Chromatography Forum

Hello,

I need to elute the target gases H2S, CO2 and H2O in the shortest time possible in presence of the natural gas interferents with their typical concentrations. The target gases will be used for detection in our new sensor.

Can you please suggest GC column to elute these target gases from the interferents using filtered air as the career gas since there will be no N or He at the customer site.?

Anadi Mukherjee, anadi@infrasign.com; (510) 815 3365

Before somebody can give you a reply, we will need to know if the non-target gases will interfere with your sensor.

Gasman

Yes, that is why we need to separate the target gases from the interferents.

You want to measure water, H2S, and CO2 in natural gas, correct?

You realize that unless you can dry the air to extremely low levels your carrier (air) will contain both CO2 and water in significant amounts (CO2 is presently about 400 ppm in air, for example) Water can vary from day to day, from weather system to weather system.

Can you use multidimensional chromatography?

If not, can you program the temperature of the oven?

I assume your sensor can tolerate the hydrocarbons passing over them. If not then you will have to heartcut the three peaks from the hydrocarbon components of natural gas, but you will still have hydrocarbon ramp peaks from your heartcuts to deal with.

Give the forum more information concerning your limitations of your detector and any restrictions of your carrier gas purification system before we go any further with this discussion.

best wishes,

Rod

Rod,

Thanks a lot for your message. Yes, we will dry the air as mush as possible, then measure the H2O and CO2 present in the air using our sensor before the air is used as a career gas. That way we can find out how much of these gases are present in the natural gas.

Yes, we will heartcut the three peaks we we measure only these from the hydrocarbon components of natural gas interferents given below. What would be a practical concentration values of the residual hydrocarbons after heartcut ?

Interferent Molecular % Range
Carbonyl Sulfide (COS) 100ppm
Methyl Mercaptan (MESH) 100ppm
Methane 75%
Ethane 6%
Propane 3%
Iso-butane 0.5%
n-Butane 1%
Iso-Pentane 0.2%
n-Pentane 0.2%
Hexanes 0.2%

Thanks again for your great help,

Cheers,
Anadi

Rod,

I would like to do the gas separation in the shortest time possible.

Yes, I can computer control the temperature of the oven.

Which process will be faster, Multidimensional Chromatography or changing temperature of the oven ?

Thanks again.

Cheers,
Anadi

You will need a two column heartcut - backflush configuration with an isothermal oven. I suggest using the N or A or R porous polymer bead packed columns, probably a 2-4 ft column and a 4-8 ft column.

The exact lengths will be determined by experiment. I am guessing a 2ft with a 6 ft column would be a place to start.

You of course will not be using metal columns due to reactivity of the H2S and the water with the metal.

By adjusting the polarity of the polymer and the temperature of the oven you may be able to heartcut the water and the H2S with one cut, and have a second cut for the CO2. Then use a less polar PP bead column to separate the H2S and the water after the heartcut.

I would start with temperatures of 90C and using the N polymer for your columns.

The water peak will shift in relation to the H2S peak as the temperature changes. I would stay in the 60-120C range. Somewhere 80-100C should be about the right temperature.

Good luck with your research and let us know what happens.

Rod

Rod,

That was a great help - I will let you know how it goes. Thanks again.

Cheers,
Anadi

h

Hydrogen is highly inflammable !

Hello,

Have you considered to use portable Micro GC to have the complete separation within less then 2 minutes, using for example Argon as carrier gas ?

Roger

Roger,
This is not about a end user or a lab but a company making an instrument.

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There is a whole different set of parameters required in this situation.

Rod

Very interesting, Rod

Thanks for this detail

Rgds
Roger