Isosteric Heat: Comparative Study between Clausius–Clapeyron, CSK and Adsorption Calorimetry Methods

Abstract

This work presents the calorimetric study of five adsorbents with different chemical and textural characteristics: MOF-199, MCM-41, SBA-15, activated carbon prepared from corn cob (GACKP) and graphite. These solids were used to establish the differences between isosteric heats evaluated by three different methods: Clausius–Clapeyron (C-C), Chakraborty, Saha and Koyama (CSK) and Adsorption Calorimetry (A-Cal). The textural characterization results show solids that have values of specific surface area between 2271 m2·g−1 for the MOF-199 and 5.2 m2·g−1 for the graphite. According to the results obtained for the isosteric heats for each sample, the magnitude varies depending on the coverage of the adsorbate and the textural characteristics of each adsorbent. Solids with an organized structure have isosteric heat values that are coincident among the three methods. Meanwhile, heterogeneous solids such as activated carbon values evaluated by the CKS and C-C have a high dispersion method regarding the adsorption calorimetry method. The results obtained show that the adsorption calorimetry, being a direct experimental measurement method, presents less dispersed data. At low quantities, the isosteric heat of nitrogen adsorption decreased in the order MOF-199, GACKP, MCM-41, SBA-15 and Graphite. The order for the isosteric heats values was coherent with the surface characteristics of each of the solids, especially with the pore size distribution. Finally, throughout the coverage examined in this work, the isosteric heats for nitrogen adsorption determined by adsorption calorimetry (A-Cal) were larger than the evaluated by C-C and CSK indirect methods of vaporization. According to the results, it is shown that the adsorption calorimetry allows values of the isosteric heats of adsorption with an error of less than 2% to be established and also reveals the complex nature of the heterogeneity or homogeneity of the adsorbent.

Understanding water activity change in oil with temperature

“…Based on these two equations, the excess enthalpy per mole water dissolved in oil, , equals to the negative isosteric heat of water absorbed in oil, . The net isosteric heat is interpreted as the difference between the heat of evaporation for the moisture in oil and the latent heat of evaporation of pure water ( Giraldo et al., 2019 ). In this study, the calculated net isosteric heat of peanut oil is equal to −14.25 kJ/mol.…”

Application of the modified Dubinin-Astakhov equation for a better understanding of high-pressure hydrogen adsorption on activated carbons

“…The heat of adsorption is generally evaluated by using the sorption isosteric method [39], which consists in applying the Clausius-Clapeyron equation to the adsorption isotherms calculated over a wide range of temperature and pressures. The latter method reliably determines the isosteric heat of adsorption [40], which ranges from 3 to 7.5 kJ mol -1 [41] for hydrogen adsorption on the Metal Organic Framework (MOF) MIL-101 and on different microporous carbon adsorbents [42]. The smallest pores contribute the most to the average heat of adsorption and are the first to be filled [43], and the heat of adsorption decreases with the surface coverage [44,45].…”

Eco-friendly removal of hexavalent chromium from aqueous solution using natural clay mineral: activation and modification effects

“…The linear plot of the two models according to Eqs. (6) and (7) are explored (as seen in Fig. 8) and the comparative data (Table 4) of the two models are analyzed.…”

“…Effluents containing chromium metal are widely discharged from various industrial processes, such as leather industry through tanning and finishing processes, mining and metallurgy [3,5], textile and dying industries, paper manufacturing, paints, wood preservation, jet aircraft, magnetic tapes, power plants and electroplating [1,3]. Therefore, for a sustainable environment these effluents must be treated in an eco-friendly manner to remove chromium ions before being discharged into water bodies [6]. Currently, several methods are available for removing this type of heavy metals from effluent such as membrane separation, flocculation, electrocoagulation and adsorption.…”