A method and system for the production of propylene from synthesis gas

Abstract

This invention belongs to the field of syngas-to-olefins technology, specifically relating to a method and system for converting syngas into propylene. After being mixed in a feedstock mixing tank, the feedstock gas first enters the first reaction unit, where it is converted into a product gas rich in propane. The product gas then enters a No. 1 separation unit for separation; unreacted syngas is returned to the feedstock mixing tank, while the separated propane gas enters the second reaction unit for alkane dehydrogenation, generating a propylene-rich product gas. The product gas then enters a No. 2 separation unit, where unreacted propane is returned to the propane dehydrogenation system, and the hydrogen generated from propane dehydrogenation is returned to the feedstock mixing tank, ultimately yielding high-purity propylene. Compared to the traditional process of producing propylene from syngas via methanol, this invention offers advantages such as a shorter process flow, lower energy consumption, and higher propylene selectivity.

Description

Technical Field

[0001] This invention belongs to the field of syngas-to-olefins technology, specifically relating to a method and system for the conversion of syngas to produce propylene. Background Technology

[0002] Propylene (C3H6) is one of the core raw materials of modern industry, mainly used in the production of polypropylene (PP), acrylonitrile, propylene oxide, cumene, etc., and widely used in plastics, fibers, rubber, coatings, pharmaceuticals and other fields. Global demand for propylene has maintained rapid growth for a long time, and traditional petroleum routes can no longer meet the demand. Converting coal into syngas and then producing propylene from syngas can realize the production of propylene from non-petroleum resources such as coal. Among these, the Fischer-Tropsch synthesis of olefins from syngas and the methanol-to-olefins (MTO) technology are relatively mature. The former has the problems of a wide carbon number distribution of the product and low propylene selectivity, while the latter requires methanol as an intermediate, resulting in a long process flow, high energy consumption and large investment.

[0003] Currently, propylene production from syngas mainly involves first converting the syngas into methanol, and then using methanol-to-propylene (MTP) technology to produce propylene. However, MTP technology suffers from drawbacks such as high investment costs, poor economic efficiency, high water consumption, and reliance on imported catalysts, hindering its industrial adoption. Therefore, developing a new technology for propylene production from syngas is of great significance in overcoming these technological bottlenecks. Summary of the Invention

[0004] To address the above problems, this invention provides a method and system for the conversion of syngas into propylene, achieving highly selective propylene production from syngas.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] The first aspect of this invention provides a method for preparing propylene from syngas, comprising the following steps: (1) In the first reaction apparatus, the synthesis gas to propane reaction is carried out under the action of catalyst I, and the synthesis gas is directly converted into propane-rich hydrocarbon products in one step. (2) Separate the product from the outlet of the first reaction device in step (1) to obtain unreacted syngas, CO2, propane and other hydrocarbon products except propane. The unreacted syngas is recycled to the first reaction device as a reaction feedstock, the CO2 is treated for emission or utilized, and the other hydrocarbons except propane are used in a graded manner. (3) The propane obtained in step (2) is sent to the second reaction unit for propane dehydrogenation reaction, and the propane is converted into a product gas rich in propylene under the action of catalyst II; (4) Separate the product from the outlet of the second reaction device in step (3) to obtain unconverted propane, H2 and propylene. The unconverted propane is recycled to the second reaction device as a raw material for reaction, and the H2 is recycled to the first reaction device as a reaction raw material.

[0007] This invention achieves the production of propylene from syngas through the tandem coupling of the syngas-to-propane reaction and the propane dehydrogenation reaction.

[0008] Based on the above technical solutions, preferably, catalyst I is a composite catalyst of metal oxide and molecular sieve; The metal oxides include ZnCr x O (1+1.5x) ZnAl x O (1+1.5x) ZnZr x Al y O (1+2x+1.5y) ZnCe x Al y O (1+2x+1.5y) ZnGa x O (1+1.5x) ZnGa x Al y O (1+1.5x+1.5y) ZnMn x Cr y O (1+1.5x+1.5y) ZnZr x O (1+2x) ZnZr x Cr y O (1+2x+1.5y) The composite oxide is formed by one or more of the following: x is in the range of 0.01-10, and y is in the range of 0.01-10; the Zn content on the surface of the metal oxide is 20%-85%; wherein the surface Zn content is quantitatively analyzed by XPS method, using the method reported in the literature (Boudevilie Y. et.al., J. Catal., 58, 52(1979); Scofield JH, J. Elec. Spec., 8, 129(1976)); it is defined as the percentage content of Zn in the surface metal elements, i.e., N Zn / (N Zn +N M )×100%, N Zn N is the molar amount of Zn on the surface. M Let M be the molar amount of surface metal M; The molecular sieve is a metal-modified molecular sieve with SiO2 coated on its surface. The metal used in the metal-modified molecular sieve is one or more of Zn, Ni, Cu, Fe, Ga, In, and Pd, and the molecular sieve is one or two of SSZ-39 molecular sieve and SSZ-13 molecular sieve.

[0009] The method of coating the surface with SiO2 is silane or siloxane treatment; The molecular formula of the silane is:

[0010] R1, R2, R3, and R4 are independently selected from hydrogen, halogen, hydroxyl, alkyl, haloalkyl, aromatic group, and haloaromatic group; The molecular formula of the siloxane is:

[0011] R5 and R6 are independently selected from hydrogen, halogen, hydroxyl, alkyl, haloalkyl, aromatic group, and haloaromatic group, and n is 2-1000.

[0012] The method of coating the surface with SiO2 is to place the molecular sieve in SiO2 slurry or sol and then impregnate, roll-coat or spray it. Based on the above technical solutions, preferably, in the metal modified molecular sieve with SiO2 coating on the surface, the mass fraction of SiO2 coating on the surface is 10-40 wt%.

[0013] Based on the above technical solution, preferably, the mass ratio of the metal oxide to the metal-modified molecular sieve coated with SiO2 is 1:4-4:1; The mixing method of the metal oxide and the metal-modified molecular sieve coated with SiO2 is physical mixing, including one of the following: solid-phase ultrafine powder mixing, particle mixing, sheet forming, and extrusion forming.

[0014] Based on the above technical solutions, preferably, the second reaction device is a fixed bed or moving bed reactor.

[0015] Based on the above technical solution, preferably, the metal-modified molecular sieve coated with SiO2 has moderately strong acidity, and the amount of moderately strong acid sites is 0.1-1.2 mmol / g. The peak temperature range of the NH3-TPD desorption peak corresponding to the moderately strong acid is 200-500℃; acetone is used as the probe molecule. 13 The C-NMR chemical shift is in the range of 210-220 ppm.

[0016] Based on the above technical solutions, preferably, the catalyst II is a Pt-based catalyst or a Cr2O3 catalyst.

[0017] Based on the above technical solution, the preferred conditions for the syngas-to-propane reaction are: reaction temperature of 360-450 ºC, reaction pressure of 1-8 MPa, and space velocity of 2000-8000 ml / g. cat / h.

[0018] Based on the above technical solutions, the preferred conditions for the synthesis of propane from syngas are: the reaction feedstock is a mixture of H2 and CO, and the molar ratio of H2 to CO is 1-4.

[0019] A second aspect of the present invention provides a system for use in the above-described method for preparing propylene from syngas, comprising: Raw material gas mixing tank, used to mix raw material gases; The first reaction apparatus is used to bring the syngas into contact with catalyst I to carry out the syngas-to-propane reaction, directly converting the syngas into propane-rich hydrocarbon products in one step. The No. 1 separation unit is used to separate the product from the outlet of the first reaction unit to obtain unreacted syngas, CO2, propane and other hydrocarbon products except propane. The unreacted syngas is recycled to the feed gas mixing tank, mixed and then reintroduced into the first reaction unit for reaction. The second reaction unit is used to contact propane with catalyst II to carry out propane dehydrogenation reaction, converting propane into a product gas rich in propylene. The No. 2 separation unit is used to separate the product from the outlet of the second reaction unit to obtain unconverted propane, H2 and propylene. The unconverted propane is recycled to the second reaction unit for further reaction, and the H2 is recycled to the feed gas mixing tank.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The method of the present invention first catalytically converts syngas into propane, and then produces propylene by propane dehydrogenation. In the process of converting CO into propane, excess oxygen is directly reacted by CO to generate CO2. Therefore, the water consumption of the reaction process is significantly reduced compared with the production of propylene from syngas via methanol.

[0021] 2. The overall propylene selectivity of the present invention is as high as 65-90%, which is higher than the 60-70% propylene selectivity in the traditional methanol-to-propylene process.

[0022] 3. The synthesis of propane from syngas is an exothermic reaction, while the dehydrogenation of propane is an endothermic reaction. The two reactions are connected in series to achieve efficient utilization of heat.

[0023] 4. The metal oxide-molecular sieve composite catalyst used in the syngas conversion of this invention has an H2 / CO ratio close to that of syngas from coal gasification. In principle, it can produce hydrogen without going through the water-gas shift reaction step, with a short process, low process water consumption, and low energy consumption. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the syngas-to-propylene system of the present invention; In the diagram: 1. Raw material gas mixing tank, 2. First reaction device, 3. Separation device #1, 4. Second reaction device, 5. Separation device #2. Detailed Implementation

[0025] The present invention will be further illustrated below by way of embodiments, but the scope of the claims of the present invention 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.

[0026] This invention provides a method for preparing propylene from syngas and a system for preparing propylene from syngas (e.g., Figure 1 (As shown), the method includes the following steps: (1) After the raw material gas is mixed in the raw material mixing tank 1, it undergoes a synthesis gas to propane reaction in the first reaction device 2 under the action of catalyst I, directly converting the synthesis gas into propane-rich hydrocarbon products in one step. In the syngas-to-propane reaction, the syngas is a mixture of H2 and CO, with a molar ratio of H2 to CO of 1-4. The reaction conditions are: syngas pressure of 1-8 MPa, reaction temperature of 360-450 ℃, and space velocity of 2000-8000 ml / g. cat / h; The catalyst I used is a composite catalyst of metal oxide and molecular sieve; wherein: the metal oxide includes ZnCr x O (1+1.5x) ZnAl x O (1+1.5x) ZnCr x Al y O (1+1.5x+1.5y) ZnMn x O (1+1.5x) ZnGa x O (1+1.5x) ZnGa x Al y O (1+1.5x+1.5y) ZnMn x Cr y O (1+1.5x+1.5y) ZnZr x O (1+2x) ZnZrx Cr y O (1+2x+1.5y) The composite oxide is formed by one or more of the following: x ranges from 0.01 to 10, and y ranges from 0.01 to 10; the Zn content on the surface of the metal oxide is 20%-85%; the molecular sieve is a metal-modified molecular sieve with SiO2 coating, wherein the metal used in the metal-modified molecular sieve is one or more of Zn, Ni, Cu, Fe, Ga, In, and Pd, and the molecular sieve is one or two of SSZ-39 molecular sieve and SSZ-13 molecular sieve; in the metal-modified molecular sieve with SiO2 coating, the mass fraction of the SiO2 coating is 10-40 wt%; the mass ratio of the metal oxide to the metal-modified molecular sieve with SiO2 coating is 1:4-4:1; the mixing method of the metal oxide and the molecular sieve is physical mixing, including one of the following: solid-phase ultrafine powder mixing, particle mixing, sheet forming, and extrusion forming. (2) The product from the outlet of the first reaction device 2 in step (1) is fed into the No. 1 separation device 3 for separation. The specific separation process can adopt the corresponding separation process known in the art to obtain unreacted synthesis gas A7, CO2A9, propane A4 and other hydrocarbon products A8 except propane. The unreacted synthesis gas A7 is recycled to the raw material gas mixing tank 1, and after mixing, it is reintroduced into the first reaction device 2 for reaction. Propane A4 enters the second reaction device 4. CO2A9 is treated for emission or utilized. Other hydrocarbon products A8 except propane are graded and utilized. (3) The propane A4 obtained in step (2) is sent to the second reaction device 4 for propane dehydrogenation reaction, and the propane is converted into propylene-rich product gas A5 under the action of catalyst II. During the propane dehydrogenation reaction, the second reaction unit can be either a fixed-bed or moving-bed reactor. The reaction conditions are: 540-650℃, atmospheric pressure, and propane space velocity of 1.0-3.0 h⁻¹. -1 .

[0027] Catalyst II can be prepared in-house or purchased using existing technologies; (4) The product from the outlet of the second reaction device 4 in step (3) is fed into the No. 2 separation device 5 for separation. Using the existing separation process in the art, unconverted propane A10, H2A11 and propylene A6 are obtained. The unconverted propane A10 is recycled to the second reaction device 4 as raw material for reaction, and H2A11 is recycled to the raw material gas mixing tank 1.

[0028] Unless otherwise specified, all devices used in the syngas-to-propylene system of the present invention can be commonly used devices with corresponding functions in the art, and will not be described in detail.

[0029] The calculation methods for propane selectivity, propylene selectivity, and overall propylene selectivity in this project are as follows: Propane selectivity, % = number of moles of CO consumed in propane production in the first reaction unit 2 / number of moles of CO consumed in the production of all hydrocarbon products; Propylene selectivity, % = number of moles of propane consumed in the production of propylene in the second reaction unit 4 / total number of moles of propane consumed in the reaction; Overall propylene selectivity, % = propane selectivity, % × propylene selectivity, % / 100.

[0030] Preparation of catalyst I: ZnCr was prepared by co-precipitation method x O (1+1.5x) Zinc nitrate and chromium nitrate were used as precursors (molar ratio Zn / Cr = 1 / 1, Zn concentration 50 mM), and mixed with ammonium carbonate in water at room temperature (ammonium carbonate was used as a precipitant, with excess ammonium carbonate or an ammonium ion to metal ion ratio of 1:1). The mixture was aged at 90°C for 5 hours, then washed, filtered, and dried. The resulting solid was calcined at 500°C in air to obtain ZnCr metal oxide, denoted as OX-1. The surface Zn content was 54%. A similar method was used to prepare ZnAl. x O (1+1.5x) ZnCr x Al y O (1+1.5x+1.5y) ZnMn x O (1+1.5x) ZnGa x O (1+1.5x) ZnGa x Al y O (1+1.5x+1.5y) ZnMn x Cr y O (1+1.5x+1.5y) ZnZr x O (1+2x) ZnZr x Cr y O (1+2x+1.5y) They are designated as OX-2, OX-3, OX-4, OX-5, OX-6, OX-7, OX-8, and OX-9, respectively. The specific surface Zn content is shown in Table 1.

[0031] Table 1. Composition and surface Zn content of different metal oxides

[0032] Preparation of SSZ-39 molecular sieve: FAU molecular sieve was used as a precursor. Organic template agent DMP was added under alkaline conditions to prepare a synthetic gel according to the molar ratio of SiO2:Al2O3:Na2O:OSDA:H2O = 30:1:8:6:1000. After stirring at room temperature until homogeneous, the gel was hydrothermally crystallized at 140 °C for 7 days. The product was cooled, washed, dried, and calcined in air at 550 °C for 5 h to obtain Na-type SSZ-39 molecular sieve. Na-SSZ-39 molecular sieve was exchanged with 1 mol / L NH4Cl solution at 80 °C for 2 h, followed by washing with deionized water until neutral. This process was repeated three times. The product was then calcined in air at 500 °C for 2 h to obtain H-SSZ-39 molecular sieve, with a moderately strong acid content of 0.98 mmol / g.

[0033] Preparation of SSZ-13 molecular sieve: Weigh an appropriate amount of NaOH and dissolve it in deionized water. Add TMAdaOH and choline chloride in a certain ratio and stir thoroughly before adding seed crystals; then add Al2(SO4)3. Add 18H2O and stir vigorously for 30 min. After stirring, add an appropriate amount of silica and continue stirring for 2 h to obtain a uniform gel. Transfer the gel to a 100 mL crystallization vessel and crystallize at 160 °C. o Crystallization was carried out at C for 4 days; after crystallization, the resulting product was filtered, washed, and then subjected to 120°C. o Dry at C for 12 h, and finally dry the product at 550 °C. o Na-SSZ-13 molecular sieve was obtained by calcining in air at C for 5 hours. Na-SSZ-39 molecular sieve was then reacted with 1 mol / L NH4Cl solution at 80°C. o The product was exchanged at C for 2 h, then washed with deionized water until neutral, and the above steps were repeated three times. The product was then calcined in air at 500 degrees for 2 h to obtain H-SSZ-13 molecular sieve with a medium strong acid content of 1.10 mmol / g.

[0034] Preparation of metal-modified and SiO2-coated molecular sieves: A certain amount of Pd precursor was dissolved in 10 ml of H2O, 5 g of SSZ-13 molecular sieve was added, stirred at room temperature for 10 h, dried, and calcined at 500℃ for 2 h to obtain Pd-modified SSZ-13 with a Pd content of 0.1 wt%; Zn, Ni, Fe, Cu, Ga, In and other precursors were dissolved in water, 5 g of SSZ-13 or SSZ-39 molecular sieve was added, stirred at room temperature for 10 h, dried, and calcined at 500℃ for 2 h to obtain Zn, Ni, Fe, Cu, Ga, In modified SSZ-13 or SSZ-39.

[0035] A certain amount of polydimethylsilane was dissolved in 100 ml of toluene and placed in a three-necked flask. 3 g of Pd-modified SSZ-13 molecular sieve was added, and the mixture was refluxed at 70 °C for 3 h. The toluene was then evaporated, the sample was dried at 110 °C, and calcined in air at 500 °C. This yielded SiO2-coated Pd-modified SSZ-13 molecular sieve. Using a similar method, SiO2-coated Zn-modified SSZ-39 molecular sieve was prepared.

[0036] A certain amount of polysiloxane (Dow Corning-550) was dissolved in 40 ml of cyclohexane and placed in a beaker. 10 g of Ni-modified SSZ-13 molecular sieve was added, and the mixture was stirred evenly at room temperature. The cyclohexane was then evaporated, the sample was dried at 110 °C, and calcined in air at 500 °C. This yielded SiO2-coated Ni-modified SSZ-13 molecular sieve. Using a similar method, SiO2-coated Cu-modified SSZ-39 molecular sieve was prepared.

[0037] A certain amount of tributylchlorosilane was dissolved in 40 ml of N,-N-dimethylformamide and placed in a beaker. 10 g of Fe-modified SSZ-13 molecular sieve was added, and the mixture was stirred evenly at room temperature. The N,-N-dimethylformamide was then evaporated, the sample was dried at 110 °C, and calcined in air at 500 °C to obtain SiO2-coated Fe-modified SSZ-13 molecular sieve. Using a similar method, SiO2-coated Ga-modified SSZ-39 molecular sieve was prepared.

[0038] Take 10 g of In-modified SSZ-13 molecular sieve, immerse it in silica sol, remove it, dry the sample at 110℃, repeat the above process 5 times, dry the sample at 110℃, and calcine it in air at 500℃ to obtain SiO2-coated In-modified SSZ-13 molecular sieve.

[0039] The properties of metal-modified SSZ-13 or SSZ-39 molecular sieves with different SiO2 coatings are shown in Table 2.

[0040] Table 2. Properties of metal-modified SSZ-13 or SSZ-39 molecular sieves with different SiO2 coatings.

[0041] Catalyst I was prepared by methods such as solid-phase ultrafine powder mixing, particle mixing, tablet forming, and extrusion forming.

[0042] Table 3. Preparation and parameter characteristics of catalyst I of the present invention

[0043] Preparation of Catalyst II: A: Preparation of K-modified Cr2O3-Al2O3 catalyst (denoted as Cat-II-1) (1) 115.44 g Cr(NO3)3·9H3O was dissolved in 60 mL of deionized water and stirred at 40 °C until completely dissolved; (2) Pour 84 g γ-Al2O3 into the impregnation solution, sonicate for 30 min to ensure that the powder is fully wetted and mixed, and let stand at room temperature for 12 h in a sealed manner to allow the metal precursor to be uniformly adsorbed. (3) Dry in an oven at 40 ℃ for 12 h, and continue drying at 120 ℃ for 4 h to completely remove residual solvent; place the product in a muffle furnace and calcine at 600 ℃ for 4 h in air atmosphere to obtain Cr2O3-Al2O3 precursor oxide; (4) 2.59 g KNO3 was dissolved in 60 mL of deionized water, and Cr2O3-Al2O3 precursor oxide was added. The mixture was stirred evenly, left to stand overnight, dried at 60 degrees for 12 h, and calcined at 600 ℃ for 2 h in air atmosphere.

[0044] B: Preparation of PtSn / Al2O3 catalyst (denoted as Cat-II-2): (1) Add a measured amount of deionized water to a beaker, then add 2 mL of concentrated hydrochloric acid, 0.84 g of chloroplatinic acid, and 0.93 g of stannous chloride in sequence, and stir magnetically until completely dissolved; (2) Pour 100 g γ-Al2O3 into the impregnation solution, sonicate for 30 min to ensure that the powder is fully wetted and mixed, and let stand at room temperature for 12 h in a sealed manner to allow the metal precursor to be uniformly adsorbed. (3) Dry in an oven at 40 ℃ for 12 h, and continue drying at 120 ℃ for 4 h to completely remove residual solvent; place the product in a muffle furnace and calcine at 500 ℃ for 4 h in air atmosphere to decompose the precursor and form metal oxides. (4) In a tube furnace, 60 mL / min of 10% H2 / N2 mixed gas is introduced, the temperature is increased to 550 ℃ at 2 ℃ / min, and the temperature is kept constant for 2 h. Then, pure nitrogen gas is switched to purge and the furnace is cooled to room temperature.

[0045] Example 1 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-1 catalyst, and the reaction conditions are: reaction temperature 380ºC, reaction pressure 4MPa, and space velocity 3000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-1, the reaction temperature is 600ºC, and the space velocity is 2h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0046] Example 2 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-2 catalyst, and the reaction conditions are: reaction temperature 380ºC, reaction pressure 6MPa, and space velocity 5000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-2, the reaction temperature is 580ºC, and the space velocity is 1.5h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0047] Example 3 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-3 catalyst, and the reaction conditions are: reaction temperature 410ºC, reaction pressure 5MPa, and space velocity 6000 ml / g. cat The catalyst II in the second reaction apparatus is Cat-II-1, the reaction temperature is 590ºC, and the space velocity is 1 h⁻¹. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0048] Example 4 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-4 catalyst, and the reaction conditions are: reaction temperature 400ºC, reaction pressure 4MPa, and space velocity 4500 ml / g. cat The second reaction apparatus used Cat-II-2 as catalyst II, with a reaction temperature of 600ºC and a space velocity of 1.7 h⁻¹. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0049] Example 5 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-5 catalyst, and the reaction conditions are: reaction temperature 430ºC, reaction pressure 3MPa, and space velocity 8000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II,1, the reaction temperature is 620ºC, and the space velocity is 2.5h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0050] Example 6 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-6 catalyst, and the reaction conditions are: reaction temperature 360ºC, reaction pressure 8MPa, and space velocity 2000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-2, the reaction temperature is 650ºC, and the space velocity is 3h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0051] Example 7 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-7 catalyst, and the reaction conditions are: reaction temperature 420ºC, reaction pressure 2MPa, and space velocity 5000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-1, the reaction temperature is 540ºC, and the space velocity is 1 h⁻¹. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0052] Example 8 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-8 catalyst, and the reaction conditions are: reaction temperature 380ºC, reaction pressure 1MPa, and space velocity 6000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-2, the reaction temperature is 580ºC, and the space velocity is 2h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0053] Example 9 This embodiment uses the above-described method to produce propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-9 catalyst, and the reaction conditions are: reaction temperature 450ºC, reaction pressure 7MPa, and space velocity 4000 ml / g. cat The second reaction apparatus used Cat-II-1 as catalyst II, with a reaction temperature of 590ºC and a space velocity of 2.3 h⁻¹. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0054] Comparative Example 1 This comparative example uses the above method to prepare propylene from syngas, and the system used is as follows: Figure 1As shown. In the first reaction apparatus, catalyst I is Cat-I-10 catalyst, and the reaction conditions are: reaction temperature 380ºC, reaction pressure 4MPa, and space velocity 3000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-1, the reaction temperature is 600ºC, and the space velocity is 2h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0055] Comparative Example 2 This comparative example uses the above method to prepare propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-11 catalyst, and the reaction conditions are: reaction temperature 380ºC, reaction pressure 4MPa, and space velocity 3000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-1, the reaction temperature is 600ºC, and the space velocity is 2h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0056] Comparative Example 3 This comparative example uses the above method to prepare propylene from syngas, and the system used is as follows: Figure 1 As shown. In the first reaction apparatus, catalyst I is Cat-I-12 catalyst, and the reaction conditions are: reaction temperature 380ºC, reaction pressure 4MPa, and space velocity 3000 ml / g. cat In the second reaction apparatus, catalyst II is Cat-II-1, the reaction temperature is 600ºC, and the space velocity is 2h / h. -1 The molar ratio of H2 / CO in the synthesis gas and the reaction results are shown in Table 4.

[0057] Table 4. Effect data of the examples and comparative examples

[0058] Catalyst I in Comparative Example 1 used an unmodified SSZ-13 molecular sieve; catalyst I in Comparative Example 2 used an SSZ-13 molecular sieve coated only with SiO2 but without metal modification; and catalyst I in Comparative Example 3 used an SSZ-13 molecular sieve modified only with Pd but without SiO2 coating. Compared with Example 1, where catalyst I used SiO2 coating and Pd modification of SSZ-13 molecular sieve, the selectivity of direct propane production from syngas was low, indicating the important role of metal modification and SiO2 coating of the molecular sieve in the syngas to propane catalyst in this syngas to propylene system.

[0059] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing propylene from syngas, characterized in that, Includes the following steps: (1) In the first reaction apparatus, the synthesis gas to propane reaction is carried out under the action of catalyst I, and the synthesis gas is directly converted into propane-rich hydrocarbon products in one step. (2) Separate the product from the outlet of the first reaction device in step (1) to obtain unreacted syngas, CO2, propane and other hydrocarbon products except propane. The unreacted syngas is recycled to the first reaction device as a reaction feedstock. (3) The propane obtained in step (2) is sent to the second reaction unit for propane dehydrogenation reaction, and the propane is converted into a product gas rich in propylene under the action of catalyst II; (4) Separate the product from the outlet of the second reaction device in step (3) to obtain unconverted propane, H2 and propylene. The unconverted propane is recycled to the second reaction device as a raw material for reaction, and the H2 is recycled to the first reaction device as a reaction raw material.

2. The method according to claim 1, characterized in that, Catalyst I is a composite catalyst of metal oxide and molecular sieve; The metal oxides include ZnCr x O (1+1.5x) ZnAl x O (1+1.5x) ZnZr x Al y O (1+2x+1.5y) ZnCe x Al y O (1+2x+1.5y) ZnGa x O (1+1.5x) ZnGa x Al y O (1+1.5x+1.5y) ZnMn x Cr y O (1+1.5x+1.5y) ZnZr x O (1+2x) ZnZr x Cr y O (1+2x+1.5y) The composite oxide is formed by one or more of the following: the value of x ranges from 0.01 to 10, and the value of y ranges from 0.01 to 10; the Zn content on the surface of the metal oxide is 20%-85%. The molecular sieve is a metal-modified molecular sieve with SiO2 coated on its surface. The metal used in the metal-modified molecular sieve is one or more of Zn, Ni, Cu, Fe, Ga, In, and Pd, and the molecular sieve is one or two of SSZ-39 molecular sieve and SSZ-13 molecular sieve.

3. The method according to claim 1, characterized in that, In the metal-modified molecular sieve with SiO2 coating, the mass fraction of SiO2 coating is 10-40 wt%.

4. The method according to claim 1, characterized in that, The mass ratio of the metal oxide to the metal-modified molecular sieve coated with SiO2 is 1:4-4:1; The mixing method of the metal oxide and the metal-modified molecular sieve coated with SiO2 is physical mixing, including one of the following: solid-phase ultrafine powder mixing, particle mixing, sheet forming, and extrusion forming.

5. The method according to claim 1, characterized in that, The second reaction device is a fixed-bed or moving-bed reactor.

6. The method according to claim 2, characterized in that, The metal-modified molecular sieve with SiO2 coating has moderately strong acidity, and the amount of moderately strong acid sites is 0.1-1.2 mmol / g.

7. The method according to claim 1, characterized in that, Catalyst II is a Pt-based catalyst or a Cr2O3 catalyst.

8. The method according to claim 1, characterized in that, The conditions for the synthesis of propane from syngas are: reaction temperature 360-450 ºC, reaction pressure 1-8 MPa, and space velocity 2000-8000 ml / g. cat / h.

9. The method according to claim 1, characterized in that, The conditions for the synthesis of propane from syngas are as follows: the reaction feedstock is a mixture of H2 and CO, with a molar ratio of H2 to CO of 1-4.

10. A system used in the method for producing propylene from syngas according to any one of claims 1-9, characterized in that, include: Raw material gas mixing tank, used to mix raw material gases; The first reaction apparatus is used to bring the syngas into contact with catalyst I to carry out the syngas-to-propane reaction, directly converting the syngas into propane-rich hydrocarbon products in one step. The No. 1 separation unit is used to separate the product from the outlet of the first reaction unit to obtain unreacted syngas, CO2, propane and other hydrocarbon products except propane. The unreacted syngas is recycled to the feed gas mixing tank. The second reaction unit is used to contact propane with catalyst II to carry out propane dehydrogenation reaction, converting propane into a product gas rich in propylene. The No. 2 separation unit is used to separate the product from the outlet of the second reaction unit to obtain unconverted propane, H2 and propylene. The unconverted propane is recycled to the second reaction unit for further reaction, and the H2 is recycled to the feed gas mixing tank.

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