Terephthalic acid

Oxidation p xylene

Oxidation of p-xylene to terephthalic acid

Terephthalic acid (TPA) is an organic compound with the formula C6H4(CO2H)2. It is a white, crystalline solid used primarily as a precursor to the polyester PET, used to make clothing and plastic bottles. TPA is an important commodity chemical, produced on a scale of several million tons per year.

Production

Terephthalic acid is principally made by oxidizing p-xylene in air, using a cobalt-manganese catalyst. The process involves several steps, including the formation of the intermediate p-toluic acid, which is further oxidized to TPA. Modern production techniques have improved the efficiency and environmental impact of TPA synthesis, notably through the development of the Amoco process, which allows for the direct oxidation of p-xylene to TPA at high yields.

Applications

The primary use of terephthalic acid is in the production of polyethylene terephthalate (PET), a polyester used in fibers for clothing, containers for liquids and foods, and in thermoforming for manufacturing. PET is synthesized by the polymerization of ethylene glycol and terephthalic acid, or its esters. TPA is also used in the production of other polyesters and in the manufacture of plasticizers, resins, and coatings.

Environmental and Health Concerns

Terephthalic acid is considered to be a low hazard substance, with the main risks associated with its dust form, which can cause respiratory irritation. In the environment, TPA is not readily biodegradable, but it is not classified as a persistent organic pollutant. However, the production and disposal of PET, which is derived from TPA, raise significant environmental concerns, particularly in terms of plastic pollution and the challenges associated with recycling PET products.

Recycling

Recycling of PET, and by extension TPA, is of growing importance in addressing environmental concerns. Chemical recycling methods have been developed to depolymerize PET back into its monomers, including terephthalic acid, which can then be purified and reused in the production of new PET. This circular approach to PET use helps to reduce waste and the consumption of raw materials.