The long-term storage stability of ethylene (C2H4) gas depends on the storage and chemical activity. Ethylene at room temperature and pressure will gradually polymerize (ca. 0.05%/ year), but at -103.7℃ liquid storage, the polymerization rate can be reduced to <0.001%/ year. According to the ASME B31.3 code, the storage pressure should be kept in 1.5-2.0 MPa (15-20 bar), the temperature range of variation is ≤±0.5℃, and 316L stainless steel container is adopted (60% greater resistance to stress corrosion cracking than 304 steel). German Linde Group data shows that its low-temperature storage tank (5000 m³ capacity) evaporation rate is only 0.02%/day, storage for 12 months after ethylene purity remains ≥99.95% (initial purity 99.99%).
The storage technology determines the degradation rate directly: the adsorption storage technology uses MOOF-74 metal-organic framework material (specific surface area 1300 m²/g), with the ability to adsorb ethylene up to 120 cm³/g at 25℃ and 3 MPa (traditional activated carbon is 45 cm³/g), and the purity loss after desorption is less than 0.005%. A paper in Nature Materials in 2023 proved that doped copper nanoparticle MOF-303 can extend the storage life of ethylene to 5 years (conventional method 2 years), but the material cost increases by 37%. The average annual energy consumption of liquid storage of ethylene (-103.7 ° C) is 18 kWh/m³ (COP≥2.5 for refrigeration systems), and the energy consumption of high-pressure gas storage (20 MPa) is 45 kWh/m³, with significant economic differences.
Impurity control is the primary method to prevent degradation: Ethylene trace oxygen (>5 ppm) will result in free radical chain reaction and give polymer formation rates (e.g., oligomers) up to 0.1%/month. Sinopec Zhenhai Refining uses two-stage molecular sieve adsorption (pore size 0.3nm) to reduce oxygen content from 100 ppm to <1 ppm, and oligomer content is only 0.003% after 18 months of storage. ASTM standard D2505 stipulates that the level of sulfides (e.g., H₂S) in the storage of ethylene must be below 0.1 ppm, otherwise, it will catalyze the decomposition
reaction (the activation energy is reduced to 80 kJ/mol).
Safety risks are rigorously controlled: the lower explosive limit (LEL) of ethylene is 2.7% (volume percentage), the storage chamber is equipped with an infrared gas detector (sensitivity ≤1 ppm, response time <2 seconds) and nitrogen inerting system (purity ≥99.999%), which replaces oxygen at a flow rate of 5 m³/min to <10% in case of leakage. The inquiry into the Yeosu Industrial Park accident in South Korea in 2022 showed that the utilization of a single-layer vacuum storage tank as opposed to a double-layer tank (single-layer tank evaporation rate 0.3%/day) resulted in the realization of an ethylene concentration of 4.5% within a closed area for 6 hours, causing an explosion, and direct losses of $45 million.
The economic tradeoff is to be calculated in total: liquid ethylene storage tank (investment cost 1.2 million /5000m)
The loss rate each year is 73,800 / ton of ethylene, and the liquid storage program saves 460,000 yuan every year. If MOF adsorption storage is used (material cost 50/kg), the total cost per ton of storage is $120 higher than the liquid one but is suitable for small-scale distributed storage scenarios.
Compliance demands Improved storage standards: ISO 21000-6:23 calls for ethylene tanks to be equipped with a real-time monitoring system (pressure error ±0.1%, temperature ±0.2 ° C) and quarterly gas chromatography (GC-FID detection limit ≤0.1 ppm). EU CLP regulations require that there be no naked flame within a 30-meter radius of the storage area, and intrinsically safe electrical equipment must be of ATEX Category 1 standard (compressive strength ≥1.5 times design pressure). Norwegian company Equinor was fined €2.8 million in 2024 for breaching storage conditions and forced to destroy 12,000 tons of ethylene stocks.
By optimizing storage technologies (i.e., low temperature + adsorption complex solutions), strict impurity control and smart monitoring, c2h4 gas (ethylene) can store for more than 5 years with a degradation rate of <0.1%, stabilizing the chemical supply chain.