Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-05-24
2002-09-17
Killos, Paul J. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06452047
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing highly pure aromatic polycarboxylic acids useful as raw materials for polyesters, polyamides and liquid crystal polymers, particularly useful for highly pure naphthalenedicarboxylic acids and highly pure biphenyldicarboxylic acids which are difficult to purify by known methods.
2. Description of the Prior Art
Aromatic polycarboxylic acids are commercially important as chemical intermediates, and have been widely used in the production of polyesters or polyamides particularly for use in manufacturing fibers, bottles and films. Among them, 2,6-naphthalenedicarboxylic acid is particularly useful as raw materials of polyethylene naphthalate (PEN) and wholly aromatic liquid crystal polymers having excellent physical properties and mechanical properties. Therefore, the demand for 2,6-naphthalenedicarboxylic acid is rapidly increasing in recent years.
The aromatic polycarboxylic acids presently used in wide industrial applications include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, etc.
It has been known that aromatic polycarboxylic acids are produced by oxidizing polyalkyl aromatic hydrocarbons such as xylene, dialkylnaphthalene and dialkylbiphenyl with molecular oxygen in a solvent such as acetic acid in the presence of heavy metal such as Co and Mn and a bromine compound under high-temperature and high-pressure conditions. The aromatic polycarboxylic acids produced by the oxidation reaction contain oxidation intermediates such as monocarboxylic acids and aldehydes and impurities such as bromine adducts derived from catalysts, colored components with undefined structure and metals such as Co and Mn derived from the oxidation catalyst.
Such aromatic polycarboxylic acids containing these impurities are unsuitable as raw materials of polyesters or polyamides, because resins produced by polymerizing such aromatic polycarboxylic acids with alcohols or amines are deteriorated in physical or mechanical properties such as heat resistance, mechanical strength and dimensional stability. Also, crude aromatic dicarboxylic acids produced by oxidizing di-substituted aromatic hydrocarbons by molecular oxygen are usually colored yellow or black, and therefore, cannot be used directly in the applications requiring high-transparency such as bottles and films. Under these circumstances, continuous studies have been made over a long period of time to develop industrially useful processes for producing highly pure aromatic polycarboxylic acids with less coloration.
Organic compounds are purified generally by distillation, recrystallization, adsorption or combination thereof. However, since aromatic polycarboxylic acids have self-decomposition temperatures lower than their boiling points, it is impossible to purify aromatic polycarboxylic acids by distillation. In addition, since aromatic polycarboxylic acids are less soluble in solvents widely used in industrial purpose, it is not easy to purify aromatic polycarboxylic acids by recrystallization. In particular, naphthalenedicarboxylic acids and biphenyldicarboxylic acids are substantially insoluble in various solvents. For these reasons, no industrially advantageous process for the production of highly pure naphthalenedicarboxylic acids or highly pure biphenyldicarboxylic acids have been developed until now.
Thus, since aromatic polycarboxylic acids themselves are difficult to purify by recrystallization, an alternative method has been proposed, in which aromatic polycarboxylic acids are first reacted with amines to form amine salts having increased solubility, and then the amine salts are purified by crystallization or treatment with activated carbon, followed by decomposing the amine salts to obtain purified aromatic polycarboxylic acids.
Japanese Patent Application Laid-Open No. 50-135062 discloses a process in which crude naphthalenedicarboxylic acid are dissolved in an aqueous aliphatic amine solution, and the resultant solution is cooled or concentrated to crystallize amine salts; Japanese Patent Application Laid-Open No. 7-118200 discloses a process in which crude naphthalenedicarboxylic acids are dissolved in a mixed solvent of amine, alcohol and water, and the resultant solution is cooled to crystallize amine salts; Japanese Patent Application Laid-Open No. 5-294891 discloses a process in which crude biphenyldicarboxylic acids are dissolved in a mixed solvent of amine and alcohol, and the resultant solution is cooled to crystallize amine salts; U.S. Pat. No. 5,565,609 discloses a process in which amine salts of aromatic dicarboxylic acids are dissolved in water and then purified by adsorption with activated carbon, and the purified amine salts are thermally decomposed in the presence of water; and U.S. Pat. No. 5,481,033 discloses a process in which salts of aromatic dicarboxylic acid and aliphatic diamine are formed in an aqueous solvent, and then crystallized to obtain purified salts.
The known crystallization methods mentioned above require heating operations for complete dissolution of salts and cooling operations for precipitation of crystals, making the methods complicated and increasing utility costs. The treatment by activated carbon requires a large amount of activated carbon primarily for decoloring. Therefore, the above purification methods of crude aromatic polycarboxylic acids through the formation of amine salts also fail to avoid complicated operations and increased production costs.
It is an object of the present invention to provide a process for producing highly pure aromatic polycarboxylic acids with less coloration from crude aromatic polycarboxylic acids at low costs in simple and industrially facilitated manners.
SUMMARY OF THE INVENTION
As a result of extensive researches on purification of crude aromatic polycarboxylic acids in view of the above objects, the inventors have found that purified crystalline amine salt of an aromatic polycarboxylic acid is obtained by the salt-forming reaction in which a crude aromatic polycarboxylic acid is mixed with an aliphatic amine and/or an alicyclic amine in the presence of a solvent under conditions which allow a substantial part of the amine salt being formed to precipitate immediately after the amine salt-formation, thereby preventing the amine salt from completely dissolving into the solvent. The present invention has been accomplished on the basis of this finding.
Thus, the present invention relates to a process for producing a highly pure aromatic polycarboxylic acid, the process comprising a salt formation step of forming a crystalline amine salt by mixing an aromatic polycarboxylic acid with an aliphatic amine and/or an alicyclic amine in the presence of a solvent under conditions which allow a substantial part of the amine salt being formed to precipitate, thereby preventing the amine salt from completely dissolving into the solvent.
In the known purification methods by recrystallization through the formation of amine salts of aromatic polycarboxylic acids, the whole amine salts are dissolved into a solvent by heating, and then the resultant solution is cooled or concentrated to precipitate purified crystals of the amine salts. The inventors have found that all organic acid components in crude aromatic polycarboxylic acids are converted into salts merely by mixing crude aromatic polycarboxylic acids with amines in an appropriate solvent without heating, and that a substantial part of the amine salt of aromatic polycarboxylic acids, i.e., excess amine salts of aromatic polycarboxylic acids exceeding the solubility to the solvent are allowed to precipitate as purified crystals immediately after the formation, while the amine salts of impurities remain dissolved in the solvent. Namely, in the process of the present invention, the amine salts are purified without creating complete dissolution state as employed in the conventional purification methods, so that highly pure aromatic polycarbo
Hashimoto Akio
Hayashi Masayoshi
Shigematsu Ryusuke
Takagawa Makoto
Antonelli Terry Stout & Kraus LLP
Killos Paul J.
Mitsubishi Gas Chemical Company Inc.
Tucker Zachary C.
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