Light hydrocarbon catalytic conversion modified molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to a light hydrocarbon catalytic conversion modified molecular sieve and a preparation method and application thereof, the modified molecular sieve comprises a molecular sieve and a composite oxide loaded on the molecular sieve, the general formula of the composite oxide is ZnO.Fe2O3. MxOy, the element M is selected from one or more of IIA family elements, IIIA family elements, IVA family elements, IVB family elements, VB family elements, VIB family elements, VIIB family elements, VIII family elements and lanthanide series elements; x and y are stoichiometric ratios, x is 1 or 2, and y is selected from 1, 2 or 3; the molar ratio of ZnO to Fe2O3 to MxOy in the composite oxide is 1: (0.5-2): (0-1); the molecular sieve comprises a five-membered ring molecular sieve. The light hydrocarbon catalytic conversion modified molecular sieve provided by the invention is beneficial to catalytic cracking of a light hydrocarbon raw material on the molecular sieve to generate low-carbon olefin and BTX; meanwhile, the composite oxide in the modified molecular sieve can effectively activate small-molecule saturated hydrocarbon, the reaction temperature of the catalytic cracking reaction of the light hydrocarbon raw material can be reduced, and the selectivity of low-carbon olefin and light aromatic hydrocarbon in the product can be improved.

Description

Technical Field

[0001] This invention belongs to the field of petrochemicals, specifically relating to a modified molecular sieve for catalytic conversion of light hydrocarbons, its preparation method, and its application. Background Technology

[0002] Ethylene, propylene, and butene can be used as basic organic chemical raw materials for the synthesis of resins, synthetic fibers, and synthetic rubber. Ethylene and propylene are mainly produced through medium-steam cracking processes of natural gas and light petroleum hydrocarbons. They can also be produced as a byproduct of gasoline and light diesel oil by using catalytic cracking (FCC) units in oil refineries, although the yield is relatively low.

[0003] CN105582999A discloses a catalyst for the catalytic cracking of naphtha to produce propylene. Based on the total weight of the catalyst, it contains 50-95% molecular sieve and 5-50% matrix. The molecular sieve comprises a first molecular sieve with a ten-membered ring two-dimensional elliptical channel structure and a second molecular sieve with a twelve-membered ring channel structure. Using this catalyst can improve the yield of propylene from naphtha catalytic cracking, and the obtained propylene / ethylene ratio is greater than 2.

[0004] Light aromatics (benzene, toluene, and xylene) are widely used in synthetic fibers, synthetic resins, synthetic rubber, and various fine chemicals. Currently, BTX mainly originates from the platinum reforming process and the steam cracking process for ethylene production. While the production of low-carbon olefins and light aromatics primarily uses light hydrocarbons as feedstock, the increasing shortage of petroleum feedstocks has made the development of processes that directly produce low-carbon olefins and light aromatics from heavy oil a research hotspot.

[0005] CN114425423A discloses a hydrocarbon conversion catalyst for producing low-carbon olefins and light aromatics. This catalyst contains zeolite, a high specific heat capacity matrix material, heat-resistant inorganic oxides, and optionally clay. By using zeolite with an MFI structure and adding manganese oxide to the matrix material, this catalyst exhibits high conversion capacity for heavy petroleum hydrocarbons, with high yields of propylene, ethylene, and light aromatics, and good selectivity for dry gas and coke. CN111068758A discloses a catalyst for increasing the production of ethylene and propylene through catalytic thermal cracking of hydrocarbons. This catalyst contains 7–70% clay, 3–70% mesoporous silica-alumina material, 5–80% inorganic oxides, and 5–60% zeolite with an MFI structure, based on the catalyst weight. This gives the catalyst a good ability to crack large molecular weight hydrocarbons, improving the production capacity of ethylene and propylene from hydrocarbon cracking.

[0006] However, the above technologies mostly use easily cracked macromolecular hydrocarbons as raw materials. Since the activation energy of cracking small molecule saturated hydrocarbons in light raw materials is high, the existing technologies still have the problem of low yield of low-carbon olefins produced by catalytic cracking of light raw materials. Summary of the Invention

[0007] The purpose of this invention is to further improve the yield of ethylene, propylene and BTX produced by catalytic conversion of light hydrocarbon feedstock rich in saturated hydrocarbons.

[0008] To achieve the above objectives, a first aspect of the present invention provides a modified molecular sieve for the catalytic conversion of light hydrocarbons, the modified molecular sieve comprising a molecular sieve and a composite oxide supported on the molecular sieve, the composite oxide having the general formula ZnO·Fe2O3·M x O y Wherein, element M is selected from one or more of Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and lanthanides; x and y are stoichiometric ratios, where x is 1 or 2, and y is selected from 1, 2, or 3; and in the composite oxide, ZnO, Fe2O3, and M... x O y The molar ratio is 1:0.5-2:0-1; the molecular sieve includes a five-membered ring molecular sieve.

[0009] Optionally, the composite oxide has a spinel structure; and / or the element M is selected from at least one of Ca, Mg, Ga, Al and Si.

[0010] Optionally, the molecular sieve further includes at least one of β-molecular sieves containing transition metals and phosphorus, and high-silica Y-type molecular sieves with or without rare earth elements; preferably, the molecular sieve includes a phosphorus-containing five-membered ring molecular sieve; preferably, the content of the five-membered ring molecular sieve in the molecular sieve is 50-100% by weight, more preferably 70-100% by weight, based on the weight of the molecular sieve.

[0011] Optionally, based on the weight of the modified molecular sieve, the modified molecular sieve comprises 90-99.99% by weight of molecular sieve and 0.01-10% by weight of composite oxide.

[0012] A second aspect of the present invention provides a method for preparing a modified molecular sieve for the catalytic conversion of light hydrocarbons. The method includes the following steps: dissolving soluble salts of zinc and iron in water, adding an organic acid to the resulting salt solution, adjusting the pH with an alkaline solution to obtain a composite metal gel solution; impregnating an equal volume of molecular sieve with the composite metal gel solution to obtain an impregnated molecular sieve; drying and calcining the impregnated molecular sieve to obtain a composite oxide-modified molecular sieve; wherein the molecular sieve comprises a five-membered ring molecular sieve; the molar ratio of the soluble salts of zinc, iron, and organic acid is 1:0.5-1:1.5-3; and the loading of the composite oxide on the modified molecular sieve, based on the metal oxide content, is 0.01-10% by weight.

[0013] Optionally, the method further includes: dissolving a soluble salt of element M1 in the water; and / or the molecular sieve is a five-membered ring molecular sieve modified with element M2; wherein element M1 and element M2 are each independently selected from one or more of Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and lanthanides; preferably, the soluble salts of zinc, iron, and element M1 are each independently selected from at least one of their nitrates, acetates, and alkoxides; preferably, the molar ratio of the soluble salt of zinc to the soluble salt of element M1 is 1:0-0.5; preferably, element M1 and element M2 are each independently selected from at least one of Ca, Mg, Ga, Al, and Si; preferably, the loading of element M2 on the molecular sieve, based on oxides, is 0-5% by weight.

[0014] Optionally, the organic acid is selected from at least one of citric acid and acetic acid; the alkaline solution is ammonia water; the pH of the composite metal gel solution is 6-8; preferably, the impregnation conditions include: an impregnation temperature of 0-40℃ and a time of 6-12 hours; preferably, the drying conditions include: a temperature of 100-200℃ and a time of 2-4 hours; preferably, the calcination includes sequentially performing a first calcination and a second calcination; the conditions for the first calcination include: a temperature of 450-500℃ and a time of 2-4 hours; the conditions for the second calcination include: a temperature of 650-750℃ and a time of 2-4 hours; optionally, the molecular sieve is a phosphorus-modified five-membered ring molecular sieve; optionally, the molecular sieve further includes at least one of β-molecular sieves containing transition metals and phosphorus, and high-silica Y-type molecular sieves with or without rare earth elements.

[0015] A third aspect of the present invention provides a light hydrocarbon catalytic conversion catalyst comprising the aforementioned light hydrocarbon catalytic conversion modified molecular sieve.

[0016] Optionally, the catalyst further includes clay and inorganic oxides; based on the weight of the catalyst, the catalyst comprises 10-100% by weight of the light hydrocarbon catalytic conversion modified molecular sieve, 0-70% by weight of clay, and 0-90% by weight of inorganic oxides; preferably, the inorganic oxides are selected from at least one of amorphous SiO2·Al2O3, SiO2, and Al2O3.

[0017] A fourth aspect of the present invention provides a method for the catalytic conversion of light hydrocarbons, the method comprising the following steps:

[0018] A light hydrocarbon feedstock is brought into contact with the aforementioned light hydrocarbon catalytic conversion catalyst in a reactor to carry out a catalytic conversion reaction; wherein the light hydrocarbon feedstock is selected from at least one of alkanes with 4-12 carbon atoms, straight-run naphtha, aviation kerosene, reformate topping oil, aromatic raffinate, and Fischer-Tropsch synthesis oil; preferably, the reactor is one or a combination of two of a fluidized bed reactor, a fixed bed reactor, and a moving bed reactor; preferably, based on the weight of the light hydrocarbon feedstock, the light hydrocarbon feedstock comprises 60-100% by weight of alkanes, 0-40% by weight of cycloalkanes, and 0-10% by weight of unsaturated hydrocarbons; more preferably, the aromatic content in the light hydrocarbon feedstock is less than 5% by weight; the temperature of the catalytic conversion reaction is 520-650°C.

[0019] Through the above technical solution, the modified molecular sieve for light hydrocarbon catalytic conversion provided by the present invention contains a five-membered ring molecular sieve, which is beneficial for light hydrocarbon feedstock to undergo catalytic cracking to generate low-carbon olefins and BTX; at the same time, the composite oxide in the modified molecular sieve can effectively activate small molecule saturated hydrocarbons, reduce the reaction temperature of the catalytic cracking reaction of light hydrocarbon feedstock, and improve the selectivity of low-carbon olefins and light aromatics in the products.

[0020] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0021] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0022] Existing technology shows that when alkenes and alkanes with the same number of carbon atoms undergo cracking reactions under the catalysis of molecular sieves, the reaction rate of alkenes is much higher than that of alkanes. Furthermore, the selectivity of low-carbon olefins among the products of catalytic cracking of olefins is higher. This indicates that catalytic cracking can be achieved at lower temperatures, thereby avoiding non-selective cracking caused by high temperatures and reducing energy consumption during the reaction process. The inventors have discovered that by introducing special active components that facilitate the activation of carbon-hydrogen bonds into the catalyst, the reaction temperature of catalytic cracking reactions of light hydrocarbons can be lowered.

[0023] A first aspect of the present invention provides a modified molecular sieve for the catalytic conversion of light hydrocarbons, the modified molecular sieve comprising a molecular sieve and a composite oxide supported on the molecular sieve, the composite oxide having the general formula ZnO·Fe2O3·M x O y Wherein, element M is selected from one or more of Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and lanthanides; x and y are stoichiometric ratios, where x is 1 or 2, and y is selected from 1, 2, or 3; and the composite oxide contains ZnO, Fe2O3, and M.x O y The molar ratio is 1:0.5-2:0-1; the molecular sieve includes a five-membered ring molecular sieve.

[0024] The modified molecular sieve for catalytic conversion of light hydrocarbons provided by this invention contains a five-membered ring molecular sieve, which is beneficial for the catalytic cracking of light hydrocarbon feedstocks to generate low-carbon olefins and BTX. At the same time, the composite oxides in the modified molecular sieve can effectively activate small molecule saturated hydrocarbons, reduce the reaction temperature of the catalytic cracking reaction of light hydrocarbon feedstocks, and improve the selectivity of low-carbon olefins and light aromatics in the products.

[0025] In embodiments of the present invention, the metal elements in the composite oxide include at least iron and zinc, and it has a spinel structure. Iron oxide readily forms an Fe2O4 spinel structure with zinc and the like, and element M can enter the spinel structure to undergo isomorphous substitution, thereby changing the active sites in the composite oxide structure.

[0026] In this invention, the composite oxide is a metal oxide containing at least zinc and iron, which is thermodynamically stable. Under catalytic cracking reaction conditions, the metal in the composite oxide is not easily lost, and the catalyst can recover its activity after regeneration and recycling.

[0027] In some embodiments of the present invention, the metal M is selected from at least one of Ca, Mg, Ga, Al and Si.

[0028] In this invention, "M" x O y "Indicates an oxide of element M, for example, M x O y It can be at least one of CaO, MgO, GaO, Al2O3 or SiO2.

[0029] In some embodiments of the present invention, the molecular sieve further includes at least one of a β molecular sieve containing transition metals and phosphorus, and a high-silica Y-type molecular sieve with or without rare earth elements.

[0030] In some embodiments of the present invention, the molecular sieve may be a phosphorus-containing five-membered ring molecular sieve to reduce Fe 3+ Reduced to Fe 2+ This improves the hydrothermal stability of the catalyst.

[0031] In some specific embodiments of the present invention, based on the weight of the molecular sieve, the content of the five-membered ring molecular sieve in the molecular sieve is 50-100% by weight, preferably 70-100% by weight.

[0032] In some embodiments of the present invention, the modified molecular sieve comprises 90-99.99% by weight of molecular sieve and 0.01-10% by weight of composite oxide, based on the weight of the modified molecular sieve.

[0033] A second aspect of the present invention provides a method for preparing a modified molecular sieve for the catalytic conversion of light hydrocarbons. The method includes the following steps: dissolving soluble salts of zinc and iron in water, adding an organic acid to the resulting salt solution, adjusting the pH with an alkaline solution to obtain a composite metal gel solution; impregnating an equal volume of molecular sieve with the composite metal gel solution to obtain an impregnated molecular sieve; drying and calcining the impregnated molecular sieve to obtain a composite oxide modified molecular sieve; wherein the molecular sieve comprises a five-membered ring molecular sieve; and the loading of the composite oxide on the modified molecular sieve is 0.01-10% by weight, calculated as a metal oxide.

[0034] In this invention, the molecular sieve includes a five-membered ring molecular sieve, which, under the shape-selective effect of the five-membered ring molecular sieve, catalytically converts light hydrocarbon feedstock into low-carbon olefins and light aromatics.

[0035] Optionally, the molecular sieve may be a phosphorus-modified five-membered ring molecular sieve.

[0036] In some other embodiments of the present invention, the molecular sieve may further include at least one of β-molecular sieves containing transition metals and phosphorus, and high-silica Y-type molecular sieves with or without rare earth elements. The content of the five-membered ring molecular sieve in the molecular sieve is 50% by weight or more, preferably 70% by weight or more.

[0037] In some embodiments of the present invention, the molar ratio of the zinc soluble salt, the iron soluble salt, and the organic acid is 1:0.5-1:1.5-3.

[0038] In an embodiment of the present invention, the method for impregnating the molecular sieve with the composite metal gel solution is an equal-volume impregnation method.

[0039] In some embodiments of the present invention, the method further includes: dissolving a soluble salt of element M1 in the water; wherein element M1 is selected from one or more of Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and the lanthanides. The composite oxides formed by element M1 with zinc and iron can also specifically activate the carbon-hydrogen bonds of saturated hydrocarbons, enabling light hydrocarbon feedstocks to be activated at lower temperatures and participate in catalytic cracking reactions, thereby increasing the yield of low-carbon olefins.

[0040] In some embodiments of the present invention, the zinc soluble salt is selected from at least one of zinc nitrates, acetates and alkoxides.

[0041] In some embodiments of the present invention, the soluble salt of iron is selected from at least one of iron nitrates, acetates and alkoxides.

[0042] In some embodiments of the present invention, the soluble salt of element M1 is selected from at least one of the nitrate, acetate and alkoxide of element M1.

[0043] The element M1 is selected from at least one of Ca, Mg, Ga, Al and Si.

[0044] In some preferred embodiments of the present invention, the molar ratio of the soluble salt of zinc to the soluble salt of element M1 is 1:0-0.5.

[0045] In some specific embodiments of the present invention, the organic acid is selected from at least one of citric acid and acetic acid, preferably citric acid.

[0046] In some specific embodiments of the present invention, the alkaline solution is ammonia water.

[0047] In some specific embodiments of the present invention, the pH of the composite metal gel solution is 6-8.

[0048] Specifically, the preparation method of the composite metal gel solution is as follows: soluble salts of zinc, iron, and element M1 are weighed according to stoichiometry and dissolved in a certain amount of distilled water. Then, an appropriate amount of citric acid is added in batches, and the solution is slowly stirred magnetically at 40-60℃ to obtain a reddish-brown transparent solution. Ethylene glycol is added to the solution and the pH value is adjusted with ammonia. The temperature is then raised to 60-100℃ to evaporate the solvent, resulting in a transparent solution with a certain viscosity and fluidity.

[0049] In other embodiments of the present invention, the molecular sieve may also be a five-membered ring molecular sieve modified with element M2. Element M2 is selected from one or more elements of Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and the lanthanides. Specifically, element M2 is selected from at least one of Ca, Mg, Ga, Al, and Si.

[0050] Preferably, the loading of element M2 on the molecular sieve is 0-5% by weight, calculated as oxides.

[0051] In some embodiments of the present invention, the impregnation conditions include: an impregnation temperature of 0-40°C and a time of 6-12 hours.

[0052] In some specific embodiments of the present invention, the drying conditions include: a temperature of 100-200°C and a time of 2-4 hours.

[0053] In some specific embodiments of the present invention, the calcination includes sequentially performing a first calcination and a second calcination; specifically, the conditions for the first calcination include: a temperature of 450-500°C and a time of 2-4 hours; the conditions for the second calcination include: a temperature of 650-750°C and a time of 2-4 hours.

[0054] A third aspect of the present invention provides a light hydrocarbon catalytic conversion catalyst comprising the aforementioned light hydrocarbon catalytic conversion modified molecular sieve.

[0055] In this invention, the light hydrocarbon catalytic conversion modified molecular sieve provided in the first aspect of this invention can be used alone as a catalyst in catalytic cracking reactions, or it can be further prepared into a catalyst with clay, heat-resistant inorganic oxides, etc.

[0056] In some embodiments of the present invention, the catalyst further includes clay and inorganic oxides; specifically, based on the weight of the catalyst, the catalyst comprises 10-100% by weight of the light hydrocarbon catalytic conversion modified molecular sieve, 0-70% by weight of clay and 0-90% by weight of inorganic oxides.

[0057] Preferably, the inorganic oxide is selected from at least one of amorphous SiO2·Al2O3, SiO2, and Al2O3.

[0058] In this invention, the light hydrocarbon catalytic conversion catalyst is a microsphere catalyst suitable for fluidized bed reactors, which can be prepared using conventional methods.

[0059] In some embodiments of the present invention, the preparation method of the light hydrocarbon catalytic conversion catalyst includes the following steps: preparing an inorganic oxide precursor (such as boehmite, alumina sol or a mixture thereof, or silica-alumina sol or gel) into a slurry with a solid content of 10-50% by weight using deionized water, and stirring evenly; adjusting the pH of the slurry to 2-4 using an inorganic acid such as hydrochloric acid, nitric acid, phosphoric acid or sulfuric acid, and then mixing it with a slurry containing 10-50% by weight of clay, stirring evenly, allowing it to stand and age at 20-80°C for 0-2 hours, then adding alumina sol or not, stirring for 0.5-1.5 hours, adding a predetermined amount of modified molecular sieve, homogenizing, spray drying, washing away free sodium ions, and drying.

[0060] In this invention, the light hydrocarbon catalytic conversion catalyst can also be suitable for fixed beds and moving beds. The preparation method is to mix the aforementioned light hydrocarbon catalytic conversion modified molecular sieve, clay and inorganic oxide in a certain proportion and then mechanically shape and form them into specific shapes and sizes.

[0061] A fourth aspect of the present invention provides a method for catalytic conversion of light hydrocarbons, the method comprising the following steps: contacting a light hydrocarbon feedstock with the aforementioned light hydrocarbon catalytic conversion catalyst in a reactor to carry out a catalytic conversion reaction; wherein the light hydrocarbon feedstock is selected from at least one of alkanes having 4-12 carbon atoms, straight-run naphtha, aviation kerosene, reformate topping oil, aromatic raffinate oil, and Fischer-Tropsch synthesis oil.

[0062] Preferably, the reactor is one or a combination of two of the following: a fluidized bed reactor, a fixed bed reactor, and a moving bed reactor.

[0063] In some embodiments of the present invention, the light hydrocarbon feedstock is rich in saturated hydrocarbons, and based on the weight of the light hydrocarbon feedstock, the light hydrocarbon feedstock includes 60-100% by weight of alkanes, 0-40% by weight of cycloalkanes and 0-10% by weight of unsaturated hydrocarbons; more preferably, the content of aromatics in the light hydrocarbon feedstock is less than 5% by weight.

[0064] In some embodiments of the present invention, the temperature of the catalytic conversion reaction is 520-650°C.

[0065] The present invention will be further described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0066] All raw materials used in the embodiments can be obtained through commercial purchase. Among them:

[0067] n-Octane (99.5% by mass), analytical grade, manufactured by CARLO ERBA Reagent Company;

[0068] ZSM-5 molecular sieve (n(SiO2):n(Al2O3)=42) is a five-membered ring molecular sieve; industrial grade, produced by Sinopec Catalyst Company Qilu Branch.

[0069] Catalyst MP051 uses phosphorus-modified five-membered ring molecular sieve as the active component; it is of industrial grade and produced by Sinopec Catalyst Company Qilu Branch. Its properties are shown in Table 1.

[0070] Table 1

[0071] MP051 catalyst <![CDATA[BET specific surface area / (m 2 / g)]]> 158 <![CDATA[Matrix area / (m 2 / g)]]> 44 <![CDATA[Micropore area / (m 2 / g)]]> 114 Total pore volume (mL / g) 0.133 Micropore volume (mL / g) 0.06 Elemental composition / weight % C 1.63 N 0.24 F 0.12 <![CDATA[Na2O]]> 0.05 <![CDATA[Al2O3]]> 30.56 <![CDATA[SiO2]]> 49.29 <![CDATA[P2O5]]> 14.33 <![CDATA[SO3]]> 0.70 <![CDATA[K2O]]> 0.08 CaO 0.07 <![CDATA[Ti2O]]> 0.06 <![CDATA[Fe2O3]]> 2.81 <![CDATA[CeO2]]> 0.06

[0072] Example 1

[0073] This embodiment illustrates the preparation method of the modified molecular sieve for the catalytic conversion of light hydrocarbons provided by the present invention, as well as the method for producing low-carbon olefins and BTX by catalytic cracking of light hydrocarbon feedstocks.

[0074] (1) The preparation method of modified molecular sieves includes the following steps:

[0075] S1. Weigh 3.56g Zn(NO3)2·6H2O and 9.70g Fe(NO3)3·9H2O and dissolve them in 10mL of distilled water to obtain a salt solution;

[0076] S2. Add 6.91g of citric acid to the salt solution in batches and stir slowly with a magnetic force at 60℃ to obtain a clear solution; add an appropriate amount of diethanol to the solution and adjust the pH value to 6-8 with ammonia water to obtain a reddish-brown transparent solution; continue to heat to 60-80℃ to evaporate the solvent to obtain a transparent solution with a certain viscosity and fluidity.

[0077] S3. Add 100g of unmodified ZSM-5 molecular sieve to the solution obtained in step S2, stir evenly, and impregnate the molecular sieve.

[0078] S4. The impregnated molecular sieve is dried at 120℃, and the dried product is calcined at 450℃ and 670℃ respectively. The modified molecular sieve obtained is denoted as M1; the molecular formula of the composite oxide is denoted as ZnFe2O4.

[0079] (2) Catalytic cracking experiments were conducted on a fixed-bed microreactor using n-octane as the light hydrocarbon feedstock and the prepared modified molecular sieve M1 as the catalyst. The reaction conditions for catalytic cracking included a reaction temperature of 600℃, a pressure of 0.1MPa, and a reaction time of 0.1s. The catalytic cracking products were analyzed, and the conversion rate of the light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the obtained products are shown in Table 2.

[0080] Example 2

[0081] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference from Example 1 is that the soluble salts and their amounts in step S1 are: 1.78 g Zn(NO3)2·6H2O, 9.70 g Fe(NO3)3·9H2O, and 0.89 g Mg(NO3)2, respectively. The obtained modified molecular sieve is denoted as M2; the molecular formula of the composite oxide is denoted as Zn. 0.5 Mg 0.5 Fe2O4.

[0082] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 2.

[0083] Example 3

[0084] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference from Example 1 is that the soluble salts and their amounts in step S1 are: 2.38 g Zn(NO3)2·6H2O, 9.70 g Fe(NO3)3·9H2O, and 0.59 g Mg(NO3)2, respectively. The obtained modified molecular sieve is designated M3; the molecular formula of the composite oxide is designated Zn. 0.67 Mg 0.33 Fe2O4.

[0085] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 2.

[0086] Example 4

[0087] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference from Example 1 is that the soluble salts and their amounts in step S1 are: 1.78 g Zn(NO3)2·6H2O, 9.70 g Fe(NO3)3·9H2O, and 0.98 g Ca(NO3)2, respectively. The obtained modified molecular sieve is designated M4; the molecular formula of the composite oxide is designated Zn. 0.5 Ca 0.5 Fe2O4.

[0088] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 2.

[0089] Example 5

[0090] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference from Example 1 is that the soluble salts and their amounts in step S1 are: 1.78 g Zn(NO3)2·6H2O, 9.70 g Fe(NO3)3·9H2O, and 0.66 g Ca(NO3)2, respectively. The obtained modified molecular sieve is designated M5; the molecular formula of the composite oxide is designated Zn. 0.67 Ca 0.33 Fe2O4.

[0091] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 2.

[0092] Example 6

[0093] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference from Example 1 is that the soluble salts and their amounts in step S1 are 3.56 g Zn(NO3)2·6H2O, 7.27 g Fe(NO3)3·9H2O, and 0.80 g AlCl3, respectively. The obtained modified molecular sieve is designated M6; the molecular formula of the composite oxide is designated ZnFe. 1.5 Al 0.5 O4.

[0094] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 2.

[0095] Example 7

[0096] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference between this embodiment and Example 1 is that the soluble salts and their amounts in step S1 are 3.56g Zn(NO3)2·6H2O, 4.85g Fe(NO3)3·9H2O, and 1.60g AlCl3, respectively. The obtained modified molecular sieve is designated as M7; the molecular formula of the composite oxide is designated as ZnFeAlO4.

[0097] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 2.

[0098] Example 8

[0099] This embodiment uses the method of Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference from Example 1 is that the ZSM-5 molecular sieve in step S3 is replaced with an equal mass of MP051 catalyst. The obtained modified molecular sieve is denoted as M8; the molecular formula of the composite oxide is denoted as ZnFe2O4.

[0100] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0101] Example 9

[0102] The modified molecular sieve M8 prepared in Example 8 was subjected to a single catalytic cracking reaction and then regenerated by coke burning. It was then tested under the same catalytic cracking reaction conditions as in Example 8, with a regeneration temperature of 680℃. The catalytic cracking products were analyzed, and the conversion rate of the light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0103] Comparative Example 1

[0104] The preparation method of the modified molecular sieve in this comparative example includes the following steps:

[0105] S1. Weigh 10.69g of Zn(NO3)2·6H2O and dissolve it in a certain amount of distilled water to obtain a clear solution;

[0106] S2. Equal volume impregnation: Add 100g of MP051 catalyst to the solution obtained in step S1, stir thoroughly, and let stand for 8 hours;

[0107] S3. The molecular sieve obtained by impregnation is dried at 120°C, and the dried product is calcined at 670°C. The modified molecular sieve obtained is denoted as DM1.

[0108] Catalytic cracking experiments were conducted in a fixed-bed microreactor using n-octane as a light hydrocarbon feedstock and the prepared modified molecular sieve DM1 as a catalyst. The reaction conditions for catalytic cracking included a reaction temperature of 600℃ and a pressure of 0.1 MPa. The catalytic cracking products were analyzed, and the conversion rate of the light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0109] Comparative Example 2

[0110] This comparative example uses the method in Comparative Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference between this example and Comparative Example 1 is that the soluble salt used in step S1 is 14.54 g Fe(NO3)3.9H2O, and the resulting modified molecular sieve is denoted as DM2.

[0111] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0112] Comparative Example 3

[0113] This comparative example uses the method in Comparative Example 1 to prepare modified molecular sieves and catalytically crack light hydrocarbon feedstocks. The difference between this example and Comparative Example 1 is that the soluble salts used in step S1 are 5.35g Zn(NO3)2·6H2O and 7.27g Fe(NO3)3·9H2O. The resulting modified molecular sieve is denoted as DM3.

[0114] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0115] Comparative Example 4

[0116] The modified molecular sieve DM3 prepared in Comparative Example 3 was subjected to a single catalytic cracking reaction and then regenerated by coke burning. It was then subjected to the same catalytic cracking reaction conditions as Comparative Example 3, with a regeneration temperature of 680℃. The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0117] Comparative Example 5

[0118] In a fixed-bed microreactor, catalytic cracking experiments were conducted using n-octane as a light hydrocarbon feedstock and unmodified ZSM-5 molecular sieve as a catalyst. The reaction conditions for catalytic cracking included a reaction temperature of 600℃ and a pressure of 0.1MPa.

[0119] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 3.

[0120] Table 2

[0121]

[0122] Table 3

[0123]

[0124] As can be seen from Tables 2 and 3, the modified molecular sieve provided by the present invention can significantly improve the conversion rate of raw materials. In particular, when ZSM-5 molecular sieve is used, the metal oxide is ZnFe2O4, and the content of metal oxide in the catalyst is 2.89% by weight, the selectivity of low-carbon ethylene, propylene, and BTX in the catalytic cracking products is significantly improved, especially the selectivity of ethylene, propylene, and BTX is greatly improved.

[0125] Example 10

[0126] This embodiment illustrates the preparation method of the light hydrocarbon catalytic conversion catalyst provided by the present invention, and the method of using the catalyst for the catalytic cracking of light hydrocarbon feedstock to produce low-carbon olefins and BTX.

[0127] (1) The preparation method of light hydrocarbon catalytic conversion catalyst includes the following steps: aluminum sol is prepared into a slurry with deionized water and stirred evenly; the pH of the slurry is adjusted to 2-4 with inorganic acid such as hydrochloric acid, nitric acid, phosphoric acid or sulfuric acid, and then mixed with slurry containing kaolin, stirred evenly, aged at 20-80℃ for 0-2h, stirred for 0.5-1.5h, the prepared modified molecular sieve M1 is added, homogenized, spray dried, free sodium ions are washed away, dried, and microsphere catalyst C1 is prepared; wherein, the weight ratio of modified molecular sieve M1, kaolin and aluminum sol is 50:40:10.

[0128] (2) Catalytic cracking experiments were conducted on the riser unit using n-octane as the light hydrocarbon feedstock and the prepared catalyst C1. The reaction conditions for catalytic cracking included: a reaction temperature of 600℃, a pressure of 0.12MPa, and a residence time of 2s for the light hydrocarbon feedstock in the riser. The catalytic cracking products were analyzed, and the conversion rate of the light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 4.

[0129] Comparative Example 6

[0130] This comparative example uses the method in Example 10 to prepare a light hydrocarbon catalytic conversion catalyst and to catalytically crack light hydrocarbon feedstock. The difference between this example and Example 10 is that the modified molecular sieve M1 is replaced with an equal mass of unmodified ZSM-5 molecular sieve, and the resulting catalyst is denoted as DC1.

[0131] The catalytic cracking products were analyzed, and the conversion rate of light hydrocarbon feedstock and the yields of low-carbon olefins and BTX in the resulting products are shown in Table 4.

[0132] Table 4

[0133]

[0134] As shown in the table above, the modified molecular sieve provided by this invention, when used in combination with amorphous silica and alumina to prepare catalysts, also helps to improve the yields of low-carbon olefins and light aromatics. Compared with unmodified ZSM-5 molecular sieves, the catalyst containing modified molecular sieves provided by this invention can significantly improve the yields of ethylene, propylene, and BTX.

[0135] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0136] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0137] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A molecular sieve modified for the catalytic conversion of light hydrocarbons, characterized in that, The modified molecular sieve comprises a molecular sieve and a composite oxide supported on the molecular sieve, wherein the general formula of the composite oxide is ZnO·Fe2O3·M x O y Wherein, element M is selected from one or more of Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and lanthanides; x and y are stoichiometric ratios, where x is 1 or 2, and y is selected from 1, 2, or 3; and the composite oxide contains ZnO, Fe2O3, and M. x O y The molar ratio is 1:0.5-2:0-1; the molecular sieve includes a five-membered ring molecular sieve.

2. The molecular sieve according to claim 1, wherein, The composite oxide has a spinel structure; and / or The element M is selected from at least one of Ca, Mg, Ga, Al and Si.

3. The molecular sieve according to claim 1 or 2, wherein, The molecular sieve also includes at least one of β molecular sieves containing transition metals and phosphorus, and high-silica Y-type molecular sieves with or without rare earth elements; Preferably, the molecular sieve comprises a phosphorus-containing five-membered ring molecular sieve; Preferably, based on the weight of the molecular sieve, the content of the five-membered ring molecular sieve in the molecular sieve is 50-100% by weight, preferably 70-100% by weight.

4. The molecular sieve according to any one of claims 1-3, wherein, Based on the weight of the modified molecular sieve, the modified molecular sieve comprises 90-99.99% by weight of molecular sieve and 0.01-10% by weight of composite oxide.

5. A method for preparing a molecular sieve modified for the catalytic conversion of light hydrocarbons, characterized in that, The method includes the following steps: Soluble salts of zinc and iron are dissolved in water, and organic acids are added to the resulting salt solutions. The pH is then adjusted with an alkaline solution to obtain a composite metal gel solution. An equal volume of molecular sieve is impregnated with the composite metal gel solution to obtain the impregnated molecular sieve. The impregnated molecular sieve is dried and calcined to obtain a composite oxide modified molecular sieve. The molecular sieve includes a five-membered ring molecular sieve; The molar ratio of the zinc soluble salt, the iron soluble salt, and the organic acid is 1:0.5-1:1.5-3; The loading of the composite oxide on the modified molecular sieve is 0.01-10% by weight, based on metal oxides.

6. The method according to claim 5, wherein, The method further includes: dissolving a soluble salt of element M1 in the water; and / or The molecular sieve is a five-membered ring molecular sieve modified with element M2; Wherein, element M1 and element M2 are each independently selected from one or more of the following groups: Group IIA, Group IIIA, Group IVA, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and the lanthanides; Preferably, the soluble salts of zinc, iron, and element M1 are each independently selected from at least one of their nitrates, acetates, and alkoxides; Preferably, the molar ratio of the soluble salt of zinc to the soluble salt of element M1 is 1:0-0.5; Preferably, element M1 and element M2 are each independently selected from at least one of Ca, Mg, Ga, Al and Si; Preferably, the loading of element M2 on the molecular sieve is 0-5% by weight, calculated as oxides.

7. The method according to claim 5, wherein, The organic acid is selected from at least one of citric acid and acetic acid; the alkaline solution is ammonia water; The pH of the composite metal gel solution is 6-8; Preferably, the impregnation conditions include: an impregnation temperature of 0-40°C and a time of 6-12 hours; Preferably, the drying conditions include a temperature of 100-200℃ and a time of 2-4 hours; preferably, the calcination includes sequentially performing a first calcination and a second calcination; the conditions for the first calcination include a temperature of 450-500℃ and a time of 2-4 hours; the conditions for the second calcination include a temperature of 650-750℃ and a time of 2-4 hours. Preferably, the molecular sieve is a phosphorus-modified five-membered ring molecular sieve; Optionally, the molecular sieve may further include at least one of β-molecular sieves containing transition metals and phosphorus, and high-silica Y-type molecular sieves with or without rare earth elements.

8. A catalyst for the catalytic conversion of light hydrocarbons, characterized in that, The catalyst comprises the light hydrocarbon catalytic conversion modified molecular sieve as described in any one of claims 1-4 or the light hydrocarbon catalytic conversion modified molecular sieve prepared by the method described in any one of claims 5-7.

9. The catalyst according to claim 8, wherein, The catalyst also includes clay and inorganic oxides; Based on the weight of the catalyst, the catalyst comprises 10-100% by weight of the light hydrocarbon catalytic conversion modified molecular sieve, 0-70% by weight of clay and 0-90% by weight of inorganic oxides. Preferably, the inorganic oxide is selected from at least one of amorphous SiO2·Al2O3, SiO2, and Al2O3.

10. A method for catalytic conversion of light hydrocarbons, characterized in that, The method includes the following steps: The light hydrocarbon feedstock is brought into contact with the light hydrocarbon catalytic conversion catalyst of claim 8 or 9 in a reactor to carry out a catalytic conversion reaction; wherein the light hydrocarbon feedstock is selected from at least one of alkanes with 4-12 carbon atoms, straight-run naphtha, aviation kerosene, reformate topping oil, aromatic raffinate oil and Fischer-Tropsch synthesis oil. Preferably, the reactor is one or a combination of two of the following: a fluidized bed reactor, a fixed bed reactor, and a moving bed reactor; Preferably, based on the weight of the light hydrocarbon feedstock, the light hydrocarbon feedstock comprises 60-100% by weight of alkanes, 0-40% by weight of cycloalkanes, and 0-10% by weight of unsaturated hydrocarbons; more preferably, the content of aromatics in the light hydrocarbon feedstock is less than 5% by weight. The temperature of the catalytic conversion reaction is 520-650℃.

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