Synthesis of Porous Inorganic Hollow Fibers without Harmful Solvents

A route for the fabrication of porous inorganic hollow fibers with high surface-area-to-volume ratio that avoids harmful solvents is presented. The approach is based on bio-ionic gelation of an aqueous mixture of inorganic particles and sodium alginate during wet spinning. In a subsequent thermal treatment, the bio-organic material is removed and the inorganic particles are sintered. The method is applicable to the fabrication of various inorganic fibers, including metals and ceramics. The route completely avoids the use of organic solvents, such as N-methyl-2-pyrrolidone, and additives associated with the currently used fiber fabrication methods. In addition, it inherently avoids the manifestation of so-called macro voids and allows the facile incorporation of additional metal oxides in the inorganic hollow fibers

Sol-gel processed magnesium-doped silica membranes with improved H2/CO2 separation

Magnesium-doped silica membranes were synthesized and a large increase in H2/CO2 permselectivity is achieved as compared to undoped silica membranes. Three magnesium concentrations were studied, namely 10, 15 and 20 mol%, in order to find the optimal Mg-concentration for the highest H2/CO2 separation performance. The physical properties of these sol-gel derived Mg-doped silica gels and membranes were characterized by dynamic light scattering, X-ray diffraction and high-resolution scanning electron microscopy. After the incorporation of magnesium into amorphous silica network, the membrane structure remained amorphous. Membrane performance was tested by single gas permeance of He, H2, CO2, N2 and CH4. With 20 mol% Mg doping, H2/CO2 permselectivity values of more than 350 were achieved with a H2 permeance of 70 × 10−9 mol m−2 s−1 Pa−1. For pure silica membranes, a H2/CO2 permselectivity of 9 was observed with a H2 permeance of 526 × 10−9 mol m−2 s−1 Pa−1

Oil-in-water emulsion separation: Fouling of alumina membranes with and without a silicon carbide deposition in constant flux filtration mode

Ceramic membranes have drawn increasing attention in oily wastewater treatment as an alternative to their traditional polymeric counterparts, yet persistent membrane fouling is still one of the largest challenges. Particularly, little is known about ceramic membrane fouling by oil-in-water (O/W) emulsions in constant flux filtration modes. In this study, the effects of emulsion chemistry (surfactant concentration, pH, salinity and Ca2+) and operation parameters (permeate flux and filtration time) were comparatively evaluated for alumina and silicon carbide (SiC) deposited ceramic membranes, with different physicochemical surface properties. The original membranes were made of 100% alumina, while the same membranes were also deposited with a SiC layer to change the surface charge and hydrophilicity. The SiC-deposited membrane showed a lower reversible and irreversible fouling when permeate flux was below 110 L m−2 h−1. In addition, it exhibited a higher permeance recovery after physical and chemical cleaning, as compared to the alumina membranes. Increasing sodium dodecyl sulfate (SDS) concentration in the feed decreased the fouling of both membranes, but to a higher extent in the alumina membranes. The fouling of both membranes could be reduced with increasing the pH of the emulsion due to the enhanced electrostatic repulsion between oil droplets and membrane surface. Because of the screening of surface charge in a high salinity solution (100 mM NaCl), only a small difference in irreversible fouling was observed for alumina and SiC-deposited membranes under these conditions. The presence of Ca2+ in the emulsion led to high irreversible fouling of both membranes, because of the compression of diffusion double layer and the interactions between Ca2+ and SDS. The low fouling tendency and/or high cleaning efficiency of the SiC-deposited membranes indicated their potential for oily wastewater treatment

Hydrothermal stability of silica, hybrid silica and Zr-doped hybrid silica membranes

Hybrid silica membranes have demonstrated to possess a remarkable hydrothermal stability in pervaporation and gas separation processes allowing them to be used in industrial applications. In several publications the hydrothermal stability of pure silica or that of hybrid silica membranes are investigated. To gain deeper insight into the mechanism of hydrothermal stability of silica-based membranes we report a comparison under identical conditions of the gas permeation performance of silica (TEOS), hybrid silica (BTESE) and Zr-doped BTESE (Zr-BTESE) membranes before and after hydrothermal treatments. First, a fast and straightforward hydrothermal stability test at 100 °C was applied to screen these membranes. The BTESE and Zr-BTESE membranes maintained their excellent performance after this test, though the TEOS membranes lost their selectivity. Second, hydrothermal tests under water gas shift (WGS) conditions were performed at different temperatures. No significant changes in permeance and selectivity were observed for BTESE derived membranes after a hydrothermal treatment at 300 °C. Surprisingly, a large reduction in carbon dioxide permeance was observed for Zr-BTESE hybrid silica membranes after a hydrothermal treatment at 200 or 300 °C, resulting in a significant increase of the H2/CO2 permselectivity from 12 to 35

Influence of the intermediate layer on the hydrothermal stability of sol-gel derived hybrid silica membranes

The hydrothermal stability of microporous silica hybrid sol-gel derived membranes is often only tested for either the mesoporous intermediate membrane layer or the microporous separation layer. In this work an investigation is done on the interaction between the intermediate γ-alumina layer and the hybrid (BTESE-derived) silica separation layer during hydrothermal treatment. Although bare γ-alumina is degraded during a hydrothermal treatment, a coating of hydrophobic BTESE on γ-alumina retains its gas separation performance, albeit with a lower mechanical adhesion between the hybrid silica separation layer and the γ-alumina intermediate layer. Applying a monoaluminumphosphate (MAP) coating between the α-alumina support and the γ-alumina layer stabilizes the γ-alumina membrane. A BTESE coating on a MAP modified γ-alumina membrane did not show any signs of delamination after hydrothermal testing. Moreover, a significant increase in the H2/N2 (perm)selectivity, factor 3, was observed for these membranes

Oil-in-water emulsion separation: Fouling of alumina membranes with and without a silicon carbide deposition in constant flux filtration mode

Ceramic membranes have drawn increasing attention in oily wastewater treatment as an alternative to their traditional polymeric counterparts, yet persistent membrane fouling is still one of the largest challenges. Particularly, little is known about ceramic membrane fouling by oil-in-water (O/W) emulsions in constant flux filtration modes. In this study, the effects of emulsion chemistry (surfactant concentration, pH, salinity and Ca2+) and operation parameters (permeate flux and filtration time) were comparatively evaluated for alumina and silicon carbide (SiC) deposited ceramic membranes, with different physicochemical surface properties. The original membranes were made of 100% alumina, while the same membranes were also deposited with a SiC layer to change the surface charge and hydrophilicity. The SiC-deposited membrane showed a lower reversible and irreversible fouling when permeate flux was below 110 L m−2 h−1. In addition, it exhibited a higher permeance recovery after physical and chemical cleaning, as compared to the alumina membranes. Increasing sodium dodecyl sulfate (SDS) concentration in the feed decreased the fouling of both membranes, but to a higher extent in the alumina membranes. The fouling of both membranes could be reduced with increasing the pH of the emulsion due to the enhanced electrostatic repulsion between oil droplets and membrane surface. Because of the screening of surface charge in a high salinity solution (100 mM NaCl), only a small difference in irreversible fouling was observed for alumina and SiC-deposited membranes under these conditions. The presence of Ca2+ in the emulsion led to high irreversible fouling of both membranes, because of the compression of diffusion double layer and the interactions between Ca2+ and SDS. The low fouling tendency and/or high cleaning efficiency of the SiC-deposited membranes indicated their potential for oily wastewater treatment.Sanitary EngineeringWater Managemen