Ethylene glycol and its Uses

Ethylene glycol (IUPAC name: ethane-1,2-diol) is an organic compound (vicinal diol) with the formula (CH2OH)2.It is mainly used for two purposes, as a raw material for the manufacture of polyester fibers and in antifreeze formulations.It is an odourless, colorless, flammable viscous liquid. Ethylene glycol has a sweet taste but is toxic in high concentrations.

Production

Industrial route

Ethylene glycol is produced from ethylene (ethylene) through the intermediate ethylene oxide.According to the chemical equation, ethylene oxide reacts with water to form ethylene glycol:

C2H4O + H2O → HO−CH2CH2−OH

The reaction can be catalyzed by acids or bases, or can occur at elevated temperatures at neutral pH.The highest yield of ethylene glycol occurs at acidic or neutral pH and a large excess of water. Under these conditions, the yield of ethylene glycol can reach 90%. The main by-products are the oligomers diethylene glycol, triethylene glycol and tetraethylene glycol.The separation of these oligomers and water is energy intensive.Produces approximately 6.7 million tons per year.Higher selectivity is achieved using Shell's OMEGA process. In the OMEGA process, ethylene oxide is first converted together with carbon dioxide (CO2) to ethylene carbonate. This ring is then hydrolyzed with a basic catalyst in a second step to produce monoethylene glycol with 98% selectivity.Carbon dioxide is released again in this step and can be returned to the process loop.Part of the carbon dioxide comes from ethylene oxide production, a part of which is fully oxidized ethylene.In countries with large coal reserves and less stringent environmental regulations, ethylene glycol is produced from carbon monoxide.Oxidative carbonylation of methanol to dimethyl oxalate offers a promising approach for the production of C.Dimethyl ethylene glycol oxalate can be converted to ethylene glycol in high yield (94.7%)[10] by hydrogenation with a copper catalyst:Because methanol is recycled, only carbon monoxide, hydrogen and oxygen are consumed. One plant with an annual capacity of 200,000 tons of ethylene glycol is located in Inner Mongolia, and a second plant with an annual capacity of 250,000 tons is located in Henan Province, China.As of 2015, there are 4 factories with a capacity of 200,000 tons/year in operation in China, and at least 17 more will be put into operation.

Uses 

Coolant and heat-transfer agent:

The primary use of ethylene glycol is as an antifreeze in coolants such as automobiles and air conditioning systems that either place the chiller or air handler outside or must be cooled below the freezing point of water.In geothermal heating/cooling systems, glycol is the fluid that transfers heat through the use of geothermal heat pumps.Ethylene glycol either takes energy from the source (lake, ocean, well) or dissipates heat to the sink, depending on whether the system is being used for heating or cooling.The specific heat capacity of pure ethylene glycol is about one-half that of water.Thus, while providing freeze protection and raising the boiling point, glycol lowers the specific heat capacity of water mixtures relative to pure water.The specific heat capacity of a 1:1 mix by mass is about 3140 J/(kg °C) (0.75 BTU/(lb °F)), three-quarters that of pure water, so the need to increase the flow rate system compared to water.Ethylene glycol mixed with water provides additional benefits to coolants and antifreezes, such as protection against corrosion and acid degradation, as well as inhibiting the growth of most microorganisms and fungi.Mixtures of ethylene glycol and water are sometimes informally referred to in the industry as ethylene glycol concentrates, compounds, mixtures, or solutions.

Anti-freeze

Pure ethylene glycol freezes at about -12 °C (10.4 °F), but when mixed with water, the mixture freezes at lower temperatures.For example, a mixture of 60% ethylene glycol and 40% water will freeze at −45 °C (−49 °F).Diethylene glycol behaves similarly.The freezing point depression of some mixtures can be explained by the colligative properties of the solution, but in highly concentrated mixtures (such as the example) deviations from ideal solution behavior are expected due to the influence of intermolecular forces.It is important to note that although purified and distilled water has a greater specific heat capacity than any mixture of antifreeze and water, commercial antifreeze usually also contains anti-corrosion additives to prevent pure water from corroding the coolant in the engine block, cylinder head Channel(s), water pump and radiator.The mixing ratio is different, depending on whether it is ethylene glycol or propylene glycol.For ethylene glycol, the mix ratios are typically 30/70 and 35/65, while for propylene glycol, the mix ratios are typically 35/65 and 40/60. It is important that the mixture is frost resistant at the minimum operating temperature.Because of its low freezing temperature, ethylene glycol is used as a deicing fluid for windshields and aircraft, as an antifreeze for automobile engines, and as a component of vitrified (anti-crystallization) mixtures used to cryopreserve biological tissues and organs.The use of ethylene glycol not only lowers the freezing point of aqueous mixtures but also raises their boiling point.This results in a widening of the operating temperature range of the heat transfer fluid at both ends of the temperature scale.The elevated boiling point is due to the fact that pure ethylene glycol has a much higher boiling point and a much lower vapor pressure than pure water.

Polymer precursor

In the plastics industry, ethylene glycol is an important precursor for polyester fibers and resins.Polyethylene terephthalate, used to make soft drink plastic bottles, is made from ethylene glycol.

Other uses

Dehydrating agent:

Ethylene glycol is used in the natural gas industry to remove water vapor from natural gas prior to further processing in much the same way as triethylene glycol (TEG).

Hydrate inhibition:

Ethylene glycol is a useful desiccant due to its high boiling point and hydrophilicity.Ethylene glycol is widely used to inhibit the formation of natural gas clathrates (hydrates) in long multiphase pipelines that transport natural gas from remote gas fields to gas processing facilities.Ethylene glycol can be recovered from natural gas and reused as an inhibitor after purification to remove water and inorganic salts.Natural gas is dehydrated by ethylene glycol. In this application, glycol flows down the top of the column and encounters an ascending mixture of water vapor and hydrocarbon gases.Dry gas exits the top of the tower.Ethylene glycol and water are separated, and ethylene glycol is recovered.In addition to removing water, ethylene glycol can also be used to lower the temperature at which hydrates are formed.The ethylene glycol used for hydration inhibition (monoethylene glycol) is typically around 80% pure, while the ethylene glycol used for dehydration (triethylene glycol) is typically 95 to over 99% pure.In addition, the injection rate of the suppressed hydrate is much lower than the circulation rate in the glycol dehydration column.