Extended Langmuir Model Research Articles

Competitive sorption of CH4, CO2 and H2O on natural coals of different rank

Competitive sorption of CH4 and CO2 from a two-component gas mixture has been studied on three coals of different rank (subbituminous coal, high-volatile bituminous coal and anthracite). On each coal, binary excess sorption isotherms were measured in the dry state and after moisture-equilibration at 53% and 97% relative humidity (RH), to investigate the effect of pre-adsorbed water on the CH4 and CO2 sorption and selectivity at 318K. Excess sorption isotherms were determined using a manometric setup and CH4/CO2 feed gas mixtures containing between 70 and 85% of CH4.The total gas (CH4+CO2) excess sorption capacity is reduced by pre-adsorbed moisture, which is most pronounced for the subbituminous coal. A large decrease in excess sorption capacity was observed for the 53% RH moisture equilibrated samples, whereas only a small further decrease was observed upon moisturization to 97% RH. The anthracite had the highest sorption capacity by far, regardless of the amount of pre-adsorbed water.All measurements show a preferential sorption of CO2 at all three moisture states. The CO2 selectivity over CH4 tends to decrease with increasing maturity and moisture content. The mean CO2 selectivity for the three investigated coals varies between 6 and 9.The extended Langmuir model for adsorption of gas mixtures is shown to be an acceptable first order approximation of the measured competitive sorption isotherm.

Single and binary adsorption of azo and anthraquinone dyes by chitosan-based hydrogel: Selectivity factor and Box-Behnken process design

Adsorption of a binary mixture of anionic dyes onto chitosan-based hydrogel (SAH) was investigated. Erichrome black T (EBT) and reactive blue 2 (RB2) were used as a model azo and anthraquinone dyes respectively. Adsorption potential of SAH was investigated under laboratory conditions as a function of initial concentration (50–400mg/L), temperate (25–55°C) and solution pH. In a single dye system, adsorption trend follows the Langmuir and pseudo second-order kinetics models. The overall rates of EBT and RB2 were noted to be controlled by film, pore and particle diffusions throughout the adsorption period. For binary dye-system, selectivity factor (A) was introduced into the extended Langmuir model, and the equilibrium data fitted well with the modified isotherm model (R2=0.96–0.99). The values of ΔG° (−17.012 to −22.473kJ/mol) of the binary dye system are within the ranges of physisorption mechanism. Box-Behnken model was utilized to estimate the competitive effects of the variables in binary dye system, and the experimental data indicates higher affinity for EBT (520.21mg/g) compared with RB2 (407.05mg/g). The reusability of SAH has proven that the adsorbent is durable and cost-effective.

Cyanoguanidine-crosslinked chitosan to adsorption of food dyes in the aqueous binary system

The dye adsorption by chitosan is considered an alternative and eco-friendly technology, however, when chitosan structure is chemically modified it can result in a more suitable adsorbent. In this work, cyanoguanidine-crosslinked chitosan (CC-chitosan) was prepared and characterized, and it was applied for the adsorption of Food Blue 2 and Food Yellow 4 in the aqueous binary system. The equilibrium curves showed adequate to fit the extended Langmuir model at different temperatures. The equilibrium results showed that the more suitable conditions for the food dye adsorption in a binary system were at 288K, and the maximum adsorption capacities were around 595–680mgg−1. Avrami model was the most appropriate to fit the kinetic behavior, and desorption was possible for two cycles. On the basis of FT-IR spectrums, it was shown that cyanoguanidine was successfully inserted on the chitosan polymeric chains. CC-chitosan was an efficient adsorbent in removing dyes from aqueous binary systems.

Removal of phenol and cyanide in multi‐substrate system using copper impregnated activated carbon (Cu‐GAC)

This study studies the process of removal of phenol and cyanide in multi‐substrate system using copper impregnated Granular Activated Carbon (Cu‐GAC). Effects of various process parameters on removal were taken into consideration. It was observed that under optimum conditions of pH 9, temperature 30°C, adsorbent dose 10 g/L, initial concentration 200 mg/L phenol and 20 mg/L cyanide and contact time 18 h, ∼91% removal of phenol and 94% removal of cyanide takes place. Among equilibrium models, Extended Freundlich model was found suitable for description of adsorption of both phenol and cyanide. The maximum adsorption capacity for phenol and cyanide, calculated by Extended Langmuir model, was 292.95 and 3.21 mg/g of Cu‐GAC, respectively. It was observed that phenol and cyanide show synergism in the process of adsorption from wastewater. Kinetic modeling of experimental data on adsorption of phenol and cyanide established the suitability of pseudo‐first and ‐second order model for adsorption of phenol and cyanide on Cu‐GAC, respectively. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1714–1723, 2015

Modeling mono- and multi-component adsorption of cobalt(II), copper(II), and nickel(II) metal ions from aqueous solution onto a new carboxylated sugarcane bagasse. Part I: Batch adsorption study

A new carboxylated-functionalized sugarcane bagasse (STA) was prepared through the esterification of sugarcane bagasse with trimellitic anhydride. The optimized synthesis conditions yield STA with a percent weight gain of 73.9% and the number of carboxylic acid groups accounted for 3.78mmol/g. STA was characterized by FTIR, elemental analysis, TGA, PZC, and SEM. Adsorption kinetics followed a pseudo-second-order model. The adsorption rate constant showed the following order: k2,Ni2+>k2,Cu2+>k2,Co2+. Four mono- and multi-component isotherm models were used to model the adsorption systems. Monocomponent experimental data were fitted to Langmuir and Sips models; whereas, multicomponent data were fitted to modified extended Langmuir and P-factor models. The maximum adsorption capacities (Qmax,mono) obtained from the Langmuir model were 1.140, 1.197, and 1.563mmol/g for Co2+, Cu2+, and Ni2+, respectively. The competitive studies demonstrated that the multicomponent adsorption capacity (Qmax,multi) was smaller than Qmax,mono, as a result of the interaction between the metal ions. Desorption studies showed that all metal ions could be fully desorbed from STA.

Binary adsorption isotherm and kinetics on debittering process of ponkan (Citrus reticulata Blanco) juice with macroporous resins

Selective removal of bitter components from ponkan juice with macroporous resins improved it sensory quality with scarcely effect on its nutritive value. Ten macroporous adsorbent resins were evaluated for their capacity in adsorbing the debittering component, and the adsorption selectivity for limonin against flavonids was estimated using coefficient αl/f. LX920 resin exhibited the highest adsorption capacity (7.96 mg/g wet resin) and selectivity coefficient αl/f (99.42) at initial limonin concentration of 24 μg/mL. The adsorption equilibrium and kinetics were isothermally generated at 25 °C under static mode condition. Langmuir isotherm model and modified extended Langmuir model were well fitted with single and binary adsorption isotherms in binary system, respectively. The solute adsorptivity KL of LX920 resin for limonin (2.81 L/g) was higher than that for flavonoids (1.10 L/g). limonin was more efficiently adsorbed onto the resin's surface. Furthermore, the pseudo-first, pseudo-second and intra-particle diffusion kinetic equations were employed to match the experimental adsorption data. Pseudo second-order and pseudo-first kinetic models were best fitted to the adsorption of limonin and flavonoids, respectively.

스트론튬과 세슘 이온의 혼합 몰비를 달리한 이성분 용액에서 제올라이트 A에 의한 경쟁 흡착: 흡착등온 및 속도해석

The adsorption characteristics of Sr ions and Cs ions in single and binary solution by zeolite A were investigated in batch experiment. The adsorption rate of Sr ions and Cs ions by zeolite A obeyed pseudo-second-order kinetic model in single and binary solution. The initial adsorption rates (h) and adsorption capacities of both ions obtained from pseudo-second-order kinetic model, and the values were decreased with increasing concentration of the competitive ions (0~1.5 mM). Also, adsorption isotherm data in binary solution were well fitted to the extended Langmuir model, the maximum adsorption capacities of Sr and Cs calculated from the model were 1.78 mmol/g and 1.64 mmol/g, respectively. The adsorption of Sr and Cs ions by zeolite A was carried out in the presence of other cations such as Na+, K+, Mg2+, and Ca2+. The results showed that the zeolite A can maintain a relatively high adsorption capacity for Sr and Cs ions and exhibits a high selectivity in the presence of competitive cations. The effect of competition had an order of Ca2+>K+>Mg2+>Na+ for Sr ions and K+>Ca2+>Na+>Mg2+ for Cs ions at the same cation concentration.

Modeling of competitive ultrasonic assisted removal of the dyes – Methylene blue and Safranin-O using Fe3O4 nanoparticles

The study was focused on the simultaneous removal of Methylene blue (MB) and Safranin-O (SO), as most together hazardous dye in wastewater, from aqueous solution by ultra-sonic-assisted adsorption onto the developed adsorbent i.e. Fe3O4 NPs. Fe3O4 NPs were synthesized, by using central composite design (CCD), the effects of variables such as pH, adsorbent dosage, MB concentration, SO concentration and contact time on binary dyes removal were examined and optimized values were found to be 6, 0.01g, 10 and 20mg/L and 2min, respectively. The very rapid removal of dyes makes this novel adsorbent as a promising tool for wastewater management applications. Different adsorption isotherm model i.e. Langmuir, Freundlich, non-modified Langmuir, modified competitive Langmuir, modified extended Langmuir, extended Freundlich and sips models are studied out of which extended-Freundlich model proved to be the best fit to equilibrium data because of correlation value (R2) is 0.99 which is very close to 1, additionally it depicts the high adsorption capacity around (89.2–91.9mgg−1). An empirical extension of competitive extended-Freundlich model was proposed to predict the simultaneous adsorption behavior of MB and SO. It was observed that pseudo-second-order equation is suitable to fit the experimental data.

Modeling the Adsorption Step during Hydrogen Purification in Gas Treatment Application

Abstract The present work is interested in modeling the adsorption step for the process of Pressure Swing Adsorption (PSA) for hydrogen purification. This work aims at modeling the adsorption of one or more compounds in a mixture at different pressures ranging from 8 to 20 bars at ambient temperature. The flow was presented by the piston model with an axial dispersion. The equilibrium isotherm was expressed by the Langmuir model for the mono-component adsorption and the model of Langmuir extended for the multi-component adsorption. Moreover, two models of kinetic transfer between the gaseous and solid phases were considered, the first-order model based on the approximation of the Linear Driving Force (LDF) and a sophisticated model which is the Surface Diffusion model (SD). As a first step, the CH4/H2 mixture adsorption on activated carbon was studied. In a second step, the adsorption of CH4/CO2/H2 on activated carbon and of CH4/N2/H2 on a 5A° molecular sieve was studied taking into consideration an interaction parameter for the extended Langmuir model. The simulation results obtained after the resolution of the equations of the model in a developed program, compared with the experimental results from previous works, show a rather satisfactory agreement on the level of stoichiometric time and kinetic mass transfer.

Competitive Retention of Sulfamethoxazole (SMX) and Sulfamethazine (SMZ) from Synthetic Solutions in a Strong Anionic Ion Exchange Resin

Numerous antibiotics such as sulfonamides have been found in effluents from drug manufacturers. Removal of pharmaceuticals by adsorption and ion exchange comprise some of the most promising techniques for the retention of these compounds from wastewaters due to their low cost, easy regeneration, and selective removal of pollutants. This article studies the removal of sulfamethoxazole (SMX) and sulfamethazine (SMZ), the most common sulfonamide antibiotics detected in municipal sewage. Lewatit MP500 (Lanxess Chemical) ion exchange resin was used to remove SMX, SMZ present in solutions. Batch experiments were carried out in cylindrical stirred tanks. Binary system solutions of equal mass concentration were prepared containing 30-250 mg/L of each compound, SMX and SMZ, and tested with an L/S ratio (mL solution/g resin) = 1000 obtained in previous experiments. Also, the adsorption of SMX mixed with trimethoprim (TMP) in batch experiments was analyzed due to the fact that both compounds are usually administered together. Equilibrium and kinetics were studied in order to characterize the operation. The adsorption equilibrium constants for SMX and SMZ were determined using a modified extended Langmuir model for multicomponent equilibrium sorption. Kinetics was analyzed using the pore diffusion model. Finally, several loading and elution cycles were carried out in fixed bed to obtain the breakthrough curves, comparing the experimental data to predicted values from a fixed bed model.

Remediation of Groundwater Polluted by Aromatic Compounds by Means of Adsorption

In this work, an experimental and modeling analysis of the adsorption of four aromatic compounds (i.e., toluene, naphthalene, o-xylene and ethylbenzene) onto a commercial activated carbon is carried out. The aim is to assess the suitability of the adsorption process for the treatment of polluted groundwater, also when a multiple contamination is detected. Batch adsorption tests from simulated polluted groundwater are performed in single-compound systems and in two binary systems (i.e., toluene + naphthalene and o-xylene + ethylbenzene), at constant temperature (20 °C) and pH (7). Experimental results in single-compound systems reveal that all of the analytes are significantly adsorbed on the tested activated carbon. In particular, toluene and naphthalene adsorption capacities are the highest and of similar value, while for o-xylene and ethylbenzene, the performances are lower. The adsorption of these compounds seems to be influenced by a combined effect of several parameters, such as hydrophobicity, molecule size, structure of the molecule, etc. Experimental results in binary systems show a different behavior of the two systems, which confirms their complexity and explains the interest in these complex adsorption systems. In particular, toluene and naphthalene are mutually competitive, while in the case of o-xylene + ethylbenzene, only the former undergoes competitive effects. The analysis of the entire experimental data set is integrated with a dedicated modeling analysis using the extended Langmuir model. For both single-compound and binary systems, this model provides acceptable results, in particular for low equilibrium concentrations, like those more commonly found in groundwater, and for the compounds involved in adsorptive competitive effects.

Molecular simulation and modelisation of methane/ethane mixtures adsorption onto a microporous molecular model of kerogen under typical reservoir conditions

The prediction of mixture adsorption is a challenging task in gas industry when dealing with shales for both resources prospect or production forecast. In this work, we used molecular simulation and models to study the adsorption of methane/ethane mixtures onto a mature kerogen model under typical reservoir conditions (338K, up to 20MPa). Using Molecular Dynamics, we first generated microporous structures of kerogen, representative of field samples. Monte Carlo simulations in the Grand Canonical ensemble were used to produce pure compound and mixture adsorption isotherms on these adsorbent structures. The ability to predict simulation results of the Ideal Adsorbed Solution model and a modified statistical mechanical derivation of the Extended Langmuir model have been studied at low pressures (up to 1MPa) where species are supposed ideal and at higher pressures (up to 20MPa) where species non-ideality is partially introduced in the models. At low pressures, the adsorption isotherms predicted by the two models are in good agreement with the results from molecular simulation, independently of the confinement. At higher pressures, this agreement is only valid for the less confined structures and worsened as the micropore size decreases.

Core flooding experiments of CO2 enhanced coalbed methane recovery

This paper presents the results of CO2 enhanced coal bed methane (ECBM) core floods on intact coal core from the Bowen Basin and the Hunter Valley, Australia, at pore pressures of 4MPa and 10MPa. The core floods involved flooding with CO2 to displace methane from the core and then reversing the flood by injecting methane to displace the CO2 from the previous flood. An important parameter for ECBM is the displacement or sweep efficiency which was estimated directly from the mass balance over the core flood. Displacement efficiencies obtained through CO2 injection were excellent with more than 99% of the CH4 recovered during the core floods. The reverse experiments in which CH4 was injected to displace CO2 were notably less effective with an average of 95% displacement obtained for the Bowen Basin core sample and only 71% displacement obtained for the Hunter Valley core sample by the end of the experiment. History matching was performed with the reservoir simulator SIMED II which used a hydrostatic permeability model, the extended Langmuir model, and a bi-disperse diffusion model. In general, good history matches were obtained between simulated and observed flow rates, mass balances, and breakthrough times demonstrating that the model could accurately represent the ECBM process. It was found that the triple porosity gas diffusion model provided an improved agreement to observations over the unipore model. Connell–Lu–Pan's hydrostatic permeability model was used in the history matching which differentiates between bulk and pore sorption strain. During the CO2 flooding experiments a change in permeability was observed as CO2 displaced CH4 in the core. As the stress conditions were constant, this was the result of the sorption strain impacting on the porosity and thus permeability. However, for the reverse core flood in which CH4 was injected to displace CO2, no permeability changes were observed, implying that pore and bulk strain were the same and thus cancelled out.

Modelling uptake and toxicity of nickel in solution to Enchytraeus crypticus with biotic ligand model theory

Protons and other cations may inhibit metal uptake and alleviate metal toxicity in aquatic organisms, but less is known about these interactions in soil organisms. The present study investigated the influence of solution chemistry on uptake and toxicity of Ni in Enchytraeus crypticus after 14 days exposure. Ca2+, Mg2+ and Na+ were found to exert significant effects on both uptake and toxicity of Ni. An extended Langmuir model, which incorporated cation competition effects, well predicted Ni uptake. The LC50{Ni2+} predicted by a developed Biotic Ligand Model matched well with observed values. These suggest that cation competition needs to be taken into account when modelling uptake and effects. The binding constants of Ni2+, Mg2+ and Na+ on the uptake and toxic action sites were similar, but for Ca2+ they differed. This indicates that the effect of Ca2+ on Ni2+ toxicity cannot simply be explained by the competition for entry into organism.

Standard Gibbs energy of adsorption and surface properties for ionic liquids binary mixtures

A classical thermodynamic model for the first time is used to derive an equation for the standard Gibbs energy of adsorption and surface properties for ionic liquids binary mixtures. Where experimental surface tension of the mixtures is available, the agreement between the calculated and the experimental data is found to be very good. Bulk mole fraction and surface tension of one of the pure component are necessary inputs for this equation. In addition, to find more information about surface structure of binary mixtures, the surface tension of binary mixtures has been studied using extended Langmuir model (EL).

An Experimental Approach to Adsorption of CO2 + CH4 Gas Mixtures Onto Coal (European RFCS CARBOLAB Research Project)

Abstract Results from adsorption experiments of CO 2 + CH 4 gas mixtures onto coal show that adsorption capacities determined with pure gas phases cannot be added to determine the total adsorption capacity of a gas mixture; and that both CO 2 and CH 4 adsorption capacities for experiments performed with gas mixtures are lower than those determined for experiments with pure gases. These results confirm that gases compete to adsorb onto coal. Results also show that the extended Langmuir model that is often used to model sorption of binary gas mixtures does not fit our experimental data. Thus, authors propose here another model.

Competitive adsorption of phenol and resorcinol onto rice husk ash

The present study deals with the adsorptive removal of phenol and resorcinol from aqueous solution onto rice husk ash. The competitive adsorption equilibrium of the binary mixtures (phenol/resorcinol) was determined by conducting batch experiments with initial concentration varying in the range of 50 to 1000 mg/L. In order to evaluate multicomponent adsorption isotherm parameters, individual adsorption equilibrium studies were also carried out. Langmuir, Freundlich and Redlich-Peterson equilibrium isotherm models were used for single compound equilibrium sorption data modeling. All three models almost similar fit for single compound equilibrium data. Binary equilibrium adsorption data and the parameter evaluated from single adsorption data were fitted to various multicomponent isotherm models by minimizing the sum of square of error. The extended Langmuir model gave the better fit to the experimental adsorption data of phenol and resorcinol from binary systems onto rice husk ash. It seems that both phenol and resorcinol compete for the same adsorption sites on rice husk ash. The net interactive effect of phenol and resorcinol on the adsorption of resorcinol by rice husk ash was found to be antagonistic.

Single-multicomponent biosorption of lead mercury chromium and arsenic onto activated sludge in batch and fixed-bed adsorber

A wide range of batch experiments were carried out for estimation of the key process parameters in competitive biosorption of Pb2+, Hg2+, Cr3+, and As5+ from simulated of wastewater onto dry activated sludge in batch adsorber. Eleven isotherm models were used for single component and five isotherm models for multicomponent systems. The Langmuir model gave the best fit for the data of single component, while the binary, ternary, and quaternary systems were fitted successfully with extended Langmuir model. An order of metal biosorption capacity onto dried activated sludge was found to be Pb2+ > Hg2+ > Cr3+ > As5+. FTIR analysis was carried out before and after biosorption. Pore diffusion coefficients required for fixed-bed design were determined by matching batch experimental data with the film-pore diffusion model at optimum agitation speed, 600 rpm and optimum weight of sewage sludge biomass. A general multicomponent rate model has been utilized to predict the fixed-bed breakthrough curves for multicomponent systems. Good agreement between the predicted theoretical breakthrough curves and the experimental results was observed. Results confirmed, from the feed containing Pb2+, Hg2+, Cr3+, and As5+, arsenic breakthrough from the column appeared first with higher overshoot, followed by chromium, mercury, and finally lead cations with no overshoot. COMSOL multiphysics software was used to solve the batch and fixed-bed models.

Studies on the adsorption behavior of CO2-CH4 mixtures using activated carbon

Separation of CO2 from CO2-CH4 mixtures is an important issue in natural gas and biogas purification. The design of such separation processes depends on the knowledge of the behavior of multicomponent adsorption, particularly that of CO2-CH4 mixtures. In this study, we present a series of experimental binary equilibrium isotherms for CO2-CH4 mixtures on an activated carbon at 293 K and compare them with predicted values using the Ideal Adsorption Solution Theory (IAST) and the Extended Langmuir (EL) model. Even at concentrations of ca. 20% for all binary isotherms, CO2 already presents higher adsorbed amounts with respect to CH4. A maximum selectivity of around 8.7 was observed for a nearly equimolar mixture at 0.1 MPa. The IAST in conjunction with the Toth equation showed slightly better results than IAST using the Langmuir equation and both showed better results than the EL model.

Use of Chitosan with Different Deacetylation Degrees for the Adsorption of Food Dyes in a Binary System

Chitosan with different deacetylation degrees was applied for the adsorption of food dyes (Acid Blue 9 and Food Yellow 3) in a binary aqueous system. The effects of deacetylation degree (DD) and pH on the food dyes adsorption were evaluated by response surface methodology (RSM). In the more adequate adsorption condition, the equilibrium curves were obtained under different temperatures, and the extended Langmuir model was fitted to the experimental data. RSM results showed that the best conditions for the adsorption of food dyes onto chitosan were DD of 95% and pH 2.5. Under these conditions, the adsorption capacities were 163.6 and 193.4 mg/g for Acid Blue 9 and Food Yellow 3, respectively. The total percentage removal was 90%. The equilibrium curves were of high affinity (H type) and the adsorption was favored by the temperature decrease. The extended Langmuir model presented satisfactory fit with the experimental equilibrium data. These results demonstrated that chitosan is an efficient adsorbent to remove dyes from binary systems.