Properties of Filter Cake Formed during Dead-End Microfiltration of O/W Emulsion

Abstract

Upward dead-end filtration tests accompanied with a sudden reduction in the cake surface during the course of filtration are proposed in order to determine the properties of the filter cake formed during microfiltration of oil-in-water (O/W) emulsion. Both upward and downward dead-end filtration tests were conducted under constant pressure conditions by using a filter having a sudden reduction in its filtration area, and the filtration characteristics between the two were compared. Consequently, it was found that the filtration rate in downward filtration was much higher than that in upward filtration as a result of cake exfoliation which occurred in downward filtration, leading to lower specific cake resistance. Moreover, when the average cake porosity was evaluated on the basis of an overall mass balance of dead-end filtration on the assumption that the cake was not exfoliated, the cake porosity in downward filtration became much lower than that in upward filtration for a similar reason. It was revealed that the correct values of cake properties were obtained from the data of upward dead-end filtration in which the exfoliation of the cake did not occur. It was necessary to consider the influence of the cake porosity in the calculation of the average specific cake resistance when an O/W emulsion was not dilute. On the basis of upward dead-end filtration tests, the power law relationship was applicable in order to represent the effects of the applied pressure on both the average volume fraction of oil droplets and the average specific resistance of the cake comprised of oil droplets. It was found that the cake formed during filtration of O/W emulsion was highly compressible due to the deformability of oil droplets. Moreover, the average volume fraction of oil droplets and the average specific resistance were kept constant throughout the course of filtration.