Method for synthesizing low-carbon olefins by one-step synthesis gas

Abstract

A one-step method for producing low-carbon olefins from syngas relates to the field of direct synthesis of low-carbon olefins from syngas, and the catalyst used includes metal oxides and AlPO-34 molecular sieves; the metal oxide is ZnAlO. x ZnGaO x ZnCrO x ZnCrAlO x ZnCrMnO x ZnCrGaO x The AlPO-34 molecular sieve is a nanosheet-like metal isomorphously substituted AlPO-34 molecular sieve with a b-axis thickness of 10–100 nm; the isomorphously substituted metal element is at least one of Ba, W, Ca, Ce, Y, Ga, Ge, La, Mg, and Sr. This invention enables the direct synthesis of low-carbon olefins from syngas with a selectivity exceeding 85%, and exhibits high stability during the reaction, demonstrating promising prospects for industrial application.

Description

Technical Field

[0001] This invention relates to the field of direct synthesis of low-carbon olefins from syngas, and more particularly to a one-step method for producing low-carbon olefins from syngas. Background Technology

[0002] Low-carbon olefins (ethylene, propylene, butene) are the most important chemical raw materials. Currently, the mainstream production route for low-carbon olefins is the petrochemical route of cracking light petroleum hydrocarbons. Developing non-oil-based resources such as coal, natural gas, carbon dioxide, and biomass as raw materials to produce syngas, and then using syngas to produce low-carbon olefins, is a feasible solution. Currently, the production of low-carbon olefins from syngas mainly adopts an indirect process, i.e., a two-step method where syngas is first converted into methanol or dimethyl ether, and then the methanol or dimethyl ether is dehydrated to produce low-carbon olefins. Developing a one-step direct catalytic conversion process from syngas to low-carbon olefins can simplify the process, reduce project investment, and improve product economic efficiency, and is currently a research hotspot in the field of syngas conversion.

[0003] Catalyst development is a key research focus in the direct catalytic conversion of syngas to low-carbon olefins. Currently, there are two main types: First, Fischer-Tropsch catalysts, represented by iron / cobalt-based catalysts, use metallic iron / cobalt or their carbides as active components. However, the reaction follows a chain growth mechanism on metal surfaces, resulting in low-carbon olefin selectivity, generally not exceeding 58% (low-carbon olefin selectivity refers to the selectivity of low-carbon olefins among organic products, the same applies throughout). Second, bifunctional catalysts formed from oxide composite molecular sieves. Currently reported bifunctional or multifunctional composite catalysts mainly use SAPO series, AlPO series, SSZ series, H-MOR, DNL-6, etc., as molecular sieve components. The selectivity of by-product alkanes is still as high as 20%~40%, and some catalysts have a methane selectivity exceeding 10%. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned problems in the prior art and provide a one-step synthesis gas method for producing low-carbon olefins, with a selectivity of over 85% for low-carbon olefins (ethylene, propylene, and butene), and exhibiting high stability during the reaction process, showing good prospects for industrial application.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for one-step synthesis of low-carbon olefins from syngas, using a catalyst comprising a metal oxide and an AlPO-34 molecular sieve (denoted as Me-AlPO-34), which are mixed by a physical means;

[0007] The metal oxide is ZnAlO x ZnGaO x ZnCrO x ZnCrAlOx ZnCrMnO x ZnCrGaO x At least one of spinel;

[0008] The AlPO-34 molecular sieve is a nanosheet-like metal isomorphous AlPO-34 molecular sieve with a relatively regular nanosheet morphology and a b-axis thickness of 10–100 nm.

[0009] In this invention, the isomorphically substituted metal element is at least one of Ba, W, Ca, Ce, Y, Ga, Ge, La, Mg, and Sr.

[0010] The weight ratio of AlPO-34 molecular sieve to metal oxide is 0.1~10, preferably 0.5~5.

[0011] The molar ratio of Al to P in the AlPO-34 molecular sieve is 0.5 to 2.0, and the molar ratio of the isomorphously substituted metal element to P is 0.01 to 1.0.

[0012] The preparation of the AlPO-34 molecular sieve includes the following steps:

[0013] 1) Add aluminum source, precursor containing metal element, phosphorus source, template agent, and crystal inhibitor to water and stir evenly, then age;

[0014] 2) Transfer the mixture obtained in step 1) into a reaction vessel for crystallization;

[0015] 3) The product obtained from the crystallization reaction is first pretreated with EDTA-2Na solution, then washed by centrifugation until the conductivity of the supernatant is lower than a certain value, and then dried.

[0016] 4) The product obtained in step 3) is calcined to obtain the AlPO-34 molecular sieve.

[0017] In step 1), the aluminum source is at least one of aluminum isopropoxide, aluminum hydroxide, boehmite, aluminum nitrate, or aluminum sulfate; the metal-containing precursor is at least one of nitrate, acetate, sulfate, oxide, halide, hydroxide, or ammonium salt containing a metal element.

[0018] In step 1), the template agent is at least one of triethylamine, tetraethylammonium hydroxide, or diisopropylethylamine; the phosphorus source is phosphoric acid; and the crystal inhibitor is at least one of urea, ethyl acetate, polyethylene glycol, or poloxamer.

[0019] The molar ratio of the template agent to the phosphorus source is 0.5~2.0, and the molar ratio of the crystal inhibitor to the phosphorus source is 0.01~0.05.

[0020] In step 1), the aging is carried out by stirring at 30~80℃ for 3~12 h; in step 2), the crystallization is carried out in a reactor at 160~220℃ for 12~144 h; in step 3), the drying is carried out at 80~150℃ for 8~48 h.

[0021] In step 3), the pretreatment involves mixing the solid product with a 0.005~0.5 mol / L EDTA-2Na solution and stirring at 40~100℃ for 1~60 minutes; the conductivity of the supernatant after centrifugation and washing of the product must be ≤10 µS / cm.

[0022] In step 4), the calcination is carried out at 450~650℃ for 2~6 hours.

[0023] In this invention, the Me-AlPO-34 molecular sieve is prepared by in-situ hydrothermal growth. Other metal ions are added to the initial gel of molecular sieve synthesis, and the molecular sieve prepared by this process is a metal isomorphously substituted AlPO-34 molecular sieve.

[0024] Furthermore, the one-step synthesis process for producing low-carbon olefins from syngas in this invention uses syngas as a reactant and catalytically converts it into low-carbon olefins in a fixed bed or moving bed. The reaction pressure is 0.5~10 MPa, preferably 2~8 MPa; the reaction temperature is 300~600℃, preferably 360~460℃; and the reaction space velocity is 500~10000 mL·g. -1 ·h -1 The preferred concentration is 1000~6000 mL·g -1 ·h -1 The syngas is a mixture of H2 and CO, with an H2 / CO volume ratio of 0.5 to 5, preferably 1 to 4; the syngas may also contain CH4, with a CH4 molar concentration of 0 to 10%; the syngas may also contain CO2, with a CO2 molar concentration of 0 to 10%; the syngas may also contain N2, with an N2 molar concentration of 0 to 10%.

[0025] In the above catalytic reactions, the selectivity of low-carbon olefins (ethylene, propylene and butene) reaches more than 85%, and the reactions exhibit high stability, showing great promise for industrial development and application.

[0026] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0027] 1) In this invention, Me-AlPO-34 molecular sieve and metal oxide are combined to form a bifunctional catalyst. In the one-step synthesis of low-carbon olefins from syngas, the selectivity of low-carbon olefins can exceed 85%, showing excellent catalytic performance. Moreover, the catalyst has high stability and is easy to scale up, and has good prospects for industrial development and application.

[0028] 2) The synthesis process of Me-AlPO-34 molecular sieve of the present invention effectively controls the crystal growth of molecular sieve in the b-axis direction by adding crystal inhibitors to the raw materials, and prepares a thin-film molecular sieve. This facilitates the rapid passage of products through the molecular sieve channels, inhibits the occurrence of side reactions, achieves highly selective synthesis of low-carbon olefins, and avoids the chain growth of carbon species in the molecular sieve channels to form carbon deposits, thereby extending the catalyst life.

[0029] 3) In this invention, the solid product after molecular sieve crystallization is treated with EDTA-2Na solution and repeatedly washed with pure water until the conductivity is low. This can effectively remove the template agent, heteroatoms and other substances remaining in the crystal phase, reduce the lattice defects of the molecular sieve framework and the blockage of substances in the pores, improve the structural integrity and stability of the molecular sieve at the molecular level, further improve the catalyst life, and achieve no deactivation phenomenon in catalytic reaction for 200 h. Attached Figure Description

[0030] Figure 1 SEM image of the prepared Mg-AlPO-34 molecular sieve;

[0031] Figure 2 XRD patterns of the prepared Mg-AlPO-34, Ca-AlPO-34, and La-AlPO-34 molecular sieves;

[0032] Figure 3 The graph shows the performance of the catalyst in Example 1 after 200 h of reaction.

[0033] Figure 4 The graph shows the performance of the catalyst in Comparative Example 1 after 100 h of reaction. Detailed Implementation

[0034] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer and more understandable, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments further illustrate the principles or features of this invention, but the scope of the claims is not limited to these embodiments. Furthermore, the embodiments only provide some conditions for achieving this objective, but do not imply that these conditions must be met to achieve this objective.

[0035] Example 1

[0036] Mg-AlPO-34 molecular sieve: Weigh 7.61 g of aluminum sulfate, 6.41 g of phosphoric acid (85wt%), 1.19 g of magnesium acetate, 12.28 g of tetraethylammonium hydroxide, and 33.36 g of polyethylene glycol, and add them one by one to a beaker containing 30 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, then stir and age at 50℃ for 10 h; transfer the above mixture to a 200 mL polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally crystallize at 180℃ for 96 h; after the material cools to room temperature, discard the upper liquid, and mix the lower solid product with 0.3 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 80℃ for 20 min, and wash repeatedly by centrifugation until the conductivity of the upper clear liquid is ≤10 µS / cm; dry the product at 150℃ for 8 hours. After h, the temperature was raised to 550℃ in a muffle furnace at a heating rate of 1℃ / min for 4 h, and the calcined product was Mg-AlPO-34 molecular sieve.

[0037] Figure 1 Here are SEM images of the prepared Mg-AlPO-34 molecular sieve, from... Figure 1 In diagram a), it can be seen that the molecular sieve exhibits a regular nanosheet morphology. Figure 1 As can be seen from b), the thickness of the b-axis is 10–100 nm. Figure 2 The XRD pattern of Mg-AlPO-34 molecular sieve shows that Mg-AlPO-34 molecular sieve has significant characteristic peaks of AlPO-34 molecular sieve.

[0038] Weigh out Mg-AlPO-34 molecular sieve powder and ZnGaO in a weight ratio of 2:1. x Metal oxide powder is ground evenly in a mortar, pressed into tablets, and then crushed into 30-60 mesh particles to obtain catalyst #1.

[0039] Catalyst #1 was evaluated using a fixed-bed reactor. The reaction conditions were: syngas H2 / CO = 2.5, pressure 5.0 MPa, and temperature 420℃. The product was split by the insulation system and sent to a gas chromatograph for online detection and analysis.

[0040] Figure 3 The performance of the catalyst was demonstrated after 200 h of reaction.

[0041] Example 2

[0042] Ge-AlPO-34 molecular sieve: Weigh 6.50 g of aluminum hydroxide, 10.67 g of phosphoric acid (85wt%), 1.32 g of germanium oxide, 11.71 g of triethylamine, and 1.67 g of urea, and add them one by one to a beaker containing 50 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, then stir and age at 40 °C for 8 h; transfer the above mixture to a 200 mL polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally crystallize at 180 °C for 96 h; after the material cools to room temperature, discard the upper liquid, and mix the lower solid product with 0.12 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 60 °C for 15 min, and wash repeatedly by centrifugation until the conductivity of the upper clear liquid is ≤10 µS / cm; after drying the product at 100 °C for 20 h, calcine it in a muffle furnace at a heating rate of 1 °C / min to 600 °C for 4 h. h, the calcination product is Ge-AlPO-34 molecular sieve.

[0043] Ge-AlPO-34 molecular sieve and ZnAlO x The metal oxides are each pressed into 30-60 mesh particles, and then the above materials are weighed and mixed evenly at a weight ratio of 1:1 to obtain catalyst #2.

[0044] Catalyst #2 was evaluated using a fixed-bed reactor. 2 g of catalyst #2 was weighed, and the air in the reactor was first replaced with N2. Then, under a 20% H2 + Ar atmosphere and normal pressure, the temperature was raised to 350℃ and held for 2 h. The reactor was then switched to syngas (H2 / CO = 2.5) and pressurized to 6.0 MPa, with the temperature adjusted to 410℃. The product was split from the heat-preservation system and analyzed online by gas chromatography.

[0045] Example 3

[0046] La-AlPO-34 molecular sieve: Weigh 20.85 g of aluminum nitrate nonahydrate, 6.41 g of phosphoric acid (85wt%), 0.45 g of lanthanum oxide, 5.62 g of triethylamine, and 1.47 g of ethyl acetate, and add them one by one to a beaker containing 25 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, then stir and age at 80 °C for 10 h; transfer the above mixture to a 200 mL polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally crystallize at 180 °C for 96 h; after the material cools to room temperature, discard the upper liquid, and mix the lower solid product with 0.18 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 60 °C for 30 min, and wash repeatedly by centrifugation until the conductivity of the upper clear liquid is ≤10 µS / cm; after drying the product at 120 °C for 10 h, calcine it in a muffle furnace at a heating rate of 1 °C / min to 550 °C for 5 h. h, the calcination product is La-AlPO-34 molecular sieve. Figure 2 The XRD pattern of the La-AlPO-34 molecular sieve shows that it exhibits significant characteristic peaks of AlPO-34 molecular sieve.

[0047] La-AlPO-34 molecular sieve and ZnCrAlO x The metal oxides are each pressed into 30-60 mesh particles, and then the above materials are weighed and mixed evenly at a weight ratio of 3:1 to obtain catalyst #3.

[0048] Catalyst #3 was evaluated using a fixed-bed reactor. 2 g of catalyst #3 was weighed, and the air in the reactor was first replaced with N2. Then, under a 20% H2 + Ar atmosphere and normal pressure, the temperature was raised to 350℃ and maintained for 2 h. The reactor was then switched to syngas (H2 / CO = 2.5) and pressurized to 4.0 MPa, with the temperature adjusted to 400℃. The product was split from the heat preservation system and analyzed online by gas chromatography.

[0049] Example 4

[0050] W-AlPO-34 molecular sieve: Weigh 6.94 g of aluminum hydroxide, 10.26 g of phosphoric acid (85wt%), 1.20 g of ammonium tungstate, 13.10 g of tetraethylammonium hydroxide, and 44.48 g of polyethylene glycol, and add them one by one to a beaker containing 40 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, then stir and age at 80℃ for 12 h; transfer the above mixture to a 200 mL polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally crystallize at 200℃ for 72 h; after the material cools to room temperature, discard the upper liquid, and mix the lower solid product with 0.35 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 80℃ for 40 min, and wash repeatedly by centrifugation until the conductivity of the upper clear liquid is ≤10 µS / cm; dry the product at 150℃ for 6 hours. After h, the temperature was raised to 550℃ in a muffle furnace at a heating rate of 1℃ / min for 6 h, and the calcined product was W-AlPO-34 molecular sieve.

[0051] Weigh out W-AlPO-34 molecular sieve powder and ZnCrMnO in a weight ratio of 1:1. x Metal oxide powder is ground evenly in a mortar, pressed into tablets, and then crushed into 30-60 mesh particles to obtain catalyst #4.

[0052] Catalyst #4 was evaluated using a fixed-bed reactor. 2 g of catalyst #4 was weighed, and the air in the reactor was first replaced with N2. Then, under a 20% H2 + Ar atmosphere and normal pressure, the temperature was raised to 350℃ and maintained for 2 h. The reactor was then switched to syngas (H2 / CO = 2.5) and pressurized to 5.0 MPa, with the temperature adjusted to 420℃. The product was split from the heat preservation system and analyzed online by gas chromatography.

[0053] Example 5

[0054] Ca-AlPO-34 molecular sieve: Weigh 15.32 g of aluminum isopropoxide, 9.61 g of phosphoric acid (85wt%), 1.97 g of calcium nitrate tetrahydrate, 15.34 g of tetraethylammonium hydroxide, and 1.50 g of urea, and add them one by one to a beaker containing 45 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, then stir and age at 40℃ for 8 h; transfer the above mixture to a 200 mL polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally crystallize at 200℃ for 72 h; after the material cools to room temperature, discard the upper liquid, and mix the lower solid product with 0.05 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 60℃ for 10 min, and wash repeatedly by centrifugation until the conductivity of the upper clear liquid is ≤10 µS / cm; dry the product at 120℃ for 8 h. After h, the temperature was raised to 600℃ in a muffle furnace at a heating rate of 1℃ / min for 4 h, and the calcined product was Ca-AlPO-34 molecular sieve. Figure 2 The XRD pattern of Ca-AlPO-34 molecular sieve shows that Ca-AlPO-34 molecular sieve has significant characteristic peaks of AlPO-34 molecular sieve.

[0055] Weigh out Ca-AlPO-34 molecular sieve powder and ZnGaO in a weight ratio of 1:1. x Metal oxide powder is ground evenly in a mortar, pressed into tablets, and then crushed into 30-60 mesh particles to obtain catalyst #5.

[0056] Catalyst #5 was evaluated using a fixed-bed reactor. 2 g of catalyst #5 was weighed, and the air in the reactor was first replaced with N2. Then, under a 20% H2 + Ar atmosphere and normal pressure, the temperature was raised to 350℃ and held for 2 h. The reactor was then switched to syngas (H2 / CO = 2.5) and pressurized to 4.5 MPa, with the temperature adjusted to 430℃. The product was split from the heat-preservation system and analyzed online by gas chromatography.

[0057] Examples 6 and 7

[0058] Y-AlPO-34 molecular sieve: Weigh 8.10 g of boehmite, 12.82 g of phosphoric acid (85wt%), 4.26 g of yttrium nitrate hexahydrate, 12.38 g of triethylamine, and 16.68 g of poloxamer, and add them one by one to a beaker containing 50 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, then age at 60 °C for 8 h; transfer the above mixture to a 200 mL polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally crystallize at 160 °C for 144 h; after the material cools to room temperature, discard the upper liquid, and mix the lower solid product with 0.4 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 80 °C for 5 min, and wash repeatedly by centrifugation until the conductivity of the upper clear liquid is ≤10 µS / cm; dry the product at 120 °C for 12 hours. After h, the temperature was raised to 550℃ in a muffle furnace at a heating rate of 1℃ / min for 5 h, and the calcined product was Y-AlPO-34 molecular sieve.

[0059] Y-AlPO-34 molecular sieve and ZnGaO x The metal oxides are each pressed into 30-60 mesh particles, and then the above materials are weighed and mixed evenly at a weight ratio of 2:1 to obtain catalyst No. 6.

[0060] Y-AlPO-34 molecular sieve powder and ZnCrO x Metal oxide powders were mixed at a weight ratio of 2:1, ground evenly in a mortar, pressed into tablets, and then crushed into 30-60 mesh particles to obtain catalyst #7.

[0061] Catalysts #6 and #7 were evaluated for their catalytic performance using a fixed-bed reactor. Two g of each catalyst were weighed, and the air in the reactor was first replaced with N2. Then, under a 20% H2 + Ar atmosphere and normal pressure, the temperature was raised to 350℃ and maintained for 2 h. The reactor was then switched to syngas (H2 / CO = 2.5) and pressurized to 6.0 MPa, with the temperature adjusted to 420℃. The product was split from the heat-preservation system and analyzed online by gas chromatography.

[0062] Examples 8 and 9

[0063] When using the No. 1 catalyst prepared in Example 1 to evaluate its catalytic performance in a fixed-bed reactor, other evaluation conditions remained unchanged, but the syngas was used with H2 / CO=2.0 for catalyst performance evaluation, which is recorded as Example 8.

[0064] Similar to Example 8, the performance of the catalyst was evaluated using syngas with an H2 / CO ratio of 4.0, and this is referred to as Example 9.

[0065] Comparative Examples 1, 2, and 3

[0066] Comparative examples 1#, 2#, and 3# were prepared for comparison in catalytic performance experiments. The only difference between the comparative examples 1#, 2#, and 3# and the catalysts in Examples 1#, 2#, and 3# is that the molecular sieve component in the comparative examples 1#, 2#, and 3# is commercially available AlPO-34 molecular sieve purchased from the catalyst factory of Nankai University. The evaluation conditions for the comparative catalysts were consistent with those in the Examples. Figure 4 The performance of catalyst #1 was demonstrated after 100 h of reaction.

[0067] Comparative Example 4

[0068] Comparative Example 4# was prepared for comparison in catalytic performance experiments. The difference between Comparative Example 4# and Example 1 is that magnesium acetate was not added during the synthesis of the molecular sieve in Comparative Example 4#, meaning that a non-metallic isomorphously substituted AlPO-34 molecular sieve was synthesized first. The calcined AlPO-34 molecular sieve was treated with 6 mL of an aqueous solution containing 1.19 g of magnesium acetate through multiple equal-volume impregnations (after each impregnation, it was dried under vacuum at 80°C for 4 h) to finally obtain a Mg-supported AlPO-34 molecular sieve. The above-mentioned supported molecular sieve was compared with ZnGaO. x Metal oxide powder was weighed at a weight ratio of 2:1, ground evenly in a mortar, compressed into tablets, and then crushed into 30-60 mesh particles to obtain the No. 4 comparative catalyst. The catalyst evaluation conditions were consistent with those in Example 1.

[0069] The catalytic reaction processes of the above embodiments and comparative examples are one-step synthesis of low-carbon olefins from syngas. Table 1 lists the specific applications of the catalysts and their performance data after 100 h of catalytic reaction.

[0070] Table 1

[0071]

[0072] Under the same catalytic reaction conditions, the reaction results of catalysts 1#, 2#, and 3# compared with those of catalysts 1#, 2#, and 3# show that the metal isomorphous AlPO-34 molecular sieve described in this invention exhibits excellent performance in improving the selectivity of the catalytic reaction, and the overall stability of the catalyst is also significantly improved.

[0073] Taking catalyst #1 and comparative example #1 as examples: After 100 h of reaction, the CO conversion rate of comparative example #1 was 27%, and the selectivity for low-carbon olefins was 73%; after 100 h of reaction, catalyst #1 showed a CO conversion rate of 42%, an increase of 15% compared to comparative example #1; and a low-carbon olefin selectivity of 86%, an increase of 13% compared to comparative example #1. The reaction results of comparative example #1 and catalyst #1 indicate that the isomorphous substitution of AlPO-34 molecular sieve described in this invention can improve the overall catalytic performance of the catalyst. Furthermore, the CO conversion rate and low-carbon olefin selectivity of comparative example #1 showed a slow decreasing trend with the progress of the reaction, while the selectivity of the byproduct methane showed a gradual increasing trend; catalyst #1 maintained a stable state of the above catalytic indicators within 200 h of reaction, indicating that the isomorphous substitution of AlPO-34 molecular sieve described in this invention also performs excellently in improving the overall stability of the catalyst. Moreover, the above-mentioned changes in catalytic performance were also observed in other catalysts and their comparative examples.

[0074] Catalysts #1, #5, and #7 all used the same metal oxide, but were paired with different Me-AlPO-34 molecular sieves. The reaction results show that AlPO-34 molecular sieves with different isomorphous metal substitutions all exhibited high selectivity for low-carbon olefins.

[0075] Both catalysts #6 and #7 use Y-AlPO-34 molecular sieves, but with different metal oxides. Under the same reaction conditions, the test results show that the matching between the molecular sieve and the metal oxide is also crucial, directly affecting the CO conversion rate and the selectivity for low-carbon olefins.

[0076] Examples 1, 8, and 9 used the same catalyst, but varied the hydrogen-to-carbon ratio of the feed gas under identical catalytic evaluation conditions. Data from 100 h of reaction showed that superior selectivity for low-carbon olefins was achieved with different feed gas compositions, demonstrating that isomorphously substituted AlPO-34 molecular sieves exhibit excellent performance in the synthesis of low-carbon olefins from syngas.

[0077] The results from Example 1 and Comparative Example 4 show that the in-situ addition of metals to isomorphically replace Al or P in the molecular sieve framework, compared with the later loading of metals onto the surface or pores of the molecular sieve by impregnation, results in a greater selectivity for low-carbon olefins in the one-step synthesis of syngas.

[0078] In summary, this invention develops a metal isomorphously substituted AlPO-34 molecular sieve with a nanosheet morphology through in-situ hydrothermal growth. This molecular sieve is then combined with metal oxides via physical mixing to form a catalyst. The catalyst exhibits high selectivity and high stability in the one-step synthesis of low-carbon olefins from syngas. Compared with existing commercial molecular sieves of the same type, the molecular sieve prepared by this invention shows significant improvements in CO conversion and low-carbon olefin selectivity. In particular, the low-carbon olefin selectivity can reach over 85%, and the overall stability of the catalyst is significantly better than that of commercial molecular sieves.

[0079] The terms and expressions used in this specification are for descriptive and not restrictive purposes only, and are not intended to exclude any equivalents of the features or components thereof represented and described.

[0080] Although several embodiments of the invention have been shown and described, the invention is not limited to the described embodiments. Rather, those skilled in the art will recognize that any modifications and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is determined by the appended claims and their equivalents.

Claims

1. A method for one-step synthesis of low-carbon olefins from syngas, characterized in that: Using syngas as a reactant, low-carbon olefins are prepared by catalytic conversion in a fixed-bed or moving-bed reactor. The reaction pressure is 0.5–10 MPa, the reaction temperature is 300–600 °C, and the reaction space velocity is 500–10000 mL·g. -1 ·h -1 The catalyst used includes metal oxides and AlPO-34 molecular sieves; the metal oxide is ZnAlO. x ZnGaO x ZnCrO x ZnCrAlO x ZnCrMnO x ZnCrGaO x At least one of spinel; the AlPO-34 molecular sieve is a nanosheet-like metal isomorphous substituted AlPO-34 molecular sieve with a b-axis thickness of 10-100 nm; the isomorphous substituted metal element is at least one of Ba, W, Ca, Ce, Y, Ga, Ge, La, Mg, and Sr; the molar ratio of Al to P in the AlPO-34 molecular sieve is 0.5-2.0, and the molar ratio of the isomorphous substituted metal element to P is 0.01-1.

0.

2. The method for one-step synthesis of low-carbon olefins from syngas as described in claim 1, characterized in that: The weight ratio of AlPO-34 molecular sieve to metal oxide is 0.1~10.

3. The method for one-step synthesis of low-carbon olefins from syngas as described in claim 1, characterized in that, The preparation of the AlPO-34 molecular sieve includes the following steps: 1) Add aluminum source, precursor containing metal element, phosphorus source, template agent, and crystal inhibitor to water and stir evenly, then age; 2) Transfer the mixture obtained in step 1) into a reaction vessel for crystallization; 3) The product obtained from the crystallization reaction is first pretreated with EDTA-2Na solution, then washed by centrifugation until the conductivity of the supernatant is lower than a certain value, and then dried. 4) The product obtained in step 3) is calcined to obtain the AlPO-34 molecular sieve.

4. The method for one-step synthesis of low-carbon olefins from syngas as described in claim 3, characterized in that: In step 1), the aluminum source is at least one of aluminum isopropoxide, aluminum hydroxide, boehmite, aluminum nitrate, or aluminum sulfate; the metal-containing precursor is at least one of nitrate, acetate, sulfate, oxide, halide, hydroxide, or ammonium salt containing a metal element.

5. The method for one-step synthesis of low-carbon olefins from syngas as described in claim 3, characterized in that: In step 1), the template agent is at least one of triethylamine, tetraethylammonium hydroxide, or diisopropylethylamine; the phosphorus source is phosphoric acid; and the crystal inhibitor is at least one of urea, ethyl acetate, polyethylene glycol, or poloxamer.

6. The method for one-step synthesis of low-carbon olefins from syngas as described in claim 3, characterized in that: The molar ratio of the template agent to the phosphorus source is 0.5~2.0, and the molar ratio of the crystal inhibitor to the phosphorus source is 0.01~0.

05.

7. A method for one-step synthesis of low-carbon olefins from syngas as described in claim 3, characterized in that: In step 1), the aging is carried out by stirring at 30~80℃ for 3~12 h; in step 2), the crystallization is carried out in a reactor at 160~220℃ for 12~144 h.

8. A method for one-step synthesis of low-carbon olefins from syngas as described in claim 3, characterized in that: In step 3), the pretreatment involves mixing the solid product with a 0.005~0.5 mol / L EDTA-2Na solution and stirring at 40~100℃ for 1~60 minutes; the conductivity of the supernatant after centrifugation and washing of the product must be ≤10 µS / cm.

9. A method for one-step synthesis of low-carbon olefins from syngas as described in claim 3, characterized in that: In step 4), the calcination is carried out at 450~650℃ for 2~6 hours.

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