A boron-containing Beta zeolite, its preparation method and application

Abstract

The present invention provides a boron-containing Beta zeolite, a preparation method thereof and an application thereof, belonging to the field of catalyst preparation. The boron-containing Beta zeolite provided by the present invention contains silicon element and boron element; the molar ratio of silicon element to boron element in the boron-containing Beta zeolite is 15-60:1. The boron element introduced in the boron-containing Beta zeolite and the adjustment of the silicon-boron ratio in the present invention reduce the high-temperature acid sites and increase the low-temperature acid sites, thereby reducing the temperature of the Beckmann rearrangement reaction, reducing the synthesis of by-products, and improving the selectivity of cyclohexanone oxime. The results of the examples show that the selectivity of cyclohexanone oxime is 82.8-99.2% when the boron-containing Beta zeolite of the present invention is used for catalysis.

Description

Technical Field

[0001] The present invention relates to the field of catalyst preparation, and particularly to a boron-containing Beta zeolite and its preparation method and application. Background Art

[0002] Caprolactam is an important chemical raw material and a monomer for preparing PA-6 and engineering plastics. At present, the production of caprolactam mainly uses fuming sulfuric acid as a catalyst and solvent for the liquid-phase Beckmann rearrangement of cyclohexanone oxime. Cyclohexanone oxime undergoes a Beckmann rearrangement reaction to form caprolactam under the catalytic action of fuming sulfuric acid at a certain temperature, and then ammonia is used to neutralize a large amount of by-product ammonium sulfate with low added value.

[0003] The process technology for the preparation of caprolactam by the Beckmann rearrangement of cyclohexanone oxime is relatively mature, with mild reaction conditions, high raw material conversion rate and product selectivity, but there are also many disadvantages. First of all, concentrated sulfuric acid will corrode equipment, and harmful substances will be discharged during the production process, which does not conform to the development concept of green environmental protection. Therefore, silicon-aluminum zeolites that do not pollute the environment have emerged as the times require. However, the selectivity of silicon-aluminum zeolites in the prior art for ketoxime is still low. Summary of the Invention

[0004] The purpose of the present invention is to provide a boron-containing Beta zeolite and its preparation method and application, and the selectivity of cyclohexanone oxime is high when using the boron-containing Beta zeolite of the present invention for catalysis.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a boron-containing Beta zeolite, which contains silicon element and boron element; the molar ratio of silicon element to boron element in the boron-containing Beta zeolite is 15-60:1.

[0007] Preferably, the boron-containing Beta zeolite is a borosilicate zeolite.

[0008] The present invention also provides a preparation method of the boron-containing Beta zeolite described in the above scheme, including the following steps:

[0009] Mix a structure-directing agent, a boron compound, a silicon source and water to carry out a sol-gel reaction to obtain a gel; the molar ratio of silicon element in the silicon source to boron element in the boron compound is 15-60:1;

[0010] Mix the gel with boron-containing Beta zeolite seeds and then carry out a hydrothermal crystallization reaction to obtain a boron-containing Beta zeolite precursor;

[0011] Calcine the boron-containing Beta zeolite precursor to obtain the boron-containing Beta zeolite.

[0012] Preferably, the structure-directing agent includes tetraalkylammonium hydroxide and / or isoalkylammonium hydroxide;

[0013] The molar ratio of the amount of substance of the structure-directing agent to the amount of substance of silicon element in the silicon source is 0.27 - 1:1.

[0014] Preferably, the silicon source includes one or more of silicon dioxide, silica sol, methyl orthosilicate, and ethyl orthosilicate.

[0015] Preferably, the boron compound includes one or more of boron chloride, boric acid, and boron oxide.

[0016] Preferably, the temperature of the hydrothermal crystallization reaction is 100 - 200 °C, and the time is 24 - 100 h.

[0017] Preferably, the temperature of the calcination is 400 - 800 °C, and the time is 5 - 10 h.

[0018] The present invention also provides the use of the boron-containing Beta zeolite described in the above solution or the boron-containing Beta zeolite prepared by the preparation method described in the above solution as a catalyst in the liquid-phase Beckmann rearrangement.

[0019] Preferably, the liquid-phase Beckmann rearrangement includes the following steps:

[0020] Mix cyclohexanone oxime, a polar organic solvent, and the boron-containing Beta zeolite to carry out the liquid-phase Beckmann rearrangement to obtain caprolactam; the temperature of the liquid-phase Beckmann rearrangement is 80 - 150 °C, and the time is 1 - 15 h.

[0021] The present invention provides a boron-containing Beta zeolite containing boron element; the molar ratio of silicon element to boron element in the boron-containing Beta zeolite is 15 - 60:1. The present invention introduces boron element into the boron-containing Beta zeolite and adjusts the silicon-boron ratio, thereby reducing the high-temperature acid sites and increasing the low-temperature acid sites, and further reducing the temperature of the Beckmann rearrangement reaction, reducing the synthesis of by-products, and improving the selectivity of cyclohexanone oxime. The results of the examples show that the selectivity of cyclohexanone oxime is 82.8 - 99.2% when catalyzed by the boron-containing Beta zeolite of the present invention. Description of the Drawings

[0022] Figure 1 XRD patterns of the boron-containing Beta zeolites of Examples 1 - 3;

[0023] Figure 2 XRD pattern of the Beta zeolite of Comparative Example 1; Detailed Description of the Invention

[0024] The present invention provides a boron-containing Beta zeolite, which contains silicon element and boron element; the molar ratio of silicon element to boron element in the boron-containing Beta zeolite is 15-60:1.

[0025] In the present invention, the molar ratio of silicon element to boron element in the boron-containing Beta zeolite is 15-60:1, preferably 30-50:1, more preferably 40-45:1. In the present invention, the boron-containing Beta zeolite is preferably a borosilicate zeolite.

[0026] The boron element introduced into the boron-containing Beta zeolite in the present invention and the adjustment of the silicon-boron ratio reduce the high-temperature acid sites and increase the low-temperature acid sites, thereby reducing the temperature of the Beckmann rearrangement reaction, reducing the synthesis of by-products, and improving the selectivity of cyclohexanone oxime.

[0027] The present invention also provides a preparation method of the boron-containing Beta zeolite described in the above scheme, including the following steps:

[0028] Mix a structure-directing agent, a boron compound, a silicon source and water to carry out a sol-gel reaction to obtain a gel; the molar ratio of silicon element in the silicon source to boron element in the boron compound is 15-60:1;

[0029] Mix the gel with the boron-containing Beta zeolite seeds and then carry out a hydrothermal crystallization reaction to obtain a boron-containing Beta zeolite precursor;

[0030] Calcine the boron-containing Beta zeolite precursor to obtain the boron-containing Beta zeolite.

[0031] In the present invention, a structure-directing agent, a boron compound, a silicon source and a polar solvent are mixed to carry out a sol-gel reaction to obtain a gel.

[0032] The mixing of the structure-directing agent, the boron compound, the silicon source and water in the present invention preferably includes: dissolving the structure-directing agent in water to obtain a structure-directing agent solution; dissolving the boron compound in the structure-directing agent solution and then adding the silicon source. In the present invention, the structure-directing agent includes tetraalkylammonium hydroxide and / or isoalkylammonium hydroxide; the tetraalkylammonium hydroxide preferably includes one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; the isoalkylammonium hydroxide preferably includes isopropylammonium hydroxide and / or isobutylammonium hydroxide. In the present invention, the concentration of the structure-directing agent solution is preferably 5-35 wt%, more preferably 10-25 wt%, and further preferably 15-20 wt%. The present invention has no special limitation on the dissolution of the boron compound, and the scheme well-known to those skilled in the art can be adopted. Specifically, stirring is used in the examples of the present invention.

[0033] In the present invention, the boron compound preferably includes one or more of boron chloride, boric acid, and boron oxide. In the present invention, the molar ratio of the amount of the structure-directing agent to the amount of silicon element in the silicon source is preferably 0.27 to 1:1, more preferably 0.4 to 0.8:1, and further preferably 0.5 to 0.6:1. In the present invention, the silicon source preferably includes one or more of silicon dioxide, silica sol, methyl orthosilicate, and ethyl orthosilicate; the silicon dioxide preferably includes fumed silica. In the present invention, the molar ratio of the silicon element in the silicon source to the boron element in the boron compound is 15 to 60:1, preferably 30 to 50:1, and more preferably 40 to 45:1.

[0034] In the present invention, the temperature of the sol-gel reaction is preferably room temperature; the time of the sol-gel reaction is preferably 0.5 to 3 h, more preferably 1.5 to 2 h. In the present invention, the sol-gel reaction is preferably carried out under stirring conditions.

[0035] After obtaining the gel, in the present invention, the gel is mixed with boron-containing Beta zeolite seeds and then subjected to hydrothermal crystallization reaction to obtain a boron-containing Beta zeolite precursor. In the present invention, the mass ratio of the total mass of the structure-directing agent, boron compound, and silicon source to the mass of the boron-containing Beta zeolite seeds is preferably 99:1. The present invention has no special limitation on the boron-containing Beta zeolite seeds, and the boron-containing Beta zeolite seeds well-known to those skilled in the art can be used. In the present invention, the mixing time is preferably 4 to 12 h.

[0036] In the present invention, the temperature of the hydrothermal crystallization is preferably 100 to 200 °C, more preferably 120 to 180 °C, and further preferably 130 to 170 °C; the time is preferably 24 to 100 h, more preferably 50 to 80 h, and further preferably 60 to 70 h.

[0037] After the hydrothermal crystallization reaction, in the present invention, the hydrothermal crystallization reaction product is preferably washed and dried to obtain the boron-containing Beta zeolite precursor. The present invention has no special limitation on the washing, and it can be washed to neutral by using a method well-known to those skilled in the art. Specifically, in the examples of the present invention, it is washed with deionized water to neutral. The present invention has no special limitation on the drying temperature, and it can be dried to constant weight by using a method well-known to those skilled in the art. Specifically, the drying temperature in the examples of the present invention is 80 to 150 °C.

[0038] After obtaining the boron-containing Beta zeolite precursor, the present invention calcines the boron-containing Beta zeolite precursor to obtain the boron-containing Beta zeolite. In the present invention, the calcination temperature is preferably 400-800 °C, more preferably 450-700 °C, and further preferably 500-600 °C; the time is preferably 5-10 h, more preferably 6-9 h, and further preferably 7-8 h. After calcination, the B element is embedded in the silicic acid framework.

[0039] The present invention also provides the use of the boron-containing Beta zeolite described in the above solution or the boron-containing Beta zeolite prepared by the preparation method described in the above solution as a catalyst in the liquid-phase Beckmann rearrangement.

[0040] In the present invention, the application includes the following steps:

[0041] Mix cyclohexanone oxime, a polar organic solvent and the boron-containing Beta zeolite to carry out liquid-phase Beckmann rearrangement to obtain caprolactam; the temperature of the liquid-phase Beckmann rearrangement is 80-150 °C, and the time is 1-15 h.

[0042] In the present invention, the polar organic solvent preferably includes one or more of acetonitrile, benzonitrile and p-tolunitrile. In the present invention, the mass ratio of the boron-containing Beta zeolite to cyclohexanone oxime is preferably 1:0.5-1.5, more preferably 1:0.6-1.2, and further preferably 0.8-1:1. In the present invention, the mass ratio of the boron-containing Beta zeolite to the solvent is preferably 1:80-200, more preferably 1:100-180, and further preferably 1:120-150. In the present invention, the temperature of the liquid-phase Beckmann rearrangement is 80-150 °C, preferably 90-130 °C, more preferably 100-120 °C; the time is 1-15 h, preferably 5-12 h, more preferably 6-10 h.

[0043] The following examples are used to illustrate in detail the boron-containing Beta zeolite and its preparation method and application provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0044] Example 1

[0045] Weigh boron chloride and put it into a beaker containing an aqueous solution of tetraethylammonium hydroxide with a concentration of 35 wt%. Stir the solution for 30 min to dissolve the boron chloride, and then slowly add silica sol under stirring to carry out a sol-gel reaction for 2 h to form a gel. The molar ratio of silicon element, boron chloride and tetraethylammonium hydroxide in the silica sol is 1:0.067:0.54;

[0046] Then, a boron-containing Beta zeolite seed crystal was added to the obtained gel (the mass ratio of the total mass of silica sol, boron chloride, and tetraethylammonium hydroxide to the mass of the boron-containing Beta zeolite seed crystal was 99:1), and then stirred for 12 h. The obtained mixture was placed in a stainless steel-lined autoclave and hydrothermally crystallized at 150 °C for 96 h. After the reaction, the obtained hydrothermal crystallization reaction product was washed with deionized water until neutral, and then dried at 90 °C to obtain a boron-containing Beta zeolite precursor;

[0047] The obtained boron-containing Beta zeolite precursor was calcined in a muffle furnace at 550 °C for 8 h to obtain a boron-containing Beta zeolite with a molar ratio of silicon element to boron element of 15.

[0048] Example 2

[0049] Boron oxide was weighed and placed in a beaker containing an aqueous solution of tetraethylammonium hydroxide with a concentration of 30 wt%. The solution was stirred for 30 min to dissolve the boron oxide, and then silica sol was slowly added under stirring for a 2-h gel reaction to form a gel. Among them, the molar ratio of silicon element, boron oxide, and tetraethylammonium hydroxide in the silica sol was 1:0.033:0.54.

[0050] Then, a boron-containing Beta zeolite seed crystal was added to the obtained gel (the mass ratio of the total mass of silica sol, boron oxide, and tetraethylammonium hydroxide to the mass of the boron-containing Beta zeolite seed crystal was 99:1), and then stirred for 12 h. The obtained mixture was placed in a stainless steel-lined autoclave and hydrothermally crystallized at 150 °C for 96 h. After the reaction, the obtained hydrothermal crystallization reaction product was washed with deionized water until neutral, and then dried at 90 °C to obtain a boron-containing Beta zeolite precursor;

[0051] The obtained boron-containing Beta zeolite precursor was calcined in a muffle furnace at 550 °C for 8 h to obtain a boron-containing Beta zeolite with a molar ratio of silicon element to boron element of 30.

[0052] Example 3

[0053] Boron chloride was weighed and placed in a beaker containing an aqueous solution of tetraethylammonium hydroxide with a concentration of 20 wt%. The solution was stirred for 30 min to dissolve the boron chloride, and then tetraethyl orthosilicate was slowly added under stirring for a 2-h gel reaction to form a gel. Among them, the molar ratio of tetraethyl orthosilicate, boron chloride, and tetraethylammonium hydroxide was 1:0.0167:0.54.

[0054] Then, boron-containing Beta zeolite seeds were added to the resulting gel (the mass ratio of the total mass of tetraethyl orthosilicate, boron oxide, and tetraethylammonium hydroxide to the mass of the boron-containing Beta zeolite seeds was 99:1), and the mixture was stirred for 12 h. The resulting mixture was placed in a stainless-steel-lined autoclave and hydrothermally crystallized at 150 °C for 96 h. After the reaction, the resulting hydrothermal crystallization reaction product was washed with deionized water until neutral, and then dried at 90 °C to obtain a boron-containing Beta zeolite precursor;

[0055] The obtained boron-containing Beta zeolite precursor was calcined in a muffle furnace at 550 °C for 8 h to obtain a boron-containing Beta zeolite with a molar ratio of silicon element to boron element of 60.

[0056] XRD analysis was performed on the boron-containing Beta zeolites of Examples 1 to 3 and Comparative Example 1, and the results are as Figure 1 and Figure 2 shown. As can be seen from Figures 1-2 it, when a small amount of boron element was doped into the boron-containing Beta zeolite framework, the diffraction peaks of the zeolite increased significantly, indicating that the introduction of boron element into the zeolite framework changed the surface structure of the catalyst.

[0057] Py-IR analysis was performed on the boron-containing Beta zeolites of Examples 1 to 3 and the zeolite of Comparative Example 1, and the results are shown in Table 1. As can be seen from Table 1, when the boron content was too high, the low-temperature acid sites decreased correspondingly.

[0058] Table 1 Py-IR analysis results of Examples 1 to 3 and Comparative Example 1

[0059]

[0060] Comparative Example 1

[0061] Pseudoboehmite was weighed and placed in a beaker containing an aqueous solution of tetraethylammonium hydroxide with a concentration of 25 wt%, and the solution was stirred for 30 min to dissolve it. Then, under stirring conditions, gaseous silicon dioxide was slowly added for a sol-gel reaction for 2 h to form a gel. Among them, the molar ratio of gaseous silicon dioxide, pseudoboehmite, and tetraethylammonium hydroxide was 1:0.033:0.54. Stir for 12 h, place the resulting mixture in a stainless-steel-lined autoclave, and hydrothermally crystallize at 150 °C for 96 h. After the reaction, the resulting hydrothermal crystallization reaction product was washed with deionized water until neutral, and then dried at 90 °C to obtain a Beta zeolite precursor;

[0062] The obtained Beta zeolite precursor was calcined in a muffle furnace at 550 °C for 12 h to obtain a Beta zeolite catalyst with a molar ratio of silicon element to aluminum element of 30.

[0063] The Beta zeolite of Comparative Example 1 was analyzed by Py-IR, and the results are shown in Table 1. As can be seen from Table 1, the common Beta zeolite only has high-temperature acid sites. When a small amount of boron element is doped into the Beta zeolite framework, the low-temperature acid sites increase significantly.

[0064] Application Example 1

[0065] 0.025 g of the boron-containing Beta zeolite of Example 1 was poured into a 50 ml round-bottom flask, and then 0.025 g of cyclohexanone oxime and 5 g of p-tolunitrile were added. Stirring was started and the mixture was heated in an oil bath to 130 °C for liquid-phase Beckmann rearrangement reaction. After 4 h, the reaction was stopped, and after cooling, centrifugation was carried out, and the upper-layer reaction solution was taken for gas chromatography analysis.

[0066] Application Examples 2-26

[0067] According to the method of Application Example 1, the boron-containing Beta zeolites prepared in Examples 2-3 were applied to the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. The specific experimental conditions and reaction results are shown in Table 2.

[0068] Comparative Application Examples 1-6

[0069] According to the method of Application Example 1, the boron-containing Beta zeolite prepared in Comparative Example 1 was applied to the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam. The specific experimental conditions and reaction results are shown in Table 3.

[0070] Table 2 Experimental conditions and results of Beckmann rearrangement in Application Examples 1-32

[0071]

[0072]

[0073] Table 3 Experimental conditions and results of Beckmann rearrangement in Comparative Application Examples 1-6

[0074]

[0075]

[0076] As can be seen from Table 2, when the boron-containing Beta zeolite provided by the present invention is applied to the liquid-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam, a conversion rate of 95.7% of cyclohexanone oxime and a selectivity of 99.2% of caprolactam can be obtained after reacting at 130 °C for 2 h (Application Example 4).

[0077] Among them, from the results of Application Examples 1 to 18 and Comparative Examples 1 to 6, it can be seen that the reaction time has an obvious effect on the activity of the catalyst: the conversion rate of cyclohexanone oxime increases to complete conversion with the extension of the reaction time, and the selectivity of the product caprolactam remains at the maximum within 2 h of the reaction. However, if the reaction time is further extended, the selectivity decreases, probably because as the reaction time extends, the reactants are gradually converted into by-products such as cyclohexanone or cyclohexanedione;

[0078] From the results of Application Examples 19 to 26, it can be seen that the reaction temperature also has an obvious effect on the activity of the catalyst: too low or too high reaction temperature is not conducive to the conversion rate of cyclohexanone oxime and the selectivity of caprolactam. The reaction temperature affects the liquid-phase rearrangement kinetics of cyclohexanone oxime. If the reaction temperature is too low, the kinetics is too slow, resulting in a low conversion rate. If the reaction temperature is too high, by-products will be formed. Only within a suitable reaction temperature range is it conducive to the rearrangement of cyclohexanone oxime to prepare caprolactam.

[0079] In addition, from the results of Comparative Application Examples 1 to 6, it can be seen that when the boron-containing Beta zeolite does not contain boron, both the conversion rate of cyclohexanone oxime and the selectivity of caprolactam are relatively low; while doping a small amount of boron element into the framework of the boron-containing Beta zeolite can improve the catalytic performance of the boron-containing Beta zeolite.

[0080] From the results of Application Examples 7 to 18, it can be seen that as the boron content increases, the selectivity of caprolactam will decrease.

[0081] Application Examples 4 to 5 show that the boron-containing Beta zeolite provided by the present invention has the most acidic sites, good catalytic effect, high conversion rate of cyclohexanone oxime, good selectivity of caprolactam, and can achieve rapid reaction. Therefore, the preparation method provided by the present invention has obvious advantages, is simple in operation, low in energy consumption, safe and has mild reaction conditions, and is suitable for industrial production.

[0082] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Application of a boron-containing Beta zeolite as a catalyst in liquid-phase Beckmann rearrangement, characterized in that, The boron-containing Beta zeolite contains silicon and boron elements; the molar ratio of silicon to boron in the boron-containing Beta zeolite is 15:1; The liquid-phase Beckmann rearrangement includes the following steps: Cyclohexanone oxime, a polar organic solvent and the boron-containing Beta zeolite are mixed for liquid-phase Beckmann rearrangement to obtain caprolactam; the temperature of the liquid-phase Beckmann rearrangement is 130 °C; The polar organic solvent is p-tolunitrile; The preparation method steps of the boron-containing Beta zeolite are as follows: A structure-directing agent, a boron compound, a silicon source and water are mixed for sol-gel reaction to obtain a gel; the molar ratio of silicon in the silicon source to boron in the boron compound is 15:1; The gel is mixed with boron-containing Beta zeolite seeds and then subjected to hydrothermal crystallization reaction to obtain a boron-containing Beta zeolite precursor; The boron-containing Beta zeolite precursor is calcined to obtain the boron-containing Beta zeolite.

2. The application according to claim 1, characterized in that, The boron-containing Beta zeolite is a borosilicate zeolite.

3. The application according to claim 1, characterized in that The structure-directing agent includes tetraalkylammonium hydroxide and / or isoalkylammonium hydroxide; The molar ratio of the amount of the structure-directing agent to the amount of silicon in the silicon source is 0.27-1:

1.

4. The application according to claim 1 or 3, characterized in that, The silicon source includes one or more of silicon dioxide, silica sol, methyl orthosilicate and ethyl orthosilicate.

5. The application according to claim 1, characterized in that, The boron compound includes one or more of boron chloride, boric acid and boron oxide.

6. The application according to claim 1, characterized in that, The temperature of the hydrothermal crystallization reaction is 100-200 °C, and the time is 24-100 h.

7. The application according to claim 1, characterized in that, The temperature of the calcination is 400-800 °C, and the time is 5-10 h.

8. The application according to claim 1, wherein The time of the liquid-phase Beckmann rearrangement is 1-15 h.

Images