Linear Adsorption Isotherm Research Articles

Adsorptive removal of technetium‐99 using macroporous poly(GMA‐co‐EGDMA) modified with diethylene triamine

AbstractThe possibility of sorption of technetium‐99 in the form of pertechnetate anion (TcO4−) and the sorption kinetics for removing TcO4− from aqueous solution by chelating polymers based on glycidyl methacrylate (GMA) were investigated. Two samples of macroporous crosslinked poly(glycidyl methacrylate‐co‐ethylene glycol dimethacrylate) (PGME), with different amount of the crosslinker (ethylene glycol dimethacrylate, EGDMA), were synthesized by suspension copolymerization and functionalized with diethylene triamine (deta). We propose that nonspecific sorption of pertechnetate anion via electrostatic interactions takes place at the protonated amino groups of macroporous crosslinked copolymer. The results of batch experiments performed at pH 1–14 showed fast sorption kinetics for removing TcO4− by amino‐functionalized PGME‐deta in a wide range of pH, that is, from 1.0 to 9.0. Almost complete removal of TcO4− (91–98%) was reached within 180 min in the stated pH range (1.0–9.0), with the sorption half‐times of under 25 min. The partitioning coefficients of linear adsorption isotherms, with 180‐min equilibrium time, reach the high values of 2130 mL g−1 and 1698 mL g−1 for the two samples of synthesized PGME‐deta. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

An analytical solution to contaminant diffusion in semi-infinite clayey soils with piecewise linear adsorption

The adsorption of contaminants onto soil particles typically is nonlinear if the contaminant concentration is sufficiently high. A simplified piecewise linear adsorption isotherm consistent with experimental results is proposed as an approximation for nonlinear adsorption behavior. This approximation allows for the use of analytical solution to model solute diffusion of contaminants that exhibit nonlinear adsorption. A moving boundary is introduced to represent significant changes in the retardation factor of clay with an increase in solute concentration. The proposed analytical solutions were validated using experimental data presented in the literature. There is negligible difference between the results obtained by the proposed analytical solution and those obtained by the linear model when C m / C 0 reached 0.5. The results also show that the model based on linear adsorption using the initial secant of the Freundlich isotherm leads to significantly lower estimated breakthrough time for the contaminant of interest than that obtained using the proposed model. The earlier breakthrough is due to an under-estimation of the amount of adsorption. The proposed method is relatively simple to apply and can be used for evaluating experimental results and verifying more complex numerical models.

Preparation of amino-modified active carbon cartridges and their use in the extraction of quercetin from Oldenlandia diffusa

Polyethyleneimine (PEI) and ethylenediamine (EDA) as modifiers were bonded on active carbon (AC) surface for specific selective extraction of quercetin from Oldenlandia diffusa. The characteristics of the modified AC materials that were obtained were investigated by field emission-scanning electron microscopy (FE-SEM) and Fourier transform infrared spectrometer (FT-IR). The interactions between quercetin and the AC materials were investigated by fitting the static adsorption data to four linear and nonlinear adsorption isotherm models. Of these four models, the Langmuir–Freundlich adsorption isotherm was proved the best for investigating quercetin on AC materials. Scatchard analysis was used to evaluate the binding properties of the AC materials for quercetin. Solvent extraction and solid-phase extraction (SPE) were optimized, and the effect of the mobile phase pH was investigated to improve the performance for the separation of quercetin on high performance liquid chromatography (HPLC). The results from the validation of the proposed analytical method demonstrated that the EDA-modified AC was the most suitable SPE cartridge for the purification of quercetin from O. diffusa.

Equilibrium and kinetics of vancomycin adsorption on polymeric adsorbent

AbstractIsolation step of vancomycin, a glycopeptide antibiotic, is usually done from fermentation broth filtrate, while its adsorption directly from the whole broth could rationalize the process. The equilibrium and kinetics of vancomycin adsorption from broth supernatant, diluted and whole broth on polymeric adsorbent was studied in this work. Experimental equilibrium data was correlated with Sips, Langmuir, Freundlich, and linear adsorption isotherms. Agreement between measured and regressed data for the first three mentioned models did not vary much and was relatively high. The maximum adsorbed amount for supernatant was higher than for fermentation broths because mycelium particles blocked adsorbent surface. Liquid film mass transfer studies showed that external mass transfer resistance could have been neglected. Diffusion of vancomycin inside adsorbent particles was acknowledged using a nonstructural, homogenous surface diffusion and bidisperse pore models. Model simulations indicated that kinetics of the process could be improved by using smaller adsorbent particles. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Natural fibers characterization by inverse gas chromatography

Vegetable fibers can be considered as naturally occurring composites, consisting mainly of cellulose, lignin and hemicellulose. Their properties are significantly affected by many factors such as variety, climate, harvesting and maturity, among others. Thus, prior to their application, the fibers should be properly characterized. In the present study, inverse gas chromatography was used to study the surface properties of several cellulosic fibers and the effect of an alkaline treatment. Dispersive surface energy ranged from 38.41mJ/m2 for piassava to 52.39mJ/m2 for assai. The studied fibers presented Lewis basic character with a Kb/Ka ratio between 1.27 and 4.00, corresponding to curaua and pita Mexicana, respectively. Based on the obtained linear adsorption isotherms, the surface area and monolayer capacity were higher for piassava. Pita Mexicana appeared to be the most heterogeneous one, with two energetic sites. The alkaline treatment of sisal increased the number of active sites for specific interactions, significantly increasing its basic character. It also increased its surface area, with a consequent decrease in the diffusion coefficient.

Adsorption Isotherms of Substituted Benzophenones on a Reverse-Phase Liquid Chromatography System: Effect of the Mobile-Phase Composition

Linear adsorption isotherms were registered by a frontal analysis method for four substituted benzophenones (BPs) using a liquid chromatography Luna C18(2) column as adsorbent. The isotherm data po...

Efficient Adsorption of Chromium(VI) Ions from Aqueous Solution onto a Low-Cost Adsorbent Developed from Limonia Acidissima (Wood Apple) Shell

The removal of chromium(VI) ions from aqueous solution was studied using Limonia acidissima (wood apple) shell activated carbon. The removal extent was found to be a maximum at a pH value of 2, with the lowcost adsorbent having an adsorption capacity of 13.74 mg/g. The material employed was characterized by scanning electron microscopy (SEM), Fouriertransform infrared spectroscopy (FT-IR) and elemental analysis. The linear Freundlich and Langmuir adsorption isotherm models were applied to describe the experimental equilibrium isotherms. The results showed that the Langmuir equation gave a better fit to the experimental data than the Freundlich equation. The pseudo-first-order and pseudo-second-order models were applied to the adsorption kinetics of Cr(VI) ions onto wood apple shell activated carbon. Thermodynamic parameters such as the standard enthalpy (ΔH0), the Gibbs' free energy (ΔG0) and the standard entropy (ΔS0) were evaluated and indicated that the sorption process was spontaneous and endothermic in nature. The results demonstrated that wood apple shell activated carbon may be effectively used for the inexpensive removal of Cr(VI) ions from aqueous solution.

Analysis and modelling of non-equilibrium sorption of aromatic micro-pollutants on GAC with a multi-compartment dynamic model

The optimisation of granular activated carbon (GAC) processes for industrial wastewater treatment requires the development of dynamic model that considers adsorption in multi-compartment porous media. In this work, the adsorption of toluene and naphthalene on GAC is investigated. Sorption equilibrium and kinetic experiments were performed at laboratory scale using low contaminant concentrations. The experimental conditions were chosen so as to simultaneously explore the different ranges of concentrations typically encountered in industrial wastewaters. The sorption behaviour was then explained through modelling taking into account the main equilibrium and transport phenomena and three adsorption compartments: the GAC particle surface, the macro- and meso-pores, and the micro-pores. The pore diffusion and solid diffusion were both considered to be coupled with a linear adsorption isotherm. With one set of four parameters adjusted for an adsorbent/contaminant pair, the model satisfactorily describes the non-equilibrium adsorption/desorption processes in different operating conditions and initial conditions.

Modelling of fixed-bed adsorption of mono-, di-, and fructooligosaccharides on a cation-exchange resin

Abstract Kinetics of fixed-bed adsorption of simple saccharides (glucose, fructose, and sucrose) and fructooligosaccharides (1-kestose, 1-nystose, and 1 F -fructofuranosyl nystose) on process-size particles of cation exchanger Amberlite™ CR1320Ca was investigated. A step-up method of frontal chromatography was used when several inlet concentration steps were made in the range of 0–20 g dm −3 . The obtained experimental data were fitted simultaneously using the general rate model with two estimated parameters, which were the distribution coefficient of linear adsorption isotherm and solid-phase diffusion coefficient. The contribution of individual transport phenomena to dispersion of adsorption fronts was discussed.

Sorption of Sulfonamides and Tetracyclines to Montmorillonite Clay

The current study investigated the sorption of sulfadimethoxine (SMT), sulfamethoxazole (SMX), tetracycline (TET), and oxytetracycline (OTC) to Na-rich montmorillonite clay in synthetic effluent (SE) and field wastewater effluent (FE). Both SMT and SMX showed a low sorption capacity and are therefore likely to be highly mobile in the environment, while the sorption of TET to clay in environmental pH range (6.5–7.5) showed similarly high adsorption capacity. Differences in sorption capacities of TET and OTC to SE or FE were attributed to the various concentrations of divalent cations in the effluents. In addition, differences in sorption of OTC or TET to SE were attributed to their different molecular structure. Moreover, the adsorption of TET in SE and FE showed linear adsorption isotherms and fitted to Freundlich model. Further experiments showed that addition of humic acid or SE to TET sorbed to clay did not enhance or suppress the sorption of TET to clay.

A Sequencing Method Applied to the Solution of a Linear Model of an Adsorption Column

This paper discusses the application of a new transient simulation method, called the sequencing method, to solve a model representing a fixed bed adsorption column. In each time step, convection and mass transfer are applied successively on the column's mesh. Numerical simulations are given for linear adsorption isotherms. These results are compared with the traditional finite difference method. The results show that the sequencing method yields excellent fluid and solid concentration profiles along the column's length and a more accurate prediction of breakthrough time than the finite difference method.

Sorption dynamics in fixed-beds of inert core spherical adsorbents including axial dispersion and Langmuir isotherm

The effects of axial dispersion and Langmuir isotherm on transient behavior of sorption and intraparticle diffusion in fixed-beds packed with monodisperse shell-type/inert core spherical sorbents are studied. The system of partial differential equations of the mathematical model is solved numerically using finite difference methods. Results are presented in the form of breakthrough curves for adsorption and desorption processes. Results reveal that the shape of the breakthrough curves is influenced by both hydrodynamic and kinetic factors. Hydrodynamic factor is governed by axial dispersion and is controlled by changes of Peclet number. Simulation results reveal that when linear adsorption isotherm is used, the effect of axial dispersion on breakthrough curves of the system is important for Peclet numbers smaller than 50, whereas, for Langmuir isotherm axial dispersion is considerable for Peclet numbers less than 80. In addition, effects of type of adsorption isotherms and size of adsorbents on breakthrough curves are investigated, and results are compared with existing reports in the pertinent literature. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Hybrid method of solution applied to simulation of pulse chromatography

In this communication, the method proposed by Cremasco et al. (2003) is applied to predict single and low concentration pulse chromatography. In previous work, a general rate model was presented to describe the breakthrough curve, where a hybrid solution was proposed for the linear adsorption. The liquid phase concentration inside the particle was found analytically and related with the bed liquid phase through Duhamel's Theorem, while the bulk-phase equation was solved by a numerical method. In this paper, this method is applied to describe pulse chromatography of solutes that present linear adsorption isotherms. The simulated results of pulse chromatography are compared with experimental ones for aromatic amino acid experiments from literature.

Environmental Media Phase-Tracking Units in the Classroom

When teaching phase partitioning concepts for solutes in porous media, and other multi-phase environmental systems, explicitly tracking the environmental media phase with which a substance of interest (501) is associated can enhance the students' understanding of the fundamental concepts and derivations. It is common to explicitly track the customary mass, length, and time based units. The expansion described here is to also track the specific media phases to which these fundamental units apply. This additional step forces students to think more carefully about concentrations and other terms. This paper presents a consistent system of notation for teaching these concepts and some examples of how this system is used. The examples presented here are based on solid-liquid partitioning and a linear Freundlich adsorption isotherm, but could also be applied to other environmental media, such as air and biological tissue, as well as other partitioning models. This approach is most appropriate for advanced undergraduate and graduate students.

Nonlinear isotherm of benzene and its derivatives by frontal analysis

Adsorption behavior of a solute is one of the most important factors to consider when designing a batch and a continuous liquid chromatographic separation process. In liquid chromatography, this behavior is based on the adsorption equilibrium between the liquid mobile-phase and solid stationary-phase. However, most retention models have been developed under a linear adsorption isotherm: very few researchers have investigated the relationship between the adsorption parameters and the mobile phase composition, and some empirical models have been introduced. In this work, adsorption isotherms were obtained by a frontal analysis for three small molecular compounds (benzene, toluene, and chlorobenzene) on a commercial C18 bonded silica column. The absorption based on the Langmuir, Freundlich, and Langmuir-Freundlich models were investigated according to changes of the composition of methanol highly enriched eluent. The calculations and analysis of the coefficients obtained for the three models confirm that the adsorption data for solutes are best modeled with the Langmuir-Freundlich isotherm. In spite of the acceptable accuracy, Langmuir and Freundlich isotherm models couldn’t satisfactorily describe the mechanism and provide objective information on the physical nature of the absorption.

Vacuum membrane distillation of the main pear aroma compound: Experimental study and mass transfer modeling

In this work, the recovery of the main pear aroma compound, ethyl 2,4-decadienoate, by means of vacuum membrane distillation is studied. A commercial hollow fiber module of polypropylene (PP) microporous membranes and a model solution of ethyl 2,4-decadienoate in ethanol–water mixtures were used in the experimental study. The effect of the operating variables, aroma feed concentration, feed flow rate, temperature and downstream pressure onto the process performance was analysed. Aroma enrichment factors up to 15 were experimentally obtained. A strong and reversible sorption of the aroma compound onto the PP material was observed. This phenomena was characterized by a linear adsorption isotherm, q a = K ads C a e , where K ads(295.96 K) = 0.27 kg kg −1 m 3 kg −1. A mathematical model able to predict the kinetics of the components separation and the partial component fluxes and enrichment factors was developed. In this model the classical gas transport mechanisms through the membrane pores, i.e. Knudsen and molecular diffusion, together with the sorption-diffusion phenomenon through the non-porous membrane portion, expressed by means of the surface diffusivity, were considered. The surface diffusivity of ethyl 2,4-decadienoate on the polypropylene was estimated to be D a s = 1.01 × 10 − 11 m 2 s − 1 at 296 K.

Investigation of the potential mobility of Pb, Cd and Cr(VI) from moderately contaminated farmland soil to groundwater in Northeast, China

The adsorption/desorption of Pb, Cd and Cr(VI) on moderately contaminated farmland soils in Northeast China and the effect of pH value on adsorption/desorption were investigated. Soil column leaching experiment was also carried out to further understand the mobility of the three metals in aeration zone of soil. Both Langmuir and Freundlich model gave good fits to the adsorption data of Pb and Cd, while the adsorption data of Cr(VI) followed linear adsorption isotherm. The adsorption/desorption of Pb, Cd and Cr(VI) obtained equilibrium in a few hours. Adsorption amounts of the three metals decreased in the order: Pb > Cd ≫ Cr(VI). Desorption of the metals was insignificant at pH 5.0. Pb and Cd adsorption increased with pH, while Cr(VI) decreased. The effect of pH on desorption was contrary to that of adsorption. Leaching experiment showed that the mobility of these metals followed the order of Cr(VI) ≫ Cd > Pb, which was consistent with the adsorption/desorption study. The results suggest that once soil is polluted by wastewater containing Pb and Cd, Pb and Cd tend to accumulating in topsoil and move downward very slowly, while the mobility of Cr(VI) in soil/groundwater system is much high because only limited amount of Cr(VI) were adsorbed by soil.

Mechanisms and factors influencing the removal of microcystin-LR by ultrafiltration membranes

In this study, we investigate the application of ultrafiltration (UF) for the removal of the cyanotoxin, microcystin-LR, and determine the dominant removal mechanisms. System variables examined included membrane characteristics, feed concentration, water recovery and operating pressure. While adsorption dominated rejection for most UF membranes, at least at early filtration times, both size exclusion and adsorption were important in removing microcystin-LR by the tight thin-film (TF) membranes. Adsorption was primarily attributed to hydrophobic interactions, although hydrogen bonding and physical surface properties such as surface roughness, thickness, and porosity may also play a role. Polysulfone membranes, the most hydrophobic membrane examined, significantly adsorbed microcystin-LR (∼91%), whereas the more hydrophilic cellulose acetate membranes adsorbed little or no microcystin-LR. The initial feed concentration had a significant influence on the adsorption capacity of TF membranes for microcystin-LR, which could be described based on a linear adsorption isotherm. An increase in water recovery and/or operating pressure led to an increase in the adsorption of microcystin-LR, probably due to increased convective transport. On the other hand, microcystin-LR rejection through size exclusion was reduced for higher water recovery and/or applied pressure.

Characterization of Cu(II) Ion Adsorption Behavior of the Polyacrylic Acid-Polyvinylidene Fluoride Blended Polymer

A blended polymer adsorbent prepared using acrylic acid and polyvinylidene fluoride was used to remove copper from aqueous solutions. The polymer was prepared using thermally induced polymerization and phase inversion. The blended polymer was characterized by X-ray diffraction analysis (XRD), environmental scanning electron microscopy (ESEM), X-ray photoelectron spectroscopy (XPS), and N 2 adsorption/desorption experiments. The sorption data was fit to linearized adsorption isotherms of the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms models. The batch sorption kinetics was evaluated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic reaction models. Δ H° is greater than 0, Δ G° is lower than 0, and Δ S° is greater than 0, which shows that the adsorption of Cu (II) by the blended polymer is a spontaneous, endothermic process. The adsorption isotherm fits better to the Freundlich isotherm model and the pseudo-second-order kinetics model gives a better fit to the batch sorption kinetics. The adsorption mechanism is assumed to be ion exchange between the cupric ion and the carboxylic acid functional group of the blended polymer.

Adsorption of methyl tert-butyl ether (MTBE) from aqueous solution by porous polymeric adsorbents

MTBE has emerged as an important water pollutant because of its high mobility, persistence, and toxicity. In this study, a postcrosslinked polymeric adsorbent was prepared by postcrosslinking of a commercial chloromethylated polymer, and a nonpolar porous polymer with comparable surface area and micropore volume to the postcrosslinked polymer was prepared by suspended polymerization. The postcrosslinked polymer, nonpolar porous polymer and chloromethylated polymer were characterized by N 2 adsorption, FTIR and XPS analysis. Results showed that postcrosslinking reaction led to the generation of a microporous postcrosslinked polymer with BET surface area 782 m 2 g −1, average pore width 3.0 nm and micropore volume 0.33 cm 3 g −1. FTIR and XPS analysis indicated the formation of surface oxygen-containing groups on the postcrosslinked polymer. The three polymers were used as adsorbents to remove aqueous methyl tert-butyl ether (MTBE). Adsorption of MTBE over the postcrosslinked polymeric adsorbent was found to follow the linear adsorption isotherm, whereas MTBE adsorption onto the nonpolar porous polymer and chloromethylated polymer followed Langmuir adsorption model. Comparison of adsorption capacities of the postcrosslinked polymer, chloromethylated polymer and nonpolar porous polymer revealed that the adsorption of MTBE from aqueous solution is dependent on both pore structure and surface chemistry of polymeric adsorbents, and the high adsorption efficiency of the postcrosslinked polymer towards MTBE is attributed to its high surface area, large micropore volume and moderate hydrophility. The process of MTBE adsorption onto the adsorbents can be well described by pseudo-second-order kinetics, and the rate of adsorption decreased at higher MTBE initial concentration.