Micron retention rating

The particle size distribution of the material and the clarity required will dictate the micron retention of the medium. Fabrics tend to have a nominal micron retention range as opposed to an absolute micron retention rating. When using precoat on a machine that leaves a residual heel of solids, a more open cloth can be used. 

Even though fibres of the above synthetic materials can be woven multifilament or monofilament, there is a trend towards the use of monofilament filter fabrics. This is so mainly because in years past it was very difficult to weave monofilaments in the fine, low-micron retention areas. Today, monofilament filter fabrics can be woven twilled down to 6 pm and plain reverse Dutch down to 14 pm. Further finishing (shrinking and calendering) can bring the particle removal rating down to the 1 pm area. 

The filter elements should remove particles of five microns, must be water-resistant, have a high flow rate capability with low pressure drop, possess high dirt-retention capacity, and be rupture-resistant. The clean pressure drop should not exceed five psig at 100 °F (38 °C). The elements must have a minimum collapse differential pressure of 50 psig. Pleated-paper elements are preferred—provided they meet these requirements. Usually, the pleated-paper element will yield the five psig clean drop when used in a filter that was sized to use depth-type elements. This result is due to the greater surface area of the pleated element, more than twice the area of a conventional stacked disc-type or other depth-type elements. 

Figure 7 is a plot of the flow rate over time for the constant volume wash step used to pass the IgG remaining in the retentate after the initial concentration of the lysate. As expected, with the lysate volume remaining constant at about 1.3 liters, there is little flow decay with time. The arrows in Figure 7 indicate the commencement of the addition of one liter aliquots of saline solution at a rate matching that of the filtrate. Five square feet of an 0.45 micron pore size filter was used for this procedure. 

Analysis. Aqueous solutions were extracted with 2 (iL of toluene In tubes used for Irradiation. Pesticide concentrations in the toluene extracts were determined directly by GLC using a 1 electron capture detector and a 15 meter X 0.53 mm (ID) bonded silicone phase (1.5 micron film thickness, 95% dlmethyl-5% diphe-nylpolyslloxane, 06-5 equivalent to SE-S) fused silica capillary column mounted in a conventional packed port. The Instrument operating conditions weret Inlet, 250 °C detector, 300 helium carrier gas flow rate, 7 nL/tnln. With a column temperature of 180 °C the dinitroanilines were completely resolved and exhibited the following retention tlmest fluchloralln (4.71 min) profluralln (4.29 min) isopropalln (11.27 min) trlfluralln (185 OC, 2.4 min). Details of the analysis of DOE, methoxychlor, methyl parathlon and -nltroanlsole are provided elsewhere (7). 

There is no distinct limit between reverse osmosis and ultra-fdtration but the latter employs lower pressures of no more than 10 bar (seldom above 6 bar) and more open membranes for separation of large molecules and ultra-fine, sub-micron solids. Henry tried to make a clear distinction between ultra-filtration and cross-flow filtration by defining the former as retention of only dissolved species from solutions (as opposed to retention of particulate material from suspensions) but this has not caught on in practice, mainly because of the fact that dissolved and undissolved (ultra-fine) soUds are often separated together. Thus, ultra-filtration is used for example for the concentration of proteins from low-cost dairy byproducts, or in the separation of emulsified oil and suspended solids from waste waters. In such processes a cake or a layer of gel would form on the membrane and reduce the filtration rates if it were not for the cross-flow characteristics of most designs, in which the suspension flows at high speed across the membrane surface and prevents cake build-up. 

For compounds eluting between dotriacontane and hexatriacontane, the 2 in the above equation was changed to a 4 to calculate indices between 3200 and 3600. The C34 hydrocarbon standard was not available. The chromatograph used was a Hewlett-Packard (HP) 5890 Series II model attached to an HP 5988 mass spectrometer, which was used to verify the identity of the spectral peaks used to produce the data presented here. The column used was an HPl capillary column with an inside diameter of 0.2 mm and a 0.33 micron film thickness of methyl silicone stationary phase. The carrier gas was helium at a flow rate of 0.9 ml/min. All measurements were made with isothermal temperature programs. The data are presented as Kovats indices followed by the column temperatures, in degrees Centigrade, used to produce the data. To reproduce the results presented in this book, the same temperature, stationary phase, carrier gas, gas flow rate, and column dimensions should be used. The Kovats indices presented here cannot be compared with indices measured with a packed column. A table of retention indices appears in Appendix E. 

---