An alkaline earth metal-doped molecular sieve catalyst, a method for preparing the same, and an application thereof

Abstract

The present application relates to the field of catalytic cracking of hydrocarbons, in particular to a kind of alkaline earth metal doped molecular sieve catalyst and its preparation method and application, the present application aims at providing a kind of assembly method of "mechanical ball milling" alkaline earth metal doped molecular sieve, alkaline earth metal component is mixed with molecular sieve by mechanical chemistry method, under the impact and shearing action of mill ball, control ball milling time and rotational speed, realize the selective doping of alkaline earth metal to the surface or channel inside of molecular sieve, the high-speed collision of mill ball can make the surface of molecular sieve produce defect and thus give alkaline earth metal more loading sites, solve the problem of uneven metal dispersion in current doping method, and the preparation process is simple and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of hydrocarbon catalyst cracking, specifically to an alkaline earth metal-doped molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Ethylene and propylene are important organic chemical raw materials, and their market demand has been steadily increasing in recent years. The largest industrial process for producing light olefins, especially ethylene, is naphtha steam cracking. This process uses high-temperature thermal cracking to break down the chain of crude oil molecules and induce dehydrogenation reactions, producing various products such as olefins, alkanes, and hydrogen. However, the application of steam cracking technology in crude oil cracking suffers from drawbacks such as high coking volume, low product selectivity, and high energy consumption, severely limiting the development of the steam cracking process for producing low-carbon olefins. Catalytic cracking, with its low reaction temperature and high yield of target products, has become the most promising technology for development and application in recent years.

[0003] Currently, a series of catalytic cracking technologies for increasing the production of low-carbon olefins have been developed in China. For example, the DCC process technology, developed by the Research Institute of Petroleum Processing (RIPP), is the first-generation heavy oil catalytic cracking technology to maximize propylene production; the TMP process technology, developed by the China University of Petroleum (East China), is a two-stage riser catalytic cracking technology for propylene production; and RIPP's CPP process technology can produce both ethylene and propylene. However, these technologies currently have significant drawbacks, primarily relying on heavy oil as feedstock. Research has found that using molecular sieves as catalysts in catalytic cracking reactions can significantly reduce reaction temperatures and lead to higher reactant conversion rates and target product selectivity.

[0004] Molecular sieve catalysts for catalytic cracking mainly include HZSM-5, Beta, MCM-41, SBA-15, Mordenite, and novel zeolites such as ITQ-2, which have been widely used in the petrochemical industry for decades. CN113751056A discloses a method for introducing a quantitative amount of non-framework aluminum into ZSM-5 molecular sieves. This method achieves precise control of the extra-framework Al content of ZSM-5 molecular sieves through equal-volume impregnation. By changing the amount of Al introduced, quantitatively constructing extra-framework Al-OH allows for controllable modulation of the Bronsted / Lewis acid content. CN113546672A discloses a catalytic cracking catalyst comprising: a modified ZSM-5 molecular sieve, a binder, and optionally a clay catalyst, exhibiting enhanced cracking ability when applied to cracking reactions. CN113548674A discloses a modified ZSM-5 molecular sieve, which comprises ZSM-5 molecular sieve and alkaline earth metal elements. When applied to catalytic cracking reactions, this modified ZSM-5 molecular sieve exhibits higher yields of low-carbon olefins and higher propylene selectivity. CN113548677A discloses a SAPO-11 and SAPO-34 composite molecular sieve modified with alkaline earth metals. Acid treatment of the alkaline earth metal and the SAPO-11 and SAPO-34 composite molecular sieve with an acid solution improves the yield and selectivity of low-carbon olefins through the synergistic effect of the alkaline earth metal and the acid centers. In recent years, numerous methods have been developed for controlling the acid properties of catalytic cracking catalysts by adding metal components. However, these methods are complex, involve an increase in the types of raw materials, and are difficult to control the location of the metal introduced into the molecular sieve, limiting the industrial application of metal-doped molecular sieve catalysts.

[0005] Currently, methods such as wet impregnation and ion exchange are commonly used to dope metal components into molecular sieve catalysts. However, these methods have drawbacks, including uneven dispersion of metal components on the support material, lack of strong interactions, easy loss of active components during the reaction process, and difficulty in effectively controlling the doping amount. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, the present invention aims to provide an alkaline earth metal-doped molecular sieve catalyst, its preparation method, and its application. The present invention utilizes a mechanochemical method to assist in the doping of alkaline earth metal components in molecular sieves, selectively adding alkaline earth metals to the outer surface of the molecular sieve catalyst, reducing side reactions, thereby enhancing the selectivity and yield of low-carbon olefins, and achieving the preparation of a molecular sieve catalyst with high catalytic cracking activity for hydrocarbons and high olefin selectivity.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for preparing an alkaline earth metal-doped molecular sieve catalyst, characterized by comprising the following steps:

[0009] (1) A sol precursor is obtained by uniformly mixing silicon source, aluminum source, alkali source and template agent in a solvent. The sol precursor is subjected to hydrothermal crystallization reaction, washed, dried and calcined to obtain molecular sieve catalyst precursor.

[0010] (2) The molecular sieve catalyst precursor obtained in step (1) is subjected to ammonium ion exchange treatment, dried and calcined to obtain the molecular sieve catalyst.

[0011] (3) Using the molecular sieve catalyst obtained in step (2) as a support, an alkaline earth metal salt compound is used to dope the molecular sieve catalyst support with alkaline earth metal elements by mechanical ball milling, and then calcination is performed to obtain the alkaline earth metal doped molecular sieve catalyst.

[0012] Preferably, the alkaline earth metal doped molecular sieve catalyst in step (3) has an alkaline earth metal doping amount of 1-20 wt% and a molecular sieve mass fraction of 80-99 wt%.

[0013] Preferably, the silicon source in step (1) is one or more of silica sol, fumed silica, sodium silicate, and tetraethyl orthosilicate, and the aluminum source is one or more of organoaluminum compounds, inorganic aluminum compounds, or hydrates.

[0014] Preferably, the alkali source in step (1) is one or more of sodium hydroxide, sodium carbonate, and potassium hydroxide, and the template agent is one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide.

[0015] Preferably, the ammonium ion exchange raw material in step (2) is one of ammonium chloride and ammonium bicarbonate.

[0016] Preferably, the alkaline earth metal salt compound mentioned in step (3) is one of magnesium nitrate, calcium nitrate, barium nitrate, and strontium nitrate.

[0017] Preferably, the hydrothermal crystallization reaction temperature in step (1) is 180°C and the reaction time is 24h.

[0018] Preferably, the ball milling speed in step (3) is 360-1000 r / min and the time is 1-3 h.

[0019] Another object of the present invention is to provide an alkaline earth metal-doped molecular sieve catalyst prepared by any of the above preparation methods.

[0020] The third objective of this invention is to provide an application of the alkaline earth metal-doped molecular sieve catalyst described above in the catalytic cracking of hydrocarbons to produce low-carbon olefins.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The purpose of this invention is to provide an assembly method for alkaline earth metal doped molecular sieves using "mechanical ball milling". The alkaline earth metal components are mixed with molecular sieves by ball milling using a mechanochemical method. Under the impact and shearing action of the milling balls, the milling time and speed are controlled to achieve selective doping of alkaline earth metals onto the surface or inside the pores of the molecular sieve. The high-speed collision of the milling balls can create defects on the surface of the molecular sieve, thereby providing more loading sites for the alkaline earth metals. This solves the problem of uneven metal dispersion in current doping methods, and the preparation process is simple and environmentally friendly.

[0023] 2. ZSM-5 molecular sieve catalysts possess a large number of... Acidic sites exhibit high reactivity in hydrocarbon cracking reactions, but excessive amounts of [unclear] in the molecular sieve [are problematic]. Acidic sites can lead to secondary reactions in the generated olefins, such as polymerization, cyclization, dehydrogenation, and aromatization, thereby reducing the selectivity and yield of low-carbon olefins. Therefore, a suitable molecular sieve catalyst for hydrocarbon catalytic cracking should have appropriate acid content and acid strength to maintain the catalyst's activation ability and avoid excessively low hydrocarbon conversion rates. By synthesizing Silicate-1 molecular sieves to reduce the catalyst's acid content and acid strength, the selectivity and yield of low-carbon olefins can be increased.

[0024] 3. Alkaline earth metal doping of molecular sieves via mechanochemical method increases the dehydrogenation components of the catalyst to improve feedstock oil conversion rate, low-carbon olefin selectivity and yield. This invention applies mechanochemical method to assist in the doping of alkaline earth metal components in molecular sieves, selectively adding alkaline earth metals to the outer surface of the molecular sieve catalyst, reducing side reactions to enhance low-carbon olefin selectivity and yield, and achieving the preparation of molecular sieve catalysts with high catalytic cracking activity and high olefin selectivity for hydrocarbons. Detailed Implementation

[0025] The following detailed description, in conjunction with embodiments of the present invention, will focus on preferred embodiments.

[0026] This invention relates to a method for preparing an alkaline earth metal-doped molecular sieve catalyst. The matrix is ​​a microporous molecular sieve, and the method for producing microporous molecular sieves is well known to researchers in the art, including ZSM-5, Silicate-1, and other molecular sieves. The molecular sieve is synthesized using a method well known to researchers in the art. The final alkaline earth metal doping amount is 1-20 wt% based on the atomic mass of the alkaline earth metal element relative to the weight of the molecular sieve, and the molecular sieve content is 80-99 wt% by weight.

[0027] Example 1

[0028] A method for preparing an alkaline earth metal-doped molecular sieve catalyst includes the following steps:

[0029] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using 1M NH4Cl solution at a mass ratio of 1:10 for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.

[0030] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.533g magnesium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Mg@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-1.

[0031] Example 2

[0032] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using 1M NH4Cl solution at a mass ratio of 1:10 for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.

[0033] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.293g calcium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ca@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-2.

[0034] Example 3

[0035] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.

[0036] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.12g strontium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Sr@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-3.

[0037] Example 4

[0038] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1MNH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0039] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.095g barium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ba@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-4.

[0040] Example 5

[0041] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1MNH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0042] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 1.06g magnesium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Mg@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-5.

[0043] Example 6

[0044] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1MNH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0045] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.586g calcium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ca@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-6.

[0046] Example 7

[0047] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0048] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.24g strontium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Sr@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-7.

[0049] Example 8

[0050] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0051] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.19g barium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ba@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-8.

[0052] Example 9

[0053] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0054] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 1.6g magnesium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Mg@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-9.

[0055] Example 10

[0056] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0057] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.88g calcium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ca@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-10.

[0058] Example 11

[0059] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0060] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.36g strontium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Sr@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-11.

[0061] Example 12

[0062] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0063] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.285g barium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ba@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-12.

[0064] Example 13

[0065] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0066] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 3.2g magnesium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min. The jar was opened and manually stirred every 30 minutes to prevent the sample from settling. The Mg@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-13.

[0067] Example 14

[0068] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0069] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 1.76g calcium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ca@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-14.

[0070] Example 15

[0071] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0072] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.72g strontium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Sr@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-15.

[0073] Example 16

[0074] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1M NH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.

[0075] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 0.57g barium nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Ba@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-16.

[0076] Comparative Example 1

[0077] 193.32 g of deionized water, 4 g of sodium hydroxide, 66.667 g of silica sol, and 13.33 g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40 °C and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180 °C for 24 h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80 °C with 1 M NH4Cl solution at a mass ratio of 1:10 for 2 h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst, named D-1.

[0078] Comparative Example 2

[0079] An in-situ hydrothermal synthesis of alkaline earth metal-doped molecular sieve catalyst was performed: 193.32 g of deionized water, 4 g of sodium hydroxide, 66.667 g of silica sol, 13.33 g of tetrapropylammonium bromide, and 1.06 g of magnesium nitrate were added to a magnetically stirred water bath at 40 °C and stirred until a homogeneous sol system was formed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 180 °C for 24 h. After crystallization, the catalyst was washed, dried, and calcined. Ammonium ion exchange was then performed for 2 h in a magnetically stirred water bath at 80 °C using a 1:10 mass ratio of 1 M NH4Cl solution. After drying and calcination, the Mg@Silicate-1 molecular sieve catalyst was obtained and named D-2.

[0080] Comparative Example 3

[0081] An in-situ hydrothermal synthesis of alkaline earth metal-doped molecular sieve catalyst was performed: 193.32 g of deionized water, 4 g of sodium hydroxide, 66.667 g of silica sol, 13.33 g of tetrapropylammonium bromide, and 0.587 g of calcium nitrate were added to a magnetically stirred water bath at 40 °C and stirred until a homogeneous sol system was formed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 180 °C for 24 h. After crystallization, the catalyst was washed, dried, and calcined. Ammonium ion exchange was then performed for 2 h in a magnetically stirred water bath at 80 °C using a 1:10 mass ratio of 1 M NH4Cl solution. After drying and calcination, the Ca@Silicate-1 molecular sieve catalyst was obtained and named D-3.

[0082] Comparative Example 4

[0083] An in-situ hydrothermal synthesis of alkaline earth metal-doped molecular sieve catalyst was performed: 193.32 g of deionized water, 4 g of sodium hydroxide, 66.667 g of silica sol, 13.33 g of tetrapropylammonium bromide, and 0.24 g of strontium nitrate were added to a magnetically stirred water bath at 40 °C and stirred until a homogeneous sol system was formed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 180 °C for 24 h. After crystallization, the catalyst was washed, dried, and calcined. Ammonium ion exchange was then performed for 2 h in a magnetically stirred water bath at 80 °C using a 1:10 mass ratio of 1 M NH4Cl solution. After drying and calcination, the Sr@Silicate-1 molecular sieve catalyst was obtained and named D-4.

[0084] Comparative Example 5

[0085] An in-situ hydrothermal synthesis of alkaline earth metal-doped molecular sieve catalyst was performed: 193.32 g of deionized water, 4 g of sodium hydroxide, 66.667 g of silica sol, 13.33 g of tetrapropylammonium bromide, and 0.19 g of barium nitrate were added to a magnetically stirred water bath at 40 °C and stirred until a homogeneous sol system was formed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 180 °C for 24 h. After crystallization, the catalyst was washed, dried, and calcined. Ammonium ion exchange was then performed for 2 h in a magnetically stirred water bath at 80 °C using a 1:10 mass ratio of 1 M NH4Cl solution. After drying and calcination, the Ba@Silicate-1 molecular sieve catalyst, named D-5, was obtained.

[0086] Results Analysis

[0087] The data for the catalytic cracking reaction of n-butane at a reaction temperature of 640℃ are shown in Table 1:

[0088] Table 1. Data on the catalytic cracking reaction of n-butane in Examples 1-16 and Comparative Examples 1-5

[0089]

[0090] Table 1 shows the data of n-butane catalytic cracking reaction in Examples 1-16 and Comparative Examples 1-5. As can be seen from the performance evaluation data of Examples 1-16 and Comparative Examples 1-5, the present invention can prepare a molecular sieve catalyst with controllable alkaline earth metal doping through a mechanochemical method, which is used for hydrocarbon catalytic cracking reaction. Under the same conditions, it has higher low-carbon olefin selectivity and low-carbon olefin yield than the comparative examples.

[0091] In summary, this invention utilizes a mechanochemical method to mix alkaline earth metal components with molecular sieves through ball milling. By controlling the milling time and rotation speed under the impact and shearing action of the milling balls, the selective doping of alkaline earth metals onto the surface or pores of the molecular sieve is achieved. The high-speed collision of the milling balls creates defects on the surface of the molecular sieve, thus providing more loading sites for the alkaline earth metals. This solves the problem of uneven metal dispersion in current doping methods. By using a mechanochemical method to dope molecular sieves with alkaline earth metals, the dehydrogenation components of the catalyst are increased, thereby improving the conversion rate of feedstock oil, the selectivity of low-carbon olefins, and the yield. This invention applies a mechanochemical method to assist in the doping of alkaline earth metal components in molecular sieves, selectively adding alkaline earth metals to the outer surface of the molecular sieve catalyst, reducing side reactions and enhancing the selectivity and yield of low-carbon olefins. This achieves the preparation of a molecular sieve catalyst with high catalytic cracking activity for hydrocarbons and high olefin selectivity.

[0092] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an alkaline earth metal doped molecular sieve catalyst, characterized by, Includes the following steps: (1) After uniformly mixing silicon source, alkali source and template agent in solvent, a sol precursor is obtained. The sol precursor is subjected to hydrothermal crystallization reaction, washed, dried and calcined to obtain molecular sieve catalyst precursor. (2) The molecular sieve catalyst precursor obtained in (1) was subjected to ammonium ion exchange treatment, dried and calcined to obtain Silicate-1 molecular sieve catalyst; (3) Using the molecular sieve catalyst obtained in (2) as a support, an alkaline earth metal salt compound is used to dope the alkaline earth metal element on the molecular sieve catalyst support by mechanical ball milling, and then calcination is performed to obtain the alkaline earth metal doped molecular sieve catalyst. (3) The ball milling speed of the mechanical ball mill is 360~1000 r / min, and the time is 1~3 h; The alkaline earth metal-doped molecular sieve catalyst is used to improve the conversion rate of n-butane, the selectivity of C2-C4 low-carbon olefins, and the yield.

2. The method for preparing an alkaline earth metal-doped molecular sieve catalyst according to claim 1, characterized by, The alkaline earth metal doped molecular sieve catalyst in step (3) has an alkaline earth metal doping amount of 1-20 wt% and a molecular sieve mass fraction of 80-99 wt%.

3. The method for preparing an alkaline earth metal-doped molecular sieve catalyst according to claim 1, characterized by, The silicon source mentioned in step (1) is one or more of silica sol, fumed silica, sodium silicate, and tetraethyl orthosilicate.

4. The method for preparing an alkaline earth metal-doped molecular sieve catalyst according to claim 1, characterized by, The alkali source mentioned in step (1) is one or more of sodium hydroxide, sodium carbonate, and potassium hydroxide, and the template agent is one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide.

5. The method of making an alkaline earth-doped molecular sieve catalyst of claim 1, wherein, The ammonium ion exchange raw material mentioned in step (2) is one of ammonium chloride and ammonium bicarbonate.

6. The method of making an alkaline earth-doped molecular sieve catalyst of claim 1, wherein, The alkaline earth metal salt compound mentioned in step (3) is one of magnesium nitrate, calcium nitrate, barium nitrate, and strontium nitrate.

7. The method of making an alkaline earth-doped molecular sieve catalyst of claim 1, wherein, In step (1), the hydrothermal crystallization reaction temperature is 180℃ and the reaction time is 24h.

8. An alkaline earth metal-doped molecular sieve catalyst prepared by the method according to any one of claims 1-7.

9. The application of the alkaline earth metal-doped molecular sieve catalyst of claim 8 in the catalytic cracking of hydrocarbons to produce low-carbon olefins.

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