Microfiltration pore size

For 8-inch diameter, brackish water membrane modules Microfiltration pore size < 0.5 microns. 

However, careful study of the spectra prior and after oil samples microfiltration revealed the presence of one or more polyconjugated species depending on pyrolysis plant construction features. It has been shown that microfiltration (pores size 2 pm) of oil samples decreased sufficiently both the quantity of microparticles and their size. In the case of the pyrolysis oil obtained from IWC plant, an ESR signal was not detected after filtration, showing that fine char particles caused the detection of paramagnetic moieties in this sample. However, the PMS content in oil samples from Aston FB, BTG and VTT plants remained constant after filtration.(Table 3). 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Membrane Cliaraeterization MF membranes are rated bvtliix and pore size. Microfiltration membranes are imiqiielv testable bv direct examination, but since the number of pores that rnav be obsen ed directlv bv microscope is so small, microscopic pore size determination is rnainlv useful for membrane research and verification of other pore-size-determining methods. Furthermore, the most critical dimension rnav not be obseiA able from the surface. Few MF membranes have neat, cvlindrical pores. Indirect means of measurement are generallv superior. Accurate characterization of MF membranes is a continuing research topic for which interested parties should consult the current literature. 

Fig. 16.2. Reverse osmosis, ultrafiltration, microfiltration and conventional filtration with distinct pore size.

Fig. 16.6. Atomic force microscope image of a polycarbonate microfiltration membrane (cyclopore), 0.2 p,m pore size.

Fig. 16.8. Atomic force microscope image of anodise microfiltration membrane, 0.2 xm pore size.

The physical characterisation of membrane structure is important if the correct membrane is to be selected for a given application. The pore structure of microfiltration membranes is relatively easy to characterise, SEM and AFM being the most convenient method and allowing three-dimensional structure of the membrane to be determined. Other techniques such as the bubble point, mercury intrusion or permeability methods use measurements of the permeability of membranes to fluids. Both the maximum pore size and the pore size distribution may be determined.1315 A parameter often quoted in manufacturer s literature is the nominal... 

S-layer ultrafiltration membranes (SUMs) are isoporous structures with very sharp molecular exclusion limits (see Section III.B). SUMs were manufactured by depositing S-layer-carrying cell wall fragments of B. sphaericus CCM 2120 on commercial microfiltration membranes with a pore size up to 1 pm in a pressure-dependent process [73]. Mechanical and chemical resistance of these composite structures could be improved by introducing inter- and intramolecular covalent linkages between the individual S-layer subunits. The uni-... 

Membrane Characterization MF membranes are rated by flux and pore size. Microfiltration membranes are uniquely testable by... 

Bubble Point Constancy. Although the exact relationship between the bubble point and the "pore size" of a microfiltration membrane is a matter of dispute (11, 12, 13, 14), nevertheless, it remains the quickest and most convenient means for demonstrating the continuing integrity of a membrane filtration system. It is consequently important that the bubble point be both reproducible (within a given range) and constant. It was, therefore, of considerable interest to discover that the bubble points of both conventional and poly(vinylidene fluoride) membranes increased with immersion time in deionized water whereas those of Tyrann-M/E and polyamide remained essentially constant (Figure 6). 

When pressurized liquid is used lo separate micrometer-size particles from fluids, the process is called microfiltration. Generally particle sizes are front 0.02 to 10 pm. Thus compared lo ultrafiltration and reverse osmosis, fluxes and pore sizes are large, osmotic pressure low. and pressures moderate. Two types of niicrofiltration processes exist, crossflow and deadend. Commercially, the former is growing at Ihe expense of the latter. 

Microfiltration. Various membrane filters have been used to remove viral agents from fluids. In some cases, membranes which have pores larger than the viral particle can be used if the filtration is conducted under conditions which allow for the adsorption of the viral particle to the membrane matrix. These are typically single-pass systems having pore sizes of 0.10—0.22 m. Under situations which allow optimum adsorption, between 10—102 particles of poliovirus (28—30 nm) were removed (34—36). The formation of a cake layer enhanced removal (35). The titer reduction when using 0.10—0.22 Jim membrane filters declined under conditions which minimized adsorption. By removal standards, these filters remove viruses at a rate on the low end of the desired titer reduction and the removal efficiency varies with differences in fluid chemistry and surface chemistry of viral agents (26). 

Particles smaller than the largest pores, but larger than the smallest pores are partially rejected, according to the pore size distribution of the membrane. Particles much smaller than the smallest pores will pass through the membrane. Thus, separation of solutes by microporous membranes is mainly a function of molecular size and pore size distribution. In general, only molecules that differ considerably in size can be separated effectively by microporous membranes, for example, in ultrafiltration and microfiltration. 

The most important property characterizing a microporous membrane is the pore diameter (d). Some of the methods of measuring pore diameters are described in Chapter 7. Although microporous membranes are usually characterized by a single pore diameter value, most membranes actually contain a range of pore sizes. In ultrafiltration, the pore diameter quoted is usually an average value, but to confuse the issue, the pore diameter in microfiltration is usually defined in terms of the largest particle able to penetrate the membrane. This nominal pore diameter can be 5 to 10 times smaller than the apparent pore diameter based on direct microscopic examination of the membrane. 

---