Effect of transmembrane pressure

The presence of organics appears to facilitate aggregate break-up. Flux decline is independent of transmembrane pressure and it is therefore assumed that the cake is not compacted. The aggregate 

Overall, the recycle experiments showed that concentration polarisation effects were negligible - if they were significant, flux would increase after permeate recycle. Concentration changes in the cell due to filtration do not seem important either. 

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The rate of phenol degradation as a function of catalyst loading in PVDF membranes and the effect of transmembrane pressure that influences the contact time substrate/catalyst, have been investigated. 

Rodgers VGJ and Sparks RE, Effect of transmembrane pressure pulsing on concentration polarization, J. Membr. Sci. 1992 68 149-168. 

Figure 7. Effect of Transmembrane Pressure and Cell Concentration on Protein Transmission a, Schematic of Amicon loplate Plate-and-Frame Device Used b Amicon loplate Plate-and-Frame Test Results...

T ransmembrane Pressure. The effect of transmembrane pressure on flux is often dependent on the influence of concentration polarization at a specified cross-flow velocity and solids loading. For MF or UF at low solids concentration and high cross-flow velocity, flux may increase linearly with TMP up to a certain threshold value (1 to 3 bar), and then remain constant or even decrease at high TMP values. This is illustrated in Fig. Athigh... 

Figure 16. Effect of transmembrane pressure on flux. Yeast concentration, dry-g/L ...

The effect of transmembrane pressure on the rejection of the TFC-SR membrane was examined and results are shown in Table 7.18. Rejection at all pressures is relatively stable, although at 7.5 bar rejection is initially lower and DOC rejection decreases with increasing pressure. 

Table 7.18 Effect of transmembrane pressure on rejection ofTFC-SK membrane (5mgL DOC FA, pH8, 0.5 mM CaOj, 1 mM NaHCO , 20 mM NaC/J.

Figure 7.40 Effect of transmembrane pressure on flux decline of CA-UF membrane (12.5 mgE HA and 2.5 mM C.aCf, pH 8).

FICU RE 16.33 Effect of transmembrane pressure on the transmembrane flux. Emulsion formulation is given in Table 16.3. 

The sensitivity of productivity or flux to transmembrane pressure (TMP) is referred to as the permeability L = flux/transmembrane pressure. TMP refers to a module average. Pure-component permeability (e.g., water permeability) refers to membrane properties while the more industrially relevant process permeability includes fouling and polarization effects. 

The objective of the present study is to develop a cross-flow filtration module operated under low transmembrane pressure drop that can result in high permeate flux, and also to demonstrate the efficient use of such a module to continuously separate wax from ultrafine iron catalyst particles from simulated FTS catalyst/ wax slurry products from an SBCR pilot plant unit. An important goal of this research was to monitor and record cross-flow flux measurements over a longterm time-on-stream (TOS) period (500+ h). Two types (active and passive) of permeate flux maintenance procedures were developed and tested during this study. Depending on the efficiency of different flux maintenance or filter media cleaning procedures employed over the long-term test to stabilize the flux over time, the most efficient procedure can be selected for further development and cost optimization. The effect of mono-olefins and aliphatic alcohols on permeate flux and on the efficiency of the filter membrane for catalyst/wax separation was also studied. 

Cross-flow filtration systems utilize high liquid axial velocities to generate shear at the liquid-membrane interface. Shear is necessary to maintain acceptable permeate fluxes, especially with concentrated catalyst slurries. The degree of catalyst deposition on the filter membrane or membrane fouling is a function of the shear stress at the surface and particle convection with the permeate flow.16 Membrane surface fouling also depends on many application-specific variables, such as particle size in the retentate, viscosity of the permeate, axial velocity, and the transmembrane pressure. All of these variables can influence the degree of deposition of particles within the filter membrane, and thus decrease the effective pore size of the membrane. 

Figure 4. Dependence of equilibrium foulant film thickness on effective transmembrane pressure...

A hemodialysis membrane with an effective area of 0.06 m, thickness of 50 ttm, and permeability of 2.96 x 10 " m is used to filter urea and other impurities from the blood. The viscosity of blood plasma is 1.2 x 10 N s/m. What is the expected filtration rate if the transmembrane pressure is 2.25 Pa ... 

Ultrafiltrates obtained using cellophane or polysulphone membranes at 20°C and a transmembrane pressure of c. 100 kPa are satisfactory, but the concentrations of citrate and calcium are slightly low due to sieving effects which are accentuated by high pressures. Dialysis of a small volume of water against at least 50 times its volume of milk (to which a little chloroform or azide has been added as preservative) at 20°C for 48 h is the most satisfactory separation procedure and agrees closely with results obtained... 

If the water flux, /p, through an RO membrane is 8 X 10 cm s under a transmembrane pressure AP = 25 atm at 25 °C, estimate the water flux of a 2.0 wt% NaCl solution under the same transmembrane pressure and temperature. You may assume that a = 1.0 and neglect the effect of the concentration polarization. 

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