Propylene oxide (PO) is a highly reactive chemical used as an intermediate for the production of numerous commercial materials. It reacts readily with compounds containing active hydrogen atoms such as alcohols, amines and acids. Its main derivatives include polyether polyols, propylene glycol (PG) and propylene glycol ethers but it has many other outlets.
Consumption of PO is dominated by its largest end use, polyether polyols. They are reacted with an isocyanate to form polyurethanes. Polyurethane end uses include flexible foams for the furniture and automotive industries, and rigid foams for appliance and building insulation. Polyols also go into non-foam applications such as coatings, adhesives, sealants and elastomers, as well as thermoplastic resins and fibres.
The growth in demand for polyether polyols is largely dependent on their use in polyurethane foam. Flexible and semi-rigid foams account for a major portion of polyols demand. In addition, a higher proportion of the polyol is used in flexible foam formulations compared to rigid foam formulations. Traditionally, rigid foams have grown faster than flexible foam due to their increasing use in insulation and structural applications.
The second largest consumer of PO is propylene glycol with monopropylene glycol (MPG) being the main product. MPG is mainly used to make unsaturated polyester resins (UPR) of which nearly three quarters are reinforced with fibre glass or mineral fillers to form fibre glass reinforced plastics (FRPs). In residential and commercial construction, FRPs are used primarily to make building panels, bathroom components, fixtures, corrosion-resistant tanks, pipes and ducts. Other uses include pleasure boats, recreational vehicles, passenger cars and trucks.
MPG is also used in coolants and antifreeze, aircraft deicing fluids and heat transfer fluids. Where there are environmental concerns, MPG is favoured over monoethylene glycol (MEG) due to its lower toxicity. MPG along with dipropylene glycol (DPG) and tripropylene glycol (TPG) are used in the fragrance, cosmetics and personal care industries as solvents, carriers, humectants and preservatives.
Polyglycols offer a wide range of formulating possibilities depending on their molecular weight. When used as functional fluids, they offer good lubricant and solvent properties. Applications include hydraulic and brake fluids, heat transfer liquids, surfactants and foam control.
Propylene glycol ethers (PGE) are formed by the reaction of PO with alcohols such as methanol, ethanol, propanol and butanol. PGEs are commonly used as solvents and coupling agents in paints and in the production of coatings, inks, resins and cleaners. PGE solvents exhibit lower toxicological effects than their ethylene glycol ether counterparts.
One producer, LyondellBasell, uses PO to make butanediol (BDO) which is consumed in the production of high performance polymers, solvents and fine chemicals.
Propylene oxide can be used as a component for a variety of surfactants for gas dispersion, detergency and friction reduction. Applications include detergents, paints, adhesives and cosmetics.
Propylene oxide can be reacted with phosphorous derivatives to create flame retardants. They can be used in polyurethane foams, textiles and floorings.
Modified carbohydrates or starches can be used in a variety of applications in the construction, paint, food and pharmaceutical industries. Hydroxypropyl starches have enhanced freeze/thaw stability that help frozen food products maintain their integrity as well as use as thickening agents and stabilisers. Industrial starches modified with PO have applications such as oil field drilling chemicals, paints and adhesives.
Other applications for PO include hydroxypropyl acrylates used in UV curable resins, inks, coatings and varnishes; isopropanolamines employed as solvents in natural gas purification, metal working fluids and cosmetics; and propylene glycol alginates made with sea weed (kelp) for use as food grade thickeners, emulsifiers and stabilisers.
Global demand for PO had been growing at 4-5%/year. Growth in Europe and the US had been around 3-4%/year while Asia, in particular China, had seen the strongest growth at 7-8%/year.
In addition, growth came to an abrupt halt when markets collapsed in the second half of 2008 due to the economic crisis. Overall sales were said to be 5% down in 2008 compared to 2007 and a further decline of 5% is expected in 2009. As a result much capacity has been temporarily idled in this period. Markets are not expected to return to pre-crisis growth levels until 2011, according to some market sources.
However, 2009 also saw the start-up of two new PO plants. BASF and Dow Chemical started up a 300,000 tonne/year joint venture plant in Antwerp, Belgium, based on a new hydrogen peroxide HPPO process. PetroRabigh, a joint venture between Saudi Aramco and Sumitomo Chemical, commissioned a 200,000 tonne/year PO plant in Saudi Arabia using Sumitomo’s cumene hydroperoxide process.
Further capacity is under construction. Dow Chemical and Thailand’s Siam Cement are building a 390,000 tonne/year plant at Mab Ta Phut using HPPO technology with start-up expected in 2011. LyondellBasell and Sinopec have formed a joint venture to build a 285,000 tonne/year plant at Ningbo, China.
Updated: October 2009. Sources: ICB Chemical Profile, 7 September 2009.
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Propylene oxide (PO) is made traditionally by chlorohydrin or epoxidation routes. In the older chlorohydrin process, propylene and chlorine react in the presence of water to form propylene chlorohydrin, which is further reacted with sodium or calcium hydroxide to obtain PO.
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