A monolithic catalyst loaded with noble metal, its preparation method and use, and a method for cracking and hydrogenating aniline tar

Abstract

The application relates to a noble metal loaded monolithic molecular sieve catalyst and a preparation method thereof and application thereof in aniline tar treatment. The noble metal loaded monolithic ZSM-5 molecular sieve catalyst is obtained by one-time forming through a water vapor assisted crystallization method with an industrial grade nanometer sponge as a carrier, the preparation process has high raw material utilization rate and few waste liquid, and a binder is not needed, the unique multilayer pore structure of micropore-mesopore-macropore strengthens adsorption and catalysis of aniline tar and carbon deposition resistance. The monolithic molecular sieve prepared based on the nanometer sponge carrier has good reaction activity, a stable mechanical structure, and enhanced heat transfer process of the reaction, and the aniline tar hydrocracking process is applied, and the monolithic molecular sieve has the characteristics of high tar cracking rate, high product selectivity, long catalyst service life and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical waste recycling, in particular to a supported noble metal monolithic catalyst, a preparation method thereof and a method for catalytic cracking and hydrogenation of aniline tar. BACKGROUND

[0002] Aniline is an important chemical raw material intermediate. There are 300 important products produced from aniline, and the main downstream products are MDI and antioxidant fields. With the continuous expansion of the downstream market MDI in recent years, the supporting aniline production capacity is continuously improved. At present, the total aniline production capacity in China has reached 4.3 million tons. In order to ensure that the purity of aniline products meets the requirements of MDI production, a large amount of tar-like high-viscosity mixture (aniline tar) will inevitably be generated during the production and refining of aniline. Aniline tar is a black viscous liquid at room temperature, which contains a small amount of light components such as aniline, aminophenol, methyl aniline, phenol, phenylenediamine and other nitrobenzene hydrogenation by-product, and the main heavy components are aminodiphenylamine and other long-chain polymers of three-ring and polycyclic aromatic hydrocarbons with larger molecular weight. At present, aniline tar is mainly treated by incineration. Although this treatment method can produce steam, the utilization rate of carbon atoms is very low, and a large amount of carbon dioxide and nitrogen oxides will be produced during the incineration process, causing great environmental pressure. Therefore, it is of great significance to reasonably utilize aniline tar, reduce environmental pollution, turn waste into treasure, and has significant environmental and economic benefits.

[0003] At present, the heavy component tar treatment method in chemical production mainly focuses on effective component physical extraction method, modification reaction method, high-temperature cracking method, catalytic cracking and hydrogenation method, etc. In comparison, the supported noble metal catalyst belongs to the low-temperature catalytic cracking and hydrogenation technology. Specifically, under the action of an acidic support and a noble metal active component, aniline tar is cracked at a relatively low temperature and further hydrogenated to generate high-value-added products cyclohexylamine and dicyclohexylamine. This technology has the characteristics of high carbon atom utilization rate, relatively mild reaction conditions, no secondary pollution, etc., and has been widely studied. At present, the research on supported metal hydrogenation cracking catalysts mainly focuses on granular or powder catalysts, which are divided into noble metal catalysts and non-noble metal catalysts. The preparation process generally involves loading noble metals (Pt, Au, Pd, Rh, etc.) or non-noble metals (Co, Ni, Ce, Sn, etc.) on molecular sieves or metal oxide supports. The catalysts prepared at present generally have the characteristics of short service life, poor thermal conductivity, low mechanical strength, and difficult regeneration.

[0004] Hydrocracking process is a typical petroleum processing process, and catalytic hydrocracking reaction is generally carried out in a fixed bed reactor, and the technical core is the catalyst. The overall process is that under the action of hydrogen and catalyst, heavy tar undergoes hydrogenation, cracking and isomerization reaction to convert into light oil, cracking gas and other effective components. At present, the catalytic hydrogenation process is relatively mature, but there are very few reports on its application in aniline tar waste liquid.

[0005] Chinese patent CN108047051A introduces a method for producing aniline and diphenylamine from aniline tar by catalytic cracking and a catalyst used therein, which includes a carrier and an active component. The carrier is a complex molecular sieve catalyst, and the active component includes Ni element and a cocatalyst. Using the catalyst can crack aniline tar to a certain extent to convert it into organic matter mainly composed of aniline and diphenylamine. However, the catalyst required in industrial application should be a particle with sufficient strength of mm or cm level, so the powdered molecular sieve must be added with a binder and then formed by extrusion or other methods. After adding the binder, the intrinsic activity of the catalyst will be reduced, and the actual effect of the nickel-based catalyst is also restricted by factors such as easy carbon deposition and deactivation of the catalyst. Since the composition of tar is complex, coke will be generated in the catalytic reforming process, which will affect the mass transfer process and reduce the service life of the catalyst.

[0006] Chinese patent CN113121311A introduces a comprehensive recovery process for aniline tar in aniline production. The aniline tar and organic acid solvent are mixed and fed into a rectification tower for hydrogenation treatment, and the tar is decomposed into small molecular substances by hydrogenolysis to produce high value-added products such as alcohol amine and solve the toxic effect of tar on the activity of the catalyst and recover the aniline catalyst. However, due to the flowability and reactivity of aniline tar itself, the conversion rate and selectivity of the reaction hydrogenation are low, and the generated products are complex, which is not conducive to subsequent separation.

[0007] US patents US5728883A and US5705700A introduce a non-supported cobalt catalyst and a method for synthesizing cyclohexylamine. The catalyst contains Co, Mn, alkaline earth metals and other metal elements. However, the reaction is carried out at a high pressure of 30 MPa, and as the reaction temperature increases, the selectivity of cyclohexylamine decreases rapidly, and the byproduct dicyclohexylamine increases significantly. Above 200℃, there is no obvious advantage in the yield of cyclohexylamine product, and industrial application is difficult. Since the cracking and hydrogenation reaction of aniline tar system is a typical high-temperature strong exothermic reaction, on the one hand, the traditional hydrogenation catalyst has poor heat conduction during the reaction, which easily causes local high temperature of the catalyst and "hot spots", making the coke generated in the fixed bed more easily accumulated on the active sites of the catalyst, further accelerating the deactivation of the catalyst and leading to a low service life. Therefore, it is believed that the traditional powder forming hydrogenation catalyst is not suitable for aniline tar system. SUMMARY

[0008] In order to solve the technical problems of poor heat conduction, low activity and low mechanical strength of the existing catalyst, the application provides a noble metal loaded monolithic catalyst and a preparation method thereof, and the catalyst has the characteristics of high activity, low pressure drop, excellent heat and mass transfer performance and long service life.

[0009] The application also provides the use of the noble metal loaded monolithic catalyst as an aniline tar cracking and hydrogenation treatment catalyst.

[0010] To achieve the above-mentioned purposes, the application provides the following solutions.

[0011] One of the technical solutions of the application is to provide a noble metal loaded monolithic molecular sieve catalyst, which is a monolithic hierarchical pore ZSM-5 molecular sieve catalyst synthesized by using a nano-sponge carrier as a carrier and a steam-assisted crystallization method.

[0012] The catalyst of the application is a one-time formed monolithic hierarchical pore ZSM-5, and the shape thereof is preferably cubic, the pore volume thereof is 0.20-0.40 cm 3 / g, the micropore volume thereof is 0.10-0.15 cm 3 / g, the mesopore volume thereof is 0.14-0.28 cm 3 / g, the specific surface area thereof is 300-400 m 2 / g, the content of the noble metal in the catalyst is 0.02-2.5 wt%, and the average particle size of the noble metal active component loaded is 1-6.9 nm.

[0013] The second technical solution of the application is to provide a preparation method of the noble metal loaded monolithic molecular sieve catalyst, which comprises the following steps.

[0014] (1) Dissolve an aluminum source in a solvent, stir, add a silicon source, and stir again to obtain a precursor solution; immerse a nano-sponge in the precursor solution, and then immerse the nano-sponge and an alkali source solution in a crystallization kettle to obtain a sponge carrier intermediate through crystallization;

[0015] (2) Add an organic structure directing agent to the sponge carrier intermediate obtained in step (1), dry, and crystallize to obtain an intermediate product;

[0016] (3) Wash, dry and calcine the intermediate product obtained in step (2) to obtain a monolithic ZSM-5 molecular sieve;

[0017] (4) The ZSM-5 molecular sieve obtained in the step (3) is impregnated with a noble metal solution, preferably equal volume impregnation, and calcined to obtain a noble metal loaded monolithic catalyst.

[0018] As a preferred scheme, the preparation method comprises the following steps:

[0019] (1) The aluminum source is dissolved in a solvent, preferably ultrasonic dissolution, and stirred at room temperature for 2-4h, then the silicon source is added, and stirred at room temperature for 4-6h to obtain a precursor solution. The nanosponge carrier cut into a suitable size is immersed in the precursor solution. The nanosponge carrier after immersion and the alkali source are separated by a stainless steel mesh and placed in a crystallization kettle for crystallization treatment. This process is repeated 3-5 times to ensure that the nanosponge carrier is loaded with sufficient silicon source and aluminum source;

[0020] (2) The nanosponge carrier intermediate obtained in the step (1) is proportionally added with an organic structure directing agent, and dried at 60-80℃ for 4-6h to obtain a nanosponge carrier containing silicon source, aluminum source and organic structure directing agent. The nanosponge carrier containing silicon source, aluminum source and organic structure directing agent is placed in a crystallization kettle for crystallization treatment to obtain an intermediate product;

[0021] (3) The intermediate product is washed, dried and calcined to remove the organic structure directing agent and the nanosponge carrier to obtain the monolithic ZSM-5 molecular sieve;

[0022] (4) The ZSM-5 molecular sieve is impregnated with a noble metal solution, preferably equal volume impregnation, and calcined to obtain a catalyst.

[0023] As a preferred scheme, the nanosponge carrier of the application is an industrial grade high density nanosponge, which has a 60-100μm large pore structure connected to each other, provides sufficient space for molecular sieve loading, and provides a transmission path for reactants and products in subsequent reactions. Preferably, the industrial grade high density nanosponge is produced by Puyang Enwovo New Material Co., Ltd.

[0024] As a preferred scheme, the nanosponge of the application is cleaned with methanol and then deionized water, and dried to remove various impurities in the carrier.

[0025] The solvent in the step (1) of the application is one or more of methanol, ethanol and acetone, and the mass ratio of the solvent to the aluminum source is (30-60):1.

[0026] The alkali source in the step (1) of the application is one or more of sodium hydroxide, potassium hydroxide and ammonia water; preferably ammonia water, the mass concentration of the alkali source solution is 5wt%-35wt%, preferably 28wt%-30wt%; and / or, the mass ratio of the alkali source solution to the nanosponge is (10-15):1.

[0027] In step (1) of the present application, the temperature of the impregnation is 60-80℃, and the time of the impregnation is 0.5-2h.

[0028] In step (1) of the present application, the pressure of the crystallization treatment is 0.7-1.2MPa, the temperature is 80-120℃, and the time is 8-12h.

[0029] In step (1) of the present application, the silicon source is one or more of ethyl silicate (TEOS), water glass, silica sol, sodium silicate, and white carbon black.

[0030] In step (1) of the present application, the aluminum source is one or more of aluminum isopropoxide, aluminum sulfate, sodium metaaluminate, and aluminum nitrate.

[0031] In step (1) of the present application, the molar ratio of the silicon source to the aluminum source is (40-280):1, preferably (50-70):1.

[0032] In step (2) of the present application, the organic structure directing agent is one or both of cetyltrimethylammonium bromide (CTAB) and hexadecyltrimethoxysilane (HTS), preferably hexadecyltrimethoxysilane (HTS), and the molar ratio of the silicon source to the organic structure directing agent is (4-50):1.

[0033] In step (2) of the present application, the pressure of the crystallization treatment is 0.7-1.2MPa, the temperature is 170-180℃, and the time is 48-60h, and the mass ratio of the water in the hydrothermal kettle to the sponge carrier is (10-15):1.

[0034] In step (3) of the present application, the medium for washing is deionized water, and the washing is repeated 3-5 times to adjust the pH to 8-9.

[0035] In step (3) of the present application, the temperature of the drying is 80-90℃, and the time of the drying is 6-8h.

[0036] In steps (3) and (4) of the present application, the temperature of the calcination is 500-600℃, the atmosphere of the calcination is air, and the time of the calcination is 3-9h.

[0037] In step (4) of the present application, the noble metal solution is one or more of chloroplatinic acid, chloropalladic acid, sodium chloropalladic acid, palladium nitrate, and palladium acetate, and the concentration is 0.1-0.6g / L, preferably 0.15-0.2g / L.

[0038] In step (4) of the present application, the temperature of the impregnation is 80-90℃, and the time is 2-8h.

[0039] The third technical solution of the present application provides application of the above-mentioned supported noble metal monolithic catalyst in aniline tar cracking hydrogenation. The application method of the monolithic multi-level pore molecular sieve catalyst in aniline tar cracking hydrogenation reaction comprises the following steps:

[0040] The aniline tar cracking hydrogenation catalyst provided by the present application is filled into a fixed bed reactor, heated to 450-600 DEG C under a flow hydrogen atmosphere of 0.3-0.8 MPa, and reduced at constant temperature for 3-5 h.

[0041] The fixed bed is cooled to the required reaction temperature, the hydrogen feed flow and the reaction pressure are adjusted, the aniline tar is preheated to 140-200 DEG C and then input into the fixed bed reactor filled with the above-mentioned catalyst for reaction, and a reaction liquid containing cyclohexylamine and dicyclohexylamine is obtained.

[0042] Preferably, the reaction temperature is 250-320 DEG C, more preferably 280-300 DEG C, and the reaction pressure is 3-5 MPa, more preferably 3.5-4 MPa.

[0043] Preferably, the molar ratio of hydrogen to aniline tar is 25-60:1, more preferably 30-35:1.

[0044] It should be noted that in the application of the above-mentioned catalyst, the number and connection scheme of the reactors for aniline tar cracking hydrogenation reaction are not particularly limited, and the reaction can be carried out in one reactor or in multiple parallel or serial reactors.

[0045] Specifically, the aniline tar comprises 8-30 wt%, preferably 15-30 wt% of aminophenol, 13-20 wt% of aniline, 25-45 wt% of aminodiphenylamine, and the rest is impurities, wherein the impurities comprise methyl aniline, diphenylamine, phenylenediamine and other heavy components with three or more rings, etc.

[0046] The reaction pressure in the present application is absolute pressure.

[0047] The positive effects of the present application are: (1) the present application provides a monolithic ZSM-5 molecular sieve catalyst synthesized based on a nanosponge carrier. The nanosponge carrier has a large interconnected pore structure, which increases the loading space and contact area of the molecular sieve catalyst, and also provides a transmission channel for the reaction raw materials and products in the subsequent reaction. (2) The one-time molding by the steam-assisted crystallization method can obtain a molecular sieve with the same shape as the original sponge carrier, and forms a multi-level pore structure of microporous-mesoporous-macroporous. The raw material utilization rate is high during the synthesis process, reducing the discharge of waste liquid and improving the green degree of the synthesis process. No binder is needed, and the reaction performance of the catalyst is better than that of the ordinary powder-formed ZSM-5 catalyst. (3) The macroporous structure provided by the nanosponge carrier and the three-dimensional multi-level pore structure formed by the combination of the structure molecular sieve strengthen the adsorption and catalysis of aniline tar, the construction of multi-level pores can effectively improve the transmission channel of the reactants and products, and the mesoporous structure can slow down the carbon deposition in the micropores and effectively enhance the stability of the catalyst, thereby improving the service life of the catalyst. Compared with the traditional powder catalyst, the monolithic molecular sieve based on the nanosponge carrier has a stable mechanical structure, increases the heat transfer process of the reaction, can effectively avoid the hot spot problem in the reaction process, and is more suitable for aniline tar cracking and hydrogenation system. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The scanning electron microscope morphology of the nanosponge carrier is shown in the figure;

[0049] Figure 2 The overall morphology of Example 1 is shown in the figure;

[0050] Figure 3 The micro-morphology of Example 1 is shown in the figure;

[0051] Figure 4 The micro-morphology of Comparative Example 1 is shown in the figure;

[0052] Figure 5 The micro-morphology of Comparative Example 2 is shown in the figure;

[0053] Figure 6 The XRD spectrum of the sample is shown in the figure;

[0054] Figure 7 The N2 adsorption-desorption isotherm of the sample is shown in the figure. DETAILED DESCRIPTION

[0055] The raw materials used in the detailed description and their sources are shown in Table 1.

[0056] Table 1 Synthesis raw materials of monolithic multi-level pore ZSM-5 molecular sieve

[0057]

[0058]

[0059] Analytical test methods

[0060] The loading of the molecular sieve was estimated by the mass change of the support before and after synthesis.

[0061] The pore structure properties were determined by a Micromeritics ASAP-2020V3.00H adsorption instrument. The specific surface area, micropore parameters and pore size distribution were calculated by BET method, t-plot method and BJH method, respectively.

[0062] The crystallization state of the sample was characterized by a D / max 2550VB / PC rotating target diffractometer.

[0063] The acid strength and acid amount of the sample were determined by a Micromeritics ChemiSorb 2720 adsorption instrument, and calculated by temperature programmed desorption (NH3-TPD) data.

[0064] The morphology of the sample was obtained by a Nova Nano SEM of FEI Company.

[0065] Example 1

[0066] (1) Nanosponge was selected as the support, and the support morphology is shown in the accompanying drawings. Figure 1 The sponge support has a three-dimensional macroporous structure interconnected with each other. The whole support was cut into small blocks of 1 cm in length, width and height, and then immersed in an excess amount of methanol solution for ultrasonic treatment for 10 min. The cut support was washed repeatedly with deionized water by ultrasonic treatment to remove impurities, and then dried in an oven at 65°C for 12 h.

[0067] (2) 0.275 g of aluminum isopropoxide AIP was ultrasonically dissolved in 16 ml of ethanol, and stirred at room temperature for 2 h. Then, 14 g of silicon source TEOS was added, and stirred at room temperature for 5 h to obtain a precursor solution. 0.15 g of the sponge support pretreated in step (1) was weighed and immersed in the precursor solution, and the immersion temperature was 60°C, and the immersion time was 2 h. The immersed sponge was placed in a crystallization kettle containing 2 g of 30% ammonia solution, and the sponge and the ammonia water were separated by a stainless steel mesh. After loading, the crystallization kettle was placed in an oven at 80°C for 12 h, and the crystallization treatment pressure was 1 MPa. The crystallization kettle was removed and quenched to room temperature, and the process was repeated for 3 times.

[0068] (3) In step (2), hexadecyltrimethoxysilane, a structure-directing agent, was added to the sponge carrier at a ratio of n(SiO2):n(HTS) = 1:0.04, and dried at 60°C for 4 hours. The resulting sponge block containing silicon source, aluminum source, and structure-directing agent was placed in a PTFE-lined crystallization vessel with 2g of distilled water at the bottom. The vessel was then steam-assisted crystallization was performed at 180°C for 48 hours at a crystallization pressure of 1.0 MPa. After synthesis, the crystallization vessel was removed and quenched to ambient temperature. The obtained product was washed 3–5 times with deionized water, the pH was adjusted to 8–9, and the product was dried at 80°C for 8 hours. Finally, it was calcined at 550°C in air for 8 hours to remove the organic structure-directing agent and the sponge carrier.

[0069] (4) The obtained monolithic molecular sieve catalyst was impregnated with an equal volume of 0.15 g / L chloroplatinic acid solution at 85 °C for 5 h, and then calcined at 550 °C in air for 7 h to complete the noble metal loading. The Pt noble metal loading was 0.5 wt%, and the average particle size was 4.8 nm.

[0070] (5) Weigh 2.5g of the monolithic catalyst, cut the bulk cubic block into smaller pieces, and fill them into a fixed-bed reactor. Fill the top and bottom with an equal volume of quartz sand. In a flowing hydrogen atmosphere (99.999%, 0.5MPa), raise the temperature from room temperature to 450℃ at a rate of 2℃ / min, and then maintain the constant temperature for 5h. After the reduction is complete, cool down to 290℃, adjust the reaction pressure to 4MPa, preheat the aniline tar to 180℃, adjust the hydrogen flow rate to the aniline tar molar ratio to 30:1, and pump the raw materials hydrogen and tar into the fixed-bed reactor filled with the above catalyst for reaction.

[0071] Example 2

[0072] (1) Nano sponges were selected as the carriers, and the morphology of the carriers is shown in the attached figure. Figure 1 As shown, the sponge carrier has an interconnected three-dimensional macroporous structure. The entire carrier was cut into small cubes with dimensions of 1 cm in length, width, and height. The cut carriers were immersed in an excess methanol solution and sonicated for 10 min. They were then repeatedly ultrasonically washed with deionized water to remove impurities from the carriers and then dried in an oven at 65°C for 12 h.

[0073] (2) 0.125 g of sodium metaaluminate was dissolved in 8 ml of methanol by ultrasonic treatment, and stirred at room temperature for 2 h. Then, 12 g of silica sol was added, and stirred at room temperature for 5 h to obtain a precursor solution. 0.15 g of the sponge carrier pretreated in step (1) was weighed and immersed in the precursor solution, and the immersion temperature was 75 °C, and the immersion time was 2 h. The sponge after immersion was placed in a crystallization kettle containing 2.25 g of 5% sodium hydroxide aqueous solution, and the sponge and the sodium hydroxide aqueous solution were separated by a stainless steel mesh. After loading, the crystallization kettle was placed in a 100 °C oven for 10 h, and the crystallization treatment pressure was 0.8 MPa. The crystallization kettle was removed and quenched to room temperature, and the process was repeated 3 times.

[0074] (3) In the sponge carrier obtained in step (2), a structure directing agent, cetyltrimethylammonium bromide, was added according to n(SiO2):n(CTAB) = 1:0.02, and dried at 60 °C for 4 h. The sponge block containing the silica source, the aluminum source and the structure directing agent was placed in a PTFE-lined crystallization kettle, 2 g of distilled water was placed at the bottom of the kettle, and steam-assisted crystallization was carried out in a 175 °C oven for 55 h, and the crystallization treatment pressure was 0.8 MPa. After the synthesis was completed, the crystallization kettle was removed and quenched to ambient temperature. The obtained product was washed repeatedly with deionized water for 3-5 times, the pH was adjusted to 8-9, the obtained product was dried at 90 °C for 6 h, and then calcined at 600 °C in an air atmosphere for 8 h to remove the organic structure directing agent and the sponge carrier.

[0075] (4) The obtained monolithic molecular sieve catalyst was impregnated with an equal volume of 0.40 g / L palladium nitrate solution at 90 °C for 8 h, and then calcined at 600 °C in an air atmosphere for 3 h to complete the noble metal loading. The Pd noble metal loading was 0.7 wt%, and the average particle size was 6.5 nm.

[0076] (5) 2.5 g of the monolithic catalyst was weighed, and the monolithic cubic block was cut into smaller block-shaped pieces and packed into a fixed bed reactor, and an equal volume of quartz sand was packed above and below. In a flowing hydrogen atmosphere (99.999%, 0.6 MPa), the temperature was increased to 500 °C at a rate of 2 °C / min from room temperature, and then kept constant for 4.5 h for reduction. After reduction, the temperature was lowered to 280 °C, the reaction pressure was adjusted to 5 MPa, the aniline tar was preheated to 200 °C, the hydrogen flow rate and the aniline tar molar ratio were adjusted to 35:1, the raw materials hydrogen and tar were pumped into the fixed bed reactor packed with the above-mentioned catalyst to carry out the reaction.

[0077] Example 3

[0078] (1) Nanosponge was selected as the carrier, and the carrier morphology was as shown in FIG. 1. Figure 1The sponge carrier has a three-dimensional macroporous structure as shown. The whole carrier was cut into small cubes with a length, width and height of 1 cm. The cut carrier was immersed in a methanol solution and ultrasonically treated for 10 min, then washed repeatedly with deionized water by ultrasonic treatment to remove impurities in the carrier, and then dried in an oven at 75°C for 10 h.

[0079] (2) 0.285 g of aluminum sulfate was ultrasonically dissolved in 15 ml of acetone, stirred at room temperature for 2.5 h, then 11 g of sodium silicate was added, stirred at room temperature for 5 h to obtain a precursor solution. 0.15 g of the sponge carrier pretreated in step (1) was weighed and immersed in the precursor solution, the immersion temperature was 80°C, and the immersion time was 2 h. The immersed sponge was placed in a crystallization kettle containing 2.25 g of 35% ammonia water solution, and the sponge and ammonia water were separated by a stainless steel mesh. After loading, the crystallization kettle was placed in a 105°C oven for 8 h, the crystallization treatment pressure was 1.1 MPa, and the crystallization kettle was removed to quench to room temperature. This process was repeated three times.

[0080] (3) According to the molar ratio of hexadecyltrimethoxysilane HTS / SiO2 of 0.06, dry at 60°C for 4 h. Put the sponge block containing the silicon source, aluminum source and structure directing agent into the PTFE-lined crystallization kettle, add 2 g of distilled water at the bottom of the kettle, and use steam-assisted crystallization in a 170°C oven for 60 h, with a crystallization treatment pressure of 1.1 MPa. After the synthesis is completed, the crystallization kettle is removed and quenched to ambient temperature. The obtained product is dried at 85°C for 7 h, and then calcined at 500°C in air for 6 h to remove the organic structure directing agent and the sponge carrier.

[0081] (4) The obtained monolithic molecular sieve catalyst was immersed in an equal volume of 0.60 g / L sodium palladium chloride solution at 80°C for 8 h, and then calcined at 600°C in air for 5 h to complete the noble metal loading. The Pd noble metal loading was 0.9 wt%, and the average particle size was 4.2 nm.

[0082] (5) Weigh 2.5 g of the monolithic catalyst, cut the monolithic cube into smaller blocks and fill them into a fixed bed reactor with equal volume of quartz sand at the top and bottom. In a flowing hydrogen atmosphere (99.999%, 0.8 MPa), the temperature was increased from room temperature to 600°C at a rate of 2°C / min, and then kept constant for 4.5 h of reduction. After reduction, the temperature was lowered to 300°C, the reaction pressure was adjusted to 3 MPa, the aniline tar was preheated to 160°C, the hydrogen flow rate was adjusted to a molar ratio of 40:1 to aniline tar, and the raw materials hydrogen and tar were pumped into the fixed bed reactor filled with the above-mentioned catalyst to carry out the reaction.

[0083] Comparative Example 1

[0084] (1) with tetraethyl orthosilicate (TEOS) as silicon source, hexadecyl trimethoxysilane (HTS) as template agent, sodium aluminate as aluminum source, and sodium hydroxide as alkali source, under stirring, the NaAlO2 and NaOH were dissolved in water and stirred, then HTS was dissolved in water, TEOS was slowly added dropwise, stirring at 80°C for 4h;

[0085] (2) The slurry prepared in step (1) was placed in a culture dish and air-dried to obtain a dry gel.

[0086] (3) The dry gel prepared in step (2) was transferred to a beaker, the beaker was added to a crystallization kettle, and water with the same mass as the dry gel was placed at the bottom of the crystallization kettle, and crystallized at 180°C for 72h, then washed, dried at 100°C, and then placed in a muffle furnace at 550°C in air for 8h. A microporous ZSM-5 powder was obtained.

[0087] Steps (4) and (5) are the same as in Example 1.

[0088] Comparative Example 2

[0089] Step (1) is the same as in Example 1

[0090] (2) With tetraethyl orthosilicate (TEOS) as silicon source, tetrapropylammonium hydroxide (TPAOH) as template agent, the precursor solution for synthesizing molecular sieve was prepared in a molar ratio of n(TEOS):n(TPAOH):n(H2O) = 1:0.3:20, stirring until clear, the precursor solution was poured into a stainless steel crystallization kettle, dynamic crystallization at 180°C for 56h, the product was separated by centrifugation and washed with deionized water, dried at 80°C, and then calcined at 550°C in air for 6h to remove the template agent to obtain a full-silicon type seed crystal. The seed crystal was ultrasonically treated to uniformly disperse in deionized water to prepare a 2wt% seed crystal suspension, ammonia was added dropwise to adjust the pH value of the suspension to 8.0, the pretreated sponge carrier was placed in the seed crystal suspension, ultrasonic immersion for 10min, and then dried in an oven at 100°C for 12h;

[0091] (3) With tetraethyl orthosilicate (TEOS) as silicon source, hexadecyl trimethoxysilane (HTS) as template agent, aluminum isopropoxide as aluminum source, and sodium hydroxide as alkali source, in a ratio of n(SiO2):n(HTS):n(Al2O3):n(NaOH):n(H2O) = 1:0.05:1 / 60:0.1:120, first NaAlO2 and NaOH were dissolved in water and stirred; then the structure directing agent TPAOH was dissolved in the solution, TEOS was slowly added dropwise, and stirred at 80°C for 4h until clear.

[0092] (4) Put the seed coated sponge carrier into 100 mL crystallization kettle, pour the mixed solution prepared in step (3) into the kettle, and crystallize at 180 °C for 45 h. After being taken out, washed, and dried at 105 °C, the sponge carrier is removed by calcining at 550 °C in a muffle furnace in air for 68 h.

[0093] (5) The obtained monolithic molecular sieve catalyst is impregnated with an equal volume of 0.15 g / L chloroplatinic acid solution at 85 °C for 5 h, and then calcined at 550 °C in air for 7 h to complete the loading of noble metal. The Pt noble metal loading is 0.4 wt%, and the average particle size is 4.5 nm.

[0094] (6) 2.5 g of the monolithic catalyst is weighed, and the monolithic cubic block is cut into smaller blocks and packed into a fixed bed reactor with equal volume of quartz sand at the top and bottom. The temperature is raised to 450 °C at a rate of 2 °C / min from room temperature in a flowing hydrogen atmosphere (99.999%, 0.5 MPa), and then kept constant for 5 h. After reduction, the temperature is lowered to 290 °C, the reaction pressure is adjusted to 4 MPa, the aniline tar is preheated to 180 °C, the hydrogen flow and the molar ratio of aniline tar are adjusted to 30:1, the raw materials hydrogen and tar are pumped into the fixed bed reactor packed with the above-mentioned catalyst to carry out the reaction.

[0095] The monolithic morphology of the catalyst of Example 1 is shown in FIG. 1, from which it can be seen that the sponge carrier has been removed by calcination, and a large amount of molecular sieve is loaded on the skeleton structure, and the molecular sieve particles are closely packed to form the monolithic catalyst. The morphologies of the samples of the examples are similar, and will not be described in detail. The micro-morphology of the catalyst of Example 1 is shown in FIG. 2, from which it can be seen that the surface of the particles of Example 1 has obvious etching, indicating that the addition of the structure-directing agent successfully constructs a hierarchical pore structure. The other examples are similar to Example 1, and will not be described in detail. Figure 2 Figure 3 As shown in FIG. 3, the molecular sieve prepared in Comparative Example 1 is a microporous molecular sieve without sponge carrier loading. Due to repeated crystallization, the molecular sieve grows multiple times to become a structure in which the two are inlaid, and the particle size is relatively large, being 2-3 μm. As shown in FIG. 4, Comparative Example 2 is a carrier molecular sieve prepared by hydrothermal synthesis. Due to the amount of water solvent and the coating process, the molecular sieve layer prepared is significantly less than the same sample prepared by the steam-assisted crystallization method, and the molecular sieve layer has a fracture and an uneven phenomenon.

[0096] As shown in FIG. 5, the molecular sieve prepared in Comparative Example 1 is a microporous molecular sieve without sponge carrier loading. Due to repeated crystallization, the molecular sieve grows multiple times to become a structure in which the two are inlaid, and the particle size is relatively large, being 2-3 μm. As shown in FIG. 4, Comparative Example 2 is a carrier molecular sieve prepared by hydrothermal synthesis. Due to the amount of water solvent and the coating process, the molecular sieve layer prepared is significantly less than the same sample prepared by the steam-assisted crystallization method, and the molecular sieve layer has a fracture and an uneven phenomenon. Figure 4 Figure 5 The crystallinity of the samples of the examples is shown in FIG. 6.

[0097] The crystallinity of the samples of the examples is shown in FIG. 6. Figure 6 ​​As shown, the MFI type structure characteristic peaks of Example 1, Example 2 and Example 3 are typical, and the crystallinity is more than 90%, which indicates that in the preparation process, each example successfully synthesizes a good ZSM-5 molecular sieve, and the nano-sponge carrier has no obvious adverse effect on the ZSM-5 crystallization process.

[0098] The isothermal adsorption and desorption curves of each example and the comparative sample are shown in FIG. 2. Figure 7 As shown, the molecular sieve pore structure parameters are shown in Table 2. Figure 7 It can be seen that the isotherms of Example 1, Example 2, Example 3 and Comparative Example 2 are a mixture of type I and type IV, and there is an obvious hysteresis loop, which is due to the capillary condensation phenomenon in the mesopore, which proves that the structure directing agent and the sponge carrier structure provided by the application successfully play a role in preparing a hierarchical pore in the synthesis process. The isotherm of Comparative Example 1 basically conforms to the conventional type I isotherm, which indicates that the pore type of the molecular sieve sample is mainly microporous. The BET surface area and pore volume of each example are greater than those of the comparative sample, and after the sponge carrier is burned off, a multi-level structure of macropore-mesopore-micropore is formed in the molecular sieve, thereby better improving the reaction performance of the catalyst.

[0099] Table 2 Pore structure parameters of different example samples

[0100]

[0101]

[0102] The acid amount data of each example and the comparative sample are shown in Table 3, and the data shows that the weak acid content and acid strength difference between Example 1, Example 2 and Example 3 is small, and the strong acid content difference is obvious. Aniline tar cracking and hydrogenation is a typical acid catalytic reaction, and the yield and selectivity of the reaction are directly affected by the acidity and acid amount of the catalyst, especially the strong acid amount, and a lower acid amount cannot provide sufficient reaction active center to ensure tar cracking. Each sample can meet the performance requirements of the catalytic reaction, but a higher strong acid amount will cause the catalyst to deactivate quickly and have a short service life. From the data, each example has an advantage.

[0103] Table 3 Acid amount data of different example samples

[0104]

[0105] The reaction conversion rate, selectivity and service life of each example and the comparative sample are shown in the table: Table 4 Reaction data of different examples

[0106]

[0107]

[0108] From the data in the table, it can be seen that the catalyst of the present application applied to the reaction of aniline tar cracking hydrogenation synthesis of cyclohexylamine and dicyclohexylamine, shows excellent catalytic performance, tar cracking rate and product selectivity is high to 100% and more than 95%, high temperature and high pressure and high hydrogen oil ratio conditions can crack macromolecular substances into small molecules of hydrocarbons, which is beneficial to aniline tar cracking hydrogenation. The tar cracking rate of the catalysts of example 1, example 2, example 3, comparative example 1 after reaction is 100%, while the tar cracking rate of comparative example 2 is 97%, which shows that the molecular sieve synthesized by steam assisted method has high loading and strong activity per unit, the product yield is example 1> example 2> example 3> comparative example 2, and is higher than that of comparative example 1 ordinary powder HZSM-5, which shows that the cubic shaped monolithic molecular sieve obtained after crystallization saves the processes of tabletting or extruding and the used binding aids, improves the preparation efficiency and the utilization rate of molecular sieve, the aromatic selectivity of the reaction is affected by the synergistic effect of catalyst acidity and diffusion, and the micropore active sites of the catalyst with multi-level pore structure of each group of examples are more exposed, and the diffusion performance is better.

[0109] The order of the length of the service life of the catalysts of each example and comparative example is example 1> example 2> example 3> comparative example 2. And the service life of the monolithic molecular sieve catalyst is longer than that of the powder molecular sieve catalyst of comparative example 1. The examples show good stability due to moderate acidity, and the unique multi-level structure of micropore-mesopore-macropore strengthens the diffusion of products and inhibits the deposition of carbon in the micropore orifice and channel. The mesopore volume of example 1 is the largest and the mesopore amount is the most, so its capacity to accommodate carbon is better, and therefore the stability is the best and the service life is the longest.

[0110] The above is only the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the method of the present application, a number of improvements and supplements can also be made, which should be considered as the protection scope of the present application.

Claims

1. A method for preparing a monolithic molecular sieve catalyst supported on noble metals, characterized in that, Includes the following steps: (1) Dissolve the aluminum source in a solvent, stir, add the silicon source, and stir again to obtain the precursor solution; place the nano sponge in the precursor solution for immersion, and after immersion, place the nano sponge and the alkaline source solution in a crystallization kettle to crystallize and obtain the sponge carrier intermediate. (2) Add an organic structure directing agent to the sponge carrier intermediate obtained in step (1), dry, crystallize, and obtain an intermediate product; (3) The intermediate product obtained in step (2) is washed, dried and calcined to obtain monolithic ZSM-5 molecular sieve; (4) The monolithic ZSM-5 molecular sieve obtained in step (3) is impregnated with a noble metal solution and then calcined to obtain a monolithic catalyst supported on noble metals. The nano-sponge is an industrial-grade high-density nano-sponge with interconnected 60-100μm macroporous structures; the crystallization in steps (1) and (2) is steam-assisted crystallization.

2. The method according to claim 1, characterized in that, The alkaline source is one or more of sodium hydroxide, potassium hydroxide, and ammonia water; and / or, the mass ratio of the alkaline source solution to the nano sponge is (10-15):

1.

3. The method according to claim 2, characterized in that, The mass concentration of the alkaline source solution is 5%-35wt%.

4. The method according to claim 3, characterized in that, The mass concentration of the alkaline source solution is 28%-30wt%.

5. The method according to claim 1, characterized in that, In step (1), the silicon source is one or more of ethyl silicate, silica sol, silica fume, water glass, and sodium silicate.

6. The method according to claim 5, characterized in that, In step (1), the aluminum source is one or more of aluminum isopropoxide, aluminum sulfate, sodium aluminate, and aluminum nitrate, and the molar ratio of silicon source to aluminum source is (40-280):

1.

7. The method according to claim 6, characterized in that, In step (1), the molar ratio of silicon source to aluminum source is (50-70):

1.

8. The method according to claim 1, characterized in that, In step (1), the crystallization treatment pressure is 0.7-1.2 MPa, the temperature is 80-120℃, and the time is 8-12 h; and / or, in step (2), the crystallization treatment pressure is 0.7-1.2 MPa, the temperature is 170-180℃, and the time is 48-60 h.

9. The method according to claim 1, characterized in that, In step (2), the organic structure directing agent is one or both of hexadecyltrimethylammonium bromide and hexadecyltrimethoxysilane; and / or, the molar ratio of silicon source to organic structure directing agent is (4-50):

1.

10. The method according to claim 1, characterized in that, In step (4), the noble metal solution is one or more of chloroplatinic acid, chloropalladium acid, sodium chloropalladium, palladium nitrate, and palladium acetate solution, with a concentration of 0.1-0.6 g / L.

11. The method according to claim 1, characterized in that, In step (4), the impregnation is an equal-volume impregnation.

12. Use of the catalyst prepared by any one of claims 1-11 as a catalyst for the hydrocracking of aniline tar.

13. A method for pyrolysis and hydrogenation of aniline tar, characterized in that, Includes the following steps: The catalyst prepared by any one of claims 1-11 is reduced at 450°C-600°C under a flowing hydrogen atmosphere of 0.3-0.8 MPa for 3-5 hours; aniline tar is preheated to 140-200°C and reacted in a fixed-bed reactor packed with the above catalyst to obtain a reaction solution containing cyclohexylamine and dicyclohexylamine.

14. The method according to claim 13, characterized in that, The reaction temperature is 250℃-320℃, and the reaction pressure is 3-5MPa.

15. The method according to claim 14, characterized in that, The reaction temperature is 280-300℃ and the reaction pressure is 3.5-4 MPa.

16. The method according to claim 13, characterized in that, The feed molar ratio of hydrogen and aniline tar is 25-60:

1.

17. The method according to claim 16, characterized in that, The feed molar ratio of hydrogen and aniline tar is 30-35:1.

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