reactivating dessicant
private
This *should* be a simple operation, but what is the best way to dry
large amounts (~5 lbs) of CaSO4 indicating desiccant?
The fisher catalog indicates drying at 218 C for an hour. When I've tried
this in a forced air oven, the top layer did turn blue ... a very pale
blue. I was expecting it to return to the same color as unused desiccant;
does this ever happen?
Putting the desiccant in a vacuum oven seemed to remove color,
putting it in a muffle furnace over the weekend actually charred some
of the desiccant. (all around 225 C)
To fully reactivate the dessicant, is it sufficient to dry the desiccant
from pink to any shade of blue or does it need to be returned to the
original color?
Another question dealing with drying agents.
The vacuum ovens I use pull outside air in through a desiccant
(CaSO4) pack when the vacuum is released. The desiccant is stored in a
cylinder roughly 5 cm by 15 cm. It looks the same as the drying tubes
plumbed into GC lines.
The arrangement I've been using passes air first through a layer
of desiccant, then through a layer of seives. I noticed the Fisher catalog
also shows the packs filled completely with desiccant. Is one arrangement
better then another for drying incoming air but not venting too slowly?
Any information would be appreciated,
Jon
Chopsly
private wrote in message ...
>Hi.
>
>This *should* be a simple operation, but what is the best way to dry
>large amounts (~5 lbs) of CaSO4 indicating desiccant?
>
>The fisher catalog indicates drying at 218 C for an hour. When I've tried
>this in a forced air oven, the top layer did turn blue ... a very pale
>blue. I was expecting it to return to the same color as unused desiccant;
>does this ever happen?
>
>Putting the desiccant in a vacuum oven seemed to remove color,
>putting it in a muffle furnace over the weekend actually charred some
>of the desiccant. (all around 225 C)
>
>To fully reactivate the dessicant, is it sufficient to dry the desiccant
>from pink to any shade of blue or does it need to be returned to the
>original color?
I use indicator grade silica gel as my dessicant. To reactivate, I dry the
dessicant, overnight at 140° C. This brings me back to my original starting
color. Since the color of the dessicant is generally an indicator of the
efficiency of the dessicant, a light blue color would work, but not as long
as an indicator with a deep blue color.