Ultrafiltration tests

As part of a downstream processing sequence, 10 m3 of a process fluid containing 20 kg m 3 of an enzyme is to be concentrated to 200 kg/m3 by means of ultrafiltration. Tests have shown that the enzyme is completely retained by a 10,000 MWCO surface-modified polysulphone membrane with a filtration flux given by ... 

Example 30.5. Ultrafiltration tests with a 1.5-cm tubular membrane at — 25,000 gave a permeate flux of 40 L/m -h and 75 percent rejection for a 5 percent polymer solution. The polymer has an average molecular weight of 30,000, and the estimated diffusivity is 5 x 10 cm s. (fl) Neglecting the effect of molecular diffusion in the pores, predict the fraction rejected for a flux of 20 L/m -h, and predict the maximum rejection, (b) Estimate the fraction rejected for the low-molecular-weight fraction of the pol3mier with M 10,000. (c) If the selective layer thickness is 0.2 fan, does molecular diffusion have a significant effect on the rejection for case (a) ... 

Ultrafiltration Tests have thus far been carried out only on one type of freshly prepared sols made from 3.25 ratio silicate by initially diluting the Si02 concentration from 5.9 to 0.59 M (350 to 59 gl ) at 0 C and at once adding this to enough dilute H2S0 and ice in a blender to obtain a sol at 0 C, pH 1.7, 16.6 mM (1000 ppm) Si02. This was at once ultrafiltered through a membrane of selected pore diameter while the ultrafilter was surrounded by ice. 

Gas chromatographic research with plasma-coated silica gel adsorbent and an ultrafiltration test of organic solutes having different molecular sizes have revealed that the polymer appears to have micropores of 2-4 nm in diameter. Control of the dissolution rate of pharmaceuticals by dianging the polymer film thickness was also attempted [72], It was found that propargyl alcohol is a very promising monomer and a few applications of this hydrophilic plasma polymer have been reported [72]. 

Effect of Microgel in Silica Sol. The most critical factor in using ultrafiltra-tion to concentrate silica sols is the presence of microgel or silica aggregates which are of the order of half a micron or more in size. Aggregates this large diffuse so slowly in comparison with single particles that they are carried by the flux to the membrane surface where they are deposited irreversibly as gel and reduce the flow of water and ions. In a series of ultrafiltration tests on a 4% SiOi sol the flux was... 

Fig. 29. Rejection of test proteins as a function of molecular weight, in a series of ultrafiltration membranes with different weight cut-offs (69).

Until the early 1960s, laboratory iavestigators rehed on dialysis for the separation, concentration, and purification of a wide variety of biologic fluids. Examples iaclude removal of a buffer from a proteia solution or concentrating a polypeptide with hyperosmotic dialysate. Speciali2ed fixtures were sometimes employed alternatively, dialysis tubes, ie, cylinders of membrane about the si2e of a test tube and sealed at both ends, were simply suspended ia a dialysate bath. In recent years, dialysis as a laboratory operation has been replaced largely by ultrafiltration and diafiltration. 

Membrane Characterization The two important characteristics of a UF membrane are its permeability and its retention characteristics. Ultrafiltration membranes contain pores too small to be tested by bubble point. Direc t microscopic observation of the surface is difficult and unreliable. The pores, especially the smaller ones, usually close when samples are dried for the electron microscope. Critical-point drying of a membrane (replacing the water with a flmd which can be removed at its critical point) is utihzed even though this procedure has complications of its own it has been used to produce a Few good pictures. 

FTIR can be used to screen membranes for fouling tendencies prior to the first ultrafiltration experiment. Screening can be done by means of a simple static adsorption test. Membranes showing greater static adsorption are expected to foul more during ultrafiltration and are disfavored. Figure 8 illustrates the FTIR results... 

Early ultrafiltration membranes had thin surface retentive layers with an open structure underneath, as shown in Fig. 20-62. These membranes were prone to defects and showed poor retention and consistency. In part, retention by these membranes would rely on large retained components in the feed that polarize or form a cake layer that plugs defects. Composite membranes have a thin retentive layer cast on top of a microfiltration membrane in one piece. These composites demonstrate consistently high retention and can be integrity-tested by using air diffusion in water. 

Comparison between the inventories in the collected fractions (the colloidal and ultrafiltered fractions) and in the starting sample often indicate that there are losses of nuclides on to the ultrafiltration cartridge. These are largely recovered by subsequent acid rinses of the ultrafilters and filtration system. It is not clear whether the recovered abundances should be considered part of the colloids retained by the filter, or solutes that have adsorbed in the system (Gustafsson et al. 1996 Andersson et al. 2001), even though test experiments with colloidally-bound " Th showed significant losses in the ultrafiltration system (Baskaran et al. 1992.)... 

These estimates, though approximate, established that — excluding sample consumption for testing — the yield could not have been less than 20% and perhaps as much as 50%. Since another 10 pg of hementin were known to have been lost into the filtrate of the initial ultrafiltration and another 5 to 10 pg into IEC peaks II and III, no less than 40% and up to 80% of the material was accounted for. 

Fractionation of the Sediment Extract. Ultrafiltration methods (17) have produced some useful data about the nominal molecular size of the active component. Crude sediment extract was filtered (Amicon, 50 psi) and separated into three fractions having the following nominal molecular fractions <10,000, <2,000, <500. The fractions were tested for hydrilla-inhibition, and the two lower M.W. fractions proved to be inactive against the plant. The fraction having a M.W. greater than 2,000 but less than 10,000 showed inhibitory action somewhat enhanced over that of the crude extract (12). 

Municipal landfill leachate typically contains dissolved organic carbon (DOC) concentrations up to several thousand (typically >1700 ppm), even in a landfill that is decades old (Christensen et al. 1998). More than 200 organic compounds have been identified in municipal landfill leachate (Paxe us 2000). Therefore, an effective chemical characterization of landfill leachate by numerous analytical techniques requires a previous isolation procedure in order to remove possible interferences. In our previous study, we tested the advantage of the ultrafiltration... 

Flat membranes from these polymers were tested for desalination and found to be of low salt rejecting type. Hov/ever, the copolymer was found to possess more than 90 per cent rejection for 1 per cent dextran solution with 10.0 gfd water flux at 200 psi thus indicating the possibility of application of these membranes in ultrafiltration and hemodialysis. 

Probstein et al (10) Investigated the use of detached strip type turbulence promoters in the ultrafiltration of bovine serum albumin in laminar flow. His apparatus is shown in Figure 27 the detached strip type promoters tested were circular cylinders with a diameter (D) approximately one-half (0.46) of the channel height and were across the center of the channel cross-section, transverse to the flow. 

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