Propylene glycol (PG) is used to make unsaturated polyester resins (UPRs), deicing and antifreeze fluids, food industry coolants, non-ionic detergents, plasticisers and hydraulic brake fluids. It is also an excellent solvent and extractant, and used as a humectant. In PG manufacture, monopropylene glycol (MPG) is the main product followed by dipropylene glycol (DPG) and tripropylene glycol (TPG).
The largest outlet for MPG is UPRs which are consumed primarily in the construction, marine and transportation industries. Nearly three-quarters of UPR is reinforced with fibre glass or mineral fillers to form fibre glass reinforced plastics (FRPs), which are tough, lightweight composites.
In residential and commercial construction, FRPs are used primarily to make building panels, bathroom components, fixtures and corrosion-resistant tanks, pipes and ducts. Other markets include the production of pleasure boats, passenger cars and trucks as well as recreational vehicles and major appliances.
In the US, western Europe and Japan, the UPR market is mature and growth has been slowing. However, general economic conditions are the main driving force behind demand and purchases of products containing FRP components are often among the first to be postponed or cancelled in an economic recession.
In addition, demand for UPRs could be hit by increased penetration from dicyclopentadiene (DCPD)-based resins. These resins use DCPD and ethylene glycol instead of phthalic anhydride and propylene glycol.
Another major use of PG is its use as an ingredient in engine coolants, deicing fluids and antifreeze. It has replaced ethylene glycol as the base fluid for aircraft deicing formulations and a coolant in the food industry. Propylene glycol is preferred over ethylene glycol due to its much lower toxicity.
Industrial grade PG is used in the production of polyglycols for hydraulic and brake fluids.
Propylene glycol is used as a solvent and extractant. Solvent applications include alkyd resins, printing inks and coatings.
Propylene glycol finds broad use as a humectant in the pharmaceutical, cosmetic, animal food and tobacco industries. Cosmetics include personal care products such as antiperspirants and deodorants. In these applications, PG keeps the moisture content of the materials in a narrow range despite fluctuations in environmental humidity.
A major use for DPG is speciality plasticisers, in particular dipropylene glycol dibenzoate. DPG and TPG have many applications in the fragrance, cosmetic and personal care industries while a fragrance-grade DPG is used as a carrier for cosmetics and fragrances. DPG is also used in the manufacture of UPRs.
Propylene glycol may see some substitution by glycerine in antifreeze and deicing applications as well as a replacement as a humectant in food applications. Glycerine is produced as a byproduct in biodiesel manufacture and the past boom in biodiesel projects has led to concerns of oversupply of glycerine.
In Europe, PG demand had been growing at 2-2.5%/year before the economic downturn. The European market is generally balanced in terms of supply and demand. However, demand in the UPR sector collapsed in late 2008 driven by the downturn in the construction and automotive sectors. The US pharmaceutical (USP) grade market has been steady while the demand in the deicing/antifreeze sector picked up in late 2008/early 2009 due to bad weather across Europe.
Growth in the US had been around 2%/year before being impacted by the economic downturn. The UPR sector had been growing at 1.5%/year with personal care segment doing somewhat better at 2.5%/year.
Asia is the world’s fastest growing region at about 6-7%/year over the longer term. Most of the new capacity planned is located in the region. China’s Zhenhai Refining and Chemical plans to build a 100,000 tonne/year PG plant at Zhejiang, downstream of its joint propylene oxide (PO) plant with LyondellBasell. The Siam Cement-Dow group plans to add a PG unit to its PO project in Thailand. Dow is also studying a PG plant at its joint venture complex with Saudi Aramco in Saudi Arabia.
In addition, there are a number of companies looking to produce PG from glycerine which is expected to become increasingly available as a byproduct of biodiesel manufacture. Archer Daniels Midland (ADM) will start up in 2010 a 100,000 tonne/year PG plant at Decatur, Illinois, using glycerine and sorbitol as raw materials. However, the Ashland Chemical-Cargill joint venture for a 65,000 tonne/year glycerine-based PG facility in Europe is believed to have been postponed. Huntsman and Dow Chemical have announced plans to make glycerine-based PG available to customers.
Updated: October 2009. Sources: ICB Chemical Profile, 7 October 2009
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Commercial production of propylene glycol is by hydration of propylene oxide. Di- and tripropylene glycols, as well as small quantities of higher glycols, are also produced in the reaction.
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