Article — Liquid Ethylene Density Calculator (kg/m³ vs Temperature)
Liquid Ethylene Density Calculator: ρ(T) from Triple to Critical Point
Liquid ethylene (C₂H₄) density ranges from 654 kg/m³ at the triple point (104 K, −169 °C) to 214 kg/m³ at the critical point (282 K, 9 °C). At the normal boiling point of −103.7 °C density is 588 kg/m³ — about 60 % of liquid water. The full curve drops sharply near T_c as liquid and vapor merge into a single supercritical fluid.
This calculator interpolates NIST saturated-liquid data across the entire liquid range. Enter temperature in °C, K, or °F. Output covers kg/m³, g/cm³, lb/ft³, plus a flag for the physical state (solid below 104 K, supercritical above 282 K).
What is liquid ethylene density?
Liquid ethylene is the condensed phase of the simplest alkene, C₂H₄, existing in a narrow window between the triple point (−169 °C) and the critical temperature (+9 °C). Its density measures how much mass packs into a given volume — essential for sizing tanks, pumps, pipelines, and heat exchangers in the petrochemical industry that produces 200 million tonnes per year.
Ethylene is the world's most-produced organic chemical. The liquid form is what tankers carry, what cracker plants discharge from cold separation, and what refrigerated trucks deliver. Density determines mass flow rate per unit pipe area and the pressure rating of every component along the way.
Liquid ethylene density formula
T_c = 282.35 K (9.20 °C)T_bp = 169.41 K (−103.74 °C)ρ_c = 214 kg/m³ρ at bp = 588 kg/m³Two correlations dominate the literature. The DIPPR equation ρ(T) = A · B^(−(1−T/T_c)^n) gives a single smooth curve fit. The Rackett equation ρ/ρ_c = Z_c^((1−T/T_c)^(2/7)) is structure-free. This calculator uses linear interpolation between NIST tabulated points — slightly more accurate near T_c, where neither correlation handles the steep gradient well.
Liquid ethylene density vs temperature
- 104 K (−169 °C, triple point) = 654 kg/m³
- 130 K (−143 °C) = 629 kg/m³
- 150 K (−123 °C) = 609 kg/m³
- 169 K (−104 °C, boiling point) = 588 kg/m³
- 200 K (−73 °C) = 548 kg/m³
- 240 K (−33 °C) = 477 kg/m³
- 260 K (−13 °C) = 422 kg/m³
- 280 K (+7 °C) = 290 kg/m³
- 282 K (+9 °C, critical point) = 214 kg/m³
The slope is mild between the triple and boiling points — about 0.5 kg/m³ per kelvin — but accelerates beyond. In the last 20 K below T_c the density nearly halves. This is the universal critical-point behavior all fluids exhibit.
Ethylene is not just an industrial feedstock — plants produce it endogenously as a gaseous hormone that triggers fruit ripening, leaf abscission, and flower senescence. The ethylene-mediated ripening of one apple in a crate can accelerate ripening across the whole shipment. Refrigerated produce containers actively scrub ethylene to delay spoilage.
Liquid ethylene near the critical point
Approaching T_c = 282 K, three things happen simultaneously. First, liquid and vapor density converge toward the critical density of 214 kg/m³. Second, surface tension drops toward zero. Third, the compressibility diverges — small pressure changes produce large volume changes.
For engineers, this critical-region behavior creates practical headaches. Pump cavitation, heat-exchanger fouling from density mismatches, and erratic level instruments all worsen near T_c. Industrial liquid-ethylene service stays well below 5 °C to keep operation in the "normal" liquid regime.
A common misconception is that enough pressure liquefies any gas. Above the critical temperature (9.2 °C for ethylene), no amount of compression produces a distinct liquid phase — only a denser supercritical fluid. To liquefy ethylene at room temperature you must first cool below 9 °C.
Storing and transporting liquid ethylene
Industrial liquid ethylene moves three ways:
Cryogenic atmospheric tanks — −104 °C, 1 to 2 bar. Standard for terminal storage and short-distance transfer. Uses double-wall vacuum-insulated tanks similar to LNG tankage.
Pressurized refrigerated tanks — 0 to 5 °C, 40 to 50 bar. The compromise for road and rail tankers. Less insulation but more steel.
Pipelines — gas phase at high pressure (60 to 90 bar) for transcontinental movement. The Gulf Coast ethylene pipeline grid handles 25 million tonnes per year.
Density at storage temperature feeds directly into tank sizing: a 5,000 m³ refrigerated tank at −100 °C holds about 2,900 tonnes; at +5 °C the same tank holds only 1,750 tonnes because density drops to ~350 kg/m³.
Liquid ethylene applications
Outside the petrochemical core, liquid ethylene serves niche roles: as a refrigerant in cryogenic chillers (between LNG and liquid nitrogen ranges), as a cryogenic coolant for low-temperature research, and as a propellant in some specialty rocket motors when paired with liquid oxygen.
Common liquid ethylene density mistakes
The frequent errors:
- Using gas density — gaseous ethylene at STP is 1.18 kg/m³, three orders of magnitude less than liquid
- Confusing with ethane or ethanol — different molecules, different densities, different boiling points
- Wrong reference state — saturation line vs subcooled vs compressed values can differ by 5 to 10 %
- Extrapolating beyond range — below 104 K ethylene is solid; above 282 K it is supercritical
- Ignoring pressure — at very high pressure (above 100 bar) liquid density rises a few percent
- Treating purity as 100 % — commercial ethylene is 99.9 %+ but contains traces of ethane and methane that alter density slightly
For quick mental estimates: liquid ethylene density in kg/m³ ≈ 590 − 1.4·(T_K − 169) over the −100 to −20 °C range. Accurate to about 5 % across that range. Beyond it use the full NIST data — the curve is too non-linear for any simple expression.
Steam crackers — the giant facilities that produce ethylene by pyrolyzing naphtha or ethane — cost 1 to 3 billion dollars each. A typical world-scale cracker handles 1.5 million tonnes per year of ethylene, which means 4,100 tonnes per day passes through the cold separation train as liquid. With density around 560 kg/m³ at typical separator conditions, that is 7,300 m³ per day of liquid — sizing tanks, pumps, and pipelines to that volumetric flow rate requires reliable density data across the full operating range.