Description, Uses, and Production

Ethylene Glycol

Wilfredo Colón-Santiago

160-58-0767 According to the Merck Index, ethylene glycol (HO(CH2) (CH2)OH) is a sweet tasting, slightly viscous fluid (at 20 °C) which is so hygroscopic that it absorbs twice its weight in water at 100% relative humidity. Interestingly enough, though it is sweet, you should not swallow it. It might cause a problem or two from the biomedical perspective. Some of its physical chemical attributes include a dipole moment of 2.20; a specific heat of .561 cal/g°C (at 20 °C); a heat of formation of –108.1 Kcal/mol; a heat of fusion of 44.7 cal/g; a heat of vaporization of 191 cal/g; a dielectric constant of 38.66 esu at 20 °C and 150 meter wavelenght; a density of 9.3 lbs/gal at 20 °C (mixing systems !@#$%^&**); a one atmosphere boiling point of 197.6 °C; a one atmosphere melting point of –13 °C; total miscibility in water, lower aliphatic alcohols, glycerol, acetic acid, acetone, similar ketones, aldehydes, pyridine, and similar coal tar bases; only slight solubility in ether; practically insoluble in benzene and its homologs.

Also, according to Merck, some of ethylene glycol’s industrial applications include its use: as an automotive radiator antifreeze (very popular); as an automotive break fluid

(also very popular); as an industrial humectant; as a solvent in the paint and plastics industries; as a softening agent for cellophane; a stabilizer for anti-pyrolytics such as soybean foam (used for the retardation of petroleum fires); in the synthesis of safety explosives, inks, glyoxal, plasticizers, resins, elastomers, synthetic fibers, synthetic waxes, and pesticides.

One production method for ethylene glycol requires the hydration of ethylene oxide, also known as oxyrane. Oxyrane is readily reactive with water. The yield can be increased if the reaction were to occur over a silver catalyst at 225 °C. Since the process flow would be above the boiling temperature of all of the reactor components, the simplest form of separation would be to cool the gas below to less than 197 °C. The vapors and liquid glycol can be separated further in an absorber from which a recycle can be returned to the reactor which contains quenching water , oxyrane, and returns some energy back to the reactor. The liquid product will surely contain water vapor contaniment. This can be distilled in a column. The water vapor separates out, while the ethylene glycol exits out the lower to middle trays. Since the process uses a great deal of water and consumes a great deal of heat, a crosscurrent system of water to process flow will achieve greater thermal efficiency. The process flow might look thus:

Process Flow diagram for the Manufacture of Ethylene Glycol from Ethylene Oxide

(Oxyrane) Sources:

1. http://ntp-server.niehs.nih.gov/htdocs/8_RoC/RAC/EthyleneOxide.html

2. http://www.ucc.ie/ucc/depts/chem/dolchem/html/comp/glycol.html