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I have a gaseous mixture (air) at a temperature of approximately 30 degrees Celsius in which the following gases are present:

  • Oxygen 0 - 25%
  • Carbon Dioxide 0 - 20%
  • Methanol 0 - 100 ppm?
  • Ethanol 0 - 100 ppm?
  • Ethylene 0 - 20 ppm

I want to measure the concentration of each of the gases individually. That is not a problem with Oxygen and Carbon Dioxide but becomes a problem with methanol, ethanol and ethylene because of the cross sensitivity most sensors have for these gases.

Methanol and Ethanol are in liquid state at the temperature of 30 degrees Celsius. In the air the Ethanol and Methanol is present as vapor.

Would it be possible to design a 'scrubber' in which we bubble the air mixture through a container of for example liquid methanol to get rid of the methanol vapor and sequentially through a container of liquid ethanol to get rid of the ethanol vapor.

I can imagine that ethanol might also dissolve in the methanol liquid? And another issue would be the volatility of the ethanol and methanol liquid since we want to prevent new vapor getting into the air stream after the scrubbing.

Do you think this would be a feasible direction to investigate further? Another way to go would be to scrub it through water maybe? If we would be able to separate those two gasses we would then be able to determine all the concentrations individually by measuring the original air mixture and the scrubbed air mixture with two different sensors.

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    $\begingroup$ A scrubber made by passing the gas through the liquids will probably increase their concentration in the gas. $\endgroup$
    – matt_black
    Commented Jul 17, 2023 at 17:10
  • $\begingroup$ Thanks for your reply. I was indeed wondering what the effect would be and thought it could go either way depending on the ratio between volatility and mass transfer. I am a bit rusty on this subject so thanks again for helping me out. $\endgroup$
    – DenmarkViking
    Commented Jul 18, 2023 at 6:12

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Try a trap filled with a high boiling point liquid, such as glycerol or propylene glycol, which would absorb the organic gases... but would require periodic replacement or heating to drive off vapors.

If you are not concerned by the slight increase in $\ce{CO2}$ that this would create, and if there is sufficient oxygen, a hot mesh of copper, or better, of a platinum metal, would catalytically oxidize the three contaminants.

Also, a cold trap, e.g. with Peltier cooling, could greatly decrease ethanol and methanol, though it would not decrease low-boiling ethylene.

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  • $\begingroup$ Thank you for your answer. I will look into the cold trap method. To be able to measure the gasses individually it is important that we only extract methanol and ethanol. By measuring both the original gas mixture and the mixture without ethanol and methanol we can then determine the ratio of the different elements in de original mixture. We have found one PID sensor that is responsive to ethylene and ethanol but not to methanol and we can use an electrochemical sensor that is responsvie to all three gasses. $\endgroup$
    – DenmarkViking
    Commented Jul 18, 2023 at 6:07

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