Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-01-19
2003-05-13
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S416000, C562S417000
Reexamination Certificate
active
06562997
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of aromatic carboxylic acid by the liquid phase oxidation of a corresponding aromatic compound having two or three oxidizable ring substituents. Specifically, this invention relates to a process for the production of aromatic carboxylic acid in by the liquid phase oxidation of a correspond aromatic compound having two or more oxidizable ring substituents wherein the oxidation solvent comprises benzoic acid and water and the process yields aromatic carboxylic acid with reduced impurity levels.
BACKGROUND OF THE INVENTION
Aromatic carboxylic acids are useful chemical compounds and are raw materials for a wide variety of manufactured articles. The most widely used commercial processes for the production of aromatic carboxylic acids involve the catalytic liquid-phase oxidation of a suitable aromatic feedstock under elevated pressure and temperature conditions. For example, ortho-xylene is oxidized to produced phthalic acid (“PA”), meta-xylene is oxidized to produce isophthalic acid (“IA”), para-xylene is oxidized to produce terephthalic acid (“TA”), 2,6-dimethynaphthalene is oxidized to produce 2,6-naphthalene dicarboxylic acid (“NDA”) and pseudocumene is oxidized to produce trimellitic acid (“TMLA”). These processes may be catalyzed by one or more heavy metal compounds, such as cobalt, manganese, zirconium, cerium or mixtures thereof. In addition, the oxidation reaction is usually promoted one or more promoter compounds, for example elemental bromine.
TA is likely the most widely produced aromatic carboxylic acid. TA is manufactured on a world-wide basis in amounts exceeding 10 billion pounds per year. A single manufacturing plant can produce 100,000 to more than 750,000 metric tons of terephthalic acid per year. TA is used, for example, to prepare polyethylene terephthalate, from which polyester fibers for textile applications and polyester film for packaging and container applications are made. Although there are competing processes, TA is most often produced by the high pressure, exothermic oxidation of para-xylene in a liquid-phase reaction using air or other source of molecular oxygen as the oxidant and catalyzed by one or more heavy metal compounds and one or more promoter compounds.
Methods for oxidizing para-xylene and other aromatic compounds using such liquid-phase oxidations are well known in the art. For example, Saffer in U.S. Pat. No. 2,833,816 discloses a method for oxidizing aromatic feedstock compounds to their corresponding aromatic carboxylic acids. Central to these processes for preparing aromatic carboxylic acids is employing an oxidation catalyst comprising a heavy metal component and a source of bromine in a liquid-phase reaction mixture including a low molecular weight monocarboxylic acid, such as acetic acid, as part of the reaction solvent. A certain amount of water is also present in the oxidation reaction solvent. Water is also formed as a result of the oxidation reaction. Although various means can be used to control the temperature of the highly exothermic oxidation reaction, it is generally most convenient to remove heat by allowing the solvent to vaporize, i.e. boil, during the oxidation reaction. Gaseous effluent from the oxidation reaction generally comprises steam, monocarboxylic acid, an ester thereof, carbon dioxide, carbon monoxide and bromine which, depending on the aromatic feedstock compound used, is mainly in the form of one or more alkyl bromide compounds, such as methyl bromide. Methyl bromide is toxic and, if discharged into the atmosphere, is believed to contribute to depletion of atmospheric ozone. It is therefore important to avoid discharge of methyl bromide into the atmosphere. Additionally, when compressed air is used as the source of molecular oxygen, the gaseous effluent contains nitrogen gas and unreacted oxygen.
In conventional manufacturing processes, TA undergoes catalytic purification to reduce the amount of impurities found therein. Purified Terephthalic Acid (“PTA”), from which fibers, bottles, films etc. are made, is obtained by the catalytic purification of crude terephthalic acid (“TA”) generated by the liquid-phase oxidation of para-xylene.
Typically, after the TA is formed by oxidation, it is crystallized and separated from its mother liquor which comprises catalyst components, acetic acid and a variety of intermediates and by-products. The crystallized TA contains a number of impurities, such as 4-carboxybenzaldehyde (“4-CBA”) and colored impurities, which are measured by the optical density (light absorption) at 400 nm (“OD400”). These impurities cause undesired effects in the polyester resin. Therefore the TA must be purified.
In a typical purification process, the crystallized TA is dissolved in deionized water at temperatures of from about 250° C. and upward. The solution is then contacted with molecular hydrogen in the presence of a hydrogenation catalyst. The solution is then cooled to crystallized the purified terephthalic acid which is then recovered, washed and dried. Using conventional processes, TA usually contains about 2000 to about 5000 ppm of 4-CBA and OD400 values of approximately 0.1. And PTA typically contains between less than about 75 ppm of 4-CBA and OD400 values of approximately 0.01.
Also, in use today are liquid-phase processes that produce Medium Grade Terephthalic Acid known as MTA. MTA can be used in many of the same applications as PTA, for example, fibers and films. MTA usually contains from about 100 to about 500 ppm of 4-CBA and may have OD400 values slightly greater than about 0.01. Although MTA contains more 4-CBA than PTA, it is produced by substantially the same oxidation process with no subsequent purification.
Conventional processes for the production of IA, PA, NDA and TMLA are similar to that for TA. In each case, the process involves the liquid-phase oxidation of an appropriate aromatic feedstock. Like the TA processes, the aromatic acids obtained from the oxidation contain impurities the level of which is reduced by some type of purification process. In the case of TMLA, the acid is often further processed through dehydration to form trimellitic anhydride.
In general, an appropriate feedstock is a benzene having two appropriately positioned oxidizable ring substituents in the case of TA, IA and PA. For TMLA a suitable feedstock is a benzene ring having oxidizable ring substituents in the 1, 2 and 4 positions. For NDA production a suitable feedstock is naphthalene having oxidizable ring substituents in the 2 and 6 positions.
What is needed is a process for the production of aromatic dicarboxylic or tricarboxylic acid in which the production of toxic methyl bromide production is minimized. The current invention provides a process for the production of aromatic dicarboxylic or tricarboxylic acid in which the formation of methyl bromide substantially reduced relative to conventional processes.
In addition, the current invention provides a process for the production of aromatic dicarboxylic or tricarboxylic acid in which catalytic purification is largely optional. As in one embodiment, to TA produced is suitable for direct conversion to PET without a separate purification step. Other advantages of the invention will become apparent upon reading the following detailed description and appended claims.
SUMMARY OF THE INVENTION
The current invention provides a continuous process for the production of aromatic carboxylic acid by the liquid phase oxidation of an aromatic feedstock with oxygen in a reaction medium comprising the aromatic feedstock, an oxidation promoter, heavy metal catalyst and solvent, the solvent comprising benzoic acid and water, wherein the oxidation is carried out in the reaction zone of a plug flow reactor and wherein at least a portion of the aromatic acid produced crystallizes in the reaction zone. In one embodiment, the oxidation promoter is bromine. In another embodiment, the heavy metal catalyst comprises cobalt, manganese, zirconium, cerium or mixtures thereof. As much as 10%, 15%, 25% or more
Abrams Kenneth J.
Bartos Thomas M.
Pandya Alpen K.
Sikkenga David L.
Zaenger Ian C.
BP Corporation North America Inc.
Hensley Stephen L.
Raymond Richard L.
Tucker Zachary C.
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