Mixed Matrix Silicone and Fluorosilicone/Zeolite 4A Membranes for Ethanol Dehydration by Pervaporation

The ability of homogeneous and mixed matrix membranes prepared using standard silicone rubber, poly(dimethylsiloxane) (PDMS), and fluorosilicone rubber, poly(trifluoropropylmethylsiloxane) (PTFPMS), to dehydrate ethanol by pervaporation was evaluated. Although PDMS is generally considered to be the benchmark hydrophobic membrane material in pervaporation, water/ethanol molar permselectivity of a pure PDMS membrane was found to be 0.89 for a feed containing 80/20 w/w ethanol/water at 50°C, indicating a slight selectivity for water. Fluorinated groups in PTFPMS improved the water-ethanol permselectivity to 1.85, but decreased the water permeability from 9.7 × 10^?12 kmol · m/m² · s · kPa in PDMS to 5.1 × 10^?12 kmol · m/m² · s · kPa (29,000 and 15,200 Barrer, respectively). These water permeabilities are attractive, particularly since the rubbery materials should not experience the steep declines in water permeability observed with most standard dehydration membranes as water concentration in the feed decreases. However, the water selectivity is lower than desired for most applications. Particles of hydrophilic zeolite 4A were loaded into both PDMS and PTFPMS matrices in an effort to boost water selectivity and further improve water permeability. Water-ethanol permselectivities as high as 11.5 and water permeabilities as high as 23.2 × 10^?12 kmol · m/m² · s · kPa were observed for the PTFPMS/zeolite 4A mixed matrix membranes?6 times higher than for the unfilled PTFPMS membrane.     

Application of Electroless Deposited Thin-Film Palladium Composite Membrane in Hydrogen Separation

Abstract

In recent years, there has been increased interest in developing inorganic and composite membranes for in-situ separation of hydrogen to achieve an equilibrium shift in catalytic membrane reactors. The productivity of these membrane reactors, however, is severely limited by the poor permeability and selectivity of available membranes. To develop a new class of permselective inorganic membranes, electroless plating has been used to deposit palladium thin-films on a microporous ceramic substrate. A palladium thin-film coating was deposited on a microporous ceramic disk (α-alumina, φ 39 mm × 2 mm thickness, nominal pore size 150 nm and open porosity ≈ 42%) by electroless deposition. The film was evaluated by SEM and EDX analysis. A steady-state counter-diffusion method, using gas chromatographic analysis, was used to evaluate the permeability and selectivity of the composite palladium membrane for hydrogen separation at temperatures from 373 to 573 K. The pressure on the high pressure side of the membrane ranged from 170 to 240 kPa and the low pressure side was maintained at 136 kPa. The measured hydrogen permeabilities at 573 K were found to be 1.462×10^?9 mol·m/m²·s·Pa^0.778, and 3.87×10^?8 mol · m/m² · s · Pa^0.501 for palladium film thicknesses of 8.5 and 12 μm, respectively. The results indicate that the membrane has both high permeability and selectivity for hydrogen and may find applications in high temperature hydrogen separation and membrane reactors.     

Treatment of Oily Waste Water Using Low-Cost Ceramic Membrane: Flux Decline Mechanism and Economic Feasibility

Abstract

This work addresses the applicability of different membrane pore blocking models for the prediction of flux decline mechanisms during dead end microfiltration (MF) of stable oil-in-water (o/w) emulsions using relatively low-cost ceramic membranes. Circular disk type membranes (52.5 mm diameter and 4.5 mm thickness) were prepared by the paste method using locally available low-cost inorganic precursors such as kaolin, quartz, calcium carbonate, sodium carbonate, boric acid, and sodium metasilicate. Characterization of the prepared membrane was done by SEM analysis, porosity determination, and pure water permeation through the membrane. Hydraulic pore diameter, hydraulic permeability, and hydraulic resistance of the membrane was evaluated as 0.7 µm, 1.94 × 10^?6 m³/m²·s·kPa and 5.78 × 10¹¹ m²/m³, respectively. The prepared membrane was used for the treatment of synthetic stable o/w emulsions of 40 and 50 mg/L crude oil concentration in batch mode with varying trans-membrane pressure differentials ranging from 41.37 to 165.47 kPa. The membrane exhibited 96.97% oil rejection efficiency and 21.07 × 10^?6 m³/m²·s permeate flux after 30 min of experimental run at 165.47 kPa trans-membrane pressure for 50 mg/L oil concentration. Different pore blocking, models such as complete pore blocking, standard pore blocking, intermediate pore blocking and cake filtration were used to gain insights into the nature of membrane fouling during permeation. The observed trends for flux decline data convey that the decrease in permeate flux was initially due to intermediate pore blocking (during 1 to 10 minutes of experimental run) followed with cake filtration (during 10 to 30 minutes of experimental run). Based on retail prices of the inorganic precursors, the membrane cost was estimated to be 130 $/m². Finally, preliminary process economic studies for a single stage membrane plant were performed for the application of the prepared membrane in industrial scale treatment of o/w emulsions. A process economics study inferred that the annualized cost of the membrane plant would be 0.098 $/m³ feed for treating 100 m³/day feed with oil concentration of 50 mg/L.     

The Fabrication and Characterization of Cellulose/Mesoporous Silica Composites Packaging Films with Adjustable Permeability by NMMO Technology

Cellulose-based composites containing various amounts of SBA-15 mesoporous silica were prepared by NMMO-technology, and their morphologies, mechanical properties, permeability for oxygen and water vapor were studied. The investigation suggested that both the modified and unmodified mesoporous silica materials can improve the elongation at break of the cellulose films. However, the incorporation of the mesoporous silica materials can reduce the tensile strength of the films, and the modified one has less effect on that than the unmodified one. The composites films with rational mechanical properties have adjustable oxygen permeability (7.90 × 10^?15–94.6 × 10^?15 cm³ · cm/cm² · s · Pa) and water vapor permeability (7.12 × 10^?13–4.10 × 10^?13 g · cm/cm² · s · Pa).     

Inkjet Printing of Microporous Silica Gas Separation Membranes

Inkjet printing was applied to manufacture silica‐based gas separation membranes, which were coated on a pore‐graduated alumina substrate with a mesoporous γ‐alumina interlayer. A silica sol diluted by 1‐propanol was used to print the membrane layer followed by thermal treatment in a rapid thermal processing furnace. The membrane thickness was varied between 30 and 110 nm by conducting one, two, and three coating steps. In the latter case, H₂ permeance in the range of 2.0 × 10^?8–3.3 × 10^?8 mol/s·m²·Pa combined with H₂/CO₂ selectivities in the range of 15–25 were achieved, proving the concept that inorganic gas separation membranes can be successfully processed by inkjet printing.     

Transport of Co(II) Ions through Di(2-ethylhexyl) Phosphoric Acid-CCl4 Supported Liquid Membranes

Abstract

A liquid membrane transport study of Co(II) using di(2-ethylhexyl) phosphoric acid (D2EPHA) as carrier and CCl₄, as diluent supported on polypropylene microporous film has been carried out. The carrier concentration in the membrane and HCl concentration in the stripping phase have been varied to see the effect on transport of Co(II) ions across the membrane. Maximum flux and permeability values of 1.23 × 10^?5 mol · m^?2 · s^?1 and 7.66 × 10^?11 m²/s, respectively, at a 0.87 mol/dm³ carrier concentration in the membrane have been found. At 1 mol/dm³ HCl concentration in the stripping phase the flux and permeability have maximum values of 1.4 mol · m^?2 · s^?1 and 5.27 × 10^?11 m²/s, respectively. The distribution coefficient of Co(II) ions into organic phase has been found to increase with increasing carrier concentration. The diffusion coefficient determined varies from 13.73 × 10^?11 to 0.83 × 10^?11 m²/s, which is the reverse order of the values of the distribution coefficient and explains the permeability of the Co(II) D2EPHA complex through the membrane.     

GAS PERMEANCE BEHAVIOR AT ELEVATED TEMPERATURE IN MESOPOROUS ANODIC OXIDIZED ALUMINA SYNTHESIZED BY PULSE-SEQUENTIAL VOLTAGE METHOD

Mesoporous anodic oxidized alumina (MAOA) capillary tubes with and without a barrier layer have been synthesized by applying a pulse-sequential voltage. The single gas permeances at an elevated temperature and the thermal and hydrothermal stabilities of MAOA were investigated. A highly oriented radial mesopore channel with pore sizes from 40 to 4 nm was formed in the MAOA tubes. Micropores with sizes from 0.4 to 0.8 nm were formed in the barrier layer. The H₂ permeance of MAOA with a barrier layer (barrier type) was approximately 540 times lower than that of MAOA without a barrier layer (block type) at 773 K. The H₂/N₂ permselectivity of the barrier type in the temperature range from 333 to 673 K was 3.4; those of the barrier type at 773 and 823 K were 4.4 and 11, respectively. On the other hand, the H₂/N₂ permselectivities of the block type were from 3.1 to 3.6 in the temperature range from 333 to 773 K. The H₂ permeance and the H₂/N₂ permselectivity of the amorphous silica membrane on the block type were 1.1 × 10^?7 mol/m² · s · Pa and 40 at 773 K, respectively. MAOA synthesized by the pulse-sequential voltage method can be applied to the mesoporous support of the gas separation membrane at elevated temperatures.     

Microwave synthesis of tubular zeolitic imidazolate framework ZIF-8 membranes for CO2/CH4 separation

The separation of CO₂/CH₄ is reported in detail by using zeolitic imidazolate framework (ZIF-8) membrane which was prepared on 3-aminopropyltriethoxysilane modified Al₂O₃ tube through microwave heating synthesis. Attributed to the preferential adsorption affinity of CO₂ over CH₄ and a narrow pore window of 0.34 nm, the ZIF-8 membrane shows high separation performances for the separation of CO₂/CH₄ mixtures. For the separation of equimolar CO₂/CH₄ mixture at 100°C and 2 bar feed (1 bar permeate) pressure, a CO₂ permeance of 1.02 × 10^?8 mol/m²· s· Pa and a CO₂/CH₄ selectivity of 6.8 are obtained, which is promising for CO₂ separation.     

Quantitative measurement of voids formed during liquid impregnation of nonwoven multifilament glass networks using an optical visualization technique

A technique based on matching the refractive index of an invading liquid to that of a fiber mat has been used to study entrapment of air (“voids”) that occurs during forced in-plane radial flow into nonwoven multifilament glass networks. The usefulness of this technique is demonstrated in quantifying and mapping the air pockets. Experiments with a series of fluids, with surface tensions varying from 28 × 10^?3 to 36 × 10^?3 N/m, viscosities from 45 × 10^?3 to 80 × 10^?3 Pa · s, and inlet flow rates from 0.15 × 10^?6 to 0.75 × 10^?6 m³/s, have shown that void content is a function of the capillary number characterizing the flow process. A critical value of capillary number Ca = 2.5 × 10^?3 identifies a zone below which void content increases exponentially with decreasing capillary number. Above this critical value, negligible entrapment of voids is observed.     

Permeability of deuterium and helium in poly(vinyl alcohol)

We report the permeabilities of deuterium and helium-4 through poly(vinyl alcohol) (PVA) over the temperature range of 25–125°C. For deuterium, permeabilities ranged from 0.5 × 10^?18 to 50 × 10^?18 mol·m/m²·s·Pa at these two extreme temperatures. Helium permeabilities were roughly five times higher. We also studied the effects of different curing temperatures and time on the deuterium permeability and found that, to within experimental error, results were the same for samples heat treated at any temperature between 100°C and 140°C. Aluminizing the samples using a special process decreased the permeabilities by a factor of at least 5. A sensitive apparatus constructed around a quadrupole spectrometer was used to measure the very low permeabilities. The apparatus is described in detail.     

Preparation of nano-zeolite tubular membrane for ethylbenzene separation from ternary mixed xylene by microwave functional coating method

The ethylbenzene separation from mixed xylene is one of the critical issues in the chemical industry. In this study, separation of ethylbenzene from ternary xylene mixtures system [ethylbenzene (EB), para-xylene (PX) and meta-xylene (MX)] was performed using a nano-zeolite coated tubular membrane system. Nano-zeolite membranes with different Si/Al ratios (Si/Al = 30, 100 and ∞) were prepared by a microwave hydrothermal method and the separation performance was compared. MFI-type nano-zeolite membranes were synthesized on alumina tubes from the randomly oriented seed layers by dip coating and functional coating using 3-chloropropyltrimethoxysilane, respectively. After the microwave-assisted secondary growth, it was observed that thinner layers of nano-zeolites were prepared by functional coating (3–4 μm) compared to the typical dip coating (6–8 μm). Ethylbenzene separation tests were performed using a comparatively high EB-containing ternary mixture feed (EB/PX/MX = 80/5/15 molar ratio). The silicalite-1 (Si/Al ratio = ∞) membrane with a functional layer shows the best ethylbenzene separation factor of 3.11 from the high EB-containing ternary mixture feed (ethylbenzene flux: 1,010.6 mol/m² s Pa ×10^?10).     

Carbon molecular sieve membranes for natural gas purification: Role of surface flow

Carbon molecular sieve membranes (CMSM) were prepared from the pyrolysis of polyimide films within a temperature range of 600°C-800°C under nitrogen stream. The membrane samples were characterized and tested for the permeation of He, CH₄, CO₂, and N₂ at different pressures and temperatures, respectively. The CMSM700 membrane (pyrolyzed at 700°C) showed an ideal selectivity of ~ 11 for N₂/CH₄ with a permeability of 2.18 × 10⁻¹⁵ mol · m/m² · s · Pa for N₂. The separation mechanism for the N₂/CH₄ pair was shown to be largely molecular sieving rather than surface flow. The membrane showed an ideal selectivity of ~ 500 for the CO₂/CH₄ pair with a CO₂ permeability of 9.72 × 10⁻¹⁴ mol · m/m² · s · Pa. The permeability of He was lower than that of CO₂, suggesting that the surface flow played a significant role in the CO₂ permeation. The updated permeability-selectivity tradeoff curves show that this CMSM membrane compared favourably with other membrane materials reported in the literature for the removal of N₂ and CO₂ from CH₄ for natural gas upgrading.     

Coupled Transport of Zr(IV) through Tri-n-butylphosphate-Xylene-Based Supported Liquid Membranes

Abstract

The transport of Zr(IV) through tri-n-butylphosphate-xylene-based liquid membranes, supported in a polypropylene hydrophobic microporous film, has been studied. The concentration of HNO₃ in the feed solution and tri-n-butylphosphate (TBP) carrier in the membrane were varied, and the flux and permeability coefficients were determined. The optimum conditions found for maximum flux were determined to be 10 mol/dm³ HNO₃ and 2.93 mol/dm³ TBP with a flux value of 12.9 × 10^?6 mol · m^?2 · s^?1. The solvent extraction study revealed that 1.25 to 3.5 protons are involved in zirconium transport, and that two molecules of TBP are involved in the complex formation. The value of protons involved varies with acid concentration. The zirconium ion transport is coupled with nitrate ions transport.     

Microporous polypropylene sheets containing polymethylsilsesquioxane filler

Plasma polymerized membranes were prepared from octamethyltrisiloxane for the purpose of separation of O₂ over N₂. The obtained membrane consisted of plasma prepared polymer layer on top of a porous polyproplene substrate. The membrane polymerized under the mild plasma condition (low power input and high monomer flow rate) showed the high permeation rate. Selectivity, however, was hardly affected by the plasma conditions. The selectivity and permeation rate obtained were 2.6 and 2.5 × 10^?10 kmol/(m²·s·Pa) (=7.5×10^?4 cm³/(cm²·s·cmHg)), respectively. This high permeation rate was attributed to the use of the monomer with the long, flexible siloxane chain and the mild plasma condition. Moreover, the membranes were prepared from a series of monomers with different siloxane chain lenghts (methoxytrimethylsilane, hexamethyldisiloxane, and octamethyltrisiloxane), and from those with different alkyl chain lenghts (methoxytrimethylsilane, propoxytrimethylsilane, and hexyloxytrimethylsilane). As the siloxane chain lenghts of the starting monomers increased and the alkyl chain lengths decreased, the permeation rates of the corresponding polymers increased. The selectivities were nearly constant regardless of the difference in the starting monomer structures. The structures of the plasma prepared polymers were analyzed by XPS and IR measurements, and discussed in relation to the membrane efficiencies. © 1994 John Wiley & Sons, Inc.     

EXPERIMENTAL STUDIES AND PARAMETER OPTIMIZATION OF SEPARATION OF COPPER USING HOLLOW FIBER–SUPPORTED LIQUID MEMBRANE

The separation of copper from a leach liquor bearing 204.59 mol/m³ Cu, 40.83 mol/m³ Zn, 33.94 mol/m³ Co, 255.58 mol/m³ Ni, and 75.72 mol/m³ (NH₄)₂SO₄ has been carried out with a hollow fiber membrane using LIX 84-I as the mobile carrier. Central composite inscribed (CCI) design was used to design the experiments. The factors considered for the CCI design were pH, LIX 84-I concentration in the membrane phase, flow rate, and acid concentration in the strip solution. A reduced quadratic model was found to fit the experimental data. Detailed analysis of the effect of different factors as well as their interaction on the extraction of copper has been done. The optimized condition for maximum copper flux was found to be pH 4.5, 39.88% LIX 84-I, 360 mL/min flow rate, and 7% H₂SO₄ in strip solution. The highest copper flux of 7.46 × 10^?5 mol/m² · s was obtained experimentally at the above conditions, which is in good agreement with the predicted value of 7.57 × 10^?5 mol/m² · s.     

Integral conversion of SO2: Hysteresis and rate discontinuities

The oxidation of SO₂ was carried out over an American Cyanamid V₂O₅ catalyst in an insulated integral reactor without significant interparticle resistances under the following conditions: 10 percent SO₂-air feed, feed temperatures in the range of 430°C to 590°C, 108 kPa pressure, and entrance temperatures of the gases in the annular heat exchanger from 400°C to 450°C, with one set of conversions being obtained without annular air flow. Gas analysis was accomplished by the oxidation of SO₂ to SO₃ with potassium permanganate. The method was fully tested before adoption. Final conversions in the range of 5 to 60 percent were observed. A hysteresis loop was found in the plane of outlet conversion versus the average feed temperature. The multiplicity is possibly stable but probably decays with the time constants in the order of days which is evident from the transient data that were obtained. A one dimensional model was able to correlate the conversion data through the Arrhenius rate parameters in the Boreskov-Sokolova⁽⁸⁾ rate expression which changed from A = 1.92 × 10⁷ m³/(s·kg) and E = 151 MJ/kmol to A = 0.344 m³/(s·kg) and E = 33.5 MJ/kmol at a calculated temperature at the surface of the catalyst of 517°C. Similar behavior has been observed in other studies concerned with basic kinetic studies over catalyst pellets. The analogy between the behavior of the catalyst pellets and the behavior of the integral reactor can thus be fully drawn with respect to hysteresis and rate discontinuities.     

Separation of Acetic Acid‐Water Mixtures through Poly(Vinyl Alcohol)/Poly(Acrylic Acid) Alloy Membranes by Using Evapomeation and Temperature Difference Evapomeation Methods

Abstract

Separation of acetic acid‐water mixtures by using evapomeation (EV) method were carried out over the full range of compositions at temperatures varying from 30 to 55°C using poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) (75/25) (v/v) alloy membranes. PVA/PAA membranes gave separation factors of 110–5711 and permeation rates of 2.3×10^?4–1.53×10^?1 kg/m²h, depending on the operation temperature and feed mixture composition. The temperature dependence of the permeation in EV was expressed by the Arrhenius type expression and the activation energy was calculated as 9.15 kcal/mol. More efficient EV technique, which is called temperature difference evapomeation method (TDEV) was also applied to PVA/PAA membranes to separate acetic acid‐water mixtures; high permeation rates (1.7×10^?3–3.0×10^?1 kg/m²h) and separation factors (1335–8924) were obtained for each of the studied feed compositions. Azeotropic mixture of acetic acid and water was also separated by TDEV method with a separation factor of 297 and permeation rate of 1.50×10^?1 kg/m²h.     

Supported Liquid Membrane Extraction Study of (MoO4)2- Ions using Tri-n-octylamine as Carrier

Abstract

The transport of (MoO₄)^2- ions across a tri-n-octylamine (TOA) xylene-based supported liquid membrane has been studied at various HCl concentrations in the feed, TOA concentrations in the membrane, and NaOH concentrations in the strip solution. The distribution coefficient and flux of the Mo(VI) ion species vary with the HCl concentration, indicating that different polymeric species of this metal ion are present in the aqueous solution. A TOA concentration increase of up to 1.308 mol/dm³ enhances flux and permeability of this metal ion, which beyond this concentration is reduced due to an increase in carrier liquid viscosity. An increase in NaOH solution concentration has been found to increase flux and permeability values. The continuous increase in pH of the feed with the transport of metal ions indicates that the (MoO₄)^2- transport does not involve a decrease or increase in concentration as a result of association of lower to higher or decomposition of higher to lower metal ions polymeric species. The optimum conditions of transport of Mo(VI) metal ions across these membranes have been found to be HCl = 0.01, [NaOH] = 1, and [TOA] = 1.308, furnishing flux and permeability values of the order of 2.49 × 10^?4 mol·m^?2·s^?1 and 2.32 × 10^?10 m²·s^?1, respectively.     

Equilibrium and kinetic studies of the extraction of chelated copper(II) anions with Aliquat 336

The equilibrium and kinetics of solvent extraction of Cu²⁺ from aqueous solutions containing equimolar EDTA with Aliquat 336 in n‐decanol and kerosene at 298 K were investigated. The concentrations of Cu²⁺ (8–50 mol m^?3), Cl^? (5–60 mol m^?3), and Aliquat 336 (20–100 mol m^?3) were varied. A semi‐empirical model with three parameters was proposed to describe the equilibrium behavior, in which the non‐idealities in both aqueous and organic phases were considered. Over the ranges studied, the model agreed reasonably well with the experimental data (standard deviation, 15%). The forward and backward reaction rate constants were determined as (5.31 ± 0.16)×10^?6 m^9/4 mol^?3/4 s^?1 and (2.62 ± 0.09)×10^?7 s^?1, respectively, at 298 K. An interfacial reaction mechanism was proposed, which revealed that the reaction between the chelated anions and trimeric amine molecules at the interface was rate limiting. The derived rate laws were consistent with the experimental results. © 2002 Society of Chemical Industry     

Performance of Low Cost Ceramic Microfiltration Membranes for the Treatment of Oil-in-water Emulsions

Using the uniaxial compaction method, ceramic disk type microfiltration membranes were fabricated using mixtures of clays to yield membranes M₁, M₂, and M₃. These were obtained with distinct compositions of raw materials at a sintering temperature of 900°C. Membrane characterization was conducted using thermogravimetric analysis (TGA), particle size distribution (PSD), X-ray diffraction (XRD), and scanning electron microscope analysis (SEM). Morphological characterization of these membranes includes the evaluation of average porosity, pore size, mechanical stability, chemical stability, and hydraulic permeance. With varying composition of the raw materials, it is observed that the average porosity and pore size of the membrane varied between 23–30% and 0.45 to 1.30 µm. For all membranes, the flexural strength varied within the range of 10-34 MPa. Chemical stability tests indicate that the membranes are stable in both acidic and basic media. The hydraulic permeance of M₁, M₂, and M₃ membranes is about 3.97 × 10^?6, 2.34 × 10^?6, and 0.37 × 10^?6 m³/m² s kPa, respectively. Further, the performance of these membranes was studied for the microfiltration of synthetic oily wastewater emulsions. Amongst all membranes, membrane, M₂ performance is satisfactory as it provides oil rejection of 96%, with high permeate flux of 0.65 × 10^?4 m³/m² s at a lower transmembrane pressure differential of 69 kPa for the oil concentration of 200 mg/L.