The answer is rather complex. First of all I should know if you would like to prepare membranes for a particular mixture, or do you have a particular polymer which is going to be investigated .

At the industrial level composite membranes with a dense PVA (few micrometers) layer are used. This layer is prepared by the plasma polymerization. 

At the lab scale (testing different polymers) you can used phase inversion technique with the evaporation of solvent (so called dry phase inversion or thermally induced). You can use also much more advanced techniques (see Rafik Karaman's answer) but I guess it is not a case.

I suggest you also to read some of my papers (most of them are available on RG) and book by Mulder (Basic Principles of Membrane Technology) or Strathmann (Introduction to Membrane Science and Technology).

If you need some additional information, please don't hesitate to contact me.

Good luck,

Wojciech Kujawski

Dear Soheila,

The following technique is most suitable for membrane fabrication in Pervaporation ( dehydartion) Process: 

Dry–wet phase inversion technique (Loeb-Sourirajan method); A number of

methods can be used to achieve phase inversion. Among these, the dry–wet phase inversion technique and thermally induced phase separation (TIPS) are the most commonly used in membrane manufacturing. The dry–wet phase inversion technique, also called the Loeb-Sourirajan technique, was used by Loeb and Sourirajan in their development of the first cellulose acetate membrane for seawater desalination. In this method, a polymer solution is prepared by mixing polymer and solvent (sometimes even nonsolvent). The solution is then cast on a suitable surface by a doctor blade to a precalculated thickness. After a partial evaporation of the solvent, the cast film is immersed in a nonsolvent medium called a gelation bath. Due to a sequence of two desolvation steps, i.e., evaporation of the solvent and solvent–nonsolvent exchange in the gelation bath, solidification of the polymer film takes place. It is desirable to choose a solvent of strong dissolving power with a high volatility. During the first step of desolvation by solvent evaporation, a thin skin layer of solid polymer is formed instantly at the top of the cast film due to the loss of solvent. In the solvent– nonsolvent exchange process that follows, the nonsolvent diffuses into the polymer solution film through the thin solid layer while the solvent diffuses out. The change in the composition of the polymer solution film during the solvent–nonsolvent exchange process, often called a composition path, 

The top skin layer can also be made porous by lowering the polymer concentration

in the casting solution and the solvent evaporation period. This is called, hereafter,

the porous skin layer. Asymmetric membranes can also be made in a tubular

form using a casting bob assembly and a hollow fiber spinneret.

Thermally induced phase separation method In this method, phase inversion is

introduced by lowering the temperature of the polymer solution. A polymer is mixed

with a substance that acts as a solvent at a high temperature and the polymer solution is cast into a film. When the solution is cooled, it enters into an immiscible region due to the loss of solvent power. Because the solvent is usually nonvolatile, it must be removed with a liquid that is miscible with the solvent but not miscible with the polymer.

For more details on other kinds of membranes, please use the following link:

file:///C:/Users/Rafik%20Karaman/Downloads/9783540739937-c1.pdf

Hoping this will be helpful,

Rafik

Hi Soheila,

it depends on the feed mixture, polymer to prepare membrane, PV temperature, feed concentration etc. Generally, for pervapration dense membranes are used, since transport is via solution diffusion. Preparing membranes by phase inversion will result in porous membranes, in order to prepare dense membrane you have to go for high polymer concentration which might reduce the fluxes.

You can better choose polymer by looking at your feed mixture. Different polymers sch as Polyvinylalcohol, sodium alginate, chitosan could be used to prepare membranes.

you can prepare either dense membranes by solution casting or composite membrane by dip, spin, spray coating on the porous support.

You can also make membranes by interfacial polymerization. 

I hope you have an idea now.

Good luck.

The answer is rather complex. First of all I should know if you would like to prepare membranes for a particular mixture, or do you have a particular polymer which is going to be investigated .

At the industrial level composite membranes with a dense PVA (few micrometers) layer are used. This layer is prepared by the plasma polymerization. 

At the lab scale (testing different polymers) you can used phase inversion technique with the evaporation of solvent (so called dry phase inversion or thermally induced). You can use also much more advanced techniques (see Rafik Karaman's answer) but I guess it is not a case.

I suggest you also to read some of my papers (most of them are available on RG) and book by Mulder (Basic Principles of Membrane Technology) or Strathmann (Introduction to Membrane Science and Technology).

If you need some additional information, please don't hesitate to contact me.

Good luck,

Wojciech Kujawski

Hello Soheila,

Are you looking for making a membrane, or are you searching for a membrane for a dehydration process?

For the last case maybe we can help you. please take a look at our web site.

If you need any more help, please let me know.

Regards, Frans Velterop, Pervatech BV

As  Wojciech Kujawski said the answer for your question is very complex,its depend upon what feed mixture are going to separate,additionally, you can used some hydrophobic membrane if your feed mixture is very diluted.In that case membrane fabrication method can be change such as if used some PDMS type of membrane,so better you decide your feed water concentration first.

For pervaporation separation dense membrane is required. In case of dehydration,hydrophilic polymer like poly(vinyalalochol) is used to prepare dense membrane. On the basis of structure dense membrane are of two types (1) Self supported membrane:It will be prepared by evaporation casting. (2) Supported membrane :In this method firstly porous support are prepared by the dry-wet immersion technique.This prepared support is coated with dense hydrophilic polymer layer by dip-coating or evaporation casting.This type of membrane use to decrease the mass transfer resistance of the membrane to enhance the flux without compromising selectivity.

Please note that in both case cross-linking reaction of dense membrane required to stabilized the membrane during swelling.