Rejuvenating desiccants in microwave oven
Greg Schmitz
Has anyone had any experience rejuvenating desiccants like Drierite or
silica gel in a microwave? Can it be done? I don't have easy access to
any other kind of oven here at CU (art history).
Thanks!
greg schmitz
gw...@columbia.edu
Note: My appoligies if this question does not belong in sci.chem. I
am not a regular reader of this group, but it seemed a logical place
to crosspost too. Reponses to technical questions in rec.photo have
in the past ben few.
Rob Toreki
gw...@ciao.cc.columbia.edu (Greg Schmitz) writes:
>
> Has anyone had any experience rejuvenating desiccants like Drierite or
> silica gel in a microwave? Can it be done? I don't have easy access to
> any other kind of oven here at CU (art history).
As long as you haven't used any noxious/toxic chemicals with what you
were drying, you can go ahead and dry it in your regular oven at home.
I'd try about 300 degrees F to start. If you have the indicating kind
of Drierite it makes things easy. Silica gel should also be no
problem. If you have used either of these for drying something other
than photo gear etc. I'd stop by the chemistry department and ask to
use their oven.
Professor Robert Toreki
Department of Chemistry
University of Kentucky
Lexington, KY 40506-0055
Paul Rubin
Greg Schmitz <gw...@ciao.cc.columbia.edu> wrote:
>
>
>Has anyone had any experience rejuvenating desiccants like Drierite or
>silica gel in a microwave? Can it be done? I don't have easy access to
>any other kind of oven here at CU (art history).
The usual technique is to use a conventional oven.
A microwave doesn't sound so good.
John De Armond
gw...@ciao.cc.columbia.edu (Greg Schmitz) writes:
>
> Has anyone had any experience rejuvenating desiccants like Drierite or
> silica gel in a microwave? Can it be done? I don't have easy access to
> any other kind of oven here at CU (art history).
Microwave works like a champ. It heats fast, dries fast and quits heating
when the desiccant is dry. A dedicated microwave is a fixture in every
nuclear plant instrumentation lab where scads of desiccant is dried
on a regular basis. The drying process can greatly be speeded up if
an aux fan is fitted to the over to speed the air changes inside the oven
but that's not really necessary.
John
--
John De Armond, WD4OQC, Marietta, GA j...@dixie.com
Performance Engineering Magazine. Email to me published at my sole discretion
Respect the VietNam Vet, for he has survived every attempt by this country
to kill him.
Ian Russell Ollmann
>
>
>silica gel in a microwave? Can it be done? I don't have easy access to
>any other kind of oven here at CU (art history).
>
>Thanks!
>
>greg schmitz
>gw...@columbia.edu
We dry mol. sieves in the microwave. It works fine, but you've got to
watch them, they actually can get hot enough to glow and fuse together.
Be nice and don't dry these sort of things in a microwave used for food. I
think we had someone dry silica that way too. If you don't have a
microwave for chemicals, just take your stuff over to the Chem building.
Any of the organic chemistry labs will not doubt let you put it in one of
their ovens overnight since they are probably on all the time anyway for
just that sort of thing.
Ian
Dominic Ryan
: In article <309jae$g...@apakabar.cc.columbia.edu> gw...@ciao.cc.columbia.edu (Greg Schmitz) writes:
: >
: >
: >Has anyone had any experience rejuvenating desiccants like Drierite or
: >silica gel in a microwave? Can it be done? I don't have easy access to
: >any other kind of oven here at CU (art history).
: >
: >Thanks!
: >
: >greg schmitz
: >gw...@columbia.edu
: We dry mol. sieves in the microwave. It works fine, but you've got to
: watch them, they actually can get hot enough to glow and fuse together.
There was a series of papers a number of years ago, one of which was in
JOC, quantitating the drying of lots of solvents by various methods
including sieves. They used tritiated water to follow the process. My
point is that one of the series discussed in detail the treatment of
sieves. It would seem that they are relatively delicate, to the extent
that heating them over 250C can virtually destroy any dessicant ability.
The amount of water taken up by the sieves falls off *drastically* over
that temperature. At the same time, they do need to be activated by
heating under vacuum to somewhere between 180C and 250C.
It is important to place them under vacuum while heating, if you don't you
won't get rid of the water. When you microwave them I would be the
trapped water in the interstitial spaces is what gets you so hot, In any
case though, glowing red suggests to me you just killed the sieves.
Sorry I don't recall those papers anymore, but they are must reading for
anyone dealing with dry solvents and intert-atmosphere techniques. (A
past life experience :-).
___________________________________________________________________________
M. Dominic Ryan (610)-270-6529 SmithKline Beecham Pharmaceuticals
Internet: ryan%phmms...@sb.com King of Prussia, PA
Bruce Hamilton
>There was a series of papers a number of years ago, one of which was in
>JOC, quantitating the drying of lots of solvents by various methods
>including sieves. They used tritiated water to follow the process. My
>point is that one of the series discussed in detail the treatment of
>sieves. It would seem that they are relatively delicate, to the extent
>that heating them over 250C can virtually destroy any dessicant ability.
>The amount of water taken up by the sieves falls off *drastically* over
>that temperature. At the same time, they do need to be activated by
>heating under vacuum to somewhere between 180C and 250C.
It's a couple of years since I posted the complete list of these papers.
The Author is David R. Burfield, and the series was called
"Dessicant efficiency in Solvent Drying". Part Nos = *x*
1. J. Org. Chem. v42, n18, 1977, p3062-3065 *1*
2. J. Appl. Chem. Biotechnol. 1978, v28, p23-30 *2*
3. J. Org. Chem. v43, n20, 1978, p3966-3968 *3*
4. Chem. Ind. (London) 15/3/1980, p240-241
5. J. Chem. Tech. Biotechnol. 1980, v30, p491-496 *4*
6. J. Org. Chem. 1981, v46, p629-631 *5*
7. J. Chem. Ed. 1982, v59, n8, p703-704 *6*
8. J. Org. Chem. 1983, v48, p2420-2422 *7*
9. J. Chem. tech. Biotechnol. 1984, v34A, p187-194 *8*
10. J. Org. Chem. 1984, v49, p3852-3854 *9*
>It is important to place them under vacuum while heating, if you don't you
>won't get rid of the water. When you microwave them I would be the
>trapped water in the interstitial spaces is what gets you so hot, In any
>case though, glowing red suggests to me you just killed the sieves.
Yes, heating Mole sieves too high will kill them. We rountinely use a GC
oven, with the molesieves in a quickfit conical flask with a drechsel top
( with ptfe threadseal tape on the ground-glass joint ). we just run the
nitrogen carrier gas through the sinter and vent it outside. Heating to
250C overnight will dry 500gms of MS. Leave carrier flowing as they cool
down - which does take a while as they are ceramics.
Another interesting trick to demonstrate how non-uniform microwave ovens
are is to coat a glass TLC plate with self-indicating silica gel. Pre-wet the
plate and then watch as parts turn pink-blue over time.
>Sorry I don't recall those papers anymore, but they are must reading for
>anyone dealing with dry solvents and intert-atmosphere techniques. (A
>past life experience :-).
Exactly - every organic chemist should read Burfield's papers. He also
wrote a neat little piece on the myth of oven dryng glassware in J. Chem.
Ed. " Oven Drying of Volumetric Glassware" which showed that calibration
of pipettes and volumetric flasks was retained up to 320C, and suggested
that 110C was OK. Unfortunately my copy just has the page no ( 1054 ),
but the other author was Glenn Hefter. I don't dry my volumetric
glassware in an oven, but it's nice to know that I can.
Bruce Hamilton
Nate Zieske
: In article <309jae$g...@apakabar.cc.columbia.edu>
: gw...@ciao.cc.columbia.edu (Greg Schmitz) writes:
: >
: > Has anyone had any experience rejuvenating desiccants like Drierite or
: > silica gel in a microwave? Can it be done? I don't have easy access to
: > any other kind of oven here at CU (art history).
: As long as you haven't used any noxious/toxic chemicals with what you
: were drying, you can go ahead and dry it in your regular oven at home.
: I'd try about 300 degrees F to start. If you have the indicating kind
: of Drierite it makes things easy. Silica gel should also be no
: problem. If you have used either of these for drying something other
: than photo gear etc. I'd stop by the chemistry department and ask to
: use their oven.
We tried drying desiccants in an oven and found that it just sticks
together in a giant clump. We reccomend the microwave, stirring every
5-10 minutes.
Nate
U of Mich
Allen Johnson
with the indicating (blue->pink) type. I ran the microwave at full power
with the desicant spread in a thin layer over the bottom of a ceramic plate
for 40 to 90 seconds, and then waited for the water vapor to dissipate (withh
the door open), and then heated again. The gell should go to a bright blue,
if indicating. If not, then placing a cold glass in the vicinity of the
gell should show condensation if the gell is still generating steam.
I have seen condensation at the start, before the plate is heated by
the steam.
Allen.
Paul WOOLMER
Ludwig Stuart
> There was a series of papers a number of years ago, one of which was
> including sieves. They used tritiated water to follow the process.
> sieves.
> past life experience :-).
and Reagent Drying. 7. Alcohols. David Burfield and Roger Smithers.
I don't know if its still avail., another good ref. is JT Baker Product
Information Bulletin, Desiccants (9/9/70)
Aldrich has a Tech. Info. Bull. #AL-134 Handling Air-Sensitive Reagents
which they stick in all their 'sure-seal' packing.
--Bill
__________________________GREETINGS FROM____________________________
L. William (Bill) Stuart Burroughs Wellcome Co.
oc...@bwco.com Organic Chemistry Division
Raleigh & Research Triangle Park, North Carolina USA
____________________________________________________________________
standard disclaimer: "Opinions expressed are my own & do not
represent those of my employer"
==========================have a nice day!==========================
Mr Richard Stowell
: >Has anyone had any experience rejuvenating desiccants like Drierite or
: >silica gel in a microwave? Can it be done? I don't have easy access to
: >any other kind of oven here at CU (art history).
: The usual technique is to use a conventional oven.
: A microwave doesn't sound so good.
Microwave works fine. I use it all the time. Use about 50% power
setting and 5-10 minutes to give the water time to be driven out. Make
sure you use a pyrex or burn proof dish. The silica gel gets HOT.
MA k.l.
it but I always scare that it is no good to my health because I use
microwave to cook a lot.
John Vinson
>Do you think it will harm your health when doing this? I would like to do
>it but I always scare that it is no good to my health because I use
>microwave to cook a lot.
by ingestion (unless you eat it by the spoonful). If you just wipe the oven
with a damp sponge after regenerating the dessicant you should have no problem.
OTOH, what are you drying? If the dessicant has adsorbed organic solvents or
other materials from whatever you're drying, they could contaminate the oven.
But I wouldn't worry about the dessicants themselves.
John
Wysard of Information
Joe Cali
kle...@cs.concordia.ca writes:
In article <CtAso...@newsflash.concordia.ca> MA k.l.,
kle...@cs.concordia.ca writes:
>Do you think it will harm your health when doing this? I would like to
do
>it but I always scare that it is no good to my health because I use
>microwave to cook a lot.
>
The common silica gel which is blue when dry and pink when wet contains a
cobalt chloride indicator. I certainly would not place it in my
microwave oven and nuke it. Silica gel is a hydrated silicate ie it has
structural water. To rejuvenate silica gel, place it in a tray spread
thinly. Cover with a towel and place in a conventional oven at about 100
degrees celcius = 212 degrees Farenheit or even less. Super heating in
microwaves is totally unnecessary. When the gel turns blue again (40-60
minutes) it's dehydrated and ready to use.
Joe Cali