Use of NH₄OAc and BMIM Br in Staged Oxidation of p-Xylene and Oxidative Treatment of CTA for Obtaining TPA with a Low Content of 4-CBA
2019
Kuznetsova, Nina I. | Kuznetsova, Lidia I. | Yakovina, Olga A. | Zudin, Vladimir N. | Bal’zhinimaev, Bair S. | Bhattacharyya, Alakananda | Walenga, Joel T.
Synthesis of terephthalic acid (TPA) with a low content of p-toluic acid and 4-carboxybenzaldehyde (4-CBA) intermediates through only oxidative procedures without hydrogenation purification is a promising approach to simplify commercial production. Here, addition of ammonium acetate (NH₄OAc) and 1-butyl-3-methylimidazolium bromide (BMIM Br) has been proposed to conduct two-step oxidation of p-xylene and oxidative treatment of crude terephthalic acid (CTA) using conventional conditions and a Co/Mn/Br catalyst. The additives enabled an efficient oxidation of undesirable intermediates due to an increase in their solubility under reaction conditions. Concentration of the catalyst, temperature and duration of the procedure were important factors affecting the oxidation. Subsequent recrystallization was advisable for further removal of the intermediates, as well as for the hydrolysis of the impure amide that was caused by bringing them into contact with nitrogen compounds. BMIM Br required a higher temperature than NH₄OAc to oxidize the intermediates, but did not generate colored impurities during the oxidation. The oxidative treatment of CTA in the presence of BMIM Br allowed to obtain an absolute white TPA with a content of 4-CBA below 300 ppm that corresponded to medium quality TPA.
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