Toluene diisocyanate (TDI) exists as two isomers; 2,4-TDI and 2,6-TDI. The most common form of TDI offered commercially is an 80/20 mixture of the 2,4- and 2,6-isomers but is also available as a 65/35 mixture as well as a pure 2,4-isomer.
The main outlet for TDI is in the manufacture of polyurethane (PU) flexible foams used in upholstery, mattresses and automotive seats. This is achieved by reacting the TDI with a polyol to produce the foam. Depending on the components selected and how they are combined, end-products with quite different properties can be achieved.
The majority of flexible foams are produced by the slabstock foaming process, in which the mixture of polyurethane raw materials is dispensed onto paper linings in an open trough, where it gradually expands into a large bun of foam. These buns are then cut into blocks or slices, which are then processed into their final form by the converter.
Another important foaming technique is the moulded foam process. Here the PU raw material mix is filled into moulds where the foam takes on the required shape without a great deal of additional processing.
Automotive seats are produced mainly from moulded foam with each car seat containing an average of 9kg of PU foam. This technique also allows up to four different hardness zones, for example the sitting area and seat wings, to be incorporated in a single process. Airline seats are also manufactured from flexible PU foams.
Smaller uses for TDI include polyurethane elastomers and coatings. PU elastomers are noted for their toughness, flexibility, strength, abrasion resistance, shock absorbency and chemical resistance. Because they are relatively expensive compared to most other elastomers, they are used in more demanding applications such as automobile bumper covers and facias, industrial rollers, sport soles and boots, and mechanical goods.
PU coatings are one of the fastest growing sectors of the paints and coatings industry. Despite their relatively high cost, they are suitable for a range of high performance applications due to their excellent durability, resistance to corrosion and abrasion, and flexibility. Markets for PU coatings include automotive refinishing, wood finishes and high performance anti-corrosion coatings.
With most of TDI’s output going into the furniture and automotive sectors, demand is sensitive to economic activity. However, long-term global demand growth for TDI is estimated at around 4-5%/year.
Growth in the US is much lower than the world average and has been adversely impacted by the slowdown in the economy. Flexible PU foams account for 88% of TDI demand in the US with transportation, furniture, carpet and bedding markets being the main outlets. Consumption of TDI is estimated to have decline by nearly 2% in 2007 compared to 2006.
Nevertheless, in the longer term, US demand is expected to grow by 2.4%/year through to 2011, according to ICIS Chemical Business (ICB). Demand is forecast to increase from 240,000 tonnes in 2007 to 263,000 tonnes in 2011. Exports in 2007 were a sizeable 185,000 tonnes while imports were negligible.
Around 38% of capacity has been shut in the US in the first half of the decade with Dow, Bayer, Huntsman and Lyondell (now LyondellBasell) closing plants. This has resulted in a balanced supply/demand situation and operating rates at a healthy mid-90% range. ICB estimates that TDI capacity in the US at 440,000 tonnes/year is barely sufficient to meet domestic demand and exports.
Demand in western Europe will also grow more slowly at GDP rates. However, growth in eastern and central Europe, Middle East and Africa will be much higher at 5-6%/year, driven by improving living standards. Growth in Asia, where China accounts for three-quarters of TDI consumption, is put at about 8%/year.
World TDI markets have also tightened considerably, partly due to closure of capacity in 2005 and 2006. This tightness is expected to continue for the next three years but markets could move into overcapacity in 2011-2012 with a number of new projects coming on-stream.
No major new capacity is planned until BorsodChem brings on-stream its 170,000 tonnes/year facility in Kazincbarika, Hungary, in the second half of 2009. BorsodChem has plans to grow its European base with the new plant.
Bayer has increased the capacity of its proposed plant in Shanghai from 160,000 tonnes/year to 300,000 tonnes/year as a result of new phosgenation technology. This project is expected to be completed in 2010. A number of other projects are also being studied in China.
A BASF and Dow Chemical joint venture is carrying out a feasibility study into the construction of a 300,000 tonnes/year TDI facility in Europe. If the study proves positive, the plant could start operating in 2011.
Dow is also conducting a feasibility study to expand TDI capacity in Brazil using a new process technology. The plant will meet demand for TDI in Latin America which is expected to grow at 1-2% above GDP through to 2015, according to Dow. A decision to proceed is expected to be made in Q4 2008 which would enable the new capacity to come on-stream in 2011.
Updated: April 2008. Source: ICB Chemical Profiles, 7 April 2008 and 21 January 2008.
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