A SAPO-11 molecular sieve composite catalyst and its application in direct conversion of synthesis gas to gasoline

Abstract

The present invention belongs to the technical field of synthesis gas for preparing gasoline, and particularly relates to a SAPO-11 molecular sieve composite catalyst and its application in the direct conversion of synthesis gas to gasoline. The catalyst comprises component I and component II, and component I and component II are compounded together in a mechanical mixing manner. The active ingredient of component I is metal oxide, and component II is SAPO-11 molecular sieve. Using synthesis gas as the reaction raw material, the conversion reaction is carried out in a fixed bed or a moving bed. The reaction process has high product yield and selectivity. The selectivity of gasoline composed of C5-C 11 can reach 70-90%, the selectivity of aromatics in C5-C 11 is less than 30%, the ratio of isoparaffin to n-paraffin (iso / n) in C5-C 11 can reach 15-60, and at the same time, the selectivity of by-product methane is less than 3%, having good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing gasoline from synthesis gas, and specifically relates to a SAPO-11 molecular sieve composite catalyst and application thereof in directly converting synthesis gas into gasoline. Background Art

[0002] With the development of economy and the improvement of living standards, people's demand for gasoline has increased sharply year by year. At the same time, due to factors such as environmental protection and health, people's requirements for gasoline quality have also increased year by year. This requires that the gasoline finally sold should have the characteristics of low olefins, low aromatics, and high isoparaffins. Therefore, it is very important to produce gasoline with high isoparaffin content. At present, the production of gasoline mainly comes from petroleum. With the increasing consumption of global petroleum resources, especially for my country, which is short of petroleum resources, more than 70% of the annual petroleum consumption depends on imports. It is of great social and strategic significance to seek an alternative process route and develop and utilize non-petroleum-based carbon resources such as coal, biomass and even CO2 to prepare gasoline, especially gasoline with high isoparaffin content.

[0003] my country is rich in coal resources. With coal as raw material, syngas (i.e., a mixture of CO and H2) is obtained through gasification, and the syngas is converted into methanol. The technical route of methanol to gasoline through dimethyl ether has matured and entered industrialization. This route provides an important route for the production of gasoline from carbon resources such as coal, biomass and even CO2. However, if the direct conversion of syngas can be achieved without the route of methanol synthesis and methanol dehydration to dimethyl ether, it can not only simplify the process flow, but also reduce unit operations, investment and energy consumption. The traditional Fischer-Tropsch route can realize the direct conversion of syngas to prepare gasoline, but its product distribution is limited by the ASF distribution, the selectivity of gasoline is less than 50%, and the octane number of the obtained gasoline is too low. The product is mainly straight-chain hydrocarbons, which need to be refined in the later stage before it can be put into use. Summary of the invention

[0004] In view of the above problems, the present invention provides a SAPO-11 molecular sieve composite catalyst and its application in the direct conversion of syngas to gasoline. The catalyst of the present invention can adjust the product of syngas conversion to gasoline, greatly improve the selectivity of gasoline in the product, and improve the ratio of isoparaffins to normal paraffins (iso / n) in the product.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] On one hand, the present invention provides a SAPO-11 molecular sieve composite catalyst, which comprises component I and component II, which are composited together by mechanical mixing, wherein the active ingredient of component I is a metal oxide, and component II is a SAPO-11 molecular sieve.

[0007] Based on the above technical solution, the specific surface area of ​​the outer surface of the SAPO-11 molecular sieve accounts for 20%-50% of the total specific surface area of ​​the molecular sieve. The specific surface area is determined by N2 physical adsorption, micropores refer to pores below 2nm, and the specific surface area of ​​the outer surface is the difference between the total specific surface area and the specific surface area of ​​micropores.

[0008] Based on the above technical solution, the SAPO-11 molecular sieve has medium-strong acid characteristics, and the amount of medium-strong acid sites is 0.05-0.5 mol / kg, preferably 0.05-0.3 mol / kg, and more preferably 0.05-0.2 mol / kg.

[0009] The acid strength is defined by the NH3-TPD peak, including three types of acidity: weak acid, medium-strong acid, and strong acid. The NH3-TPD is based on the position of the desorption peak of NH3. The position of the desorption peak refers to the test conditions under standard test conditions, under the test conditions of the ratio of sample mass w to carrier gas flow rate f (w / f) = 100g·h / L and a heating rate of 10℃ / min. TCD records the thermal conductivity signal of desorbed NH3, draws a desorption curve, and divides the inorganic solid into three types of acid strength according to the apex of the curve peak position. Weak acid refers to the acid position with NH3 desorption temperature less than 275℃; medium-strong acid refers to the acid position with NH3 desorption temperature between 275-500℃; strong acid refers to the acid position with NH3 desorption temperature greater than 500℃. Acetone is used as a probe molecule. 13 The C-NMR chemical shifts were in the range of 210-220 ppm.

[0010] Based on the above technical solution, the preparation method of the SAPO-11 molecular sieve comprises the following steps:

[0011] (1) Mix di-n-propylamine, silicon source, aluminum source, phosphoric acid and water, and age at room temperature for 2-24 hours;

[0012] (2) transferring the gel obtained in step (1) to a hydrothermal reactor and rotating the reaction mixture at 180-200° C. and a rotation speed of 10-60 rpm / min for crystallization for 24-48 hours;

[0013] (3) After the crystallization is completed, the reactor is cooled to room temperature in a water bath, centrifuged, washed, and the obtained precipitate is dried and then calcined in air at 500-700° C. for 1-12 h to obtain the SAPO-11 molecular sieve.

[0014] Based on the above technical solution, the silicon source includes one of silica sol, fumed silica, silica gel, tetraethyl orthosilicate, and white carbon black, and the aluminum source includes aluminum isopropoxide or pseudo-boehmite.

[0015] Based on the above technical scheme, the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the phosphoric acid is calculated as P2O5, n(SiO2) / n(Al2O3)=0.3, n(DPA) / n(Al2O3)=1.4, n(H2O) / n(Al2O3)=50, and n(P2O5) / n(Al2O3)=1.

[0016] Based on the above technical solution, the metal oxide is Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Mn b Al (1-a-b) O x 、Zn a Cr b Al (1-a-b) O x 、Zn a Cr b Mn (1-a-b) O x One or more of the above, wherein the value range of x is 0.7 to 3.7, the value range of a is 0-1, and the value range of a+b is 0-1; a, b, (1-a), (1-ab), and x in the present invention only represent the relative proportions of the chemical composition of the elements in the metal oxide, and all metal oxides with the same proportion are regarded as the same metal oxide; the Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Mn b Al (1-a-b) O x 、Zn a Cr b Al (1-a-b) O x 、Zn a Cr b Mn (1-a-b) O x The specific surface area is 5-250m 2 / g, preferably 50-250m 2 / g.

[0017] Based on the above technical solution, the weight ratio between the active ingredient in component I and component II is 0.1-20, preferably 0.3-5.

[0018] Another aspect of the present invention provides a method for directly converting synthesis gas into gasoline, wherein the synthesis gas is used as a reaction raw material, the conversion reaction is carried out on a fixed bed or a moving bed, and the catalyst used is the above-mentioned composite catalyst.

[0019] Based on the above technical scheme, based on the above technical scheme, the pressure of the synthesis gas is 0.5-10MPa, preferably 1-8MPa; the reaction temperature is 300-600℃, preferably 320-450℃; the space velocity is 300-12000mL / g / h, preferably 500-5000mL / g / h; the synthesis gas is a H2 / CO mixed gas, and the H2 / CO ratio is 0.2-3.5, preferably 0.5-2.5.

[0020] The beneficial effects of the present invention are:

[0021] 1. The catalyst of the present invention is different from the traditional Fischer-Tropsch synthesis technology. It utilizes the strategy of active center separation and uses a specific oxide + SAPO-11 molecular sieve to form a bifunctional catalyst, which can separate CO activation and CC coupling on two active centers, thereby breaking the limitation of product selectivity in traditional Fischer-Tropsch and obtaining high gasoline selectivity without being restricted by the ASF model.

[0022] 2. The SAPO-11 molecular sieve synthesized by the method of the present invention has a high ratio of the external surface area to the total surface area, so that the gasoline selectivity in the synthesis gas conversion reaction product is high, and the C5-C 11 The gasoline selectivity of the composition can reach 70-90%, C5-C 11 The selectivity of aromatics is less than 30%, especially C5-C 11 The ratio of isoparaffins to normal paraffins (iso / n) can reach 15-60, while the methane selectivity is extremely low, less than 3%, and the products can be separated without deep cooling, which greatly reduces the energy consumption and cost of separation and has a high application prospect.

[0023] 3. The metal oxide, the active component of component I in the catalyst, has a higher specific surface area, so there are more active sites on the surface of the metal oxide, which is more conducive to the catalytic reaction.

[0024] 4. The role of component II in the catalyst is, on the one hand, to convert the active gas phase intermediates produced by component I into gasoline by coupling with component I. The effect of component II on the equilibrium pulling of the series reaction can promote the activation and conversion of synthesis gas by component I, thereby improving the conversion rate. On the other hand, the special structure of the molecular sieve in component II used in the present invention can promote the formation of gasoline and is beneficial to the formation of isoparaffins, thereby highly selectively obtaining a gasoline component with a high isoparaffin content.

[0025] 5. Using component I or component II described in the present invention separately cannot achieve the function of the present invention at all. For example, the methane selectivity in the product of component I alone is very high, and the conversion rate is very low, while component II alone can hardly activate and convert synthesis gas. Only when component I and component II work together can efficient synthesis gas conversion be achieved and excellent selectivity be obtained. This is because component I can activate synthesis gas to generate specific active gas phase intermediates, and the intermediates diffuse into the pores of component II through the gas phase. Due to the 1D ten-membered ring straight-through pores and specific acidity of the SAPO-11 molecular sieve selected by the present invention, the active gas phase intermediates generated by component I can be further activated and converted into gasoline. Due to the special pore structure of component II, the product has special selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The SEM images of the two groups are shown in Figure 2, where a is the result of 25,000 times magnification and b is the result of 20,000 times magnification;

[0027] Figure 2 The SEM image of sample 4 was magnified 10,000 times. DETAILED DESCRIPTION

[0028] The present invention is further described below by way of examples, but the scope of the claims of the present invention is not limited by these examples. Meanwhile, the examples only provide partial conditions for achieving this purpose, but do not mean that these conditions must be met to achieve this purpose.

[0029] The specific surface area of ​​the sample can be tested by nitrogen or argon physical adsorption method.

[0030] The metal oxide of the present invention can be obtained by purchasing commercially available metal oxides with high specific surface area, or by the following method:

[0031] 1. Preparation of Catalyst Component I

[0032] Synthesis of Zn with high specific surface area by coprecipitation a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Mn b Al (1-a-b) O x 、Zn a Cr b Al (1-a-b) O x 、Zn a Cr b Mn (1-a-b) Ox Zinc nitrate, aluminum nitrate, chromium nitrate, and manganese nitrate are used as precursors, and one or more of ammonium carbonate, ammonium bicarbonate, and sodium carbonate are used as precipitants. The precursors are mixed in water at room temperature, and then transferred to a water bath pot with a temperature range of 50-90°C, and a precipitant is added (wherein the precipitant feed ratio is 100-150% of the theoretical amount); the mixed solution is aged, and then taken out for washing, filtering, and drying. The obtained solid is calcined in an air atmosphere to obtain a metal oxide with a high specific surface area. The specific samples and their preparation conditions are shown in Table 1 below.

[0033] Table 1 Preparation and performance parameters of high specific surface area metal oxides

[0034]

[0035] 2. Preparation of Component II SAPO-11

[0036] The hydrothermal method is used to synthesize SAPO-11 molecular sieve. The specific preparation process is as follows:

[0037] According to n(SiO2) / n(Al2O3)=0.3, n(DPA) / n(Al2O3)=1.4, n(H2O) / n(Al2O3)=50, n(P2O5) / n(Al2O3)=1.

[0038] Dipropylamine (DPA), silica sol (silicon dioxide content 30wt%), aluminum isopropoxide, phosphoric acid (85wt%), and deionized water are mixed and stirred at room temperature according to the above-mentioned feed ratio, and then aged at room temperature for 4h under vigorous stirring. The obtained gel is transferred to a hydrothermal kettle and rotated for crystallization at 200℃ for 24h. After the crystallization is completed, the reactor is quenched to room temperature in a water bath, and centrifuged and washed repeatedly until the pH of the supernatant is 7. The obtained precipitate is first dried in a 70℃ oven for 6h and then transferred to a 110℃ oven for drying overnight. Then, it is calcined in air at 600℃ for 6h to obtain the desired SAPO-11.

[0039] By changing the type, ratio and rotation speed of the precursors, various SAPO-11 molecular sieves can be obtained, as shown in Table 2, which are defined as points 1 to 5. The molecular sieves described in Table 3 are all synthesized according to the feed ratio in Table 3 and processed by the above-mentioned processing steps.

[0040] Table 2 Preparation and performance parameters of different SAPO-11 molecular sieves

[0041]

[0042]

[0043] 3. Morphological characterization of catalysts

[0044] SEM tests were performed on some catalysts to characterize their morphology. The SEM images of the two catalysts are shown in Figure 2. Figure 1 As shown, the SEM images of the four Figure 2 shown.

[0045] from Figure 1 It can be clearly seen from the SEM results that the SAPO-11 molecular sieve synthesized by the method of the present invention finally forms an aggregate composed of a large number of lamellar molecular sieve crystals stacked on each other, and finally presents a petal-like morphology, produces a large number of stacked pores, and exposes a large number of external surface sites. Figure 2 The SEM image in the middle is a conventional statically synthesized SAPO-11 molecular sieve. It can be clearly seen from the results in the figure that the statically synthesized molecular sieve mainly forms large aggregate particles, lacks sufficient stacking structure, and the aggregate itself has very little exposed external surface.

[0046] 4. Preparation of Catalyst

[0047] Add component I and component II in the required proportion into the container, and utilize one or more of the extrusion force, impact force, shear force, friction force, etc. generated by the high-speed movement of these materials and / or containers to achieve the purpose of separation, crushing, mixing, etc., and realize the conversion of mechanical energy, thermal energy and chemical energy by adjusting the temperature and carrier gas atmosphere, and further adjust the interaction between different components.

[0048] During the mechanical mixing process, the mixing temperature can be set at 20-100°C, and the mixing can be carried out in an atmosphere or directly in air, and the atmosphere is selected from any of the following gases:

[0049] a) Nitrogen and / or inert gas;

[0050] b) a mixture of hydrogen and nitrogen and / or an inert gas, wherein the volume of hydrogen in the mixture is 5-50%;

[0051] c) a mixture of CO and nitrogen and / or an inert gas, wherein the volume of CO in the mixture is 5-20%;

[0052] d) A mixed gas of O2 and nitrogen and / or an inert gas, wherein the volume of O2 in the mixed gas is 5-20%, and the inert gas is one or more of helium, argon, and neon.

[0053] Mechanical mixing can be performed by one or more of mechanical stirring, ball milling, shaking mixing, and mechanical grinding, as follows:

[0054] Mechanical stirring: In a stirring tank, use a stirring rod to mix component I and component II. The degree of mixing of component I and component II can be adjusted by controlling the stirring time (5min-120min) and speed (30-300 rpm).

[0055] Ball milling: The abrasive and catalyst are rolled at high speed in the grinding tank to produce strong impact and crushing on the catalyst, so as to disperse and mix components I and II. By controlling the ratio of abrasive (material can be stainless steel, agate, quartz. Size range: 5mm-15mm) to catalyst (mass ratio range: 20-100:1).

[0056] Shaking table mixing method: pre-mix component I and component II and put them into a container; mix component I and component II by controlling the reciprocating oscillation or circular oscillation of the shaker; achieve uniform mixing by adjusting the oscillation speed (range: 1-70 rpm) and time (range: 5min-120min).

[0057] Mechanical grinding method: pre-mix component I and component II and put them into a container; under a certain pressure (range: 5 kg-20 kg), the grinding tool and the mixed catalyst are moved relative to each other (speed range: 30-300 rpm) to achieve uniform mixing.

[0058] The specific catalyst preparation and its parameter characteristics are shown in Table 3.

[0059] Table 3 Preparation of catalysts and their parameter characteristics

[0060]

[0061]

[0062]

[0063] 5. Catalytic Reaction Examples

[0064] The fixed bed reaction is used as an example, but the catalyst is also suitable for moving bed reactors. The device is equipped with a gas mass flow meter and an online product analysis chromatograph (the tail gas of the reactor is directly connected to the quantitative valve of the chromatograph for periodic real-time sampling and analysis).

[0065] 0.6 g of the catalyst of the present invention is placed in a fixed bed reactor, the air in the reactor is replaced with Ar, and then the temperature is raised to 300° C. in a H2 atmosphere, synthesis gas (H2 / CO molar ratio = 0.2-3.5) is switched, the pressure of the synthesis gas is 0.5-10 MPa, the temperature is raised to a reaction temperature of 300-600° C., and the space velocity of the reaction raw gas is adjusted to 300-12000 ml / g / h. The product is analyzed by online chromatography.

[0066] Changing the temperature, pressure, space velocity and the molar ratio of H2 / CO in the synthesis gas can change the reaction performance. 11 The gasoline selectivity of the composition can reach 70-90%, C5-C 11 The ratio of isoparaffin to normal alkane (iso / n) can reach 15-60. Table 4 lists the specific application of the catalyst and its effect data. 11 Both selectivity and CH4 selectivity are its selectivity among all hydrocarbons.

[0067] Table 4 Specific application of catalyst and its effect data

[0068]

[0069]

[0070] Comparative Example 1 Catalyst component I is Zn 0.33 Al 0.67 O 1.33 Component II is a conventional statically synthesized SAPO-11 molecular sieve (4). Through its SEM electron microscopy results, it can be found that the molecular sieve synthesized by the conventional method eventually forms large aggregate particles that are tightly packed, so that the molecular sieve has less exposed external surface, and the ratio of its external surface specific surface area to the total specific surface area of ​​the molecular sieve is low. Therefore, the value of iso / n in the final reaction result is very low, 13.

[0071] Comparative Example 2 Catalyst component I is Zn 0.33 Al 0.67 O 1.33 Component II is a conventional SAPO-11 molecular sieve available on the market. In its specific surface area results, the ratio of external surface specific surface area to total specific surface area is also very low, similar to the statically synthesized SAPO-11 molecular sieve. This indicates that the aggregate particles are larger in size and the exposed external surface is too small. Therefore, the iso / n value in the final reaction result is very low, 10.

[0072] The reaction results of the above embodiment and comparative examples 1-2 show that the SAPO-11 molecular sieve is synthesized by the rotary synthesis method and coupled with the oxide to perform a one-step synthesis gas to gasoline performance evaluation. The gasoline selectivity of the obtained product is as high as 70-90%, and the C5-C 11 The selectivity of aromatics is less than 30%, C5-C 11The ratio of isoparaffins to normal paraffins (iso / n) can reach 15-60, and the selectivity of byproduct methane is less than 3%; the ratio of the specific surface area of ​​the molecular sieve's outer surface to the total specific surface area can be affected by simply adjusting the rotation rate of the synthesis process, thereby affecting the ratio of isoparaffins to normal paraffins in the gasoline product. The performance of the rotationally synthesized SAPO-11 molecular sieve is far superior to that of the ordinary statically synthesized SAPO-11 and commercial SAPO-11 molecular sieves.

[0073] Comparative Example 3 The catalyst only contains component I, namely Zn 0.33 Al 0.67 O 1.33 , which has a very low CO conversion rate, and the hydrocarbons in the product are mainly CH4, with almost no C5-C 11 components, indicating that the gasoline production effect of the present invention cannot be achieved by using only the oxide components.

[0074] The catalyst of Comparative Example 4 contains only component II, i.e., SAPO-11 molecular sieve synthesized by 2 rotations, which does not have the ability to convert CO and does not have the performance of synthesizing gasoline from synthesis gas, indicating that the use of molecular sieve components alone cannot achieve the gasoline production effect of the present invention.

[0075] In summary, the use of a simple rotational synthesis method to synthesize SAPO-11 molecular sieves can more effectively produce gasoline with a high isoparaffin content, which cannot be achieved by using only oxide components or only molecular sieve components.

Claims

1. A method for directly converting synthesis gas into gasoline, characterized in that: The synthesis gas is used as the reaction raw material, and the conversion reaction is carried out on a fixed bed or a moving bed. The catalyst used includes component I and component II, which are mechanically mixed together. The active component of component I is a metal oxide, and component II is a SAPO-11 molecular sieve. The metal oxide is Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Mn b Al (1-a-b) O x 、Zn a Cr b Al (1-a-b) O x 、Zn a Cr b Mn (1-a-b) O x One or more of the following, wherein the value range of x is 0.7-3.7, the value range of a is 0-1, and the value range of a+b is 0-1; the Zn a Cr (1-a) O x 、Zn a Al (1-a) O x 、Zn a Mn b Al (1-a-b) O x 、Zn a Cr b Al (1-a-b) O x 、Zn a Cr b Mn (1-a-b) O x The specific surface area is 5-250m 2 / g; The specific surface area of ​​the outer surface of the SAPO-11 molecular sieve accounts for 20%-50% of the total specific surface area of ​​the molecular sieve; The preparation method of the SAPO-11 molecular sieve comprises the following steps: (1) Mix di-n-propylamine, silicon source, aluminum source, phosphoric acid and water, and age at room temperature for 2-24 hours; (2) transferring the gel obtained in step (1) to a hydrothermal reactor and rotating the reaction mixture at 180-200° C. and 10-60 rpm / min for crystallization for 24-48 hours; (3) After the crystallization is completed, the reactor is cooled to room temperature in a water bath, centrifuged, washed, and the obtained precipitate is dried and then calcined in air at 500-700° C. for 1-12 h to obtain the SAPO-11 molecular sieve.

2. The method according to claim 1, characterized in that The SAPO-11 molecular sieve has medium-strong acid characteristics, and the amount of medium-strong acid sites is 0.05-0.5 mol / kg.

3. The method according to claim 1, characterized in that: The silicon source includes one of silica sol, fumed silica, silica gel, tetraethyl orthosilicate, and white carbon black, and the aluminum source includes aluminum isopropoxide or pseudo-boehmite.

4. The method according to claim 1, characterized in that: The silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, and the phosphoric acid is calculated as P2O5, n(SiO2) / n(Al2O3)=0.3, n(DPA) / n(Al2O3)=1.4, n(H2O) / n(Al2O3)=50, n(P2O5) / n(Al2O3)=1.

5. The method according to claim 1, characterized in that: The weight ratio between the active ingredient in component I and component II is 0.1-20.

6. The method according to claim 1, characterized in that: The pressure of the synthesis gas is 0.5-10MPa; the reaction temperature is 300-600°C; the space velocity is 300-12000mL / g / h; the synthesis gas is a H2 / CO mixed gas, and the H2 / CO ratio is 0.2-3.5.

Images