Dialysis Dialysis Dialysis uses a semipermeable membrane to separate species by virtue of their different diffusion rates in the membrane. The feed solution or dialyzate, which contains the solutes to be separated, flows on one side of the membrane and the solvent or diffusate stream on the other side. Some solvent may diffuse across the membrane in the opposite direction, which reduces the performance by diluting the dialyzate. In practice it is used to seperate species that differ appreciably in size, which have a reasonably large difference in diffusion rates.
Solute fluxes depend on the concentration gradient in the membrane.
Hence, dialysis is characterized by low flux rates, in comparison to other membrane processes, such as reverse osmosis and ultrafiltration, membrane processes that depend on applied pressure. A common type of equipment configuration used in liquid membrane processes is the flat plate, which is similar to a filter press. Vertical solid membranes are placed in between alternate liquor and solvent feed frames, with the liquor to be dialyzed being fed to the bottom and the solvent to the top of these frames. The dialyzate and the diffusate are removed through channels located at the top and bottom of the frames, respectively. The most important type consists of many small tubes or very fine hollow fibers arranged in a bundle like a heat exchanger.