Process for the preparation of trimellitic acid triesters

Abstract

This invention relates to the field of fine chemicals technology, specifically to a method for preparing trimellitic acid triester. The method includes: (1) adding a catalyst and an alcohol to crude trimellitic acid, heating under reflux, and separating water to obtain a reactant; (2) mixing the reactant with water, separating the layers to obtain an oil phase; (3) removing the alcohol from the oil phase to obtain trimellitic acid triester; wherein the catalyst is selected from at least one of protic acids, Lewis acids, and solid polyacids; the alcohol is selected from at least one of C4-C10 alcohols; and the crude trimellitic acid product contains at least 5 wt% acetic acid. The residual acetic acid in the crude trimellitic acid product, in the presence of the catalyst, reacts with the alcohol to form acetate ester, which acts as a dehydrating agent. The acetate ester, alcohol, and water form a ternary azeotropic compound that removes water from the reaction system, increasing the conversion rate of esterification.

Description

Technical Field

[0001] This invention relates to the field of fine chemicals technology, and specifically to a method for preparing trimellitic acid triester. Background Technology

[0002] The current production process involves: high-temperature, high-pressure air oxidation of trimellitene to obtain trimellitic acid under conditions of cobalt acetate, manganese acetate, and tetrabromoethane as catalysts and acetic acid as solvent; removal of the solvent and water to obtain trimellitic anhydride; and finally, esterification of the trimellitic anhydride and alcohol under acidic conditions to form trimellitic acid triester. The shortcomings of this process are:

[0003] When trimellitic acid is oxidized, some oxidation products are produced, as follows:

[0004]

[0005] And the decarboxylation products at high temperatures, as follows:

[0006]

[0007] There are even some rearrangement products, as follows:

[0008]

[0009] These byproducts, during the dehydration process, can form mixed anhydrides with the main product trimellitic acid, as well as products formed by cross-dehydration between multiple acids, thus reducing the yield of trimellitic anhydride.

[0010] In existing technologies, acetic acid needs to be recovered after oxidation, requiring significant heat and refrigerant. After removing the solvent acetic acid and water by vacuum distillation, the product is recovered under reduced pressure. However, the high-boiling-point substances formed by the cross-dehydration of multiple acids are difficult to distill off, resulting in ash residue after distillation. The catalyst is completely encapsulated in this residue and cannot be recovered. This leads to problems such as low selectivity of trimellitic anhydride products, numerous and difficult-to-separate byproducts, and difficulty in catalyst recovery. The reaction between trimellitic anhydride and alcohols also requires dehydration by a dehydrating agent to improve esterification conversion. Commonly used dehydrating agents such as toluene or xylene readily undergo Friedel-Crafts alkylation reactions with alcohols under these reaction conditions. Summary of the Invention

[0011] The purpose of this invention is to overcome the problems of low product selectivity, numerous and difficult-to-separate byproducts, and difficult-to-recover catalysts in the prior art, and to provide a method for preparing trimellitic acid triester. This method has the advantages of high product selectivity, few byproducts, low heat consumption and refrigerant consumption, and the ability to recover the catalyst.

[0012] To achieve the above objectives, the present invention provides a method for preparing trimellitic acid triester, the method comprising:

[0013] (1) Add catalyst and alcohol to crude trimellitic acid product, heat under reflux and separate water to obtain reaction material;

[0014] (2) The reactants are mixed with water and then separated into layers to obtain the oil phase;

[0015] (3) Remove the alcohol from the oil phase to obtain trimellitic acid triester;

[0016] The catalyst is selected from at least one of protic acids, Lewis acids, and solid polyacids;

[0017] The alcohol is selected from at least one of C4-C10 alcohols;

[0018] In the crude trimellitic acid product, the acetic acid content is not less than 5 wt%.

[0019] Through the above technical solution, the residual acetic acid in the crude trimellitic acid product reacts with alcohol in the presence of a catalyst to form acetate, which acts as a dehydrating agent. The acetate, alcohol, and water form a ternary azeotropic compound that removes moisture from the reaction system, thus improving the esterification conversion rate. Compared with existing technologies, this method has the following advantages:

[0020] 1. Trimethicone has good selectivity and no dehydration products of trimellitic acid and other byproducts, which improves the yield of trimelliticone.

[0021] 2. It reduces the number of times acetic acid is recovered, and reduces the use of heat sources and refrigerants;

[0022] 3. The catalyst can be recycled and reused, reducing the formation of waste residue;

[0023] 4. No additional water-removing agent is required. Attached Figure Description

[0024] Figure 1 This is the 1H NMR spectrum of tributyl trimellitate prepared in Example 1;

[0025] Figure 2 This is the carbon spectrum of tributyl trimellitate prepared in Example 1;

[0026] Figure 3 This is the mass spectrum of tributyl trimellitate prepared in Example 1;

[0027] Figure 4 This is the 1H NMR spectrum of tri-n-octyl trimellitate prepared in Example 2;

[0028] Figure 5 This is the carbon spectrum of tri-n-octyl trimellitate prepared in Example 2;

[0029] Figure 6 This is the mass spectrum of tri-n-octyl trimellitate prepared in Example 2;

[0030] Figure 7 This is the 1H NMR spectrum of triisooctyl trimellitate prepared in Example 3;

[0031] Figure 8 This is the carbon spectrum of triisooctyl trimellitate prepared in Example 3;

[0032] Figure 9 This is the mass spectrum of triisooctyl trimellitate prepared in Example 3. Detailed Implementation

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] This invention provides a method for preparing trimellitic acid triester, the method comprising:

[0035] (1) Add catalyst and alcohol to crude trimellitic acid product, heat under reflux and separate water to obtain reaction material;

[0036] (2) The reactants are mixed with water and then separated into layers to obtain the oil phase;

[0037] (3) Remove the alcohol from the oil phase to obtain trimellitic acid triester; the catalyst is selected from at least one of protic acid, Lewis acid and solid polyacid;

[0038] The alcohol is selected from at least one of C4-C10 alcohols;

[0039] In the crude trimellitic acid product, the acetic acid content is not less than 5 wt%.

[0040] Using the preparation method described in this invention, the residual acetic acid in the crude trimellitic acid product reacts with an alcohol in the presence of a catalyst to form acetate, which acts as a dehydrating agent. The acetate, alcohol, and water form a ternary azeotropic compound that removes water from the reaction system, thus increasing the esterification conversion rate. Using the preparation method described in this invention: 1. Tritrimethylenetetramine has good selectivity, with no dehydration products of trimellitic acid and other byproducts, thus improving the yield of tritrimethylenetetramine; 2. It reduces the number of acetic acid recovery cycles, reducing the use of heat sources and refrigerants; 3. The catalyst can be recycled and reused, reducing the formation of waste residue; 4. No additional dehydrating agent is required.

[0041] According to a preferred embodiment of the present invention, in step (1), the reactants are obtained by atmospheric pressure heating and reflux followed by water separation or by reduced pressure heating and reflux followed by water separation. In this invention, there is no particular limitation on the pressure of reduced pressure heating and reflux.

[0042] In step (3), the oil phase from step (2) is subjected to atmospheric or vacuum distillation to remove the alcohol from the oil phase, yielding trimellitic acid triester. In this invention, there is no particular limitation on the pressure of vacuum distillation; for example, it can be a pressure not exceeding 1000 Pa, such as 400-600 Pa.

[0043] In this invention, the range of types of protic acids that can be selected is relatively wide. According to a preferred embodiment of this invention, the protic acid is selected from at least one of concentrated sulfuric acid, methanesulfonic acid, p-toluenesulfonic acid, and concentrated phosphoric acid.

[0044] In this invention, the range of Lewis acids that can be selected is relatively wide. According to a preferred embodiment of this invention, the Lewis acid is selected from at least one of stannous oxide, titanium dioxide, zirconium oxide, aluminum trichloride, ferric chloride, and boron trifluoride.

[0045] According to a preferred embodiment of the present invention, the solid polyacid is selected from at least one of phosphotungstic heteropolyacid and phosphotomolybdic heteropolyacid.

[0046] According to a preferred embodiment of the present invention, the catalyst is selected from concentrated sulfuric acid, methanesulfonic acid, concentrated phosphoric acid, stannous oxide, and phosphotungstic heteropoly acid.

[0047] In this invention, the range of C4-C10 alcohols is relatively wide, for example, it can be at least one of n-butanol, n-octanol, 2-ethylhexanol (isooctanol), and isononol. Preferably, the alcohol is selected from at least one of n-butanol, n-octanol, and isooctanol.

[0048] According to a preferred embodiment of the present invention, when the alcohol is n-butanol, the catalyst is selected from concentrated sulfuric acid and / or phosphoric acid.

[0049] According to a preferred embodiment of the present invention, when the alcohol is n-octanol, the catalyst is selected from methanesulfonic acid.

[0050] According to a preferred embodiment of the present invention, when the alcohol is isooctyl alcohol, the catalyst is selected from at least one of concentrated sulfuric acid, methanesulfonic acid and phosphotungstic heteropoly acid.

[0051] In this invention, the amount of catalyst can be selected from a wide range. According to a preferred embodiment of this invention, the amount of catalyst, calculated based on trimellitic acid, is 0.11-0.3 eq.

[0052] In this invention, the amount of alcohol used can be selected from a wide range. According to a preferred embodiment of this invention, the amount of alcohol used is 6-30 eq, based on trimellitic acid.

[0053] According to a preferred embodiment of the present invention, step (3) further includes: after depressurization, adding an acid remover and a decolorizing agent to remove acid and decolorize; preferably, the acid remover is selected from at least one of alkaline earth metal oxides, preferably magnesium oxide; the decolorizing agent is activated carbon.

[0054] According to a preferred embodiment of the present invention, the crude trimellitic acid product contains 10-15 wt% acetic acid.

[0055] In this invention, the crude trimellitic acid product mainly contains trimellitic acid, acetic acid and water, as well as trace amounts of some byproducts obtained from the oxidation of trimellitene, such as monomethyl oxidation products, dimethyl oxidation products and trimellitic acid decarboxylation products.

[0056] According to a preferred embodiment of the present invention, the crude trimellitic acid product contains 75-85% trimellitic acid, 10-15% acetic acid, and 1-5% water, based on the total weight of trimellitic acid.

[0057] In this invention, the source of the trimellitic acid is not particularly limited and can be any conventional source in the art. For example, the material after trimellitene oxidation is cooled and crystallized, and then centrifuged to obtain crude trimellitic acid. The mother liquor is then dehydrated with a dehydrating agent and recycled. By using the aforementioned method, the catalyst in the mother liquor can be recovered and reused, reducing the formation of waste residue.

[0058] According to a preferred embodiment of the present invention, the dehydrating agent is selected from at least one of molecular sieve, silica gel, activated alumina, anhydrous sodium sulfate, anhydrous magnesium sulfate and anhydrous calcium chloride.

[0059] According to a preferred embodiment of the present invention, the crude trimellitic acid is obtained by: a reaction of trimellitene with cobalt acetate and manganese acetate as the main catalysts and tetrabromoethane as the co-catalyst, under air oxidation conditions of 1.5-3.0 MPa and 160-220°C. The oxidized material is then cooled and crystallized, and centrifuged to obtain crude trimellitic acid. In this invention, the mass ratio of Co, Mn, and Br in the catalyst used to obtain the trimellitic acid is 1:(1.5-2.5):(2-3).

[0060] According to a preferred embodiment of the present invention, the temperature of atmospheric pressure heating reflux or depressurization heating reflux is 130-140°C.

[0061] According to a preferred embodiment of the present invention, the method for preparing the trimellitic acid triester includes:

[0062] (1) Pyrite undergoes air oxidation at 1.5-3.0 MPa and 160-220 °C with cobalt acetate and manganese acetate as the main catalysts and tetrabromoethane as the co-catalyst. The oxidized material is cooled and crystallized, and then centrifuged to obtain crude trimellitic acid. After the oxidation reaction of pyrite is completed, the material is cooled to precipitate insoluble matter, which is then centrifuged to obtain crude trimellitic acid. The mother liquor is dehydrated with a dehydrating agent and then directly recycled. Cobalt acetate and manganese acetate are dissolved in the mother liquor and are recovered together. The mother liquor can be recycled four times before vacuum distillation to recover acetic acid.

[0063] (2) Add catalyst and alcohol to crude trimellitic acid. Low-boiling alcohols, such as butanol, are directly heated under reflux and water is separated by a water separator. High-boiling alcohols, such as octanol and isooctanol, are heated under reduced pressure under reflux and water is separated by a water separator.

[0064] (3) Cool, add water to the reaction system, separate the phases, and discard the aqueous phase;

[0065] (4) The oil phase is subjected to vacuum to recover alcohol, and then magnesium oxide and activated carbon are added in a 1:1 ratio. The mixture is stirred at 100-120℃ for 0.5 hours to remove residual acid and decolorize. The product, trimellitic acid triester, is obtained by vacuum filtration.

[0066] The present invention will be described in detail below through embodiments.

[0067] In the following examples, APHA stands for Platinum-Cobalt Colorimetric Unit.

[0068] In the following examples, the crude trimellitic acid product was prepared by the following method:

[0069] Trimethylbenzene was subjected to air oxidation at 2 MPa and 160-220 °C with cobalt acetate and manganese acetate as the main catalysts and tetrabromoethane as the co-catalyst, and the mass ratio of Co, Mn and Br was 1:2:2. The oxidized material was cooled and crystallized, and then centrifuged to obtain crude trimellitic acid. The mother liquor was dehydrated and recovered using anhydrous magnesium sulfate.

[0070] Example 1

[0071] (1) 1.27 g of trimellitene, cobalt acetate and manganese acetate as the main catalysts, and tetrabromoethane as the co-catalyst (wherein the mass ratio of Co, Mn and Br is 1:2:2), were subjected to air oxidation reaction at 2 MPa and 160-220 °C. The oxidized material was cooled and crystallized, and centrifuged to obtain 2.6 g of crude trimellitic acid (containing 2.0 g of trimellitic acid, 0.3 g of acetic acid, and 0.1 g of water). The yield was 90.0% based on trimellitene.

[0072] (2) Add crude trimellitic acid to a three-necked flask, add a water separator, add 21.15 g of n-butanol, stir at room temperature for 10 minutes, add 60 μL of 98% concentrated sulfuric acid, stir and reflux at 130°C for 12 hours to separate water.

[0073] (3) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0074] (4) The oil phase was subjected to reduced pressure (0.1 mPa) and 135 °C to recover n-butanol until no liquid distilled out. Magnesium oxide and 3 g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120 °C for 0.5 hours for decolorization. A Buchner funnel was filled with 12 mm thick diatomaceous earth as a filter aid, and the product, tributyl trimellitic acid, was obtained by reduced pressure filtration. The yield, based on trimellitic acid, was 93.7%. The flash point was 193 °C, the tributyl trimellitic acid content was 99.5 wt%, the acid value was 0.1 mg / Kg, the color was 20 (APHA), and the volume resistivity was 1.0 x 10⁻⁶. 11 Ω·cm.

[0075] Figure 1 This is the 1H NMR spectrum of tributyl trimellitate prepared in Example 1; Figure 2 This is the carbon spectrum of tributyl trimellitate prepared in Example 1; Figure 3 This is the mass spectrum of tributyl trimellitate prepared in Example 1; ¹H NMR (400MHz, CDCl₃) δ 8.40 (d, J = 1.7Hz, 1H), 8.20 (dd, J = 8.0, 1.7Hz, 1H), 7.76 (d, J = 8.0Hz, 1H), 4.36 (dt, J = 13.2, 6.7Hz, 6H), 1.82–1.69 (m, 6H), 1.04–0.90 (m, 9H). ¹³C NMR (101MHz, CDCl3) δ 167.23, 166.69, 165.06, 136.34, 132.70, 132.17, 131.98, 130.10, 128.87, 65.92, 65.86, 65.54, 30.67, 30.54, 30.51, 19.23, 19.18, 19.16, 13.73, 13.71. HRMS calculated value C 21 H 30 O6, 378.2042, found value C 21 H 31 O6, 379.2147. (By...) Figure 1 , Figure 2 , Figure 3 The results show that the n-butyl trimellitate product obtained by the preparation method described in this invention has high purity.

[0076] Example 2

[0077] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 37.1g of n-octanol, stir at room temperature for 10 minutes, add 60uL of 98% concentrated sulfuric acid, stir and reflux at 140℃ for 6 hours; then stir and reflux at 140℃ for 6 hours under a pressure of 0.1mPa to separate water.

[0078] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0079] (3) The oil phase was subjected to reduced pressure (400-600 Pa, 210℃) to recover n-octanol until no more liquid distilled off. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the mixture was filtered under reduced pressure to obtain the product, trioctyl trimellitate. The flash point was 240℃, the trioctyl trimellitate content was 99.0wt%, the acid value was 0.2mg / Kg, the color was 45 (APHA), and the volume resistivity was 7.0 x 10⁻⁶. 10 Ω·cm.

[0080] Figure 4 This is the 1H NMR spectrum of tri-n-octyl trimellitate prepared in Example 2; Figure 5 This is the carbon spectrum of tri-n-octyl trimellitate prepared in Example 2; Figure 6 This is the mass spectrum of tri-n-octyl trimellitate prepared in Example 2; ¹H NMR (400MHz, CDCl₃) δ 8.40 (d, J = 1.7Hz, 1H), 8.20 (dd, J = 8.0, 1.7Hz, 1H), 7.77 (d, J = 8.0Hz, 1H), 4.35 (dt, J = 13.4, 6.7Hz, 6H), 1.84–1.70 (m, 6H), 1.49–1.22 (m, 30H), 0.93–0.86 (m, 9H). ¹³C NMR (101MHz, CDCl3)δ167.26,166.72,165.08,136.32,132.70,132.16,132.00,130.11,128.88,66.25,66.19,65.86,31.80,29.26,29.25,29.24,29.21,28.63,28.52,28.49,25.99,25.95,22.66,14.10.HRMS calculated value C 33 H 54 O6, 546.3920, found value C 33 H 55 O6, 547.3976. (By...) Figure 4, Figure 5 , Figure 6 The results show that the n-octyl trimellitate product obtained by the preparation method described in this invention has high purity.

[0081] Example 3

[0082] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 37.1g of 2-ethylhexanol, stir at room temperature for 10 minutes, add 60uL of 98% concentrated sulfuric acid, stir and reflux at 140℃ for 6 hours; under a pressure of 0.1mPa, stir and reflux at 140℃ to separate water for 6 hours.

[0083] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes, separate the layers, and collect the oil phase.

[0084] (3) The oil phase was subjected to reduced pressure to 400-600 Pa and 150-180℃ to recover 2-ethylhexanol until no liquid distilled out. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, triisooctyl trimellitate, was obtained by reduced pressure filtration. The flash point was 245℃, the ester content was 99.5wt%, the acid value was 0.15mg / Kg, the color was 35 (APHA), and the volume resistivity was 1.0 x 10⁻⁶. 12 Ω·cm.

[0085] Figure 7 This is the 1H NMR spectrum of triisooctyl trimellitate prepared in Example 3; Figure 8 This is the carbon spectrum of triisooctyl trimellitate prepared in Example 3; Figure 9 The mass spectrum of triisooctyl trimellitate prepared in Example 3; 1 H NMR(400MHz, CDCl3) δ8.40(d,J=1.6Hz,1H),8.21(dd,J=8.0,1.8Hz,1H),7.75(d,J=8.0Hz,1H), 4.26(ddt,J=17.3,11.0,5.6Hz,6H),1.82–1.63(m,4H),1.56–1.23(m,24H),1.01–0.83(m,18H). 13C NMR (101MHz, CDCl3) δ 167.40, 166.65, 165.14, 136.62, 132.65, 132.12, 132.07, 130.05, 128.84, 68.51, 68.36, 67.94, 38.87, 38.72, 38.68, 30.52, 30.35, 30.33, 28.98, 28.93, 28.91, 23.95, 23.76, 23.72, 23.00, 22.98, 14.08, 11.10, 10.99, 10.97. HRMS calculated C 33 H 54 O6, 546.3920, found value C 33 H 55 O6, 547.4025. (By...) Figure 7 , Figure 8 , Figure 9 The results show that the triisooctyl trimellitate product obtained by the preparation method described in this invention has high purity.

[0086] Example 4

[0087] (1) Add 2.6g of crude trimellitic acid (2.0g of trimellitic acid; 0.3g of acetic acid; 0.1g of water) to a three-necked flask, add a water separator, add 21.15g of n-butanol, stir at room temperature for 10 minutes, add 125uL of 99% methanesulfonic acid, stir and reflux at 130℃ to separate water for 12 hours.

[0088] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0089] (3) The oil phase was subjected to reduced pressure to 0.1 mPa, and n-butanol was recovered at 135℃ until no liquid distilled out. Magnesium oxide and 3 g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12 mm thick diatomaceous earth as a filter aid, and the product, tributyl trimellitate, was obtained by reduced pressure filtration. The flash point was 193℃, the tributyl trimellitate content was 99.0 wt%, the acid value was 0.12 mg / Kg, the color was 20 (APHA), and the volume resistivity was 1.2 x 10⁻⁶. 11 Ω·cm.

[0090] Example 5

[0091] (1) Add 2.6 g of crude trimellitic acid (2.0 g of trimellitic acid; 0.3 g of acetic acid; 0.1 g of water) to a three-necked flask, add a water separator, add 45 mL (0.285 mol) of n-octanol, stir at room temperature for 10 minutes, add 125 μL of 99% methanesulfonic acid, stir and reflux at 140 °C for 6 hours; then stir and reflux at 140 °C for 6 hours under a pressure of 0.1 MPa to separate water.

[0092] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0093] (3) The oil phase was subjected to reduced pressure (400-600 Pa, 210℃) to recover n-octanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours to decolorize. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, tri-n-octyl trimellitate, was obtained by reduced pressure filtration. The flash point was 240℃, the tri-n-octyl trimellitate content was 99.4wt%, the acid value was 0.16mg / Kg, the color was 30 (APHA), and the volume resistivity was 8.0 x 10⁻⁶. 10 Ω·cm.

[0094] Example 6

[0095] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 37.1g of 2-ethylhexanol, stir at room temperature for 10 minutes, add 125uL of 99% methanesulfonic acid, stir and reflux at 140℃ for 6 hours; then stir and reflux at 140℃ for 6 hours under a pressure of 0.1mPa to separate water.

[0096] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes, separate the layers and collect the oil phase;

[0097] (3) The oil phase was subjected to reduced pressure (400-600 Pa, 150-180℃) to recover 2-ethylhexanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours to decolorize. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, triisooctyl trimellitate, was obtained by reduced pressure filtration. The flash point was 245℃, the triisooctyl trimellitate content was 99.6wt%, the acid value was 0.14mg / Kg, the color was 30 (APHA), and the volume resistivity was 1.2 x 10⁻⁶. 12 Ω·cm.

[0098] Example 7

[0099] (1) Add 2.5g of crude trimellitic acid (2.0g of trimellitic acid; 0.28g of acetic acid; 0.1g of water) to a three-necked flask, add a water separator, add 21.15g of n-butanol, stir at room temperature for 10 minutes, add 98uL of 99% phosphoric acid, stir and reflux at 130℃ to separate water for 12 hours.

[0100] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0101] (3) The oil phase was subjected to reduced pressure (0.1 mPa) and 135℃ to recover n-butanol until no liquid distilled out. Magnesium oxide and 3 g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12 mm thick diatomaceous earth as a filter aid, and the product, tributyl trimellitate, was obtained by reduced pressure filtration. The flash point was 193℃, the tributyl trimellitate content was 99.2 wt%, the acid value was 0.13 mg / Kg, the color was 25 (APHA), and the volume resistivity was 1.3 x 10⁻⁶. 11 Ω·cm.

[0102] Example 8

[0103] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 45mL (0.285mol) of n-octanol, stir at room temperature for 10 minutes, add 98uL of 99% phosphoric acid, stir and reflux at 140℃ for 6 hours; then stir and reflux at 140℃ for 6 hours under a pressure of 0.1mPa to separate water.

[0104] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0105] (3) The oil phase was subjected to reduced pressure (400-600 Pa) and 210℃ to recover n-octanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, tri-n-octyl trimellitate, was obtained by reduced pressure filtration. The flash point was 240℃, the tri-n-octyl trimellitate content was 98.9wt%, the acid value was 0.18mg / Kg, the color was 20 (APHA), and the volume resistivity was 6.0 x 10⁻⁶. 10 Ω·cm.

[0106] Example 9

[0107] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 44mL (0.285mol) of 2-ethylhexanol, stir at room temperature for 10 minutes, add 98uL of 99% phosphoric acid, stir and reflux at 130℃ for 6 hours; then stir and reflux at 130℃ for 6 hours under a pressure of 0.1mPa to separate water.

[0108] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0109] (3) The oil phase was subjected to reduced pressure (400-600 Pa) and 150-180℃ to recover 2-ethylhexanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, triisooctyl trimellitate, was obtained by reduced pressure filtration. The flash point was 245℃, the triisooctyl trimellitate content was 97.6wt%, the acid value was 0.20mg / Kg, the color was 35 (APHA), and the volume resistivity was 1.0 x 10⁻⁶. 11 Ω·cm.

[0110] Example 10

[0111] (1) Add 2.5g of crude trimellitic acid (2.0g of trimellitic acid; 0.28g of acetic acid; 0.1g of water) to a three-necked flask, add a water separator, add 14.10g of n-butanol, stir at room temperature for 10 minutes, add 0.26g of stannous oxide, stir and reflux at 130℃ to separate water for 12 hours.

[0112] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0113] (3) The oil phase was subjected to reduced pressure (0.1 mPa) and 135 °C to recover n-butanol until no liquid distilled out. Magnesium oxide and 3 g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120 °C for 0.5 hours for decolorization. A Buchner funnel was filled with 12 mm thick diatomaceous earth as a filter aid, and the product, tributyl trimellitate, was obtained by reduced pressure filtration. The flash point was 193 °C, the tributyl trimellitate content was 95.8 wt%, the acid value was 0.23 mg / Kg, the color was 45 (APHA), and the volume resistivity was 1.2 x 10⁻⁶. 10 Ω·cm.

[0114] Example 11

[0115] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.35g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 24.75g of n-octanol, stir at room temperature for 10 minutes, add 0.26g stannous oxide, heat to 140℃ and stir under reflux for 6 hours; then under 0.1mPa pressure, stir under reflux at 140℃ for 6 hours to separate water.

[0116] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes, separate the layers, and collect the oil phase.

[0117] (3) The oil phase was subjected to reduced pressure (400-600 Pa) and 210℃ to recover n-octanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours to decolorize. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, tri-n-octyl trimellitate, was obtained by reduced pressure filtration. The flash point was 240℃, the tri-n-octyl trimellitate content was 95.7wt%, the acid value was 0.38mg / Kg, the color was 45 (APHA), and the volume resistivity was 5.2 x 10⁻⁶. 10 Ω·cm.

[0118] Example 12

[0119] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 24.75g of 2-ethylhexanol, stir at room temperature for 10 minutes, add 0.26g stannous oxide, stir and reflux at 130℃ for 6 hours; then stir and reflux at 130℃ for 6 hours under a pressure of 0.1mPa to separate water.

[0120] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0121] (3) The oil phase was subjected to reduced pressure to 400-600 Pa and 150-180℃ to recover 2-ethylhexanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon were added in a 1:1 ratio, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, triisooctyl trimellitate, was obtained by reduced pressure filtration. The flash point was 245℃, the triisooctyl trimellitate content was 94.5wt%, the acid value was 0.45mg / Kg, the color was 50 (APHA), and the volume resistivity was 0.9 x 10⁻⁶. 10 Ω·cm. APHA is the unit of colorimetric hue for platinum-cobalt.

[0122] Example 13

[0123] (1) Add 2.5g of crude trimellitic acid (2.0g trimellitic acid; 0.28g acetic acid; 0.1g water) to a three-necked flask, add a water separator, add 21.15g of n-butanol, stir at room temperature for 10 minutes, and then add phosphotungstic heteropoly acid (H3PW). 12 O 40 0.275g of nH2O was stirred and refluxed at 130℃ for 12 hours to separate the water.

[0124] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0125] (3) The oil phase was subjected to reduced pressure to 0.1 mPa, and n-butanol was recovered at 135℃ until no liquid distilled out. Magnesium oxide and 3 g of activated carbon (1:1 ratio) were added, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12 mm thick diatomaceous earth as a filter aid, and the product, tributyl trimellitate, was obtained by reduced pressure filtration. The flash point was 193℃, the tributyl trimellitate content was 98.8 wt%, the acid value was 0.18 mg / Kg, the color was 19 (APHA), and the volume resistivity was 2.4 x 10⁻⁶. 11 Ω·cm.

[0126] Example 14

[0127] (1) Add 2.5 g of crude trimellitic acid (2.0 g trimellitic acid; 0.28 g acetic acid; 0.1 g water) to a three-necked flask, add a water separator, add 45 mL (0.285 mol) of n-octanol, stir at room temperature for 10 minutes, and then add phosphotungstic heteropoly acid (H3PW). 12 O 40 0.275 g of nH2O was heated to 140°C and stirred under reflux for 6 hours; then, under a pressure of 0.1 MPa, the mixture was stirred under reflux at 140°C for 6 hours to separate the water.

[0128] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0129] (3) The oil phase was subjected to reduced pressure to 400-600 Pa and 210℃ to recover n-octanol until no liquid distilled out. Magnesium oxide and 3g of activated carbon were added in a 1:1 ratio, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, tri-n-octyl trimellitate, was obtained by reduced pressure filtration. The flash point was 240℃, the tri-n-octyl trimellitate content was 98.4wt%, the acid value was 0.16mg / Kg, the color was 20 (APHA), and the volume resistivity was 7.8 x 10⁻⁶. 9 Ω·cm.

[0130] Example 15

[0131] (1) Add 2.5 g of crude trimellitic acid (2.0 g trimellitic acid; 0.28 g acetic acid; 0.1 g water) to a three-necked flask, add a water separator, add 44 mL (0.285 mol) of 2-ethylhexanol, stir at room temperature for 10 minutes, and then add phosphotungstic heteropoly acid (H3PW). 12 O 40 Add 0.275g of nH2O and stir and reflux at 130℃ for 6 hours; then stir and reflux at 130℃ for 6 hours under a pressure of 0.1mPa to separate the water.

[0132] (2) Add water to separate the layers, collect the oil phase, add 10% sodium carbonate aqueous solution and stir for 15 minutes to separate the layers, collect the oil phase;

[0133] (3) The oil phase was subjected to reduced pressure to 400-600 Pa and 150-180℃ to recover 2-ethylhexanol until no liquid distilled off. Magnesium oxide and 3g of activated carbon were added in a 1:1 ratio, and the mixture was stirred at 100-120℃ for 0.5 hours for decolorization. A Buchner funnel was filled with 12mm thick diatomaceous earth as a filter aid, and the product, triisooctyl trimellitate, was obtained by reduced pressure filtration. The flash point was 245℃, the triisooctyl trimellitate content was 99.5wt%, the acid value was 0.25mg / Kg, the color was 50 (APHA), and the volume resistivity was 0.9 x 10⁻⁶. 12 Ω·cm.

[0134] Example 16

[0135] The method of Example 1 is the same, except that in step (1), the crude trimellitic acid product contains 0.2g of acetic acid; specifically:

[0136] (1) 2.6 g of crude trimellitic acid (containing 2.0 g of trimellitic acid, 0.2 g of acetic acid, and 0.1 g of water) was added to a three-necked flask, a water separator was added, 21.15 g of n-butanol was added, and the mixture was stirred at room temperature for 10 minutes. Then, 60 μL of 98% concentrated sulfuric acid was added, and the mixture was stirred and refluxed at 130°C for 12 hours to separate the water. The remaining conditions were the same as in Example 1.

[0137] The product has a flash point of 193℃, a tributyl trimellitate content of 96.8wt%, an acid value of 0.20 mg / kg, a color of 26 (APHA), and a volume resistivity of 1.3 x 10⁻⁶. 11 Ω·cm.

[0138] Example 17

[0139] The method of Example 1 is the same, except that in step (1), the crude trimellitic acid product contains 0.47g of acetic acid; specifically:

[0140] (1) 2.6 g of crude trimellitic acid (containing 2.0 g of trimellitic acid, 0.47 g of acetic acid, and 0.08 g of water) was added to a three-necked flask, a water separator was added, 21.15 g of n-butanol was added, and the mixture was stirred at room temperature for 10 minutes. Then, 60 μL of 98% concentrated sulfuric acid was added, and the mixture was stirred and refluxed at 130 °C for 12 hours to separate the water. The remaining conditions were the same as in Example 1.

[0141] The product has a flash point of 193℃, a tributyl trimellitate content of 96.1 wt%, an acid value of 0.35 mg / kg, a color of 34 (APHA), and a volume resistivity of 1.5 x 10⁻⁶. 11 Ω·cm.

[0142] Comparative Example 1

[0143] (1) 1.27 g of pseudotrimethylbenzene, cobalt acetate and manganese acetate as the main catalysts, and tetrabromoethane as the co-catalyst (wherein, the mass ratio of Co, Mn and Br is 1:2:2), were subjected to air oxidation reaction at 2 MPa and 160-220 °C.

[0144] (2) After oxidation, the system is heated to 220-230℃ for melting and dehydration, and then subjected to vacuum distillation at 42.66 kPa until no liquid distills out. Finally, it is cooled to obtain trimellitic anhydride, with a yield of 75.2% based on trimellitene.

[0145] Compared with Example 1 (the yield of tributyl trimellitate was 84.3% based on trimellitene), Comparative Example 1 used existing technology to separate trimellitic anhydride, which had a low yield. Triellitic anhydride was then esterified with alcohol, further reducing the yield of trimellitic triester. It can be seen that the preparation method described in this invention has achieved significant progress.

[0146] Comparative Example 2

[0147] The method of Example 10 differs in that, in step (1), the crude trimellitic acid product contains 4.4 wt% acetic acid, specifically:

[0148] (1) 2.5 g of crude trimellitic acid (2.0 g of trimellitic acid; 0.11 g of acetic acid; 0.10 g of water) was added to a three-necked flask, a water separator was added, and 14.10 g of n-butanol (0.19 mol, 17.4 mL, 20 eq) was added. After stirring at room temperature for 10 minutes, 0.26 g of stannous oxide (0.0019 mol, 0.2 eq) was added, and the mixture was stirred and refluxed at 130 °C for 12 hours to separate the water.

[0149] The remaining conditions were the same as in Example 10, and the product tributyl trimellitate was obtained.

[0150] Tributyl trimellitate has a flash point of 193℃, an ester content of 84.5 wt%, an acid value of 0.25 mg / kg, a color of 61 (APHA), and a volume resistivity of 1.4 x 10⁻⁶. 6 Ω·cm.

[0151] Example 18

[0152] The dehydrated mother liquor obtained from the preparation of crude trimellitic acid was analyzed for cobalt and manganese ion concentrations. Cobalt acetate and manganese acetate were added according to a ratio (Co, Mn, and Br mass ratio of 1:2:2), followed by air oxidation at 2 MPa and 160-220 °C. The oxidized material was cooled and crystallized, then centrifuged to obtain crude trimellitic acid. The yield, based on trimellitene, was 90.1%, showing no significant difference compared to Comparative Example 1. This demonstrates that the solvent and catalyst in the preparation method described in this invention can be directly recycled and reused, representing a significant advancement.

[0153] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing trimellitic acid triester, characterized in that, The method includes: (1) Add catalyst and alcohol to crude trimellitic acid, heat under reflux and separate water to obtain reaction material; (2) The reactants are mixed with water and then separated into layers to obtain the oil phase; (3) Remove alcohol from the oil phase by vacuum distillation. After vacuum distillation, add acid remover and decolorizing agent to remove acid and decolorize to obtain trimellitic acid triester. The alcohol is selected from n-butanol, n-octanol, or isooctanol; When the alcohol is n-butanol, the catalyst is selected from concentrated sulfuric acid and / or phosphoric acid; when the alcohol is n-octanol, the catalyst is selected from methanesulfonic acid; when the alcohol is isoooctanol, the catalyst is selected from at least one of concentrated sulfuric acid, methanesulfonic acid, and phosphotungstic heteropolyacid. Source of crude trimellitic acid: The material after oxidation of trimellitene is cooled and crystallized, and then centrifuged to obtain crude trimellitic acid. The mother liquor is dehydrated by a dehydrating agent and then recycled. The crude trimellitic acid product contains 75-85 wt% trimellitic acid, 10-15 wt% acetic acid, and 1-5 wt% water. The amount of catalyst used is 0.11-0.3 eq, based on trimellitic acid; the amount of alcohol used is 6-30 eq.

2. The preparation method according to claim 1, wherein, In step (1), the reactants are obtained by heating and refluxing under normal pressure and separating water or heating and refluxing under reduced pressure and separating water.

3. The preparation method according to claim 1, wherein, The acid remover is selected from at least one of alkaline earth metal oxides; the decolorizing agent is activated carbon.

4. The preparation method according to claim 1, wherein, The dehydrating agent is selected from at least one of molecular sieves, silica gel, activated alumina, anhydrous sodium sulfate, anhydrous magnesium sulfate, and anhydrous calcium chloride.

5. The preparation method according to claim 2, wherein, In step (1), the temperature of reflux under normal pressure or reflux under reduced pressure is 130-140℃.

Images