Henry’s Law Pressure Limitations

Question

I’m trying to decide if I can I expect Henry’s Law to be an effective way to estimate how the solubility of a gas in a liquid solution will change if I decrease the pressure.

I know Henry’s is best applied where temperatures are not too low, pressures are not too high, and the solute is very dilute in the liquid solution.

My application is about 40 C and very dilute in the liquid phase, so I’m not really worried about those factors as much. But the pressure is 430 psig (with the gas of interest being a large portion of that).

I know it’s different for every system, but what do we generally consider low/moderate/high pressures for ideal gas/Henry’s application? Do you think Henry’s would still be an accurate predictor here? Okay but starting to deviate a bit? Or likely quite off base?

I haven’t really found any good rules of the thumb on this. Working on getting this modeled so won’t ultimately be assuming simple proportionality for design, but just trying to do a quick check ahead of those results.

Answer 1

I believe Henry's law would be good for a rough estimate and indeed might be very accurate in your case. At your suggested pressure, though, the gas phase will likely deviate from ideality and require some correction.

For very high pressures, Krichevsky and Kasarnovsky (J. Am. Chem. Soc., 57, 2168–2171 (1935)) derived a pressure-corrected version of Henry's law that they found accurate for "nitrogen and hydrogen in water at a pressure up to 1000 atmospheres and temperatures from 0 to 100°"C. It adds another parameter (the partial molar volume of gas in liquid), values of which may or may not be available for your system of interest. The Krichevsky-Kasarnovsky equation still has the same caveats as Henry's law, except for the pressure restriction.