# where can I find experimental compressibility factor values?

I am interested in experimental compressibility factors for various gases, such as methane and carbon monoxide. Not only for standard pressures and room temperature, but in a range from 1 to a few 1000 bars and various temperatures. Where can I get them? I've done a quick google search, but they seem to be well hidden.

EDIT: Perhaps a better question is where can I find second, third, fourth, fifth... virial coefficient for these 2 gases? I am interested at 2 temperatures: 200 K and 287 K. I found some so far, but not at 287 K.

• Googled "compressibility factor of methane", got this as first hit encyclopedia.airliquide.com/Encyclopedia.asp seems to have data you need for CH4 and CO as well as a ton of other gases. Seems like not every gas has compressibility factor info but at least for CH4 and CO it's there – orthocresol Aug 25 '16 at 9:12
• Perhaps I am being dumb, but it only states the Z at 1 atm which is of little use to me, because I am interested at Z from 1-1000 bar. – sanjihan Aug 25 '16 at 9:53
• Oh, I see, that's different then. – orthocresol Aug 25 '16 at 9:57
• Virial coefficients and compressiblity factors differ when calculated by different gas equations. – Akshar Gandhi Aug 25 '16 at 11:29
• Why don't you just use the law of corresponding states and modifications thereof, based on reduced temperature, reduced pressure, and ascentric factors. This is in practically every thermo book. – Chet Miller Aug 25 '16 at 12:03

The NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) is a program that can calculate the thermodynamic and transport properties of some important fluids and their mixtures. It was developed by the National Institute of Standards and Technology (NIST) and is commercially available as NIST Standard Reference Database 23 here.

For example, the following selected results have been obtained with REFPROP Version 9.0. The number of digits is set to the default value (5 digits), which are not necessarily significant.

Methane
Temperature: 200.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99369
2nd Virial Coef.: −0.0065173 m³/kg
3rd Virial Coef.: 0.000015219 (m³/kg)²

Methane
Temperature: 287.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99802
2nd Virial Coef.: −0.0029520 m³/kg
3rd Virial Coef.: 0.000010232 (m³/kg)²

Carbon monoxide
Temperature: 200.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99739
2nd Virial Coef.: −0.0015501 m³/kg
3rd Virial Coef.: 0.0000035524 (m³/kg)²

Carbon monoxide
Temperature: 287.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99952
2nd Virial Coef.: −0.00040865 m³/kg
3rd Virial Coef.: 0.0000027781 (m³/kg)²

REFPROP can also be used to plot the results, for example for carbon monoxide:

• This is great. Is there an option to also get the 4th and 5th virial coefficient? And if so, do you mind posting it? – sanjihan Aug 25 '16 at 12:47
• @sanjihan I can only find the second and third coefficient in REFPROP. I guess, in general, the value for the fourth coefficient is rarely available. – Loong Aug 25 '16 at 12:59
• @sanjihan You might also be interested in the book Virial Coefficients of Pure Gases and Mixtures. (I did not check the content.) – Loong Aug 25 '16 at 13:00