Bhuma Rajagopalan, University of Kansas, 1530 W, 15th street room # 4132 Learned Hall, Lawrence, KS 66045, Bala Subramaniam, Center for Environmentally Beneficial Catalysis/Chemical Engineering, University of Kansas, 1501 Wakarusa Dr., Suite A-110, Lawrence, KS 66047, and Daryle H. Busch, CEBC/Chemistry, University of Kansas, 1501 Wakarusa Drive, Lawrence, KS 66047.
Terephthalic acid is a monomer for the polymerization of polyethylene terephthalate (PET), feedstock for the manufacture of plastics, films and fibers. The commercial process utilizes a catalytic system consisting of cobalt-manganese and bromine that affords product in both high yield and purity. However, the use of air as the oxidant source and the corrosive nature of the halide catalyst-solvent system leads to corrosion, safety, environmental issues. The unique properties of CO2 -based reaction media provide opportunities to address the abovementioned issues by providing tunable transport properties and solubilities (gases and catalysts). This work systematically investigates the addition of CO2 to the acetic acid-based reaction medium for the production of terephthalic acid using the commercial catalytic system. The effect of CO2 addition was studied in terms of p-xylene conversion, terephthalic acid yield and purity over a wide range of temperatures along with safety aspects. Further, the product separation advantages afforded by CO2 (as an antisolvent) will also be presented. The efficacy of a novel catalytic system consisting of cobalt and N-hydroxy succinamide will also be evaluated under milder temperatures (80°C) in CO2 expanded acetic acid and compared with the conventional process.