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immobilization on the carbonaceous surface, adsorption heat is one of the fundamental parameters. To ascertain the values of the adsorption enthalpy, courses of adsorption isotherms measured at different temperatures are often analysed, so offering information on

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represents a measure of the strength of these interactions. Therefore, adsorption heats bring information about heterogeneity of the adsorption sites on the surface of the adsorbent. In addition, knowledge of the adsorption heat is very important for the

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showed their efficiency as air dehumidifier [ 18 ]. An understanding of the process of adsorption of water vapor on solid surfaces requires knowledge of both the adsorbed amounts and the adsorption heats. The heats of adsorption allow an assessment of the

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of phase transition [ 3 ], enthalpy of combustion [ 4 ], adsorption heat [ 5 ], enthalpy of formation [ 6 ], heat of salt hydration [ 7 ], solution enthalpy [ 8 ], and thermal conductivity [ 9 ] present only a few characteristic examples of parameters

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Abstract  

Adsorption isotherms of n-butane on a granulated activated carbon were measured by two different but complementary experimental methods: calorimetry and gravimetry. Adsorption heats were determined in different ways. For the system studied, the experimental results prove that the adsorbent offers a homogeneous site distribution. Besides, there can be differences between the adsorption heat values which might come from the way they are obtained (by calculation or direct measurements).

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Abstract  

The heats of hydration reactions for MgCl2⋅4H2O and MgCl2⋅2H2O include two parts, reaction enthalpy and adsorption heat of aqueous vapor on the surfaces of magnesium chloride hydrates. The hydration heat for the reactions MgCl2⋅4H2O+2H2O→MgCl2⋅6H2O and MgCl2⋅2H2O+2H2O→MgCl2⋅4H2O, measured by DSC-111, is –30.36 and –133.94 kJ mol–1,respectively. The adsorption heat of these hydration processes, measured by head-on chromatography method, is –13.06 and –16.11 kJ mol–1, respectively. The molar enthalpy change for the above two reactions is –16.64 and –118.09 kJ mol–1, respectively. The comparison between the experimental data and the theoretical values for these hydration processes indicates that the results obtained in this study are quite reliable.

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Abstract  

The adsorption heat of the stoichiometric displacement process for the adsorption of a solute in a liquid-solid system was investigated. On the basis of the SDM-A and the rule of the additivity of energy, an expression which describes the dependence of the adsorption enthalpy on the nature and concentration of the solute, and on the solvent and adsorbent, was derived. The adsorption heat determined for the solute with the traditional method can be divided into two independent fractions, relating to the adsorption of the solute and to the desorption of the solvent. Experimental data on both isotherms from the literatures and precise calorimetry were used to test the adsorption heat and its fractions computed quantitatively via the equations presented in this study, and a satisfactory degree of conformity between them was obtained.

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Abstract  

The influence of microporous carbon surface oxidation on energetics of methane adsorption at 308 K is discussed. Obtained adsorption heats and integral molar entropies of the adsorbate show that microporous carbon surface oxidation changes the methane adsorption process. This is probably resulted by the existence of an endothermic effect during adsorption in oxidized carbon micropores.

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Abstract  

The role of calorimetry in adsorption is shortly reviewed. The differences between calorimetric adsorption heats and those calculated from Clausius-Clapeyron equation for the systems ethanol-activated carbons are presented. Obtained results, together with the results presented previously for other adsorbates, confirm that calorimetry is indispensable for a real thermodynamical description of the adsorption process in this type of system.

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Adsorption micro calorimeter

Design and electric calibration

Journal of Thermal Analysis and Calorimetry
Authors: V. García-Cuello, J. Moreno-Pirajan, L. Giraldo-Gutiérrez, K. Sapag, and G. Zgrablich

Abstract  

In this work, it is described an innovative heat flux micro calorimeter Tian-Calvet type designed to measure adsorption heats and reactions as well as adsorption isotherms. It consists in an adsorption instrument for volumetric gases, which is coupled to the micro calorimeter. The changes in the pressure are monitored by means of high sensitivity and high precision pressure transducers. The micro calorimeter has thermo elements that work by a Seebeck effect, in a twin cells system. The cells are inside a box in which the temperature can be adjusted from 77 to 300 K. The sensitiveness of the calorimeter is established by applying a perfectly known electric work. The results corresponding to the electric calibration, the base line stability determination and the time constant in the equipment are shown.

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