Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-08-22
2002-09-10
Richter, Johann (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S414000
Reexamination Certificate
active
06448436
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an integrated process for the manufacture of polymer grade 2,6-naphthalene dicarboxylic acid (2,6-NDA). Moreover, the invention allows an economic route to 2,6-naphthalene dicarboxylic acid, the preferred monomer for the production of polyethylenenaphthalate (PEN), via relatively inexpensive feedstock comprising methylnaphthalene feedstock. Methylnaphthalene is found in substantial concentration in cracked light gas oil (CLGO) produced as a by-product of ethylene production when heavy gas oil is the feedstock to the ethylene production unit. Methylnaphthalene is also produced in petroleum refineries, both in the light gas oil produced in refinery catalytic cracking operations, and in the bottom fractions of reformate from catalytic reforming operations. Coal tar, such as that produced in the steel industry, also contains methylnaphthalene. Another source of methylnaphthalene is the heavy aromatic stream generated by the UOP-BP Cyclar® process that converts liquified petroleum gases to aromatics.
The process disclosed herein 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. It also produces the preferred monomer, naphthalene dicarboxylic acid (NDA), rather than naphthalene dicarboxylate (NDC), and optionally allows linkage to a PEN process without isolation and drying of NDA crystals.
BACKGROUND OF THE INVENTION
Naphthalene dicarboxylic acids are useful as intermediates leading to various industrial chemicals, dyestuffs and the like. Polyesters prepared from 2,6 naphthalene dicarboxylic acid and ethylene glycol, such as polyethylenenaphthalate (PEN), have excellent heat resistance, gas barrier, and mechanical properties as compared with polyethylene terephthalate. 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 order to prepare high quality PEN it is desirable to use purified 2,6-naphthalene dicarboxylic acid.
Methods for producing 2,6 naphthalene dicarboxylic acid are known in the art. One method is the oxidation of an alkyl or acyl substituted aromatic compound to the corresponding aromatic carboxylic acid using a heavy metal catalyst in the liquid phase. For example, U.S. Pat. Nos. 2,833,816; 3,856,855; 3,870,754; 4,933,491; and 4,950,786 disclose such oxidation methods.
In U.S. Pat. No. 3,856,855 there is disclosed a process for the preparation of NDA which consists essentially of oxidizing dimethylnaphthalene with molecular oxygen at a temperature within the range of 100° C. to 160° C. under an oxygen partial pressure of from about 2 to 8 atm in acetic acid of an amount of at least 4 parts by wt. per part by wt of dimethylnaphthalene in the presence of a Co/Mn/Br catalyst.
More recently, U.S. Pat. No. 5,292,934 disclosed a method for preparing an aromatic carboxylic acid by oxidizing an aromatic compound having at least one oxidizable alkyl or acyl group with oxygen in the presence of a low molecular weight carboxylic acid solvent and a heavy metal at a temperature of about 250° F. to 450° F., heating the product to about 550° F., and recovering the carboxylic acid.
The primary disadvantage of the methods that involve direct oxidation to 2,6NDA, is that impurities are trapped in the 2,6NDA oxidation product which forms upon oxidation as a solid in the oxidation solvent. In order to remove these impurities to a sufficiently low level acceptable for polymerization, the 2,6NDA product must be purified via multiple steps. These steps typically involve esterification, so that the resulting end product is 2,6naphthalene dicarboxylate, an ester, rather than the preferred 2,6napthalene dicarboxylic acid. Another disadvantage is that the methods referenced above require expensive base feedstocks and subsequent difficult synthesis reactions in order to prepare the feed for the oxidation to crude 2,6NDA.
Alternatively, naphthalene monocarboxylic acid and naphthalene dicarboxylic acids other than 2,6-naphthalene dicarboxylic acid can be converted to 2,6-NDA using a disproportionation reaction in the case of the monocarboxylic acids or a rearrangement reaction in the case of other naphthalene dicarboxylic acids. Henkel and Cie first patented a reaction of naphthoic acid salts to 2,6NDA in the late 1950s. (See U.S. Pat. No. 2,823,231 and U.S. Pat. No. 2,849,482).
U.S. Pat. No. 2,823,231 discloses a method of producing naphthalene 2,6-dicarboxylic acid from a naphthalene-monocarboxylic acid which comprises converting said naphthalene-monocarboxylic acid into a corresponding mono-alkali metal salt, heating said mono-salt to a temperature above about 360° C. and below the temperature at which substantial decomposition of the starting material and reaction product takes place, in an inert atmosphere of carbon dioxide and nitrogen and converting the dialkali metal salt of naphthalene 2,6-dicarboxylic acid formed thereby into free naphthalene 2,6-dicarboxylic acid by acidification of said di-alkali metal salt with a strong mineral acid.
Other patents have claimed improvements in particular aspects of the rearrangement type of reaction. U.S. Pat. No. 4,820,868 claims improvements in yield of 2,6-naphthalene dicarboxylic acid for specific isomers subjected to a rearrangement reaction.
U.S. Pat. No. 3,766,258 claims an improvement in yield in a process for carboxylation of metallic salts of aromatic mono-, di-, or polycarboxylic acids in the presence of a metal halide catalyst and acid binding agent, the improvement consisting of using, in addition to a heavy metal catalyst, a basic metal carbonate comprising cupric carbonate or chromium carbonate.
U.S. Pat. No. 3,671,578 discloses a process for preparing 2,6-naphthalene dicarboxylic acid which enables the re-use of alkali in the alkali salt of the starting naphthalene carboxylic acid formed by the rearrangement reaction.
U.S. Pat. No. 3,952,052 discloses separation of metal salts of polycarboxylic acids by flash evaporation of the dispersant, where the dispersant is selected from biphenyl, terphenyl, quaterphenyl, and isomers and mixtures thereof.
U.S. Pat. No. 3,631,096 claims improvements in the yield of polycarboxylic acid salts by carrying out the transformation process in an inert atmosphere and in the presence of a transformation catalyst having present therewith as an adjuvant an ammonium salt of an aromatic acid.
There have been a number of references in the art which describe work relating to improved methods of purifying crude 2,6-naphthalene dicarboxylic acid. U.S. Pat. No. 3,888,921 provides a method for purifying a crude 2,6 NDA by preparing a dialkali salt, precipitating 40 to 97 mol %. of the dialkali 2,6 NDA as a monoalkali salt, and converting the precipitate to 2,6NDA.
The production of terephthalic acid provides additional relevant information regarding the art in this field. For example, U.S. Pat. No. 4,430,511 discloses an improvement in a method of producing terephthalic acid which comprises forming aggregates of crystals by direct precipitation and mixing the crystals with terphenyl to form a low viscosity slurry and transporting the slurry to a disproportionation reactor.
In the art relating to producing terephthalic acid it is also known to remove contaminants from the catalyst used in the process. For example, in U.S. Pat. No. 4,263,451, carbon impurities are removed from Zno & oxides of carbon by passing the effluent through a filter which collects the oxides of carbon.
U.S. Pat. No. 2,927,130 provides a method of recovering terephthalic acid from an aqueous solution containing alkali salts of terephthalates.
Canadian Patent
Blackbourn Robert Lawrence
Brewer Steve Edward
Brownscombe Thomas Fairchild
Buechele James Laurel
Chen Ye-Mon
Mossi & Ghisolfi Overseas, S. A.
Renner Kenner Greive Bobak Taylor & Weber
Richter Johann
Zucker Paul A.
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