Cellulose acetate membranes ratio

Figure 2b. Experimental data on the effect of operating pressure and average pore size on membrane surface on solute separation and (PR)/(PWP) ratio for the reverse osmosis system cellulose acetate membrane-p-chlorophenol-water fill...

The effect of casting solution composition on flux and rejection of formamide-modified cellulose acetate membranes is shown in Figure 1, illustrating the general capability of this membrane type as function of solvent concentration. Membranes of casting solution composition cellulose diacetate/acetone/ formamide 23/52/25 (solvent-to-polymer ratio 2.26) were used as reference membranes in this work. 

The frictional force is expressed by a function of the ratio of a distance associated with sterlc repulsion at the Interface, to the pore radius. The frictional function Increases steeply with increase in the latter ratio. The method of calculating reverse osmosis separation data by using the surface potential function and the frictional function so generated, in conjunction with the transport equation is illustrated by examples involving cellulose acetate membranes of different porosities and AO nonionized organic solutes in single solute aqueous solution systems. 

Figure 6.3.33. Effect of pressure ratio, y, on the permeate mole fraction of oxygen through a cellulose acetate membrane (a = 6) for a feed mixture of O2-N2,...

Case (1) You have a cellulose acetate membrane having a value of (Qo /Qnj) = 6.0. What will be the permeate composition for a pressure ratio, y = 0 ... 

Deposition of polyelectrolytes Lajimi et al. [56] explored the surface modification of nanofiltration cellulose acetate (CA) membranes by alternating layer-by-layer deposition of acidic chitosan (CHI) and sodium alginate (AEG) as the cationic and anionic polyelectrolyte, respectively. The supporting CA membranes were obtained by a phase separation process from acetone/formamide. The permeation rate of salted solutions was found to be higher than that of pure water. The rejection of monovalent salt was decreased, while that of divalent salt remained constant so that the retention ratio increased. Increasing the concentration of feed solutions enhanced this selectivity effect. 

The support medium provides the matrix in which protein separation takes place. Various types of support media are used in electrophoresis and range from pure buffer solutions in a capfilary to insoluble gels (e.g., sheets, slabs, or columns of starch, agarose, or polyacrylamide), or membranes of cellulose acetate. Gels are cast in a solution of the same buffer to be used in the procedure and may be used in a horizontal or vertical direction. In either case, maximum resolution is achieved if the sample is applied in a very fine starting zone. Separation is based on differences in charge-to-mass ratio of the proteins and, depending on the pore size of the medium, possibly molecular size. 

Equation (26.46) shows that the water flux increases strongly with the pressure difference AP, and the selectivity increases also, since the salt flux does not depend on AP. Experiments confirm these trends, but the salt rejection with cellulose acetate is not as high as predicted. The water content C is about 0.2 g/cm , and tracer tests show 10 cmVs- Diffusion tests of NaCl in dense polymer films indicate = 0.035 and = 10 cm s- The fluxes and cannot be predicted accurately for an asymmetric membrane, because the skin thickness z is not known. However, the ratio of fluxes is independent of z, and the predicted salt... 

Figure 9-42. Gas-separation selectivity of the acetate cellulose polymer membrane 5(nHe/ncH<) as function of the microwave discharge energy (dose) deposited during total duration of treatment microwave pulse power 2 kW pulse duration 100 fis gas pressure in the microwave discharge chamber 2 Torr nitrogen/oxygen ratio in the plasma gas N2 02 =4 1 flow rate of the plasma gas 40 cm /s. The same dose can be achieved at different values of average microwave power -b, 10 W (pulsing period 20 ms) o, 20 W (pulsing period 10 ms) , 100 W (pulsing period 2 ms).

Several classes of polymeric materials are found to perform adequately for blood processing, including cellulose and cellulose esters, polyamides, polysulfone, and some acrylic and polycarbonate copolymers. However, commercial cellulose, used for the first membranes in the late 1940 s, remains the principal material in which hemodialysis membranes are made. Membranes are obtained by casting or spinning a dope mixture of cellulose dissolved in cuprammonium solution or by deacetylating cellulose acetate hollow fibers [121]. However, polycarbonate-polyether (PC-PE) block copolymers, in which the ratio between hydrophobic PC and hydrophilic PE blocks can be varied to modulate the mechanical properties as well as the diffusivity and permeability of the membrane, compete with cellulose in the hemodialysis market. 

If this assumption is seriously in error, the actual mixed gas mobility selectivity of cellulose acetate may be even lower than indicated by the diffiisivity ratios in Table 20.3-1. Polymers such as cellulose acetate which are solubility selectors may tend to display plasticization-type responses in the permeability versus pressure plots such as that shown in Fig. 20.3-2h. More detailed sorption and diffiision data on a single, well-characterized film sample for this interesting system are needed badly to investigate these effects further. Understanding the principles at play in the case of cellulose acetate may permit expansion of the ranks of such solubility selecting materials for possible use as thin-film composite membranes or in blending with other, more plasticization-resistant membrane materials. 

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