Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.


%mol - CO2

%mol - CO2

Struggling with some very basic composition math...

I'm looking to calculate the percentage of CO2 in a volume flow based on %mol CO2.

Information is as follows:

Rate: 128,865 Nm3/hr
Composition (vol%): 4.3%mol CO2


Is it as simple as 128,865 * .043 =5,541 Nm3/hr - CO2.

Which can than be converted to kg/hr as follows:

5,541 Nm3/hr * 1977 kg/m3 ~= 10,955kg/hr

RE: %mol - CO2

Yes, it's that simple, but 1977 kg/m3 for CO2 does not make sense. From wiki:

1562 kg/m3 (solid at 1 atm and −78.5 °C)
1101 kg/m3 (liquid at saturation −37°C)
1.977 kg/m3 (gas at 1 atm and 0 °C)

See what I mean?

Good luck,

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: %mol - CO2

Thank you for the quick response.

Sorry, fat finger mistake. I was going for 1.977kg/m3.

RE: %mol - CO2

A "safer" Way would be to convert Nm3 to kmol directly and Them ude CO2 molweight to calc massflow


RE: %mol - CO2

Just to clarify. The factor 22.414 L/mol refers to an ideal gas at 1 atmosphere of pressure
and at 0 °C. At 1 bar, it would be ~ 22.711 L/mol.

RE: %mol - CO2

Disagree with your clarification (or splitting hairs dont really know), Nm3 is in reality a unit that refers to no. of mols (for any gas). A Nm3 can in really be any given number of moles since there is no universal definition, but following the most common definition: 0ºC, 0 barg (1.01325 bar a) this is 22.414 l/mol

RE: %mol - CO2

22.414 L/mol is for an ideal gas at 0 oC and 1 atm. At these conditions, the factor for CO2 is ~22.263 L/mol.

RE: %mol - CO2

@25362, and this is where i disagree. A Nm3 CO2 has the same no. mols as any other Nm3 of any other gas!

RE: %mol - CO2

Here are some examples of "real" gases at 0oC and 1 atm, conditions usually referred as normal, in L/mol:

SO2 21.856
H2S 22.187
CH4 22.361
O2 22.392
N2 22.404
Ne 22.425
H2 22.428

One can see the differences, however small, because of their cuasi-ideality at normal conditions..

RE: %mol - CO2

true, but when you refer to 1 Nm3 of SO2 you have just as many mol SO2 as when you refer to 1Nm3 of CH4 (and that would be 44.6158)

RE: %mol - CO2

Wrong! With 1 Nm3 at 0oC and 1 atm, of each gas, the numbers of moles are not the same, for example:

CH4 44.722
SO2 45.755
and for n-butane
C4H10 46.518 (in this case the deviation from ideality is more than 4%)

RE: %mol - CO2


Your statement would imply all real gases have the same Z compression factor, which is not the case.

RE: %mol - CO2

25362 is referring to actual (real) gases while MortenA refers to the ideal gas case.
Is it sunny outside? No, I want a hamburger for dinner.

Process Engineer, MSChE

RE: %mol - CO2

EmmanuelTop, MortenA postings tell a different -erroneous- story. Bon appetit!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close