Sciencemadness Discussion Board

Using 3A Molecular Sieves to dry gases

Tdep - 5-12-2016 at 02:36

Is it possible to use molecular sieves to dry gasses like chlorine and ammonia? It would be useful to me if possible. I need some dry gasses, and passing large amounts of wet gas through a chemical drying agent tends to start to clump and clog up the line. I know I can get around that in some ways but the thought of using a column of sieves seems simple.

Can ammonia and chlorine stick in the pores of the sieves? Chlorine seems rather big, but ammonia seems small enough. But even more in general, if you had a big molecule, could you dry the gas stream of it with 3A sieves? It seems like obviously you can, but I can't find any note of it online really, so am I missing something?

Aqua-regia - 5-12-2016 at 03:26

I think this were A wrong way. Molecularsieves working slow, and concepted for liquid.

Sulaiman - 5-12-2016 at 05:07

oxygen concentrators use 5A or 13X zeolites/sieves to absorb nitrogen in preference to oxygen,
in the gas phase.

Dan Vizine - 12-12-2016 at 10:03

Molecular sieves are not designed for such uses.

Chlorine is best dried by bubbling through concentrated H2SO4. As with most all amines, ammonia is best preliminarily dried over sodium or potassium hydroxide. Final drying usually involves sodium metal, if it must be rigorous.

BromicAcid - 12-12-2016 at 10:10

Yes, they could be used that way but that is not a traditional use for sieves. I have used them successfully to dry nitrogen that most would have already considered 'dry'. My initial worry was that they dry somewhat slowly compared to standard drying agents for gases. However, on reflection I cannot say that is truly the case. To test our sieves would would take a standard weight of sieves and pour in a set amount of water and swirl and look at the heat of the 'reaction' to see if they were fresh enough, the heat evolution was very fast and exothermic so I suppose the hydration is somewhat fast.
Quote: Originally posted by Dan Vizine  
As with most all amines, ammonia is best preliminarily dried over sodium or potassium hydroxide. Final drying usually involves sodium metal, if it must be rigorous.


Although not the best method of preparation, ammonia does react with sodium at room temp to produce the amide.

Dan Vizine - 12-12-2016 at 15:29

Quote: Originally posted by BromicAcid  
Yes, they could be used that way but that is not a traditional use for sieves. I have used them successfully to dry nitrogen that most would have already considered 'dry'. My initial worry was that they dry somewhat slowly compared to standard drying agents for gases. However, on reflection I cannot say that is truly the case. To test our sieves would would take a standard weight of sieves and pour in a set amount of water and swirl and look at the heat of the 'reaction' to see if they were fresh enough, the heat evolution was very fast and exothermic so I suppose the hydration is somewhat fast.

Quote: Originally posted by Dan Vizine  
As with most all amines, ammonia is best preliminarily dried over sodium or potassium hydroxide. Final drying usually involves sodium metal, if it must be rigorous.


Although not the best method of preparation, ammonia does react with sodium at room temp to produce the amide.


You think molecular sieves will handle wet chlorine? Nitrogen is one thing, chlorine another.

We use sieves to dry our glovebox atmospheres to sub-ppm levels, so, yes, they can obviously dry gasses.

Sodium, or it's [final] product, sodamide, is exactly how ammonia is dried:

http://www.worldofchemicals.com/chemicals/chemical-propertie...

"It is the reagent of choice for the drying of ammonia and is also widely used as a strong base in organic chemistry, often in liquid ammonia solution"



[Edited on 13-12-2016 by Dan Vizine]