Development of silica RO membranes

Silica based membranes have been developed by using a counter diffusion CVD method. Effects of alkyl groups in the silica precursors and deposition temperatures had investigated in order to control pore sizes of the silica membranes. In this study, this type of a silica membrane was applied for RO separation. Effects of silica sources, deposition temperatures and post treatments had been investigated. Tetramethoxysilane (TMOS), Ethyltrimethoxysilane (ETMOS) and Phenyltrimethoxysilane (PhTMOS) were used as silica precursors. A counter diffusion CVD method was carried out for 90 min at 270 - 600degC on γ-alumina capillary substrates (effective length: 50 mm, φ: 4 nm: NOK Co.). O3 or O2 was introduced into the inside of the substrate at the O2 rate of 0.2 L min-1. Ion beam irradiation was carried out for a post treatment using Os at 490 MeV for 1.0 x 1010 ions cm-2 or 3.0 x 1010 ions cm-2. Single gas permeance was measured by using H2, N2 and SF6. RO tests were employed at 3.0 or 5.4 MPa for 100 mg L-1 of feed NaCl solution. First, effects of the silica sources were investigated. The total fluxes increased by increasing N2 permeance through the silica membrane deposited by ETMOS. The maximum NaCl rejection was 28.2% at 12.2 kg m-2 h-1 of the total flux through the membrane deposited at 270degC. N2 permeance was 9.6 x 10-9 mol m-2 s-1 Pa-1. While, total fluxes through the membrane deposited by using PhTMOS were smaller than those through the ETMOS membranes. The phenyl groups for the PhTMOS membrane must be important for the hydrophobic properties through the membrane. Next, effects of ion beam irradiation were tested for the TMOS membranes. Water is difficult to permeate through the TMOS membranes due to the low N2 permeance through the membrane (3.1 x 10-11 mol m-2 s-1 Pa-1). N2 permeance increased to 7.3 x 10-9 mol m-2 s-1 Pa-1 by the irradiation. Irradiation amounts had little effects on N2 permeance. However, NaCl rejections were -124% (0.37 kg m-2 h-1) and 52% (0.98 kg m-2 h-1) for the irradiations at 1.0 x 1010 ions cm-2 and 3.0 x 1010 ions cm-2, respectively. Detailed structure investigations were required for the further discussions. (author)