A process for the preparation of chloro-phthalic acid

Abstract

The application discloses a preparation method of chlorophthalic acid, which comprises the following steps: contacting a raw material liquid containing chloro-o-xylene with an oxidant and an oxidation reaction catalyst, and generating an oxidation reaction to prepare the chlorophthalic acid; wherein the oxidant comprises methyl nitrite and oxygen. The method can fully utilize methyl nitrite, which is an important intermediate in a coal-to-ethylene glycol process. The methyl nitrite and the oxygen are used as the oxidant, so that the chloro-o-xylene can be efficiently oxidized to prepare the chlorophthalic acid under mild conditions.

Description

Technical Field

[0001] The present application relates to a method for preparing chlorophthalic acid, belonging to the field of fine chemicals. Background Art

[0002] Chlorophthalic anhydride mainly refers to 3-chlorophthalic anhydride and 4-chlorophthalic anhydride, which are widely used in polyimide, medicine, dyes and other fields. In recent years, they have also been widely used in some fine chemical preparation fields.

[0003] Methods for preparing chlorinated phthalic anhydride include: phthalic anhydride chlorination with hypochlorous acid, chlorination with mononitrophthalic anhydride with chlorine gas, catalytic oxidation of monochloro-o-xylene with air, vapor-phase chlorination of phthalic anhydride, and aromatization of monochloro-tetrahydro- or hexahydrophthalic anhydride. Among these, the chlorination with hypochlorous acid is the most widely used method in industrial production. However, this method requires a long reaction time, produces numerous byproducts, and results in low product yields.

[0004] The catalytic oxidation of monochloro-o-xylene in air is an effective route for producing monochlorophthalic anhydride. However, current catalytic oxidation methods primarily rely on gas-phase oxidation, which operates at reaction temperatures of 420-480°C, exothermic and presents safety risks. Overoxidation is prone to occur, and selectivity is difficult to control. Liquid-phase homogeneous selective oxidation of hydrocarbons using air or oxygen as oxygen sources is the most competitive technology and a focus of scientific and industrial attention.

[0005] Summary of the Invention

[0006] Ethylene glycol is a major petrochemical product, primarily used in antifreeze and the production of PET polyester. Currently, ethylene glycol is primarily produced using a petrochemical process: ethylene is epoxidized to produce ethylene oxide, which is then hydrated to produce ethylene glycol. This process consumes significant amounts of petroleum resources and is energy-intensive for dehydration and separation. The development and application of coal chemical technology has provided a new non-petroleum-based route for the production of ethylene glycol. Methyl nitrite is a key intermediate in the coal-to-ethylene glycol process, occurring in large quantities both in the ethylene glycol production process and in the treatment of the by-product, dilute nitric acid. It is readily available, readily available, and inexpensive. Therefore, leveraging the oxidizing properties of methyl nitrite to achieve the stoichiometric oxidation of chloro-o-xylene to chlorophthalic acid offers a novel approach to producing chlorophthalic acid. This approach has significant practical implications for reducing the production cost of chlorophthalic acid and improving the comprehensive utilization of intermediates in coal-to-ethylene glycol production.

[0007] According to one aspect of the present application, a method for preparing chlorophthalic acid is provided. The method can fully utilize methyl nitrite, an important intermediate in the coal-to-ethylene glycol process. By using methyl nitrite as an oxidant, chloro-o-xylene can be efficiently converted into chlorophthalic acid under mild conditions using a non-precious metal catalyst.

[0008] Optionally, the preparation method includes: contacting a raw material liquid containing chloro-o-xylene with an oxidant and an oxidation reaction catalyst to produce an oxidation reaction to obtain the chlorophthalic acid, wherein the oxidant includes methyl nitrite and oxygen.

[0009] Optionally, the oxidant is a mixture of methyl nitrite and oxygen.

[0010] The method can fully utilize the intermediates in the coal-to-ethylene glycol process and realize the co-production with the coal-to-ethylene glycol process.

[0011] The method can realize the preparation of chlorophthalic acid by oxidizing chloro-o-xylene with methyl nitrite, and the conversion rate of chlorophthalic acid is high.

[0012] Optionally, the chloro-o-xylene is selected from one or both of 3-chlorotoluene and 4-chlorotoluene.

[0013] Optionally, the methyl nitrite gas comes from a coal-to-ethylene glycol process.

[0014] Optionally, the molar ratio of methyl nitrite to oxygen is 1 to 10;

[0015] Optionally, the molar ratio of methyl nitrite to oxygen is 2-5.

[0016] Optionally, the upper limit of the molar ratio of methyl nitrite to oxygen can be independently selected from 2:1, 5:1, and 10:1, and the lower limit can be independently selected from 1:1, 2:1, and 5:1.

[0017] Optionally, the solvent in the raw material liquid containing chloro-o-xylene is selected from at least one of acetic acid, ethanol, methanol, acetonitrile, and dimethyl phthalate, wherein the mass fraction of the chloro-o-xylene in the solvent is 5 to 50 wt%;

[0018] Optionally, the mass percentage of the chloro-o-xylene in the solvent is 10 to 40 wt %.

[0019] Optionally, the upper limit of the mass percentage of the chloro-o-xylene in the solvent can be independently selected from 10wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 50wt%, and the lower limit can be independently selected from 5wt%, 10wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%.

[0020] Optionally, the oxidation reaction catalyst is a transition metal salt.

[0021] Optionally, the oxidation reaction catalyst is a non-precious metal catalyst.

[0022] Optionally, the oxidation reaction catalyst is selected from at least one of chromium chloride, vanadium oxychloride, copper nitrate, cerium nitrate, and sodium bromide.

[0023] Optionally, the content of the oxidation reaction catalyst in the raw material liquid containing chloro-o-xylene is 1 to 50 wt %, based on the amount of chloro-o-xylene in the raw material liquid;

[0024] Optionally, the content of the oxidation reaction catalyst in the chloro-o-xylene raw material solution is 10 to 30 wt%;

[0025] Optionally, the upper limit of the content of the oxidation reaction catalyst in the chloro-o-xylene raw material solution can be independently selected from 2wt%, 6wt%, 10wt%, 20wt%, 30wt%, 40wt%, and 50wt%, and the lower limit can be independently selected from 1wt%, 2wt%, 6wt%, 10wt%, 20wt%, 30wt%, and 40wt%.

[0026] As a specific embodiment, the method for preparing chlorophthalic acid at least comprises: contacting a raw material liquid containing an oxidant of methyl nitrite and oxygen and chloro-o-xylene with an oxidation reaction catalyst in a reactor to carry out an oxidation reaction to obtain chloro-o-xylene.

[0027] Optionally, the reactor is a tank reactor;

[0028] Optionally, the reactor is a pressure-resistant autoclave reactor with mechanical stirring.

[0029] Optionally, the reaction temperature of the oxidation reaction is in the range of 100 to 220° C., the reaction pressure is in the range of 0.2 to 2.0 MPa, and the reaction time is in the range of 1.0 to 5.0 h.

[0030] Alternatively, the upper limit of the reaction temperature may be independently selected from 140°C, 180°C, 200°C, and 220°C, and the lower limit may be independently selected from 100°C, 140°C, 180°C, and 200°C;

[0031] Alternatively, the upper limit of the reaction pressure may be independently selected from 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, 1.2 MPa, 1.5 MPa, and 2.0 MPa, and the lower limit may be independently selected from 0.2 MPa, 0.4 MPa, 0.6 MPa, 0.8 MPa, 1 MPa, 1.2 MPa, and 1.5 MPa;

[0032] Optionally, the upper limit of the reaction time can be independently selected from 2h, 3h, 4h, and 5h, and the lower limit can be independently selected from 1h, 2h, 3h, and 4h;

[0033] Optionally, the reaction temperature of the oxidation reaction is in the range of 120 to 200° C., the reaction pressure is in the range of 0.2 to 1.0 MPa, and the reaction time is in the range of 2.0 to 4.0 h.

[0034] The beneficial effects of this application include:

[0035] 1) The present application provides a method for preparing chlorophthalic acid, which uses methyl nitrite and oxygen as oxidants to oxidize a raw material containing chloro-o-xylene to chlorophthalic acid through catalytic oxidation. The method is environmentally friendly, easy to operate, has a high conversion efficiency to chlorophthalic acid, and chlorophthalic acid is easily separated from the reaction raw materials. The oxidant used in the method can be methyl nitrite, an intermediate product in the coal-to-ethylene glycol process, which is convenient for use in conjunction with existing coal-to-ethylene glycol processes to achieve large-scale industrial production.

[0036] 2) The method for preparing chlorophthalic acid provided herein employs a batch reaction and a kettle-type reactor, which helps reduce production costs and facilitates industrial production. The entire reaction process is carried out under mild conditions, significantly reducing the equipment requirements for the reaction and possessing broad prospects for industrial application.

[0037] 3) As a nitrogen oxide, methyl nitrite has a more efficient oxidation performance than molecular oxygen. DETAILED DESCRIPTION

[0038] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0039] Unless otherwise specified, the raw materials and catalysts in the examples of this application were purchased from commercial sources, and all reagents used were of analytical grade.

[0040] In the embodiment, methyl nitrite gas comes from a coal-to-ethylene glycol plant; acetic acid, ethanol, methanol, acetonitrile, and dimethyl phthalate are purchased from Tianjin Komeo Company; chloro-o-xylene is purchased from Shanghai Aladdin Reagent Company; chromium chloride, vanadium trichloride, copper nitrate, cerium nitrate, and sodium bromide are purchased from Shanghai Sinopharm Reagent Company.

[0041] In the examples, the oxidation catalyst was dried under vacuum at 120° C. for 2 to 12 hours before use.

[0042] In the embodiment, the catalytic oxidation of chloro-o-xylene to produce chlorophthalic acid is carried out in a pressure-resistant autoclave reactor. The catalyst, chloro-o-xylene, and reaction solvent are added to the autoclave reactor in proportion. The reaction unit is heated to a certain temperature, and a mixed gas of methyl nitrite and oxygen is introduced to the reaction pressure to carry out the oxidation reaction. After the reaction is completed, the autoclave is vented and opened. The resulting solid-liquid two-phase product is completely dissolved and fixed to volume with acetic acid and ethyl acetate. The contents of chloro-o-xylene and chlorophthalic acid are analyzed by gas chromatography equipped with a thermal conductivity detector, and the conversion rate of chloro-o-xylene and the yield of chlorophthalic acid are calculated using an internal standard method.

[0043] The conversion rate and yield in the examples of this application are calculated as follows:

[0044] Conversion rate of chloro-o-xylene = (moles of chloro-o-xylene before reaction - moles of chloro-o-xylene after reaction) / moles of chloro-o-xylene before reaction * 100%

[0045] Yield of chlorophthalic acid = moles of chlorophthalic acid / moles of converted chloro-o-xylene * 100%

[0046] Example 1: Oxidation of chloro-o-xylene by methyl nitrite to produce chlorophthalic acid using different transition metal catalysts

[0047] Different transition metal catalysts were added into the reactor to verify the catalytic activity.

[0048] 5g of 3-chloro-o-xylene, 25g of acetic acid as solvent; oxidant composition: methyl nitrite and oxygen, 5:1 molar ratio. Reaction temperature: 180°C, reactor pressure: 0.6 MPa, reaction time: 3 hours.

[0049] The results obtained on different transition metal catalysts are shown in Table 1.

[0050] Table 1 Oxidation of chloro-o-xylene by methyl nitrite to produce chlorophthalic acid by different catalysts

[0051]

[0052] As shown in Table 1, chromium chloride, vanadium oxychloride, and sodium bromide catalysts exhibited excellent catalytic performance for the oxidation of 3-chloro-o-xylene. Other catalysts, such as copper, cerium, and their mixtures, performed poorly. Under optimized conditions, chromium chloride, vanadium oxychloride, and sodium bromide were selected as the catalysts for the reaction.

[0053] Example 2 Effect of different chromium chloride feeding amounts on the catalytic oxidation of chloro-o-xylene by methyl nitrite to produce chlorophthalic acid

[0054] Different masses of chromium chloride were added into the reactor to verify the catalytic activity.

[0055] 3-chloro-o-xylene 5 g, solvent acetic acid 25 g, vanadium oxytrichloride 0.5 g, sodium bromide 0.3 g; oxidant composition: methyl nitrite and oxygen, molar ratio 5:1. Reaction temperature 180 °C, reactor pressure 0.6 MPa; reaction time 3 hours.

[0056] The results obtained with different amounts of chromium chloride are shown in Table 2.

[0057] Table 2 Influence of the amount of chromium chloride on the catalytic oxidation of methyl nitrite to produce chlorophthalic acid from chloro-o-xylene

[0058] Example Chromium chloride, g Conversion Rate % Selectivity% Yield % 2-1 0.1 58.1 31.7 18.4 2-2 0.2 75.4 36.3 27.4 2-3 0.5 89.9 42.9 38.6 2-4 1.0 97.3 45.5 44.2 2-5 2.0 99.6 45.6 45.4

[0059] As can be seen from the results in Table 2, increasing the amount of catalyst chromium chloride increases the selectivity and conversion, but when the concentration of the substrate reaches 20%, the increase in selectivity is no longer significant.

[0060] Example 3 Influence of the amount of sodium bromide on the reaction

[0061] Different amounts of sodium bromide were added to the reactor to verify the catalytic activity.

[0062] 3-chloro-o-xylene 5 g, solvent acetic acid 25 g, vanadium oxytrichloride 0.5 g, sodium bromide 0.3 g; oxidant composition: methyl nitrite and oxygen, molar ratio 5:1. Reaction temperature 180 °C, reactor pressure 0.6 MPa; reaction time 3 hours.

[0063] Table 3 Influence of the amount of sodium bromide on the oxidation reaction

[0064] Example Sodium bromide, g Conversion Rate % Selectivity% Yield % 3-1 0.05 39.1 31.2 12.2 3-2 0.1 67.0 39.1 26.2 3-3 0.3 89.9 42.9 38.6 3-4 0.5 93.7 44.7 41.9 3-5 1 95.4 31.5 30.1

[0065] As can be seen from the results in Table 3, sodium bromide has a significant promoting effect on the reaction. In the probe reaction of the oxidation of 3-chloro-o-xylene, the selectivity and conversion increase with the amount of sodium bromide within a certain range, but when the amount of sodium bromide increases to a certain extent, the selectivity decreases.

[0066] Example 4 Influence of the content of methyl nitrite and oxygen in the oxidant on the reaction

[0067] Different molar ratios of methyl nitrite and oxygen were mixed to verify the catalytic activity.

[0068] 3-chloro-o-xylene 5 g, solvent acetic acid 25 g, vanadium oxytrichloride 0.5 g, sodium bromide 0.3 g; oxidant composition: methyl nitrite and oxygen, molar ratio 5:1. Reaction temperature 180 °C, reactor pressure 0.6 MPa; reaction time 3 hours.

[0069] The results obtained with different ester oxygen ratios are shown in Table 4.

[0070] Table 4 Results of oxidation of chloro-o-xylene to chloro-phthalic acid by methyl nitrite under different ester / oxygen ratios

[0071] Example Ester oxygen ratio Conversion rate (%) Selectivity (%) 4-1 1 93 18.6 4-2 2 90 35.1 4-3 5 89.9 42.9 4-4 10 63 46.8

[0072] As can be seen from the results in Table 4, the molar ratio of methyl nitrite to oxygen has a significant effect on the conversion rate of chloro-o-xylene and the yield of chloro-phthalic acid. As the ester / oxygen ratio increases, the conversion rate of chloro-o-xylene gradually decreases. The reason may be that the decrease in oxygen content affects the activation process of the substrate in the oxidation reaction, thereby reducing the conversion rate. In addition, as the ester / oxygen ratio increases, the yield of chloro-phthalic acid increases significantly, which indicates that compared to oxygen, methyl nitrite has higher reactivity and is more conducive to the production of target products, reducing the content of intermediate products.

[0073] Example 5 Effect of reaction temperature

[0074] The catalytic activity was verified by changing the reaction temperature.

[0075] 3-chloro-o-xylene 5 g, solvent acetic acid 25 g, vanadium oxytrichloride 0.5 g, chromium chloride 0.5 g, sodium bromide 0.3 g; the oxidant composition is methyl nitrite and oxygen, the molar ratio is 5:1. The reaction kettle pressure is 0.6 MPa, and the reaction time is 3 hours.

[0076] The reaction results under different temperatures are shown in Table 5.

[0077] Table 5 Results of oxidation of chloro-o-xylene to chloro-phthalic acid by methyl nitrite under different reaction temperatures

[0078] Example Temperature Conversion Rate % Selectivity% Yield % 5-1 100 12.5 No diacid detected 0 5-2 140 69.5 10.2 7.1 5-3 180 89.9 42.9 38.6 5-4 200 99.9 38.5 38.5

[0079] As can be seen from the results in Table 5, the reaction temperature has a significant effect on the conversion rate of chloro-o-xylene. Temperature is important for the conversion rate and selectivity of the reaction. If the temperature is too low, the conversion rate is too low, and the selectivity of the diacid is low. If the temperature is too high, excessive oxidation generates a large amount of by-products.

[0080] Example 6 Effect of reaction pressure

[0081] The catalytic activity was verified by changing the reaction pressure.

[0082] 3-chloro-o-xylene 5 g, solvent acetic acid 25 g, vanadium oxytrichloride 0.5 g, chromium chloride 0.5 g, sodium bromide 0.3 g; the oxidant composition is methyl nitrite and oxygen, the molar ratio is 5:1. The reaction temperature is 180°C, and the reaction time is 3 hours.

[0083] The reaction results under different pressures are shown in Table 6.

[0084] Table 6 Results of oxidation of chloro-o-xylene to chloro-phthalic acid by methyl nitrite under different reaction pressures

[0085] Example Pressure (MPa) Conversion Rate % Selectivity% Yield % 6-1 0.2 45.5 29.7 13.5 6-2 0.4 51.3 35.5 18.2 6-3 0.6 89.9 42.9 38.6 6-4 1.0 90.2 43.6 39.3

[0086] From the results in Table 6, it can be seen that the reaction pressure has a significant effect on the conversion rate of chloro-o-xylene. Lower pressure is not conducive to the conversion rate and selectivity of the reaction. However, when the pressure is greater than 0.6 MPa, the conversion rate and selectivity do not change much.

[0087] Example 7 Effect of reaction time

[0088] The catalytic activity was verified by varying the reaction time.

[0089] 5g of 3-chloro-o-xylene, 25g of acetic acid, 0.5g of vanadium oxytrichloride, 0.5g of chromium chloride, and 0.3g of sodium bromide; the oxidant is methyl nitrite and oxygen in a molar ratio of 5:1. The reaction temperature is 180°C and the reaction pressure is 1.0 MPa.

[0090] The reaction results under different pressures are shown in Table 7.

[0091] Table 7 Oxidation of chloro-o-xylene to chlorophthalic acid by methyl nitrite at different reaction times

[0092]

[0093] As shown in Table 7, extending the reaction time can improve the conversion of chloro-o-xylene to a certain extent. However, for the yield of chlorophthalic acid, there is a process of first increasing and then decreasing. This may be caused by the competition between the intermediate product conversion and the side reaction.

[0094] Example 8 Effect of Solvent

[0095] The catalytic activity was verified by changing the reaction solvent.

[0096] 5g of 3-chloro-o-xylene, 0.5g of vanadium oxytrichloride, 0.5g of chromium chloride, and 0.3g of sodium bromide; the oxidant is methyl nitrite and oxygen in a molar ratio of 5:1. The reaction temperature is 180°C, the reaction pressure is 1.0 MPa, and the reaction time is 3h.

[0097] The reaction results under different solvent conditions are shown in Table 8.

[0098] Table 8 Oxidation of chloro-o-xylene by methyl nitrite to produce chlorophthalic acid in different solvents

[0099]

[0100] As shown in Table 8, acetic acid exhibits relatively good catalytic effects. Other low-boiling-point solvents, such as methanol and acetonitrile, show little catalytic effect. High-boiling-point ester solvents also exhibit poor results. However, mixtures of acetic acid and high-boiling-point solvents exhibit some catalytic activity. The presence of a high-boiling-point solvent can alleviate some later separation issues.

[0101] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing chlorophthalic acid, characterized in that: The preparation method comprises: contacting a raw material liquid containing chloro-o-xylene with an oxidant and an oxidation reaction catalyst to generate an oxidation reaction to produce the chlorophthalic acid; the oxidation reaction catalyst is selected from at least one of chromium chloride, vanadium trichloride, copper nitrate, cerium nitrate, and sodium bromide; Wherein, the oxidant comprises methyl nitrite and oxygen, and the molar ratio of the methyl nitrite to oxygen is 1-10.

2. The preparation method according to claim 1, characterized in that The chloro-o-xylene is selected from one or both of 3-chloro-o-xylene and 4-chloro-o-xylene.

3. The preparation method according to claim 1, characterized in that The methyl nitrite gas comes from the coal-to-ethylene glycol process.

4. The preparation method according to claim 1, characterized in that The molar ratio of methyl nitrite to oxygen is 2 to 5.

5. The preparation method according to claim 1, characterized in that The solvent in the raw material liquid containing chloro-o-xylene is selected from at least one of acetic acid, ethanol, methanol, acetonitrile, and dimethyl phthalate, wherein the mass fraction of the chloro-o-xylene in the solvent is 5-50 wt%.

6. The preparation method according to claim 1, characterized in that The mass percentage of the chloro-o-xylene in the solvent is 10-40 wt %.

7. The preparation method according to claim 1, characterized in that The content of the oxidation reaction catalyst in the raw material liquid containing chloro-o-xylene is 1-50 wt%, based on the amount of chloro-o-xylene in the raw material liquid.

8. The preparation method according to claim 1, characterized in that The content of the oxidation reaction catalyst in the chloro-o-xylene raw material liquid is 10-30 wt%.

9. The preparation method according to claim 1, characterized in that The oxidation reaction is carried out in a tank reactor.

10. The preparation method according to claim 1, characterized in that The reaction temperature of the oxidation reaction is in the range of 100-220° C., the reaction pressure is in the range of 0.2-2.0 MPa, and the reaction time is in the range of 1.0-5.0 h.

11. The preparation method according to claim 1, characterized in that The reaction temperature of the oxidation reaction is in the range of 120-200° C., the reaction pressure is in the range of 0.2-1.0 MPa, and the reaction time is in the range of 2.0-4.0 h.

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