Bubble nucleation in core–shell structured molten oxide-based membranes with combined diffusion-bubbling oxygen mass transfer: experiment and theory

Abstract

Oxygen-selective membranes are likely to play a leading part in the future separation processes relevant to energy engineering. A newly developed molten copper and vanadium oxide-based diffusion-bubbling membrane with core–shell structure and fast combined oxygen mass transfer is a promising candidate for efficient oxygen separation. In this work, the oxygen bubble nucleation and transport properties of the diffusion-bubbling membrane were experimentally and theoretically studied. Bubble size distribution and cumulative oxygen flux have been plotted as functions of oxygen partial pressure. The relationship between the bubble density, oxygen partial pressure, and oxygen permeation flux was established. The oxygen flux and bubble density vary in the ranges of 3.2 × 10⁻⁸–1.4 × 10⁻⁷ mol cm⁻² s⁻¹ and 1.3 × 10¹³–5.8 × 10¹³ m⁻³ at ΔP_O2 = 0.1–0.75 atm, respectively. The mechanisms of homogeneous, heterogeneous, pseudo-classical and non-classical nucleation are reviewed within the framework of the Cahn–Hilliard model. It is shown that the homogeneous nucleation mechanism is most likely in the membrane core. The estimated values of the interfacial tension, energy barrier, and rate nucleation are 0.02 J m⁻², 5 kT, and 4 × 10²⁹ m⁻³ s⁻¹, respectively.