A method for catalyzing ethanol and benzene to ethylbenzene by adopting nanosheet molecular sieve

Abstract

A method for preparing ethylbenzene by using nanosheet molecular sieve as catalyst, the hydrogen type nanosheet molecular sieve is broken and loaded into a fixed bed reactor, benzene and ethanol are used as raw materials, nitrogen is used as carrier gas, the reaction is carried out at 280-350 DEG C and 0.1-1.0 MPa; the hydrogen type nanosheet molecular sieve is ZSM-5 molecular sieve, the length of b axis direction is 70-100 nm, the length ratio L b / L a is less than 0.40. The method for preparing ethylbenzene provided by the application can be directly used for catalyzing ethanol and benzene to prepare ethylbenzene without secondary treatment such as modification of acid, alkali and alkali metal and rare earth metal elements based on the special structure of the nanosheet molecular sieve with ultra-short b axis, can ensure that the product is desorbed and diffused from the surface of the catalyst in time, reduces the probability of deep reaction of the product molecules, realizes high selectivity of the product ethylbenzene, and reduces the cracking and other side reactions.

Description

Technical Field

[0001] This invention belongs to the field of ethylbenzene preparation technology, specifically relating to a method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieves as catalysts. Background Technology

[0002] Ethylbenzene is an important chemical raw material, primarily used in the production of styrene, which in turn produces polystyrene, engineering plastics, and styrene-butadiene rubber. Currently, the main industrial method for producing ethylbenzene is the alkylation of benzene with dry gas. The main processes include the AlCl3 liquid-phase alkylation method and the molecular sieve gas-phase alkylation method. The molecular sieve gas-phase alkylation method mainly uses ZSM-5 molecular sieve as a catalyst to catalyze the alkylation reaction of ethylene (US3751504, US3751506, US4016218, and US4547605) or ethanol (CN102274746A, CN101450888A) with benzene to produce ethylbenzene. This method has advantages such as being non-corrosive, pollution-free, having a simple process, and being able to recover the heat of reaction.

[0003] ZSM-5 zeolite molecular sieves are widely used in chemical production and materials due to their regular pore structure, suitable acidity, and good stability. ZSM-5 molecular sieves possess acidic sites, enabling them to simultaneously catalyze reactions such as ethanol dehydration to ethyl cations, benzene alkylation, and alkyl cracking. Therefore, conventional ZSM-5 molecular sieve-catalyzed ethanol and benzene alkylation reactions often produce significant amounts of byproducts such as toluene, xylene, and cumene. This is partly because ethanol undergoes dehydration at the acidic sites within the ZSM-5 molecular sieve pores to generate ethyl cations, which then undergo carbocation cracking, alkylating with benzene to produce toluene, xylene, or other byproducts, or further side reactions. On the other hand, the catalytic performance of the catalyst is also affected by the pore structure. Conventional ZSM-5 catalysts have very small pores, which can easily impair mass transfer. Since the ethylbenzene product generated from the alkylation reaction of ethanol and benzene may not promptly desorb from the catalyst surface and diffuse outwards from the pores, the ethylbenzene product can also continue to undergo side reactions to produce toluene and xylene. Furthermore, the ethanol alkylation reaction generates a large amount of water, and conventional ZSM-5 has poor hydrothermal stability, making its structure prone to collapse and deactivation during this reaction. These factors can all lead to side reactions, thus affecting the selectivity of ethylbenzene.

[0004] Currently, researchers typically employ post-processing methods, namely, modifying conventional ZSM-5 molecular sieves to improve the selectivity of ethylbenzene and reduce byproducts. Commonly used research methods include adjusting the surface acidity of ZSM-5 molecular sieves by adding additives, loading alkali metals, rare earth metals, etc. [Wei Huirong. Journal of Zhengzhou University (Engineering Science), 1992, 13(2): 60-65; CN101450888A], and adjusting the surface pore structure of ZSM-5 molecular sieves by steam treatment, acid treatment, alkali treatment, etc. [Li Jianjun et al. Journal of Xiamen University (Natural Science Edition), 2012, 51(5): 882-887; Sun Linping. Dalian University of Technology, 2010(D); CN102274746A]. Such post-processing methods result in uneven secondary pore formation, and the formed pores are prone to collapse. The released Si and Al will block the pores and hinder reaction mass transfer. At the same time, the post-processing method is cumbersome and time-consuming. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieves. The nanosheet molecular sieves used have a short b-axis, enabling high selectivity for ethylbenzene at lower temperatures and higher space velocities, while also suppressing the formation of ethyl cracking products.

[0006] A method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieve catalysis is as follows: After crushing the hydrogen-form nanosheet molecular sieve, it is loaded into a fixed-bed reactor, using benzene and ethanol as raw materials, and nitrogen as carrier gas, and reacting at 280-350℃ and 0.1-1.0MPa. The hydrogen-type nanosheet molecular sieve is a ZSM-5 molecular sieve, with a length of 70-100 nm along the b-axis and a length ratio L between the b-axis and a-axis. b / L a Less than 0.40.

[0007] Preferably, the molar ratio of benzene to ethanol is (6-10):1, and the ethanol mass hourly space velocity is 0.2-1.5 h⁻¹. -1 .

[0008] Preferably, the hydrogen-form nanosheet molecular sieve is prepared by the following method: (1) Dissolve aluminum source and alkali source in deionized water, stir until clear, add template agent, stir until clear, then add silicon source dropwise, stir for 2-4 hours, finally add alcohol solvent, continue stirring for 1-2 hours to obtain molecular sieve precursor; (2) The molecular sieve precursor obtained in step (1) is placed in a hydrothermal synthesis reactor and sealed, and crystallized at 120-180℃ for 4-24h; (3) After crystallization, solid-liquid separation is performed. The separated solid is washed with deionized water until neutral, and then dried and calcined. (4) The molecular sieve obtained in step (3) is subjected to ion exchange to obtain hydrogen-type nanosheet molecular sieve. Preferably, the alcohol solvent is one of methanol, ethanol, isopropanol, and n-butanol.

[0009] Preferably, the amount of silicon source is SiO2, the amount of aluminum source is Al2O3, the amount of alkali source is NaOH, and the molar ratio of silicon source, aluminum source, template agent, alcohol solvent, alkali source and deionized water in step (1) is 30: (0.3-1.0): (5-30): (300-2000): (0.5-3): (300-4000).

[0010] Preferably, the aluminum source is at least one selected from aluminum isopropoxide, aluminum hydroxide, aluminum sulfate, aluminum nitrate, and sodium aluminate; The silicon source is at least one of tetraethyl orthosilicate, silica sol, and silica. The alkali source is selected from at least one of alkali metal hydroxides; The template agent is tetrapropylammonium hydroxide.

[0011] Preferably, the drying in step (3) is performed at 80-100℃ for 8-10 hours; the calcination in step (3) is performed at 400-600℃ for 5-8 hours.

[0012] Preferably, the specific operation of step (4) is as follows: the molecular sieve is mixed with 1 mol / L NH4Cl solution at a mass ratio of 1:(20-25), stirred and refluxed at 80-90℃ for 5-6h for ion exchange, centrifuged and dried at 100-105℃ for 5h; the above operation is repeated twice, and calcined at 500-600℃ for 5-6h.

[0013] Advantages of this invention: (1) The method for preparing ethylbenzene provided by the present invention is based on the special structure of the ultrashort b-axis of nanosheet molecular sieve. It can be used directly to catalyze the preparation of ethylbenzene from ethanol and benzene without secondary treatment such as acid, alkali and alkali metal and rare earth metal element modification. It can ensure that the product after the reaction is desorbed and diffused from the catalyst surface in time, reduce the probability of the product molecules continuing to undergo deep reaction, achieve high selectivity of the product ethylbenzene, and reduce side reactions such as cracking. (2) Compared with conventional ZSM-5 molecular sieves, which require post-treatment steps such as alkali metal loading modification, high temperature steam and phosphoric acid treatment to achieve high selectivity of ethylbenzene at higher temperatures, the present invention greatly reduces the catalyst preparation time and improves efficiency. Attached Figure Description

[0014] Figure 1 X-ray diffraction pattern of the nanosheet molecular sieve prepared in Example 1; Figure 2 Scanning electron microscope image of the nanosheet molecular sieve prepared in Example 1; Figure 3 X-ray diffraction pattern of the nanosheet molecular sieve prepared in Example 2; Figure 4 Scanning electron microscope image of the nanosheet molecular sieve prepared in Example 2. Detailed Implementation

[0015] Example 1 Hydrogen-form nanosheet molecular sieves were prepared by the following method: (1) Sodium aluminate is used as the aluminum source, sodium hydroxide as the alkali source, tetraethyl orthosilicate as the silicon source, tetrapropylammonium hydroxide as the template agent, and ethanol is selected as the alcohol solvent; sodium aluminate and sodium hydroxide are dissolved in deionized water and stirred until clear, then tetrapropylammonium hydroxide is added and stirred until clear, then tetraethyl orthosilicate is added dropwise and stirred for 2 hours, and finally ethanol is added and stirred for another 2 hours to obtain the molecular sieve precursor; wherein, 0.16 g of sodium aluminate is used, the amount of silicon source is SiO2, the amount of aluminum source is Al2O3, the amount of alkali source is NaOH, and the molar ratio of silicon source, aluminum source, template agent, alcohol solvent, alkali source and deionized water is 30:1:5:300:0.5:4000; (2) The molecular sieve precursor obtained in step (1) was placed in a hydrothermal synthesis reactor and sealed, and crystallized at 180°C for 4 h. (3) After crystallization, solid-liquid separation is performed. The separated solid is washed with deionized water until neutral, then dried at 80°C for 10 h and calcined at 400°C for 8 h to obtain molecular sieve. (4) The molecular sieve obtained in step (3) is mixed with 1 mol / L NH4Cl solution at a mass ratio of 1:20, stirred and refluxed at 90°C for 5 h for ion exchange, centrifuged and dried at 105°C for 5 h; the above operation is repeated twice, and calcined at 500°C for 6 h to obtain hydrogen-type nanosheet molecular sieve. The obtained hydrogen-form nanosheet molecular sieves were analyzed by XRD and SEM, respectively. Figure 1 and Figure 2 ;Depend on Figure 1 It can be seen that it is a typical characteristic peak of ZSM-5, belonging to ZSM-5 molecular sieve, with no other impurity peaks appearing, indicating good crystallinity; from Figure 2It can be seen that its morphology is nanosheet-like and uniform in size. The lengths along the a-axis, b-axis, and c-axis are statistically analyzed, and the average value is taken as the length of each axis. The lengths along the a-axis, b-axis, and c-axis are found to be 330 nm, 85 nm, and 1440 nm, respectively. The ratio of the length along the b-axis to the a-axis is L. b / L a It is 0.25.

[0016] Example 2 Hydrogen-form nanosheet molecular sieves were prepared by the following method: (1) Sodium aluminate is used as the aluminum source, sodium hydroxide as the alkali source, tetraethyl orthosilicate as the silicon source, tetrapropylammonium hydroxide as the template agent, and n-butanol is selected as the alcohol solvent; sodium aluminate and sodium hydroxide are dissolved in deionized water and stirred until clear. Then, tetrapropylammonium hydroxide is added and stirred until clear. Then, tetraethyl orthosilicate is added dropwise and stirred for 4 hours. Finally, n-butanol is added and stirred for 1 hour to obtain the molecular sieve precursor. Sodium aluminate is 0.05 g, the amount of silicon source is SiO2, the amount of aluminum source is Al2O3, and the amount of alkali source is NaOH. The molar ratio of silicon source, aluminum source, template agent, alcohol solvent, alkali source and deionized water is 30: 0.3: 30: 2000: 3: 300. (2) The molecular sieve precursor obtained in step (1) is placed in a hydrothermal synthesis reactor and sealed, and crystallized at 120°C for 24 h; (3) After crystallization, solid-liquid separation is performed. The separated solid is washed with deionized water until neutral, then dried at 100°C for 8 hours and calcined at 600°C for 5 hours to obtain molecular sieve. (4) The molecular sieve obtained in step (3) is mixed with 1 mol / L NH4Cl solution at a mass ratio of 1:25, stirred and refluxed at 80°C for 6 h for ion exchange, centrifuged and dried at 100°C for 5 h; the above operation is repeated twice, and calcined at 600°C for 5 h to obtain hydrogen-type nanosheet molecular sieve. The obtained hydrogen-form nanosheet molecular sieves were analyzed by XRD and SEM, respectively. Figure 3 and Figure 4 ;Depend on Figure 3 It can be seen that it is a typical characteristic peak of ZSM-5, belonging to ZSM-5 molecular sieve, with no other impurity peaks appearing, indicating good crystallinity; from Figure 4 It can be seen that its morphology is nanosheet-like and uniform in size. The lengths along the a-axis, b-axis, and c-axis are statistically analyzed, and the average value is taken as the length of each axis. The lengths along the a-axis, b-axis, and c-axis are found to be 610 nm, 75 nm, and 4200 nm, respectively. The ratio of the length along the b-axis to the a-axis is L. b / L a It is 0.12.

[0017] Example 3 A method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieve catalysis is as follows: The hydrogen-form nanosheet molecular sieve obtained in Example 1 is crushed, sieved, and 20-40 mesh hydrogen-form nanosheet molecular sieves are loaded into a fixed-bed reactor. Benzene and ethanol are used as raw materials, and nitrogen is used as the carrier gas. The reaction is carried out at 320℃ and 1.0 MPa. The molar ratio of benzene to ethanol is (6-10):1, and the ethanol mass hourly space velocity is 0.2-1.5 h⁻¹. -1 The carrier gas nitrogen flow rate was 50 mL / min; the specific reaction conditions and results are shown in Table 1.

[0018] Table 1. Reaction conditions and results of hydrogen-type nanosheet molecular sieve catalyzing the production of ethylbenzene from ethanol and benzene in Example 1. Note: The molar ratio in Table 1 is the molar ratio of benzene to ethanol, and the space velocity is the mass space velocity of ethanol.

[0019] As shown in Table 1, the conversion rates of ethanol were all above 99%, the selectivity of the main product ethylbenzene was all greater than 90%, the selectivity of ethylbenzene (ethylbenzene includes ethylbenzene and ortho, meta, and para-diethylbenzene) was greater than 96%, and the xylene content in the products was low, with the lowest being 660 ppm.

[0020] Example 4 A method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieve catalysis is as follows: The hydrogen-form nanosheet molecular sieve obtained in Example 1 is crushed, sieved, and 20-40 mesh hydrogen-form nanosheet molecular sieves are loaded into a fixed-bed reactor. Benzene and ethanol are used as raw materials, nitrogen is used as the carrier gas, and the reaction is carried out at 280-350℃ and 0.1-1.0 MPa. The molar ratio of benzene to ethanol is 6:1, and the ethanol mass hourly space velocity (HHSV) is 1.0 h⁻¹. -1 The carrier gas nitrogen flow rate was 50 mL / min; the specific reaction conditions and results are shown in Table 2.

[0021] Table 2. Reaction conditions and results of hydrogen-form nanosheet molecular sieve catalyzing the production of ethylbenzene from ethanol and benzene in Example 2. As shown in Table 2, the conversion rates of ethanol were all above 99%, the selectivity of the main product ethylbenzene was all greater than 92%, the selectivity of ethylbenzene (ethylbenzene includes ethylbenzene and ortho, meta, and para-diethylbenzene) was greater than 94%, and the xylene content in the products was low, with the lowest being 730 ppm.

[0022] Comparative Example Commercially available conventional ZSM-5 molecular sieve (commercial Nankai ZSM-5 catalyst) was used.

[0023] The commercial Nankai ZSM-5 catalyst (denoted as 1#) and the hydrogen-type nanosheet molecular sieve prepared in Example 1 (denoted as 2#) were used to catalyze the production of ethylbenzene from ethanol and benzene. The specific method is as follows: After crushing the catalyst, it was sieved to obtain 20-40 mesh samples, which were then loaded into a fixed-bed reactor. Benzene and ethanol were used as raw materials, and nitrogen was used as the carrier gas. The reaction was carried out at 300°C and 1.0 MPa. The molar ratio of benzene to ethanol was 6:1, and the ethanol mass hourly space velocity (HHSV) was 0.5 h⁻¹. -1 The carrier gas nitrogen flow rate was 50 mL / min; the specific reaction conditions and results are shown in Table 3.

[0024] Table 3. Reaction conditions and results of hydrogen-form nanosheet molecular sieves and comparative catalysis of ethanol and benzene to ethylbenzene in Example 1. As shown in Table 3, compared with the hydrogen-type nanosheet ZSM-5 molecular sieve provided by the present invention, conventional ZSM-5 molecular sieves exhibit lower conversion rates of benzene and ethanol when used to prepare ethylbenzene from ethanol and benzene. The selectivity of the main product, ethylbenzene, is significantly reduced, while the content of the byproduct, xylene, is significantly increased. This indicates that the nanosheet ZSM-5 molecular sieve has better activity and selectivity than conventional ZSM-5 molecular sieves, verifying the superiority of the catalyst of the present invention.

Claims

1. A method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieves as catalysts, characterized in that: After the hydrogen-type nanosheet molecular sieve is crushed, it is loaded into a fixed-bed reactor and reacted with benzene and ethanol as raw materials and nitrogen as carrier gas at 280-350℃ and 0.1-1.0MPa. The hydrogen-type nanosheet molecular sieve is a ZSM-5 molecular sieve, with a length of 70-100 nm along the b-axis and a length ratio L between the b-axis and a-axis. b / L a Less than 0.40; The molar ratio of benzene to ethanol is (6-10):1, and the ethanol mass hourly space velocity is 0.2-1.5 h⁻¹. -1 ; The hydrogen-form nanosheet molecular sieve was prepared by the following method: (1) Dissolve aluminum source and alkali source in deionized water, stir until clear, add template agent, stir until clear, then add silicon source dropwise, stir for 2-4 hours, finally add alcohol solvent, continue stirring for 1-2 hours to obtain molecular sieve precursor; (2) The molecular sieve precursor obtained in step (1) is placed in a hydrothermal synthesis reactor and sealed, and crystallized at 120-180℃ for 4-24 h; (3) After crystallization, solid-liquid separation is performed. The separated solid is washed with deionized water until neutral, then dried and calcined to obtain molecular sieve. (4) The molecular sieve obtained in step (3) is subjected to ion exchange to obtain hydrogen-type nanosheet molecular sieve; The alcohol solvent is one of methanol, ethanol, isopropanol, and n-butanol; The amount of silicon source is SiO2, the amount of aluminum source is Al2O3, and the amount of alkali source is NaOH. In step (1), the molar ratio of silicon source, aluminum source, template agent, alcohol solvent, alkali source and deionized water is 30: (0.3-1.0): (5-30): 300: (0.5-3): (300-4000) or 30: (0.3-1.0): (5-30): 2000: (0.5-3): (300-4000).

2. The method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieves as catalyzed according to claim 1, characterized in that: The aluminum source is at least one of aluminum isopropoxide, aluminum hydroxide, aluminum sulfate, aluminum nitrate, and sodium aluminate; The silicon source is at least one of tetraethyl orthosilicate, silica sol, and silica. The alkali source is selected from at least one of alkali metal hydroxides; The template agent is tetrapropylammonium hydroxide.

3. The method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieves as catalyzed according to claim 2, characterized in that: The drying in step (3) is performed at 80-100℃ for 8-10 hours; the calcination in step (3) is performed at 400-600℃ for 5-8 hours.

4. The method for producing ethylbenzene from ethanol and benzene using nanosheet molecular sieves as described in claim 3, characterized in that: The specific operation of step (4) is as follows: Mix the molecular sieve with 1 mol / L NH4Cl solution at a mass ratio of 1:(20-25), stir and reflux at 80-90℃ for 5-6 hours for ion exchange, centrifuge and dry at 100-105℃ for 5 hours; repeat the above operation twice and calcine at 500-600℃ for 5-6 hours.

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