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Critical Pressure and Temperature of common materials

Including air, ammonia, methane, water

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1. Definition of the critical point
2. Data table

1. Definition of the critical point : What is the critical point


The critical point is actually the end point of the liquid / vapor equilibrium curve. Beyond the critical point, there is no more a difference in between the liquid and vapor phase and both merge in a same phase, supercritical. Beyond the critical point, the substance becomes supercritical.

The critical point is illustrated on the graph below [1] :

Figure 1 : phase diagram showing the critical point

Note : other critical points than the liquid / vapor one exist but are less studied. Generally, when referring to the critical point, one refer to the liquid-vapor critical point.

2. Data table of critical pressure and temperature [2]
Critical pressure Pc Critical temperature Tc
Material Formula psia bar (abs) °F °c k = Cp/Cv
Acetic Acid CH3-CO-OH 841 58 612 322 1.15
Acetone CH3-CO-CH3 691 47.6 455 235 -
Acetylene C2H2 911 62.9 97 36 1.26
Air O2+N2 547 37.8 -222 -141 1.4
Ammonia NH3 1638 113 270 132 1.33
Argon A 705 48.6 -188 -122 1.67
Benzene C6H6 701 48.4 552 289 1.12
Butane C4H10 529 36.5 307 153 1.09
Carbon Dioxide CO2 1072 74 88 31 1.3
Carbon Monoxide CO 514 35.5 -218 -139 1.4
Carbon Tetrachloride CCl4 661 45.6 541 283 -
Chlorine Cl2 1118 77 291 144 1.36
Ethane C2H6 717 49.5 90 32 1.22
Ethyl Alcohol C2H5OH 927 64 469 243 1.13
Ethylene CH2=CH2 742 51.2 50 10 1.26
Ethyl Ether C2H5-O-C2H5 522 36 383 195 -
Fluorine F2 367 25.3 -247 -155 1.36
Helium He 33.2 2.29 -450 -268 1.66
Heptane C7H16 394 27.2 513 267 -
Hydrogen H2 188 13 -400 -240 1.41
Hydrogen Chloride HCl 1199 82.6 124 51 1.41
Isobutane (CH3)CH-CH3 544 37.5 273 134 1.1
Isopropyl Alcohol CH3-CHOH-CH3 779 53.7 455 235 -
Methane CH4 673 46.4 -117 -83 1.31
Methyl Alcohol H-CH2OH 1156 79.6 464 240 1.2
Nitrogen N2 492 34 -233 -147 1.4
Nitrous Oxide N2O 1054 72.7 99 37 1.3
Octane CH3-(CH2)6-CH3 362 25 565 296 1.05
Oxygen O2 730 50.4 -182 -119 1.4
Pentane C5H12 485 33.5 387 197 1.07
Phenol C6H5OH 889 61.3 786 419 -
Phosgene COCl2 823 56.7 360 182 -
Propane C3H8 617 42.6 207 97 1.13
Propylene CH2=CH-CH3 661 45.6 198 92 1.15
Refrigerant 12 CCl2F2 582 40.1 234 112 1.14
Refrigerant 22 CHClF2 713 49.2 207 97 1.18
Sulfur Dioxide SO2 1142 78.8 315 157 1.29
Water H2O 3206 221 705 374 1.32


Source
[1] Wikipedia, uploaded by Matthieumarechal
[2] Masoneilan