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Verfahrenstechnik und Technische Chemie Das Forum für die Chemie jenseits von Reagenzgläsern und Glaskolben. Hier können Probleme der Reaktionstechnik sowie der thermischen und mechanischen Stoffwandlungs- und Trennprozesse diskutiert werden.

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Alt 03.12.2001, 15:06   #1   Druckbare Version zeigen
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Terephthalic Acid/Terephthalsäure (AMOCO-Verfahren)

Für eine Simulation benötige ich Daten zur Terephtalsäure-Herstellung nach dem Amoco-Verfahren. Hat jemand nähere Infos zu diesem Thema oder weiss einen guten Link?

Schwimmbutz
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Alt 03.12.2001, 15:53   #2   Druckbare Version zeigen
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Hallo Schwimmbutz,
das Einzige was ich finden konnte war das hier:

Google

Is nicht viel aber besser als nix

Geändert von PCRManiac (03.12.2001 um 15:58 Uhr)
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Alt 03.12.2001, 16:25   #3   Druckbare Version zeigen
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das habe ich auch schon gefunden, leider wird man da nur an die BP weiter geleitet und deren Site bietet nicht viel bis überhaupt gar nix.
Trotzdem Danke

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Alt 03.12.2001, 18:33   #4   Druckbare Version zeigen
schlumpf  
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schau mal nach in der Ullstein-Enzyklopaedie der Technischen Chemie (sollte in jeder Unibibliothek vorhanden sein).

Und: Amoco? waren das nicht die, die die Bretagne eingeoelt haben?
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Alt 03.12.2001, 18:42   #5   Druckbare Version zeigen
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3.1. Amoco Oxidation

About 70 % of the terephthalate feedstock used worldwide is produced with a catalyst system discovered by Scientific Design [5] , [6] . Almost 100 % of new plants use this reaction. A separate company, Mid-Century Corporation, was established to market this technology, and subsequently purchased by Amoco Chemical. Amoco developed a commercial process, as did Mitsui Petrochemical, now Mitsui Sekka. Mitsui was an early licensee of Mid-Century. Both Amoco and Mitsui participate in joint-venture companies, and both have licensed the process. Licensees are distributed around the world, and some have relicensed the process to other companies.
A soluble cobalt – manganese – bromine catalyst system is the heart of the process. This yields nearly quantitative oxidation of the p-xylene methyl groups with small xylene losses [7] . Acetic acid is the solvent, and oxygen in compressed air is the oxidant. Various salts of cobalt and manganese can be used, and the bromine source can be HBr, NaBr, or tetrabromoethane [79-27-6] among others. The highly corrosive bromine – acetic acid environment requires the use of titanium-lined equipment in some parts of the process.
A feed mixture of p-xylene, acetic acid, and catalyst is continuously fed to the oxidation reactor (Fig. (1)). The feed mixture also contains water, which is a byproduct of the reaction. The reactor is operated at 175 – 225 °C and 1500 – 3000 kPa. Compressed air is added to the reactor in excess of stoichiometric requirements to provide measurable oxygen partial pressure and to achieve high p-xylene conversion. The reaction is highly exothermic, releasing 2×108 J per kilogram p-xylene reacted. Water is also released. The reaction of 1 mol p-xylene with 3 mol dioxygen gives 1 mol terephthalic acid and 2 mol water. Only four hydrogen atoms, representing slightly over 2 wt % of the p-xylene molecule, are not incorporated in the terephthalic acid.
Owing to the low solubility of terephthalic acid in the solvent, most of it precipitates as it forms. This yields a three-phase system : solid terephthalic acid crystals ; solvent with some dissolved terephthalic acid ; and vapor consisting of nitrogen, acetic acid, water, and a small amount of oxygen. The heat of reaction is removed by solvent evaporation. A residence time up to 2 h is used. Over 98 % of the p-xylene is reacted, and the yield to terephthalic acid is > 95 mol %. Small amounts of p-xylene and acetic acid are lost, owing to complete oxidation to carbon oxides, and impurities such as oxidation intermediates are present in reactor effluent. The excellent yield and low solvent loss in a single reactor pass account for the near universal selection of this technology for new plants.
The oxidation of the methyl groups occurs in steps, with two intermediates, p-toluic acid [99-94-5] and 4-formylbenzoic acid [619-66-9] . While 4-formylbenzoic acid is the IUPAC name of the intermediate, it is customarily referred to as 4- carboxybenzaldehyde (4-CBA).

4-Formylbenzoic acid is troublesome, owing to its structural similarity to terephthalic acid. It co- crystallizes with terephthalic acid and becomes trapped and inaccessible for completion of the oxidation. Up to 5000 ppm 4-formylbenzoic acid can be present, and this necessitates a purification step to make the terephthalic acid suitable as a feedstock for polyester production.
The slurry is passed from the reactor to one or more surge vessels where the pressure is reduced. Solid terephthalic acid is then recovered by centrifugation or filtration, and the cake is dried and stored prior to purification. This is typically referred to as crude terephthalic acid, but is > 99 % pure.
Vapor from the reactor is condensed in overhead heat exchangers, and the condensate is refluxed to the reactor. Steam is generated by the condensation and is used as a heating source in other parts of the process. Oxygen-depleted gas from the condensers is scrubbed to remove most uncondensed vapors. Similar to the reactor condensate, liquid from centrifuges or filters is sent to solvent recovery. Since the centrifugate or filtrate contains dissolved species, it is first sent to a residue still. Vapor from the still and other vents from throughout the oxidation process are sent to a solvent dehydration tower. The tower removes the water formed in the reaction as the overhead stream, and the acetic acid from the tower bottom is combined with fresh acetic acid to make up for process losses, and returned to the process.
Isophthalic acid is also produced by this process from m-xylene. Because isophthalic acid is several times more soluble than terephthalic acid, much less precipitates in the reactor. Consequently, isophthalic acid from this process contains much less 3-formylbenzoic acid, since it tends to stay in solution where complete oxidation can occur. Further purification was not carried out in the past, but a purified grade that is now being produced will become the standard.

ð Continued ...


[5] Mid-Century Corp., US 2 833 816, 1955 (R. S. Barker, S. A. Soffer).
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Alt 03.12.2001, 18:49   #6   Druckbare Version zeigen
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3.2. Amoco Purification

The purification process developed by Amoco Chemical [8] and used on terephthalic acid from the Amoco oxidation process supplies over 60 % of the terephthalate feedstock for polyester production (Fig. (2)).
Crude terephthalic acid is unsuitable as a feedstock for polyester, primarily owing to the 4-formylbenzoic acid impurity concentration. There are also yellow impurities and residual amounts of catalyst metals and bromine. The Amoco purification process removes 4-formylbenzoic acid to < 25 ppm, and also gives a white powder from the slightly yellow feed.
It is necessary to make all impurities accessible to reaction, so the crude terephthalic acid is slurried with water and heated until it dissolves entirely. A solution of at least 15 wt % is obtained, and this requires a temperature ³ 260 °C. The solution passes to a reactor where hydrogen is added and readily dissolves. The solution is contacted with a carbon-supported palladium catalyst. Reactor pressure is held above the vapor pressure of water to maintain a liquid phase.
The 4-formylbenzoic acid is converted to p-toluic acid in the reactor, and some colored impurities are hydrogenated to colorless compounds. The reaction is highly selective ; loss of terephthalic acid by carboxylic acid reduction or ring hydrogenation is < 1 %.
After reaction, the solution passes to a series of crystallizers where the pressure is sequentially decreased [9] . This results in a stepped temperature reduction, and crystallization of the terephthalic acid. The more soluble p-toluic acid formed in the reactor, and other impurities, remain in the mother liquor. After leaving the final crystallizer, the slurry undergoes centrifugation and/or filtration to yield a wet cake, and the cake is dried to give a free-flowing terephthalic acid powder as the product. Over 98 wt % of the incoming terephthalic acid is recovered as purified product.
As with the Amoco oxidation, this purification process is also used with isophthalic acid.

ð Continued ...


[8] Standard Oil Company (Indiana), US 3 584 039, 1967 (D. H. Meyer).
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Was sich überhaupt sagen läßt, läßt sich klar sagen; und wovon man nicht sprechen kann, darüber muß man schweigen.

L.Wittgenstein.
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Alt 05.12.2001, 09:42   #7   Druckbare Version zeigen
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Vielen Dank für die Texte, haben mich ein Stück weitergebracht. Kannst Du mir vielleicht sagen, wo Du diese Infos her hast (Buchtitel, Site, etc.)

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