Preparation method and application of a bromobiphenyl composite catalyst

Abstract

The invention discloses a preparation method and application of a bromobiphenyl composite catalyst, and in particular relates to a bromobiphenyl composite catalyst for catalytic oxidation of trimellitic acid in liquid phase air by trimethylol and a preparation method thereof. Brominated alkanes and biphenyl compounds are used as raw materials, low-carbon organic acids are used as solvents, and peroxide catalysts are used to undergo a bromination reaction to generate a bromobiphenyl composite catalyst in one step, the main components of which include monobromobiphenyl compounds, polybromobiphenyl compounds and isomers thereof. The bromobiphenyl composite catalyst has the characteristics of high activity, fast rate, and low dosage. Compared with traditional catalysts for liquid phase catalytic oxidation of trimethylol, it has the advantages of higher yield of the target product of the catalytic reaction, lower side reactions and impurity content.

Description

Technical Field

[0001] The invention relates to the technical field of chemical engineering, and in particular to a preparation method and application of a bromobiphenyl composite catalyst. Background Art

[0002] Trimellitic anhydride (TMA) is an important chemical raw material, widely used in surfactants, plasticizers, curing agents, coatings, etc. At present, the method for producing TMA is the liquid-phase air oxidation of trimethylol. This method uses metal acetate and bromide as catalysts, adds trimethylol and solvent acetic acid into the oxidation tower, and then introduces air at about 200°C and 2.0MPa for high-temperature and high-pressure reaction. The reaction is completed to generate trimellitic acid, which is then dehydrated to generate TMA.

[0003] The main problems faced by the liquid-phase air oxidation of trimethylbenzene are high impurity content and low TMA yield. The reaction is a free radical chain reaction. Bromide is the initiator of the reaction. At high temperature, bromide will produce bromine radicals, which will trigger the chain reaction. Methyl groups will generate carboxyl groups under the chain reaction rules. In the process of trimethylbenzene being oxidized to trimellitic acid, all three methyl groups on the aromatic ring must be oxidized to carboxyl groups. Taking tetrabromoethane as an example, when the two methyl groups of trimethylbenzene have been oxidized to carboxyl groups, the third methyl group is difficult to be oxidized due to the electron-withdrawing effect of the two carboxyl groups. Therefore, the activity in the latter stage of the reaction is low, resulting in more TMA impurities and low yield.

[0004] Biphenyl is a strong electron-donating group, which weakens the electron-withdrawing effect of the carboxyl group to a certain extent and promotes the further oxidation of the third methyl group. Therefore, when the bromide is a bromobiphenyl substance, the activity of the latter stage of the reaction is promoted. The invention discloses a bromobiphenyl composite catalyst, which improves the TMA yield and reduces the impurity content compared with the traditional catalyst.

[0005] CN106957218 B discloses a solid phase synthesis method of polybrominated diphenyl ether monomers. The synthesis method of polybrominated diphenyl ethers comprises the following steps: brominated phenol undergoes a dehydration coupling reaction under the catalysis of a solid acid such as SiO2-TiO2, SiO2-A12O3 or TiO2-ZrO3 to obtain polybrominated diphenyl ethers.

[0006] CN116514631A discloses a method for synthesizing high-purity 4-bromo-4'-propylbiphenyl, wherein 4-bromobiphenyl and propionyl chloride are used as reaction raw materials, polyphosphoric acid is used as an acylating agent, and a Friedel-Crafts acylation reaction is performed at 0-10°C to synthesize 4-bromo-4'-propionylbiphenyl.

[0007] In the study of the synthesis process of 4,4'-dibromobiphenyl, Wang Yujing et al. used biphenyl and liquid bromine as raw materials, 1,2-dichloroethane as solvent, and a homemade catalyst to synthesize a high-purity organic intermediate 4,4'-dibromobiphenyl through a catalytic substitution / addition reaction. Summary of the invention

[0008] One of the technical problems to be solved by the present invention is the low triacid yield and high impurity content in the prior art. A bromobiphenyl composite catalyst for liquid-phase air oxidation of trimethylol is provided, which has the advantages of high triacid 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 bromobiphenyl composite catalyst corresponding to the first technical problem.

[0010] The present invention relates to a bromobiphenyl composite catalyst for liquid-phase air catalytic oxidation of trimellitic acid to trimethylbenzene and a preparation method thereof. Brominated alkanes and biphenyl compounds are used as raw materials, low-carbon organic acids are used as solvents, and organic peroxide catalysts are used to generate a bromination reaction to generate a bromobiphenyl composite catalyst in one step. The main components include monobromobiphenyl compounds, polybromobiphenyl compounds and isomers thereof, and the catalyst has a synergistic catalytic effect on the liquid-phase air catalytic oxidation reaction of trimethylbenzene to prepare trimellitic acid. The catalyst has the characteristics of fast catalytic rate and small catalytic dosage. Compared with traditional catalysts for liquid-phase catalytic oxidation of trimethylbenzene, the catalyst has the advantages of higher product yield and low impurity content.

[0011] Preferably, the general structural formula of the brominated alkane is as follows:

[0012] R1-Brn

[0013] Wherein R1 is an alkane having 1 to 8 carbon atoms, and n is the number of Br substituents.

[0014] Preferably, the biphenyl compound is composed of unit bodies of the following structure, and the number of unit bodies n≥2;

[0015]

[0016] Wherein R represents a substituent on the unit body, and the types include but are not limited to alkyl, hydroxyl, carboxyl, etc., and the number of carbon atoms in the substituent is 0 to 4.

[0017] Preferably, the low-carbon organic acid refers to a monobasic organic acid with a carbon number of 1 to 8.

[0018] Preferably, the composite catalyst main component comprises a compound having the following structural characteristics:

[0019]

[0020] Where n means that the biphenyl compound is composed of n units of the above structure, and the number of units n ≥ 2;

[0021] R represents a substituent on the unit body, and its types include but are not limited to alkyl, hydroxyl, carboxyl, etc., and the number of carbon atoms in the substituent is 0 to 4;

[0022] m represents the number of substitutions of Br atoms;

[0023] Taking n=2, m=2, and R as H atom as an example, the structure of the composite catalyst is as follows:

[0024]

[0025] The mass fraction of the main product 4,4'-dibromobiphenyl (a) is 60% to 90%, and the mass fraction of other isomers (a1 to a11) is 10% to 40%.

[0026] The invention also discloses a method for preparing a bromobiphenyl composite catalyst, comprising the following steps: firstly, adding a low-carbon organic acid and an organic peroxide catalyst into a three-necked flask, adding a biphenyl compound under stirring, and then dripping brominated alkane into the three-necked flask through a separatory funnel, controlling the stirring rate to 200-1000 rpm during the dripping process to fully mix the reaction raw materials, and after reacting for 4-6 hours, obtaining a composite catalyst for liquid-phase air catalytic oxidation of trimethylol.

[0027] The bromination reaction equation described in the preparation method is:

[0028]

[0029] Where n represents the number of Br substituents, n' (n' ≥ 2) represents the number of biphenyl compound units, and m represents the number of Br atoms substituted.

[0030] The reaction catalyst is an organic peroxide, including but not limited to benzoyl peroxide, acetylacetone peroxide, etc. The reaction temperature is 30 to 80° C. and the reaction time is 3 to 6 hours.

[0031] The reaction equation of trimethylol disproportionation

[0032]

[0033] Trimellitic acid decarboxylation reaction equation

[0034]

[0035] Preferably, the bromobiphenyl composite catalyst can be applied to the process of preparing trimellitic acid by liquid-phase air oxidation of trimellitic acid, and has the advantages of high product yield and low impurity content compared with traditional catalysts.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The bromobiphenyl composite catalyst of the present invention has the characteristics of high activity, fast rate, small dosage, etc. Compared with the traditional catalyst for liquid-phase catalytic oxidation of trimethylol, it has the advantages of higher yield of the target product of the catalytic reaction, lower side reactions and impurity content.

[0038] 2. The present invention improves the stability of the bromine initiator at high temperatures. Tetrabromoethane is unstable at high temperatures and is prone to oxidative decomposition to produce bromophosgene, resulting in tetrabromoethane loss, so fewer bromine free radicals are generated.

[0039]

[0040] 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.

[0041]

[0042] 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.

[0043]

[0044] 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

[0045] 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.

[0046] Unless otherwise specified, the raw materials used in the present invention are all conventional products purchased from the market.

[0047] Example 1

[0048] Taking tetrabromoethane as raw material, first add 100 mL of acetic acid and 0.0285 g of benzoyl peroxide catalyst into a three-necked flask, add 12.4 g of biphenyl under stirring, and then add 9.68 mL of tetrabromoethane 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, the bromobiphenyl composite catalyst is obtained.

[0049] Example 2

[0050] Taking 1,2-dibromopropane as raw material, first add 100 mL of acetic acid and 0.0285 g of benzoyl peroxide catalyst into a three-necked flask, add 12.4 g of biphenyl under stirring, and then add 9.68 mL of 1,2-dibromopropane 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, the bromobiphenyl composite catalyst is obtained.

[0051] Example 3

[0052] Taking tetrabromoethane as raw material, first add 100 mL of acetic acid and 0.0285 g of acetylacetone peroxide catalyst into a three-necked flask, add 12.4 g of biphenyl under stirring, and then add 9.68 mL of tetrabromoethane 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, the bromobiphenyl composite catalyst is obtained.

[0053] Example 4

[0054] Taking 1,2-dibromopropane as raw material, first add 100 mL of acetic acid and 0.0285 g of benzoyl peroxide catalyst into a three-necked flask, add 12.4 g of biphenyl under stirring, and then add 9.68 mL of 1,2-dibromopropane 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 6 hours, the bromobiphenyl composite catalyst is obtained.

[0055] Example 5

[0056] Taking tetrabromoethane as raw material, first add 100 mL of acetic acid and 0.0285 g of benzoyl peroxide catalyst into a three-necked flask, add 12.4 g of p-terphenyl under stirring, and then add 9.68 mL of tetrabromoethane dropwise into the three-necked flask through a separatory funnel. During the addition, the stirring rate is controlled at 400 rpm to fully mix the reaction raw materials. After reacting for 4 hours, the bromobiphenyl composite catalyst is obtained.

[0057] Performance Evaluation

[0058] The performance evaluation method of the composite catalyst for the liquid-phase air catalytic oxidation of trimethylol prepared above is as follows: 30 mL of the composite catalyst, 200 mL of trimethylol, 600 mL of acetic acid, 1.25 g of cobalt acetate, and 1.25 g of manganese acetate are added to a reactor, and a certain amount of air is introduced. 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.

[0059] Comparative Example

[0060] The composite catalyst was compared with the common cobalt-manganese catalyst. 200 mL of trimethylol, 600 mL of acetic acid, 1.25 g of cobalt acetate and 1.25 g of manganese acetate were added to the reactor as raw materials, and a certain amount of air was introduced. The catalytic oxidation reaction occurred at 200 ° C and 2.0 MPa. The reaction was 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) were determined. The relevant research results are shown in Table 1.

[0061] Table 1 Target product yield and by-product content

[0062]

[0063] Table 2 Composition and content of composite catalyst in Example 1

[0064] composition 4,4'-Dibromobiphenyl 4,4'-Dibromobiphenyl isomers Cobalt acetate Manganese acetate Content / wt% 81.56 8.25 5.1 5.1

[0065] 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. An application of a bromobiphenyl composite catalyst, characterized in that: The bromobiphenyl composite catalyst is used in the preparation of trimellitic acid by liquid-phase air catalytic oxidation of trimethylbenzene, which has the effect of promoting the oxidation of the third methyl group of trimethylbenzene. The preparation method of the bromobiphenyl composite catalyst comprises the following steps: Using brominated alkanes and biphenyl compounds as raw materials, low-carbon organic acids as solvents, and organic peroxides as catalysts, a bromination reaction occurs to generate a brominated biphenyl composite catalyst; The catalyst is mainly composed of monobrominated biphenyl compounds, polybrominated biphenyl compounds and their isomers, and has a synergistic catalytic effect on the liquid-phase air catalytic oxidation reaction of trimellitic acid from trimellitic toluene. The low-carbon organic acid refers to a monobasic organic acid with a C number of 1 to 8; The composite catalyst mainly comprises compounds having the following structural characteristics: Wherein n' indicates that the biphenyl compound is composed of n' units of the above structure, and the number of units n' ≥ 2; R represents a substituent on the unit body, and its types include alkyl, hydroxyl, and carboxyl. The number of carbon atoms in the substituent is 0 to 4; m represents the number of substitutions of Br atoms; The general structural formula of the brominated alkane is as follows: R1-Brn Where R1 is an alkane with a carbon number of 1 to 8, and n is the number of Br substituents; The biphenyl compound is composed of the following structural units, and the number of units n' is ≥ 2, ; Where R represents a substituent on the unit body, and the types include alkyl, hydroxyl, and carboxyl. The number of carbon atoms in the substituent is 0 to 4; The bromination reaction has the following reaction equation: ； Where n represents the number of Br substituents, n' represents the number of biphenyl compound units, n'≥2, and m represents the number of Br atoms substituted; The organic peroxide includes benzoyl peroxide and acetylacetone peroxide, the reaction temperature is 30-80°C, and the reaction time is 3-6h; 30 mL of bromobiphenyl composite catalyst, 200 mL of trimethylol, 600 mL of acetic acid, 1.25 g of cobalt acetate and 1.25 g of manganese acetate were added into a reaction kettle, and a certain amount of air was introduced to cause a catalytic oxidation reaction at 200° C. and 2.0 MPa.

2. The use of a brominated biphenyl composite catalyst according to claim 1, characterized in that: The preparation method of the bromobiphenyl composite catalyst also includes the following specific steps: Firstly, low-carbon organic acid and organic peroxide catalyst are added into a three-necked flask, biphenyl compounds are added under stirring, and then brominated alkane is added dropwise into the three-necked flask through a separatory funnel. During the dropping process, the stirring rate is controlled at 200-1000 rpm to fully mix the reaction raw materials. After reacting for 4-6 hours, a composite catalyst for liquid-phase air catalytic oxidation of trimethylol is obtained.

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