Reasons for bubbling during low-current operation of ion exchange membranes! ! !
Thread Content
This post was last edited by sunjl1981 on 2013-1-6 at 23:57. As the title suggests, could everyone explain in principle why ion exchange membranes develop bubbles when operating at low currents for a long time? :o This post was last edited by limingshuguang on 2007-12-11 09:16 ] # ， ， &
As far as I know, foaming of the ion exchange membrane under low current conditions occurs mostly in processes with natural circulation. This is mainly because the distribution of brine in cells with natural circulation depends not only on the internal structure of the cells but also on the mixing of brine caused by the upward movement of bubbles during normal operation. During low-current operation, the number of bubbles generated per unit time decreases, reducing the effect of bubble agitation; as a result, some brine remains stagnant, and the low local brine concentration causes bubbles to form on the ion exchange membrane. This post was last edited by limingshuguang on 2007-12-11 09:15.]
In ion-exchange membrane electrolysis, since the transport number of sodium ions in the membrane is greater than that in the anolyte, the concentration of sodium ions at and near the membrane surface is lower than that in the entire anolyte; therefore, a sufficient amount of sodium ions must be supplied through diffusion. As the concentration of the anolyte decreases, the sodium ions on or near the membrane surface eventually drop to 0. At a certain current, when the concentration of the anode solution drops to a critical value, the voltage rises sharply, the purity of chlorine decreases, and bubbles form on the membrane. On the other hand, if the concentration of the anolyte exceeds the designed level, the membrane will shrink and the voltage will rise; therefore, it is necessary to keep the anolyte concentration within the designed range.
No wonder foreigners specifying our electrolytic cells require that the operating time at 4KA should not exceed 4 hours. I’ve learned it, thank you. :lol