Double-zeolite system composite catalyst as well as preparation method and application thereof

Abstract

The invention discloses a double-zeolite system composite catalyst and a preparation method and application thereof, and belongs to the technical field of synthesis of hydrocarbon compounds, the double-zeolite system composite catalyst is composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies, the two different products refer to propane and butane, and the molecular sieves comprise beta, SSZ-13 and SAPO-34. According to the invention, carbon dioxide and hydrogen are used as raw materials, a ZnCr bimetallic catalyst and two molecular sieves with different product tendencies are compounded to form the bifunctional catalyst, the liquefied petroleum gas is directly synthesized under the reaction conditions of 350 DEG C and 5 MPa, and accurate regulation and control of the relative proportion of propane and butane in the LPG product can be realized. By regulating and controlling the relative mass of the double molecular sieves and accurately controlling the relative content of propane and butane in the LPG product, the large-range regulation of the weight ratio of propane to butane between 0.53 and 4.31 is successfully realized, meanwhile, the equipment investment can be reduced, the energy consumption can be reduced, the operation cost can be reduced, few byproducts are produced, and the economic benefit is remarkable.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthesis of hydrocarbon compounds, and relates to a method for synthesizing hydrocarbon compounds by hydrogenating carbon dioxide, and specifically to a double zeolite system composite catalyst and a method for accurately and dynamically regulating the components of LPG in the carbon dioxide hydrogenation product. Background Art

[0002] As the world's population increases, the demand for LPG (Liquefied Petroleum Gas) fuel is also growing. It is estimated that the annual production of LPG will reach 350 million tons in 2030 and will remain at 400 million tons by 2050. With the rapid growth of market demand for LPG and the decreasing availability of cheap and easy-to-collect petroleum resources, countries around the world are actively developing new technologies for LPG production.

[0003] With the increasing development of petrochemical resources and the development of society, the environmental problems caused by carbon dioxide emissions are becoming increasingly serious. Carbon dioxide emission reduction and resource utilization have become the focus of attention of countries around the world. How to convert carbon dioxide into LPG is undoubtedly of great significance for carbon dioxide emission reduction, conversion and utilization, and solving the LPG raw material problem.

[0004] In actual industrial production, the desired product may not be a single chemical or a chemical with a fixed composition, but also a mixture containing variable components. Taking LPG as an example, considering the difference in cost and the difference in boiling points of propane and butane, LPG suppliers need to adjust the ratio of propane and butane in LPG according to temperature and season. In addition, as an engine fuel, different proportions of LPG have been shown to be closely related to the combustion noise, emissions and knock characteristics of dual-fuel engines. It is worth noting that a propane and butane mixture with an appropriate proportion exhibits higher comprehensive performance than the two gases alone, so controllable regulation of product distribution is crucial.

[0005] At present, in the process of carbon dioxide hydrogenation, there are certain technical problems in achieving precise adjustment of product distribution and pursuing high selectivity of specific hydrocarbons. Therefore, finding a technology for producing LPG by carbon dioxide hydrogenation with high conversion rate and high selectivity, and adjusting the specific ratio of propane and butane in LPG, is not only of great significance to the resource utilization of carbon dioxide, but also solves the problem of LPG resource shortage and subsequent specific application of the industry. Summary of the invention

[0006] In view of the problems of low selectivity, low carbon dioxide conversion rate and difficult control of the ratio of propane and butane in the existing carbon dioxide hydrogenation to LPG, the present invention proposes a method for applying a double zeolite system composite catalyst to the carbon dioxide hydrogenation to LPG, and simultaneously adjusting the ratio of propane and butane in LPG. The synthesis method has the characteristics of high CO2 conversion rate, high LPG selectivity and controllable propane and butane ratio.

[0007] The concept of the present invention is: using carbon dioxide and hydrogen as raw materials, using a composite catalyst composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies, under certain reaction conditions, directly synthesizing LPG and regulating the ratio of propane and butane. Its reaction route mainly undergoes four steps: CO2 hydrogenation to synthesize methanol, methanol dehydration to synthesize light olefins, and light olefin hydrogenation to synthesize LPG. It not only greatly improves the conversion efficiency of carbon dioxide, but also has the characteristics of high LPG selectivity and controllable propane and butane ratio.

[0008] In order to solve the above technical problems, the first aspect of the present invention provides a composite catalyst, which is composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies, wherein the two different products are propane and butane, and the molecular sieves include β, SSZ-13 and SAPO-34; the methanol synthesis catalyst includes a ZnCr bimetallic catalyst.

[0009] Specifically, the composite catalyst of the present invention is composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies. The methanol synthesis catalyst includes a ZnCr bimetallic catalyst. The oxygen vacancies on the interface of ZnO and ZnCr2O4 are more conducive to CO2 adsorption and the formation of reaction intermediates HCOO* and H3CO* than the oxygen vacancies on the pure spinel phase, thereby accelerating the methanol synthesis reaction. The two high-conversion molecular sieves with different product tendencies refer to a combination of β and SSZ-13, or a combination of β and SAPO-34, so that the ratio of propane and butane can be controllably adjusted.

[0010] The SiO2 / Al2O3 of the molecular sieve β is 20-50; the SiO2 / Al2O3 of the molecular sieve SAPO-34 is 0.1-0.5; and the SiO2 / Al2O3 of the molecular sieve SSZ-13 is 10-30.

[0011] As a further improvement of the above scheme, the molar ratio of Zn / Cr in the ZnCr bimetallic catalyst is 1:2-5:1, preferably 1:2, 1:1, 3:1, 5:1, respectively denoted as 1Zn2Cr, 1Zn1Cr, 3Zn1Cr, 5Zn1Cr.

[0012] The ZnCr bimetallic catalyst with different Zn / Cr ratios is synthesized by coprecipitation. The coprecipitation process is as follows: a soluble Zn salt and a soluble Cr salt are used as Zn source and Cr source respectively, and the soluble mixture is dissolved in 100mL-200mL deionized water and stirred according to the Zn / Cr molar ratio of 1:2, 1:1, 3:1, and 5:1. An alkali salt that can be completely decomposed under air conditions at 400°C is used as a precipitant and dissolved in 100mL-300mL deionized water. The two solutions are added dropwise to 50mL-100mL deionized water at 60°C-80°C for stirring, and the pH of the system is maintained at 7-8. When any one of the solutions is exhausted, the reaction is completed, and the resulting turbid solution is aged at 60°C-80°C for 1-3 hours, washed and filtered to a pH of 7, dried at 60°C-80°C overnight, and the catalyst is calcined at 400°C-600°C for 4-6 hours to obtain a ZnCr bimetallic catalyst.

[0013] As a further improvement of the above scheme, the β and SSZ-13 molecular sieves are converted to H type (proton type) by ion exchange before use, which are recorded as Hβ and HSSZ-13 (except SAPO-34 molecular sieve).

[0014] As a further improvement of the above scheme, the mass ratio of the methanol synthesis catalyst to the molecular sieve Hβ and HSSZ-13 (or SAPO-34) is 1:(0-3):(0-3).

[0015] The second aspect of the present invention provides a method for preparing the composite catalyst, comprising the following steps:

[0016] (1) Convert the selected molecular sieve to H type (except SAPO-34 molecular sieve) by ion exchange method;

[0017] (2) Mixing the methanol synthesis catalyst with the H-type molecular sieve prepared in step (1) and / or with the SAPO-34 molecular sieve to obtain a composite catalyst.

[0018] As a further improvement of the above scheme, the modification process of the ion exchange is: 1g-5g of the molecular sieve is treated with 2mol / L-5mol / L (NH4)2CO3 solution at 60℃-90℃ for 3-6 hours. The ion exchange process is repeated 2-4 times. Subsequently, the obtained product is filtered, washed and dried. Finally, the dried product is calcined at 400℃-800℃ for 2-6 hours to obtain the target product H-type molecular sieve.

[0019] As a further improvement of the above scheme, the methanol synthesis catalyst and the two molecular sieves with different product tendencies are mixed in a powder mixing manner.

[0020] Preferably, the powder mixing process is: freely mix the methanol synthesis catalyst and two different product-prone molecular sieves according to the use requirements, and then grind, tablet and crush into 20-40 mesh.

[0021] The third aspect of the present invention provides a method for synthesizing LPG with adjustable propane and butane ratio in the product, which is produced by converting carbon dioxide and hydrogen as reaction gases under the action of a composite catalyst; the composite catalyst is composed of a methanol synthesis catalyst, an SSZ-13 or SAPO molecular sieve that tends to produce propane, and a β molecular sieve that tends to produce butane.

[0022] Preferably, the molar ratio of hydrogen to carbon dioxide is (1-4):1, more preferably, the molar ratio of hydrogen to carbon dioxide is (2-3):1.

[0023] As a further improvement of the above scheme, the method for synthesizing LPG comprises the following steps:

[0024] The composite catalyst is placed in a reactor, hydrogen is introduced, and the temperature is increased; then the reaction gas is introduced, the pressure and temperature are increased to react, and LPG is obtained.

[0025] Specifically, during the synthesis process, the purpose of introducing hydrogen first is mainly to reduce the active metal components in the methanol synthesis catalyst.

[0026] Preferably, the temperature is raised to 260°C-400°C; more preferably, the temperature is raised to 300°C-380°C.

[0027] Preferably, the flow rate of the reaction gas is 1000 mL / min. -1 h -1 -6000mLg -1 h -1 More preferably, the flow rate of the reaction gas is 2000mLg -1 h -1 -4000mLg -1 h -1 .

[0028] Preferably, the pressure is increased to 3MPa-6MPa; more preferably, the pressure is increased to 4MPa-5MPa.

[0029] As a further improvement of the above scheme, the method for controlling the ratio of propane to butane comprises the following steps:

[0030] The purpose of regulating the propane-butane ratio in the product is achieved by changing the mass ratio of SSZ-13 or SAPO-34 molecular sieves with higher propane selectivity and β molecular sieves with higher butane selectivity.

[0031] Compared with the prior art, the above solution of the present invention has at least the following technical effects or advantages:

[0032] The composite catalyst of the invention is composited by a methanol synthesis catalyst and two molecular sieves with different product tendencies. The methanol synthesis catalyst comprises a ZnCr bimetallic catalyst. The oxygen vacancies on the interface of ZnO and ZnCr2O4 are more conducive to CO2 adsorption and the formation of reaction intermediates HCOO* and H3CO* than the oxygen vacancies on the pure spinel phase, thereby accelerating the methanol synthesis reaction. The two high-conversion molecular sieves with different product tendencies include a combination of β and SSZ-13 and a combination of β and SAPO-34, so that the ratio of propane and butane can be controlled and adjusted.

[0033] When the composite catalyst of the present invention is used to synthesize LPG by hydrogenation of carbon dioxide, the CO2 conversion rate can reach up to 30%, the LPG selectivity can reach up to 80%, and the propane / butane mass ratio can be successfully adjusted in a wide range between 0.53 and 4.31. This method solves the problems of subsequent product separation and mixing, facilitates use in multiple scenarios, and can reduce equipment investment, energy consumption, and operating costs, and has few by-products and significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The SEM images of the ZnCr bimetallic catalysts with different ratios in Example 1;

[0035] Figure 2 The XPS O1s spectra of the ZnCr bimetallic catalysts with different ratios in Example 1;

[0036] Figure 3 CO2-TPD-MS spectra of ZnCr bimetallic catalysts with different ratios in Example 1;

[0037] Figure 4 These are SEM images of SSZ-13-15 molecular sieve before and after ion exchange in Example 4. (a), (b), and (c) are photos of SSZ-13-15 molecular sieve at 1,000, 40,000, and 100,000 magnifications, respectively, before ion exchange; (d), (e), and (f) are photos of HSSZ-13-15 molecular sieve at 1,000, 40,000, and 100,000 magnifications, respectively, after ion exchange;

[0038] Figure 5 These are SEM images of the β-30 molecular sieve before and after ion exchange in Example 4. (a), (b), and (c) are photos of the β-30 molecular sieve before ion exchange at 1,000 times, 40,000 times, and 100,000 times, respectively; (d), (e), and (f) are photos of the β-30 molecular sieve after ion exchange at 1,000 times, 40,000 times, and 100,000 times, respectively;

[0039] Figure 6The pyridine infrared spectra of SSZ-13-15 molecular sieve before and after ion exchange in Example 4. (a) SSZ-13-15 molecular sieve before ion exchange; (b) HSSZ-13-15 molecular sieve after ion exchange;

[0040] Figure 7 The pyridine infrared spectra of β-30 molecular sieve before and after ion exchange in Example 4. (a) β-30 molecular sieve before ion exchange; (b) Hβ-30 molecular sieve after ion exchange;

[0041] Figure 8 The XRD patterns of SSZ-13 molecular sieve before and after ion exchange in Example 4;

[0042] Fig. 9 The XRD patterns of the β-30 molecular sieve before and after ion exchange in Example 4;

[0043] Fig.10 This is the SEM image of SAPO-34 in Example 6. DETAILED DESCRIPTION

[0044] The present invention is described in detail below in conjunction with the examples, so that the technical personnel of the relevant technical field can understand the present invention. It is necessary to point out here that the examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. The non-essential improvements and adjustments made to the present invention by the skilled person in the relevant field according to the above invention content should still belong to the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods that are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0045] In order to evaluate the catalytic performance of the prepared catalyst, a fixed bed reactor with an inner diameter of 6 mm was used. Before the reaction, the catalyst was reduced with 20 mL / min of pure H2 at 400°C for 10 hours. After the reduction, the reactor was cooled to room temperature. Then, CO2 / H2 / Ar (volume ratio 27.0 / 68.0 / 5.0) reaction gas was charged into the reactor, and the system temperature and pressure were gradually increased to 350°C and 5.0 MPa, respectively, with GHSV=2000 mLg -1 h -1 (Relative to the weight of Zn-Cr). Two online gas chromatographs (GL Sciences GC320 and Shimadzu GC-2014) were used to identify gas phase products: one was equipped with a thermal conductivity detector (TCD, GC320) and an activated carbon column for the analysis of Ar, CO, CH4 and CO2; the other was equipped with a flame ionization detector (FID, GC-2014) and an HP-PLOT-Q capillary column for the analysis of light hydrocarbons.

[0046] SSZ-13 molecular sieve: commercial molecular sieve, Nankai Catalyst Factory.

[0047] SAPO-34 molecular sieve: commercial molecular sieve, Nankai Catalyst Factory.

[0048] β molecular sieve: commercial molecular sieve, Nankai Catalyst Factory.

[0049] Powder mix: first mix the powders of the components required for the catalyst together, then press them into tablets and granules.

[0050] Granular mix: The components required for the catalyst are compressed into granules separately and then the granules are mixed together.

[0051] The present invention will be further described below in conjunction with embodiments:

[0052] Example 1

[0053] A methanol synthesis catalyst, specifically a ZnCr bimetallic catalyst, wherein the molar ratio of Zn:Cr is 1:2, 1:1, 3:1, or 5:1.

[0054] A method for preparing a methanol synthesis catalyst, wherein Zn(NO3)2·6H2O and Cr(NO3)3·9H2O are used as Zn source and Cr source, respectively. A coprecipitation method is used to synthesize ZnCr bimetallic catalysts with different Zn / Cr ratios. Na2CO3 is used as a precipitant. A mixture of Zn(NO3)2·6H2O and Cr(NO3)3·9H2O with a Zn / Cr molar ratio of 1:2 (10.0 g, 26.9 g), 1:1 (10.0 g, 13.5 g), 3:1 (10.0 g, 4.5 g) and 5:1 (10.0 g, 2.7 g) is dissolved in 100 mL of deionized water and stirred, and 27 g, 18 g, 11 g and 10 g of Na2CO3 are dissolved in 200 mL of deionized water, respectively. The two solutions are added dropwise into deionized water at 60°C and stirred, and the pH is kept at 8. When any one of the solutions was consumed, the reaction was completed, and the resulting turbid solution was aged at 60°C for 1 hour, washed and filtered to a pH of 7. After drying at 60°C overnight, the catalyst was calcined at 400°C for 5 hours to obtain a methanol synthesis catalyst.

[0055] Application of a methanol synthesis catalyst in the synthesis of LPG by hydrogenation of carbon dioxide comprises the following steps:

[0056] The methanol synthesis catalyst of this embodiment was weighed to a mass of 0.3 g, and the temperature was raised to 400 ° C at a rate of 1.5 ° C / min under H2 gas flow, and then reduced for 10 hours. The H2 flow rate was 20 mL / min. After the reduction was completed; the reaction temperature was reduced to 350 ° C, and then carbon dioxide and hydrogen raw gas were introduced, and the pressure was increased to 5.0 MPa. The total gas flow rate was 2000 mL g -1 h -1 , the molar ratio of H2 to CO2 is 2.5:1.

[0057] By changing the molar ratio of Zn:Cr in the methanol synthesis catalyst, the catalyst activity and product selectivity were investigated at the same temperature, pressure and flow rate. The test results are shown in Table 1, where: C2 P Selectivity for C2 alkanes; C2-C4 ＝ The selectivity of C2-C4 olefins; C3 P Selectivity for propane; C4 P Selectivity for butane; C3 P –C4 P For C3 P and C4 P sum.

[0058] Table 1 Effect of different molar ratios on reaction performance

[0059]

[0060]

[0061] As shown in Table 1, by changing the molar ratio of Zn:Cr, it is found that among the ZnCr bimetallic catalysts, 3Zn1Cr exhibits the best catalytic performance, with a carbon dioxide conversion rate of 19.2% and a selectivity of 80.5% for methanol and dimethyl ether.

[0062] pass Figure 1 The SEM of the ZnCr bimetallic catalyst shows that the Zn and Cr elements in different proportions are evenly distributed, indicating that the metal sites are well dispersed during the synthesis process. Oxygen vacancies play a very important role in the adsorption and activation of carbon dioxide during the methanol synthesis process. Figure 2 The XPS O1s spectra of ZnCr bimetallic catalysts with different ratios showed that the content of oxygen vacancies decreased with the increase of Zn content. This is because 1Zn1Cr and 1Zn2Cr contain more spinel phases, and spinel phase ZnCr2O4 is more likely to produce oxygen vacancies, so it shows a larger oxygen vacancy content. Figure 3The following are the CO2-TPD-MS spectra of ZnCr bimetallic catalysts with different proportions. The results show that 1Zn2Cr and 1Zn1Cr with more oxygen vacancies adsorb less CO2 than 3Zn1Cr and 5Zn1Cr. This is because the excess oxygen density on ZnCr2O4 will weaken the adsorption of carbon dioxide to a certain extent. At the same time, with the increase of ZnO phase, there are more ZnO / ZnCr2O4 interfaces in 3Zn1Cr and 5Zn1Cr catalysts. This is because the interfacial oxygen vacancies have lower binding energy for CO2 than the oxygen vacancies in the spinel phase. Therefore, combined with the effects of oxygen vacancy density and binding energy, 3Zn1Cr exhibits the best catalytic performance.

[0063] The results showed that the introduction of ZnO had little effect on the structural properties of the oxide itself, but the presence of ZnO affected the interaction between CO2 and ZnCr2O4, thereby greatly improving the catalytic performance of the catalyst. The oxygen vacancies on the surface of the reduced ZnCr2O4 were the active sites for the CO2 activation reaction, while the excessively high Zn / Cr ratio made the proportion of ZnCr2O4 too low, which in turn led to a decrease in the catalytic performance of the catalyst. Therefore, 3Zn1Cr exhibited the best catalytic performance.

[0064] Example 2

[0065] A composite catalyst is composed of a methanol synthesis catalyst and a product-oriented molecular sieve. The methanol synthesis catalyst is specifically a ZnCr bimetallic catalyst with a Zn:Cr molar ratio of 3:1. The high-conversion molecular sieve with a product tendency is specifically a β molecular sieve. The specific mass ratio of the methanol synthesis catalyst to the molecular sieve is 1:2.

[0066] A method for preparing a composite catalyst comprises the following steps:

[0067] (1) Weigh 5g of molecular sieve β-25, β-30, and β-40 respectively, dissolve in 100mL of 3mol / L (NH4)2CO3 solution, stir in a water bath at 70℃ for 3 hours, and repeat the ion exchange process 3 times. Subsequently, the obtained zeolite is filtered, washed, and dried at 80℃. Finally, the zeolite is calcined at 600℃ for 6 hours to obtain Hβ-25, Hβ-30, and Hβ-40 molecular sieves. 25, 30, and 40 in β-25, β-30, and β-40 refer to different silicon-aluminum ratios of β molecular sieves.

[0068] (2) The methanol synthesis catalyst 3Zn1Cr and the Hβ-25, Hβ-30, and Hβ-40 molecular sieves obtained in step (1) are respectively tableted and crushed into 20-40 mesh sizes, and then mixed with Hβ molecular sieves with different silicon-aluminum ratios at the same mass ratio to obtain the composite catalyst of this embodiment.

[0069] A method for synthesizing LPG comprises the following steps:

[0070] The composite catalyst of this embodiment was weighed and placed in a stainless steel fixed bed reactor (the mass of the methanol synthesis catalyst 3Zn1Cr was kept constant at 0.3 g), and the temperature was raised to 400 ° C at a rate of 1.5 ° C / min under H2 gas flow, and then reduced for 10 hours, the H2 flow rate was 20 mL / min, and after the reduction was completed; the reaction temperature was 350 ° C, and then carbon dioxide and hydrogen raw gas were introduced, and the pressure was increased to 5.0 MPa, and the total gas flow rate was 2000 mL g -1 h -1 , the molar ratio of H2 to CO2 is 2.5:1.

[0071] By changing the silicon-aluminum ratio of the molecular sieve, the changes in catalyst activity, product selectivity and propane-to-butane ratio at the same temperature, pressure and flow rate were explored. The test results are shown in Table 2, where: C2 P Selectivity for C2 alkanes; C2-C4 ＝ The selectivity of C2-C4 olefins; C3 P Selectivity for propane; C4 P Selectivity for butane; C5 + The selectivity for all products with carbon numbers above 5.

[0072] Table 2 Effect of different silicon-aluminum ratios of Hβ molecular sieves on reaction performance

[0073]

[0074] As can be seen from Table 2, the mixture of 3Zn1Cr catalyst and Hβ-30 molecular sieve has a higher CO2 conversion rate and selectivity for the target product LPG. The CO2 conversion rate reaches 26.34%, the CO selectivity is 47.64%, and the selectivity for the target product LPG is 78.57%. At the same time, it can be found that at various silicon-aluminum ratios, Hβ molecular sieve only shows a higher selectivity for butane. The internal ratio of LPG produced by this method cannot meet the scenario with a higher propane usage ratio.

[0075] Example 3

[0076] A composite catalyst is composed of a methanol synthesis catalyst and a product-oriented molecular sieve, wherein the methanol synthesis catalyst is specifically a ZnCr bimetallic catalyst with a Zn:Cr molar ratio of 3:1, and a product-oriented high-conversion molecular sieve includes SSZ-13 and SAPO-34 molecular sieves, and the specific mass ratio of the methanol synthesis catalyst to the molecular sieve is 1:2.

[0077] A method for preparing a composite catalyst comprises the following steps:

[0078] (1) Weigh 5g of molecular sieves SSZ-13-15, SSZ-13-20, and SSZ-13-30 respectively, dissolve in 100mL of 4mol / L (NH4)2CO3 solution, stir in a water bath at 70°C for 3 hours, and repeat the ion exchange process 3 times. Subsequently, the obtained zeolite is filtered, washed, and dried at 80°C. Finally, the zeolite is calcined at 600°C for 6 hours to obtain HSSZ-13-15, HSSZ-13-20, and HSSZ-13-30 molecular sieves. 15, 20, and 30 in SSZ-13-15, SSZ-13-20, and SSZ-13-30 represent different silicon-aluminum ratios of SSZ-13 molecular sieves, respectively.

[0079] (2) The methanol synthesis catalyst 3Zn1Cr and the HSSZ-13-15, HSSZ-13-20, HSSZ-13-30 molecular sieves and SAPO-34 molecular sieves prepared in step (1) are respectively pressed into tablets, crushed into 20-40 mesh, and mixed with HSSZ-13 molecular sieves and SAPO-34 molecular sieves with different silicon-aluminum ratios at the same mass ratio to obtain the composite catalyst of this embodiment.

[0080] A method for synthesizing LPG comprises the following steps:

[0081] The composite catalyst of this embodiment was weighed and placed in a stainless steel fixed bed reactor (the mass of the methanol synthesis catalyst 3Zn1Cr was kept constant at 0.3 g), and the temperature was raised to 400 ° C at a rate of 1.5 ° C / min under H2 gas flow, and then reduced for 10 hours, the H2 flow rate was 20 mL / min, and after the reduction was completed; the reaction temperature was 350 ° C, and then carbon dioxide and hydrogen raw gas were introduced, and the pressure was increased to 5.0 MPa, and the total gas flow rate was 2000 mL g -1 h -1 , the molar ratio of H2 to CO2 is 2.5:1.

[0082] By changing the silicon-aluminum ratio of HSSZ-13 molecular sieve, the changes in catalyst activity, product selectivity and propane-to-butane ratio at the same temperature, pressure and flow rate were explored. The test results are shown in Table 3, where: C2 P Selectivity for C2 alkanes; C2-C4 ＝ The selectivity of C2-C4 olefins; C3 P Selectivity for propane; C4 P Selectivity for butane; C5 + The selectivity for all products with carbon numbers above 5.

[0083] Table 3 Effect of different silicon-aluminum ratios on reaction performance

[0084]

[0085] It can be seen from Table 3 that the mixture of 3Zn1Cr catalyst and HSSZ-13-15 molecular sieve has a higher CO2 conversion rate and selectivity for the target product LPG. The CO2 conversion rate reaches 24.71%, the CO selectivity is 53.6%, and the selectivity for the target product LPG is 74.54%. At the same time, it can be found that at various silicon-aluminum ratios, HSSZ-13 and SAPO-34 molecular sieves only show higher selectivity for propane. The internal proportion of LPG produced by this method cannot meet the scenario with a higher proportion of butane.

[0086] Example 4

[0087] A composite catalyst is composed of a methanol synthesis catalyst and a molecular sieve. The methanol synthesis catalyst is specifically a ZnCr bimetallic catalyst with a Zn:Cr molar ratio of 3:1. The molecular sieves include SSZ-13-15, HSSZ-13-15, β-30 and Hβ-30 molecular sieves. The specific mass ratio of the methanol synthesis catalyst to the molecular sieve is 1:2.

[0088] A method for preparing a composite catalyst comprises the following steps:

[0089] (1) Weigh 5 g of molecular sieve SSZ-13-15 and β-30 respectively, dissolve in 100 mL of 3 mol / L (NH4)2CO3 solution, stir in a water bath at 70°C for 3 hours, and repeat the ion exchange process 3 times. Subsequently, the obtained zeolite is filtered, washed, and dried at 80°C. Finally, the zeolite is calcined at 600°C for 6 hours to obtain HSSZ-13-15 and Hβ-30 molecular sieves.

[0090] (2) The methanol synthesis catalyst 3Zn1Cr and the HSSZ-13-15 and Hβ-30 molecular sieves obtained in step (1) are respectively tableted and crushed into 20-40 mesh sizes, and then mixed with the SSZ-13-15 and β-30 molecular sieves before ion exchange at the same mass ratio to obtain the composite catalyst of this embodiment.

[0091] A method for synthesizing LPG comprises the following steps:

[0092] The composite catalyst of this embodiment was weighed and placed in a stainless steel fixed bed reactor (the mass of the methanol synthesis catalyst 3Zn1Cr was kept constant at 0.3 g), and the temperature was raised to 400 ° C at a rate of 1.5 ° C / min under H2 gas flow, and then reduced for 10 hours, the H2 flow rate was 20 mL / min, and after the reduction was completed; the reaction temperature was 350 ° C, and then carbon dioxide and hydrogen raw gas were introduced, and the pressure was increased to 5.0 MPa, and the total gas flow rate was 2000 mL g -1 h -1 , the molar ratio of H2 to CO2 is 2.5:1.

[0093] By changing the acid sites of SSZ-13-15 and β-30, the catalyst activity, product selectivity and propane to butane ratio at the same temperature, pressure and flow rate were investigated. The test results are shown in Table 4, where: C2 P Selectivity for C2 alkanes; C2-C4 ＝ The selectivity of C2-C4 olefins; C3 P Selectivity for propane; C4 P Selectivity for butane; C5 + The selectivity for all products with carbon numbers above 5.

[0094] Table 4 Effect of different composite catalysts on reaction performance

[0095]

[0096] As shown in Table 4, both SSZ-13-15 and β-30 had a positive effect on the catalytic process after ion exchange, and the conversion rate of carbon dioxide and the selectivity to LPG were improved. Figure 4 SEM images of SSZ-13-15 molecular sieve before and after ion exchange Figure 5 From the SEM images of β-30 molecular sieves before and after ion exchange, it can be seen that the surface of the molecular sieve after ion exchange becomes rougher, and compared with commercial molecular sieves, its dispersion is more uniform, making its surface structure and overall distribution more conducive to contact with CO2 gas molecules, so it also has a better carbon dioxide conversion rate. Figure 6 Pyridine infrared spectrum of SSZ-13-15 molecular sieve before and after ion exchange Figure 7 The pyridine infrared spectra of β-30 molecular sieve before and after ion exchange show that the acid content of the molecular sieve after ion exchange has been significantly improved compared with the molecular sieve before ion exchange, which is more conducive to the subsequent hydrogenation reaction. Figure 8 , Fig. 9 As shown in the figure, the ion exchange did not damage the molecular sieve structure, so the selectivity for propane and butane did not change.

[0097] Example 5

[0098] A composite catalyst is composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies. The methanol synthesis catalyst is specifically a ZnCr bimetallic catalyst with a Zn:Cr molar ratio of 3:1. Two high-conversion molecular sieves with different tendencies include β and SSZ-13. The methanol synthesis catalyst and the two molecular sieves are mixed in powder form in a specific mass ratio of 1:(0-3):(0-3).

[0099] A method for preparing a composite catalyst comprises the following steps:

[0100] (1) Weigh 5 g of molecular sieve β-30 and SSZ-13-15, respectively, and dissolve them in 100 mL of 3 mol / L (NH4)2CO3 solution, respectively, and stir in a water bath at 70°C for 3 hours. The ion exchange process is repeated 3 times. Subsequently, the obtained zeolite is filtered, washed, and dried at 80°C. Finally, the zeolite is calcined at 600°C for 6 hours to obtain Hβ-30 and HSSZ-13-15 molecular sieves.

[0101] (2) The methanol synthesis catalyst 3Zn1Cr and the Hβ-30 and HSSZ-13-15 molecular sieves prepared in step (1) were respectively tableted and crushed into 20-40 mesh sizes, and the powders were mixed by changing different mass ratios to obtain the composite catalyst of this embodiment.

[0102] A method for synthesizing LPG capable of regulating the ratio of propane to butane in a product comprises the following steps:

[0103] The composite catalyst of this embodiment was weighed and placed in a stainless steel fixed bed reactor (the mass of the methanol synthesis catalyst 3Zn1Cr was kept constant at 0.3 g), and the temperature was raised to 400 ° C at a rate of 1.5 ° C / min under H2 gas flow, and then reduced for 10 hours, the H2 flow rate was 20 mL / min, and after the reduction was completed; the reaction temperature was 350 ° C, and then carbon dioxide and hydrogen raw gas were introduced, and the pressure was increased to 5.0 MPa, and the total gas flow rate was 2000 mL g -1 h -1 , the molar ratio of H2 to CO2 is 2.5:1.

[0104] The mass ratio of methanol synthesis catalyst to two molecular sieves with different product tendencies was changed to explore the changes in catalyst activity, product selectivity and propane-to-butane ratio at the same temperature, pressure and flow rate. The test results are shown in Table 5, where: C2 P Selectivity for C2 alkanes; C2-C4 ＝ The selectivity of C2-C4 olefins; C3 P Selectivity for propane; C4 P Selective for butane; others include C5 + Selectivity for hydrocarbons and isomers of C3 and C4 hydrocarbons.

[0105] Table 5 Effect of different mass ratios on reaction performance and product ratio

[0106]

[0107]

[0108] It can be seen from Table 5 that under the same reaction conditions, the adjustable degree of propane / butane in the dual zeolite system depends on the ratio of each zeolite. At the same time, by increasing the mass of the corresponding zeolite, LPG containing more propane or butane can be produced. In addition, it is worth noting that the LPG composition seems to be only related to the relative mass ratio of the two zeolites, and has no obvious relationship with the ratio of the two zeolites to 3Zn1Cr. For example, when 3Zn1Cr:β-30:SSZ-13-15 is 1:1:1 and 1:1.5:1.5, the ratio of propane to butane is similar, which strongly proves the limitation of adjusting the product by a single zeolite. By changing the mass ratio between the dual molecular sieves, the controllable adjustment of the propane to butane ratio between 0.53 and 1.82 was successfully achieved.

[0109] Example 6

[0110] A composite catalyst is composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies. The methanol synthesis catalyst is specifically a ZnCr bimetallic catalyst with a Zn:Cr molar ratio of 3:1. Two high conversion molecular sieves with different tendencies include β and SAPO-34. The specific mass ratio of the methanol synthesis catalyst to the two molecular sieves is 1:(0-3):(0-3). The SEM picture of SAPO-34 is as follows Fig.10 shown.

[0111] A method for preparing a composite catalyst comprises the following steps:

[0112] (1) Weigh 5 g of molecular sieve β-30, dissolve in 100 mL of 3 mol / L (NH4)2CO3 solution, stir in a water bath at 70°C for 3 hours, and repeat the ion exchange process 3 times. Subsequently, the obtained zeolite is filtered, washed, and dried at 80°C. Finally, the zeolite is calcined at 600°C for 6 hours to obtain Hβ-30 molecular sieve, and SAPO-34 is not subjected to ion exchange treatment.

[0113] (2) The methanol synthesis catalyst 3Zn1Cr and the Hβ-30 and SAPO-34 molecular sieves prepared in step (1) were respectively tableted and crushed into 20-40 mesh sizes, and the powders were mixed by changing different mass ratios to obtain the composite catalyst of this embodiment.

[0114] A method for synthesizing LPG capable of regulating the ratio of propane to butane in a product comprises the following steps:

[0115] The composite catalyst of this embodiment was weighed and placed in a stainless steel fixed bed reactor (the mass of the methanol catalyst was kept constant at 0.3 g), and then reduced for 10 hours at a rate of 1.5 ° C / min under H2 gas flow to 400 ° C, and the H2 flow rate was 20 mL / min. After the reduction was completed; the reaction temperature was 350 ° C, and then carbon dioxide and hydrogen raw gas were introduced, and the pressure was increased to 5.0 MPa, and the total gas flow rate was 2000 mL g -1 h -1 , the molar ratio of H2 to CO2 is 2.5:1.

[0116] The mass ratio of methanol synthesis catalyst to two molecular sieves with different product tendencies was changed to explore the changes in catalyst activity, product selectivity and propane-to-butane ratio at the same temperature, pressure and flow rate. The test results are shown in Table 6, where: C2 P Selectivity for C2 alkanes; C2-C4 ＝ The selectivity of C2-C4 olefins; C3 P Selectivity for propane; C4 P Selective for butane; others include C5 + Selectivity for hydrocarbons and isomers of C3 and C4 hydrocarbons.

[0117] Table 6 Effect of different mass ratios on reaction performance and product ratio

[0118]

[0119] Table 6 draws the same conclusion as Table 5. Since SAPO-34 has the highest preference for propane, the synergistic effect of Hβ and SAPO-34 increases the upper limit of the propane / butane ratio from 1.82 to 4.31 compared with the system constructed by Hβ and HSSZ-13 zeolite.

[0120] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A double zeolite system composite catalyst, characterized in that: The invention is composed of a methanol synthesis catalyst and two molecular sieves with different product tendencies; wherein the two different products are propane and butane; the molecular sieves include β, SSZ-13 and SAPO-34; and the methanol synthesis catalyst includes a ZnCr bimetallic catalyst.

2. A dual zeolite system composite catalyst according to claim 1, characterized in that: The molecular sieve β and SSZ-13 are converted into proton-type molecular sieves Hβ and HSSZ-13 by ion exchange before use; the two molecular sieves with different product tendencies specifically refer to a combination of Hβ and HSSZ-13 after ion exchange, or a combination of Hβ and SAPO-34 after ion exchange.

3. A dual zeolite system composite catalyst according to claim 2, characterized in that: The mass ratio of the methanol synthesis catalyst to Hβ and HSSZ-13, or to Hβ and SAPO-34 is 1:(0-3):(0-3).

4. A dual zeolite system composite catalyst according to claim 1, characterized in that: The molar ratio of Zn / Cr in the ZnCr bimetallic catalyst is 1:2-5:

1.

5. A dual zeolite system composite catalyst according to claim 4, characterized in that: The ZnCr bimetallic catalyst with different Zn / Cr ratios is synthesized by a coprecipitation method. The coprecipitation process comprises the following steps: using a soluble Zn salt and a soluble Cr salt as a Zn source and a Cr source respectively, dissolving the soluble mixture in deionized water according to the Zn / Cr molar ratio and stirring; using an alkali salt as a precipitant and dissolving it in deionized water; dropping the two solutions into the deionized water at 60-80°C and stirring, during which the pH value of the system is kept at 7-8, and when any one of the solutions is exhausted, the reaction is completed, and the obtained turbid liquid is aged at 60-80°C for 1-3 hours, washed and filtered to a pH value of 7, dried at 60-80°C, and then calcined at 400-600°C for 4-6 hours to obtain the ZnCr bimetallic catalyst.

6. A method for preparing a dual zeolite system composite catalyst according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) using an ion exchange method to treat industrial molecular sieves SSZ-13 and β to obtain proton-type HSSZ-13 and Hβ molecular sieves; (2) Mixing the methanol synthesis catalyst with the proton-type HSSZ-13 and Hβ molecular sieves obtained in step (1), and / or with the SAPO-34 molecular sieve to obtain a composite catalyst.

7. The preparation method according to claim 6, characterized in that: The ion exchange treatment process is as follows: 1g-5g of molecular sieves SSZ-13 and β are treated with 2mol / L-5mol / L (NH4)2CO3 solution at 60℃-90℃ for 3-6 hours, and the ion exchange process is repeated 2-4 times; the obtained products are filtered, washed and dried; and calcined at 400℃-800℃ for 2-6 hours to obtain proton-type HSSZ-13 and Hβ molecular sieves.

8. A method for synthesizing LPG, characterized in that: The LPG is converted with carbon dioxide and hydrogen as reaction gases under the action of a catalyst; the catalyst used is the double zeolite system composite catalyst described in any one of claims 1-5.

9. The method for synthesizing LPG according to claim 8, characterized in that: The catalyst is placed in a reactor, hydrogen is introduced, and the temperature is increased; then the reaction gas is introduced, the pressure and temperature are increased to react, and LPG is obtained; the molar ratio of hydrogen to carbon dioxide in the reaction gas is (1-4):1; the temperature range of the two heatings is 260℃-400℃; the flow rate of the reaction gas is 1000mLg - 1 h -1 -6000mLg -1 h -1 ;Increase pressure to 3MPa-6MPa.

10. The method for synthesizing LPG according to claim 8, characterized in that: By using the double zeolite system composite catalyst according to any one of claims 1 to 5, the propane / butane mass ratio in LPG is controlled between 0.53 and 4.31.

Images