Gas Permeation Experiment

After all tlte gases are tested, the permeation cell is opened and the mask removed from the permeation cell. The digital image of the masked CMS is shown in Fig. 5.14. 

Syed Mohd STC (2004) Foramtion and characterization of polyacrylonitrile (PAN) carbon hollow fiber membranes for gas separation. Master of Engineering Thesis, University Technology Malaysia, Skudai, Johor, Malaysia 

Ismail AF, Dunkin IR, Gallivan SL, Shilton SJ (1999) Production of super selective polysul-fone hollow fiber membranes for gas separation. Carbon 40 (23) 6499-6506 

Williams PJ (2006) Analysis of factors influenceingthe performance of CMS membranes for gas separation. PhD thesis, Georgia Institute of Technology, Atlanta, GA, USA 

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In the discussion of concentration polarization to this point, the assumption is made that the volume flux through the membrane is large, so the concentration on the permeate side of the membrane is determined by the ratio of the component fluxes. This assumption is almost always true for liquid separation processes, such as ultrafiltration or reverse osmosis, but must be modified in a few gas separation and pervaporation processes. In these processes, a lateral flow of gas is sometimes used to change the composition of the gas on the permeate side of the membrane. Figure 4.14 illustrates a laboratory gas permeation experiment using this effect. As the pressurized feed gas mixture is passed over the membrane surface, certain components permeate the membrane. On the permeate side of the membrane, a lateral flow of helium or other inert gas sweeps the permeate from the membrane surface. In the absence of the sweep gas, the composition of the gas mixture on the permeate side of the membrane is determined by the flow of components from the feed. If a large flow of sweep gas is used, the partial... 

Based on the gas permeation experiments, Fernandez et al. [59] concluded that parameters Kq and Bq are independent of the gas... 

Some more module configurations are reported for use in MD. Lawson and Lloyd [77] have designed a laboratory-scale MD module as shown in Figure 19.13, where the membrane was sandwiched between the two half-cells, and several hose clamps held the module together. The total area available is 9.7 cm and the smooth transitions at the module entrance as well as exit allow achievement of relatively high Reynolds numbers, whereby conventional boundary layer equations are applicable. The module does not require a support in low pressure-drop applications such as DCMD. Wider permeate channels would require a support for VMD experiments. A porous sintered stainless steel material has been used for the gas permeation experiments. 

The effects of feed pressure on C02 flux and permeability, H2 flux, and C02/H2 selectivity were investigated using a membrane with a thickness of -60pm on the BHA microporous Teflon support. The feed pressures ranged from 1.5 to 2.8atm. Temperature was maintained at 110°C, and water rates were kept at 0.03cc/min for both the feed side and sweep side. The feed gas consisted of 20% C02,40% H2, and 40% N2 (on dry basis) with a feed gas rate of about 60cc/min in the gas permeation experiments. 

From gas permeation experiments (see Chapter 9) it was found that before template removal even very thin layers (1-2 pm) could be produced in a gastight state. After template removal a good membrane quality could be obtained with somewhat thicker layers. To obtain high quality, defect-free MFI membranes, two subsequent hydrothermal treatments resulting in a total layer thickness of about 3-4 pm give best results with excellent separation properties. 

Gas permeation experiments with xylenes indicate some catalytic activity which point to acid sites, not present in pure silicalite (Al/Si = 0) but which are present when Al is built into the silicalite lattice. This indicates the occurrence of some reaction between the precursor solution and the a-alumina support during hydrothermal synthesis. 

Gas permeation experiments were carried out at 3()3 773K by using single or binary gas systems of hydrogen and nitrogen, etc. The membrane was fixed in a stainless steel(SS316) reactor placed in an electrical furnace. 

Gas permeation experiments were performed in the temperature range of 35-300°C. The feed stream was pressurized, while downstream pressure was maintained at atmospheric pressure no sweep gas was used. The permeate flow rate was determined by a soap-film meter. 

Gas permeation experiment A constant volume technique was used to measure the gas permeability (12). After mounting a membrane in a permeation cell, the cell system was evacuated and its leak rate was checked, which was typically 45 mTorr/hr. The true pressure increase data were obtained by substracting the leak from the measured pressure increase. The permeability P was calculated from the slope of a plot of pressure vs time t at steady state. 

A battery of single-gas permeation experiments using molecules with different kinetic diameters is used to gauge the effective pore size in defect-free membranes... 

Thronghont all of the gas permeation experiments, it was noticed that the gas permeance was independent of the feed pressure in other words, the gas permeance was independent of Therefore, the diffusive mechanism seems to dominate the gas transport throngh the membrane pores, revealing the fact that the prepared mem-branes in this stndy have small pore sizes. Accordingly, the gas permeance will be described after omitting the viscous term in Equation 6.1 as (Equation 6.2) (Khayet et al. 2005a Qtaishat et al. 2009a,b) ... 

This test was therefore useful in evaluating the ratio (reILp). Some of the gas permeation experiments were duplicated using different manbrane sheets made from the same casting solution batch in order to evaluate the variance of the obtained values from one batch to another. Moreover, for each membrane, the measurement of the gas flow rate was made three times at a given gas pressure and the average value was reported as the membrane permeance. 

It has been found, for a wide range of solntes in glassy and rubbery polymers, that S varies with T, where Ti is the critical tanperature of the solute [31]. This correlation was found to apply for PlM-1, as can be seen in Figure 2.6, which includes S values from IGC and S values derived from gas permeation experiments. Figure 2.6 also includes data for the previous champion amongst monbiane polymers, PTMSP [32], and the results show that PlM-1 exhibits the largest solubility coefficients of all polymers studied in this way. This confirms the exceptional affinity that PlM-1 has for small molecules. 

Defect-free membranes comprising zeolites and amorphous glassy perfluoropolymers can be prepared by modifying the surface of the filler. The pure gas permeation experiments of a series of Teflon AF 1600 membranes with various amounts of 80 and 350nm silicalite-1 crystals cannot be interpreted on the basis of the Maxwell model, but are compatible with a model in which a barrier to transport exists on the zeolite surface and a lower density polymer layer surrounds the crystals. With a small zeolite size (80nm) the low density layers around the crystals may coalesce and form percolation paths of lesser resistance and less selectivity. Silicalite-1 crystals improve the CO2/CH4 selectivity of Hyflon AD60X, and drive the N2/CH4 selectivity beyond the Robeson s upper bound. It also turns out that the presence of silicaUte-l crystals, like fumed silica, promote the inversion of the methane/butane selectivity of Teflon AF2400 in mixed gas experiments. 

For moderate transmembrane pressure difference, that is, up to about 650 kPa, and for temperatures not higher than 400°C the microstructured metallic plate having straight channels 200-500 pm wide provided good mechanical support even for the thinnest membranes tested. Moreover, mixed gas permeation experiments revealed that concentration polarization effects are expected to be subordinate [129]. 

Gas permeation experiments were carried out for carbon dioxide, oxygen and nitrogen. The method used to measure the gas permeability was the constant pressure or variable volume method. For the measurements a home-made system was used [32]. It comprised a two-compartment flat sheet permeability cell. The feed stream circulates in the bottom compartment tangentially to the composite films and permeates through them to be collected in the top compartment where a flowmeter is connected. Due to the asymmetry of the composites the permeation experiments were carried out both for the top and bottom surfaces of the composite films facing the feed stream. 

The authors are thankful to Dr. Corinne Chappey (UMR 6270 CNRS, Rouen, France) for the technical insight and support in gas permeation experiments. 

The following quantities are known from the gas permeation experiments with silicone rubber film, porous polyethersulfone substrate membrane, and silicone rubber/polyethersulfone laminated membrane ... 

The miscibility of PMMA with bisphenol chloral polycarbonate (BCPC) has been studied using gas-permeation experiments [99]. Gas permeability coefficients for... 

Table 7.1 Experimental results from single gas permeation experiments...

The results of the gas permeation experiments are as follows. Since the Knudsen number, A/J, where A is the mean free path and d is the pore diameter, is 10-70 for the membrane and for the tested gases, the gas flow through the membrane pore should be in Knudsen flow regime. The flux through the membrane can then be calculated from the pore size, pore length and the transmembrane pressure difference. Surprisingly, the experimental permeation data revealed that they are at least... 

In pure, non-hydrocarbon gas permeation experiments (H, He, Ne, N2, O2, Ar, CO2, Xe), Holt et al. foimd an dependence in permeabihty. That is, light gases diffuse faster, in proportion to the molecule s thermal velocity va k T/Mf . The above relationship is usually associated with Knudsen diffusion for the following reasons The self diffusion eoefficient, ZX, of a gas molecules is simply vA, where A is its mean free path. Thus the permeability could be explained if one assumes ... 

Gas permeation. The gas permeation experiments were performed with a difriision cell consisting of two compartments for feed and sweep gas (1). The plasma treated membranes were sandwiched between the two compartments. The membrane area was 9.7 cm. The feed gas (a mixture of CO2 and CH4, CO2 mol fraction 0.05, total... 

A more in-depth elucidation of the mechanism of permselective membranes can be done by using the Nemst-Planck/Poisson equations. As a model system, the gold nanoporous membranes introduced by Martin et al. were used however, the surface charge was established by their chemical modification with self-assembled monolayers (SAMs) of chemisorbed electrically charged thiol derivatives. The average pore diameters of such membranes can be very precisely determined with gas permeation experiments based on the kinetic theory of gases ... 

Cu-BTC MOF125 (Figure 5b) as additive in an asymmetric membrane of Matrimid 9725 or of 3 1 Matrimid /polysulfone Utrason S 6010 N blend showed a higher CO2 permeance compared to the unfilled membrane in mixed gas permeation experiments.binary... 

An asymmetric membrane from MIL-53(A1) (Figure 7b) (or Cu-BTC or ZIF-8, see above and Table 1) and Matrimid 9725 showed a higher CO2 permeability than the unfilled membrane in mixed gas permeation experiments. Preferentially, permeation of CO2 increased with the filler loading for all thre MOFs in the binary gas mixtures CO2/CH4 and CO2/N2 with CO2 concentrations from 10 to 75vol.%. Yet, the CO2 selectivity increased only slightly in the case of Cu-BTC or MIL-53(A1) and remained almost constant for ZIF-8. Under the same conditions, the CO2 permeability remained invariant with the type of MOF for the CO2/N2 gas mixture. The CO2/CH4 selectivity acoj/cn, dropped linearly when the CO2 fraction increased from 10 to 75vol.% for all three MOFs. The decrease in selectivity was essentially independent of the MOF filler content. 

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