PEP Review IX-1-4
Terephthalic Acid from p-Xylene through Terephthalonitrile
Published: September 1973
There are several commercial routes for the production of fiber-grade terephthalic acid or dimethyl terephthalate. The main process step in these routes is either the liquid phase oxidation of an aromatic hydrocarbon, usually p-xylene, or the rearrangement of the salt of an aromatic carboxylic acid, e.g., dipotassium phthalate. One type of process commercially produces (by ammoxidation of p-xylene) terephthalonitrile as an intermediate. A route of this type was evaluated in Supplement A (January 1967) to Process Economics Program Report No. 9, Terephthalic Acid and Dimethyl Terephthalate.
The first step in the process is the production of terephthalonitrile by the ammoxidation of p-xylene. The terephthalonitrile is then converted to bis(2-hydroxyethyl)terephthalate. The estimated capital and production costs for this process were compared with estimated costs for one of the conventional routes and it was concluded that the terephthalonitrile route could be competitive if the ammonia/p-xylene feed mol ratio was 4.0, fluidized bed reactors were used in the ammoxidation step, and disposal of waste streams was not costly.
Recently, the Lummus Company revealed a process to make fiber-grade terephthalic acid from p-xylene in which terephthalonitrile is an intermediate.