Di(2-ethylhexyl) phthalate (DEHP) is one of the most cost effective and widely available general purpose plasticisers. It is used mainly for making PVC soft and pliable and it accounts for around 15% of all plasticiser usage in Western Europe.
DEHP (CAS No [117-81-7]) is also known as di-octyl phthalate (DOP). It is the phthalate ester of the alcohol 2-ethyl hexanol, which is normally manufactured by the dimerisation of butyraldehyde, the butyraldehyde itself being synthesised from propylene.
DEHP is a plasticiser which offers a good all-round performance and is therefore used for a great many cost-effective, general purpose products including building material such as flooring, cables, profiles and roof membranes, as well as medical products such as blood bags and dialysis equipment.
DEHP possesses reasonable plasticising efficiency, fusion rate and viscosity (of great importance for plastisol applications).
The content of DEHP in flexible polymer materials varies but is often around 30% (w/w).
All manufacturers of phthalate esters use similar processes. DEHP is produced by the esterfication of phthalic anhydride with 2-ethyl-hexanol. This reaction occurs in two successive steps. The first reaction step results in the formation of monoester by alcoholysis of phthalic acid. This step is rapid and proceeds to completion.
The second step involves the conversion of the monoester to the di-ester. This is a reversible reaction and proceeds more slowly than the first.
To shift the equilibrium towards the di-ester, the reaction water is removed by distillation. Elevated temperatures and a catalyst accelerate the reaction rate. Depending on the catalyst used, the temperature in the second step varies from 140°C to 165°C with acid catalysts and from 200°C to 250°C with amphoteric catalysts. Variations in purity may occur depending on catalyst, reactant alcohol and process type.
Excess alcohol is recovered and recycled and DEHP is purified by vacuum distillation and/or activated charcoal. The reaction sequence is performed in a closed system. This process can be run continuously or batchwise.
- More background information on DEHP is available in the EU Risk Assessment Reports