Permeate flux

Membranes made by interfacial polymerization have a dense, highly cross-linked interfacial polymer layer formed on the surface of the support membrane at the interface of the two solutions. A less cross-linked, more permeable hydrogel layer forms under this surface layer and fills the pores of the support membrane. Because the dense cross-linked polymer layer can only form at the interface, it is extremely thin, on the order of 0.1 p.m or less, and the permeation flux is high. Because the polymer is highly cross-linked, its selectivity is also high. The first reverse osmosis membranes made this way were 5—10 times less salt-permeable than the best membranes with comparable water fluxes made by other techniques. 

Using this simplified model, CP simulations can be performed easily as a function of solution and such operating variables as pressure, temperature, and flow rate, usiag software packages such as Mathcad. Solution of the CP equation (eq. 8) along with the solution—diffusion transport equations (eqs. 5 and 6) allow the prediction of CP, rejection, and permeate flux as a function of the Reynolds number, Ke. To faciUtate these calculations, the foUowiag data and correlations can be used (/) for mass-transfer correlation, the Sherwood number, Sb, is defined as Sh = 0.04 S c , where Sc is the Schmidt... 

For very small AP, flux is linear with pressure. Figure 7 shows a graph of flux versus pressure. Curve A is the pure water flux from equation 1, curve B is the theoretical permeate flux (TPE) for a typical process. As the gel layer forms, the flux deviates from the TPF following equation 7 and curve D results. Changing the hydrodynamic conditions changes K and results in a different operating curve, curve C. 

Electroultrafiltration has been demonstrated on clay suspensions, electrophoretic paints, protein solutions, oil—water emulsions, and a variety of other materials. Flux improvement is proportional to the appHed electric field E up to some field strength E where particle movement away from the membrane is equal to the Hquid flow toward the membrane. There is no gel-polarization layer and (in theory) flux equals the theoretical permeate flux. It... 

Theory Cross-flow-elecfrofiltration can theoretically be treated as if it were cross-flow filtration with superimposed electrical effects. These electrical effects include elecfroosmosis in the filter medium and cake and elecfrophoresis of the particles in the shiny. The addition of the applied electric field can, nowever, result in some quahta-tive differences in permeate-flux-parameter dependences. 

The membrane resistance for CF-EF can be defined by specifying two permeate fluxes as... 

The resistances, when incorporated into equations descriptive of cross-flow filtration, yield the general expression for the permeate flux for particulate suspensions in cross-flow-electrofiltration systems. 

FIG. 22-29 Qualitative effects of Reynolds number and applied-electric-field strength on the filtration permeate flux J. Dashed lines indicate large particles (radial migration dominates) solid lines, small particles (particle diffusion dominates). 

The net pressure differential across a membrane, taking into consideration the osmotic pressure is given by (AP - AH), and hence, the expression for the permeate flux is ... 

What should be the pressure aeross an ultrafiltration module, in order to achieve a permeate flux of 400 Liter/m -day. The clean membrane resistance is 2.4 X 10 1/m. 

A RO stage can be used to reduce salinity and related parameters for high standard industrial reuse using the former UF effluent as feed stream. A pilot plant with 0.4 m h constant permeate flux capacity has been used in this demonstration. Table 7 summarizes the main technical characteristics of this plant. In order to increase the overall system recovery ratio while maintaining an acceptable... 

Although the trend in the viscosity of the system tended to decrease, which facilitated filtration, a gel occasionally appeared during the filtration and a polarisation layer was always formed. The first line (1-5 h) of Figure 4 is based on an assay in which the filtration started after a reaction time of 1.5 hours, when there were still polymers and the viscosity of the system was high. A sharp decrease in the permeate flux was obtained because a gel appeared among the hollow fibers, as did a polarisation layer. The second line (4-11 h) of Figure 4 is from an assay in which the filtration started after a reaction time of 4.5 hours, when there were no polymers and the viscosity of the system was low. In this experiment no sharp decrease in the permeate flux was obtained and no gel appeared between the hollow fibers. Only the appearance of the polarisation layer was responsible for the decrease of the flux from 250 mL/h (initial flux) to almost 200 mL/h. 

E > Ec, increases in permeate flux rate are due only to electroosmosis in the filtration medium. 

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. 

FIGURE 15.7 Variation of permeate flux against time on stream when 1-dodecanol was added to catalyst/wax slurry. 

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