FLOW OF DILUTE, SUBMICRON EMULSIONS IN GRANULAR POROUS-MEDIA - EFFECTS OF PH AND IONIC-STRENGTH

The effects of pH and ionic strength on the flow of dilute, sub-micron emulsions of n-hexadecane in water through sand beds were studied exp erimentally to determine the mechanism of transport under different ph ysicochemical conditions. The effluent concentration of the oil phase and the drop size distribution were measured along with the permeabili ty of the porous medium at different pH and ionic strengths. The effec t of pH was studied at a constant ionic strength of 5 x 10(-4) M. At h igh pH values, no entrapment of the emulsion in the porous medium is s een, owing to significant repulsion among the emulsion droplets themse lves and between the droplets and the sand grains. At low pH values, t here is an attractive interaction between the droplets and the porous medium. Consequently, deposition and coalescence of the emulsion occur within the porous medium, leading to effective pore blockage and redu ction in permeability. The effect of ionic strength was studied in the range 5 x 10(-4)-10(-1) M at a constant pH of 8.3. Substantial permea bility reductions were observed at high ionic strengths owing to the d ecrease in the thickness of the electrical double layers, and a reduct ion in the zeta potential of the emulsion droplets and the sand grains . The permeability reduction increases with increasing ionic strength. This work demonstrates that, depending on the surface chemical effect s, the permeability of a porous medium can be considerably reduced by the flow of emulsions even when the drop size is much smaller than the pore size.