Jacketed dessicant

Wondering everyones opinion on heating a jacketed filter dryer. I’ve heard opposing theories… Getting a jacketed spool for one isn’t that much more but I’m wondering if anyone thinks its not necessary? Also size… Anyone think too big is ever too big/counter productive?

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We use a 3" jacketed spool for our filter dryer (BizzyBee style), works great!

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How long of a spool? I thought Ive seen some of bizzy that are like 6x48!

How often are you replacing your beads?

I think my spool is like 3" by 24"/36" or something like that. We regenerate every 5-6 columns/runs or so. Replace beads or regenerate in oven every couple months.

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Cool. Still just curious. Some people say heating it with the jacket is just releasing the moisture… some say it helps it absorb the moisture.

We heat it with the jacket while pulling full vacuum to regenerate the beads.

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How hot are you going though when heating the jacket to reactivate your sieve beads. I Have read that you need to be at like 250-300C when doing a normal cook of them then into a vac oven for an hour under full vac. I feel we aren’t reaching hot enough temps when cooking in the jacket. Also how long are you heating and pulling vac when doing this.

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same here, we remove the beads and regen them @400 f for an hour. After the beads are regenerated we cool them under vaccum, then they are loaded into the filter dryer.

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I’ve read that too but never felt the need to do it. 180-200F at full vac for a couple hours in the spool seemed to work well enough. We’ve opened it up and tested the beads and verified that they are still active many times as well. Full change out or true regen in oven every couple months seems to be sufficient for our process.


How are you testing them?

Couple things you can do:

  1. Keep indicator beads at the top, so you can visually check for color change/etc.
  2. Place a small quantity of beads on a gloved hand, and add roughly two volume equivalents of water. If the sieves are fully active they will become too hot to hold, even through the glove.
  3. Can weigh the beads before/after vacuum drying. Just to see how much moisture you had left. We often see there is almost no loss in weight at 450F at full vac overnight.

We find it easier to have multiple desiccant tubes pre-packed and sealed so we can swap them out very quickly and just keep running. The spent tubes can be emptied out and dehydrated in a vacuum oven under heat once they have been swapped out with the spare.

Personally I would assume that the increased heat while under operation would make it harder for the beads to trap the gas, as the gas would have more energy to escape…

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From the fifth edition of Purification of Laboratory Chemicals, Armarego and Chai,

Molecular sieves:
Molecular sieves are types of adsorbents composed of crystalline zeolites (sodium and calcium aluminosilicates). By heating them, water of hydration is removed, leaving holes of molecular dimensions in the crystal lattices. These holes are of uniform size and allow the passage into the crystals of small molecules, but not of large ones.
This sieving action explains their use as very efficient drying agents for gases and liquids. The pore size of these sieves can be modified (within limits) by varying the cations built into the lattices. The four types of molecular sieves currentlyavailable are:

Type 3A sieves. A crystalline potassium aluminosilicate with a pore size of about 3 Angstroms. This type of molecular sieves is suitable for drying liquids such as acetone, acetonitrile, methanol, ethanol and 2-propanol, and drying gases such as acetylene, carbon dioxide, ammonia, propylene and butadiene. The material is supplied as beads or pellets.

Type 4A sieves. A crystalline sodium aluminosilicate with a pore size of about 4 Angstroms, so that, besides water, ethane molecules (but not butane) can be adsorbed. This type of molecular sieves is suitable for drying chloroform, dichloromethane, diethyl ether, dimethylformamide, ethyl acetate, cyclohexane, benzene, toluene, xylene, pyridine and diisopropyl ether. It is also useful for low pressure air drying. The material is supplied as beads, pellets or powder.

Type 5A sieves. A crystalline calcium aluminosilicate with a pore size of about 5 Angstroms, these sieves adsorb larger molecules than type 4A. For example, as well as the substances listed above, propane, butane, hexane, butene, higher n-olefins, n-butyl alcohol and higher n-alcohols, and cyclopropane can be adsorbed, but not branched-chain C^ hydrocarbons, cyclic hydrocarbons such as benzene and cyclohexane, or secondary and tertiary alcohols, carbon tetrachloride or boron trifluoride. This is the type generally used for drying gases, though organic liquids such as THF and dioxane can be dried with this type of molecular sieves.

Type 13X sieves. A crystalline sodium aluminosilicate with a pore size of about 10 Angstroms which enables many branched-chain and cyclic compounds to be adsorbed, in addition to all the substances removed by type 5A sieves.

They are unsuitable for use with strong acids but are stable over the pH range 5-11.
Because of their selectivity, molecular sieves offer advantages over silica gel, alumina or activated charcoal, especially in their very high affinity for water, polar molecules and unsaturated organic compounds. Their relative efficiency is greatest when the impurity to be removed is present at low concentrations. Thus, at 25° and a relative humidity of 2%, type 5A molecular sieves adsorb 18% by weight of water, whereas for silica gel and alumina the figures are 3.5 and 2.5% respectively. Even at 100° and a relative humidity of 1.3% molecular sieves adsorb about 15% by weight of water.
The greater preference of molecular sieves for combining with water molecules explains why this material can be used for drying ethanol and why molecular sieves are probably the most universally useful and efficient drying agents. Percolation of ethanol with an initial water content of 0.5% through a 144 cm long column of type 4A molecular sieves reduced the water content to lOppm. Similar results have been obtained with pyridine.

The main applications of molecular sieves to purification comprise:

  1. Drying of gases and liquids containing traces of water.
  2. Drying of gases at elevated temperatures.
  3. Selective removal of impurities (including water) from gas streams.
    (For example, carbon dioxide from air or ethene; nitrogen oxides from nitrogen; methanol from diethyl ether. In general, carbon dioxide, carbon monoxide, ammonia, hydrogen sulfide, mercaptans, ethane, ethene, acetylene (ethyne), propane and propylene are readily removed at 25°. In mixtures of gases, the more polar ones are preferentially adsorbed).

The following applications include the removal of straight-chain from branched-chain or cyclic molecules. For example, type 5A sieves will adsorb n-butyl alcohol but not its branched-chain isomers. Similarly, it separates n- tetradecane from benzene, or n-heptane from methylcyclohexane.
The following liquids have been dried with molecular sieves: acetone, acetonitrile, acrylonitrile, allyl chloride, amyl acetate, benzene, butadiene, w-butane, butene, butyl acetate, n-butylamine, /i-butyl chloride, carbon tetrachloride, chloroethane, l-chloro-2-ethylhexane, cyclohexane, dichloromethane, dichloroethane, 1,2- dichloropropane, 1,1-dimethoxyethane, dimethyl ether, 2-ethylhexanol, 2-ethylhexylamine, n-heptane, n-hexane, isoprene, isopropyl alcohol, diisopropyl ether, methanol, methyl ethyl ketone, oxygen, n-pentane, phenol, propane, n-propyl alcohol, propylene, pyridine, styrene, tetrachloroethylene, toluene, trichloroethylene and xylene. In addition, the following gases have been dried: acetylene, air, argon, carbon dioxide, chlorine, ethene, helium, hydrogen, hydrogen chloride, hydrogen sulfide, nitrogen, oxygen and sulfur hexafluoride.
After use, molecular sieves can be regenerated by heating at between 300°-350° for several hours, preferably in a stream of dry inert gas such as nitrogen or preferably under vacumm, then cooling in a desiccator. Special precautions must be taken before regeneration of molecular sieves used in the drying of flammable solvents. However, care must be exercised in using molecular sieves for drying organic liquids. Appreciable amounts of impurities were formed when samples of acetone, 1,1,1-trichloroethane and methyl-f-butyl ether were dried in the liquid phase by contact with molecular sieves 4A (Connett Lab Pract 21 545 7972). Other, less reactive types of sieves may be more suitable but, in general, it seems desirable to make a preliminary test to establish that no unwanted reaction takes place. Useful comparative data for Type 4A and 5A sieves are in Table 19. (from pages 28-29)

n-Butane [106-97-8] M 58.1, m -135°, b -0.5°. Dried by passage over anhydrous Mg(ClO4)2 and molecular sieves type 4A. Air was removed by prolonged and frequent degassing at -107°. (from page 143)

Link to download the book,


Cool. That makes sense to me as well, thats why I was confused on the topic. What size do you use? Im thinking about going 4x24 or 36

We’ve been using two 2"x36" tubes, one for each master vapor pump on each unit. Engineers from the manufacturer always recommended using a narrower longer tube because the gas’ tendency to flow in a laminar fashion would mean that the desiccant around the outer edges of the tube wouldn’t saturate evenly.

I’ve always been of the position that a 4" tube would do just fine though and that it would expand to fill the cavity well enough to saturate the desiccant around the outer edges and would be open to using larger ones though…

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That does make sense… Im sure there a certain point where bigger isn’t always better. Im currently 2x12 but I want to mount it on a rack so I can go bigger. Running dual cmep I’m wondering if I should do a 2x36 each…

I’d say that’s not a bad plan.

i’m running 3x24 dryers. replaced every 20 tubes of wet, or 60 dry tubes 4x48.


What tempature would you have your molecular sieve jacket set to while actively recovering from roughly 30psi.

I use the same warm water circulator that is on my collection base.

so 78-100F depending on how gently I’m blowing/how much of a hurry I’m in.

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