Foam control using a fluidized bed of hydrophobic particles

Applications of foams and foaming are found in many industries such as the flotation of minerals, enhanced oil recovery, drilling in oil reservoirs; i nsulation, construction and refining processes such as vacuum distillation and delay-coker reactors. However, foaming and defoaming are not yet unders tood. Foams trap gas, and are not wanted in many applications. It has been found that foaming may be strongly suppressed by fluidizing hydrophilic par ticles in the bubbly mixture below the foam, in a cold slit bubble reactor. This suppression is achieved by increasing the wetted area of the solid's surface (walls and particles), by bed expansion and by decreasing the gas h old-up by increasing the effective density of the liquid-solid mixture. Never before has a fluidized bed been used to study the antifoam action of hydrophobic particles. In this work, we fluidized hydrophobic;and hydrophil ic versions of two different sands in a slit bubble reactor. We found that the hydrophobic sands suppress the foam substantially better than their hyd rophilic counterparts. We also observed that, when foam is not present in t he reactor (i.e. at high liquid velocities), the gas hold-up in the bubbly mixture was higher for the hydrophobic version of one sand. This result may be explained in terms of attachment of the particles onto the air bubbles, which increases the residence time of the gas phase. On the other hand, th e gas hold-up in the bubbly mixture for the hydrophobic version of the othe r sand was smaller. A possible explanation is that the bubble adhesion to a non-wettable particle, leads to a decrease in the apparent density of the particle, which in turn is responsible for a larger bed expansion and small er gas hold-up compared with wettable particle systems. These results sugge st that the degree of hydrophobicity matters. Hydrophobic particles appear to break, and not only suppress foam; and they may have a wider application. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.