A process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation

Abstract

The present application relates to the technical field of low carbon olefin preparation, and discloses a method for preparing propylene and butene through direct conversion of carbon dioxide hydrogenation, comprising the following steps: (1) preparing mesoporous SAPO-14 molecular sieve by adopting a gel aluminum-rich crystallization method; the molar ratio of SiO2, Al2O3 and P2O5 in the raw material of the gel aluminum-rich crystallization method is 0.02-0.2:1.1-1.8:1; (2) mixing the mesoporous SAPO-14 molecular sieve and metal oxide to obtain a catalyst; (3) using a mixed gas of carbon dioxide and hydrogen as raw material, and contacting the catalyst to perform catalytic reaction to prepare propylene and butene. The present application adopts metal oxide and mesoporous SAPO-14 molecular sieve to perform compounding and coupling to obtain a catalyst, which has a higher specific surface area and more active sites, is more conducive to the catalytic reaction, and can obtain higher propylene and butene selectivity and catalytic stability.

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 propylene and butene by directly converting carbon dioxide and hydrogen. BACKGROUND

[0002] Low-carbon olefin refers to olefin with carbon atom number less than or equal to 4 (ethylene, propylene and butene). At present, the production of low-carbon olefin mainly adopts the petrochemical route of light hydrocarbon (ethane, naphtha, light diesel) cracking. Due to the increasing shortage of petroleum resources and the long-term high price of crude oil, the development of low-carbon olefin industry will encounter more and more raw material problems by relying on the tubular cracking furnace process of petroleum light hydrocarbon as raw material only. The low-carbon olefin production process and raw materials must be diversified. In addition, the traditional olefin production process route is highly dependent on fossil energy, and about 1.5-2 tons of CO2 are emitted per ton of olefin produced. It is of great significance for energy saving and economic benefit to catalytically convert CO2 into low-carbon olefin, a high-value chemical product, through hydrogenation reaction.

[0003] At present, there are mainly two technical routes for preparing low-carbon olefin from CO2: one is the improved Fischer-Tropsch synthesis route, taking carbon monoxide as an intermediate. However, due to the limitation of Anderson-Schulz-Flory (ASF) distribution rule, the product distribution is too wide, resulting in a low-carbon olefin selectivity usually less than 58%, and problems of high selectivity of carbon monoxide and by-product methane. The second is the methanol-mediated route, which uses a metal oxide / molecular sieve composite catalyst. By physical mixing, the two processes of CO2 activation and carbon-carbon bond formation are decoupled, breaking through the selectivity limitation, and the selectivity of low-carbon olefin is improved to more than 80%, so it becomes a more promising mainstream technical direction.

[0004] The team of Academician Li Can of Dalian Institute of Chemical Physics developed a ZnZr solid solution oxide / Zn modified SAPO-34 molecular sieve bifunctional catalyst, which realized the high selective conversion of CO2 into low-carbon olefin (low-carbon olefin selectivity of 80%, CO2 conversion rate of 12.6%) under the reaction conditions close to industrial production, and showed excellent stability and sulfur poisoning resistance (CO2 hydrogenation to high-value products via heterogeneous catalysis, ACSCatalysis, 2017, 7, 8544). From the perspective of industrial separation process, the energy consumption of subsequent separation of olefin products from CO2 hydrogenation is one of the key factors affecting the overall process economy. The existing CO2 hydrogenation technology has a wide product distribution (containing C1, C2 and C 5+The separation difficulty and energy consumption problems are more prominent. In the above research, the ethylene content in the product is relatively high (about 25%), and the ethylene needs to be effectively separated through multi-stage cryogenic separation, which significantly increases the energy consumption. If propylene and butene products can be obtained with high selectivity, deep cooling separation is not needed, which greatly reduces the energy consumption and cost of separation, and has great application value.

[0005] In addition, the prior art also discloses the application of SAPO-14 molecular sieve in the preparation of low-carbon olefins by carbon dioxide hydrogenation. For example, a catalyst for synthesizing low-carbon olefins by CO2 hydrogenation reaction and its preparation and application are disclosed in CN119857524A. The catalyst comprises active component A and core-shell structure B@C. The active component A is a metal oxide which has catalytic activity for synthesizing low-carbon olefins by CO2 hydrogenation reaction. In the core-shell structure B@C, B is SAPO molecular sieve (optionally SAPO-14 molecular sieve), and C is selected from one or more of B2O3, SiO2, Al2O3, TiO2, ZrO2, kaolin and montmorillonite. However, the patent only discloses the selectivity of the catalyst for C2-C4 olefins, which still contains ethylene, and cannot obtain propylene and butene products with high selectivity. In addition, the SAPO-14 molecular sieve also has the problem of poor stability, which affects the application of the technology. SUMMARY

[0006] To solve the above technical problems, the present application provides a method for directly converting carbon dioxide hydrogenation to prepare propylene and butene, which adopts metal oxide and mesoporous SAPO-14 molecular sieve to obtain a catalyst. The catalyst has a higher specific surface area and more active sites, which is more conducive to the catalytic reaction and can obtain higher propylene and butene selectivity and catalytic stability.

[0007] The object of the present application is achieved by the following technical solutions:

[0008] The present application provides a method for directly converting carbon dioxide hydrogenation to prepare propylene and butene, which comprises the following steps:

[0009] (1) Mesoporous SAPO-14 molecular sieve is prepared by gel aluminum-rich crystallization method, and the specific surface area of the mesopore is 50-120 m 2 / g; the molar ratio of SiO2, Al2O3 and P2O5 in the raw material of the gel aluminum-rich crystallization method is 0.02-0.2:1.1-1.8:1;

[0010] (2) The mesoporous SAPO-14 molecular sieve and metal oxide are mixed to obtain a catalyst; the metal oxide is InZr x O (1+1.5x) , GaZr xO (1+1.5x) ZnCr x O (1+1.5x) ZnAl x O (1+1.5x) ZnGa x O (1+1.5x) ZnZr x O (1+1.5x) x is in the range of 0.1-10;

[0011] (3) using a mixture of carbon dioxide and hydrogen as raw material, and contacting with a catalyst to prepare propylene and butene.

[0012] The catalyst in the application is obtained by compounding metal oxide and mesoporous SAPO-14 molecular sieve. The metal oxide has a high specific surface area and more active sites, which is more conducive to the catalytic reaction. The SAPO-14 molecular sieve is one kind of 8-ring small pore molecular sieve, and the size of the elongated AFN cage is 5.3x10.05 Å, and the size of the 8-membered ring aperture is 4.6x1.9 Å, 4.9x2.1 Å and 4.0x3.3 Å. The unique cage structure is particularly conducive to the generation of C3 and C4 products.

[0013] On the one hand, the mesoporous SAPO-14 molecular sieve used in the application can be coupled with the metal oxide to further convert the active gas intermediates generated by the metal oxide to obtain propylene and butene. Due to the effect of the SAPO-14 molecular sieve on pulling the series reaction equilibrium, the activation and conversion of carbon dioxide and hydrogen by the metal oxide can be promoted, thereby improving the conversion rate. On the other hand, compared with the conventional SAPO-14 molecular sieve, the mesoporous SAPO-14 molecular sieve prepared by the gel aluminum-rich crystallization method has a higher mesoporous specific surface area, which can provide a larger accommodation space for carbon species, effectively solving the problem of small AFN cage space (5.3x10.05 Å), thereby significantly improving the stability of the catalytic reaction, and the selectivity of propylene and butene is further improved.

[0014] The application directly converts carbon dioxide and hydrogen into propylene and butene in one step, and the selectivity of low-carbon olefins can reach 75-90%, the selectivity of propylene and butene can reach 65-80%, the selectivity of propylene and butene in low-carbon olefins can reach 84-90%, the ratio of propylene and butene is between 2.5-3.5, and the selectivity of byproduct methane is low (<12%), which has a good application prospect.

[0015] As a preferred, the molar ratio of SiO2, Al2O3 and P2O5 in the raw material of the gel aluminum-rich crystallization method is 0.1-0.2:1.1-1.8:1.

[0016] Preferably, the mass ratio of the metal oxide to the mesoporous SAPO-14 molecular sieve is 0.1-20:1, more preferably 0.3-5:1.

[0017] Preferably, the specific surface area of the mesopores in the mesoporous SAPO-14 molecular sieve is 60-100 m 2 / g.

[0018] Preferably, the mesoporous SAPO-14 molecular sieve has a medium-strong acid characteristic, and the molar amount of the medium-strong acid sites is 0.1-0.6 mol / kg, more preferably 0.1-0.4 mol / kg, and further preferably 0.3-0.4 mol / kg.

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

[0020] The NH3-TPD is based on the desorption peak position of NH3, and the desorption peak position refers to that under standard test conditions, at a sample mass w to carrier gas flow rate f ratio (w / f) = 100 g•h / L, under a test condition of a temperature rising speed of 10 ℃ / min, 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 an acid site with a NH3 desorption temperature less than 245 ℃; medium-strong acid refers to an acid site with a NH3 desorption temperature of 245-500 ℃; and strong acid refers to an acid site with a NH3 desorption temperature greater than 500 ℃.

[0021] Preferably, the specific surface area of the metal oxide is 100-150 m 2 / g.

[0022] The x in the chemical formula of the metal oxide only represents the relative proportion of the chemical composition of the elements in the metal oxide.

[0023] Preferably, the gel-rich aluminum crystallization method comprises the following steps: mixing a silicon source, an aluminum source, a phosphorus source, a template agent, and water, stirring and aging, and then performing rotary crystallization after temperature rising; after the reaction is completed, washing, drying, and performing aerobic calcination to obtain the mesoporous SAPO-14 molecular sieve.

[0024] Preferably, the stirring and aging time is 1-3 h; the rotary crystallization temperature is 150-200 ℃, and the time is 40-60 h; and the aerobic calcination temperature is 500-700 ℃, and the time is 5-7 h.

[0025] As preferred, the catalytic reaction is carried out on a fixed bed or a moving bed, the reaction temperature is 300-500 DEG C, more preferably 380-500 DEG C; the space velocity of the mixed gas is 300-12000 mL / g / h, more preferably 1000-10000 mL / g / h, further preferably 3000-10000 mL / g / h.

[0026] As preferred, the molar ratio of the carbon dioxide and the hydrogen is 1:0.2-4.5, more preferably 1:0.5-3.5.

[0027] As preferred, the pressure of the mixed gas is 0.5-10 MPa, more preferably 1-5 MPa; the mixed gas further comprises an inert gas.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] (1) The catalyst in the present application is obtained by compounding and coupling metal oxides with mesoporous SAPO-14 molecular sieves, and the mesoporous SAPO-14 molecular sieves have higher mesoporous specific surface area and moderate acid sites, so that the catalyst obtained by coupling the mesoporous SAPO-14 molecular sieves with the metal oxides has higher specific surface area and more active sites, and is more conducive to the catalytic reaction, and the selectivity of propylene and butene is further improved.

[0030] (2) The preparation process of the catalyst in the present application is simple and the conditions are mild, the selectivity of propylene and butene in the product is higher, which can reach 65-80%, and the selectivity of the byproduct methane is low (<12%), which greatly improves the technical economy; and the product scheme can be customized according to market needs, and the ratio of propylene and butene can be changed between 2.5-3.5 by adjusting the reaction conditions. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is the X-ray diffraction spectrum of the molecular sieve prepared in Example 2.

[0032] Figure 2 It is the catalytic reaction stability evaluation of Example 2 and Comparative Example 4.

[0033] Figure 3 It is the nitrogen adsorption-desorption graph of the molecular sieve prepared in Example 2. DETAILED DESCRIPTION

[0034] 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.

[0035] 1. Metal oxide

[0036] (1) Metal oxides CuAl2O4, ZnO, FeO are commercially available. The 10% FeO+InZr2O4 catalyst is obtained by mixing FeO and InZr2O4, and FeO accounts for 10% of the total mass of FeO+InZr2O4.

[0037] (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 the feeding 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.

[0038] The metal oxide in the application is prepared according to the above 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 oxide is one or more 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) , and the value range of x is 0.1-10. The specific surface area of the metal oxide is 5-150 m 2 / g.

[0039] Table 1 Preparation parameters of metal oxides

[0040]

[0041] 2. Molecular sieve

[0042] (1) SAPO-34 molecular sieve, ZSM-5 molecular sieve and MOR molecular sieve are commercially available.

[0043] (2) The preparation method of the conventional SAPO-14 molecular sieve comprises the following steps: tetraethyl orthosilicate, aluminum isopropoxide, phosphoric acid and deionized water are weighed according to the molar ratio of SiO2:Al2O3:P2O5:IPA:H2O = 0.1:1.0:1.0:1.38:80, mixed at room temperature, and then the template agent isopropylamine (IPA) is added dropwise; after stirring and 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 rotated for crystallization for 50 h; after crystallization, the water bath is rapidly cooled to room temperature, repeated centrifugal washing is performed until the supernatant pH is 7 at the end of washing, the precipitate is dried at 90ºC for 12 h, and then calcined in air at 600ºC for 6 h, to obtain the conventional SAPO-14 molecular sieve.

[0044] (3) The preparation method of the mesoporous SAPO-14 molecular sieve comprises the following steps: tetraethyl orthosilicate, aluminum isopropoxide, phosphoric acid and deionized water are weighed according to the molar ratio of SiO2:Al2O3:P2O5:IPA:H2O = x (x = 0.03, 0.10, 0.15, 0.20):y (y = 1.15, 1.3, 1.45, 1.6):1.0:1.38:80, mixed at room temperature, and then the template agent isopropylamine (IPA) is added dropwise; after stirring and aging at 30ºC for 2 h, it is transferred to a stainless steel hydrothermal kettle, heated to a certain temperature at a heating rate of 2ºC / min, and rotated for crystallization; after crystallization, the water bath is rapidly cooled to room temperature, repeated centrifugal washing is performed until the supernatant pH is 7 at the end of washing, the precipitate is dried at 90ºC for 12 h, and then calcined in air at 600ºC for 6 h, to obtain the mesoporous SAPO-14 molecular sieve.

[0045] The mesoporous SAPO-14 molecular sieve prepared by the gel-rich aluminum crystallization method used in the present application is a self-prepared molecular sieve, and here the hydrothermal synthesis is taken as an example, and the specific preparation parameters are shown in Table 2, and the remaining conditions are the same. The specific surface area of the mesoporous SAPO-14 molecular sieve is 50-120 m 2 / g; the mesoporous SAPO-14 molecular sieve has a medium-strong acid characteristic, and the molar amount of the medium-strong acid site is 0.005-0.6 mol / kg. The medium-strong acid can be tested by H spectrum of solid nuclear magnetic resonance, NH3-TPD, infrared, chemical titration and the like, but the testing method of the acid is not limited to the above testing methods.

[0046] Table 2 Preparation parameters of SAPO-14 molecular sieve

[0047]

[0048] 3. Catalyst

[0049] The metal oxide and the molecular sieve in the required proportion are added into a container for mechanical mixing to obtain the catalyst. One or more than two of the extrusion force, impact force, cutting force, friction force and the like generated by the high-speed movement of the material and / or the container are used to achieve the purposes of separation, crushing, mixing and the like. 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.

[0050] In specific embodiments 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.

[0051] In specific embodiments of the present application, mechanical mixing can be carried out by one or more of mechanical stirring, ball milling, shaking table mixing and mechanical grinding, as follows:

[0052] 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.

[0053] b) Ball milling: The abrasive and 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, thereby achieving 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.

[0054] c) Shaking table oscillation: The metal oxide and the molecular sieve are pre-mixed and 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 time (range: 5-120 min), uniform mixing and adjustment of the relative distance are achieved.

[0055] d) Mechanical grinding: The metal oxide and the molecular sieve are pre-mixed and loaded into a container. Under a certain pressure (range: 5-20 kg), the relative movement (rate range: 30-300 rpm) between the grinding tool and the mixed catalyst is achieved to adjust the particle size and the relative distance of the catalyst and to achieve uniform mixing.

[0056] 4. Catalytic reaction

[0057] The catalytic reaction is carried out in a fixed bed reactor or a moving bed reactor, which is equipped with a gas mass flow meter, an online product analysis chromatograph (the tail gas of the reactor is directly connected with a 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 mixed gas of carbon dioxide and hydrogen is used as the raw material to contact the catalyst to carry out the catalytic reaction, the molar ratio of carbon dioxide to hydrogen is 1:0.2-4.5, the reaction temperature is 300-500℃, the pressure of the mixed gas is 0.5-10 MPa, and the space velocity of the mixed gas is 300-12000 mL / g / h.

[0058] Examples 1-12 and Comparative Examples 1-12

[0059] (1) Metal oxides are prepared by a precipitation method, and the specific preparation parameters are shown in Table 1; or commercially available metal oxides are used;

[0060] (2) Mesoporous SAPO-14 molecular sieves are prepared by a gel aluminum-rich crystallization method, and the specific preparation parameters are shown in Table 2; or commercially available molecular sieves are used;

[0061] (3) The metal oxides and molecular sieves in the required proportions are added to a container for mechanical mixing to obtain a catalyst, and the specific catalyst preparation and its parameter characteristics are shown in Tables 3 and 4;

[0062] (4) Carbon dioxide and hydrogen are used as raw materials to contact the catalyst to carry out the 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℃ in a H2 atmosphere, the mixed gas 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 of 300-500℃, and the space velocity of the mixed gas is adjusted to 300-12000 mL / g / h. The specific parameters of the catalytic reaction are shown in Table 5, and the products are detected and analyzed by an online chromatograph.

[0063] Table 3 Preparation parameters of the catalyst in Examples 1-12

[0064]

[0065] Table 4 Preparation parameters of the catalyst in Comparative Examples 1-12

[0066]

[0067] Table 5 Catalytic reaction parameters used in Examples 1-12 and Comparative Examples 1-12

[0068]

[0069] Table 6. Application effect data of catalysts in Examples 1-12 and Comparative Examples 1-12 (30h)

[0070]

[0071] As shown in Table 6, Examples 1-12 demonstrate that by changing the temperature, pressure, space velocity, and the molar ratio of H2 / CO2 in the catalytic reaction, the final catalytic effect will vary, but the overall catalytic activity, selectivity, and stability are high. After 30 hours of reaction, the CO2 conversion rate can still reach 30-40%, and after 30 hours, the selectivity of low-carbon olefins (one or more of ethylene, propylene, and butene) in hydrocarbon products can reach 75-90%, the selectivity of propylene and butene in hydrocarbon products can reach 65-80%, and the selectivity of propylene and butene in low-carbon olefins can reach 80-90%, with a molar ratio of propylene to butene between 2.5 and 3.5. Due to the low hydrogenation activity on the catalyst surface, the large-scale generation of methane is avoided, resulting in low methane selectivity (<12%).

[0072] like Figure 1 The image shows the X-ray diffraction pattern of the molecular sieve prepared in Example 2, which exhibits diffraction peaks typical of the AFN topology. Figure 3 The attached figure shows the nitrogen adsorption-desorption of the molecular sieve prepared in Example 2, which is a typical type IV isotherm. Figure 1 and Figure 3 This demonstrates the successful synthesis of mesoporous SAPO-14 molecular sieves.

[0073] The comparative results of Comparative Example 1 and Example 2, Comparative Example 2 and Example 3, and Comparative Example 3 and Example 4 show that molecular sieves with different topologies significantly modulate the product selectivity. The molecular sieve used in Comparative Example 1 was the commercially available SAPO-34, which has a three-dimensional intersecting channel, an eight-membered ring pore diameter, and a pore size of 3.8 Å, suitable for C2-C4 hydrocarbons, but with low selectivity for propylene and butene. The molecular sieve used in Comparative Example 2 was the commercially available ZSM-5, which has a three-dimensional ten-membered ring topology and a larger pore size of 5.6 Å. The products are mainly C4 hydrocarbons and even longer-chain hydrocarbons, with low selectivity for low-carbon olefins. The molecular sieve used in Comparative Example 3 was the commercially available MOR catalyst, which has a one-dimensional twelve-membered ring topology. Although the pore size is very large, reaching 6.5 × 7.0 Å, it also contains side pockets with eight circular pores. The pocket depth is shallower than that of SAPO-34 pockets, so it mainly produces ethylene with two carbon atoms. The selectivity for propylene and butene is lower than that of Comparative Example 1.

[0074] Comparative Example 4 and Example 2 were compared. The molecular sieve in Comparative Example 4 was SAPO-14 prepared by a conventional method, which had a smaller mesopore specific surface area (only 32 m 2 / g), and the selectivity of the low carbon olefins in the reaction product was low, and the total selectivity of propylene and butylene was not high, and the selectivity of methane was high. As shown in Figure 1, which was a catalytic stability evaluation diagram of the catalysts in Comparative Example 4 and Example 2, it could be obviously seen that the catalytic activity of the catalyst in Comparative Example 4 was significantly deactivated after 30 h of reaction. Figure 2

[0075] Comparative Examples 5-7 and Example 2 were compared. The molecular sieve used in Comparative Examples 5-7 was mesoporous SAPO-14 molecular sieve with different acid amounts. From the reaction results, it could be seen that too low acid amount would significantly reduce the conversion rate of CO2, and too high acid amount would cause the selectivity of the byproduct low carbon alkane in the product to increase, and the selectivity of propylene and butylene to decrease.

[0076] Comparative Examples 8-9 and Example 1 were compared. The catalyst used in Comparative Example 8 was only metal oxide without molecular sieve, the reaction conversion rate was very low, and the product was mainly byproduct dimethyl ether, methane, etc., and almost no propylene and butylene were generated. The catalyst used in Comparative Example 9 was only molecular sieve without metal oxide, and since the molecular sieve had no ability to activate CO2, the catalytic reaction had almost no activity. Comparative Examples 8-9 showed that the catalytic reaction effect was poor when only metal oxide or molecular sieve was used, and completely did not have the excellent reaction performance described in the application.

[0077] Comparative Example 10 and Example 4 were compared. The oxide in the catalyst used in Comparative Example 10 was Cu-based oxide, the reaction conversion rate was very low, and the product was mainly byproduct methane, and the selectivity of C2-C4 hydrocarbons was very low. Comparative Example 11 and Example 5 were compared. The oxide in the catalyst used in Comparative Example 11 was single-component ZnO, which had a large crystal grain size, a low specific surface area (<1 m 2 / g), and no partial reduction O defect structure on the surface, the reaction conversion rate was very low, and the hydrogenation was serious, and the product was mainly methane. Comparative Example 12 and Example 1 were compared. The oxide in the catalyst used in Comparative Example 12 also contained 10 % FeO component, the reaction product was mainly methane, the selectivity of propylene and butylene was very low, and the selectivity of low carbon olefins was also obviously lower than that of Example 1. This was because the FeO in the catalyst was reduced to generate iron carbide phase during the reaction, and thus the reaction process became a traditional Fischer-Tropsch synthesis technical route. The product distribution obeyed the ASF distribution, and no longer met the requirements of the application. The technical effects of the application could not be achieved. The reaction results of Comparative Examples 10-12 showed that the oxide component in the catalyst was very important for preparing low carbon olefins with high selectivity.

[0078] ​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 the present application specification, 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 process for the direct conversion of carbon dioxide by hydrogenation to produce propylene and butylenes, characterized in that, It comprises the following steps: (1) a mesoporous SAPO-14 molecular sieve is prepared by using a gel aluminum-rich crystallization method, the specific surface area of the mesoporous is 50-120 m 2 / g; the raw materials of the gel aluminum-rich crystallization method are weighed according to the molar ratio of SiO2, Al2O3 and P2O5 as 0.02-0.2:1.1-1.8:1; the gel aluminum-rich crystallization method comprises the following steps: the silicon source, the aluminum source, the phosphorus source, the template agent and water are mixed, stirring and aging are performed, and then rotating crystallization is performed after temperature rising; after the reaction is completed, washing, drying and aerobic calcination are performed to obtain the mesoporous SAPO-14 molecular sieve; (2) mixing the mesoporous SAPO-14 molecular sieve and a metal oxide to obtain a catalyst; the metal oxide is one or more 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) , and x is in the range of 0.1-10; (3) using mixed gas containing carbon dioxide and hydrogen as raw gas, and contacting with catalyst to carry out catalytic reaction to prepare propylene and butene.

2. The process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation according to claim 1, characterized in that, The mass ratio of the metal oxide to the mesoporous SAPO-14 molecular sieve is 0.1-20:

1.

3. The process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation according to claim 1, characterized in that, The molar amount of the medium-strong acid site in the mesoporous SAPO-14 molecular sieve is 0.1-0.6 mol / kg.

4. The process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation according to claim 1, characterized in that, The specific surface area of the metal oxide is 100-150 m 2 / g.

5. The process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation according to claim 1, characterized in that, The stirring aging time is 1-3 h; the rotating crystallization temperature is 150-200℃, and the time is 40-60 h.

6. The process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation according to claim 1, characterized in that, The aerobic roasting temperature is 500-700℃, and the time is 5-7 h.

7. The process for the direct conversion of carbon dioxide to propylene and butylenes by hydrogenation according to claim 1, characterized in that, The catalytic reaction temperature is 300-500℃, and the mixed gas space velocity is 300-12000 mL / g / h.

8. The process for the direct conversion of carbon dioxide to propylene and butylenes by means of its hydrogenation according to claim 1 or 7, characterized in that, The molar ratio of the carbon dioxide to the hydrogen is 1:0.2-4.

5.

9. Process for the direct conversion of carbon dioxide to propylene and butylenes by means of its hydrogenation according to claim 1 or 7, characterized in that, The pressure of the mixed gas is 0.5-10 MPa.

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