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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?

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    $\begingroup$ 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. $\endgroup$
    – Aniruddha Deb
    Oct 22, 2020 at 12:37
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    $\begingroup$ 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... $\endgroup$
    – Ivan Neretin
    Oct 22, 2020 at 12:42
  • $\begingroup$ @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. $\endgroup$
    – A. Kvåle
    Oct 22, 2020 at 16:41
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    $\begingroup$ I guess it is good to go as sold. $\endgroup$
    – Ivan Neretin
    Oct 22, 2020 at 19:28
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    $\begingroup$ 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. $\endgroup$
    – matt_black
    Oct 22, 2020 at 20:42

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In the oil and gas industry, glycols are used in a scrubber to remove water from natural gas [methane] for a number or reasons: water is very soluble in glycols, water is extracted into “dry” glycols due to equilibrium forces, and there is efficient contact between the gases and the liquid. Another huge part of the stribber is the regeneration portion of the system, the stripper – getting to the point of your question. Heat is applied to the water/glycol mixture after having been in contact with the “wet” methane, driving off the water and regenerating the sorbent, the glycol. The glycol can then be recycled. Although I have described this as a batch process, the actual process is continuous.
In an industrial setting, “throwing something away” is used as a last resort.
Below is a schematic of a glycol dehydrator and regeneration unit.

enter image description here https://www.sciencedirect.com/science/article/pii/S2352484719301039#fig1

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  • $\begingroup$ This is a good answer and my question was perhaps badly worded. I know that the triethylene glycol is circulating through the system, going through a heating process so as to evaporate away the water it had attained. Thing is, what I'm wondering about is, does the TEG need to be made anhydrous before it is even used? If I had completely normal TEG on me right now, would it work as a desiccant, or would it need to be treated like Epsom salt? $\endgroup$
    – A. Kvåle
    Oct 22, 2020 at 16:46
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    $\begingroup$ @A.Kvåle, Does the TEG need to be anhydrous before it ever used? If you purchase pure TEG with no or minimal water, then It could be use. It can be purchased from Aldrich as 99% pure. sigmaaldrich.com/catalog/product/aldrich/… $\endgroup$
    – Hal
    Oct 22, 2020 at 17:28
  • $\begingroup$ Then again, when you have a factory with a huge scrubbing facility, you don't buy from Aldrich. $\endgroup$
    – Ivan Neretin
    Oct 22, 2020 at 19:27
  • $\begingroup$ Correct, as a scientist in the laboratory Aldrich might be a place to start. In a refinery TEG by the tank car load might be needed, The point of the Aldrich comment was to show that 99% TEG was available on the market and would not need dehydration to begin with. $\endgroup$
    – Hal
    Oct 22, 2020 at 19:47

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