Behavior in environment, which includes transportation (the distance and ways that chemicals get moved from producer to user companies) and when released into the environment, their effects on the biosphere and human health and safety.

Profile: Mono-ethylene glycol

When you read about ethylene glycol in the press, mono-ethylene glycol is usually the subject. It is the most important of a family of chemical building blocks used in industrial chemistry throughout the world.

CHEMISTRY: Alcohol.
The compound is a colorless, viscous fluid with a syrupy sweet taste and no odor.  As any alcohol, ethylene (more precisely mono-ethylene) glycol dissolves easily in water in any concentration.

USES: Chemical intermediate, many uses.
Ethylene glycol is a building block used to make polyester fabrics and furnishings, plastic food containers and antifreeze. Globally, about 55 percent of ethylene glycol made each year is used to make polyester fibers. Another 25 percent is used to make polyethylene terephthalate (PET) plastic packaging and drinking bottles. In the United States, antifreeze is the largest use of ethylene glycol.

PROCESS: Energy-intensive, petrochemical-based.
Manufacturers make ethylene glycol by exposing ethylene oxide to water and separating it and related glycols by distillation.  Manufacturers can tweak production efficiency by making the reactor environment acidic or using catalysts at somewhat lower water temperature. But, generally, only about 90 percent of inputs produce mono-ethylene glycol.  Byproducts include di-ethylene glycol (DEG) and tri-ethylene glycol (TEG). These related chemicals have their own uses in industry. Distillation used to separate final products requires lots of electricity to heat the water.

BEHAVIOR IN ENVIRONMENT: Transported widely, toxic when released.
The ability of ethylene glycol to dissolve easily in water has consequences for human health and environmental safety. A detailed account of ethylene glycol hazards and mitigation is in an upcoming post.

Profile: Di-ethylene and tri-ethylene glycols

These glycols are related to mono-ethylene glycol. Often they are produced in the same chemical process as MEG.

CHEMISTRY: Alcohols.
Like ethylene glycol, these compounds dissolve easily in water. However, they are heavier, are more viscous and boil at higher temperatures than ethylene glycol. Properties of tri-ethylene glycol resemble those of DEG, but it is heavier. Tri-ethylene glycol is also distinguished by its antibacterial properties.

USES: Chemical intermediates, many uses
Di-ethylene glycol is used to produce textiles and plastics and is a component in brake fluid, lubricants, wallpaper strippers, artificial fog solutions, and personal care products. Although dilute solutions of di-ethylene glycol can be used as a coolant, mono-ethylene glycol is used much more often. Tri-ethylene glycol is used in air conditioners and to prevent water collecting in natural gas pipelines. This form of glycol can also be used as a plasticizer for vinyl and an additive in hydraulic fluid, smoke machines and brake fluids.

PROCESS: Energy-intensive, petrochemical-based
Di- and tri-ethylene glycols are produced by exposing ethylene oxide to water. They can be produced as a byproduct of mono-ethylene glycol production or from basic raw materials. Depending on process conditions, varying amounts of mono-, di- and tri-ethylene glycols are produced. Inputs, resource requirements and effluents are similar to those in ethylene glycol production.

BEHAVIOR IN ENVIRONMENT: Transported widely, not considered toxic when handled carefully
Neither di- nor tri-ethylene glycol is considered a health hazard when handled using industry-standard safety standards. So, they can be stored in ordinary carbon steel containers. However, for ease of handling and to maintain its purity, special precautions should be taken. A future post will discuss glycol behavior in the evironment in more detail.

Profile: Propylene glycol

Although chemically related to other glycols, propylene glycol differs from them in how they are made, used and cleaned up.

CHEMISTRY: Alcohol
Propylene glycol is a clear, colorless liquid with the consistency of syrup. It dissolves easily in water and many other liquids. It is practically odorless and tasteless. It’s stable at room temperatures and isn’t explosive.

USES: Many applications for human and industrial use
Propylene glycol is produced in pharmaceutical, industrial and regular grades. Pharmaceutical grade propylene glycol must satisfy the requirements of US and European Pharmacopoeia standards because it is used in food, feed and personal care products. Other uses include pharmaceuticals, solvents, and preservative in food and tobacco products. Propylene glycol is also used as an alternative aircraft de-icing fluid.

PROCESSES:  Inorganic and organic alternatives:
INORGANIC: Expose propylene oxide to water under heat and pressure. Di- and tri-propylene glycols, as well as small quantities of higher glycols, are also produced in the reaction. The amount of water is controlled to favor propylene glycol production. The reaction mixture is dehydrated by evaporation and the various glycols separated by distillation.
ORGANIC: proprietary catalytic process converts glycerin into propylene glycol.  The reaction between glycerin and hydrogen takes place at high temperature and pressure over a unique catalyst to produce propylene glycol and water.  About 20 percent of the inputs is converted to propylene glycol, which is then purified to either industrial-grade or USP-specifications-grade product by using a proprietary separation method.

BEHAVIOR IN ENVIRONMENT: Transported widely, few health or safety risks when handled carefully.
Propylene glycol’s physical properties make it a low explosions or fire risk when moved and handled according to industry and government standards. However, it can pose health risks at high-dose accidental exposure. Our next post describes glycol health and environmental risks in detail.