Study of adsorption from binary liquid mixtures on thermally treated activated carbon (original) (raw)
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Adsorption from binary liquid mixtures on commercial activated carbons
Carbon, 1995
Adsorption from binary liquid mixtures of completely miscible components of different polarity was studied, in order to characterize the adsorption properties of commercial activated carbons. The excess adsorption isotherms were measured for three binary liquid systems: acetone + n-heptane, acetone + benzene, and benzene + n-heptane on four activated carbons of various ash content. Textural characteristics of the adsorbents were determined on the basis of the adsorption/desorption isotherms of argon at 77.5 K. The relationship between the extent of adsorption from the liquid phase as well as the shape of the adsorption isotherms and various parameters characterizing the investigated activated carbons are discussed. A good agreement is found as far as the actual surface area of the materials is concerned.
Study of Adsorption Equilibria in the Systems Ternary Liquid Mixtures–Modified Activated Carbons
Journal of Colloid and Interface Science, 1999
The adsorption abilities of commercial activated carbon after thermal and chemical treatment were investigated. The chemical character of carbon surfaces was determined by applying the thermogravimetric method, measurement of adsorption isotherms of water vapor, and the process of neutralization of surface functional groups. Total amounts of oxygen and nitrogen in all carbon samples were estimated by elemental analysis. Adsorption-desorption isotherms of benzene vapor were used to determine the parameters of the Dubinin-Radushkevich equation characterizing the porous structure of investigated carbons. These analyses show that chemical modification of carbon samples leads to strong differentiation of the chemical character of adsorbent surfaces; however, the porous structures show distinct similarity. In order to study the adsorption equilibria from liquid phase, the adsorption isotherms were measured for ternary mixtures of benzene, diethyl ketone, and n-heptane on all carbons. A strong effect of the chemical character of the carbon surface on liquid adsorption was found and discussed for all systems.
Adsorption properties of two different activated carbons, steam and chemically activated, respectively, were examined by inverse gas chromatography (IGC). The influence of acid, basic and combined washings, carried out in order to remove ashes, on the adsorption properties of these materials was also tested using this technique. Chemical and textural characterization was carried out by nitrogen adsorption, ICP-MS and temperature programmed desorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined by IGC. Washing procedures (specially those involving acid washing) removes almost completely the mineral ashes of the carbons. Concerning to the effect on porous structure, this procedures only affect significantly to the properties of chemically activated carbon, with increases of micropore volume of up to 43%. The steam activated carbon shows the best adsorptive behaviour, with an enthalpy of adsorption up to 16% higher than the corresponding to chemically activated one, as well as a large amount of micropores. The removal of these ashes enhances the adsorption of studied compounds, especially for alkanes and chlorinated ones. Washing procedures also modify the chemical structure of the organic functionalities, but this effect does not seem to be very important on the adsorption properties of these materials.
An IGC Study of the Role of Washing Procedures on the Adsorption Properties of Activated Carbons
Inverse gas chromatography (IGC) was used to study the influence of different washing treatments (acid, basic and combined washings) on the adsorption properties of two different activated carbons (steam-and chemically-activated). Chemical and textural characterization was carried out by the use of nitrogen adsorption, ICP-MS and temperature programmed desorption methods. The adsorption capacity and the interaction strength (sub-divided into dispersive and specific components) were determined by IGC.
Adsorption characteristic study of activated carbons down to 4.5 k
Materials Today: Proceedings, 2018
Adsorption characteristic study of different activated carbon samples are performed at low temperature down to 5 K by using cryocooler based low temperature facility with a micropore analyzer. This facility is now operational at Institute for plasma research (IPR). It comprises of a commercial micro pore analyzer for sample characterization at 77 K and a GM cryocooler cooling unit forholding the sample at any temperature < 77 K. The sample holder is connected to the micro-pore analyzer measurement unit through a small diameter tube for gas dosing and equilibrium pressure measurement. A PID control based temperature controller unit along with temperature sensors and heatersare used to regulate and maintain the temperature of the sample cell at any temperature between 4.5 K and 77 K. Among different kinds ofactivated carbon samples studied, the surface area and pore width for carbon cloths are found to be 3438 m 2 /gm (at 4.5 K), and it increases with lowering the temperature down to 4.5 K from 77.0 K.
Characterizations of Activated Carbon–Methanol Adsorption Pair Including the Heat of Adsorptions
Journal of Chemical & Engineering Data, 2015
This paper presents adsorption isotherms and isosteric heats of adsorption for methanol vapor adsorption for two commercially available activated carbon samples207EA granules and WS-480 pellets (Calgon Carbon, U.S.A.)which were also fully characterized using nitrogen sorption at 77 K. The heat of adsorption of methanol as a function of loading was determined using the Clausius−Clapeyron approach with isotherms obtained at 5°C, 15°C, and 25°C. The isosteric heats of adsorption increased sharply at the small coverage due to increasing effect of condensation heat with coverage. The heat reached a maximum and then varies little with loading, with the average values at around 46.6 kJ/mol for 207EA and 45.1 kJ/mol for WS-480. The higher heats of adsorption for the former activated carbon reflect its more microporous nature (around 78 % compare to 62 % for WS-480 activated carbon). The heat of adsorption data is also comparable to that obtained elsewhere for other activated carbons.
Adsorption and desorption kinetics of n-octane and n-nonane vapors on activated carbon
Langmuir, 1999
This investigation has involved the study of the adsorption and desorption kinetics of two n-alkanes on a wood-based active carbon (BAX950). The adsorption and desorption characteristics of n-octane vapor on the activated carbon were investigated over the relative pressure (p/p o) range 0-0.97 for temperatures in the range 288-313 K in a static vapor system. The adsorption characteristics of n-nonane were studied over the relative pressure range 0-0.97 and temperature range 303-323 K. The adsorption and desorption kinetics were studied with different amounts of preadsorbed n-octane for set changes in relative vapor pressure (p/p o). The desorption kinetics were much slower than the corresponding adsorption kinetics for the same pressure step. The rate constants for adsorption increased with increasing relative pressure and surface coverage. The kinetic data for adsorption were used to calculate the activation energies for each increase in relative pressure. The activation energy was highest at low p/p o and decreased with increasing p/p o until a maximum was reached at p/p o ∼0.075. n-Nonane adsorption showed similar trends in adsorption kinetics and activation energies to the n-octane adsorption. The results are discussed in terms of diffusion in the pore structure in relation to the adsorption isotherm and mechanism.
Analysis of some adsorption experiments with activated carbon
Chemical Engineering Science, 1976
A simple method is proposed whereby the film transfer coefficient and coefficient of diffusion in the particles may be determined from finite bath adsorption experiments. The method also makes it possible to separate pore and surface diffusion. Under certain conditions it is also possible to determine the influence of particle phase concentration on the surface diffusivity. The method is based on models describing the instationary diffusion in the solids. Data from six different adsorption systems were analysed using this method. The adsorbed components were: phenol, paranitrophenol, parachlorophenol, bensoic acid, phenylacetic acid and 24dichlorophenoxyacetic acid. In all systems surface diffusion was the determining transport mechanism in the particles. In the system phenol and phenylacetic acid the surface diffusion coefficient increased by about a factor 3 with an increase in surface concentration of about 40%. For parachlorophenol the increase was somewhat less. For the other systems there was no significant increase. The increase in diffusivity is explained by a decrease in bonding forces with increasing concentration.
Characterization of Activated Carbons Using Liquid Phase Adsorption
"A modification of the Dubinin–Radushkevich pore filling model by incorporation of the repulsive contribution to the pore potential, and of bulk non-ideality, is proposed in this paper for characterization of activated carbon using liquid phase adsorption. For this purpose experiments have been performed using ethyl propionate, ethyl butyrate, and ethyl isovalerate as adsorbates and the microporous–mesoporous activated carbons Filtrasorb 400, Norit ROW 0.8 and Norit ROX 0.8 as adsorbents. The repulsive contribution to the pore potential is incorporated through a Lennard–Jones intermolecular potential model, and the bulk-liquid phase non-ideality through the UNIFAC activity coefficient model. For the characterization of activated carbons, the generalized adsorption isotherm is utilized with a bimodal gamma function as the pore size distribution function. It is found that the model can represent the experimental data very well, and significantly better than when the classical energy–size relationship is used, or when bulk non-ideality is neglected. Excellent agreement between the bimodal gamma pore size distribution and DFT-cum-regularization based pore size distribution is also observed, supporting the validity of the proposed model."
Competitive adsorption of a benzene–toluene mixture on activated carbons at low concentration
Carbon, 2006
Previous studies of the adsorption of benzene and toluene at low concentration showed that both porosity and surface chemistry of the activated carbon play an important role. This paper analyses the adsorption behaviour of a mixture of VOCs (benzene-toluene) on AC, due to the lack of information regarding the adsorption of mixtures. Thus, the performance of chemically activated carbons, physically activated carbon with steam and commercial samples is studied. This study shows that chemically activated carbons have better performance than the other samples, showing much higher adsorption capacities, breakthrough times and separation times. Porosity is a key factor and those activated carbons with higher volumes of micropores exhibit higher adsorption capacities and breakthrough times. This work also analyses the state of the adsorbed phase resulting from the mixture adsorption and comparison of the composition of the adsorbed hydrocarbons with that predicted by the ideal adsorption solution theory (IAST), shows good agreement.