Separation in dialysis is due to concentration gradient and is used for the separation of small solutes from large synthetic or biological macromolecules. The membrane material retains larger molecules due to steric reasons, while the smaller solutes freely diffuse through the membranes, eventually leveling out concentration differences. If the osmotic pressure is different between the two phases, solvent molecules will also diffuse through the membrane, to reach equilibrium. Dialysis is used primarily in the treatment of patients with renal failure and also in the separation ofproteins and other macromolecules from salts in pharmaceutical and biochemical applications.

Figure 13.10 Pervaporation assembly.
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