Reduced graphene oxide/metal oxide nanoparticles composite membranes for highly efficient molecular separation

Graphene oxide(GO) membranes play an important role in various nanofiltration applications including desalination, water purification, gas separation, and pervaporation. However, it is still very challenging to achieve both high separation efficiency and good water permeance at the same time. Here, we synthesized two kinds of GO-based composite membranes i.e. reduced GO(rGO)@MoO_2 and rGO@WO_3 by in-situ growth of metal nanoparticles on the surface of GO sheets. They show a high separation efficiency of ～100% for various organic dyes such as rhodamine B, methylene blue and evans blue, along with a water permeance over 125 Lm~(-2) h~(-1) bar~(-1). The high water permeance and rejection efficiency open up the possibility for the real applications of our GO composite membranes in water purification and wastewater treatment. Furthermore, this composite strategy can be readily extended to the fabrication of other ultrathin molecular sieving membranes for a wide range of molecular separation applications.     

永磁式异步磁力耦合器漏磁系数计算

针对磁路法、有限元法及磁力线闭合回路法计算永磁式异步磁力耦合器(Permanent Magnetic AsynchronousCoupling,PMAC)漏磁系数的各种缺陷,将积分法与区域划分法相结合,对PMAC进行漏磁系数分析与计算。按PMAC永磁体的漏磁通路径对其进行几何图形划分与归纳,并按几何图形所形成的积分路径建立漏磁导数理模型,保证了漏磁系数计算的完整性及通用性。所提出的方法适于计算机编程,可对PMAC的励磁系统进行结构参数分析与优化。     

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.     

Hydrogen permeation measurements of Pd and Pd-Cu membranes using dynamic pressure difference method

Hydrogen permeation across membranes is measured using a dynamic pressure difference method. In the method, a transient system for continuously monitoring hydrogen flux of a membrane is conducted. Three different membranes, consisting of two pure palladium (Pd) membranes with different thicknesses and one palladium-copper (Pd-Cu) membrane supported by porous stainless steel (PSS) tubes, are taken into account. Three different operating temperatures of 320, 350 and 380 °C as well as two different initial pressure differences of 5 and 10 atm are considered to evaluate the effects of the operating parameters upon the hydrogen permeation. The results suggest that a threshold of pressure difference is always exhibited at the end of the permeation process, regardless of which membrane is tested. The hydrogen permeation rate can be predicted well for the pressure exponent in the range of 0.1-1.0; however, the optimal pressure exponent is located between 0.5 and 0.8. The theoretical analysis indicates that the characteristic time of hydrogen permeation in the present system ranges from 245 to 460 s and the entire permeation period is longer than the characteristic time by an order of magnitude. In regard to the effect of membrane temperature on the permeation, the activation energies of the three membranes range from 11 to 18 kJ mol⁻¹.     

Numerical characterization on concentration polarization of hydrogen permeation in a Pd-based membrane tube

Sieverts’ law has been extensively employed to evaluate hydrogen permeation rate across a hydrogen-permeable membrane based on the concept of continuous stirred tank reactor (CSTR). However, when the hydrogen permeation rate is high to a certain extent, concentration polarization will appear in a membrane tube which results in the deviation of hydrogen permeation rate from Sieverts’ law. Under such a situation, the nature of mass transfer in a membrane tube is characterized by plug flow reactor (PFR) rather than CSTR. To figure out the feasibility of Sieverts’ law, a two-dimensional numerical method is developed to simulate the phenomena of concentration polarization for hydrogen permeation in a Pd-based membrane tube. Four important parameters affecting hydrogen permeation are taken into account; they include the pressure difference, H₂ molar fraction in the influence, Reynolds number and membrane permeance. The predictions indicate that increasing pressure difference or membrane permeance facilitates H₂ permeation rate; concentration polarization is thus triggered. Alternatively, when Reynolds number or H₂ molar fraction decreases along with a higher permeance, the deviation of PFR from CSTR grows, even though H₂ permeation rate declines. From the obtained results, it is concluded that the H₂ permeation rate can be predicted by Sieverts’ law if the H₂ permeation ratio is no larger than 30%.     

Preparation of supported palladium membrane and separation of hydrogen

Palladium acetate was sublimed at a reduced pressure at 400°C., carried into the macropores of the porous wall of an α-alumina support tube and was decomposed there. A thin palladium membrane which was thus formed showed a hydrogen permeance of 10⁶ mol·m²·s¹.-Pa¹ and a hydrogen/nitrogen permselectivity higher than 1000. The membrane was stable against hydrogen embrittlement even when the permeation temperature was varied between 100 and 300°C., and it was stable to sulfur or chlorine. To test the ability of this system for the separation of hydrogen and deuterium, a palladium disk was used instead of the prepared membrane since a definite membrane thickness was necessary for calculation. When H₂ and D₂ permeated through the membrane independently, the H/D permselectivity was approximately 7 at 150–200°C under a feed side pressure of 0.4 MPa and a permeate side pressure of 0.1 MPa. When a mixture of H₂ and D₂ was fed, the H/D permselectivity was reduced to 1.2–1.6.     

Facilitated transport separation of propylene–propane: Experimental and modeling study

Supported liquid membrane, as one type of facilitated transport membranes, was used for the separation of propylene–propane mixtures. The effect of trans-membrane pressure and carrier concentration on membrane separation performance were evaluated in terms of mixed-gas selectivity, propylene and propane permeances and propylene and propane permeation fluxes. A general dimensionless model for the transport of components across the membrane was proposed and solved numerically by orthogonal collocation method. Experimental results showed that for a 70:30 (vol.%) propylene–propane mixture, at pressure 120 kPa and carrier concentration 20 wt.%, a propylene permeation flux of 1.46 × 10⁻⁴ mol/m² s was obtained. Mathematical results are in well agreement with experimental results. The average deviation between experimental and modeling results was found to be 5.3% for propylene permeation flux and 0.03% for propane permeation flux.     

Oxidation-bonded SiC membrane for microfiltration

Porous SiC is a proven viable material for microfiltration membranes, but its application has been limited by high fabrication cost. In this study, the oxidation bonding technique was used for the first time to fabricate SiC microfiltration membrane. The study was divided into two parts: optimization of the slurry used to dip coat the SiC particles over a porous SiC ceramic support and controlling the oxidation behaviour of SiC with respect to temperature. The oxidation behaviour during different thermal treatments was related to pore morphology and ultimately the membrane permeance. By coating the clay-bonded SiC support with oxidation-bonded SiC and sintering the coating at 1100 °C for 1 h, we prepared a defect-free microfiltration membrane with pure-water membrane permeance of >210 L m^?2 h^?1 bar^?1, an average pore size of 93 nm, and a narrow pore-size distribution.     

Polymeric amine membrane materials for carbon dioxide (CO2)/methane (CH4) separation

Carbon dioxide separation from methane using membrane technology is getting attraction, and polymeric membranes are the most prominent polymer membrane materials. However, the existing polymeric membranes performance is inadequate due to trade-off limitation open new windows to explore. Therefore, in this study, amine polymeric membrane (APM) has been fabricated by the addition of different concentration (5 wt.% and 15 wt.%) of diethanolamine (DEA). The developed amine polymeric membranes have been characterized in term of morphology and thermal analysis using field emission scanning electron microscope and thermogravimetric analyzer, respectively. The permeance and selectivity have been determined by using pure carbon dioxide (CO₂) and methane (CH₄). Also, the effect of amine concentration on permeance and selectivity has been studied. The results confirmed the symmetric and homogenous structure and thermal stability of membranes up to 490 °C. The maximum percent increase by the 15 wt.% addition of diethanolamine is 102.08 % at 10 bar pressure.     

Preparation and characterization of palladium ceramic alumina membrane for hydrogen permeation

In this study, a tubular palladium membrane has been prepared by an electroless plating method using palladium II chloride as a precursor with the intent of not having a completely dense film since its application does not require high hydrogen selectivity. The support used was a 15 nm pore sized tubular ceramic alumina material that comprised of 77% alumina and 33% titania. It has dimensions of 7 mm inner and 10 mm outer diameters respectively. The catalyst was deposited on the outside tube surface using the electroless deposition process. The membrane was morphologically characterized using scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDXA) and liquid nitrogen adsorption/desorption analysis (BET) to study the shape and nature of the palladium plating on the membrane. The catalytic membrane was then inserted into a tubular stainless-steel holder which was wrapped in heating tapes so as to enable the heating of the membrane in the reactor. The gases used for permeation tests comprised H₂, N₂, O₂ and He. Permeation tests were out at 573 K and at pressure range between 0.05 and 1 barg. The results showed that hydrogen displayed a higher permeation when compared to other gases that permeated through the membrane and its diffusion is also thought to include solution diffusion through the dense portions of the palladium in addition to Knudsen, convective and molecular sieving mechanisms occurring through cracks and voids along the grain boundaries. While high hydrogen selectivity is critically important in connection with hydrogen purification for fuel cells and in catalytic membrane reactors used to increase the yield of thermodynamically limited reactions such as methane steam reforming and water–gas shift reactions whereby the effective and selective removal of the H₂ produced from the reaction zone shifts the equilibrium, it is not so important in situations in which the membrane has catalytic activity such that it is possible to carryout the reaction in situations where the premixed reactants are forced-through the membrane on which the catalysts is attached. This type of catalytically active membranes is novel and has not been tested in gas-solid-liquid reactions and liquid-solid reactions before. With such a reactor configuration, it is possible to achieve good feed stream distribution and an optimal usage of the catalytic material. The preparation and characterization of such membrane catalysts has gained increased interest in the process industries because it can be adapted to carryout the chemical reactions if one of the reactants is present in low concentration and an optimal reactant distribution results in a better utilization of the active catalytic material. However, there are concerns in terms of the high cost of palladium membranes and research on how to fabricate membranes with a very low content of the palladium catalyst is still ongoing. Work is currently underway to deploy the Pd/Al₂O₃ membrane catalysts for the deoxygenating of water for downhole injection for pressure maintenance and in process applications.