Method for modifying zsm-5 zeolite to increase ethylene to propylene ratio in catalytic cracking products, the resulting zeolite and applications thereof

Abstract

The present application relates to the field of molecular sieve modification, in particular to a ZSM-5 molecular sieve modification method for improving the ethylene propylene ratio in catalytic cracking products and the molecular sieve and application thereof. The modification method provided by the present application includes: subjecting ZSM-5 molecular sieve and an alkali source to hydrothermal reaction; the alkali source is selected from one or both of ammonia water or urea. + The present application greatly shortens the alkali treatment time while saving resources; and because the alkali is relatively mild, the framework structure of the treated ZSM-5 molecular sieve is not damaged, so that the molecular sieve surface and micropore and mesopore properties are effectively controlled, the acid density of the molecular sieve is stabilized, the acid strength is improved, the efficiency of preparing low-carbon olefins by catalytic cracking is improved, and more importantly, the ethylene propylene ratio (E / P) of the reaction is improved, and the ethylene yield is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of molecular sieve modification, in particular to a ZSM-5 molecular sieve modification method for improving the ethylene / propylene ratio in catalytic cracking products, the molecular sieve obtained by the method and the application thereof. BACKGROUND

[0002] Low-carbon olefins such as ethylene and propylene are important organic chemical raw materials, and are known as the cornerstone of modern chemical industry. The ethylene industry is the core of the petrochemical industry, and ethylene products account for more than 75% of petrochemical products, and play an important role in the national economy. At present, the catalytic cracking process for preparing low-carbon olefins is increasingly highlighting its advantages. Compared with thermal cracking, the catalytic cracking process can greatly reduce the restrictions on raw materials, and under the action of the catalyst, the activation energy of hydrocarbon cracking can be effectively reduced, carbon emissions can be reduced, the yield of low-carbon olefins can be effectively improved, and the product distribution can be adjusted. As the core of the catalytic cracking reaction process, the catalyst has an important influence on the product distribution. ZSM-5 molecular sieve has high hydrothermal stability and shape selectivity, and has a wide range of adjustable silicon-aluminum ratio, and is the best choice as a catalytic cracking catalyst. In the catalytic cracking of hydrocarbons to produce olefins, the acid properties and texture properties of ZSM-5 molecular sieve have an important influence on its catalytic performance, so people are committed to the microstructure regulation of ZSM-5 molecular sieve. Among them, catalytic cracking is an acid-catalyzed reaction, the acid properties of ZSM-5 molecular sieve affect the conversion rate of raw materials and the selectivity of low-carbon olefins in the product, and also affect the stability of the molecular sieve. Fewer external surface strong acid sites are conducive to reducing the formation of external carbon deposition, prolonging the service life and stability of the catalyst; in addition, the microporous structure of ZSM-5 molecular sieve provides the necessary shape-selective conditions for the production of low-carbon olefins, and on this basis, mesoporous structures can be introduced by alkali treatment to adjust the acid distribution of the molecular sieve, which is conducive to regulating the ethylene / propylene ratio (E / P) in the catalytic cracking product, improving the diffusion performance of the intermediate product, reducing the secondary reaction of the product, and prolonging the service life of the catalyst.

[0003] Patent CN104445261A discloses a method for preparing a multi-level hole ZSM-5 zeolite by simple NaOH treatment. ZSM-5 molecular sieve is prepared and then treated with alkali, and cellulose is used as a template agent for secondary synthesis, so that the molecular sieve has micropores of 0.5-0.6 nm and ordered mesopores of 4-10 nm. This method can avoid the defects of single pore structure, improve the mass transfer efficiency, and has a wide application prospect in the field of petrochemical industry; however, the treatment depth is not easy to control, and the secondary synthesis material is easy to block the molecular sieve pores, cover part of the active centers, and affect the catalytic performance.

[0004] Patent CN109201106A discloses a method for treating HZSM-5 molecular sieve with Na2CO3 and tetrapropylammonium hydroxide (TPAOH), which introduces a certain amount of mesoporous structure, effectively reduces the adverse effects of micropore diffusion resistance on mass transfer, reduces the generation of coke, and increases the aromatic hydrocarbon yield by 7.3%; however, this technology greatly damages the microporous structure of HZSM-5, which affects the shape selectivity of the molecular sieve, and Na + A complicated ion exchange and calcination process is also required.

[0005] Z Wang et al. used NaHCO3 to treat ZSM-5, which increased the mesoporous structure by nearly one time while maintaining the original framework, formed a hierarchical structure combining micropores and mesopores, and reduced the diffusion resistance (Hierarchical zeolites obtained by alkaline treatment for enhanced n-pentane catalytic cracking[J]. Fuel, 2022, 313). However, this method has more by-products and the conversion rate of the catalytic reaction is reduced by 8.5% compared with the ZSM-5 molecular sieve before modification, which obviously reduces the conversion capacity of the molecular sieve.

[0006] Patent CN107954443A discloses a method for treating ZSM-5 molecular sieve with n-propylamine and hydrochloric acid in combination and repeatedly, which introduces mesoporous structure into the ZSM-5 molecular sieve, improves the pore distribution of the molecular sieve after Al removal, effectively controls the pore structure of the obtained molecular sieve, and improves the diffusion capacity of the product; however, this technology has complex experimental steps, high energy consumption of repeated calcination, washing, and drying, and the combination of acid treatment and alkali treatment repeatedly causes great loss of the molecular sieve, greatly damages the micropores, reduces the content of micropores, and thus reduces the selectivity of the molecular sieve. SUMMARY

[0007] Therefore, the technical problem to be solved by the present application is to provide a ZSM-5 molecular sieve modification method for improving the ethylene / propylene ratio in the catalytic cracking product, the obtained molecular sieve, and the application thereof. The modification method provided by the present application can adjust the acid distribution of the ZSM-5 molecular sieve, the modified ZSM-5 molecular sieve obtained by the method is applied to a hydrocarbon cracking reaction, the obtained product has a high ethylene / propylene ratio, and has a high yield of low-carbon olefins.

[0008] The present application provides a ZSM-5 molecular sieve modification method for improving the ethylene / propylene ratio in the catalytic cracking product, which comprises:

[0009] hydrothermally reacting the ZSM-5 molecular sieve and an alkali source;

[0010] The alkali source is selected from one or both of ammonia water and urea.

[0011] The ZSM-5 molecular sieve in the present application adopts a molecular sieve with a moderate silicon-aluminum ratio and a small crystal size. Specifically, the silicon-aluminum ratio of the ZSM-5 molecular sieve in the present application is 20-200, preferably 100-150; and the crystal size of the ZSM-5 molecular sieve is 100-800 nm. The alkali source in the present application is selected from one or both of ammonia water or urea, and is specifically preferably selected from one or both of ammonia water, urea or bio-fermented urea.

[0012] The present application performs a hydrothermal reaction on the ZSM-5 molecular sieve and the alkali source, and specifically, a mixed solution of the alkali source and the ZSM-5 molecular sieve is subjected to a hydrothermal reaction. The present application first obtains a mixed solution of the ZSM-5 molecular sieve and the alkali source, which is obtained by mixing a ZSM-5 molecular sieve solution and an alkali source solution; or by mixing a ZSM-5 molecular sieve solution and an alkali source; or by mixing a ZSM-5 molecular sieve solution and an alkali source solution; or by mixing a ZSM-5 molecular sieve and an alkali source in a solvent. The mixed solution of the ZSM-5 molecular sieve and the alkali source in the present application refers to a mixed aqueous solution of the ZSM-5 molecular sieve and the alkali source, and the ZSM-5 molecular sieve solution or the alkali source solution refers to a ZSM-5 molecular sieve aqueous solution or an alkali source aqueous solution.

[0013] The alkali source in the present application is preferably in the form of an alkali source solution. In some embodiments of the present application, the ZSM-5 molecular sieve is added to the alkali source solution, and a mixed solution of the ZSM-5 molecular sieve and the alkali source is obtained after uniform mixing. In one embodiment, the alkali source is added to water and stirred until completely dissolved to obtain an alkali source solution, and then the ZSM-5 molecular sieve is added to the alkali source solution to obtain a mixed solution of the ZSM-5 molecular sieve and the alkali source; a mixed solution of the ZSM-5 molecular sieve and the alkali source is obtained; the stirring temperature in the present application is 20-100°C, and the stirring time is 1-10 h.

[0014] The concentration of the alkali source and the concentration of the ZSM-5 molecular sieve in the present application both refer to their respective concentrations in the water used in the hydrothermal reaction, that is, their respective proportions in the solvent water added to the above-mentioned mixed solution. It is assumed herein that the addition of the alkali source and the molecular sieve solid does not cause a change in volume. The concentration of the alkali source in the present application is 0.01 mol / L-2 mol / L, preferably 0.1 mol / L-2 mol / L; and the concentration of the ZSM-5 molecular sieve is 50 g / L-400 g / L, preferably 80 g / L-220 g / L.

[0015] The application obtains a mixed solution of ZSM-5 molecular sieve and an alkali source, and then performs hydrothermal reaction on the mixed solution. The temperature of the hydrothermal reaction is 100-200 DEG C, preferably 150-170 DEG C; the time of the hydrothermal reaction is 6-60 hours, preferably 45-50 hours. After the hydrothermal reaction, the application further includes drying the product obtained after the hydrothermal reaction to obtain modified ZSM-5 molecular sieve; the temperature of the drying is 50-200 DEG C, and the time is 8-24 hours.

[0016] The application provides a modification method, which can modify ZSM-5 molecular sieve by hydrothermal treatment with ammonia water or urea as an alkali source, can increase mesoporous properties of the molecular sieve while retaining microporous characteristics of the molecular sieve, can increase acid strength while stabilizing acid density of the molecular sieve, and can adjust acid distribution of the molecular sieve. The treatment technology is simple, convenient and practical.

[0017] The application provides a modified ZSM-5 molecular sieve obtained by the above method. The application further provides a molecular sieve catalyst, which includes the modified ZSM-5 molecular sieve obtained by the above method. The molecular sieve catalyst is an alkali-treated ZSM-5 molecular sieve catalyst, which is obtained by grinding, tabletting and screening the modified ZSM-5 molecular sieve. The tabletting pressure is 5-40 MPa. The particle size of the molecular sieve catalyst is 10-80 mesh, preferably 20-40 mesh. The modified ZSM-5 molecular sieve provided by the application has high conversion rate when used as an active component in catalytic cracking, especially in catalytic cracking of hydrocarbons to produce olefins, can adjust product distribution, can improve selectivity of low-carbon olefins ethylene, propylene and butene in catalytic cracking products, and especially can improve the ratio of ethylene to propylene (E / P).

[0018] The application further provides application of the catalyst in catalytic cracking of hydrocarbons to improve the ratio of ethylene to propylene. Specifically, the application provides a hydrocarbon cracking method, which includes: catalytically cracking hydrocarbons under the action of the above molecular sieve catalyst to obtain cracking products. Preferably, the catalytic cracking is performed in a reactor; the reactor is a fixed bed reactor or a fluidized bed reactor; the temperature of the catalytic cracking is 600-650 DEG C; the application introduces a carrier gas in the catalytic cracking process, and the carrier gas is nitrogen; the pressure is normal pressure; the space velocity is 2-10 h -1 The hydrocarbons are alkanes or olefins; and the cracking products include low-carbon olefins, such as ethylene and propylene.

[0019] The application provides a ZSM-5 molecular sieve modification method for improving the ethylene propylene ratio in catalytic cracking products, and a molecular sieve and application thereof. The method provided by the application can obtain modified ZSM-5 molecular sieve, and the alkali-treated ZSM-5 molecular sieve catalyst prepared by further preparing the modified ZSM-5 molecular sieve can be used in the catalytic cracking of hydrocarbons to prepare olefins. The ammonia and urea used in the process of modifying the ZSM-5 molecular sieve do not introduce Na + , and the time of alkali treatment is greatly shortened while resources are saved; and because the alkalinity is relatively mild, the framework structure of the treated ZSM-5 molecular sieve is not damaged, so that the surface and micropore and mesopore properties of the molecular sieve are effectively controlled, the acid strength of the molecular sieve is improved while the acid density of the molecular sieve is stabilized, the efficiency of preparing low-carbon olefins by catalytic cracking is improved, and more importantly, the ethylene to propylene ratio (E / P) of the reaction is improved, and the yield of ethylene is increased. The problems of the traditional alkali-treated molecular sieve, such as the fact that NaOH greatly damages the micropores of the molecular sieve, and the fact that Na2CO3 and NaHCO3 can introduce Na + , and the like, need to be solved. In addition, the ZSM-5 molecular sieve modification process and the preparation process of the molecular sieve catalyst are both simple and efficient, from the raw material cost, urea and ammonia water are more cost-effective, and the alkali treatment process is simpler and more efficient. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the evaluation device of the catalyst of the embodiment of the application;

[0021] Figure 2 It is an XRD graph of the catalyst obtained by treating the ZSM-5 molecular sieve with urea in Example 2;

[0022] Figure 3 It is an electron microscope graph of the molecular sieve in Comparative Example 1;

[0023] Figure 4 It is an electron microscope graph of the ZSM-5 molecular sieve treated with urea in Example 2;

[0024] Figure 5 It is an electron microscope graph of the ZSM-5 molecular sieve treated with Na2CO3 in Comparative Example 8;

[0025] Figure 6 It is an electron microscope graph of the ZSM-5 molecular sieve treated with NaOH in Comparative Example 4;

[0026] Figure 7 It is an ammonia temperature programmed desorption curve graph of the products in some embodiments and comparative examples of the application. DETAILED DESCRIPTION

[0027] This invention discloses a method for modifying ZSM-5 molecular sieves to increase the ethylene-propylene ratio in catalytic cracking products, the resulting molecular sieve, and its applications. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired results. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art will clearly be able to modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0028] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and compounds described are commercially available unless otherwise specified.

[0029] The sources of raw materials are shown in Table 1:

[0030] Table 1

[0031]

[0032]

[0033] Evaluation and analysis methods:

[0034] (1) The reaction performance evaluation of the catalyst was carried out in a continuous flow fixed bed reactor, as follows: Figure 1 As shown, Figure 1 This is a schematic diagram of the catalyst evaluation device according to an embodiment of the present invention; wherein, the reference numerals are: 1. n-hexane; 2. micro-feed pump; 3. nitrogen; 4. gas flow meter; 5. heating furnace; 6. catalyst; 7. gas chromatograph.

[0035] The reaction tube has an inner diameter of 10 mm and a length of 400 mm. The catalyst loading is 0.5 g, and both ends are filled with quartz wool. Before the reaction, the reactor is purged with N2 for 2 hours. The reactants are pumped into the reactor using a micro-pump, mixed with the carrier N2 before entering the reactor. The product at the reactor outlet is split into two streams: one portion is incubated and directly enters the gas chromatograph for online quantitative analysis, while the other portion is directly vented. The catalyst evaluation conditions are: 600–650 °C, atmospheric pressure, reactants are alkanes or olefins or a mixture of both, and the feed mass hourly space velocity (WHSV) is 8 h⁻¹. -1 The products were analyzed online by gas chromatography.

[0036] (2) Product distribution and calculation method

[0037] When using n-hexane as a raw material, the conversion rate and selectivity of n-hexane are calculated according to the following formulas 1 and 2, respectively:

[0038]

[0039] In formula 1, is the mass fraction of n-hexane in the raw material;

[0040] is the mass fraction of n-hexane in the product;

[0041]

[0042] In formula 2, w CiHjt is the mass fraction of a certain substance in the product.

[0043] The application is further described below in combination with examples:

[0044] Example 1

[0045] 0.075 g of urea was configured into a solution with 12.5 mL of water, and the solution was slowly added dropwise into 1.25 g of ZSM-5 with a silicon-aluminum ratio of 100, and the mixture was fully stirred for 2 h, and then the mixture was transferred into a 50 mL high-temperature reaction kettle, and static reaction was carried out at 160 ℃ for 48 h, and then the reaction kettle was cooled to room temperature in air, the reaction kettle cover was opened, and drying was carried out at 120 ℃ for 7 h to obtain a molecular sieve product. The catalyst was pressed into a sheet at 20 MPa, and particles with a size of 20-40 mesh were obtained for evaluation.

[0046] Example 2

[0047] 1.5 g of urea was configured into a solution with 50 mL of water, and the solution was slowly added dropwise into 5 g of ZSM-5 with a silicon-aluminum ratio of 100, and the mixture was fully stirred for 2 h, and then the mixture was transferred into a 150 mL high-temperature reaction kettle, and static reaction was carried out at 160 ℃ for 48 h, and then the reaction kettle was cooled to room temperature in air, the reaction kettle cover was opened, and drying was carried out at 120 ℃ for 7 h to obtain an intermediate powder. The catalyst was pressed into a sheet at 20 MPa, and particles with a size of 20-40 mesh were obtained for evaluation. The obtained catalyst was subjected to XRD testing, as shown in Figure 2 Figure 2 FIG. 2 is an XRD pattern of the catalyst obtained by treating ZSM-5 with urea in Example 2. It can be known from the figure that the ZSM-5 treated with urea all has ZSM-5 framework characteristic diffraction peaks near 2θ = 7.9°, 8.8°, 22.9°, 23.9°, and 24.4°, indicating that the framework structure of the ZSM-5 is not destroyed by urea treatment. Figure 2

[0048] Example 3

[0049] ​​A solution of 12 g of urea and 200 mL of water was prepared, and the solution was slowly added to 20 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 500 mL high-temperature reactor, reacted statically for 48 h at 160°C, cooled to room temperature in air, and dried at 120°C for 7 h to obtain a molecular sieve product. The catalyst was pressed into a tablet at 20 MPa, and particles with a size of 20-40 mesh were obtained for evaluation.

[0050] Example 4

[0051] A solution of 1.5 g of bio-fermented urea and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature reactor, reacted statically for 48 h at 160°C, cooled to room temperature in air, and dried at 120°C for 7 h to obtain a molecular sieve product. The catalyst was pressed into a tablet at 20 MPa, and particles with a size of 20-40 mesh were obtained for evaluation.

[0052] Example 5

[0053] A solution of 6 g of bio-fermented urea and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature reactor, reacted statically for 48 h at 160°C, cooled to room temperature in air, and dried at 120°C for 7 h to obtain a molecular sieve product. The catalyst was pressed into a tablet at 20 MPa, and particles with a size of 20-40 mesh were obtained for evaluation.

[0054] Example 6

[0055] A solution of 0.7 g of aqueous ammonia and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature reactor, reacted statically for 48 h at 160°C, cooled to room temperature in air, and dried at 120°C for 7 h to obtain a molecular sieve product. The catalyst was pressed into a tablet at 20 MPa, and particles with a size of 20-40 mesh were obtained for evaluation.

[0056] Example 7

[0057] A solution of 3.5 g of urea and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature autoclave for static reaction at 160°C for 48 h. After cooling to room temperature in air, the autoclave was opened, and the product was dried at 120°C for 7 h. The catalyst was tabletted at 20 MPa, and the particles were sieved to 20-40 mesh to obtain a catalyst for evaluation.

[0058] Example 8

[0059] A solution of 0.3 g of urea and 0.7 g of aqueous ammonia and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature autoclave for static reaction at 160°C for 48 h. After cooling to room temperature in air, the autoclave was opened, and the product was dried at 120°C for 7 h. The catalyst was tabletted at 20 MPa, and the particles were sieved to 20-40 mesh to obtain a catalyst for evaluation.

[0060] Example 9

[0061] A solution of 1.5 g of urea and 3.5 g of aqueous ammonia and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature autoclave for static reaction at 160°C for 48 h. After cooling to room temperature in air, the autoclave was opened, and the product was dried at 120°C for 7 h. The catalyst was tabletted at 20 MPa, and the particles were sieved to 20-40 mesh to obtain a catalyst for evaluation.

[0062] Example 10

[0063] A solution of 1.5 g of urea and 50 mL of water was prepared, and the solution was slowly added to 5 g of ZSM-5 with a silica-alumina ratio of 200, stirred for 2 h, and then transferred to a 150 mL high-temperature autoclave for static reaction at 120°C for 48 h. After cooling to room temperature in air, the autoclave was opened, and the product was dried at 120°C for 7 h. The catalyst was tabletted at 20 MPa, and the particles were sieved to 20-40 mesh to obtain a catalyst for evaluation.

[0064] Example 11

[0065] A solution of 1.5 g urea and 50 mL water was prepared, and the solution was slowly added to 5 g ZSM-5 with a silica-alumina ratio of 200, stirred for 2 h, and then transferred to a 150 mL high-temperature reaction kettle for static reaction at 140°C for 48 h. After cooling to room temperature in air, the kettle cover was opened, and the product was dried at 120°C for 7 h. The catalyst was pressed into a tablet at 20 MPa, and the particles with a size of 20-40 mesh were obtained for evaluation.

[0066] Example 12

[0067] A solution of 1.5 g urea and 50 mL water was prepared, and the solution was slowly added to 5 g ZSM-5 with a silica-alumina ratio of 200, stirred for 2 h, and then transferred to a 150 mL high-temperature reaction kettle for static reaction at 140°C for 48 h. After cooling to room temperature in air, the kettle cover was opened, and the product was dried at 120°C for 7 h. The catalyst was pressed into a tablet at 20 MPa, and the particles with a size of 20-40 mesh were obtained for evaluation.

[0068] Example 13

[0069] A solution of 1.5 g urea and 50 mL water was prepared, and the solution was slowly added to 5 g ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature reaction kettle for static reaction at 180°C for 24 h. After cooling to room temperature in air, the kettle cover was opened, and the product was dried at 120°C for 7 h. The catalyst was pressed into a tablet at 20 MPa, and the particles with a size of 20-40 mesh were obtained for evaluation.

[0070] Example 14

[0071] A solution of 1.5 g urea and 50 mL water was prepared, and the solution was slowly added to 5 g ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and then transferred to a 150 mL high-temperature reaction kettle for static reaction at 180°C for 36 h. After cooling to room temperature in air, the kettle cover was opened, and the product was dried at 120°C for 7 h. The catalyst was pressed into a tablet at 20 MPa, and the particles with a size of 20-40 mesh were obtained for evaluation.

[0072] Example 15

[0073] A solution of 1.5 g urea in 50 mL water was prepared, and the solution was slowly added to 5 g ZSM-5 with a silica-alumina ratio of 100, and the mixture was stirred for 2 h, and then the mixture was transferred to a 150 mL high-temperature reactor, and reacted statically at 180 °C for 60 h, and then cooled to room temperature in air, and the reactor cover was opened, and dried at 120 °C for 7 h to obtain a molecular sieve product. The catalyst was pressed into a sheet at 20 MPa, and sieved into particles of 20-40 mesh to obtain a catalyst for evaluation.

[0074] Example 16

[0075] A solution of 24 g urea in water was prepared to 400 mL, and stirred until the urea was completely dissolved, and the prepared urea solution was slowly added to 80 g ZSM-5 with a silica-alumina ratio of 100, and the mixture was transferred to a high-temperature reactor, and reacted statically at 160 °C for 48 h, and then cooled to room temperature in air, and the reactor cover was opened, and dried at 120 °C for 10 h, and then 100 g of SB powder was added, and after mixing evenly, 20 g of sesbania powder was added, and 100 g of citric acid and 100 mL of nitric acid were added, and after stirring evenly, extruded into strips, and dried at 100 °C, and then calcined at 550 °C for 6 h to obtain a modified shaped molecular sieve catalyst.

[0076] Example 17

[0077] A solution of 24 g urea in water was prepared to 400 mL, and stirred until the urea was completely dissolved, and the prepared urea solution was slowly added to 80 g ZSM-5 with a silica-alumina ratio of 100, and the mixture was transferred to a high-temperature reactor, and reacted statically at 160 °C for 48 h, and then cooled to room temperature in air, and the reactor cover was opened, and dried at 120 °C for 10 h, and then 100 g of kaolin was added, and after mixing evenly, 20 g of glycerol was added, and 100 g of citric acid and 100 mL of nitric acid were added, and after stirring evenly, extruded into strips, and dried at 100 °C, and then calcined at 550 °C for 6 h to obtain a modified shaped molecular sieve catalyst.

[0078] Example 18

[0079] A solution of 24 g urea in water was prepared to 400 mL, and stirred until the urea was completely dissolved, and the prepared urea solution was slowly added to 80 g ZSM-5 with a silica-alumina ratio of 100, and the mixture was transferred to a high-temperature reactor, and reacted statically at 160 °C for 48 h, and then cooled to room temperature in air, and the reactor cover was opened, and dried at 120 °C for 10 h, and then 100 g of kaolin was added, and after mixing evenly, 20 g of sesbania powder was added, and 200 g of oxalic acid was added, and after stirring evenly, extruded into strips, and dried at 100 °C, and then calcined at 550 °C for 6 h to obtain a modified shaped molecular sieve catalyst.

[0080] Example 19

[0081] A solution of 1.5 g urea and 50 mL water was prepared and slowly added to 5 g ZSM-5 with a silica-alumina ratio of 100, stirred for 10 h, and then transferred to a 100 mL autoclave for static reaction at 160 °C for 48 h. The mixture was cooled to room temperature in air, the autoclave was opened, and the product was dried at 120 °C for 7 h. The catalyst was tabletted at 20 MPa, sieved to 20-40 mesh particles, and the catalyst was obtained for evaluation. The prepared catalyst was subjected to steam aging treatment. The catalyst was subjected to steam treatment at 800 °C in a self-built small fixed bed reactor, a flat pump was used, the mass space velocity was 18 h -1 The water inlet was 4 h.

[0082] Example 20

[0083] A solution of 1.5 g urea and 50 mL water was prepared and slowly added to 5 g ZSM-5 with a silica-alumina ratio of 100, stirred for 10 h, and then transferred to a 100 mL autoclave for static reaction at 160 °C for 48 h. The mixture was cooled to room temperature in air, the autoclave was opened, and the product was dried at 120 °C for 7 h. The catalyst was tabletted at 20 MPa, sieved to 20-40 mesh particles, and the catalyst was obtained for evaluation. The prepared catalyst was subjected to steam aging treatment. The catalyst was subjected to steam treatment at 800 °C in a self-built small fixed bed reactor, a flat pump was used, the mass space velocity was 18 h

[0084] Comparative Example 1 (ZSM-5 as received)

[0085] ZSM-5 molecular sieve powder was tabletted at 20 MPa, sieved to 20-40 mesh particles, and the catalyst was obtained for evaluation.

[0086] Comparative Example 2 (simple base treatment)

[0087] A solution of 1.5 g urea and 50 mL water was prepared and slowly added to 5 g ZSM-5 with a silica-alumina ratio of 100, stirred for 10 h, and then transferred to a 100 mL autoclave for static reaction at 160 °C for 48 h. The mixture was cooled to room temperature in air, the autoclave was opened, and the product was dried at 120 °C for 7 h. The catalyst was tabletted at 20 MPa, sieved to 20-40 mesh particles, and the catalyst was obtained for evaluation. The prepared catalyst was subjected to steam aging treatment. The catalyst was subjected to steam treatment at 800 °C in a self-built small fixed bed reactor, a flat pump was used, the mass space velocity was 18 h

[0088] Comparative Example 3 (simple hydrothermal without adding base)

[0089] Mix 1 g of NaOH with 50 mL of water and slowly add to 5 g of ZSM-5 with a silica to alumina ratio of 100, stir well for 2 h, transfer the mixture to a 150 mL high temperature autoclave, react statically at 160 °C for 48 h, cool to room temperature in air, open the autoclave lid, and dry at 120 °C for 7 h to obtain the molecular sieve product. Press the catalyst into a pellet at 20 MPa, sieve the pellet to obtain particles of 20-40 mesh, and obtain the catalyst for evaluation.

[0090] Comparative Example 4

[0091] Mix 1 g of NaOH with 50 mL of water and slowly add to 5 g of ZSM-5 with a silica to alumina ratio of 100, stir well for 2 h, transfer the mixture to a 150 mL high temperature autoclave, react statically at 160 °C for 48 h, cool to room temperature in air, open the autoclave lid, and dry at 120 °C for 7 h to obtain the molecular sieve product. Press the catalyst into a pellet at 20 MPa, sieve the pellet to obtain particles of 20-40 mesh, and obtain the catalyst for evaluation.

[0092] Comparative Example 5

[0093] Mix 7.59 g of TPAOH with 50 mL of water and slowly add to 5 g of ZSM-5 with a silica to alumina ratio of 100, stir well for 2 h, transfer the mixture to a 150 mL high temperature autoclave, react statically at 160 °C for 48 h, cool to room temperature in air, open the autoclave lid, and dry at 120 °C for 7 h to obtain the molecular sieve product. Press the catalyst into a pellet at 20 MPa, sieve the pellet to obtain particles of 20-40 mesh, and obtain the catalyst for evaluation.

[0094] Comparative Example 6

[0095] Mix 2.1 g of NaHCO3 with 50 mL of water and slowly add to 5 g of ZSM-5 with a silica to alumina ratio of 100, stir well for 2 h, transfer the mixture to a 150 mL high temperature autoclave, react statically at 160 °C for 48 h, cool to room temperature in air, open the autoclave lid, and dry at 120 °C for 7 h to obtain the molecular sieve product. Press the catalyst into a pellet at 20 MPa, sieve the pellet to obtain particles of 20-40 mesh, and obtain the catalyst for evaluation.

[0096] Comparative Example 7

[0097] 2.65 g of Na2CO3 was mixed with 50 mL of water and added slowly to 5 g of ZSM-5 with a silica-alumina ratio of 100, stirred for 2 h, and the mixture was transferred to a 150 mL high-temperature reactor, reacted statically at 160°C for 48 h, cooled to room temperature in air, the reactor cover was opened, and dried at 120°C for 7 h to obtain a molecular sieve product. The catalyst was pressed into a tablet at 20 MPa, and the 20-40 mesh particles were sieved to obtain a catalyst for evaluation.

[0098] The results of the hydrocarbon catalytic cracking to olefin reaction of the examples and comparative examples are shown in Table 2.

[0099] Table 2

[0100]

[0101]

[0102] As can be seen from Table 2, the method adopted in the present application improves the selectivity of low-carbon olefins in catalytic cracking to prepare low-carbon olefins, and the yield of ethylene is increased by more than 6%, effectively improving the E / P of the catalytic cracking product, and it is found that the utilization rate of the sample molecular sieve treated by the method of the present application is increased by more than 10%.

[0103] The texturing properties of some of the example and comparative example samples are shown in Table 3.

[0104] Table 3

[0105]

[0106] In Table 3, the superscript a represents the BET method, i.e. the BET specific surface area (S BET a ) calculated by the BET method;

[0107] The superscript b represents the total pore volume (V total b ) calculated at a relative pressure (p / p0) = 0.99;

[0108] The superscript c represents the pore surface area or pore volume obtained by the t-plot method, where S micro c is the micropore surface area, S external c is the external surface area, V micro c is the micropore volume;

[0109] The superscript d represents the mesopore volume (V mesod The value is obtained by subtracting the micropore volume from the total pore volume.

[0110] The acid properties of some of the examples and comparative samples are shown in Table 4.

[0111] Table 4

[0112]

[0113] Tables 3 and 4 show that ZSM-5 molecular sieves, after being treated with urea, form mesoporous structures while retaining a high microporous structure, thus achieving high shape selectivity and excellent diffusion performance, suppressing secondary reactions to the greatest extent; increasing acidity and acid strength, increasing the conversion rate of catalytic cracking reactions, and improving the yield of low-carbon olefins in hydrocarbon catalytic cracking reactions, while also effectively increasing the E / P ratio in the products.

[0114] Figures 3-5 These are electron microscope images of some embodiments and comparative examples of the present invention, wherein... Figure 3 This is an electron micrograph of the original molecular sieve sample from Comparative Example 1. Figure 4 This is an electron micrograph of ZSM-5 molecular sieve treated with urea in Example 2. Figure 5 The image shows an electron micrograph of the ZSM-5 molecular sieve treated with Na2CO3 in Comparative Example 8. Figure 6 Electron micrograph of ZSM-5 molecular sieve treated with NaOH in Comparative Example 4. Figure 3 and Figure 4 Observations revealed little difference in morphology between the original molecular sieve and the urea-treated ZSM-5 molecular sieve from Example 2, indicating that the treatment conditions of this method are milder and cause less alteration to the morphology of the molecular sieve. Figure 5 It was found that in Comparative Example 8, treatment of ZSM-5 molecular sieve with Na2CO3 caused deformation and blurring of the edges between molecular sieve particles, as well as surface depressions. This may be due to the Na2CO3 dissolving the silicon in the molecular sieve framework and on the surface. Figure 6 It was found that, in Comparative Example 4, the surface morphology of ZSM-5 molecular sieve treated with NaOH differed significantly from that of the urea-modified sample. Etching occurred on the grain surface, and some amorphous substances were generated. This may be due to the stronger alkalinity of NaOH, which caused excessive dissolution of both the framework and non-framework silicon in the molecular sieve. Other examples and photographs are also available. Figure 4 Similarly, the present invention will not list them all.

[0115] Figure 7 These are ammonia desorption curves for some embodiments and comparative examples of the present invention. Curve 1 represents Comparative Example 4, curve 2 represents Example 16, curve 3 represents Comparative Example 3, curve 4 represents Comparative Example 1, curve 5 represents Example 2, and curve 6 represents Comparative Example 3. From... Figure 7It can be seen that the samples treated by alkali and modified have low temperature and high temperature desorption peaks corresponding to the desorption temperature range of weak acid and strong acid sites. The total acid amount of the urea hydrothermal treated sample of Example 2 is increased by more than 18% compared with the untreated sample of Comparative Example 1. The urea treated sample has a stronger alkali and a lower temperature, which causes the removal of Si atoms in the framework of the molecular sieve, generates mesopores, improves the accessibility of the acid sites of the molecular sieve, and leads to an increase in the acid density of the molecular sieve. The acid amount and acid strength of the sample treated by sodium hydroxide in Comparative Example 4 are reduced, thereby reducing the catalytic performance of the molecular sieve. The sodium hydroxide treated molecular sieve first removes the framework defects (hydroxyl pits and internal silicon hydroxyl groups), and then removes the Si atoms in the framework, which causes the removal of the Si atoms in the framework of the molecular sieve, generates mesopores, improves the accessibility of the acid sites of the molecular sieve, and leads to an increase in the acid density of the molecular sieve. - The attack on the framework of the molecular sieve causes the change in the acid properties of the molecular sieve. The urea treatment of the present application increases the acid amount and acid strength of the molecular sieve, obtains a higher strong acid / weak acid ratio, improves the selectivity of low carbon olefins, effectively adjusts the E / P of the cracking products, and makes the molecular sieve catalyst exhibit excellent catalytic stability.

[0116] In summary, the alkali treated ZSM-5 molecular sieve catalyst provided by the present application has a suitable micropore / mesopore ratio, improves the conversion rate of the catalytic cracking reaction, the yield of low carbon olefins, and especially the yield of ethylene. The stability of the molecular sieve structure and the stability of the acid structure are greatly enhanced, and the reaction stability of the molecular sieve catalyst is further improved, so that the molecular sieve catalyst is applied to the preparation of low carbon olefins by catalytic cracking of hydrocarbons.

[0117] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can make equivalent replacements or changes to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A process for cracking hydrocarbons, characterized in that, The method comprises the following steps: catalytically cracking hydrocarbons under the action of a molecular sieve catalyst to obtain cracking products; The molecular sieve catalyst is a modified ZSM-5 molecular sieve prepared by the following steps: The ZSM-5 molecular sieve and an alkali source are subjected to a hydrothermal reaction to obtain a modified ZSM-5 molecular sieve; the ZSM-5 molecular sieve has a silicon-aluminum ratio of 100-150; and the ZSM-5 molecular sieve has a crystal grain size of 100 nm-800 nm; The alkali source is selected from one or both of ammonia water and urea; The concentration of the alkali source is 0.01 mol / L-2 mol / L; The concentration of the ZSM-5 molecular sieve is 50-400 g / L.

2. The method of claim 1, wherein, The concentration of the alkali source is 0.1 mol / L-2 mol / L; The concentration of the ZSM-5 molecular sieve is 80-220 g / L.

3. The method of claim 1, wherein, The temperature of the hydrothermal reaction is 100 DEG C-200 DEG C, and the time of the hydrothermal reaction is 6 h-60 h.

4. The method of claim 3, wherein, The temperature of the hydrothermal reaction is 150 DEG C-170 DEG C, and the time of the hydrothermal reaction is 45 h-50 h.

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