# Must a desiccant be made anhydrous before it can be used for drying?

I'm writing about the treatment of methane gas, and in one part of the process, the methane gas is dried in a tank called a scrubber. Here, a desiccant called triethylene glycol is used.

Thinking about another desiccant, magnesium sulfate heptahydrate (Epsom salt), the water must be taken away through evaporation before the salt can be used for drying. The chemical must be anhydrous, so that it'll steal away all the water from the object in need of drying.

However, is this the case with triethylene glycol? Must it be made anhydrous before it can be used for drying, or is its attraction to water molecules great enough to begin with?

• answering the general question, no, conc. $\ce{H2SO4}$ is a dessicant that does not need to be made anhydrous for it to have dessicating properties. Not too sure about triethylene glycol though. Oct 22 '20 at 12:37
• What are you going to do with your triethylene glycol once it consumes as much water as it can? Throw it away? No, that's not how things are done... Oct 22 '20 at 12:42
• @IvanNeretin How does my question imply that I'm under the impression the triethylene glycol must be thrown away afterwards? I know that the triethylene glycol is circulated and heated up after it has collected the water. This heating up makes the water molecules evaporate away, and then the triethylene glycol can be used again. However, my question is, before it is even used, must it be heated to the extent that all hydrates in the substance are removed, making it some kind of anhydrous triethylene glycol? Also, triethylene glycol can become toxic waste if the benzene amount is too high. Oct 22 '20 at 16:41
• I guess it is good to go as sold. Oct 22 '20 at 19:28
• All desiccants will eventually saturate at some level of water. MAny can be effective desiccants with moderate water loads below the saturation level. Few need to be completely dry to work effectively. So, no, 'anhydrous' is not usually required. Oct 22 '20 at 20:42