Bubble point measurement

Figure 10.6 Pore size estimation by bubble point measurement.

Figure 7.4 Membrane pore diameter from bubble point measurements versus Bacillus prodigiosus concentration [1], Reprinted from W.J. Elford, The Principles of Ultrafiltration as Applied in Biological Studies, Proc. R. Soc. London, Ser. B 112, 384 (1933) with permission from The Royal Society, London, UK...

The apparatus used to measure membrane bubble points is shown in its simplest form in Figure 7.7 [4], Bubble point measurements are subjective, and different operators can obtain different results. Nonetheless the test is quick and simple and is widely used as a manufacturing quality control technique. Bubble point measurements are also used to measure the integrity of filters used in critical pharmaceutical or biological operations. 

Bubble point measurements are most useful to characterize sheet stock or small membrane filters. The technique is more difficult to apply to formed membrane cartridges containing several square feet of membrane because diffusive flow of... 

Table 7.1 Properties of liquids commonly used in bubble point measurements. The conversion factor divided by the bubble pressure (in psi) gives the maximum pore size (in im)...

Figure 7.7 Bubble point measurements (a) exploded view of filter holder (b) test apparatus and (c) typical bubble patterns produced. From Brock [4]. Courtesy of Thomas D. Brock...

Although bubble point measurements can be used to determine the pore diameter of membranes using Equation (7.1), the results must be treated with caution. Based on Equation (7.1), a 0.22-pm pore diameter membrane should have a bubble point of about 200 psig. In fact, based on the bacterial challenge test, a 0.22-pm pore diameter membrane has a bubble point pressure of 40-60 psig, depending on the membrane. That is, the bubble point test indicates that the membranes has a pore diameter of about 1 pm. 

When the wetting fluid is expelled from the largest pore, a bulk gas flow will be detected on the downstream side of the filter system (Fig. 7). The bubble point measurement determines the pore size of the filter membrane, i.e., the larger the pore the lower the bubble point pressure. Therefore, filter manufacturers specify the bubble point limits as the minimum allowable bubble point. During an integrity test, the bubble point test has to exceed the set minimum bubble point. 

The bubble point measurement is recognized as an ASTM procedure (F316-80 [26] and E128-61 [27]). This technique allows the determination of pore diameters and the presence of defects in the membrane. Bubble point is based on Jurin s law. If a porous membrane is impregnated with a liquid (e.g., water, alcohol) each pore has a meniscus of condensate at the gas-liquid interface which opposes the flux of gas. To unblock the pores a pressure Ap must be applied. According to the Jurin s law, the smaller the pores, the higher the pressure required... 

A majority of commonly used inorganic membranes are composites consisting of a thin separation barrier on porous support (e.g., Membralox zirconia and alumina membrane products). Inorganic MF and UF membranes are characterized by their narrow pore size distributions. This allows the description of their separative performance in terms of their true pore diameter rather than MW CO value which can vary with operating conditions. This can be advantageous in comparing the relative separation performance of two different membranes independent of the operating conditions. MF membranes, in addition, can be characterized by their bubble point pressures. Due to their superior mechanical resistance bubble point measurements can be extended to smaller diameter MF membranes (0.1 or 0.2 pm) which may have bubble point pressure in excess of 10 bar with water. 

Figure 3.22 shows the bubble point measured with isopropanol (IPA) on polyvinylidene difluoride UF membranes with MWCO s between 10,000 and 1,000,000. A 300,000 MWCO membrane (F300) should have an estimated effective pore size of 0.02 ju yet the bubble point indicates a maximum pore size in the skin over 0.4 ju. This is one reason why UF membranes can be less retentive for bacteria than MF membranes. However, Figure 3.22 also indicates that a 10,000 MWCO membrane can have a (I.P.A.) bubble point of 100 psi. Equation 3 of Chapter 2 may be used to calculate a maximum pore diameter of 0.12 jtt which should be retentive for all bacteria. Indeed, small laboratory discs of these membranes can be subjected to high challenge levels of bacteria with absolute retention (zero passage). However, industrial scale UF modules often employ 10 to 100 square feet of membrane area it is difficult to manufacture a pinhole-free module with this much area. Broken fibers, bubbles in glue-line seals, and other defects provide leak paths for bacteria. 

The apparatus employed for the investigation is based on a modified version of the dew and bubble-point method of phase-boundary determination. By altering the standard procedure, solid-liquid-vapor and solid-vapor equilibria data can be determined along with the vapor-liquid data in the same basic apparatus used for dew and bubble-point measurements. The method presented here is a slight variation of the method presented by Kurata and Kohn [ ] and similar to that of Donnelly and Katz p]. 

Microfiltration membranes, possessing pores in the range 0.1-2 pm, ag relatively easy to characterise (see chapter IV). The main techniques employed are Scanning Electron Microscopy (SEM). bubble-point measurements, mercury poromeiry and... 

Bubble point measurement Figure 2.9 Gas permeability apparatus. 

Table 4.2 Results of bubble point measurements through plane forTGP-H-060 with different Teflon contents...

Each data point represents the average of measurements at three independent, random locations on the screen surface. Also plotted is the methanol/water contact angle data from Addesso and Lund (1997) obtained using the Whilhelmy plate method. Reasonable agreement exists between the data sets. Methanol mass fraction values in this work were chosen consistent with mass fractions from bubble point measurements. Contact angle measurements for mixtures here are also in qualitative agreement with previously... 

Bubble point measurements were repeated at similar tank pressures and/or temperatures for repeatability and consistency Because screen pore sizes may vary slightly due to screen manufacturing variations or defects, it was also desired to repeat measurements to verify that... 

The scatter in Figures 6.7b and 6.8b from previous bubble point measurements made by Jurns and McQuillen (2008) could be explained by potential temperature differences between the bulk fluid and the screen however, temperature sensors directly moimted on the screen were not incorporated for those tests. None of the historical measurements used screen side temperatures to deduce bubble point. In Figures 6.7 and 6.8, the apparent scatter in the data is not a result of experimental uncertainty. Rather, it is due to the fact... 

Jurns, J.M., McQuillen, J.B., Gaby, J.D., Sinacore, S.A., 2007. Bubble point measurements with liquid methane of a screen channel capillary liquid acquisition device. In NASA-TM-2009-215494, 54A JANNAF... 

Pore size distribution and bubble point measurement of the membranes were carried out using a capillary flow porometer (Porous Materials Inc., USA). The membranes were first wetted with Galwick solution and then placed in the holder. Measurements were made in a wet up, dry up operating mode. 

JAN Jang, Y.-S. and Byim, H.-S., Cloud-point and bubble-point measurement for the poly(2-butoxyethyl acrylate) + cosolvent mixture and 2-butoxyethyl acrylate in supercritical fluid solvents, J. Chem. Eng. Data, 59, 1391, 2014. 

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