WO2016090612A1

WO2016090612A1 - Synthesis method for mesoporous and microporous sapo-34 molecular sieve

Info

Publication number: WO2016090612A1
Application number: PCT/CN2014/093624
Authority: WO
Inventors: 王婵; 杨淼; 田鹏; 刘中民; 桑石云; 杨越
Original assignee: 中国科学院大连化学物理研究所
Priority date: 2014-12-11
Filing date: 2014-12-11
Publication date: 2016-06-16

Abstract

Disclosed is a synthesis method for a mesoporous and microporous SAPO-34 molecular sieve. In the method, a SAPO-34 molecular sieve with a mesoporous and microporous composite structure is obtained by using an organic silicon compound containing a quaternary ammonium cation as a silicon source and a structure directing agent simultaneously, in combination with the use of a seed crystal. The prepared SAPO-34 molecular sieve is used as a catalyst in an MTO reaction and shows an excellent catalytic performance, and the catalyst life is notably prolonged.

Description

Method for synthesizing medium microporous SAPO-34 molecular sieve

Technical field

The present application relates to a method for preparing a microporous SAPO-34 molecular sieve, and the use of the prepared molecular sieve as a catalyst in the reaction of converting oxygenates into light olefins.

Background technique

Molecular sieve is a microporous solid material with a crystalline structure, with regular microporous structure, medium strong acidity, high specific surface and high thermal stability. It is widely used in the fields of catalysis, adsorption and separation. The high reaction shape selectivity of molecular sieve micropores makes them highly selective for specific reactions. However, the single microporous structure reduces the mass transfer efficiency, resulting in low utilization rate of the active site of the catalyst, which is highly prone to occur in the catalytic reaction. Carbon is inactivated.

SAPO-34 is a chabazite-type (CHA) molecular sieve with an eight-membered ring ellipsoidal cage and a three-dimensional cross-cell structure formed by a double six-membered ring stacked in an ABC manner. The pore size is 0.38×0.38 nm, and the cage size is 1.0×0.67 nm. , belongs to small pore molecular sieve. SAPO-34 exhibits excellent catalytic properties in methanol to olefin (abbreviated as MTO) reactions due to its suitable pore structure, acid properties, excellent thermal stability and hydrothermal stability. At present, many work has shown that multi-stage pores SAPO-34 and nano-SAPO-34 can effectively prolong the life of SAPO-34 in MTO reaction (Chemical Communication, 2009, 3282; Journal of Materials Chemistry, 2010, 20, 3227; Microporous And Mesoporous Materials, 2012, 164, 214; Chemical Communication, 2014, 50, 6502; Chemistry of Materials, 2014, 26, 4552; Applied Catalysis A: General 2012, 437-438, 120; Journal of Physical Chemistry C, 2013, 117, 8214).

Various synthetic methods such as soft templating, hard templating and post-treatment have been applied to the preparation of multistage pore SAPO-34 molecular sieves. The soft template method has proven to be a very effective method for synthesizing multi-stage pore molecular sieves due to its simple operation and variety of soft templates. However, the introduction of mesoporous templates often leads to phase separation of micropores and mesopores. This is mainly due to the fact that the mesoporous structure is usually crystallized faster, such as MCM-41 and SBA-15, which is generally crystallization at 100-140 ° C for 24 hours, while the crystallization of the microporous molecular sieve is introduced after the introduction of the mesoporous template. The crystallization rate is severely slowed down, and it usually takes more than 48 hours to crystallize. This is a serious mismatch with the crystallization rate of the mesoporous structure, so the product of the soft template synthesis is often a mixture of microporous crystals and amorphous.

Summary of the invention

According to an aspect of the present application, there is provided a method for synthesizing a mesoporous SAPO-34 molecular sieve, which is obtained by using an organosilicon compound containing a quaternary ammonium cation as a silicon source and a structure directing agent in combination with the use of a seed crystal. Microporous composite structure of SAPO-34 molecular sieve. The prepared SAPO-34 molecular sieve is used as a catalyst in the MTO reaction, exhibits excellent catalytic performance, and the catalyst life is significantly prolonged.

The method for synthesizing the microporous SAPO-34 molecular sieve is characterized in that the mesoporous SAPO-34 is synthesized by a hydrothermal method in the presence of an organosilicon compound containing a quaternary ammonium cation and a seed crystal of SAPO-34. Molecular sieves.

Preferably, the organosilicon compound containing a quaternary ammonium cation is a silicone surfactant containing a quaternary ammonium cation.

The organosilicon compound containing a quaternary ammonium cation functions as a partial silicon source and/or a mesoporous mold. Plate.

Preferably, the organosilicon compound containing a quaternary ammonium cation is selected from at least one of the compounds having the chemical structural formula of Formula I:

Wherein n is any positive integer between 1 and 6; R ¹ , R ² , R ³ , R ⁴ and R ^{5 are} independently selected from an alkyl group having 1 to 10 carbon atoms; and R ^{6 is} selected from a carbon atom. The number is 1 to 22 alkyl groups; X ^- is at least one selected from the group consisting of halogen anions. Preferably, n is any positive integer between 2 and 4; and R ¹ , R ² , R ³ , R ⁴ and R ^{5 are} independently selected from an alkyl group having 1 to 5 carbon atoms. Further preferably, in the formula I, n=3; R ¹ is a methyl group; R ² is a methyl group; R ³ is a methyl group; R ⁴ is a methyl group; R ⁵ is a methyl group; and R ^{6 is} selected from carbon atoms. Is an alkyl group of 12 to 22; X ^- is Br ^- .

The alkyl group is a group formed by the loss of any hydrogen atom on any linear alkane, any branched alkane or any of the cycloalkane molecules.

According to a preferred embodiment of the present application, the method for synthesizing the mesoporous SAPO-34 molecular sieve comprises at least the following steps:

a) After dissolving the organosilicon compound containing a quaternary ammonium cation in water, an aluminum source, a phosphorus source, an organic amine, and a silicon compound containing no quaternary ammonium cation are sequentially added to obtain a mixture having the following molar ratio:

P ₂ O ₅ : Al ₂ O ₃ : SiO ₂ : organic amine: H ₂ O = 0.6 to 1.4: 0.6 to 1.4: 0.2 to 1.2: 1.5 to 3.0: 50 to 200;

b) adding SAPO-34 seed crystals to the mixture obtained in step a), mixing uniformly at 130-240 ° C Crystallization for 1 to 72 hours;

c) After the crystallization is finished, the solid product is separated, washed, and dried to obtain the mesoporous SAPO-34 molecular sieve.

In the mixture of step step a), the amount of the aluminum source is in terms of the number of moles of Al ₂ O ₃ , that is, 1/2 of the mole of the aluminum element contained in the aluminum source; the amount of the phosphorus source is in the molar amount of P ₂ O ₅ The number is 1/2 of the number of moles of phosphorus contained in the phosphorus source; the organosilicon compound containing a quaternary ammonium cation and the silicon compound containing no quaternary ammonium cation are used as a common silicon source, and the amount of SiO ₂ is added. The sum of the number of moles of silicon contained in the organosilicon compound containing a quaternary ammonium cation and the silicon compound containing no quaternary ammonium cation; the number of moles of the organic amine in terms of the number of moles per mole, and the number of moles of water The number of moles in itself.

Preferably, the molar ratio of the organosilicon compound containing the quaternary ammonium cation in the step a) to the silicon compound not containing the quaternary ammonium cation is an organosilicon compound containing a quaternary ammonium cation in terms of the number of moles of the silicon element: no season The silicon compound of the ammonium cation is 1 to 30:10. Further preferably, the molar ratio of the organosilicon compound containing the quaternary ammonium cation in the step a) to the silicon compound not containing the quaternary ammonium cation is an organosilicon compound containing a quaternary ammonium cation in terms of the number of moles of the silicon element: The silicon compound of the quaternary ammonium cation = 2 to 10:10.

Preferably, the phosphorus source in step a) is selected from at least one of phosphoric acid, metaphosphoric acid, phosphate, and phosphite.

Preferably, the aluminum source in step a) is selected from at least one of aluminum isopropoxide, pseudoboehmite, and aluminum hydroxide.

Preferably, the silicon compound containing no quaternary ammonium cation in step a) is selected from at least one of tetraethyl orthosilicate, silica sol, and silica.

Preferably, the organic amine in step a) is selected from the group consisting of tetraethylammonium hydroxide (abbreviated as TEAOH), At least one of triethylamine (abbreviated as TEA), diethylamine (abbreviated as DEA), and morpholine (abbreviated as MOR).

Preferably, the crystallization time in the step b) is 2 to 24 hours.

Preferably, the mass ratio of the SAPO-34 seed crystal in step b) to the mixture obtained in step a) is from 0.001 to 0.6:1. Further preferably, the upper limit of the mass ratio range of the mixture of SAPO-34 and the mixture obtained in step a) in step b) is selected from the group consisting of 0.6:1, 0.4:1, 0.3:1, 0.1:1, and the lower limit is selected from 0.001:1, 0.01. : 1, 0.03: 1, 0.05: 1, 0.07: 1.

Preferably, the SAPO-34 molecular sieve has a crystallite size of 50 nm to 1 μm.

Preferably, the SAPO molecular sieve has a mesoporous composite structure having a micropore specific surface area of 300 to 600 m ² /g and a mesoporous specific surface area of 100 to 300 m ² /g.

According to still another aspect of the present application, there is provided an acid catalyst characterized in that the mesoporous SAPO-34 molecular sieve synthesized according to any of the above methods is obtained by calcination in air at 400 to 700 °C.

According to still another aspect of the present application, there is provided a catalyst for the conversion of an oxygenate to an olefin, characterized in that the mesoporous SAPO-34 molecular sieve synthesized according to any of the above methods is obtained by calcination in air at 400 to 700 °C.

The beneficial effects that can be produced by the present invention include at least:

(1) According to the method provided by the present application, the prepared SAPO-34 molecular sieve has a microporous mesoporous composite structure.

(2) According to the method provided by the present application, the particle size of the prepared SAPO-34 molecular sieve is 50 nm - 1 μm.

(3) According to the method provided by the present application, the prepared SAPO-34 molecular sieve exhibits excellent catalytic performance in the MTO reaction, and the catalyst life is remarkably prolonged.

DRAWINGS

1 is a scanning electron micrograph of a sample obtained in Example 1.

2 is a scanning electron micrograph of a sample obtained in Comparative Example 1.

Figure 3 is a scanning electron micrograph of the sample obtained in Comparative Example 2.

Detailed ways

The present application is described in detail below by way of examples, but the application is not limited thereto.

Unless otherwise specified, the test conditions in the examples were as follows: The elemental composition was measured by a Magix-601 type ray fluorescence analyzer (XRF) manufactured by Philips.

X-ray powder diffraction phase analysis (XRD) was carried out using an X'Pert PRO X-ray diffractometer from the PANalytical Company of the Netherlands, a Cu target, a Kα radiation source (λ = 0.15418 nm), a voltage of 40 kV, and a current of 40 mA.

The SEM morphology analysis was performed using a SU8020 scanning electron microscope from the Scientific Instrument Factory of the Chinese Academy of Sciences.

The N ₂ physical adsorption analysis was measured using a Micromeritics ASAP Model 2020 physical adsorption analyzer from Micron, USA.

The organosilicon compound containing a quaternary ammonium cation used in the examples is selected from the group consisting of n = 3 in the formula I, R ¹ is a methyl group, R ² is a methyl group, R ³ is a methyl group, and R ⁴ is a methyl group, R ⁵ is a methyl group, R ^{6 is} selected from an alkyl group having 12 to 22 carbon atoms; and X ^- is a compound of Br ^- abbreviated as OS-R ⁶ . For example, "OS-12" means that the chemical structure is n=3 in formula I, R ¹ is methyl, R ² is methyl, R ³ is methyl, R ⁴ is methyl, R ⁵ is methyl, X ^- An organosilicon compound containing a quaternary ammonium cation in which Br ^- and R ⁶ are dodecyl groups.

Example 1

The ratio of raw material ingredients, crystallization conditions and sample element composition are shown in Table 1. The specific ingredients process is as follows:

21.6 g of OS-12 (72% by mass) and 89.8 g of deionized water were mixed and stirred for 5 hours, and 14.0 g of pseudoboehmite (72.5% by mass of Al ₂ O ₃ ), 23.0 g of phosphoric acid were sequentially added. (H ₃ PO ₄ mass percentage 85%), 30.6 g triethylamine (TEA mass percentage 99%), 8.6 g silica sol (SiO ₂ mass percent 31%), stirred and aged for 24 hours, The component molar ratio was 1.0 P ₂ O ₅ : 1.0 Al ₂ O ₃ : 0.76 SiO ₂ : 3.0 TEA: 50 H ₂ O of the SAPO gel in which the molar ratio of OS-12 to silica sol was 7:10. Further, 18.8 g of SAPO-34 seed crystal was added to the above gel, and the mixture was stirred at room temperature for 12 hours, and the gel was transferred to a stainless steel reaction vessel. After the reaction vessel was placed in an oven, the temperature was programmed to 150 ° C for 24 hours. After completion of the reaction, the solid product was centrifuged, washed repeatedly with deionized water, and dried in air at 110 ° C to obtain a raw powder.

The morphology of the obtained sample was characterized by scanning electron microscopy. The electron micrograph was as shown in Fig. 1. The obtained sample was a cubic particle having a rough surface of about 400 nm.

The original powder samples were subjected to XRD analysis, and the results are shown in Table 2. The results indicate that the synthesized product has the characteristics of the SAPO-34 structure.

The obtained samples were subjected to elemental composition analysis by XRF, and the results are shown in Table 1.

Table 1 Molecular sieve synthesis ingredients, crystallization conditions and element composition table

Table 2 XRD of the sample of Example 1

Comparative example 1

The proportion of the ingredients and the crystallization process were the same as in Example 1, except that the organosilicon compound OS-12 containing a quaternary ammonium cation was not added, and the organosilicon compound OS-12 containing a quaternary ammonium cation was replaced with a silica sol containing the same SiO ₂ mole number.

The morphology of the obtained sample was characterized by scanning electron microscopy. The electron micrograph is shown in Fig. 2, which is a large crystal grain with a smooth surface of about 1 μm.

Comparative example 2

The proportion of ingredients and the crystallization process were the same as in Example 1, but without the addition of SAPO-34 seeds.

The morphology of the sample was characterized by scanning electron microscopy. The electron micrograph is shown in Figure 3. A large number of amorphous forms exist.

Examples 2 to 14

The specific proportion of ingredients and crystallization conditions are shown in Table 1, and the specific batching process is the same as in Example 1.

The samples obtained in Examples 2 to 14 were subjected to XRD analysis. The data results were close to those in Table 2, that is, the peak positions and shapes were the same, and the relative peak intensity fluctuated within ±10% depending on the synthesis conditions, indicating that the synthesized product had SAPO-34. The characteristics of the structure.

The samples obtained in Examples 2 to 14 were subjected to XRF elemental composition analysis, and the results are shown in Table 1.

The morphology of the samples obtained in Examples 2 to 14 was analyzed by scanning electron microscopy, and the obtained electron micrographs were similar to those of Fig. 1.

Example 15

The samples obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were subjected to air baking at 600 ° C for 2 hours, and then subjected to N ₂ physical adsorption analysis. The results are shown in Table 3, showing that not only micropores but also mesopores were present in the samples obtained in Examples 1 to 7.

Table 3 Specific surface area and pore volume of the sample

Example 16

The samples of Examples 1 to 7 and Comparative Examples 1 and 2 were subjected to air baking at 600 ° C for 2 hours, and then tableted and crushed to 20 to 40 mesh. A 0.3 g sample was weighed into a fixed bed reactor and evaluated for MTO reaction. The reaction was carried out by a nitrogen gas activation at 550 ° C for 1 hour and then cooling to 450 ° C. Methanol was carried by nitrogen, the flow rate of nitrogen was 42 ml/min, and the mass velocity of methanol was 2.9 h ^-1 . The reaction product was analyzed by on-line gas chromatography (Varian 3800, FID detector, capillary column PoraPLOT Q-HT). The results are shown in Table 4. It can be seen that the samples obtained in Examples 1 to 7 using the technical solutions of the present application have greatly improved the life of the catalyst as compared with the samples obtained in Comparative Examples 1 and 2.

Table 4 Results of methanol conversion to olefins in samples

a. methanol conversion rate of 100% reaction time

b. The highest (ethylene + propylene) selectivity when 100% methanol conversion

The present application is disclosed in the above preferred embodiments, but is not intended to limit the scope of the claims. Any one of ordinary skill in the art can make various possible changes and modifications without departing from the spirit of the present application. The scope should be determined by the scope defined by the claims of the present application.

Claims

A method for synthesizing microporous SAPO-34 molecular sieve, characterized in that the mesoporous SAPO-34 is synthesized by a hydrothermal method in the presence of an organosilicon compound containing a quaternary ammonium cation and a seed crystal of SAPO-34 Molecular sieves.
The method according to claim 1, wherein said organosilicon compound containing a quaternary ammonium cation is at least one selected from the group consisting of compounds having a chemical structural formula of formula I:

Wherein n is any positive integer between 1 and 6; R 1 , R 2 , R 3 , R 4 and R 5 are independently selected from an alkyl group having 1 to 10 carbon atoms; and R 6 is selected from a carbon atom. The number is 1 to 22 alkyl groups; X - is at least one selected from the group consisting of halogen anions.
The method according to claim 2, wherein n = 3 in the formula I; R 1 is a methyl group; R 2 is a methyl group; R 3 is a methyl group; R 4 is a methyl group; and R 5 is a methyl group. R 6 is selected from an alkyl group having 12 to 22 carbon atoms; and X - is Br - .
The method of claim 1 including at least the following steps:

a) After dissolving the organosilicon compound containing a quaternary ammonium cation in water, an aluminum source, a phosphorus source, an organic amine, and a silicon compound containing no quaternary ammonium cation are sequentially added to obtain a mixture having the following molar ratio:

P 2 O 5 : Al 2 O 3 : SiO 2 : organic amine: H 2 O = 0.6 to 1.4: 0.6 to 1.4: 0.2 to 1.2: 1.5 to 3.0: 50 to 200;

b) adding SAPO-34 seed crystals to the mixture obtained in step a), mixing uniformly, and crystallization at 130-240 ° C for 1 to 72 hours;

c) After the crystallization is finished, the solid product is separated, washed, and dried to obtain the mesoporous SAPO-34 molecular sieve.
The method according to claim 4, wherein the molar ratio of the organosilicon compound containing the quaternary ammonium cation to the silicon compound not containing the quaternary ammonium cation in the step a) is in the range of the molar amount of the silicon element, and is a season containing Ammonium cation organosilicon compound: silicon compound containing no quaternary ammonium cation = 1 to 30:10.
The method according to claim 4, wherein the phosphorus source in step a) is at least one selected from the group consisting of phosphoric acid, metaphosphoric acid, phosphate, and phosphite; and the aluminum source in step a) is selected from the group consisting of At least one of aluminum isopropoxide, pseudoboehmite, and aluminum hydroxide; the silicon compound containing no quaternary ammonium cation in step a) is selected from the group consisting of ethyl orthosilicate, silica sol, and silica. At least one.
The method according to claim 4, wherein the organic amine in the step a) is at least one selected from the group consisting of tetraethylammonium hydroxide, triethylamine, diethylamine and morpholine.
The method according to claim 4, wherein the mass ratio of the SAPO-34 seed crystal to the mixture obtained in the step a) in the step b) is from 0.001 to 0.6:1.
An acid catalyst characterized in that the mesoporous SAPO-34 molecular sieve synthesized by the method according to any one of claims 1 to 8 is obtained by calcination in air at 400 to 700 °C.
A catalyst for the conversion of an oxygen-containing compound to an olefin, characterized in that the medium-microporous SAPO-34 molecular sieve synthesized by the method according to any one of claims 1 to 8 is obtained by calcination in air at 400 to 700 °C.