3. Processes

The quality of terephthalic acid, produced industrially in the 1950s, was unsuitable for the manufacture of PET as a result:

• the presence of prohibitive impurities;

• unsuitable crystal morphology (size and shape of crystals). The insoluble crystals were too small and required a very large quantity of glycol to form a conveyable paste, which led to very high levels of diethylene glycol (5%) and an additional cost that put a strain on the economics of the process.

For this reason, the first PET production units in the 1950s-1960s used batch processes based on DMT, a raw material that could be distilled under reduced pressure, and therefore easily purified, and miscible with glycol in the molten state. Productivity ranged...