Membrane surface porosity

A large membrane surface porosity (e), large pore radii (r), and a low tortuosity (t), together with a low membrane thickness Ax, are advantageous. The influence of the viscosity (iq) is important when the temperature is varied a lower viscosity is obtained at higher temperatures, which results in higher fluxes. An increase of the temperature by 1°C corresponds to a flux increase of 2-2.5%. For concentrated solutions or solutions with high salinity, the osmotic pressure An should be substracted from the applied pressure AP. The flux equation then becomes... 

All symbols are defined at the end of the paper. Equation 10 defines the pure water permeability constant A for the membrane which is a measure of its overall porosity eq 12 defines the solute transport parameter D /K6 for the membrane, which is also a measure of the average pore size on the membrane surface on a relative scale. The Important feature of the above set of equations is that neither any one equation in the set of equations 10 to 13, nor any part of this set of equations is adequate representation of reverse osmosis transport the latter is governed simultaneously by the entire set of eq 10 to 13. Further, under steady state operating conditions, a single set of experimental data on (PWP), (PR), and f enables one to calculate the quantities A, Xy 2> point... 

Figure 12. Variations of S for alcohols, aldehydes, ketones, and ethers and In A for nonionized polar organic solutes with -parameter for the polymeric membrane material as a function of surface porosity (correlations with C in centimeters/sec-ond and A in gram-moles hJ) centimeter /second atm) (56)...

Porous Membrane DS Devices. The applicability of a simple tubular DS based on a porous hydrophobic PTFE membrane tube was demonstrated for the collection of S02 (dilute H202 was used as the scrubber liquid, and conductometric detection was used) (46). The parameters of available tubular membranes that are important in determining the overall behavior of such a device include the following First, the fractional surface porosity, which is typically between 0.4 and 0.7 and represents the probability of an analyte gas molecule entering a pore in the event of a collision with the wall. Second, wall thickness, which is typically between 25 and 1000 xm and determines, together with the pore tortuosity (a measure of how convoluted the path is from one side of the membrane to the other), the overall diffusion distance from one side of the wall to the other. If uptake probability at the air-liquid interface in the pore is not the controlling factor, then items 1 and 2 together determine the collection efficiency. The transport of the analyte gas molecule takes place within the pores, in the gas phase. This process is far faster than the situation with a hydrophilic membrane the relaxation time is well below 100 ms, and the overall response time may in fact be determined by liquid-phase diffusion in the boundary layer within the lumen of the membrane tube, by liquid-phase dispersion within the... 

The surface porosity is equal to the ratio of the pore area to membrane area multiplied by the number of pores. In most cases volume flux through ceramic membranes can be best described by the Kozeny-Carman relationship, which corresponds to a system of close packed spheres (see Figure 6.8a) ... 

Pmi, Pm2 6 the partial pressures of vapor (water) at the membrane surfaces on the feed and permeate sides, respectively Kiji is the membrane coefficient that is a function of membrane properties (pore size, thickness, porosity, and tortuosity), properties of the vapor transported across the membrane (molecular weight and diffusivity) and temperature gradient... 

A novel idea for the production of water is by the combination of MD and membrane crystallization [ 139], where the salt is concentrated on the feed side to a point close to super-samration, thereby inducing nucleation of crystals. Recently Gryta and Morawski [140] performed experiments using polypropylene capillary membranes with pore diameters ranging between 0.2 and 0.6 p.m, and 70% porosity. They found crystallization to occur at the membrane surface, but by increasing the distillate temperature to 328 K, the problem was eliminated and stable flux restored. 

Diffusion coefficient of solute in the membrane, m /s Diffusion coefficient of solvent in the membrane, m /s Quanhty difference Surface porosity... 

Several attempts to characterize quantitatively pore structures in ultrafiltration membranes have been described in the literature. Preusser(lJ analyzed surface porosities of Amicon membranes, using a carbon replica technique and a high-resolution transmission electron microscopy (TEM). A similar approach was... 

The physicochemical criteria approach to reverse osmosis separations Involving the surface excess free energy of solvation for ionized and nonlonized solutes has been demonstrated by this work to include nonaqueous solutions. The parameters and correlations presented in this work permit the prediction of reverse osmosis separations and permeation rates for different alkali metal halides for cellulose acetate OEastman E-398) membranes of different surface porosities from only a single set of experimental data for a sodium chloride-methanol reference feed solution system. 

Reverse osmosis separations of 12 alkali meteil halides in methanol solutions have been studied using cellulose acetate membranes of different surface porosities. Data for surface excess free energy parameters for the ions and ion pairs Involved have been generated for the above mend>rane material-solution systems. These data offer a means of predicting the performance of cellulose acetate membranes in the reverse osmosis treatment of methanol solutions involving the above ions from only a single set of experimental data. 

Transport of the gaseous species from the donor to the acceptor stream depends on several parameters, e.g., temperature, ionic strength, surface tension, contact time between the solutions and the semi-permeable medium, the characteristics of this medium (active surface, porosity, thickness), the partition coefficient between the fluid and the membrane,... 

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