GY-Ethylene Oxide

Appearance and odour

 Colourless gas; a colourless clear mobile liquid under pressure; sweet, ethereal and irritating odour

 Odour threshold about 260 ppm (GHC) / 433 ppm (ITRC); far above the occupational exposure limit of 1 ppm, so odour is unreliable and must not be used to detect a leak

Melting / freezing point

approx. −111.7 °C (BASF) / −111 °C (ICSC) / −112.46 °C (literature)

At 101.3 kPa; slight differences between sources

Boiling point

10.7 °C (BASF, GHC) / 10.4 °C (ICSC, literature)

 At 101.3 kPa. The atmospheric boiling point of about 10 °C is below normal summer ambient temperature, so the substance must be kept in pressure vessels at ambient temperature

Density

 Liquid approx. 0.88 g/cm³ (20 °C); gas approx. 1.9 kg/m³

 Relative density (water = 1) about 0.88; gas density at 101.3 kPa

Vapour density

 approx. 1.52 (BASF) / 1.5 (ICSC)

 Air = 1. Heavier than air, so a leak may travel along the ground and through low-lying areas to distant ignition sources and flash back

Vapour pressure

approx. 175.2 kPa (1 752 hPa) at 20 °C (BASF) / approx. 146 kPa at 20 °C (ICSC)

 The two sources differ and both are quoted. Vapour pressure rises steeply with temperature, so storage temperature must be tightly controlled ; the pressure at 50 °C is markedly higher, so an adequate design margin is required

 Flash point

approx. −57 °C (BASF) / < −18 °C (ITRC)

The extremely low flash point means any flammable concentration at ambient temperature is far above it, which is the primary fire characteristic of the substance

Autoignition temperature

approx. 429 °C

 BASF, ICSC and the literature agree (429 °C)

Explosion limits

3 % – 99.99 % (v/v) (BASF) / 3 % – 100 % (ICSC, GB/T 13098) / 2.6 % – 100 % (GHC)

The upper limit approaches 100 %, so almost any air–vapour ratio lies within the explosive range. This is the most striking difference from other flammable gases (propylene 2 % – 11 %, butadiene 2 % – 12 %)

Critical parameters

approx. 195.8 °C / approx. 7.19 MPa

Critical density about 0.315 g/cm³. The critical temperature is comparatively low, so ambient-temperature compression liquefies the substance , and ambient-pressure liquefaction dominates storage and transport practice

Solubility in water

Miscible with water in all proportions

 BASF states "miscible"; also readily soluble in ethanol, diethyl ether, acetone, benzene and most organic solvents. Full miscibility means a spill spreads readily with water and hydrolyses slowly to ethylene glycol

Partition coefficient

 log Pow approx. −0.3

 n-Octanol / water; very low lipophilicity, with no bioaccumulation potential

Hydrolysis

Slow hydrolysis, half-life t₁/₂ 290.4 h

 At 25 °C and pH 7.4; in water the substance is eliminated mainly by hydrolysis and volatilisation , both markedly accelerated by the presence of acid or base

Other constants

 The three-membered oxygen ring is highly strained and extremely reactive; combustion products CO and CO₂

 The epoxide group is a strong electrophile and ring-opens rapidly with compounds containing active hydrogen (water, alcohols, ammonia, amines and acids); incomplete combustion markedly increases carbon monoxide formation

Stability and incompatibilities

A chemically unstable gas (Chem. Unst. Gas A); incompatible with acids, bases, alcohols, ammonia, amines, water, strong oxidising agents and various metal chlorides

 BASF self-classifies the substance as a chemically unstable gas under H230, "may react explosively even in the absence of air" . Heat or contamination (rust, alkalis, acids, metal chlorides) may trigger violent exothermic decomposition or polymerisation, and in a closed vessel the pressure rise may rupture the container with explosive force