Adsorption Isotherms Of Phenol Research Articles

Separating Surface and Solvent Effects and the Notion of Critical Adsorption Energy in the Adsorption of Phenolic Compounds by Activated Carbons

A modified form of the Freundlich equation in which the solute equilibrium concentration is normalized with respect to the solute solubility is analyzed and applied to adsorption isotherms of phenol, 4-nitrophenol, 4-chlorophenol, and 2-chlorophenol at different values of pH on commercial activated carbon before and after oxidation. The analysis confirms the importance of normalizing the solute equilibrium concentration when analyzing the adsorption isotherms, and it is suggested that a parameter, K(F10), obtained by taking 10% solubility as the reference point when applying the Freundlich equation, is probably the best comparative estimate of the relative adsorption capacity of the carbon for different phenolic compounds. In combination with the Freundlich exponent, n(F), estimates of the adsorption capacity at any other reference point can then be obtained. Analysis of the experimental results also indicates a need to distinguish between two regimes of adsorption, characterized by an adsorption energy, E(ads), greater than or less than a critical value, E(ca). When E(ads) > E(ca), the shape of the adsorption isotherm is determined by solute-solid interactions. On the other hand, when E(ads) < E(ca), solute-solution interactions become more important.

Heterogeneity of activated carbons with different surface chemistry in adsorption of phenol from aqueous solutions

The heterogeneity of activated carbons is investigated on the basis of adsorption isotherms of phenol from dilute aqueous solutions at different values of pH in the solution. The original carbon studied was prepared from polyethyleneterephtalate (PET). Its various oxygen surface functionalities were systematically changed by additional nitric acid and heat treatments. The Dubinin–Astakhov adsorption-isotherm equation was used to evaluate the parameters characterizing the adsorption of phenol from dilute water solutions on activated carbon surfaces. Adsorption energy distribution functions were calculated by the INTEG algorithm, based on a regularization method. Analysis of distribution functions for activated carbons provides significant comparative information about their energetic heterogeneity. Moreover, a comparison of the resulting energies obtained from the distributions can be made with enthalpic data.

Experimental and modeling study of adsorption in preparative monolithic silica column

The hydrodynamic, equilibrium and kinetics of adsorption in a silica-based monolithic preparative column Chromolith Prep. Si (Merck KgaA, Germany) have been studied. The inverse size-exclusion chromatography with polystyrene standards of narrow molecular size distribution and small tracer molecule has been used to measure the external and total porosity of the monolithic column. The column permeability was calculated according to the Darcy law for laminar flow. The efficiency of the monolithic column was characterized through the height equivalent to a theoretical plate (HETP) of phenol, ethyl vanillin and dimethyl phthalate. The separation efficiency does not decrease in the region of high flow rates. The adsorption isotherms of phenol, ethyl vanillin and dimethyl phthalate measured by frontal analysis were linear in the investigated concentration range. The 2D single channel mathematical model has been applied to describe the adsorption dynamics. The model assumes parabolic velocity profile, axial and radial diffusion in the monolith channel, linear driving force model for the mass transfer in the monolith channel skeleton wall and linear adsorption equilibrium. The model gives good prediction of the experimental breakthrough curves.

Adsorption Mechanism in RPLC. Effect of the Nature of the Organic Modifier

The adsorption isotherms of phenol and caffeine were acquired by frontal analysis on two different adsorbents, Kromasil-C18 and Discovery-C18, with two different mobile phases, aqueous solutions of methanol (MeOH/H2O = 40/60 and 30/70, v/v) and aqueous solutions of acetonitrile (MeCN/H2O = 30/70 and 20/80, v/v). The adsorption isotherms are always strictly convex upward in methanol/water solutions. The calculations of the adsorption energy distribution confirm that the adsorption data for phenol are best modeled with the bi-Langmuir and the tri-Langmuir isotherm models for Kromasil-C18 and Discovery-C18, respectively. Because its molecule is larger and excluded from the deepest sites buried in the bonded layer, the adsorption data of caffeine follow bi-Langmuir isotherm model behavior on both adsorbents. In contrast, with acetonitrile/water solutions, the adsorption data of both phenol and caffeine deviate far less from linear behavior. They were best modeled by the sum of a Langmuir and a BET isotherm models. The Langmuir term represents the adsorption of the analyte on the high-energy sites located within the C18 layers and the BET term its adsorption on the low-energy sites and its accumulation in an adsorbed multilayer system of acetonitrile on the bonded alkyl chains. The formation of a complex adsorbed phase containing up to four layers of acetonitrile (with a thickness of 3.4 A each) was confirmed by the excess adsorption isotherm data measured for acetonitrile on Discovery-C18. A simple interpretation of this change in the isotherm curvature at high concentrations when methanol is replaced with acetonitrile as the organic modifier is proposed, based on the structure of the interface between the C18 chains and the bulk mobile phase. This new model accounts for all the experimental observations.

Kinetics of phenol oxidation in a trickle bed reactor over active carbon catalyst

AbstractThe wet air oxidation of phenol over a commercial active carbon catalyst was studied in a trickle bed reactor (TBR) in the temperature and oxygen partial pressure ranges of 120–160 °C and 0.1–0.2 MPa, respectively. The performance of the active carbon was compared in terms of phenol and COD destruction. The weight change of active carbon due to reaction was also measured. Finally, oxic phenol adsorption isotherms were assessed in batch conditions at 25, 125 and 160 °C. In order to use the conversion data obtained from the TBR for a kinetic study, special care was taken to check the kinetic control in the TBR experiments. Several kinetic models including power law or Langmuir–Hinshelwood expressions were considered to describe the catalytic oxidation of phenol over active carbon. The simple power law model with first order dependence on both phenol and oxygen concentration predicted satisfactorily the experimental data not only over the entire range of operating conditions studied, but also outside its validity range. Copyright © 2005 Society of Chemical Industry

Determination of the adsorption capacity of activated carbon made from coffee grounds by chemical activation with ZnCl 2 and H 3PO 4

In order to evaluate the adsorptive capacities of granular activated carbon produced from coffee grounds by chemical activation, the adsorption of different phenols and acid and basic dyes, has been carried out. The comparison with a commercial activated carbon has been made. Adsorption isotherms of phenols and dyes (acid and basic) onto produced and commercial granular activated carbons were experimentally determined by batch tests. Both Freundlich [1] and Langmuir [2] models are well suited to fit the adsorption isotherm data. As a result, the coffee grounds based activated carbon may be promising for phenol and dye removal from aqueous streams.

Removal of Phenol by Using Montmorillonite, Clinoptilolite and Hydrotalcite

This work is to study the removal of phenol from aqueous solutions by adsorption using three different adsorbents, clinoptilolite, montmorillonite, and hydrotalcite (HT). Except for montmorillonite, the other adsorbents were treated. Clinoptilolite was modified using cetyltrimethylammonium bromide (CTAB) and hydrotalcite was calcined by heating to 550∘C. Adsorption isotherms of phenol on all of the mentioned adsorbents was determined by using the batch equilibration technique and indicated that, the adsorption behavior could be modelled by using the Modified Freundlich equation. The differences observed in the isotherms were explained by the variations in adsorbent-adsorbate interactions under the effects of the different surface structures of adsorbents and the pH dependent ionization behavior of phenol. Calcined hydrotalcite (HTC) was found to be the best among the studied adsorbents since it can adsorb 52% of phenol from a solution containing initially 1 g/L phenol for the 1/100 adsorbent solution ratio while the others can adsorb only 8% of phenol for the same concentration and adsorbent solution ratio.

Tris(2,2′-bipyridine)ruthenium(II)-clays as adsorbents for phenol and chlorinated phenols from aqueous solution

The adsorptive properties of tris(2,2′-bipyridine)ruthenium(II)-clay intercalation compounds, which were synthesized through cation exchange reactions from synthetic saponite (Sumecton SA), synthetic fluoro-tetrasilicic mica and montmorillonite (Kunipia F) for phenols were investigated. The adsorption isotherms of phenols for the tris(2,2′-bipyridine)ruthenium(II)-clays from aqueous solutions followed Langmuir type, indicating strong adsorbate–adsorbent interactions. The basal spacings of the tris(2,2′-bipyridine)ruthenium(II)-clays did not change through the adsorption of phenols. This means that the adsorbed phenols existed in the interlayer nanopore created by the tris(2,2′-bipyridine)ruthenium(II) in the interlayer space of the tris(2,2′-bipyridine)ruthenium(II)-clays. The adsorbed amounts of phenols varied depending upon the nature of clays. One of the factors responsible for the variation in the adsorbed amounts is the layer charge density of smectites. Relatively low-layer charge density of saponite led to relatively large pore volume in the interlayer space. The adsorbed amounts of 2,4-dichlorophenol for the tris(2,2′-bipyridine)ruthenium(II)-saponite and the tris(2,2′-bipyridine)ruthenium(II)-montmorillonite were the largest among three phenols. It is thought that the interactions between tris(2,2′-bipyridine)ruthenium(II) cation and phenols played an important role in the adsorption of these phenols.

Adsorption of organic compounds onto activated carbons from recycled vegetables biomass.

The removal of organic species from aqueous solution by activated carbons is investigated. The latter ones are prepared from olive husks and almond shells. A wide range of surface area values are obtained varying temperature and duration of both carbonization and activation steps. The adsorption isotherm of phenol, catechol and 2,6-dichlorophenol involving the activated carbons prepared are obtained at 25 degrees C. The corresponding behavior is quantitatively correlated using classical isotherm, whose parameters are estimated by fitting the equilibrium data. A two component isotherm (phenol/2,6-dichlorophenol) is determined in order to test activated carbon behavior during competitive adsorption.

Adsorption Isotherms for Phenol Onto Activated Carbon

This laboratory study investigated the effectiveness of two types of activated carbons (ACs), NORIT Granular Activated Carbon (NAC 1240) and NORIT Granular Activated Carbon 010 (NAC 010), for the removal of phenol from aqueous solutions. The study was carried out under batch mode at different initial concentrations (10-60 mg/I) and at temperature of 30°C. The adsorption isotherm parameters for the Langmuir and Freundlich models were determined using the adsorption data. It was found that both the Langmuir and the Freundlich isotherms described well the adsorption behavior of phenol on NAC 010, while the Freundlich isotherm described very well the adsorption of phenol on NAC 1240.

Adsorption of phenol and chlorophenols on hexadecyltrimethylammonium-and tetramethylammonium-montmorillonite from aqueous solutions

Batch experiments were carried out at 25°C to obtain the adsorption isotherms of phenol, 2-cholorophenol, 4-chlorophenol and 2,4-dichlorophenol on hexadecyltrimethylammonium-exchanged-and tetramethylammonium-exchanged-montmorillonite (HDTMA-M and TMA-M) prepared from Wyoming bentonite SWy-2. The isotherms were interpreted principally using the Freundlich model. The reaction orders (n) and Freundlich constants (k F) for the adsorption of an adsorbate on HDTMA-M and TMA-M remain approximately constant against the variation of adsorbate to adsorbent ratios. Then value for most of the phenolic adsorbates on HDTMA-M is close to unity, indicating Langmuir-type adsorption but that on TMA-M is variable among different phenolic adsorbates. The degree of adsorption of phenolic compounds on HDTMA-M is primarily controlled by the hydrophobicity of the adsorbates but those on TMA governed by the complicated combinations of size, shape and hydrophobicities of the adsorbates. The estimated model parameters for the adsorption isotherms on HDTMA-M are in disagreement with those of earlier workers probably because of the differences in experimental conditions. This study also estimated the model parameters on TMA-M, which are not available in the literature.

Effects of the surface chemistry of carbon materials on the adsorption of phenol–aniline mixtures from water

The adsorption behavior of phenol, aniline and phenol–aniline mixtures in water over carbonaceous material surfaces has been studied. The adsorbents used were: a mesoporous high surface area graphite (HSAG) and a microporous activated carbon (AC). Aliquots of AC were treated with HCl and H2F2 to remove inorganic surface impurities. Furthermore, samples of HSAG and AC were subjected at 1173 K, to inert He flow, in order to eliminate surface oxygen groups. Apparent surface areas, surface oxygen groups and, zero point of charge of the adsorbent surfaces have been determined. All the adsorption isotherms of phenol and aniline on HSAGs are adequately fitted by Freundlich type isotherms, while on ACs, the extended Langmuir equation provides a better description of the experimental results. This fact reveals the importance of the textural characteristics (i.e., pore sizes) on the adsorption behavior. The presence of oxygen surface groups affects the adsorption behavior. Their effect depends on the amount of these groups that are present on the adsorbent surface and on the nature of the adsorbate molecule. In the case of HSAG, aniline is adsorbed to a larger extent than phenol for all the studied phenol–aniline mixtures. The opposite trend was found for ACs. Elimination of oxygen groups, originally present in larger amounts on the HSAG surface than on AC, produces an inversion in the selectivity adsorption of the mixtures. That is, more phenol than aniline is adsorbed on the surface of heat-treated HSAG (HSAGT).

Surface heterogeneity of six commercial brands of end-capped C18-bonded silica. RPLC separations.

Single component adsorption isotherms of phenol and caffeine were measured on six different commercial brands of end-capped C(18)-bonded silica columns (five monomeric bonded phases: Kromasil, Waters Symmetry, Phenomenex, Hypersil, and Chromolith from Merck; one polymeric bonded phase, Vydac) with the same methanol/water solution (30/70, v/v) as the mobile phase. Adsorption data were acquired by frontal analysis (FA) for all these columns in the same way. Depending on their solubility in the mobile phase, the concentrations used ranged between 1 and 100 g/L and between 0.35 and 35 g/L for phenol and caffeine, respectively. Twenty-two adsorption data points were recorded over these ranges. In each case, the best isotherm model accounting for all sets of adsorption data is the bi-Langmuir model, all columns behaving as heterogeneous adsorbents despite the endcapping. Depending on the column, the high-energy sites accounts for between 30 and 40% and between 4 and 7% of the total saturation capacity for phenol and caffeine, respectively. Except for the polymeric phase (Vydac), the ratio of the adsorption constants on the high- and low-energy sites is constant at around 10 for both phenol and caffeine, corresponding to an average adsorption energy difference of 5 kJ/mol between these two sites. The exact nature of the high-energy sites is illustrated by the following properties: (i) they have a very low selectivity for caffeine, with alpha(caffeine/phenol) close to 0.4 for the five monomeric columns, which suggests the complete derivatization of residual silanols; (ii) the high-energy sites account for a large fraction of the surface area of these packing materials (35% for phenol, 6% for caffeine); (iii) there is a small adsorption energy difference between high and low adsorption energy sites (5 kJ/mol); and (iv) the adsorption constants increase with increasing surface coverage of the monomeric columns. Thus, the high energy sites cannot be residual free silanols of the bare silica. More likely, they are related to the local heterogeneity of the C(18)-bonded-layer structure. Caffeine is more strongly retained on the low-energy sites than phenol (the product q(s,) (1)b(1) is larger for caffeine) but the contribution of the high-energy sites (q(s,) (2)b(2)) is markedly lower for caffeine than for phenol, despite the larger value of the adsorption constant, b(2). Because of a larger molecular size, caffeine cannot penetrate as deeply as phenol inside the bonded layer. This explains the paradox of a stronger retention for phenol than for caffeine on end-capped C(18)-bonded stationary phases.

Adsorption–desorption isotherm hysteresis of phenol on a C 18-bonded surface

Single component adsorption and desorption isotherms of phenol were measured on a high-efficiency Kromasil-C 18 column ( N=15 000 theoretical plates) with pure water as the mobile phase. Adsorption isotherm data were acquired by frontal analysis (FA) for seven plateau concentrations distributed over the whole accessible range of phenol concentration in pure water (5, 10, 15, 20, 25, 40, and 60 g/l). Desorption isotherm data were derived from the corresponding rear boundaries, using frontal analysis by characteristic points (FACP). A strong adsorption hysteresis was observed. The adsorption of phenol is apparently modeled by a S-shaped isotherm of the first kind while the desorption isotherm is described by a convex upward isotherm. The adsorption breakthrough curves could not be modeled correctly using the adsorption isotherm because of a strong dependence of the accessible free column volume on the phenol concentration in the mobile phase. It seems that retention in water depends on the extent to which the surface is wetted by the mobile phase, extent which is a function of the phenol concentration, and of the local pressure rate, which varies along the column, and on the initial state of the column. By contrast, the desorption profiles agree well with those calculated with the desorption isotherms using the ideal model, due to the high column efficiency. The isotherm model accounting best for the desorption isotherm data and the desorption profiles is the bi-Langmuir model. Its coefficients were calculated using appropriate weights in the fitting procedure. The evolution of the bi-Langmuir isotherm parameters with the initial equilibrium plateau concentration of phenol is discussed. The FACP results reported here are fully consistent with the adsorption data of phenol previously reported and measured by FA with various aqueous solutions of methanol as the mobile phase. They provide a general, empirical adsorption model of phenol that is valid between 0 and 65% of methanol in water.

Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons

Physical properties of activated carbons prepared from pinewood at different activation times (0.5, 1.5, 2.7, and 4.0 h) in steam at 900 °C were studied. The adsorption equilibria and kinetics of three dyes and three phenols (phenol, 3-chlorophenol, and o-cresol) from aqueous solutions on such carbons were then examined at 30 °C. The adsorption isotherms of phenols could be well fitted by the Freundlich equation, and those of dyes were adequately described by the Langmuir–Freundlich equation. The effect of microporosity of the carbons on adsorption capacity was explored. Four simplified kinetic models including pseudo-first-order equation, pseudo-second-order equation, intraparticle diffusion model, and the Elovich equation were selected to follow the adsorption processes. The adsorption of all six adsorbates could be best described by the Elovich equation. The kinetic parameters of this best-fit model were calculated and discussed.

A Study of the Influence of Hydrophobicity of Activated Carbon on the Adsorption Equilibrium of Aromatics in Non-Aqueous Media

The effect of hydrophobicity on the adsorption of aromatics on metal-free activated carbons was studied. Adsorption isotherms for phenol, aniline, benzene, and xylene were generated in cyclohexane and heptane media, using seven carbons with different surface heterogeneity. The hydrophobicity of these carbons was probed using flow microcalorimetry (FMC). Surface polarity and solvent and adsorbate hydrophobicity were found to influence the adsorption capacity. For adsorbates that do not form hydrogen bonds with oxygen on the carbon surface, higher surface acidity lowers adsorption capacity due to increased polarity. In contrast, for adsorbates that can form hydrogen bonds with surface oxygen, the capacity is enhanced at higher surface acidities. A higher solvent hydrophobicity was found to decrease capacity for all the aromatic adsorbates studied, except at high surface polarity, where the effect of the solvent was found to be minimal.

Heterogeneity of active carbons in adsorption of phenol aqueous solutions

Energetic heterogeneity of activated carbons prepared from bituminous coals is investigated on the basis of adsorption isotherms of phenol from the dilute aqueous solutions. The Langmuir–Freundlich (L–F) equation has been used to estimate the monolayer capacity values of carbons studied. Adsorption energy distribution functions have been calculated by using algorithm INTEG based on a regularization method. Analysis of these functions for carbons provided significant comparative information about their heterogeneity.

Fitting adsorption isotherms to the distribution data determined using packed micro-columns for high-performance liquid chromatography

Knowing the adsorption isotherms of the components of a mixture on the chromatographic system used to separate them is necessary for a better understanding of the separation process and for the optimization of the production rate and costs in preparative high-performance liquid chromatography (HPLC). Currently, adsorption isotherms are usually measured by frontal analysis, using conventional analytical columns. Unfortunately, this approach requires relatively large quantities of pure compounds, and hence is expensive, especially in the case of pure enantiomers. In this work, we investigated the possible use of packed micro-bore and capillary HPLC columns for the determination of adsorption isotherms of benzophenone, o-cresol and phenol in reversed-phase systems and of the enantiomers of mandelic acid on a Teicoplanin chiral stationary phase. We found a reasonable agreement between the isotherm coefficients of the model compounds determined on micro-columns and on conventional analytical columns packed with the same material. Both frontal analysis and perturbation techniques could be used for this determination. The consumption of pure compounds needed to determine the isotherms decreases proportionally to the second power of the decrease in the column inner diameter, i.e. 10 times for a micro-bore column (1 mm I.D.) and 100 times for capillary columns (0.32 mm I.D.) with respect to 3.3 mm I.D. conventional columns.

Electro-Activation of Granular Carbon from Olive Mill Solid Residue

A technique for activation of granular activated carbon (GAC) is presented based on the electrochemical method. In this study, we investigate the effectiveness of the electroactivated GAC in removing phenol from water and determine the optimum conditions for activation. Electro-activation of the GAC appears to be an interesting technique; it requires a short electro-activation time Ta = 30 min and an optimum potential ranging from +200 mV/SCE to 400 mV/SCE. Phenol adsorption isotherms gave a limiting adsorption capacity Qm dependent on the applied potential, which at potential E=+300 mV/SCE was improved by about 55%, giving Qm = 75 mgphenol g−1 GAC.

Effects of dissolved oxygen and surfactant treatment on the sorptive capacity of a local soil for phenol

The soil used in this study was found to have 24% clay (Muscovite) and a surface area of 173 m2/g. Hexadecyl‐trimethyl‐ammonium bromide (HDTMA) surfactant was mixed with the soil in order to investigate its effect on the soil sorptive capacity. Fourier transform infrared spectroscopy (FTIR) spectrums showed interaction between the soil and HDTMA. Phenol adsorption isotherms conducted for the soil under different combinations of HDTMA and dissolved oxygen (DO) revealed that both HDTMA and DO enhance the adsorption capacity of the soil for phenol. HDTMA‐induced increase of 48.5% and 312% in the soil sorptive capacity was attained at a residual phenol concentration of 100 g/1 under anoxic and oxic conditions, respectively. On the other hand, DO increased the soil sorptive capacity by 26% and 249% at 100 mg/1 phenol residual concentration for untreated and treated samples, respectively. The sorptive capacity enhancement was investigated at different residual phenol concentrations. DO without HDTMA treatment caused a constant enhancement around 40%. Up to a residual phenol concentration of 240 mg/1, DO caused an additional capacity enhancement over that treated with HDTMA only. Above the aforementioned residual concentration, an opposite trend was observed.