Terephthalic acid from phthalic anhydride

Whereas benzene and toluene serve as the raw materials for a wide range of products, applications for the three xylene isomers, o-, m- and p-xylene, are basically limited to chemicals arising through oxidation, i.e. phthalic anhydride (PA) from o-xylene, isophthalic acid from m-xylene and terephthalic acid from p-xylene. 

In addition to the use of p-xylene as a raw material in the production of tere-phthalic acid, processes were also operated in the past to produce terephthalic acid from toluene and phthalic anhydride. 

Smdies of the thermal degradation of several aromatic acids have been reported. Phthalic acid (80), but not isophthalic acid (81) or terephthalic acid (82), decomposes via dehydration to its anhydride at 140-160 °C. However, (81) and (82) and benzoic acid are thermally stable below 200 °C. Dissociation constants of all 19 isomers of methyl-substimted benzoic acids (83) have been measured in methanol and DMSO. From the pA a values, the substiment effects of the methyl groups were calculated and tentatively divided into polar and steric effects. Also, in the case... 

There are only two top 50 chemicals, terephthalic acid and dimethyl terephthalate, derived from /7-xylene and none from o- or m-xylene. But phthalic anhydride is made in large amounts from o-xylene. 

For the esterification of terephthalic acid with ethylene glycol at 473 K, SO /TiCh calcined at 773 K is much more active than SiC -A Ch as shown in Fig. 6 [60]. The SO /TiCh showed a maximum activity when calcined at 573 K for the esterification of oleic acid with glycerol and of propionic acid with butanol at 403 K [61], where the active sites were attributed to Bronsted acid sites from a correlation between the activity and the Bronsted acidity. The esterification of phthalic anhydride with 2-ethylhexanol to form dioctyl phthalate is also efficiently catalyzed by solid super-acids, the selectivity being more than 90% [62]. The... 

On the other hand, although o-phthalic acid, or rather its anhydride, had long been produced in enormous amounts for use in the manufacture of alkyd resins, the para derivative was less well known and not available on a large scale. The synthesis is a straightforward one, however, from p-xylene, which is oxidized to terephthalic acid, either by means of nitric acid in the older process or by air (catalyzed) in the newer one. In the early years this compound then was converted to the easily purified dimethyl ester in order to obtain a colorless polymer adequate for the manufacture of commercially acceptable fibers. 

Polymer concretes show excellent mechanical properties and chemical resistance compared with conventional cement concretes. Polymer concretes can be cured quickly by the use of curing agents. Thus, the applications of polymer concretes are being increased. One of the popular polymers for polymer concretes is unsaturated polyester (UPE) resin. The properties of UPE resin can be modified by changing its molecular features. For the synthesis of the resin, phthalic anhydride or isophthalic acid as well as maleic anhydride can be employed to modify the mechanical properties or hydrothermal resistance. Terephthalic acid which is also used for the synthesis of poly ethylene terephthalate (PET) enhances the thermal resistance of the cured UPE resin. However, the synthesis of unsaturated polyester resin from terephthalic acid is difficult. One method to synthesize unsaturated polyester from terephthalic acid is the use of recycled PET. 

In 1968 U.S. production of p- and o-xylene was estimated at 1.3 billion and 0.97 billion pounds per year respectively. Production figures for m-xylene have never been published by the Tariff Commission. Its use has, however, remained quite small in relation to p- and o-xylene. It is expected that domestic demand for both p- and o-xylene will continue to increase. Terephthalic acid is the key component required for production of polyester film and fibers and is presently produced only from p-xylene. Phthalic anhydride is produced from both naphthalene and o-xylene. Although o-xylene is not expected to replace naphthalene entirely, its use for phthalic anhydride manufacture is expected to increase. 

Poly(ethylene terephthalate) is a linear polyester obtained from the reaction of difunctional monomers. Branched or network polyesters are obtained if at least one of the reagents is tri- or multifunctional. This can be achieved either by the use of polyols such as glycerol in the case of saturated polyesters (glyptal) or by the use of unsaturated dicarboxyhc acids such as maleic anhydride in the ease of unsaturated polyester. In the preparation of glyptal, glycerol and phthalic anhydride reaet to form a viseous liquid initially, which on further reaction hardens as a result of network formation (Equation 2.31). 

Polyarylate oximates (PAO) were prepared from various diketoximes (DKO) and dichloride anhydrides of wo-phthalic (CAIP) and terephthalic acids (CAT). Synthesis of polyarylate oximates was earned out by low temperature eatalytic-acceptor polyeondensation, with triethylamine as catalyst (Fig.l)... 

One of the most important selective oxidation processes in the production of chemicals is the side chain oxidation of alkyl aromatics, which are then further reacted to higher value products that end up in a variety of polymer compositions and specialised chemicals.The largest oxyfunctionalised aromatic products with regard to world production are terephthalic acid, phthalic anhydride and benzoic acid which are produced worldwide with capacities of >30,000, 5,000 and 500 kt a respectively. Worldwide production capacities for benzaldehyde and pyromel-litic dianhydride do not rise above 50 kt a In smaller capacities as specialty chemicals for the pharmaceutical industry, halo-substituted oxyfunctionalized aromatics are also produced. Of the aforementioned products, phthalic anhydride and pyromellitic dianhydride are produced from gas-phase processes using V20s-Ti02 catalysts and a liquid-phase alternative process does not appear immediately desirable. On the other hand, terephtalic and benzoic acids, and benzaldehyde are... 

The terephthalate plasticizer DEHTP, first commercialized around 1975 as Eastman DOTP, is very similar in structure to DEHP except that the substitution of the aromatic ring is at the 1,4 position versus the 1,2 position of the aromatic ring. The structure of DEHTP is also shown in Pig. 24.1. Terephthalates are prepared by the esterification of terephthaUc acid or by the transesterification of dimethyl terephthalate with aliphatic alcohols such as butanol or 2-ethyl hexanol. Although DEHTP can be produced from terephthalic acid in a traditional DEHP esterification plant with minor modifications to the process, this process is not as efficient as the esterification of phthalic anhydride and manufacturing capacity reductions of >50% are realized. Transesterification of dimethyl terephthalate is a much faster reaction. However, this process will require significant process modifications to a traditional DEHP manufacturing unit. One benefit with this chemistry is that it does not lead to a significant drop in production capacity. The main problem with this route is the limited availability of dimethyl terephthalate in many locations. 

Xylenes are used inter alia as solvents, for example in the USA 180,000 t p.a. [13] and in Japan 90,000 t [33], particularly in the paint and printing ink industries (see also [5]). In eastern Europe it is also used for numerous applications in the shoe industry, o-xylene (besides naphthalene) is mainly oxidized to phthalic anhydride from which dyestuffs, phthalodinitrile and - by esterification with alcohols - plasticizers and raw materials for paints and varnishes are obtained [36, 38]. p-xylene is oxidized and processed with methanol to terephthalic acid dimethyl ester, from which polyesters are made [36, 38, 39]. For example, in 1972 2.9 million t polyester fibres were produced worldwide [39] and in 1979 more than 5 million t, which corresponds to 2.8 million t of p-xylene [30 a]. Polystyrene and copolymers (including expanded plastics) in particular are polymerized from styrene, and the world annual production of these products around 1975 was about 5 million t [39, 40],... 

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