A process for the preparation of ethylene propylene using a catalyst which selectively passivates acid sites

Abstract

The present application relates to the technical field of low carbon olefin preparation, and discloses a method for preparing ethylene propylene by using a catalyst for selectively passivating acid sites, comprising the following steps: S1, synthesizing a molecular sieve raw powder by using a hydrothermal method; adding the molecular sieve raw powder into an aqueous solution of a metal salt, performing ion exchange, and then drying and oxygen roasting to obtain a metal salt modified molecular sieve, wherein the molecular sieve is SAPO-17, SAPO-34 or SAPO-35, and the metal salt is a sodium salt and / or a potassium salt; S2, mechanically mixing the metal salt modified molecular sieve with a metal oxide to obtain a catalyst; S3, contacting a mixed gas of hydrogen and carbon dioxide with the catalyst to perform a reaction to prepare ethylene and propylene. By adopting the strategy of selectively shielding the acid sites on the outer surface of the molecular sieve by the metal salt and the strategy of using the metal oxide to be compounded and coupled, the carbon dioxide conversion rate and the selectivity of ethylene and propylene in the product are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of low-carbon olefin preparation, and in particular to a method for preparing ethylene propylene by using a catalyst with selectively passivated acid sites. BACKGROUND

[0002] Currently, the technical route of CO2 hydrogenation to low-carbon olefins mainly includes two categories: one is the methanol intermediate route, that is, CO2 is first hydrogenated to synthesize methanol, and then converted into low-carbon olefins through a methanol-to-olefin process; the other is an improved Fischer-Tropsch synthesis route, that is, CO2 is converted into carbon monoxide (CO) through a reverse water gas shift reaction (RWGS), and then C-C chain growth is realized through a Fischer-Tropsch synthesis (FTS) reaction to generate olefins. Among them, the dual-functional catalyst is the core of the methanol intermediate route, and its performance directly determines the reaction efficiency and product selectivity. In current research, molecular sieves are widely used to construct a dual-functional catalytic system due to their adjustable pore structure, shape-selective selectivity and surface acidity, forming a synergistic catalytic mode of "metal active center-molecular sieve".

[0003] SAPO series molecular sieves show potential in inhibiting methane by-product and improving the selectivity of low-carbon olefins due to their weak surface acidity and various topological structures. Professor Sun Yuhang and Professor Gao Peng's team of Shanghai Institute of Higher Research, Chinese Academy of Sciences, designed an In2O3 / SAPO-34 dual-functional catalyst, which can realize the high-selectivity synthesis of low-carbon olefins (CO2 conversion rate is 34.1%, and the olefin selectivity in total hydrocarbons is 76.9%) (Direct conversion of CO2 into liquid fuels with high selectivity over a bifunctional catalyst, Nature Chemistry, 2017, 9, 1019). However, the selectivity of ethylene and propylene in the olefin product is usually 55-65%. Compared with butene, ethylene and propylene are important basic raw materials in the petrochemical industry, and have higher economic value and practical application significance. Therefore, improving the selectivity of ethylene and propylene in low-carbon olefins has more application value and practical significance. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a method for preparing ethylene propylene by using a catalyst with selectively passivated acid sites. By adopting the strategy of selectively shielding the acid sites on the outer surface of the molecular sieve with metal salts, the secondary conversion of ethylene and propylene into low-carbon alkanes and C 4+ hydrocarbons can be effectively inhibited, thereby greatly improving the selectivity of ethylene and propylene in the product; at the same time, the molecular sieve with selectively passivated acid sites is compounded and coupled with metal oxides, which is more conducive to the catalytic reaction, promotes the activation and conversion of carbon dioxide, and further improves the conversion rate.

[0005] The object of the present application is achieved by the following technical solutions.

[0006] The present application provides a method for preparing ethylene propylene by using a catalyst for selectively passivating acidic sites, comprising the following steps:

[0007] S1, using a hydrothermal method to synthesize a molecular sieve raw powder; adding the molecular sieve raw powder into an aqueous solution of a metal salt, performing ion exchange, and then drying and oxygen roasting to obtain a metal salt modified molecular sieve with a content of medium-strong acid sites of 0.05-0.3 mol / kg, wherein the molecular sieve is SAPO-17, SAPO-34 or SAPO-35, and the metal salt is a sodium salt and / or a potassium salt;

[0008] S2, mechanically mixing the metal salt modified molecular sieve with a metal oxide, wherein the metal oxide is at least one of InZr x O (1+1.5x) , GaZr x O (1+1.5x) , ZnCr x O (1+1.5x) , ZnAl x O (1+1.5x) , ZnGa x O (1+1.5x) and ZnZr x O (1+1.5x) , wherein the value of x is 0.1-10, to obtain a catalyst;

[0009] S3, contacting a mixed gas of hydrogen and carbon dioxide with the catalyst to perform a reaction to prepare ethylene and propylene.

[0010] In the carbon dioxide hydrogenation reaction, while the reaction products diffuse out of the pores of the molecular sieve of the bifunctional catalyst, ethylene and propylene are prone to secondary conversion at the acid sites on the outer surface to obtain butene and C 4+ hydrocarbons, thereby resulting in a low ethylene propylene selectivity. Therefore, the present application selectively passivates the outer surface of the molecular sieve by using a metal salt solution. Since the template agent added during the synthesis of the molecular sieve has not been removed by roasting, the template agent still remains in the pores of the molecular sieve raw powder, and thus the metal salt can selectively passivate the outer surface of the molecular sieve. Then, the molecular sieve is roasted to remove the template agent, and sufficient acid sites still exist in the pores of the molecular sieve. By controlling the content of the acid sites in the passivated molecular sieve and the type of the metal salt, a higher CO2 conversion rate and ethylene propylene selectivity can be achieved.

[0011] Therefore, the application can realize selective passivation of the outer surface of the molecular sieve, on the one hand, the acid sites inside the molecular sieve channel are reserved, the catalyst still has high catalytic activity and CO2 conversion rate, on the other hand, the content of the acid sites on the outer surface of the molecular sieve is reduced, the secondary conversion of ethylene propylene on the outer surface is reduced in a targeted manner, and the ethylene propylene selectivity is improved. At the same time, the metal oxide is coupled with the molecular sieve after selective passivation of the acid sites, the metal oxide has a high specific surface area and more active sites, which is more conducive to the catalytic reaction, promotes the activation and conversion of carbon dioxide and thus improves the conversion rate.

[0012] Preferably, in S1, the molar ratio of SiO2, Al2O3 and P2O5 in the raw material of the hydrothermal synthesis method is 0.1:1.0:1.0-1.2.

[0013] Preferably, in S1, the hydrothermal synthesis method specifically comprises: mixing a silicon source, an aluminum source, a phosphorus source and water, adding a template agent and aging, then performing temperature rising crystallization, and drying to obtain a molecular sieve raw powder.

[0014] Preferably, the template agent comprises cyclohexylamine, cyclohexyl imine or tetraethylammonium hydroxide; the aging is performed at room temperature for 1-3 hours; and the temperature rising crystallization is performed by rising the temperature to 150-200 DEG C for 60-80 hours.

[0015] Preferably, in S1, the sodium salt is sodium nitrate or sodium chloride; and the potassium salt is potassium nitrate or potassium chloride.

[0016] Preferably, in S1, the concentration of the metal salt aqueous solution is 0.05-3 mol / L, more preferably 0.5-3 mol / L; and the ion exchange is performed by rising the temperature to 60-90 DEG C for 5-15 hours.

[0017] Preferably, in S1, the aerobic roasting is performed by rising the temperature to 500-700 DEG C for 5-7 hours.

[0018] Preferably, in S1, the content of the medium-strong acid sites in the metal salt modified molecular sieve is 0.1-0.3 mol / kg, more preferably 0.2-0.3 mol / kg.

[0019] The acid strength is defined by NH3-TPD peaks, including weak acid, medium-strong acid and strong acid.

[0020] The NH3-TPD is according to the desorption peak position of NH3, the position of the desorption peak refers to that under the standard test conditions, under the test conditions of the ratio (w / f) of the sample mass w to the carrier gas flow rate f = 100 g•h / L, a TCD records the thermal conductivity signal of desorbed NH3, a desorption curve is drawn, and the inorganic solid is divided into three acid strengths according to the peak position vertex of the curve. Weak acid refers to the acid site with a NH3 desorption temperature less than 245 DEG C; medium-strong acid refers to the acid site with a NH3 desorption temperature of 245-500 DEG C; and strong acid refers to the acid site with a NH3 desorption temperature greater than 500 DEG C.

[0021] Preferably, in S2, the specific surface area of the metal oxide is 5-150 m 2 / g.

[0022] Preferably, in S2, the mass ratio of the metal salt modified molecular sieve to the metal oxide is 0.1-20:1, more preferably 0.3-5:1.

[0023] Preferably, in S3, the reaction conditions are as follows: the temperature is 300-500 DEG C, more preferably 300-450 DEG C; the pressure of the mixed gas is 0.5-10 MPa, more preferably 1-8 MPa; the space velocity of the mixed gas is 300-10000 mL•g -1 •h -1 , more preferably 500-9000 mL•g -1 •h -1 , further preferably 500-6000 mL•g -1 •h -1 .

[0024] Preferably, in S3, the molar ratio of H2 / CO2 in the mixed gas is 0.2-4.5, more preferably 0.3-3.5.

[0025] The present application directly converts carbon dioxide and hydrogen into ethylene and propylene in one step, and the selectivity of low-carbon olefins can reach 82-90%, the selectivity of ethylene and propylene can reach 78-86%, the ratio of ethylene and propylene is between 0.8 and 1.7, and the selectivity of byproduct methane is low (<10%), which has good application prospect.

[0026] Preferably, the process for directly converting carbon dioxide and hydrogen into ethylene and propylene is carried out under the preferred reaction conditions, when the reaction temperature is 300-450 DEG C, the space velocity is 1000-6000 mL•g -1 •h -1 , and the molar ratio of H2 / CO2 is 0.3-3.5, the selectivity of ethylene and propylene is 82-86%, and the selectivity of byproduct methane is <8%.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) The strategy of selectively shielding the acid sites on the outer surface of the molecular sieve by metal salt can effectively inhibit the secondary conversion of ethylene and propylene into low-carbon alkanes and C 4+ hydrocarbons, thereby greatly improving the selectivity of ethylene and propylene in the products;

[0029] (2) The molecular sieve after selective passivation of the metal oxide and the acid sites is compounded and coupled, the metal oxide has a high specific surface area and more active sites, which is more conducive to the catalytic reaction and promotes the activation and conversion of carbon dioxide, thereby improving the conversion rate;

[0030] (3) The preparation process of the catalyst is simple and the conditions are mild, and the selectivity of ethylene and propylene can reach 78-86%, greatly improving the technical and economic efficiency; and by adjusting the reaction conditions, the ratio of ethylene and propylene can be changed between 0.8-1.5, which is conducive to the change of product price. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 NH3-TPD graph of the molecular sieve prepared for Example 2 and Comparative Example 2.

[0032] Figure 2 Pyridine infrared spectrum of the molecular sieve prepared for Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0033] The technical solutions of the present application are illustrated by specific examples below, but the protection scope of the present application is not limited thereto.

[0034] I. Catalyst component I (metal oxide)

[0035] (1) The metal oxides CuAl2O4, ZnO and FeO are commercially available. The 10 % FeO+InZr2O4 catalyst is obtained by mixing FeO and InZr2O4, and the mass fraction of FeO in the total FeO+InZr2O4 is 10 %.

[0036] (2) The preparation method of the metal oxide comprises the following steps: two of zinc nitrate, chromium nitrate, aluminum nitrate, zirconium nitrate, indium nitrate and gallium nitrate are used as precursors, the precursors and ammonium carbonate are mixed in water at room temperature, wherein ammonium carbonate is used as a precipitant, and the molar ratio of ammonium ion to metal ion is 1:1 (or, optionally, ammonium carbonate is in excess); the obtained mixed solution is aged, taken out after aging is completed, and then washed, filtered and dried in sequence; the obtained solid is calcined in an air atmosphere to obtain the metal oxide.

[0037] The metal oxides in the present application are prepared according to the above-mentioned precipitation method, and the specific parameter conditions used in the preparation process are shown in Table 1, and the remaining conditions are the same. The metal oxides are InZr x O (1+1.5x) , GaZr x O (1+1.5x) , ZnCr x O (1+1.5x) , ZnAl x O (1+1.5x) , ZnGa x O (1+1.5x) and ZnZr x O (1+1.5x) , and the value of x is in the range of 0.1-10. The specific surface area of the metal oxide is 5-150 m 2 / g.

[0038] Table 1 Preparation parameters of metal oxides

[0039]

[0040] II. Catalyst component II (molecular sieve)

[0041] SAPO-17, SAPO-34 and SAPO-35 molecular sieves are all 8 circular ring small pore molecular sieves, and the pore opening sizes thereof are 3.6*5.1 nm, 3.6*4.8 nm and 3.8*3.8 nm, respectively. The SAPO-17, SAPO-34 and SAPO-35 molecular sieves of component II of the present application can be commercially available products or self-prepared molecular sieves, and here, hydrothermal synthesis is taken as an example.

[0042] The medium-strong acid described in the present application can be tested by H spectrum of solid nuclear magnetic, NH3-TPD, infrared, chemical titration and the like. The testing method of the acidity is not limited to the above-mentioned testing methods.

[0043] (1) SAPO-17 molecular sieve

[0044] According to the molar ratio of SiO2:Al2O3:P2O5:CHA:H2O = 0.1:1.0:1.0:1.38:80, silicasol (mass concentration of 30%), pseudo-boehmite, phosphoric acid and deionized water are weighed, mixed at room temperature, and then template agent cyclohexylamine (CHA) is added dropwise; after aging at 30ºC for 2 h, it is transferred to a stainless steel hydrothermal kettle, heated to 200ºC at a heating rate of 2ºC / min, and crystallized for 96 h; after crystallization is completed, it is rapidly cooled to room temperature in a water bath, repeatedly centrifuged and washed until the supernatant pH is 7 at the end of washing, and the precipitate is dried at 90ºC for 12 h to obtain molecular sieve raw powder. A part of the molecular sieve raw powder is calcined at 600ºC in air for 6 h to obtain SAPO-17 molecular sieve.

[0045] (2) SAPO-34 molecular sieve

[0046] According to the molar ratio of SiO2:Al2O3:P2O5:TEAOH:H2O = 0.1:1.0:1.2:2.0:40, silicasol (mass concentration of 30%), pseudoboehmite, phosphoric acid, and deionized water were weighed and mixed at room temperature, then template agent tetraethylammonium hydroxide (TEAOH) was added dropwise. After stirring and aging at 30ºC for 2 h, it was transferred to a stainless steel hydrothermal kettle, heated to 180ºC at a heating rate of 2ºC / min for crystallization for 50 h. After crystallization was completed, it was rapidly cooled to room temperature in a water bath, repeatedly centrifuged and washed until the supernatant pH was 7 at the end of washing, and the precipitate was dried at 90ºC for 12 h to obtain the molecular sieve raw powder. A portion of the molecular sieve raw powder was calcined at 600ºC in air for 6 h to obtain the SAPO-34 molecular sieve.

[0047] (3) SAPO-35 molecular sieve

[0048] According to the molar ratio of SiO2:Al2O3:P2O5:HMI:H2O = 0.1:1.0:1.0:1.2:50, silicasol (mass concentration of 30%), aluminum isopropoxide, phosphoric acid, and deionized water were weighed and mixed at room temperature, then template agent cyclohexylamine (HMI) was added dropwise. After stirring and aging at 30ºC for 2 h, it was transferred to a stainless steel hydrothermal kettle, heated to 200ºC at a heating rate of 2ºC / min for crystallization for 48 h. After crystallization was completed, it was rapidly cooled to room temperature in a water bath, repeatedly centrifuged and washed until the supernatant pH was 7 at the end of washing, and the precipitate was dried at 90ºC for 12 h to obtain the molecular sieve raw powder. A portion of the molecular sieve raw powder was calcined at 600ºC in air for 6 h to obtain the SAPO-35 molecular sieve.

[0049] (4) Metal salt modified molecular sieve

[0050] Taking sodium salt as an example, sodium nitrate or sodium chloride was dissolved in deionized water to prepare a sodium salt aqueous solution with a certain concentration. The above-mentioned molecular sieve raw powder (SAPO-17, SAPO-34, or SAPO-35) was dried in a vacuum oven at 120ºC for 12 h or more. Then 10 g of the molecular sieve raw powder was added to the prepared sodium salt aqueous solution, and ion exchange was carried out at a certain temperature. After that, the solid product was centrifuged and washed with deionized water for 3 times. Finally, the obtained solid was dried at 110ºC overnight, and calcined at 600ºC in air for 6 h to obtain the sodium salt modified molecular sieve.

[0051] Other metal salt modified molecular sieves were prepared by the same preparation method as described above, and the specific preparation parameters are shown in Table 2.

[0052] Table 2 Preparation of metal salt modified molecular sieve and its performance parameters

[0053]

[0054] III. Catalyst

[0055] The catalyst is obtained by adding the metal oxide and the molecular sieve in the required proportions into a container and mechanically mixing them. One or more than one of the extrusion force, impact force, cutting force, friction force, etc. generated by the high-speed movement of the material and / or the container is used to achieve the purpose of separation, crushing, mixing, etc. The conversion of mechanical energy, thermal energy and chemical energy is achieved by adjusting the temperature and the carrier gas atmosphere, and the interaction between different components is further adjusted.

[0056] In a specific embodiment of the present application, the mixing temperature during mechanical mixing can be set to 20-100°C, and the mixing can be carried out in an atmosphere or directly in air. The atmosphere is selected from any of the following gases: a) nitrogen and / or inert gas; b) a mixture of hydrogen and nitrogen and / or inert gas, wherein the volume of hydrogen in the mixture is 5-50%; c) a mixture of CO and nitrogen and / or inert gas, wherein the volume of CO in the mixture is 5-20%; d) a mixture of O2 and nitrogen and / or inert gas, wherein the volume of O2 in the mixture is 5-20%. The inert gas is one or more of helium, argon and neon.

[0057] In a specific embodiment of the present application, the mechanical mixing can be carried out by one or more of mechanical stirring, ball milling, shaking table mixing and mechanical grinding, which are as follows:

[0058] a) Mechanical stirring: In a stirring tank, the metal oxide and the molecular sieve are mixed by using a stirring rod. By controlling the stirring time (5-120 min) and the stirring rate (30-300 rpm), the mixing degree and the relative distance of the metal oxide and the molecular sieve can be adjusted.

[0059] b) Ball milling: The abrasive, the metal oxide and the molecular sieve are tumbled at high speed in a milling tank to produce strong impact and crushing on the catalyst, so as to achieve the dispersion and mixing of the metal oxide and the molecular sieve. By controlling the mass ratio of the abrasive (the material can be stainless steel, agate or quartz, and the size range is 5-15 mm) to the catalyst (20-100:1), the particle size of the catalyst can be adjusted.

[0060] c) Shaking table oscillation: The metal oxide and the molecular sieve are pre-mixed and then loaded into a container. By controlling the reciprocating oscillation or the circular oscillation of the shaking table, the mixing of the metal oxide and the molecular sieve is achieved. By adjusting the oscillation speed (range: 1-70 rpm) and the oscillation time (range: 5-120 min), the uniform mixing and the adjustment of the relative distance are achieved.

[0061] d) Mechanical grinding: the metal oxide and the molecular sieve are premixed and loaded into a container; under a certain pressure (range: 5-20 kg), the mixed catalyst is subjected to relative motion (rate range: 30-300 rpm) by a grinding tool to achieve the effects of adjusting the particle size, relative distance and achieving uniform mixing of the catalyst.

[0062] 4. Catalytic reaction

[0063] The catalytic reaction is carried out in a fixed bed reactor or a moving bed reactor, and the reactor is equipped with a gas mass flow meter, an online product analysis chromatograph (the tail gas of the reactor is directly connected to the quantitative valve of the chromatograph for periodic real-time sampling analysis). Inert gas (one or more of helium, argon and neon) is used to replace the air in the reactor, and a mixture of carbon dioxide and hydrogen is used as the raw material to contact the catalyst for catalytic reaction, the molar ratio of carbon dioxide to hydrogen is 1:0.2-4.5, the reaction temperature is 300-500°C, the pressure of the mixed gas is 0.5-10 MPa, the space velocity of the mixed gas is 500-10000 mL•g -1 •h -1 .

[0064] Examples 1-13 and Comparative Examples 1-11

[0065] S1, the metal oxide is prepared by a precipitation method, and the specific preparation parameters are shown in Table 1; or, a commercially available metal oxide is used;

[0066] S2, the molecular sieve or the metal salt modified molecular sieve is prepared by the above preparation method, and the specific preparation parameters are shown in Table 2; or, a commercially available molecular sieve is used;

[0067] S3, the metal salt modified molecular sieve and the metal oxide are mechanically mixed to obtain a catalyst, and the specific catalyst preparation and its parameter characteristics are shown in Tables 3 and 4;

[0068] S4, carbon dioxide and hydrogen are used as raw materials to contact the catalyst for catalytic reaction. 2 g of catalyst is placed in a fixed bed reactor, argon is used to replace the air in the reactor, and then the reactor is heated to 300°C in a H2 atmosphere, the mixture of carbon dioxide and hydrogen (H2 / CO2 molar ratio = 0.2-4.5) is switched, the pressure of the mixed gas is 0.5-10 MPa, the temperature is raised to the reaction temperature 300-500°C, and the space velocity of the mixed gas is adjusted to 500-10000 mL•g -1 •h -1 . The specific parameters of the catalytic reaction are shown in Table 5, and the product is detected and analyzed by an online chromatograph.

[0069] Table 3 Preparation parameters of the catalyst in Examples 1-13

[0070]

[0071] Table 4 Preparation parameters of catalysts in Comparative Examples 1-11

[0072]

[0073] Table 5 Catalytic reaction parameters adopted in Example 1-13 and Comparative Examples 1-11

[0074]

[0075] Table 6 Application effect data (10 h) of catalysts in Example 1-13 and Comparative Examples 1-11

[0076]

[0077] As shown in Table 6, after 10 h of continuous reaction in a fixed bed reactor, it is tested that, by changing the temperature, pressure, space velocity and molar ratio of H2 / CO2 in the mixed gas of the catalytic reaction, the final catalytic effect will be different, but the overall catalytic activity, ethylene propylene selectivity is high, and the methane selectivity is low. Specifically, the CO2 conversion rate reaches 30-50%, the selectivity of low-carbon olefins (one or more of ethylene, propylene and butene) in the hydrocarbon product can reach 82~90%, the selectivity of ethylene and propylene in the hydrocarbon product can reach 78~86%, the molar ratio of ethylene and propylene is between 0.8~1.7, and the methane selectivity is <10%.

[0078] As shown in Table 6, Comparative Example 1 relative to Example 1, Comparative Example 2 relative to Example 2, and Comparative Example 3 relative to Example 3, the molecular sieve in the catalysts adopted is SAPO-17, SAPO-34 and SAPO-35 without passivation of the outer surface acid sites, respectively. The reaction results of Comparative Examples 1-3 show that, the molecular sieve without passivation of the outer surface acid sites, the selectivity of low-carbon olefins in the reaction product is low, the total selectivity of ethylene and propylene is not high, and the methane selectivity is high. This is because the secondary conversion of ethylene occurs on the outer surface acid sites, resulting in a high selectivity of C 4+ . Figure 1 The NH3-TPD graph of the molecular sieve prepared in Example 2 (part 5) and Comparative Example 2 (part 2) is shown in Table 6, which shows that the number of medium-strong acid sites after surface passivation treatment is reduced. As shown in Table 6, the pyridine infrared spectrum of the molecular sieve prepared in Example 1 (part 4) and Comparative Example 1 (part 1) shows that the characteristic peak of B acid is significantly reduced, which proves that the number of acid sites on the outer surface after passivation treatment is significantly reduced. Figure 2

[0079] As shown in Table 6, Comparative Example 1 relative to Example 1, Comparative Example 2 relative to Example 2, and Comparative Example 3 relative to Example 3, the molecular sieve in the catalysts adopted is SAPO-17, SAPO-34 and SAPO-35 without passivation of the outer surface acid sites, respectively. The reaction results of Comparative Examples 1-3 show that, the molecular sieve without passivation of the outer surface acid sites, the selectivity of low-carbon olefins in the reaction product is low, the total selectivity of ethylene and propylene is not high, and the methane selectivity is high. This is because the secondary conversion of ethylene occurs on the outer surface acid sites, resulting in a high selectivity of C 4+ .

[0080] The molecular sieve in Comparative Example 4 has a significantly lower concentration of aqueous sodium nitrate solution used in the ion exchange process relative to Example 1, and the acid site content of the molecular sieve is still relatively high. As can be seen from the reaction results, the ethylene propylene selectivity is significantly reduced. This is because the low concentration of metal salt cannot completely exchange the acid sites on the outer surface, and thus the ethylene propylene is further converted into low carbon alkanes and C 4+ The molecular sieve in Example 13 has an increased concentration of aqueous sodium nitrate solution used in the ion exchange process relative to Example 1. As can be seen from the reaction results, the ethylene propylene selectivity is comparable to that of Example 1. This is because the concentration of metal salt in Example 1 is already able to completely passivate the acid sites on the outer surface, and the acid sites have been maintained at a low level. Further increasing the concentration of the metal salt has little effect on the reaction performance.

[0081] The metal salts used in Comparative Examples 5 and 6 are rubidium nitrate and cesium chloride, respectively. As can be seen from the reaction results, the CO2 conversion rate gradually decreases, and the ethylene propylene selectivity also decreases in Comparative Examples 5-6 relative to Example 1. This is because the ionic radius of rubidium ions and cesium ions is larger than that of sodium ions. Larger metal ions block the pore openings, causing diffusion limitations, and thus the technical effects of the present application cannot be achieved. The reaction results of Comparative Examples 4-6 show that controlling the acid site content of the passivated molecular sieve and the type of metal salt are crucial for achieving higher CO2 conversion rates and ethylene propylene selectivity.

[0082] Comparative Examples 7-8 have catalysts containing only metal oxides, without molecular sieves, relative to Example 4. The CO2 reaction conversion rate is very low, and the products are mainly dimethyl ether, methane and other byproducts, and the ethylene propylene selectivity is very low. The catalyst used in Comparative Example 8 contains only molecular sieves, without metal oxides. Since the molecular sieves have no ability to activate CO2, the catalytic reaction has almost no activity. The reaction results of Comparative Examples 7-8 show that the catalysts containing only Component I or Component II have poor reaction effects, and do not have the excellent reaction performance described in the present application.

[0083] Comparative Example 9 has a catalyst with Cu-based oxides as the metal oxides relative to Example 4. The reaction conversion rate is very low, and the products are mainly methane and other byproducts, and the C2-C4 hydrocarbon selectivity is very low. Comparative Example 10 has a catalyst with single-component ZnO as the metal oxides relative to Example 5. The ZnO crystal grain size is large, and the specific surface area is low (<1 m 2 / g) and no partially reduced O-defect structures on the surface, the CO2 conversion is very low and the hydrogenation is severe, and the product is mainly methane. Comparative Example 11 uses the same catalyst as Example 1, except that the oxide component also contains 10% FeO component. The reaction product is mainly methane, and the selectivity of low carbon olefins and ethylene and propylene is very low, because the FeO in the catalyst is reduced to form iron carbide phase during the reaction, and thus the reaction process becomes a traditional Fischer-Tropsch synthesis technology route, and the product distribution obeys the ASF distribution. The reaction results of Comparative Examples 9-11 show that the oxide component in the catalyst used is essential for the preparation of high selectivity low carbon olefins.

[0084] The above merely describes the preferred embodiments of the present application, and is not intended to limit the patent scope of the present application, and any equivalent structure or equivalent process transformation made by using the present application description, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing ethylene propylene using a catalyst that selectively passivates acidic sites, characterized in that, Includes the following steps: S1. After mixing silicon source, aluminum source, phosphorus source and water, add template agent and age, then heat and crystallize, and dry to obtain molecular sieve raw powder. Molecular sieve powder is added to a metal salt aqueous solution for ion exchange, followed by drying and aerobic calcination to obtain a metal salt modified molecular sieve with a medium-strong acid site content of 0.05~0.3 mol / kg, wherein the molecular sieve is SAPO-17, SAPO-34 or SAPO-35, and the metal salt is sodium salt and / or potassium salt. S2. Mechanically mix the metal salt-modified molecular sieve with a metal oxide, wherein the metal oxide is InZr. x O (1+1.5x) GaZr x O (1+1.5x) ZnCr x O (1+1.5x) ZnAl x O (1+1.5x) ZnGa x O (1+1.5x) and ZnZr x O (1+1.5x) At least one of the following, wherein x takes the value of 0.1 to 10, is used to obtain a catalyst; S3. A mixture of hydrogen and carbon dioxide is brought into contact with a catalyst to react and produce ethylene and propylene.

2. The method for preparing ethylene propylene using a catalyst with selectively passivated acidic sites according to claim 1, characterized in that, The template agent includes cyclohexylamine, cyclohexylimine, or tetraethylammonium hydroxide; the aging is carried out at room temperature for 1-3 hours.

3. The method for preparing ethylene propylene using a catalyst with selectively passivated acidic sites according to claim 1 or 2, characterized in that, The temperature-raising crystallization involves raising the temperature to 150~200℃ and crystallizing for 60~80 hours.

4. The method for preparing ethylene propylene using a catalyst that selectively passivates acidic sites according to claim 1, characterized in that, In S1, the sodium salt is sodium nitrate or sodium chloride; the potassium salt is potassium nitrate or potassium chloride.

5. The method for preparing ethylene propylene using a catalyst that selectively passivates acidic sites according to claim 1, characterized in that, In S1, the concentration of the metal salt aqueous solution is 0.05~3 mol / L; the ion exchange is carried out by heating to 60~90℃ and holding for 5~15 h.

6. The method for preparing ethylene propylene using a catalyst with selectively passivated acidic sites according to claim 1, 4, or 5, characterized in that, In S1, the aerobic roasting involves heating to 500~700℃ and holding at that temperature for 5~7 hours.

7. The method for preparing ethylene propylene using a catalyst with selectively passivated acidic sites according to claim 1, 4, or 5, characterized in that, In S2, the mass ratio of the metal salt modified molecular sieve to the metal oxide is 0.1~20:

1.

8. The method for preparing ethylene propylene using a catalyst with selectively passivated acidic sites according to claim 1, characterized in that, In S3, the reaction conditions are: temperature 300~500℃, mixed gas pressure 0.5~10 MPa, and mixed gas space velocity 300~10000 mL•g. -1 •h -1 .

9. The method for preparing ethylene propylene using a catalyst with selectively passivated acidic sites according to claim 1 or 8, characterized in that, In S3, the molar ratio of H2 / CO2 in the mixed gas is 0.2~4.5.

Images