Azeotropic mixtures may be broken by membrane distillation

✍ Scribed by H. Udriot; A. Araque; U. von Stockar

• Book ID: 103955694
• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 693 KB
• Volume: 54
• Category: Article
• ISSN: 0923-0467
• DOI: 10.1016/0923-0467(93)02814-d

✦ Synopsis

The feasibility of removing water from azeotropic mixtures is explored. Akhough the selectivity of membrane distillation processes is largely determined by vapor liquid equilibria (VLE), differences in diffusion rates across the membrane and an eventual additional gas gap may shift the selectivity away from unity, the value expected for azeotropes. Experiments in a plate-and-frame membrane distillation module, with azeotropic mixtures of HCl&.O and of propionic acid/H20, yielded retention selectivities of the solute between 0.6 and 0.8. They could be decreased by increasing the length of the diffnsion path, but the permeation flnx decreased also. For the HCl/HaO system, the apparent azeotropic point in membrane distillation was shifted to higher acid strength, whereas it disappeared altogether for the propionic acid/ water system. Prelkinary design considerations indicate that membrane clWhation might be utilized analogously to pervaporation in order to break azeotropes, and that membrane distillation might complement pervaporation for mixtures with higher water contents.