Ethylene glycol: properties industrial uses hazards and safe handling

Ethylene glycol, also known as monoethylene glycol (MEG), is a chemical compound widely used in industry for its versatile properties. It is a colorless, sweet-tasting, but highly toxic liquid. Its predominant use is in the formulation of antifreeze and coolants, as well as in the production of polyester fibers.

However, its handling requires rigorous precautions due to the risks it poses to human health and the environment. This article discusses its main physicochemical properties, industrial applications, associated hazards, relevant regulations and detection technologies, along with emerging sustainable alternatives.

Physicochemical properties of ethylene glycol

Ethylene glycol (C₂H₆O₂) has a simple molecular formula composed of two hydroxyl groups, which gives it a high hygroscopic capacity and miscibility with water. It has a density of 1.11 g/cm³, a boiling point of 197.3 °C and a freezing point of -12.9 °C. Its viscosity and low freezing point make it an ideal ingredient for cooling fluids. In addition, it is soluble in alcohols and acetone, but not very volatile, which favors its use in closed systems. The following image shows the structural and molecular formula of this compound.

How is ethylene glycol produced?

Ethylene glycol is produced from ethylene by means of a petrochemical process known as Project OMEGA, developed by Shell Global Solutions, which has revolutionized this technology, achieving high selectivity and energy efficiency. The following flow chart explains each stage of the process, aligned with the best chemical and engineering practices.

What is the OMEGA process to produce ethylene glycol?

Obtaining ethylene glycol by ethylene oxide (EO) carbonation:

The OMEGA process consists of two main steps:

• Controlled oxidation of ethylene to form ethylene oxide (EO).
• Hydrolysis of ethylene oxide to obtain monoethylene glycol (MEG), with an efficiency of more than 99.5%.

Stage 1: Synthesis of ethylene oxide

Ethylene (C₂H₄) reacts with oxygen (O₂) in the presence of a silver catalyst supported on alumina. This exothermic reaction takes place in a gas-phase multi-tube reactor (unit 1 in the diagram). Some ethylene can overoxidize to CO₂ and water, but in the OMEGA process ethyl chloride is added as a moderator, reducing this effect.

Stage 2: Ethylene oxide recovery

After the reaction, the gaseous mixture passes through a recovery system that includes:

• Absorber (2): separates EO from other gases.
• Strippers and columns (3-4): remove light compounds.
• CO₂ removal (6-7): captured carbon dioxide is reused to synthesize ethylene carbonate.

Stage 3: Synthesis of ethylene glycol

In this stage, ethylene oxide reacts with recycled CO₂ to form ethylene carbonate (unit 6), which is then hydrolyzed in reactors (7) to produce monoethylene glycol (MEG) and regenerate CO₂. These reactions are carried out in liquid phase with homogeneous catalysts.

Reactions:

C₂H₄O + CO₂ → C₃H₄O₃ (ethylene carbonate)
C₃H₄O₃ + H₂O → HOC₂H₄OH + CO₂ (MEG)

Stage 4: Purification of monoethylene glycol

The produced MEG passes through a water removal column (8) and then through a purification column (9). In these units, the by-products are separated, and the catalyst is recovered and recycled to the system. Finally, the purified MEG is cooled (10) and can be used directly or stored.

Advantages of the OMEGA process

The OMEGA process offers a number of advantages in the production of monoethylene glycol (MEG): High efficiency, reaching a selectivity of 99.5 % towards MEG, which minimizes the formation of unwanted by-products such as diethylene glycol. In addition, it significantly reduces energy consumption due to the reduced need for distillation. Another considerable aspect is the effective recycling of both carbon dioxide and catalysts, which improves the sustainability and cost-effectiveness of the process.

Industrial applications of ethylene glycol

Coolants and antifreeze

One of the most widespread applications of ethylene glycol is its use in engine cooling systems, where it acts as an antifreeze fluid. Thanks to its ability to lower the freezing point of water, it protects engines in cold climates and improves heat transfer in cooling systems.

Production of polyesters

Ethylene glycol is an essential raw material in the production of polyethylene terephthalate (PET), used in the manufacture of bottles, packaging, textile fibers and plastic films. In this process, it reacts with terephthalic acid to form a high-performance polymer, which is widely demanded by the food and textile industries.

Other applications

It is also used as a solvent in the formulation of inks, paints, brake fluids and wetting agents. In the electronics industry, it is used as a medium for thermal control of heat-sensitive components.

Health and environmental hazards

Ethylene glycol poses serious health hazards. Its ingestion, even in small amounts, can cause kidney damage, neurological damage and even death. The toxic effects are due to its metabolites, such as oxalic acid, which crystallizes in the kidneys. Chronic exposure by inhalation or dermal contact can also cause irritation and respiratory problems.

From an environmental point of view, it is a polluting substance if released without control, as it can affect water bodies and soils, altering aquatic ecosystems due to its slow biodegradation under anaerobic conditions.

Transportation and storage regulations

The handling of ethylene glycol is regulated by various international standards. According to the Occupational Safety and Health Administration (OSHA), it should be handled with respiratory and eye protection, avoiding prolonged skin contact. The National Fire Protection Association (NFPA) classifies ethylene glycol as a level 1 flammable, 2 health hazard and 0 reactivity. Under the Globally Harmonized System (GHS), it is assigned the category of acute toxic (oral, category 4) and with a hazard warning.

The EPA regulates its environmental management to prevent contamination. Internationally, regulations vary, but they coincide in prioritizing safety and environmental protection, making it essential for companies to comply with these guidelines in order to operate safely and legally. Storage should be in hermetically sealed containers, in ventilated areas, away from sources of ignition and incompatible substances, such as strong oxidizing agents.

Leak detection systems in chemical plants

In industrial facilities, early detection of ethylene glycol leaks is essential to prevent accidents and minimize environmental impacts. Continuous monitoring systems include infrared sensors and electrochemical detectors that can alert to the presence of vapors in the environment. In addition, more advanced technologies such as thermal imaging cameras or portable mass spectrometry allow rapid assessment in hard-to-reach areas.

Proper maintenance of valves, piping and pumps, along with regular inspections, are key practices to ensure asset integrity and prevent accidental releases.

Safer and more sustainable alternatives

With the move towards a greener chemical industry, alternatives to ethylene glycol derived from renewable sources have been developed. Bio-glycols, such as plant-based propylene glycol, offer significantly lower toxicity and a more benign environmental profile. These compounds are compatible with many industrial applications, including refrigerants, cosmetics and food, making them viable options to replace ethylene glycol in certain contexts.

Case study: ethylene glycol leak at thermal plant

In 2023, a thermal power plant in South America experienced a significant ethylene glycol leak from a heat exchanger. The cause was internal corrosion of a carbon steel pipe that had not been inspected in the past three years. The fluid spilled into a containment trench, but some of it reached the storm drain system.

The immediate consequence was the suspension of operations and the activation of an emergency environmental protocol. Elevated levels of contaminants were identified in a nearby stream, which led to the imposition of regulatory sanctions.

The subsequent action plan included replacing materials with stainless steel, implementing infrared detection sensors, and updating the predictive maintenance program with on-line corrosion monitoring. This incident underscores the importance of reliability, maintenance and asset integrity, fundamental pillars in the prevention of industrial failures.

Ethylene glycol involvement in the chemical industry

Although sometimes confused with vinyl chloride processes, ethylene glycol is not directly involved in PVC production. PVC is manufactured through a chain that starts with the reaction of ethylene with chlorine to form ethylene dichloride (EDC), which undergoes pyrolysis to obtain vinyl chloride monomer (VCM), and finally polymerizes to obtain PVC.

Where ethylene glycol does play a critical role is in the production of PET, as explained above. This differentiation is important for understanding the structure of petrochemical value chains.

Conclusion

Ethylene glycol is a key substance in multiple industries for its physicochemical properties, especially as an antifreeze and feedstock in the production of polyesters. However, its toxicity and contamination potential require careful and regulated handling. The incorporation of monitoring technologies, regulatory compliance and the transition to safer alternatives are the pillars of responsible and sustainable ethylene glycol management.

Frequently asked questions about ethylene glycol (FAQ)

What is ethylene glycol and what is its main use?

1. Ethylene glycol (MEG) is a chemical compound widely used as an antifreeze, coolant and raw material in the manufacture of polyesters and PET resins.

2. How is ethylene glycol produced from ethylene?

It is obtained by a two-step process: oxidation of ethylene to form ethylene oxide, followed by hydrolysis of ethylene oxide or, in the OMEGA process, by intermediate formation of ethylene carbonate.

3. What are the benefits of the OMEGA process in the production of ethylene glycol?

The OMEGA process achieves high selectivity (99.5 % towards MEG), reduces energy consumption and minimizes the formation of by-products such as diethylene glycol, which improves the efficiency and sustainability of the process.

4. What are the risks involved in handling ethylene glycol?

Ethylene glycol is toxic if inhaled or ingested. It requires safe handling, personal protective equipment and compliance with environmental and industry regulations.

References

1. American Chemistry Council. (2021). Ethylene Glycol Product Stewardship Summary. Retrieved from https://www.americanchemistry.com/industry-groups/ethylene-glycols
2. Wikipedia, OMEGA process, (accessed 29^th Apr 2024).
3. Shell, OMEGA process (accessed 29^th Apr 2024).
4. Intratec Solutions, 14^th Sep 2023, Ethylene Glycol from Ethylene (Carbonation without EO By-Product) | Economic Analysis, Medium.