Thermal deactivation kinetics and thermodynamics of a silica gel using surface area data
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CitationSarıkaya, Y., Ceylan, H., Önal, M. ve Pekdemir, A. D. (2020). Thermal deactivation kinetics and thermodynamics of a silica gel using surface area data. Journal of Thermal Analysis and Calorimetry, Springer.
A new calculation method was presented using surface area data for the thermal analysis of adsorbents. Five parts from a silica gel (Hypersil) were heated at the temperatures of 500, 640, 700, 770, and 850 degrees C, respectively, for 16 h. The maximum adsorption capacity as liquid nitrogen volume (0.930 cm(3) g(-1)), monolayer capacity (0.093 cm(3) g(-1)), surface area (A(H) = 245 m(2) g(-1)), number of monolayer (10) in the multimolecular adsorption, and heat of the first layer (3300 J mol(-1)) were evaluated from the nitrogen adsorption data obtained at - 196 degrees C. Surface area (A) of the preheated samples was determined similarly. The assumed parameters k=-(partial derivative A/partial derivative T)(p)/A and K= (1 - a)/a were calculated for each preheating temperature, where a = A/A(H) is the relative decrease in the surface area by the thermal deactivation, because thekandKsupplying Arrhenius equations and van't Hoff equation behave as reaction rate constant and equilibrium constant, respectively. The activation energy for the thermal deactivation of the silica gel was calculated as E# = 27330 J mol(-1)from the slope of a straight line which is plotted according to the Arrhenius equation. The enthalpy change (Delta H-0 = 28936 J mol(-1)) and entropy change (Delta S-0=47.42 J mol(-1) K-1) for the same case were, respectively, evaluated from the slope and intercept of a straight line which is plotted according to the van't Hoff equation. Accordingly, temperature dependence of the Gibbs energy is written as Delta G(0)=Delta H-0-T Delta S-0=28936-47.42T by the SI units. The spontaneous nature of the deactivation was discussed using the last relationship.
SourceJournal of Thermal Analysis and Calorimetry
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