Mono terephthalate

Enzymatically released aromatic PET degradation products can be monitored by UV detection at 240-255 nm, following separation by reversed-phase high performance liquid chromatography (HPLC). Soluble hydrolysis products of PET films, fibers, and cyclic PET trimers (CTR) that have been identified include TPA, mono(2-hydroxyethyl) terephthalate (MHET), Z A(2-hydroxyethyl terephthalate) (BHET), 1,2-ethylene-mono-terephthalate-OTono(2-hydroxyethyl terephthalate) (EMT), and 1,2-ethylene-/ A-terephthalate (EBT) [8, 33, 38, 40, 90, 102] (Fig. 1). 

The emission spectrum of the irradiated PET yarn, when excited by 342 nm energy is totally dominated by the 460 nm emission, which has been attributed to the presence of mono-hydroxy-terephthalate, with only a shoulder as evidence of the residual fluorescence from the terephthalate units (Figure 9). 

PET is a polycondensation polymer based on the reaction of terephthalic acid (TA) and mono-ethylene glycol (MEG) or alternatively with di-methyl terephtha-late (DMT) plus MEG (Figure 10). 

Fig. 1. Biodegradation of dimethyl terephthalate (DMT) by Pasteurella multocida Sa in the presence of ethanol. Ester hydrolysis of DMT involves a transesterification of mono-methyl terephthalate (MMT), and the formation of monoethyl terephthalate (MET).

If PET used for making bottles were just the product of combinations of terephthalate and mono- or diethylene glycol, the commercial depolymerization would... 

When one methyl group has been oxidised, 4-toluic acid is formed. This intermediate is soluble in the solvent used, acetic acid. In the next step it is oxidised to terephthalic acid, which is almost insoluble in acetic acid. The intermediate product is 4-formylbenzoic acid. This cocrystallises with the final product. Since it is a mono-acid it will cause a termination of the polymerising chain. 

High molecular weights are needed to obtain strong materials. Thus, the presence of mono-acids is detrimental to the quality of terephthalic acid and they have to be carefully removed. One approach involves a second oxidation carried out at higher temperatures and the other method involves reduction of the formylbenzoic acid to toluic acid. The latter is more soluble and stays behind in the liquid. The reduction is done with a palladium catalyst on carbon support. This method gives the highest quality terephthalic acid. 

As outlined above a purity of only 99.5% is not sufficient for a polymer feedstock and the mono-acid intermediate has to be removed either by oxidation under more forcing conditions (Mitsubishi) or reduction (Amoco). In the Amoco process (not shown) the crude di-acid is dissolved in water (275 °C) (15 % weight) and hydrogenated over a palladium on carbon catalyst. The intermediate 4-formylbenzoic acid is hydrogenated to 4-toluic acid which has a much higher solubility and does not cocrystallise with terephthalic acid. The solution is carefully cooled while the product crystallises and the by-product remains in the water. The final content of 4-formylbenzoic acid is as low as 15... 

Mono esters of dicarboxylic acids.1 Aliphatic straight-chain dicarboxylic acids when adsorbed on alumina react with diazomethane to form monomethyl esters in quantitative yield. Terephthalic acid, isophthalic acid, and 1,4-cyclohexanedi-carboxylic acid are also converted selectively to the monomethyl esters. However, phthalic acid does not show any enhanced selectivity under these conditions. Evidently selectivity for monoesterification results from adsorption of one of the acid groups on alumina. 

Results obtained for two mixed plastics are summarized in Table 4. A balance exists between process temperature, plastics feed rate, and product yields (67). For example, lower temperatures increase wax formation due to incomplete depolymerization. Slower feed rates and increased residence times reduce wax formation and increase the yield of liquids. The data summarized in Table 4 illustrate that the addition of PET to a HDPE PP PS mixture changes the performance of the Conrad process. Compared to the reference HDPE PP PS mixture, increased amounts of solids are formed. These are 95% terephthalic acid and 5% mono- and bis-hydroxyethyl esters. At higher temperatures, apparendy enough water remains to promote decarboxylation. 

A special case in terms of application of rotary kiln technology is the pyrolysis of mono fractions such as styrene, PMMA, polycarbonate, or polyethylene terephthalate. Polymethylmethacrylate is an example illustrate the advantages in using fluidized beds or rotary kilns. The feed material does not have a heteroatom problem and the pyrolysis product can easily be handled as a monomer source instead of feedstock. Therefore the... 

BHET = bis(2-hydroxyethyl)terephthalate EG = ethylene glycol DEG = diethylene glycol TA = terephthalic acid MHET = mono-(2-hydroxyethyl)terephthalate. 

Cyclic dimer (0.1). terephthaiic acid (0.5). benzoic acid (6). hydroquinone (40.5). and various fragments of the main chain benzene, phenol, benzaldehyde. biphenyl, benzoquinone. 4-hydrox henylbenzoate. benzoic aod. mono and di(4-hydroxyphenyl) terephthalate. terephihaNc add. terephthaldehydic add. short cham fragments... 

The effects of dicarboxylate [R(COONa)2] ions on the PNO-catalyzed IPTC reactions of PhCOCl and sodium dicarboxylates in H2O/CH2CI2 medium were investigated on selected dicarboxylate ions including oxalate, malonate, maleate, fumarate, succinate, adipate, nonanedioate, phthalate, isophthalate, and terephthalate [190]. In general, the observed products included mono- and bis-(benzoyloxycarbonyl) compounds, benzoic anhydride, and benzoic acid, which depended on the molecular structure of the dicarboxylate ion. Four types of dicarboxylate ions were classified according to the distribution of products shown as follows ... 

There arc numerous examples of product selectivity, many of which involve mono-and disubslituted aromatics formed over ZSM-5 (MFI) catalysts (22-24). One of the early examples was xylene isomerization. Xylene can be formed over MFI catalysts via the acid-catalyzed reaction between methanol and toluene (see Fig. 10.3). According to thermodynamics the equilibrium distribution of o-, m-, and p-isomers is 26 51 23, which is different from the industrial demand as the p-isomer is a feedstock for terephthalic acid, a monomer for PET. However, very high selectivities of p-xylene can be obtained over MFT materials primarily because the diffusion of p-xylene is faster in the MFI pores compared to the other two isomers. 

Table 1. Glass transition temperatures, melting temperatures, and clearing temperatures of selected mono- and disubstituted poly-(p-phenylene terephthalate) esters with flexible substituents.

A selection of monosubstituted and disub-stituted poly-(/ -phenylene-terephthalate)s is compared in Table 2. Poly(p-phenylene-terephthalate)s with methyl, methoxy, chlo-ro, or bromo substituents on either the hy-droquinone or the terephthalic acid moiety exhibit melting temperatures of 350 °C or higher. Thermotropic liquid crystalline behavior is observed in these samples, although it is in the range of thermal decomposition. A comparison of the mono- and diphenyl substituted polyesters reveals an important trend. The monosubstituted poly-(p-phenylene-terephthalate) with the phenyl substituent in the hydroquinone moiety melts at 346 °C, also forming a nematic melt up to a clearing temperature of... 

Two cold ring fractions were obtained. The upper fraction contained benzoic acid, terephthaldehydic acid, terephthalic acid, mono-3-butenyl terephthalate, butylene terephthalate cyclic dimer, and H0(C=0)Ph(C=0)0(CH2)40(C=0)Ph(C=0)0H. The lower cold ring fraction consisted of short-chain fragments containing anhydride groups. 

Hexamethylcyclotrisiloxane (D3) (Toshiba Silicone Co.) was distilled over CaHa-Butyllithium (Nacalai Tesque, 1.6mol/L in hexane) was filtered with a G4 glass filter. A lithium salt of bis[p-(dimethylhydroxysilyl)phenyl]ether was prepared according to the method detailed elsewhere. 3-Trimethylsiloxypropyldimethylchlorosilane, 2., was prepared by the method detailed elsewhere. Tetrahydrofuran (THF) (Nacalai Tesque) was distilled firom the blue sodium/benzophenone solution. 1-Methylpyrrolidine (Nacalai Tesque) was distilled over CaH2. Tosyl chloride and dimethylaminopyridine (Nacalai Tesque) were recrystallized firom ethyl acetate. Mono and plurifunctional carboxylates used in the present study were sodium benzoate, sodium terephthalate, sodium and lithium salts of trimesic acid and pyrromelitic acid. They were either purchased or prepared by the standard neutralization method with sodium or lithium hydroxides. Deionized water (chromatography grade, Nacalai Tesque) was used as received. 

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