hereto a novel contactor was designed and good process control, working with pure CO2 and small particle diameters enabled the measurement of intrinsic kinetics. A mathematical model describing convection, diffusion and reaction rate inside a particle confirmed the absence of mass and heat transfer limitations in the experiments. Linear driving force and Toth-isotherm reaction rate equations are evaluated for the CO2 adsorption process studied. The results show that the experimental particle loading with time could not be described by the linear driving force models. On the other hand, the Toth reaction rate equation, consistent with the Toth isotherm to describe the adsorption equilibrium, showed a very good fit to the experimental data. This shows that a rate based isotherm equation is necessary for prediction of both adsorption rate and equilibrium loading. It also implies that there is a strong correlation between the kinetic rate parameters found and the adsorption equilibrium parameters used, which was confirmed in this study.

Removal of Fluoride and Arsenate from Aqueous Solutions by Aluminum-Modified Guava Seeds

The contamination of groundwater by arsenic and fluoride is a major problem worldwide, causing diseases in the population that uses these waters for their consumption. Therefore, the removal of these types of pollutants from groundwater is a very important issue. In this work, the removal of arsenate and fluoride from aqueous solutions by using aluminum-modified guava seeds (Al-GSs) was evaluated. Batch-type adsorption experiments were carried out with aqueous solutions of As(V) and F− and Al-GSs. The kinetic and equilibrium parameters of adsorption were determined, as well as the effects of adsorbent dose and pH. The adsorbent was characterized by scanning electron microscopy and infrared spectroscopy in order to determine its morphology and the functional groups present in the material. The results showed that hydroxyl and carboxyl are the main groups involved in the adsorption of As(V) and F−. The fluoride adsorption kinetics indicate that the equilibrium time was reached at 150 min and it can be described by the Lagergren model, while for As(V) the equilibrium time was lower (120 min) and the kinetic data were fitted well to the pseudo-second-order model. The Langmuir-Freundlich model can describe the adsorption equilibrium data in all cases. The fluoride adsorption capacity by Al-GS was 0.3445 mg/g, and for As(V) it was 4 mg/g. It can be established that the removal of arsenates and fluoride in Al-GSs is due to chemisorption on a heterogeneous surface.

Transient effectiveness factor. Simultaneous determination of kinetic, diffusion and adsorption equilibrium parameters in porous catalyst particles under diffusion control conditions

A method to determine kinetics, diffusion and adsorption equilibrium parameters simultaneously in porous catalyst particles, where a first order chemical reaction occurs under diffusion control conditions in batch reactor, was proposed. The method is based on the use of observable magnitudes from a few experiments in a well stirred batch reactor. By means of a model considering the accumulation of reactant in the catalyst particles, the transient effectiveness factor allows analyzing the time response of systems with different adsorption capacities. The analysis basis and consequent methodology are more general and precise that those resulting from the conventional assumption, which consider that the concentration profiles in the particles, fulfill the steady state condition. Once an initial period elapsed after the reactant injection, the transient effectiveness factor reaches a pseudo-equilibrium state, condition under which an analytical expression can be used to describe the evolution of the reactant concentration in the fluid phase as a function of time. The parameters characterizing that expression of the dynamic response of the reactor, i.e., the exponential decaying constant and the concentration extrapolated at time zero, allow using data from a few experiments to determine the corresponding system’s diffusion, adsorption and chemical reaction parameters under reaction conditions.

Adsorption Equilibrium, Kinetics, and Thermodynamic Studies of Fluoride Adsorbed by Tetrametallic Oxide Adsorbent

This study investigated the performance of fluoride adsorption onto a specific tetrametallic oxide adsorbent Fe–Al–Ce-Ni (FACN) and the effect of temperature on adsorption performance. The adsorption performance was determined by adsorption equilibrium, kinetics, and thermodynamic parameters. The adsorption, kinetic, and thermodynamic parameters were compared alternatively. The fluoride adsorption capacity was obtained from four different adsorption isotherm models, namely, Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R), and Freundlich was found to best fit model. Fluoride removal rate using adsorption (0.27 min–1) was obtained faster than reactive adsorption (0.04 min–1). Several thermodynamic parameters such as enthalpy, Gibbs free energy, entropy (ΔS > 0), and adsorption activation energy were calculated which demonstrated the feasibility and spontaneity (ΔG < 0) and exothermic nature of (ΔH < 0) the fluoride adsorption process. The adsorption process was controlled by a physical mechanis...

Effect of light on the kinetics and equilibrium of the textile dye (Reactive Red 120) adsorption by Helianthus annuus hairy roots

The study demonstrates for the first time that light influences the adsorption equilibrium and kinetics of a dye by root culture system. The azo dye (Reactive Red 120) adsorption by the hairy roots of H. annuus followed a pseudo first-order kinetic model and the adsorption equilibrium parameters were best estimated using Langmuir isotherm. The maximum dye adsorption capacity of the roots increased 6-fold, from 0.26 mg g−1 under complete dark conditions to 1.51 mg g−1 under 16/8 h light/dark photoperiod. Similarly, adsorption rate of the dye and removal (%) also increased in the presence of light, irrespective of the initial concentration of the dye (20–110 mg L−1). The degradation of the azo dye upon adsorption by the hairy roots of H. annuus was also confirmed. In addition, a strategy for simultaneous dye removal and increased alpha-tocopherol (industrially relevant) production by H. annuus hairy root cultures has been proposed and demonstrated.

Interconversion and chromatographic separation of carbohydrate stereoisomers on polystyrene-divinylbenzene resins

Mutarotation of sugars causes distorted and splitted peaks in liquid chromatography. The shape of the elution profile is affected by the different anomeric and isomeric forms in solution. The rate of interconversion between the different forms relative to the propagation velocity in the column determines the extent of the distortion. This interplay of interconversion reaction and chromatographic separation was examined both experimentally and theoretically. Elution profiles resulting from pulse injections of glucose and fructose solutions at different flow rates and temperatures were analyzed both qualitatively and quantitatively. Adsorption equilibrium and reaction kinetic parameters were estimated by a simple fitting procedure, based on peak elution times and area ratios obtained from the analysis of the experimental profiles. To enhance the accuracy of the model parameters further, estimated reaction kinetic parameters were provided as an initial guess for inverse fitting to elution profiles, using a numeric mass balance model. Simulations with the numeric model, based on the enhanced parameters, allowed a very precise description of the experimental profiles. Accuracy of the fitted parameters was further confirmed through comparison with literature values. Reaction rate constants for the adsorbed phase were calculated and interpreted based on apparent rate constant values determined in this work, and on literature data for aqueous solutions.

Thermodynamics of krypton adsorption on microporous carbon adsorbent at high pressures

The behavior of the thermodynamic functions for the adsorption system krypton—microporous carbon sorbent ACC is described. The dependences of the differential molar isosteric heat of adsorption, entropy, enthalpy, heat capacity, and differential molar energy of the adsorption system on the adsorption equilibrium parameters were studied over the temperature range from 178 to 393 K and at pressures ranging from 1 to 6•106 Pa. Consideration of the non-ideality of gas phase and non-inertness of the adsorbent leads to a temperature dependence of the thermodynamic functions of the studied adsorption system, especially in the range of high pressures of the adsorptive. The non-ideality of the gas phase and the energetics of the adsorbent—adsorbate system exert the most significant effect on the thermodynamic functions. The non-inertness of the adsorbent in the investigated range of parameters of the adsorption system has a weak effect on the thermodynamic functions of adsorption. In the region of high filling of ACC micropores, the entropy increases, indicating the existence of processes, which change the structure of the adsorbate in the micropores, in particular, to form associates.

Using the Equilibrium and Thermodynamic Parameters of Copper Adsorption in some Calcareous Soils

Using the Equilibrium and Thermodynamic Parameters of Copper Adsorption in some Calcareous Soils

Amides as a model system of low molar mass algal organic matter. Influence on the adsorption of p-nitrophenol on activated carbon

In this study, the adsorption equilibrium and diffusivity parameters of p-nitrophenol were estimated for water containing different concentrations of secondary amides. Commercial powdered activated carbon was used as an adsorbent. The external mass transfer coefficient (kf), the surface diffusion coefficient (Ds) and the standard free Gibbs energy were calculated for p-nitrophenol in the presence of different secondary amide concentrations. The analysis established that there are correlations between structural parameters of amides, on the one hand, and diffusion and thermodynamic parameters for p-nitrophenol adsorption process, on the other. It was noticed that voluminous hydrophobic amides decreased the adsorption capacity of p-nitrophenol on activated carbon. On the basis of the results obtained for external mass transfer coefficients, it is assumed that amides cause the reduction of adsorption capacity of p-nitrophenol onto activated carbon by concentrating at the solid/liquid interface.

Transesterification of propylene glycol methyl ether in chromatographic reactors using anion exchange resin as a catalyst

Reactive chromatography using an anion exchange resin is proposed for a transesterification reaction of propylene glycol methyl ether (DOWANOL™ PM) with ethyl acetate to produce propylene glycol methyl ether acetate (DOWANOL™ PMA). This reaction is studied in batch and chromatographic reactors catalyzed by an anion exchange resin. Several anion exchange resins are tested and compared based on the performance of resin as an adsorbent and a catalyst. A chromatographic column is packed with a selected catalyst, AMBERLITE™ IRA904, and both reaction and chromatographic elution are studied at different temperatures and feed concentrations. The resulting chromatograms are fitted to a mathematical model to obtain adsorption equilibrium and reaction kinetic parameters by the inverse method. Compared to esterification investigated in a previous study, transesterification has advantages such as a higher conversion at lower temperature and easy removal of the byproduct which may lead to higher productivity. Deactivation of anion exchange resins is observed and potential solutions are suggested.

STERIC MASS ACTION MODEL FOR LACTOFERRIN ADSORPTION IN CRYOGEL WITH IMMOBILIZED COPPER IONS

Parameters of equilibrium adsorption obtained from experiments using immobilized metal affinity chromatography (IMAC) were used to evaluate the applicability of the steric mass-action (SMA) model to describe the adsorption of lactoferrin to cryogel resin under different conditions. The adsorption of lactoferrin on continuous supermacroporous cryogel with immobilized Cu2+ ions was evaluated in batch adsorption experiments at different pH (6-8) and temperature (293-313 K) values. Estimated values of the equilibrium constant (K) and characteristic number of binding sites (n) showed that these parameters decreased with increasing ionic strength, pH and temperature, while the nonlinear parameter, the steric factor (σ), increased with increasing ionic strength and temperature. Expressions correlating these parameters with pH, ionic strength and temperature were then derived.

High performance liquid chromatography of substituted aromatics with the metal-organic framework MIL-100(Fe): Mechanism analysis and model-based prediction

Metal-organic framework (MOF) MIL-100(Fe) with well-defined thickness was homogenously coated onto the outer surface of magnetic microparticles via a liquid-phase epitaxy method. The as-synthesized MIL-100(Fe) was used as stationary phase for high-performance liquid chromatography (HPLC) and separations of two groups of mixed aromatic hydrocarbons (toluene, styrene and p-xylene; acetanilide, 2-nirtoaniline and 1-naphthylamine) using methanol/water as mobile phase were performed to evaluate its performance. Increasing water content of the mobile phase composition can greatly improve the separations on the expense of a longer elution time. Stepwise elution significantly shortens the elution time of acetanilide, 2-nirtoaniline and 1-naphthylamine mixtures, while still achieving a baseline separation. Combining the experimental results and in-depth modeling using a recently developed chromatographic software (ChromX), adsorption equilibrium parameters, including the affinities and maximum capacities, for each analyte toward the MIL-100(Fe) are obtained. In addition, the pore diffusivity of aromatic hydrocarbons within MIL-100(Fe) was determined to be 5×10−12m2s−1. While the affinities of MIL-100(Fe) toward the analyte molecules differs much, the maximum capacities of the analytes are in a narrow range with q*MOFmax,toluene=3.55molL−1, q*MOFmax,styrene or p-xylene=3.53molL−1, and q*MOFmax,anilines=3.12molL−1 corresponding to approximately 842 toluene and 838 styrene or p-xylene, and 740 aniline molecules per MIL-100(Fe) unit cell, respectively.

Criterion of Occurrence of Filtration Convection of a Mixture with Account of Equilibrium and Nonequilibrium Adsorption

Convective stability of a binary mixture in a porous medium has been studied with account taken of equilibrium and nonequilibrium adsorption. The regularities of the influence of the parameters of equilibrium adsorption and of kinetic coefficients in the case of nonequilibrium adsorption on the conditions of occurrence of convection have been established. A comparison of the results with the case of the absence of adsorption has been presented.

Comparison of 2-amino benzyl alcohol adsorption onto activated carbon, silicon carbide nanoparticle and silicon carbide nanoparticle loaded on activated carbon

In the present study, the adsorption of 2-amino benzyl alcohol from aqueous solutions onto three adsorbents: activated carbon (AC), silicon carbide nanoparticles (SiC-NPs) and modified activated carbon using silicon carbide nanoparticle (SiC-AC) was studied. Several instrumental and experimental methods such as thermal gravimetric analysis, proximate analysis, X-ray powder diffraction, scanning electron microscope, Fourier transforms infrared, N2 adsorption isotherms, point of zero charge and Bohem titration were employed to determine the physicochemical properties of raw material, activated carbon, silicon carbide and modified activated carbon, respectively. The results show that the activated carbon is composed mainly of micropores, and the Brunauer–Emmett–Teller surface area was obtained as 1253.92 (m2.g−1). Experimental and instrumental data show that the attachment of silicon carbide nanoparticles changed the chemical and textural surface properties of the activated carbon. The experimental data were fitted to conventional kinetic and thermodynamic models. The equilibrium adsorption parameters reveal that the higher adsorption capacity was found in activated carbon. Additionally, in the regeneration of adsorbent, it was shown that all three adsorbents retained up to 98% of their pristine adsorption performance.