Experimental measurements of the volumetric liquid mass transfer and bubble size distribution in a vertically oriented semi-batch gas-liquid Taylor-Couette vortex reactor with radius ratio eta = r(i)/r(o) = 0.75 and aspect ratio Gamma = h/(r(o) - r(i)) = 40 were performed, and the results are presented for axial and azimuthal Reynolds number ranges of Re-a = 11.9-143 and Re-Theta = 0-3.5 x 10(4), respectively. Based on these data, power-law correlations are presented for the dimensionless Sauter mean diameter, bubble size distribution, bubble ellipticity, and volumetric mass transfer coefficient in terms of relevant parameters including the axial and azimuthal Reynolds numbers. The interaction between wall-driven Taylor vortices and the axial passage of buoyancy-driven gas bubbles leads to significantly different dependencies of the mass transfer coefficient on important operating parameters such as inner cylinder angular velocity and axial superficial gas velocity than has been observed in horizontally oriented gas-liquid Taylor vortex reactors. In general, the volumetric mass transfer coefficients in vertical Taylor vortex reactors have a weaker dependence upon both the axial and azimuthal Reynolds numbers and are smaller in magnitude than those observed in horizontal Taylor vortex reactors or in stirred tank reactors. These findings can be explained by differences in the size and spatial distribution of gas bubbles in the vertically oriented reactor in comparison with the other systems. (C) 2015 Elsevier B.V. All rights reserved.