Size-selection filtration

Results of test work with this filter, producing cakes of 1 mm thickness using a 3 mm clearance, have been pubUshed (33,34). The cake formed on the medium was generally stable, giving high filtration rates over long periods of time, and the precoat type cake did not blind with time. There was no evidence of any size selectivity of the process the only exception was conventional filter aids which were preferentially picked up by the rotating fluid. This... 

All filters require a filter medium to retain solids, whether the filter is for cake filtration or for filter-medium or depth filtration. Specification of a medium is based on retention of some minimum parficle size at good removal efficiency and on acceptable hfe of the medium in the environment of the filter. The selection of the type of filter medium is often the most important decision in success of the operation. For cake filtration, medium selection involves an optimization of the following factors ... 

Data collected for each run Included cation concentration using ICP and H concentration by titration. Filtering characteristics were determined using solid and liquid yield rates, as well as back pressures during the filtration cycle. The filter cake was characterized by moisture content and particle size. Selected samples of the cake were analyzed using SEM to determine average particle size and shape. 

Edwards, A., B.S. Daniels, and W.M. Deen. 1999. Ultra structural model for size selectivity in glomerular filtration. Am.J. Physiol. 276 F892-902. 

Membrane pore size rating refers to the size of a specific particle to be retained by the filter with a specific degree of efficiency. Pore size will affect the flow rate, back pressure, and life of the filter. Membrane pore size is outlined in Table 9 and selected on the basis of the applications requirements. The size and amount of particles to be filtered from the sample can also affect the pore size selection. Most applications in the isolation of drug impurities and degradants would either require prefiltration to remove large clumps of insoluble excipients or a filtration/clarification step prior to FIPLC, and would be chosen on these bases.71... 

Colloidal filtration is selected as the dip-coating mechanism for the first trials in the development path. This means that cake filtration should occur when the suspension comes into contact with the substrate. So the particle size in the suspension should not be much smaller than 1 pm (approximately 4 times less than the mean pore size in the substrate) otherwise too much penetration and clogging of the substrate occurs prior to cake build-up. This would give rise to an extra high interfacial flow resistance during application of the MF membrane. 

When the mass of carrier material is large relative to that of the enzyme, the physical and chemical properties of the carrier (Table 6-5) will, in large part, determine properties of the resultant immobilized enzyme. Often, the carrier will impart mechanical strength to the enzyme, allowing repetitive recovery by simple filtration of the solid particles and reuse of the enzyme. The degree of porosity and pore volume will determine the resistance to diffusion and molecular size selectivity of the biocatalyst. When used in non-aqueous media, dispersion of the enzyme over a large surface area can greatly increase its activity. Table 6-3 summarizes many of the key properties and considerations for enzyme carrier materials. 

Figure 13.28 Mechanism of size exclusion chromatography (a) size selectivity as a function of pore and analyte sizes and (b) Separation process on a Gel-Filtration Column. (Adapted with permission from Phenomenex, Inc.)...

Microporous membranes are often used in many processes to remove impurities or contaminants through size-selective filtration. The breath figures method also finds application in this field, specially the approaches that facilitate the easy transfer to other supports. Another prerequisite is the formation of through pores that penetrate from the top of the layer to the bottom and the use of ice support favors this fact. For example, highly uniform membranes of PS-h-PDMAEMA have been prepared with pores on the micrometer scale for size-selective separation. The films were prepared by casting at an air-ice interface and easily transferred onto other supports [219]. Miktoarm star copolymers with proper water wettability and mechanical stability have been used to fabricate separation membranes also using ice substrate [131]. Moreover, the breath figures approach has been employed to build polymer membranes on structured substrates in order to obtain hierarchically structured microsieves [208]. 

Yang et al. synthesized a thin film with an ordered standing cylinder structure from BCP SA and transferred the film to a porous support to fabricate highly selective membranes with ordered nanochannels for virus filtration [70]. The top thin layer derived from BCP SA provided size-selective pores at the nanoscale. 

We investigated the deposited material using cryo-SEM to reveal the formation of a porous gel-like layer with relatively uniform pores (Fig. 13c-e). The structure was strikingly reminiscent of that of filtration membranes, motivating us to investigate the system as a size-selective separation membrane. Assuming that it possesses... 

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