W. S. Winston Ho

Facilitated transport of olefins in Ag+-containing polymer membranes

Abstract Synthesis of new poly(vinyl alcohol)-containing silver nitrate membranes is described. The membrane showed high olefin flux and olefin/paraffin selectivity. For this membrane, the effects of water saturation, silver nitrate content, total retenate pressure and permeate partial pressure on butene fluxes were investigated. For the facilitated transport of butenes and propylene in the membrane, we determined the mass transfer resistances due to complexation and decomplexation and thus obtained the “true” permeability which is independent of membrane thickness. Based on the mass transfer resistances and permeability, a transport model can be used to relate flux and selectivity to separation process conditions. Also investigated was the stability of the membrane.

Extraction of Uranium from Wet Process Phosphoric Acid by Liquid Membranes

Abstract The liquid membrane process can effectively separate and concentrate uranium from wet process phosphoric acid and is economically superior to solvent extraction systems. The paper describes the process, compares it to other extraction schemes, and shows how it can be used for uranium recovery. A mathematical model useful for design purposes is presented and the effect of important variables is discussed.

Extraction of phenolic compounds and organic acids by liquid membranes

Abstract Liquid membrane emulsions were used to extract phenolic compounds and organic acids from their aqueous solutions. The emulsions contained caustic as the reactive agent. When the phenolic compounds and organic acids permeated through the liquid membranes into the emulsion droplets, they reacted with caustic and became ionized. The ionized species could not permeate through the liquid membranes and therefore were held in the emulsion droplets. The conclusions of this recent investigation are: (1) More than 99% of phenol and cresols can be extracted in less than 1 minute. (2) Acetic and propionic acids can also be extracted but at much slower rates. However, if the amount of caustic is not sufficient to react with all the permeating compounds, the acids will be extracted preferentially to the phenols. (3) The acids can only be extracted at low pH (acidic) whereas the phenolic compounds can be extracted at pH of 7. (4) The extraction rates for phenol and acetic acid are the same in individual-compound and binary-mixture permeations. (5) The extraction can be described by a mass transfer model.

Sterically-hindered amines for acid-gas absorption

Abstract This paper reviews sterlcally-hindered amines for removal of add gases such as CO2 and H2S from gaseous streams. Steric hindrance of amines reduces carbamate stability. Moderately hindered amines are characterized by high rates of CO2 absorption and high capacities for CO2. The moderately hindered amine in use with organic solvent has considerably higher capacity than the conventional amine-solvent system for simultaneous removal of CO2and H2S from synthesis gas and natural gas. A severely-hindered-amine absorbent, characterized by a very low rate of CO2absorption, has much higher capacity and selectivity than the current industry standard, methyldiethanolamine, for selective removal of H2S from CO2-containing streams. Use of hindered amines represents new advances in gas treating. Hindered amines save energy and capital in gas treating significantly. In addition, hindered amines used commercially have much better stability than conventional amines. As of today, fourteen commercial plants use hin...

Preparation of Uniform-Sized Multiple Emulsions and Micro/Nano Particulates for Drug Delivery by Membrane Emulsification

Much attention has in recent years been paid to fine applications of drug delivery systems, such as multiple emulsions, micro/nano solid lipid and polymer particles (spheres or capsules). Precise control of particle size and size distribution is especially important in such fine applications. Membrane emulsification can be used to prepare uniform-sized multiple emulsions and micro/nano particulates for drug delivery. It is a promising technique because of the better control of size and size distribution, the mildness of the process, the low energy consumption, easy operation and simple equipment, and amendable for large scale production. This review describes the state of the art of membrane emulsification in the preparation of monodisperse multiple emulsions and micro/nano particulates for drug delivery in recent years. The principles, influence of process parameters, advantages and disadvantages, and applications in preparing different types of drug delivery systems are reviewed. It can be concluded that the membrane emulsification technique in preparing emulsion/particulate products for drug delivery will further expand in the near future in conjunction with more basic investigations on this technique.

Removal and Recovery of Metals and Other Materials by Supported Liquid Membranes with Strip Dispersion

Abstract: This paper reviews recent advances in supported liquid membranes (SLMs) with strip dispersion for removal and recovery of metals including chromium, copper, zinc, and strontium; it also discusses potential applications of SLMs for removal and recovery of other materials, including cobalt and penicillin G. The technology for chromium that we developed, not only removes the Cr(VI) from about 100–1,000 ppm to less than 0.05 ppm in the treated effluent allowable for discharge or recycle, but also recovers the chromium product at a high concentration of about 20% Cr(VI) (62.3% Na2CrO4) suitable for resale or reuse. In other words, we have achieved the goals of zero discharge and no sludge. The stability of the SLM is ensured by a modified SLM with strip dispersion, where the aqueous strip solution is dispersed in the organic membrane solution in a mixer. The strip dispersion formed is circulated from the mixer to the membrane module to provide a constant supply of the organic solution to the membrane pores. The copper SLM system that we have identified, not only removed the copper from 150 ppm in the inlet feed to less than 0.15 ppm in the treated feed, but also recovered the copper at a high concentration of greater than 10,000 ppm in the strip solution. For the zinc SLM system identified, zinc at an inlet feed concentration of 550 ppm was removed to less than 0.3 ppm in the treated feed, whereas a high zinc concentration of more than 17,000 ppm was recovered in the strip solution. For strontium removal, we synthesized a family of new extractants, alkyl phenylphosphonic acids. The SLM removed radioactive 90Sr to the target of 8 pCi/L or lower from feed solutions of 300–1,000 pCi/L. The SLM removed cobalt from about 525 ppm to 0.7 ppm in the treated feed solution, concentrating it to at least 30,000 ppm in the aqueous strip solution. Concerning penicillin G recovery, the SLM removed penicillin G from a feed of 8,840 ppm and concentrated it to a high concentration of 41,011 ppm in the aqueous strip solution with a high recovery of about 93%.

A biodegradable, immunoprotective, dual nanoporous capsule for cell-based therapies

To demonstrate the transplantation of drug-secreting cells with immunoprotection, a biodegradable delivery device combining two nanoporous capsules is developed using secretory alkaline phosphatase gene (SEAP) transfected mouse embryonic stem (mES) cells as a model system. The outer capsule is a poly (ethylene glycol) (PEG)-coated poly (epsilon-caprolactone) (PCL) chamber covered with a PEG grafted PCL nanoporous membrane made by phase inversion technique. SEAP gene transfected mES cells encapsulated in alginate-poly-L-lysine (AP) microcapsules are placed in the PCL capsule. Both nanoporous capsules showed good immunoprotection in the IgG solution. In microcapsules, mES cells could form a spheroid embryonic body (EB) and grow close to the microcapsule size. The secreted SEAP from encapsulated mES cells increased gradually to a maximum value before reaching a steady level, following the cell growth pattern in the microcapsule. Without microcapsules, mES cells only formed a monolayer in the large PCL capsule. The secreted SEAP release was very low. The integrated device showed a similar cell growth pattern to that in microcapsules alone, while the SEAP release rate could be regulated by the pore size of the large capsule. This integrated device can achieve multi-functionalities for cell-based therapy, i.e. a 3-D microenvironment provided by microcapsules for cell growth, superior immunoprotection and controllable release performance provided by the two nanoporous membranes, and good fibrosis prevention by PEG surface modification of the large capsule.

Prediction of flux and selectivity in pervaporation through a membrane

Flux and selectivity in pervaporation through a membrane can be predicted via the solution-diffusion mechanism by the use of solubility and diffusivity models. The solubility model developed takes into account the free energy contributions in the mixture system of multicomponent penetrants and a polymer from combinatorial-entropy, free-volume, interactional-enthalpy, and elastic factors. The diffusivity model developed is the hybrid model that combines the key features of the free-volume and molecular models. In the hybrid model, penetrant molecular thickness and polymer molecular parameters are used to determine the term equivalent to the preexponential factor of the free-volume model, and the free-volume expression is used to relate penetrant diffusivity to penetrant size and the free volume of the mixture system including concentration contributions from the multicomponent penetrants. Both the solubility and diffusivity models have been verified with the sorption of single-component aromatic vapors in a semicrystalline polyethylene film. Based on the single-component solubility and diffusivity model parameters determined from the sorption, the prediction of flux and selectivity is in line with experimental data obtained from the perva-poration of a mixture of toluene, p-xylene, and mesitylene through the polyethylene film at various temperatures and different permeate pressures. The effects of temperature on flux and selectivity are investigated via both the model prediction and experiments. Also predicted are the effects of permeate vapor pressure on flux and selectivity, and the concentration and diffusivity profiles across the membrane.

Rapid crystallization of faujasitic zeolites: mechanism and application to zeolite membrane growth on polymer supports.

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications.

Use of a nanoporous biodegradable miniature device to regulate cytokine release for cancer treatment

The clinical management of locally recurrent or unresectable malignant melanoma continues to pose a significant challenge. These lesions are typically painful and currently available treatments, such as repeated intratumoral injections of interferon-alpha (IFN-α), are costly and inconvenient. Nanotechnology offers promise as a novel means of drug delivery. A capsule-like nanoporous miniature device (NMD) based on a biodegradable polymer, poly(polycaprolactone) (PCL) was developed for controlling the local delivery of immunological agents to the tumor microenvironment. The device consists of a nanoporous release gate, a fabricated drug reservoir loaded with IFN-α and a protective layer. To improve the biocompatibility of the device, a hydrophilic poly(ethylene glycol) monoacrylate was applied to the outside wall of the device via covalent bonding techniques. Microscopic visualization of the nanoporous gate from in vitro experiments exhibited good pore stability over a two-month period. In vitro experiments demonstrated a constant release rate of IFN-α from the NMD and showed that the release rate could be regulated by the gate area. The released IFN-α was biologically functional. Cytokine-containing supernatants from release experiments phosphorylated signal transducer and activator of transcription (STAT1) in peripheral blood mononuclear cells. Subcutaneous implantation of the NMDs was well tolerated and associated with an anti-tumor effect in a human xenograft model of melanoma. There was no evidence of a significant inflammatory response to the NMD or encapsulation of the NMD by fibrosis. These experiments show that the NMD can be fabricated and employed in vivo as a versatile drug delivery platform.