Method for producing purified phthalonitriles and method for purifying phthalonitriles

Abstract

There has been a need for a method for producing a purified phthalonitrile, by said method a high-purity phthalonitrile being able to be stably obtained with high yield for a long period of time, and a method for purifying a phthalonitrile. The present invention provides a method for producing a purified phthalonitrile, said method being characterized by comprising: a production reaction step wherein a reaction product gas containing a phthalonitrile and a cyanobenzamide is obtained by reacting ammonia, oxygen and xylene in the presence of a catalyst; a collection step wherein a collection liquid is obtained by bringing the reaction product gas into contact with an organic solvent that has a lower boiling point than the phthalonitrile; a separation step wherein the collection liquid is distilled by a high boiling point fraction-separating column, thereby obtaining a gas that contains the phthalonitrile and the organic solvent from the column top, while obtaining a bottom liquid that contains a cyanobenzamide from the column bottom, said bottom liquid having a phthalonitrile content of 90% by mass or less; a combustion step wherein the thus-obtained bottom liquid is subjected to combustion, while being kept in a liquid state; and a rectification step wherein a purified phthalonitrile is obtained by removing the organic solvent from the gas that has been obtained from the column top.

Description

[Technical field]

[0001] The present invention relates to a method for producing purified phthalonitriles and a method for purifying phthalonitriles, and more particularly to a method for producing purified phthalonitriles and a method for purifying phthalonitriles obtained by an ammoxidation reaction. [Background technology]

[0002] A method of reacting a carbocyclic or heterocyclic compound having an organic substituent with ammonia and an oxygen-containing gas in the presence of a catalyst is called ammoxidation. In the ammoxidation reaction, a gas-phase catalytic flow reaction is generally adopted. Nitrile compounds such as phthalonitriles are produced by the ammoxidation reaction. Phthalonitriles are useful as raw materials for the production of synthetic resins, agricultural chemicals, etc., and as intermediate raw materials for amines, isocyanates, etc. Various methods for separating phthalonitriles from the reaction product gas generated by the ammoxidation reaction have been disclosed.

[0003] For example, Non-Patent Document 1 discloses a method in which isophthalonitrile in a reaction product gas is collected with an organic solvent, the collected liquid is then fed to a solvent recovery tower, the solvent is removed from the top of the tower, crude isophthalonitrile is recovered from the bottom of the tower, and the crude isophthalonitrile is then fed to a purification tower, and purified isophthalonitrile is recovered from the top of the tower. However, the method described in Non-Patent Document 1 is prone to loss of phthalonitriles.

[0004] Patent Document 1 also discloses a method for producing isophthalonitrile, in which isophthalonitrile in a reaction product gas produced by an ammoxidation reaction is collected with an organic solvent, high boiling point impurities are separated in a first distillation step, and the organic solvent is volatilized and separated in a second distillation step to extract isophthalonitrile. However, there is room for improvement in terms of stably obtaining high purity phthalonitriles in high yield over a long period of time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4929523 [Non-patent literature]

[0006] [Non-Patent Document 1] Process Handbook published by the Japan Petroleum Institute (1976) MGC-Badger Isophthalonitril Process Summary of the Invention [Problem to be solved by the invention]

[0007] There is a demand for a method for producing purified phthalonitriles and a method for purifying phthalonitriles, which enable phthalonitriles to be obtained stably over a long period of time.

[0008] In addition, there is a need to establish a method for treating a liquid containing by-products in an ammoxidation reaction in order to stably obtain phthalonitriles over a long period of time.

[0009] Furthermore, there is a demand for a method for producing purified phthalonitriles and a method for purifying phthalonitriles, which can stably produce high-purity phthalonitriles in high yield over a long period of time. [Means for solving the problem]

[0010] The present inventors have conducted extensive research into a method for extracting purified phthalonitriles from a mixed gas of phthalonitriles and impurities produced by an ammoxidation reaction. As a result, they have found that after removing high-boiling-point impurities, phthalonitriles are separated from organic solvents and the like, and the high-boiling-point impurities are recovered in a liquid state and incinerated, thereby preventing deterioration of the bottom liquid, and thus phthalonitriles can be stably obtained for a long period of time, and preferably, while reducing the loss of phthalonitriles due to deterioration, solidification and clogging due to deterioration of the bottom liquid can be prevented, and thus high-purity phthalonitriles can be stably obtained in high yield for a long period of time, leading to the completion of the present invention.

[0011] According to the present invention, the following is provided: [1] a reaction step of reacting ammonia, oxygen and xylene in the presence of a catalyst to obtain a reaction product gas containing phthalonitriles and cyanobenzamides; a collecting step of contacting the reaction product gas with an organic solvent having a boiling point lower than that of the phthalonitriles to obtain a collected liquid; a separation step of distilling the collected liquid in a high boiling point separation column to obtain a gas containing the phthalonitriles and the organic solvent from the top of the column and a bottom liquid having a phthalonitrile content of 90 mass% or less and containing cyanobenzamides from the bottom of the column; A combustion treatment step in which the obtained column bottom liquid is combusted while still in a liquid state; and A rectification step in which the organic solvent is removed from the gas obtained from the top of the column to obtain purified phthalonitriles. A method for producing purified phthalonitriles, comprising the steps of: [2] The method for producing purified phthalonitriles according to the above [1], wherein in the separation step, the liquid residence time at the bottom of the column is 72 hours or less, the distillation pressure is 12 kPa or less, and the temperature at the bottom of the column is 200 to 230°C. [3] The steps from the production reaction step to the rectification step are carried out continuously, In the production reaction step, the reaction product gas further contains tolunitriles, The method for producing purified phthalonitriles according to the above [1] or [2], wherein the tolunitriles are recovered and used as the organic solvent in the collecting step. [4] The method for producing purified phthalonitriles according to the above [3], wherein the tolunitriles are meta-tolunitrile, para-tolunitrile, or a mixture thereof. [5] The method for producing purified phthalonitriles according to any one of the above [1] to [4], wherein the cyanobenzamides are 3-cyanobenzamide, 4-cyanobenzamide, or a mixture thereof. [6] The method for producing purified phthalonitriles according to any one of the above [1] to [5], wherein the phthalonitriles are isophthalonitrile, terephthalonitrile, or a mixture thereof. [7] a collection step of contacting a reaction product gas containing phthalonitriles and cyanobenzamides with an organic solvent having a boiling point lower than that of the phthalonitriles to obtain a collection liquid; a separation step of distilling the collected liquid in a high boiling point separation column to obtain a gas containing the phthalonitriles and the organic solvent from the top of the column and a bottom liquid having a phthalonitrile content of 90 mass% or less and containing cyanobenzamides from the bottom of the column; A combustion treatment step in which the obtained column bottom liquid is combusted while still in a liquid state; and A rectification step in which the organic solvent is removed from the gas obtained from the top of the column to obtain purified phthalonitriles. A method for purifying phthalonitriles, comprising: [8] The method for producing purified phthalonitriles according to any one of the above [1] to [6], wherein the combustion treatment step further comprises generating water vapor by utilizing heat generated by the combustion treatment. [9] The method for producing purified phthalonitriles according to the above [8], wherein the combustion treatment step further comprises transporting a column bottom liquid using a pipe, and the temperature of the pipe is maintained by using the water vapor.

[10] The method for producing purified phthalonitriles according to the above [8] or [9], wherein the steam is used as a heat source in the collection step, the separation step or the rectification step.

[11] A method for producing phthalonitriles by an ammoxidation reaction, in which a liquid to be treated containing 90 mass % or less of phthalonitriles, cyanobenzamides, and an organic solvent is subjected to combustion treatment while still in a liquid state. Effect of the Invention

[0012] According to the present invention, there are provided a method for producing purified phthalonitriles and a method for purifying phthalonitriles, which enable phthalonitriles to be stably obtained over a long period of time.

[0013] Also provided is a method for treating a by-product-containing liquid in an ammoxidation reaction, which allows phthalonitriles to be stably obtained over a long period of time.

[0014] Furthermore, according to the present invention, there are provided a method for producing purified phthalonitriles and a method for purifying phthalonitriles, which can stably produce high-purity phthalonitriles in high yield over a long period of time. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow diagram showing an example of a production method of the present invention. [Diagram 2] FIG. 1 is a diagram showing a flow of an experimental example. [Diagram 3] FIG. 4 is a flow chart showing another example of the manufacturing method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Method of producing purified phthalonitrile> One aspect of the present invention relates to a method for producing purified phthalonitriles. The method includes (1) a reaction step of obtaining a reaction product gas containing phthalonitriles and impurities by an ammoxidation reaction, (2) a collection step of contacting the reaction product gas with an organic solvent to obtain a collection liquid, (3) a separation step of distilling the collected liquid in a high boiling separation tower to obtain a gas containing phthalonitriles and an organic solvent from the top of the tower and recovering a bottom liquid containing high boiling impurities such as cyanobenzamides from the bottom of the tower, (4) a combustion treatment step of combusting the recovered bottom liquid while it is in a liquid state, and (5) a rectification step of removing the organic solvent and the like from the gas obtained from the top of the tower to obtain purified phthalonitriles. Hereinafter, the method for producing the present invention will be described with reference to FIG. 1, but the method for producing the present invention is not limited to the embodiment shown in FIG. 1.

[0017] (1) Formation reaction process In the production reaction step, an ammoxidation reaction is carried out by reacting xylene, ammonia and oxygen. In FIG. 1, the production reaction step is carried out in an ammoxidation reactor designated by A.

[0018] Since the ammoxidation reaction generates a large amount of heat of reaction, it is preferable to employ a gas-phase fluidized bed reaction in order to obtain a uniform temperature distribution in the reactor. As the reactor, various types of fluidized bed reactors can be used.

[0019] For the ammoxidation reaction, known catalysts can be used, such as a catalyst containing V-Cr-B-Mo oxides described in JP-A-11-209332 and a catalyst containing Fe-Sb-V oxides described in JP-A-9-71561.

[0020] Oxygen is generally supplied by supplying an oxygen-containing gas, such as air, which is a mixture of oxygen and other gases, to a reactor. As the oxygen-containing gas, a gas obtained by further enriching air with oxygen may be used. A diluent such as nitrogen or carbon dioxide may also be used in combination. The amount of oxygen used is preferably 3 times or more by mole, more preferably 4 to 100 times by mole, per mole of xylene. If the amount used is too small, the yield of phthalonitriles may decrease. If the amount used is too large, the space-time yield may decrease.

[0021] Xylene includes ortho-xylene, meta-xylene, and para-xylene, and meta-xylene is preferred. When ammoxidation is carried out using air, the concentration of xylene in the raw gas supplied to the reactor is preferably 0.2 to 10% by volume, more preferably 0.5 to 5% by volume. If the concentration of xylene is too high, the yield of phthalonitriles may decrease. If the concentration of xylene is too low, the space-time yield may decrease.

[0022] Ammonia of industrial grade can be used. The amount of ammonia used is preferably 2 to 20 times by mole, more preferably 6 to 15 times by mole, relative to xylene. If the amount used is too small, the yield of phthalonitriles may decrease. If the amount used is too large, the space-time yield may decrease.

[0023] Ammonia can be mixed with xylene and supplied to the reactor as shown in Figure 1. In addition, under the condition of avoiding the explosion range (combustion range), a part of the oxygen-containing gas can be further mixed with the mixed gas of ammonia and xylene and supplied.

[0024] The reaction temperature of the ammoxidation is preferably 300 to 500° C., more preferably 330 to 470° C. If the reaction temperature is too low, the conversion rate may be low, whereas if the reaction temperature is too high, the amount of by-products such as carbon dioxide gas and hydrogen cyanide may increase, resulting in a decrease in the yield of phthalonitriles.

[0025] The reaction pressure may be normal pressure, elevated pressure, or reduced pressure, but is preferably in the range of normal pressure (atmospheric pressure, usually 0.1013 MPa in absolute pressure) to 0.3 MPa, and more preferably 0.2 to 0.3 MPa.

[0026] When a catalyst is used, the contact time between the reaction gas and the catalyst depends on conditions such as the molar ratio of ammonia and oxygen-containing gas to xylene and the reaction temperature, but is usually in the range of 0.3 to 30 seconds.

[0027] (1) In the production reaction step, a reaction product gas containing phthalonitriles and impurities is obtained.

[0028] Phthalonitriles include, for example, isophthalonitrile, terephthalonitrile, or a mixture thereof.

[0029] Among the impurities contained in the reaction gas, cyanobenzamides are high-boiling impurities having a boiling point higher than that of phthalonitriles, preferably isophthalonitrile. Examples of cyanobenzamides include 3-cyanobenzamide, 4-cyanobenzamide, and mixtures thereof. Other than cyanobenzamides, meta-toluamide and 3-cyanobenzoic acid may also be contained.

[0030] The reaction product gas may contain low-boiling impurities having a boiling point lower than that of phthalonitriles, preferably isophthalonitrile. Examples of the low-boiling impurities include tolunitriles. Examples of the tolunitriles include metatolunitrile, paratolunitrile, or a mixture thereof. In addition to tolunitriles, low-boiling impurities may also be contained.

[0031] When low boiling point impurities such as tolunitriles are by-produced, it is preferable to continuously carry out the steps from (1) the reaction for production to (5) the rectification step, recover the low boiling point impurities such as tolunitriles by-produced in the reaction for production (1) and use them as an organic solvent in the collection step (2).

[0032] (2) Collection process Next, the reaction product gas is contacted with an organic solvent to obtain a collection liquid. In FIG. 1, the (2) collection step is carried out in a collection tower indicated by B. That is, the reaction product gas leaving the ammoxidation reactor A is introduced into the collection tower B and contacted with the organic solvent. An absorption section consisting of a tray or a packed bed may be installed in the upper part of the collection tower as shown in FIG. 1. In this case, the organic solvent is supplied from the upper part of the collection tower.

[0033] The organic solvent to be used has a boiling point lower than that of the phthalonitriles. At least one selected from the group consisting of alkylbenzenes, heterocyclic compounds, aromatic nitrile compounds, and heterocyclic nitrile compounds is preferred, and at least one selected from the group consisting of alkylbenzenes, heterocyclic compounds, aromatic nitrile compounds, and heterocyclic nitrile compounds, which has high solubility of the phthalonitriles and is inactive to the phthalonitriles, is more preferred.

[0034] Specific examples of the organic solvent include meta-xylene, pseudocumene, mesitylene, ethylbenzene, methylpyridine, benzonitrile, meta-tolunitrile, para-tolunitrile, cyanopyridine, etc. These organic solvents can be used alone or in combination. Meta-tolunitrile is particularly preferred.

[0035] As described above, the low-boiling impurities generated in the reaction generation step (1) may be used as the organic solvent.

[0036] The temperature of the absorption column is set so that the absorption liquid (sometimes called the liquid phase at the bottom of the column) accumulated at the bottom of the column is at or below the boiling point. More specifically, in (2) the absorption step, the composition of the liquid phase at the bottom of the column is determined by the amount of reaction product gas from the ammoxidation reactor A and the amount of organic solvent supplied to the absorption column B, and the temperature of the bottom of the absorption column is set so that the liquid phase at the bottom of the column of each composition is at or below the boiling point.

[0037] The pressure in the absorption column may be normal pressure, elevated pressure, or reduced pressure, but is usually set within the range of normal pressure to the ammoxidation reaction pressure.

[0038] In addition to the (1) production reaction step, high-boiling impurities other than the above-mentioned cyanobenzamides such as meta-toluamide and 3-cyanobenzoic acid may also be generated in the (2) collection step.

[0039] In the (2) collection step, the reaction product gas is blown into the liquid phase at the bottom of the collection tower. As a result, the phthalonitriles in the reaction product gas are dissolved in an organic solvent together with high-boiling impurities such as cyanobenzamides and, in some cases, low-boiling impurities, and are collected. On the other hand, unreacted ammonia, hydrophilic by-products such as hydrogen cyanide, carbon dioxide, water, carbon monoxide, nitrogen, oxygen, etc. are not collected in the organic solvent and are separated as exhaust gas. The exhaust gas is discharged from the top of the collection tower. The collected liquid is extracted from the bottom of the collection tower and is used in the subsequent (3) separation step.

[0040] (3) Separation process In the separation step, high boiling impurities are removed from the collected liquid. Specifically, the collected liquid is distilled in a high boiling separation tower (shown as C in Fig. 1) to obtain a gas containing phthalonitriles, an organic solvent, and, in some cases, low boiling impurities from the top of the tower, while a bottom liquid containing high boiling impurities is recovered from the bottom of the tower.

[0041] In the (3) separation step, a distillation apparatus such as a packed column, a plate column, a flash drum, etc. can be used. In addition, the (3) separation step can be carried out under reduced pressure in a batch or continuous manner.

[0042] The bottom liquid may contain phthalonitriles. Specifically, the content of phthalonitriles is 90% by mass or less. The content of phthalonitriles is preferably 60% by mass or less, more preferably 40% by mass or less, even more preferably 20% by mass or less, particularly preferably 10% by mass or less, and most preferably less than 10% by mass. The lower limit of the content of phthalonitriles is not particularly limited, but is preferably 5% by mass or more. The preferred method for determining the content is gas chromatography. The content is preferably determined after the separation step is completed.

[0043] The bottom liquid is recovered in liquid form.

[0044] The bottom liquid may contain high-boiling impurities such as cyanobenzamides and phthalonitriles, but phthalonitriles are unstable to heat in the presence of impurities such as cyanobenzamides, ammoxidation catalysts, and metals, and are prone to deterioration such as amidation and polymerization. The longer the time exposed to high temperatures and the higher the temperature exposed, the more likely and severe the deterioration will be. Therefore, in order to perform the (3) separation step quickly and at as low a temperature as possible, it is preferable to control the conditions in the high-boiling separation tower, specifically, the bottom temperature, the residence time of the bottom liquid at the bottom, and the distillation pressure. This makes it difficult for the deterioration of phthalonitriles to progress, suppresses the rise in the melting point of the components contained in the bottom liquid, and suppresses the increase in the viscosity of the bottom liquid. As a result, it is believed that the loss of phthalonitriles due to the deterioration of phthalonitriles can be suppressed. It is also believed that solidification and blockage due to the deterioration of the bottom liquid can be prevented.

[0045] Specifically, the distillation pressure of the column bottom liquid is preferably 12 kPa or less, more preferably less than 12 kPa, and particularly preferably less than 8 KPa. The lower limit of the distillation pressure is not particularly limited, but is preferably 5 kPa or more.

[0046] The temperature of the bottom liquid is preferably 200 to 230° C., more preferably 210 to 230° C., and particularly preferably 220 to 230° C. If the temperature of the bottom liquid is lower than 200° C., it is lower than the melting point of high-boiling impurities such as cyanobenzamides, and there is a risk that the bottom liquid will solidify.

[0047] The liquid residence time of the bottom liquid is preferably less than 96 hours, particularly preferably 72 hours or less. The lower limit of the liquid residence time is not particularly limited as long as it is 0 hours or more, but is preferably 12 hours or more, particularly preferably 24 hours or more, and most preferably 48 hours or more.

[0048] It is preferable that the distillation pressure of the bottom liquid is 5 to 12 kPa, the temperature is 200 to 230°C, and the liquid residence time is 12 to 72 hours, it is more preferable that the distillation pressure of the bottom liquid is 5 to less than 12 kPa, the temperature is 210 to 230°C, and the liquid residence time is 12 to 72 hours, and it is particularly preferable that the distillation pressure of the bottom liquid is 5 to less than 8 KPa, the temperature is 220 to 230°C, and the liquid residence time is 12 to 72 hours.

[0049] The liquid residence time can be calculated according to the following formula: X=B / A In the formula, X (Hr) represents the liquid residence time, and A (m 3 / Hr) is the discharge rate of the bottom liquid, and B(m 3 ) indicates the amount of liquid held at the bottom of the high boiling separation tower. As shown in Figure 3, when steam is generated using heat generated by the combustion process and this steam is supplied to the high boiling separation tower, B indicates the amount of liquid held at the bottom of the high boiling separation tower, the bottom liquid circulation pipe extending from the bottom, and the reboiler.

[0050] The liquid recovered from the bottom of the tower is sent to the (4) combustion process, while the gas recovered from the top of the tower is sent to the (5) rectification process.

[0051] (4) Combustion treatment process The resulting bottom liquid is subjected to the (4) combustion treatment step. In the present invention, the bottom liquid is transferred to an incinerator in a liquid state without solidifying or vaporizing as much as possible, and is combusted there.

[0052] The bottom liquid is maintained in a temperature range higher than the melting point and lower than the boiling point during transportation to the incinerator. As a means for maintaining the bottom liquid in this temperature range while transporting it, a known means such as heating the pipe through which the bottom liquid passes with a heater or the like may be used. Preferably, the bottom liquid is passed through the inside of a double pipe, and a temperature-maintaining fluid such as steam is passed through the outside.

[0053] It is preferable to use a pump to transport the bottom liquid and supply it to the incinerator.

[0054] Any known incinerator can be used, such as a horizontal cylindrical furnace or a vertical cylindrical furnace. The bottom liquid is preferably combusted by blowing it in liquid form into the incinerator through a nozzle.

[0055] The heat generated by the combustion process can be used to generate steam. For example, a water drum, a pipe through which water passes (hereafter referred to as the water pipe), and a steam-water drum are installed in the incinerator (boiler) that burns the bottom liquid, and steam is generated by heating the water in the water pipe with the heat generated by the combustion. The generated steam is sent out of the incinerator through an insulated steam pipe.

[0056] The generated steam can be used for various purposes. For example, by arranging a steam pipe between the combustion treatment equipment and the bottom liquid pipe and sending steam to the bottom liquid pipe, the temperature of the bottom liquid during transfer can be maintained. A double pipe is used as the bottom liquid pipe. As shown in FIG. 3, the bottom liquid pipe is structured to circulate the bottom liquid while discharging a portion of it, and it is preferable to provide a reboiler (also called a heat exchanger; omitted in FIG. 3) in the circulation section of the bottom liquid pipe and supply steam to the reboiler.

[0057] In addition, by disposing a steam pipe between the combustion treatment equipment and the collected liquid pipe extending from the collection tower B, the high boiling point separation tower C, or the rectification tower D, it is possible to use steam as a heat source in the (2) collection step, (3) separation step, or (5) rectification step.

[0058] Furthermore, by arranging a steam pipe to the pipe for purified phthalonitriles extending from the distillation column D, steam can be used as a heat source to prevent the purified phthalonitriles from solidifying below their melting point. A double pipe is used as the pipe for purified phthalonitriles. As shown in FIG. 3, the pipe for purified phthalonitriles is structured to circulate the purified phthalonitriles while discharging a part of it, and it is preferable to provide a reboiler (also called a heat exchanger, omitted in FIG. 3) in the circulation section of the pipe for purified phthalonitriles and supply steam to the reboiler.

[0059] (5) Rectification process On the other hand, referring to FIG. 1, the gas obtained from the top of the column in the separation step (3) contains not only the desired phthalonitriles but also other components such as organic solvents and low boiling point impurities. Therefore, in the rectification step (5), the phthalonitriles are separated from these other components. Specifically, distillation is performed in a rectification tower (shown as D in FIG. 1) to remove other components from the top of the column, and the desired purified phthalonitriles are recovered in liquid form from the bottom of the column.

[0060] When the gas obtained in the (3) separation step is supplied to the (5) rectification step, the phthalonitriles and other components such as the organic solvent may be supplied in a gaseous state or may be condensed and supplied in a liquid state. It is preferable to supply them in a gaseous state since this can reduce the amount of energy used.

[0061] The operating pressure of the distillation column is preferably reduced pressure. Specifically, the operating pressure of the distillation column is selected as a high vacuum condition within a range in which phthalonitriles do not precipitate in the column. For example, the pressure of the distillation column when m-tolunitrile is used as the organic solvent is preferably in the range of 5 to 10 kPa. If the following conditions are satisfied: phthalonitriles are in contact with a sufficient amount of organic solvent in the distillation column, the main component of the condensation section is the solvent and the temperature is low, there is no vapor pressure of phthalonitriles in the condensation section, and phthalonitriles do not scatter in the vacuum exhaust system, a scrubber between the condensation section and the vacuum exhaust section may not be necessary.

[0062] When tolunitriles are contained in the other components, it is preferable that the separated and recovered tolunitriles are reused as an organic solvent in the collection step (2). For reuse, it is preferable that the tolunitriles are cooled by a heat exchanger and stored in an intermediate tank as shown in FIG. 1.

[0063] <Method for refining phthalonitriles> The present invention also provides a method for purifying phthalonitriles. a collecting step of contacting a reaction product gas containing phthalonitriles and cyanobenzamides with an organic solvent having a boiling point lower than that of the phthalonitriles to obtain a collected liquid; a separation step of distilling the collected liquid in a high boiling point separation column to obtain a gas containing the phthalonitriles and the organic solvent from the top of the column and a bottom liquid having a phthalonitrile content of 90 mass% or less and containing cyanobenzamides from the bottom of the column; A combustion treatment step in which the obtained column bottom liquid is combusted while still in a liquid state; and A rectification step for removing the organic solvent from the gas to obtain purified phthalonitriles. Includes. The details of the collection step, separation step, combustion treatment step and rectification step are as described above in the description of the production method of the present invention.

[0064] <Processing method> Furthermore, the present invention provides a method for burning and treating a liquid to be treated, which contains 90% by mass or less of phthalonitriles, cyanobenzamides, and an organic solvent, while it is in a liquid state when phthalonitriles are produced by an ammoxidation reaction (hereinafter, this method may be referred to as the treatment method of the present invention). When the treatment method of the present invention is carried out during the production or purification of phthalonitriles by an ammoxidation reaction, stable production or purification can be carried out over a long period of time, and preferably stable production or purification can be carried out over a long period of time with little loss of isophthalonitriles.

[0065] The details of the ammoxidation reaction, the phthalonitriles, the cyanobenzamides and the organic solvent are as described in the description of the production method of the present invention. The details of the treatment are as described in the (4) combustion treatment step in the description of the production method of the present invention.

[0066] In one embodiment of the treatment method of the present invention, the liquid to be treated is preferably a column bottom liquid produced by the production method of the present invention or the purification method of the present invention.

[0067] The treatment method of the present invention preferably includes a separation step of distilling a collected liquid containing phthalonitriles, cyanobenzamides, and an organic solvent in a high boiling point separation column to obtain a gas containing the phthalonitriles and the organic solvent from the top of the column and a bottoms liquid having a phthalonitrile content of 90 mass% or less and containing cyanobenzamides from the bottom of the column, and a combustion treatment step of combusting the obtained bottoms liquid while it is in a liquid state. The details of the separation step and the combustion treatment step are as described above in the description of the production method of the present invention.

[0068] In the separation step, the content of phthalonitriles in the column bottom liquid is preferably 60% by mass or less, more preferably 40% by mass or less, even more preferably 20% by mass or less, particularly preferably 10% by mass or less, and most preferably less than 10% by mass. The lower limit of the content of phthalonitriles is not particularly limited, but is preferably 5% by mass or more. The suitable measurement conditions and method are as described in the description of the production method of the present invention.

[0069] In the separation step, the distillation pressure of the column bottom liquid is preferably 12 kPa or less, more preferably less than 12 kPa, and particularly preferably less than 8 KPa. The lower limit of the distillation pressure is not particularly limited, but is preferably 5 kPa or more.

[0070] In the separation step, the temperature of the column bottom liquid is preferably from 200 to 230°C, more preferably from 210 to 230°C, and particularly preferably from 220 to 230°C.

[0071] In the separation step, the liquid residence time of the bottom liquid is preferably less than 96 hours, particularly preferably 72 hours or less. The lower limit of the liquid residence time is not particularly limited as long as it is 0 hours or more, but is preferably 12 hours or more, particularly preferably 24 hours or more, and most preferably 48 hours or more.

[0072] In the separation step, the distillation pressure of the bottom liquid is preferably 5 to 12 kPa, the temperature is 200 to 230°C, and the liquid residence time is 12 to 72 hours, more preferably the distillation pressure of the bottom liquid is 5 to less than 12 kPa, the temperature is 210 to 230°C, and the liquid residence time is 12 to 72 hours, and particularly preferably the distillation pressure of the bottom liquid is 5 to less than 8 KPa, the temperature is 220 to 230°C, and the liquid residence time is 12 to 72 hours. EXAMPLES

[0073] In the following, the present invention will be described in detail with reference to experimental examples, although the present invention is not limited to these examples.

[0074] [Experimental Example 1] Using a mixture containing 73.5 wt% m-tolunitrile, 25 wt% isophthalonitrile, 1 wt% cyanobenzamide (3-cyanobenzamide) and 0.5 wt% other components, distillation purification and separation of isophthalonitrile was performed according to the flow shown in Figure 2. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 12 kPa and a bottom temperature of 200° C. The concentration of isophthalonitrile in the bottom liquid was 55.7 wt%, cyanobenzamide was 26.7 wt%, and others were 17.6 wt%. The bottom liquid was kept at 200°C for 72 hours and still retained its fluidity. The bottom liquid was then pumped through a double-walled pipe (outer: steam at about 230°C) and blown into a horizontal cylindrical furnace with a nozzle for incineration. There was no blockage in the pipes, and incineration was possible.

[0075] [Experimental Example 2] Using a mixed liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 8 kPa and a bottom temperature of 215° C. The concentration of isophthalonitrile in the bottom liquid was 35.7 wt%, cyanobenzamide was 33.1 wt%, and others were 31.2 wt%. The bottom liquid was kept at 215°C for 72 hours, and still retained its fluidity. Thereafter, the bottom liquid was sent to an incinerator in the same manner as in Experimental Example 1, and was incinerated without any clogging of the piping.

[0076] [Experimental Example 3] Using a mixed liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 5 kPa and a bottom temperature of 230° C. The concentration of isophthalonitrile in the bottom liquid was 7.5 wt%, cyanobenzamide was 56.7 wt%, and others were 35.8 wt%. The bottom liquid was kept at 230°C for 72 hours, and still retained its fluidity. Thereafter, the bottom liquid was sent to an incinerator in the same manner as in Experimental Example 1, and was incinerated without any clogging of the piping.

[0077] [Comparative Example 1] Using a mixed liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 12 kPa and a bottom temperature of 200° C. The concentration of isophthalonitrile in the bottom liquid was 55.7 wt%, cyanobenzamide was 26.7 wt%, and others were 17.6 wt%. When the bottom liquid was kept at 200°C for 96 hours, it lost its fluidity. An attempt was made to send it to an incinerator in the same manner as in Experimental Example 1, but this was not possible.

[0078] [Comparative Example 2] Using a mixed liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 8 kPa and a bottom temperature of 215° C. The concentration of isophthalonitrile in the bottom liquid was 35.7 wt%, cyanobenzamide was 33.1 wt%, and others were 31.2 wt%. When the bottom liquid was kept at 215°C for 96 hours, it lost its fluidity. An attempt was made to send it to an incinerator in the same manner as in Experimental Example 1, but this was not possible.

[0079] [Comparative Example 3] Using a mixed liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle of the high bp separation column. The distillation conditions were a top pressure of 5 kPa and a bottom temperature of 230° C. The concentration of isophthalonitrile in the bottom liquid of the high bp separation column was 7.5 wt%, cyanobenzamide was 56.7 wt%, and others were 35.8 wt%. When the bottom liquid was kept at 230°C for 96 hours, it lost its fluidity. An attempt was made to send it to an incinerator in the same manner as in Experimental Example 1, but this was not possible.

[0080] In Experimental Examples 1 to 3, the bottom liquid maintained its fluidity even after the retention. This indicates that the melting point of the bottom liquid was lower than the temperature of the bottom liquid. The bottom liquid that maintains its fluidity can be sent to an incinerator. As a result, it is possible to avoid clogging of the piping and to stably produce phthalonitriles over a long period of time, as well as stably purify phthalonitriles over a long period of time. On the other hand, in Comparative Examples 1 to 3, the bottom liquid after retention lost fluidity. This indicates that the melting point of the bottom liquid was higher than the temperature of the bottom liquid. As a result, the piping was clogged, making it impossible to send the bottom liquid to the incinerator.

[0081] The compositions and melting points of the column bottom liquid before and after retention in Experimental Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 1 below. The composition of the bottom liquid before and after retention was measured by gas chromatography. Specifically, the bottom liquid was sampled and cooled to room temperature, then crushed and dissolved in a solvent, and analyzed by gas chromatography. Shimadzu GC-2025 (Shimadzu Corporation) was used as the measuring device. A Flame Ionization Detector (FID) was used as the detector, and helium gas was used as the carrier gas. [Table 1]

[0082] It is apparent from Table 1 that the bottom liquids of Experimental Examples 1 to 3 were more inhibited from altering due to retention than the bottom liquids of Comparative Examples 1 to 3.

[0083] [Reference example 1] Using a liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 8 kPa and a bottom temperature of 215° C. The concentration of isophthalonitrile in the bottom liquid was 35.7 wt%, cyanobenzamide was 33.1 wt%, and others were 31.2 wt%. The bottom liquid was kept at 215°C for 72 hours and still fluid. However, when the bottom liquid was removed from the system, the high boiling point liquid solidified and became difficult to handle.

[0084] [Reference example 2] Using a mixed liquid having the same composition as in Experimental Example 1, isophthalonitrile was purified and separated by distillation according to the flow shown in FIG. The above mixture was supplied to the middle stage of the high boiling separation column. The distillation conditions were a top pressure of 8 kPa and a bottom temperature of 215° C. The concentration of isophthalonitrile in the bottom liquid was 35.7 wt%, cyanobenzamide was 33.1 wt%, and others were 31.2 wt%. The high boiling liquid maintained its fluidity at the bottom of the column at a temperature of 215°C. When the bottom liquid was quickly removed from the system, it solidified and became difficult to handle.

[0085] When phthalonitriles containing tolunitriles as the main low-boiling impurities and cyanobenzamides as the main high-boiling impurities are distilled to obtain purified phthalonitriles, the bottom liquid of the distillation column can be prevented from solidifying and clogging. Therefore, the method of the present invention can stably obtain high-quality isophthalonitrile for a long period of time. Therefore, the method of the present invention can produce phthalonitriles industrially in an extremely advantageous manner, and the present invention is of great industrial significance. [Explanation of symbols]

[0086] A: Ammoxidation reactor, B: Collection tower, C: High boiling point separation tower, D: Rectification tower

Claims

1. a reaction step of reacting ammonia, oxygen and xylene in the presence of a catalyst to obtain a reaction product gas containing phthalonitriles and cyanobenzamides; a collecting step of contacting the reaction product gas with an organic solvent having a boiling point lower than that of the phthalonitriles to obtain a collected liquid; a separation step of distilling the collected liquid in a high boiling separation column without adding any aromatic hydrocarbon liquid having an initial boiling point of 299 to 399°C, thereby obtaining a gas containing the phthalonitriles and the organic solvent from the top of the column and obtaining a column bottom liquid having a phthalonitrile content of more than 0 mass% and not more than 90 mass% and containing cyanobenzamides from the bottom of the column; A combustion treatment step in which the obtained column bottom liquid is combusted while still in a liquid state; and A rectification step in which the organic solvent is removed from the gas obtained from the top of the column to obtain purified phthalonitriles. Including, A method for producing purified phthalonitriles, characterized in that the content of components other than phthalonitriles and cyanobenzamides in the column bottom liquid is more than 0 mass% and 64.7 mass% or less.

2. The method for producing purified phthalonitriles according to claim 1, wherein in the separation step, the liquid residence time at the bottom of the column is 72 hours or less, the distillation pressure is 12 kPa or less, and the temperature at the bottom of the column is 200 to 230° C.

3. The steps from the production reaction step to the rectification step are carried out continuously, In the production reaction step, the reaction product gas further contains tolunitriles, The method for producing purified phthalonitriles according to claim 1 or 2, wherein the tolunitriles are recovered and used as the organic solvent in the collecting step.

4. The method for producing purified phthalonitriles according to claim 3, wherein the tolunitriles are metatolunitrile, paratolunitrile, or a mixture thereof.

5. The method for producing purified phthalonitriles according to any one of claims 1 to 4, wherein the cyanobenzamides are 3-cyanobenzamide, 4-cyanobenzamide, or a mixture thereof.

6. The method for producing purified phthalonitriles according to any one of claims 1 to 5, wherein the phthalonitriles are isophthalonitrile, terephthalonitrile, or a mixture thereof.

7. a collecting step of contacting a reaction product gas containing phthalonitriles and cyanobenzamides with an organic solvent having a boiling point lower than that of the phthalonitriles to obtain a collected liquid; a separation step of distilling the collected liquid in a high boiling separation column without adding any aromatic hydrocarbon liquid having an initial boiling point of 299 to 399°C, thereby obtaining a gas containing the phthalonitriles and the organic solvent from the top of the column and obtaining a column bottom liquid having a phthalonitrile content of more than 0 mass% and not more than 90 mass% and containing cyanobenzamides from the bottom of the column; A combustion treatment step in which the obtained column bottom liquid is combusted while still in a liquid state; and A rectification step in which the organic solvent is removed from the gas obtained from the top of the column to obtain purified phthalonitriles. Including, A method for purifying phthalonitriles, characterized in that the content of components other than phthalonitriles and cyanobenzamides in the column bottom liquid is more than 0 mass% and 64.7 mass% or less.

8. The method for producing purified phthalonitriles according to any one of claims 1 to 6, wherein the combustion treatment step further comprises generating water vapor by utilizing heat generated by the combustion treatment.

9. The method for producing purified phthalonitriles according to claim 8, wherein the combustion treatment step further comprises transferring a bottom liquid through a pipe, and the temperature of the pipe is maintained by using the steam.

10. The method for producing purified phthalonitriles according to claim 8 or 9, wherein the steam is used as a heat source in the collection step, the separation step, or the rectification step.

11. A method for producing phthalonitriles by an ammoxidation reaction, comprising the steps of: burning a liquid to be treated, the liquid containing more than 0 mass % but not more than 90 mass % of phthalonitriles, cyanobenzamides, and an organic solvent while the liquid is in a liquid state; The liquid to be treated is a column bottom liquid obtained by the following steps, in which the content of components other than phthalonitriles and cyanobenzamides is more than 0 mass% and 64.7 mass% or less. a reaction step of reacting ammonia, oxygen and xylene in the presence of a catalyst to obtain a reaction product gas containing phthalonitriles and cyanobenzamides; a collecting step of contacting the reaction product gas with an organic solvent having a boiling point lower than that of the phthalonitriles to obtain a collected liquid; a separation step of distilling the collected liquid in a high boiling point separation tower without adding any aromatic hydrocarbon liquid having an initial boiling point of 299 to 399°C, to obtain a gas containing the phthalonitriles and the organic solvent from the tower top, and obtaining a tower bottom liquid having a phthalonitrile content of more than 0 mass% and not more than 90 mass% and containing cyanobenzamides from the tower bottom.

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