Method for producing xylylenediamine

Abstract

The method for producing a xylylenediamine comprises: a first hydrogenation step for supplying dicyanobenzene and a hydrogen-containing gas G1 to a reactor in the presence of a catalyst having hydrogenation capacity and obtaining xylylenediamine by hydrogenation of the dicyanobenzene; a treatment step for interrupting hydrogenation, supplying a hydrogen-containing gas G2 containing a recycled gas to the reactor, and bringing the catalyst that has undergone the first hydrogenation step into contact with the hydrogen-containing gas G2; and a second hydrogenation step for resuming hydrogenation in the presence of the catalyst that has undergone the treatment step. The recycled gas is obtained by removing at least a part of the organic compounds from exhaust gas discharged from the reactor after the contact.

Description

Method for producing xylylenediamine

[0001] The present invention relates to a method for producing xylylenediamine.

[0002] Xylylenediamine is useful as a raw material for polyamide resins, curing agents, etc., and as an intermediate raw material for isocyanate resins, etc. A typical method for producing xylylenediamine is to hydrogenate dicyanobenzene in the presence of a catalyst. As a specific example, Patent Document 1 proposes that a catalyst whose activity has decreased due to use in the hydrogenation reaction of dicyanobenzene is regenerated by the following steps (1) and (2), and then reused as a catalyst in a reaction system: (1) a step of contacting the catalyst with a hydrogen-containing gas for one hour or more at a temperature in the range of 140 to 200°C, with an average temperature of 180°C or less; and (2) a step of further contacting the contact-treated catalyst with a hydrogen-containing gas at a temperature in the range of 200 to 500°C.

[0003] Patent No. 4561063

[0004] The method described in Patent Document 1 is advantageous because it allows for the reuse of catalysts with reduced activity, thereby enabling a significant reduction in catalyst costs. However, Patent Document 1 does not fully consider the composition of the gas used to treat the catalyst, and therefore there is still room for improvement in terms of production efficiency.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing xylylenediamine in the hydrogenation of dicyanobenzene, which allows the catalyst to be used for a long period of time and has excellent production efficiency.

[0006] As a result of extensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by treating the exhaust gas during the catalyst regeneration process and then contacting it with a used catalyst, and thus completed the present invention.

[0007] That is, the present invention encompasses the following aspects: [1] A method for producing xylylenediamine, comprising: a first hydrogenation step of supplying dicyanobenzene and a hydrogen-containing gas G1 to a reactor in the presence of a catalyst having hydrogenation ability and hydrogenating the dicyanobenzene to obtain xylylenediamine; a treatment step of interrupting the hydrogenation, supplying a hydrogen-containing gas G2 containing a recycle gas to the reactor, and contacting the catalyst that has undergone the first hydrogenation step with the hydrogen-containing gas G2; and a second hydrogenation step of resuming the hydrogenation in the presence of the catalyst that has undergone the treatment step, wherein the recycle gas is obtained by removing at least a portion of the organic compounds from the exhaust gas that has been contacted and is discharged from the reactor. [2] A method for producing xylylenediamine according to [1], wherein the recycle gas is obtained by removing at least a portion of the organic compounds from the exhaust gas using a gas-liquid separator. [3] A method for producing xylylenediamine according to [2], wherein the temperature at which the exhaust gas is supplied to the gas-liquid separator is 5°C to 80°C. [4] The method for producing xylylenediamine according to any one of [1] to [3], wherein in the treatment step, the contact temperature between the hydrogen-containing gas G2 and the catalyst that has undergone the first hydrogenation step is 200°C to 500°C. [5] The method for producing xylylenediamine according to any one of [1] to [4], wherein the hydrogen concentration of the hydrogen-containing gas G2 is 1 vol% or more. [6] The method for producing xylylenediamine according to any one of [1] to [5], wherein in the treatment step, at least a portion of the catalyst is subjected to washing with a solvent before the hydrogen-containing gas G2 is supplied to the reactor. [7] The method for producing xylylenediamine according to any one of [1] to [6], wherein the reactor is a fixed-bed reactor. [8] The method for producing xylylenediamine according to any one of [1] to [7], wherein the catalyst contains nickel and / or cobalt.

[0008] According to the present invention, there can be provided a method for producing xylylenediamine in which the catalyst can be used for a long period of time in the hydrogenation of dicyanobenzene and which is excellent in production efficiency.

[0009] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be carried out by appropriately modifying it within the scope of its gist.

[0010] <Method for Producing Xylylenediamine> The method for producing xylylenediamine of this embodiment (hereinafter also referred to as the "production method of this embodiment") includes: a first hydrogenation step in which dicyanobenzene and a hydrogen-containing gas G1 are supplied to a reactor in the presence of a catalyst having hydrogenation ability (hereinafter also simply referred to as the "catalyst") and xylylenediamine is obtained by hydrogenating the dicyanobenzene; a treatment step in which the hydrogenation is interrupted, a hydrogen-containing gas G2 containing a recycle gas is supplied to the reactor, and the catalyst that has undergone the first hydrogenation step is brought into contact with the hydrogen-containing gas G2; and a second hydrogenation step in which the hydrogenation is resumed in the presence of the catalyst that has undergone the treatment step. The recycle gas is obtained by removing at least a portion of the organic compounds from the exhaust gas discharged from the reactor after the contact. Because the production method of this embodiment is configured in this manner, the catalyst can be used for a long period of time in the hydrogenation of dicyanobenzene and production efficiency is excellent.

[0011] (First hydrogenation step) In the first hydrogenation step, dicyanobenzene and hydrogen-containing gas G1 are supplied to a reactor in the presence of a catalyst having hydrogenation ability, and xylylenediamine is obtained by hydrogenating the dicyanobenzene. The method and reaction conditions for such hydrogenation (hydrogenation reaction) are not particularly limited, and various known methods and conditions can be adopted, but typical examples will be described below.

[0012] Dicyanobenzene refers to a compound in which at least two hydrogen atoms of benzene are substituted with nitrile groups, and examples thereof include isophthalonitrile and terephthalonitrile. Furthermore, compounds in which, in addition to the substitution with nitrile groups, further substitution is made with a halogen atom such as fluorine or chlorine, an alkyl group such as methyl or ethyl, or an alkoxy group such as methoxy or ethoxy can also be used, such as 2-chloroterephthalonitrile, 5-methylisophthalonitrile, and 4-methylisophthalonitrile. These compounds can be hydrogenated to obtain the corresponding xylylenediamine.

[0013] In this embodiment, the hydrogenation reaction is preferably carried out under liquid-phase conditions, and a reaction solvent is preferably used in this case. The reaction solvent is not particularly limited, and various solvents that are stable under the hydrogenation reaction conditions can be used. Specific examples include hydrocarbon solvents such as toluene, xylene, and trimethylbenzene; ether solvents such as tetrahydrofuran and dioxane; lower aliphatic amide solvents such as dimethylformamide and dimethylacetamide; alcohol solvents such as methanol, ethanol, and propanol; and ammonia. Two or more of these solvents may be selected and used in combination. Because the use of ammonia can increase the yield of xylylenediamine, it is preferable to select ammonia as part of the solvent. The amount of the solvent used is not particularly limited, but is preferably 1 to 99 parts by mass, more preferably 1.5 to 99 parts by mass, per part by mass of dicyanobenzene.

[0014] The hydrogen-containing gas G1 used in the hydrogenation reaction of dicyanobenzene may contain, in addition to hydrogen, impurities that are not involved in the reaction, such as methane and nitrogen. However, from the viewpoint that reducing the impurity concentration makes it easier to ensure the necessary hydrogen partial pressure and avoids increasing the total reaction pressure, the hydrogen concentration is preferably 50 mol% or more.

[0015] In this embodiment, the catalyst having hydrogenation ability may be a known supported or unsupported metal catalyst, a Raney catalyst, or other hydrogenation catalyst. A catalyst containing at least one metal selected from nickel, cobalt, palladium, ruthenium, and rhodium as the active metal component is preferred, and among these, a catalyst containing nickel and / or cobalt is more preferred. In the case of a supported catalyst, examples of the carrier used include alumina, silica, titania, and zirconia. If necessary, the catalyst may be modified by adding at least one component selected from the group consisting of Li, Na, K, Rb, Cs, Be, Ca, Ba, Ti, Cu, Cr, Zn, Mn, Mg, Fe, Ga, Ge, Nb, Ir, Pt, Bi, Al, Si, In, Sr, Ce, and Mo.

[0016] In this embodiment, in order to maximize the performance of the catalyst, the catalyst may be subjected to a reduction treatment (activation treatment) before being used for hydrogenation. Such reduction treatment may be carried out under various known conditions.

[0017] In this embodiment, an additive may be added during the hydrogenation reaction for the purpose of accelerating the reaction, improving the yield, etc. Examples of the additive include hydroxides and alcoholates of alkali metals or alkaline earth metals, and specific examples include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc.

[0018] The hydrogenation reaction may be carried out in either a fixed bed or a suspension bed, and may be either a batch or continuous system, and a reactor corresponding to such a system can be used. In this embodiment, a fixed bed continuous flow system is preferred due to its simplicity, and a reactor corresponding to such a system is preferably used. That is, in this embodiment, the reactor is preferably a fixed bed reactor. The reaction temperature of the hydrogenation reaction is preferably 20 to 250°C, more preferably 20 to 200°C, and the hydrogen pressure is preferably 0.5 to 30 MPa, more preferably 1 to 20 MPa. The reaction temperature of the hydrogenation reaction can be specified as the catalyst layer temperature during the reaction. When hydrogenation is carried out using a suspension bed, the amount of catalyst used is preferably 0.1 to 200 parts by mass per 100 parts by mass of the raw material dicyanobenzene. When hydrogenation is carried out using a fixed bed, the raw material dicyanobenzene is preferably supplied at a rate of 0.01 to 1,000 parts by mass / hour per 100 parts by mass of the catalyst.

[0019] In the hydrogenation reaction, from the viewpoint of producing xylylenediamine more efficiently, it is preferable to increase the degree of progress of the hydrogenation reaction of nitrile groups to aminomethyl groups, and it is preferable to select reaction conditions that maintain low concentrations of dicyanobenzene and cyanobenzylamine in the liquid obtained after the hydrogenation reaction. Specifically, the amount of cyanobenzylamine in the reaction product obtained after the hydrogenation reaction is preferably maintained at 5.0 mass% or less, more preferably 1.0 mass% or less, and even more preferably 0.2 mass% or less. The reaction product after removing the solvent from the reaction liquid discharged from the reactor is preferably within the above range. Furthermore, the conversion of dicyanobenzene is preferably 99.50% or more, more preferably 99.90% or more, and even more preferably 99.95% or more.

[0020] (Treatment Step) In the treatment step, the hydrogenation is interrupted, and a hydrogen-containing gas G2 containing a recycled gas is supplied to the reactor, and the catalyst that has undergone the first hydrogenation step is brought into contact with the hydrogen-containing gas G2. In this embodiment, when the catalyst is subjected to hydrogenation, its activity decreases over time. That is, in this embodiment, the catalyst immediately after the first hydrogenation step is treated as having decreased activity compared to the catalyst immediately before being subjected to the first hydrogenation step. In this embodiment, by carrying out the treatment step, the catalyst that has undergone the first hydrogenation step is brought into contact with the hydrogen-containing gas G2, thereby reactivating the catalyst (also referred to herein simply as "regeneration" or "regeneration treatment"). This not only makes it possible to achieve the desired reaction results in the subsequent second hydrogenation step, but also results in excellent production efficiency. The inventors speculate as follows as to the reason for this, but the present invention is not limited to the following content.

[0021] As described above, the catalyst in this embodiment loses activity after the first hydrogenation step. Therefore, in order to continue producing xylylenediamine without deteriorating the reaction results, it is important to perform a catalyst regeneration treatment. Reasons for the decline in catalyst activity include the accumulation of high-boiling compounds generated by the hydrogenation reaction on the catalyst. In the regeneration treatment, the catalyst is regenerated by contacting a hydrogen-containing gas with the catalyst, reducing the carbon content of the high-boiling compounds through hydrocracking, vaporizing them, and removing them. Thus, in addition to the hydrogen used in the hydrogenation performed to produce xylylenediamine, hydrogen is also required for hydrocracking in the regeneration treatment. Therefore, there is room for improving production efficiency by reducing the amount of hydrogen used in the latter treatment. The present inventors investigated the direct recycling of the hydrogen-containing gas (exhaust gas) used in the regeneration treatment, but found that this would not maintain the desired reaction results. This is thought to be because the exhaust gas contains organic compounds such as benzene (typically liquid organic compounds), and when the exhaust gas is re-supplied into the reactor, these organic compounds decompose on the catalyst surface, raising the catalyst layer temperature and adversely affecting catalytic performance. Based on the above, the inventors conducted further studies and found that by removing the organic compounds from the exhaust gas and reusing it as a recycled gas, the catalyst can be regenerated while reducing the amount of hydrogen used, thereby maintaining the desired reaction results while improving production efficiency. As described above, the production method of this embodiment employs a two-stage hydrogenation reaction and includes a treatment step between the first and second hydrogenation steps. This eliminates the need to change the hydrogenation conditions in the second hydrogenation reaction from those in the first hydrogenation step, allowing xylylenediamine to be produced continuously over a long period of time and with excellent production efficiency.

[0022] In the treatment step, it is preferable to wash at least a part of the catalyst with a solvent before supplying the hydrogen-containing gas G2 to the reactor. When such washing is performed, the regeneration treatment of the catalyst in the treatment step tends to be further promoted. From the same viewpoint, it is preferable to separate and remove liquid components present in the reactor before washing the catalyst.

[0023] In the present embodiment, the timing to interrupt the hydrogenation can be determined taking into consideration the composition of the reaction liquid (the reaction liquid discharged from the reactor after removing the solvent) and the state of the reactor, but is not limited to the following. For example, the timing can be determined based on the fact that, in the first hydrogenation step, the amount of 3-cyanobenzylamine in the reaction liquid has reached a predetermined amount or more, or the differential pressure between the inlet and outlet of the catalyst layer in the reactor has reached a predetermined value or more.

[0024] In the treatment step, the contact temperature between the hydrogen-containing gas G2 and the catalyst that has undergone the first hydrogenation step is preferably 200°C to 500°C. When the contact temperature is 200°C or higher, the effect of the regeneration treatment tends to be enhanced, and when the contact temperature is 500°C or lower, temperature-related catalyst deterioration tends to be prevented. The contact temperature in the treatment step refers to the steady-state temperature after the catalyst temperature rise process described below, and can be specified as the catalyst layer temperature in the reactor. Regarding the contact temperature and the treatment time length in this embodiment, taking into consideration the type of catalyst and the degree of activity decline, it is preferable to extend the treatment time, particularly when the degree of activity decline of the catalyst that has undergone the first hydrogenation step is significant. In this embodiment, it is preferable to maintain a contact temperature of 200°C to 500°C for 3 to 300 hours.

[0025] In the treatment step, the temperature rise rate of the catalyst during contact of the hydrogen-containing gas G2 with the catalyst that has undergone the first hydrogenation step is preferably 40°C / min or less (including zero), more preferably 30°C / min or less, and even more preferably 20°C / min or less. In this embodiment, as described above, the contact temperature is preferably 200 to 500°C, but the hydrogen-containing gas G2 can also be contacted with the catalyst at less than 200°C before reaching that temperature range. In this case, too, it is preferable to control the temperature rise rate of the catalyst to 40°C / min or less.

[0026] In the treatment step, the supply rate of the hydrogen-containing gas G2 is not particularly limited and can be adjusted appropriately depending on the type of catalyst, its usage history, and the catalyst temperature. From the viewpoint of appropriately controlling the rate of temperature rise of the catalyst, the supply rate of the hydrogen-containing gas G2 in the treatment step is preferably 0.001 to 2000 NL / h (N: standard condition (0°C, 1 atmosphere)) per 1 kg of catalyst, and more preferably 0.001 to 1000 NL / h.

[0027] The hydrogen-containing gas G2 may contain any component other than hydrogen, for example, an inert impurity that does not interfere with catalyst regeneration. Examples of such impurities include, but are not limited to, methane and nitrogen. The hydrogen pressure of the hydrogen-containing gas G2 is preferably 0.01 kPa to 30 MPa, and more preferably 0.1 kPa to 15 MPa. When the hydrogen partial pressure is set low (for example, 0.1 MPa or less), it is convenient and preferable to use an inert diluent gas such as nitrogen.

[0028] In the treatment step, the contact temperature is preferably set to 200 to 500°C, but the following treatment (hereinafter also referred to as "pretreatment") may be carried out before setting the temperature within this range. That is, the hydrogen-containing gas G2 may be contacted with the catalyst that has been subjected to the first hydrogenation step at a temperature in the range of 140 to 200°C with an average temperature of 180°C or less for one hour or more. In this case, the catalyst tends to be regenerated more efficiently, and heat generation and gas generation due to the regeneration treatment tend to be reduced.

[0029] The average temperature in the pretreatment refers to the time-average temperature in the pretreatment carried out at 140 to 200°C, and is defined as the value obtained by dividing the temperature integrated over time by the treatment time length. When carrying out the pretreatment, the temperature may be changed during the treatment within the range of 140 to 200°C, for example, a constant temperature holding step and a temperature increase or decrease step may be combined. The treatment time for the pretreatment may be 1 to 20 hours.

[0030] In the pretreatment, the rate of increase in catalyst temperature when hydrogen-containing gas G2 is supplied is preferably 40°C / min or less (including zero), more preferably 30°C / min or less, and particularly preferably 20°C / min or less.

[0031] In the pretreatment, the supply rate of the hydrogen-containing gas G2 is not particularly limited and can be adjusted appropriately depending on the type of catalyst, its usage history, and the catalyst temperature. From the viewpoint of appropriately controlling the rate of temperature rise of the catalyst, the supply rate of the hydrogen-containing gas G2 in the pretreatment is preferably 0.001 to 2000 NL / h (N: standard condition (0°C, 1 atmosphere)) per 1 kg of catalyst, and more preferably 0.001 to 1000 NL / h.

[0032] The composition of the hydrogen-containing gas G2 when the contact temperature is set to 200 to 500° C. may be the same as or different from the composition of the hydrogen-containing gas G2 during pretreatment.

[0033] The recycled gas in the treatment step is obtained by removing at least a portion of the organic compounds from the exhaust gas discharged from the reactor after the contact. The operation for removing at least a portion of the organic compounds from the exhaust gas is not particularly limited, but examples include adsorption, absorption, and gas-liquid separation. As described above, the organic compounds in this embodiment may typically contain liquid organic compounds, and therefore a gas-liquid separator is preferably used. That is, in this embodiment, from the viewpoint of increasing the efficiency of removing organic compounds from the exhaust gas while avoiding excessive equipment burden, it is preferable to remove at least a portion of the organic compounds from the exhaust gas using a gas-liquid separator to obtain the recycled gas. From the same viewpoint as above, in this embodiment, the temperature of the exhaust gas supplied to the gas-liquid separator is preferably 5°C to 80°C. The gas-liquid separator is not particularly limited, and various known separators can be used.

[0034] The hydrogen-containing gas G2 in the treatment step is not particularly limited as long as it contains a recycled gas, and can be adjusted to various compositions. In this embodiment, from the viewpoint of improving the efficiency of the catalyst regeneration treatment, the hydrogen concentration of the hydrogen-containing gas G2 is preferably 1 vol% or more. Furthermore, in this embodiment, the upper limit of the hydrogen concentration of the hydrogen-containing gas G2 is not particularly limited, and may be, for example, 90 vol% or less.

[0035] In this embodiment, the timing to terminate the treatment process can be determined taking into consideration the degree of removal of high-boiling-point compounds that may accumulate on the catalyst, but is not limited to the following. For example, the timing can be determined based on the fact that the hydrogen concentration of the hydrogen-containing gas G2 and the hydrogen concentration of the exhaust gas have become approximately the same during the treatment process. In other words, when the hydrogen concentration of the hydrogen-containing gas G2 and the hydrogen concentration in the exhaust gas become approximately the same, it suggests that the high-boiling-point compounds that may accumulate on the catalyst have already been sufficiently removed.

[0036] (Second Hydrogenation Step) In the second hydrogenation step, the hydrogenation is resumed in the presence of the catalyst that has undergone the treatment step. In this embodiment, the catalyst has been reactivated by undergoing the treatment step, and therefore the desired reaction results can be achieved in the second hydrogenation step as in the first hydrogenation step. The hydrogenation conditions in the second hydrogenation step can be the same as those described in the first hydrogenation step. Since the second hydrogenation step is a step subsequent to the treatment step, the catalyst can be said to be in a sufficiently reduced state, and therefore, in the second hydrogenation step, it is preferable to carry out hydrogenation without performing the reduction treatment (activation treatment) that can be optionally performed in the first hydrogenation step.

[0037] As described above, the production method of this embodiment may include the first hydrogenation step, the treatment step, and the second hydrogenation step, and may optionally include various additional steps.

[0038] In the production method of this embodiment, as an additional step subsequent to the first hydrogenation step, the treatment step, and the second hydrogenation step, an additional treatment step may be carried out under the same conditions as the treatment step in order to continue the production of xylylenediamine for an even longer period of time, and then an additional hydrogenation step may be carried out under the same conditions as the first hydrogenation step. As a specific example, the production method of this embodiment may include, as an additional step subsequent to the first hydrogenation step, the treatment step, and the second hydrogenation step, an additional treatment step in which the hydrogenation in the second hydrogenation step is interrupted, a hydrogen-containing gas containing the above-mentioned recycle gas is supplied to a reactor, and the hydrogen-containing gas is brought into contact with the catalyst that has undergone the second hydrogenation step, and an additional hydrogenation step in which the hydrogenation is resumed in the presence of the catalyst that has undergone the additional treatment step. In the production method of this embodiment, as an additional step subsequent to the first hydrogenation step, the treatment step, and the second hydrogenation step, the additional treatment step and the additional hydrogenation step may be repeated in this order one or more times.

[0039] In the production method of this embodiment, after the first hydrogenation step, the treatment step, and the second hydrogenation step, or after the first hydrogenation step, the treatment step, and the additional step subsequent to the second hydrogenation step, a purification step may be carried out in a purification column or the like installed downstream of the reactor outlet in order to increase the purity of the xylylenediamine. The purification step can be carried out using various known conditions.

[0040] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples.

[0041] [Example 1] (1) First hydrogenation step A tubular vertical hydrogenation reactor (made of SUS304, inner diameter 32 mm) was packed with 180 g of a commercially available Raney cobalt catalyst having a cobalt content of 53 mass%, and an activation treatment was carried out by passing a 10% hydrogen-containing gas through the reactor at 320 NmL / min for 16 hours at 280°C. After the activation treatment, the system was cooled, and hydrogen gas was injected into the reactor to maintain a constant pressure of 8 MPaG, and the catalyst layer temperature was maintained at 60°C by external heating. A hydrogenation reaction was carried out by passing a mixture of isophthalonitrile and liquid ammonia (isophthalonitrile:liquid ammonia = 5:95 (mass ratio)) through the catalyst at 2.25 g / h while flowing hydrogen gas (hydrogen-containing gas G1) from the top of the reactor at a flow rate of 118 NmL / min (reaction temperature 60°C; raw material dicyanobenzene was supplied at a rate of 0.0625 mass parts / hour per 100 mass parts of catalyst). 48 hours after the start of the reaction, a sample of the reaction liquid discharged from the reactor was taken and heated to 80°C under normal pressure to remove the liquid ammonia. The composition of the reaction liquid after removal of the liquid ammonia was 97.0 mass% metaxylylenediamine and 0.08 mass% 3-cyanobenzylamine, with no isophthalonitrile detected. The reaction was then continued, and it was confirmed that the concentration of 3-cyanobenzylamine in the reaction liquid after removal of the liquid ammonia reached 0.2 mass%.

[0042] (2) Treatment Step As described above, when the concentration of 3-cyanobenzylamine in the reaction solution after removal of liquid ammonia reached 0.2% by mass, the supply of the mixed solution of isophthalonitrile and liquid ammonia and hydrogen gas was stopped, and the hydrogenation reaction was interrupted. Thereafter, liquid ammonia alone was passed through at 5.0 g / h for 1 hour to wash the catalyst. The catalyst layer temperature was cooled to 40°C or below, the reactor pressure was returned to atmospheric pressure, and then a 10% hydrogen-containing gas was passed through the reactor at 32 NmL / min. The exhaust gas discharged from the reactor was supplied to a gas-liquid separator installed downstream of the reactor outlet. A portion of the exhaust gas that passed through the gas-liquid separator was returned to the reactor inlet at 288 NmL / min using a compressor as a recycled gas (recycle gas obtained by removing at least a portion of the organic compounds from the exhaust gas discharged from the reactor), and a total of 320 NmL / min of gas (hydrogen-containing gas G2: hydrogen concentration 1 vol% to 10 vol%) was passed through the reactor. The reactor was then heated to raise the catalyst layer temperature to 280°C over 2 hours. After performing the regeneration treatment for a total of 16 hours, including the temperature-raising time, heating was stopped and the regeneration treatment was terminated (contact time at a contact temperature of 280°C for 14 hours). The gas supply temperature to the gas-liquid separator during the regeneration treatment was 25°C. After the regeneration treatment was completed, the liquid recovered in the gas-liquid separator was examined, and it was found that 13.6 g of benzene, 7.1 g of heptane, and 0.5 g of meta-xylene had been collected. The amount of hydrogen gas newly used in the treatment process was 3.1 NL in total.

[0043] (3) Second hydrogenation step After the step (2) above, the hydrogenation reaction was restarted under the same reaction conditions as in the step (1) above. The composition of the reaction liquid obtained 48 hours after the restart of the hydrogenation reaction and after removal of liquid ammonia was 95.2% by mass of metaxylylenediamine, 0.12% by mass of 3-cyanobenzylamine, and no isophthalonitrile was detected, showing results almost similar to those in the step (1) above.

[0044] Comparative Example 1 The steps up to (3) were carried out in the same manner as in Example 1, except that no gas-liquid separator was installed on the downstream side of the reactor in (2) above. As a result, the composition of the reaction liquid obtained 48 hours after resumption of the hydrogenation reaction in (3) above and after removal of liquid ammonia contained 95.5% by mass of metaxylylenediamine and no isophthalonitrile was detected, but the content of 3-cyanobenzylamine had increased significantly to 0.52% by mass, indicating a decrease in catalytic activity.

[0045] Comparative Example 2 The same procedures as in Example 1 were carried out up to the step (3) above, except that in the step (2) above, a gas-liquid separator was not installed downstream of the reactor, and after venting a 10% hydrogen-containing gas into the reactor at 320 NmL / min, the exhaust gas discharged from the reactor was not reused (it was not returned to the reactor as a recycled gas). As a result, the composition of the reaction liquid obtained 48 hours after resuming the hydrogenation reaction in the step (3) above after removing the liquid ammonia was 96.9% by mass of metaxylylenediamine, 0.08% by mass of 3-cyanobenzylamine, and no isophthalonitrile was detected, showing results almost similar to those of Example 1. However, a total of 30.7 Nl of hydrogen gas was newly used in the treatment step, which was a larger amount of hydrogen than in Example 1.

[0046] This application is based on a Japanese patent application (Patent Application No. 2023-108290) filed on June 30, 2023, the contents of which are incorporated herein by reference.

Claims

1. A method for producing xylylenediamine, comprising: a first hydrogenation step of supplying dicyanobenzene and a hydrogen-containing gas G1 to a reactor in the presence of a catalyst having hydrogenation ability, and obtaining xylylenediamine by hydrogenating the dicyanobenzene; a treatment step of interrupting the hydrogenation, supplying a hydrogen-containing gas G2 containing a recycled gas to the reactor, and contacting the catalyst that has undergone the first hydrogenation step with the hydrogen-containing gas G2; and a second hydrogenation step of resuming the hydrogenation in the presence of the catalyst that has undergone the treatment step, wherein the recycled gas is obtained by removing at least a portion of the organic compounds from the exhaust gas discharged from the reactor after the contact.

2. The method for producing xylylenediamine according to claim 1, wherein at least a portion of the organic compounds is removed from the exhaust gas using a gas-liquid separator to obtain the recycled gas.

3. The method for producing xylylenediamine according to claim 2, wherein the temperature of the exhaust gas supplied to the gas-liquid separator is 5°C to 80°C.

4. The method for producing xylylenediamine according to claim 1 or 2, wherein in the treatment step, the contact temperature between the hydrogen-containing gas G2 and the catalyst that has been subjected to the first hydrogenation step is 200°C to 500°C.

5. A method for producing xylylenediamine according to claim 1 or 2, wherein the hydrogen concentration of the hydrogen-containing gas G2 is 1 vol % or more.

6. The method for producing xylylenediamine according to claim 1 or 2, wherein in the treatment step, at least a portion of the catalyst is subjected to washing with a solvent before the hydrogen-containing gas G2 is supplied to the reactor.

7. The method for producing xylylenediamine according to claim 1 or 2, wherein the reactor is a fixed bed reactor.

8. The method for producing xylylenediamine according to claim 1 or 2, wherein the catalyst contains nickel and / or cobalt.