Development and permeation properties of SiO2-ZrO2 nanofiltration membranes with a MWCO of < 200

SiO2-ZrO2 (5/5, 3/7) nanofiltration membranes with a low molecular weight cut-off (MWCO) were fabricated by coating different Si/Zr molar ratios of 5/5 and 3/7 sols from large to small colloidal sol sizes on cylindrical alpha-alumina porous supports with firing at 550 degrees C. The pore sizes of the membranes were controlled by the SiO2-ZrO2 colloidal sol sizes used for the top layer. SiO2-ZrO2 membranes with a MWCO of less than 60, and 160-180 for neutral solutes, showed water permeabilities of (0.2-0.4) x10(-12) and (1.9-2.7) x10(-12) m(3)/(m(2) s Pa), respectively. The solute rejections were strongly dependent on the type of solute; the rate of rejection for alcohols was much higher than that for either glycols or sugars. SiO2-ZrO2 membranes with a low MWCO showed hydrothermal stability and high nanofiltration performance in water at 90 degrees C. The water permeabilities of membranes increased from 2.5x10(-12) to 11.9x10(-12) m(3)/(m(2) s Pa) in operating temperatures from 25 to 90 degrees C, while the MWCO increased slightly from 150 to 210. This indicates that SiO2-ZrO2 membranes with a low MWCO showed excellent nanofiltration performance at high temperatures. The permeation properties for nanofiltration membranes were analyzed using the Spiegler-Kedem equation.