Enlargement of oil droplets by using asymmetric structure of polyvinylidene fluoride membranes

Abstract

This work demonstrates a study for enlarging the oil droplets by using the asymmetric polyvinylidene fluoride (PVDF) membranes in a cross-flow membrane filtration system. The membranes were fabricated from PVDF/DMA/LiCl: 10/88/2% wt. and coagulated in the ethanol solutions at concentrations of 0, 10, 20, and 30% v/v. The alkaline-surfactant-polymer (ASP) produced water was simulated and tested as the feed solutions. Results indicate that the variation of the ethanol concentrations did not affect the membrane porosity and thickness remarkably while control the membrane surface pore size significantly. The water permeation flux increased with the average membrane surface pore size when increasing the ethanol concentrations in the coagulation baths from 10 to 30% v/v. However, the membrane surface pore sizes have no notable effect on the enlargement of the oil droplets because at least 50% of the membrane pores were larger than the oil droplets in the feed solutions. Coalescence of the oil droplets did occur due to the tortuous pore structures of the asymmetric membranes especially when the filtration process was pressurized. At least 65% of the coalesced oil droplets in permeate having the diameters exceeding 1.0 μm. The resistance to the permeation increased with the transmembrane pressure due to more oil droplets accumulated on the membrane pores.