Microporous Hydrophobic Polypropylene Research Articles

Mass Transfer and Fluid Hydrodynamics in Sealed End Hydrophobic Hollow Fiber Membrane Gas-liquid Contactors

Hollow fiber membrane modules have been extensively used as gas-liquid contactor devices to provide a high surface area within a small volume. Hollow fiber membrane contactors have been demonstrated in a wide range of application such as in gas stripping and gas absorption. In this study the performance of sealed end hydrophobic microporous hollow fiber membranes contactors were evaluated to remove dissolved oxygen from water via vacuum degassing process. Hollow fibers membranes used in the experiment were hydrophobic microporous polypropylene of 650 μm in outer diameter, 130 μm wall thickness and nominal pore size of 0.2 μm. Based on the experimentalresult the sealed end membrane contactor can remove oxygen from water as high as 3.4-gram oxygen per square meter of membrane area per hour. The oxygen flux decreases with increasing module-packing density for the same water velocity. The same effect also occurred for the mass transfer coefficient of the membrane contactors. The mass transfer coefficients were independent of fiber length within the range of study. Hydrodynamics analysis of the contactors showed that at the same Reynolds number pressure drops increase with increasing packing density due to an increase in friction between fibers and water.

Filtering of Low-Level Radioactive Wastewater by Means of Vacuum Membrane Distillation

The rapid development of nuclear power plants (NPPs) in China has caused increasing attention to be paid to the treatment of low-level radioactive wastewaters (LLRWs). One possibility is the application of vacuum membrane distillation (VMD). In this study, a commercial hydrophobic microporous polypropylene membrane was investigated with respect to nuclide decontamination and permeate flux performance in the VMD process. The results demonstrate that vacuum pressure has the most obvious influence on permeate flux, followed by feed temperature and feed velocity. Despite the influence of operational parameters, effective nuclide filtering can be achieved with average decontamination factor (DF) values consistently higher than 1700. The salt concentration in the feed solution decreases the permeate flux and nuclide filtering. However, the VMD process still offers high average DF values of 6000 for Cs(I), 3700 for Sr(II), and 8300 for Co(II), even when the feed salt concentration reaches 80 g L−1. After operation at a high salt concentration, there is no obvious variation in the chemical composition on the membrane surface based on the attenuated total reflectance–Fourier transform infrared spectra. A brief comparison shows that the process integrating reverse osmosis and VMD is a promising method for treating LLRWs and minimizing radioactive waste in NPPs.

Application of pseudo-emulsion-based hollow fiber strip dispersion for the extraction of p-nitrophenol from aqueous solutions

ABSTRACTThe extraction of p-nitrophenol (PNP) from aqueous solutions through a pseudo-emulsion hollow fiber strip dispersion (PEHFSD) system was conducted in a microporous hydrophobic polypropylene hollow fiber membrane contactor. For the optimization of the process variables, face-centered central composite design (FCCD) has been used. It was observed that initial feed concentration, carrier composition and stripping phase concentration were the three FCCD factors, which influenced the nitrophenol extraction. Using the optimized process conditions for the separation of PNP, experiments were also performed for the separation of other nitrophenols through PEHFSD system. By the FCCD design and analysis, almost 99% extraction of all three nitrophenols was achieved at optimum conditions. A mass transfer model was also developed and aqueous and membrane resistances were evaluated as 196.46 s cm−1 and 50.14 s cm−1, respectively.

Synergistic extraction of cobalt and nickel ions by supported liquid membranes with a mixture of TIOA and TBP

In this work, the selective separation of cobalt from acidic media, containing both equimolar and non-equimolar mixtures of cobalt and nickel by supported liquid membranes (SLMs), was investigated using Alamine 308 (tri-isooctylamine, TIOA) as the carrier. The liquid membrane consisted of the desired concentration of an extractant (Alamine 308), a modifier (TBP), and a diluent (chloroform). The membrane support was microporous hydrophobic polypropylene Celgard 2500. Parameters, such as the feed solution pH, modifier (TBP) concentration, temperature, stirring speeds, extractant (Alamine 308) concentration, stripping solution type, and the complexing reagent (NH4SCN) concentration were experimentally studied and the optimum conditions were determined. The permeation coefficients (P) and initial fluxes of cobalt were calculated. A separation factor of cobalt over nickel was calculated from the experimental measurements.

Cobalt(II) membrane-extraction by DP-8R/Exxsol D100 using pseudo-emulsion based hollow fiber strip dispersion (PEHFSD) processing

The transport of cobalt(II) from acidic sulphate solutions through PEHFSD was investigated using the extractant DP-8R in Exxsol D100. The acidic feed solution containing Co(II) was passed through the tube side, and pseudo-emulsions of DP-8R/Exxsol D100 and sulphuric acid was passed through the shell side in counter-current mode, using a single microporous hydrophobic polypropylene hollow fiber contactor for extraction and stripping. In PEHFSD the aqueous strip (sulphuric acid) solution was dispersed in the organic membrane solution in a reservoir tank with an impeller stirrer to form a strip dispersion. This pseudo-emulsion phase is circulated from the tank to the membrane module to provide a constant supply of the carrier solution to the membrane micropores. Several hydrodynamic and chemical parameters, such as variation in feed pH (3–7), cobalt concentration in feed (0.17–1.7 × 10 −3 M), carrier concentration (0.16–1.28 M), etc., were investigated. Mass transfer modelling was performed and the validity of the model was evaluated with experimental data. Moreover, the system was applied in the cobalt purification of synthetic lithium solutions derived from the processing of rechargeable batteries, with cobalt/lithium separation factor values around 25.

Non-Dispersive Solvent Extraction and Stripping of Neodymium (III) using a Hollow Fiber Contactor with TODGA as the Extractant

Membrane based non-dispersive solvent extraction (NDSX) of Nd(III) from aqueous nitric acid medium was carried out using a commercial liquid-liquid extraction system consisting of an extra-flow hollow fiber module with about 10,000 microporous hydrophobic polypropylene capillaries with an effective surface area of 1.4 m2. The NDSX operation was carried out by pumping about 1 g/L Nd(III) solutions at a fixed nitric acid concentration of 3.57 M through the tube side and organic solvent (tetra-n-octyl-3-oxapentane-diamide (TODGA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fiber capillaries. NDSX studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Conditions for quantitative extraction and stripping were also identified. Reproducibility of the results from multiple runs was found to be excellent after five different identical runs.

Electrochemical characteristics of a new electric double layer capacitor with acidic polymer hydrogel electrolyte

The article presents the results of a study on activated carbon fiber cloth (AC) and a hydrophobic microporous polypropylene (PP) membrane, both chemically modified with acidic acetone aldol condensation products, and on testing their use as an electrode material and separator in electric double layer capacitors (EDLCs). Polymer hydrogel used was based on poly(acrylamide) (PAAM), H2SO4 and water. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy. As a result, the capacitor with polymer hydrogel was found to exhibit similar capacitance as that with the H2SO4 aqueous solution and an excellent high-rate dischargeability. At the 4000th cycle of potential cycling (0.5Ag−1) the specific capacitance of 132Fg−1 was obtained with a energy density of 3.45Whkg−1 at a power density of 56Wkg−1. The above results provide valuable information to explore the novel composition of EDLCs.

Grafting effect on the wetting and electrochemical performance of carbon cloth electrode and polypropylene separator in electric double layer capacitor

Activated carbon (AC) fiber cloths and hydrophobic microporous polypropylene (PP) membrane, both modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation, and filled with saturated lithium hydroxide solution were used as electrodes, a separator and electrolyte in electric double layer capacitors (EDLCs). The modification process changed the hydrophobic character of AC and PP materials to hydrophilic, made them wettable and serviceable as components of an electrochemical capacitor. The presence of poly(acrylic acid) on the AC and PP surface was confirmed by SEM and XPS methods. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy. At the 1000th cycle of potential cycling (1 A g −1) the specific capacitance of 110 F g −1 was obtained with a specific energy of 11 Wh kg −1 at power density of 1 kW kg −1. The above results provide valuable information which may be used when developing novel compositions of EDLCs.

New design of electric double layer capacitors with aqueous LiOH electrolyte as alternative to capacitor with KOH solution

Activated carbon (AC) fiber cloths and a hydrophobic microporous polypropylene (PP) membrane, both modified with lithiated acetone oligomers, were used as electrodes and a separator in electric double layer capacitors (EDLCs) with aqueous lithium hydroxide (LiOH) as the electrolyte. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry (CV), galvanostatic charge–discharge cycle tests and impedance spectroscopy (EIS), compared with a case of the capacitor with aqueous potassium hydroxide (KOH) as an electrolyte. As a result, the capacitor with LiOH aqueous solution and a modified separator and electrodes was found to exhibit higher specific capacitance, maximum energy stored and maximum power than that with KOH aqueous solution.

Selective separation of cobalt and nickel by supported liquid membranes

The selective separation of cobalt from acidic media, containing both equimolar and nonequimolar mixtures of cobalt and nickel, was examined by supported liquid membranes using Alamine 336 as mobile carrier dissolved in various diluents. The membrane support was microporous hydrophobic polypropylene Celgard 2500 (25 μm thick, 0.209 × 0.054 μm pore size and 55% porosity). Acetic acid-Na acetate buffer was used for the adjustment of the feed pH which was critical. Various parameters were experimentally studied and the optimum conditions were determined.

Separation of Phenol from Aqueous Streams by a Composite Hollow Fiber Based Pervaporation Process Using Polydimethyl siloxane (PDMS)/Polyether-Block-Amide (PEBA) as Two-Layer Membranes

In order to simultaneously achieve both high permselectivity and permeability (flux) for the recovery of aromatic compounds such as phenol from aqueous streams, a composite organophilic hollow fiber based pervaporation process using PDMS/PEBA as two-layer membranes has been developed. The process employed a hydrophobic microporous polypropylene hollow fiber, having thin layers of silicones (PDMS) and PEBA polymers coating on the inside diameter. The composite membrane module is used to investigate the pervaporation behavior of phenol in water in a separate study; and that of a mixture of phenol, methanol, and formaldehyde in an aqueous stream (a typical constituent of wastewater stream of phenol-formaldehyde resin manufacturing process) in another study. The fluxes of phenol and water increase relatively linearly with increasing concentration especially at low feed concentration, and exhibit a near plateau with further increase in concentration. As a result, the phenol/water separation factor decreases as the feed concentration increases. Significant improvement in phenol/water separation factor and phenol flux is achieved for this two-layer (PDMS/PEBA) membranes as compared to that achieved using only PDMS membrane. The phenol and water fluxes and the separation factor are highly sensitive to permeate pressure as all decrease sharply with increase in permeate pressure. For this membrane, an increase in temperature increases the separation factor, and also permeation fluxes of phenol and water. An increase in feed-solution velocity does not have a significant effect on phenol and water fluxes, and also on the separation factor at least within the range of the feed-solution velocity considered. In the study of pervaporation behavior of a typical constituent of wastewater stream of phenol-formaldehyde resin manufacturing process, phenol permeation shows a much higher flux and a higher increase in flux with increase in concentration is also exhibited as compared to that exhibited by methanol permeation. This thus indicates that the membrane is more permeable to phenol than to methanol and formaldehyde.

Electric double layer capacitors with polymer hydrogel electrolyte based on poly(acrylamide) and modified electrode and separator materials

Activated carbon fiber cloths (AC) and hydrophobic microporous polypropylene (PP) membrane, both modified by acetone aldol condensation products, and filled with polymer hydrogel were used as electrodes, separator and electrolyte in electric double layer capacitors (EDLCs). Polymer hydrogel used was based on poly(acrylamide) (PAAM), KOH and water. Electrochemical characteristics of EDLCs were investigated by cyclic voltammetry and galvanostatic charge–discharge cycle tests and also by impedance spectroscopy, compared with a case of the capacitor with only a KOH aqueous solution used as an electrolyte. As a result, the capacitor with polymer hydrogel was found to exhibit higher capacitance than that with the KOH aqueous solution and an excellent high-rate dischargeability. The above results provide valuable information to explore novel composition of EDLCs.

Transport of thorium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor

Membrane based non-dispersive solvent extraction (NDSX) of Th(IV) from aqueous nitric acid medium was carried out using di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH) using a commercial hollow fiber module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out with pumping various concentrations of nitric acid (1–6 M) containing Th(IV) through the tube side and organic extractant (usually 1.1 M DHOA in NPH) through the shell side of the hollow fibre capillaries at aqueous and organic phase flow rates of 3.5 mL/s and 4.5 mL/s, respectively. Extraction studies were performed under different hydrodynamics conditions and the overall mass transfer was evaluated under cuonter-current flow condition. The percentage NDSX of Th(IV) increased with the increase in the extractant concentration (from 0.1 M DHOA to 1.1 M DHOA) as well as with nitric acid concentration (from 1 M to 6 M). Stripping studies were carried out using both distilled water as well as oxalic acid as the strippant. The possibility of the separation of U from Th was also evaluated.

Separation of volatile organic compounds (BTEX) from aqueous solutions by a composite organophilic hollow fiber membrane-based pervaporation process

A new composite hollow fiber membrane module, employing hydrophobic microporous polypropylene hollow fibers, having a thin layer of cross-linkable vinyl-terminated silicone rubber, polydimethylsiloxane (PDMS) coated on the inside diameter has been developed. A perfect-coated pin-hole or leak free module has been achieved in this process. The separation of mixture of benzene, toluene, ethyl benzene and xylene (BTEX) (representative of an industrially significant family of aromatic hydrocarbon chemicals produced from industrial wastes) from water using the newly developed composite membrane was investigated. In this study, the permeation process employed bore-side feed flow. The influence of feed-solution velocity, permeate pressure, temperature, feed concentration and membrane thickness (based on wt% of PDMS in coating solution) on the membrane separation efficiency, permeation behaviour and performance were systematically investigated. The BTEX flux was found to increase with increase in feed-solution velocity, and the performance of this membrane has been found to improve as the driving force across the membrane decreases. That is, the optimum permeate pressure is in the range 80–100 mm Hg, when the BTEX flux is still at its maximum plateau value and the water flux is small. Increasing the permeate pressure reduces the operating cost while the separation is enhanced. As expected, the permeation fluxes of both BTEX and water were found to increase with increase in temperature and feed concentration, and a plateau value was obtained for water flux with further increase in concentration and temperature. Arrhenius plot of BTEX, water and total fluxes against reciprocal of absolute temperature shows good linearity and thus indicates the results agree with the Arrhenius effect of temperature on fluxes. The overall activation energies of pervaporation were found to be 54 and 33 kJ/mol for BTEX and water permeation fluxes, respectively. The observed enrichment in BTEX increases with increasing membrane thickness.

Au(I) extraction by LIX-79/ n-heptane using the pseudo-emulsion-based hollow-fiber strip dispersion (PEHFSD) technique

The extraction of Au(I) from alkaline cyanide solutions through PEHFSD was conducted in a microporous hydrophobic polypropylene hollow-fiber membrane contactor. The organic extractant LIX-79 ( N, N-bis(2-ethyl hexyl)guanidine) in n-heptane was used. The alkaline cyanide feed solution containing Au(I) was passed through the tube side, and pseudo-emulsions of LIX-79/ n-heptane and NaOH were passed through the shell side in counter-current mode, using a single microporous hydrophobic polypropylene hollow-fiber contactor for extraction and stripping. In PEHFSD the aqueous strip (0.2 M NaOH) solution is dispersed in the organic (12% LIX-79/ n-heptane) membrane solution in a container with a mixing arrangement (impeller stirrer) designed to form a strip dispersion. The strip dispersion is circulated from the mixer to the membrane module to provide a constant supply of the LIX-79/ n-heptane solution to the membrane pores. Various hydrodynamic and chemical parameters, such as variation in feed pH; gold cyanide concentration in feed; variation in concentrations of NaOH, LIX-79/ n-heptane and Au(I); variation in feed, strip and LIX-79/ n-heptane volume ratios and variation in feed and strippant flow rates, were investigated. Mass transfer modeling was performed and the validity of the model was evaluated with experimental data and found to tie in well with theoretical values. It was possible to concentrate Au(I) in product (NaOH) using the PEHFSD technique.

Usefulness of microporous hydrophobic polypropylene membranes after plasma-induced graft polymerization of acrylic acid for high-power nickel–cadmium batteries

Commercial microporous polypropylene (PP) membranes were modified by plasma-induced graft polymerization of acrylic acid (AAc) under UV irradiation. Under optimized conditions obtained membranes are hydrophilic and may be serviceable as separator in nickel–cadmium cell. Electrolytic resistance of modified membranes is evaluated and compared with that of commercial separators: conventional cellophane separation and hydrophilic polypropylene separation (Celgard 3501). This paper reports the maximum power test data for nickel–cadmium cells equipped with different separators. Cells with modified PP membrane show very good high-rate performance.

Novel solvent-resistant hydrophilic hollow fiber membranes for efficient membrane solvent back extraction

The advantages of employing hydrophilic hollow fiber membranes for efficient membrane solvent back extraction are explored via novel solvent-resistant hydrophilic hollow fiber membranes. The mass transfer rate of solute in membrane-based solvent extraction is controlled by boundary layer resistances and the membrane resistance. The membrane resistance can be reduced by preferentially filling the membrane pores with the phase preferred by the solute. In membrane solvent back extraction (MSBE) reactive or otherwise, it is preferable to have the pores of the membrane filled with aqueous phase. There are almost no solvent resistant hydrophilic membranes available having the required pore sizes to provide stable aqueous–organic interface at higher organic phase pressures. To that end, Nylon 6 hydrophilic porous hollow fiber membranes were coated on the inner diameter (i.d.) via insolubilization of polyethylenimine (PEI) by crosslinking to reduce the pore size. The coating provided a stable immobilized organic–aqueous interface over a reasonable range of breakthrough pressures. Back extraction of acetic acid from methyl isobutyl ketone into water was used as a model system for non-reactive extraction. Back extraction of phenol from methyl isobutyl ketone into caustic solutions was used as a model system for reactive extraction. Transport rates of phenol and acetic acid in coated hydrophilic fibers have been compared with those in hydrophobic microporous polypropylene and non-coated hydrophilic hollow fiber membranes. The novel solvent-resistant hydrophilic membranes provided better performance for nondispersive MSBE. This study also illustrated the enhancement of mass transfer coefficients in membrane solvent back extraction when the membrane pores are filled with aqueous phase.

Transport of uranium from nitric acid solution by non-dispersive solvent extraction using a hollow fibre contactor

Summary Membrane based non-dispersive solvent extraction (NDSX) of U(VI) from aqueous nitric acid medium was carried out using a commercial hollow fibre module containing microporous hydrophobic polypropylene capillaries. The NDSX operation was carried out by pumping U(VI) solutions at varying concentrations of nitric acid (1-5 M) through the tube side and organic solvent (di-n-hexyl octanamide (DHOA) in normal paraffin hydrocarbon (NPH)) through the shell side of the hollow fibre capillaries. Extraction studies were performed under different hydrodynamic conditions and the overall mass transfer was evaluated under counter-current flow conditions. Counter-current mode was found to be better as compared to the co-current mode. The U(VI) mass transfer rates were positively influenced by the nitric acid as well as DHOA concentrations.

Characterization of a mini membrane inlet mass spectrometer for on‐site detection of contaminants in both aqueous and liquid organic samples

A mini membrane inlet mass spectrometer (mini-MIMS) of a total weight of 12 kg was constructed using a miniature Multipole mass spectrometer, a small vacuum system and a flexible flat sheet membrane inlet, where the exposed membrane area can be changed by a factor of 80. The variable membrane area together with the possibility of operating the Multipole at pressures up to 1 x 10(-3) Torr made it possible to test the system with three microporous membranes (cellulose, polyether sulfone and polypropylene) normally not compatible with standard electron ionization MIMS systems and a standard non-porous polydimethylsiloxane membrane. We found that the hydrophilic cellulose and polyether sulfone membranes had selectivity characteristics opposite to those of the standard silicone membrane. They demonstrated preferential detection of hydrophilic compounds in hydrophobic organic solvents, whereas the silicone membrane preferentially detects hydrophobic organic compounds in aqueous solution. Using the cellulose membrane, organic contaminants and water could be detected in organic solvents at 10-100 ppm levels by weight, the relative high detection limits primarily caused by interference from a high chemical background from the solvent. When being used with the standard silicone membrane the mini-MIMS behaved just like most standard MIMS systems with detection limits of volatile organic compounds in water at concentrations just below 1 ppm. The hydrophobic microporous polypropylene membrane was not found to be useful with the mini-MIMS.

Application of Hollow Fiber Contactor in Nondispersive Solvent Extraction of Pu(IV) by TBP

Data on dispersion‐free solvent extraction (DFSX) of Pu(IV) from acidic nitrate media using microporous hydrophobic polypropylene hollow fiber membrane contactor with tri‐n‐butylphosphate (TBP) employing as an extractant are being presented. The DFSX operation was carried out with various concentration of TBP in n‐dodecane by passing acidic feed containing Pu (IV) through the tube side at the flow rate of 5.83 cm3 s−1 and organic extractant through the shell side at the flow rate of 1.53 cm3s−1. Extraction studies were performed under different hydrodynamic conditions and the overall mass‐transfer coefficient was evaluated with countercurrent flow condition. It was possible to extract and concentrate Pu(IV) from aqueous phase by employing this technique. For back extracting the Pu, uranous nitrate and hydroxylamine hydrochloride solution as strippants were examined, which flowed through the tube side (flow rate: 6.11 cm3 s−1) and the loaded organic was passed through the shell side with the flow rate of 1.66 cm3s−1. Results revealed that ∼80% of Pu(IV) from oxalate supernatant waste could be extracted by utilizing this technique.