WO2008019584A1

WO2008019584A1 - A PROCESS FOR SYNTHESIZING SAPO-34 MOLECULAR SIEVE ENRICHED WITH Si(4Al) STRUCTURE IN THE FRAMEWORK

Info

Publication number: WO2008019584A1
Application number: PCT/CN2007/002333
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: CN101121530A; CN101121530B

Abstract

Provided is a process for synthesizing SAPO-34 molecular sieve enriched with Si(4Al) structure in the framework, Si coordination environment is Si(4Al) structure in the molecular sieve framework. The synthesis process could control the form and amount of Si coordination environment by adjusting the addition ratio of silicon in the initial gel for synthesis, thereby SAPO-34 molecular sieve mainly having Si(4Al) coordination environment is synthesized. The molecular sieve is used as MTO catalyst after being baked and could improve efficiently the selectivity of ethene and propene.

Description

SAPO-34 molecular sieve synthesis method with skeleton rich in SW4A1) structure

Technical field

The invention relates to a method for synthesizing SAPO-34 molecular sieve with a skeleton rich in Si(4Al) structure. The molecular sieve is calcined and used in methanol to produce an olefin catalyst, which can effectively improve the selectivity of ethylene and propylene. Background technique

In 1984, UCC developed a new series of silicoaluminophosphate molecular sieves (SAPO-n) (USP 4,440,871). SAPO molecular sieves are a class of crystalline silicoaluminophosphates, consisting of P0 ₄ +, A10 ₄ —, and The tetrahedron of Si0 ₄ constitutes a three-dimensional skeleton structure. 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 olefin (MTO) reaction, such as SAPO-17, SAPO-18, SAPO-34, SAPO, has begun. -44, etc., which have a pore size of about 0.43 nm, are a preferred 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 composed of Α10 ₂ ·tetrahedron and Ρ0 ₂ + tetrahedron in strict proportion of 1:1, the whole skeleton is electrically neutral, there is no obvious Briinsted acid (tannic acid) center, and the whole The acidity is very weak. When aluminum phosphate backbone introduced Si atoms forming the molecular sieve SAPO-n, the backbone Α10 _₂ ·, Ρ0 ₂ ⁺ and Si0 ₂ tetrahedral connected in three kinds, the backbone produces a net negative charge, molecular sieves have acidic protons. Similar to the silicoalumino molecular sieve, there are 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 molecular sieves and the analysis of skeletal structure, Si-0-Al structure has many forms in the skeleton. Si atoms can be connected with 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 acidic 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 is likely to make methanol. Incomplete conversion, medium-strength acid centers can limit alkanes And the formation of aromatic hydrocarbons is beneficial to increase the selectivity of low-carbon olefins such as ethylene and propylene.

It is generally believed that the crystallization process of the SAPO-type molecular sieve follows the silicon substitution mechanism (J. Phys. Chem., 1994, 98, 9614-9618; J. Phys. Chem., 1994, 98, 4878-4883), first producing an AlPO molecular sieve, The silicon atoms enter the molecular sieve skeleton by means of isomorphous substitution. There are two substitution modes: (1) Si substitution P; (2) 2Si substitution P+Alo For SAPO-34 molecular sieve, the silicon content in the gel will affect the synthesis of SAPO- The coordination environment of 34 molecular sieve skeleton Si, in the case of low silicon content, the synthesis of SAPO-34 is carried out by replacing the skeleton phosphorus atom by silicon alone to form Si(4Al) structure; while at high silicon content, there is In the second method, 2Si simultaneously replaces a pair of A1+P atoms to form a plurality of silicon structural units such as Si(3Al), Si(2Al), Si(lAl), and Si(OAl). The result of silicon substitution of phosphorus is to generate a negative skeleton charge to form a B-acid center of a certain strength; silicon can simultaneously form a plurality of skeleton charge distributions to form a B-acid center of different strength.

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 invention, there is provided a method of synthesizing a SAPO-34 molecular sieve having a framework rich in Si(4Al) structure, the method comprising the steps of:

a) preparing a first gel mixture comprising SiO ₂ , A _{1 2} 0 ₃ , P ₂ 0 ₅ and water;

b) adding a templating agent to the first gel mixture to obtain a second gel mixture;

c) crystallization of the second gel mixture at a constant temperature between 100 and 250 Torr under autogenous pressure to obtain a solid product;

d) washing the solid product to neutral with water and drying to obtain the original powder of SAPO-34 molecular sieve; and e) calcining the original powder of SAPO-34 molecular sieve in air at 400-600 ° C for 3-8 hours to obtain a skeleton rich SAPO-34 molecular sieve with Si(4Al) structure,

Where the first gel mixture is in molar ratio,

SiO ₂ /Al ₂ O ₃ = 0.01~<0.2;

Ρ ₂ 0 ₅ / Α1 ₂ Ο ₃ = 0·5~15; H ₂ 0/ A1 ₂ 0 ₃ = 10~100;

Wherein, in the second gel mixture, by molar ratio, R/A1 ₂ 0 ₃ = 1 to 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 SiO ₂ in the step a) is derived from a mixture of one or both of a silica sol and white carbon black.

In a preferred aspect of the invention, in the step a), A1 ₂ 0 _{3 is} derived from a mixture of one or both of activated alumina and pseudoboehmite.

In another preferred aspect of the invention, P ₂ 0 ₅ in the step a) is derived from phosphoric acid.

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

In another aspect of the invention, there is provided a SAPO-34 molecular sieve obtained according to the method described above. In another preferred aspect of the invention, the Si/Al molar ratio in the SAPO-34 molecular sieve framework is

0.05~0.11.

In still another aspect of the invention, the use of the SAPO-34 molecular sieve as described above for the methanol to olefin reaction is provided. DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an XRD chart of a product synthesized under different silicon content conditions in Example 1 of the present invention. Figure 2: ²⁹ Si NMR spectrum of samples Nos. SP34-1, SP34-2, SP34-3 and SP34-4 in Example 2, Comparative Example 2. detailed description

It is an object of the present invention to provide a composite of different Si(OAl), Si(lAl), Si(2Al), Si(3Al) and Si(4Al) by adjusting the ratio of addition of silicon in the initial gel. The method of environmental SAPO-34 molecular sieve, thereby achieving the purpose of modulating the strength and number of acid centers on the surface of the molecular sieve.

Another object of the present invention is to synthesize a SAPO-34 molecular sieve having a skeleton rich in Si(4Al) structure. The synthesized molecular sieve with Si(4Al) as the main coordination environment can be used to improve the selectivity of ethylene and propylene by calcination and methanol for the catalyst.

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 having a skeleton rich in Si(4Al) structure, which synthesizes the proportion of silicon added to the initial gel by modulation, thereby controlling the shape The morphology and quantity of the Si coordination environment of the molecular sieve framework were synthesized, and the SAPO-34 molecular sieve with the Si (4Al) structure of the skeleton Si coordination environment was synthesized;

The molar ratio of each component of the initial gel mixture is:

Si0 ₂ /Al ₂ 0 ₃ = 0.1 -2.0;

P ₂ 0 ₅ / Α1 ₂ Ο ₃ = 0.5~15;

H ₂ 0/ A1 ₂ 0 ₃ = 10~100;

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

In the method, the templating agent is one or a mixture of two of triethylamine and diethylamine. In the method described, the low Si content of the SAPO-34 molecular sieve is adjusted by adjusting the initial gel silica-alumina ratio, and the skeleton Si/Al molar ratio is 0.05 to 0.15.

In the method, the synthesized low silicon content SAPO-34 molecular sieve skeleton Si coordination environment is a Si (4Al) structure.

In the method described, the synthesized SAPO-34 molecular sieve catalyst with Si(4Al) as a coordination environment is applied to the methanol to olefin reaction, which can effectively improve the selectivity of ethylene and propylene.

The invention is characterized in that a low silicon content SAPO-34 molecular sieve having only a Si(4Al) coordination environment can be synthesized by adjusting the proportion of silicon in the initial gel.

The invention synthesizes and synthesizes the Si coordination environment on the surface of SAPO-34 molecular sieve, can adjust the kind and number of coordination environment of molecular sieve skeleton Si, and selects and controls the synthesis of SAPO-34 molecular sieve catalyst with Si(4Al) as the main coordination environment. The reaction of methanol to olefin can increase the selectivity of ethylene and propylene, and can greatly improve the life of the catalyst.

The specific steps of the method of the present invention for synthesizing a Si(4Al)-rich coordination environment SAPO-34 molecular sieve are:

a) preparing a first gel mixture of synthetic SAPO-34 molecular sieve;

b) adding a metered templating agent to the first gel mixture obtained in step a) to obtain a second gel mixture; c) loading the second gel mixture obtained in step b) into a lining of polytetrafluoroethylene In a stainless steel synthesis kettle, it is hermetically heated to a crystallization temperature, and is subjected to constant temperature crystallization under autogenous pressure. After the crystallization is completed, the solid product is separated by centrifugation, washed with deionized water to neutrality, and dried in air at 120 ° C to obtain a raw powder of SAPO-34 molecular sieve; d) the original SAPO-34 molecular sieve obtained in the step c) The powder was calcined in 400-60 CTC air for 3-8 hours to obtain a SAPO-34 molecular sieve catalyst.

The invention selectively controls the synthesis of the oxide molar ratio of each component of the SAPO-34 molecular sieve gel mixture with Si(4Al) as the main coordination environment: Si0 ₂ /Al ₂ 0 ₃ = 0.1-0.5;

P ₂ 0 ₅ / A1 ₂ 0 ₃ = 0.5- 15;

H ₂ 0/ A1 ₂ 0 ₃ = 10 - 100;

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

In the present invention, SiO _{2 is} derived from a mixture of one or both of silica sol and white carbon; A1 ₂ 0 _{3 is} derived from a mixture of one or both of activated alumina and pseudoboehmite; P ₂ 0 _{5 is} derived from phosphoric acid .

The templating agent in the present invention is one of triethylamine and diethylamine, or a mixture of two.

The crystallization conditions of the SAPO-34 molecular sieve selected by the invention to control the synthesis of Si(4Al) as the main coordination environment are: crystallization temperature is 100-250 ° C; crystallization time is 2-120 hours.

In the present invention, the SAPO-34 molecular sieve rich in Si(4Al) structure means SAPO-34 molecular sieve having a Si(4Al) structure content of 70 to 100%. The invention is described in detail below by way of examples.

Example 1

1.65 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 69.5 g of H ₂ 0 were mixed and stirred to obtain a first gel mixture. To the first gel mixture, 30.3 g of TEA (TEA is triethylamine) was added, and stirred well to obtain a second gel mixture. The second gel mixture was placed in a stainless steel synthesizing tank lined with polytetrafluoroethylene, sealed and heated to a closed heating of 200 ° C, and subjected to constant temperature crystallization under autogenous pressure 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 raw powder of SAPO-34 molecular sieve, which was called SP34-1.

Further, 3.31 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 68.3 g of H ₂ 0 were mixed and stirred to obtain a first gel mixture. To the first gel mixture, 30.3 g of TEA (TEA is triethylamine) was added, and stirred well to obtain a second gel mixture. The second gel mixture was placed in a stainless steel synthesizer lined with polytetrafluoroethylene, sealed and heated to a sealed heat of 200 ° C, and subjected to constant temperature crystallization under autogenous pressure 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 raw powder of SAPO-34 molecular sieve, which was called SP34-2. Comparative example 1

4.41 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 to obtain a first gel mixture. To the first gel mixture, 30.3 g of TEA (TEA is triethylamine) was added, and charged The mixture was stirred to obtain a second gel mixture. The second gel mixture was placed in a stainless steel synthetic kettle lined with polytetrafluoroethylene, sealed and heated to a closed heat of 20 (TC, under autogenous pressure, and subjected to constant temperature crystallization for 12 hours. Then, the solid product was centrifuged, It was washed with deionized water to neutrality. After drying in I20'C air, XRD analysis was carried out as shown in Fig. 1, and the original powder of SAPO-34 molecular sieve was obtained, which was called SP34-3.

Separately, 13.2 g of silica sol, 20.6 g of phosphoric acid, 13.6 g of pseudoboehmite and 61.1 g of H ₂ 0 were mixed and stirred to obtain a first gel mixture. To the first gel mixture, 30.3 g of TEA (TEA is triethylamine) was added, and stirred well to obtain a second gel mixture. The second gel mixture was placed in a stainless steel synthesis vessel lined with polytetrafluoroethylene, sealed and heated to a sealed heating to 200 ° C, and subjected to constant temperature crystallization under autogenous pressure 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 raw powder of SAPO-34 molecular sieve, which was called SP34-4. Example 2

The sample No. SP34-1 and SP34-2 obtained in Example 1 were subjected to ²⁹ Si solid nuclear magnetic characterization, and the molecular sieve skeleton Si coordination environment was measured. The results are shown in Fig. 2.

When the Si0 ₂ /Al ₂ 0 ₃ molar ratio in the gel is 0.075 and 0.15, the synthesized Si34-1 and SP34-2 molecular sieve skeleton Si coordinates to Si(4Al) structure, and the skeleton Si/Al molar ratio is 0.06 and 0.11. . Comparative example 2

Comparative Example 1 was obtained with the number SP4-3; the SP4-4 sample was subjected to ²⁹ Si solid nuclear magnetic characterization, and the molecular sieve skeleton Si coordination environment was measured. The results are shown in Fig. 2.

When the molecular sieve framework Si SP34-3 ligand gel Si0 _₂ Al ₂ 0 ₃ molar ratio of / is synthesized with 0.20 Si (4Al) and Si (3Al) structure, its skeleton Si / Al molar ratio of 0.12; and when condensable When the molar ratio of Si0 ₂ /Al ₂ 0 _{3 in the} rubber is 0.60, the synthesized Si344 molecular sieve skeleton Si has a structure of Si(4Al)Si(3Al)Si(2Al), Si(lAl) and Si(OAl). The skeleton Si/Al molar ratio was 0.19. Example 3

The sample No. SP34-1, SP34-2 obtained in 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 particulate catalyst was separately charged into a reactor, activated by nitrogen at 550 ° C for 1 hour, and then cooled to 450 ° C for reaction. Nitrogen was used as a diluent gas to carry the raw material methanol, the nitrogen flow rate was 40ml/min, and the methanol weight space velocity was 2.011. The composition of the material was analyzed by on-line gas chromatography, and the results are shown in Table 1.

The results show that when the Si coordination environment of the SAPO-34 molecular sieve catalyst is Si(4Al), the selectivity of ethylene and propylene is higher and the catalyst life is longer. Table 1

No. SP34-1 SP34-2

Feed time (min) 240 240

Methanol conversion rate (wt%) 100 100

Product distribution (wt%)

CH ₄ 1.44 1.02

C ₂ H ₄ 47.33 48.10

C ₂ H ₆ 0.23 0.29

C ₃ H ₆ 42.05 41.55

C ₃ H ₈ 0.46 1.15

C ₄ ⁺ 6.34 5.69

C ₅ + 2.15 2.20

∑C ₂ ⁼ -C ₃ ⁼ 89.38 89.65

Lifetime *(min) 240-260 240-260

* Refers to the cumulative feed time when the methanol conversion is 100%. Comparative example 3

The sample No. 1 obtained in Comparative Example 1 was SP34-3, and the sample of SP34-4 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 particle catalyst was separately charged into the reactor, activated by nitrogen at 550 ° C 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 2.

The results show that when there are many Si coordination environments in the skeleton of the synthesized SAPO-34 molecular sieve catalyst, the selectivity of ethylene and propylene in the product is reduced, and the catalyst life is shortened. Table 2

No. SP34-3 SP34-4 Feed time nin) 120 120 Methanol conversion rate (%) 100 100 Product distribution (wt%)

CH ₄ 0.76 0.96

C ₂ H ₄ 39.93 39.75

C ₂ H ₆ 0.29 0.81

C ₃ H ₆ 43.09 43.07

C ₃ H ₈ 2.84 3.94

C ₄ ⁺ 8.83 7.81

C ₅ ⁺ 4.26 3.66

∑C ₂ ⁼ -C ₃ ⁼ 83.03 82.83 Life*(min) 120-140 120-140

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

Claims

Rights request

A method for synthesizing SAPO-34 molecular sieve rich in Si(4Al) structure, the method comprising the steps of:

c) crystallization of the second gel mixture at a constant temperature between 100 and 250 ° C under autogenous pressure to obtain a solid product;

d) The solid product is washed with water to neutrality and dried to obtain a raw powder of SAPO-34 molecular sieve; and e) 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 SAPO-34 molecular sieve with Si(4Al) structure,

Where the first gel mixture is in molar ratio,

SiO ₂ /Al ₂ O ₃ = 0.01 ~<0.2;

P ₂ 0 ₅ / Α1 ₂ Ο ₃ = 0.5~15;

H ₂ 0/ A1 ₂ 0 ₃ = 10~100;

Wherein, in the second gel mixture, by molar ratio, R/A1 ₂ 0 ₃ = 1 to 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 in the step a) the SiO _{2 is} derived from a mixture of one or both of a silica sol and white carbon black.

4. The method according to claim 1, wherein in the step a) A] ₂ 0 _{3 is} derived from a mixture of one or both of activated alumina and pseudoboehmite.

5. The method according to claim 1, wherein in the step a), P ₂ 0 _{5 is} derived from phosphoric acid.

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

7. A SAPO-34 molecular sieve obtained by the process of claim 1.

8. The SAPO-34 molecular sieve according to claim 7, wherein the Si/Al molar ratio in the skeleton is 0.05~

0.11.

9. Use of SAPO-34 molecular sieve according to claim 7 in methanol to olefin reaction.