Purification method of 2, 6-naphthalene dicarboxylic acidTechnical Field
The invention relates to the technical field of chemical production, in particular to a purification method of 2, 6-naphthalene dicarboxylic acid.
Background
2, 6-naphthalene dicarboxylic acid is an important raw material for synthesizing a plurality of high value-added fine chemicals and polyester materials, and can be used for preparing various high-performance plastics and thermotropic liquid crystal polymers. Currently, the most important field of application of 2, 6-naphthalenedicarboxylic acid is the synthesis of polyethylene naphthalate (PEN). PEN is a novel polyester material, and compared with the polyester material polyethylene terephthalate (PET) which is widely applied at present, PEN has more excellent performance and wider application range. Besides the synthesis of PEN, 2, 6-naphthalene dicarboxylic acid is an important intermediate for synthesizing a functional polymer PBN and a liquid crystal polymer LCP, can be used as a raw material of polyester fibers, polyamides and polythioester fibers, and is also an important raw material in the industries of medicines, electronics, pesticides, dyes and the like.
At present, the methods for producing 2, 6-naphthalenedicarboxylic acid mainly include Henkel method, carboxyl group transfer method, dialkylnaphthalene oxidation method, methylnaphthoyl oxidation method and the like. Among them, dialkyl naphthalene oxidation and methyl naphthalene oxidation are most industrially used. The preparation of 2, 6-naphthalenedicarboxylic acid by the dialkylnaphthalene oxidation method or the methylnaphthalene acylation oxidation method requires liquid-phase oxidation in a Co-Mn-Br catalyst system, and the product contains trimellitic acid, aldehyde derivatives (e.g., 6-formyl-2-naphthoic acid, 2-methyl-6-naphthoaldehyde, etc.), 2-naphthoic acid, bromo-2, 6-naphthalenedicarboxylic acid, benzoic acid, etc. Therefore, the 2, 6-naphthalenedicarboxylic acid must be purified to meet the quality requirements of the polymer grade.
The existing methods for purifying 2, 6-naphthalene dicarboxylic acid mainly comprise an alkali dissolution and acid precipitation method, a solvent recrystallization method, an esterification and hydrolysis method, a catalytic hydrogenation method and the like. The alkali-soluble acid-out method is a method of separating 2, 6-naphthalenedicarboxylic acid from other impurities by adjusting the pH of the solution using the solubility of di-salt of 2, 6-naphthalenedicarboxylic acid and the insolubility of mono-salt of 2, 6-naphthalenedicarboxylic acid. However, the method has a disadvantage that it is difficult to ensure complete conversion of di-salt of 2, 6-naphthalenedicarboxylic acid into mono-salt of 2, 6-naphthalenedicarboxylic acid by controlling the pH, which affects the yield. Meanwhile, there is a report on a method of adding acetone to an alkali solution of 2, 6-naphthalenedicarboxylic acid, heating and refluxing to precipitate disodium naphthalenedicarboxylate, dissolving the crystals in water, and adjusting pH to precipitate 2, 6-naphthalenedicarboxylic acid, thereby improving the yield and purity of 2, 6-naphthalenedicarboxylic acid. However, acetone has a low boiling point (56.5 ℃), is extremely volatile during use, causes explosive vapor, and increases purification cost and unsafe factors. The solvent recrystallization method, the esterification hydrolysis method, the catalytic hydrogenation method and the like need to use organic solvents, hydrogen, high temperature and other conditions, have complex process and high cost, and are not suitable for industrial application. Therefore, it is very important to find a method for purifying 2, 6-naphthalenedicarboxylic acid which has simple process, high safety, and high product yield and purity and is suitable for industrial production.
Disclosure of Invention
Aiming at the problems of complex process, poor safety and further improvement of yield and purity of the existing 2, 6-naphthalenedicarboxylic acid purification method, the invention provides a 2, 6-naphthalenedicarboxylic acid purification method.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a method for purifying 2, 6-naphthalenedicarboxylic acid comprising the steps of:
adding the 2, 6-naphthalenedicarboxylic acid crude product into a strong alkali ethanol water solution, uniformly mixing, adding activated carbon for decoloring, performing suction filtration, adding hydrochloric acid into the obtained filtrate to adjust the pH to 1.0-1.5, performing suction filtration, washing, and drying to obtain the 2, 6-naphthalenedicarboxylic acid product.
Compared with the prior art, the method for purifying the 2, 6-naphthalenedicarboxylic acid provided by the invention uses the strong base-ethanol aqueous solution as a solvent for dissolving the crude 2, 6-naphthalenedicarboxylic acid, so that the 2, 6-naphthalenedicarboxylic acid is completely converted into a form of the 2, 6-naphthalenedicarboxylic acid di-salt dissolved in water, impurities insoluble in a strong base-ethanol aqueous solution system are separated out, the aldehyde derivative, the reaction raw material methylnaphthalene and the like are always dissolved in the system in the purification process and cannot be separated out, the pH value of the system is adjusted to 1-1.5 subsequently, so that the 2, 6-naphthalenedicarboxylic acid di-salt is converted into the 2, 6-naphthalenedicarboxylic acid as much as possible and cannot be separated out, and acidic substances such as trimellitic acid, benzoic acid and the like are separated out, so that the purity and yield of the product are remarkably improved, heating reflux is not required in the purification process, the process is simplified, and the energy consumption is reduced. According to the purification method of 2, 6-naphthalenedicarboxylic acid provided by the invention, the specific solvent is selected and the pH value is adjusted to 1.0-1.5, so that the yield of the prepared 2, 6-naphthalenedicarboxylic acid product is over 93%, recrystallization is not needed, the purity can reach 99.9%, heating reflux is not needed, the production process is simplified, the production efficiency and the production safety are improved, and the purification method is suitable for large-scale industrial production.
Preferably, the strong base is sodium hydroxide.
Preferably, the concentration of the strong base in the ethanol water solution of the strong base is 0.07-0.09mol/L.
Preferably, the ethanol content of the ethanol aqueous solution of the strong base is 15-25% by volume.
Preferably, the mass ratio of the ethanol aqueous solution of the strong base to the crude 2, 6-naphthalenedicarboxylic acid is 3-4.
The optimized solvent and the addition amount are beneficial to converting the 2, 6-naphthalenedicarboxylic acid into the form of disodium salt thereof, so that the 2, 6-naphthalenedicarboxylic acid is fully dissolved, impurities which are insoluble in a strong base-ethanol water system are removed, and impurities such as aldehyde derivatives, reaction raw material methylnaphthalene and the like are fully dissolved in the system and can not be separated out all the time in the purification process; in addition, under the condition of subsequently adjusting the pH value to 1.0-1.5, the disodium salt of the 2, 6-naphthalenedicarboxylic acid can be converted into the 2, 6-naphthalenedicarboxylic acid as much as possible, and trimellitic acid, benzoic acid and 6-formyl 2-naphthalenedicarboxylic acid are ensured not to be separated out along with the 2, 6-naphthalenedicarboxylic acid, so that the yield and the purity of the product are remarkably improved.
Preferably, the mass ratio of the activated carbon to the crude 2, 6-naphthalenedicarboxylic acid is 1-5.
Preferably, the decolorizing time of adding activated carbon is 0.5-1h.
The optimized adding amount and the decoloring time of the active carbon can remove impurities in the crude 2, 6-naphthalene dicarboxylic acid product as much as possible under the condition of using the active carbon as little as possible, and the final product has white color, so that the quality of the product is improved, the subsequent filtration is facilitated, the filtration time is shortened, and the production efficiency is improved.
Preferably, the hydrochloric acid is commercially available concentrated hydrochloric acid in chemical purity. And slowly dripping concentrated hydrochloric acid into the system under the stirring condition, and adjusting the pH value of the system to be 1.0-1.5.
The purification method is carried out at room temperature, heating reflux and cooling crystallization are not needed, so that the production energy consumption is greatly reduced, and the used solvents are only ethanol and water, so that toxic and hazardous wastes are not generated.
Preferably, the crude 2, 6-naphthalene dicarboxylic acid is prepared by using 2-alkyl-6-acyl naphthalene or 2, 6-dialkyl naphthalene as a raw material through liquid phase oxidation.
The 2, 6-dinaphthalene formic acid crude product is prepared by taking 2-alkyl-6-acylnaphthalene or 2, 6-dialkyl naphthalene as a raw material, co-Mn as a catalyst, br as an accelerant, reaction temperature of about 200 ℃ and reaction pressure of about 3MPa through liquid phase oxidation.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
A method for purifying 2, 6-naphthalenedicarboxylic acid:
weighing 10g of crude 2, 6-naphthalenedicarboxylic acid (purity 86.21%), adding 35g of sodium hydroxide-ethanol aqueous solution, after complete dissolution, adding 30g of activated carbon, stirring and decoloring for 1h, carrying out suction filtration to separate out the activated carbon, slowly dropwise adding concentrated hydrochloric acid into the obtained filtrate under the stirring condition until the pH value is 1.0, carrying out suction filtration separation, washing with water and drying to obtain 8.10g of 2, 6-naphthalenedicarboxylic acid product, wherein the purity of HPLC is 99.9%.
Wherein, the concentration of the sodium hydroxide in the sodium hydroxide-ethanol solution is 0.08mol/L, and the volume percentage content of the ethanol is 20 percent.
Example 2
A method for purifying 2, 6-naphthalenedicarboxylic acid:
weighing 10g of 2, 6-naphthalenedicarboxylic acid crude product (with the purity of 84.52%), adding 30g of sodium hydroxide-ethanol aqueous solution, after complete dissolution, adding 10g of activated carbon, stirring and decoloring for 1h, carrying out suction filtration to separate out the activated carbon, slowly dropwise adding concentrated hydrochloric acid into the obtained filtrate under the stirring condition until the pH value is 1.5, carrying out suction filtration separation, washing with water and drying to obtain 7.89g of 2, 6-naphthalenedicarboxylic acid product, wherein the HPLC purity is 99.9%.
Wherein, the concentration of the sodium hydroxide in the sodium hydroxide-ethanol solution is 0.09mol/L, and the volume percentage content of the ethanol is 15 percent.
Example 3
A method for purifying 2, 6-naphthalenedicarboxylic acid:
weighing 10g of 2, 6-naphthalenedicarboxylic acid crude product (with the purity of 81.35%), adding 40g of sodium hydroxide-ethanol aqueous solution, after complete dissolution, adding 50g of activated carbon, stirring and decoloring for 0.5h, carrying out suction filtration to separate out the activated carbon, slowly dropwise adding concentrated hydrochloric acid into the obtained filtrate under the stirring condition until the pH value is 1.2, carrying out suction filtration separation, washing and drying to obtain 7.58g of 2, 6-naphthalenedicarboxylic acid product, wherein the HPLC purity is 99.9%.
Wherein, the concentration of the sodium hydroxide in the sodium hydroxide-ethanol solution is 0.07mol/L, and the volume percentage content of the ethanol is 25 percent.
Comparative example 1
A method for purifying 2, 6-naphthalenedicarboxylic acid:
weighing 10g of 2, 6-naphthalenedicarboxylic acid crude product (purity 86.21%), adding 35g of 0.08mol/L sodium hydroxide aqueous solution, after complete dissolution, adding 30g of activated carbon, stirring and decoloring for 1h, performing suction filtration to separate out the activated carbon, slowly dropwise adding concentrated hydrochloric acid into the obtained filtrate under the stirring condition until the pH value is 2.0, performing suction filtration separation, washing and drying to obtain 7.67g of 2, 6-naphthalenedicarboxylic acid product, wherein the HPLC purity is 91.5%.
Comparative example 2
A method for purifying 2, 6-naphthalenedicarboxylic acid:
weighing 10g of 2, 6-naphthalenedicarboxylic acid crude product (purity 86.21%), adding 35g of sodium hydroxide-methanol aqueous solution, after complete dissolution, adding 30g of activated carbon, stirring and decoloring for 1h, carrying out suction filtration to separate out the activated carbon, slowly dropwise adding concentrated hydrochloric acid into the obtained filtrate under the stirring condition until the pH value is 1.0, carrying out suction filtration and separation, washing and drying to obtain 7.85g of 2, 6-naphthalenedicarboxylic acid product, wherein the HPLC purity is 94.5%.
Wherein, the concentration of the sodium hydroxide in the sodium hydroxide-methanol solution is 0.08mol/L, and the volume percentage content of the methanol is 20 percent.
In conclusion, the purification method of 2, 6-naphthalenedicarboxylic acid provided by the invention has the advantages of simple process, no need of special equipment, low energy consumption and good safety, the purity of the 2, 6-naphthalenedicarboxylic acid can reach 99.9%, the yield can reach more than 93%, and the purification method is an environment-friendly purification method and has wide application prospect.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.