WATER ELECTROLYSIS AND PRESSURE-DROP BEHAVIOR IN A 3-DIMENSIONAL ELECTRODE

Water electrolysis from acidified solution was used as a model system to investigate the net contribution of hydrogen bubbles to the pressur e drop increase in a three-dimensional electrode. A bed of silvered gl ass beads in both fixed and fluidized state was used, assuming an unch anging particle surface during the experiments. Pressure drop behaviou r with time was measured for different experimental conditions and pre sented relative to the pressure drop determined for a bubble free bed. Parameters, such as current density, electrolyte velocity and particl e size, greatly influence the relative pressure drop behaviour in the three-dimensional electrode. A sudden increase in the pressure drop oc curs with the appearance of a gas phase in the bed, reaching a constan t value (plateau) after a certain time; this plateau corresponds to st eady state conditions. The pressure drop increases with increasing cur rent density. This increase is in the range 40-150% relative to the bu bble free electrolyte flow through the bed. Electrolyte flow-rate also strongly influences the pressure drop in the hydrogen evolving fixed bed electrode. It was observed that the relative pressure drop decreas es with increasing electrolyte velocity. At higher flow rates, peaks o ccur on the pressure drop-time curves, indicating the existence of cha nneling inside the bed in which spouting occurs. The time to reach the pressure drop plateau decreases with increasing electrolyte velocity as do the time intervals corresponding to maximum pressure drop values . At the minimum fluidization velocity the peaks disappear and the rel ative pressure drop decreases with time, tending to approach a constan t value. For hydrogen evolution in the fluidized bed, the pressure dro p is lower than that measured in the absence of gas, and reason for th is decrease being the gas hold-up in the bed.