Hi all
I am trying to get a known standard of methanol-air mixture which is saturated at room temperature. In my experiment trials using 125ml gas bubbler with methanol pool of 50 ml, I get different concentrations of methanol samples collected into teddler bags at 10 , 20, 30 , 45 min, All of these are unsaturated mixtures when analysed by GC-TCD. My question is about, when this process will reach steady state and when will my GC-TCD show me a constant area peak for methanol? Also how do i ensure saturation of air with methanol?
Thanks in advance.
Hi.
First, I would drop the Tedlar bags. They are well known for not storing methanol (and other volatiles) properly. I have experienced it myself and it's described in the literature. See for example: https://pubs.acs.org/doi/full/10.1021/es950582y?src=recsys
If your goal is to saturate air with methanol, then you could pipette into a vial and seal it. Wait a couple of hours after you start seeing condensates on the walls and analyse the headspace. Do this for some vials and analyse them after different time intervals and you will know when you reached equilibrium.
For indication, the vapour pressure of methanol at 25 C is about 18 kPa. You can use liquid injections of known amounts of methanol and compare the peak area with the gas samples. Don't forget to use Raoult's law for correction of the presence of water in the air.
Cheers!
Thanks for the article for reference and suggestions too.
I want to send this steady state mixture of methanol-air of fixed concentration that is coming out from the bubbler to a reactor at controlled flow-rates. I want it to be a continuous process and in such case, when do we ensure steady state if not equilibrium, is my question. In my experiments, I see the concentration of methanol in air reducing with time. I want to know the reason.
Thanks
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