About Pervaporation

سه شنبه, 26 خرداد 1394 نوشته شده توسط  Admin In Weblog

Pervaporation is derived from the two processes of permeation of water or an organic through a membrane and then evaporation to the vapor phase. Pervaporation is used in many industries, such as chemical and food process


The most important part of Pervaporation is the membrane. Membranes select one of the phases and passes it through. This means one the other phase would be richer over time. Although the other phase does pass through the membranes also but the transport rate for this phase would be lower.  This transport rate would define the term of “selectivity” of the membrane which is a very important factor in membrane manufacture and design. Two values characterize a membrane:

• selectivity 

• The permeate flux across the membrane


The driving force for the transport of one component through the membrane is by means of chemical potential difference of permeate (v) and the feed (l)/retenate. “The retentate is the remainder of the feed leaving the membrane feed chamber, which is not permeated through the membrane. The chemical potential can be expressed in terms of fugacity, given by Raoult's law for a liquid and by Dalton's law for (an ideal) gas. During operation, due to removal of the vapor-phase permeate, the actual fugacity of the vapor is lower than anticipated on basis of the collected (condensed) permeate.” (From Wikipedia)

Raising the temperature in the liquid feed side would help the permeate component and thus increases membrane flux so in most Pervaporation processes the feed stream is heated and then is driven to the membrane module. Permeation of one component would cause temperature loss so the feed liquid should be re heated. Some pervaporation devices have internal heating devices like steam coils or heating elements and others have external heat exchangers that are in line with the circulation of the feed and keeps up the temperature at a desired level. Pervaporation devices also use vacuum pumps to reduce pressure on the permeate side of the membranes to remove the permeate side and to increase flux. To trap the permeate condensers are used which mainly reduce temperatures as low as -150 degrees with liquid nitrogen.

Vapor permeation: 

Vapor permeation is not that different from Pervaporation and it is governed by the same rules, yet 

Using vapor instead of liquid would actually help the flux and selectivity by a reasonable degree. 


خواندن 341446 دفعه آخرین ویرایش در چهارشنبه, 17 تیر 1394 ساعت 15:32
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