i suggest  Al-Asheh et al (2004) Chemical Engineering Research and Design, 82(A7): 855–864

http://ac.els-cdn.com/S0263876204725630/1-s2.0-S0263876204725630-main.pdf?_tid=5eac43d0-eb28-11e4-9304-00000aacb360&acdnat=1429952114_b16fba7e446b3f8c2833222ddb3b5ed8

Thanks a lot for the reference 

The kinetic diameter of water molecule is 2.9 A so using molecular sieves of 3A size is good. To activate molecular sieves you have to keep them constantly at a temperature of 300-400 degrees

Muhammad,

  As already mentioned, activation of the molecular sieve will require appropriate bed temperature.   This temperature is dependent on the type of adsorbent, and also the material being adsorbed.  Enough heat has to be provided to increase the temperature of the material being adsorbed, and the adsorbent itself.  The adsorbate has to be vaporized.  For each type of adsorbent it would also be important to be mindful of the type of adsorbent material and what heating profile is desirable in order to ensure that the integrity of the adsorbent is maintained for a reasonable number of cycles.  3A, 4A, up to 13X sieves require temperatures in the range of 170 - 315 deg C.  A quick check with the supplier is recommended to ensure you are in the right range.

I would recommend 4A size molecular sieves Heated at 200 for three hours and then 400 for another three hours

Suitable methods are calcination at normal pressure or in vacuum (usually in oil-pump vacuum) http://www.sigmaaldrich.com/chemistry/chemicalsynthesis/learning-center/technical-bulletins/al-1430/molecular-sieves.html

Vacuum drying is much faster (~20 min) and need lower temperatures ( 200oC of heating bath is enough for all types)

3A-type is best, 4A is satisfactory for water

Sieves are a beautiful invention, as I’ve said before.  At 10-20% w/v, 3A molecular sieves will dry every common solvent except acetone as well or significantly better than a solvent still [1, 2].  A bottle of sieves/solvent is also far less likely to catch on fire and is far cheaper to maintain (no argon or water lines).

Unfortunately, sieves are shipped saturated with water and must be dried before use.  Sieves actually absorb water at 120 degC, so a conventional drying oven is not up to the task.

Conventional wisdom is that heating to 300 degC or greater at atmospheric pressure will dry sieves, and this temperature can be reduced somewhat under vacuum [3].  Experimentally I had some success heating to ~200 degC overnight in a vacuum oven, but was never quite sure that the sieves were fully active [4].

Holding the sieves at 350 degC for 3.5 hours is the right amount of overkill.  While this is a temperature out of reach of most drying ovens, it barely hits “medium” on the temperature setting of a glassblower’s annealing oven.