Permeation Of Other Gases Research Articles

Water vapor permeation and its influence on gases through a zeolite-4A membrane

It is known that water adsorption in zeolites can severely affect the adsorption and, thus, the permeation of other gases. This work proposes an investigation about the contributions of both surface and gas translation diffusion on permeation of some light gases (H2, CH4 and CO) in the presence of water for the 4A zeolite within a wide range of temperature (300–700 K). As main results, the contributions of the two considered diffusional mechanisms and their relative weights are determined, showing in a quantitative way that the presence of water vapor significantly reduces the adsorption of the other species. The extent to what this effect influences the overall permeation process is reported considering the variation of temperature, allowing a good prediction of the permeance decrease of H2, CH4 and CO when mixed with water vapor. The water adsorption drives the permeation of the water itself, and, in the meantime, hinders the adsorption and, hence, the permeation of the other gases.

Humidified Gas Stream Separations at High Temperatures Using Matrimid 5218

Most industrially relevant high temperature gas separations (≥150°C) of either carbon dioxide (flue gas) or hydrogen (syn-gas) must be performed in the presence of water vapor. At ambient temperatures, water vapor can permeate easily through most polymeric membranes and can influence the permeation of other gases through interaction with the polymer, such as swelling and clustering. At higher temperatures, water vapor can be destructive to polymer membranes by changing the polymer structure that can result in diminished gas separation performance. Little data has been reported on the influence of water vapor in gas separations at >100°C because most polymers are not stable at temperature. Many high performance (HP) polymers are able to endure high temperatures and aggressive chemical conditions. For example, polyimides are promising HP polymers that effectively separate permanent gases at temperatures higher than 150°C under dry conditions. In this report, the analysis of selected HP polymers in humidified gas streams (2–4 vol% water) shows that they can perform modest separations at ambient temperatures. In general, it was observed that water vapor permeability is greater than other tested gases. Additionally, the permeabilities of the analyte gases were somewhat influenced by the presence of humidity and their selectivities were significantly lower, as compared to corresponding experiments performed in the absence of water. To elucidate the role of water vapor in gas transport, energy of activation of permeation (Ep) values were obtained for Matrimid 5218 from 30–200°C in a humidified mixed gas stream, and it was found that the selectivities are nearly identical to dry gas streams at 150°C. This data suggests that water vapor functions as a gas and only slightly decreases selectivity of the other gases at elevated temperatures. As a result, economic wet gas separations may be possible using these materials if the gas stream is kept at higher temperature (≥150°C), which is assisted by the inherent stability of the membranes.

Microporous sol–gel derived aminosilicate membrane for enhanced carbon dioxide separation

A new aminosilicate, sol–gel derived microporous inorganic membrane has been developed for enhanced CO 2 separation in applications such as removal of metabolic CO 2 from the breathing loop of the NASA extravehicular mobility unit (EMU), natural gas purification, or CO 2 capture from coal-fired power plant emissions. This membrane consists of an inorganic, amorphous silica matrix of pore size 4–5 Å, containing randomly dispersed amine ( NH 2) functional groups in order to enhance its CO 2 selectivity, due to preferential adsorption of CO 2 in the membrane pore walls and simultaneous blocking of permeation of other gases (O 2, N 2 and CH 4). It is found that the gas feed condition during permeation (partial pressure of CO 2, relative humidity), post-synthetic treatments and aging, affect significantly the separation performance of the membranes. At this stage of development, with feeds of 1–20 vol.% CO 2 and 0–40% relative humidity at 22 °C, the highest CO 2:N 2 separation factor was in the range 100–200, while the CO 2 permeance was in the range 0.1–1.5 cm 3 (STP)/(cm 2 min atm). The results suggest that controlling the membrane pore size and method of activation of amine groups are the most critical factors for improving the CO 2-permselectivity of the membrane.

Characterization of track etched membranes by gas permeation

The application of polymeric membrane in combination with the metallic films can be used for the gas purification; in particular, the hydrogen where the molecular size is very small. The affinity of hydrogen to certain metals assists the flow of hydrogen, however, restricts the permeation of other gases. However, the flow rate is very small in the dense membranes. Attempts have been made to etch the nuclear tracks of the polymeric membranes in a very controlled way to achieve the conical etched tracks to meet the vertex. This has been characterized by gas permeation measurements.

Characterization of nuclear tracks by positron annihilation and gas permeation

The application of polymeric membrane in combination with metallic films can be used for gas purification in particular for hydrogen where the molecular size is very small. The affinity of hydrogen to certain metals assists the flow of hydrogen, although it restricts the permeation of other gases. However, the flow rate is very small in dense membranes. Attempts have been made to generate nuclear tracks in polymeric membranes to control the gas flow. These tracks can be characterized by positron lifetime spectroscopy and gas permeation measurements. The long lifetime of ortho-positronium gives the estimate of size of the track-free volume of the order of 0.25 nm . The nuclear tracks can be modified by a chemical etching process. The chemical etching normally takes place from both sides of the membrane. When the etched pits from both sides meet, a rapid increase in gas permeation is observed. The size of the nano opening of the track has been observed for two different gases hydrogen and carbon dioxide, which have a molecular size of 0.2 and 0.4 nm , respectively.

Nanofilter for hydrogen purification

The application of polymeric membranes in combination with metallic films can be used for gas purification, in particular hydrogen (Int J Hydrogen Energy 27(2) (2002) 905), whose molecules are very small. The affinity of hydrogen to certain metals supports its flow, but restricts the permeation of other gases. However, the flow rate is very small in dense membranes. Attempts have been made to etch nuclear tracks created in polymeric foils, from both sides in a very controlled way such that conical etched pits meet at their vertices. This has been characterized by gas permeation measurements. The low density of 10 6 – 10 8 tracks/ cm 2 is generated by a 60 MeV carbon ion beam at the NSC Pelletron, New Delhi. The primary ion fluence of 10 10/ cm 2 was reduced by means of a gold absorber foil. The gas flow rate has shown a considerable improvement along with the selectivity of hydrogen over the carbon dioxide where the molecular sizes of 0.21 and 0.4 nm , respectively, are separable.

On the Permeability of Silicone Rubber to Acetylene

Abstract Very high rates have been reported for the permeation of acetylene through silicone rubber. Measurements in this laboratory, while consistent with the reported data for the permeation of other gases through silicone rubber, do not confirm the rates reported for acetylene.