Pervaporation is a method for the separation of mixtures of liquids by partial vaporization through a non-porous membrane. ... Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... An artificial membrane, also called a synthetic membrane, is a membrane prepared for separation tasks in laboratory and industry. ...

Theory

The membrane acts as a selective barrier between the two phases, the liquid phase feed and the vapor phase permeate. It allows the desired component(s) of the liquid feed to transfer through it by vaporization. Typically, the upstream side of the membrane is at ambient pressure and the downstream side is under vacuum to allow the evaporation of the selective component after permeation through the membrane. The fractionation process is mainly due to polarity differences, and not to the volatility difference of the components in the feed. The word is derived from the two basic steps of the process, firstly the permeation through the membrane by the permeate, then its evaporation into the vapor phase. This process is used by a number of industries for several different processes, including purification and analysis, due to its simplicity and in-line nature. Evaporation is the process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. ... The polarity of an object is, in general, its physical alignment of atoms. ... Membrane introduction mass spectrometry (MIMS) is a method of introducing analytes into the mass spectrometers vacuum chamber via a permeable membrane. ... In-line expansion or inlining for short is a compiler optimization which expands a function call site into the actual implementation of the function which is called, rather than each call transferring control to a common piece of code. ...

The driving force for transport of different components is provided by a chemical potential difference between the liquid feed/retentate and vapor permeate at each side of the membrane. 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. It should be noted that 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. Separation of components (e.g. water and ethanol) is based on a difference in transport rate of individual components through the membrane. This transport mechanism can be described using the solution-diffusion model, based on the rate/ degree of dissolution of a component into the membrane and its velocity of transport (expressed in terms of diffusivity) through the membrane, which will be different for each component and membrane type leading to separation.

Pervaporation is effective for diluting solutions containing trace amounts of the component to be removed. Based on this, hydrophilic membranes are used for dehydration of alcohols containing small amounts of water and hydrophobic membranes are used for removal/recovery of trace amounts of organics from aqueuous solutions. Pervaporations is a very mild process and hence very effective for separation of those mixtures which can not survive the harsh conditions of distillation. The adjective hydrophilic describes something that likes water (from Greek hydros = water; philos = friend). ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ...

Applications

• Solvent Dehydration: dehydrating the ethanol/water and isopropanol/water azeotropes
• Continuous water removal from condensation reactions such as esterifications
• Membrane introduction mass spectrometry

Esterification is the general name for a chemical reaction in which two chemicals (typically an alcohol and an acid) form an ester as the reaction product. ... Membrane introduction mass spectrometry (MIMS) is a method of introducing analytes into the mass spectrometers vacuum chamber via a permeable membrane. ...

External links

• www.membrane-guide.com suppliers, products, news and facts for engineers involved in the design or the operation of pervaporation systems.