Monthly Science: Silica Gel Regeneration

Last month’s basement safe log showed the humidity (blue trace) relentlessly rising:

Replacing that bag emptied the dried silica gel stash, so I piled six saturated bags in the oven for an overnight regeneration with the oven set to “Warm”, which the IR thermometer reported as 140 °F or so at the bag surface. They sat on cooling racks atop cookie sheets that pretty much filled two oven shelves, with good air flow across their tops and minimal flow between bags and cookie sheet.

The last time around, I spread the beads directly on the cookie sheets. That seemed like a lot of effort, so I wanted to see how the low-labor alternative worked.

The two upper-left bags in each group had a pair of bulldog clips holding them closed. The larger bags hold 500 g of “dry” silica gel and the center bag in the lower row was a smaller mesh bag:

The big bags lost a bit under 130 g during 10 hours, call it 12 g/h, and felt slightly damp on their lower surface.

I cranked the oven to 230 °F, the lowest actual heat setting, for 210 °F on the bag surface. That got rid of the last 30 g in three hours; another hour brought them to pretty nearly their dry weight of 507 g (gross, with bag / staples / clips).

Drying being an exponential process, it looks like an overnight bake at “230 °F” will do the trick without melting the bags; the lower temperature doesn’t quite get the job done.