Physical properties, heating values, and vapor pressures for common hydrocarbons.
| Component | MW | Tc(°F) | Pc(psia) | SG | ω |
|---|---|---|---|---|---|
| Methane | 16.04 | -116.6 | 666.4 | 0.300 | 0.011 |
| Ethane | 30.07 | 90.1 | 706.5 | 0.356 | 0.099 |
| Propane | 44.10 | 206.0 | 615.0 | 0.507 | 0.152 |
| i-Butane | 58.12 | 274.9 | 527.9 | 0.563 | 0.181 |
| n-Butane | 58.12 | 305.6 | 548.8 | 0.584 | 0.200 |
| i-Pentane | 72.15 | 369.1 | 490.4 | 0.625 | 0.227 |
| n-Pentane | 72.15 | 385.7 | 488.6 | 0.631 | 0.252 |
| n-Hexane | 86.18 | 453.7 | 436.9 | 0.664 | 0.301 |
| n-Heptane | 100.2 | 512.8 | 396.8 | 0.688 | 0.350 |
| n-Octane | 114.2 | 564.2 | 360.6 | 0.707 | 0.399 |
| Component | MW | Tc(°F) | Pc(psia) | SG | ω |
|---|---|---|---|---|---|
| Nitrogen | 28.01 | -232.5 | 493.0 | 0.809 | 0.037 |
| CO₂ | 44.01 | 87.9 | 1070.6 | 0.818 | 0.274 |
| H₂S | 34.08 | 212.7 | 1306.0 | 0.784 | 0.090 |
| Water | 18.02 | 705.4 | 3206.2 | 1.000 | 0.344 |
| Helium | 4.00 | -450.3 | 32.9 | 0.138 | -0.390 |
| Hydrogen | 2.02 | -399.9 | 187.5 | 0.071 | -0.216 |
| Oxygen | 32.00 | -181.4 | 731.4 | 1.141 | 0.022 |
| Air | 28.96 | -221.3 | 546.7 | 1.000 | 0.035 |
| Component | HHV (Btu/scf) | LHV (Btu/scf) | HHV (MJ/m³) | LHV (MJ/m³) |
|---|---|---|---|---|
| Methane | 1010 | 909 | 37.7 | 33.9 |
| Ethane | 1770 | 1619 | 66.1 | 60.4 |
| Propane | 2520 | 2315 | 94.0 | 86.4 |
| i-Butane | 3253 | 3002 | 121.3 | 112.0 |
| n-Butane | 3262 | 3011 | 121.7 | 112.4 |
| i-Pentane | 4001 | 3699 | 149.3 | 138.0 |
| n-Pentane | 4011 | 3709 | 149.7 | 138.4 |
| n-Hexane | 4756 | 4404 | 177.4 | 164.3 |
| Hydrogen | 325 | 275 | 12.1 | 10.3 |
| Component | A | B | C | Range (°F) |
|---|---|---|---|---|
| Methane | 6.61184 | 389.93 | 436.03 | -296 to -117 |
| Ethane | 6.80266 | 656.40 | 433.65 | -183 to 90 |
| Propane | 6.82973 | 813.20 | 432.48 | -44 to 206 |
| n-Butane | 6.83029 | 945.90 | 428.61 | 31 to 306 |
| n-Pentane | 6.85296 | 1064.84 | 426.25 | 97 to 386 |
| n-Hexane | 6.87601 | 1171.17 | 423.87 | 156 to 454 |
| Water | 8.07131 | 1730.63 | 402.57 | 32 to 212 |
| Abbreviation | Description | Units |
|---|---|---|
| MW | Molecular Weight | lb/lbmol |
| Tc | Critical Temperature | °F |
| Pc | Critical Pressure | psia |
| SG | Specific Gravity (gas relative to air @ 60°F) | dimensionless |
| ω | Acentric Factor (Pitzer) | dimensionless |
| HHV | Higher Heating Value (gross) | Btu/scf or MJ/m³ |
| LHV | Lower Heating Value (net) | Btu/scf or MJ/m³ |
Critical Point (Tc, Pc): The temperature and pressure at which liquid and vapor phases become indistinguishable. Above Tc, no amount of pressure can liquefy the gas. Critical properties are essential for equation of state calculations (Peng-Robinson, SRK).
Molecular Weight (MW): Mass per mole of substance. Used for converting between mass and molar flow rates, and calculating gas density.
Specific Gravity (SG): Ratio of gas density to air density at standard conditions (60°F, 14.7 psia). For liquids, relative to water at 60°F. Used in flow calculations and pipeline sizing.
Acentric Factor (ω): Pitzer's factor measuring how much a molecule's behavior deviates from simple spherical molecules (like noble gases). Higher values indicate more complex molecular shapes or polarity. Used in cubic equations of state.
Heating Values: HHV (Higher/Gross) includes latent heat of water vapor condensation. LHV (Lower/Net) assumes water remains as vapor. Use HHV for sales gas contracts; LHV for combustion efficiency calculations.
Source: GPSA, NIST Chemistry WebBook