Ethylene Glycol

① What is Ethylene Glycol?

Ethylene glycol, also known as glycol, 1,2-ethylene glycol or ethylene glycol, is the simplest aliphatic diol and a major bulk basic organic chemical feedstock. At normal temperature and pressure it is a colorless, clear, odorless viscous liquid with a sweet taste. It is not highly flammable, with a flash point of 116°C, and is classified as a harmful chemical.

Ethylene glycol is miscible with water, ethanol and acetone in any proportion, and is slightly soluble in diethyl ether. Its chemical properties are active: the molecule contains two hydroxyl groups and can undergo esterification, etherification, polycondensation, oxidation, dehydration and other reactions. Ethylene glycol vapor is slightly heavier than air. If ingested by humans, it produces toxic metabolites that damage the kidneys and the central nervous system.

It is both an important antifreeze and hygroscopic solvent and an indispensable core monomer for polyester polymer synthesis. It is widely used in polyester fiber, bottle-grade resin, antifreeze, surfactants, fine chemicals, pharmaceutical intermediates and other fields, and is a key basic raw material in the chemical industry chain. Under the GHS hazard classification it is an acute oral hazard and a specific target organ toxicant on repeated exposure. UN number: UN3082, Packing Group III.

② Industrial Parameters of Ethylene Glycol

The impurities of polyester-grade ethylene glycol fully meet the requirements of the Chinese national industrial premium-grade standard GB/T 4649-2018. In industrial production, the hydration reaction is followed by multi-column distillation and thin-film evaporation to remove water and by-products such as diethylene glycol and triethylene glycol, giving the qualified finished product.

③ Ethylene Glycol Industrial Characteristics and Applications in China

Industrial characteristics: oil-based and coal-based dual routes in parallel, deeply bound to the polyester industry chain.

There are two mainstream process routes for domestic ethylene glycol: the petroleum-based ethylene-ethylene oxide hydration route and the coal-based ethylene glycol route (oxalate process), the latter being a distinctive Chinese process route with a huge total capacity. Capacity is concentrated in large coastal refining-chemical bases and northwestern coal chemical bases. Ethylene glycol output closely follows the operating rates of ethylene units and coal chemical units. China still has a certain degree of import dependence, and crude oil and coal prices directly determine the production cost of ethylene glycol. Many refining and chemical enterprises have built an integrated "ethylene glycol-PTA-polyester" layout, supplying their own feedstock to the downstream fiber industry.

Core synthetic material application: polyester is by far the largest consumption direction.

More than 90% of domestic ethylene glycol consumption goes to the polyester industry, including PET filament/staple textile fibers, PET bottle chips (beverage packaging) and PET film (photovoltaic, packaging), which are the core drivers of ethylene glycol demand. The remainder is used to produce unsaturated polyester resins and alkyd resins, serving the plastics and coatings industries.

Antifreeze solvent and fine chemical applications: used as antifreeze for automobiles and industrial plants and as refrigerant media; used as a hygroscopic agent and gas dehydration agent; used to produce ethylene glycol ethers, plasticizers and surfactants; also used as an analytical reagent, capacitor dielectric and explosive feedstock, supporting the development of the domestic fine chemical industry.

④ International Industrial Characteristics and Applications of Ethylene Glycol

Industrial landscape: globally dominated by the petroleum-based ethylene oxide hydration route, with capacity concentrated in oil- and gas-resource-rich regions.

More than 90% of the world's ethylene glycol is produced by direct hydration of ethylene oxide from ethylene. The Middle East and North America, relying on cheap ethane/ethylene feedstocks, host numerous large ethylene glycol plants and are the world's main exporting regions. There are almost no large-scale coal-based ethylene glycol projects overseas. The ethylene glycol supply cycle fluctuates with the operating rates of global ethylene cracker units.

Developed regions: developed regions focus on high-end fine chemicals and specialty materials.

Apart from polyester consumption, the European and American markets use ethylene glycol more for synthesizing high-end glycol ether solvents, specialty surfactants, pharmaceutical intermediates and specialty polyesters. In the North American market, the share of antifreeze and industrial cooling media consumption is higher than in other regions. In Europe, constrained by environmental regulations, some categories of glycol ethers are subject to tighter control and are shifting toward high-value-added derivatives.

Global trade and regionally differentiated applications: the Asia-Pacific region is the world's largest ethylene glycol consumer market; the Middle East is the world's largest ethylene glycol exporting region, exporting large volumes to China and Southeast Asia; developing countries lacking large ethylene plants rely on imported ethylene glycol to meet their polyester and antifreeze solvent needs; globally, polyester demand dominates the ethylene glycol price cycle.

⑤ Production Methods of Ethylene Glycol by Country/Region

Ethylene oxide direct hydration (global mainstream; adopted on a large scale in China, Europe/US, the Middle East, Japan and Korea):

Ethylene oxide, obtained by oxidation of ethylene, reacts with excess water in direct liquid-phase hydration in a tubular reactor under pressure (about 2.23 MPa) at 190-200°C to produce ethylene glycol, with diethylene glycol, triethylene glycol and polyethylene glycol formed as by-products. The dilute reaction liquor is concentrated in thin-film evaporators, dehydrated and purified by multi-column distillation to give polyester-grade ethylene glycol. This process delivers high product quality and is suitable for large-scale polyester feedstock production; its drawbacks are that the feedstock depends on ethylene and the various polyethylene-glycol-series by-products require distillation separation.

Coal-based oxalate process (coal-to-ethylene glycol, a distinctive large-scale industrialized process of China):

Using coal as feedstock, gasification produces CO and hydrogen; CO is catalytically coupled to give dimethyl oxalate, which is then hydrogenated to ethylene glycol. The route does not depend on petroleum ethylene resources and is suitable for coal-rich regions; part of the product quality can reach polyester grade. Its drawbacks are the large plant investment, the high requirements on catalysts, and that impurity control is the key technical point. Overseas there are only a few pilot demonstration units, with no large-scale commercial operation.

Ethylene oxide sulfuric acid-catalyzed hydration (an early eliminated process, now largely discontinued):

Ethylene oxide and water are hydrated under sulfuric acid catalysis at 60-80°C and low pressure; the reaction liquor is neutralized with alkali, evaporated and concentrated, and distilled to purify ethylene glycol. This process suffers from severe equipment corrosion, large amounts of waste gas/waste water/waste residue and high product impurities, and has been essentially phased out in all countries, retaining only historical reference value.

Other early laboratory processes - direct hydration of ethylene, hydrolysis of dichloroethane and the formaldehyde synthesis route - did not achieve large-scale industrialization and have only theoretical reference value.

⑥ Upstream Products of Ethylene Glycol

Main process - ethylene oxide direct hydration (accounting for 90%+ of global capacity):

Upstream for the coal-based ethylene glycol route (oxalate hydrogenation process): coal; oxygen; carbon monoxide; hydrogen; methyl nitrite; coupling catalysts and hydrogenation catalysts.

Upstream for the eliminated sulfuric acid-catalyzed hydration process: ethylene oxide, sulfuric acid and caustic soda (for neutralization).

Utilities: steam, circulating cooling water and nitrogen (protective gas).

⑦ Downstream Products of Ethylene Glycol (100 in total, with CAS numbers)