Hye Ryeon Lee

Preparation and characterization of methyl-modified hybrid silica membranes for gas separation

Abstract The methyl-modified hybrid silica sols with methyltriethoxysilane and tetraethoxysilane were successfully prepared using alkaline (NH3 and tetra-methyl-ammonium hydroxide (TMAH)) and acid catalysts (HCl and CH3COOH) and characterized with thermogravimetric analysis, Fourier transform infra-red, and water contact angle. The methyl-modified silica film showed hydrophobic property with water contact angles over 90° under alkaline or acid catalyst. The methyl-modified silica membranes were fabricated and evaluated with He, H2, N2, C3H8, and SF6 at 200°C. He gas permeance for hybrid silica membranes was in the range of 0.61–1.91 × 10−6 mol m−2 s−1 Pa−1, while He/SF6 and N2/SF6 permeance ratios of acid-catalyzed membranes was quite higher than those of alkaline catalyzed. Pore size (d p) of membranes were evaluated with normalized Knudsen-based permeance method, and the order of pore size for methyl-modified silica membranes can be estimated as follows: HCl-catalyzed membrane < acetic acid-catalyzed me...

Study on Preparation and Hydrophobicity of MTES Derived Silica Sol and Gel

The synthesis of hydrophobic sol by one-step sol-gel process ammonia catalyzed was investigated. The water molar ratio and catalyst molar ratio were discussed to prevent phase segregation during the hydrolysis and co-condensation of the organic and inorganic precursors. The reactant system with water molar ratio 70 could make the reaction rate of MTES slightly less than that of TEOS, so that the hydrolysis - condensation – gelling reaction with MTES and TEOS as co-precursors could be synchronously. With the increase of the MTES/TEOS molar ratio, the reaction rate of the silica sol preparation decreased, the hydrophobicity of the sol and gel increased as the molar ratio MTES/TEOS change from 0.5~4. But the hydrophobicity of the methyl-modified silica sol and gel prepared with pure MTES in the sol-gel process were slightly lower than that of the methyl-modified silica sol and gel prepared with MTES and TEOS as co-precursors.

Fabrication of SiO2–ZrO2 (50/50) membranes on the porous stainless steel-tube support for pervaporation

AbstractThe SiO2–ZrO2 membranes were fabricated with silica–zirconia sols on a porous stainless steel-tube support (O.D. = 10 mm, length = 20 mm, 316L SUS, Mott Corp. USA) by a dipping–rolling–freezing–fast drying (DRFF) and/or soaking–rolling–freezing–fast drying (SRFF) method. After coating of SiO2–ZrO2 sol, single gas permeation characteristics (He, H2, and N2) for SiO2–ZrO2 membranes were evaluated at room temperature, and the pervaporation experiments were performed at a specified feed isopropyl alcohol concentration of 90 wt% at 50°C with silica–zirconia membranes. The morphology of surface and the cross sections of the membrane were investigated with FE-SEM analysis. Judging from FE-SEM analysis, the surface of silica–zirconia membrane on the PSS tube support was denser, and the number of surface defects considerably reduced than DRFF method, and the additional modification via the SRFF significantly diminished surface defects, which could not be avoided during the DRFF step. The membrane the silic...

Preparation and Gas Permeation Properties of Silica Membranes on Porous Stainless Steel-Tube Supports

Silica membranes with high permeability were prepared using colloidal and polymeric silica sols on a porous stainless steel-tube support by a DRFF and SRFF method. Silica sols were derived with tetraethylorthosilicate (TEOS) by sol-gel method and analyzed with DLS, FE-SEM, and N2 adsorption. The coating of the intermediate layer with colloidal silica sol on the stainless steel-tube support led to a denser surface morphology of the membrane along with a considerable reduction in the number of surface defect. As the polymeric silica sol enclosed the colloidal silica sol with spherical par-ticles during the SRFF method, the separation-layer-coated silica membrane showed a denser surface than the intermediate layer. Moreover, the silica membranes showed high hydrogen gas permeability of (6.63-9.21) × 10-5 mol⋅m-2⋅s-1⋅Pa-1 with low H2/N2 perm-selectivity (2.9-3.1) at room temperatures.