A zsm-22 molecular sieve / high clay core-shell type catalyst, its preparation method and application

Abstract

The application belongs to the technical field of molecular sieve catalysts, and particularly relates to a ZSM-22 molecular sieve / high clay core-shell type catalyst, a preparation method and application thereof. The preparation method of the catalyst comprises the following steps: (1) preparation of a ZSM-22 molecular sieve precursor solution: mixing a silicon source, an aluminum source, an alkali source, a template agent and water until uniform to obtain a reaction precursor solution; (2) in-situ crystallization: first performing low-temperature aging on a mixture of the reaction precursor solution and high clay microspheres, and then performing a hydrothermal crystallization reaction to obtain ZSM-22 molecular sieve / high clay raw powder; (3) post-treatment: mixing the ZSM-22 molecular sieve / high clay raw powder with an aqueous solution containing NH4+ and performing a reaction, and then performing solid-liquid separation, washing, drying and calcination on the mixture after the reaction to obtain a primary modified product, and repeating the step to obtain the catalyst. The catalyst can be used for the synthesis of dimethylamine and has high selectivity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of molecular sieve catalysts, and particularly relates to a ZSM-22 molecular sieve / high clay core-shell type catalyst, a preparation method and application thereof. BACKGROUND

[0002] Dimethylamine is a colorless flammable gas or liquid, has ammonia odor at high concentration or compressed liquefaction, has fish oil odor at low concentration, is easily soluble in water, soluble in ethanol and diethyl ether, and is toxic. Dimethylamine is an important organic chemical raw material, and is mainly used for pesticides, medicines, rubber accelerators, fatty tertiary amines, industrial solvents, dimethylacetamide and organic intermediates. At present, dimethylamine is mainly obtained by gas phase contact reaction of methanol and ammonia in a fixed bed, and the catalyst is an acidic catalyst with dehydration and ammoniation function, such as γ-Al2O3, aluminum silicate, molecular sieve and the like. Under the action of such catalysts, the reaction is thermodynamically balanced, and the amount of trimethylamine generated is high. In recent years, the demand for dimethylamine as a raw material for dimethylformamide production is increasing worldwide, and therefore, how to improve the yield of dimethylamine has attracted widespread attention.

[0003] In addition, in order to easily form a complex azeotropic system among dimethylamine, monomethylamine and trimethylamine from the reaction products, and to separate the target product dimethylamine therefrom, very complex and large distillation equipment is required, and the energy consumption and cost of separation and recovery process are extremely high, and it is urgent to improve the reaction and separation process and reduce the energy consumption of product separation and purification. SUMMARY

[0004] In order to solve the above technical problems, one of the purposes of the present application is to provide a catalyst for synthesizing dimethylamine, which is a "core-shell" structure molecular sieve type catalyst, has the characteristics of controllable active component and pore structure, high catalytic activity and high selectivity, and by using the catalyst, high-purity dimethylamine can be directly obtained by using a fluidized bed reactor and multi-stage condensation separation equipment.

[0005] Another purpose of the present application is to provide a preparation method of the catalyst, which is prepared by using a low-temperature in-situ crystallization method, and has the characteristics of simple operation, low energy consumption and simple equipment requirements.

[0006] To achieve the above-mentioned purposes, one of the technical solutions provided by the present application is as follows:

[0007] The present application provides the following technical solution: a method for preparing the ZSM-22 molecular sieve / high clay core-shell type catalyst, comprising the following steps:

[0008] (1) Preparation of ZSM-22 molecular sieve precursor solution: mixing a silicon source, an aluminum source, an alkali source, a template agent and water until uniform to obtain a reaction precursor solution;

[0009] (2) In-situ crystallization: the mixture of the reaction precursor solution and the kaolin microspheres is first subjected to low-temperature aging, and then subjected to hydrothermal crystallization reaction to obtain ZSM-22 molecular sieve / kaolin raw powder;

[0010] (3) Post-treatment: the ZSM-22 molecular sieve / kaolin raw powder is mixed with an aqueous solution containing NH4 + , and the mixture after the reaction is subjected to solid-liquid separation, washing, drying and calcination to obtain a primary modified product; the post-treatment step (3) is repeated to obtain the core-shell structured ZSM-22 / kaolin spherical catalyst.

[0011] Preferably, in step (1), the molar ratio of each component in the ZSM-22 molecular sieve precursor solution is n (silicon source) : n (aluminum source) : n (alkali source) : n (template) : n (H2O) = (60-80) : 1 : (10-15) : (2-4) : (1500-2000).

[0012] Preferably, in step (1), the silicon source is at least one of silica sol, tetraethyl orthosilicate and white carbon black.

[0013] Preferably, in step (1), the aluminum source is at least one of pseudo-boehmite, aluminum sulfate octadecahydrate and sodium metaaluminate.

[0014] Preferably, in step (1), the alkali source is at least one of NaOH and KOH.

[0015] Further preferably, in step (1), the alkali source is a mixture of NaOH and KOH, and the mass ratio of NaOH to KOH is (3-4) : 1.

[0016] Preferably, in step (1), the template is at least one of ethylenediamine, 1,6-hexanediamine and n-butylamine.

[0017] Further preferably, in step (1), the template is a mixture of ethylenediamine and 1,6-hexanediamine, and the mass ratio of ethylenediamine to 1,6-hexanediamine is (1-2) : 1.

[0018] In step (1) of the present application, the adding mode and adding sequence of the silicon source, aluminum source, alkali source and template are not required, and the complete dissolution and uniform mixing of each component are ensured.

[0019] Preferably, in step (2), the mass ratio of the precursor solution to the kaolin microspheres is (2.5-5) : 1.

[0020] Preferably, in step (2), the microsphere size of the kaolin microspheres is 50-250 nm.

[0021] Preferably, in step (2), the aging temperature is 80-90℃, and the aging time is 8-12h.

[0022] Preferably, in step (2), the crystallization temperature is 120-140℃, and the crystallization time is 36-48h.

[0023] Preferably, in step (2), after the crystallization reaction, the solid-liquid separation, washing and drying steps are further performed. Specifically, the washing is performed by using deionized water, the drying temperature is 100-120℃, and the drying time is 2-4h.

[0024] Preferably, in step (2), the dynamic condition is not particularly required, and it is appropriate to realize the relative movement of the precursor solution and the kaolin microspheres in the crystallization process. For example, the ultrasonic or stirring method is used to realize the uniform dispersion of ions or molecules in the solution.

[0025] Preferably, in step (3), the aqueous solution containing NH4 + is an aqueous solution of (NH4)2SO4 or NH4Cl.

[0026] Preferably, in step (3), the aqueous solution containing NH4 + is an aqueous solution of (NH4)2SO4 or NH4Cl. + Preferably, in step (3), the concentration of NH4 + in the aqueous solution containing NH4 + is 0.1-0.2wt%.

[0027] Preferably, in step (3), the mass ratio of the ZSM-22 molecular sieve / kaolin raw powder to the aqueous solution containing NH4 + is (0.05-0.1):1.

[0028] Preferably, in step (3), the reaction temperature of the mixing reaction of the molecular sieve / kaolin raw powder and the aqueous solution containing NH4 + is 90-95℃, and the reaction time is 0.5-4h.

[0029] Preferably, in step (3), the temperature of the calcination process is 450-550℃, and the time is 2-4h.

[0030] In the present application, in steps (1), (2) and (3), the separation, washing and drying methods can be the conventional purification methods in the art, and are not particularly limited, as long as the purposes can be achieved. For example, the mixture solution obtained after the reaction is suction filtered, then repeatedly washed, and finally dried.

[0031] Another technical solution of the present application provides a catalyst prepared by the above method, wherein the diameter of the core microspheres is 50-250nm, and the thickness of the shell layer is 10-50nm.

[0032] Another technical scheme of the present application provides application of the above catalyst in preparation of dimethylamine, and the specific operation steps include: taking methanol and ammonia as raw materials, and making gas phase catalytic reaction in a fluidized bed to obtain crude dimethylamine product, and then purifying the crude product through multi-stage condensation separation equipment to obtain dimethylamine product.

[0033] Preferably, the methanol is gasified through a preheater and mixed with ammonia and then fed into the fluidized bed reactor from the bottom, and the reaction temperature is 300-350 DEG C, and the molar ratio of methanol to ammonia is (2-2.5):1.

[0034] Preferably, the multi-stage separation equipment is sequentially connected with dimethylamine collection device, trimethylamine collection device and methylamine collection device, and the temperature in the three-stage system of the multi-stage condensation separation equipment is controlled at 6-8 DEG C, 2-4 DEG C and (-4)-(-2) DEG C respectively.

[0035] Compared with the prior art, the preparation method of the ZSM-22 molecular sieve / high clay core-shell type catalyst provided by the present application has the following beneficial effects:

[0036] (1) The present application provides a ZSM-22 / high clay core-shell type catalyst for synthesizing dimethylamine, which is directly synthesized without subsequent molding process, solves the problem that the powdered molecular sieve cannot be directly applied to industrial production, and has the characteristics of controllable active component and pore structure, high catalytic activity and high selectivity. The ZSM-22 molecular sieve in the catalyst has shape selectivity, which destroys the thermodynamic equilibrium among methylamine, dimethylamine and trimethylamine, and greatly improves the selectivity of dimethylamine. Through the post-processing process, the content of alkali metal ions in the ZSM-22 molecular sieve can be controlled, and the pore size of the molecular sieve can be adjusted, so that the largest molecular size trimethylamine is difficult to be removed from the pore, thereby increasing the selectivity of dimethylamine.

[0037] (2) The catalyst provided by the present application is used for dimethylamine synthesis, which solves the problems of poor heat transfer effect of traditional fixed bed catalyst and insufficient contact between raw materials and active sites of the catalyst; the multi-stage condensation separation device directly connected with the fluidized bed can directly separate methylamine, dimethylamine and trimethylamine, avoids complex and large-scale distillation equipment after the fixed bed reactor, reduces energy consumption and saves cost. DETAILED DESCRIPTION

[0038] In order to make the purpose and technical scheme of the embodiments of the present application clearer, the technical scheme of the present application will be described clearly and completely in combination with the embodiments of the present application. Before the specific embodiments of the present application are described, it should be understood that the protection scope of the present application is not limited to the following specific embodiments; and it should also be understood that the terms used in the embodiments of the present application are used for describing the specific embodiments, but not for limiting the protection scope of the present application.

[0039] The application will be described in detail below by examples. In the following examples and comparative examples,

[0040] Silica sol, aluminum sulfate octadecahydrate, NaOH, KOH, ethylenediamine, 1,6-hexanediamine, NH4Cl, white carbon black, sodium aluminate were purchased from Wacker.

[0041] Example 1

[0042] (1) Preparation of ZSM-22 molecular sieve precursor solution: 140 g of silica sol, 6.66 g of aluminum sulfate octadecahydrate, 3.6 g of NaOH, 1.68 g of KOH, 1.08 g of ethylenediamine and 1.39 g of 1,6-hexanediamine were completely dissolved in 324 g of water and uniformly mixed to obtain a reaction precursor solution system;

[0043] (2) In-situ crystallization: the above reaction precursor solution was uniformly mixed with 135 g of 150 nm kaolin microspheres, aged at 85°C for 10 h, then the temperature was increased to 130°C, and hydrothermal crystallization reaction was carried out under dynamic conditions for 40 h, then filtered, washed with deionized water, dried at 120°C to obtain ZSM-22 molecular sieve / kaolin raw powder;

[0044] (3) Post-treatment: 7.5 g of ZSM-22 molecular sieve / kaolin raw powder was placed in 100 g of 0.1 wt% NH4Cl aqueous solution containing NH4+, and reacted at 92°C for 1 h, then filtered, washed with deionized water, dried at 120°C, and calcined at 500°C for 3 h to obtain a primary modified product; step (3) was repeated to obtain a ZSM-22 / kaolin spherical catalyst with a “core-shell” structure. +

[0045] Example 2

[0046] (1) Preparation of ZSM-22 molecular sieve precursor solution: 120 g of silica sol, 6.66 g of aluminum sulfate octadecahydrate, 3.2 g of NaOH, 1.12 g of KOH, 0.6 g of ethylenediamine and 1.16 g of 1,6-hexanediamine were completely dissolved in 360 g of water and uniformly mixed to obtain a reaction precursor solution system;

[0047] (2) In-situ crystallization: the above reaction precursor solution was uniformly mixed with 111 g of 250 nm kaolin microspheres, aged at 80°C for 8 h, then the temperature was increased to 120°C, and hydrothermal crystallization reaction was carried out under dynamic conditions for 36 h, then filtered, washed with deionized water, and dried at 120°C to obtain ZSM-22 molecular sieve / kaolin raw powder;

[0048] (3) Post-treatment: 10 g of ZSM-22 molecular sieve / kaolin raw powder was placed in 100 g of 0.15 wt% NH4Cl aqueous solution containing NH4+, and reacted at 92°C for 1 h, then filtered, washed with deionized water, dried at 120°C, and calcined at 500°C for 3 h to obtain a primary modified product; step (3) was repeated to obtain a ZSM-22 / kaolin spherical catalyst with a “core-shell” structure. + ​The primary modified product was obtained by the following steps: the mixture of 140 g of silica sol, 1.39 g of 1,6-hexanediamine, 0.5 g of ZSM-22 seeds, 0.5 g of kaolin seeds, and 0.5 g of NaY zeolite seeds was stirred at 90 °C for 2 h in an aqueous NH4Cl solution, suction filtration, deionized water washing, drying at 120 °C, and calcination at 450 °C for 2 h.

[0049] Example 3

[0050] The experiment was performed according to the method of Example 1, except that 140 g of silica sol was replaced by 182 g of tetraethyl orthosilicate.

[0051] Comparative Example 1

[0052] The experiment was performed according to the method of Example 1, except that 1.39 g of 1,6-hexanediamine was replaced by the same number of moles of ethylenediamine to obtain a comparative catalyst.

[0053] Comparative Example 2

[0054] The experiment was performed according to the method of Example 1, except that the crystallization temperature was replaced by 180 °C to obtain a comparative catalyst.

[0055] Comparative Example 3

[0056] The experiment was performed according to the method of Example 1, except that the 92 °C reaction for 1 h in the post-treatment condition was replaced by a 98 °C reaction for 10 h to obtain a comparative catalyst.

[0057] Comparative Example 4

[0058] The experiment was performed according to the method of Example 1, except that step (2) was performed as follows: the above reaction precursor solution was uniformly mixed with 135 g of kaolin microspheres of 150 nm, heated to 130 °C, and hydrothermally crystallized under dynamic conditions for 50 h, suction filtration, deionized water washing, drying at 120 °C to obtain ZSM-22 molecular sieve / kaolin raw powder.

[0059] Comparative Example 5

[0060] The experiment was performed according to the method of Example 1, except that step (2) was performed as follows: the above reaction precursor solution was uniformly mixed with 135 g of kaolin microspheres of 150 nm, 100 °C aging for 10 h, and then heated to 130 °C, hydrothermally crystallized under dynamic conditions for 50 h, suction filtration, deionized water washing, drying at 120 °C to obtain ZSM-22 molecular sieve / kaolin raw powder.

[0061] Comparative Example 6

[0062] The experiment was carried out according to the method of Example 1, except that the operation of step (1) was as follows: (1) Preparation of ZSM-22 molecular sieve precursor solution: 40 g of silica sol, 6.66 g of aluminum sulfate octadecahydrate, 3.6 g of NaOH, 1.68 g of KOH, 1.08 g of ethylenediamine and 1.39 g of 1,6-hexanediamine were completely dissolved in 324 g of water and uniformly mixed to obtain a reaction precursor solution system.

[0063] Comparative Example 7

[0064] The experiment was carried out according to the method of Example 1, except that the operation of step (1) was as follows: 120 g of silica sol, 8.23 g of aluminum sulfate octadecahydrate, 3.6 g of NaOH, 1.68 g of KOH, 1.08 g of ethylenediamine and 1.39 g of 1,6-hexanediamine were completely dissolved in 324 g of water and uniformly mixed to obtain a reaction precursor solution system.

[0065] Catalyst performance evaluation

[0066] Methanol and ammonia were used as raw materials to carry out a gas phase catalytic reaction in a fluidized bed reactor. The specific operation conditions were as follows: 50 g of catalyst was loaded into the fluidized bed reactor, methanol was gasified by a preheater, mixed with ammonia, and then entered the fluidized bed reactor from the bottom to prepare a crude dimethylamine product, and then the crude product was separated by a multi-stage condensation separation device to obtain a dimethylamine product. Among them, the reaction temperature in the fluidized bed reactor was 320℃, the molar ratio of methanol to ammonia was 2.2:1, and the gas inlet speed was 10 g / min.

[0067] The reaction product was quantitatively analyzed by 1H-NMR and gas chromatography equipped with a mass selective detector and a flame ionization detector. The performance test results of the catalyst prepared in each example and comparative example are shown in Table 1.

[0068] Table 1 Performance comparison of different catalysts

[0069] Catalyst [SA BET , m 2 / g]]> Methanol conversion, % Dimethylamine selectivity, % Example 1 234 99.5 50.5 Example 2 206 92.2 65.1 Example 3 215 96.2 72.5 Comparative Example 1 196 91.2 54.2 Comparative Example 2 175 72.1 49.6 Comparative Example 3 191 87.3 52.1 Comparative Example 4 168 78.4 42.6 Comparative Example 5 181 81.5 38.7 Comparative Example 6 147 65.7 35.3 Comparative Example 7 138 58.6 32.6

[0070] The above is only an embodiment of the present application, which is described in detail and specifically, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application.

Claims

1. A method for preparing ZSM-22 molecular sieve / kaolin core-shell catalyst, comprising the following steps: (1) Preparation of ZSM-22 molecular sieve precursor solution: The silicon source, aluminum source, alkali source, template agent and water are mixed until homogeneous to obtain the reaction precursor solution; (2) In-situ crystallization: The mixture of the reaction precursor liquid and kaolin microspheres is first aged at low temperature, and then subjected to hydrothermal crystallization reaction to obtain ZSM-22 molecular sieve / kaolin raw powder; (3) Post-processing: The ZSM-22 molecular sieve / kaolin raw powder is mixed with NH4-containing + The aqueous solution was mixed and reacted. After the reaction, the mixture was subjected to solid-liquid separation, washing, drying and calcination to obtain a primary modified product. The aforementioned step (3) was repeated to obtain a core-shell structured ZSM-22 / kaolin spherical catalyst. The aging temperature mentioned in step (2) is 80-90°C. o C, aging time is 8-12 hours; the crystallization temperature is 120-140°C. o C, crystallization time is 36-48h; The molar ratio of each component in the ZSM-22 molecular sieve precursor solution is nsilicon source: naluminum source: nalkali source: ntemplate agent: nH2O = (60-80): 1: (10-15): (2-4): (1500-2000).

2. The method according to claim 1, wherein in step (1), the template agent is at least one of ethylenediamine, 1,6-hexanediamine and n-butylamine.

3. According to the method of claim 1, after the crystallization reaction in step (1) is completed, solid-liquid separation, washing and drying steps are also performed.

4. The method according to claim 1, wherein in step (1), the silicon source is at least one of silica sol, tetraethyl orthosilicate and silica.

5. The method according to claim 1, wherein in step (1), the aluminum source is at least one of boehmite, aluminum sulfate octahydrate, and sodium aluminate.

6. The method according to claim 1, in step (3), the ZSM-22 molecular sieve / kaolin raw powder and NH4-containing + The mass ratio of the aqueous solution is (0.05-0.1):

1.

7. The core-shell catalyst prepared by the method according to any one of claims 1-6, wherein the core microspheres have a diameter of 50-250 nm and a shell thickness of 10-50 nm.

8. The application of the core-shell catalyst prepared by the method according to any one of claims 1-6 in the preparation of dimethylamine, wherein the specific operating steps include: Dimethylamine crude product is prepared by gas-phase catalytic reaction of methanol and ammonia in a fluidized bed. The crude product is then purified by multi-stage condensation separation equipment to obtain dimethylamine product.