Processing of DEHP
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.