Composite hollow fiber membranes for CO2 capture

Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material.The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO₂. The composite PVAm/PSf HF membranes having a 0.7–1.5 μm PVAm selective layer, showed CO₂/N₂ selectivity between 100 and 230. The selectivity was attributed to the CO₂ facilitated transport imposed by PVAm selective layer. The CO₂ permeance changed from 0.006 to 0.022 m³(STP)/(m² bar h) in direct correlation with CO₂ permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO₂ partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO₂/N₂ selectivity ranged between 20 and 500 and the CO₂ permeance from 0.11 to 2.3 m³(STP)/(m² bar h) depending on the operating conditions.For both PVAm/PSf and PVAm/PPO membranes, the CO₂ permeance was similar with the CO₂ permeance of uncoated hollow fiber supports, confirming that the CO₂ diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO₂ diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO₂ diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 μm PVAm top layer becomes the CO₂ diffusion rate limiting step.     

Bromine recovery with hollow fiber gas membranes

Gas membranes supported by microporous hollow fibers have been used to concentrate bromine from a variety of brines similar to seawater. The bromine transport is governed by diffusion in the brine, and hence is almost independent of membrane properties except the surface area per volume. In some cases, this type of membrane can be an alternative to packed towers, simultaneously carrying out both absorption and stripping.     

Fabrication of Matrimid/polyethersulfone dual-layer hollow fiber membranes for gas separation

We have developed almost defect-free Matrimid/polyethersulfone (PES) dual-layer hollow fibers with an ultra-thin outer layer of about 10 × 10⁻⁶ m (10 μm), studied the effects of spinneret and coagulant temperatures and dope flow rates on membrane morphology and separation performance, and highlighted the process similarities and differences between single-layer and dual-layer hollow fiber fabrications. The compositions of the outer and inner layer dopes were 26.2/58.8/15.0 (in wt.%) Matrimid/NMP/methanol and 36/51.2/12.8 (in wt.%) PES/NMP/ethanol, respectively. It is found that 25 °C for both spinneret and coagulant is a better condition, and the fibers thus spun exhibit an O₂/N₂ selectivity of 6.26 which is within the 87% of the intrinsic value and a calculated apparent dense-layer thickness of about 2886 × 10⁻¹⁰ m (2886 Å). These dual-layer membranes also have impressive CO₂/CH₄ selectivity of around 40 in mixed gas tests. The scanning electron microscopy (SEM) studies show that low coagulant temperatures produce dual-layer hollow fibers with an overall thicker thickness and tighter interfacial structure which may result in a higher substructure resistance and decrease the permeance and selectivity simultaneously. The elemental analysis of the interface skins confirms that a faster inter-layer diffusion occurs when the fibers are spun at higher spinneret temperatures. Experimental results also reveal that the separation performance of dual-layer hollow fiber membranes is extremely sensitive to the outer layer dope flow rate, and the inner layer dope flow rate also has some influence. SEM pictures indicate that the macrovoid formation in dual-layer asymmetric hollow fiber membranes is quite similar to that in single-layer ones. It appears that macrovoids observed in this study likely start from local stress imbalance and weak points.     

Eco-friendly and protective natural dye from red prickly pear (Opuntia Lasiacantha Pfeiffer) plant

New natural dye extracted from red prickly pear was used for dyeing wool with different types of mordents. The effect of mordant concentration on the color strength was discussed; the results obtained indicated that the color strength decreases with the increase of mordant concentration. The effect of the dye bath pH, salt concentration, dyeing temperature and dyeing time was also studied. The color strength and the dye uptake have exhibited high values. Good fastness properties of the dyed fabric were achieved.Antimicrobial activity of wool fabric dyed with this dye was tested according to diffusion agent. Test organisms as Escherichia coli, Bacillus subitilus, Pseudomons aeruginosa and Staphylococcus aureus were used and the results indicated that the samples exhibited a high inhibition zone.According to the available literature, this is the first report concerning a natural dye for fabric from fruits of red prickly pear plants.     

Electrospun nanofibrous membranes embedded with aerogel for advanced thermal and transport properties

The primary purpose of cold weather clothing is to shield the wearer from the extremities of the external environment. The thermal properties of nanofibers and their potential applications have tremendous scope and application in this area. The objective of this study was to investigate the mechanisms of heat transfer through fibrous insulation where the fiber diameter was less than 1 μm. Electrospinning process was used to produce flexible polyurethane and polyvinylidene fluoride nanofibers embedded with silica aerogel. The thermal and transport behavior of the samples was evaluated, and results were statistically analyzed. Presence of aerogel particles were confirmed through microscopic examination. Thermal behavior was investigated by using thermogravimetric analysis and differential scanning calorimetry. The results showed that the polyvinylidene fluoride nanofibrous membranes embedded with aerogel obtained a good thermal stability with lower weight loss than polyurethane nanofibrous membranes. The glass transition and melting point was not affected by the aerogel content in the layers, validating that polymers are not miscible. The increase in duration of electrospinning led to higher web thickness, which resulted in considerable decrease in air permeability. Considerable improvement of thermal insulation was observed by increasing the number and the weight per unit area of both nanofibrous membranes. The results confirmed increase in thermal insulation by embedding silica aerogel in nanofibrous membranes. With reference to the results, it could be concluded that nanofibers embedded with aerogel are good for thermal insulation in cold weather conditions. Thermal insulation battings incorporating nanofibers could possibly decrease the weight and bulk of current thermal protective clothing.     

Preparation and thermal properties of palmitic acid/expanded graphite/carbon fiber composite phase change materials for thermal energy storage

Using palmitic acid (PA), expanded graphite (EG), and carbon fiber (CF) as raw materials, PA/EG/CF composite phase change materials (CPCMs) with diverse CF contents were invented by melt blending approach. The effects of different ratios on thermal properties were studied by experimental characterization and testing. Scanning electron microscopy images displayed that PA was adsorbed in the pores of the EG surface, while CF was disorderly but uniformly embedded in the interior and surface of pores. The chemical stability and thermal decomposition stability of CPCM at low temperature were proved by Fourier transform infrared spectrometer and thermogravimetric analyzer results, respectively. According to the law of heat storage/release time and latent heat variation, the optimal ratio scheme was determined, and its heat storage/release time was 65% and 59% lower than pure PA, respectively. The form-stable materials were prepared by compression forming method, and thermal cycling experiment results demonstrated that the higher the content of CF, the stronger the inhibition of mass loss. Based on the experimental results, the PA/EG/CF CPCM has the advantages of stable phase transition, strong stability, and fast heat storage and release rate, so it has a marvelous application prospect in the field of low-temperature heat storage engineering.

     

Permeability and thermal properties of PDMS/LDPE multilayer composite membranes

This work reports on the preparation and properties of polydimethylsiloxane (PDMS)/low‐density polyethylene (LDPE) multilayer composite polymer membranes (MCPM) for gas separation applications. The membranes were produced by combining sequential coating with melt‐extrusion/salt leaching techniques. In particular, the gas sorption and permeation properties at different pressure (40–90 psig) and temperature (27–55 °C) are reported with morphology and thermogravimetric properties. The results show that a 20 μm PDMS layer was able to penetrate the microporous LDPE surface layer substrate leading to improved interfacial adhesion. Based on the different gases (CO₂, CH₄, and C₃H₈) solubility, permeability, and diffusivity obtained, these membranes are seen as good candidates for industrial gas separations. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1045–1052     

Eco-friendly fast synthesis and thermal degradation of optically active polyamides under microwave accelerating conditions

<正>An optically active bulky aromatic diacid chiral monomer,(2S)-4-[(4-methyl-2-phthalimidylpentanoyl-amino) benzoylamino]isophthalic acid(1),containing a rigid phthalimide and flexible L-leucine pendent group was synthesized in five steps.A fast and clean method for direct polyamidation reaction of monomer 1 with various aromatic diamines under microwave irradiation and conventional heating was performed.The polymerization reactions provided optically active polyamides with high yields and inherent viscosities in the range of 0.36-0.74 dL/g.Their thermal properties were evaluated by thermogravimetric analysis(TGA) and differential scanning calorimetry.TGA thermograms show that the polymers are thermally stable,10%weight loss temperatures are in excess of 385℃,and char yields at 800℃are higher than 56%.The data obtained from TGA were used to study the kinetics of thermal decomposition of the resulting polymers. The interpretation of kinetic parameters(E,ΔH,ΔS andΔG) of thermal decomposition stages was evaluated using Coats and Redfern equation.     

Preparation of PFSA/PSf hollow fiber composite membranes with recovered PFSA for the pervaporation separation of EtOH/H_2O

Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration(UF) membrane as substrate with recovered PFSA.The composite membranes were applied to the pervaporation separation of 95% ethanol(EtOH)/H2O mixture.SEM images show that the thickness of the PFSA skin layer of the composite membranes is about 2 μm,much thinner than those of other PFSA composite membranes revealed in the literatures.Effects of annealing temperature,c...     

The fabrication of hollow fiber membranes with double-layer mixed-matrix materials for gas separation

The concept of fabricating hollow fibers with double-layer mixed-matrix materials using the same polymeric matrix has been demonstrated for gas separation. Polyethersulfone (PES)–beta zeolite/PES–Al₂O₃ dual-layer mixed-matrix hollow fiber membranes with enhanced separation performance have been fabricated. This study presents an innovative approach of utilizing low cost PES and Al₂O₃ to replace expensive polyimides as the supporting medium for dual-layer mixed-matrix hollow fibers and eliminating interlayer de-lamination problems. The incorporations of 20 wt% beta zeolite in the outer selective layer and 60 wt% Al₂O₃ in the inner layer coupled with spinning at high elongational draw ratios yield membranes with an O₂/N₂ selectivity of 6.89. The presence of Al₂O₃ particles enables the membrane to retain its porous substructure morphology in the course of annealing above the glass transition temperature of PES. Moreover, spinning at high elongational draw ratios results in the re-distribution of Al₂O₃ particles towards both edges of the inner layer. Not only do the permeance and selectivity of the fibers increase, but also greater mechanical properties and lower degree of shrinkages are obtained. Therefore, the combination of PES–beta zeolite and PES–Al₂O₃ nanoparticles with a reasonable draw ratio may be another promising approach to produce hollow fibers with double-layer mixed-matrix materials.     

Preparation of PFSA/PSf hollow fiber composite membranes with recovered PFSA for the pervaporation separation of EtOH/H2O

Perfluorosulfonic acid/Polysulfone(PFSA/PSf) hollow fiber composite membranes have been prepared by dip-coating method using PSf ultrafiltration (UF) membrane as substrate with recovered PFSA. The composite membranes were applied to the pervaporation separation of 95% ethanol (EtOH)/H₂O mixture. SEM images show that the thickness of the PFSA skin layer of the composite membranes is about 2 μm, much thinner than those of other PFSA composite membranes revealed in the literatures. Effects of annealing temperature, coating solution concentration and counter-ions of PFSA on the pervaporation performances of the composite membranes were investigated. The total flux decreases and separation factor increases with the increase of annealing temperature. The highest permeation flux of 3230 g m^?2 h^?1 and a separation factor of 5.4 is obtained for the composite membrane annealed at 80°C. The lowest permeation flux of 396 g m^?2 h^?1 and a separation factor of 27.7 is obtained for the composite membrane annealed at 160°C. The permeation performances of the PFSA/PSf composite membrane are evidently influenced by the counter-ions of PFSA. The flux sequence of the PFSA/PSf composite membranes with different counter-ions is H⁺>Li⁺>Ca²⁺>Mg²⁺>Na⁺>K⁺>Ba²⁺>Fe³⁺>Al³⁺, and the separation factor sequence is H⁺<Li⁺<Al³⁺<Na⁺<Mg²⁺<Ca²⁺<K⁺<Ba²⁺<Fe³⁺. The apparent activation energy ΔE _app values of the composite membranes with different counter-ions were calculated by Arrhenius law. The sequence of ΔE _app values for the membranes with monovalent counter-ions is Li⁺>Na⁺>K⁺. There are very little variations of ΔE _app values between the composite membranes with three divalent counter-ions (Mg²⁺, Ca²⁺ and Ba²⁺), and the ΔE _app values of the composite membranes with two trivalent counter-ions (Fe³⁺ and Al³⁺) are relatively high.     

Mechanical and thermal properties of Acacia leucophloea fiber/epoxy composites: Influence of fiber loading and alkali treatment

In this work, the influence of fiber content and alkali treatment on the mechanical and thermal properties of Acacia leucophloea fiber-reinforced epoxy composites was studied. Ten composite samples were fabricated by varying fiber content (5, 10, 15, 20, and 25 wt%); both untreated and treated fiber were soaked in a 5% NaOH solution for 45 min by using hand-layup method. The composite reinforced with 20 wt% treated fiber content exhibited better mechanical properties and thermal properties. Fourier transform infrared analysis, morphological analysis by atomic force microscope, and scanning electron microscope of composites were also performed.     

Preparation and characterization of inorganic hollow fiber membranes

Inorganic hollow fiber membranes were prepared by spinning a polymer solution containing suspended aluminum oxide (Al₂O₃) powders to a hollow fiber precursor, which is then sintered at elevated temperatures. In spinning these hollow fiber precursors, polyethersulfone (PESf), N-methyl-2-pyrrolidone (NMP), and polyvinyl pyrrolidone (PVP) were used as a polymer binder, a solvent, and an additive, respectively. The inorganic hollow fiber membranes prepared were characterized using scanning electron microscope (SEM), gas permeation techniques Coulter porometer, and gravimetric analysis. Some primary factors affecting the structure and performance of the membranes such as the sintering temperature and the ratio of the aluminum oxide to the PESf polymer binder were studied extensively. The prepared inorganic membranes show an asymmetric structure, which is similar to the conventional polymeric membranes prepared from the same phase-inversion technique. The inorganic hollow fiber membrane with a higher porosity and better mechanical strength could be prepared by blending the spinning solution with a smaller amount of aluminum oxide powder.     

Eco-friendly synthesis of ZnO nanorods using Cycas pschannae plant extract with excellent photocatalytic,antioxidant, and anticancer nanomedicine for lung cancer treatment

The tunable ZnO nanorods (NRs) are produced due to the phytochemicals present in Cycas pschannae leaves which act as reducing and stabilizing agents. The confirmations of the ZnO NRs were validated using different characterization techniques: X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer, Emmett and Teller (BET), scanning electron microscopy–Energy Dispersive X-Ray Analysis (EDX), UV–visible spectroscopy, Raman spectroscopy, and transmission electron microscopy. The ZnO NRs show unique surface area and low particle size. Photocatalytic activity was measured and found to be 50.75% at low concentrations and 78.33% at high concentrations. The antioxidant activity of the ZnO NRs also showed promising results for their use in free radical scavenging. In vitro toxicity studies using zebrafish embryos was performed to evaluate the toxic nature of it and the obtained result confirmed its non-toxic nature. In addition, ZnO anticancer potential was verified using the A549 lung cancer cell line. Cytotoxic assessments of ZnO NRs were performed via 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), and neutral red uptake assays to examine the cell death cycle on the A549 lung cancer cell. Dose-dependent apoptosis and necrosis were confirmed by Lactate dehydrogenase (LDH) assay. It was also confirmed that ZnO NRs induce Reactive oxygen species (ROS) and apoptosis inside cancer (A549) cells via different intrinsic gene expression. Thus, based on this research it is evident that an effective ecofriendly, nontoxic potential anticancer drug can be synthesized using C. pschannae leaf extract.     

Fabrication of multi-layer composite hollow fiber membranes for gas separation

Using multilayer composite hollow fiber membranes consisting of a sealing layer (silicone rubber), a selective layer (poly(4-vinylpyridine)), and a support substrate (polysulfone), we have determined the key parameters for fabricating high-performance multilayer hollow fiber composite membranes for gas separation. Surface roughness and surface porosity of the support substrate play two crucial roles in successful membrane fabrication. Substrates with smooth surfaces tend to reduce defects in the selective layer to yield composite membranes of better separation performance. Substrates with a high surface porosity can enhance the permeance of composite membranes. However, SEM micrographs show that, when preparing an asymmetric microporous membrane substrate using a phase-inversion process, the higher the surface porosity, the greater the surface roughness. How to optimize and compromise the effect of both factors with respect to permselectivity is a critical issue for the selection of support substrates to fabricate high-performance multilayer composite membranes. For a highly permeable support substrate, pre-wetting shows no significant improvement in membrane performance. Composite hollow fiber membranes made from a composition of silicone rubber/0.1–0.5 wt% poly(4-vinylpyridine)/25 wt% polysulfone show impressive separation performance. Gas permeances of around 100 GPU for H₂, 40 GPU for CO₂, and 8 GPU for O₂ with selectivities of around 100 for H₂/N₂, 50 for CO₂/CH₄, and 7 for O₂/N₂ were obtained.     

Electroconvection in systems with heterogeneous ion-exchange membranes after thermal modification

It is found that the variations in the structure (morphology and microrelief) and chemical composition of surface of heterogeneous ion-exchange membranes as a result of thermal modification have different effects on the current—voltage characteristics and conditions for the generation of electroconvective instability at the membrane/solution interface under intense current modes. After thermal treatment of strongly acidic sulfocation-exchange membrane, which is characterized by a low catalytic activity in the reaction of water dissociation and a high thermal stability of fixed groups, a fraction of conducting surface area increases and the membrane microrelief develops. As a result, the diffusion limiting current density increases and the length of plateau of the current—voltage curve decreases. Therewith, the thickness of the region of electroconvective instability of solution in the near-membrane region increases and the polarization of electromembrane system, at which the mode of unstable electroconvection is reached, decreases. The thermodestruction of strongly basic anion-exchange membranes, conversely, leads to suppression of electroconvection and an increase in the length of plateau of the current—voltage curve due to the formation of fixed weakly basic amino groups, which are catalytically active in the reaction of water dissociation. A linear correlation is found between the dimensions of the region of electroconvective instability and a fraction of weakly basic functional amino groups in the composition of strongly basic membranes.     

Thermodynamic potential of a high-concentration hybrid photovoltaic/thermal plant for co-production of steam and electricity

Journal of Thermal Analysis and Calorimetry - A thermodynamic model was developed to assess the energetic performance of a dual receiver concentrated photovoltaic/thermal plant for the...     

Synthesis, characterization and thermal studies on cellulose acetate membranes with additive

Cellulose acetate (CA) membranes are used in ultrafiltration applications, although they show low chemical, mechanical and thermal resistance. In order to prepare membranes with improved properties, modification of cellulose acetate with polyethelene glycol (PEG 600) has been attempted. In this study, CA has been mixed with PEG 600 as an additive in a polar solvent. The effects of CA composition and additive concentration given by a mixture design of experiments on membrane compaction, pure water flux, water content and membrane hydraulic resistance have been studied and discussed. The efficiency of protein separation by the developed CA membranes have been quantified using model proteins such as pepsin, egg albumin (EA) and bovine serum albumin (BSA). The thermal stability of the developed membranes prepared with PEG 600 additive has also been investigated using thermogravimetric analysis and differential scanning calorimetry.     

Thermal behavior and thermal stabilization of guanidine hydrochloride-modified acrylic fiber for preparation of low-cost carbon fiber

Journal of Thermal Analysis and Calorimetry - A commercial textile-grade acrylic fiber was modified with guanidine hydrochloride for the preparation of low-cost carbon fibers. Thermal behavior of...