Sr-composite molecular sieve catalyst and preparation method and application thereof

Abstract

The invention relates to the technical field of organic synthesis and discloses a Sr-composite molecular sieve catalyst as well as a preparation method and application thereof. The prepared ZSM-5 and SAPO-34 are subjected to composite modification, and the binder, the filler and the peptizing agent are introduced, so that the mechanical strength, the thermal stability and the forming performance of the catalyst are improved; by introducing the Sr metal salt, the too strong acidity of the molecular sieve can be reduced, side reactions caused by the too strong acidity are reduced, generation of carbon deposition can be inhibited, the catalyst can keep good stability in the long-term reaction process, and the service life of the catalyst is prolonged. The Sr-composite molecular sieve catalyst prepared by the method has the characteristics of excellent catalytic activity, high low-carbon olefin selectivity, strong stability and long service life, is highly in line with large-scale industrial production requirements, and shows remarkable economic value and wide industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, specifically to an Sr-composite molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Low-carbon olefins are important basic chemical raw materials. Methanol-to-olefins (MTO) is a key technology for producing low-carbon olefins via non-petroleum cracking routes, which can effectively alleviate the current contradiction between oil supply and demand. In the MTO reaction, SAPO-34 molecular sieve is a commonly used catalyst, but it has obvious limitations: its eight-membered ring microporous structure restricts the diffusion of aromatic hydrocarbon intermediates, causing these intermediates to accumulate in the pores. This not only causes pore blockage but also covers the acidic active sites of the catalyst, ultimately leading to carbon deposition and deactivation, significantly shortening the catalyst lifetime.

[0003] To address this issue, modification of SAPO-34 molecular sieves has become an important research direction. Appropriate modification can suppress coking reactions, reduce the frequency of catalyst circulation between the reactor and regenerator, and thus extend its service life. However, single modification methods have many shortcomings, such as easily leading to damage to the molecular sieve crystal structure, easy deposition of modified species, and difficulty in enriching surface chemical properties. In contrast, composite molecular sieves, as an emerging catalytic material, exhibit excellent performance in numerous catalytic reactions. They not only enhance the properties of molecular sieves... The synergistic effect of acids and Lewis acids enhances catalytic efficiency; it can also shorten the distance between different active components, allowing reactant molecules to reach active sites more quickly and accelerating the reaction process, providing a new approach to solving the bottleneck problem of MTO catalysts.

[0004] Patent application CN 105439788 B discloses a method for improving the olefin selectivity of the product in the methanol-to-olefins reaction. This method involves loading a SAPO-34 catalyst into a reactor, pre-purging with nitrogen at a rate of 50 mL / min for 2-3 hours at 500°C, and then purging with nitrogen at a mass hourly space velocity (HHSV) of 1 h⁻¹ under conditions of 350-550°C and 0.01 MPa-0.3 MPa. -1 Methanol and an additive are mixed and introduced into a reactor to react and produce olefins. This method can be used to improve the olefin selectivity of the product. However, the SAPO-34 catalyst used in this invention has poor stability and a short service life. Therefore, there is an urgent need to develop a catalyst with strong stability and long service life in the methanol-to-olefin process. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor stability, low service life, and low olefin selectivity of existing SAPO-34 catalysts in the catalytic production of low-carbon olefins from methanol, and to provide a Sr-composite molecular sieve catalyst, its preparation method, and its application. The Sr-composite molecular sieve catalyst prepared by the method described in this invention exhibits excellent catalytic activity, high selectivity for low-carbon olefins, strong stability, and long service life, highly meeting the needs of large-scale industrial production and demonstrating significant economic value and broad industrial application prospects.

[0006] To achieve the above objectives, the present invention provides a method for preparing Sr-composite molecular sieve catalysts, the method comprising the following steps:

[0007] (1) Mix the first aluminum source, phosphorus source, first silicon source, morpholine and water and perform the first aging, then perform the first hydrothermal crystallization reaction on the obtained first sol to obtain the first mixture;

[0008] (2) Mix the second aluminum source, sodium source, second silicon source, tetrapropylammonium hydroxide and water, then adjust the pH of the resulting mixture to 10-12, then carry out the second aging, and then carry out the second hydrothermal crystallization reaction of the resulting second sol to obtain the second mixture;

[0009] (3) The first mixture and the second mixture are mixed and subjected to a third hydrothermal crystallization reaction to obtain a composite molecular sieve dispersion. Then, the composite molecular sieve dispersion, binder, filler and adhesive are mixed, and then the mixture is successively shaped, dried and calcined to obtain a composite molecular sieve catalyst.

[0010] (4) The Sr metal salt is loaded onto the composite molecular sieve catalyst by impregnation, and then washed, dried and calcined in sequence.

[0011] Preferably, in step (1), the first aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, the first silicon source is calculated as SiO2, and the molar ratio of the first aluminum source, the phosphorus source, the first silicon source, morpholine and water is 1:(0.5-1.2):(0.3-1):(1-5):(50-100).

[0012] Preferably, in step (1), the conditions for the first aging include: a temperature of 20-25°C and a time of 10-14 hours.

[0013] Preferably, the conditions for the first hydrothermal crystallization reaction include: a temperature of 180-220°C and a time of 20-30 hours.

[0014] Preferably, in step (2), the second aluminum source is calculated as Al2O3, the sodium source is calculated as Na2O, the second silicon source is calculated as SiO2, and the molar ratio of the second aluminum source, the sodium source, the second silicon source, tetrapropylammonium hydroxide and water is 1:(30-60):(130-170):(45-60):(250-350).

[0015] Preferably, in step (2), the conditions for the second aging include: a temperature of 20-25°C and a time of 10-14 hours.

[0016] Preferably, the conditions for the second hydrothermal crystallization reaction include: a temperature of 160-200℃ and a time of 4-8h.

[0017] Preferably, in step (3), the weight ratio of the first mixture to the second mixture is 1.5-3:1.

[0018] Preferably, the weight ratio of the composite molecular sieve dispersion, the binder, the filler, and the adhesive solvent is (20-70):(12.5-50):(1-6):1.

[0019] Preferably, the binder is selected from at least one of kaolin, alumina, aluminosilicate compounds and boehmite.

[0020] Preferably, the filler is selected from at least one of guar gum powder, cellulose and graphite powder.

[0021] Preferably, the adhesive solvent is selected from at least one of hydrochloric acid, nitric acid, acetic acid, and citric acid.

[0022] Preferably, in step (3), the conditions for the third hydrothermal crystallization reaction include: a temperature of 160-200℃ and a time of 16-20h.

[0023] Preferably, the calcination conditions include: a heating rate of 1-5℃ / min, a temperature of 500-700℃, and a time of 4-10h.

[0024] Preferably, in step (4), the process of loading the Sr metal salt onto the composite molecular sieve catalyst by impregnation includes: impregnating the composite molecular sieve catalyst in an Sr metal salt impregnation solution, then stirring at a constant temperature of 70-85°C for 1-2 hours, and then letting it stand at 20-25°C for 2-3 hours.

[0025] Preferably, the concentration of the Sr metal salt impregnation solution is 0.5-2.5 wt%.

[0026] Preferably, the Sr metal salt is selected from at least one of strontium acetate chlorate, strontium nitrite, and strontium nitrate.

[0027] Preferably, in step (4), the calcination conditions include: a heating rate of 1-5℃ / min, a temperature of 500-700℃, and a time of 4-10h.

[0028] A second aspect of the present invention provides an Sr-composite molecular sieve catalyst prepared by the above method.

[0029] A third aspect of the present invention provides a method for preparing olefins from methanol, the method comprising: reacting methanol in the presence of the above-described Sr-composite molecular sieve catalyst to generate olefins.

[0030] The method described in this invention uses morpholine to guide the formation of SPAO-34 molecular sieve, controlling the pore structure and crystal morphology of the molecular sieve to form a regular eight-membered ring pore structure; it uses tetrapropylammonium hydroxide to guide the synthesis of ZSM-5 molecular sieve, adjusting the pore structure and crystal size of ZSM-5; and it performs composite modification on ZSM-5 and SAPO-34 with different topological structures and acid site distributions to achieve complementary advantages between the two molecular sieves. The synthesized composite molecular sieve can form abundant active centers and produce a multi-level pore structure and a synergistic effect of composite phase interface.

[0031] Secondly, the method described in this invention can improve the mechanical strength, thermal stability and molding performance of the catalyst by introducing binders, fillers and adhesives, thereby ensuring the high efficiency and stability of the Sr-composite molecular sieve catalyst in the methanol-to-olefins reaction.

[0032] Furthermore, the method described in this invention, by introducing Sr metal salt, not only reduces the excessive acidity of the molecular sieve and minimizes side reactions caused by excessive acidity, but also inhibits the formation of carbon deposits, enabling the catalyst to maintain good stability during long-term reactions and extending its service life. This results in Sr-composite molecular sieve catalysts prepared by this method exhibiting excellent catalytic activity, high selectivity for low-carbon olefins, strong stability, and long service life, highly meeting the needs of large-scale industrial production and demonstrating significant economic value and broad industrial application prospects. Detailed Implementation

[0033] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] The preparation method of the Sr-composite molecular sieve catalyst of the present invention includes the following steps:

[0036] (1) Mix the first aluminum source, phosphorus source, first silicon source, morpholine and water and perform the first aging, then perform the first hydrothermal crystallization reaction on the obtained first sol to obtain the first mixture;

[0037] (2) Mix the second aluminum source, sodium source, second silicon source, tetrapropylammonium hydroxide and water, then adjust the pH of the resulting mixture to 10-12, then carry out the second aging, and then carry out the second hydrothermal crystallization reaction of the resulting second sol to obtain the second mixture;

[0038] (3) The first mixture and the second mixture are mixed and subjected to a third hydrothermal crystallization reaction to obtain a composite molecular sieve dispersion. Then, the composite molecular sieve dispersion, binder, filler and adhesive are mixed, and then the mixture is successively shaped, dried and calcined to obtain a composite molecular sieve catalyst.

[0039] (4) The Sr metal salt is loaded onto the composite molecular sieve catalyst by impregnation, and then washed, dried and calcined in sequence.

[0040] In this invention, the first mixture is a molecular sieve stock solution containing SPAO-34 molecular sieve, and the second mixture is a molecular sieve raw material solution containing ZSM-5 molecular sieve.

[0041] In the method described in this invention, step (1) does not limit the type of the first aluminum source; it can be a commercially available product or prepared using methods conventional in the art. In some specific embodiments, the first aluminum source is boehmite and / or sodium aluminate.

[0042] In the method described in this invention, step (1) does not limit the type of phosphorus source; it can be a commercially available product or prepared using methods conventional in the art. In some specific embodiments, the phosphorus source is phosphoric acid.

[0043] In the method described in this invention, step (1) does not limit the type of the first silicon source; it can be a commercially available product or prepared using methods conventional in the art. In some specific embodiments, the first silicon source is tetraethyl orthosilicate.

[0044] In the method described in this invention, in step (1), morpholine is used as a template agent to guide the formation of SPAO-34 molecular sieve, control the pore structure and crystal morphology of the molecular sieve, and make it form a regular eight-membered ring pore structure.

[0045] In some embodiments, in step (1), in order to further improve the catalytic activity, low-carbon olefin selectivity, stability and service life of the Sr-composite molecular sieve catalyst, in a preferred case, the first aluminum source is based on Al2O3, the phosphorus source is based on P2O5, the first silicon source is based on SiO2, and the molar ratio of the first aluminum source, the phosphorus source, the first silicon source, morpholine and water is 1:(0.5-1.2):(0.3-1):(1-5):(50-100), preferably 1:(0.6-1):(0.4-0.8):(1.5-4):(55-95), and more preferably 1:(0.7-0.9):(0.5-0.7):(2-3):(60-90).

[0046] In some specific embodiments, the specific process of mixing the first aluminum source, the phosphorus source, the first silicon source, morpholine and water and performing the first aging in step (1) includes: mixing the phosphorus source and water, then adding the first aluminum source and the first silicon source under stirring at 20-25°C, stirring for 20-40 minutes, and then adding morpholine and performing the first aging.

[0047] In some specific implementations, in step (1), the first aging time can be 10-14 hours, preferably 11-13 hours.

[0048] In some specific embodiments, in step (1), the conditions for the first hydrothermal crystallization reaction include: a temperature of 180-220°C, preferably 190-210°C, and a time of 20-30h, preferably 22-25h.

[0049] In the method described in this invention, step (2) does not limit the type of the second aluminum source; it can be a commercially available product or prepared using conventional methods in the art. Preferably, the second aluminum source is at least one of sodium aluminate, boehmite, and aluminum isopropoxide.

[0050] In the method described in this invention, step (2) does not limit the type of sodium source; it can be a commercially available product or prepared using methods conventional in the art. In some specific embodiments, the sodium source is sodium hydroxide.

[0051] In the method described in this invention, step (2) does not limit the type of the second silicon source; it can be a commercially available product or prepared using methods conventional in the art. In some specific embodiments, the second silicon source is tetraethyl orthosilicate.

[0052] In the method described in this invention, in step (2), using tetrapropylammonium hydroxide as a template agent can guide the synthesis of ZSM-5 molecular sieves and can also adjust the pore structure and crystal size of ZSM-5.

[0053] In some embodiments, in step (2), in order to further improve the catalytic activity, low-carbon olefin selectivity, stability and service life of the Sr-composite molecular sieve catalyst, in a preferred case, the second aluminum source is based on Al2O3, the sodium source is based on Na2O, the second silicon source is based on SiO2, and the molar ratio of the second aluminum source, the sodium source, the second silicon source, tetrapropylammonium hydroxide and water is 1:(30-60):(130-170):(45-60):(250-350), preferably 1:(33-55):(135-165):(48-59):(260-340), and more preferably 1:(35-50):(140-160):(50-58):(280-330).

[0054] In some specific embodiments, the process of mixing the second aluminum source, the sodium source, the second silicon source, tetrapropylammonium hydroxide and water in step (2) includes: stirring and mixing the second aluminum source, the sodium source and water for 20-40 minutes, and then adding the second silicon source and tetrapropylammonium hydroxide under stirring at 20-25°C.

[0055] In the method described in this invention, in step (2), the pH value of the obtained mixture is adjusted to 10-12, preferably 10.5-11.5. In some embodiments, sulfuric acid may be used to adjust the pH value of the mixture.

[0056] In some specific implementations, in step (2), the second aging time can be 10-14 hours, preferably 11-13 hours.

[0057] In some specific embodiments, in step (2), the conditions for the second hydrothermal crystallization reaction include: the temperature can be 160-200℃, preferably 170-190℃; the time can be 4-8h, preferably 5-7h.

[0058] In some embodiments, in step (3), in order to further improve the catalytic activity, low-carbon olefin selectivity, stability and service life of the Sr-composite molecular sieve catalyst, preferably, the weight ratio of the first mixture to the second mixture is 1.5-3:1, more preferably 1.8-2.8:1, and more preferably 2-2.5:1. As a specific example, the weight ratio of the first mixture to the second mixture can be 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1 or 2.5:1.

[0059] In some specific embodiments, in step (3), the conditions for the third hydrothermal crystallization reaction include: the temperature can be 160-200℃, preferably 170-190℃; the time can be 16-20h, preferably 17-19h.

[0060] In some specific embodiments, the specific process of step (3) further includes: after the product of the third hydrothermal crystallization reaction is naturally cooled, it is first filtered and then membrane separated to obtain a composite molecular sieve dispersion with a water content of 15-35 wt%.

[0061] In the method described in this invention, the addition of the binder, the filler and the adhesive in step (3) can further improve the mechanical strength, thermal stability and molding performance of the Sr-composite molecular sieve catalyst, thereby ensuring the high efficiency and stability of the Sr-composite molecular sieve catalyst in the methanol-to-olefins reaction.

[0062] In the method described in this invention, step (3) does not limit the type of adhesive; various adhesives commonly used in the art can be used. Preferably, the adhesive is selected from at least one of kaolin, alumina, aluminosilicate compounds, and boehmite. More preferably, the adhesive is kaolin.

[0063] In the method described in this invention, step (3) does not limit the type of filler; various fillers commonly used in the art can be used. Preferably, the filler is selected from at least one of guar gum powder, cellulose, and graphite powder. More preferably, the filler is guar gum powder.

[0064] In the method described in this invention, step (3) does not limit the type of adhesive solvent; various adhesive solvents commonly used in the art can be used. Preferably, the adhesive solvent is selected from at least one of hydrochloric acid, nitric acid, acetic acid, and citric acid. More preferably, the adhesive solvent is citric acid.

[0065] In some embodiments, in step (3), in order to further improve the mechanical strength, thermal stability and molding performance of the Sr-composite molecular sieve catalyst, thereby ensuring the high efficiency and stability of the Sr-composite molecular sieve catalyst in the methanol-to-olefins reaction, in a preferred case, the weight ratio of the composite molecular sieve dispersion, the binder, the filler and the adhesive solvent is (20-70):(12.5-50):(1-6):1, preferably (30-60):(15-40):(2-5):1, and more preferably (35-50):(20-30):(2.5-4):1.

[0066] In some specific embodiments, in step (3), the drying conditions include: the temperature can be 90-120℃, preferably 100-110℃; the time can be 1-10h, preferably 2-5h.

[0067] In some specific embodiments, in step (3), the calcination conditions include: the heating rate can be 1-5℃ / min, preferably 1.5-4℃ / min; the temperature can be 500-700℃, preferably 530-600℃; and the time can be 4-10h, preferably 5-9h.

[0068] In the method described in this invention, the introduction of Sr metal salt in step (4) not only reduces the excessive acidity of the molecular sieve and minimizes side reactions caused by excessive acidity, but also inhibits the formation of carbon deposits, enabling the Sr-composite molecular sieve catalyst to maintain good stability during long-term reactions and extending its service life. Preferably, the Sr metal salt is selected from at least one of strontium acetate, strontium chlorate, strontium nitrite, and strontium nitrate. More preferably, the Sr metal salt is strontium acetate.

[0069] In some specific embodiments, in step (4), the process of loading the Sr metal salt onto the composite molecular sieve catalyst by impregnation includes: impregnating the composite molecular sieve catalyst in an Sr metal salt impregnation solution, then stirring at a constant temperature of 70-85°C for 1-2 hours, and then letting it stand at 20-25°C for 2-3 hours.

[0070] In some specific embodiments, in step (4), the Sr metal salt impregnation solution is a mixture of the Sr metal salt and water, and the concentration of the Sr metal salt impregnation solution can be 0.5-2.5 wt%, preferably 0.8-2.3 wt%, and more preferably 1-2 wt%. Specifically, the concentration of the Sr metal salt impregnation solution can be 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2 wt%.

[0071] In this invention, in step (4), the solid-liquid ratio of the composite molecular sieve catalyst to the Sr metal salt impregnation solution is not emphasized. It is only necessary to ensure that the composite molecular sieve catalyst is completely immersed in the Sr metal salt impregnation solution throughout the impregnation process.

[0072] In some specific embodiments, in step (4), the drying conditions include: the temperature can be 90-120℃, preferably 100-110℃; the time can be 1-10h, preferably 2-5h.

[0073] In some specific embodiments, in step (4), the calcination conditions include: the heating rate can be 1-5℃ / min, preferably 1.5-4℃ / min; the temperature can be 500-700℃, preferably 550-650℃; and the time can be 4-10h, preferably 5-9h.

[0074] The present invention also provides an Sr-composite molecular sieve catalyst prepared by the above method. This catalyst has the characteristics of excellent catalytic activity, high selectivity for low-carbon olefins, strong stability and long service life, which is highly compatible with the needs of large-scale industrial production and shows significant economic value and broad industrial application prospects.

[0075] The present invention further provides a method for preparing olefins from methanol, the method comprising: reacting methanol in the presence of the above-mentioned Sr-composite molecular sieve catalyst to generate olefins.

[0076] In some embodiments, the reaction is carried out in a fixed-bed reactor. Before the reaction, the Sr-composite molecular sieve catalyst is loaded into the fixed-bed reactor, and then methanol is introduced. The methanol is reacted and converted into olefins through the Sr-composite molecular sieve catalyst bed.

[0077] In some specific embodiments, the reaction conditions include: a temperature of 400-600℃, preferably 450-550℃; and a pressure of 0.1-10 MPa, preferably 1-5 MPa. Specifically, the reaction temperature can be 450℃, 470℃, 500℃, 520℃, or 550℃; and the reaction pressure can be 1 MPa, 2 MPa, 3 MPa, 4 MPa, or 5 MPa. In this invention, the pressure is gauge pressure.

[0078] In some specific embodiments, to further improve the selectivity of olefins, it is necessary to limit the weight hourly space velocity (WHSV) of methane. Specifically, the preferred WHSV of methane is 0.1-20 h⁻¹. -1 More preferably 1-15h -1 Further preferred is 2-10h -1 As a specific example, the weight hourly space velocity (WHSV) of methane can be 2 h⁻¹. -1 3h -1 4h -1 5h -1 6h -1 7h -1 8h -1 9h -1 or 10h -1 .

[0079] The following examples further illustrate the Sr-composite molecular sieve catalyst, its preparation method, and its application according to the present invention. The examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0080] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0081] In the following examples and comparative examples, boehmite and sodium aluminate are calculated as Al2O3, phosphoric acid as P2O5, sodium hydroxide as Na2O, and tetraethyl orthosilicate as SiO2.

[0082] Example 1

[0083] (1) Mix 85% phosphoric acid and water, then add boehmite and tetraethyl orthosilicate sequentially under stirring at 25°C, stir for 30 min, then add morpholine, continue stirring and aging for 12 h to obtain the first sol, then pour the first sol into the first reactor, hydrothermally crystallize at 200°C for 24 h, cool to room temperature to obtain the first mixture; wherein, the molar ratio of boehmite, phosphoric acid, tetraethyl orthosilicate, morpholine and water is 1:0.8:0.6:2.5:75;

[0084] (2) Sodium aluminate, sodium hydroxide and water are mixed and stirred for 30 min. Then, under stirring at 25 °C, tetraethyl orthosilicate and tetrapropylammonium hydroxide are added dropwise. The pH of the system is adjusted to 11 with 98% sulfuric acid. The mixture is stirred and aged for 12 h to obtain the second sol. The second sol is then poured into the second reaction vessel and hydrothermally crystallized at 180 °C for 6 h. After cooling to room temperature, the second mixture is obtained. The molar ratio of sodium aluminate, sodium hydroxide, tetraethyl orthosilicate, tetrapropylammonium hydroxide and water is 1:42.5:150:54:305.

[0085] (3) The first mixture and the second mixture were mixed at a weight ratio of 2.2:1 and poured into the third reactor. The mixture was stirred at 25°C for 30 min and then hydrothermally crystallized at 180°C for 18 h. After the reaction was completed, the mixture was cooled, filtered, and then washed and separated by membrane separation to obtain a composite molecular sieve dispersion with a water content of 25%. Then, 55 g of composite molecular sieve dispersion, 37.5 g of kaolin, 4 g of guar gum powder and 1.5 g of citric acid were mixed, stirred, kneaded and shaped, and then dried at 105°C for 4 h. Then, the temperature was increased to 550°C at a heating rate of 2°C / min and calcined for 6 h. The mixture was then cooled to room temperature to obtain the composite molecular sieve catalyst.

[0086] (4) 2g of composite molecular sieve catalyst was placed in 50mL of strontium acetate aqueous solution with a concentration of 1.5wt%, stirred at 75℃ for 1.5h, and allowed to stand at 25℃ for 2.5h. The catalyst was then removed, filtered and washed, dried at 105℃ for 4h, and then heated to 600℃ at a heating rate of 3℃ / min. The catalyst was calcined for 6h and cooled to room temperature to obtain Sr-composite molecular sieve catalyst S1.

[0087] (5) The Sr-composite molecular sieve catalyst S1 was loaded into a fixed-bed reactor, and methanol was used as raw material. The reaction was carried out at a temperature of 500°C, a pressure of 3 MPa, and a methanol weight hourly space velocity of 6 h⁻¹. -1 Under the specified conditions, the raw materials were passed through the Sr-composite molecular sieve catalyst S1 bed and reacted for 30 min. The reaction products were then analyzed.

[0088] Example 2

[0089] (1) Mix 85% phosphoric acid and water, then add boehmite and tetraethyl orthosilicate sequentially under stirring at 25°C, stir for 20 min, then add morpholine, and continue stirring and aging for 11 h to obtain the first sol. Then pour the first sol into the first reactor and hydrothermally crystallize at 190°C for 25 h, and cool to room temperature to obtain the first mixture; wherein, the molar ratio of boehmite, phosphoric acid, tetraethyl orthosilicate, morpholine and water is 1:0.7:0.5:2:60;

[0090] (2) Sodium aluminate, sodium hydroxide and water are mixed and stirred for 20 min. Then, under stirring at 25 °C, tetraethyl orthosilicate and tetrapropylammonium hydroxide are added dropwise. The pH of the system is adjusted to 10.5 with 98% sulfuric acid. The mixture is stirred and aged for 13 h to obtain the second sol. The second sol is then poured into the second reactor and hydrothermally crystallized at 170 °C for 7 h. After cooling to room temperature, the second mixture is obtained. The molar ratio of sodium aluminate, sodium hydroxide, tetraethyl orthosilicate, tetrapropylammonium hydroxide and water is 1:35:140:50:280.

[0091] (3) The first mixture and the second mixture were mixed at a weight ratio of 2:1 and poured into the third reactor. The mixture was stirred at 25°C for 20 min and then hydrothermally crystallized at 170°C for 19 h. After the reaction was completed, the mixture was cooled, filtered, and then washed and separated by membrane separation to obtain a composite molecular sieve dispersion with a water content of 15%. Then, 52.5 g of composite molecular sieve dispersion, 30 g of kaolin, 3.75 g of guar gum powder and 1.5 g of citric acid were mixed, stirred, kneaded and shaped, and then dried at 105°C for 4 h. Then, the temperature was increased to 530°C at a heating rate of 1.5°C / min and calcined for 9 h. After cooling to room temperature, the composite molecular sieve catalyst was obtained.

[0092] (4) 2g of composite molecular sieve catalyst was placed in 50mL of strontium acetate aqueous solution with a concentration of 1wt%, stirred at 70℃ for 2h, and allowed to stand at 25℃ for 3h. The catalyst was then removed, filtered and washed, dried at 105℃ for 4h, and then heated to 550℃ at a heating rate of 1.5℃ / min. The catalyst was calcined for 9h and cooled to room temperature to obtain Sr-composite molecular sieve catalyst S2.

[0093] (5) The Sr-composite molecular sieve catalyst S2 was loaded into a fixed-bed reactor, and methanol was used as raw material. The reaction was carried out at a temperature of 450°C, a pressure of 1 MPa, and a methanol weight hourly space velocity of 2 h⁻¹. -1 Under the specified conditions, the raw materials were passed through the Sr-composite molecular sieve catalyst S2 bed and reacted for 30 min. The reaction products were then analyzed.

[0094] Example 3

[0095] (1) Mix 85% phosphoric acid and water, then add boehmite and tetraethyl orthosilicate sequentially under stirring at 25°C, stir for 40 min, then add morpholine, and continue stirring and aging for 13 h to obtain the first sol. Then pour the first sol into the first reactor and hydrothermally crystallize at 210°C for 22 h, and cool to room temperature to obtain the first mixture; wherein, the molar ratio of boehmite, phosphoric acid, tetraethyl orthosilicate, morpholine and water is 1:0.9:0.7:3:90;

[0096] (2) Sodium aluminate, sodium hydroxide and water are mixed and stirred for 40 min. Then, under stirring at 25 °C, tetraethyl orthosilicate and tetrapropylammonium hydroxide are added dropwise. The pH of the system is adjusted to 11.5 with 98% sulfuric acid. The mixture is stirred and aged for 11 h to obtain the second sol. The second sol is then poured into the second reaction vessel and hydrothermally crystallized at 190 °C for 5 h. After cooling to room temperature, the second mixture is obtained. The molar ratio of sodium aluminate, sodium hydroxide, tetraethyl orthosilicate, tetrapropylammonium hydroxide and water is 1:50:160:58:330.

[0097] (3) The first mixture and the second mixture were mixed at a weight ratio of 2.5:1 and poured into the third reactor. The mixture was stirred at 25°C for 40 min and then hydrothermally crystallized at 190°C for 17 h. After the reaction was completed, the mixture was cooled, filtered, and then washed and separated by membrane separation to obtain a composite molecular sieve dispersion with a water content of 35%. Then, 75 g of composite molecular sieve dispersion, 45 g of kaolin, 6 g of guar gum powder and 1.5 g of citric acid were mixed, stirred, kneaded and shaped, and then dried at 105°C for 4 h. Then, the temperature was increased to 600°C at a heating rate of 4°C / min and calcined for 5 h. The mixture was then cooled to room temperature to obtain the composite molecular sieve catalyst.

[0098] (4) 2g of composite molecular sieve catalyst was placed in 50mL of strontium acetate aqueous solution with a concentration of 2wt%, stirred at 85℃ for 1h, and then allowed to stand at 25℃ for 2h. The catalyst was then removed, filtered and washed, dried at 105℃ for 4h, and then heated to 650℃ at a heating rate of 4℃ / min. The catalyst was calcined for 5h and cooled to room temperature to obtain Sr-composite molecular sieve catalyst S3.

[0099] (5) The Sr-composite molecular sieve catalyst S3 was loaded into a fixed-bed reactor, and methanol was used as raw material. The reaction was carried out at a temperature of 550°C, a pressure of 5 MPa, and a methanol weight hourly space velocity of 10 h⁻¹. -1 Under the specified conditions, the raw materials were passed through the Sr-composite molecular sieve catalyst S3 bed and reacted for 30 min. The reaction products were then analyzed.

[0100] Example 4

[0101] The method described in Example 1 was implemented, except that in step (1), the molar ratio of boehmite, phosphoric acid, tetraethyl orthosilicate, morpholine and water was 1:0.8:0.6:3.2:75, and the Sr-composite molecular sieve catalyst S4 was finally obtained. The Sr-composite molecular sieve catalyst S4 was used to catalyze the preparation of olefins from methanol.

[0102] Example 5

[0103] The method described in Example 1 was implemented, except that in step (2), the molar ratio of sodium aluminate, sodium hydroxide, tetraethyl orthosilicate, tetrapropylammonium hydroxide and water was 1:42.5:150:60:305, and the Sr-composite molecular sieve catalyst S5 was finally obtained. The Sr-composite molecular sieve catalyst S5 was used to catalyze the preparation of olefins from methanol.

[0104] Example 6

[0105] The method described in Example 1 is implemented, except that in step (3), the weight ratio of the first mixture and the second mixture is 1.8:1, and the Sr-composite molecular sieve catalyst S6 is finally obtained. The Sr-composite molecular sieve catalyst S6 is used to catalyze the preparation of olefins from methanol.

[0106] Example 7

[0107] The method described in Example 1 was implemented, except that in step (3), 52.5g of composite molecular sieve dispersion, 52.5g of kaolin, 3.75g of guar gum powder and 1.5g of citric acid were mixed to finally obtain Sr-composite molecular sieve catalyst S7, and Sr-composite molecular sieve catalyst S7 was used to catalyze the preparation of olefins from methanol.

[0108] Example 8

[0109] The method described in Example 1 was implemented, except that in step (4), the concentration of the strontium acetate aqueous solution was 2.8 wt%, and the Sr-composite molecular sieve catalyst S8 was finally obtained. The Sr-composite molecular sieve catalyst S8 was used to catalyze the preparation of olefins from methanol.

[0110] Example 9

[0111] The method described in Example 1 was carried out, except that in step (5), the reaction temperature was 400°C, the reaction pressure was 0.1 MPa, and the weight hourly space velocity of methanol was 0.1 h⁻¹. -1 .

[0112] Example 10

[0113] The method described in Example 1 was carried out, except that in step (5), the reaction temperature was 600°C, the reaction pressure was 10 MPa, and the weight hourly space velocity of methanol was 20 h⁻¹. -1 .

[0114] Example 11

[0115] The method described in Example 1 was carried out, except that in step (5), the reaction temperature was 550°C, the reaction pressure was 5 MPa, and the weight hourly space velocity of methanol was 10 h⁻¹. -1 .

[0116] Comparative Example 1

[0117] The method described in Example 1 was carried out, except that step (1) was not performed. The composite molecular sieve catalyst D1 was finally obtained and used to catalyze the preparation of olefins from methanol.

[0118] Comparative Example 2

[0119] The method described in Example 1 was carried out, except that step (2) was not performed. The composite molecular sieve catalyst D1 was finally obtained and used to catalyze the preparation of olefins from methanol.

[0120] Comparative Example 3

[0121] The method described in Example 1 was implemented, except that in step (3), kaolin, guar gum powder and citric acid were not added, and Sr-composite molecular sieve catalyst D3 was finally prepared, and Sr-composite molecular sieve catalyst D3 was used to catalyze the preparation of olefins from methanol.

[0122] Comparative Example 4

[0123] The method described in Example 1 was carried out, except that step (4) was not performed. The composite molecular sieve catalyst D4 was finally obtained and used to catalyze the preparation of olefins from methanol.

[0124] Test case

[0125] (1) In this invention, the content of each component in the reaction products obtained by the examples and comparative examples is analyzed simultaneously using a dual-channel detector of gas chromatography, and the peak area normalization method is used for quantitative analysis of the products. The propylene yield when the methanol conversion rate is 100% is calculated. The results are shown in Table 1.

[0126] (2) The present invention tested the reaction time to maintain a methanol conversion rate of over 95%, and then tested the lifespan of the Sr-composite molecular sieve catalysts prepared in Examples 1-11 and Comparative Examples 1-3, as well as the composite molecular sieve catalyst prepared in Comparative Example 4. The results are shown in Table 1.

[0127] Table 1

[0128]

[0129]

[0130] As can be seen from the results in Table 1, the Sr-composite molecular sieve catalyst prepared by the method described in this invention has the characteristics of excellent catalytic activity, high selectivity for low-carbon olefins, strong stability and long service life, which are highly compatible with the needs of large-scale industrial production and show significant economic value and broad industrial application prospects.

[0131] Compared to Example 1, in the preparation of Sr-composite molecular sieve catalysts, Examples 4 and 5 changed the amount of morpholine and tetrapropylammonium hydroxide added, respectively. Excess morpholine and tetrapropylammonium hydroxide may lead to problems such as overly complex pore structure, incomplete crystallization, and changes in acidic sites. Example 6 changed the weight ratio of the first mixture and the second mixture in step (3), which caused the catalyst to lose the balance between catalytic activity and stability. Example 7 changed the amount of kaolin added in step (3), resulting in poor stability. Example 8 changed the concentration of strontium acetate aqueous solution in step (4). Excessive Sr may lead to problems such as reduced acidic sites, pore blockage, and decreased activity. Comparative Example 3 did not have step (3), resulting in reduced stability. All of these will affect the yield of propylene and the catalytic life to a certain extent.

[0132] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing an Sr-composite molecular sieve catalyst, characterized in that, The method includes the following steps: (1) Mix the first aluminum source, phosphorus source, first silicon source, morpholine and water and perform the first aging, then perform the first hydrothermal crystallization reaction on the obtained first sol to obtain the first mixture; (2) Mix the second aluminum source, sodium source, second silicon source, tetrapropylammonium hydroxide and water, then adjust the pH of the resulting mixture to 10-12, then carry out the second aging, and then carry out the second hydrothermal crystallization reaction of the resulting second sol to obtain the second mixture; (3) The first mixture and the second mixture are mixed and subjected to a third hydrothermal crystallization reaction to obtain a composite molecular sieve dispersion. Then, the composite molecular sieve dispersion, binder, filler and adhesive are mixed, and then the mixture is successively shaped, dried and calcined to obtain a composite molecular sieve catalyst. (4) The Sr metal salt is loaded onto the composite molecular sieve catalyst by impregnation, and then washed, dried and calcined in sequence.

2. The method according to claim 1, characterized in that, In step (1), the first aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, the first silicon source is calculated as SiO2, and the molar ratio of the first aluminum source, the phosphorus source, the first silicon source, morpholine and water is 1:(0.5-1.2):(0.3-1):(1-5):(50-100).

3. The method according to claim 1 or 2, characterized in that, In step (1), the conditions for the first aging include: a temperature of 20-25°C and a time of 10-14 hours; and / or The conditions for the first hydrothermal crystallization reaction include: a temperature of 180-220℃ and a time of 20-30h.

4. The method according to claim 1, characterized in that, In step (2), the second aluminum source is calculated as Al2O3, the sodium source is calculated as Na2O, the second silicon source is calculated as SiO2, and the molar ratio of the second aluminum source, the sodium source, the second silicon source, tetrapropylammonium hydroxide and water is 1:(30-60):(130-170):(45-60):(250-350).

5. The method according to claim 1 or 4, characterized in that, In step (2), the conditions for the second aging include: a temperature of 20-25°C and a time of 10-14 hours; and / or The conditions for the second hydrothermal crystallization reaction include: a temperature of 160-200℃ and a time of 4-8 hours.

6. The method according to claim 1, characterized in that, In step (3), the weight ratio of the first mixture to the second mixture is 1.5-3:1; and / or The weight ratio of the composite molecular sieve dispersion, the binder, the filler, and the adhesive solvent is (20-70):(12.5-50):(1-6):1; Preferably, the binder is selected from at least one of kaolin, alumina, silica-alumina compounds, and boehmite; Preferably, the filler is selected from at least one of guar gum powder, cellulose, and graphite powder; Preferably, the adhesive solvent is selected from at least one of hydrochloric acid, nitric acid, acetic acid, and citric acid.

7. The method according to claim 1 or 6, characterized in that, In step (3), the conditions for the third hydrothermal crystallization reaction include: a temperature of 160-200℃ and a time of 16-20h; and / or The calcination conditions include: a heating rate of 1-5℃ / min, a temperature of 500-700℃, and a time of 4-10h.

8. The method according to claim 1, characterized in that, In step (4), the process of loading Sr metal salt onto the composite molecular sieve catalyst by impregnation includes: impregnating the composite molecular sieve catalyst in Sr metal salt impregnation solution, then stirring at a constant temperature of 70-85℃ for 1-2 hours, and then letting it stand at 20-25℃ for 2-3 hours. Preferably, the concentration of the Sr metal salt impregnation solution is 0.5-2.5 wt%. Preferably, the Sr metal salt is selected from at least one of strontium acetate, strontium chlorate, strontium nitrite, and strontium nitrate.

9. The method according to claim 1 or 8, characterized in that, In step (4), the calcination conditions include: a heating rate of 1-5℃ / min, a temperature of 500-700℃, and a time of 4-10h.

10. The Sr-composite molecular sieve catalyst prepared by the method according to any one of claims 1-9.

11. A method for preparing olefins from methanol, characterized in that, The method comprises reacting methanol in the presence of the Sr-composite molecular sieve catalyst of claim 10 to generate olefins.

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