TDI chemistry and production

Toluene diisocyanate (TDI) is an aromatic diisocyanate and exists in two isomers: 2,4 TDI and 2,6 TDI.


TDI Types

TDI type Description  Form at room temperature
TDI 65/35 Contains 2,4/2,6 isomers in the ratio of 65/35  Water clear liquid material
TDI 80/20 Contains 2,4/2,6 isomers in the ratio of 80/20 Water clear liquid material
TDI 100 Contains 2,4 isomers in 99% Water clear liquid material
Modified TDI Partially reacted TDI isomers giving versatility in handling and properties Water clear liquid material
The main outlet for TDI is in the manufacture of polyurethane flexible foams used in upholstery, mattresses and vehicle seats.
Flexible foam for furniture is produced by a slabstock foaming process. The resulting foam slabs are cut into shapes, which are then combined with materials such as springs or webbing to produce finished products.
PU flexible foam is the only cushioning foam used in upholstered seating. Different foam grades can be used to achieve different degrees of comfort, durability, support etc. It is also used in bedding for wadding and padding. Increasingly, full polyurethane foams are also penetrating the sprung mattress market.
The transport/automotive seating sector is also an important market. This application uses moulded rather than slabstock foam.


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Production process

The main commercial route for the manufacture of TDI starts with the nitration of toluene using nitric acid to produce dinitrotoluene (DNT), followed by catalytic hydrogenation to toluene diamine (TDA). The toluene diamine is dissolved in an inert solvent and reacted with phosgene to produce a crude TDI solution. The crude solution of TDI is fractionated to remove any unreacted phosgene, solvent and hydrogen chloride before being distilled under vacuum.

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