Finger-like Pore Structure Research Articles

Preparation of hollow fiber composite membrane for carbon dioxide/methane separation via orthogonal experimental design

Coating active layer on a porous support membrane was an effective method to prepare composite membranes with both high permeability and selectivity for gas separation. However, most of the investigations are focused on the choice and optimization of novel active materials. In this paper, an orthogonal experimental method was used to optimize the structure of the polysulfone (PSF) support membrane. Polyvinylamine (PVAm) and polyvinyl alcohol (PVA) were blended and used as the active materials of hollow fiber composite membranes for the separation of CO2/CH4. The preparation parameters including additives content (A), polymer content (B), weight-average molecular weight of additives (C) and solvent concentration in bore fluid (D) were investigated. The results of statistical analysis indicated that the effects of these preparation parameters on the permeance and selectivity of CO2/CH4 both gradually weakened in the order of B, A, C and D. FESEM observation showed that PSF support membrane with the typical double finger-like pore structure could get a high separation factor and high CO2 permeance, rather than a single finger-like pore structure on the outer skin. The optimization of preparation parameters was as follows: PSF:PEG-400:DMAC (wt%)=19:5:76 and 10 wt% DMAC in bore fluid. Under the optimal preparation conditions, the resultant composite membrane exhibited a more excellent permselectivity of CO2/CH4 than commercial Prism membrane under low pressure (≤0.4 MPa).

Study on the effects and properties of PVDF/FEP blend porous membrane

Polyvinylideneflouride (PVDF)/poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) blend flat-sheet membranes were fabricated by the immerged phase-inversion method. Micro–nanometer scale FEP particles were introduced into PVDF/N,N-dimethylacetamide (DMAc) casting solution. Effects of FEP content on the rheology behavior of casting solution and performances of PVDF/FEP blend membranes were investigated respectively. Results shown that: (1) With FEP content increasing, the viscosity of casting solution decreased while the value of non-Newtonian index n increased. When FEP content was 60wt.%, the value of n reached as high as 0.903 which demonstrated that the casting solution exhibited good Newtonian flowing property; (2) with FEP content increasing, the porosity and permeability of blend membranes increased obviously while the liquid entrance pressure (LEP) decreased. Blend membranes' cross-section morphologies shown that the increase in FEP content aided the formation of a larger and deeper finger-like pore structure; and (3) with FEP content increasing, mechanical strength of blend membranes decreased while the water contact angle increased at first then decreased.

Performance of PSf Ultrafiltration Membrane: Effect of Different Nonsolvent on Coagulation Medium

One of the big challenges in developing a good asymmetric membrane is macrovoid formation that leads to reduction of rejection value. The most common method to reduce or suppress macrovoid formation is by addition of controlled solvent to the coagulation bath. Therefore, the effect of difference coagulants based on dissolved KCl (monovalent) and dissolved Na2SO4(divalent) with different concentration onto asymmetric Polysulfone (PSf) ultrafiltration membrane was investigated in this work. The PSf ultrafiltration membranes were prepared by using phase inversion method using these two immerse aqueous solutions. The performances of membranes were evaluated via pure water flux (distilled water) and solute rejection (humic acid). Results on the cross section revealed that the structure of membrane show a straight pattern of bigger finger-like pore structure from top to bottom layer tend to reduce with at the same time the diameter of finger-like pore structure also increased, as salt medium of coagulant increases. These obviously shown by permeation values for both salt mediums were higher compared to without salt coagulant. This reduction of finger-like structure at bottom layer occurred along together with the formation of sponge shape structure. The growth of thick sponge shape is strongly influence by kinetic phase inversion of salt coagulant that also creates resistance to permeation mechanism. However the intense salt coagulant medium can cause the bigger sponge structure that will slightly reduce rejection and increase the permeation. This was proved by the rejection of KCl medium started to increase at 1-3% but slightly reduced at 4%. Based on the result analysis demonstrated that the ideal membrane with highest rejection and good permeation values was membrane immersed into 1% Na2SO4 coagulation medium.

La 0.8 Sr 0.2 Cr 0.5 Fe 0.5 O 3−δ (LSCF)–Zr 0.8 Y 0.2 O 2−δ (YSZ) based multilayer membrane for CO 2 decomposition

Abstract A La 0.8 Sr 0.2 Cr 0.5 Fe 0.5 O 3− δ (LSCF)–Zr 0.8 Y 0.2 O 2− δ (YSZ) based multilayer membrane was fabricated by a combination of dual-layer phase inversion tape casting, slurry coating and co-sintering. LSCF–YSZ was adopted as the oxygen separation layer. A porous YSZ substrate with a continuous transitional finger-like pore structure was prepared, and a LSCF–YSZ active layer with a fine sponge-like pore structure was introduced between the functional LSCF–YSZ oxygen separation layer and YSZ substrate. The asymmetric membrane exhibits good chemical stability and acceptable oxygen permeation under stringent conditions. An oxygen permeation flux of 0.041, 0.068 and 0.15 ml(STP)cm −2 min −1 was gained at 900 °C for operation under air/argon, CO 2 /CH 4 and CO 2 /H 2 gradient, respectively. The apparent activation energy for oxygen permeation was 175.61±18.45, 97.21±2.94 and 79.41±6.26 kJ/mol under air/argon, CO 2 /CH 4 and CO 2 /H 2 gradients respectively. The preliminary results show that the membrane may be promising for applications in the recycling of CO 2 and treatment of hydrocarbons.

Synthesis and characterization of flat-sheet thin film composite forward osmosis membranes

Forward osmosis (FO) technology has become increasingly attractive in the past decades for water related applications and will likely continue to develop rapidly in the future. This calls for the development of high performance FO membranes. Thin film composite (TFC) polyamide FO membranes with tailored support structure were prepared in the current study. The porous polysulfone substrates with finger-like pore structures were prepared via phase inversion, and the polyamide rejection layers were synthesized by interfacial polymerization. The resulting TFC FO membranes had small structural parameters ( s = 0.67–0.71 mm) due to the thin cross-section, low tortuosity, and high porosity of the membrane substrates. Meanwhile, their rejection layers exhibited superior separation properties (higher water permeability and better selectivity) over commercial FO membranes. When the rejection layer is oriented towards the draw solution, FO water flux as high as 54 L/m 2 h can be achieved with a 2 M NaCl draw solution while maintaining relatively low solute reverse diffusion. Comparison of the synthesized TFC FO membranes with commercial FO and RO membranes reveals the critical importance of the substrate structure, with straight finger-like pore structure preferred over spongy pore structure to minimize internal concentration polarization. In addition, membranes with high water permeability and excellent selectivity are preferred to achieve both high FO water flux and low solute flux.