Easy and Efficient Drying of Molecular Sieve and Silica Gel Pellets.

Everyone probably has had the experience of working in a lab and being told the importance of that dry solvent and yet the bottle with the magical molecular sieve at the bottom just gets topped up and no one can seem to remember it ever being regenerated, right? Maybe it's time to regenerate those pellets!

3A zeolite ceramic molecular sieve pellets used for solvent drying in the EM lab can only absorb so much water and then need to be heated to 250C to regenerate by driving off the water. Most lab ovens are rated 1 to 2 kW and barely get to 250C. This is both marginal for drying and wastes a lot of energy to bake out a small volume of sieves. The baking is very easily accomplished using a heating mantle driven by a Variac (Variable AC Autotransformer) or some other power control device. Every lab/department seems to have both of these items lurking in back corners. For the 380 Watt Heating Mantle shown, the Variac set to "60" gives the right temperature; measure once with a thermocouple placed in the molecular sieve to find the proper setting and it should remain the same for that heating mantle..


Operation Notes.

Heating Mantle with cover

Heating Mantle showing aluminum cup with silica gel

A "Variac", or Variable AC autotransformer to control input power to the heating mantle. The heating mantle shown above required a setting of "60" (about half of line voltage) to reach 260C.

Dale A. Callaham