Terephthalic acid Subject

PETP flakes produced from used soft drinks bottles were subjected to alkaline hydrolysis in aqueous sodium hydroxide. A phase transfer catalyst (trioctylmethylammonium bromide) was used to enable the depolymerisation reaction to take place at room temperature and under mild conditions. The effects of temperature, alkali concentration, PETP particle size, PETP concentration and catalyst to PETP ratio on the reaction kinetics were studied. The disodium terephthalate produced was treated with sulphuric to give terephthalic acid of high purity. A simple theoretical model was developed to describe the hydrolysis rate. 17 refs. 

Terephthalic acid (TA) (diacid) is now the major monomer used in the production of PET. It is produced on a world-wide scale and is available in a number of purities. These can be generally referred to as PTA (pure TA), MTA (medium purity TA) or CTA (cmde TA). These descriptions are subjective and used in different ways by manufacturers. The purity of TA is the self-limiting process in PET manufacture. The major impurity in any TA grade is 4-carboxybenzaldehyde and it is a chain growth inhibitor. As the level of impurity increases less reaction can take place. From a food contact point of view the purity or impurities in the TA is important. Both US and EU law state that monomers should be of good technical quality but do not define what that technical quality should be. If no other information is available the... 

In recent years, the relaxation and yield behavior of amorphous semi-aromatic polyamides has been the subject of a detailed analysis at the molecular level [1-6], Two series of materials were investigated, so-called SAPA-R and SAPA-A (Table 1). In the SAPA-R series, the chemical structure is based on isophthalic or terephthalic acid and 2-methyl 1,5-pentanediamine. In the SAPA-A series, the chemical formulae include isophthalic or terephthalic acid residues, diamino dimethylcyclohexylmethane residues, and lactam-12 sequences. 

Polyester fibres, specifically PETP, possess high thermal stability and sufficient resistance to light effect and atmospheric action. However, effect of high temperatures, to which PETP is subjected in the process of synthesis and processing into products, may cause thermal destruction of polymer and in the absence of oxygen. Decrease of molecular mass, increase of end groups quantity, extraction of volatile products, the main of which are terephthalic acid, acetaldehyde and carbon oxide are observed at PETP thermal destruction. Besides these substances, anhydride groups, benzoic acid, p-acetyl-benzoic acid, ketones, acetals are identified in the compound mixture of the products of thermal decay [34]. 

It is produced from para-xylene and ethylene. The p-xylene is converted into either dimethyl terephthalate or terephthalic acid, and the ethylene into ethylene glycol. These monomers are then polymerized by a condensation process, producing water as the byproduct molecule if terephthalic acid is used, and methanol if dimethyl terephthalate is used. Following the condensation polymerization, the molecular weight is increased by solid-stating, in which the dried and crystallized resin chips from the original polymerization are subjected to high temperature and vacuum. 

The repeat unit of the PET molecule, the product of a condensation reaetion of terephthalic acid and ethylene glycol, was shown in Fig. 2.3 and is repeated here in Fig. 5.20. For their study, Illers and Breuer chose a commercial product with no detectable initial crystallinity, and removed all traces of residual stress as well as any previously existing water by appropriate prolonged thermal treatments above the glass-transition temperature of 67 °C. Different levels of crystallinity in samples were then obtained by nine separate isothermal crystallization protocols at temperatures ranging from 70 to 245 °C for pre-selected times until equilibrium crystallinities ranging from 0 to 46% were achieved in each case. Only samples subjected to temperatures above 86 °C showed X-ray evidence of crystallinity. 

The decarbonylation of aromatic aldehydes catalyzed by Pd on carbon seems to be fairly general. Anisole was obtained in 94% yield by the treatment of p-methoxyben-zaldehyde at 243 °C for 1 h using 1% Pd on carbon. In order to remove p-formylben-zoic acid formed in a smaU amount in the oxidation of p-xylene to terephthalic acid, the oxidation product containing the aldehyde is subjected to Pd-catalyzed decarbonylation and formylbenzoic acid is converted to benzoic acid, which can be separated from terephthalic acid easily (Scheme 14). 

Polyfethylene terephthalate) 2GT.— The formation of 2GT from the direct interaction of terephthalic acid with ethylene glycol rather than the transesterification process formerly used, has been the subject of several papers. These have dealt with the production of high purity terephthalic acid, the rheological aspects of its processing and analysis of reaction mixtures by gel permeation chromatography. The formation of 2GT and characterization of the derived fibres from the direct interaction of ethylene oxide with terephthalic acid has also been described. ... 

Aerobic oxidation of alkylbenzenes is a promising subject in industrial chemistry. Many bulk chemicals such as terephthalic acid, phenol, benzoic add, and so on are... 

Such polymers contain repeat units based on ethylene glycol (and indeed other glycols such as 1, 4-butane diol) and terephthalic acid and proportions of isophthalic acid. Allen and co-workers [118] developed a precise quantitative method for determining such units in terylene. The sample is subject to an alkaline hydrolysis and glycol and acidic products after conversion to the trimethylsilyl derivatives are analysed by gas chromatography. 

It is occasionally advantageous to be able to subject fatty acids in the unesterified form to GC analysis. In this instance, acidic liquid phases such as DEGS containing 3 % phosphoric acid, FFAP ("free fatty acid phase"), Carbowax 20M -terephthalic acid or the structurally related phase, SP-1000 , are used (see Section F.8). 

Poly(butylene terephthalate) is also subject to analogous side reactions [128], the formation of 1-butenyl end groups (Scheme 3.4) followed by splitting-off of 1,3-butadiene or tetrahydrofuran (Scheme 3.5). This latter reaction is not affected by the metallic catalyst, but is catalyzed by the carboxyl end groups, making production of PBT by direct esterification of terephthalic acid and 1,4-butanediol disadvantageous. 

Mitsubishi Chemical Industries, Ltd. practiced a Henkel II technology starting with toluene to produce benzoic acid. Reaction of benzoic acid with potassium hydroxide resulted in potassium benzoate, which was subjected to a disproportionation reaction to produce dipotassium terephthalate and benzene. Dipotassium terephthalate reacted with sulfuric acid, and the resulting terephthahc acid was recovered by filtration and drying (65,66). Here, dipotassium sulfate was the by-product. 

Detection and result The chromatogram was dried in a stream of warm air for 10 min, immersed in the reagent solution for 3 s and then subjected to intense UV radiation (high pressure lamp, A = 365 nm) for up to 10 min. Terephthalic (hRf 0 - 5), pimelic (hRf 55), suberic (hRf 60), sebacic (hRf 65 — 70) and benzoic acids (hRf 70 — 75) together with sorbic, malic, adipic, citric, tartaric, lactic and fumaric acids only exhibited a reaction on silica gel layers at higher concentrations. 4-Hydroxybenzoic, salicylic and acetylsalicylic acids fluoresced light blue after irradiation. The detection limit per chromatogram zone was 0.5 pg for salicylic acid and more than 5 pg for benzoic acid. 

The reaction shown is an oversimplification and items such as shifting the equilibrium toward methanol, catalyst poisoning, and pressure/temperature tradeoffs need to be considered and are the subject of a text [3]. Methanol has many uses as a solvent and is the major component of windshield washer fluid. However, most methanol is converted to other commodity chemicals such as acetic acid, formaldehyde, or dimethyl terephthalate. It can also be used directly as a fuel additive, as a component in the synthesis of biodiesel or converted to dimethyl ether or methyl-t-butyl ether (MTBE), two fuel additives. 

---