Liquid Ethylene Density Calculator

Compute the temperature-dependent mass density, specific volume, and batch weight of saturated cryogenic liquid ethylene (ethene, C2H4) across industrial boiling and storage regimes using calibrated thermodynamic state correlations.

Technical Guide to Liquid Ethylene Density & Cryogenic States

Ethylene (IUPAC name: ethene, chemical formula C2H4) is the foundational monomer of modern organic chemistry and industrial plastics manufacturing, serving as the essential precursor to high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene dichloride, and polyester precursors. Under ambient atmospheric conditions of 20 degrees Celsius and 101.325 kilopascals, pure ethylene is a colorless, highly flammable gas lighter than air. Consequently, industrial supply chains compress and refrigerate the fluid into a cryogenic liquid state to achieve high bulk storage density for marine transport, rail shipments, and pipeline buffer vessels.

Liquid ethylene exists across a finite thermodynamic window bounded by its triple point temperature of -169.15 degrees Celsius (104.00 Kelvin) and its critical temperature of 9.20 degrees Celsius (282.35 Kelvin). Within this cryogenic operating range, the physical density of liquid ethylene varies significantly as a function of temperature. Accurate density data is indispensable for process custody transfer metering, relief valve sizing, marine carrier boil-off management, and slurry polymerization reactor feed control.

Mathematical Formulation: The Modified Rackett Model

Saturated liquid densities of pure hydrocarbons are accurately determined through the Rackett equation of state, an established empirical thermodynamic model formulated for liquids along their vapor-liquid coexistence curve:

Density (rho) = A / ( B ^ ( 1 + ( 1 - T / Tc ) ^ D ) )

Where the parameters are defined as:

rho: Liquid mass density in kilograms per cubic meter (kg/m3) or grams per cubic centimeter.
T: Operating temperature in Kelvin (K).
Tc: Critical temperature of ethylene, standardized at 282.35 Kelvin (9.20 degrees Celsius).
A: Critical density parameter (214.15 kg/m3).
B: Rackett compressibility constant Zra, calibrated for ethylene at 0.2818.
D: Scaling exponent, evaluated at 0.2857 (or 2/7).

For molar-volume evaluations, the Rackett equation solves for molar volume (Vm) using the universal gas constant (R = 8.31446 J/(mol·K)), critical pressure (Pc = 50.42 bar), and critical temperature (Tc = 282.35 K). Dividing the molecular weight of ethylene (28.054 g/mol) by the resulting molar volume yields mass density directly.

Key Reference States for Liquid Ethylene

Engineers and bulk logistics operators rely on three primary benchmark states:

Normal Boiling Point (-103.7 degrees Celsius / 169.45 Kelvin): At standard 1 atmosphere pressure, saturated liquid ethylene has a density of approximately 568.6 kg/m3 (35.50 lb/cu ft). This serves as the worldwide shipping benchmark for insulated cryogenic ocean vessels.
Triple Point Limit (-169.15 degrees Celsius / 104.00 Kelvin): Coexistence of solid crystals, liquid, and vapor at 0.0012 bar. Density reaches its maximum liquid value of approximately 654.7 kg/m3 (40.87 lb/cu ft) due to cold thermal contraction.
Critical Point (9.20 degrees Celsius / 282.35 Kelvin): At 50.42 bar absolute pressure, the meniscus separating liquid and gas disappears. The density reaches the critical value of 214.2 kg/m3 (13.37 lb/cu ft). Above this temperature, liquid ethylene cannot exist regardless of applied pressure.

Step-by-Step Instructions: How to Use the Tool

Enter the Process Temperature: Type your target temperature into the liquid temperature input box. Select your desired input unit: Celsius (°C), Kelvin (K), or Fahrenheit (°F).
Set the Batch Volume (Optional): If you need to determine the total mass in a storage sphere, tank car, or pipeline section, enter the volume and choose cubic meters, liters, US gallons, or cubic feet.
Choose the Phase Assumption: Select either saturated liquid coexistence or normal boiling equilibrium.
Click Calculate: Click the solid green Calculate button. The tool executes the Rackett model, checks for sub-critical temperature validity, and displays both the primary density and an itemized engineering conversion table.
Reset or Export: Use the Reset button to clear inputs, Share to send the link, or Print to isolate and format the calculation onto a single A4 sheet.

Industrial Applications in Process Engineering

Accurate liquid ethylene density computation is essential across chemical processing facilities:

Marine Cargo Loading & IGC Code Compliance: The International Gas Carrier (IGC) Code mandates that liquefied gas tanks must never become liquid-full during transit. Marine surveyors compute the maximum allowable filling limits using the calculated liquid density at the design relief valve pressure.
Pipeline Custody Transfer: Ethylene is bought and sold on a mass basis (metric tons or pounds). Coriolis or ultrasonic flow meters record volumetric throughput, which process computers multiply by live calculated density to generate commercial billing data.
Polymerization Reactor Feed Systems: In HDPE slurry loop reactors and high-pressure LDPE autoclaves, monomer mass feed rates dictate polymer melt index and chain branching. Facilities employ live density conversions alongside our Molar Mass Calculator and Density Calculator.
Boil-Off Gas (BOG) Compression: Heat ingress into insulated cryogenic storage tanks causes continuous vaporization. Plant engineers model phase equilibria using the Clausius-Clapeyron Equation Calculator to size re-liquefaction compressor loops.

Frequently Asked Questions (FAQ)

1. What is the density of liquid ethylene at its normal boiling point?

At its atmospheric boiling point of -103.7 degrees Celsius (-154.7 degrees Fahrenheit) under 101.325 kPa, pure saturated liquid ethylene has a density of approximately 568.6 kilograms per cubic meter (0.5686 g/cm3 or 35.50 pounds per cubic foot).

2. Can ethylene be liquefied at room temperature?

No. Ethylene cannot exist as a liquid at room temperature (20 to 25 degrees Celsius) under any amount of applied pressure because its critical temperature is 9.20 degrees Celsius (48.56 degrees Fahrenheit). Above this temperature, it exists exclusively as a supercritical fluid or dense gas.

3. Why does liquid ethylene density drop significantly near 9 degrees Celsius?

As liquid ethylene approaches its critical temperature of 9.20 degrees Celsius, thermal kinetic energy causes large volumetric expansion. The liquid expands until its density matches the vapor phase density at the critical point (214.2 kg/m3).

4. What is the specific volume of liquid ethylene?

Specific volume is the mathematical inverse of mass density (1 / density). At ethylene's normal boiling point of -103.7 degrees Celsius, the specific volume is approximately 0.001759 cubic meters per kilogram (1.759 liters per kilogram or 0.02817 cubic feet per pound).

5. Does liquid ethylene float on water?

Yes. Saturated liquid ethylene has a density between 560 and 655 kg/m3 across its cryogenic envelope, making it significantly less dense than liquid water (1,000 kg/m3). In the event of a surface spill, it floats while boiling rapidly.

6. How does subcooling affect liquid ethylene density?

Subcooling increases density in two ways: lowering the liquid temperature causes thermal contraction, while applying mechanical pressure above the saturation pressure compresses the liquid, producing small additional density gains.

7. What is the molecular weight of ethylene used in density conversions?

The molecular weight of ethylene (C2H4) is 28.054 grams per mole, comprising two carbon atoms (approximately 12.011 g/mol each) and four hydrogen atoms (approximately 1.008 g/mol each).

8. Why is ethylene transported at cryogenic temperatures rather than under pressure at ambient temperature?

Because ethylene's critical temperature is 9.2 degrees Celsius, keeping it liquefied at ambient temperatures is impossible without crossing into supercritical regimes requiring thick-walled vessels rated above 50 bar. Refrigerated transport at -104 degrees Celsius near atmospheric pressure allows light, economical cargo tanks.

9. What is the Rackett equation?

The Rackett equation is an empirical thermodynamic formulation that relates saturated liquid molar volume to critical temperature, critical pressure, and a compound-specific compressibility factor along the vapor-liquid saturation curve.

10. What is the lowest temperature at which liquid ethylene can exist?

The lowest temperature is the triple point of ethylene at -169.15 degrees Celsius (104.00 Kelvin), where solid, liquid, and vapor phases coexist in equilibrium. Below this temperature, ethylene freezes solid.