Author Topic: Mystery drying agent?  (Read 2343 times)

0 Members and 1 Guest are viewing this topic.

nitrous351

  • Guest
Mystery drying agent?
« on: June 24, 2003, 06:28:00 AM »
I need some help with this please... I have access to a dessiccant (free), but I don't know what it is. It comes in a rectangular, sealed brown pouch. The beads inside are off-white/grey, and some of them are blue (indicator). I know it's dessiccant because I use it in a machine to prevent ice buildup in sub-zero temperatures. The texture of the beads is a lot like chalk...they're not smooth like silica beads. I put about 200g in a plastic bucket, and poured about 200 mL of water on top. The resulting reaction was exothermic, with the evolution of a white gas (hydrogen gas). The blue beads turned grey, and the off-white beads turned brownish. Anybee have any ideas what my mystery drying agent is? If nobee can identify it, does anybee think it would be safe to try in a dream for the crystallization of mdma from xylene? Thanks...
PS- there are no labels on the pouches...just lot numbers and such.
EDIT: ok after some intense searching, I found out I have some molecular sieve 4 angstrom. I read rhodium's post on drying agents, and the links he gave, but no direct answers for this question: is this material safe to use for the crystallization in xylene? ie, will it react chemically (other than with the water?)If it can be used, do I just add it in small bits til the solution is no longer cloudy (since they're beads they won't clump) thanks peace


baalchemist

  • Guest
Why don't you just spend $2 on some epson...
« Reply #1 on: June 26, 2003, 04:30:00 AM »
Why don't you just spend $2 on some epson salts and forget that other crap.


Rhodium

  • Guest
Molecular sieves
« Reply #2 on: June 26, 2003, 04:34:00 AM »
Molecular sieves is one of the best drying agents you can get, and it is completely reusable (heat them to 250°C for 2h).
I highly reccommend it for your non-polar solvents (unless they are really wet (as in >1%), then you should pre-dry them with MgSO4 first (xylene will always have less than 1% water, or it will sink to the bottom).

The molecular sieves does not react with anything, it works because it is full of tiny pores, which are of the perfect size to trap water molecules, but not any larger organics (such as xylene). I cannot guarantee that the indicator dye will not leach, so if the beads are large enough for it to be feasible, pick out the blue beads first.

nitrous351

  • Guest
thanks...
« Reply #3 on: June 26, 2003, 06:16:00 AM »
I don't want to spend the extra $2 for salts because it's really more than $2. My time is worth something too right? If I use epsom salts, I have to put them in the oven, then break up the cake, then store them in an acetone/heat-dried jar, etc... Why go through all that when I have free access to molecular sieves, which are better? Thanks for your help Rhodium...you da man! peace


calcium

  • Guest
Preparing Mol Sieves for 1st use...
« Reply #4 on: June 26, 2003, 02:15:00 PM »
Do Molecular Sieves need to be heated prior to initial use, or just to regenerate them after they've been used? I've got a sealed 2.5 kilo container of 4A sieves which, if I'm not mistaken, are useful for drying air and non-polar solvents. 3A sieves dry alcohols. Having 3A & 4A sieves on hand, it seems, would handle most bees drying needs.
     Rhodium, thanks for the tip on pre-drying very wet solvents. If my question has been answered already I appologize, but I sure have searched high and low for info on this topic.

Rhodium

  • Guest
Pre-activation of new molecular sieves
« Reply #5 on: June 26, 2003, 03:29:00 PM »
Usually you don't need to pre-activate new sieves, unless you need to dry solvents for Grignard reactions or other organometallic purposes... It's definitely okay if you just want to use the solvents for gassing.

wyndowlicker

  • Guest
Leach!
« Reply #6 on: June 30, 2003, 07:58:00 PM »
Ive heard that they will also take in the color of your ketone,making it a  weaker yellow color.Will this have any effect on the final product? :P


Buster_Hymen

  • Guest
The way to tell if your sieves are good is to...
« Reply #7 on: July 01, 2003, 08:14:00 AM »
The way to tell if your sieves are good is to put a few in the palm of your hand and let a single drop of water fall onto them. You should feel a brief surge of heat. If the sieves are really dry, it will almost be painful, but only for a second. Don't remember who, but somebody here at the Hive (props to you!) recommended this method. I tried it, and it works. Water-saturated sieves will not create any heat when you do this.

>I've got a sealed 2.5 kilo container of 4A sieves which,
>if I'm not mistaken, are useful for drying air and non-polar solvents.
>3A sieves dry alcohols.

I don't think this is true.

The "A" means "angstroms", or wavelength (Å), and refers to the pore size of the sieve. Pore size determines which size molecules will be "sucked up".

For example, 3Å sieves are used to absorb water because the water molecule is 3Å or less in size, I believe. You would use them to remove water from solvents OR gases. Similarly, 4Å sieves would be useful for absorbing molecules that are larger than water (alcohols maybe? I'm not sure).

Somebody will correct me if I'm wrong, but I'm pretty sure you want to use 3Å sieves to remove water from anything -- solvents, free-bases, gases, etc.

nitrous351

  • Guest
shit
« Reply #8 on: July 01, 2003, 06:04:00 PM »
According to this link,

http://www.sigmaaldrich.com/Brands/Aldrich/Technical_Bulletins/AL_143/Molecular_Sieves.html

Buster is correct. I guess the 4A's would pick up water, but would the pores bee so big that they would pick up my product?


calcium

  • Guest
mol sieve info
« Reply #9 on: July 01, 2003, 09:18:00 PM »
I found the following information online concerning what can be dried with what molecular sieve... hope it helps.

-Typical Applications for Molecular Sieve


TYPE 3A: Potassium Ion with pore diameter of 3 Angstroms

ORGANIC LIQUIDS: Acetone, Acetonitrile, Methanol, Ethanol, 2-Propanol

GASES: Acetylene, Carbon Dioxide, Ammonia, Propylene, Butadiene,

Cracked Gas


TYPE 4A: Sodium Ion with pore diameter of 4 Angstroms

ORGANIC LIQUIDS: Chloroform, Dichloromethane, Diethyl Ether,

Dimethylformamide, Ethyl Acetate, Cyclohexane, Benzene, Toluene,

Xylene, Pyridine, Diisopropyl Ether

GASES: Natural Gas, Low pressure Air Drying


TYPE 5A: Calcium Ion with pore diameter of 5 Angstroms

ORGANIC LIQUIDS: Tetrahydrofuran, Dioxane


TYPE 13X: Sodium Ion with pore diameter of 10 Angstroms

GASES: Air plant feed purification to remove water and carbon dioxide simultaneously, Cracked Gas

GC_MS

  • Guest
molecular sieves
« Reply #10 on: July 09, 2003, 10:49:00 AM »
I was checking a new chem supplier for prices of 0.4 nm molecular sieves, and noticed that they offered several forms of it:

- powder
- 1.6 mm pellets
- 3.2 mm pellets
- beads (with or without moisture indicator)

Does one form offer a certain advantage over the other, or is it just another way of draining more money from clients?


Rhodium

  • Guest
mol sieves powder/pellet difference
« Reply #11 on: July 09, 2003, 11:42:00 PM »
The powder is "faster" as it has a larger surface area, but the larger pellets are easier to handle (you simply decant your solvent from these, as opposed to filter the powder off).

methyl_ethyl

  • Guest
exothermic? why
« Reply #12 on: July 10, 2003, 03:30:00 AM »
The way to tell if your sieves are good is to put a few in the palm of your hand and let a single drop of water fall onto them. You should feel a brief surge of heat. If the sieves are really dry, it will almost be painful, but only for a second

     What causes this exothermic, evolution?  I will try this first thing in the morning.  I have been wondering this for a while?  I am probably just silly.  But I can not figure what would cause the heat....  8)


Aurelius

  • Guest
Heat of hydration
« Reply #13 on: July 10, 2003, 07:37:00 AM »
the heat is caused by the formation of adducts between the sieve and water.  weak (most of the time) bonds are formed between the drying material and the water, this is how the water is held, making it possible to remove water (nearly) completely.


methyl_ethyl

  • Guest
OOOUCH!!!
« Reply #14 on: July 11, 2003, 08:56:00 PM »
Thank you, Aurelius, I just tried ~10-15 4 Angstrom seives in the palm of my hand, and dripped ~5mL of water into the palm of my hand and there was some serious heat to be felt, after about three seconds I had to fling them out of my hand it was so hot.
     I know I am easily amused,  ;)  Thanks for the lesson in heat of hydration.  Very interesting....  8)


yellium

  • Guest
Molsieves get hot for the same reason ...
« Reply #15 on: July 11, 2003, 10:27:00 PM »
Molsieves get hot for the same reason dissolving h2so4 in water (or dissolving naoh in water) is exothermic: bond formation. Formation of a lot of hydrogen bonds yields a lot of energy.