Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbon through cellulose pyrolysis as well as preparation method and application of Fe-ZSM-5 molecular sieve catalyst

Abstract

The invention relates to a Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbon through cellulose pyrolysis as well as a preparation method and application of the Fe-ZSM-5 molecular sieve catalyst. A preparation method of a Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbon through cellulose pyrolysis comprises the following steps: (1) dissolving TPAOH, aluminum hydroxide and tetraethoxysilane in deionized water, stirring for 3-4 hours, adding ferric nitrate, stirring until a compact solution is formed, and heating and crystallizing to obtain a crystallized product; (2) washing the crystallized product to be neutral, drying, and calcining for the first time; and (3) carrying out ion exchange, washing and drying on the product after the first calcination, and carrying out second calcination. According to the Fe-ZSM-5 molecular sieve catalyst as well as the preparation method and the application thereof, the Fe-ZSM-5 molecular sieve is prepared through a one-step hydrothermal synthesis method, cellulose is converted into chemicals within an extremely short time by adopting a rapid pyrolysis method, and the Fe-ZSM-5 molecular sieve catalyst has excellent monocyclic aromatic hydrocarbon selectivity and can be used as a catalyst for preparing the hydrocracking catalyst. The invention provides a new possible way for designing an efficient Fe-based ZSM-5 molecular sieve catalyst for high-value conversion of cellulose.

Description

Technical Field

[0001] The present invention belongs to the technical field of molecular sieve catalysts, and in particular to an Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbons by pyrolysis of cellulose, and a preparation method and application thereof. Background Art

[0002] The rapid depletion of fossil fuel reserves and increasingly serious environmental problems highlight the urgent need to find sustainable alternatives to produce valuable chemicals and energy. Lignocellulosic biomass is the most abundant renewable organic carbon resource on Earth and is mainly composed of three components, of which cellulose accounts for 40-60%. Cellulose can be converted into energy, fuel or chemicals through processes such as pyrolysis, gasification and liquefaction, making it a powerful alternative to traditional energy. Among these conversion methods, pyrolysis is a key technology for efficient and clean utilization of biomass, which can directly convert it into liquid fuel or bio-oil. However, bio-oil is a complex mixture of organic compounds such as acids, aldehydes, ketones, alcohols, sugars, furans and phenolic compounds. Its instability, high oxygen content and acidity pose challenges to practical applications.

[0003] Upgrading bio-oil to more valuable products through catalytic fast pyrolysis shows significant potential in addressing these challenges. High-value chemicals such as benzene, phenols, furans, and light olefins can be selectively produced by using various catalysts. Among these products, light aromatics, especially benzene, toluene, and xylenes (BTX), have significant economic value due to their wide application as gasoline additives, solvents, and raw materials for the production of rubber, plastics, fibers, and resins. Among various catalysts, ZSM-5 has attracted much attention due to its unique properties. Its acidity, microporous structure, and shape selectivity make it highly effective in promoting the conversion of cellulose into high-value products.

[0004] The catalytic performance of ZSM-5 can be improved by introducing metals to tune its acidity and deoxygenation capabilities, enhancing its selectivity towards aromatics. Among these metals, modification with iron significantly improves the yield and quality of bio-oil by converting complex oxygenated compounds into valuable hydrocarbons. Moreover, the abundance and cost-effectiveness of iron make it an ideal choice for this application. Although iron has been identified as a catalytically active center, there is still no consensus on its specific nature, the evolution of iron species during catalyst preparation, and its exact role in the catalytic mechanism, highlighting the need for further research.

[0005] Therefore, in order to effectively improve the catalytic pyrolysis efficiency and bio-oil quality, it is crucial to further clarify the specific role of iron sites in cellulose catalytic pyrolysis and develop a catalytic system that can quickly and efficiently convert cellulose to produce high-value chemicals. Traditional methods usually result in low iron utilization, which reduces pyrolysis efficiency.

[0006] In view of this, the present invention proposes an Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbons by pyrolysis of cellulose and a preparation method and application thereof, which is an Fe-ZSM-5 molecular sieve catalyst, which introduces iron into the zeolite framework by isomorphic substitution and + ), thus showing excellent catalytic performance in the preparation of monocyclic aromatic hydrocarbons by catalytic pyrolysis of cellulose. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a Fe-ZSM-5 molecular sieve catalyst, wherein iron is introduced into the zeolite framework by isomorphous substitution and charged compensating cations (Na + ) Increase the content and dispersion of active iron species in the ZSM-5 zeolite framework.

[0008] In order to achieve the above purpose, the technical solution adopted is:

[0009] A method for preparing a Fe-ZSM-5 molecular sieve catalyst for preparing aromatics by pyrolysis of cellulose, comprising the following steps:

[0010] (1) dissolving TPAOH, aluminum hydroxide and tetraethoxysilane in deionized water, stirring for 3-4 hours, adding ferric nitrate, stirring until a dense solution is formed, and crystallizing at 165-175° C. for 4-6 days to obtain a crystalline product;

[0011] (2) washing the crystalline product to neutrality, drying it, and then calcining it for the first time;

[0012] (3) The product after the first calcination is subjected to ion exchange, washed, dried, and subjected to a second calcination to obtain the Fe-ZSM-5 molecular sieve catalyst.

[0013] Furthermore, in the step (1), the molar ratio of TPAOH: ferric nitrate: aluminum hydroxide: tetraethoxysilane in the dense solution is x: 0.6: 1.2: 50, x = 3, 5, 7, 9.

[0014] Furthermore, the step (1) further comprises: adding sodium hydroxide, mixing evenly, and then adding ferric nitrate.

[0015] Furthermore, in the step (1), the molar ratio of TPAOH, ferric nitrate, sodium hydroxide, aluminum hydroxide and tetraethoxysilane in the dense solution is 7:y::2:1.2:50; y=0.6, 0.7, 1, 1.2.

[0016] Furthermore, in the step (2), the temperature of the first calcination is 540-550° C. and the time is 4-6 hours;

[0017] The temperature of the second calcination is 550-750°C and the time is 4-6h.

[0018] Furthermore, in the step (2), the first calcination temperature is 550° C. and the time is 4 h;

[0019] The second calcination temperature was 750°C and the time was 6 h.

[0020] Furthermore, in the step (2), the ion exchange process is: the product after the first calcination is ion exchanged with 1 mol / L NH4Cl solution at 70-90°C.

[0021] Another object of the present invention is to provide a Fe-ZSM-5 molecular sieve catalyst prepared by the above-mentioned preparation method.

[0022] Another object of the present invention is to provide the application of the above-mentioned Fe-ZSM-5 molecular sieve catalyst in the preparation of monocyclic aromatic hydrocarbons by pyrolysis of cellulose. By utilizing rapid catalytic pyrolysis technology, cellulose can be converted into chemicals with high added value in a relatively short period of time, and has excellent aromatic hydrocarbon selectivity, thereby expanding the application field of cellulose.

[0023] Furthermore, the method for preparing monocyclic aromatic hydrocarbons by pyrolysis of cellulose is as follows: a quartz basket containing pretreated cellulose is temporarily suspended on the top of a quartz tube, a Fe-ZSM-5 molecular sieve having a certain proportion to cellulose is placed on a catalyst bed, 50 mL / min of argon is used as a carrier gas, and the basket is placed in a constant temperature zone of a pyrolysis furnace at a pyrolysis and catalytic temperature of 500-550°C for 5-10 minutes of pyrolysis reaction.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. In the technical solution of the present invention, the incorporation of iron into the zeolite framework by isomorphous substitution provides a more effective method, ensuring uniform distribution and preventing the formation of larger iron oxide particles and iron clusters. After template removal and secondary heat treatment, Fe 3+ The migration from coordination-saturated sites into the zeolite channels results in the formation of highly dispersed isolated iron species, leading to high catalytic activity.

[0026] 2. In the technical solution of the present invention, by introducing Na + Effect of Na as a charge-balancing cation on the migration of iron species and the formation of active iron species in the isostructurally substituted Fe-ZSM-5 framework. + The introduction of can promote the incorporation of more isolated iron species into the zeolite framework and promote their migration from the framework to the zeolite channel. The resulting molecular sieve catalyst exhibits excellent catalytic performance in the preparation of monocyclic aromatic hydrocarbons by catalytic pyrolysis of cellulose.

[0027] 3. Conventional pyrolysis products of cellulose will produce a large amount of oxygen-containing compounds. The catalyst in the technical solution of the present invention has a significant promoting effect on deoxygenation and aromatization, and the selectivity of aromatics in the product is relatively high; and a rapid pyrolysis method can be used, which greatly shortens the reaction time and realizes efficient utilization of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the XRD of the prepared molecular sieve;

[0029] Figure 2 It is the TEM and SEM of Na-FeZ5-550 and FeZ5-550;

[0030] Figure 3 is the Uv-vis of the prepared molecular sieve;

[0031] Figure 4 (a) is the product distribution diagram of the prepared Na-40FeZ5-550, Na-120FeZ5-550, 40FeZ5-550, 120FeZ5-550 molecular sieves for rapid catalytic pyrolysis of cellulose and (b) is the product distribution diagram of the prepared FeZ5-550, FeZ5-750, Na-FeZ5-550, Na-FeZ5-750 molecular sieves for rapid catalytic pyrolysis of cellulose. In the figure, MAH represents monocyclic aromatic hydrocarbons; PAH represents polycyclic aromatic hydrocarbons; BTEX is the abbreviation of (Benzene, Toluene, Ethylbenzene, Xylene), and its value is the sum of the values ​​of Benzene, Toluene, Ethylbenzene, and Xylene. DETAILED DESCRIPTION

[0032] In order to further illustrate the Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbons by pyrolysis of cellulose and its preparation method and application, and to achieve the intended purpose of the invention, the Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbons by pyrolysis of cellulose and its preparation method and application, its specific implementation method, structure, characteristics and efficacy are described in detail below in combination with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0033] The following will further introduce in detail the Fe-ZSM-5 molecular sieve catalyst for preparing aromatics by pyrolysis of cellulose and its preparation method and application in combination with specific embodiments of the present invention:

[0034] The present invention discloses a Fe-ZSM-5 molecular sieve catalyst for preparing aromatic hydrocarbons by pyrolysis of cellulose, and a preparation method and application thereof, wherein iron is introduced into the zeolite framework by isomorphic substitution, and a charge compensation cation (Na + ) Increase the content and dispersion of active iron species in the ZSM-5 zeolite framework, convert cellulose into chemicals in a very short time by rapid catalytic pyrolysis, and have excellent aromatic selectivity, which proposes a new possible path for the industrial application of cellulose and explores a new application mode of cellulose.

[0035] In order to achieve the above purpose, the technical solution adopted is:

[0036] A method for preparing a Fe-ZSM-5 molecular sieve catalyst for preparing aromatics by pyrolysis of cellulose, comprising the following steps:

[0037] (1) dissolving TPAOH, aluminum hydroxide and tetraethoxysilane in deionized water, stirring for 3-4 hours, adding ferric nitrate, stirring until a dense solution is formed, and crystallizing at 165-175° C. for 4-6 days to obtain a crystalline product;

[0038] (2) washing the crystalline product to neutrality, drying it, and then calcining it for the first time;

[0039] (3) The product after the first calcination is subjected to ion exchange, washed, dried, and subjected to a second calcination to obtain the Fe-ZSM-5 molecular sieve catalyst.

[0040] Preferably, in the step (1), the molar ratio of TPAOH: ferric nitrate: aluminum hydroxide oxysilane in the dense solution is x: 0.6: 1.2: 50, x = 3, 5, 7, 9.

[0041] Preferably, the step (1) further comprises: adding sodium hydroxide, mixing evenly, and then adding ferric nitrate.

[0042] Further preferably, in the step (1), the molar ratio of TPAOH, ferric nitrate, sodium hydroxide, aluminum hydroxide and tetraethoxysilane in the dense solution is 7:y::2:1.2:50; y=0.6, 0.7, 1, 1.2.

[0043] In the above technical solution, tetrapropylammonium hydroxide (TPAOH) is used as a template, and by introducing or not introducing charge compensating cations (Na + ) and secondary calcination to prepare Fe-ZSM-5 molecular sieve catalysts with different iron species distribution. + The catalyst was prepared by increasing the amount of TPAOH and keeping Si / OH=50 / 9, with the other steps being the same.

[0044] Preferably, in the step (2), the temperature of the first calcination is 540-550° C. and the time is 4-6 hours;

[0045] The temperature of the second calcination is 550-750°C and the time is 4-6h.

[0046] Further preferably, in the step (2), the temperature of the first calcination is 550° C. and the time is 4 h;

[0047] The second calcination temperature was 750°C and the time was 6 h.

[0048] Preferably, in the step (2), the ion exchange process is: the product after the first calcination is ion exchanged with 1 mol / L NH4Cl solution at 70-90°C.

[0049] A Fe-ZSM-5 molecular sieve catalyst is prepared by the above-mentioned preparation method.

[0050] The application of the above-mentioned Fe-ZSM-5 molecular sieve catalyst in the preparation of monocyclic aromatic hydrocarbons by pyrolysis of cellulose can convert cellulose into chemicals with high added value in a relatively short period of time, thus expanding the application field of cellulose.

[0051] Preferably, the method for preparing monocyclic aromatic hydrocarbons by pyrolysis of cellulose is as follows: a quartz basket containing pretreated cellulose is temporarily suspended on the top of a quartz tube, a Fe-ZSM-5 molecular sieve having a certain ratio with cellulose is placed on a catalyst bed, 50 mL / min of argon is used as a carrier gas, and the basket is placed in a constant temperature zone of a pyrolysis furnace at a pyrolysis and catalytic temperature of 500-550°C for 5-10 minutes of pyrolysis reaction.

[0052] Example 1.

[0053] Preparation of Na + The specific steps of Fe-ZSM-5 are as follows:

[0054] (1) Dissolve 33.75 deionized water and TPAOH in a polytetrafluoroethylene beaker, place it in a magnetic stirrer, and stir at 400 rpm. Then add aluminum hydroxide (Al(OH)3) and tetraethyl orthosilicate (TEOS, adamas, 99wt%) to the beaker in turn and keep stirring for 3 hours. Then add sodium hydroxide, stir for 3 hours, then add ferric nitrate nonahydrate, and continue stirring for 40 minutes to obtain a dense solution. The molar ratio of TPAOH, ferric nitrate, sodium hydroxide, aluminum hydroxide, and tetraethoxysilane in the dense solution is 7:0.6:2:1.2:50, that is, the molar ratio of each component in the catalyst preparation process is required to be 7TPAOH:0.3Fe2O3:Na2O:0.6Al2O3:50SiO2.

[0055] (2) The dense solution was placed in a 100 ml polytetrafluoroethylene lined autoclave for hydrothermal crystallization at 170°C for 5 days. After the hydrothermal crystallization was completed, the product was centrifugally washed with deionized water until neutral, and dried at 80°C for 10 hours to obtain Na-FeZ5-AS.

[0056] (3) Na-FeZ5-AS was first calcined at 550 °C for 4 h to remove the organic template in the pores and promote the migration of part of the iron from the framework.

[0057] (4) In order to obtain H-type ZSM-5 molecular sieve and continue to regulate the evolution of iron species in the zeolite framework, a second calcination was carried out. The process is as follows: the catalyst after the first calcination was first subjected to ion exchange three times with 1 mol / L NH4Cl solution at 70°C, each time for 4 hours (1g of solid was added to every 100mL of solution). After washing and drying with deionized water, it was divided into two parts and calcined at 550°C and 750°C for 6 hours respectively. The final material was named Na-FeZ5-T, where T represents the second calcination temperature (550°C and 750°C).

[0058] Example 2.

[0059] Preparation without introducing Na + The specific operation steps are the same as those in Example 1, except that:

[0060] Because the introduction of OH- is reduced, the amount of TPAOH added is increased, and Si / OH=50 / 9 is maintained, and the other synthesis conditions are the same. The molar ratio of TPAOH: ferric nitrate: aluminum hydroxide: tetraethoxysilane in the dense solution is 9:0.6:1.2:50, that is, the molar ratio of each component in the catalyst preparation process is required to be 9TPAOH:0.3Fe2O3:0.6Al2O3:50SiO2.

[0061] The final material was named FeZ5-T, where T again represents the second calcination temperature (550°C and 750°C).

[0062] The material obtained after hydrothermal crystallization, washing and drying but not calcined was named FeZ5-AS.

[0063] Example 3.

[0064] In order to compare the effect of iron, a catalyst without iron was prepared. The specific operation steps are as follows:

[0065] (1) The operation steps are the same as those in Example 1. The difference is that:

[0066] No iron salt was added, and the secondary calcination was only carried out at 550 °C. The final catalyst was named Na-Z5.

[0067] (2) The operation steps are the same as those in Example 2. The difference is that:

[0068] No iron salt and sodium hydroxide were added, and the secondary calcination was only carried out at 550°C. The final catalyst was named Z5.

[0069] Example 4.

[0070] The initial impregnation method synthesizes Fe / Z5. The specific steps are as follows:

[0071] First, weigh 2g Z5 and 0.144g ferric nitrate nine hydrate into a 50ml glass beaker, add 5ml deionized water, put in a magnet, and place it on a heated magnetic stirrer and stir at room temperature for 2h. In order to make the iron more dispersed on the surface of the molecular sieve, an ultrasonic-assisted method was used, that is, after stirring for 2h, the beaker was placed in an ultrasonic cleaner, and ultrasonicated at a power of 100Hz and a temperature of room temperature for 30min. After the ultrasonication, it was placed on a magnetic stirrer again and stirred at 50℃ for 10h to completely evaporate the water. The completely dried powder was calcined at 540℃ in a muffle furnace for 4h to obtain iron-impregnated Fe / Z5.

[0072] Example 5.

[0073] Compare the effects of the silicon-aluminum ratio of Fe-ZSM-5 zeolite catalyst on its catalytic performance in pyrolysis of cellulose to produce aromatics.

[0074] (1) Introduction of Na + Fe-ZSM-5

[0075] Method: The specific operation steps are as follows: the same as in Example 1, except that the molar ratio of TPAOH, ferric nitrate, sodium hydroxide, aluminum hydroxide, and tetraethoxysilane in the dense solution is as follows: the ratio is 7:0.6:2:m:50, m=1.2, 0.4.

[0076] And after only one calcination, the final materials were named Na-40FeZ5-550 and Na-120FeZ5-550.

[0077] (2) No introduction of Na + Fe-ZSM-5

[0078] Method: The specific operation steps are as follows: the molar ratio of TPAOH: ferric nitrate: aluminum hydroxide: tetraethoxysilane in the dense solution is as follows: the ratio is 7: 0.6: n: 50, n = 1.2, 0.4.

[0079] After only one calcination, the final materials were named 40FeZ5-550 and 120FeZ5-550.

[0080] Example 6.

[0081] The catalysts Na-Z5, Z5, FeZ5-AS, FeZ5-550, FeZ5-750, Na-FeZ5-AS, Na-FeZ5-550, Na-FeZ5-750, Na-40FeZ5-550, Na-120FeZ5-550, 40FeZ5-550, and 120FeZ5-550 prepared in Examples 1-5 were tested.

[0082] (1)XRD

[0083] The catalyst was characterized by XRD. Figure 1 shown.

[0084] Figure 1 XRD of the prepared molecular sieves shows that all the synthesized materials show the characteristic diffraction peaks of the MFI zeolite structure, indicating that the isomorphous substitution of iron for aluminum in the zeolite lattice does not destroy the crystal framework of the molecular sieve. The introduction of sodium hydroxide significantly improves the crystallinity of the ZSM-5 framework, which is proved by the sharper and stronger diffraction peaks of the NaZ5 series samples than the Z5 series (without sodium hydroxide).

[0085] (2) SEM, TEM

[0086] TEM and SEM tests of Na-FeZ5-550 and FeZ5-550 prepared in Example 1-2 showed the following results: Figure 2 shown.

[0087] Depend on Figure 2It can be seen that the introduction of iron and sodium hydroxide changed the crystallization kinetics of zeolite, resulting in the formation of different zeolite morphologies. Scanning electron microscopy showed that the size of Na-FeZ5-550 was about (700nm) and its surface was smooth, while FeZ5-550 had a smaller particle size and a rougher surface. Based on the TEM results, the possibility of the presence of large Fe2O3 nanoparticles in the fresh material can be ruled out.

[0088] (3)Uv-vis

[0089] Methods: UV-Vis DRS measurements were performed using a Shimadzu UV-3600 UV / Vis / NIR microspectrophotometer equipped with a diffuse reflectance accessory to determine the iron content in the Fe-ZSM-5 samples. To reduce light absorption, the samples were diluted 1:4 with barium sulfate. The instrument background was removed by subtracting the spectrum of a blank run (pure barium sulfate).

[0090] result: Figure 3 The UV-vis spectra of the prepared molecular sieve provide more conclusive evidence for the nature of the iron species in the synthesized Fe-modified ZSM-5 catalyst. The UV-vis spectra show that the absorption intensity of Na-FeZ5-AS in the uncalcined sample is high in the range of 200-250nm, indicating that Na + After calcination at 550°C, the absorption of Na-FeZ5-550 in the range of 200-250nm and 250-350nm was strong, indicating that the iron species inside and outside the framework were more stable and dispersed, while the absorption intensity of FeZ5-550 decreased and significantly enhanced in the range of 350-450nm and ≥450nm, indicating that more iron species aggregated to form Fe x O y After calcination at 750℃, the absorption of both samples decreased in the 200-250nm range, but the decrease of Na-FeZ5-750 was smaller, and the iron species in the framework were more stable; in the 250-350nm range, the absorption of Na-FeZ5-750 was higher, and the iron species were less aggregated, while the absorption of FeZ5-750 was further weakened, and more iron species aggregated to form Fe x O y In general, the introduction of sodium hydroxide significantly improved the stability of iron species and inhibited the migration and aggregation of iron species during calcination.

[0091] (4) Product distribution

[0092] Methods: Cellulose and catalyst were used in a rapid catalytic pyrolysis experiment at a mass ratio of 1:1.

[0093] After drying cellulose with a particle size of 90 microns at 110°C, it is placed in a hanging basket, and a catalyst is added to the catalyst bed. After reaching the pyrolysis temperature, the hanging basket is lowered to the constant temperature zone of the reactor for catalytic pyrolysis reaction. The specific conditions are: the pyrolysis furnace is heated to 550°C, the retention time is 10 minutes, and the pyrolysis gas after the reaction is completed goes out from the lower end of the reaction tube and enters the condensation collection tube, where the liquid phase product is condensed, and the non-condensable gas is collected through the gas sampling bag. The gas product. After 10 minutes, the pyrolysis reaction is basically completed. The liquid product collected in the condenser tube is dissolved in tetrahydrofuran and collected with a collection bottle. It is then evaluated using an Agilent 8890-5977B gas chromatograph / mass spectrometer equipped with an HP-5MS capillary column. The test temperature range is: 50°C for 4 minutes, the heating rate is 5°C / min; 210°C, the heating rate is 10°C / min; 280°C for 10 minutes. The NIST mass spectrum database provides information on the resulting chemicals. The yield of the compound was determined by the absolute peak area under the same conditions, and the percentage of the peak area to the total peak area of ​​all test compounds was used to compare the relative content of each compound. The catalysts were FeZ5-550, FeZ5-750, Na-FeZ5-550, Na-FeZ5-750, and Fe / Z5 prepared in Examples 1, 2, and 4.

[0094] result: Figure 4 (a) is the product distribution diagram of the rapid catalytic pyrolysis of cellulose by the prepared Na-40FeZ5-550, Na-120FeZ5-550, 40FeZ5-550, and 120FeZ5-550 molecular sieves; (b) is the product distribution diagram of the rapid catalytic pyrolysis of cellulose by the prepared FeZ5-550, FeZ5-750, Na-FeZ5-550, and Na-FeZ5-750 molecular sieves. As shown in Figure (a), the sample with the highest aluminum content (Si / Al=40) exhibits the highest deoxygenation ability and selectivity for aromatics, regardless of whether Na is introduced or not. + As shown in Figure (b), the conventionally prepared Na-FeZ5-750 has the highest selectivity for BTEX, accounting for 41.3% of the total aromatics, and the selectivity of aromatic compounds is 90.1%; compared with the conventional iron-impregnated molecular sieve, the total aromatics selectivity is significantly increased.

[0095] Example 7.

[0096] The specific steps are as follows:

[0097] (1) Preparation and introduction of Na + Fe-ZSM-5

[0098] The operation steps are the same as those in Example 1, except that:

[0099] TPAOH, aluminum hydroxide and tetraethoxysilane were dissolved in deionized water, stirred at 300 rpm for 4 h, and ferric nitrate was added and stirred until a dense solution was formed, and crystallized at 165° C. for 6 days.

[0100] The first calcination temperature was 540 °C and the time was 6 h;

[0101] The second calcination temperature was 600°C and the time was 5 h.

[0102] (2) After drying cellulose with a particle size of 90 μm at 110° C., place it in a hanging basket, add the Fe-ZSM-5 molecular sieve catalyst prepared in (1) (the mass ratio of catalyst to cellulose is 1:1) and place it in the catalyst bed. After reaching the pyrolysis temperature, lower the hanging basket to the constant temperature zone of the reactor for catalytic pyrolysis reaction. The specific conditions are: the pyrolysis furnace is heated to 500° C. and the retention time is 8 minutes.

[0103] Example 8.

[0104] The specific steps are as follows:

[0105] (1) Preparation without introducing Na + Fe-ZSM-5

[0106] The operation steps are the same as those in Example 3, except that:

[0107] TPAOH, aluminum hydroxide and tetraethoxysilane were dissolved in deionized water, stirred at 500 rpm for 3.5 h, iron nitrate was added, stirred until a dense solution was formed, and crystallized at 175 °C for 4 days.

[0108] The first calcination temperature was 545 °C and the time was 5 h;

[0109] The second calcination temperature was 700°C and the time was 4 h.

[0110] (2) After drying cellulose with a particle size of 90 μm at 110° C., place it in a hanging basket, add the Fe-ZSM-5 molecular sieve catalyst prepared in (1) (the mass ratio of catalyst to cellulose is 1:1) and place it in the catalyst bed. After reaching the pyrolysis temperature, lower the hanging basket to the constant temperature zone of the reactor for catalytic pyrolysis reaction. The specific conditions are: the pyrolysis furnace is heated to 540° C. and the retention time is 5 min.

[0111] Example 9.

[0112] Compare the effects of the ratio of each component in the dense solution on the catalyst.

[0113] (1) Introduction of Na + Fe-ZSM-5

[0114] Method: The specific operation steps are the same as those in Example 1, except that the molar ratio of TPAOH, ferric nitrate, sodium hydroxide, aluminum hydroxide, and tetraethoxysilane in the dense solution is as follows:

[0115] (1) The ratio is 7:0.7:2:1.2:50. Result: The iron content is too high and the solution in the beaker solidifies.

[0116] (2) The ratio is 7:1:2:1.2:50. Result: The iron content is too high and the solution in the beaker solidifies.

[0117] (3) The ratio is 7:1.2:2:1.2:50. Result: The iron content is too high and the solution in the beaker solidifies.

[0118] (2) No introduction of Na + Fe-ZSM-5

[0119] Method: The specific operation steps are as follows. The same as in Example 2, except that the molar ratio of TPAOH: ferric nitrate: aluminum hydroxide: tetraethoxysilane in the dense solution is as follows:

[0120] (1) The ratio is 3:0.6:1.2:50. Result: TEOS cannot be completely hydrolyzed, and the solution has solidified before adding ferric nitrate.

[0121] (2) The ratio is 5:0.6:1.2:50. Result: TEOS cannot be completely hydrolyzed, and the solution has solidified before adding ferric nitrate.

[0122] (3) The ratio is 7:0.6:1.2:50. Result: TEOS cannot be completely hydrolyzed, and the solution has solidified before adding ferric nitrate.

[0123] It can be seen from this that the raw material ratio of the catalyst synthesis stock solution is very important to its density and fluidity, and the solidification of the solution will affect the subsequent hydrothermal synthesis.

[0124] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a Fe-ZSM-5 molecular sieve catalyst for preparing aromatics by pyrolysis of cellulose, characterized in that: The following steps are involved: (1) dissolving TPAOH, aluminum hydroxide and tetraethoxysilane in deionized water, stirring for 3-4 hours, adding ferric nitrate, stirring until a dense solution is formed, and crystallizing at 165-175° C. for 4-6 days to obtain a crystalline product; (2) washing the crystalline product to neutrality, drying it, and then calcining it for the first time; (3) The product after the first calcination is subjected to ion exchange, washed, dried, and subjected to a second calcination to obtain the Fe-ZSM-5 molecular sieve catalyst.

2. The preparation method according to claim 1, characterized in that: In the step (1), the molar ratio of TPAOH: ferric nitrate: aluminum hydroxide: tetraethoxysilane in the dense solution is x: 0.6: 1.2: 50, x = 3, 5, 7, 9.

3. The preparation method according to claim 1, characterized in that: The step (1) further comprises: adding sodium hydroxide, mixing evenly, and then adding ferric nitrate.

4. The preparation method according to claim 3, characterized in that: In the step (1), the molar ratio of TPAOH, ferric nitrate, sodium hydroxide, aluminum hydroxide and tetraethoxysilane in the dense solution is 7:y:2:1.2:50; y=0.6, 0.7, 1, 1.

2.

5. The preparation method according to claim 1, characterized in that: In the step (2), the first calcination temperature is 540-550°C and the time is 4-6h; The temperature of the second calcination is 550-750°C and the time is 4-6h.

6. The preparation method according to claim 5, characterized in that: In the step (2), the first calcination temperature is 550° C. and the time is 4 hours; The second calcination temperature was 750°C and the time was 6 h.

7. The preparation method according to claim 1, characterized in that: In the step (2), the ion exchange process is: the product after the first calcination is ion exchanged with 1 mol / L NH4Cl solution at 70-90°C.

8. A Fe-ZSM-5 molecular sieve catalyst, characterized in that: The preparation method is described in any one of claims 1 to 7.

9. Use of the Fe-ZSM-5 molecular sieve catalyst according to claim 8 in the preparation of monocyclic aromatic hydrocarbons by pyrolysis of cellulose.

10. The use according to claim 9, characterized in that: The method for preparing monocyclic aromatic hydrocarbons by pyrolysis of cellulose is as follows: a quartz basket containing pretreated cellulose is temporarily suspended on the top of a quartz tube, the Fe-ZSM-5 molecular sieve is placed on a catalyst bed, 50 mL / min of argon is used as a carrier gas, and the basket is placed in a constant temperature zone of a pyrolysis furnace at 500-550° C. for pyrolysis reaction for 5-10 minutes.

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