Oxidation of Purified Terephthalic Acid

Case 1 Catalytic Oxidation of Purified Terephthalic Acid 7.2.1. Introduction 

Terephthalic acid (TA) produced in a purified form (PTA) is used almost exclusively in the manufacture of polyethylene terephthalate (PET polyester) fibers. A smaller percentage of PTA is used for the manufacture of polyester films, polybutylene terephthalate resins and barrier resins for carbonated beverage bottles. Between 1994 and 1998, global PTA capacity increased by 62%, from lOmilfionto 17 million metric tons. Approximately 70% of worldwide PTA capacity is located in the Asia-Pacific region.  

The vent gases from purified terephthalic acid (PTA) plants contain CO, methyl bromide (MeBr) and various VOCs from the partial oxidation reaction of p-Xylene to terephthalic acid. Catalytic oxidation has been accepted as the most effective technology to control these emissions. Various catalytic components and carriers (or supports) were investigated in order to develop catalysts capable of controlling emissions at lower temperatures to reduce energy consumption. 

Production of PTA requires two separate processes, one to synthesize crude TA and one to purify crude TA. The predominant process for crude TA manufacture 

Air emissions from PTA production mostly come from the reactor vent gas of the TA production stage. There are no VOC emissions associated with the purification of TA. After passing through aqueous adsorbers, the reactor vent gas still contains the VOCs of p-xylene, acetic acid, methyl acetate, toluene, benzene, methyl bromide and CO. With increasingly stringent environmental regulations combined with the expansion of PTA capacity, more and more PTA plants are required to further reduce air emissions from the adsorber vent gas. 

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