Optimized Liquid-Phase Oxidation

Abstract

Disclosed is an optimized process and apparatus for more efficiently and economically carrying out the liquid-phase oxidation of an oxidizable compound. Such liquid-phase oxidation is carried out in a bubble column reactor that provides for a highly efficient reaction at relatively low temperatures. When the oxidized compound is para-xylene and the product from the oxidation reaction is crude terephthalic acid (CTA), such CTA product can be purified and separated by more economical techniques than could be employed if the CTA were formed by a conventional high-temperature oxidation process.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of application Ser. No. 11 / 154,219, entitled “Optimized Liquid-Phase Oxidation,” filed on Jun. 16, 2005, which claims priority to U.S. Provisional Application Ser. No. 60 / 606,808, filed Sep. 2, 2004 and 60 / 631,346, filed Nov. 29, 2004, the disclosures of which are incorporated herein by reference in their entirety to the extent they do not contradict statements herein.FIELD OF THE INVENTION [0002] This invention relates generally to a process for the liquid-phase, catalytic oxidation of an aromatic compound. One aspect of the invention concerns the partial oxidation of a dialkyl aromatic compound (e.g., para-xylene) to produce a crude aromatic dicarboxylic acid (e.g., crude terephthalic acid), which can thereafter be subjected to purification and separation. Another aspect of the invention concerns an improved bubble column reactor that provides for a more effective and economical liquid-phase oxidation ...

AI Technical Summary

Benefits of technology

The present invention relates to a crude terephthalic acid composition and a slurry composition containing the same. The crude terephthalic acid composition has a low amount of impurities such as 4,4-dicarboxystilbene, isophthalic acid, 2,6-dicarboxyfluorenone, and benzoic acid. The slurry composition also has a low amount of impurities such as isophthalic acid, phthalic acid, trimellitic acid, and benzoic acid. The process for making the crude terephthalic acid composition involves oxidizing para-xylene in a liquid phase of a multi-phase reaction medium containing a reaction zone and withdrawing a slurry containing solid crude terephthalic acid particles from the reaction zone. The slurry composition has a high percentage transmittance at 340 nanometers. The technical effects of the invention are to provide a crude terephthalic acid composition with low impurities and a slurry composition with high purity.

Problems solved by technology

If the liquid phase of the multi-phase reaction medium contains an insufficient concentration of molecular oxygen (i.e., if certain portions of the reaction medium are “oxygen-starved”), undesirable side-reactions can generate impurities and / or the intended reactions can be retarded in rate.

If the liquid phase of the reaction medium contains too little of the oxidizable compound, the rate of reaction may be undesirably slow.

Further, if the liquid phase of the reaction medium contains an excess concentration of the oxidizable compound, additional undesirable side-reactions can generate impurities.

For example, CSTRs have a relatively high capital cost due to their requirement for expensive motors, fluid-sealed bearings and drive shafts, and / or complex stirring mechanisms.

Further, the rotating and / or oscillating mechanical components of conventional CSTRs require regular maintenance.

The labor and shutdown time associated with such maintenance adds to the operating cost of CSTRs.

However, even with regular maintenance, the mechanical agitation systems employed in CSTRs are prone to mechanical failure and may require replacement over relatively short periods of time.

CTA contains relatively high levels of impurities (e.g., 4-carboxybenzaldehyde, para-toluic acid, fluorenones, and other color bodies) that render it unsuitable as a feedstock for the production of PET.

Although effective, this type of conventional purification process can be very expensive.

Individual factors contributing to the high cost of conventional CTA purification methods include, for example, the heat energy required to promote dissolution of the CTA in water, the catalyst required for hydrogenation, the hydrogen stream required for hydrogenation, the yield loss caused by hydrogenation of some terephthalic acid, and the multiple vessels required for multi-step crystallization.

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