Filtration conditions

Direct interception refers to a sieve-type mechanism in which contaminants larger than the filter pore size are directly trapped by the filter. This sieve retention mechanism of particle arrest is the mechanism of choice and occurs owing to geometric or spatial restraint. This type of particle arrest is considered to be absolute, that is, it is independent of filtration conditions. 

A PVDF membrane filter has been shown to remove >10 particles of vims for vimses >50 nm independent of fluid type (8). Vimses smaller than 50 nm are not removed as efficientiy but are removed in a predictable manner which correlates to the vims particle size. The chemistry of the suspending fluid affects titer reduction for vimses <50 nm owing to other removal mechanisms, such as adsorption, coming into play. The effects of these other mechanisms can be minimized by using filtration conditions that minimize adsorption. 

Pressure leaf filters are used to separate much the same lands of slurries as are filter presses and are used much more extensively than filter presses for filter-aid filtrations. They should be seriously considered whenever uniformity of production permits long-time operation under essentially constant filtration conditions, when thorough washing with a minimum of hquor is desired, or when vapors or fumes make closed construction desirable. Under such conditions, if the filter medium does not require frequent changing, they may show a considerable advantage in cycle and labor economy over a filter press, which has a lower initial cost, and advantages of economy and flexibility over continuous vacuum filters, which have a higher first cost. 

The term r/ax, is a constant and independent of filtration conditions. We find that the ratio of constant C2 at pressure 1.5 atm. to constant C, for the process under pressure at 0. 5atm. is as follows Then A2/A, = 10... 

Parameters q and W are variables when filtration conditions are changed. Coefficient (rj, is a function of pressure (rj, = f(P). The exact relationship can be derived from experiments in a device called a compression-permeability cell. Once this relationship is defined, the integral of the right hand side of the above equation may be evaluated analytically. Or, if the relationship is in the form of a curve, the evaluation may be made graphically. The interrelation between W and P, is established by the pump characteristics, which define q = f(W) in the integral. Filtration time may then be determined from dq/dt = W, from which we may state ... 

The difficulty becomes accentuated by several other requirements that cannot be achieved through the selection of a single filter medium. Therefore, selection is often reduced to determining the most reasonable compromise between different, mutually contradictory requirements as applied to the filter medium at a specified set of filtration conditions. Because of this, some problems should be solved before final medium selection. For example, should attempts be made to increase filtration rate or filtrate purity Is cost or medium life more important In some cases a relatively more expensive filter medium, such as a synthetic cloth, is only suitable... 

Parameters q and W are variables when filtration conditions change. Coefficient (ry,)x is a function of pressure ... 

The filtration conditions (i.e., the rate and time of filtration) should be established in preliminary experiments. The two major considerations are (1) filter washing must be sufficient to minimise the nonspecific retention of radiologand by the filter and (2) the time course of filtration should be sufficiently short that dissociation of the radioligand from its receptor is avoided. In these studies, it is important to have a preliminary estimate of the dissociation rate, i.e., k i in equation23. For a simple exponential reaction, the half-time of dissociation (t./,) is related to the dissociation rate constant by t./, = 0.693/k i... 

The case stndy of the SP development of an HPLC assay method for an OTC prodnct derived from natural materials illustrates the importance of optimizing both the extraction and filtration conditions to fully recover all the labile active components in the formulation. The HPLC gradient assay method, which separates all active ingredients from other... 

Figure 8 shows a typical F4PLC chromatogram of the tablet extract illustrating the complexity of the sample, which contains numerous natural components, excipients and additives. During the SP method development, it was found that extraction with a neutral aqueous buffer was problematic due the loss of one of the active ingredients by hydrolysis. The use of the PTFE filter was also important because this hydrolysis product, which is highly hydrophobic, was absorbed by nylon filters under the filtration conditions. 

Using the optimized filtration conditions, filter a blank sample solution (sample solvent) to determine whether any materials are leached or extracted from the filter s membrane or housing. The response from the filtered sample solvent should not be greater than 1.0% of the average response for the unfiltered standard solution. In addition, for separative finish (e.g., HPLC), no peaks should coelute with the principal peak of the chromatogram. 

At the ZPC maximum hydrophobic characteristics of the coal are exhibited. One can establish better froth flotation, flocculation, and/or filtration conditions if this point is known. 

Data for some filter media are shown in Table 11.6. Although these porosities and permeabilities are of unused materials, the relative values may be useful for comparing behaviors under filtration conditions. Permeability Kp normally is the property... 

There is much evidence, however, that the resistivity behavior of a cake under filtration conditions may be different from that measured in a CP cell. The literature is reviewed by Wakeman... 

Filtration conditions were studied in a process of producing dyes. The filtration phenomenon is expressed with these four factors ... 

Ognier, S., Wisniewski, C. and Grasmick, A. (2004) Membrane bioreactor fouling in sub-critical filtration conditions a local critical flux concept. Journal of Membrane Science, 229, 171-177. 

There is much evidence, however, that the resistivity behavior of a cake under filtration conditions may be different from that measured in a CP cell. The literature is reviewed by Wakeman (1978). CP cell data are easily obtained and may be of value in a qualitative sense as an indication of the sensitivity of resistivity to pressure, but apparently are not of acceptable engineering accuracy for the design of filtration equipment. The deduction of resistivities fi om filtration tests is illustrated in Example 11.1. 

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