Processes Amoco

Purified terephthahc acid became commercially available from Amoco Chemical Co. in 1965, by which time a considerable polyester industry based on dimethyl terephthalate had already developed. The Amoco process involves purification of cmde terephthahc acid by a separate step to attain the high product purity required for polyester manufacture. The Amoco technology is the most-used worldwide, but other processes have been developed and are operating commercially. 

Acetaldehyde can be used as an oxidation-promoter in place of bromine. The absence of bromine means that titanium metallurgy is not required. Eastman Chemical Co. has used such a process, with cobalt as the only catalyst metal. In that process, acetaldehyde is converted to acetic acid at the rate of 0.55—1.1 kg/kg of terephthahc acid produced. The acetic acid is recycled as the solvent and can be isolated as a by-product. Reaction temperatures can be low, 120—140°C, and residence times tend to be high, with values of two hours or more (55). Recovery of dry terephthahc acid follows steps similar to those in the Amoco process. Eastman has abandoned this process in favor of a bromine promoter (56). Another oxidation promoter which has been used is paraldehyde (57), employed by Toray Industries. This leads to the coproduction of acetic acid. 2-Butanone has been used by Mobil Chemical Co. (58). 

Amoco Purification Process. The Amoco process is used to purify terephthaHc acid produced by the brornine-promoted air oxidation of Nxylene. The main impurity in the oxidation product is 4-formylbenzoic acid] [619-66-9] and the Amoco process removes this to less than 25 ppm. Metals and colored organic impurities are also almost completely removed by the purification. 

Since going online in 1993, the joint venture has reaped large dividends from the P15/P18 blocks of Holland s Rijn field, some 40 km (25 miles) from Rotterdam. BP-Amoco processes 13 MMm (500 MMft ) of natural gas from the field each day also, nearly 2,000 m (12,300 bbl) of condensate are produced daily. The project marks the first time Dutch gas has been produced to sales specification at an offshore location. Seven reservoirs, developed separately, are tied back... 

Maruzen (1) A process for making terephthalic acid from/j-. ylcnc. Similar to the Amoco process but yielding a purer product in one stage. Operated in Japan by Matsuyama Chemical Company. 

Another, highly selective oligomerisation reaction of ethene should be mentioned here, namely the trimerisation of ethene to give 1-hexene. Worldwide it is produced in a 0.5 Mt/y quantity and used as a comonomer for ethene polymerisation. The largest producer is BP with 40 % market share utilizing the Amoco process, formerly the Albemarle (Ethyl Corporation) process. About 25 % is made by Sasol in South Africa where it is distilled from the broad mixture of hydrocarbons obtained via the Fischer-Tropsch process, the conversion of syn-gas to fuel. The third important process has been developed by Phillips. 

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... 

Terephthalic acid is commonly abbreviated TA or TPA. The abbreviation PTA (P = pure) is reserved for the product of 99% purity for polyester manufacture. For many years polyesters had to be made from dimethyl terephthalate (DMT) because the acid could not be made pure enough economically. Now either can be used. TA is made by air oxidation of /7-xylene in acetic acid as a solvent in the presence of cobalt, manganese, and bromide ions as catalysts at 200°C and 400 psi. TA of 99.6% purity is formed in 90% yield. This is called the Amoco process. 

Benzoic acid is an important chemical intermediate which can also be used as a phenol precursor by decarbonylation in the presence of copper catalysts (Lummus process). It is produced industrially by oxidation of toluene by air in the presence of cobalt catalysts (Dow and Amoco processes equation 240). The reaction can be carried out without solvent, or in an acetic acid solvent. The oxidation of toluene without solvent uses a cobalt octoate catalyst and operates at higher temperature (180-200 CC). Yields of benzoic acid are about 80% for ca. 50% toluene conversion.361 In an acetic acid solution and in the presence of cobalt acetate, the reaction occurs at lower temperature conditions (110-120 °C) and gives higher yields in benzoic acid (90%).83,84... 

In the Amoco process, p-xylene is oxidized at 200 °C under 15-20 atm in acetic acid and in the presence of a catalyst consisting of a mixture of cobalt acetate (5% weight of the solution), manganese acetate (1%) and ammonium bromide. Owing to the highly corrosive nature of the reaction mixture, special titanium reactor vessels are required. One of the main difficulties of this process is to remove the intermediate oxidation products such as p-toluic acid or p-carboxybenzal-dehyde which contaminate TPA obtained by precipitation from the reaction medium. A series of recrystallization and solvent extraction apparatus is required to obtain fiber grade TPA with 99.95% purity. The overall yield in TPA is ca. 90% for a 95% conversion of p-xylene. 

The Dynamit Nobel process produces dimethyl terephthalate (DMT) by a complicated series of oxidation and esterification stages (equation 241).83,84,86 In the oxidation section, p-xylene is oxidized at 150°C and 6 atm without solvent and in the presence of cobalt octoate to TPA and p-toluic acid. These oxidation products are sent to another reactor for esterification by methanol at 250 °C and 30 atm. Fiber grade DMT is purified by several recrystallizations, and monoesters are recycled to the oxidation reactor. The overall yield in DMT is about 80%, which is lower than in the Amoco process. However, this process is competitive because it is not corrosive and requires lower investments. It provides high-quality fiber-grade dimethyl terephthalate. 

Production of t-amylbenzene proceeds at 313 K with high conversion (99.9%) and selectivity (99.6%). Another commercial application is the Amoco process for production of polyester intermediates such as 2,6-naphthalenedicarboxylic acid (NDA) [34]. NDA is produced in a 45 0001year-1 plant at Decatur, Alabama, USA. In the first reaction step, o-xylene is reacted with butadiene to form 5-(o-tolyl)-2-... 

The advantage of the Amoco process is that high-purity terephthalic acid is produced in one step. The solubility of terephthalic acid in acetic acid is low its separation with high purity by crystallization is therefore relatively easy. However, the corrosive nature of the acids and the relatively drastic conditions make it necessary to use special material of construction for the reactors. 

The substitution of aluminium for boron in zeolites leads to a material with decreased Broensted acidity. These properties have been successfully applied in industrial processes, such as the Assoreni (methyl tertiobuthylether into methanol and isobutene) and Amoco processes (xylene isomerization and ethylbenzene conversion) [1-3]. Recently, the methanol conversion, the alkylation of toluene with methanol and the xylene isomerization on borosilicalites were critically analyzed [4]. 

The air oxidation of p-xylene to TEA appears on the surface to be similar to the Witten process in that it uses a homogeneously dissolved cobalt/manganese catalyst system. The TEA process, originally referred to as the Mid-Century (cf. [9], [10]) and now as the Amoco process, is actually quite different from the Witten process described above. The Amoco process uses acetic acid as a solvent for the oxidation reactions and bromine as a free- radical source, proceeds to TEA from p-xylene in one step, operates at 175-230 °C/l-2 MEa, obtains overall yields of approximately 95 %, and of course does not involve an esterification step [9-12]. 

The roles of manganese in TPA manufacture are better understood than in the Witten process, and include decomposition of the CH2COOH radical (derived from the acetic acid solvent) and regeneration of the bromine atom promoter [13], In an effort to eliminate halogen compounds which are highly corrosive to oxidation equipment, use of acetaldehyde [14] and paraldehyde [15] has been developed. These aldehyde promoters are ultimately converted to acetic acid in high yield. For economic reasons, these aldehyde processes have been abandoned in favor of the bromine-promoted Amoco process. 

The Maruzen Oil process operates in similar conditions to those of the Amoco process,... 

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