A Pd/α-Al2O3 composite membrane was prepared on a porous α-Al2O3 disk via the thermal decomposition of bis(hexafluoroacetylacetonato)Pd(II), Pd(hfac)2. Pd(hfac)2 was dissolved in supercritical CO2 at 303 K, supplied to the substrate, and thermally decomposed at 403 and 443 K. The decomposition of Pd(hfac)2 at 443 K resulted in a sufficient pore filling of substrate with Pd as well as the formation of a thin Pd top layer. The hydrogen flux through this membrane was about 1.7 times than that of a electro-less plating Pd membrane with about 20 μm thick. Hydrogen permeation was governed by the solution-diffusion mechanism which gave a high separation selectivity.

Porous solids were obtained from self-assembled deposits of silica nanoparticles used as templates to form 3-D porous membranes. The effect of the solvent chemistry on the morphology of the deposits was investigated. The parameters of interest are surface tension and ionic strength of the solvent, due to electrostatic and capillary interactions. Deposits of nanoparticles of different sizes were obtained for a variety of conditions. The deposits were imaged using SEM and showed distinctive structures for each of the solvent chemistries. The phenomenon is consistent with the DVLO theory and calculations of capillary interaction energy.

The mesoscopic framework describing single-component diffusion through microporous materials is extended here to characterize binary diffusion in the absence of intermolecular forces. Two diffusion mechanisms, single-file diffusion characteristic of confined pore structures and species-species exchange consistent with diffusion modes in less-confined pore topologies, are incorporated at the Master Equation level. Derived fundamentally via rigorous coarse-graining of the underlying Master Equation, the binary mesoscopic relation is validated via direct comparison to gradient continuous time Monte Carlo (G-CTMC) simulations. We further show the capability of this fundamentally derived model to capture the macroscopic diffusion phenomenon of ‘overshoot’ or ‘roll-up’ in the transient uptake and flux. Exploration of the species-species exchange mechanism reveals its strong effect on the transient ‘overshoot’ behavior through relaxation of the constrained single-file diffusion.

Novel preparation process of V-Ni alloys for hydrogen purification membrane using chemical transport was investigated. Vanadium, NH4Cl, and PtCl2 as evaporating source were put in one side of a fused-silica tube, and Ni substrate was put in the other side. The fused-silica tube was sealed in vacuo, and set in a furnace with temperature gradients. Evaporating source temperature was 1173–1273 K. Substrate temperature was 3–100 K higher than the evaporating source temperature. This process consists of formation of HCl from NH4Cl and PtCl2, chemical transport of vanadium under temperature gradient via chlorides in the presence of HCl, and diffusion of the transported V into the Ni substrate. EDX line profile of cross section of the substrates after the process demonstrated that V diffused into the Ni substrates. Distribution of V concentration in the substrates was dependent on the substrate temperature and the temperature difference between the substrate and the evaporating source. Heating condition was optimized to obtain homogeneous V-Ni alloy. When the substrate temperature and evaporating-source temperature were 1228 K and 1223 K, respectively, V diffused homogeneously into the Ni substrate with thickness of 20 μm, and V concentration attained in the substrate was higher than 70at%.

A numerical model is presented for analyzing the propagation of ionic concentrations and electrical potential in space and time in the solution ion-exchanging membrane system. Diffusion and migration according to the Nernst-Planck (NP) flux equation govern the transport of ions, and the electrical interaction of the species is described by the Poisson (P) equation. These two equations and the continuity equation form a system of partial non-linear differential equations that is solved numerically. As a result of the physicochemical properties of the system, both the contact/boundary potential and the diffusion potential contribute to the overall membrane potential. It is shown that interpreting the electrical potential of ion-exchanging membranes exclusively in terms of boundary potential at steady-state is incorrect. The Nernst-Planck-Poisson (NPP) model is general and applies to ions of any charge in space and time domains.

This work developed a metal-reinforced ceramic membrane processing approach [by using perovskite La0.2Sr0.8 CoO3-x (LSCO-80) as the model membrane] with the aim of overcoming the membrane-cracking problem. A thin layer of Ag/Pd alloy was incorporated into the LSCO-80 membrane made by dip coating and sintering. It is not viable to obtain a Pd/Ag alloy film using the co-plating method because Ag+ ion strongly inhibits chemical reduction of Pd2+ ion, and the alkaline plating bath causes severe etching of LSCO-80. This obstacle was circumvented through a layer-by-layer deposition procedure, in which Ag and Pd layers were deposited subsequently onto LSCO membrane. The Ag and Pd layers undergo alloying when the laminar structure was subjected to calcinations at 1000°C. It was found that the Pd/Ag alloy drifts beneath into pores in the LSCO layer. The resultant metal-ceramic composite membrane shows excellent structural integrity and free of micro-cracks.

Virus filtration is increasingly used in the biopharmaceutical industry, but capacity and fouling remain problematic. Experimental studies were conducted in dead-end, stirred filtration cells with Viresolve 180 polyvinylidene fluoride membranes using the protein bovine serum albumin. Data were obtained for membranes in two different flow orientations, with the selective “skin” layer oriented on either the upstream surface or downstream relative to the fluid flow. Compaction of the substructure occurs when the skin layer is downstream, leading to a significant increase in membrane resistance. Concentration polarization in the bulk solution or membrane substructure caused a substantial increase in the protein sieving coefficient, with this effect being greatest when the flow entered through the substructure. Fouling is primarily due to the deposition of large protein aggregates. The effect of this fouling on the flux was reduced when the skin layer was oriented downstream since the substructure acted as a prefilter. These results demonstrate that the membrane morphology and orientation play a critical role in determining the overall performance of virus filtration membranes.

For methanol oxidative dehydrogenation to formaldehyde, the performance of the packed-bed membrane reactor (PBMR) is compared with that of the conventional fixed-bed reactor (FBR) over a wide range of operating conditions. The reaction was studied in three reactor configurations: the conventional FBR and the packed-bed membrane reactor, with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined and incorporated in a PBMR model. Both experimental data and model considerations demonstrate that the PBMR enhances reactant conversion and selectivity.

Small oscillations in CO production were observed experimentally. Their amplitude was taken as a basis for comparison of packed-bed operation instability. The likely source of oscillatory behavior is the non-uniformity in reaction conditions along the reactor. It was found that membrane distributed feed, by providing a more uniform reactor operation, is an effective remedy from these instabilities.

It is found, both by simulations and experimental observations, that relative reactor performance depends strongly on the operating conditions. Using formaldehyde yield as the basis for optimization, optimal reactor performances are determined to be in the order: PBMR-O > FBR > PBMR-M. Further PBMR productivity enhancement is possible by optimizing the membrane feed distribution pattern.

The present work is aimed at developing uniform nanoporous carbon membranes on porous stainless steel supports. Thin layers of polyfurfuryl alcohol are applied on the stainless steel supports using spin coating method. Nanoporous carbon is obtained by pyrolyzing polyfurfuryl alcohol films under inert atmosphere. Uniform nanoporous carbon membranes were obtained by repeated spin coating and pyrolysis of polyfurfuryl alcohol on the stainless steel supports. The morphology of the membranes was examined using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). It was shown that there is direct correlation between the morphology and the selectivity of the membranes. SEM and AFM show the presence of globular domains during the formation of carbon membranes. The selectivity increased with the decrease in the size of the globules. It was also shown that the annealing of the membrane affected both the morphology and the selectivity of the membrane.

Recent data from the literature dealing with the influence on oxygen transport of porous nanophase ion conducting ceramics are reviewed, and then transposed to the design of mesoporous nanophase ceria-based membranes. Mesoporous CeO2/Al2O3 and Gd doped CeO2 membranes containing Pd and Pt nanoparticles were prepared using the sol-gel process. Permeation of N2 and O2 single gases was studied in a temperature range 20–500°C. Permeation measurements indicate an activated oxygen transport in agreement with the literature data. A synergetic effect of the noble metal nanoparticles on oxygen transport has been evidenced, in relation with the triple phase boundary concept. However, these membranes do not perform totally the preferential oxygen transport predicted by the theory. Several directions are proposed for membrane improvement, in particular concerning pore and grain optimal sizes.

Thin films derived from nanocrystal cores and functionalized linkers provide large surface-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial ion fluxes associated with redox reactivity and structural properties of such films using cyclic voltammetry, electrochemical quartz-crystal nanobalance, surface infrared reflection spectroscopy, and X-ray photoelectron spectroscopy. Films from gold nanocrystals of 2 nm core sizes and 11-mercaptoundecanoic acid were studied as a model system. First, the film coated on electrode surface displays redox-like voltammetric waves characteristic of the deprotonation-reprotonation of the carboxylic acid groups in the nanostructured network. This process is accompanied by mass changes. Secondly, the film exhibits capability for the complexation of copper ions via the nanostructured carboxylate framework. This process is also accompanied by interfacial fluxes of electrolyte cations across the electrode | film | electrolyte interface which compensate electrostatically the fixed negative charges in the reduction process.

Mixed ionic electronic conducting perovskite type oxides are promising materials for potential use in various applications such as in fuel cells and membranes for air separation. An important issue in the development of the perovskites is the structural, chemical and mechanical stability of these materials at high temperatures and reducing environments (oxygen partial pressure from 0.21 to 10−17 atm) encountered in membrane reactors. SrFeO3 oxides doped with La on the A-site and Cr on the B-site showed high strength at room temperature in air. The strength degrades rapidly with an increase in temperature in air as compared to in N2 and CO2/CO environment. Fracture in the material is characterized by non-equilibrium segregation of elements within the grains. The observations provide valuable structure-property correlation as applicable to the long-term behavior of the material in advanced catalytic membrane reactors.