A catalyst for preparing meta-xylylenediamine and a preparation method thereof

Abstract

A catalyst for preparing meta-phenylenediamine, comprising a carrier and an active component and an auxiliary agent attached to the carrier; the active component is a mixture formed by mixing Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:(1-3):(2-3):(1-3):2:(0.8-1.2):(0.3-0.5):0.4; the auxiliary agent is a mixture formed by mixing Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:(1-3):(0.8-1.2):(0.1-0.3):0.2:(0.8-1.2):(0.2-0.4). The catalyst has high catalytic activity, stability, and selectivity, and has a long service life, can significantly improve production efficiency, reduce production costs, and is conducive to industrial application.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a catalyst for preparing meta-xylylenediamine and a preparation method thereof. Background Art

[0002] Meta-phenylenediamine is an important organic raw material intermediate, mainly used in the manufacture of epoxy resin curing agent, rubber additives, photosensitive plastics, polyurethane resins and coatings. In addition, it can also be used in pesticides, fiber finishing agents, rust inhibitors, lubricants, etc. It is a widely used and high value-added fine chemical. The market demand is still large.

[0003] At present, m-xylylenediamine is mostly produced by catalytic hydrogenation of isophthalonitrile, and the catalysts used are commonly Raney nickel, modified Raney nickel or amorphous nickel, etc., and the metal nickel content of these catalysts reaches more than 60%, and the manufacturing cost is high. Other existing catalysts also have more or less fine particles, easy pulverization, poor separation effect, high production cost, poor safety, easy loss, easy side reactions, large dosage, short life, unsatisfactory selectivity and activity and other technical defects.

[0004] In order to solve the above problems, the Chinese invention patent with the authorization announcement number CN114797870B discloses a catalyst for hydrogenating isophthalonitrile to prepare meta-phenylenediamine, wherein the catalyst has Ni and Co as active components and silica sol or aluminum sol as carrier, wherein the Ni content is 0.1%-50% of the catalyst mass, and the Co content is 0.1%-25% of the catalyst mass. The invention also discloses its preparation method and application. The catalyst of the invention is a high-performance hydrogenation catalyst with a uniform distribution of a bimetallic alloy layer prepared by a two-step method of peptization complexation and coordination adsorption. The bimetallic alloy catalyst prepared by the novel two-step method adopted in the invention exhibits excellent catalytic performance in the reaction process of hydrogenating isophthalonitrile to prepare meta-phenylenediamine, with a 100% conversion rate, a selectivity of up to 99.6%, and a test stability of 1000 hours. However, its selectivity and catalytic activity still need to be further improved. And it also has technical defects such as easy sintering and easy carbon deposition.

[0005] Therefore, the development of a catalyst for preparing meta-xylylenediamine and its preparation method which has high catalytic activity, stability and selectivity, long service life, can significantly improve production efficiency, reduce production costs, and is conducive to industrial application meets market demand, has broad market value and application prospects, and is of great significance to promoting the development of catalytic hydrogenation technology. Summary of the invention

[0006] The main purpose of the present invention is to provide a catalyst for preparing meta-xylylenediamine, which has high catalytic activity, stability and selectivity, long service life, can significantly improve production efficiency, reduce production costs, and is conducive to industrial application, and a preparation method thereof.

[0007] To achieve the above purpose, the present invention provides a catalyst for preparing meta-phenylenediamine, comprising a carrier and active components and auxiliary agents attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:(1-3):(2-3):(1-3):2:(0.8-1.2):(0.3-0.5):0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:(1-3):(0.8-1.2):(0.1-0.3):0.2:(0.8-1.2):(0.2-0.4).

[0008] Preferably, the rare earth is a mixture of Sc, Y, Gd, and Tb in a mass ratio of 1:(0.6-1):(0.3-0.6):(0.1-0.3).

[0009] Preferably, the content of the active component is 4-23% of the total mass of the catalyst.

[0010] Preferably, the content of the auxiliary agent is 2-7% of the total mass of the catalyst.

[0011] Preferably, the carrier is at least one of molecular sieve, diatomaceous earth and activated alumina.

[0012] Preferably, the molecular sieve is at least one of SBA-15 molecular sieve and MCM-48 molecular sieve; and the activated alumina is X-ρ type alumina.

[0013] Preferably, the carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trihydroxymethyl methacrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting at 60-70° C. in an inert gas atmosphere for 3-5 hours, and then removing the solvent by rotary evaporation to obtain a surface-modified carrier.

[0014] Preferably, the mass ratio of the carrier, organic solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, and initiator is (3-5):(10-25):(0.1-0.2):0.1:0.1:(0.003-0.0.005).

[0015] Preferably, the organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; the initiator is azobisisobutyronitrile; and the inert gas is any one of nitrogen, helium, neon, and argon.

[0016] Another object of the present invention is to provide a method for preparing the catalyst for preparing meta-xylylenediamine, comprising the following steps: mixing the chloride salts of the active components and the auxiliary components according to a ratio, adding them into water, dispersing them evenly, impregnating the surface-modified carrier for 10-20 hours, taking them out and drying them at 100° C. to constant weight, and then reducing and activating them in pure hydrogen at 390-420° C. and normal pressure for 3-6 hours to obtain the catalyst for preparing meta-xylylenediamine.

[0017] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0018] (1) The method for preparing the catalyst for preparing m-xylylenediamine disclosed in the present invention has simple process, convenient operation, high preparation efficiency and finished product qualification rate, low energy consumption, low dependence on equipment, is suitable for continuous large-scale production, and has high promotion and application value.

[0019] (2) The catalyst for preparing m-phenylenediamine disclosed in the present invention comprises a carrier and an active component and an auxiliary agent attached to the carrier; the active component is a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:(1-3):(2-3):(1-3):2:(0.8-1.2):(0.3-0.5):0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:(1-3):(0.8-1.2):(0.1-0.3):0.2:(0.8-1.2):(0.2-0.4). Through the mutual coordination and joint action of the various components, the prepared catalyst has high catalytic activity, stability, and selectivity, and a long service life, which can significantly improve production efficiency, reduce production costs, and is conducive to industrial application.

[0020] (3) The catalyst for preparing m-phenylenediamine disclosed in the present invention has a carrier that undergoes surface modification during the preparation process, and simultaneously introduces alkoxy silicon, amphoteric organic ion salts, hydroxyl groups and amide groups on the surface, which can increase the carrier loading rate, improve the dispersion uniformity of active ingredients and additives on the carrier surface, and further improve the catalytic activity and service life, and increase the reaction rate, reaction conversion rate and selectivity. DETAILED DESCRIPTION

[0021] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art may think of other obvious variations. Example 1

[0022] A catalyst for preparing meta-xylylenediamine comprises a carrier and active components and auxiliary agents attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:1:2:1:2:0.8:0.3:0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:1:0.8:0.1:0.2:0.8:0.2.

[0023] The rare earth is a mixture of Sc, Y, Gd and Tb in a mass ratio of 1:0.6:0.3:0.1; the content of the active component is 10% of the total mass of the catalyst; the content of the auxiliary agent is 3% of the total mass of the catalyst; the carrier is a molecular sieve; and the molecular sieve is an SBA-15 molecular sieve.

[0024] The carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting at 60° C. for 3 hours in an inert gas atmosphere, and removing the solvent by rotary evaporation to obtain a surface-modified carrier; the mass ratio of the carrier, the organic solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and the initiator is 3:10:0.1:0.1:0.1:0.003; the organic solvent is dimethyl sulfoxide; the initiator is azobisisobutyronitrile; and the inert gas is nitrogen.

[0025] A preparation method of the catalyst for preparing meta-xylylenediamine comprises the following steps: mixing the chloride salts of the active component and the auxiliary agent according to a proportion, adding them into water, dispersing them uniformly, impregnating a surface-modified carrier for 10 hours, drying them at 100° C. to constant weight after taking them out, and then reducing and activating them in pure hydrogen at 390° C. and normal pressure for 3 hours to obtain the catalyst for preparing meta-xylylenediamine. Example 2

[0026] A catalyst for preparing meta-xylylenediamine comprises a carrier and active components and auxiliary agents attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:1.5:2.2:1.5:2:0.9:0.35:0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:1.5:0.9:0.15:0.2:0.9:0.25.

[0027] The rare earth is a mixture of Sc, Y, Gd, and Tb in a mass ratio of 1:0.7:0.4:0.15; the content of the active component is 12% of the total mass of the catalyst; the content of the auxiliary agent is 4% of the total mass of the catalyst; and the carrier is diatomaceous earth;

[0028] The carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trihydroxymethyl methacrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting at 62° C. in an inert gas atmosphere for 3.5 hours, and then removing the solvent by rotary evaporation to obtain a surface-modified carrier. A surface-modified carrier; the mass ratio of the carrier, organic solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt, and initiator is 3.5:15:0.13:0.1:0.1:0.0035; the organic solvent is N,N-dimethylformamide; the initiator is azobisisobutyronitrile; and the inert gas is helium.

[0029] A preparation method of the catalyst for preparing meta-xylylenediamine comprises the following steps: mixing the chloride salts of the active components and the auxiliary components according to a proportion, adding them into water, dispersing them evenly, impregnating a surface-modified carrier for 13 hours, taking them out and drying them at 100° C. to constant weight, and then reducing and activating them in pure hydrogen at 400° C. and normal pressure for 4 hours to obtain the catalyst for preparing meta-xylylenediamine. Example 3

[0030] A catalyst for preparing meta-phenylenediamine comprises a carrier and active components and auxiliary agents attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:2:2.5:2:2:1:0.4:0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:2:1:0.2:0.2:1:0.3.

[0031] The rare earth is a mixture of Sc, Y, Gd, and Tb in a mass ratio of 1:0.8:0.45:0.2; the content of the active component is 15% of the total mass of the catalyst; the content of the auxiliary agent is 5% of the total mass of the catalyst; the carrier is activated alumina; and the activated alumina is X-ρ type alumina.

[0032] The carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting at 65° C. for 4 hours in an inert gas atmosphere, and then removing the solvent by rotary evaporation to obtain a surface-modified carrier; the mass ratio of the carrier, the organic solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and the initiator is 4:19:0.15:0.1:0.1:0.004; the organic solvent is N-methylpyrrolidone; the initiator is azobisisobutyronitrile; and the inert gas is neon.

[0033] A method for preparing a catalyst for preparing meta-xylylenediamine comprises the following steps: mixing the chloride salts of the active components and the auxiliary components according to a proportion, adding them into water, and after uniform dispersion, immersing a surface-modified carrier for 15 hours, taking them out and drying them at 100° C. to constant weight, and then reducing and activating them in pure hydrogen at 405° C. and normal pressure for 4.5 hours to obtain the catalyst for preparing meta-xylylenediamine. Example 4

[0034] A catalyst for preparing meta-xylylenediamine comprises a carrier and active components and auxiliary agents attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:2.5:2.8:2.5:2:1.1:0.45:0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:2.5:1.1:0.25:0.2:1.1:0.35.

[0035] The rare earth is a mixture of Sc, Y, Gd, and Tb in a mass ratio of 1:0.9:0.55:0.25; the content of the active component is 17% of the total mass of the catalyst; the content of the auxiliary agent is 6% of the total mass of the catalyst; the carrier is a mixture of molecular sieve, diatomaceous earth, and activated alumina in a mass ratio of 1:2:3; the molecular sieve is a mixture of SBA-15 molecular sieve and MCM-48 molecular sieve in a mass ratio of 3:5; the activated alumina is X-ρ type alumina.

[0036] The carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trihydroxymethyl methacrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting at 68° C. in an inert gas atmosphere for 4.5 hours, and then evaporating to remove the solvent to obtain a surface-modified carrier; the carrier, the organic solvent The mass ratio of the solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and the initiator is 4.5:24:0.18:0.1:0.1:0.0045; the organic solvent is a mixture of dimethyl sulfoxide, N,N-dimethylformamide and N-methylpyrrolidone in a mass ratio of 1:2:3; the initiator is azobisisobutyronitrile; and the inert gas is argon.

[0037] A preparation method of the catalyst for preparing meta-xylylenediamine comprises the following steps: mixing the chloride salts of the active components and the auxiliary components according to a proportion, adding them into water, dispersing them uniformly, impregnating a surface-modified carrier for 18 hours, taking them out and drying them at 100° C. to constant weight, and then reducing and activating them in pure hydrogen at 415° C. and normal pressure for 5.5 hours to obtain the catalyst for preparing meta-xylylenediamine. Example 5

[0038] A catalyst for preparing meta-phenylenediamine comprises a carrier and active components and auxiliary agents attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb and Co in a mass ratio of 1:3:3:3:2:1.2:0.5:0.4; the auxiliary agent is a mixture of Ir, Zn, Cr, Hf, Ta, Al and Ga in a mass ratio of 0.6:3:1.2:0.3:0.2:1.2:0.4.

[0039] The rare earth is a mixture of Sc, Y, Gd and Tb in a mass ratio of 1:1:0.6:0.3; the content of the active component is 20% of the total mass of the catalyst; the content of the auxiliary agent is 7% of the total mass of the catalyst; the carrier is a molecular sieve; and the molecular sieve is an SBA-15 molecular sieve.

[0040] The carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting at 70° C. in an inert gas atmosphere for 5 hours, and removing the solvent by rotary evaporation to obtain a surface-modified carrier; the mass ratio of the carrier, the organic solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and the initiator is 5:25:0.2:0.1:0.1:0.0.005; the organic solvent is dimethyl sulfoxide; the initiator is azobisisobutyronitrile; and the inert gas is nitrogen.

[0041] A preparation method of the catalyst for preparing meta-xylylenediamine comprises the following steps: mixing the chloride salts of the active component and the auxiliary agent according to a proportion, adding them into water, dispersing them uniformly, impregnating a surface-modified carrier for 20 hours, drying them at 100° C. to constant weight after taking them out, and then reducing and activating them in pure hydrogen at 420° C. and normal pressure for 6 hours to obtain the catalyst for preparing meta-xylylenediamine.

[0042] Comparative Example 1

[0043] The present invention provides a catalyst for preparing meta-xylylenediamine and a preparation method thereof, which are similar to Example 1, except that Os, Nb, Hf and Ta are not added.

[0044] Comparative Example 2

[0045] The present invention provides a catalyst for preparing meta-xylylenediamine and a preparation method thereof, which are similar to Example 1, except that Sr, Sb, Al and Ga are not added.

[0046] The catalysts of each example were crushed into 30 meshes and loaded into a continuous flow packed bed reactor. High-purity hydrogen was introduced at a system pressure of 0.5 MPa and a temperature of 450°C. The hydrogen gas space velocity was 1500 h -1 , reduction for 2 hours. The temperature was lowered to 105°C, the pressure was raised to 8.0MPa, and a DMF liquid ammonia solution of isophthalonitrile was pumped in by a horizontal flow pump. The liquid hourly space velocity of isophthalonitrile was 0.5h -1, the molar ratio of hydrogen to isophthalonitrile is 10:1. Among them, in the DMF liquid ammonia solution of isophthalonitrile, the molar ratio of isophthalonitrile to DMF is 1:10, and the molar ratio of isophthalonitrile to liquid ammonia is 1:5; the reaction products were analyzed by gas chromatography, and the calculation statistics showed that the catalyst was operated for 1000h and 2000h respectively, and the conversion rate of isophthalonitrile and the selectivity of meta-xylylenediamine were .

[0047] Table 1

[0048]

[0049] As can be seen from Table 1, the catalyst for preparing m-xylylenediamine disclosed in the embodiment of the present invention has better catalytic activity and selectivity, and better stability than the comparative example product; the addition of Os, Nb, Hf, Ta, Sr, Sb, Al and Ga is beneficial to improving the above properties.

[0050] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A catalyst for preparing meta-xylylenediamine, characterized in that: It includes a carrier and active components and additives attached to the carrier; the active components are a mixture of Ru, Os, Ni, Nb, rare earth, Sr, Sb, and Co in a mass ratio of 1:(1-3):(2-3):(1-3):2:(0.8-1.2):(0.3-0.5):0.4; the additives are a mixture of Ir, Zn, Cr, Hf, Ta, Al, and Ga in a mass ratio of 0.6:(1-3):(0.8-1.2):(0.1-0.3):0.2:(0.8-1.2):(0.2-0.4); the rare earth is a mixture of Sc, Y, Gd, and Tb in a mass ratio of 1:(0.6-1):(0.3-0.6):(0.1-0.3); The carrier is a surface-modified carrier; the preparation method of the surface-modified carrier comprises the following steps: dispersing the carrier in an organic solvent, adding N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and an initiator thereto, stirring and reacting for 3-5 hours at 60-70° C. in an inert gas atmosphere, and then removing the solvent by rotary evaporation to obtain a surface-modified carrier; the mass ratio of the carrier, the organic solvent, N-trimethylolmethyl acrylamide, vinyl trimethoxysilane, 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt and the initiator is (3-5):(10-25):(0.1-0.2):0.1:0.1:(0.003-0.0.005).

2. The catalyst for preparing meta-xylylenediamine according to claim 1, characterized in that: The content of the active component is 4-23% of the total mass of the catalyst.

3. The catalyst for preparing meta-xylylenediamine according to claim 1, characterized in that: The content of the auxiliary agent is 2-7% of the total mass of the catalyst.

4. The catalyst for preparing meta-xylylenediamine according to claim 1, characterized in that: The carrier is at least one of molecular sieve, diatomaceous earth and activated alumina.

5. The catalyst for preparing meta-xylylenediamine according to claim 4, characterized in that: The molecular sieve is at least one of SBA-15 molecular sieve and MCM-48 molecular sieve; the activated alumina is X-ρ type alumina.

6. The catalyst for preparing meta-xylylenediamine according to claim 1, characterized in that: The organic solvent is at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; the initiator is azobisisobutyronitrile; and the inert gas is any one of nitrogen, helium, neon, and argon.

7. A method for preparing a catalyst for preparing meta-xylylenediamine according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: mixing the active component and the chloride salt of each component of the auxiliary agent according to a proportion, adding the mixture into water, and evenly dispersing the mixture, and then impregnating the surface-modified carrier for 10-20 hours, taking the mixture out and drying it at 100° C. to a constant weight, and then reducing and activating the mixture in pure hydrogen at 390-420° C. and normal pressure for 3-6 hours to obtain a catalyst for preparing m-phenylenediamine.

Images