Statistically modeled adsorption isotherms for the multilayer gas molecules adsorbed on non-porous solid adsorbents of two and three groups sites

The adsorption isotherms with each saturation vapor pressure factor (c_s1, c_s2 or c_s3) for two groups of sites in two cases of the multilayer and for three groups of sites in one case of the multilayer are derived statistically in heterogeneous non-porous solid adsorbents without interactions among the adsorbed molecules. When some sites of BET isotherm are substituted by less energetic sites, the two-group isotherm obtained by the substitution shows less adsorption over the whole range of relative pressure than the BET isotherm prior to the substitution, at any combined values of f₁ with M₁ of the two-group isotherm with the same saturation vapor pressure factor. A method to get the monolayer sites (v_m) from the ratios of the experimental isotherm to the theoretical isotherm at the whole relative vapor pressure minimizing the standard error is suggested. Our two- or three-group isotherms calculated through many experimental adsorption isotherm data selected appropriately provide larger values of v_m than those obtained from BET isotherms. Differential heat vs. v/v_m and Bose-Condensation heat are mentioned.     

Preparation and Characterization of Activated Carbon from Chestnut Shell and its Adsorption Characteristics for Lead

Activated carbons were prepared from chestnut shell by phosphoric acid activation and the prepared activated carbons were used to remove lead(II) from aqueous solutions. The effects of impregnation ratio (IR) and activation temperature on activated carbon production were investigated. The produced activated carbons were characterized by N₂ adsorption, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques. The highest surface area (1611 m²/g) and total pore volume (0.7819 cm³/g) were obtained at a carbonization temperature of 500°C with an impregnation ratio of 3/1. The resulting activated carbon was used for removal of lead(II) from aqueous solution. The effects of temperature, contact time, and adsorbent dosage were investigated. The adsorption isotherm studies were carried out and the obtained data were analyzed by the Langmuir, Freundlich, and Temkin equations. The rate of adsorption was found to conform to the pseudo-second-order kinetic model. The Langmuir isotherm equation showed better fit for all temperatures and the maximum adsorption capacities of lead(II) was obtained as 138.88 mg/g at 45°C.     

A new model for water adsorption in porous ceramics

This research proposes a new isotherm model that is derived for adsorption of clustering and condensable vapors on mesoporous ceramics. The adsorption characteristics of water vapor on both experimental data and isotherm model were investigated over the relative pressure ranging from 0 to 0.95. The applicability of the model was evaluated by significance of fitting parameters. For each adsorption isotherm there are five parameters (m, q _f , K _f , q _m and K _m ). The comparison of modeling fit with experimental data was used as the methodology for selecting the most informative and the best-fitting model. The experimental testing results showed that this model is able to describe all possible behaviors of the water adsorption isotherm displaying type IV classification. The model is based on the forming and growth of the water molecule clusters and capillary condensation mechanism in mesopore. The findings suggest a significant tool for understanding the behavior of water adsorption in humidity-control porous ceramics.     

Adsorption characteristics of carbonized bark for phenol and pentachlorophenol

The potential of using carbonized slash pine bark as a substitute for activated carbon was examined in this study. The bark was carbonized by slow heating in nitrogen for 6·5 h to 672°C. The BET-N₂ surface area, average micropore and mesopore diameter, and micropore volume were 332 m² g⁻¹ 21·7 Å, and 0·125 cm³ g⁻¹, respectively. The adsorption capacities for phenol and pentachlorophenol (PCP) at pH 2 and pH 8 were evaluated. The Langmuir equation provided a slightly better fit than the Freundlich equation to two sets of phenol data. The calculated Freundlich constants, K = 0·41–0·58 mmol/g/(mmol dm⁻³)^1/n and 1/n = 0·30–0·41, were lower and higher, respectively, than literature values for activated carbons. The adsorption capacity of the carbonized bark was much lower for PCP than for phenol. The protonated and anionic PCP isotherms were Type II or III, respectively, in the Brunauer classification. The BET equation provided the best fit to protonated PCP isotherm data. The anionic PCP data were fitted to both the BET model and an equation used in the literature to represent phosphate adsorption on activated carbons. Non-linear regression of the data for both phenol and PCP adsorption with the Freundlich, Langmuir and BET equations generally gave more accurate param-eters, compared with the use of linearized equations to obtain the parameters. © 1998 SCI.     

Preparation and characterization of spherical activated carbons from oil agglomerated bituminous coals for removing organic impurities from water

A new and simple method of producing of spherical activated carbons (SACs) from different bituminous coals, i.e., gas coal, gas-coking coal and orthocoking coal, is presented. Coal agglomerates of spherical shape obtained by oil agglomeration using rapeseed oil and linseed oil, were subjected to carbonization and activation with steam at 850 °C. The SACs prepared from gas-coking coal (hvAb) agglomerates were characterized by the best developed porous structure with surface area S_BET of about 800 m²/g and pore volume of 0.40 cm³/g. The adsorption capacity of the produced SACs was determined in terms of substituted phenolic compounds. The adsorption of 2-chlorophenol (OCP), 4-chlorophenol (PCP) and 4-nitrophenol (PNP) from aqueous solutions was studied under a static conditions on the SAC prepared from gas-coking coal agglomerated using rapeseed oil. At high concentrations of the solute the adsorption behavior of OCP was found to be different in comparison to PCP and PNP. The adsorption of the two last phenolic compounds on the selected SAC is very well described by Langmuir adsorption model. For OCP a two-stepped adsorption isotherm was obtained. The Langmuir isotherm equation fits very well only for the first stage of the OCP adsorption.     

The complete identity of the isotherm equations of dubinin and john for determination of the volume and degree of microporosity of carbon

Complete identity of adsorption isotherms of Dubinin and John is proved by showing that the slope D of Dubinin equation is equal to slope D₀ of Dubinin type equation derived from John's isotherm and also showing that the terms involved in D and D₀ are fundamentally the same. It is shown that the degree of microporosity is proportional to n the slope of John's isotherm. B the measure of microporosity in Dubinin equation is inversely proportional to n. The advantages of John's isotherm are also given.     

Studies on the Adsorption of Traces of Zirconium on Manganese Dioxide from Acid Solutions

Abstract

The adsorption of zirconium on manganese dioxide from nitric and perchloric acid solutions has been investigated at different concentrations of electrolyte, adsorbent, and adsorbate. The effect of other cations and anions on adsorption has been studied. Fluoride, citrate, oxalate, molybdate, tartrate, carbonate, phosphate, Fe(III), Sr(II), Zn(II), Cr(III), and Mg(II) drastically reduce adsorption. Adsorption of other metal ions on the oxide has been measured under identical conditions. Based on these data, separation of zirconium from a number of elements, including cobalt, zinc, caesium, neodymium and lutetium, can be achieved. Zirconium adsorption follows Freundlich's equation C _Ads = AC ^1/n Bulk with the values of 1/n = 0.92 and A = 40 mmol/g. Thus manganese dioxide can be used for the separation and preconcentration of zirconium from dilute solutions.     

Preparation and Evaluation of Fullers Earth Beads for Removal of Cesium from Waste Streams

Abstract

Fullers earth beads and cylinders were prepared using chitosan and sodium silicate as binders, respectively, for removal of cesium ion from aqueous solutions. The cost of the adsorbent is expected to be significantly lower as the raw materials are low cost materials and readily available. The adsorbents were characterized by SEM, EDS, and x‐ray microanalysis. Adsorption capacity of the beads was evaluated under both batch and dynamic conditions. The adsorption capacity for Fullers earth beads was found to be 26.3 mg/g of adsorbent at 293 K when the liquid phase concentration of cesium was 1000 mg/L. The adsorption capacity of Fullers earth cylinder was found to be higher than that of beads, however, it was concluded that the alkaline nature of the cylinder precipitated out cesium increasing its capacity. The capacity of Fullers earth beads decreased by almost 62% when 1 mol/L NaCl and 2.25 mmol/L of strontium were present in the solution. The Freundlich, the Langmuir isotherm equations, and a modified Polanyi's equation were used to correlate the data. The isosteric heats of adsorption suggested the heterogeneity of the surface and multilayer coverage. The first order reversible kinetic model adequately described the dynamic system during the adsorption process. The adsorption (k₁) and desorption (k₂) rate constants were evaluated from the dynamic model.     

Sorption of ruthenium by dipropylmethyl-2-(N,N-diisobutyl) acetamidoammonium iodide impregnated Amberlite XAD-4 resin from nitric acid medium

Dipropylmethyl-2-(N,N-diisobutyl)acetamidoammonium iodide has been impregnated on Amberlite XAD-4 resin and investigated for sorption of Ru from nitric acid medium. Equilibrium sorption data for Ru uptake were represented well by the Langmuir isotherm equation (R² = 0.98) compared to Freundlich isotherm equation (R² = 0.86). The maximum monolayer coverage (Q₀) value of 6.25 mg/g as obtained from Langmuir isotherm was close to the experimental value (5.63 mg/g). The heterogeneity parameter (1/n) = 0.37 obtained from the slope of Freundlich isotherm indicates slight heterogeneity in sorption process. Aqueous solutions of 5% ammonia or 10% sodium hydroxide were found suitable for desorption. The method can be applied for separation of Ru from acidic waste solutions.     

Study of the CO2 adsorption isotherms on El Hicha clay by statistical physics treatment: microscopic and macroscopic investigation

ABSTRACT

CO₂ introduction in deep aquifers based on adsorption phenomena represents geological tanks that reduce CO₂ emission. Thus, investigating carbon dioxide adsorption on rocks is becoming more interesting. In our work, carbon dioxide adsorption on El Hicha clay is extensively studied. Experimental data for CO₂ adsorption on this clay are given for the first time. All the corresponding parameters are simulated and interpreted using the multilayer model with two interaction energies. The effect of the key parameters involved in the adequate model on the isotherm curves are thus elucidated and interpreted. The formulation of this model is based on statistical physic formalism. Several hypotheses involving some physicochemical parameters which describe perfectly the adsorption process are used.

The characteristic parameters of the adsorption isotherm such as the number of carbon dioxide molecules per site (n), the receptor site densities (N_M), the number of adsorbed layers (N_L) and the energetic parameters (-ε₁) and (-ε₂) are estimated for the studied systems by a nonlinear least square regression. These parameters are discussed and interpreted considering their temperature dependence. In order to provide new macroscopic interpretations of adsorption mechanisms, three thermodynamic functions are also determined such as the entropy, the internal energy and the free enthalpy of Gibbs from experimental data. Thus, we prove theoretically and experimentally that CO₂ adsorption on El Hicha clay is feasible, spontaneous and exothermic in nature.     

Dilute solution properties of hydrophobically associating polyacrylamide: fitted by different equations

In this paper six different equations were used to fit the data of dilute solution of both nonionic (PBAM3) and ionic (PBAMS) hydrophobically associating polyacrylamide with and without the addition of NaCl. The results showed that Fedors equation was the most accurate equation to describe the dilute solution properties of these kinds of polymers. The lower value of the polymer concentration parameter (C_m) in Fedors equation was corresponded to the higher value of the constant k in Schulz-Blaschke equation for PBAM3 system. Two types of polymers had anti-polyelectrolyte effect. In dilute solution the PBAMS polymer chains had a more extended conformation than those of PBAM3 due to the existence of ionic groups.     

Removal of basic dyes from aqueous solutions using natural clay

Adsorption properties of natural clay (from Eski?ehir of Turkey) were investigated by depending on different adsorption conditions such as different initial dye concentrations and contact times. The chemical composition of the natural clay was analyzed by X-ray fluorescence spectrometry (XRF). The removal of basic dyes such as Nile Blue (NB) and Brilliant Cresyl Blue (BCB) from aqueous solutions using natural clay in this study was described. After the equilibrium adsorption time of 8 h, the adsorption capacities for NB and BCB reach about 25 mg/g and 42 mg/g, respectively. Lagergren kinetic equation was used to test the experimental data to examine the controlling mechanism of adsorption processes. Adsorption data of the BCB and NB onto natural clay were fitted well by the pseudo-first-order model. The adsorption isotherms data were correlated with the Freundlich equation and the Freundlich constants K_f (mg/g) and n (intensity of adsorption) were calculated. The r² (regression coefficients) values were 0.9835 and 0.9849 for NB and BCB, respectively. The adsorption capacities of natural clay for NB and BCB have the following order: BCB > NB.     

Adsorption characteristics of sericite for cesium ions from an aqueous solution

To efficiently remove cesium ions from aqueous solution, sericite was used as a novel adsorbent. The silanol (SiO₂) and aluminol (Al₂O₃) groups in sericite are likely to play an important role in adsorption process. The maximum adsorption capacity (q_m) and adsorption constant (K_L) for cesium ions obtained from the Langmuir isotherm model were 6.68 mg/g and 0.227 L/mg, respectively and regression curve fit well with the experimental data as the 0.965 of correlation coefficients (r²). However, when the Freundlich isotherm model was used correlation coefficient (r²) was 0.973. Therefore, it was concluded that Freundlich model fits equilibrium data better than Langmuir model. When the 6.0 g/L of sericie concentration was added to aqueous solution, cesium ions were removed by about 80% and the increase was not happened above 6.0 g/L of sericite concentration any more. The process was determined as exothermic reaction because the removal efficiency of cesium ions decreased as temperature increased. Furthermore, all adsorption was completed in 120 min and comparing the pseudo first and second-order kinetic models indicates that the adsorption of cesium ions using sericite follows well the pseudo-second-order kinetics.     

Statistical condensation adsorption isotherms of gas molecules adsorbed on porous adsorbents, surface monolayer adsorption isotherms and hysteresis phenomena

Condensation adsorption isotherms of type IV (or V) according to BDDT classification on porous adsorbents composed of one or two groups of adsorption sites are derived statistically. When Β_c1 (or Β_c2) is less than unity, the isotherm becomes type IV, and when it is greater than unity, the isotherm becomes type V. It is understood that the negative sign(-) of the additional adsorption energy, q, in the nth layer in deriving those theoretical isotherms plays a decisive role on the horizontally flat approach to the axis of the isotherm near the saturation vapor pressure. The values of the surface area can be calculated easily. The pore radii of all the adsorbents which we have obtained by using the derived isotherms with respect to the appropriately selected experimental data agree with those obtained by using the Kelvin equation. Many surface mono-layer adsorption isotherms are obtained in the process of deriving the various adsorption isotherms. From them we can learn that the surface sites are not adsorbed completely even near the saturated vapor pressure, and we can find the range of error by comparing them with v_ms of the BET equation. We could mention through judging the results of a great deal of the experimental isotherm data of types IV and V that “the cause of hysteresis phenomena of the condensation adsorption-desorption of gases is originated from the deviation from the thermodynamically reversible adsorption-desorption process in the condensation adsorption-desorption of gases”.     

Multilayer adsorption and capillary condensation processes by mesoporous silica

Detailed examination of the sigmoidal adsorption isotherm for physisorption of inert nitrogen vapor on mesoporous silica has been analyzed in terms of the Polanyi sorption potential (excess surface work) decrease with respect to the amount adsorbed. The multilayer sorption isotherm is analyzed in terms of two parameters: (1) An initial sorption potential, E(0), and (2) an intensity term, n(m), related to the statistical monolayer capacity). The linear trend is noted up to ca. 6 monolayer equivalents. At pressures corresponding to menisci radii, capillary condensation commences and increases in accord with the fractal roughness of the surfaces and/or interparticulate voids. The merits of the autoshielding potential model for physisorption is discussed.     

Adsorption of Acetaldehyde,Propionaldehyde, and Butyraldehyde on Molecular Sieve 13X

Abstract

Adsorption isotherms for acetaldehyde, propionaldehyde, and butyraldehyde on Davison molecular sieve 13X were determined gravimetrically at three temperatures. The isoteric heat of adsorption of acetaldehyde and propionaldehyde decreased initially with the increase in loading, then increased up to a certain point after which it decreased again. For butyraldehyde the heat of adsorption initially increased and then decreased with increased loading. The equilibrium adsorption data reduce to a single characteristic curve when correlated according to Polanyi's potential theory. Recently proposed isotherm equations for heterogeneous surfaces by Sircar and Hines et al. were used to correlate the isotherm data. The BET equation gave a good correlation of the data for a relative pressure range of 0.05 ≤ P/P, ≤ 0.25. The monolayer surface coverage and surface area were calculated by the Langmuir and the BET equations. The Langmuir equation consistently provided a larger estimate of the surface area than did the BET equation.     

Adsorption of phosgene and chloroform by activated and impregnated carbons

Equilibrium adsorption and desorption isotherm data at room temperature have been obtained for phosgene and chloroform vapors on BPL grade activated carbon, ASC whetlerite and four ASB impregnated carbons. Isotherm data were plotted in the form of the Dubinin-Polanyi equation. Experimental affinity coefficients (β_ex) for phosgene with chloroform as a reference, were calculated for all the carbons except ASC whetlerite from the slopes (k) of the Dubinin-Polanyi plot, and were compared with the theoretical affinity coefficients (β_th) in order to assess the adsorption capabilities of different adsorbents. In the case of phosgene on ASC whetlerite carbon, significant chemisorption takes place along with physical adsorption and the resulting isotherm shows non-linear behavior. Attempts were made to separate the chemisorption contribution from the total adsorption and thus assess β_ex for the physical adsorption contribution.     

Removal of methylene blue from aqueous solution by a carbon-microsilica composite adsorbent

Microsilica, one kind of industrial solid waste material, was utilized firstly to prepare a carbon-microsilica composite adsorbent (CMS). The prepared adsorbent was characterized with XPS, SEM and Gas sorption experiments. The results indicated the SO₃H groups, which are very effective in capturing cationic organic dye, were introduced onto the surface of CMS; the Brunauer-Emmett-Teller (BET) surface area (S _BET ) and total pore volume (V _total ) of CMS reach 51m²/g and 0.045 cm³/g, respectively. Meanwhile, the possibility of the utilization of the adsorbent for removal of methylene blue (MB) from aqueous solution was investigated. The effect of pH, contact time and initial MB concentration for MB removal were studied. Equilibrium data were modeled using the Langmuir, Freundlich and Dubinin-Radushkevich equations to describe the equilibrium isotherms. It was found that data fit to the Langmuir equation better than the Freundlich equation. Maximum monolayer adsorption capacity was calculated at different temperatures (298, 308, and 318 K) reach 251.81, 283.76 and 309.70 mg/g, respectively. It was observed that adsorption kinetics obeys the pseudo-first-order equation.