Kinetic studies on the CuO/γ-Al₂O₃ sorbent regeneration by methane - Topochemical approach

CuO impregnated γ-Al₂O₃ support provides convenient adsorption and regeneration characteristics. These features give the potential to regard this chemisorption process as more effective, feasible and widely accepted than lime and limestone scrubbing in the removal of SO₂ from the outlet gases. Thermogravimetric tests on the regeneration of the CuO/γ-Al₂O₃ exhausted sorbent (first stage of the regeneration, CuSO₄ → Cu⁰) with methane were conducted. Commercially available 1/8″ γ-Al₂O₃ spheres, loaded with 5.8 wt % of Cu were investigated. The tests concerning the isothermal regeneration kinetics were performed at temperatures: T = 700, 727 and 750 K, while a 20 cm³ min^-1 flow of pure methane was used. To select the mechanism of the regeneration reaction, as well as to evaluate their kinetic parameters of the rate equations, the TGA data were compared with the series of theoretical topochemical kinetic models as advocated by Gardner, Hancock and Sharp's approach. The kinetic mechanism of the regeneration reaction in the initial stage of the process may be originally interpreted as the combination of both boundary-surface-controlled reaction (contracting sphere) and the first-order kinetics models. Various diffusion limited kinetic equations have proved useful for the description of the final stage of the process. Both proposed models (two kinetic and four diffusion ones) fit fairly well to the experimental data (in their limited validity ranges) obtained in all three temperature values studied.