A method for recycling the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid.

Abstract

This invention discloses a method for recovering and utilizing the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid. The method includes the following steps: (1) filtering the product obtained from the oxidation reaction of synthesized 2,6-naphthalenedicarboxylic acid at a temperature greater than 80°C to obtain oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product; (2) hydrogenating oxidation mother liquor A in the presence of a hydrogenation catalyst to obtain hydrogenated oxidation mother liquor AH; (3) supplementing the hydrogenated oxidation mother liquor AH with a catalyst and organic solvent to serve as the reaction mother liquor, and continuing to introduce reaction raw materials and sufficient gas containing free oxygen for oxidation reaction. The method for recovering and utilizing the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid provided by this invention can maximize the recovery rate of the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid and reduce the impact of impurities in the mother liquor on product purity.

Description

Technical Field

[0001] This invention relates to a method for recycling the mother liquor from the oxidation of 2,6-naphthalenedicarboxylic acid. Background Technology

[0002] Polyethylene naphthalate (PEN) is a new polyester variety commercialized in the 1990s, formed by the polycondensation of dimethyl 2,6-naphthalenedicarboxylate (NDC) or 2,6-naphthalenedicarboxylic acid (NDA) with ethylene glycol (EG). Like traditional polyester (PET), PEN can be processed into films, fibers, hollow containers, and sheets. However, PEN exhibits superior physical and mechanical properties, gas barrier properties, chemical stability, and resistance to heat, UV radiation, and other harmful substances compared to PET. Due to its excellent overall performance and broad potential market, it has attracted the attention of the global polyester industry. The key technology in PEN polyester production is the synthesis technology of its monomer, 2,6-naphthalenedicarboxylic acid.

[0003] Currently, industrially, 2,6-NDA is synthesized only through air-liquid phase oxidation using 2,6-dimethylnaphthalene as a raw material, under a Co-Mn-Br catalyst. For example, US5183933 uses 2,6-dimethylnaphthalene (2,6-DMN) to produce 2,6-NDA with a yield of 93%. However, considering the cost of raw materials, 2,6-diisopropylnaphthalene (2,6-DIPN) has a more significant advantage. Therefore, the 2,6-DIPN oxidation method for preparing 2,6-NDA has greater development potential. For instance, US4709088 uses a semi-continuous method, continuously adding 2,6-DIPN to a mixture of catalyst and solvent at a certain rate, followed by 2 hours of deep oxidation after the feed is complete, achieving a 2,6-NDA yield of 91.7 mol%, but requiring a very large amount of catalyst. In addition, impurities have a significant impact on subsequent polymerization reactions. Numerous experiments have found that the main impurities in the oxidation products of 2,6-DIPN are 2-formyl-6-naphthoic acid (2,6-FNA) and 2-acetyl-6-naphthoic acid (2,6-ANA). The content of these two impurities has a great influence on the performance and color of the polymer.

[0004] The presence of impurities, particularly 2-acetyl-6-naphthoic acid (2,6-ANA), limits the recovery and reuse of the oxidation mother liquor from the synthesis of 2,6-naphthalenedicarboxylic acid from 2,6-diisopropylnaphthalene. Excessive recovery of the mother liquor inevitably affects the purity of subsequent products. Summary of the Invention

[0005] This invention addresses the problem that the recovery rate of the oxidation mother liquor used in the synthesis of 2,6-naphthalenedicarboxylic acid is limited by the impurities it contains, and proposes a method for recovering and utilizing the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid. This aims to further improve the recovery rate of the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid and reduce the impact of impurities in the mother liquor on product purity.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for recycling the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid, comprising the following steps:

[0007] (1) The product obtained from the oxidation reaction of synthesized 2,6-naphthalenedicarboxylic acid was filtered at a temperature greater than 80°C to obtain oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product;

[0008] (2) The mother liquor A of oxidation is hydrogenated in the presence of a hydrogenation catalyst to obtain the hydrogenated mother liquor AH;

[0009] (3) After adding catalyst and organic solvent to the hydrogenated oxidation mother liquor AH, it is used as the reaction mother liquor. Then, the reaction raw materials and sufficient gas containing free oxygen are continuously introduced to carry out the oxidation reaction.

[0010] Furthermore, the product obtained from the oxidation reaction in step (1) is preferably filtered at 85-100°C, and even more preferably at 85-90°C.

[0011] Further, the oxidation reaction process for synthesizing 2,6-naphthalenedicarboxylic acid described in step (1) is as follows: acetic acid solvent and catalyst are added to a reaction vessel; the reactants and sufficient gas containing free oxygen are introduced into the reaction vessel to carry out the reaction. The reactants are 2,6-diisopropylnaphthalene, the mass ratio of catalyst to 2,6-diisopropylnaphthalene is 1-2, and the mass ratio of acetic acid solvent to catalyst is 5-7.

[0012] Furthermore, the catalyst contains any one or more compounds of Co, Mn, Br, and K.

[0013] Furthermore, the gas containing free oxygen is air.

[0014] Further, the reaction conditions for the oxidation reaction in step (1) are: temperature 160-210℃, pressure 1-3MPa, and the ratio of air filling rate to raw material 2,6-diisopropylnaphthalene feed rate is (8-15):1 (L / g).

[0015] Further, the reaction conditions for the hydrogenation reaction in step (2) are: reaction temperature 80-130℃, reaction pressure 1-3MPa, reaction time 15-45min, and the hydrogen charging rate is related to the mass of the oxidation mother liquor A. Usually, the hydrogen charging rate corresponding to 1kg of oxidation mother liquor A is 10-15ml / min.

[0016] Furthermore, the hydrogenation catalyst in step (2) is a supported metal catalyst, and any suitable support can be selected, preferably coconut shell activated carbon.

[0017] Furthermore, the metal in the supported metal catalyst is at least one or more selected from Pd and Ru, and its loading amount is 0.1%-1% based on the catalyst mass and the metal element, preferably 0.3%-0.6%.

[0018] Furthermore, in step (3), the amount of reactant introduced is 0.5-2 times the weight of the oxidizing reactant in step (1), the amount of catalyst added is 5%-10% of the initial catalyst weight, and the amount of solvent added is 5%-10% of the initial solvent weight.

[0019] Furthermore, the reaction conditions for the oxidation reaction in step (3) are the same as those for the oxidation reaction in step (1).

[0020] The method for recycling the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid provided by this invention can maximize the recycling rate of the oxidation mother liquor of 2,6-naphthalenedicarboxylic acid and reduce the impact of impurities in the mother liquor on the purity of the product. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but it should be understood that the specific embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection.

[0022] In this invention, the crude 2,6-naphthalenedicarboxylic acid yield (%) = the mass of the dried crude 2,6-naphthalenedicarboxylic acid obtained from the oxidation reaction / (the theoretical mass of 2,6-naphthalenedicarboxylic acid obtained from the oxidation of 2,6-diisopropylnaphthalene) * 100%.

[0023] In this invention, the purity analysis of the product 2,6-naphthalenedicarboxylic acid was performed using liquid chromatography with external standard method.

[0024]

Example 1

[0025] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 60min. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90℃ to obtain 8369.54g of oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D, which was dried and weighed to be 934.68g. Oxidation mother liquor A was added to a hydrogenation reactor. At the same time, 5g of 0.5wt% Pd / C catalyst was added to the catalyst basket in the reactor. The reactor was closed and the temperature and pressure were increased. The reaction temperature was controlled at 110℃ and the reaction pressure at 1.8MPa. Hydrogen gas was introduced at a rate of 100ml / min and the reaction was carried out for 25min. After the reaction was completed, oxidation mother liquor AH was obtained. The reaction mother liquor AH was transferred to an oxidation reactor.

[0026] 31.11g Co(OAc)2·4H2O, 30.63g Mn(OAc)2·4H2O, 29.75g KBr, 36.75g CH3COOK and 770g acetic acid were added to the oxidation reactor.

[0027] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 60 min. Oxidation mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0028] For ease of comparison, the analysis results are listed in Table 1.

[0029]

Example 2

[0030] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 60min. After the reaction, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 100℃ to obtain 8375.58g of oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D, which was dried and weighed to be 931.62g. Oxidation mother liquor A was added to a hydrogenation reactor. At the same time, 5g of 0.5wt% Pd / C catalyst was added to the catalyst basket in the reactor. The reactor was closed and the temperature and pressure were increased. The reaction temperature was controlled at 85℃ and the reaction pressure at 1.2MPa. Hydrogen gas was introduced at a rate of 100ml / min and the reaction was carried out for 45min. After the reaction was completed, oxidation mother liquor AH was obtained. The reaction mother liquor AH was transferred to an oxidation reactor.

[0031] 31.11g Co(OAc)2·4H2O, 30.63g Mn(OAc)2·4H2O, 29.75g KBr, 36.75g CH3COOK and 770g acetic acid were added to the oxidation reactor.

[0032] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 60 min. Oxidation mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0033] For ease of comparison, the analysis results are listed in Table 1.

[0034]

Example 3

[0035] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 60min. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90℃ to obtain 8369.54g of oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D, which was dried and weighed to be 934.68g. Oxidation mother liquor A was added to a hydrogenation reactor. At the same time, 5g of 0.6wt% Ru / C catalyst was added to the catalyst basket in the reactor. The reactor was closed and the temperature and pressure were increased. The reaction temperature was controlled at 130℃ and the reaction pressure at 2.5MPa. Hydrogen gas was introduced at a rate of 100ml / min and the reaction was carried out for 15min. After the reaction was complete, oxidation mother liquor AH was obtained. The reaction mother liquor AH was transferred to an oxidation reactor.

[0036] 31.11g Co(OAc)2·4H2O, 30.63g Mn(OAc)2·4H2O, 29.75g KBr, 36.75g CH3COOK and 770g acetic acid were added to the oxidation reactor.

[0037] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 60 min. Oxidation mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0038] For ease of comparison, the analysis results are listed in Table 1.

[0039]

Example 4

[0040] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 60min. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90℃ to obtain 8369.54g of oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D, which was dried and weighed to be 934.68g. Oxidation mother liquor A was added to a hydrogenation reactor. At the same time, 5g of 0.5wt% Pd / C catalyst was added to the catalyst basket in the reactor. The reactor was closed and the temperature and pressure were increased. The reaction temperature was controlled at 110℃ and the reaction pressure at 1.8MPa. Hydrogen gas was introduced at a rate of 100ml / min and the reaction was carried out for 25min. After the reaction was completed, oxidation mother liquor AH was obtained. The reaction mother liquor AH was transferred to an oxidation reactor.

[0041] 24.89g Co(OAc)2·4H2O, 24.50g Mn(OAc)2·4H2O, 23.80g KBr, 29.40g CH3COOK and 770g acetic acid were added to the oxidation reactor.

[0042] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 60 min. Oxidation mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0043] For ease of comparison, the analysis results are listed in Table 1.

[0044]

Example 5

[0045] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 60min. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90℃ to obtain 8369.54g of oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D, which was dried and weighed to be 934.68g. Oxidation mother liquor A was added to a hydrogenation reactor. At the same time, 5g of 0.5wt% Pd / C catalyst was added to the catalyst basket in the reactor. The reactor was closed and the temperature and pressure were increased. The reaction temperature was controlled at 110℃ and the reaction pressure at 1.8MPa. Hydrogen gas was introduced at a rate of 100ml / min and the reaction was carried out for 25min. After the reaction was completed, oxidation mother liquor AH was obtained. The reaction mother liquor AH was transferred to an oxidation reactor.

[0046] 18.67g Co(OAc)2·4H2O, 18.38g Mn(OAc)2·4H2O, 17.85g KBr, 22.05g CH3COOK and 770g acetic acid were added to the oxidation reactor.

[0047] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 60 min. Oxidation mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0048] For ease of comparison, the analysis results are listed in Table 1.

[0049]

Comparative Example 1

[0050] 311.25g Co(OAc)₂·4H₂O, 306.25g Mn(OAc)₂·4H₂O, 297.5g KBr, 367.5g CH₃COOK, and 7700g acetic acid were mixed and added to a reactor. The mixture was then stirred and heated to 200℃, with the reactor pressure controlled at 2.75MPa. 1000g of 2,6-diisopropylnaphthalene was first heated to a molten state and then added to the reactor at a rate of 10g / min, while air was simultaneously introduced at a rate of 100L / min for the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained for another 60min. After the reaction was completed, the reaction product mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 90℃ to obtain 8369.54g of oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product D, which was dried and weighed to be 934.68g.

[0051] Add the mother liquor A to the oxidation reactor and continue to add 31.11g Co(OAc)2·4H2O, 30.63g Mn(OAc)2·4H2O, 29.75g KBr, 36.75g CH3COOK and 770g acetic acid.

[0052] Stirring was started and the temperature was raised to 200℃. The pressure in the reactor was controlled at 2.75 MPa. Then, 1000 g of molten 2,6-diisopropylnaphthalene was added to the reactor at a rate of 10 g / min, while air was introduced at a rate of 100 L / min to carry out the reaction. After the 2,6-diisopropylnaphthalene feed was completed, the reaction temperature and pressure were maintained and the reaction continued for 60 min. Oxidation mother liquor A1, filtrate B1, filter cake C1, and crude 2,6-naphthalenedicarboxylic acid product D1 were obtained.

[0053] For ease of comparison, the analysis results are listed in Table 1.

[0054] [Comparative Example 2]

[0055] Same as Example 1, except that after the reaction, the mixture containing crude 2,6-naphthalenedicarboxylic acid was filtered at 60°C. The analytical results are listed in Table 1.

[0056] Table 1

[0057]

[0058] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recovering and utilizing the mother liquor from the oxidation of 2,6-naphthalenedicarboxylic acid, characterized in that, Includes the following steps: (1) The product obtained from the oxidation reaction of synthesized 2,6-naphthalenedicarboxylic acid was filtered at a temperature greater than 80°C to obtain oxidation mother liquor A and crude 2,6-naphthalenedicarboxylic acid product; (2) The mother liquor A of oxidation is subjected to hydrogenation reaction in the presence of a hydrogenation catalyst to obtain hydrogenated mother liquor AH; (3) After adding catalyst and organic solvent to the hydrogenated oxidation mother liquor AH, it is used as the reaction mother liquor. Then, the reaction raw materials and sufficient gas containing free oxygen are continuously introduced to carry out the oxidation reaction. The oxidation reaction process for synthesizing 2,6-naphthalenedicarboxylic acid described in step (1) is as follows: acetic acid solvent and catalyst are added to the reaction vessel; the reaction raw material and sufficient gas containing free oxygen are introduced into the reaction vessel to carry out the reaction; the reaction raw material is 2,6-diisopropylnaphthalene; The reaction conditions for the hydrogenation reaction in step (2) are: reaction temperature 80-130℃, reaction pressure 1-3MPa, reaction time 15-45min, and hydrogen charging rate of 10-15ml / min for every 1kg of oxidizing mother liquor A.

2. The method according to claim 1, characterized in that, The product obtained from the oxidation reaction in step (1) is filtered at 85-100℃.

3. The method according to claim 2, characterized in that, The product obtained from the oxidation reaction in step (1) is filtered at 85-90℃.

4. The method according to claim 1, characterized in that, In the oxidation reaction for synthesizing 2,6-naphthalenedicarboxylic acid described in step (1), the mass ratio of the catalyst to 2,6-diisopropylnaphthalene is 1-2, and the mass ratio of the solvent acetic acid to the catalyst is 5-7.

5. The method according to claim 4, characterized in that, The catalyst contains any one or more compounds of Co, Mn, Br, and K.

6. The method according to claim 4, characterized in that, The gas containing free oxygen is air.

7. The method according to claim 1, characterized in that, The reaction conditions for the oxidation reaction in step (1) are: temperature 160-210℃, pressure 1-3MPa, and the ratio of air filling rate to raw material 2,6-diisopropylnaphthalene feed rate is (8-15):1 L / g.

8. The method according to claim 1, characterized in that, The hydrogenation catalyst mentioned in step (2) is a supported metal catalyst, and the support is coconut shell activated carbon.

9. The method according to claim 8, characterized in that, The metal in the hydrogenation catalyst in step (3) is at least one or more selected from Pd and Ru, and its loading is 0.1%-1% based on the mass of the catalyst and the metal element.

10. The method according to claim 9, characterized in that, The hydrogenation catalyst mentioned in step (3) has a loading of 0.3%-0.6% based on the catalyst mass and the metal element content.

Images