Polyethersulfone Hollow Fiber Research Articles

Formation of ultrathin high-performance polyethersulfone hollow-fiber membranes

We have demonstrated, for the first time, that ultrathin skin-layer hollow-fiber membranes with a skin layer of 474 Å can be prepared using mainly a one-polymer and one-solvent system. This is one of the thinnest skin-layer asymmetric hollow-fiber membranes that have ever been reported in the literature for air and gas separation. This work implies that, in order to yield a high-permeance polyethersulfone (PES) membrane with a skin layer of approximately 500 Å, the addition of non-solvents into spinning dopes may not be the pre-condition to form ultrathin skin-layer hollow-fiber membranes for gas separation. The keys to fabricate ultrathin skin-layer hollow-fiber membranes are (1) to control the chemistry of the internal coagulant and the borefluid flow rate and (2) to have a dope exhibiting significant chain entanglement. The newly developed polyethersulfone (PES) hollow fibers have an O 2 N 2 selectivity of 5.80 with a permeance of 9.3 × 10 −6 cc(STP)/cm 2 s cmHg for O 2 at room temperature. The skin layer thickness was calculated to be 474 Å. These hollow fibers were wet-spun from a 35 75 (weight ratio) PES/ N-methyl-pyrrolidone (NMP) dope using water as the external coagulant and 80 20 NMP/H 2O as the bore fluid. The hollow fiber must be coated with a silicone elastomer. This work also suggests that in order to yield a high-permeance PES membrane with a skin layer of approximately 500 Å, there might not exist a critical solvent molar volume when preparing the dope solvent mixture, as previously suggested by the Permea research group. SEM observation of skin nodules suggests that the skin layer thickness is less than 700 Å.

Flat‐sheet and hollow fiber membrane bioreactors: A study of the kinetics and active site conformational changes of immobilized papain including sorption studies of reaction constituents

AbstractPapain, a sulfhydryl protease has been immobilized on flat‐sheet modified polysulfone membranes and hydroxyethyl cellulose coated polyethersulfone hollow fibers. Amidase activity of the enzyme in solution on the membranes has been assayed. Immobilized papain on the modified polysulfone membrane and the hollow fibers retains 12% and 25% of its activity (with 1 mmol dm−3 substrate) in solution, respectively. Loading experiments revealed decreased activity on the modified polysulfone membrane with increased enzyme loading. Adsorption experiments for the reaction product, p‐nitroaniline, have been performed and an attempt has been made to correct for this in activity calculations. Apparent Michaelis–Menten parameters were determined for the modified polysulfone and hollow fibers with both Km and Vmax being lower in the immobilized cases. Electron paramagnetic resonance study of the changes in active site conformation of an enzyme on a hollow fiber membrane are reported for the first time. Experiments using the sulfhydryl‐specific (1‐oxyl‐2,2,5,5‐teetrahyl‐Δ3‐pyrroline‐3‐methyl)methanethiolsulfonate spin label depicted the presence of two subpopulations of immobilized papain on the hollow fibers, one of them active and one denatured.

Effect of the Addition of Fructose on the Pervaporation of Ethanol/Water Mixtures by Silicone-Rubber-Coated Polyethersulfone Membranes

Abstract Composite hollow fiber membranes were prepared by coating polyethersulfone hollow fibers with silicone rubber. The hollow fiber membranes so produced were found to be water selective when they were used for the separation of feed ethanol/water mixtures by pervaporation. When fructose was added to feed ethanol/water mixtures, a decrease in permeation rate and an increase in water selectivity were observed. The decrease in the permeation rate was possible to assume, but the noticed increase in water selectivity was against our expectation, since the vapor pressure of water decreases while that of ethanol increases when sugars are added to mixtures of ethanol and water. Water selectivity of the membrane was enhanced with an increase in the amount of fructose in the feed.

Pore size and pore size distribution on the surface of polyethersulfone hollow fiber membranes

Hollow fiber membranes were prepared by the solution spinning technique from polyethersulfone polymer. Investigations were made on the effect of the nature of internal coagulants on the ultrafiltration performance. It was found that both solute PEG separation and permeation rate decrease with an increase in the carbon number of the carboxylic acid additive when the acid/water mixtures are used as internal coagulants. A method was developed to evaluate the mass transfer coefficient on the feed side of the membrane. The pore size and the pore size distribution at the internal surface of the hollow fiber were established using transport equations based on the surface force-pore flow model.

Characterization of composite membranes by their non-equilibrium thermodynamic transport parameters

Composite reverse osmosis membranes were prepared by interfacially polymerizing aromatic polyamide discriminating layers on the inside surface of microporous polyethersulfone hollow fibers and on the surface of flat sheet polysulfone ultrafilters. The salt rejection and flux of these membranes were measured at various feed pressures. From these measurements, the membrane reflection coefficients, salt permeances and hydraulic permeances were estimated. Neither the polysulfone ultrafilters nor the microporous polyethersulfone hollow fibers possessed any inherent salt rejecting capability. Both had a hydraulic permeance at least two orders of magnitude greater than that of the respective composite membranes. Consequently, it was concluded that the estimated transport parameters for both composite membranes were characteristics exclusively of thier polyamide discriminating layers. Comparison of these transport parameters generated insight into structural and functional aspects of the membrane that could not be visualized by scanning electron microscopy.

A hollow fiber membrane probe for the measurement of the hydrogen concentration in a liquid

A new method is introduced to measure the hydrogen concentration in liquids by applying a polyethersulfone hollow fiber membrane as a probe. Hydrogen rapidly diffuses through the fiber wall after which it is carried to a thermal conductivity detector by an inert gas flow. Stationary measurements in a pure hydrogen atmosphere as well as in a silicone oil are conducted. Polyethersulfone was shown to be more suitable as fiber material for a selective hydrogen probe than polysulfone. From nonstationary measurements it could be concluded that the response time of the polyethersulfone probe is fast enough to monitor the hydrogen concentration during instationary processes which involve hydrogen, like gas—liquid or liquid—solid mass transfer and homogeneous/heterogeneous reactions.