Effect of the pH of emulsion on ultrafiltration of oil products and nonionic surfactants

The structure and properties of a water–oil emulsion have been studied. The ultrafiltration of the water–oil emulsion has been performed with the use of spiral wound and hollow fiber membranes to separate the emulsion into a filtrate and a concentrate. The effect of pH on the following performance characteristics of the ultrafiltration process has been studied: the efficiency and the degree of separation of oil products and nonionic surfactants. It was found that an increase in the pH value of the emulsion decreased the efficiency of membranes and the degree of separation of nonionic surfactants. It has been found that a Raifil UF membrane effectively rejects oil products from acidic emulsion and, on the contrary, an EMU 45-300 membrane is effective in an alkaline medium. This behavior has been associated with to a positive surface charge of the EMU 45-300 membrane. The maximum efficiencies and degrees of separation of oil products and nonionic surfactants from emulsions with the use of the Raifil UF ultrafiltration membrane and the EMU 45-300 membrane have been attained in the pH ranges from 2.1 to 2.9 and from 2.2 to 2.5, respectively. After ultrafiltration, the size of particles in the filtrate increased by a factor of about 18 due to the coalescence of oil particles in the near-membrane layer because of polarization effects. The increase in the particle size of the dispersed phase in the filtrate can also be explained by a positive surface charge of polysulfonamide membranes.