Closely linking a NDA process with a pen process

Details Closely linking a NDA process with a pen process Closely linking a NDA process with a pen process

2000-08-22

2001-10-02

Acquah, Samuel A. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S308000, C528S499000, C528S500000, C528S501000, C560S076000, C560S077000, C560S100000

Reexamination Certificate

active

06297348

ABSTRACT:

FIELD OF INVENTION
This invention relates to the production of 2,6-naphthalene dicarboxylic acid (hereinafter abbreviated as 2,6-NDA) and to the production of polyethylene naphthalate (hereinafter abbreviated as PEN). More particularly this invention makes it possible for the first time to eliminate the drying and solids handling portions of a process for preparing 2,6-NDA and pump the 2,6-NDA in an aqueous slurry directly into to a process for making PEN. This invention also relates to the preparation of 2,6- NDA pure enough for polymerization.
BACKGROUND OF THE INVENTION
Films, fibers and other shaped articles prepared from PEN display improved strength and thermal properties relative to other polyester materials. High strength fibers made from PEN can be used to make tire cords and films made from PEN are advantageously used to manufacture magnetic recording tape and components for electronic applications. In comparison with polyethylene terephthalate, PEN is excellent, for example, in mechanical strength and heat stability. PEN is used for films for magnetic tapes, for films for packaging, and for condensers. In recent years it has been used for photograph supports because of its dimensional stability in the form of a thin film.
2,6-NDA and ethylene glycol are the raw materials for producing PEN. The methods for producing PEN are the esterification process and the direct polymerization process, each of which can be carried out batchwise or continuously. Currently in the art the esterification process is more commonly used, but usually employs as the raw material a salt of 2,6-NDA, 2,6-naphthalene dicarboxylate (hereinafter abbreviated 2,6-NDC). 2,6-NDC is often in crystal form with impurities trapped in the structure. 2,6-NDC is used, because there have been no processes available in the art to produce polymerization grade 2,6-NDA, the preferred monomer for making PEN. The availability of a process for making polymer grade 2,6-NDA would make it possible to pursue the preferred route to PEN. This would represent a revolutionary advance in the art. PEN produced by such a process would be much more economical.
It is also known in the art that all previous processes for producing NDA and NDC deliver a solid product that is usually shipped to the polymer manufacturing plant. Though 2,6-NDA is the preferred monomer, handling of NDA particles is still difficult and expensive. In addition, particle size can be critical where dry handling of solids is practiced.
U.S. Ser. No. 4,755,587, for example, discusses the problem of handling solids and claims advantages using very small porous pellets.
Copending U.S. Ser. No. 60/151,577, filed of even date, and incorporated by reference herein in its entirety, discloses a process for producing 2,6-NDA of polymer grade. The new process is unique in many respects. Of particular importance, the new process can operate using relatively impure methylnaphthalene feedstock with respect to organic hydrocarbon impurities, allows for debromination of the oxidation product in the liquid phase, and avoids the isolation of purified naphthoic acid.
The advent of a process for making polymer grade 2,6-NDA, suitable for direct use in a PEN process without esterification, or solids drying and handling and the associated problems of particle size control is of tremendous value in the art. Such a process constitutes a very significant advance in the art, is much more economical, and is capable of producing polymer grade 2,6-NDA that could be slurried directly into a PEN process. This eliminates problems with solids handling, including the major expense of transporting the 2,6-naphthalene dicarboxylate solids. This constitutes a tremendous advance in the art.
SUMMARY
In accordance with the foregoing the present invention is a process for close coupling of a process for making 2,6-NDA and a process for making PEN that has not previously been possible in the art. The invention comprises directly pumping an aqueous slurry of 2,6-NDA, generated in a process for producing 2,6 NDA, into a process for producing PEN. Alternatively, the invention also comprises adding water to 2,6-NDA of polymer quality, which may or may not be already wetted with water, and pumping the resulting slurry of 2,6-NDA directly into a process for producing PEN.
The process comprises:
Pumping an aqueous slurry of polymer grade 2,6-NDA directly into a process for making PEN, either by directly pumping a stream from a 2,6 NDA process into a PEN process, or by adding water to polymer grade 2-6-NDA prior to pumping the resulting slurry to the PEN process.
Removing the slurry water during the first esterification reaction at the same time the water produced by the esterification reaction is removed.
The following advantages are realized by the disclosed process:
The process allows for the elimination of costly drying equipment that would otherwise be associated with the final steps of the 2-6 NDA process. Through the invention, equipment typically required in the PEN process, such as dense phase or paste make-up facilities, is also eliminated.
Through the inclusion of additional water in the first stage of esterification, the final PEN product is expected to be very low in diethylene glycol concentration. Diethylene glycol is a known contaminant in PEN.


REFERENCES:
patent: 4755587 (1988-07-01), Rinehart

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