WO2014047807A1

WO2014047807A1 - Sapo-44 molecular sieves and synthesis method thereof

Info

Publication number: WO2014047807A1
Application number: PCT/CN2012/082011
Authority: WO
Inventors: 田鹏; 樊栋; 刘中民; 苏雄; 张莹; 杨越
Original assignee: 中国科学院大连化学物理研究所
Priority date: 2012-09-26
Filing date: 2012-09-26
Publication date: 2014-04-03

Abstract

The present invention relates to SAPO-44 molecular sieves and to a synthesis method thereof. The invention is characterized in that the micropores of the molecular sieves contain a hexamethyleneimine template agent, the surface of the molecular sieve crystal body is slightly silicon-rich, and the ratio of external surface silicon contents to the bulk silicon contents of the crystal body is 1.50 to 1.01. Said molecular sieves, following calcination in air at 400〜700°C, can be used as a catalyst for acid-catalyzed reactions and oxygenate-to-olefin reactions.

Description

SAPO-44 molecular sieve and synthesis method thereof

The invention belongs to the field of SAPO molecular sieves, and particularly relates to a SAPO-44 molecular sieve and a synthetic method thereof. Background technique

In 1984, U.S. Union Carbide Corporation (UCQ developed a series of SAPO molecular sieves (USP 4440871). This molecular sieve is a type of crystalline silicoaluminophosphate with a three-dimensional framework consisting of Ρ0 ₂ ⁺ , Α10 ₂ Π Si〇 ₂ The composition of the structure is SAPO-34, which is composed of eight rings and has an orifice of 0.38 nm x 0.38 nm. SAPO-34 molecular sieves produce low-carbon olefins in methanol due to their suitable acidity and pore structure. The MTO) exhibits excellent catalytic performance and has received much attention.

SAPO-34 molecular sieves are generally hydrothermally synthesized using water as a solvent in a closed autoclave. The synthetic components include an aluminum source, a silicon source, a phosphorus source, a templating agent, and deionized water. Available as silicon source with silica sol, active silica and orthosilicate, aluminum source with activated alumina, pseudoboehmite and alkoxy aluminum. The ideal source of silicon and aluminum is silica sol and pseudo-thin water. Aluminite; Phosphorus source generally uses 85% phosphoric acid. Common templating agents include tetraethylammonium hydroxide (TEAOH), morpholine (MOR), piperidine (Piperidine), isopropylamine (i-PrNH2), triethylamine (TEA;), diethylamine (DEA). , dipropylamine, etc. and mixtures thereof. SAPO-44 has a similar framework structure (CHA) to SAPO-34, but there are some differences in the XRD spectra. SAPO-44 is typically synthesized using cyclohexylamine as a template.

Hexamethyleneimine (HMI) is commonly used as a structure directing agent for the synthesis of SAPO-35 molecular sieves in the synthesis of SAPO molecular sieves. Chinese patent 200710175273.X reported the synthesis of SAPO-35 using HMI as a template. The initial synthesis mixture needs to be gelled at 35-100 ^Q C. The synthesis ratio is (0.5-1.8) R: (0.05-2) Si0 ₂ : 1A1 ₂ 0 ₃ : (0.5-1.5 ) P ₂ 0 ₅ : ( 10- 150) H ₂ 0, crystallized at 150-210 ° C for 0.5-500 h. The SAPO-35 molecular sieve belongs to the LEV structure, which is formed by stacking double six-membered rings in the order of AABCCABBC. The CHA structure is formed by stacking double six-membered rings in AABBCC order. It can be seen that there is a big difference in the structure between the two. In general, the synthesis of SAPO molecular sieves requires organic amine/ammonium as a structure directing agent. An organic amine can synthesize molecular sieves of various structures under different conditions. Similarly, a molecular sieve can be synthesized using a variety of different organic amines. But so far, the relationship between the structure of the organic amine and the molecular sieve structure it is directed to is not very clear. Although a lot of researchers have done a lot of research and experiment in this area, and have made some progress, it is still very difficult to predict between the structure-directing agent and the molecular sieve structure it produces. Most of the organic amines required for molecular sieve synthesis have been discovered experimentally.

In the synthesis of SAPO molecular sieves, several researchers reported that the synthesized molecular sieves have the characteristics of surface-rich silicon. This is mainly due to the fact that the initial gel system of SAPO molecular sieves is generally acidic or near-neutral. As crystallization proceeds, phosphoric acid is gradually consumed (crystallization to form molecular sieves) resulting in an increase in the pH of the synthesis system. The silicon source usually exists in the form of a polymerized state at the initial stage of crystallization. Due to its lower isoelectric point, as the pH of the synthetic system increases, the silicon oxide will gradually depolymerize to form a low-concentration silicon species, thereby allowing silicon to participate. The proportion of the skeleton forming the SAPO molecular sieve is increased, resulting in the phenomenon that the surface of the molecular sieve crystallite is rich in silicon. For example, we used diethylamine synthesis in the early stage.

SAPO-34 found that silicon is unevenly distributed in SAPO-34 molecular sieve crystals, increasing its content from core to shell, and the outer surface silicon content (molar ratio Si/(Si+Al+PX» and bulk bulk silicon) The ratio of contents is 1.41 (Microporous and Mesoporous Materials, 2008, 114(1 -3): 4163). Akolekar et al. found that the ratio of surface silicon content to bulk silicon content is as high as 6-10 for SAPO-44. (Colloids and Surfaces A: Physicochemical and Engineering Aspects 146 (1999) 375-386). In general, SAPO molecular sieves generally exhibit the characteristics of silicon-rich surface, but it is worth noting that even the same SAPO Molecular sieves, the composition of their surface elements and bulk phase will also vary greatly depending on the synthesis conditions and the templating agent used.

Generally, in the SAPO molecular sieve, as the silicon content increases, the coordination environment of silicon will also transition from the initial simple Si (4Al) to a variety of silicon environments (Si = 0-4) (different SAPO molecular sieves in its skeleton) The maximum amount of single silicon dispersion allowed is different, see Phys. Chem., 1994, 98, 9614). The change of silicon coordination environment causes a large change in acid concentration and acid strength. The acid strength has the following order: Si(lAl) >Si(2Al)>Si(3Al)> Si(4Al). On the other hand, with the appearance of silicon islands in the framework of SAPO molecular sieves, the amount of acid center produced by each silicon atom decreases (1 for Si(4Al) and less than 1 for many silicon environments), that is, acid density. reduce. Can be imagined If the SAPO molecular sieve is an acid catalyst, if the distribution of silicon in the crystallite grains is not uniform, the acid properties will also be non-uniform, which will inevitably have an important influence on the catalytic performance of the molecular sieve. If the molecular sieve grains are rich in silicon, the silicon coordination environment near the outer shell region of the crystal grains is relatively complicated compared with the inside. Weckhuysen et al. have reported that in the methanol to olefin reaction (MTO), the reaction is first carried out in the near outer surface region of the SAPO-34 grains. As the reaction progresses, a large carbonaceous material gradually forms and blocks the pores, causing the interior of the grains. Product diffusion is more difficult (Chemistiy - A European Journal, 2008, 14, 1 1320-1 1327; J. Catal., 2009, 264, 77-87). This also indicates that the acidic environment on the outer surface of the molecular sieve grains is particularly important for the catalytic reaction. It is of great significance to find a method to effectively control the degree of silicon enrichment on the surface of molecular sieves. Summary of the invention

The object of the present invention is to provide a SAPO-44 molecular sieve whose anhydrous chemical composition can be expressed as: mSDA. (Si _x Al _y P _z )0 ₂ , wherein: SDA is hexamethyleneimine; m represents each Molar (Si _x Al _y P _z ) 0 ₂ corresponds to the number of moles of organic amine, m = 0.1~0.5; x, y, z represent the molar fractions of Si, Al, and P, respectively, and the ranges are x = 0.01 to 0.60, respectively. y=0.2~0.60, z=0.2~0.60, and x+y+z=l. The surface of the molecular sieve crystal is slightly rich in silicon, and the ratio of silicon content on the outer surface (Si/(Si+Al+P) molar ratio;) to the bulk silicon content of the crystal is 1.50~1.01, preferably 1.40~1.02, more preferably 1.35 -1.03, more preferably 1.30~1.03. The increase in the amount of silicon from the core to the shell in the SAPO-44 molecular sieve crystal may be uniform or non-uniform.

It is still another object of the present invention to provide a method for synthesizing SAPO-44 molecular sieves.

It is still another object of the present invention to provide an SAPO-44 molecular sieve and an acid-catalyzed reaction catalyst or an oxygen-containing compound converted to an olefin-reactive catalyst prepared by the above method.

It is still another object of the present invention to provide a gas adsorbent which is synthesized by the above method and which is prepared from the SAPO-44 molecular sieve.

The technical problem to be solved by the present invention is that hexamethyleneimine (hereinafter referred to as hydrazine) is directly used as a structure-directing agent, and a phosphorus source, a silicon source and an aluminum source used in conventional molecular sieve synthesis are used as raw materials, and synthesized under hydrothermal conditions. Pure phase SAPO-44 molecular sieve, and the surface of the synthesized molecular sieve crystal is slightly rich in silicon, the ratio of silicon content on the outer surface (Si/(Si+Al+P;) molar ratio) to the bulk silicon content of the crystal is 1.45-1.01 The inventors found through experiments that by adding a small amount of surfactant to the synthesis system and adopting a method of temperature-changing crystallization, the synthetic SAPO-44 molecular sieve can be effectively reduced. The surface is rich in silicon.

The invention is characterized in that the preparation process is as follows - a) mixing a silicon source, an aluminum source, a phosphorus source, deionized water, a surfactant and SDA to form an initial gel mixture having the following molar ratio:

Si0 ₂ /Al ₂ 0 ₃ =0.01 〜 1;

Ρ ₂ Ο ₅ /Α1 ₂ Ο ₃ = 0.5 - 1.5;

H ₂ 0/A1 ₂ 0 ₃ = 30-130;

SDA/Al ₂ O ₃ = 2.0 ~ 6 _;

BM/A1 ₂ 0 ₃ = 0.01- 0.10;

Wherein SDA is hexamethyleneimine and BM is a surfactant;

b) The initial gel mixture obtained in step a) is charged into a synthesis kettle, sealed, and heated to 190 ~ 23 CTC for crystallization at autogenous pressure for l~15h;

c) lowering the crystallization temperature to 160 ~ 180 ° C crystallization under autogenous pressure l~15h;

d) After the crystallization is completed, the solid product is centrifuged, washed with deionized water to neutrality, and dried to obtain SAPO-44 molecular sieve.

The step a) the silicon source in the initial gel mixture is a mixture of one or a combination of silica sol, active silica, orthosilicate, metakaolin; aluminum source is aluminum salt, activated alumina, a mixture of one or any of alkoxyaluminum, metakaolin; a phosphorus source of one or a mixture of any of orthophosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, organic phosphide or phosphorus oxide The surfactant is dodecyltrimethylammonium chloride, tridecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, pentadecyltrimethylammonium chloride, ten Hexacyclotrimethylammonium chloride, dodecyltrimethylammonium bromide, tridecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, pentadecyltrimethyl amine bromide, cetyl trimethyl ammonium bromide any one or several of the mixing step a) the initial gel mixture SDA and A1 ₂ 0 ₃ molar ratio of SDA A1 ₂ 0 ₃ = 2.5 - 5.0, more preferably SDA / A1 ₂ 0 ₃ = 3.0 - 4.5 _D

Said step a) the initial gel mixture of H ₂ 0 and A1 ₂ 0 ₃ molar ratio of _{_{_{H 2 0 / A1 2 0 3}}} = 35 ~ 100 o

The step a) the molar ratio of BM to A1 ₂ 0 ₃ in the initial gel mixture is BM/A1 ₂ 0 ₃ = 0.03^0.08. The crystallization temperature in the step b) is 195 to 225 ° C, the crystallization time is 1 to 12 h, the preferred crystallization temperature is 211-225 ° C, and the crystallization time is 1 to 10 ho.

The crystallization temperature in the step c) is 165 to 175 ° C, and the crystallization time is 3 to 12 h.

The present invention also relates to a catalyst for acid-catalyzed reaction which is obtained by calcining in an air of 400 to 700 ° C by SAPO-44 molecular sieve as described above or SAPO-44 molecular sieve synthesized according to the above method.

The present invention also relates to a catalyst for the conversion of an oxygen-containing compound to an olefin which is obtained by calcining the above-mentioned SAPO-44 molecular sieve or SAPO-44 molecular sieve synthesized according to the above method through 400 to 70 (TC air).

The present invention also relates to a gas adsorbent which is obtained by firing the above-mentioned SAPO-44 molecular sieve or SAPO-44 molecular sieve synthesized according to the above method in air at 400 to 700 °C. The beneficial effects that can be produced by the present invention include:

(1) Obtaining a SAPO-44 molecular sieve with hexamethyleneimine as a template, and having the characteristics of slightly rich silicon on the surface of the crystal, silicon content on the outer surface (molar ratio Si/(Si+Al+P and crystal) The ratio of bulk silicon content is between 1.50 and 1.01.

(2) The prepared SAPO-44 molecular sieve exhibits excellent catalytic performance and gas adsorption separation performance in the catalytic reaction. DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a scanning electron micrograph (SEM) of a product synthesized in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION The bulk element composition was measured using a PANalytical XTert PRO X-ray diffractometer (XRF), a Cu target, a Κα radiation source (λ = 0.15418 nm), a voltage of 40 KV, and a current of 100 mA.

The surface element composition XPS was measured by X-ray photoelectron spectrometer Thermo ESCALAB 250X1 (using monochromator ΑΙΚα as the excitation source), and the surface charge of the sample surface was corrected by using A12p=74.7eV on the sample surface A1203 as an internal standard. The invention is described in detail below by way of examples, but the invention is not limited to the examples. Example 1

The molar ratio of the raw materials and the crystallization conditions are shown in Table 1. The specific batching process is as follows. 16.4 g of phosphoric acid (H ₃ P0 ₄ mass% 85%) is mixed with 30 g of deionized water, stirred uniformly, and then 5.7 g of silica sol (Si〇 ₂ mass percent 30%) is added, strongly Stir for lh. 21.5 g of hexamethyleneimine HMI (99% by mass) was added to the previous mixture, sealed and stirred for 30 mm to obtain a homogeneous mixture, denoted as A. In addition, 10 g of pseudoboehmite (A1 ₂ 0 ₃ mass percent 72.5%), 1.29 g of cetyltrimethylammonium bromide (CTAB) and 20.9 g of deionized water were mixed and mixed, and added to the mixture A. After the mixture was uniformly stirred and stirred for 30 mm, the gel was transferred to a stainless steel reactor. The molar ratio of each component of the synthesis system was 3.0 HMI: 0.4 SIO ₂ : 1A1 ₂ O ₃ : 1P ₂ O ₅ : 0.05 CTAB: 50H ₂ O.

The synthesis kettle was heated to 230 ^Q C for 2 h, and then cooled to 170 ° for 10 h. After the crystallization is completed, the solid product is centrifuged, washed, and dried in an air of ioo ° C to obtain a raw powder. The sample was subjected to XRD analysis, and the results showed that the synthesized product had the characteristics of CHA structure, and the XRD data are shown in Table 2. The XRD results of Examples 2-10 are close to those of Example 1, that is, the peak positions are the same, and the relative peak intensities of the peaks vary slightly with the synthesis conditions and the ratio of the feed, fluctuating within ±10%, indicating that the synthesized product is SAPO-44. Molecular sieves. The SEM results of the sample are shown in Figure 1.

The surface and bulk elemental compositions of the molecular sieve products were analyzed by XPS and XRF. The ratio of the outer surface silicon content to the bulk silicon content is shown in Table 1. Example 1 The bulk element of the sample was Alo.49Po.40Si. .11.

The CHN elemental analysis of the original powder sample of Example 1 showed a CN molar ratio of 6.05. The CHN elemental analysis result is normalized to the inorganic element composition determined by XRF, and the composition of the molecular sieve raw powder is obtained.

The ¹³ C MAS NMR analysis of the original powder sample revealed only the carbon resonance peak belonging to the HMI, and no characteristic carbon resonance peak belonging to CTAB was observed. These results indicate that CTAB did not enter the final synthetic product. Table 1 Molecular sieve synthesis ingredients and crystallization conditions table * Feeding molar composition

EXAMPLES - Local Temperature Crystallization Low Temperature Crystallization Si /Si w

匪I aluminum source pity source silicon source H ₂ 0 BM ^e

1 3.0 1 1 0.4 50 0.05 230°C 2h 170°C lOh 1.29

2 2.0 Γ 0.5 0.2 ^b 35 0.02 225°C 7h 175°C 8h 1.35

3 2.2 Γ 0.7 0.3 ^d 45 0.10 211°C l Oh 165°C 8h 1.28

4 2.5 1 0.8 0.1 50 0.03 195°C 12h 170°C lOh 1.40

5 4.5 1 1.2 0.6 80 0.01 190°C 15h 160°C 15h 1.45

6 5.0 1 1.5 0.8 100 0.05 200°C l Oh 180°C 8h 1.41

7 6.0 1 1.5 1.0 130 0.08 211°C 15h 180°C lh 1.25

8 3.0 1 1 0.4 50 0.08 230°C lh 170°C 12h 1.30

9 3.0 1 1 0.4 50 0.05 230°C 4h 180°C lOh 1.10

10 3.0 1 1 0.3 50 0.05 215°C 5h 160°C 8h 1.35

*: The aluminum source is pseudo-boehmite (A1 ₂ 0 ₃ mass percentage 72.5%), the phosphorus source is phosphoric acid (H ₃ P0 ₄ mass percentage 85%), and the silicon source is silica sol (Si0 ₂ mass) a content of 30%); a: aluminum source is γ-alumina, Α1 ₂ 0 ₃ mass percentage 93%; b: tetraethoxysilane is silicon source; _C: aluminum source is aluminum isopropoxide; d: The silicon source is fumed silica (Si0 ₂ mass percent 93%); e: BM is a surfactant, the BM of Examples 1 to 5 is CTAB, and the BM of Examples 6-9 are respectively dodecyl Trimethylammonium chloride, tridecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, pentamethyltrimethylammonium chloride and hexadecyltrimethylammonium chloride The BM of Example 10 is a mixture of dodecyltrimethylammonium bromide and CTAB in a molar ratio of 1/1. Table 2 XRD results of the sample of Example 1

1 9.3839 9.42484 98.06

2 12.8501 6.8893 19.03

3 15.9553 5.55484 65.43

4 17.4034 5.09575 11.86

5 18.8856 4.69902 11.24

6 20.5578 4.32043 100

7 21.7095 4.09376 22.75

8 22.3866 3.97146 5.36

9 22.9278 3.87891 11.85 10 24.478 3.63666 62.39

11 25.917 3.43792 29.31

12 27.6348 3.228 9.82

13 29.4733 3.03069 3.39

14 30.2097 2.95847 19.87

15 30.5999 2.92163 53.69

16 32.9821 2.71585 3.65

17 34.5379 2.597 4.06

18 35.5404 2.52601 9.06

19 39.6681 2.27216 3.17

20 42.2638 2.13843 3.24

21 43.338 2.08788 4.53

22 47.7474 1.90486 4.89

23 48.517 1.87642 6.24

24 50.235 1.81471 9.2

25 53.4032 1.71569 3.85

26 54.0128 1.69776 2.66

27 56.103 1.63937 4.53

28 59.3137 1.55677 3.04 Example 2-10

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

The synthesized samples were subjected to XRD analysis, and the results showed that the products synthesized in Examples 2-10 had

The structural characteristics of SAPO-44, XRD data results are close to Table 2, that is, the peak position and shape are the same, and the peak relative peak intensity fluctuates within ±10% depending on the synthesis conditions.

The surface and bulk elemental compositions of the molecular sieve products were analyzed by XPS and XRF. The ratio of the outer surface silicon content to the bulk silicon content is shown in Table 1. Example 10 The bulk element of the sample is

Α1ο.5θΡθ.42 θ. 8.

The CHN elemental analysis of the original powder samples of Examples 2-10 showed that the c N molar ratio was

6.0 ± 0.05 fluctuations. The composition of CHN elements and the composition of inorganic elements obtained by XRF are returned Once, the composition of the original molecular sieve powder was 0.12HMI<Si. . . . ₇ Al. . ₄₉ P. ₄₃ )0 ₂ , 0.13HMI Si ₀ . ₁₀ Al ₀ . ₅₅ P ₀ . ₃₅ )O ₂ , 0.14HMI'(Si.. ₀₅ Al.. ₅₃ P.. ₄₂ )O ₂ , 0.15HMI Si ₀ . ₁₄ Al ₀ .4 ₇ Po.39)0 ₂ , 0.16HMI.(Si.. ₂₁ Al.. ₄ P ₃₉ )O ₂ , 0.20HMI Si ₀ . ₂₈ Al ₀ . ₃₈ P ₀ .34)O ₂ , 0.18 HMI Si ₀ . ₁₀ Alo.48Po.42)0 ₂ , 0.16HMI Si ₀ . ₁₁ Al ₀ .4 ₉ Po.4o)0 ₂ , 0.17HMI.(Si.. ₈ Al.. ₅ .P.. ₄₂ ) O ₂ .

The ¹³ C MAS NMR analysis of the original powder samples of Examples 2-10 revealed only the carbon resonance peak belonging to the HMI, and no characteristic carbon resonance peak belonging to CTAB was observed. These results indicate that CTAB did not enter the final synthetic product. Example 11

3 g of the synthetic sample of Examples 1-10 was placed in a plastic beaker, and 3 ml of a 40% hydrofluoric acid solution was added to dissolve the molecular sieve skeleton in an ice water bath, and then 15 ml of carbon tetrachloride was added to dissolve the organic matter therein. The organic matter was analyzed by GC-MS to show that the organic matter contained therein was hexamethyleneimine. Example 12

The synthetic sample of Example 1 was cured, and then epoxy resin was cured, and then polished on a polishing machine. Using a line scan mode of SEM-EDX, a crystal face close to the crystal core was selected for composition analysis from the core to the shell. The results show that the 8^8 atomic ratio of the crystal core region is about 0.19, and the Si/Al atomic ratio near the surface region is about 0.28.

The synthesized sample of Example 10 (SEM showed a rhombohedral morphology, grain size 1-5 μιη), epoxy resin cured, and then polished on a polishing machine, using a line scan mode of SEM-EDX, selected close to the crystal core The crystal face is analyzed from the core to the shell. The results show that the Si/Al atomic ratio in the core region of the crystal is about 0.14, and the Si/Al atomic ratio near the surface region is about 0.21. Comparative example 1

The specific batch ratio and batching process are the same as in Example 10. The crystallization conditions were changed to 215 ^Q C for 13 h. The synthesized sample was analyzed by XRD, and the results showed that it was close to Table 2, that is, the peak position and the peak shape were the same, indicating that the synthesized product had the characteristics of the SAPO-44 structure. The relative crystallinity of the sample was 89% as compared with the sample of Example 1 (the crystallinity of the sample of Example 1 was defined as 100%). Relative crystallinity = (Ii + + Is lOOQ / oW + Ι ₂ ' + Ι ₃ ') (Ι^ Ι ₂ and Ι ₃为₃ is the strongest three diffraction peak heights in the XRD spectrum of the sample 1 of Comparative Example 1, 1 ₂ ' and 1 ₃ ' are the strongest three diffraction peak heights in the XRD spectrum of the sample of Example 1.)

XPS and XRF were used to analyze the surface and bulk element composition of the molecular sieve product. The bulk phase element of the sample 1 was Al^P S^ and the ratio of silicon content to bulk silicon content was Si /Si body phase = 2. 5 . Comparative example 2

The specific proportion of ingredients and the batching process were the same as in Example 10, and the addition of the surfactant was omitted. The XRD analysis of the synthesized sample showed that it was close to Table 2, that is, the peak position and the peak shape were the same, indicating that the synthesized product had the characteristics of SAPO-44 structure. The relative crystallinity of the sample was 95% as compared with the sample of Example 1 (the crystallinity of the sample of Example 1 was defined as 100%).

XPS and XRF were used to analyze the surface and bulk element composition of the molecular sieve product. The ratio of silicon content on the outer surface to the content of bulk silicon was Si / outside / Si body phase = 2.0. Comparative example 3

The specific proportion of ingredients and the batching process were the same as in Example 10, the addition of the surfactant was omitted, and the crystallization process became 215 ^Q C crystallization for 5 h.

The XRD analysis of the synthesized sample showed that it was close to Table 2, that is, the peak position and the peak shape were the same, indicating that the synthesized product had the characteristics of SAPO-44 structure. The relative crystallinity of the sample was 75% as compared with the sample of Example 1 (the crystallinity of the sample of Example 1 was defined as 100%).

XPS and XRF were used to analyze the surface and bulk elemental composition of the molecular sieve product. The outer surface silicon content and bulk silicon content ratio Si outer /Si body phase = 1.8. Example 13

The sample obtained in Example 9 was used as a propylene adsorbent. The adsorption isotherm of the sample was measured on ASAP2020 by Micromeritics, USA. The adsorbed gases were propene (99.99%) and propane (99.99%). In order to avoid the influence of the physically adsorbed water on the adsorption test in the molecular sieve, the sample was air-fired at 600 ° C for 4 hours before the isotherm test, and then further processed in ASAP2020 under the condition that it was extremely low. Vacuum degree (5x10-3 Under mmHg), increase to 350 ° C at a ramp rate of rC / min for 8 hours. The temperature of the gas adsorption was controlled by a constant temperature water bath (accuracy: plus or minus 0.05 ^Q C), and the adsorption temperature was 298 K. The results showed that the adsorption amount of the sample to propylene and propane was 2.0 and 1.0 mmol/g, respectively (at a pressure of 10 kPa). The adsorption selectivity calculated therefrom was propylene/propane = 2.0.

The sample after the adsorption test was subjected to vacuum adsorption treatment at room temperature for 30 mm on an ASAP2020 apparatus, and then subjected to adsorption adsorption isotherm measurement. The adsorption amount of the sample to the propene and propane was 2.05 and

l .lmmol / g (pressure is lOlkPa). The sample has good regenerability and can be regenerated under very mild conditions. Example 14

The samples obtained in Example 10 and Comparative Example 1 were calcined at 600 ° C for 4 hours, and then tableted and crushed to 20 to 40 mesh. The l.Og sample was weighed into a fixed bed reactor for evaluation of the ethanol dehydration reaction. The reaction was carried out by activating nitrogen gas at 550 ° C for 1 hour and then cooling to 260 ° C. The ethanol was carried by nitrogen, the flow rate of nitrogen was 60 ml/mm, and the weight of ethanol was 2.0^. The reaction product was analyzed by on-line gas chromatography (Varian 3800, FID detector, capillary column PoraPLOT Q-HT). The results showed that the conversion of the sample of Example 10 was 100%, and the selectivity of the ethylene was 100%. Comparative Example 1 The conversion rate of the sample was 72%, and the selectivity of ethylene was 89%. The product also contained hydrocarbon by-products such as methane. Example 15

The samples obtained in Example 10 and Comparative Example 1 were subjected to air baking at 600 ° C for 4 hours, and then tableted and crushed to 20 to 40 mesh. The l.Og sample was weighed into a fixed bed reactor for MTO reaction evaluation. The reaction was carried out by a nitrogen gas activation at 550 ° C for 1 hour and then cooling to 450 ° C. The pump was fed with 60 wt% aqueous methanol, and the weight of methanol was 2.5 h. The reaction product was analyzed by on-line gas chromatography (Varian 3800, FID detector, capillary column PoraPLOT). Table 3 sample methanol conversion to olefin' hydrocarbon reaction results

Life selectivity (% by mass) *

Sample

(mill) CH ₄ C2H4 C ₂ C3H C3H8 c ₄ ⁺ c ₅ ⁺ C2H4+C3H6

180 2.0 44.3 1.0 40.5 2.0 8.1 2.1 84.8 Example 10

Compared

130 2.3 41.8 1.0 38.7 2.5 11.6 2.1 80.5 Example 1

* 100% methanol conversion rate (ethylene propylene) selectivity

Claims

Rights request

1. A SAPO-44 molecular sieve, characterized in that the anhydrous chemical composition of the molecular sieve is expressed as: mSDA- (Si _x _Aly P _z )0 ₂ , where:

SDA is hexamethyleneimine;

m represents the number of moles of organic amine per mole ^1^1^)0 ₂ , m=0.1~0.5;

x, y, and z represent the mole fractions of Si, Al, and P respectively, and their ranges are x=0.01~0.60, y=0.2~0.60, z=0.2~0.60, and x+y+z=l.

2. The SAPO-44 molecular sieve according to claim 1, characterized in that the surface of the molecular sieve crystal is slightly rich in silicon, and the ratio of the silicon content on the outer surface to the bulk silicon content of the crystal is 1.50~1.01, preferably 1.40~1.02, and more Preferably it is 1.35~1.03, more preferably 1.30~1.03, where the silicon content is the molar ratio of Si/(Si+Al+P).

3. The SAPO-44 molecular sieve according to claim 1, characterized in that the silicon content in the SAPO-44 molecular sieve crystal increases uniformly from the core to the shell.

4. The SAPO-44 molecular sieve according to claim 1, characterized in that the silicon content in the SAPO-44 molecular sieve crystal increases unevenly from the core to the shell.

5. A method for synthesizing the molecular sieve of claim 1, the method comprising the following steps: a) Mixing silicon source, aluminum source, phosphorus source, deionized water, surfactant and SDA to form a molar ratio as follows Initial gel mixture:

Si0 ₂ /Al ₂ 0 ₃ =0.01 ~ 1;

Ρ ₂ Ο ₅ /Α1 ₂ Ο ₃ = 0.5~ 1.5;

H ₂ 0/A1 ₂ 0 ₃ = 30-130;

SDA/Al ₂ O ₃ = 2.0 ~ 6;

ΒΜ/Α1 ₂ Ο ₃ = 0Ό1~0.10;

Among them, SDA is hexamethyleneimine and BM is surfactant;

b) Put the initial gel mixture obtained in step a) into the synthesis kettle, seal it, raise the temperature to 190 ~ 23 CTC and crystallize under autogenous pressure for 1 ~ 15 hours;

c) Reduce the crystallization temperature to 160~18(TC and crystallize under autogenous pressure for 1~15h;

d) After crystallization is complete, the solid product is separated by centrifugation, washed with deionized water until neutral, and dried to obtain SAPO-44 molecular sieve.

6. The method according to claim 5, characterized in that the silicon source in the initial gel mixture of step a) is one or any of silica sol, activated silica, orthosilicate, metakaolin. A mixture of several; the aluminum source is one or a mixture of any of several types of aluminum salt, activated alumina, aluminum alkoxide, metakaolin; the phosphorus source is orthophosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, organic phosphorus One or any mixture of compounds or phosphorus oxides; the surfactant is dodecyltrimethylamine chloride, tridecyltrimethylamine chloride, tetradecyltrimethylchloride amine, pentadecyltrimethylamine chloride, cetyltrimethylamine chloride, dodecyltrimethylamine bromide, tridecyltrimethylamine bromide, tetradecane One or any mixture of trimethylamine bromide, pentadecyltrimethylamine bromide and cetyltrimethylamine bromide.

7. The method according to claim 5, characterized in that the molar ratio of SDA and Al ₂ 0 ₃ in the initial gel mixture of step a) is SDA/Al ₂ O ₃ =2.5~5.0, preferably 3.0~ 4.5.

8. The method according to claim 5, characterized in that the molar ratio of H ₂ 0 and A1 ₂ 0 ₃ in the initial gel mixture of step a) is H ₂ 0/A1 ₂ 0 ₃ = 35~: 100 .

9. The method according to claim 5, characterized in that the molar ratio of BM to A1 ₂ 0 ₃ in the initial gel mixture of step a) is BM/A1 ₂ 0 ₃ = 0.03^0.08.

10. The method according to claim 5, characterized in that the crystallization temperature in step b) is 195~225°C, preferably 211~225°C, and the crystallization time is 1~12h, preferably 1~10h.

11. The method according to claim 5, characterized in that the crystallization temperature in step c) is 165-175 °C, and the crystallization time is 3 to 12 hours.

12. A catalyst for an acid-catalyzed reaction, characterized in that the SAPO-44 molecular sieve according to any one of claims 1-4 or the SAPO-44 molecular sieve synthesized according to any method of claims 5-11 is passed through 400 It is obtained by roasting in air at ~700 V.

13. A catalyst for the reaction of converting oxygenated compounds to olefins, characterized in that the SAPO-44 molecular sieve according to any one of claims 1-4 or the SAPO-44 synthesized according to any method of claims 5-11 44 molecular sieve is obtained by roasting in air at 400 ~ 700°C.

14. A gas adsorbent, characterized in that the SAPO-44 molecular sieve according to any one of claims 1 to 4 or the SAPO-44 molecular sieve synthesized according to any method of claims 5 to 11 is passed through 400-700 °C by roasting in air.