Thermal deactivation kinetics and thermodynamics of a silica gel using surface area data
Journal of Thermal Analysis and Calorimetry, cilt.146, sa.4, ss.1505-1510, 2021 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 146 Sayı: 4
- Basım Tarihi: 2021
- Doi Numarası: 10.1007/s10973-020-10132-z
- Dergi Adı: Journal of Thermal Analysis and Calorimetry
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
- Sayfa Sayıları: ss.1505-1510
- Anahtar Kelimeler: Kinetics, Silica gel, Surface area, Thermal deactivation, Thermodynamics
- Maltepe Üniversitesi Adresli: Evet
Özet
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 °C, respectively, for 16 h. The maximum adsorption capacity as liquid nitrogen volume (0.930 cm3 g−1), monolayer capacity (0.093 cm3 g−1), surface area (AH = 245 m2 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 °C. Surface area (A) of the preheated samples was determined similarly. The assumed parameters k= - (∂A/ ∂T) p/ A and K= (1 - a) / a were calculated for each preheating temperature, where a= A/ AH is the relative decrease in the surface area by the thermal deactivation, because the k and K supplying 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 (Δ H= 28936 J mol−1) and entropy change (Δ S= 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 Δ G= Δ H- TΔ S= 28936 - 47.42 T by the SI units. The spontaneous nature of the deactivation was discussed using the last relationship.