Method for preparing low-carbon olefin from synthesis gas through one-step method

Abstract

The invention discloses a method for preparing low-carbon olefin from synthesis gas through a one-step method, and relates to the field of direct preparation of low-carbon olefin from synthesis gas, and an adopted catalyst comprises a metal oxide and an AlPO-34 molecular sieve; the metal oxide is at least one of ZnAlOx, ZnGaOx, ZnCrOx, ZnCrAlOx, ZnCrMnOx and ZnCrGaOx spinel, and the metal oxide is at least one of ZnAlOx, ZnGaOx, ZnCrOx, ZnCrAlOx and ZnCrGaOx spinel; the AlPO-34 molecular sieve is a nanosheet-shaped metal isomorphous substituted AlPO-34 molecular sieve, and the b-axis thickness of the AlPO-34 molecular sieve is 10-100 nm; the isomorphous substituted metal element is at least one of Ba, W, Ca, Ce, Y, Ga, Ge, La, Mg and Sr. According to the method, the synthesis gas is directly used for preparing the low-carbon olefin, the selectivity can reach 85% or above, high stability is shown in the reaction process, and the method has a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the field of direct preparation of light olefins from synthesis gas, and in particular to a method for preparing light olefins from synthesis gas in one step. Background Art

[0002] Light olefins (ethylene, propylene, butene) are the most important chemical raw materials. The current mainstream light olefin production route is the petrochemical route of petroleum light hydrocarbon cracking. It is a feasible solution to develop non-oil-based resources such as coal, natural gas, carbon dioxide, biomass, etc. as raw materials to produce synthesis gas, and then produce light olefins from synthesis gas. At present, the production of light olefins from synthesis gas mainly adopts the indirect process, that is, the synthesis gas is first used to produce methanol or dimethyl ether, and the methanol or dimethyl ether is then dehydrated to produce light olefins in two steps. The development of a one-step process for direct catalytic conversion of synthesis gas to produce light olefins can simplify the process, reduce project investment, and improve product economic benefits. It is a research hotspot in the current field of synthesis gas conversion.

[0003] Catalyst development is the research focus of the process technology for direct catalytic conversion of synthesis gas to light olefins. Currently, it mainly includes the following two types: one is the Fischer-Tropsch synthesis catalyst represented by iron / cobalt-based catalysts, which use metal iron / cobalt or their carbides as active components, but the reaction process follows the chain growth reaction mechanism of the metal surface, and the selectivity of light olefins is low, generally not exceeding 58% (light olefin selectivity refers to the selectivity of light olefins in organic products, the same below). The second is a bifunctional catalyst formed by oxide composite molecular sieves. The bifunctional or multifunctional composite catalysts reported so far, the molecular sieve components are mainly SAPO series, AlPO series, SSZ series, H-MOR, DNL-6, etc., the selectivity of by-product alkanes is still as high as 20%~40%, and the methane selectivity of some catalysts exceeds 10%. Summary of the invention

[0004] The purpose of the present invention is to solve the above-mentioned problems in the prior art and to provide a method for preparing light olefins from synthesis gas in one step. The selectivity of light olefins (ethylene, propylene and butene) can reach more than 85%, and the method exhibits high stability during the reaction, which has good industrial application prospects.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for preparing low-carbon olefins from synthesis gas in one step, wherein the catalyst used includes a metal oxide and an AlPO-34 molecular sieve (denoted as Me-AlPO-34), which are mixed in a physical manner;

[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 nano-sheet-shaped metal isomorphous substituted AlPO-34 molecular sieve having a relatively regular nano-sheet morphology and a b-axis thickness of 10 to 100 nm.

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

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

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

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

[0013] 1) adding an aluminum source, a precursor containing a metal element, a phosphorus source, a template agent, and a crystal inhibitor into water, stirring the mixture evenly, and aging the mixture;

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

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

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

[0017] In step 1), the aluminum source is at least one of aluminum isopropoxide, aluminum hydroxide, pseudo-boehmite, aluminum nitrate or aluminum sulfate; the metal element-containing precursor is at least one of nitrate, acetate, sulfate, oxide, halide, hydroxide or ammonium salt of the 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 to the P element in the phosphorus source is 0.5-2.0, and the molar ratio of the crystal inhibitor to the P element in the phosphorus source is 0.01-0.05.

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

[0021] In step 3), the pretreatment is to mix the solid product with 0.005-0.5 mol / L EDTA-2Na solution, and stir at 40-100°C for 1-60 minutes; the conductivity of the supernatant after centrifugal washing of the product needs to be ≤10 µS / cm.

[0022] In step 4), the calcination is performed at 450-650° C. for 2-6 h.

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

[0024] Furthermore, the one-step synthesis gas to light olefins process of the present invention uses synthesis gas as a reaction raw material, and catalytic conversion is carried out on a fixed bed or a moving bed to prepare light olefins, the reaction pressure is 0.5-10 MPa, preferably 2-8 MPa; the reaction temperature is 300-600°C, preferably 360-460°C; the reaction space velocity is 500-10000 mL·g -1 ·h -1 , preferably 1000~6000mL·g -1 ·h -1 The synthesis gas is H 2 and CO mixture, H 2 The volume ratio of / CO is 0.5-5, preferably 1-4; the synthesis gas may also contain CH 4 , CH 4 The molar concentration in the synthesis gas is 0-10%; the synthesis gas may also contain CO 2 , CO 2 The molar concentration in the synthesis gas is 0-10%; the synthesis gas may also contain N 2 , N 2 The molar concentration in the synthesis gas is 0~10%.

[0025] In the above-mentioned catalytic reaction, the selectivity of low-carbon olefins (ethylene, propylene and butene) reaches more than 85%, and it shows high stability during the reaction process, and has good prospects for industrial development and application.

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0027] 1) In the present invention, the Me-AlPO-34 molecular sieve is composited with a metal oxide to form a bifunctional catalyst. In the one-step process of preparing light olefins from synthesis gas, the selectivity of light olefins can exceed 85%, showing excellent catalytic performance. The catalyst has high stability and is easy to scale up and prepare, and has good industrial development and application prospects.

[0028] 2) The synthesis process of the Me-AlPO-34 molecular sieve of the present invention effectively controls the crystal growth of the molecular sieve in the b-axis direction by adding a crystal inhibitor to the raw material, and prepares a thin-flaky structure molecular sieve, which is conducive to the rapid passage of the product through the molecular sieve pores, inhibits the occurrence of side reactions, realizes the highly selective synthesis of light olefins, and also avoids the chain growth of carbon species in the molecular sieve pores to form carbon deposits, thereby extending the catalyst life.

[0029] 3) In the present invention, the solid product after crystallization of the molecular sieve is treated with EDTA-2Na solution and repeatedly washed with pure water until the conductivity is low, which 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 200 h of catalytic reaction without deactivation. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0032] Figure 3 This is the performance diagram of the catalyst in Example 1 after 200 h of reaction;

[0033] Figure 4 This is the performance diagram of the catalyst in Comparative Example 1 after 100 h of reaction. DETAILED DESCRIPTION

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The present invention further illustrates the principles or features of the present invention through embodiments, but the scope of the claims of the present invention is not limited by these embodiments. At the same time, the embodiments only provide some conditions for achieving this purpose, but do not mean that these conditions must be met to achieve this purpose.

[0035] Example 1

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

[0037] Figure 1 The SEM image of the prepared Mg-AlPO-34 molecular sieve is shown in Figure 2. Figure 1 In a), we can see that the molecular sieve presents a regular nanosheet morphology. Figure 1 ) in b), where the b-axis thickness is 10 to 100 nm. Figure 2 The XRD diagram of Mg-AlPO-34 molecular sieve is included, and it can be seen that Mg-AlPO-34 molecular sieve has significant characteristic peaks of AlPO-34 molecular sieve.

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

[0039] The catalytic performance of catalyst 1# was evaluated using a fixed bed reactor. The reaction conditions were synthesis gas H 2 / CO=2.5, pressure 5.0 MPa, temperature 420℃, the product is diverted from the insulation system into the gas chromatography online detection and analysis.

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

[0041] Example 2

[0042] Ge-AlPO-34 molecular sieve: weigh 6.50 g aluminum hydroxide, 10.67 g phosphoric acid (85wt%), 1.32 g germanium oxide, 11.71 g triethylamine, and 1.67 g urea, add them one by one in the above order into a beaker containing 50 mL pure water and stir evenly; stir at room temperature for 2 h, then stir and age at 40°C for 8 h; transfer the above mixed solution to a 200 mL polytetrafluoroethylene liner hydrothermal autoclave, and hydrothermally crystallize at 180°C for 96 h; after the material cools to room temperature, pour out the upper liquid, 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 it several times by centrifugal washing until the conductivity of the upper clear liquid is ≤10 µS / cm; dry the product at 100°C for 20 h, and heat it to 600°C in a muffle furnace at a heating rate of 1°C / min for 4 h. h, the calcined product is Ge-AlPO-34 molecular sieve.

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

[0044] The catalytic performance of catalyst 2# was evaluated using a fixed bed reactor. Weigh 2 g of catalyst 2# and first 2 The air in the reactor was replaced, and then the 2 +Ar atmosphere, heated to 350 °C under normal pressure and maintained for 2 h, then switched to synthesis gas (H 2 / CO=2.5) to 6.0 MPa, and the temperature was adjusted to 410° C. The product was diverted from the heat preservation system to the gas chromatography online detection and analysis.

[0045] Example 3

[0046] La-AlPO-34 molecular sieve: weigh 20.85 g aluminum nitrate nonahydrate, 6.41 g phosphoric acid (85wt%), 0.45 g lanthanum oxide, 5.62 g triethylamine, and 1.47 g ethyl acetate, add them one by one in the above order into a beaker containing 25 mL pure water and stir evenly; stir at room temperature for 2 h, then stir and age at 80°C for 10 h; transfer the above mixed solution to a 200 mL polytetrafluoroethylene liner hydrothermal autoclave and hydrothermally crystallize at 180°C for 96 h; after the material cools to room temperature, pour out the upper liquid, 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 it several times by centrifugal washing until the conductivity of the upper clear liquid is ≤10 µS / cm; after the product is dried at 120°C for 10 h, heat it to 550°C in a muffle furnace at a heating rate of 1°C / min for 5 h, and then calcine it at 1000 °C for 10 h. h, the calcined product is La-AlPO-34 molecular sieve. Figure 2 The XRD diagram of La-AlPO-34 molecular sieve is included, and it can be seen that La-AlPO-34 molecular sieve has obvious characteristic peaks of AlPO-34 molecular sieve.

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

[0048] The catalytic performance of catalyst 3# was evaluated using a fixed bed reactor. Weigh 2 g of catalyst 3# and first 2 The air in the reactor was replaced, and then the 2 +Ar atmosphere, heated to 350 °C under normal pressure and maintained for 2 h, then switched to synthesis gas (H 2 / CO=2.5) to 4.0 MPa, and the temperature was adjusted to 400° C. The product was diverted from the heat preservation system to the gas chromatography online detection and analysis.

[0049] Example 4

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

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

[0052] The catalytic performance of catalyst 4# was evaluated using a fixed bed reactor. Weigh 2 g of catalyst 4# and first 2 The air in the reactor was replaced, and then the 2 +Ar atmosphere, heated to 350 °C under normal pressure and maintained for 2 h, then switched to synthesis gas (H 2 / CO=2.5) to 5.0 MPa, and the temperature was adjusted to 420° C. The product was diverted from the insulation system to the gas chromatography online detection and analysis.

[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, add them one by one in the above order into a beaker containing 45 mL of pure water and stir evenly; stir at room temperature for 2 h, and then stir and age at 40°C for 8 h; transfer the above mixed solution to a 200 mL polytetrafluoroethylene liner hydrothermal autoclave, and hydrothermally crystallize at 200°C for 72 h; after the material cools to room temperature, pour out the upper liquid, mix the lower solid product with 0.05 mol / L EDTA-2Na solution at a weight ratio of 1:20, stir at 60°C for 10 min, and wash several times by centrifugal washing until the conductivity of the upper clear liquid is ≤10 µS / cm; dry the product at 120°C for 8 h later, the temperature was raised to 600 °C in a muffle furnace at a heating rate of 1 °C / min and calcined for 4 h. The calcined product was Ca-AlPO-34 molecular sieve. Figure 2 The XRD diagram of Ca-AlPO-34 molecular sieve is included, and it can be seen that Ca-AlPO-34 molecular sieve has significant characteristic peaks of AlPO-34 molecular sieve.

[0055] Weigh Ca-AlPO-34 molecular sieve powder and ZnGaO x The metal oxide powder is placed in a mortar and ground evenly, then pressed into tablets, and then crushed into 30-60 mesh particles to obtain 5# catalyst.

[0056] The catalytic performance of catalyst 5# was evaluated using a fixed bed reactor. Weigh 2 g of catalyst 5# and first 2 The air in the reactor was replaced, and then the 2 +Ar atmosphere, heated to 350 °C under normal pressure and maintained for 2 h, then switched to synthesis gas (H 2 / CO=2.5) to 4.5 MPa, and the temperature was adjusted to 430° C. The product was diverted from the heat preservation system to the gas chromatography online detection and analysis.

[0057] Embodiment 6, 7

[0058] Y-AlPO-34 molecular sieve: Weigh 8.10 g of pseudo-boehmite, 12.82 g of phosphoric acid (85 wt%), 4.26 g of yttrium nitrate hexahydrate, 12.38 g of triethylamine, and 16.68 g of poloxamer, add them one by one into a beaker containing 50 mL of pure water in the above order and stir evenly; stir at room temperature for 2 h, and then stir and age at 60 ° C for 8 h; transfer the above mixed solution to a 200 mL polytetrafluoroethylene liner hydrothermal autoclave and hydrothermally crystallize at 160 ° C for 144 h; after the material cools to room temperature, pour out the upper liquid, 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 it several times by centrifugal washing until the conductivity of the upper clear liquid is ≤10 µS / cm; the product is dried at 120 ° C for 12 h later, the temperature was raised to 550 °C in a muffle furnace at a heating rate of 1 °C / min and calcined for 5 h. The calcined product was Y-AlPO-34 molecular sieve.

[0059] Y-AlPO-34 molecular sieve and ZnGaO x The metal oxides are individually tableted to form 30-60 mesh particles, and then the above materials are weighed and mixed evenly in a weight ratio of 2:1 to obtain a 6# catalyst.

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

[0061] The catalytic performance of 6# and 7# catalysts was evaluated using a fixed bed reactor. Weigh 2 g of 6# and 7# catalysts and first 2 The air in the reactor was replaced, and then the 2 +Ar atmosphere, heated to 350 °C under normal pressure and maintained for 2 h, then switched to synthesis gas (H 2 / CO=2.5) to 6.0 MPa, and the temperature was adjusted to 420° C. The product was diverted from the heat preservation system to the gas chromatography online detection and analysis.

[0062] Embodiment 8, 9

[0063] When the catalytic performance of catalyst No. 1 prepared in Example 1 was evaluated in a fixed bed reactor, other evaluation conditions remained unchanged, but the synthesis gas was H 2 The performance of the catalyst was evaluated at / CO=2.0, which is recorded as Example 8.

[0064] Same as in Example 8, the synthesis gas used was H 2 The performance of the catalyst was evaluated at 40 °C / CO = 4.0, which is recorded as Example 9.

[0065] Comparative Examples 1, 2, and 3

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

[0067] Comparative Example 4

[0068] Comparative Example 4# was prepared as a comparison for the catalytic performance experiment. The difference between Comparative Example 4# and Example 1 is that the molecular sieve in Comparative Example 4# was not added with magnesium acetate during the synthesis process, that is, the AlPO-34 molecular sieve without metal isomorphous substitution was synthesized first. The above-mentioned calcined AlPO-34 molecular sieve was treated by multiple equal volume impregnations using 6 mL of an aqueous solution containing 1.19 g of magnesium acetate (after each impregnation, it was dried at 80°C and vacuum dried for 4 h), and finally the AlPO-34 molecular sieve loaded with metal Mg was obtained. The above-mentioned loaded molecular sieve was mixed with ZnGaO x Metal oxide powder was weighed at a weight ratio of 2:1, placed in a mortar and ground evenly, pressed into tablets, and then crushed into 30-60 mesh particles to obtain a 4# comparative catalyst. The catalyst evaluation conditions were the same as those in Example 1.

[0069] The catalytic reaction process of the above-mentioned embodiments and comparative examples is a one-step process for preparing light olefins from synthesis gas. Table 1 lists the specific applications of the catalysts and their performance data when the catalytic reaction is carried out for 100 h.

[0070] Table 1

[0071]

[0072] Under the same catalytic reaction conditions, it can be seen from the reaction results of 1#, 2#, 3# catalysts and 1#, 2#, 3# comparative examples that the metal isomorphously substituted AlPO-34 molecular sieve of the present invention performs excellently in improving the selectivity of the catalytic reaction, and the overall stability of the catalyst is also significantly improved.

[0073] Take 1# catalyst and 1# comparative example as examples: when the reaction of 1# comparative example was carried out for 100 hours, the CO conversion rate was 27% and the selectivity of light olefins was 73%; when the reaction of 1# catalyst was carried out for 100 hours, the CO conversion rate was 42%, which was 15% higher than that of 1# comparative example; the selectivity of light olefins was 86%, which was 13% higher than that of 1# comparative example. The reaction results of 1# comparative example and 1# catalyst show that the metal isomorphous substitution of AlPO-34 molecular sieve of the present invention can improve the overall catalytic performance of the catalyst. In addition, the CO conversion rate and light olefin selectivity of 1# comparative example show a slow downward trend as the reaction proceeds, while the selectivity of by-product methane shows a gradual upward trend; as the reaction of 1# catalyst proceeds, the above catalytic indicators can maintain a stable trend within 200 hours of reaction, indicating that the metal isomorphous substitution of AlPO-34 molecular sieve of the present invention also performs well in improving the overall stability of the catalyst. In addition, the above-mentioned change in catalytic performance is reflected in other catalysts and their comparative examples.

[0074] Catalysts 1#, 5#, and 7# use the same metal oxide with different Me-AlPO-34 molecular sieves. From the reaction results, it can be seen that AlPO-34 molecular sieves with different metal isomorphous substitutions can all show higher selectivity for light olefins.

[0075] Catalyst 6# and catalyst 7# both use Y-AlPO-34 molecular sieve, but use different metal oxides. Under the same reaction conditions, the test results show that the matching between molecular sieve and metal oxide is also crucial, which directly affects the CO conversion rate and the selectivity of light olefins.

[0076] Example 1, Example 8 and Example 9 use the same catalyst, and under the same catalytic evaluation conditions, the hydrogen-to-carbon ratio of the feed gas is changed. From the result data of the reaction for 100 h, it can be seen that better selectivity for light olefins can be obtained under different feed gas compositions, indicating that the metal isomorphously substituted AlPO-34 molecular sieve has excellent performance in preparing light olefins from syngas.

[0077] It can be seen from the results of Example 1 and Comparative Example 4 that the isomorphous substitution of Al or P in the molecular sieve framework by in-situ addition of metals is more advantageous in the selectivity of light olefins in the one-step synthesis gas to light olefin reaction than loading the metals on the molecular sieve surface or in the pores by impregnation at a later stage.

[0078] In summary, the present invention has developed a metal isomorphously substituted AlPO-34 molecular sieve with a nano-flake morphology through an in-situ hydrothermal growth method. The molecular sieve is physically mixed with a metal oxide to form a catalyst, and the catalyst exhibits high selectivity and high stability in the one-step synthesis gas to light olefin reaction. Compared with the existing commercial molecular sieves of the same type, the molecular sieve prepared by the present invention has significantly improved CO conversion rate, light olefin selectivity, etc. In particular, the light olefin selectivity can reach more than 85%, and the overall stability of the catalyst is significantly better than that of the commercial molecular sieve.

[0079] The terms and expressions used in this specification are used as terms and expressions of description only and not of limitation, and there is no intention in the use of these terms and expressions to exclude any equivalents of the features represented and described or their components.

[0080] Although several embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. On the contrary, those skilled in the art should be aware that any modifications and improvements can be made to these embodiments without departing from the principles and spirit of the present invention, and the protection scope of the present invention is determined by the attached claims and their equivalents.

Claims

1. A method for preparing light olefins from synthesis gas in one step, characterized in that: Synthesis gas is used as the reaction raw material to catalytically convert light olefins on a fixed bed or moving bed. The reaction pressure is 0.5~10 MPa, the reaction temperature is 300~600℃, and the reaction space velocity is 500~10000 mL·g -1 ·h -1 The catalyst used includes metal oxide and AlPO-34 molecular sieve; the metal oxide is ZnAlO x 、ZnGaO x 、ZnCrO x 、ZnCrAlO x 、ZnCrMnO x 、ZnCrGaO x At least one of spinels; the AlPO-34 molecular sieve is a nano-sheet metal isomorphously substituted AlPO-34 molecular sieve with a b-axis thickness of 10 to 100 nm; the isomorphously substituted metal element is at least one of Ba, W, Ca, Ce, Y, Ga, Ge, La, Mg, and Sr.

2. The method for preparing light olefins from synthesis gas in one step according to claim 1, characterized in that: The weight ratio of the AlPO-34 molecular sieve to the metal oxide is 0.1-10.

3. The method for preparing light olefins from synthesis gas in one step according to claim 1, characterized in that: The molar ratio of Al element to P element in the AlPO-34 molecular sieve is 0.5-2.0, and the molar ratio of the isomorphously substituted metal element to the P element is 0.01-1.

0.

4. The method for preparing light olefins from synthesis gas in one step according to claim 1, characterized in that: The preparation of the AlPO-34 molecular sieve comprises the following steps: 1) adding an aluminum source, a precursor containing a metal element, a phosphorus source, a template agent, and a crystal inhibitor into water, stirring the mixture evenly, and aging the mixture; 2) transferring the mixture obtained in step 1) into a reaction vessel for crystallization; 3) The product obtained by the crystallization reaction is pretreated with an EDTA-2Na solution, then centrifuged and washed until the conductivity of the supernatant is lower than a certain value, and then dried; 4) Calcine the product obtained in step 3) to obtain the AlPO-34 molecular sieve.

5. The method for preparing light olefins from synthesis gas in one step according to claim 4, characterized in that: In step 1), the aluminum source is at least one of aluminum isopropoxide, aluminum hydroxide, pseudo-boehmite, aluminum nitrate or aluminum sulfate; the metal element-containing precursor is at least one of nitrate, acetate, sulfate, oxide, halide, hydroxide or ammonium salt of the metal element.

6. The method for preparing light olefins from synthesis gas in one step according to claim 4, 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.

7. The method for preparing light olefins from synthesis gas in one step according to claim 4, characterized in that: The molar ratio of the template agent to the P element in the phosphorus source is 0.5-2.0, and the molar ratio of the crystal inhibitor to the P element in the phosphorus source is 0.01-0.

05.

8. The method for preparing light olefins from synthesis gas in one step according to claim 4, characterized in that: In step 1), the aging is carried out by stirring at 30-80° C. for 3-12 h; in step 2), the crystallization is carried out in a reactor at 160-220° C. for 12-144 h.

9. The method for preparing light olefins from synthesis gas in one step according to claim 4, characterized in that: In step 3), the pretreatment is to mix the solid product with 0.005-0.5 mol / L EDTA-2Na solution, and stir at 40-100°C for 1-60 minutes; the conductivity of the supernatant after centrifugal washing of the product needs to be ≤10 µS / cm.

10. The method for preparing light olefins from synthesis gas in one step according to claim 4, characterized in that: In step 4), the calcination is performed at 450-650° C. for 2-6 h.

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