Porous Stainless Steel Hollow Fibers Research Articles

Porous stainless steel hollow fiber-supported ZIF-8 membranes via FCDS for hydrogen/carbon dioxide separation

MOF membranes show great potential in gas separation, but there are still great difficulties in industrialization due to current complex and time-consuming synthesis methods. We successfully synthesized a series of ZIF-8 membranes on the polydopamine (PDA)-modified porous stainless steel hollow fiber substrates within 20 min using the fast current drive synthesis (FCDS) method. When the applied current density is 0.76 mA/cm2, the prepared 10 cm-length ZIF-8 hollow fiber membrane exhibits a selectivity of 14 for H2/CO2 and H2 permeance of 1.9 × 10-10 mol/(m2·s·Pa) with good stability during 120 h continuous separation. This work extends the fast and facile FCDS method for growing ZIF-8 membranes from disk-shaped substrates to cambered hollow fiber substrates and makes significant sense for accelerating MOF membranes' industrialization.

Strict molecular sieving over electrodeposited 2D-interspacing-narrowed graphene oxide membranes

To separate small molecules/species, it’s crucial but still challenging to narrow the 2D-interspacing of graphene oxide (GO) membranes without damaging the membrane. Here the fast deposition of ultrathin, defect-free and robust GO layers is realized on porous stainless steel hollow fibers (PSSHFs) by a facile and practical electrophoresis deposition (ED) method. In this approach, oxygen-containing groups of GO are selectively reduced, leading to a controlled decrease of the 2D channels of stacked GO layers. The resultant ED-GO@PSSHF composite membranes featured a sharp cutoff between C2 (ethane and ethene) and C3 (propane and propene) hydrocarbons and exhibited nearly complete rejections for the smallest alcohol and ion in aqueous solutions. This demonstrates the versatility of GO based membranes for the precise separation of various types of mixtures. At the same time, a robust mechanical strength of the ED-GO@PSSHF membrane is also achieved due to the enhanced interaction at GO/support and GO/GO interfaces.

Modification of porous stainless steel hollow fibers by adding TiO2, ZrO2 and SiO2 nano-particles

Using 316L stainless steel powder (SSP) with a nominal particle size of 25 μm, porous stainless steel hollow fibers (SSHFs) have been prepared via dry-wet spinning of a particle-loaded casting solution based on non-solvent induced phase inversion, followed by temperature programming sintering. The morphology and performances were characterized by the maximum/mean pore size, SEM, porosity, density, shrinkage, pure water flux and mechanical strength. Subsequently, SSHFs were modified by adding TiO2, ZrO2 and SiO2 nano-particles for the first time. The morphology of SSHFs relied on not only the SSP contents, but also the contents of TiO2, ZrO2 and SiO2 nano-particles. The corresponding results demonstrated that SSHFs with TiO2 nano-particles possessed excellent properties, especially for mechanical strength having a more than 100 % increase and a maximum pore size of 4.5 μm. What’s more, nano-particles also reduced the defects of SSHFs’ structure, which could be observed from SEM images.

Preparation of spiral porous stainless steel hollow fiber membranes by a modified phase inversion–sintering technique

The practical use of inorganic hollow fibre membranes has been limited by their brittleness. When assembled inside a membrane module for high temperature applications, the unavoidable thermal expansion or shrinkage would break the membrane. To overcome this problem, in this paper, spiral-shaped porous stainless steel (PSS) hollow fiber membranes have been developed via a modified phase inversion–sintering technique using 316L stainless steel powder as the membrane material, polysulfone as the polymeric binder and N-methylpyrrolidone as the solvent, respectively. The effects of sintering conditions on the hollow fiber properties have been investigated extensively to optimize the preparation. In order to obtain the desired porous structure, high performance and appropriate mechanical strength, the PSS hollow fiber precursors should be calcined in O2-free sintering atmosphere between 1050°C and 1100°C. Under the optimal sintering conditions, the resultant PSS hollow fibre membranes have a bimodal pore size distribution of 0.1–3μm diameter, high mechanical strength of 290–600MPa, and the nitrogen permeances ranged between 2.23×10−4 and 2.84×10−5molm−2s−1Pa−1. When two sides are fixed by sealant, such spiral hollow fiber membranes are able to flexibly expand by 20% and shrink by at most 57% of its original length, thus suitable for variable high-temperature operations as they can offset the thermal expansion and contraction caused by the temperature change.

Sintering of the Immersion-Induced Porous Stainless Steel Hollow Fiber Membranes

Porous stainless steel (PSS) hollow fiber membranes have been fabricated by an immersion induced phase inversion and sintering technique. This paper is mainly focused on the sintering process. The influences of the sintering atmosphere as well as the sintering temperature and dwelling time on the microstructure, mechanical strength, and the permeation properties of the hollow fiber have been extensively investigated. Experimental results indicate that a H2-containing sintering atmosphere favors the formation of highly permeable porous PSS membranes with desirable mechanical strength. But the sintering atmosphere with H2 concentration larger than 25% is not necessary as it yields a marginal improvement on the membrane performances. For a sufficient sintering, the sintering temperature should be controlled between 1050 and 1100°C, which ensures not only a desirable mechanical strength but also good membrane porosity. For cost effective and less time consuming, sintering time can be controlled within two hours. The resultant PSS hollow fibers satisfy the longstanding criteria of porous supports for gas separation membranes in terms of high porosity, high fluid permeance and robustness to withstand stress.

Effect of polymer and additive on the structure and property of porous stainless steel hollow fiber

Porous stainless steel hollow fiber has been widely used due to its high mechanical strength, excellent thermal conductivity and good sealing properties compared with other porous supports. We successfully prepared porous stainless steel hollow fibers using polyacrylonitrile (PAN) as polymer via dry-wet spinning followed by sintering through temperature programming method. The PAN concentration had an obvious impact on the structure and property of porous stainless steel hollow fiber even if it would be burned off during sintering. The results showed that the morphology could be tuned by adjusting the concentration of PAN. With increasing PAN concentration in casting solution for spinning, the viscosity was increased dramatically, resulting in much compact structures with high pure water flux (higher than 3×105 L·m−2·h−1·Pa−1). A more dense structure could be obtained by adding additive polyvinylpyrrolidone (PVP) as viscosity enhancer.

Preparation of porous stainless steel hollow fibers by robotic fiber deposition

Inorganic membranes can be used under harsh operating conditions such as corrosive environments and high temperatures. We propose a new method for producing porous stainless steel hollow fiber membranes using phase-inversion robotic fiber deposition. The method uses a suspension consisting of stainless steel powder, polymer and solvent which is extruded through a concentric nozzle. By a non-solvent induced phase inversion process the hollow fiber is solidified after extrusion. This technique allows the production of accurate continuous patterns in a one-step process. The resulting green stainless steel hollow fibers are quite stiff and the obtained green patterns can easily be transferred without any deformation. A low amount of organic additives (2wt%) is used resulting only in a limited shrinkage after sintering. The prepared hollow fibers in this study had outer diameters between 1 and 4mm and wall thicknesses of 200 to 700μm. It was found that the diameter to wall thickness ratio had an effect on the uniformity of the wall thickness. Therefore this ratio should preferably be larger than eight for stainless steel. The morphology of the obtained fibers was characterized and the effect of the sintering temperature on properties such as porosity, mechanical strength and nitrogen permeation was investigated.

Carbon nanofibers in catalytic membrane microreactors

Abstract In this study, we report on the fabrication and operation of new hybrid membrane microreactors for gas–liquid–solid (G–L–S) reactions. The presented reactors consist of porous stainless steel tubes onto which carbon nanofibers (CNFs) are grown as catalyst support, all encapsulated by a gas permeable coating. Such reactors benefit from a controlled G–L–S interface of a membrane reactor and high surface area of carbon nanofibers as catalyst support. Preparation steps such as porous stainless steel hollow fiber fabrication, CNF growth on the stainless steel surface, palladium catalyst immobilization and an outer gas permeable polymeric coating steps are presented. The fabricated microreactors have high surface area, mechanical strength and catalytic activity for nitrite reduction in water. Results proved high nitrite reduction performance of these reactors, even without the presence of palladium (Pd) or additional hydrogen (H 2) supply. Our results suggest intrinsic reductant properties and catalytic activity of the reactors, which make them very suitable for hydrogenation reactions.

Porous stainless steel hollow fibers with shrinkage-controlled small radial dimensions

A method is presented for the preparation of thin (∼250 μm) porous stainless steel hollow fiber membranes based on dry–wet spinning of a particle-loaded polymer solution followed by heat treatment. Extraordinarily small radial dimensions were achieved by controlled shrinkage during thermal treatment. Above the glass transition temperature of the polymer, the dynamics of surface energy-driven viscous flow allow regulated reduction of the macrovoid volume, resulting in a substantial decrease in the final fiber diameter.

Porous stainless steel hollow fiber membranes via dry–wet spinning

Porous stainless steel hollow fibers have been prepared via the dry–wet spinning process, based on phase inversion of a particle loaded polymer solution, followed by sintering. The morphology of the green fibers combines sponge like structures and macro voids, and is related to the dynamics of the phase inversion process. The morphology can be tuned by changing the spinning conditions and the composition of the spinning mixture. In analogy to their ceramic counterparts the morphology of the stainless steel fibers is preserved during sintering, apart from shrinkage due to densification. At a length scale comparable to the diameter of the steel particles the microstructure and related pore size distribution are more strongly affected by the sintering temperature, as compared to their ceramic counterparts. Sintering the stainless hollow fibers at temperatures > 1100 °C results in a sharp decrease in nitrogen permeance and an increase in bending strength, due to densification. The strength (∼1 GPa) and nitrogen permeance (0.1 mmol m −2 Pa −1 s −1 at 21 °C) of stainless steel fibers sintered at 1050–1100 °C are superior as compared to their ceramic counterparts. The excellent properties of the stainless steel hollow fibers make them suitable as membrane (supports) for applications involving harsh environments.