Denitrated cellulose membrane

Example 3.4.5 Calculate the membrane mass-transfer coefficients and the permeability coefficients of two solutes, sodium sulfate and sucrose, through a microporous light denitrated cellulose membrane whose properties, along with those of the two solutes, are provided below (Lane and Higgle, 1959). The temperature is 20 °C, and dilute aqueous solutions are under consideration with essentially no convection through the membrane. For sodium sulfate M = 142 diffusion coefficient in water = 7.7 x 10 cm /s density />, = 2.698 g/cm. For sucrose Mj = 342 diffusion coefficient in water =... 

Through a microporous denitrated cellulose membrane, the separation factor for two solutes, sodium sulfate and sucrose, has to be determined for the case of simple diffusion with no convection. The properties of the membrane, the operating conditions and the solute properties are available in Example 3.4.5. 

The membrane is critically important in osomometry. Selection of a membrane involves reconciliation of high permeability toward the solvent with virtual impermeability to the smallest polymer molecules present in the sample. Membranes of cellulose are most widely used. Commercially Regenerated cellulose film is a common source. The undried gel cellophane film is often preferred, but the dry film may be swollen in water (or in aqueous solutions of caustic or zinc chloride ) to satisfactory porosity. Useful cellulose membranes may also be prepared by denitration of nitrocellulose films/ and special advantages have been claimed for bacterial cellulose films. The water in the swollen membrane in any case may be replaced by a succession of miscible organic solvents ending with the one in which osmotic measurements are to be made. Membranes of varying porosity may be... 

The substances generally used as osmotic membranes include collodion (nitrocellulose of 11-13.5 per cent nitrogen) regenerated cellulose, obtained by denitration of collodion gel cellophane that has never permitted to dry after manufacture bacterial cellulose, obtained by the action of certain strains of bacteria rubber, poly (vinyl alcohol) polyurethances poly (vinyl butyral) and polychlorotrifluoroethylene. At present gel cellophane is most widely used. 

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