Partial oxidation of ethane to syngas in an oxygen-permeable membrane reactor

A perovskite-type oxide of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) with mixed electronic and oxygen ionic conductivity at high temperatures was used as an oxygen-permeable membrane. A tubular membrane of BSCFO made by extrusion method has been used in the membrane reactor to exclusively transport oxygen for the partial oxidation of ethane (POE) to syngas with catalyst of LiLaNiO/γ-Al₂O₃ at temperatures of 800–900 °C. After only 30 min POE reaction in the membrane reactor, the oxygen permeation flux reached at 8.2 ml cm⁻² min⁻¹. After that, the oxygen permeation flux increased slowly and it took 12 h to reach at 11.0 ml cm⁻² min⁻¹. SEM and EDS analysis showed that Sr and Ba segregations occurred on the used membrane surface exposed to air while Co slightly enriched on the membrane surface exposed to ethane. The oxygen permeation flux increased with increasing of concentration of C₂H₆, which was attributed to increasing of the driving force resulting from the more reducing conditions produced with an increase of concentration of C₂H₆ in the feed gas. The tubular membrane reactor was successfully operated for POE reaction at 875 °C for more than 100 h without failure, with ethane conversion of ∼100%, CO selectivity of >91% and oxygen permeation fluxes of 10–11 ml cm⁻² min⁻¹.     

Gas permeation properties of poly(lactic acid)

The need for the development of polymeric materials based on renewable resources has led to the development of poly(lactic acid) (PLA) which is being produced from a feedstock of corn rather than petroleum. The present study examines the permeation of nitrogen, oxygen, carbon dioxide, and methane in amorphous films of PLA cast from solution. The properties of PLA are compared to other commodity plastics and it is shown that PLA permeation closely resembles that of polystyrene. At 30°C, N₂ permeation in PLA is 1.3 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and the activation energy is 11.2 kJ/mol. For oxygen the corresponding values are 3.3 (10⁻¹⁰ cm³(STP) cm/cm² s cm Hg) and 11.1 kJ/mol. The values for carbon dioxide permeation are 1.2 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and 6.1 kJ/mol. For methane values of 1.0 (10⁻¹⁰ cm³ (STP) cm/cm² s cmHg) and an activation energy of 13.0 kJ/mol are found. Studies with pure gases show that polymer chain branching and small changes in l:d stereochemical content have no effect on permeation properties. Crystallinity is found to dominate permeation properties in a biaxially oriented film. The separation factor for a CO₂/CH₄ mixed gas system is measured between 0 and 50°C and does not deviate significantly from the calculated ideal separation factor; at 0°C the separation factor is 16, a value that suggests continued studies of PLA as a separation medium are warranted.     

Separation performance of polyimide composite membrane prepared by dip coating process

The effects of the preparation conditions in a dip coating process on polyimide composite membranes have been investigated. Polyimide precursor obtained from pyromellitic dianhidride (PMDA) and 4,4′-oxydianiline (ODA) was mixed with triethylamine and poly(amic acid)tri-ethylamine salt (PAA salt) was made. An asymmetric polyimide membrane (PI-2080) as a supporting membrane was dipped in a PAA salt (concentration 0–5 wt.%) methanol solution. The coating layers of PAA salt were converted to these of polyimide by annealing at 200°C for 3 h in an ordinary vacuum oven.The performance of the polyimide composite membrane was evaluated by gas permeation (N₂, O₂, CO₂, at 1 kg/cm²) and pervaporation (feed: a 95 vol.% ethanol aqueous solution at 30–60°C). The composite membranes prepared using a coating solution of 5 wt.% PAA salt showed the CO₂/N₂ selectivity of over 25 on gas permeation, and separation factor α (H₂O/EtOH) of over 800 with a total flux of 0.21 kg/m² h on pervaporation.     

Oxygen permeation through (Bi2O3)0.74(SrO)0.26–Ag (40% v/o) composite

The dense dual phase composite membrane made from strontium-stabilized bismuth oxide and silver, (Bi₂O₃)_0.74(SrO)_0.26–Ag (40% v/o), was investigated. The composite was found to exhibit very high electrical conductivity at the room temperature, revealing that the silver phase has formed electron-conducting networks in the oxide matrix. The composite shows much improved oxygen permeability compared with the bismuth oxide alone. An oxygen flux of 5×10⁻⁸ mol cm⁻² s⁻¹ was observed for a 1.00 mm thick composite at 700°C with oxygen partial pressures of the feed and permeate side at 0.209, 0.0024 atm, respectively. Combination of electrical conductivity and oxygen permeation measurements reveals that oxygen-ion conduction through the oxide phase of the composite is the rate-limiting step for oxygen permeation.     

Ultrafiltration of soybean oil/hexane extract by porous ceramic membranes

This study investigated the ultrafiltration of soybean oil/hexane extract (miscella) using porous ceramic membrane. The evaporation energy can be saved in the soybean oil production by pre-separating a portion of hexane through the ceramic membrane. Raw soybean oil/hexane extract with 33 wt% of oil was used without pretreatment. A cross-flow ultrafiltration was performed using an anodisc membrane with a pore diameter of 0.02 μm and thickness of ∼1 μm. The concentrations of oil/hexane mixture were measured by UV adsorption at a wavelength of 458 nm. The separation mechanism was suggested to be the hindrance diffusion of soybean oil. Agitation in the feed side significantly increased the rejection of soybean oil. A small stage cut could also yield a higher rejection. Above observations were attributed to the reduction of concentration polarization by increasing the shear rate and small permeate flux, respectively. The optimum separation was achieved under the conditions of 4 kg/cm² transmembrane pressure, 0.04 stage cut and 120 rpm agitation speed. The concentration of soybean oil decreased from 33 wt% of feed to 27 wt% in permeate, that is, near 20% rejection. A gel-layer polarization model was proposed to estimate the gel concentration and thickness. The gel concentration was found 43–53 wt%. Agitating feed side reduced gel thickness, thus enhanced the rejection and permeate flux.     

Preparation of palladium membranes from the reaction of Pd(C3H3)(C5H5) with H2: wet-impregnated deposition

A new technique to prepare a palladium membrane for high-temperature hydrogen permeation was developed: Pd(C₃H₃)(C₅H₅) an organometallic precursor reacted with hydrogen at room temperature to decompose into Pd crystallites. This reaction together with sintering treatment under hydrogen and nitrogen in sequence resulted in the formation of dense films of pure palladium on the surface of the mesoporous stainless steel (SUS) support. Under H₂ atmosphere the palladium membrane could be sintered at 823 K to form a skin layer inside the support pores. The hydrogen permeance was 5.16×10⁻² cm³ cm⁻² cm Hg⁻¹ s⁻¹ at 723 K. H₂/N₂ selectivity was 1600 at 723 K.     

Effects of the feed solution concentration on the separation degree in Donnan dialysis for binary systems of amino acids

The separations of amino acids by Donnan dialysis using an ion-exchange membrane were studied. Donnan dialytic experiments were carried out using an anion-exchange membrane, glutamic acid–phenylalanine or glutamic acid–alanine mixed solutions as the feeds, and sodium hydroxide solutions as the stripping ones. The initial concentrations of the two kinds of amino acids in the feed solutions were equal and in the range of 0.5–50 mol m⁻³. The amino acid fluxes were measured for each feed solution. Above the feed concentration of 10 mol m⁻³, the glutamic acid flux was over 100 times greater than that of the other amino acid, and it was found that the Donnan dialysis was applicable to the separation of the amino acids. On the other hand, below 10 mol m⁻³, the amino acid fluxes varied in a complicated manner with the concentration, and below 1 mol m⁻³ there was little difference between the fluxes of the two amino acids.Furthermore, after soaking the membrane in solutions having the same concentrations as the feed in the Donnan dialysis, uptake of the amino acids into the membrane was also measured. By comparing the experimental results of both the flux and uptake of the amino acids, the reason why the flux varied in a complicated manner with the concentration was discussed.     

Modelling of mass transfer in facilitated supported liquid membrane transport of copper(II) using MOC-55 TD in Iberfluid

The transport of copper(II) through a supported liquid membrane using MOC-55 TD (oxime derivative), dissolved in Iberfluid, as a carrier has been studied. A physico-chemical model is derived to describe the transport mechanism which consists of: diffusion process through the feed aqueous diffusion layer, fast interfacial chemical reaction and diffusion through the membrane. The experimental data can be explained by mathematical equations describing the rate of transport. The mass transfer coefficient was calculated from the described model as 2.8×10⁻³ cm s⁻¹, the thickness of the aqueous boundary layer as 2.6×10⁻³ cm⁻¹ and the membrane diffusion coefficient of the copper-containing species as 1.2×10⁻⁸ cm² s⁻¹.     

Hollow fiber supported liquid membrane: a novel technique for separation and recovery of plutonium from aqueous acidic wastes

Low plutonium content acidic waste is generated in nuclear chemical facilities. Study was initiated to develop hollow fiber supported liquid membrane (HFSLM) technique for quantitative separation and recovery of plutonium (Pu) from such wastes using tri-n-butyle phosphate (TBP) in dodecane as carrier. Hollow fiber test module was fabricated using 20 lumens of 33.91 cm² surface area and 9 cm length. After satisfactory testing of the hydrodynamic condition of the module, it was operated at a flow rate of 3 ml min⁻¹ on recycling mode with acidic waste solution containing Pu=8 mg dm⁻³, uranium=15 dm⁻³, gross β⁻=49.33 mCi dm⁻³, gross γ=15.73 mCi dm⁻³ and acidity 3 M HNO₃. In presence of various fission products, selective permeation of Pu(IV) through the bundle of hollow fiber test module was observed to be more than 90% into a stripping phase consisting 0.1 M NH₂OH·HCl in 0.3 M HNO₃. A model is presented to describe the transport mechanism and to evaluate the mass transfer coefficient. The radiation stability was also tested by exposing the membrane upto irradiation level of 1 M rad. Potentiality of the method for the selective separation of plutonium from acidic waste is, thus, clearly seen.     

Noise and ac impedance analysis of ion transfer kinetics at the micro liquid/liquid interface

Fluctuation analysis was utilized to determine the TEA ion transfer kinetics across the water/1,2-dichloroethane interface. The obtained data were compared with those derived from electrochemical impedance spectroscopy experiments using the same electrolytic cell. The apparent standard rate constants k_s determined by these two techniques have a similar value. The average value k_s = 0.37 cm s^− 1 is comparable with the previously reported value k_s = 0.2 cm s^− 1. The experimental approach utilizing a thick wall glass micro-capillary to fix the interface exhibits a very small stray capacitance value, proving this system to be suitable for determining the kinetics of the fast ion transfer across a liquid/liquid interface. Application of a method employing a small perturbation signal prevents polarization of the inner capillary surface by current flowing through the cell. The induced polarization of the capillary can affect ion concentration at the interface due to electroosmosis and thus make the kinetic data evaluation difficult or erroneous.     

Fabrication of supported Si3N4 membranes using the pyrolysis of liquid polysilazane precursor

The fabrication process is described of supported microporous Si₃N₄ membranes, prepared by pyrolytically decomposing organo-substituted polysilazane precursor. The membrane had a composite asymmetric structure consisting of a mechanically strong porous Si₃N₄ support which had 42 vol% pores between 0.4 and 0.52 μm, coated with an intermediate and one or two thin active top layers. The individual layers were fabricated by the conventional dip-coating technique.Permeation experiments with He, N₂ and CO₂ have been performed to determine the gas transport characteristics and separation performance of the processed membranes. The permeation is pressure-independent, indicating no viscous flow in the supported top layer. The proposed process has made it possible to prepare membranes with He permeation rates of ≥5.3×10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and He/N₂ permselectivities of ≥2.0, even in the membrane with one top layer. It is also demonstrated from separation experiments, that the membrane with high quality top layer has the separation factors of 4.7 for He/N₂ and of the theoretical of Knudsen flow for CO₂/N₂.     

Pervaporation separation of water–acetic acid mixtures through poly(vinyl alcohol)-silicone based hybrid membranes

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. The remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as crosslinking agent. The membrane containing 1:2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10⁻² kg/m² h at 30 °C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values, obtained for water permeation being lower than those of acetic acid permeation values, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal as due to higher selective nature of membranes. Further, the activation energy values for permeation of water and diffusion of water are almost equivalent, suggesting that both diffusion and permeation contribute almost equally to the pervaporation process. The negative heat of sorption values (ΔH_s) for water in all the membranes suggests the Langmuir's mode of sorption.     

Experimental evaluation of a uniform transmembrane pressure crossflow microfiltration unit for the concentration of micellar casein from skim milk

A uniform transmembrane pressure (UTMP) crossflow microfiltration (CFMF) system maintains a low but uniform transmembrane pressure (ΔP_TM) with high crossflow velocity (CFV), which reduces fouling and cake build-up, and improves the utilization of available filtration area. A CFMF system, with a 0.2 μm nominal pore size ceramic filter, filtration area 0.184 m², was operated in both UTMP and non-UTMP modes. The two modes were compared for their effectiveness in maintaining a steady flux during the separation of casein micelles from skim milk up to a concentration factor (CF) 10 at 50°C. Experiments were performed at an average CFV of 7.2 m s⁻¹ and ΔP_TM from 89 to 380 kPa. Up to CF 4 the non-UTMP mode maintained a slightly better flux and process time than the UTMP mode, but reached the minimally acceptable flux (below 0.005 kg m⁻² s⁻¹) at CF 6. Depending upon the ΔP_TM maintained, the UTMP mode approached the minimal flux at CF 7 or 10 depending upon the combination of ΔP_TM and CFV used. Cake resistance (R_cm) was modified to include the effect of an increase in retentate viscosity with concentration. R_cm increased for the non-UTMP mode and decreased for the UTMP mode with a decrease in the ratio of permeation flux/wall shear stress (J_p/τ_w) (which occurred as the retentate gets concentrated). This indicated that the cake formed during the non-UTMP mode of operation was more compact and durable (harder to erode) than in the UTMP mode. A central composite rotatable design estimated the optimal operating region at a CFV of 7.1 m s⁻¹ and ΔP_TM of 241±10 kPa to achieve maximum flux and a high concentration.     

Construction of a universal model for non-invasive identification of penicillins for injection using near-infrared diffuse reflectance spectroscopy

A universal NIR model for identification of 24 types of penicillins for injection has been developed. A total of 194 batches of 24 products from 87 manufacturers in China were used in the study. The classification model is a principal component analysis (PCA) based model consisting of a primary identification library with four sub-libraries. The spectral frequency regions used were 6000–6400 cm⁻¹ and 8400–8900 cm⁻¹ in the main library, 6000–6800 cm⁻¹ in sub-library 1, 4100–12,000 cm⁻¹ in sub-libraries 2 and 3, and 6200–6400 cm⁻¹ and 4700–5000 cm⁻¹ in sub-library 4. The data preprocessing method is the first derivative with nine-point smoothing followed by vector normalization. The distances between spectra were calculated using factors 2–5 for the primary identification library, factors 4–7 for sub-library 1, and factor 2 for sub-libraries 2–4. The specificity of the model was validated, and it had a correct identification rate of approximately 99%. This study has not only confirmed, but also improved the strategy described in our early report (Chong et al. (2009) [11]) to build such a library for the identification of different medicines by NIR.     

Dispersed phase back transport during ultrafiltration of cutting oil emulsions with a spinning membrane disc geometry

A commercial centrifugal rotary membrane module was used for the ultrafiltration of oil–water emulsions (droplet radius 50–3000 nm). This configuration can achieve high shear rates (>10⁵ s⁻¹) which are decoupled from the bulk recirculation rate. Fluxes were in the pressure controlled regime above 600 rpm with transmembrane pressures up to 345 kPa. The pressure dependent flux behaviour suggests that concentration polarization or gel formation was minimal. The dominant back transport mechanism was determined by comparing various back transport mechanisms to the permeation drag force. Back transport mechanisms included Brownian diffusion, shear induced diffusion, lateral migration, viscous drag, centrifugal and DLVO forces. The effect of the membrane surface porosity and Sherwood's correction for Stokes's law on the permeation drag were also studied. Viscous drag was the dominant force on droplet sizes between 50–1000 nm and was the only mechanism which could overcome the permeation drag force. Lateral migration was significant for droplets between 1000–3000 nm which were present in small quantities.     

Characteristics of inclusions in topaz from Serrinha pegmatite (Medina granite,Minas Gerais State,SE Brazil) studied by Raman spectroscopy

Eastern Brazilian Pegmatite Province includes many topaz-bearing pegmatitic bodies. Residual melts from the Fe–K-rich alkaline Medina granite (ca. 500 Ma) formed the Serrinha pegmatite—a system of branched thin pegmatite veins hosted by pink facies of the parent granite. The colourless topaz from Serrinha pegmatite contains both mineral and fluid inclusions. Microcline (513, 476, 456 cm⁻¹), albite (507, 479, 457 cm⁻¹), topaz (926, 858, 267, 239 cm⁻¹), quartz (463 cm⁻¹), rutile (610, 444 cm⁻¹), wolframite (884 cm⁻¹) and uranophane (968, 788 cm⁻¹) represent solid inclusions formed by fluid-induced processes from the pneumatolytic (∼600–400 °C) to hydrothermal (<400 °C) stages of pegmatite crystallization. Fluid inclusions are mainly liquid or liquid-gas, which contain CO₂ (marker bands ∼1388 cm⁻¹ and ∼1285 cm⁻¹) and traces of methane (2917 cm⁻¹). They are mainly of primary and pseudo-secondary origin, indicating tectonic quiescence during and after topaz crystallization (in agreement with the post-collisional nature of the parent granite). Topaz crystallized in high temperature conditions of the pneumatolytic stage at a depth around 8.5–10.0 km.     

Determination of inorganic and total mercury by vapor generation atomic absorption spectrometry using different temperatures of the measurement cell

A simple and inexpensive laboratory-built flow injection vapor generation system coupled to atomic absorption spectrometry (FI-VG AAS) for inorganic and total mercury determination has been developed. It is based on the vapor generation of total mercury and a selective detection of Hg^2 + or total mercury by varying the temperature of the measurement cell. Only the inorganic mercury is measured when the quartz cell is at room temperature, and when the cell is heated to 650 °C or higher the total Hg concentration is measured. The organic Hg concentration in the sample is calculated from the difference between the total Hg and Hg^2 + concentrations. Parameters such as the type of acid (HCl or HNO₃) and its concentration, reductant (NaBH₄) concentration, carrier solution (HCl) flow rate, carrier gas flow rate, sample volume and quartz cell temperature, which influence FI-VG AAS system performance, were systematically investigated. The optimized conditions for Hg^2 + and total Hg determinations were: 1.0 mol l^− 1 HCl as carrier solution, carrier flow rate of 3.5 ml min^− 1, 0.1% (m/v) NaBH₄, reductant flow rate of 1.0 ml min^− 1 and carrier gas flow rate of 200 ml min^− 1. The relative standard deviation (RSD) is lower than 5.0% for a 1.0 μg l^− 1 Hg solution and the limit of quantification (LOQ, 10 s) is 55 ng g^− 1. Certified samples of dogfish muscle (DORM-1 and DORM-2) and non-certified fish samples were analyzed, using a 6.0 mol l^− 1 HCl solution for analyte extraction. The Hg^2 + and CH₃Hg⁺ concentrations found were in agreement with certified ones.     

Hydrogen isotope separation with an alkaline membrane fuel cell

The separation of deuterium from a hydrogen–deuterium mixture was carried out using an alkaline membrane fuel cell (AMFC) with a Pt catalyst. This novel use of an AMFC to separate deuterium from a mixture of H₂ and D₂ was demonstrated by the production of deuterium-enriched water during power generation by the AMFC. The deuterium separation factor increased with output current (i) to a maximum value of 1.64 attained at i = 30 mA cm^− 2.     

Immobilized glycerol-based liquid membranes in hollow fibers for selective CO2 separation from CO2–N2 mixtures

Glycerol-based liquid membranes immobilized in the pores of hydrophilic microporous hollow fibers have been studied for selective separation of CO₂ from a mixed gas (CO₂, N₂) feed having low concentrations of CO₂ characteristic of gases encountered in space walk and space cabin atmosphere. The immobilized liquid membranes (ILMs) investigated consist of sodium carbonate–glycerol or glycine-Na–glycerol solution. Based on the performances of such liquid membranes in flat hydrophilic porous substrates [Chen et al., Ind. Eng. Chem. Res. 38 (1999) 3489; Chen et al., Ind. Eng. Chem. Res. 39 (2000) 2447], hollow fiber-based ILMs were studied at selected CO₂ partial pressure differentials (Δp_CO2 range 0.36–0.50 cmHg), relative humidities (RH range 45–100%), as well as carrier concentrations. The sodium carbonate concentration was primarily 1.0 mol/dm³; the glycine-Na concentration was 3.0 mol/dm³. The sweep gas was always dry helium and it flowed on the shell side. Very high CO₂/N₂ selectivities were observed with porous polysulfone microfiltration membranes as substrate. As in the case of flat film-based ILMs (see references above), feed side RH is an important factor determining the ILM performances. Generally, lower permeances and greater CO₂/N₂ selectivity values were observed at lower feed stream RHs. When the feed side average RH=60%, p_CO2,f=0.005 atm and glycine-Na concentration was 3.0 M, the CO₂/N₂ separation factor observed was over 5000. Prolonged runs lasting for 300 h showed that the hollow fiber-based ILM permeation performances were stable.     

Studies on polypyrrole modified nafion membrane for vanadium redox flow battery

In order to prevent the vanadium crossover and preferential water transfer in all-vanadium redox flow battery (VRFB), three methods – electrolyte soaking, oxidation polymerisation and Electrodeposition, were used to modify Nafion 117 membranes using pyrrole. The surface of the modified membranes was uniform and even, and the membranes were characterised in terms of morphology, membrane area resistance, vanadium permeability and water transfer property. The properties of all the modified membranes were improved greatly. The membranes modified by Electrodeposition showed a best combination of the membrane resistance, vanadium permeability and water transfer property, the experimental results showed that the V(IV) ion permeability of polypyrrole modified Nafion membranes by Electrodeposition at the conditions of 0.025 mA cm⁻² and 0 ^°C for 60 min reduced more than 5 times from 2.87 × 10⁻⁶ cm² min⁻¹ to 5.0 × 10⁻⁷cm² min⁻¹, and the water transfer property decreased more than 3 times from 0.72 ml/72 h cm² to 0.22 ml/72 h cm². All above properties made the modified Nafion membranes more applicative in the VRFB system. This paper also reported other methods for Nafion membrane modification and the influences of the deposition conditions on the properties of the membrane selectivity and water transfer.