Maximum effective pore diameter

Figure 22.1.9. Relationship between maximum effective pore diameter and toluene concentration.

According to de Lange typical porosities of about 37% are obtained with a bi-modal pore size distribution having a maximum at an effective pore diameter... 

For any LAD mesh type, a pore throat defines the point within the pore where cross-sectional area is a minimum for a gas or vapor bubble to pass through the wetted screen, while the pore mouth defines the point where area is a maximum. The effective pore diameter, and thus bubble point pressure, is related to the pore throat. Statistically, the screen breaks down when a gas bubble passes through the largest pore throat, and thus path of least resistance, of the LAD screen. Likewise, the largest pore mouth controls the screen reseal pressure. 

The results of the MIP analyses of the bulk polymers are illustrated in Figure 1.7. It could be demonstrated that the polymerization time is capable of influencing the shape of the pore distribution itself, rather than shifting a narrow macropore distribution (and thus the pore-size maximum) along the scale of pore diameter (see effect of the porogenic solvent in Section 1.3.2.2 and Figure 1.5). On... 

The effectiveness factors and n, defined as the ratios of the actual reaction rates at time 0 to the maximum reaction rates on a clean catalyst, are obtained nEmerically from equations [4] -[9]. An explicit finite difference method was used to solve the partial differential equations without further simplifications. Densities, porosities and clean catalyst pore diameters were measured experimentally. The maximum coke content is assumed to be that which fills the pore completely. The tortuosity is taken as 2.3, as discussed by Satterfield et al. (14). 

Yeast can be separated from an ethanol fermentation broth by porous ceramic membranes with backflushing [Matsumoto et al., 1988]. Tubular alumina membranes with a nominal pore diameter of 1.6 pm were demonstrated to be effective for this application with a maximum permeate flux of 1,1(X) IVhr-m with backflushing. The permeate flux increases with increasing feed rale (or crossflow velocity) and TMP and with decreasing yeast concentration. Various backflushing techniques were investigated and the reverse flow of filtrate (instead of air) either by pressure from the permeate side... 

Previous pilot plant operations have shown that the effectiveness of carbon adsorption processes in removing humic substances from raw water sources is limited. Most of the commercially available active carbons with high specific surface, iodine index and phenol index have a pore size distribution with a maximum of pores of a relatively low average diameter. For reason the adsorption capacity and rate towards larger-sized molecules is quite low. This was one of the incentives for the authors to start a search for alternative activated carbons. This paper will deal with the evaluation of a first generation of such activated carbons on the basis of widely used adsorption tests and an experimental comparison of their capacity towards several humic substances. 

Similar observations were reported by Toulhoat and Plumail [38], who found HDV and hydrodeasphaltene reactions to pass through a maximum as the pore size increases. Up to ca 20 nm pore diameter, mass transfer appeared to limit access to the pore system. Above this value, the effective surface area dropped away as a result of increasing pore diameter to give a reduction in the overall rate of HDM. 

Since the effective pore size is estimated from the molecular diameter of globular proteins which are retained 90% by the membrane, it is obvious that larger pores do exist. The measurement of a membrane s bubble point (see the section on the bubble point test in Chapter 2) permits calculation of the maximum pore size in the skin of the membrane. 

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. 

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