Pure Terephthalic Acid (PTA) is a white powder-substance used extensively in the production of plastics and polyester products like fibers or films. The material is produced in a pressurized reactor where acetic acid and xylene are combined chemically in the presence of catalyst.
The majority of the PTA emissions come from this reactor, although there are small emissions sources from these facilities that could also emit VOCs and/or HAPs.
Gas-phase byproducts of the PTA reaction are CO2 (carbon dioxide), CO (carbon monoxide), water vapor, methyl acetate, unreacted xylene, acetaldehyde and small concentrations of methyl bromide.
These gas phase emissions are routed to a pressurized absorber where the gases are scrubbed with water to reduce emissions. The remaining air emissions are then routed to an abatement device.
A PTA plant in the Middle East was looking to expand production from 420 metric tons to 700 metric tons per year.
An existing catalytic oxidizer with two reactor modules was only designed to treat a total flow of 67,000 SCFM (106,000 Nm3/h). Rather than return to the catalytic style oxidizer they were familiar with, this plant decided that the RTO technology would be the better solution.
In order to provide optimum performance they installed two RTOs with the capacity to handle 127,000 SCFM (200,000 Nm3/h) of total airflow. The RTOs share some common components such as a main system stack and electrical controls but are capable of operating independently during routine maintenance or slow production.
When compared to the old catalytic oxidizer, the new RTOs collectively emit 5,000 fewer tons per year of CO2 emissions and 5 tons each year of NOX emissions, which corresponds to approximately 10 MMBTU/hr of reduced auxiliary fuel consumption.
The plant essentially doubled the capacity of the abatement device, lowered operating costs and reduced their carbon footprint all while achieving greater than 98% destruction of the targeted pollutants.
In addition, there are no ongoing catalyst replacement costs, saving a significant amount of money maintenance expenditures.
Most of the recent PTA expansions have occurred in the Middle East, India and Asia where these plants are in close proximity to the plastic products made from the material.
However, the low cost for carbon-based precursors will likely bring more of this PTA manufacturing back to the United States where manufacturers can also take advantage of the new air pollution control technologies and techniques.