Reactant absorption from dispersed bubbles in packed bed electrochemical reactors.

Interfacial areas and mass transfer coefficients were measured in cocurrent upward gas-liquid flow over a packed bed electrode consisting of 1.2 mm glassy carbon particles. Specific areas were measured by chemical absorption of 0(2) into Na(2)S0(3) solutions, and volumetric mass transfer coefficients were measured by physical desorption of 0(2) into N(2) bubbles. Areas were found to be in the range of 4 x 10(3) to 2 x 10(5)m(-1), much higher than have been previously reported. High areas were related to the use of concentrated electrolytes and small particles. Bubble size was found to depend primarily on liquid flow rate. As a result of high areas, volumetric mass transfer coefficients k(L)a(G) were also high (0.1 K(L)a(G) 0.75 s(-1)). Mass transfer coefficients K(L) were small, however. For the smaller bubble dispersions, mass transport was diffusion controlled. Differences between the absorption behavior of porous electrodes and packed bed absorption columns were described.