Process for the hydrogenation of nitrile compounds

Abstract

This invention relates to the field of hydrogenation technology for nitrile compounds, specifically to a method for hydrogenating nitrile compounds. The method includes the following steps: (a) mixing a solution containing a nitrile compound with a hydrogen feedstock, and then subjecting the mixture to a hydrogenation reaction to obtain a hydrogenated product; (b) separating the hydrogenation product from step (a) into a gas phase and a liquid phase, with a portion of the gas phase recycled back to the hydrogen feedstock and a portion of the liquid phase recycled back to the solution containing the nitrile compound. By recycling a portion of the gaseous and liquid phase reaction products back to the feedstock before mixing, side reactions can be effectively suppressed and the accumulation of heavy components during the reaction process can be avoided. This solves the problems of low selectivity, unstable operation, short expected catalyst lifespan, poor equipment safety, and poor process stability in the preparation of amine compounds in existing technologies. It can be used for the industrial continuous production of amine compounds such as m-phenylenediamine.

Description

Technical Field

[0001] This invention relates to the field of hydrogenation technology of nitrile, and more specifically to a method for hydrogenating nitrile compounds. Background Technology

[0002] m-Phenylated dimethylamine (MXDA) is an important monomer for synthesizing high-end materials, with three main applications: First, it is used as a low-temperature, low-toxicity (LD50 1.0 g / kg), low-viscosity epoxy resin curing agent, exhibiting fast curing speed at room temperature and good heat resistance, water resistance, and chemical resistance. Second, it is used to synthesize poly(m-phenylene adipamide) (nylon MXD6), which has high high-temperature strength and elasticity, high deformation temperature, low thermal expansion coefficient, and good barrier properties. Third, it is used to synthesize isophthaloethylene diisocyanate (XDI) polyurethane resin, producing coatings with high hardness, low toxicity, and excellent yellowing resistance. Additionally, it can be used to synthesize high-end electronic curing agents such as 1,3-diaminomethylcyclohexane.

[0003] Currently, MXDA production technology all adopts the continuous hydrogenation method of isophthalonitrile (IPN). The main technical bottleneck is the selectivity and stability control of the complex reaction network by the fixed-bed catalyst. At the same time, because ammonia substances are involved, higher requirements are placed on the process route design and equipment design and selection of the entire reaction. The main side reactions of the entire reaction include: (1) Insufficient hydrogenation: the intermediate product imine is generated, which is extremely reactive and easily polymerized. (2) Excessive hydrogenation: 3-methylbenzylamine, m-xylene, etc. are generated. (3) Condensation deamination: the amino group attacks the imine as a nucleophile, generating high-boiling substances such as secondary amines, tertiary amines, and cross-linked amines, which affect the selectivity and yield of the reaction. The adsorption of high-boiling substances on the catalyst surface further reduces the adsorption of imine, which may lead to catalyst deactivation.

[0004] As can be seen above, the hydrogenation of isophthalonitrile to prepare m-phenylenediamine involves numerous side reactions, many of which are strongly exothermic. If the heat of reaction cannot be removed in time, not only will the number of side reactions increase, but more seriously, the generated heavy components will directly adhere to the surface of the catalyst, leading to a decrease in catalyst activity. This affects the catalyst's lifespan, as well as the quality and yield of the product. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of low catalyst life and low reaction efficiency in the hydrogenation of nitrile compounds, especially isophthalonitrile, in the existing technology, and to provide a hydrogenation method for nitrile compounds that has high reaction efficiency and long catalyst life.

[0006] To achieve the above objectives, the present invention provides a method for hydrogenating nitrile compounds, the method comprising the following steps: (a) mixing a solution containing nitrile compounds with a hydrogen feedstock, and subjecting the mixed material to a hydrogenation reaction to obtain a hydrogenation product; (b) separating the hydrogenation product in step (a) into a gas phase and a liquid phase, wherein a portion of the gas phase is recycled back to the hydrogen feedstock and a portion of the liquid phase is recycled back to the solution containing nitrile compounds.

[0007] Through the above technical solution, the present invention has the following advantages: By recycling some of the gas-phase and liquid-phase reaction products back to the raw materials before mixing, side reactions can be effectively suppressed and the accumulation of heavy components during the reaction process can be avoided. This solves the problems of low selectivity, unstable operation, short expected catalyst life, poor equipment safety and process stability in the preparation of amine compounds in the existing technology. It can be used for the industrial continuous production of amine compounds such as m-phenylenediamine.

[0008] In a preferred embodiment, an ammonia solution of nitrile compounds, especially isophthalonitrile, is subjected to two-stage catalytic hydrogenation to produce amine compounds. Compared to the first hydrogenation reaction, the second hydrogenation reaction can ensure high reaction efficiency by increasing the reaction temperature and reducing the feed space velocity.

[0009] In a more preferred embodiment, by using an optimized bubbling fixed bed and externalizing the gas-liquid mixer, the reactor can be switched in a timely manner when a certain mixer becomes blocked, thus ensuring a stable feed to the reactor and further improving the reaction efficiency. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a reaction system and process according to a preferred embodiment of the present invention; Figure 2 This is a schematic diagram of a gas-liquid mixer according to a preferred embodiment of the present invention.

[0011] Explanation of reference numerals in the attached figures A-Ingredient Dispensing Kettle B-Preheater C-Gas-Liquid Mixer D-First Stage Reactor E-Primary Separator F-Condenser G-Secondary Separator H-Boost Pump I-Gas-Liquid Mixer J-Secondary Reactor K-Condenser L-First stage separator M- Condenser N-Secondary Separator O-Ammonia Recovery Tower 1-Nitrile compounds 2-Nitrile solution 3-Preheated nitrile solution 4- Fresh gas phase 5-Hydrogen Feedstock 6-Materials after hydrogenation reaction 7-E separated gas phase Partial liquid phase after 8-E separation The other liquid phase after 9-E separation 10-Hydrogen Feedstock 11-Re-hydrogenated material 12- L separated gas phase 13-L separated liquid phase 14-N separated gas phase Another part of the mixed gas phase separated from 15-G and N; A portion of the mixed gas phase containing 16-G and N separated; 17-amine products 18-Amino 19-solvent Detailed Implementation The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0012] This invention provides a method for hydrogenating nitrile compounds, the method comprising the following steps: (a) mixing a solution containing nitrile compounds with a hydrogen feedstock, and subjecting the mixed material to a hydrogenation reaction to obtain a hydrogenation product; (b) separating the hydrogenation product from step (a) into a gas phase and a liquid phase, wherein a portion of the gas phase is recycled back to the hydrogen feedstock and a portion of the liquid phase is recycled back to the solution containing nitrile compounds.

[0013] By recycling some of the gas-phase and liquid-phase reaction products back to the raw materials before mixing, side reactions can be effectively suppressed and the accumulation of heavy components during the reaction process can be avoided. This solves the problems of low selectivity, unstable operation, short expected catalyst life, poor equipment safety and process stability in the preparation of amine compounds in the existing technology. It can be used for the industrial continuous production of amine compounds such as m-phenylenediamine.

[0014] According to a preferred embodiment of the present invention, in step (b), 50-95%, preferably 60-90%, of the gas phase is recycled back to the hydrogen feedstock. By adopting the aforementioned preferred embodiment, the selectivity of amine compounds and catalyst lifetime, as well as process stability and equipment safety, can be further improved.

[0015] According to a preferred embodiment of the present invention, in step (b), 70-97%, preferably 80-92%, of the liquid phase is recycled back to the solution containing the nitrile compound. By adopting the aforementioned preferred embodiment, the selectivity of the amine compound and the catalyst lifetime, as well as the process stability and equipment safety, can be further improved.

[0016] According to a preferred embodiment of the present invention, the method further includes step (c): the remaining gas phase and the remaining liquid phase in step (b) are mixed a second time, and the mixed material is then subjected to further hydrogenation. By adopting the aforementioned preferred scheme, the selectivity of amine compounds and the catalyst lifetime, as well as process stability and equipment safety, can be further improved.

[0017] According to a preferred embodiment of the present invention, the product stream from the re-hydrogenation is separated into a gas phase and a liquid phase. The gas phase is recycled back to the gas phase in step (b), and the liquid phase is subjected to distillation to recover the solvent and the hydrogenation product. By adopting the aforementioned preferred scheme, the selectivity of amine compounds and the catalyst lifetime, as well as the process stability and equipment safety, can be further improved.

[0018] According to a preferred embodiment of the present invention, the material space velocity of the hydrogenation reaction in step (a) is 4-24 h higher than that of the material space velocity of the re-hydrogenation reaction in step (c). -1 For example, it could be 4 hours. -1 6 h -1 10 h -1 15 h -1 20 h -1 Optimal high 6-20 h -1 The material space velocity is the liquid volume space velocity. By adopting the aforementioned preferred scheme, the selectivity of amine compounds and the catalyst lifetime, as well as the process stability and equipment safety, can be further improved.

[0019] According to a preferred embodiment of the present invention, the temperature of the hydrogenation reaction in step (a) is 2-100°C lower than the temperature of the re-hydrogenation in step (c), for example, it can be 4°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc., preferably 4-50°C lower. By adopting the aforementioned preferred embodiment, the selectivity of amine compounds and the catalyst lifetime, as well as the process stability and equipment safety, can be further improved.

[0020] In this invention, the conditions for the hydrogenation reaction can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for the hydrogenation reaction include: a pressure of 2.0-15 MPa, preferably 4-10 MPa; a temperature of 60-180°C, preferably 60-120°C; and a liquid hourly space velocity of 2-25 h⁻¹. -1 Preferably 4-20 h -1 The molar ratio of hydrogen to nitrile compounds is 5-50, preferably 10-40. In this invention, the conditions for re-hydrogenation are available in a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for re-hydrogenation include: a pressure of 2.0-15 MPa, preferably 6-12 MPa; a temperature of 70-180°C, preferably 80-160°C; and a liquid hourly space velocity of 0.1-10 h⁻¹. -1 Preferably 0.5-8 h -1 The molar ratio of hydrogen to nitrile compounds is 25-150, preferably 40-120.

[0021] In this invention, there is no particular limitation on the concentration of nitrile compounds in the solution containing nitrile compounds. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, in the solution containing nitrile compounds, the nitrile compounds account for 5-50% by total mass, preferably 8-20%; and the solvent accounts for 50-95%, preferably 80-92%.

[0022] In this invention, the solvent in the solution containing nitrile compounds can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solvent is liquid ammonia, preferably the liquid ammonia contains no more than 100 ppm of water.

[0023] In this invention, a wide range of nitrile compounds can be selected. The following is an illustrative example, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the nitrile compound is an arylalkyl nitrile, preferably a C6-C12 isophthalic nitrile. The advantages of this invention are illustrated using isophthalonitrile as an example.

[0024] In this invention, no particular limitation is placed on the catalysts used for the hydrogenation reaction and the re-hydrogenation. Generally, catalysts commonly used in the art are used. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the hydrogenation reaction and the re-hydrogenation are each carried out independently in the presence of a non-precious metal catalyst.

[0025] In this invention, the range of non-precious metal catalysts that can be selected is relatively wide. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the non-precious metal catalyst is selected from at least one of silicon-based catalysts, nickel-based catalysts, and nickel-cobalt bimetallic catalysts.

[0026] According to a preferred embodiment of the present invention, the separation in steps (b) and (c) includes: firstly performing a primary separation; then, condensing the gas phase after primary separation and performing a secondary separation; returning the liquid phase after secondary separation to the primary separation; outputting the liquid phase obtained from the primary separation as a liquid phase; and outputting the gas phase obtained from the secondary separation as a gas phase. By adopting the aforementioned preferred scheme, the selectivity of amine compounds and the catalyst lifetime, as well as process stability and equipment safety, can be further improved.

[0027] According to a preferred embodiment of the present invention, the hydrogenation reaction and re-hydrogenation in the hydrogenation method are carried out independently in a fixed bubbling bed reactor. Preferably, the fixed bubbling bed reactor includes, from bottom to top, a lower head, a cylinder, and an upper head. The cylinder includes, from bottom to top, a gas-liquid redistribution unit, a catalyst support unit, and a catalyst compaction unit. The gas-liquid redistribution unit, the cylinder, and the lower head together form a pre-distribution zone for pre-distribution of the feedstock. The gas-liquid redistribution unit, the cylinder, and the catalyst support unit together form a redistribution zone for redistribution of the feedstock. The catalyst support unit, the cylinder, and the catalyst compaction unit together form a catalytic reaction zone for catalytic reaction of the feedstock from the redistribution zone. The catalyst compaction unit, the cylinder, and the upper head together form a product enrichment zone for collecting the product from the catalytic reaction zone. By adopting the aforementioned preferred embodiment, the selectivity of amine compounds and the catalyst lifetime, as well as process stability and equipment safety, can be further improved.

[0028] According to a preferred embodiment of the present invention, a raw material inlet is provided on the cylinder below the gas-liquid redistribution unit of the fixed bubbling bed reactor. The inlet pipeline extends to the center of the reactor and then bends downward at 60-120°, preferably downward at 80-100°.

[0029] In this invention, there are no particular limitations on the mixing method. According to a preferred embodiment of the invention, the first mixing and the second mixing are carried out independently in a gas-liquid mixer. Preferably, the mixer is selected from at least one of a Venturi gas-liquid mixer, an orifice plate gas-liquid mixer, and a cyclone gas-liquid mixer, specifically as follows: Figure 2 As shown. By adopting the aforementioned preferred scheme, the selectivity of amine compounds and catalyst lifetime, as well as process stability and equipment safety, can be further improved.

[0030] In this invention, the output liquid stream needs to be treated with ammonia recovery. An ammonia recovery tower, i.e., a distillation tower, is used to recover ammonia from the liquid stream and extract the target product. The distillation conditions include: top pressure of 1-2 MPa; top temperature of 20-60°C; bottom temperature of 80-180°C; and reflux ratio of 0.1-5.

[0031] This invention provides a method for hydrogenating nitrile compounds, wherein the method comprises, for example, Figure 1 The process, as shown in the apparatus, includes: mixing nitrile compound 1 and solvent 19 in a mixing tank A to prepare nitrile solution 2; preheating the solution in preheater B to obtain preheated nitrile solution 3; mixing this preheated solution with recycled gas phase 16 and fresh gas phase 4; and then injecting the mixture, along with hydrogen feedstock 5, into a gas-liquid mixer C for further mixing. The mixed material is then injected through the feedstock inlet into the pre-reaction zone of primary reactor D, where it undergoes a hydrogenation reaction in contact with the catalyst. The hydrogenated material 6 is output from the top of the reactor and sent to primary separator E for separation. The separated gas phase 7 passes through primary cooler F and enters secondary separator G for further separation. A portion of the liquid phase 8 separated in primary separator E is recycled back to nitrile feedstock 3, while the remaining portion 9 is sent to secondary gas-liquid mixer I. The liquid phase separated in secondary separator G is recycled back to... In primary separator E, the gas phases separated from secondary separators G and N are pressurized by booster pump H and divided into two parts: one part is the circulating gas phase 16, and the other part 15 is used as hydrogen feedstock 10 for secondary reactor J. This mixture is then mixed with a portion of the liquid phase 9 from primary separator E and injected into secondary reactor J for re-hydrogenation. The re-hydrogenated material 11 is output from the top of the reactor and sent to primary separator L for separation. The gas phase 12 separated in primary separator L passes through secondary cooler M and enters secondary separator N for further separation. The liquid phase separated in secondary separator N is recycled back to primary separator L. The liquid phase 13 separated in primary separator L is sent to ammonia recovery tower O for distillation to obtain amine products 17 and ammonia 18. Ammonia 18 is cooled by cooler K and returned to the batching vessel as solvent 19. The gas phase 14 separated in secondary separator N is mixed with the gas phase separated in secondary separator G.

[0032] The present invention will be described in detail below through examples. In the following examples, the conversion rate of isophthalonitrile is calculated as: (1 - molar amount of remaining isophthalonitrile after reaction / molar amount of isophthalonitrile before reaction) × 100%.

[0033] The selectivity of m-phenylenediamine is calculated as: (molar amount of m-phenylenediamine produced / molar amount of all products) × 100%; The isophthalonitrile raw material is a commercially available product from Shandong Dacheng Biochemical Co., Ltd. Unless otherwise specified in the examples, all measurements are by mass.

[0034] Example 1 In a mixing tank, isophthalonitrile is prepared into an 8% solution with a liquid phase flow rate of 100 kg / h. After preheating, it is mixed with the circulating liquid phase from the primary reactor and fed into the primary gas-liquid mixer as the liquid phase feedstock. Fresh hydrogen feedstock is mixed with circulating hydrogen and fed into the primary gas-liquid mixer as the gas phase feedstock. The total hydrogen flow rate is 14 Nm³ / h. After thorough mixing of the gas and liquid phases, the mixture enters the primary reactor. The operating pressure is 4 MPa, the operating temperature is 60 °C, the molar ratio of hydrogen to isophthalonitrile is 10, and the liquid hourly space velocity is 4 h⁻¹. -1 The reaction products enter the first-stage separator (first-stage reactor) through the top outlet for the first-stage gas-liquid separation. The temperature of the first-stage separator is 30°C. The bottom liquid phase product is split into two streams, with the discharge flow rate of the first-stage reaction liquid phase product accounting for 20% of the total discharge flow rate, and the recirculation flow rate of the first-stage reaction liquid phase product accounting for 80% of the total discharge flow rate. The gas phase product, after being condensed by the first-stage condenser, enters the second-stage separator (first-stage reactor) for the second-stage gas-liquid separation. The operating temperature of the second-stage separator is 0°C. The top gas phase is split into two streams: one stream is the first-stage reaction gas phase recirculation, accounting for 60%, which, after being pressurized by a booster pump, is combined with fresh hydrogen from the outside as the gas phase feedstock and enters the first-stage reaction gas-liquid mixer; the other stream is the first-stage reaction gas phase discharge, which serves as the gas phase feedstock for the second-stage reaction and enters the second-stage gas-liquid mixer.

[0035] The liquid and gas phase feeds from the first reactor are thoroughly mixed in a two-stage gas-liquid mixer and then enter the second-stage reactor through a 90° bend. After passing through a gas-liquid redistributor, they enter the catalyst bed for reaction. The second-stage reaction pressure is 6 MPa, the reaction temperature is 80°C, and the liquid hourly space velocity is 0.5 h⁻¹. -1， The molar ratio of hydrogen to isophthalonitrile is 40. The reaction products enter the primary gas-liquid separator at the top outlet of the reactor for gas-liquid separation, with an operating temperature of 40°C. The gaseous products are condensed in a secondary condenser and then enter the secondary gas-liquid separator for further gas-liquid separation, with an operating temperature of 0°C. The liquid products enter an ammonia recovery tower for ammonia removal. The ammonia recovery tower has a top pressure of 1.2 MPa, a top temperature of 20°C, a bottom temperature of 140°C, and a reflux ratio of 1. The ammonia gas from the top of the tower is condensed in an ammonia condenser and then fed into a mixing tank with isophthalonitrile for mixing. The bottom product is crude MXDA.

[0036] The gas-liquid mixers used are all Venturi-type gas-liquid mixers, such as... Figure 2 As shown, the gas-liquid phase is fed vertically.

[0037] Reaction results: After two-stage reaction, the conversion rate of isophthalonitrile was 99.8%, and the selectivity of isophthalic acid was 98.5%.

[0038] Example 2 In a mixing tank, isophthalonitrile is prepared into a 10% solution with a liquid phase flow rate of 100 kg / h. After preheating, it is mixed with the circulating liquid phase from the primary reactor and fed into the primary gas-liquid mixer as the liquid phase feedstock. Fresh hydrogen feedstock is mixed with circulating hydrogen and fed into the primary gas-liquid mixer as the gas phase feedstock. The total hydrogen flow rate is 43.8 Nm³ / h. After thorough mixing of the gas and liquid phases, the mixture enters the primary reactor. The operating pressure is 7 MPa, the operating temperature is 90 °C, the molar ratio of hydrogen to isophthalonitrile is 25, and the liquid hourly space velocity is 12 h⁻¹. -1 The reaction products enter the first-stage separator (first-stage reactor) through the top outlet for the first-stage gas-liquid separation. The temperature of the first-stage separator is 50°C. The bottom liquid phase product is split into two streams, with the discharge flow rate of the first-stage reaction liquid phase product accounting for 15% of the total discharge flow rate, and the recirculation flow rate of the first-stage reaction liquid phase product accounting for 85% of the total discharge flow rate. The gas phase product, after being condensed by the first-stage condenser, enters the second-stage separator (first-stage reactor) for the second-stage gas-liquid separation. The operating temperature of the second-stage separator is 15°C. The top gas phase is split into two streams: one is the first-stage reaction gas phase recirculation, accounting for 80%, which, after being pressurized by a booster pump, is combined with fresh hydrogen from the outside as the reaction gas phase feedstock and enters the first-stage reaction gas-liquid mixer; the other is the first-stage reaction gas phase discharge, which serves as the gas phase feedstock for the second-stage reaction and enters the second-stage gas-liquid mixer.

[0039] The liquid and gas phase feeds from the first reactor are thoroughly mixed in a two-stage gas-liquid mixer and then enter the second-stage reactor through a 90° bend. After passing through a gas-liquid redistributor, they enter the catalyst bed for reaction. The second-stage reaction pressure is 9 MPa, the reaction temperature is 120°C, and the liquid hourly space velocity is 2 h⁻¹. -1 The molar ratio of hydrogen to isophthalonitrile is 80. The reaction products enter the first gas-liquid separator at the top outlet of the reactor for gas-liquid separation, with an operating temperature of 60°C. The gaseous products are condensed in a second-stage condenser and then enter the second gas-liquid separator for further gas-liquid separation, with an operating temperature of 15°C. The liquid products enter an ammonia recovery tower for ammonia removal, with a top pressure of 1.6 MPa, a top temperature of 30°C, a bottom temperature of 160°C, and a reflux ratio of 3. The ammonia gas from the top of the tower is condensed in an ammonia condenser and then fed into a mixing tank with isophthalonitrile for mixing. The bottom product is crude MXDA.

[0040] The gas-liquid mixers used are all orifice plate type gas-liquid mixers, such as... Figure 2 As shown, the gas-liquid phase is fed vertically.

[0041] Reaction results: After two-stage reaction, the conversion rate of isophthalonitrile was 99.9%, and the selectivity of isophthalic acid was 99.0%.

[0042] Example 3 In a mixing tank, isophthalonitrile is prepared into a 20% solution with a liquid phase flow rate of 100 kg / h. After preheating, it is mixed with the circulating liquid phase from the primary reactor and fed into the primary gas-liquid mixer as the liquid phase feedstock. Fresh hydrogen feedstock is mixed with circulating hydrogen and fed into the primary gas-liquid mixer as the gas phase feedstock. The total hydrogen flow rate is 140 Nm³ / h. After thorough mixing of the gas and liquid phases, the mixture enters the primary reactor. The operating pressure is 10 MPa, the operating temperature is 120 °C, the molar ratio of hydrogen to isophthalonitrile is 40, and the liquid hourly space velocity is 20 h⁻¹. -1 The reaction products enter the first-stage separator (first-stage reactor) through the top outlet for the first-stage gas-liquid separation. The temperature of the first-stage separator is 80℃. The bottom liquid phase product is split into two streams, with the discharge flow rate of the first-stage reaction liquid phase product accounting for 20% of the total discharge flow rate, and the recirculation flow rate of the first-stage reaction liquid phase product accounting for 80% of the total discharge flow rate. The gas phase product, after being condensed by the first-stage condenser, enters the second-stage separator (first-stage reactor) for the second-stage gas-liquid separation. The operating temperature of the second-stage separator is 30℃. The top gas phase is split into two streams: one is the first-stage reaction gas phase recirculation, accounting for 90%, which, after being pressurized by a booster pump, is combined with fresh hydrogen from the outside as the reaction gas phase feedstock and enters the first-stage reaction gas-liquid mixer; the other is the first-stage reaction gas phase discharge, which serves as the gas phase feedstock for the second-stage reaction and enters the second-stage gas-liquid mixer.

[0043] The liquid and gas phase feeds from the first reactor are thoroughly mixed in a two-stage gas-liquid mixer and then enter the second-stage reactor through a 90° bend. After passing through a gas-liquid redistributor, they enter the catalyst bed for reaction. The second-stage reaction pressure is 12 MPa, the reaction temperature is 160 °C, and the liquid hourly space velocity is 8 h⁻¹. -1 The molar ratio of hydrogen to isophthalonitrile is 120. The reaction product enters the first gas-liquid separator at the top outlet of the reactor for gas-liquid separation at a temperature of 90°C. The gaseous product is condensed in a second condenser and then enters the second gas-liquid separator for further gas-liquid separation at a temperature of 30°C. The liquid product enters an ammonia recovery tower for ammonia removal. The top pressure of the ammonia recovery tower is 1.8 MPa, the top temperature is 40°C, the bottom temperature is 180°C, and the reflux ratio is 5. The ammonia gas at the top of the tower is condensed in an ammonia condenser and then fed into a mixing tank with isophthalonitrile for mixing. The bottom product is crude MXDA.

[0044] The gas-liquid mixers used are all cyclone type gas-liquid mixers, such as... Figure 2 As shown, the gas-liquid phase is fed vertically.

[0045] Reaction results: After two-stage reaction, the conversion rate of isophthalonitrile was 99.9%, and the selectivity of isophthalic acid was 999.3%.

[0046] Example 4 Same as Example 1, except that the concentration of phthalonitrile in the feed is 15%.

[0047] Reaction results: After two-stage reaction, the conversion rate of isophthalonitrile was 90.1%, and the selectivity of isophthalic dimethylamine was 92.3%.

[0048] Example 5 Same as Example 1, except that the temperature in the second reactor is the same as that in the first reactor, which is 60°C.

[0049] Reaction results: After two-stage reaction, the conversion rate of isophthalonitrile was 89.7%, and the selectivity of isophthalic diamine was 90.5%.

[0050] Example 6 Same as Example 1, except that no secondary reaction is performed, and 20% of the flow rate of the liquid phase product at the bottom of the first separator is discharged as product.

[0051] Reaction results: After the first-stage reaction, the conversion rate of isophthalonitrile was 85.5%, and the selectivity of isophthalic dimethylamine was 85.7%.

[0052] Example 7 Same as Example 1, except that the liquid space velocity in the second reactor is the same as that in the first reactor, which is 4 h⁻¹. -1 .

[0053] Reaction results: After two-stage reaction, the conversion rate of isophthalonitrile was 92.1%, and the selectivity of isophthalic dimethylamine was 94.3%.

[0054] Comparative Example 1 Similar to Example 1, except that the gas phase after the first separation (including the gas phase after the second separation) is not recycled and is directly output from the system, and the liquid phase after the first separation is used as feed for the secondary reaction.

[0055] Reaction results: The conversion rate of isophthalonitrile was 80.4%, and the selectivity of isophthalic dimethylamine was 80.6%.

[0056] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for hydrogenating nitrile compounds, characterized in that, The method includes the following steps: (a) A solution containing a nitrile compound is first mixed with a hydrogen feedstock, and the mixture is subjected to a hydrogenation reaction to obtain a hydrogenation product; (b) Separate the hydrogenation product from step (a) into a gas phase and a liquid phase, with part of the gas phase recycled back to the hydrogen feedstock and part of the liquid phase recycled back to the solution containing nitrile compounds.

2. The hydrogenation method according to claim 1, wherein, In (b), 50-95%, preferably 60-90%, of the gas phase recycled back into the hydrogen feedstock; and / or 70-97%, preferably 80-92%, of the liquid phase is recycled back to the solution containing the nitrile compound.

3. The hydrogenation method according to claim 1 or 2, wherein, The method further includes step (c): the remaining gas phase and the remaining liquid phase in step (b) are mixed for the second time, and the mixed material is then hydrogenated again; Preferably, the product stream of the re-hydrogenation is separated into a gas phase and a liquid phase. The gas phase is recycled back to the gas phase in step (b), and the liquid phase is distilled to recover the solvent and the hydrogenation product.

4. The method according to any one of claims 1-3, wherein, The material space velocity (WHV) of the hydrogenation reaction in step (a) is 4-24 h higher than that of the re-hydrogenation reaction in step (c). -1 Preferred high 6-20 h -1 .

5. The method according to any one of claims 1-4, wherein, The temperature of the hydrogenation reaction in step (a) is 2-100°C lower than the temperature of the re-hydrogenation in step (c), preferably 4-50°C lower.

6. The method according to any one of claims 1-5, wherein, In the method, The conditions for hydrogenation reactions include: a pressure of 2.0-15 MPa, preferably 4-10 MPa; and / or a temperature of 60-180°C, preferably 60-120°C; and / or a liquid hourly space velocity of 2-25 h⁻¹. -1 Preferably 4-20 h -1 The molar ratio of hydrogen to nitrile compounds is 5-50, preferably 10-40. and / or The conditions for re-hydrogenation include: a pressure of 2.0-15 MPa, preferably 6-12 MPa; and / or a temperature of 70-180°C, preferably 80-160°C; and / or a liquid hourly space velocity of 0.1-10 h⁻¹. -1 Preferably 0.5-8 h -1 The molar ratio of hydrogen to nitrile compounds is 25-150, preferably 40-120.

7. The method according to any one of claims 1-6, wherein, In the solution containing nitrile compounds, the nitrile compounds account for 5-50% by total mass, preferably 8-20%; the solvent accounts for 50-95%, preferably 80-92%; preferably, The solvent is liquid ammonia, preferably with a water content of no more than 100 ppm; and / or The nitrile compound is an arylalkyl nitrile, preferably a C6-C12 isophenylenedialkyl nitrile.

8. The method according to any one of claims 1-7, wherein, The hydrogenation reaction and the re-hydrogenation are each carried out independently in the presence of a non-noble metal catalyst; preferably, The non-precious metal catalyst is selected from at least one of silicon-based catalysts, nickel-based catalysts, and nickel-cobalt bimetallic catalysts.

9. The method according to any one of claims 1-8, wherein, The separation in steps (b) and (c) includes the following independent steps: firstly, a primary separation is performed; the gas phase after primary separation is condensed and then a secondary separation is performed; the liquid phase after secondary separation is returned to the primary separation; the liquid phase obtained from primary separation is output as the liquid phase; and the gas phase obtained from secondary separation is output as the gas phase.

10. The method according to any one of claims 1-9, wherein, In the hydrogenation method, the hydrogenation reaction and re-hydrogenation are carried out independently in a bubbling fixed-bed reactor. Preferably, the bubbling fixed-bed reactor includes, from bottom to top, a lower head, a cylindrical body, and an upper head. The cylindrical body includes, from bottom to top, a gas-liquid redistribution unit, a catalyst support unit, and a catalyst compaction unit. The gas-liquid redistribution unit, the cylindrical body, and the lower head together form a pre-distribution zone for pre-distribution of the feedstock. The gas-liquid redistribution unit, the cylindrical body, and the catalyst support unit together form a redistribution zone for redistribution of the feedstock. The catalyst support unit, the cylindrical body, and the catalyst compaction unit together form a catalytic reaction zone for catalytic reaction of the feedstock from the redistribution zone. The catalyst compaction unit, the cylindrical body, and the upper head together form a product enrichment zone for collecting the product from the catalytic reaction zone. and / or The first and second mixing are carried out independently in a gas-liquid mixer, preferably selected from at least one of a Venturi gas-liquid mixer, an orifice plate gas-liquid mixer, and a vortex gas-liquid mixer.

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