Composite membranes for hydrophobic pervaporation: study with the toluene–water system

Composite membranes were utilized for hydrophobic pervaporation. Experiments were carried out with the toluene–water system using composite membranes (PERVAP®1060 and PERVAP®1070) and the results were analysed. The chosen membranes were characterised using a positron annihilations technique to measure free volume. In order to study solute–membrane interactions, the diffusion coefficient of toluene with in the membrane and Flory–Huggins interaction parameters (surface thermodynamic approach through contact angle measurement) were estimated. Influences of operating conditions (downstream pressure, feed toluene concentration, feed temperature) were observed on pervaporate fluxes (toluene and water) and pervaporate concentration of toluene.
The selectivities of the chosen composite membranes were observed to be lower compared to known values of selectivities for dense PDMS membrane, suggesting the role played by the support layer in this regard. Individual fluxes of toluene and water increase with increase in feed temperature; however, fluxes decrease with increase in downstream pressure. Further, pervaporate concentration of toluene increases with increase in feed concentration. Similar expected trends were observed; but in case of PERVAP®1070, the toluene flux attained a plateau with increase in feed toluene concentration. Such a trend confirmed the presence of an extra component (possibly zeolites) in the skin layer of PERVAP®1070. A simple resistance-in-series model, along with the solution-diffusion model were employed for mathematical analysis of the results. Model predictions with experimental values showed close agreements for the PERVAP®1060 membrane while deviations were observed for the PERVAP®1070 membrane.

Read Full text at

http://www.geocities.com/castro_che2000/membrane1.pdf

Recovery of uranium(VI) from acidic wastes using tri-n-octylphosphine oxide and sodium carbonate based liquid membranes

Acidic wastes containing low concentrations of uranium are generated during uranium purification and processing. This study has been initiated to develop a suitable emulsion liquid membrane (ELM) technique for selective separation and recovery of uranium from such wastes using tri-n-octylphosphine oxide (TOPO) in paraffin as a carrier and sodium carbonate as a stripping agent. The waste, having a composition of nearly 600 ppm U(VI), 360 ppm Fe(III), 325 ppm Ca(II), 390 ppm Mg(II) at an acidity of 1.2 M HNO3, was used as the feed phase. A comparison of ELM extraction was done between synthetically prepared uranyl feed solution and acidic wastes. Various factors that affect the emulsion stability as well as percentage extraction of uranium have been optimized in order to obtain maximum concentration of uranium from acidic wastes. An attempt was made to recover uranium without making any substantial changes to the wastes composition. In presence of various metal ions, selective permeation of uranyl ions through liquid membrane was observed to be more than 70%. Batch type extractions of U(VI) by the ELM method were performed to simulate a two-stage counter extraction and the experimental findings suggest that the U(VI) concentration in the final raffinate can be lowered to below 50 ppm. Potential of the method for the selective separation of U(VI) from acidic wastes is, thus, established.

Read Full Text at

http://www.geocities.com/castro_che2000/liquid2_membrane.pdf

Membrane reactor for the production of hydrogen and higher hydrocarbons from methane over Ru/Al2O3 catalyst

It is known that higher alkanes can be produced from methane over Ru, Pt or Co supported on silica by using a two-step reaction sequence. In this investigation, a dense Pd/Ag flat membrane reactor (FMR) and a traditional reactor (TR) are analysed referring to experimental data. The two-step reaction over Ru-based catalyst was chosen as a model reaction to be investigated. The experiments carried out in this study confirm that, using a membrane reactor, it is possible to obtain consumed methane values greater than the ones obtained in a TR for the first step operating at the same experimental conditions. A direct consequence should be an increase of the yield in higher hydrocarbons. In addition, this work shows that the membrane reactor performances can be improved by properly tuning the operating conditions. Experimental results of this work are compared with both experimental data obtained in a previous work using a dense Pd/Ag tubular membrane reactor (TMR) and experimental data reported in the literature.

Read Full Text at

http://www.geocities.com/castro_che2000/membrane_reactor.pdf

Pd–Ag membrane reactors for water gas shift reaction

Pd–Ag thin wall permeators have been obtained by coating ceramic porous tubes with thin Pd–Ag metal foils (50 μm). A procedure of cold rolling and annealing has been used for producing thin metal foils. These membranes and membrane reactors have been proposed to recover hydrogen (and its isotopes) from tritiated water by using the water gas shift reaction, and by the reverse reaction (CO2 conversion) for applications in the fusion reactor fuel cycle.
The rolled membranes have been tested at 135–360 °C with a hydrogen transmembrane pressure in the range 130–180 kPa and hydrogen flow rates up to 1.02×10−4 mol s−1. Both a complete hydrogen selectivity and a good chemical and physical stability have been observed through long-term tests. The tests on the membrane reactors have been carried out at the temperature of 325–330 °C with a feed pressure of 100 kPa; in particular, reaction conversion values close to 100% (well above the equilibrium value, about 80%) have been attained with the water gas shift reaction. These tests have demonstrated their applicability to the fusion fuel cycle as well as to the hydrogenation or dehydrogenation processes involving the use or the production of highly pure hydrogen.

Read Full Text at

http://www.geocities.com/castro_che2000/Pd-Ag_membrane.pdf

Experimental studies on treatment of distillery effluent by liquid membrane extraction

Emulsion liquid membrane (ELM) as a technique for effluent treatment has received wide attention in recent years due to its ease of operation, lower power consumption and modular design. Odorous distillery effluent was treated for removal of acetic acid (solute) using ELM in a batch process. The effect of agitator speed, duration of agitation, xylene concentration in the membrane phase, membrane to external phase (M/E) ratio on the reduction of solute, concentration of biological oxygen demand (BOD) and chemical oxygen demand (COD) in the external phase has been studied. At 110 rpm, 4% xylene concentration and M/E ratio of 0.8, a maximum recovery of 44% solute and minimum values of BOD and COD of 96 and 927 ppm, respectively, in the external phase were observed. The experiment was also conducted in a York-Schiebel column at 110 rpm and the BOD and COD of treated effluent were 94 and 900 ppm, respectively, which is almost the same as that in a batch process.

Read Full Text at

http://www.geocities.com/castro_che2000/liquid_membrane.pdf

Effect of fluidization conditions on the membrane permeation rate in a membrane assisted fluidized bed

The effects of fluidization conditions on the membrane permeation rate in a membrane assisted fluidized bed (MAFB) employing micro-porous membranes have been studied experimentally in a square fluidized bed, equipped with vertical ceramic membranes positioned in a staggered arrangement. First, the morphological parameters of the membranes have been determined with separate experiments and the membrane gas permeation rates could be well described with the dusty gas model. Secondly, the effects of the fluidization conditions, such as the particle size, superficial gas velocity and freeboard pressure on the membrane permeate flow rate have been measured. The membrane permeation rates from the fluidized bed could be well described by taking into account the local pressure drop over the membrane, where the local pressure inside the fluidized bed was evaluated as the hydrostatic head using the average bed porosity.

Read Full Text at

http://www.geocities.com/castro_che2000/fluidized_membrane.pdf

Analytic solution of the Maxwell–Stefan equations for multicomponent permeation across a zeolite membrane

We develop an analytic solution of the Maxwell–Stefan equations describing steady-state diffusion of n-component mixtures across a zeolite membrane. In the development of the analytic solution we assume Langmuirian behaviour of the pure components and that the mixture sorption can be calculated from the multicomponent Langmuir isotherm. Explicit expressions are derived for calculation of steady-state fluxes and the loading profiles in the membrane. The utility of the developed solution is illustrated by means of two illustrative examples involving permeation of alkane mixtures across an MFI membrane.

Read full text at

http://www.geocities.com/castro_che2000/zeolite2_membrane.pdf

Intrinsic kinetics of first-order reactions in photocatalytic membranes and layers

Heterogeneous photocatalysts, in the form of particles immobilized in permeable membranes or in layers covering supports, are under development for production of ultrapure water for use in semiconductor fabrication and other applications. Concentration and light intensity gradients present within a photocatalyst layer will cause local reaction rates to vary within the layer, complicating determination of intrinsic kinetics. Analytical solutions are obtained here for arbitrary networks of two or more species that undergo first-order reactions in photocatalyst layers. First-order or pseudo-first-order behavior should be obtained at the very low contaminant concentrations encountered in water ultrapurification. Experimental data can be analyzed using the solutions to obtain estimates of intrinsic rate coefficients for two flow configurations: (1) water and reactants flow through a photocatalyst layer, (2) water flows past one face of a photocatalyst layer into which reactants diffuse, with the other face sealed. A set of experimental data in the literature is analyzed and an estimate of the intrinsic reaction rate coefficient is obtained. The analytical solutions show that, when reactants flow through a photocatalyst layer, the same outlet composition is obtained for the same total incident light intensity, regardless of how the incident intensity is distributed between the two faces of the layer. When reactants diffuse into a photocatalyst layer, greater conversion can be obtained for light incident on the face over which water flows than for light incident on the sealed face. Greater conversion is obtained for reactant flow through a photocatalyst layer than for reactant diffusion into the layer.

Read full text at

http://www.geocities.com/castro_che2000/photo_membrane.pdf

A new proton-conducting porous silicon membrane for small fuel cells

In this paper, we report the fabrication of a new miniature fuel cell (FC) for portable applications based on a Nafion®-filled porous silicon membrane. This technique allows to combine advantages of Nafion® such as good proton conduction and silicon such as easy serial and parallel integration. Other advantages are the integration of gas feed and electrical contacts into the membrane etching process thanks to simple KOH wet etching processes and metal sputtering and the possibility of encapsulation. Moreover, with this technique we hope to reduce the lateral water diffusion through the membrane which is a problem with Nafion® membranes. All the results have been obtained at room temperature and gas feed (H2) is provided by the electrolysis of a NaOH solution.

Read full text at
http://www.geocities.com/castro_che2000/silicon_membrane.pdf

Preparation of hollow fiber poly(ether block amide)/polysulfone composite membranes for separation of carbon dioxide from nitrogen

The separation of carbon dioxide from nitrogen is relevant to flue gas treatment for greenhouse gas emission control. This study deals with the preparation of hollow fiber poly(ether block amide) (PEBA)/polysulfone (PSf) composite membranes for CO2/N2 separation. PEBA 2533 copolymer was shown to be a good permselective membrane material for CO2/N2 separation. At 25 °C and 100 psig, a CO2 permeability of about 260 Barrer and a CO2/N2 selectivity of 32 were obtained. The thin-film hollow fiber PEBA/PSf composite membrane comprising of a thin PEBA skin layer (<5 name="hit5">membranes were investigated. Defect-free PEBA/PSf composite membranes with an inside and an outside diameters of 350 and 600 μm, respectively, have been obtained which showed a CO2 permeance of 61 GPU and a CO2/N2 selectivity close to the intrinsic selectivity of the PEBA dense membrane. It was shown that the N2 permeability is essentially independent of the pressure, whereas CO2 permeability tends to increase with an increase in gas pressure, presumably due to plasticization of the membrane caused by the relatively high solubility of CO2 in the membrane.

FULL TEX at http://www.geocities.com/castro_che2000/titanium.pdf

If you can not open that link and you want to read this journal.

Please contact me at castro_che2000@yahoo.com

The effect of diffusion direction on the permeation rate of hydrogen in palladium composite membranes

The experimentally measured hydrogen permeability of a composite Pd/porous stainless steel membrane was found to be influenced by the direction of permeation. For pure hydrogen, the direction from the stainless steel support to the metal film gave the higher hydrogen permeance. However, for a hydrogen/nitrogen mixture the opposite effect was obtained. Simulation results showed that while permeation from the support to the metal gave the expected Sieverts’ law value of the pressure exponent of 0.5, that from the metal to the support gave a higher value for this exponent of approximately 0.66.

full text at

http://www.geocities.com/castro_che2000/composite_membranes.pdf

If you can not open that link and you want to read this journal.

Please contact me at castro_che2000@yahoo.com

Pervaporation properties of PDMS membranes for removal of benzene from aqueous solution: Experimental and modeling

Polydimethylsiloxane (PDMS) pervaporation membranes were employed to remove benzene from aqueous solution. A predictive model was proposed based on solution-diffusion mechanism to predict mass transfer during pervaporation process. The solubility of components in the membrane was described by UNIFAC-FV model, and the diffusion coefficients in polymeric membrane were calculated by free volume theory. The effects of feed concentration and operating temperature on pervaporation properties were investigated to validate the model. It has shown that the proposed model can be applied to select membrane materials and predict the permeation flux and selectivity of components through the polymeric membrane.
FULL TEXT at
http://www.geocities.com/castro_che2000/PDMS_membrane.pdf

Technical and economical evaluation of a zeolite membrane term based heptane hydroisomerization process

An industrial scale heptane hydroisomerization process was simulated based on a concept of two reactors and a zeolite membrane. A product stream containing tribranched, and part of the dibranched C7 isomers with octane number up to 92 is predicted. The economics of the process shows an investment cost of 40 million euros, with the membrane unit as the main cost driver. The technical and economical feasibility of this industrial scale heptane hydroisomerization process depends mainly on further development and performance of zeolite membranes.

FULL TEXT at

http://www.geocities.com/castro_che2000/zeolite_membrane.pdf

Hydrolysis of sucrose by radiation grafted sulfonic acid membranes

The hydrolysis of sucrose to glucose and fructose by poly(tetrafluoroethylene-co-perfluorovinyl ether)-graft-polystyrene sulfonic acid (PFA-g-PSSA) membranes was investigated. The membranes were prepared by simultaneous radiation-induced grafting of styrene onto poly(tetrafluoroethylene-co-perfluorovinyl ether) (PFA) films using γ-radiation followed by sulfonation with chlorosulfonic mixture. The kinetics of the reaction was determined for various membranes in batch mode and the reaction rate constants were obtained in a temperature range of 40–70 °C. The catalytic activity of the membranes was found to be dependent on the reaction temperature and the concentration of the sulfonic acid groups in the membranes. The results of this work suggest that PFA-g-PSSA membranes have strong potential to replace liquid sulfuric acid and ion exchange resins in sugar hydrolysis processes.

FULL TEXT at
http://www.geocities.com/castro_che2000/hydrolysis.pdf

Treatment of titanium white waste acid using ceramic microfiltration membrane

The aim of the research was to study the clarification of titanium white waste acid by ceramic microfiltration membrane. The main focus was the effect of high concentration FeSO4 and flocculant of polyacrylamide (PAA) on the filtration. The influence of operating parameters such as transmembrane pressure, cross-flow velocity, concentration and temperature on filtration process was also investigated. The results showed that hydrated TiO2 in waste acid can be successfully recovered by ceramic membrane microfiltration and an excellent clarification effect was achieved. The high concentration of FeSO4 in waste acid complicates the effect of temperature on the filtration process. When the temperature decreased to less than 293 K, crystallization of FeSO4 may occur in the membrane pores, hence it is difficult to regenerate the membrane. Flocculation by modified PAA, of which the concentration was less than 5 ppm, slightly increased the membrane flux. Further addition of flocculants might cause adsorption fouling of the membrane and resulted in decrease of flux. The membrane flux was also affected by other parameters. Analyses of filtration resistances indicated that the cake resistance was the main component of the fouling resistance and was 68–80% of the total resistance. The analyses gave more quantitative understanding into the effects of the operating parameters on the filtration.

FULL TEX at
http://www.geocities.com/castro_che2000/titanium.pdf

If you can not open that link and you want to read this journal.
Please contact me at castro_che2000@yahoo.com

Membranes for solubility-based gas separation applications

The use of membranes in gas separations has grown at a very rapid pace in recent times. One particularly interesting application of gas separation with membranes is the removal of dilute heavy organics from light gas streams such as the removal of solvents from the exhaust of different process industries. For such applications separations are achieved using the solubility-selective mode in which preferential permeation of the heavier organic molecules is desired. This article aims to review some of the recent advancements in the field of membranes for solubility-based gas separations. The development of different inorganic, polymeric and hybrid membrane materials in light of the opportunities and challenges are presented.

FULL TEXT at

http://www.geocities.com/castro_che2000/membrane.pdf

Gold and Silica-Coated Gold Nanoparticles as Thermographic Labels for DNA Detection

The infrared emissivity of Au and silica-coated Au nanoparticles (Au NPs) deposited on indium tin oxide substrates was investigated. NPs were irradiated with laser light at a frequency close to the Au plasmon resonance band, and the blackbody radiation emitted as a result was monitored with an IR camera equipped with an InAs array detector. The differences in temperature before and after laser irradiation were recorded (T-jumps) and were found to be directly proportional to the number of particles present on the slide and to the laser power used in the experiment. Coating Au NPs with silica increased the measured T-jumps 2-5 times, depending on the thickness of the silica shell. This was in agreement with the observation that silica has a much higher IR emissivity than Au. Both Au and silica-coated Au NPs were then tested as labels for thermographic DNA detection. Target DNA concentrations as low as 100 pM were recorded when Au NPs were used as labels and as low as 10 pM when silica-coated Au NPs were used.

FULL TEXT at
http://www.geocities.com/castro_che2000/silica.pdf