Analysis of impurities in crude and highly-purified terephthalic acid by capillary electrophoresis

Abstract

Neste trabalho, foi desenvolvido um método simples e rápido, utilizando eletroforese capilar (CE), para a análise simultânea de 4-carboxibenzaldeído (4-CBA), ácido p-toluóico (pTOL) e ácido benzóico (BZ), em lotes industriais de ácido tereftálico cru (CTA) e purificado (PTA). As condições eletroforéticas de análise foram: tampão tetraborato a 20 mmol L -1 (pH 9), injeção hidrodinâmica (5 s, 17 kPa), tensão aplicada de +30 kV e detecção direta em 200 nm.Foram analisados cinco lotes de CTA e quatro lotes de PTA nos teores de 4-CBA e pTOL pela metodologia proposta e as metodologias utilizadas na empresa Tereftalatos Mexicanos S.A. (TEMEX), que são cromatografia gasosa para pTOL e polarografia para 4-CBA, mostrando concordância entre os valores encontrados. Os níveis de BZ foram determinados apenas pela metodologia CE, apresentando no CTA, valores compreendidos entre 60 e 300 ppm, enquanto que no PTA, 5 a 7 ppm. Várias impurezas derivadas da oxidação incompleta do p-xileno foram investigadas, constatando-se a presença do ácido 4-hidroximetilbenzóico por comparação com padrões.In this work, a simple and fast capillary electrophoresis method for the simultaneous analysis of 4-carboxybenzaldehyde (4-CBA), p-toluic acid (pTOL) and benzoic acid (BZ) in industrial batches of crude (CTA) and highly-purified (PTA) terephthalic acid was developed. The electrophoretic conditions comprise: 20 mmol L -1 tetraborate buffer at pH 9, hydrodynamic injection (5 s/17 kPa), applied voltage of +30 kV and direct UV detection at 200 nm.The concentrations of 4-CBA and pTOL in five batches of CTA and four batches of PTA as determined by the proposed CE methodology were in agreement with the results from gas chromatography and polarography methods in current use in Tereftalatos Mexicanos S.A. (TEMEX). Levels of BZ were determined only by the CE methodology and ranged from 60 -300 ppm in CTA and 5 -7 ppm in PTA. Several impurities deriving from the incomplete oxidation of p-xylene were investigated. So far the positive identification of 4-hydroxymethylbenzoic acid was accomplished by comparison with pure standards.

Impact of MTA blend % in melt spinning process and polyester properties

“…The PTA route, which is easier to handle, transport and cheaper, and allows for very quick reaction times than the DMT route. That's why the PTA route is preferable in industrial applications [6][7][8][9][10][11]. In the PTA route, mono ethylene glycol and purified terephthalic acid (PTA), and moderately purified terephthalic acid (MTA) are used as raw materials to make PET.…”