Membrane pore size experiments

Table 25.2 Membrane Pore Size Experiment on Muzzle Residue...

Table 25.3 Membrane Pore Size Experiment on Clothing (one shot)...

The mean free path, /, of the C02 molecules at the temperatures and pressures of the permeation experiment are by far smaller than the membrane pore size, d, that is, d, /.. Then, Knudsen flow is not possible since the determining process is gaseous laminar flow through the membrane pores [18]. It is therefore feasible to apply Darcy s law for gaseous laminar flow (Equations 10.19 through 10.23). 

Some authors (7, ) have used measured parameters of solute and solvent transport for calculation of membrane pore size distributions. Difficulties associated with this approach are of both experimental and theoretical nature. The experiments need to be carried out under conditions that minimize or eliminate effects of boundary phenomena (polarization) and of solute adsorption (fouling) on the measured coefficients. This is rarely done. An even more serious obstacle in this approach is the absence of quantitative and valid relations between measured transport parameters and the size parameters of a "representative pore."... 

The CNTs, both single-walled nanotubes (SWNT) and multi-walled nanotubes (MWNT) prepared by chemical vapor deposition (CVD) and arc-discharge (AD) methods, respectively, were purchased from Iljin Nanotech, Co., Korea. For proton and electron irradiation experiments, CNTs sheets were prepared as shown in Figure 2 by filtration of the CNT solution mixed in dimethylformamide through a cellulose membrane (pore size 0.45 pm). The thickness of the CNT sheets was approximately 0.5 mm, and they were 47 mm in diameter. After drying in a vacuum oven at 80 °C for 24 hours, CNT sheets (Figure 2) were obtained. These sheets were used in the radiation experiments, and were used for analysis such as SEM, Raman spectroscopy and XPS without any further treatment. For a dispersion test, a CNT powder was used instead of the CNT sheets. 

When the membrane pore size is relatively small, the retention is governed by steric effect and the retention sequence is in the same order that of hydrated ions size, which is close to pore size [26,28]. In addition to that, the retention sequence observed during nanohltration experiment can be in the same order that of hydration energy, that is, the ion with the highest hydration energy is the most retained [34,35]. 

In some instances, however, the use of a finer pore-sized membrane provides hi er stable fluxes over longer periods than is found with coarser membranes. This is particularly true when the suspended sohds particle size is close enough to the membrane pore size for internal filter clogging to occur. Figure 10.10 illustrates an experiment conducted with two polymer membranes and a very low concentration latex su ension, with particle size in the range 0,2-2 pm. 

The phenomeiion above describes reverse osmosis. Here, a liquid with a higher concentration of electrolyte is driven through a membrane (pore sizes are on the order of 3 nm), and the exiting solvent contains much less electrolyte. The reverse osmosis membranes usually have an of 0.995. Calculate the corresponding ipj. The present treatment is from Jacazio et al. (1972), who also compared theory to experiments. 

Internal pressure hollow fiber ultrafiltration membrane was used in the experiment. The membrane material is modified PVC with effective membrane area of 40 m, the inner diameter and outer diameter of the hollow fiber is 1.0 mm and 1.5 mm, respectively, and the average membrane pore size is 0.01 xm, the molecular weight cutoff (MWCO) is 100 Ku. 

Instead, membrane filtration may be used to sterilise the nutrient in this experiment. This can be accomplished by drawing the nutrient from a mixing jar and forcing it through an in-line filter (0.2 p,m pore size) either by gravity or with a peristaltic pump. The sterilised medium is fed into an autoclaved nutrient jar with a rubber stopper fitted with a filtered vent and a hooded sampling port. 

Experiments in 500 ml Erlenmeyer flasks and Fernbach flasks contained 200 ml and 1 L of EPl and EP2 medium respectively. Inocuia added to these cultures was 2 ml of spore suspension (5.0 optical density at 540 nm) for each 100 ml EP medium. All cultures were grown at 37°C in a shaking incubator (New Brunswik Sci. Co., USA), at 200 rpm. Then 10 ml of sample were withdrawn each 24 h during fermentation and immediately filtered through Millipore membranes of 0.45 pm pore size these cell-free filtrates were used for enzymatic assays and extracellular protein determinations by the Lowry method (14). Experiments in the 14 L fermentor (Microgen Fermentor New Brunswik Sci. Co., USA) were carried with lOL of fermentation medium EP2 and inoculum added was IL of mycelium grown 24 h in... 

Surprisingly, intuition fails to predict the behavior of the same solute and solvent in a membrane with a uniform pore size larger than both the solvent and solute. The expectation that such a membrane will provide no rejection of the solute has been refuted repeatedly. Indeed, careful experiments indicate that partial rejection of the solute occurs even when the solute is considerably smaller (say 1/1 Oth as large as the pore size) (Miller, 1992 Deen, 1987 Ho and Sirkar, 1992 Happel and Brenner, 1965). The extent of rejection increases monotonically to the total rejection limit as the solute size approaches the pore size. These effects arise both from entropic suppression of partitioning and from augmented hydrodynamic resistance to transport through the fine pores. Thus, in this case, for a porous membrane, thermodynamic partitioning can play a role in the physical chemical processes of transport. 

Although the results were not definitive, it is clear that substantial amounts of NG passed through both the 1.2- and 0.8-pm filters, although the initial filter retained the bulk in each test. (There were no membrane filters with a pore size less than 0.45 pm in the laboratory at the time of the test. It would have been interesting to repeat the experiment incorporating the smaller pore size filters, such as 0.2 pm.) It is suspected that NG is present as both vapor and particulate matter, the particulate matter having a wide size range. 

After the pore-size was established, the membranes were treated in a steel reactor with a Simulated Ambient Steam Reforming Atmosphere (SASRA) for 100 hrs at 600°C with H2O/CH4 = 3/1 (by volume) at 2.5 MPa total pressure. Heating and cooling was performed in an argon atmosphere at the same total pressure at a rate of 1 °C/min. In a few experiments a pure steam treatment was carried out at 0.2 MPa total pressure at 150°C or 300°C in the same manner as for SASRA treatment. A pure CO2 treatment was done likewise, but at 500°C at 1.2 MPa pressure. 

Before and after experiments the pore sizes of the membranes were measured by permpo-rometry [16], a technique based on blocking of smaller pores by capillary condensation of cyclohexane and the simultaneous measurement of the permeance of oxygen gas through the larger, open pores. The measurements are performed at 20°C on an area of 8.5 10 4 m2. The pore size distribution (Kelvin radii) is determined in the desorption stage using the Kelvin equation. More details on the permporometry technique can be found in [17] and all experimental details of the permporometry apparatus are presented in [16],... 

To determine the change in pore size of a mesoporous membrane during CVI, the pore-size was measured before and after a CVI-experiment by permporometry. Typical results are shown in Figure 4, in which raw permporometry data are shown before and after CVI with SiAc4. 

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