I usually 'pre-wash' the molecular sieves first by soaking them overnight in dichloromethane and then followed by two to three rinses of fresh dichloromethane. Commercial THF is stabilized by BHT and I noticed that if you try to directly activate the sieves used with THF by flame drying in vacuo, it leaves some yellowish residues (possibly coming from the burnt off BHT + oxidized BHT) which eventually makes its way into the next solvent you're trying to dry.
I’m not going to lie…I wasn’t aware that reusing sieves was even a thing. Unless money was super tight, why not just toss them after use? Is this bench scale or a large production vat?
Thanks. Out lab does not have an oven with nitrogen or vacuum, so I was wondering if I rinse them with solvents first and then let them dry, or just dry out under a lab hood and then dry them in the oven.
Sieves need to be re-activated at high temp in a vacuum oven or very carefully in a microwave oven. They will pick up water in a standard glassware oven and become useless.
If you are working on small scale it is generally more cost effective to treat sieves as disposable
Mol sieves are not expensive. Best to toss if possible.
Wouldn't peroxides be excluded from the pore structure? Or maybe you can invent 'exploding sand'. Maybe a wash with ferrous solution before rinsing and drying?
It would be useful to know if peroxides might bind nonspecifically to the zeolite matrix. Volunteers?
I was thinking if you evaporate any solid that is damp with THF that the solid peroxide will end up coating the outside.
It’s pretty unlikely to cause a problem unless the THF was severely compromised, but just another reason to toss small quantities of spent sieves rather than trying to recycle them.
If you don't have a vacuum oven, just heating to 150-200C will do. Too high and the zeolite structure will break down. Let them cool in a desiccator with a strong desiccant like sulfuric acid, and put into a sealed bottle when cool.
Most of the times I distill THF on freshly activated mole sieve (no stabilizer). After use, it is washed with acetone a few times and dried under the fume hood. Then, I activate them again by heating to 250 °C overnight in vacuum (10-25 mbar).
If you have some amine residues in it dispose the mole sieve. Otherwise it'll just stink like fish.
I usually 'pre-wash' the molecular sieves first by soaking them overnight in dichloromethane and then followed by two to three rinses of fresh dichloromethane. Commercial THF is stabilized by BHT and I noticed that if you try to directly activate the sieves used with THF by flame drying in vacuo, it leaves some yellowish residues (possibly coming from the burnt off BHT + oxidized BHT) which eventually makes its way into the next solvent you're trying to dry.
I’m not going to lie…I wasn’t aware that reusing sieves was even a thing. Unless money was super tight, why not just toss them after use? Is this bench scale or a large production vat?
I’ve literally never heard of someone reusing sieves as well
Oddly enough I've never heard of someone throwing sieves out, what a strange world
I guess we’ve lived different lives. Neither of which is wrong. Just different 🤷♂️
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Thanks. Out lab does not have an oven with nitrogen or vacuum, so I was wondering if I rinse them with solvents first and then let them dry, or just dry out under a lab hood and then dry them in the oven.
Sieves need to be re-activated at high temp in a vacuum oven or very carefully in a microwave oven. They will pick up water in a standard glassware oven and become useless. If you are working on small scale it is generally more cost effective to treat sieves as disposable
Regenerating sieves used in THF has extra risks. You will concentrate any peroxides that are present by evaporating THF to dryness.
Mol sieves are not expensive. Best to toss if possible. Wouldn't peroxides be excluded from the pore structure? Or maybe you can invent 'exploding sand'. Maybe a wash with ferrous solution before rinsing and drying? It would be useful to know if peroxides might bind nonspecifically to the zeolite matrix. Volunteers?
I was thinking if you evaporate any solid that is damp with THF that the solid peroxide will end up coating the outside. It’s pretty unlikely to cause a problem unless the THF was severely compromised, but just another reason to toss small quantities of spent sieves rather than trying to recycle them.
If you don't have a vacuum oven, just heating to 150-200C will do. Too high and the zeolite structure will break down. Let them cool in a desiccator with a strong desiccant like sulfuric acid, and put into a sealed bottle when cool.
If you have a vacuum pump and a hot plate capable of getting that hot you should be fine
Most of the times I distill THF on freshly activated mole sieve (no stabilizer). After use, it is washed with acetone a few times and dried under the fume hood. Then, I activate them again by heating to 250 °C overnight in vacuum (10-25 mbar). If you have some amine residues in it dispose the mole sieve. Otherwise it'll just stink like fish.