CRITICAL-ASSESSMENT OF THE DYNAMIC DOUBLE-RESPONSE METHOD FOR MEASURING KLA - EXPERIMENTAL ELIMINATION OF DISPERSION EFFECTS

A survey of measuring techniques for k(L)a is presented which eliminate the dispersion effects in both phases in various equipments (agitated vessels, bubble and packed columns). The double-response method (DRM) attempts to overcome the lack of knowledge of the gas-phase mixing in agitated vessels by measuring the off-gas transient. However, the correctness of the method depends on the hardly acceptable assumption that the dispersion consists of a monosized bubbles. The correctness of the DRM is tested here experimentally by comparison of k(L)a measured by this method with those obtained by the dynamic pressure method and the steady-state sulphite feeding method using pure oxygen, the correctness of which was proven earlier. The measurements were done in water (coalescent batch), a 0.5 M Na2SO4 solution (non-coalescent batch), and in a solution of 1%wt carboxymethylcellulose in 0.5 M Na2SO4 (viscous non-coalescent batch). In non-coalescent and viscous batches, the DRM yields up to 94% lower k(L)a compared to the correct methods.