WO2008019583A1

WO2008019583A1 - A PROCESS FOR SYNTHESIZING SAPO-34 MOLECULAR SIEVE ENRICHED WITH A Si(4Al) STRUCTURE IN THE SKELETON

Info

Publication number: WO2008019583A1
Application number: PCT/CN2007/002332
Authority: WO
Inventors: Lei Xu; Zhongmin Liu; Peng Tian; Aiping Du; Lixin Yang; Cuiyu Yuan
Original assignee: Dalian Institute Of Chemical Physics Chinese Academy Of Sciences
Priority date: 2006-08-08
Filing date: 2007-08-03
Publication date: 2008-02-21
Also published as: CN101121528A

Abstract

A process for synthesizing SAPO-34 molecular sieve enriched with a Si(4Al) structure in the skeleton relates to molecular sieve synthesis technology, the molecular sieve synthesized by the process predominately has Si(4Al) structure in skeleton Si coordination environment. In the present process, the fluorides are added to a starting synthesis gel to control a manner in which Si enters into molecular sieve skeleton, thereby to reduce the formation of Si(0Al), Si(1Al), Si(2Al) and Si(3Al) coordination structure and to facilitate the entrance of Si into molecular sieve skeleton in Si(4Al) coordination form. The synthesized SAPO-34 molecular sieve enriched with a Si(4Al) structure is used as MTO catalyst after being baked and could improve efficiently the selectivity of ethene and propene.

Description

The framework is rich in Si (4AD structure of SAPO-34 molecular sieve synthesis method)

Technical field

The invention relates to a method for synthesizing SAPO-34 molecular sieve rich in Si(4Al) structure, relating to the technical field of molecular sieve synthesis, wherein the Si coordination environment in the molecular sieve skeleton synthesized by the method is mainly Si(4Al) structure, and the relative content thereof is 70 -100%. Background technique

In 1984, UCC developed a series of new silica-alumina series molecular sieves (SAPO-n) (USP 4,440,871). Phosphorus-alumina SAPO molecular sieves are composed of phosphorus, silicon, aluminum and oxygen. Molecular sieves of the zeolitic structure. The structure unit composed of a P0 _₂ +, Si0 ₂ tetrahedra and Α10 ₂ · anhydrous chemical composition can be expressed as:

In the above formula, R is a templating agent present in the micropores of the molecular sieve crystal, m is the number of moles of R, x, y, z are the molar fractions of Si, Al, and P, respectively, and satisfies x + y + z = l. With the advent of the silicoaluminophosphate series of molecular sieves, the use of such small pores of moderately acidic molecular sieves for the methanol to light olefin (MTO) reaction, such as SAPO-17, SAPO-18, SAPO-34, has begun. , SAPO-44 molecular sieves, which have a pore size of about 0.43 nm, are a good type of shape-selective catalyst. Among them, SAPO-34 molecular sieve exhibits excellent catalytic performance in MTO reaction due to its suitable acidity and pore structure.

The acidity of the SAPO type molecular sieve can be regarded as caused by the substitution of Si into the framework of the aluminum phosphate molecular sieve by substitution. The aluminum phosphate molecular sieve Α1Ρ0 ₄ -η is formed by AK tetrahedron and P0 ₂ + tetrahedron in strict proportion of 1:1. The whole skeleton is electrically neutral, has no obvious B acid center, and the overall acidity is very weak. When a Si atom is introduced into the aluminum phosphate framework to form a SAPO-n molecular sieve, the skeleton is formed by three tetrahedrons of AKV, P0 ₂ + and Si0 ₂ , and the skeleton generates a net negative charge, so that the molecular sieve has a protonic acidity. Similar to the silicoalumino molecular sieve, there are also only two ways of bonding Si in the SAPO molecular sieve, one in the form of Si-0-Al and the other in the form of Si-0-Si. From the formation principle of the molecular sieve and the analysis of the skeleton structure, the Si-0-Al structure has various forms in the skeleton. The Si atoms can be connected to 0 to 4 aluminum atoms through oxygen to form various Si coordination structures, which can be represented separately. It is Si(0Al), Si(lAl), Si(2Al), Si(3Al), Si(4Al). Theoretically, the acid center strength of different silicon-aluminum structures is enhanced in the order of Si(OAl), Si(4Al), Si(3Al), Si(2Al), Si(lAl), so the strength of the acid center in the molecular sieve framework The number and number are closely related to the structure and number of the skeleton silicon atoms (J. Phys. Chem, 1997, 101, 5249-5262), that is, the skeleton silicon content of the SAPO molecular sieve and the coordination environment have a strong influence on its acidity. For SAPO-34 molecular sieve catalyst, the strength and number of acid centers in the molecular sieve framework directly affect the MTO catalytic performance of SAPO-34 molecular sieve. The acidic acid center is more favorable for the formation of alkane molecules, and the acidity of the weak acid center may make methanol. Incomplete conversion, medium-strength acid centers can limit the formation of terpene and aromatics, and contribute to the selectivity of low-carbon olefins such as ethylene and propylene.

In 1998, Abbad et al. (Microporous and Mesoporous Materials, 1998, 21, 12-18) synthesized pure SAPO-31 molecular sieves using fluorinated liquid containing HF. They believed that HF could not only mineralize, but also It acts like a templating agent to structure and stabilize the molecular sieve structure. Liu Hongxing et al. (Acta catalysis, 2003, 24, 279-283) added HF to the synthesis of SAPO-34 molecular sieves. It is believed that fluoride ions increase the crystallinity of molecular sieves and facilitate the formation of larger specific surface and pore volume. SAPO-34 molecular sieves using Si(4Al) as the main coordination form for the synthesis of ruthenium ions have not been reported.

Therefore, there is a need for a SAPO-34 molecular sieve having a skeleton rich in Si(4Al) structure and a preparation method thereof, which is advantageous for improving the selectivity of low-carbon olefins such as ethylene and propylene in an MTO reaction. Summary of the invention

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for synthesizing SAPO-34 molecular sieve having a skeleton rich in Si(4Al) structure.

Another object of the present invention is to provide a SAPO-34 molecular sieve having a skeleton rich in Si(4Al) structure. The present invention has been completed through intensive work by the inventors.

Specifically, in one aspect of the present invention, there is provided a method for synthesizing a SAPO-34 molecular sieve rich in Si(4Al) structure, wherein the relative amount of Si(4Al) structure in the molecular sieve skeleton accounts for 70-100 of the Si coordination environment. %; This method includes the following steps:

a) preparing a gel mixture containing fluoride, SiO ₂ , A1 ₂ 0 ₃ , P ₂ 0 ₅ , a templating agent, and water;

b) crystallization of the gel mixture at a constant temperature between 1000-250 ° C under autogenous pressure to obtain a solid product;

c) The solid product is washed with water to neutrality and dried to obtain a raw powder of SAPO-34 molecular sieve; d) the raw powder of SAPO-34 molecular sieve is calcined in air at 400-600 ° C for 3-8 hours to obtain a skeleton rich in Si (4Al) structure of SAPO-34 molecular sieve,

Wherein, in the gel mixture, in molar ratio:

F7 Al ₂ O ₃ = 0.0! ~ 2.0;

SiO ₂ /Al ₂ O ₃ = 0.1 to 2.0; Ρ ₂ Ο ₅ / Α1 ₂ Ο ₃ = 0.5~15;

H ₂ 0/ A1 ₂ 0 ₃ = 10~100;

R/- Al ₂ 0 ₃ = l~5, wherein R is a templating agent.

In a preferred aspect of the invention, the templating agent is one of triethylamine and diethylamine, or a mixture of the two.

In another preferred aspect of the invention, the fluoride is a soluble acid or salt of a fluoride ion.

In still another preferred aspect of the invention, the fluoride is one of HF and NH ₄ F, or a mixture of the two.

In a preferred aspect of the invention, the crystallization time in the step b) is from 2 to 120 hours.

In another preferred aspect of the invention, in the Si coordination environment in the SAPO-34 molecular sieve rich in Si(4Al) coordination structure, based on the relative content percentage of the Si coordination environment: the molar percentage content of Si(4Al) 70~100%; Si(3Al) has a molar percentage of 0~30%; Si(2Al) has a molar percentage of 0~20%; Si(lAl) has a molar percentage of 0~10%; Si( The molar percentage of OAl) is 0 to 5%, provided that the ratio of the molar percentage content of Si(4Al), Si(3Al), Si(2Al), Si(lAl), and Si(OAl) is 100%.

In another aspect of the invention, the invention provides a SAPO-34 molecular sieve having a framework rich in Si(4Al) structure prepared by the process as described above.

In another aspect of the present invention, the present invention provides a SAPO-34 molecular sieve having a skeleton rich in Si(4Al) structure, wherein in a Si coordination environment in a SAPO-34 molecular sieve rich in Si(4Al) coordination structure According to the relative content percentage of Si coordination environment: the content of Si (4Al) is 70~100% _{; the} content of Si (3Al) is 0~30%; the content of Si (2Al) is 0~ 20%; Si (lAl) has a molar percentage of 0 to 10%; Si (OAl) has a molar percentage of 0 to 5%, provided that: Si(4Al), Si(3Al), Si(2Al), Si The ratio of the molar percentage content of (lAl) to Si (OAl) is 100%.

In still another aspect of the present invention, the present invention provides the use of a SAPO-34 molecular sieve having a skeleton-rich Si(4Al) structure as described above for the methanol to olefin reaction. DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a XRD chart of a product synthesized under different HF ratio conditions and Comparative Example 1 in the absence of HF in Example 1 of the present invention.

Figure 2: XRD spectrum of the product synthesized under different HF ratio conditions and Comparative Example 2 without HF in Example 4 of the present invention. Figure 3: XRD spectrum of the synthesized product in different NH ₄ F ratios in Example 7 of the present invention. detailed description

The object of the present invention is to analyze the influence of the strength and number of surface acid center of SAPO-34 molecular sieve on the reaction performance of methanol to olefin (MTO), and provide a synthetic method of SAPO-34 molecular sieve with Si (4Al) structure. In the synthetic molecular sieve gel mixture, fluoride is added to control the Si into the molecular sieve skeleton, and the SAPO-34 molecular sieve with Si(4AI) as the main coordination form is synthesized, thereby achieving the purpose of adjusting the acid center strength and number on the surface of the molecular sieve.

In order to achieve the above object, the technical solution of the present invention is to provide a method for synthesizing a SAPO-34 molecular sieve rich in Si (4Al) structure, and a Si (4Al) structure of a Si coordination environment in the molecular sieve skeleton has a relative content of 70 -100%; a gel mixture of a SAPO-34 molecular sieve having a synthetic skeleton rich in Si(4Al) structure, including a fluoride, a templating agent, a silicon source, an aluminum source, a phosphorus source, and water;

By adding fluoride to the SAPO-34 synthetic gel mixture, the way of Si entering the molecular sieve skeleton is controlled, and Si is promoted to form a Si(4Al) coordination form into the molecular sieve skeleton, reducing Si(OAl), Si(lAl), Si. (2Al), formation of a coordination environment of Si(3Al)-.

In the method, the templating agent is one of or a mixture of triethylamine and diethylamine. In the method, the fluoride is a soluble acid or salt of a fluoride ion.

In the method, the fluoride is one or a mixture of two of HF, NF.

In the method, the Si coordination environment of the SAPO-34 molecular sieve rich in Si(4Al) coordination structure is calculated by the relative content percentage of the Si coordination environment: Si(4Al) is 70~100; Si(3Al) It is 30~0; Si(2AI) is 20~0; Si(lAl) is 10~0; Si(OAl) is 5~0.

In the method described, the operation steps are:

a) preparing a gel mixture of SAPO-34 molecular sieve by formulating fluoride, templating agent, silicon source, aluminum source, phosphorus source and water;

b) the fluorine-containing ion gel mixture obtained in the step a) is placed in a stainless steel synthetic kettle lined with polytetrafluoroethylene, sealed and heated to a crystallization temperature, and subjected to constant temperature crystallization under autogenous pressure; to be crystallized After completion, the solid product is separated by centrifugation, washed with deionized water to neutrality, and dried in air at 120 ° C to obtain a raw material rich in Si (4Al) structure SAPO-34 molecular sieve;

c) The SAPO-34 molecular sieve raw powder obtained in the step b) is calcined in air at 500-600 ° C for 3-8 hours to obtain a SAPO-34 molecular sieve catalyst rich in Si (4Al) structure. In the method, the molar ratio of each component oxide of the gel mixture in the step a) is -F7 Al ₂ O ₃ = 0.01 to 2.0.

SiO ₂ /Al ₂ O ₃ = 0.1 to 2.0;

Ρ2θ ₅ / Α1 ₂ Ο ₃ = 0.5~15;

Η ₂ Ο / Α _{1 2} Ο ₃ = 10~100;

_{_{R / A1 2 0 3 = 1~5}} , R is a templating agent.

In the method, the crystallization temperature in the step b) is 100-250 ° C, and the crystallization time is 2-120 hours. In the method described, the synthesis of the Si(4Al)-rich SAPO-34 molecular sieve catalyst obtained by the synthesis is used to effectively increase the selectivity of ethylene and propylene when the methanol is used for the olefin reaction.

The invention is characterized in that the structure of the molecular sieve is restricted by the interaction of the F ion and the gel component.

The formation of a coordination environment of Si(OAl), Si(lAl), Si(2Al), and Si(3Al) promotes the entry of Si into the molecular sieve skeleton in a coordinated form of Si(4Al).

The controlled synthesis of the coordination coordination environment of the SAPO-34 molecular sieve framework Si can improve the coordination structure of the Si(4Al) framework of the molecular sieve framework, thereby adjusting the acid center strength and number of the SAPO-34 molecular sieve. The choice of controlling the synthesis of Si(4Al)-rich SAPO-34 molecular sieve catalyst for the methanol to olefin reaction can improve the selectivity of ethylene and propylene and greatly improve the life of the catalyst.

The invention is described in detail below by way of examples.

Example 1

Initial gel fraction _{_{3.0TEA: 0.6SiO 2: P 2 0}} 5: A1 2 0 3: 50H 2 O: xHF (TEA triethylamine templating agent, x = 0.09, 0.22, 0.33 , 0.45, 0.65, 0.75, 1.00) Configure the gel mixture. First, 30.3 g of TEA, 13.2 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 73.9 g of H ₂ 0 were mixed and stirred uniformly, and then 0.45 g, Ug, 1.65 g, 2.25 g, 3.25, 3.75 and 5.0 g were respectively added. For 40% aqueous HF solution, continue to stir into a gel mixture, put the gel mixture into a synthetic tank filled with polytetrafluoroethylene, heat it to 200 °C, and auto-crystallization for 12 hours under autogenous pressure. . Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C. XRD analysis was carried out as shown in Fig. 1, and the original powder of SAPO-34 molecular sieve (No. SPF34-1, SPF34-) was obtained. 2, SPF34-3, SPF34-4; SPF34-5, SPF34-6 and SPF34-7, which correspond to x=0.09, 0.22, 0.33, 0.45, 0.65, 0.75 and 1.00, respectively. Comparative Example 1 (no HF)

With an initial gel ratio of 3.0TEA: 0.6SiO ₂ : P ₂ 0 ₅ : A1 ₂ 0 _{3 :} 50H ₂ O (TEA is a triethylamine template) Place the gel mixture. Mix 30.3 g of TEA, 13.2 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 73.9 g of H ₂ 0, stir well to form a uniform gel, and put it into a synthetic tank lined with polytetrafluoroethylene, and heat it to 200. 'C, under constant pressure, crystallized for 12 hours. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C, and XRD analysis was carried out as shown in Fig. 1 to obtain a SAPO-34 molecular sieve raw powder (No. SP34). Example 2

The sample No. SP34 obtained in Example I was numbered SPF34-1, SPF34-2, SPF34-3 and Comparative Example 1 was subjected to ²⁹ Si solid nuclear magnetic characterization to determine the Si coordination environment of the molecular sieve skeleton, and the relative contents of various Si coordination structures. As shown in Table 1.

Table 1

Sample HF/Al ₂ 0 ₃ (mol) relative content of silicon coordination structure (%)

Si(4Al) 54.2

SP34 Si(3Al) 19.7

Si(OAl) 26.1

Si(4Al) 81.2

SPF34-1 0.09 Si(3Al) 10.3

Si(OAl) 8.5

Si(4Al) 96.4

SPF34-2 0.22

Si(3Al) 3.6

Si(4AI) 98.5

SPF34-3 0.33

Si(3Al) 1.5 Example 3

The sample No. SP34 obtained in Example 1 and having the numbers SPF34-1, SPF34-2, SPF34-3 and Comparative Example 1 was calcined at 550 ° C for 4 hours to obtain a SAPO-34 molecular sieve catalyst for methanol-to-olefin catalytic reaction. 0.6 g of a sample of 20-40 mesh granules of catalyst was separately charged into the reactor, and activated at 55 (TC for 1 hour with nitrogen gas, and then cooled to 450 ° C. The nitrogen was used as a diluent gas to carry the raw material methanol, and the nitrogen flow rate was 40ml/min, methanol weight space velocity 2.01^. The composition of the reaction product was analyzed by online gas chromatography. The results are shown in Table 2. Shown.

The results showed that the SPF34-1 sample synthesized in the initial gel at a molar ratio of HF/A1 ₂ 0 ₃ had no change in the selectivity of ethylene and propylene in the reaction product. When the initial gel had a HF/A1 ₂ 0 ₃ molar ratio greater than 0.22, the synthesized SPF34-2 and SPF34-3 samples showed a significant increase in ethylene and propylene selectivity.

Table 2

No. SP34 SPF34-1 SPF34-2 SPF34-3

HF/Al ₂ 0 ₃ (mol) 0.00 0.09 0.22 0.33 Feed time (min) 120 160 200 220 Methanol conversion (wt%) 100 100 100 100 Product distribution (wt%)

CH ₄ 0.93 1.02 1.23 0.89

C ₂ H ₄ 40.29 40.41 45.66 47.66

C ₂ H ₆ 0.84 0.97 0.86 0.69

C ₃ H ₆ 39.55 39.04 37.49 37.41

C ₃ H ₈ 4.04 4.80 3.45 2.83

C ₄ ⁺ 9.72 9.59 8.13 7.50

C ₅ ⁺ 4.63 4.17 3.18 3.02

∑C ₂ =-C ₃ ⁼ 79.84 79.45 83.15 85.07 Lifetime ¹¹¹ (min) 120-140 160-180 200-220 220-240

* Refers to the cumulative feed time when the methanol conversion is 100%. Example 4

Initial gel fraction _{_{3.0TEA: 0.2SiO 2: P 2 0}} 5: A1 2 0 3: 50H 2 O: xHF (TEA triethylamine templating agent, x = 0.04, 0.09, 0.12 , 0.21, 0.34) arranged condensate Glue mixture. First, 30.3 g of TEA, 4.4 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 67.5 g of H ₂ 0 were mixed and stirred uniformly, and then 0.2 g, 0.45 g, 0.6 g, 1.05 g and 1.7 g were respectively added to a concentration of 40^. The % aqueous solution of 1% was continuously stirred into a gel, placed in a synthetic PTFE-lined synthetic kettle, sealed and heated to 200 ° C, and subjected to constant temperature crystallization under autogenous pressure for 24 hours. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C. XRD analysis was carried out as shown in Fig. 2 to obtain SAPO-34 molecular sieve raw powder (No. SPF34-8, SPF34- 9, SPF34-10, SPF34-11; SPF34-12). Comparative Example 2 (no HF)

The gel mixture was formulated at an initial gel ratio of 3.0 TEA: 0.2 SiO _{2 :} P ₂ 0 ₅ : A1 ₂ 0 ₃ : 50H ₂ O (TEA is a triethylamine templating agent). First, 30.3 g of TEA, 4.4 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 67.5 g of H ₂ 0 were mixed, and the mixture was further stirred to form a gel, which was placed in a synthetic PTFE-lined synthetic kettle, and sealed and heated. 200'C, under constant pressure, crystallized for 12 hours. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C, and XRD analysis was carried out as shown in Fig. 2 to obtain a SAPO-34 molecular sieve raw powder (No. SP34-2). Example 5

The No. SPF34-9 obtained in Example 4 and the No. SP34-2 sample obtained in Comparative Example 2 were subjected to ²⁹ Si solid nuclear magnetic characterization, and the molecular sieve skeleton Si coordination environment was determined. The relative contents of various Si coordination structures are shown in Table 3. .

table 3

Si(4Al) 98.4

SP34-2 ―

Si(3Al) 1.6

Si(4Al) 100

SPF34-9 0.09

Si(3Al) 0

Example ⁶

The sample No. SP34-2 obtained in Example 4, which was numbered SPF34-8, SPF34-9, SPF34-10, SPF34-11, SPF34-12 and Comparative Example 2, was calcined at 550 ° C for 4 hours to obtain SAPO-34 molecular sieve. The catalyst is used for methanol to olefin catalytic reaction. A sample of 0.6 g of a 20-40 mesh particulate catalyst was separately charged into a reactor, activated by nitrogen at 550 ° C for 1 hour, and then cooled to 450 Torr for reaction. The raw material methanol was carried with nitrogen as a diluent gas, the nitrogen flow rate was 40 ml/min, and the methanol weight space velocity was 2.0 h. The composition of the reaction product was analyzed by on-line gas chromatography, and the results are shown in Table 4.

The results show that the selectivity of ethylene and propylene in the HF/A1 ₂ ₃ molar ratio of the initial gel is significantly higher, and the catalyst life is prolonged. Table 4

― No. SP34-2 SPF34-8 SPF34-9 SPF34-10 SPF34-11 SPF34-12

HF/A1 ₂ 0 ₃ (molar ratio) 0 0.04 0.09 0.12 0.21 0.34 Feed time (min) 120 220 220 220 260 280 Methanol conversion (wt%) 100 100 100 100 100 100 Product distribution (wt%)

CH ₄ 0.71 0.77 1.05 1.36 1.32 0.99

C ₂ H ₄ 40.12 48.96 50.86 51.83 52.52 52.76

C ₂ 3⁄4 0.30 0.33 0.37 0.42 0.47 0.38

C ₃ H ₆ 42.38 40.47 39.24 37.78 37.86 37.34

C ₃ H ₈ 1.62 1.54 1.46 1.42 1.55 1.45

C ₄ + 10.39 6.05 5.56 5.46 5.13 5.19

C ₅ ⁺ 4.48 1.88 1.46 1.73 1.15 1.89

∑C ⁼ ₂ -C ⁼ 3 82.50 89.43 90.10 89.61 89.38 90.10 Life*(min) 120-140 220-240 220-240 220-240 260-280 280-300

* Refers to the cumulative feed time when the methanol conversion is 100%. Example 7

The gel mixture was formulated at an initial gel ratio of 3.0 TEA: 0.2 SiO ₂ : P ₂ 0 ₅ : A1 ₂ 0 _{3 :} 50H ₂ O: xNH ₄ F (TEA as a template, χ=0.05, 0.10, 0.20). First 30.3gTEA, 4.4g silica sol, 20.6 g of phosphoric acid, 13.6 g of boehmite and pseudoboehmite 67.5gH ₂ 0 were mixed and stirred uniformly, and then were added 0.475g, 0.95g, and 1.9 _g of a concentration of 40% ^> ¾ ^ aq The mixture was further stirred to form a gel, placed in a synthetic PTFE-lined synthetic kettle, sealed and heated to 200 ° C, and subjected to constant temperature crystallization for 24 hours under autogenous pressure. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C. XRD analysis was carried out as shown in Fig. 3 to obtain SAPO-34 molecular sieve raw powder (No. SPF34-a, SPF34- b, SPF34-c). Example 8

The sample No. SPF34-b obtained in Example 7 and the sample No. SP34-2 obtained in Comparative Example 2 were subjected to ²⁹ Si solid nuclear magnetic characterization, and the molecular sieve skeleton Si coordination environment was determined. The relative contents of various Si coordination structures are shown in Table 5. . table 5

Sample NI^F/A OaCmol) Silicon coordination structure Relative content (%)

Si(4Al) 98.4

SP34-2 one

Si(3Al) 1.6

Si(4Al) 100

SPF34-b 0.10

Si(3Al) 0 Example 9

The sample No. SP34-2 obtained in Example 7 and designated as SPF34-a, SPF34-b and Comparative Example 2 was calcined at 550 ° C for 4 hours to obtain a SAPO-34 molecular sieve catalyst for methanol-to-olefin catalytic reaction. A sample of 0.6 g of a 20-40 mesh particulate catalyst was separately charged into a reactor, activated by nitrogen at 55 CTC for 1 hour, and then cooled to 450 ° C for reaction. The raw material methanol was carried with nitrogen as a diluent gas, the nitrogen flow rate was 40 ml/min, and the methanol weight space velocity 2.011 was analyzed by on-line gas chromatography. The results are shown in Table 6.

Table 6

No. SP34-2 SPF34-a SPF34-b

_{_{_{NH 4 F / Al 2 0 3}}} (mol) 0 0.05 0.10

Feed time (min) 120 240 180 Methanol conversion rate (wt%) 100 100 100

C3⁄4 0.71 1.07 1.66

C ₂ H ₄ 40.12 50.49 47.06

C ₂ H ₆ 0.30 0.43 0.32

C _{3 3⁄4} 42.38 39.26 40.19

C ₃ H _g 1.62 1.74 1.80

C ₄ H _g 10.39 5.61 6.21

C4H10 4.48 1.40 2.76

∑C ₂ ⁼ ~C ₃ ⁼ 82.50 89.75 87.25

Lifetime *(min) 120-140 240-260 180-200

* refers to the cumulative time of feed when the methanol conversion is 100%. The results show that the selectivity of ethylene and propylene in the product synthesized in the initial gel with NH ₄ F/A1 ₂ ₃ molar ratio greater than 0.05 is significantly improved, and the catalyst life is prolonged.

Claims

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1. A method for synthesizing SAPO-34 molecular sieve rich in Si(4Al) structure, wherein the relative amount of Si(4Al) structure in the molecular sieve skeleton accounts for 70-100% of the Si coordination environment; the method comprises the following steps:

a) preparing a gel mixture containing fluoride, SiO ₂ , A1 ₂ 0 ₃ , P ₂ 0 ₅ , a templating agent and water;

c) the solid product is washed with water to neutrality and dried to obtain a raw powder of SAPO-34 molecular sieve;

d) SAPO-34 molecular sieve raw powder is calcined in 400-60 (TC air for 3-8 hours to obtain SAPO-34 molecular sieve with Si(4Al) structure.

Wherein, in the gel mixture, in molar ratio:

F7 Al ₂ O ₃ = 0.01~2.0;

SiO ₂ /Al2O ₃ = 0.1~2,0;

Ρ ₂ Ο ₅ / Α1 ₂ Ο ₃ = 0·5~15;

0/ Α1 ₂ 0 ₃ = 10~100;

_{_{R / A1 2 0 3 = 1~5}} , wherein R is a templating agent.

2. The method according to claim 1, wherein the templating agent is one of triethylamine and diethylamine, or a mixture of two.

3. A method according to claim 1 wherein said fluoride is a soluble acid or salt of a fluoride ion.

4. The method according to claim 1, wherein the fluoride is one of HF and NH ₄ F, or a mixture of two.

5. A method according to claim 1 wherein the crystallization time in said step b) is from 2 to 120 hours.

6. The method according to claim 1, wherein in the Si coordination environment in the SAPO-34 molecular sieve rich in Si(4Al) coordination structure, based on the relative content percentage of the Si coordination environment: Si(4Al) The molar percentage content is 70~100%; the content of Si(3Al) is 0~30%; the molar content of Si(2Al) is 0~20%; the molar content of Si(lAl) is 0~10% The molar percentage of Si(OAl) is 0 to 5%, provided that the ratio of the molar percentage of Si(4Al), Si(3Al), Si(2Al), Si(lAl), and Si(OAl) is 100. %.

7. A SAPO-34 molecular sieve rich in Si(4Al) structure, wherein the relative content of the Si coordination environment is in the Si coordination environment in the SAPO-34 molecular sieve rich in Si(4Al) coordination structure. Meter: Si (4Al) The percentage content of Si (3Al) is 0~30%; the content of Si(2Al) is 0~20%; the content of Si(lAl) is 0~10% _; molar percentage of Si (OAl) is 0~5%, with the proviso that: Si (4Al), Si ( 3Al), Si (2Al), the molar ratio of the percentage content of the Si (lAl) and Si (OAl) 100 %.

The use of the SAPO-34 molecular sieve rich in Si(4Al) structure according to claim 7 for the methanol to olefin reaction.