JP5318595B2 - Method for producing 2,6-naphthalenedicarboxylic acid - Google Patents

Description

  The present invention includes a step of reacting a di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid with a basic alkali metal compound and acidifying the resulting solution of a dialkali metal salt of 2,6-naphthalenedicarboxylic acid. The production method of 2,6-naphthalenedicarboxylic acid.

  2,6-naphthalenedicarboxylic acid (hereinafter, 2,6-naphthalenedicarboxylic acid is sometimes referred to as 2,6-NDA) is important as a monomer for various polymers such as polyethylene naphthalate, liquid crystalline polyester, and polyamide. A compound. Further, di-lower alkyl esters such as dimethyl ester of 2,6-naphthalenedicarboxylic acid (hereinafter, di-lower alkyl esters of 2,6-naphthalenedicarboxylic acid may be referred to as 2,6-NDC) From the viewpoint of physical properties and ease of use as a monomer, it is widely used as a monomer for various polymers in the same manner as 2,6-NDA.

  Conventionally, as a method for producing 2,6-NDA, an alkyl group and / or an acyl group is obtained by using naphthalene substituted at the 2,6-position with an alkyl group and / or an acyl group and using a heavy metal such as cobalt or manganese as a catalyst. A production method is known in which is oxidized with molecular oxygen. However, the crude 2,6-NDA obtained by this method cannot be used directly as a monomer for a polymer because it contains impurities such as aldehyde-type intermediates and oxidized polymers.

  For this reason, various purification methods have been studied for the crude 2,6-NDA obtained by the above method.

  For example, by esterifying crude 2,6-NDA with a lower alcohol such as methanol to 2,6-NDC, and then purifying 2,6-NDC by distillation, recrystallization, etc., followed by decomposition of the ester group, Methods for obtaining high purity 2,6-NDA are generally known.

  As a method for producing high purity 2,6-NDA by decomposing the ester group of 2,6-NDC, a method of decomposing the ester group with an acid catalyst, a method of decomposing the ester group with water under specific conditions, In addition, a method of decomposing an ester group with a basic catalyst has been proposed.

  As a method for decomposing an ester group with an acid catalyst, there is known a method for decomposing an ester group of 2,6-NDC in the presence of an acid catalyst and an aliphatic carboxylic acid to obtain 2,6-NDA of high purity. (See Patent Document 1). However, this method has a problem that a long time is required for the reaction and aliphatic carboxylic acid esters are generated as a by-product in the ester group decomposition step.

  The method for decomposing ester groups with water under certain conditions includes the presence of a sufficient amount of water to solubilize at least about 10% of the 2,6-NDA produced at the reaction temperature under liquid phase conditions. Below, a method of hydrolyzing the ester group of 2,6-NDC at a reaction temperature of at least 450 degrees Fahrenheit (232 degrees Celsius) is known (see Patent Document 2). However, this method requires a very high temperature of 450 degrees Fahrenheit or higher, and the reaction is performed at a temperature higher than the boiling point of water.

  As a method of decomposing an ester group with a basic catalyst, a solution of a salt of 2,6-NDA is obtained by decomposing the ester group with a basic compound using water and / or an organic solvent, and then by acid precipitation. , 6-NDA is known (see Patent Documents 3 to 6).

  However, in these methods, since the obtained 2,6-NDA contains a large amount of alkali metal, when used as a raw material for a polymer material such as polyester, the behavior during the polymerization reaction is caused by the catalytic action of the alkali metal. And the problem that it becomes difficult to control the physical properties of the resulting polymer material, and the operation of recovering 2,6-NDA from the slurry after acid deposition is difficult because very fine crystals are precipitated during acid precipitation. There's a problem.

JP-A-6-256256 JP-T 6-505512 JP-A-3-240750 JP 2005-272423 A JP 2005-272424 A JP 2005-272425 A

  The object of the present invention is that it does not require violent conditions such as high temperature and high pressure, and in a simple process without using a special apparatus, high-purity 2,6-NDA with a low alkali metal content can be obtained in a short time. It is to provide a method of manufacturing.

  The present inventors react 2,6-NDC with a basic alkali metal compound in the presence of a solvent to obtain a 2,6-NDA dialkali metalate solution, and then acidify it. As a result of intensive studies on a process for producing 2,6-NDA comprising steps, alcohol produced as a by-product by reaction of 2,6-NDC and a basic alkali metal compound and alcohol contained in the reaction solvent are After distilling off the 6-NDA dialkali metal salt solution, the reaction solution was subjected to acid precipitation to find that high-purity 2,6-NDA with a low alkali metal content can be easily prepared. The invention has been completed.

〔Ｉ〕
［式中、Ｒは分岐を有してもよい炭素原子数１〜６のアルキル基を表す］。 That is, this invention provides the manufacturing method of 2, 6- naphthalene dicarboxylic acid including the process of the following (1)-(3):
(1) A di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid represented by the formula [I] and a basic alkali metal compound are selected from water or a mixed solvent of water and an alcohol having 1 to 6 carbon atoms. Reacting in the presence of an aqueous solvent to obtain a dialkali metal salt solution of 2,6-naphthalenedicarboxylic acid;
(2) in step (1), during and / or after the reaction, the step of distilling off the alcohol by-produced by the reaction and the alcohol contained in the solvent to 2% by weight or less of the reaction solution; and
(3) A step of subjecting a solution of a dialkali metal salt of 2,6-naphthalenedicarboxylic acid from which alcohol has been distilled off in step (2) to acid precipitation;

[I]
[Wherein R represents an alkyl group having 1 to 6 carbon atoms which may have a branch].

  In the present specification and claims, the term “lower” means 1 to 6 carbon atoms.

  According to the method of the present invention, high-purity 2,6-NDA with a low alkali metal content can be produced in a short time.

  The 2,6-NDC represented by the formula [I] used in the present invention may be obtained by any conventionally known method. For example, by oxidizing naphthalene substituted at the 2,6-position with an alkyl group and / or acyl group with a heavy metal such as cobalt or manganese as a catalyst, the alkyl group and / or acyl group is oxidized with molecular oxygen. The obtained crude 2,6-NDA can be obtained by reacting with a lower alcohol in the presence of an acid catalyst such as sulfuric acid or p-toluenesulfonic acid.

  Preferable specific examples of 2,6-NDC represented by the formula [I] used in the present invention include 2,6-naphthalenedicarboxylic acid dimethyl ester, 2,6-naphthalenedicarboxylic acid diethyl ester, 2,6- Naphthalenedicarboxylic acid di-n-propyl ester, 2,6-naphthalenedicarboxylic acid di-iso-propyl ester, 2,6-naphthalenedicarboxylic acid di-n-butyl ester, 2,6-naphthalenedicarboxylic acid di-iso-butyl ester Examples thereof include one or more compounds selected from the group consisting of esters, 2,6-naphthalenedicarboxylic acid di-n-pentyl ester, and 2,6-naphthalenedicarboxylic acid di-n-hexyl ester.

  Among these specific examples of 2,6-NDC, 2,6-naphthalenedicarboxylic acid dimethyl ester is particularly preferable because it is easily available.

  In the present invention, as a solvent for reacting 2,6-NDC and a basic alkali metal compound, an aqueous solvent selected from water or a mixed solvent of water and an alcohol having 1 to 6 carbon atoms is used. Preferably, as the aqueous solvent, an aqueous alcohol solution containing water or an alcohol having 1 to 6 carbon atoms in an amount of 10% by weight or less is used. When the content of the alcohol having 1 to 6 carbon atoms exceeds 10% by weight, it takes a long time to distill the alcohol.

  Specific examples of the alcohol having 1 to 6 carbon atoms include methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, n-pentyl alcohol, and n-hexyl alcohol. One or more types selected from the group can be mentioned.

  Among these alcohols having 1 to 6 carbon atoms, it is preferable to use methanol alone because it is easily dissolved in water and is easily available and inexpensive.

  The amount of the solvent used in the present invention is not particularly limited as long as the reaction between 2,6-NDC represented by the formula [I] and the basic alkali metal compound proceeds well, but relative to the weight of 2,6-NDC 3 to 10 times weight is preferable, 4 to 8 times weight is more preferable, and 5 to 7 times weight is particularly preferable. When the solvent is less than 3 times the weight, it is difficult to stir the reaction solution.

  In the present invention, the basic alkali metal compound used for decomposing the ester group of 2,6-NDC includes, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate. One or more types selected from the group can be mentioned.

  Among these basic alkali metal compounds, it is preferable to use sodium hydroxide or potassium hydroxide because of reactivity, availability, and low cost.

  The basic alkali metal compound may be solid when charged into the reaction system, or may be in the form of a solution dissolved in water or an aqueous solution of an alcohol having 1 to 6 carbon atoms.

  The amount of the basic alkali metal compound used is 1 to 2. ester of 2,6-NDC represented by the formula [I]. It is preferably 0 to 5.0 equivalents, and more preferably 1.0 to 2.0 equivalents.

  In the present invention, the temperature at which the 2,6-NDC represented by the formula [I] is reacted with the basic alkali metal compound is not particularly limited as long as the reaction proceeds well, but is preferably 40 to 200 ° C., preferably 60 to 150 degreeC is more preferable and 80-120 degreeC is especially preferable. When the reaction temperature exceeds the boiling point of the solvent, the reaction may be carried out using a pressure device.

  The reaction between 2,6-NDC and the basic alkali metal compound is not particularly problematic if carried out in air or in an inert gas atmosphere, but may be carried out in an inert gas atmosphere such as nitrogen or helium. preferable.

  The reaction time between 2,6-NDC and the basic alkali metal compound is typically 1 to 50 hours, preferably 2 to 20 hours, more preferably, depending on the type and amount of the solvent used and the reaction temperature. It takes 3-10 hours.

  The analysis means for confirming the completion of the reaction between 2,6-NDC and the basic alkali metal compound is not particularly limited. For example, it can be confirmed by analyzing the reaction solution by high performance liquid chromatography.

  The reaction of 2,6-NDC with a basic alkali metal compound is carried out with 95 mol% or more, preferably 98 mol% or more, more preferably 99 mol% or more of 2,6-NDA with 2,6-NDA being charged. This may be done until it is converted to a dialkali metal salt.

  According to the present invention, from the reaction solution of 2,6-NDC and a basic alkali metal compound, an alcohol by-produced by the reaction of 2,6-NDC and the basic alkali metal compound during and / or after the reaction. 2,6-NDA dialkali metal salt solution obtained by reaction after distilling off alcohol contained in the solvent to 2% by weight or less, preferably 1.5% by weight or less of the reaction solution Acidified.

  The alcohol concentration in the solvent in the reaction solution after distilling off the alcohol was obtained by taking a part of the reaction solution as a sample, measuring the alcohol content in the reaction solution using a conventional method such as gas chromatography, It can be calculated based on the amount of 2,6-NDA dialkali metal salt and unreacted 2,6-NDC contained in the liquid.

  The method for distilling off the alcohol is not particularly limited, and the reaction liquid may be heated and the generated vapor may be discharged out of the reaction tank system through a distillation pipe connected to the reaction tank used for the reaction. At this time, the same amount of water as the amount of alcohol distilled is added.

  The distillation of the alcohol may be started during the reaction or may be started after the end of the reaction, and the alcohol concentration in the reaction solution before being subjected to acid precipitation is 2% by weight or less, preferably 1.5% by weight. It only has to be as follows.

  The temperature at which the reaction vessel is heated when the alcohol is distilled off is the same as the temperature at which 2,6-NDC reacts with the basic alkali metal compound.

  The solution of 2,6-NDA dialkali metal salt obtained by reacting 2,6-NDC with a basic alkali metal compound and distilling off the alcohol as described above is then subjected to an acid precipitation step. Provided.

  For the 2,6-NDA dialkali metal salt solution before acid precipitation, if necessary, by filtration treatment for removing insoluble foreign matter, activated carbon for removing coloring substances, metals, etc. An adsorbent treatment may be performed.

  In the present invention, the step of acidifying the 2,6-NDA dialkali metal salt solution may be carried out in the same reaction vessel following the step of reacting 2,6-NDC with a basic alkali metal compound, It may be carried out after transferring a solution of 2,6-NDA dialkali metal salt to a separately prepared reaction vessel.

  Although the acid used at an acid precipitation process is not specifically limited, A mineral acid is used suitably. Examples of the mineral acid include binary acids such as hydrochloric acid and hydrofluoric acid, and oxo acids such as sulfuric acid, nitric acid, phosphoric acid, and perchloric acid. Also, organic acids such as acetic acid and propionic acid can be used.

  The amount of these acids to be used is preferably 1.0-2.0 equivalents, more preferably 1.1-1.5 equivalents relative to the 2,6-NDA dialkali metal salt, and 1.1-1. Two equivalents are particularly preferred.

  The temperature during acid precipitation is preferably 30 to 200 ° C, more preferably 80 to 120 ° C, and particularly preferably 90 to 110 ° C.

  The acid precipitation time varies depending on the scale of the reaction, but is preferably 50 to 70 minutes, more preferably 55 to 65 minutes.

  The acid precipitation is not particularly problematic if carried out in air or in an inert gas atmosphere, but is preferably carried out in an inert gas atmosphere such as nitrogen or helium.

  The 2,6-NDA slurry obtained by acid precipitation is separated and recovered from the slurry by conventional methods such as centrifugation and filtration with a filter press. The separated 2,6-NDA is dried after being washed with cold water or hot water as necessary.

  The 2,6-NDA thus obtained is suitably used as a raw material for various chemical products, but has a low purity of alkali metal and high purity, so that liquid crystalline polyester, polyethylene naphthalate, polyamide, etc. It is particularly suitably used as various polymer monomers.

  The alkali metal content of 2,6-NDA obtained by the method of the present invention is preferably less than 100 ppm, more preferably less than 70 ppm.

  Hereinafter, the present invention will be described in detail by way of examples.

Example 1
Charge 171.5 g of 2,6-naphthalenedicarboxylic acid dimethyl ester, 848.9 g of water, 8.6 g of methanol, and 119.6 g of 48% NaOH aqueous solution to a 2 L flask equipped with a stirrer, a reflux condenser and a thermometer. The mixture was heated to 98 ° C. or higher and stirred at a speed of 250 rpm to obtain a reflux state. Distillation of the distillate was started 4 hours after the internal temperature reached 90 ° C., and maintained for 7 hours to obtain a sodium 2,6-naphthalenedicarboxylate aqueous solution. The amount of distillate was 83 g, and the methanol concentration in the distillate was 33%.

  After cooling this aqueous solution to 50 ° C. and filtering off the slightly remaining raw material (insoluble matter), the mother liquor was transferred to the same 2 L flask, and 566 g of water and 83 g of water having the same amount as the distillate were added. . The methanol concentration in the aqueous 2,6-naphthalenedicarboxylate solution was 1.4% by weight. The aqueous solution was heated to 90 ° C. while stirring at 250 rpm, and 107.1 g of 62% sulfuric acid was added dropwise over about 60 minutes. The temperature was raised to 99 ° C. over 30 minutes from the start of dropping, and thereafter the same temperature was maintained until the end of dropping to obtain a white slurry liquid of 2,6-naphthalenedicarboxylic acid. The slurry was cooled to 50 ° C. and then separated into solid and liquid.

  This solid content was dried with a blast dryer at 120 ° C. to obtain 151.0 g of a solid (yield 99.8%). As a result of HPLC analysis, 2,6-naphthalenedicarboxylic acid was 98%, and 2,6-naphthalenedicarboxylic acid dimethyl ester as a raw material was not detected. The amount of Na element contained in 2,6-naphthalenedicarboxylic acid was determined by atomic absorption analysis to be 54 ppm.

Example 2
2,6-naphthalenedicarboxylic acid was produced in the same manner as in Example 1 except that the stirring speed during the reaction was 300 rpm. During the reaction, the amount of distillate was 104 g, the methanol concentration was 28.8%, and the methanol concentration in the aqueous 2,6-naphthalenedicarboxylate solution before 62% sulfuric acid was added was 1.2% by weight.

  The solid content of the obtained 2,6-naphthalenedicarboxylic acid was 151.1 g (yield 99.8%), and 2,6-naphthalenedicarboxylic acid dimethyl ester as a raw material was not detected. The amount of Na element contained in 2,6-naphthalenedicarboxylic acid was determined by atomic absorption analysis to be 49 ppm.

Comparative Example 1
During the reaction, 2,6-naphthalenedicarboxylic acid was produced in the same manner as in Example 1 except that the distillate was not withdrawn and the maximum temperature after adding 62% sulfuric acid was 97 ° C. During the reaction, the methanol concentration in the aqueous 2,6-naphthalenedicarboxylate solution before dropping 62% sulfuric acid was 3.0% by weight.

  The solid content of the obtained 2,6-naphthalenedicarboxylic acid was 151.1 g (yield 99.8%), and 2,6-naphthalenedicarboxylic acid dimethyl ester as a raw material was not detected. The amount of Na element contained in 2,6-naphthalenedicarboxylic acid was determined by atomic absorption analysis to be 100 ppm.

  As described above, when the distillate was withdrawn during the reaction, the obtained 2,6-naphthalenedicarboxylic acid had a low Na element content, but the distillate was not withdrawn. In this case, the obtained 2,6-naphthalenedicarboxylic acid had a high content of Na element.

Claims (4)

A process for producing 2,6-naphthalenedicarboxylic acid, comprising the following steps (1) to (3):
(1) A di-lower alkyl ester of 2,6-naphthalenedicarboxylic acid represented by the formula [I] and a basic alkali metal compound are mixed with water or an alcohol having 1 to 6 carbon atoms in an amount of 10% by weight or less. Reacting in the presence of an aqueous alcohol solution to obtain a dialkali metal salt solution of 2,6-naphthalenedicarboxylic acid;
(2) in step (1), during and / or after the reaction, the step of distilling off the alcohol by-produced by the reaction and the alcohol contained in the solvent to 2% by weight or less of the reaction solution; and
(3) A step of subjecting a solution of a dialkali metal salt of 2,6-naphthalenedicarboxylic acid from which alcohol has been distilled off in step (2) to acid precipitation;

[I]
[Wherein R represents an alkyl group having 1 to 6 carbon atoms which may have a branch]. In the reaction of step (1), the amount of aqueous solvent, according to claim 1 which is 3 to 10 times by weight relative to the weight of the di-lower alkyl ester of 2,6-naphthalene dicarboxylic acid of the formula [I] A method for producing 2,6-naphthalenedicarboxylic acid as described in 1). Basic alkali metal compound is sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, according to claim 1 or 2 sodium bicarbonate, and is at least one compound selected from the group consisting of potassium bicarbonate Of 2,6-naphthalenedicarboxylic acid.   The method for producing 2,6-naphthalenedicarboxylic acid according to any one of claims 1 to 3, wherein the alkali metal content of 2,6-naphthalenedicarboxylic acid obtained after the acid precipitation in step (3) is less than 70 ppm.