It was shown for the first time that the conditions of thermal treatment of the casting solution significantly affect the morphology and transport properties of porous, flat, and hollow fiber polysulfone (PSf) membranes. It is ascertained that the main solution components that are subjected to thermo-oxidative destruction are the pore-forming agent polyethylene glycol (PEG) and solvent N-methyl-2-pyrrolidone (NMP). It is proved that hydroxyl groups of PEG actively react in the process of the casting solution thermo-oxidative destruction. It is shown that despite the chemical conversion taking place in the casting solution, their stability towards coagulation virtually does not change. The differences in the membrane morphology associated with the increase of thermal treatment time at 120 °C are not connected to the thermodynamic properties of the casting solutions, but with the kinetics of the phase separation. It is revealed that the change of morphology and transport properties of membranes is connected with the increase of the casting solution viscosity. The rise of solution viscosity resulted in the slowdown of the phase separation and formation of a more densely packed membrane structure with less pronounced macropores. It is determined experimentally that with the increase of casting solution thermal treatment time, the membrane selective layer thickness increases. This leads to the decrease of gas permeance and the rise of the He/CO₂ selectivity for flat and hollow fiber membranes. In the case of hollow fibers, the fall of gas permeance is also connected with the appearance of the sponge-like layer at the outer surface of membranes. The increase of selectivity and decline of permeance indicates the reduction of selective layer pore size and its densification, which agrees well with the calculation results of the average membrane density. The results obtained are relevant to any polymeric casting solution containing NMP and/or PEG and treated at temperatures above 60 °C.

For the development of high efficiency porous supports for composite membrane preparation, polysulfone (PSf) hollow fiber membranes (outer diameter 1.57 mm, inner diameter 1.12 mm) were modified by air plasma using the low temperature plasma treatment pilot plant which is easily scalable to industrial level and the Piranha etch (H₂O₂ + H₂SO₄). Chemical and plasma modification affected only surface layers and did not cause PSf chemical structure change. The modifications led to surface roughness decrease, which is of great importance for further thin film composite (TFC) membranes fabrication by dense selective layer coating, and also reduced water and ethylene glycol contact angle values for modified hollow fibers surface. Furthermore, the membranes surface energy increased two-fold. The Piranha mixture chemical modification did not change the membranes average pore size and gas permeance values, while air plasma treatment increased pore size 1.5-fold and also 2 order enhanced membranes surface porosity. Since membranes surface porosity increased due to air plasma treatment the modified membranes were used as efficient supports for preparation of high permeance TFC membranes by using poly[1-(trimethylsilyl)-1-propyne] as an example for selective layer fabrication.

Convection–diffusion mass transfer in a gas–liquid membrane contactor based on porous polysulfone hollow fiber membranes with a mesoporous ( dpore~ 2 nm) structure of the separation layer has been...

In relation to the demand for asymmetric porous hollow fiber membranes to be used in gas–liquid membrane contactors designed for operation in organic media, polysulfone membranes of this type have been prepared and subsequently modified to impart oleophobic properties to their surface. The structure and properties of the membranes have been characterized using various techniques, such as optical and scanning electron microscopy, and by measuring contact angles and the permeability of helium, carbon dioxide, and hexane. The surface properties of the membranes have been modified by etching with a mixture of hydrogen peroxide and sulfuric acid or coating with a perfluorinated acrylic copolymer. In the latter case, modified membrane samples have shown a significant reduction in wettability with both water and organic liquids. The hexane permeability data indicate the absence of hexane flow through the membrane modified with perfluorinated acrylic copolymer until a gauge pressure of about 1 atm. The results of the study lead to the conclusion that these membranes can find use in gas–liquid membrane contactors, e.g., for the removal of dissolved gases from liquid hydrocarbons.

Fabrication of highly efficient composite gas separation membranes involves selection and pretreatment of the support material. In the present work, porous support pretreatment was for the first time studied for deposition of thin selective layers made from highly permeable organosilicon polymers. Asymmetric polysulfone hollow fiber membranes with mesoporous skin layer structure were employed as supports. It was shown that preliminary impregnation of the support pores is essential for composite membranes fabrication. If poly[1-(trimethylsilyl)-1-propyne] layers from casting solution are deposited onto the polysulfone support without impregnation, the casting solution penetrates the mesoporous layer to a depth of > 1 μm, thus predominantly (> 90%) contributing the overall mass transfer resistance, as estimated by the resistance-in-series model. Such membranes provide relatively poor transport properties: carbon dioxide permeance is 0.2-0.3 m³/(m²hbar). Preliminary impregnation of porous support by distilled water or aqueous glycerol solution prevents casting solution penetration into porous support and results in defect-free thin polymer layer. According to SEM, the deposited selective layer thickness is less than 1 μm. Composite membranes fabricated via this technique provide permeance increase more than order of magnitude. The composite membranes with poly[1-(trimethylsilyl)-1-propyne] and polydimethylsiloxane selective layers show high transport properties in gas-liquid membrane contactors.