Terephthalic acid, production

Fig. 2. Terephthalic acid production by catalytic, liquid-phase air oxidation of -xylene.

Figure 15.12. Simple flow-scheme for terephthalic acid production...

Polyester Polyols. Initially polyester polyols were the preferred raw materials for polyurethanes, but in the 1990s the less expensive polyether polyols dominate the polyurethane market. Inexpensive aromatic polyester polyols have been introduced for rigid foam applications. These are obtained from residues of terephthalic acid production or by transesterification of dimethyl terephthalate (DMT) or poly (ethylene terephthalate) (PET) scrap with glycols. 

Purified Terephthalic Acid Production Alternative Energy Development... 

In the case of terephthalic acid production by oxidation with air, an addition of Zr, Fe, and Ni produces high conversions of p-xylene to almost colorless terephthalic acid [17, 18]. In this context other catalyst components such as Ce, W, Mo, V, Cr, Be, Al, Bi, Cd, Fe, Pd, and Nd are claimed [18]. 

Kingsley JP, Rohy AK, Litz LM. (1994) Terephthalic acid production. U.S. Patent 5,371,283. 

Amemiya, T., Hayashi, K. Industrial Development of Terephthalic Acid Production in Japan Sixth World Petroleum Congress, Frankfurt/Main, June 19-26 (1963), Verein zur Forderung des 6.Welt-Erd61-Kongresses, Hamburg... 

The alkylation of toluene with methanol has been investigated for many years as a potential alternative route to / - Qflene, ethylbenzene, and styrene. Conventional / -xylene production from petroleum reformate requires costly purification and separation from jQ lene isomers and other aromatics. A process that selectively produces /)-xylene could have a significant commercial impact by eliminating the need for p-xylene separation. Furthermore, styrene or ethylbenzene production from methanol and toluene is desired as part of the development of processes based on Cl feedstocks rather than ethylene or propylene feedstocks [48], Para- xyl ae is used primarily in terephthalic acid production, a major component of polyester manufacture. 

Those polymers which are the condensation product of two different monomers are named by applying the preceding rules to the repeat unit. For example, the polyester formed by the condensation of ethylene glycol and terephthalic acid is called poly(oxyethylene oxyterphthaloyl) according to the lUPAC system, as well as poly (ethylene terephthalate) or polyethylene terephthalate. 

Purified terephthalic acid and dimethyl terephthalate are used as raw materials for the production of saturated polyesters. During 1993, the combined worldwide production of purified terephthafic acid plus dimethyl terephthalate exceeded 14 x 10 t (42), which is 80% of the total benzenepolycarboxyfic acid production. Terephthafic acid is also produced ia technical or cmde grades which are not pure enough for manufacture of poly(ethylene terephthalate). In almost all cases, the technical-grade material is immediately converted to purified terephthafic acid or dimethyl terephthalate, which together are the articles of commerce. 

Like terephthalic acid, isophthalic acid is used as a raw material in the production of polyesters. Much of the isophthaUc acid is used for unsaturated polyesters, whereas terephthaUc acid is used almost exclusively in saturated (thermoplastic) polyesters. However, a considerable amount of isophthaUc acid is used as a minor comonomer in saturated polyesters, where the principal diacid is terephthaUc acid. The production volume of isophthaUc acid is less than 2% that of terephthahc. IsophthaUc acid was formerly produced in technical or cmde grades and only a small amount was purified. Now, however, it is all purified to a standard similar to that of terephthahc acid. 

The combined filtrates are heated nearly to boiling and acidified with a solution of 108 ml. of concentrated sulfuric acid (sp. gr. 1.84) in 400 ml. of water. After the mixture has been cooled to room temperature, the tcrephthalic acid is filtered and washed by stirring on the filter with three successive 100-ml. portions of cold water. The product is dried in an evaporating dish on a steam bath. The yield of terephthalic acid which sublimes at 800 or higher without melting is 105-109 g. (84-88%) (Notes 2 and 3). 

The high yields of ethyl ester obtainable from the product attest its purity. A mixture of 50 g. of terephthalic acid, 500 ml. of absolute ethyl alcohol, and 25 ml. of sulfuric acid was boiled for 16 hours and then distilled to half its volume and poured into dilute aqueous sodium carbonate. There was obtained 56.7 g. of diethyl terephthalate (m.p. 42-44°), and from the wash water there was recovered 4.6 g. of terephthalic acid these materials account for 93.3% of the original substance. 

With each succeeding year in the 1950s and 1960s there was a swing away from coal and vegetable sources of raw materials towards petroleum. Today such products as terephthalic acid, styrene, benzene, formaldehyde, vinyl acetate and acrylonitrile are produced from petroleum sources. Large industrial concerns that had been built on acetylene chemistry became based on petrochemicals whilst coal tar is no longer an indispensable source of aromatics. 

The oldest of these materials, a poly (trimethylhexamethylene terephthal-amide) was first marketed by Dynamit Nobel in the mid-1960s (Trogamid T). It is a condensation product of trimethylhexamethylenediamine and terephthalic acid (or its dimethyl ester) (Figure 18.25). In practice a 1 1 mixture of 2,2,4- and 2,4,4-trimethyldiamines is used, this being produced from acetone via iso-phorone, trimethyladipic acid and trimethyladiponitrile. 

From the above comments it will be expected that terephthalic acid would be an important intermediate in the production of linear crystallisable polyesters, and so it has proved. 

A similar product is Kodar PETG 6703 in which one acid (terephthalic acid) is reacted with a mixture of glycols (ethylene glycol and 1,4-cyclohexylene glycol). A related glass-reinforced grade (Ektar PCTG) has also been offered. 

Toluene (methyl benzene) QH5CH3 Automotive fuels additive, organic solvent, production of benzene, styrene, and terephthalic acid... 

Colbalt Hydrogenations of solid fuels and fuel oils Manufacture of terephthalic acid High pressure production of aldehydes Lung irritation (hard metal disease) respiratory sensitization... 

The phthalic acid and benzoic acid are reacted to form a reaction intermediate. The reaction intermediate is dissolved in sulfuric acid, which precipitates terephthalic acid (TPA). Fifty percent of the TPA is sold as a product and 50 percent is further processed at your facility into polyester fiber. The TPA Is treated with ethylene glycol to form an intermediate product, which is condensed to polyester. 

Your company manufactures terephthalic acid, a listed chemical, both for sale/distribution as a commercial product and for on-site use/processino as a feedstock in the polyester process. Because it is a reactant, it is also processed. See Figure D for how this information would be reported in Part III, Section 3 of Form R. 

An alternative route to PET is by the direct reaction of terephthalic acid and ethylene oxide. The product bis(2-hydroxyethyl)terephthalate reacts in a second step with TPA to form a dimer and ethylene glycol, which is released under reduced pressure at approximately 300°C. 

A similar oxidation is employed industrially for the preparation of the terephthalic acid used in the production of polyester fibers. Approximately 5 million tons per year of p-xylene are oxidized, using air as the oxidant and Co(lll) salts as catalyst. 

PET is the polyester of terephthalic acid and ethylene glycol. Polyesters are prepared by either direct esterification or transesterification reactions. In the direct esterification process, terephthalic acid is reacted with ethylene glycol to produce PET and water as a by-product. Transesterification involves the reaction of dimethyl terephthalate (DMT) with ethylene glycol in the presence of a catalyst (usually a metal carboxylate) to form bis(hydroxyethyl)terephthalate (BHET) and methyl alcohol as a by-product. In the second step of transesterification, BHET... 

The principal solvolysis reactions for PET are methanolysis with dimethyl terephthalate and ethylene glycol as products, glycolysis with a mixture of polyols and BHET as products, and hydrolysis to form terephthalic acid and ethylene glycol. The preferred route is methanolysis because the DMT is easily purified by distillation for subsequent repolymerization. However, because PET bottles are copolyesters, the products of the methanolysis of postconsumer PET are often a mixture of glycols, alcohols, and phthalate derivatives. The separation and purification of the various products make methanolysis a cosdy process. In addition to the major product DMT, methanol, ethylene glycol, diethylene glycol, and 1,4-cyclohexane dimethanol have to be recovered to make the process economical.1... 

Hydrolysis, although a simple method in theory, yields terephthalic acid (TPA), which must be purified by several recrystallizations. The TPA must be specially pretreated to blend with ethylene glycol to form premixes and slurries of the right viscosities to be handled and conveyed in modern direct polyesterification plants. Hie product of the alkaline hydrolysis of PET includes TPA salts, which must be neutralized with a mineral acid in order to collect the TPA. That results in the formation of large amounts of inorganic salts for which commercial markets must be found in order to make the process economically feasible. There is also the possibility that the TPA will be contaminated with alkali metal ions. Hydrolysis of PET is also slow compared to methanolysis and glycolysis.1... 

Methanolysis products are separated and purified by distillation. BHET, the monomer obtained by PET glycolysis, is normally purified by melt filtration under pressure. One of the problems encountered in neutral hydrolysis of PET is that the terephthalic acid isolated contains most of the impurities initially present in the PET waste. Hence very elaborate purification processes are required to obtain terephthalic acid of commercial purity. 

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