Continuous catalytic process for the preparation of pyromellitic dianhydride by anthracene directed conversion

Abstract

This invention belongs to the fields of coal chemical engineering, fine organic synthesis, and heterogeneous catalysis, and discloses a continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride. The method of this invention is a continuous catalytic route from anthracene to symmetrical octahydroanthracene and then to pyromellitic dianhydride. Addressing the problems of high raw material costs, single anthracene conversion pathway, low selectivity in the synthesis of symmetrical octahydroanthracene, and poor oxidation directionality in existing pyromellitic dianhydride production methods, this invention provides a mild, high-yield, and environmentally friendly method for the directional conversion of anthracene to prepare pyromellitic dianhydride.

Description

Technical Field

[0001] This invention belongs to the fields of coal chemical engineering, fine organic synthesis and heterogeneous catalysis technology, and relates to a continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride. Background Technology

[0002] Anthracene is an abundant polycyclic aromatic hydrocarbon in coal tar, and its structure highly matches the carbon skeleton of homohydric anhydride, making it an ideal non-petroleum-based raw material. However, direct oxidation of anthracene easily produces a mixture of anthraquinones, tribenzoic acid, etc., making it impossible to directionally obtain homohydric anhydride. In existing technologies, anthracene hydrogenation is mostly full hydrogenation or low-selectivity partial hydrogenation, making it difficult to obtain symmetrical octahydroanthracene with high selectivity; there are few reports on high-efficiency liquid-phase catalytic systems and processes for the oxidation of symmetrical octahydroanthracene to homohydric anhydride. Pyromellitic dianhydride (PMDA) is a core monomer for the preparation of high-end polyimides, high-temperature insulating materials, epoxy resin curing agents, and high-temperature plasticizers, and is widely used in aerospace, electronics, membrane materials, and other fields, with continuously growing market demand. Traditional homohydric anhydride production uses mesitylene as a raw material, which is obtained through air oxidation, and suffers from problems such as reliance on petroleum-based raw materials, high prices, harsh oxidation conditions, and easy carbon deposition and deactivation of the catalyst.

[0003] Chinese patent CN105772034A states that metal sulfides are the main catalysts used in the traditional anthracene hydrogenation process. This process requires harsh reaction conditions with high temperature and pressure, and can lead to sulfur loss and contamination of the reaction products.

[0004] Chinese patent CN118788380A describes a one-step method for preparing symmetrical octahydroanthracene catalysts via selective hydrogenation and cyclotransfer isomerization of phenanthrene. However, this method utilizes a noble metal Pt / HBeta catalyst, resulting in low selectivity for the octahydroanthracene product and high catalyst cost, making industrialization difficult.

[0005] Chinese patent CN120243006A describes the selective oxidation of mesitylene in air to produce pyromellitic dianhydride. The catalyst preparation involves uniformly mixing vanadium pentoxide and an aqueous solution of a soluble metal salt or ionic liquid with a phosphoric acid solution, followed by hydrothermal treatment at 200°C for 24 hours to prepare mixture I. Titanium dioxide is then added to mixture I and stirred to obtain mixture II. Mixture II is dried, shaped, and calcined at 650°C for 24 hours to obtain the catalyst. The catalyst preparation process is complex and time-consuming.

[0006] Chinese patent CN115228462B reports a gas-phase oxidation method for preparing pyromellitic dianhydride from mesitylene. The catalyst requires calcination at 1100–1300 °C and undergoes extrusion and spraying processes, making the preparation conditions complex and demanding. Furthermore, this reaction is a complex heterogeneous catalytic process accompanied by numerous side reactions, resulting in a low yield of the pyromellitic dianhydride product.

[0007] This invention uses anthracene, a coal tar byproduct, as a raw material to replace petroleum-based mesitylene, significantly reducing costs. A directed, continuous catalytic process partially hydrogenates anthracene to prepare symmetrical octahydroanthracene, which is then oxidized to homohydric anhydride. This two-step continuous catalytic process is green, producing no waste acid or heavy metal pollution. The catalyst is simple to prepare, and the raw materials are widely available and low-cost, making it suitable for industrial scale-up. It achieves a complete directed conversion from anthracene to symmetrical octahydroanthracene to homohydric anhydride, filling a technological gap. The technical route is complete and efficient, and can be applied on a large scale in industrial production. Summary of the Invention

[0008] This invention provides a continuous catalytic route of "anthracene → symmetrical octahydroanthracene → pyromellitic dianhydride". It addresses the problems of high raw material cost, single anthracene conversion pathway, low selectivity of symmetrical octahydroanthracene synthesis, and poor oxidation directionality in existing dianhydride production methods. It provides a mild, high-yield, green and environmentally friendly method for the directional conversion of anthracene to prepare dianhydride.

[0009] The technical solution of the present invention: A continuous catalytic method for the directional conversion of anthracene to pyromellitic dianhydride includes the following steps: Step 1: Using anthracene, a byproduct of coal tar, as raw material and decahydronaphthalene as solvent, a catalyst is loaded into a fixed-bed reactor for selective hydrogenation. The reaction conditions are controlled to selectively hydrogenate symmetrical octahydroanthracene and the byproduct. The solvent is recovered and reused after concentration, and the product is obtained by distillation. The catalyst is 25 wt.% Ni / Nb2O5-SiO2.

[0010] The reaction temperature in the aforementioned reaction conditions is 230-270℃.

[0011] The reaction pressure in the aforementioned reaction conditions is 2-6 MPaH2.

[0012] The reaction space velocity under the aforementioned reaction conditions is 0.5-2 h⁻¹. -1 .

[0013] In the reaction system, the mass fraction of anthracene, a coal tar byproduct, is 3-8 wt.%.

[0014] Step 2: Selective oxidation of the symmetrical octahydroanthracene obtained in Step 1 to prepare pyromellitic dianhydride; using the Mn-Co-Ce-V composite oxide synthesized with sucrose as a chelating agent as a catalyst, air as an oxidant, and acetonitrile as a reaction solvent, liquid-phase selective oxidation was carried out in a high-pressure reactor, the reaction conditions were adjusted, and the product was collected to obtain pyromellitic dianhydride.

[0015] The preparation method of the Mn-Co-Ce-V composite oxide is as follows: using the sol-gel method, sucrose is used as a chelating agent. Metal salt, sucrose and deionized water are mixed, with a metal salt:sucrose molar ratio of 1:(0.5~1.5). The mixture is stirred thoroughly and dried continuously in an oven at 100℃ for 12 hours. The dried sample is then calcined in air at 550℃ for 2 hours to obtain the Mn-Co-Ce-V composite oxide. The metal salts are NiCl2·6H2O, CoCl2·6H2O, CeCl3·7H2O, and NH4VO3.

[0016] The reaction temperature in the aforementioned reaction conditions is 180-220℃.

[0017] The reaction pressure in the aforementioned reaction conditions is 1.5-3.0 MPa.

[0018] The reaction time in the aforementioned reaction conditions is 3-8 hours.

[0019] The beneficial effects of this invention are as follows: This invention achieves a conversion rate of >99.0% and a selectivity of >87% for pyromellitic dianhydride through the directional conversion of anthracene via continuous catalysis. The two-step continuous catalysis process is green, produces no waste acid, has a simple catalyst preparation method, utilizes widely available and low-cost raw materials, and exhibits high product selectivity, making it suitable for industrial scale-up. Attached Figure Description

[0020] Figure 1 The graph shows the effect of reaction pressure on the catalytic activity of anthracene. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below in conjunction with the technical solutions and accompanying drawings.

[0022] Example 1 Preparation of 20wt.% Ni / Nb2O5-SiO2 catalyst; The niobium pentoxide-silica (Nb₂O₅-SiO₂) support was prepared by mechanical mixing. 5.0 g of silica and 5.0 g of niobium pentoxide were weighed and thoroughly ground and mixed. Then, 9.909 g of Ni(NO₃)₂·6H₂O and deionized water were added to a 100 mL beaker, followed by impregnation with the Nb₂O₅-SiO₂ support. The resulting sample was continuously dried in an oven at 100 °C for 12 h. After drying, the sample was calcined in air at 550 °C for 5 h to obtain the catalyst precursor. The catalyst precursor was then treated in a hydrogen atmosphere at a reduction temperature of 450 °C for 2 h to obtain the supported metal catalyst. The prepared sample was designated as 20 wt.% Ni / Nb₂O₅-SiO₂.

[0023] Example 2 Weigh 0.1 g of 20 wt.% Ni / Nb₂O₅-SiO₂ catalyst and load it into a fixed-bed reactor. Set the reaction temperature to 250 °C, the reaction pressure to 5 MPaH₂, and the fixed-bed reaction space velocity to 1.5 h⁻¹. -1 The anthracene mass fraction was 6 wt.%. After checking the airtightness of the apparatus, the hydrogenation reaction was initiated. The reaction products were collected, and the conversion rate and product selectivity of anthracene were tested. The conversion rate of anthracene was 99.9%, with symmetrical octahydroanthracene being the predominant hydrogenation product, and the selectivity for symmetrical octahydroanthracene was 92.6%.

[0024] Example 3 The conditions are the same as in Example 2, except that the reaction temperature is set to 230°C.

[0025] Example 4 The conditions are the same as in Example 2, except that the reaction temperature is set to 270°C.

[0026] Table 1. Effect of different reaction temperatures on the catalytic activity of anthracene partial hydrogenation.

[0027] At lower reaction temperatures, the conversion rate of anthracene is lower, and the hydrogenation activity is weaker; low temperatures are also unfavorable for H2 activation. Excessively high temperatures lead to lower selectivity for symmetrical octahydroanthracene and increased selectivity for the over-hydrogenated product, perhydroanthracene. Therefore, 250℃ is a suitable reaction temperature.

[0028] Example 5 The conditions are the same as in Example 2, except that the reaction pressure is set to 2 MPa.

[0029] Example 6 The conditions are the same as in Example 2, except that the reaction pressure is set to 6 MPa.

[0030] Specific experimental parameters and reaction yields are shown in Table 2.

[0031] Table 2. Effect of different reaction pressures on the catalytic activity of anthracene partial hydrogenation.

[0032] Reaction pressure has a significant impact on product selectivity. Lower reaction pressures result in lower anthracene conversion rates, lower hydrogen concentrations, and weaker hydrogenation activity. Higher reaction pressures lead to increased selectivity for the over-hydrogenated product, perhydroanthracene.

[0033] Example 7 The conditions are the same as in Example 2, except that the reaction space velocity is changed to 0.5 h⁻¹. -1 .

[0034] Example 8 The conditions are the same as in Example 2, except that the reaction space velocity is changed to 2.0 h⁻¹. -1 .

[0035] Table 3. Effect of different reaction space velocities on the catalytic activity of anthracene partial hydrogenation.

[0036] Examples 9-10 The conditions were the same as in Example 2, except that the mass fractions of anthracene reactants were 3 wt.% and 8 wt.%, respectively. Specific experimental parameters and reaction yields are shown in Table 4.

[0037] Table 4. Effect of different anthracene mass fractions on the catalytic activity of anthracene partial hydrogenation.

[0038] Anthracene preferentially undergoes hydrogenation at the 9,10 positions via parallel adsorption on 20% Ni / Nb₂O₅-SiO₂ to form 9,10-dihydroanthracene, followed by stepwise hydrogenation rearrangement to generate symmetrical octahydroanthracene. Next, the symmetrical octahydroanthracene is subjected to selective oxidation of the side chain and ring hydrogens under the action of a complex metal oxide, aromatization to form a tetracarboxylic acid structure, and dehydration to cyclization and pyromellitic dianhydride.

[0039] Example 11 The catalyst was prepared using the sol-gel method. A mixture of metal salt (Me) and sucrose (Su) was added, with a molar ratio of 1:1. In a 100 mL beaker, 2.3769 g NiCl₂·6H₂O, 2.3793 g CoCl₂·6H₂O, 3.7258 g CeCl₃·7H₂O, and 1.1698 g NH₄VO₃ were added, followed by 13.68 g sucrose and water. The mixture was stirred thoroughly to dissolve the precipitate. The resulting sample was dried overnight at room temperature, then dried in a 100 °C oven for 12 h. After drying, the sample was calcined in a muffle furnace at 550 °C for 2 h in an air atmosphere. The prepared sample was designated Mn-Co-Ce-V (Me:Su = 1:1).

[0040] Using air as the oxidant and acetonitrile as the reaction solvent, liquid-phase selective oxidation was carried out in a high-pressure reactor: reaction temperature: 200℃, air pressure: 2.0 MPa, reaction time: 5 h, mass fraction of symmetrical octahydroanthracene: 5 wt.%. After the reaction, the reaction products were collected, and the conversion rate and product selectivity of symmetrical octahydroanthracene were tested. The conversion rate of symmetrical octahydroanthracene was 99.9%, the oxidation product was mainly pyromellitic dianhydride, and the selectivity of pyromellitic dianhydride was 87.1%.

[0041] Example 12 The conditions were the same as in Example 10, except that the composition of sucrose (Su) was adjusted to obtain a Mn-Co-Ce-V (Me:Su=1:0.5) catalyst.

[0042] Example 13 The conditions were the same as in Example 10, except that the composition of sucrose (Su) was adjusted to obtain a Mn-Co-Ce-V (Me:Su=1:1.5) catalyst.

[0043] Table 5. Effect of different catalyst compositions on the catalytic activity of symmetric octahydroanthracene oxidation to prepare pyromellitic dianhydride.

[0044] Using readily available and inexpensive sucrose as a catalyst, experimental results showed that sucrose-based catalysts promoted the reaction. As the amount of sucrose added gradually increased, the selectivity of pyromellitic dianhydride first increased and then decreased. The oxidation effect was optimal when the molar ratio of metal salt to sucrose was 1:1. When the molar ratio of metal salt to sucrose increased to 1:1.5, the thickness of the carbon layer after calcination increased, making it difficult to remove effectively, thus reducing the catalyst activity and resulting in poorer oxidation.

[0045] Example 14 The conditions were the same as in Example 11, except that the reaction temperature was investigated and set to 180°C. Example 15 The conditions were the same as in Example 11, except that the reaction temperature was investigated and set to 220°C. After the reaction was completed, the reaction products were collected and analyzed; the yield and composition of the products were calculated. Specific experimental parameters and reaction yields are shown in Table 6.

[0046] Table 6. Effect of different reaction temperatures on the catalytic activity of symmetric octahydroanthracene oxidation.

[0047] Experimental results show that increasing the reaction temperature promotes catalytic oxidation, but excessively high temperatures can also lead to over-oxidation, converting pyromellitic dianhydride into pyromellitic acid.

[0048] Example 16 The conditions are the same as in Example 11, except that the reaction pressure is set to 1.5 MPa. Example 17 The conditions were the same as in Example 11, except that the reaction pressure was set to 3 MPa. Specific experimental parameters and reaction yields are shown in Table 7.

[0049] Table 7. Effect of different reaction pressures on the catalytic activity of symmetric octahydroanthracene oxidation.

[0050] Example 18 The conditions are the same as in Example 11, except that the reaction time is changed to 3 hours.

[0051] Example 19 The conditions are the same as in Example 11, except that the reaction time is changed to 8 hours.

[0052] Specific experimental parameters and reaction yields are shown in Table 8.

[0053] Table 8. Effect of different reaction times on the catalytic activity of symmetric octahydroanthracene oxidation.

[0054] Extending the reaction time allows the reaction to proceed fully. Increasing the reaction time from 3 hours to 5 hours significantly improves the catalytic activity. However, extending the reaction time to 8 hours does not significantly change the conversion rate of symmetrical octahydroanthracene, and the selectivity of pyromellitic dianhydride decreases. It is speculated that with further reaction time, pyromellitic dianhydride reacts further with the catalyst to form pyromellitic acid. Therefore, we selected 5 hours as the optimal reaction time.

[0055] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride, characterized in that, The steps are as follows: Step 1: Using anthracene, a byproduct of coal tar, as raw material and decahydronaphthalene as solvent, a catalyst is loaded into a fixed-bed reactor for selective hydrogenation. The reaction conditions are controlled to selectively hydrogenate symmetrical octahydroanthracene and the byproduct. The solvent is recovered and reused after concentration, and the product is obtained by distillation. Step 2: Selective oxidation of the symmetrical octahydroanthracene obtained in Step 1 to prepare pyromellitic dianhydride; using the Mn-Co-Ce-V composite oxide synthesized with sucrose as a chelating agent as a catalyst, air as an oxidant, and acetonitrile as a reaction solvent, liquid-phase selective oxidation was carried out in a high-pressure reactor, the reaction conditions were adjusted, and the product was collected to obtain pyromellitic dianhydride.

2. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step one, the catalyst is 25 wt.% Ni / Nb2O5-SiO2.

3. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step one, the reaction temperature in the reaction conditions is 230-270℃.

4. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step one, the reaction pressure in the reaction conditions is 2-6 MPaH2.

5. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step one, the reaction space velocity in the reaction conditions is 0.5-2 h⁻¹. -1 .

6. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step one, the mass fraction of anthracene, a coal tar byproduct, in the reaction system is 3-8 wt.%.

7. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step two, the preparation method of the Mn-Co-Ce-V composite oxide is as follows: using the sol-gel method, sucrose is used as a chelating agent. Metal salt, sucrose and deionized water are mixed, with a metal salt:sucrose molar ratio of 1:(0.5~1.5). The mixture is stirred thoroughly and dried continuously in an oven at 100℃ for 12 hours. The dried sample is then calcined in air at 550℃ for 2 hours to obtain the Mn-Co-Ce-V composite oxide.

8. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step two, the reaction temperature in the reaction conditions is 180-220℃.

9. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step two, the reaction pressure in the reaction conditions is 1.5-3.0 MPa.

10. The continuous catalytic method for the directional conversion of anthracene to prepare pyromellitic dianhydride according to claim 1, characterized in that, In step two, the reaction time in the reaction conditions is 3-8 hours.

Images