Ethylene Glycol
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Product Description
Ethylene glycol (ethane-1,2-diol; C₂H₆O₂; HOCH₂CH₂OH) is the simplest, highest-volume diol: a colourless, syrupy, hygroscopic liquid that is completely miscible with water and possesses a high boiling point (197 °C) and low freezing point (–13 °C). These characteristics, together with its ready biodegradability and low volatility, make it the active component of most automotive and HVAC antifreeze/coolants, aircraft de-icing fluids, hydrate inhibitors for natural-gas pipelines, and heat-transfer media in solar-thermal and geothermal loops. Chemically the molecule behaves as a bidentate alcohol, undergoing stepwise catalytic oxidation (→ glycoaldehyde → glycolic acid → oxalic acid), esterification with terephthalic acid to give polyethylene terephthalate (PET) for bottles and polyester fibre, etherification to glycol-ether solvents for paints and brake fluids, and dehydration to 1,4-dioxane; its high polarity and hydrogen-bonding capacity also suit it as a solvent, plasticiser and humectant in inks, adhesives, cosmetics and capacitor electrolytes. Although only moderately toxic to aquatic life, ethylene glycol is acutely hazardous to mammals because hepatic alcohol dehydrogenase converts it to calcium-chelating oxalic acid, causing metabolic acidosis, renal failure and death at human doses as low as 1 g kg⁻¹; fomepizole or ethanol infusion plus dialysis is therefore the standard antidote. Global capacity now exceeds 45 Mt yr⁻¹, with ~65 % dedicated to PET production and ~20 % to antifreeze; emerging research is extending its role as a next-generation, CO₂-derived C₂ feedstock for microbial biorefineries that upgrade waste PET or syngas-based EG into fuels and value-added chemicals.
Other Information
Comparison with Other Glycols
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Propylene Glycol (PG): Less toxic and approved for food and pharmaceutical use. Used where human/animal exposure is likely (e.g., aircraft de-icing, food processing).
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Di-ethylene Glycol (DEG) & Tri-ethylene Glycol (TEG): Higher boiling points, used as desiccants for gas dehydration and solvents.
Synthesis and Production
1. Traditional (Fossil-Based) Routes (Still Dominant)
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Ethylene Oxide Hydration: The primary industrial method, accounting for ~90% of global capacity. It involves the hydrolysis of ethylene oxide (derived from petroleum-based ethylene) with water at high temperature and pressure.
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C₂H₄O (EO) + H₂O → HO-CH₂-CH₂-OH
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Coal/Syngas Route: Primarily used in China, this method involves gasification of coal to syngas, which is converted to dimethyl oxalate and then hydrogenated to EG.
2. Emerging Sustainable/Circular Routes (2024-2025)
The production landscape is rapidly shifting towards renewable and circular pathways to reduce carbon emissions.
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Catalytic Hydrogenolysis of Carbohydrates: Uses cellulose, glucose, or starch as a feedstock. This process, commercialized at pilot scale (e.g., Avantium), involves retro-aldol and hydrogenation steps.
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Electrosynthesis from Glycerol: A promising lab-scale process using paired electrolysis to upgrade biodiesel by-product glycerol into EG with high efficiency and significantly lower CO₂ emissions.
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PET Chemical Recycling (Glycolysis): A circular economy route where PET plastic waste is depolymerized using EG to recover the monomer (BHET), which can be repurposed, effectively creating "recycled" EG with near-zero emissions.
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Direct CO₂ Electroreduction: An emerging technology that uses renewable electricity and CO₂ to produce EG, though it currently suffers from low selectivity.
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Syngas-to-Methanol Route: Uses CO₂-derived syngas, converted via methanol and formaldehyde to EG, and has been demonstrated at pilot scale.
Uses and Applications
1. Primary Industrial Uses
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Polyester Production (≈65% of market): The dominant use as a precursor for Polyethylene Terephthalate (PET), found in textiles (polyester fiber), plastic bottles, and films.
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Antifreeze and Coolants (≈20% of market): Its ability to significantly lower the freezing point and raise the boiling point of water makes it ideal for automotive engine coolants, de-icing fluids for aircraft and runways, and heat-transfer fluids in HVAC systems.
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Chemical Intermediate and Solvents (≈8% of market): Used to produce glycol ethers, plasticizers, resins (alkyd, unsaturated polyester), and as a solvent in paints, inks, dyes, and industrial cleaners. Also used in hydraulic and brake fluids.
2. Other Applications
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Gas Dehydration: Used to remove water vapor from natural gas streams and to suppress hydrate formation in pipelines.
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Other Niche Uses: Humectant in paper/tobacco, carrier for fragrances and explosives, component in electrolytic capacitors, and cryoprotectant for biological specimen preservation.
Chemical and Physical Properties
1. Chemical Identity
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IUPAC Name: Ethane-1,2-diol
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Molecular Formula: C₂H₆O₂
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CAS Number: 107-21-1
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Molar Mass: 62.07 g/mol
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Structure: HO–CH₂–CH₂–OH (a vicinal diol)
2. Physical Properties
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Appearance: Colorless, odorless, viscous (syrupy), hygroscopic liquid with a sweet taste.
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Melting Point: -12.9 °C
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Boiling Point: 197.3 °C (high due to extensive hydrogen bonding)
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Density: 1.113 g/cm³ at 20°C
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Solubility: Fully miscible with water, alcohols, and many polar solvents.
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Viscosity: 16.1 mPa·s at 20°C (higher than water)
3. Chemical Properties
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Reactivity: Contains two hydroxyl groups, enabling typical alcohol reactions.
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Esterification: With terephthalic acid to form PET.
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Oxidation: Can be oxidized stepwise to glycolaldehyde, glycolic acid, glyoxylic acid, and oxalic acid.
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Etherification: Can form mono- and di-ethers (e.g., glycol ethers).
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Hygroscopicity: Highly hygroscopic, readily absorbing moisture from the atmosphere.
Safety and Handling
1. Toxicity and Health Hazards
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Highly Toxic if Ingested: The sweet taste poses a risk of accidental poisoning. The human lethal dose is estimated at ~1.0–1.5 mL/kg (approx. 70 mL for an adult).
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Mechanism of Poisoning: Metabolized in the liver by alcohol dehydrogenase to glycolic and oxalic acids. This causes severe metabolic acidosis. Oxalic acid binds with calcium to form calcium oxalate crystals, leading to acute kidney failure and potential death.
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Stages of Poisoning:
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Neurological (30 min - 12 hrs): Appears inebriated (dizziness, slurred speech, nausea).
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Cardiopulmonary (12 - 24 hrs): Tachycardia, hypertension, heart failure.
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Renal (24 - 72 hrs): Flank pain, oliguria, acute kidney failure.
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2. Safe Handling and First Aid
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Personal Protective Equipment (PPE): Wear gloves, goggles, and work in well-ventilated areas to avoid prolonged skin contact or inhalation of mists.
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Storage: Store in clearly marked, sealed containers away from oxidizers, heat, and sparks. Carbon steel or stainless-steel tanks are acceptable.
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Antidotes and Treatment: Immediate medical attention is critical.
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Fomepizole: The preferred antidote, which inhibits alcohol dehydrogenase.
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Ethanol: Can be used if fomepizole is unavailable.
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Hemodialysis: Often required to remove EG and its metabolites from the blood.
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Regulatory Exposure Limits:
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OSHA PEL (Ceiling): 50 ppm
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ACGIH TLV-C: 50 ppm
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