Evaluation of adsorption properties of zeolites using inverse gas chromatography: comparison with immersion calorimetry (original) (raw)
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Chemical Engineering Journal, 2002
Inverse gas chromatography has been used to evaluate the adsorption parameters ( H, S and G) of some probes, each representing a class of organics (n-hexane, cyclohexane and benzene) on 4A and 13X zeolites. The adsorption parameters of the probes on 4A were determined in the finite concentration region, and those on 13X were determined in the infinite dilution region. The interactions between the probes and the surface were discussed in the light of determined thermodynamic parameters of adsorption. It was found that the adsorption isotherms for 4A conform with the Langmuir equation and benzene exhibits more negative H than for n-hexane and cyclohexane on both 4A and 13X. Also, interactions of the benzene and n-hexane with 13X were found to be stronger than that on 4A.
The scope of this work is to carry out a systematic comparison of inverse gas chromatography (IGC) and microcalorimetry as tools for the study of the gas-phase adsorption of organic vapours (using hexane as model compound) on zeolitic materials (using different Mn, Co and Fe-exchanged NaX and CaA zeolites). Adsorption isotherms were recorded using both techniques in the temperature range of 150-250 • C, being observed that the shape of the isotherms obtained with the dynamic (IGC) and static (microcalorimetry) techniques was surprisingly similar in the pressure range at which both techniques are applicable (low surface coverages). Concerning to the measurement of the strength of the adsorption, calorimetric data provide two parameters related to the adsorption enthalpy: the initial differential heat and the isosteric adsorption enthalpy. A great coincidence was found between the last one and the adsorption enthalpy determined by IGC (4-20% of difference, depending on the studied material). The behaviour of the initial differential heat depends strongly on the studied material, being in some cases closely related to the other two parameters and temperature-independent (in the case on Mn-exchanged zeolites), whereas for the Co-CaA and Fe-CaA zeolites, it is temperature-dependent, being not correlated with the other parameters in this case. The main conclusion of this work is that IGC is an attractive alternative to the static microcalorimetric data for obtaining information on the adsorption of organic compounds on microporous materials.
Characterization of Co, Fe and Mn-exchanged zeolites by inverse gas chromatography
The adsorption of several alkanes, cyclic hydrocarbons, aromatic hydrocarbons and chlorinated compounds on NaX, CaA, and exchanged Co, Mn and Fe zeolites as adsorbents was investigated. Zeolite composition and structure was determined by ICP-mass spectroscopy, XRD, and nitrogen adsorption. Adsorption parameters (enthalpy of adsorption and free energy of adsorption) as well as dispersive surface energy interaction and specific interaction parameters were determined for each solute-adsorbent system by inverse gas chromatography (IGC). The original zeolites NaX and CaA show the higher values of enthalpy of adsorption but specific interactions depend on the metal exchanged. Zeolites Mn-NaX and Co-NaX exhibit the strongest interactions with benzene, whereas zeolite Co-CaA shows the strongest interactions with chlorinated compounds. The trivalent cation (Fe 3+ ) does not affect the either the adsorption efficiency or specific interaction.
Characterization of Zeolites by Gas Adsorption at Low Pressures
MRS Proceedings, 1987
The nitrogen and argon adsorption isotherms of three different zeolites, calcium A, ZSM-5, and sodium Y were obtained at 77.3 and 87.5 K. Using a continuous volumetric technique high resolution data was obtained in the Henry's Law region of the isotherm at relative pressures below 10−1 P/Po. The data for the two adsorbates indicates that nitrogen, due to its quadrupole moment, shows a high degree of localized adsorption, which makes it difficult to differentiate among zeolites of different pore sizes. Argon, on the other hand, can be used to identify zeolites of different pore sizes. The argon data was used in conjunction with the Horvath-Kawazoe model to obtain a pore size distribution of the zeolite.
Chemical Physics Letters, 2001
The adsorption properties of ethylene on H-Faujasite (H-FAU) and H-ZSM-5 zeolites have been investigated by both the cluster and embedded cluster approaches at the MP2 and B3LYP levels of theory using the 6-31G(d, p) basis set. The eects of the Madelung potential were found to be important. The calculated MP2 adsorption energy of)13.55 kcal=mol for the C 2 H 4 =H-ZSM-5 complex is larger than that of)8.2 kcal=mol for the C 2 H 4 =H-FAU complex. This is consistent with the experimental observation that the ZSM-5 is more acidic than that of FAU zeolite. The adsorption energy for the C 2 H 4 =H-FAU complex is comparable with the experimental estimate of about)9 kcal=mol for ethylene adsorbed on the H-FAU zeolite.
Adsorption-journal of The International Adsorption Society, 2010
Two different experimental methods have been used for studying equilibrium adsorption of water vapour on zeolite 13X based on thermogravimetry and a novel technique using mass spectrometry. Good agreement can be found between experimental data of the adsorption isobars from these two methods. Also the isosteric heat of adsorption of this system has been determined from the equilibrium data. Water adsorption has been measured under a variety of operation conditions of the cooling systems, i.e. pressures from 12.28 to 73.84 mbar and temperatures from 50 to 230 °C.
Zeolites as Adsorbents of Atmospheric and Water Pollutants
2011
In this study, adsorption of atmospheric and water pollutants on chosen zeolites has been studied. N2O and CO have been adsorbed from the gas phase on ZSM-5 and MOR zeolites. The adsorption of water pollutants: phenol, nicotine and pharmaceutically active compounds (salicylic acid, acetylsalicylic acid and atenolol) have been probed on ZMS-5, and clinoptilolite. The adsorbents have been used as synthesized or after modification procedures. The adsorption was studied at 303 K, by titration microcalorimetry, employed to obtain the heats evolved as a result of adsorption either from the gas or liquid phase. Adsorption experiments were performed under the same conditions. The maximal adsorption capacities of investigated solids against specific pollutants have been determined; the effect of zeolite‘ modification have been considered, too. The obtained results show that zeolites can be used effectively in the removal of investigated atmospheric or water pollutants.
Journal of chromatography. A, 2014
Adsorption isotherm data of some alkyl aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) measured in the temperature range of 423-523K on a partially dealuminated faujasite type DAY F20 zeolite by inverse gas chromatography are presented in this work. The temperature dependent form of Tóth's equation has been fitted to the multiple temperature adsorption isotherms of benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene with standard deviations of 4.6, 5.0, 5.9, 4.3, 5.1 and 6.3mmolkg(-1) and coefficients of determinations (r(2)) of 0.977, 0.971, 0.974, 0.975, 0.991 and 0.991, respectively. The gas-solid equilibria and modeling were interpreted on the basis of the interfacial properties of the zeolite, by dispersive, specific and total surface energy heterogeneity profiles and distributions of the adsorbent measured by surface energy analysis.