Study of modelling transmembrane pressure and gel resistance in ultrafiltration of oily emulsion

This article deals with water removal from oil-in-water emulsion by an ultrafiltration membrane at different transmembrane pressures. The membrane intrinsic resistance and gel resistance are analyzed and determined based on the resistance-in-series theory. The experimental results show that the effect of pressure on the permeate flux depends greatly on variations of the membrane properties, feed emulsion concentration and feed emulsion temperature. At lower emulsion concentration the flux increases with an increase in pressure. At higher emulsion concentration the concentration polarization becomes very serious. The flux is slightly influenced by pressure as the operating pressure is over a critical value. The COD values and oil concentrations in the permeate were reduced greatly when the transmembrane pressure was not over the critical pressure, however, on the contrary to the pressure is over the critical pressure. In addition, the model describing the relation of gel resistance and pressure is presented and analyzed by the experimental data. The results show that this model has a good agreement with calculated values.

(1) An increase in the transmembrane pressure and temperature can improve the permeate flux. At a lower emulsion concentration (0.5%), the concentration polarization is not obvious, the permeate flux increases with an increase in the pressure. At a higher emulsion concentration (5%) above 2 bar the flux is controlled by the gel layer. (2) An increase in the temperature can enhance the flux at lower or higher emulsion concentrations too. (3) According to the model between the gel resistance and transmembrane pressure, it was found that the gel resistance increases with increasing pressure, and increasing temperature may reduce the gel resistance. (4) Using the selected membrane, the COD and oil concentrations in the permeate were reduced greatly. However, their oil concentrations and COD values increase obviously as the transmembrane pressure is over the critical pressure. Therefore, the selection of transmembrane pressure should be controlled below the critical pressure in order to reach the discharge standard of wastewater.