Gas holdup, bubble size distribution, and mass transfer in an airlift reactor with ceramic membrane and perforated plate distributor

The airlift reactor is one of the most commonly used gas-liquid two-phase reactors in chemical and biological processes. The objective of this study is to generate different-sized bubbles in an internal loop airlift reactor and characterize the behaviours of the bubbly flows. The bubble size, gas holdup, liquid circulation velocity, and the volumetric mass transfer coefficient of gas-liquid two-phase co-current flow in an internal loop airlift reactor equipped with a ceramic membrane module (CMM) and a perforated-plate distributor (PPD) are measured. Experimental results show that CMM can generate small bubbles with Sauter mean diameter d(32) less than 2.5 mm. As the liquid inlet velocity increases, the bubble size decreases and the gas holdup increases. In contrast, PPD can generate large bubbles with 4 mm < d(32) < 10 mm. The bubble size and liquid circulation velocity increase as the superficial gas velocity increases. Multiscale bubbles with 0.5 mm < d(32) < 10 mm can be generated by the CMM and PPD together. The volumetric mass transfer coefficient k(L)a of the multiscale bubbles is 0.033-0.062 s(-1), while that of small bubbles is 0.011-0.057 s(-1). Under the same flow rate of oxygen, the k(L)a of the multiscale bubbles increases by up to 160% in comparison to that of the small bubbles. Finally, empirical correlations for k(L)a are obtained.