A catalyst for the liquid-phase oxidation of terephthalic acid and its application

Abstract

This invention provides a catalyst for the liquid-phase oxidation of terephthalic acid and its application. The catalyst comprises a cobalt salt, a zirconium salt, a bromine-containing compound, and an auxiliary agent; the mass ratio of Co, Zr, Br, and the auxiliary agent in the catalyst is 500:(250–350):(500–1200):(30–80); the auxiliary agent is selected from compounds with the structure shown in formula (1), wherein R is selected from C1–C4 alkyl groups. The catalyst for the liquid-phase oxidation of terephthalic acid provided by this invention has a low Br content and good catalytic performance; its application in the liquid-phase oxidation of p-xylene to terephthalic acid can reduce the impurity content in the product and effectively improve the product yield.

Description

Technical Field

[0001] This invention belongs to the field of terephthalic acid preparation technology, specifically relating to a catalyst for the liquid-phase oxidation preparation of terephthalic acid and its application. Background Technology

[0002] Terephthalic acid (PTA) is an important organic chemical intermediate, mainly used in the synthesis of polyester PET, and can be used in industries such as chemical fibers, textiles, light industry, and construction. Currently, the mainstream PTA production process consists of two steps: p-xylene (PX) oxidation and crude terephthalic acid (CTA) hydrogenation purification. The main purpose of CTA hydrogenation purification is to hydrogenate p-carboxybenzaldehyde (4-CBA) to p-methylbenzoic acid (p-TA) in a hydrogen atmosphere under the action of a palladium-on-carbon catalyst. Subsequent multiple crystallization purifications yield polymer-grade terephthalic acid (PTA) product.

[0003] Industrially, PX oxidation typically uses a Co-Mn-Br ternary mixture as a catalyst (Co-Mn is the main catalyst, and bromine-containing compounds are auxiliary agents), acetic acid-water as a solvent, and air as the oxidant under specific temperature and pressure conditions. PX oxidation is a free radical reaction, and bromide ions are excellent promoters of free radical reactions; a certain amount of bromine is beneficial to the reaction and can increase the yield of terephthalic acid. However, high levels of bromide ions can cause corrosion to reactor equipment and pipelines, requiring the use of titanium alloys in the reactor vessel, thus increasing the construction cost of PTA plants. Furthermore, the emission of toxic bromide gases increases the difficulty of treating the oxidation tail gas system and causes environmental pollution. Therefore, developing a low-bromine, high-efficiency PX oxidation catalyst system is crucial.

[0004] US Patent US7985875B2 (Process for preparing aromatic polycarboxylicacid by liquid phase oxidation) discloses a catalyst comprising an ionic liquid containing bromine or iodine, which can be used for the liquid oxygen oxidation of aromatics (especially the liquid phase oxidation of p-xylene to terephthalic acid) to avoid the use of a special corrosion-resistant reactor; however, the terephthalic acid produced using this catalyst has a high content of impurities (e.g., 4-CBA). Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a catalyst for the liquid-phase oxidation preparation of terephthalic acid and its application, in order to solve the technical problem of high bromine content in the catalyst system for the liquid-phase oxidation preparation of terephthalic acid in the prior art.

[0006] The objective of this invention is mainly achieved through the following technical solutions.

[0007] In a first aspect, the present invention provides a catalyst for the liquid-phase oxidation preparation of terephthalic acid, comprising a cobalt salt, a zirconium salt, a bromine-containing compound, and an auxiliary agent; wherein the mass ratio of Co, Zr, Br, and the auxiliary agent in the catalyst is 500:(250-350):(500-1200):(30-80);

[0008] The adjuvant is selected from compounds with the structure shown in formula (1).

[0009]

[0010] R is selected from C1 to C4 alkyl groups.

[0011] The catalyst for the liquid-phase oxidation preparation of terephthalic acid provided by this invention can significantly reduce the Br content in the catalyst by adding an appropriate amount of auxiliary agent to the cobalt-zirconium system, and has good catalytic performance.

[0012] In this invention, the amount of additives added will significantly affect the catalytic performance of the catalyst and should be controlled within a suitable range.

[0013] According to some embodiments of the present invention, the adjuvant includes at least one of 1-butyl-3-methylimidazole chloride and 1-ethyl-3-methylimidazole chloride.

[0014] According to some embodiments of the present invention, the mass ratio of Co, Zr, Br and auxiliaries in the catalyst is 500:(250-350):(500-900):(30-80).

[0015] According to some embodiments of the present invention, the mass ratio of Co, Zr, Br and auxiliaries in the catalyst is 500:(250-350):(500-700):(30-80).

[0016] According to some embodiments of the present invention, the cobalt salt includes cobalt acetate.

[0017] According to some embodiments of the present invention, the zirconium salt includes zirconium acetate.

[0018] In this invention, there is no particular limitation on the type of bromine-containing compound, which can be any conventional bromine-containing compound in the art.

[0019] According to some embodiments of the present invention, the bromine-containing compound includes at least one of inorganic bromides and bromine hydrocarbons.

[0020] According to some embodiments of the present invention, the inorganic bromide includes at least one of hydrogen bromide and alkali metal bromide.

[0021] According to some embodiments of the present invention, the bromohydrocarbon includes at least one selected from naphthalene bromide, tetrabromoethane, tetrabromopropane, and tetrabromobutane.

[0022] According to some embodiments of the present invention, the bromine-containing compound includes naphthalene bromide.

[0023] In this invention, there are no particular limitations on the number and position of bromine substitutions in naphthalene bromide. For example, 1-naphthalene bromide or 1,4-dibromonaphthalene can be selected, but is not limited to.

[0024] In a second aspect, the present invention provides the application of the catalyst described in the first aspect in the liquid-phase oxidation of p-xylene to prepare terephthalic acid.

[0025] According to some embodiments of the present invention, the application includes: oxidizing p-xylene with an oxidant in a solvent in the presence of the catalyst to obtain terephthalic acid.

[0026] According to some embodiments of the present invention, the solvent includes acetic acid.

[0027] In this invention, the solvent may further include a small amount of water. Adding a small amount of water to acetic acid can inhibit its combustion. The appropriate amount of water in acetic acid is readily known to those skilled in the art; for example, the mass ratio of acetic acid to water in the solvent is 100:2.

[0028] According to some embodiments of the present invention, the oxidant is a gas containing elemental oxygen, such as oxygen, air, an oxygen-nitrogen mixture, an oxygen-air mixture, etc.

[0029] According to some embodiments of the present invention, the oxidant is air.

[0030] According to some embodiments of the present invention, the oxidant space velocity (the ratio of gas volume flow rate to reactant volume) is 2 to 4 h⁻¹. -1 .

[0031] In this invention, there are no particular limitations on the liquid-phase oxidation reaction conditions of p-xylene, which can be conventional oxidation conditions in the art.

[0032] According to some embodiments of the present invention, the conditions for the oxidation reaction include: a temperature of 150–220°C, preferably 170–200°C; a pressure of 0.5–2 MPa, preferably 0.9–1.5 MPa; and a time of 0.5–4 h, preferably 1–2 h.

[0033] Thirdly, the present invention provides a method for preparing terephthalic acid by liquid-phase oxidation of p-xylene, comprising: under the condition of the catalyst described in the first aspect, p-xylene and an oxidant undergo an oxidation reaction in a solvent to obtain terephthalic acid.

[0034] According to some embodiments of the present invention, the solvent includes acetic acid.

[0035] According to some embodiments of the present invention, the oxidant is a gas containing elemental oxygen, such as oxygen, air, an oxygen-nitrogen mixture, an oxygen-air mixture, etc.

[0036] According to some embodiments of the present invention, the oxidant is air.

[0037] According to some embodiments of the present invention, the oxidant space velocity (the ratio of gas volume flow rate to reactant volume) is 2 to 4 h⁻¹. -1 .

[0038] In this invention, there are no particular limitations on the liquid-phase oxidation reaction conditions of p-xylene, which can be conventional oxidation conditions in the art.

[0039] According to some embodiments of the present invention, the conditions for the oxidation reaction include: a temperature of 150–220°C, preferably 170–200°C; a pressure of 0.5–2 MPa, preferably 0.9–1.5 MPa; and a time of 0.5–4 h, preferably 1–2 h.

[0040] According to some embodiments of the present invention, the method may further include: hydrogenating the oxidation reaction product. Hydrogenation is generally carried out in a hydrogen atmosphere and under the action of a palladium-on-carbon catalyst, which can hydrogenate p-carboxybenzaldehyde (4-CBA) in the oxidation reaction product to p-methylbenzoic acid (p-TA), followed by multiple crystallization purifications to obtain polymer-grade terephthalic acid (PTA) product.

[0041] Compared with the prior art, the present invention can achieve at least the following beneficial effects:

[0042] The catalyst for the liquid-phase oxidation of terephthalic acid provided by this invention has a low Br content and good catalytic performance; when used in the liquid-phase oxidation of p-xylene to terephthalic acid, it can reduce the impurity content in the product and effectively improve the product yield. Detailed Implementation

[0043] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for illustrating this patent and do not limit the scope of protection of this invention in any way.

[0044] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.

[0045] In the following examples, the effect of the catalyst was evaluated by calculating the content of impurity 4-CBA in the crude terephthalic acid product and the yield of terephthalic acid. The higher the yield of terephthalic acid and the lower the content of 4-CBA, the better the catalytic performance of the catalyst.

[0046] Example 1

[0047] The oxidation reaction is carried out in a 1L titanium high-pressure stirred tank, equipped with a reflux condenser.

[0048] (1) First, add the following materials to the reactor: 20g PX, 100g acetic acid, 2g water, and catalyst (cobalt acetate, zirconium acetate, 1-naphthalene bromide, and 1-butyl-3-methylimidazole chloride). The materials contain 500ppmw cobalt, 250ppmw zirconium, 700ppmw (as Br) 1-naphthalene bromide, and 40ppmw 1-butyl-3-methylimidazole chloride. The catalyst formulation is shown in Table 1.

[0049] (2) Seal the container and purge it with nitrogen gas three times.

[0050] (3) Maintain a continuous nitrogen flow at a mass hourly space velocity (MHV) of 3 h⁻¹. -1 The pressure was 1.3 MPa, and the temperature was raised to 188°C.

[0051] (4) Switch to air, mass hourly space velocity is 3h -1 The pressure was 1.3 MPa, and the reaction was maintained for 1 hour.

[0052] (5) After the reaction is complete, switch to nitrogen gas, turn on the circulating cooling water, and cool to room temperature.

[0053] (6) The obtained solid product was washed multiple times with acetic acid and aqueous solution. A portion of the solid product was dissolved in dimethyl sulfoxide and analyzed by liquid chromatography. The analysis results are shown in Table 2. The tail gas was analyzed by infrared online analysis. The tail oxygen content was controlled between 3% and 6%, and the CO and CO2 contents were controlled between 1% and 1.5%.

[0054] Example 2

[0055] The material is essentially the same as in Example 1, except that it contains 500 ppmw of cobalt, 350 ppmw of zirconium, 600 ppmw (as Br) of 1-naphthalene bromide and 75 ppmw of 1-butyl-3-methylimidazole chloride.

[0056] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0057] Example 3

[0058] It is basically the same as Example 1, except that 700 ppmw (calculated as Br) of 1-bromonaphthalene in the material is replaced with 700 ppmw (calculated as Br) of 1,4-dibromonaphthalene.

[0059] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0060] Example 4

[0061] It is basically the same as Example 1, except that 700 ppmw (calculated as Br) of 1-bromonaphthalene in the material is replaced with 700 ppmw (calculated as Br) of hydrogen bromide.

[0062] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0063] Example 5

[0064] The process is essentially the same as in Example 1, except that 700 ppmw (calculated as Br) of 1-bromonaphthalene in the material is replaced with 700 ppmw (calculated as Br) of tetrabromoethane.

[0065] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0066] Example 6

[0067] It is basically the same as Example 1, except that the 40 ppmw of 1-butyl-3-methylimidazole chloride in the material is replaced with 40 ppmw of 1-ethyl-3-methylimidazole chloride.

[0068] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0069] Comparative Example 1

[0070] The process is essentially the same as in Example 1, except that the catalyst consists of cobalt acetate, manganese acetate and hydrogen bromide, and the material contains 500 ppmw of cobalt, 250 ppmw of manganese and 1000 ppmw (as Br) of hydrogen bromide.

[0071] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0072] Comparative Example 2

[0073] It is basically the same as Comparative Example 1, except that 1000 ppmw (calculated as Br) of hydrogen bromide in the material is replaced with 700 ppmw (calculated as Br) of 1-bromonaphthalene.

[0074] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0075] Comparative Example 3

[0076] The process is essentially the same as in Example 1, except that the catalyst consists of cobalt acetate, manganese acetate, 1-bromonaphthalene and 1-butyl-3-methylimidazole chloride, and the 250 ppmw zirconium in the material is replaced with 250 ppmw manganese.

[0077] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0078] Comparative Example 4

[0079] The process is essentially the same as in Example 1, except that the catalyst consists of cobalt acetate, zirconium acetate and 1-bromonaphthalene, and the material does not contain 40 ppmw of 1-butyl-3-methylimidazole chloride.

[0080] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0081] Comparative Example 5

[0082] It is basically the same as Example 1, except that the amount of 1-butyl-3-methylimidazole chloride in the material is changed from 40 ppmw to 100 ppmw.

[0083] The catalyst formulation is shown in Table 1, and the product analysis results are shown in Table 2.

[0084] Table 1 Catalyst Formulation

[0085]

[0086] Table 2 Product Analysis Results

[0087]

[0088]

[0089] As shown in Tables 1 and 2, in the catalyst system for the liquid-phase oxidation of terephthalic acid provided by this invention, cobalt acetate and zirconium acetate are used as the main catalysts, and appropriate amounts of auxiliary agents are introduced. When the amount of bromine source used in the catalyst is 600-700 ppmw, the content of the impurity 4-CBA in the product is lower than that in the traditional Co / Mn / Br system when the bromine content is 1000 ppmw, resulting in a higher product yield. Therefore, it can be seen that the catalyst for the liquid-phase oxidation of terephthalic acid provided by this invention has a lower Br content and better catalytic effect.

[0090] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A catalyst for the liquid-phase oxidation preparation of terephthalic acid, characterized in that, The catalyst comprises cobalt salt, zirconium salt, bromine-containing compound and promoter; the mass ratio of Co, Zr, Br and promoter in the catalyst is 500:(250-350):(500-1200):(30-80); The adjuvant is selected from compounds with the structure shown in formula (1). R is selected from C1 to C4 alkyl groups.

2. The catalyst according to claim 1, characterized in that, The adjuvant includes at least one of 1-butyl-3-methylimidazole chloride and 1-ethyl-3-methylimidazole chloride; And / or, the mass ratio of Co, Zr, Br and promoter in the catalyst is 500:(250-350):(500-900):(30-80), preferably 500:(250-350):(500-700):(30-80).

3. The catalyst according to claim 1 or 2, characterized in that, The cobalt salt includes cobalt acetate.

4. The catalyst according to any one of claims 1-3, characterized in that, The zirconium salt includes zirconium acetate.

5. The catalyst according to any one of claims 1-4, characterized in that, The bromine-containing compound includes at least one of inorganic bromides and bromohydrocarbons.

6. The catalyst according to claim 5, characterized in that, The inorganic bromide includes at least one of hydrogen bromide and alkali metal bromides; and / or, the bromohydrocarbon includes at least one of naphthalene bromide, tetrabromoethane, tetrabromopropane, and tetrabromobutane. Preferred, The bromine-containing compounds include naphthalene bromide.

7. The use of the catalyst according to any one of claims 1-6 in the liquid-phase oxidation of p-xylene to prepare terephthalic acid.

8. A method for preparing terephthalic acid by liquid-phase oxidation of p-xylene, characterized in that, The method comprises: in the presence of the catalyst described in any one of claims 1-6, reacting p-xylene with an oxidant in a solvent to produce terephthalic acid.

9. The method according to claim 8, characterized in that, The solvent includes acetic acid; And / or, the oxidant is a gas containing elemental oxygen.

10. The method according to claim 8 or 9, characterized in that, The conditions for the oxidation reaction include: a temperature of 150–220°C, preferably 170–200°C; and a pressure of 0.5–2 MPa, preferably 0.9–1.5 MPa.

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