Method for preparing diphenyl tetracarboxylic acid based on palladium-carbon catalyst and activation method of palladium-carbon catalyst

Abstract

This invention provides a method for preparing biphenyl tetracarboxylic acid based on a palladium-on-carbon catalyst and an activation method for the palladium-on-carbon catalyst, belonging to the field of catalyst regeneration technology. This invention selects inexpensive mixed sodium chlorophthalic acid as raw material and water as solvent. An activator is added to the system before the palladium-on-carbon catalyst is added, which helps to avoid poisoning and deactivation of the palladium-on-carbon catalyst. Then, a coupling reaction occurs under the action of a reducing agent, followed by acidification and purification to obtain 3,3',4,4'-biphenyl tetracarboxylic acid. Simultaneously, this invention activates the used palladium-on-carbon catalyst in the presence of an activator. The operation is simple, eliminates the need for palladium leaching, reduces palladium loss during recovery, and realizes the resource utilization of the palladium-on-carbon catalyst, resulting in high economic and environmental benefits. Moreover, the method provided by this invention has good activation effect; the activated palladium-on-carbon catalyst can be reused at least 15 times, greatly reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of catalyst regeneration technology, specifically to a method for preparing biphenyl tetracarboxylic acid based on a palladium-on-carbon catalyst and a method for activating the palladium-on-carbon catalyst. Background Technology

[0002] 3,3',4,4'-Biphenyltetracarboxylic dianhydride is an important monomer for the preparation of polyimides, and it can polymerize with various amines to form polyimides. Polyimides, as a special engineering material, possess numerous advantages such as a wide operating temperature range, chemical resistance, high strength, and excellent flexibility and adaptability. In recent years, with the rapid development of flexible displays, the market for high-end electronic-grade polyimide films is poised for rapid expansion. Therefore, various key intermediates for polyimide preparation will also face significant market demand.

[0003] In existing technologies, 3,3',4,4'-biphenyltetracarboxylic acid is typically obtained by catalytic coupling, acidification, and purification of 4-chlorophthalic acid. This 3,3',4,4'-biphenyltetracarboxylic acid is then dehydrogenated to prepare 3,3',4,4'-biphenyltetracarboxylic dianhydride. In the production of 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4-chlorophthalic acid, sodium hydroxide, water, and a catalyst are usually mixed, and a reducing agent is added dropwise to the resulting reaction system for catalytic coupling. The catalyst used in this step is usually a palladium-on-carbon catalyst. This catalyst deactivates rapidly during use, and its activity decreases significantly after one use. Using a deactivated catalyst directly affects the product yield and quality; therefore, the catalyst must be discarded after one use, resulting in high costs.

[0004] There are many methods for treating deactivated palladium-on-carbon catalysts, and different methods can be used depending on the degree of deactivation. For example, Chinese patent CN89101887.5 discloses a method for reactivating palladium-on-carbon catalysts, specifically involving contacting the catalyst with hot water at 200–350°C for 0.5–10 hours, then with cool water below 100°C for 0.5–10 hours, and finally with a concentrated alkaline solution for 1–10 hours to complete the reactivation process. This type of treatment method is suitable for palladium-on-carbon catalysts with a relatively mild degree of deactivation, but the operation is complex. For palladium-on-carbon catalysts with a severe degree of deactivation or complete deactivation, the method of extracting palladium from the catalyst is generally used. For example, Chinese patent CN95104435.4 discloses a method for recovering palladium from a heavily deactivated palladium-on-carbon catalyst. Specifically, the palladium-on-carbon catalyst is placed in a roasting furnace for oxidative roasting. The resulting roasting ash is then acid-boiled with sulfuric acid solution to remove impurities. The purified ash is then leached with palladium using a chlorination method. The leachate is further purified by cation exchange resin exchange, and the exchange solution is purified by ammonia complexation. Finally, it is reduced to obtain sponge palladium. This method has the disadvantages of being complex to operate and polluting the environment. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing biphenyl tetracarboxylic acid based on a palladium-on-carbon catalyst and an activation method for the palladium-on-carbon catalyst. The method provided by this invention is simple to operate, environmentally friendly, and the treated palladium-on-carbon catalyst can be reused at least 15 times.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing 3,3',4,4'-biphenyltetracarboxylic acid based on a palladium-on-carbon catalyst, comprising the following steps:

[0008] A first mixture of mixed sodium chlorophthalate, sodium hydroxide and water is obtained; the mixed sodium chlorophthalate includes sodium 4-chlorophthalate and sodium 4,5-chlorophthalate.

[0009] The activator is mixed with the first mixture to obtain a second mixture; the activator is hydroxylamine hydrochloride or an aqueous solution of hydrazine hydrate with a concentration of 10-80 wt%.

[0010] The palladium-on-carbon catalyst is mixed with the second mixture to obtain a third mixture.

[0011] The third mixture is mixed with a reducing agent in a fourth process, followed by coupling reaction, acidification and purification, to obtain 3,3',4,4'-biphenyltetracarboxylic acid.

[0012] Preferably, the mass ratio of the mixed sodium chlorophthalate, activator and palladium on carbon catalyst is 100:(0.2-0.3):(0.2-0.3).

[0013] Preferably, the mass ratio of the mixed sodium chlorophthalate, sodium hydroxide and water is 100:(80-90):(400-500).

[0014] Preferably, the reducing agent is a water-glycerol-hydroxylamine mixture, wherein the mass ratio of water, glycerol and hydroxylamine in the reducing agent is (6-7.5):1:(1.5-2); and the mass ratio of the mixed sodium chlorophthalate salt to the reducing agent is 100:(110-130).

[0015] Preferably, when the second mixing is performed, the temperature of the first mixture is 90-95°C;

[0016] During the third mixing, the temperature of the second mixture is 90–95°C;

[0017] The fourth mixing involves adding a reducing agent dropwise to the third mixture; the dropping rate of the reducing agent is 12-16 g / h; during the addition of the reducing agent, the temperature of the third mixture is 95-105°C.

[0018] Preferably, the temperature of the coupling reaction is 95–105°C, the time of the coupling reaction is 0.5–1.5 h, and the time of the coupling reaction begins from the time the reducing agent is completely added.

[0019] This invention provides a method for activating a palladium-on-carbon catalyst, comprising the following steps:

[0020] The palladium catalyst to be activated is mixed with an activator and activated; the palladium catalyst to be activated is a solid material obtained by solid-liquid separation of the product system obtained after the coupling reaction in the above technical solution; the activator is a mixture of methanol aqueous solution, hydrazine hydrate aqueous solution and formic acid.

[0021] Preferably, the concentration of the methanol aqueous solution is 45-55 wt%, and the concentration of the hydrazine hydrate aqueous solution is 20-80 wt%; the mass ratio of the methanol aqueous solution, hydrazine hydrate aqueous solution and formic acid in the activator is (40-50):1:(8-10).

[0022] Preferably, the mass ratio of the palladium catalyst to be activated to the activator is 1:(5-15).

[0023] Preferably, the activation treatment is performed at a temperature of 60–70°C for 1–2 hours.

[0024] This invention provides a method for preparing biphenyl tetracarboxylic acid based on a palladium-on-carbon catalyst, comprising the following steps: firstly mixing a mixed sodium chlorophthalate, sodium hydroxide, and water to obtain a first mixture; the mixed sodium chlorophthalate includes sodium 4-chlorophthalate and sodium 4,5-chlorophthalate; secondly mixing an activator with the first mixture to obtain a second mixture; the activator is hydroxylamine hydrochloride or an aqueous solution of hydrazine hydrate with a concentration of 10-80 wt%; thirdly mixing the palladium-on-carbon catalyst with the second mixture to obtain a third mixture; and fourthly mixing the third mixture with a reducing agent, followed by coupling reaction, acidification, and purification to obtain 3,3',4,4'-biphenyl tetracarboxylic acid. This invention selects inexpensive mixed sodium chlorophthalic acid as raw material, uses water as solvent, and adds an activator to the system before adding the palladium on carbon catalyst to avoid poisoning and deactivation of the palladium on carbon catalyst. Then, a coupling reaction is carried out under the action of a reducing agent, and 3,3',4,4'-biphenyltetracarboxylic acid can be obtained after acidification and purification.

[0025] This invention provides a method for activating a palladium-on-carbon catalyst, comprising the following steps: mixing the palladium-on-carbon catalyst to be activated with an activating agent and performing activation treatment; the palladium-on-carbon catalyst to be activated is a solid material obtained by solid-liquid separation of the product system obtained after the coupling reaction in the method described above; the activating agent is a mixture of methanol aqueous solution, hydrazine hydrate aqueous solution, and formic acid. This invention activates the used palladium-on-carbon catalyst in the presence of an activating agent, which is simple to operate, eliminates the need for palladium leaching, reduces palladium loss during recovery, and realizes the resource utilization of the palladium-on-carbon catalyst, resulting in high economic and environmental benefits; moreover, the method provided by this invention has good activation effect, and the activated palladium-on-carbon catalyst can be reused at least 15 times, greatly reducing production costs. Detailed Implementation

[0026] This invention provides a method for preparing 3,3',4,4'-biphenyltetracarboxylic acid based on a palladium-on-carbon catalyst, comprising the following steps:

[0027] A first mixture of mixed sodium chlorophthalate, sodium hydroxide and water is obtained; the mixed sodium chlorophthalate includes sodium 4-chlorophthalate and sodium 4,5-chlorophthalate.

[0028] The activator is mixed with the first mixture to obtain a second mixture; the activator is hydroxylamine hydrochloride or an aqueous solution of hydrazine hydrate with a concentration of 10-80 wt%.

[0029] The palladium-on-carbon catalyst is mixed with the second mixture to obtain a third mixture.

[0030] The third mixture is mixed with a reducing agent in a fourth process, followed by coupling reaction, acidification and purification, to obtain 3,3',4,4'-biphenyltetracarboxylic acid.

[0031] Unless otherwise specified, all raw materials used in this invention are commercially available products well known to those skilled in the art.

[0032] This invention involves mixing a mixed sodium chlorophthalate, sodium hydroxide, and water to obtain a first mixture. In this invention, the mixed sodium chlorophthalate (SCP) comprises sodium 4-chlorophthalate and sodium 4,5-chlorophthalate; preferably, it also comprises sodium 3-chlorophthalate, sodium 3,4-chlorophthalate, and sodium phthalate; more preferably, it also comprises other impurities. In this invention, the SCP preferably contains 80.5 wt% of 4-chlorophthalic acid monosodium salt, 11.6 wt% of 4,5-chlorophthalic acid monosodium salt, 0.1 wt% of 3-chlorophthalic acid monosodium salt, 0.26 wt% of 3,4-chlorophthalic acid monosodium salt, and 7.5 wt% of sodium phthalate monosodium salt, with other impurities comprising 0.04 wt%. The SCP used in this embodiment was purchased from Ningjin County Haitai Chemical Co., Ltd. In this invention, the sodium hydroxide is specifically caustic soda flakes; the water is preferably pure water. In this invention, the mass ratio of the mixed chlorophthalic acid monosodium salt, sodium hydroxide, and water is preferably 100:(80-90):(400-500), more preferably 100:(82-85):(420-450); the mass of the mixed chlorophthalic acid monosodium salt is based on dry weight. In this invention, the first mixing is preferably carried out under stirring and heating conditions. The specific stirring and heating conditions are not particularly limited, as long as the sodium chlorophthalate monosodium salt is fully dissolved and the components are fully and evenly mixed.

[0033] After obtaining the first mixture, the present invention further mixes the activator with the first mixture to obtain a second mixture. In the present invention, the activator is hydroxylamine hydrochloride or an aqueous solution of hydrazine hydrate with a concentration of 10-80 wt%, preferably 20-70 wt%, more preferably 30-60 wt%, and even more preferably 40-50 wt%. In the present invention, the activator can prevent chloride ion poisoning (from SCP) in the palladium on carbon catalyst. In the present invention, the mass ratio of the mixed sodium chlorophthalate to the activator is preferably 100:(0.2-0.3), more preferably 100:(0.25-0.3). In the present invention, the second mixing is preferably carried out under stirring conditions to ensure that all components are fully and uniformly mixed. In this invention, when the second mixing is carried out, the temperature of the first mixture is preferably 90-95°C, more preferably 93-95°C. In this invention, the activator is preferably added to the first mixture at 90-95°C. When the activator is added, the temperature of the first mixture is controlled at 90-95°C, and then mixed with the palladium-on-carbon catalyst. This helps to ensure that the activator has a good activation effect on the palladium-on-carbon catalyst and prevents the palladium-on-carbon catalyst from being poisoned instantly upon addition.

[0034] After obtaining the second mixture, the present invention further mixes the palladium catalyst on carbon with the second mixture to obtain the third mixture. In the present invention, the palladium content in the palladium catalyst on carbon is preferably 5-10 wt%, more preferably 5-7 wt%. In the present invention, the mass ratio of the mixed sodium chlorophthalate to the palladium catalyst on carbon is preferably 100:(0.2-0.3), more preferably 100:(0.25-0.3); the mass of the palladium catalyst on carbon is on a dry basis. In the present invention, during the third mixing, the temperature of the second mixture is preferably 90-95°C, more preferably 93-95°C; the present invention preferably adds the palladium catalyst on carbon to the second mixture at 90-95°C. Controlling the temperature of the second mixture at 90-95°C when adding the palladium catalyst on carbon helps ensure that the activator fully activates the palladium catalyst on carbon.

[0035] After obtaining the third mixture, the present invention further mixes the third mixture with a reducing agent in a fourth mixture, and then sequentially performs coupling reaction, acidification, and purification to obtain 3,3',4,4'-biphenyltetracarboxylic acid. In the present invention, the reducing agent is preferably a water-glycerol-hydroxylamine mixture, and the mass ratio of water, glycerol, and hydroxylamine in the reducing agent is preferably (6-7.5):1:(1.5-2), more preferably (6.5-7):1:(1.5-2), specifically 6.5:1:1.5 or 7:1:2. In the present invention, the mass ratio of the mixed sodium chlorophthalate salt to the reducing agent is preferably 100:(110-130), more preferably 100:(120-125). In this invention, the fourth mixing involves adding a reducing agent dropwise to the third mixture. The dropping rate of the reducing agent is preferably 12–16 g / h, more preferably 12.5–15.7 g / h, and even more preferably 13–15.6 g / h. During the addition of the reducing agent, the temperature of the third mixture is preferably 95–105°C, more preferably 95–100°C. This invention preferably adds the reducing agent at a temperature of 95–105°C and a rate of 12–16 g / h to ensure a suitable reaction rate.

[0036] In this invention, the temperature of the coupling reaction is preferably 95-105°C, more preferably 95-100°C; the time of the coupling reaction is preferably 0.5-1.5 h, more preferably 1 h; the time of the coupling reaction begins from the time the reducing agent is completely added.

[0037] Following the coupling reaction, the present invention preferably performs solid-liquid separation on the product system obtained after the coupling reaction, and then acidifies the resulting liquid material. The solid material obtained from the solid-liquid separation is the used palladium-on-carbon catalyst, which can be reused after activation treatment. The activation treatment method will be described in detail later. The present invention does not have a particular limitation on the solid-liquid separation method; any method well known to those skilled in the art can be used, such as filtration. In the present invention, the acid reagent used for acidification is preferably hydrochloric acid, and the concentration of the hydrochloric acid is preferably 20-30 wt%. The acidification preferably involves adjusting the pH value of the liquid material to 0.5-1, more preferably 0.5-0.8.

[0038] After acidification, the present invention purifies the resulting acidified system. The purification method preferably includes: solid-liquid separation of the acidified system, followed by washing and drying of the resulting solid material to obtain 3,3',4,4'-biphenyltetracarboxylic acid. The present invention does not specifically limit the solid-liquid separation method; any method well-known to those skilled in the art, such as filtration, can be used. In the present invention, the solid-liquid separation is preferably carried out at 80–90°C, more preferably at 85–90°C. In the present invention, the washing reagent is preferably hot water, and the temperature of the hot water is preferably 60–80°C, more preferably 70–80°C; the washing is preferably performed to wash the solid material until the pH value is 5.5–6.5. The present invention does not specifically limit the drying process; any method that ensures the material is sufficiently dried is acceptable.

[0039] This invention provides a method for activating a palladium-on-carbon catalyst, comprising the following steps:

[0040] The palladium catalyst to be activated is mixed with an activator and activated; the palladium catalyst to be activated is a solid material obtained by solid-liquid separation of the product system obtained after the coupling reaction in the above technical solution; the activator is a mixture of methanol aqueous solution, hydrazine hydrate aqueous solution and formic acid.

[0041] In this invention, the palladium-on-carbon catalyst to be activated is the solid material obtained by solid-liquid separation of the product system after the coupling reaction in the above-described technical solution. That is, it is based on the catalytic preparation of 3,3',4,4'-biphenyltetracarboxylic acid using palladium-on-carbon catalyst. The used palladium-on-carbon catalyst (referred to as the recycled catalyst) can be regenerated by activation treatment, and then it can be used to catalyze the preparation of 3,3',4,4'-biphenyltetracarboxylic acid.

[0042] In this invention, the activator is a mixture of methanol aqueous solution, hydrazine hydrate aqueous solution, and formic acid; the concentration of the methanol aqueous solution is preferably 45-55 wt%, more preferably 50 wt%; the concentration of the hydrazine hydrate aqueous solution is preferably 20-80 wt%, more preferably 30-70 wt%, further preferably 35-60 wt%, and even more preferably 40-50 wt%; the mass ratio of methanol aqueous solution, hydrazine hydrate aqueous solution, and formic acid in the activator is preferably (40-50):1:(8-10), more preferably 50:1:8 or 40:1:8. In this invention, the activator can alleviate the chloride ion poisoning symptoms of the palladium-on-carbon catalyst to be activated.

[0043] In this invention, the mass ratio of the palladium catalyst to be activated to the activator is preferably 1:(5-15), more preferably 1:(8-11), and even more preferably 1:(9-10); the palladium catalyst to be activated is on a dry basis.

[0044] In this invention, the activation temperature is preferably 60–70°C, more preferably 65–67°C; the activation treatment is specifically carried out under reflux conditions; and the activation time is preferably 1–2 hours, more preferably 1.5–2 hours. The preferred activation conditions under these conditions allow for the full release of the catalyst's activity, thus completing catalyst regeneration.

[0045] After the activation treatment, the present invention preferably performs solid-liquid separation on the obtained activation system, and the resulting solid material is the activated palladium-on-carbon catalyst, denoted as the activated catalyst. The present invention does not specifically limit the method of solid-liquid separation; any method well known to those skilled in the art can be used, such as filtration. In the present invention, the solid-liquid separation is preferably carried out at 60–80°C, more preferably at 70–75°C.

[0046] The recovered catalyst is activated using the method described above in this invention. The resulting activated catalyst can be reused in the coupling reaction for the catalytic preparation of 3,3',4,4'-biphenyltetracarboxylic acid. When using the activated catalyst, it is preferable to add a new palladium-on-carbon catalyst. The amount of the new palladium-on-carbon catalyst added is preferably 10-20% of the initial catalyst mass, more preferably 12-15%. In this invention, the activated catalyst can be reused at least 15 times in the coupling reaction for the catalytic preparation of 3,3',4,4'-biphenyltetracarboxylic acid, and the palladium-on-carbon catalyst recovery rate reaches 95%.

[0047] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0048] The mixed sodium chlorophthalate (SCP) used in the following examples and comparative examples was purchased from Ningjin County Haitai Chemical Co., Ltd., wherein the content of sodium 4-chlorophthalate was 80.5 wt%, the content of sodium 4,5-chlorophthalate was 11.6 wt%, the content of sodium 3-chlorophthalate was 0.1 wt%, the content of sodium 3,4-chlorophthalate was 0.26 wt%, the content of sodium phthalate was 7.5 wt%, and the content of other impurities was 0.04 wt%.

[0049] Example 1

[0050] Add 80g of caustic soda flakes to 400g of pure water, then add 100g of SCP dry product. Heat to 95℃ under stirring. After complete dissolution, add 0.3g of activator (30wt% hydrazine hydrate aqueous solution), stir well, and then add 0.3g of catalyst dry base (palladium on carbon catalyst with 5wt% palladium content). After the catalyst addition is complete, begin dropwise addition of 125g of reducing agent (obtained by mixing water, glycerol, and hydroxylamine in a mass ratio of 6.5:1:1.5). Maintain the system temperature at 103℃ during the dropwise addition process. The addition is completed in 8 hours. The reaction was then carried out at 103℃ for 1 hour. After the reaction, the resulting product system was filtered at 90℃ to obtain 0.67g of filter cake (the catalyst used in the reaction, which was recovered and reused, denoted as the recovered catalyst). The filtrate was adjusted to pH 0.7 with 30wt% hydrochloric acid, and then filtered at 85℃. The filter cake was washed with 80℃ hot water to pH 5.5, and then dried to obtain 62.5g of product. The content of 3,3',4,4'-biphenyltetracarboxylic acid in the product was found to be 99.53wt%.

[0051] A 50wt% methanol aqueous solution, a 40wt% hydrazine hydrate aqueous solution, and formic acid were mixed in a mass ratio of 50:1:8 to obtain an activator. 0.67g of the recovered catalyst was mixed with 6g of the activator, and the mixture was heated to 67°C and refluxed for 2 hours. After activation, the mixture was filtered at 60°C to obtain 0.65g of filter cake, which is the activated catalyst.

[0052] The activated catalyst was reused for further reactions, with 20% new catalyst added for each reaction, while other conditions remained unchanged. The specific reuse results are shown in Table 1, where the yield deviation from the new catalyst is calculated as (weight of biphenyltetracarboxylic acid - 62.5) / 62.5 × 100%. Table 1 shows that the catalyst activated using the method provided by this invention can be reused.

[0053] Table 1. Catalyst Application Results

[0054]

[0055]

[0056] Example 2

[0057] Add 80g of caustic soda flakes to 450g of pure water, then add 100g of SCP dry product. Heat to 95℃ under stirring. After complete dissolution, add 0.3g of activator (hydroxylamine hydrochloride), stir well, and then add 0.25g of catalyst dry base (palladium on carbon catalyst with a palladium content of 5wt%). After the catalyst addition is complete, begin dropwise addition of 130g of reducing agent (obtained by mixing water, glycerol, and hydroxylamine in a mass ratio of 7:1:2). Maintain the system temperature at 100℃ during the dropwise addition process. Complete the dropwise addition in 10 hours, then maintain the temperature at 100℃. The reaction was carried out at a constant temperature for 1 hour. After the reaction, the resulting product system was filtered at 90°C to obtain 0.68 g of filter cake (the catalyst used in the reaction, which was recovered and reused, denoted as the recovered catalyst). The filtrate was adjusted to pH 0.5 with 25 wt% hydrochloric acid, and then filtered at 80°C. The filter cake was washed with hot water at 60°C to pH 5.7, and then dried to obtain 62.2 g of product. The content of 3,3',4,4'-biphenyltetracarboxylic acid in the product was detected to be 99.51 wt%.

[0058] A 50wt% methanol aqueous solution, a 40wt% hydrazine hydrate aqueous solution, and formic acid were mixed in a mass ratio of 40:1:8 to obtain an activator. 0.68g of the recovered catalyst was mixed with 7g of the activator, and the mixture was heated to 67°C and refluxed for 2 hours. After activation, the mixture was filtered at 65°C to obtain 0.66g of filter cake, which is the activated catalyst.

[0059] The activated catalyst was reused for further reactions, with 15% new catalyst added for each reaction, while other conditions remained unchanged. The specific reuse results are shown in Table 2, where the yield deviation from the new catalyst is calculated as (weight of biphenyltetracarboxylic acid - 62.5) / 62.5 × 100%. Table 2 shows that the catalyst activated using the method provided by this invention can be reused.

[0060] Table 2 Catalyst Application Results

[0061]

[0062] Comparative Example 1

[0063] The procedure is the same as in Example 1, except that the activator is omitted, as detailed below:

[0064] Take 80g of caustic soda flakes and put them into 400g of pure water. Then add 100g of SCP dry product and heat to 95℃ under stirring. After it is completely dissolved, add 0.3g of catalyst dry base (palladium on carbon catalyst with a palladium content of 5wt%). After the catalyst is added, start to add 125g of reducing agent (prepared by mixing water, glycerol and hydroxylamine in a mass ratio of 6.5:1:1.5). Keep the temperature of the system at 100℃ during the drop addition process. The drop addition is completed in 8 hours. Then keep the reaction at 100℃ for 1 hour. After the reaction was completed, the resulting product system was filtered at 90°C to obtain 0.65 g of filter cake (which was the catalyst used in the reaction process, recovered and reused, and denoted as the recovered catalyst). The filtrate was adjusted to pH 0.9 with 25 wt% hydrochloric acid, and then filtered at 90°C. The filter cake was washed with hot water at 650°C to pH 5.8, and then dried to obtain 62.6 g of product. The content of 3,3',4,4'-biphenyltetracarboxylic acid in the product was detected to be 99.51 wt%.

[0065] A 50wt% methanol aqueous solution, a 40wt% hydrazine hydrate aqueous solution, and formic acid were mixed in a mass ratio of 50:1:8 to obtain an activator. 0.65g of the recovered catalyst was mixed with 6g of the activator, and the mixture was heated to 67°C and refluxed for 2 hours. After activation, the mixture was filtered at 60°C to obtain 0.65g of filter cake, which is the activated catalyst.

[0066] The activated catalyst was reused to continue the reaction, with 20% new catalyst added for each reaction, while other conditions remained unchanged. The specific reuse results are shown in Table 3, where the yield deviation from the new catalyst is calculated as (weight of biphenyltetracarboxylic acid - 62.5) / 62.5 × 100%. Table 3 shows that the catalyst provided in Comparative Example 1 cannot be reused.

[0067] Table 3 Catalyst Application Results

[0068]

[0069] Comparative Example 2

[0070] The procedure is the same as in Example 1, except that the step of activating the recovered catalyst is omitted; the recovered catalyst is used directly, as detailed below:

[0071] Add 80g of caustic soda flakes to 400g of pure water, then add 100g of SCP dry product. Heat to 95℃ under stirring. After complete dissolution, add 0.3g of activator (30wt% hydrazine hydrate aqueous solution), followed by 0.3g of catalyst dry base (palladium on carbon catalyst with 5wt% palladium content). After the catalyst addition is complete, begin dropwise addition of 125g of reducing agent (obtained by mixing water, glycerol, and hydroxylamine in a mass ratio of 6.5:1:1.5). Maintain the system temperature at 100℃ during the dropwise addition process. The addition is completed in 8 hours. Afterwards, [further details to be added]. The reaction was carried out at 00℃ for 1 hour. After the reaction, the resulting product system was filtered at 90℃ to obtain 0.66g of filter cake (the catalyst used in the reaction, which was recovered and reused, denoted as the recovered catalyst). The filtrate was adjusted to pH 0.85 with 25wt% hydrochloric acid, and then filtered at 80℃. The filter cake was washed with 60℃ hot water to pH 5.8, and then dried to obtain 62.4g of product. The content of 3,3',4,4'-biphenyltetracarboxylic acid in the product was found to be 99.50wt%.

[0072] The recovered catalyst was reused for further reactions, with 20% new catalyst added for each reaction, while other conditions remained unchanged. The specific reuse results are shown in Table 1, where the yield deviation from the new catalyst is calculated as (weight of biphenyltetracarboxylic acid - 62.5) / 62.5 × 100%. Table 4 shows that the catalyst provided in Comparative Example 2 cannot be reused.

[0073] Table 4. Catalyst Application Results

[0074]

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing 3,3',4,4'-biphenyltetracarboxylic acid based on palladium on carbon catalyst, comprising the following steps: A first mixture of mixed sodium chlorophthalate, sodium hydroxide and water is obtained; the mixed sodium chlorophthalate includes sodium 4-chlorophthalate and sodium 4,5-chlorophthalate. The activator is mixed with the first mixture to obtain a second mixture; the activator is hydroxylamine hydrochloride or an aqueous solution of hydrazine hydrate with a concentration of 10-80 wt%. The palladium-on-carbon catalyst is mixed with the second mixture to obtain a third mixture. The third mixture is mixed with a reducing agent in a fourth mixture, and then subjected to coupling reaction, acidification and purification in sequence to obtain 3,3',4,4'-biphenyltetracarboxylic acid; The mass ratio of the mixed sodium chlorophthalate, activator, and palladium on carbon catalyst is 100:(0.2~0.3):(0.2~0.3). The reducing agent is a water-glycerol-hydroxylamine mixture, wherein the mass ratio of water, glycerol and hydroxylamine in the reducing agent is (6~7.5):1:(1.5~2); and the mass ratio of the mixed sodium chlorophthalate salt to the reducing agent is 100:(110~130).

2. The method according to claim 1, characterized in that, The mass ratio of the mixed sodium chlorophthalate, sodium hydroxide and water is 100:(80~90):(400~500).

3. The method according to claim 1, characterized in that, During the second mixing, the temperature of the first mixture is 90~95℃; During the third mixing, the temperature of the second mixture is 90~95°C; The fourth mixing involves adding a reducing agent dropwise to the third mixture; the dropping rate of the reducing agent is 12~16 g / h; during the addition of the reducing agent, the temperature of the third mixture is 95~105℃.

4. The method according to claim 3, characterized in that, The coupling reaction is carried out at a temperature of 95~105℃ and for a time of 0.5~1.5h, starting from the time when the reducing agent is completely added.

5. An activation method for a palladium-on-carbon catalyst, comprising the following steps: The coupling reaction is carried out by any one of claims 1 to 4, and the solid material obtained by solid-liquid separation of the product system after the coupling reaction is the palladium-on-carbon catalyst to be activated. The palladium-on-carbon catalyst to be activated is mixed with an activator and activated. Then, solid-liquid separation is performed, and the resulting solid material is the activated palladium-on-carbon catalyst. The activator is a mixture of methanol aqueous solution, hydrazine hydrate aqueous solution and formic acid; the concentration of the methanol aqueous solution is 45~55wt%, and the concentration of the hydrazine hydrate aqueous solution is 20~80wt%; the mass ratio of methanol aqueous solution, hydrazine hydrate aqueous solution and formic acid in the activator is (40~50):1:(8~10).

6. The activation method according to claim 5, characterized in that, The mass ratio of the palladium catalyst to be activated to the activator is 1:(5~15).

7. The activation method according to claim 5 or 6, characterized in that, The activation treatment is performed at a temperature of 60-70°C for 1-2 hours.

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