Assistance Needed On Calculating Hydrogen Gas Volume

[ooiuniscience]

Dear all and respective expert,

Good days to everyone! Hope everyone are doing great!

I'm conducting watersplitting reaction to generate hydrogen. The H2 gas generated after 1 hour reaction will be cumulated at headspace (volume headspace = 10ml) and the H2 gas will be transferred into online-GC by using peristaltic pump for quantification.

The sample loop volume of GC is 1ml and the measured-hydrogen concentration in that 1ml sample loop after calibrate with known-standard gas is 100ppm. Can I determine the “TOTAL AMOUNT OF H2 GAS GENERATED IN 10ml HEADSPACE” in such a way (which is proportional):

TOTAL AMOUNT OF H2 GAS GENERATED IN 10ml HEADSPACE = 10ml x 100ppm / 1ml

P/s corrects me if I’m no correct.

Hopefully anyone of you can shed a light on this base on your expertise.

Jeff Ooi

[chromatographer1]

If I understand your situation from your explanation correctly (and I have been known to fail) it appears you are meaning hydrogen in matrix of air saturated with water vapor and calibrating the hydrogen content of the headspace with a standard containing hydrogen in an unknown matrix.

While it is possible the errors in dealing with non-ideal gases may not be LARGE (>30% ?) they may be larger than you wish to claim as an accurate determination in the total hydrogen in your 10mL of headspace. Assuming the sampling of the headspace is proportional then you should be able to claim an amount of hydrogen has been generated.

The assumption is of course, you are dealing with ideal gases which you are not, by the way.

best wishes,

Rod

[ooiuniscience]

If I understand your situation from your explanation correctly (and I have been known to fail) it appears you are meaning hydrogen in matrix of air saturated with water vapor and calibrating the hydrogen content of the headspace with a standard containing hydrogen in an unknown matrix.

While it is possible the errors in dealing with non-ideal gases may not be LARGE (>30% ?) they may be larger than you wish to claim as an accurate determination in the total hydrogen in your 10mL of headspace. Assuming the sampling of the headspace is proportional then you should be able to claim an amount of hydrogen has been generated.

The assumption is of course, you are dealing with ideal gases which you are not, by the way.

best wishes,

Rod

Hi Rod,

Thanks for your time in responding.

My reactor headspace is indeed composed of water vapor, Hydrogen gas, Oxygen gas and Nitrogen gas (as matrix that have identical purity with my GC carrier gas).

Yes, i agree with you the possible error due to non-ideal gas would be large. But a lot of hydrogen researchers also conduct their measurement at 15Degree Celsius and 1 atm. Then if i used Dalton partial pressure law (P1V1=P2V2) to calculate do you think is it valid?

Hope to hear your comments.

[chromatographer1]

If you can calibrate using a known concentration std in a similar matrix with a TCD , or you have an HID which is fairly uniform in its sensitivity to different gases on a molar basis, and you know the pressure, temperature, and the volume of the reactor contents before you sample it and reduce the pressure to 1 ATM at the time of injection of a known volume in your sample loop, then you should be able to calculate the amount of hydrogen in your reactor as you have described.

Good luck,

Rod