Purification of terephthalic acid (PTA)
Terephthalic acid is a precursor to the polyester PET, used to make plastic bottles and clothing. Crude terephthalic acid is produced by catalytic air oxidation of p-xylene. During this process, unwanted by-products are formed. One in particular, 4-carboxybenzaldehyde (4-CBA), needs to be removed, as it is a colored compound.
Therefore, the crude terephthalic acid is purified in a fixed-bed reactor using Clariant’s H2MAX® catalyst: the colored by-products are hydrogenated to uncolored and water-soluble substances. In the end, the purified terephthalic acid (PTA) has typically less than 20 parts-per-million (ppm) of 4-CBA.
H2MAX® catalysts contain palladium, a precious metal. Clariant produces the catalysts with a unique production technology that assures their activity remain stable for a long time. For precious metal catalysts, it is important that they preserve as much as possible of the valuable metal during operation. H2MAX® retains more palladium during its lifetime than other state-of-the-art catalysts. This means that customers save money, as they need to buy less palladium.