p-Xylene Oxidation to Terephthalic Acid: New Trends

Abstract

Large-scale terephthalic acid production from the oxidation of p-xylene is an especially important process in the polyester industry, as it is mainly used in polyethylene terephthalate (PET) manufacturing, a polymer that is widely used in fibers, films, and plastic products. This review presents and discusses catalytic advances and new trends in terephthalic acid production (since 2014), innovations in terephthalic acid purification processes, and simulations of reactors and reaction mechanisms.

Keywords: oxidation; p-xylene; polyethylene terephthalate; terephthalic acid.

Figure 1

Applications of terephthalic acid (1,4-benzenedicarboxylic acid, TPA). Adapted from [1].

Scheme 1

Reaction pathway and products obtained for the oxidation of p-xylene.

Figure 2

Example of the aza-crowned dihydroxamic acid, n = 0–4. Adapted from [21].

Figure 3

Iron(II) C-scorpionate complex structure. Adapted from [23].

Scheme 2

Proposed mechanism for the oxidation of p-xylene catalyzed by a C-scorpionate iron(II) complex. Adapted from [23].

Figure 4

Structures of iron(III) containing bis-(2-pyridymethyl)amine) (BMPA) and derivatives. Adapted from [24].

Figure 5

Structure of the osmium(VI) nitride complex. Adapted from [25].

Figure 6

Structure of an iron(II) complex bearing a tetradentate bis(pyridyl-N-heterocyclic carbene) ligand. Adapted from [26].

Scheme 3

Proposed mechanism for the oxidation of 1,4-dihydroxymethylbenzene. Adapted from [27].

Figure 7

Structure of the copper(II) complexes derived from aroylhydrazone N’-(di(pyridin-2-yl)methylene)pyrazine-2-carbohydrazide; (A) Complex [Cu₂(μ-1κN³,2κN²O-L)(Cl)₃(MeOH)] (B) 1D polymer [Cu₃(μ₃-1κN³,2κN²O,3κNL)(μ-NO₃)(NO₃)₃(H₂O)₃]n·nNO₃. Adapted from [29].

Figure 8

Structure of the 1-benzyl-4-N,N-dimethylaminopyridinium salt. Adapted from [30].

Scheme 4

Reaction mechanism proposed by Hwang et al. for p-xylene oxidation in CH₃CN-H₂O with ozone upon UV light irradiation. Adapted from [31].

Scheme 5

Mechanism of p-xylene photooxidation catalyzed by anthraquinone derivative with O₂ under visible light. Adapted from [32].

Figure 9

Structure of the vanadium(IV) C-scorpionate complex. Adapted from [43].

Scheme 6

Reaction pathway for the oxidation of p-cymene, with low oxidation products in the orange box and high oxidation products in the green box. Adapted from [52].

Scheme 7

The mechanism proposed for the oxidation of p-xylene, which is catalyzed by Co-BTC/NDHPI X = CH₃, COOH. Adapted from [53].

Figure 10

Flow sheet of an industrial hydropurification plant for TPA. Adapted from [68].

Figure 11

Flow sheet of the industrial hydropurification plant for TPA with improved PID control. Adapted from [68].

Scheme 8

Reaction mechanism for the reaction of DFT-derived p-xylene. Adapted from [25].

Scheme 9

Reaction pathway and products obtained for the hydrogenation of 4-CBA.

Scheme 10

Reaction pathway and the product obtained for the decarbonylation of 4-CBA.

Figure 12

Representation of the (A) opposed-flow reactor and (B) tubular reactor, where elements labeled H are heating blocks. Adapted from [74].