A method for preparing a composite catalyst for liquid-phase air catalytic oxidation of trimethylol

Abstract

The invention discloses a preparation method of a composite catalyst for liquid-phase air catalytic oxidation of trimellitic acid. The composite catalyst uses liquid bromine, cobalt bromide, manganese bromide and other inorganic substances and biphenyl compounds as main raw materials, and uses acetic acid as both a reaction raw material and a solvent. A bromination reaction occurs at a certain temperature to generate a composite catalyst composed of cobalt acetate, manganese acetate, hydrogen bromide, bromobiphenyl and acetic acid, and the reaction system does not require post-processing such as separation and purification. Compared with traditional catalysts, the catalyst improves the activity of liquid-phase air oxidation reaction of trimellitic acid, reduces the occurrence of decarboxylation and disproportionation side reactions, and improves the yield of trimellitic acid.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to a method for preparing a composite catalyst for liquid-phase air catalytic oxidation of trimethylol. Background Art

[0002] The process of liquid-phase air oxidation of trimellitic acid with trimethylbenzene uses trimethylbenzene as raw material, acetic acid as solvent, cobalt acetate, manganese acetate and tetrabromoethane as catalysts, and introduces air or oxygen to react at about 200°C and 2.0MPa. The product trimellitic acid is dehydrated to obtain trimellitic anhydride (TMA). The tetrabromoethane catalyst in the existing process has poor thermal stability and is easily oxidized or decomposed at high temperatures, resulting in poor activity in the latter stage of the reaction, resulting in low TMA yield and many impurities.

[0003] In the process of oxidizing trimellitic acid to tolyltrimethylbenzene, the methyl groups on the aromatic ring all need to be oxidized to carboxyl groups, and the difficulty of oxidizing different methyl groups is different. When the catalyst is tetrabromoethane, after the two methyl groups on the trimellitic acid are oxidized to carboxyl groups, the third methyl group is difficult to be oxidized to carboxyl groups due to the electron-withdrawing effect of the already generated carboxyl groups. In order to solve the problem of difficult oxidation in the latter stage and low yield of trianhydride under the existing catalyst conditions, it is urgent to develop a new catalyst to improve the yield of trianhydride.

[0004] CN114289075A discloses a cobalt manganese bromine catalyst for oxidizing p-xylene and a preparation method thereof. The catalyst components include cobalt salt, manganese salt and bromine-containing compound, and also include potassium salt and palladium-containing compound. The synthesis method of the catalyst is to add cobalt salt, manganese salt, potassium salt, bromine-containing compound and palladium-containing compound into acetic acid solution and mix them to prepare the cobalt manganese bromine catalyst. This synthesis method is physical mixing and no chemical reaction occurs.

[0005] CN101402624A discloses a method for producing trimellitic anhydride by liquid-phase air staged oxidation of trimellitic anhydride, which uses cobalt acetate, manganese acetate and tetrabromoethane as catalysts and improves the reaction activity by adding the catalyst in batches.

[0006] CN110560110B discloses a catalyst for the oxidation of trimethylbenzene to synthesize trimethylbenzene anhydride. A supported catalyst with vanadium and titanium as the main catalytic elements, wherein the active components of the catalyst include at least one of vanadium, titanium, IIIA group elements, and IIB group elements and non-metallic elements. The catalyst is synthesized by dissolving the active components in oxalic acid to prepare a precursor, then applying it to a carrier, and calcining the carrier at a high temperature to obtain a supported catalyst. This synthesis method has relatively difficult production steps and is mainly used for the gas-phase air oxidation of trimethylbenzene. Summary of the invention

[0007] The invention discloses a composite catalyst and a preparation method thereof, which are used to solve the problem that the third methyl group of trimethylbenzene is difficult to oxidize.

[0008] One of the technical problems to be solved by the present invention is that the existing catalyst has difficulty in the rear-end oxidation of trimethylol, which causes the occurrence of decarboxylation reaction and disproportionation reaction, affecting the quality and purity of the product obtained by the oxidation of trimethylol. The composite catalyst provided by the present invention has the advantages of high rear-end oxidation activity, high trianhydride yield and low impurity content.

[0009] The second technical problem to be solved by the present invention is to provide a method for preparing a composite catalyst in view of the problem of back-end oxidation.

[0010] The invention discloses a method for preparing a composite catalyst for the liquid-phase air catalytic oxidation of trimellitic acid. Liquid bromine, cobalt bromide, manganese bromide and biphenyl compounds are used as main reaction raw materials, and acetic acid is used as a reaction raw material and a solvent. The composite catalyst containing cobalt acetate, manganese acetate, hydrogen bromide and brominated biphenyl is directly synthesized in a one-step method. The composite catalyst can be directly used for the liquid-phase air oxidation of trimellitic acid to form trimellitic acid.

[0011] When the bromine catalyst is brominated biphenyl, since biphenyl is a strong electron-donating group, it weakens the electron-withdrawing effect of the carboxyl group to a certain extent, thereby promoting the further oxidation of the third methyl group. Compared with traditional catalysts, the composite catalyst improves the activity of the liquid-phase air oxidation reaction of trimellitic acid, reduces the occurrence of decarboxylation and disproportionation side reactions, and improves the yield and purity of trimellitic acid.

[0012] Preferably, the biphenyl compound is composed of unit bodies of the following structure, and the number of unit bodies n≥2;

[0013]

[0014] Wherein R represents a substituent on the unit body, the types of which include but are not limited to alkyl, hydroxyl, and carboxyl, and the number of carbon atoms in the substituent is 0 to 4.

[0015] Preferably, the brominated biphenyl is composed of unit bodies of the following structure, and the number of unit bodies n is ≥ 2;

[0016]

[0017] Wherein m represents the number of Br atoms substituted, m = 1 to 5n.

[0018] The bromination reaction that occurs with different reactants is also different. The bromination reaction equations that occur with liquid bromine, cobalt bromide, and manganese bromide as raw materials are as follows:

[0019] (1) Using liquid bromine as raw material:

[0020]

[0021] The reaction temperature is 20-60°C, the reaction pressure is normal pressure, and the reaction time is 2-5h;

[0022] The main components of the composite catalyst are hydrogen bromide and brominated biphenyl.

[0023] The reaction catalyst is a metal bromide, including but not limited to iron tribromide, aluminum tribromide, and the like.

[0024] (2) Using cobalt bromide as raw material:

[0025]

[0026] The reaction temperature is 20-60°C, the reaction pressure is normal pressure, and the reaction time is 2-5h;

[0027] The main components of the composite catalyst are cobalt acetate, hydrogen bromide and brominated biphenyl.

[0028] The reaction catalyst is a metal bromide, including but not limited to iron tribromide, aluminum tribromide, and the like.

[0029] (3) Using manganese bromide as raw material:

[0030]

[0031] The reaction temperature is 20-60°C, the reaction pressure is normal pressure, and the reaction time is 2-5h;

[0032] The main components of the composite catalyst are manganese acetate, hydrogen bromide and brominated biphenyl.

[0033] The reaction catalyst is a metal bromide, including but not limited to iron tribromide, aluminum tribromide, and the like.

[0034] The reaction equation of trimethylol disproportionation:

[0035]

[0036] Trimellitic acid decarboxylation reaction equation:

[0037]

[0038] The composite catalyst disclosed by the invention comprises the following components by mass fraction: 50% to 90% of brominated biphenyl; 0% to 25% of cobalt acetate; 0% to 25% of manganese acetate; and 0% to 20% of hydrogen bromide.

[0039] With liquid bromine as raw material, acetic acid and ferric bromide catalyst were first added into a three-necked flask, biphenyl was added under stirring, and then the liquid bromine was dripped into the three-necked flask through a separatory funnel. During the dripping process, the stirring rate was controlled at 400 rpm to fully mix the reaction materials. After reacting for 4 to 6 hours, a composite catalyst for liquid-phase air oxidation of trimethylol was obtained.

[0040] With cobalt bromide as the raw material, acetic acid and ferric bromide catalyst were first added into a three-necked flask, and biphenyl and cobalt bromide were added under stirring to fully mix the reaction materials. After reacting for 4 to 6 hours, a composite catalyst for liquid-phase air oxidation of trimethylol was obtained.

[0041] With manganese bromide as the raw material, acetic acid and ferric bromide catalyst were first added into a three-necked flask, and biphenyl and manganese bromide were added under stirring to fully mix the reaction materials. After reacting for 4 to 6 hours, a composite catalyst for liquid-phase air oxidation of trimethylol was obtained.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. Compared with traditional catalysts, the composite catalyst prepared by the present invention has the advantage that the composite catalyst is a mixed solution and can be directly used as a composite catalyst for the liquid-phase air oxidation of trimethylolbenzene; the activity of the liquid-phase air oxidation reaction of trimethylolbenzene is improved, the occurrence of decarboxylation and disproportionation side reactions is reduced, and the yield of trimellitic acid is improved.

[0044] 2. Improved the stability of bromine initiator at high temperature. Tetrabromoethane is unstable at high temperature and is prone to oxidative decomposition to produce bromophosgene, resulting in tetrabromoethane loss, so less bromine free radicals are produced;

[0045]

[0046] Due to the stability of the benzene ring, brominated biphenyl can exist stably at high temperatures and can produce more bromine free radicals during the reaction;

[0047]

[0048] 3. During the oxidation of trimethylbenzene, when two methyl groups have been oxidized to carboxyl groups, the third methyl group is difficult to be oxidized due to the electron-withdrawing effect of the carboxyl group. Biphenyl is an electron-donating group, and the addition of bromobiphenyl is conducive to weakening the electron-withdrawing effect of the carboxyl group and promoting the oxidation of the third methyl group.

[0049]

[0050] The methyl group loses electrons due to oxidation. The electron cloud density of the substance is relatively large, the electron transition is easy, and the binding ability of the electron is relatively weak, so it is easy to be captured by the oxidant. The electron-withdrawing effect of the carboxyl group causes the electron cloud density of the methyl group to decrease, making oxidation more difficult. The electron-donating effect of the biphenyl group weakens the electron-withdrawing effect of the carboxyl group, making the methyl group remain easily oxidized. DETAILED DESCRIPTION

[0051] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0053] Example 1

[0054] Taking liquid bromine as raw material, first add 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst into a three-necked flask, add 9.56 g of biphenyl under stirring, and then add 10.24 mL of liquid bromine dropwise into the three-necked flask through a separatory funnel. During the dropping process, the stirring rate is controlled at 400 rpm to fully mix the reaction raw materials. After reacting for 4 hours, a composite catalyst for liquid-phase air oxidation of trimethylol is obtained.

[0055] Example 2

[0056] Using cobalt bromide as raw material, first add 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst into a three-necked flask, then add 9.56 g of biphenyl and 12.44 g of cobalt bromide under stirring, mix the reaction materials thoroughly, and react for 4 hours to obtain a composite catalyst for liquid-phase air oxidation of trimethylol.

[0057] Example 3

[0058] Taking manganese bromide as raw material, first add 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst into a three-necked flask, then add 9.56 g of biphenyl and 12.44 g of manganese bromide under stirring, mix the reaction materials thoroughly, and react for 4 hours to obtain a composite catalyst for liquid-phase air oxidation of trimethylol.

[0059] Example 4

[0060] With liquid bromine and cobalt bromide as raw materials, firstly, 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst were added into a three-necked flask, and then 9.56 g of biphenyl and 6.22 g of cobalt bromide were added under stirring. Then, 5.12 mL of liquid bromine was added dropwise into the three-necked flask through a separatory funnel. During the addition, the stirring rate was controlled at 400 rpm to fully mix the reaction materials. After reacting for 4 hours, a composite catalyst for liquid-phase air oxidation of trimethylol was obtained.

[0061] Example 5

[0062] With liquid bromine and manganese bromide as raw materials, first add 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst into a three-necked flask, then add 9.56 g of biphenyl and 6.22 g of manganese bromide under stirring, then add 5.12 mL of liquid bromine dropwise into the three-necked flask through a separatory funnel. During the dropping process, the stirring rate is controlled at 400 rpm to fully mix the reaction materials. After reacting for 4 hours, a composite catalyst for liquid-phase air oxidation of trimethylol is obtained.

[0063] Example 6

[0064] With liquid bromine, cobalt bromide and manganese bromide as raw materials, first add 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst into a three-necked flask, then add 9.56 g of biphenyl, 4.15 g of cobalt bromide and 4.15 g of manganese bromide under stirring, then add 3.14 mL of liquid bromine dropwise into the three-necked flask through a separatory funnel. During the dropping process, the stirring rate is controlled at 400 rpm to fully mix the reaction materials. After reacting for 4 hours, a composite catalyst for liquid-phase air oxidation of trimethylol is obtained.

[0065] Performance Evaluation

[0066] The catalytic oxidation performance evaluation method of the composite catalyst for liquid-phase air oxidation of trimethylol prepared in the above embodiments is as follows: 30 mL of the composite catalyst, 200 mL of trimethylol and 600 mL of acetic acid solvent are added to a reactor, a certain amount of air is introduced, and a catalytic oxidation reaction occurs under the conditions of 200°C and 2.0 MPa. The reaction is terminated after 4 hours, and the mass yield of the target product and the content of by-products (phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid) are determined.

[0067] Table 1 Target product yield and by-product content

[0068]

[0069] Table 2 Composition and content of composite catalyst in Example 6

[0070]

[0071] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a composite catalyst for liquid-phase air catalytic oxidation of trimethylol, characterized in that: The following steps are involved: With liquid bromine, cobalt bromide and manganese bromide as raw materials, first add 100 mL of acetic acid and 0.0162 g of ferric bromide catalyst into a three-necked flask, then add 9.56 g of biphenyl, 4.15 g of cobalt bromide and 4.15 g of manganese bromide under stirring, then add 3.14 mL of liquid bromine dropwise into the three-necked flask through a separatory funnel. During the dropping process, the stirring rate is controlled at 400 rpm to fully mix the reaction materials. After reacting for 4 hours, a composite catalyst for liquid-phase air oxidation of trimethylol is obtained.

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