WO2012071891A1

WO2012071891A1 - Method for synthesizing small crystal size sapo-34 molecular sieve

Info

Publication number: WO2012071891A1
Application number: PCT/CN2011/076578
Authority: WO
Inventors: 田鹏; 刘中民; 樊栋; 齐越; 张莹
Original assignee: 中国科学院大连化学物理研究所
Priority date: 2010-11-29
Filing date: 2011-06-29
Publication date: 2012-06-07
Also published as: CN102275948A; CN102275948B

Abstract

Provided is a method for synthesizing small crystal size SAPO-34 molecular sieve, wherein mixing aluminum source, silicon source, organic amine and a part of water firstly, pretreating the mixture solution under autogenous pressure at an elevated temperature for a period of time, adding a mixture solution of phosphor source and the rest part of water in situ at the elevated temperature, and then crystallizing and synthesizing to obtain the small crystal size SAPO-34.

Description

Method for synthesizing small crystal SAPO-34 molecular sieve

The invention relates to a method for synthesizing a small-grain SAPO-34 molecular sieve. Background technique

In 1984, UCC developed a series of SAPO molecular sieves (USP 4440871). The molecular sieve is a type of crystalline silicoaluminophosphate whose three-dimensional skeleton structure is composed of P0 ₂ +, A10 ₂ - and Si0 ₂ tetrahedrons. Among them, SAPO-34 is a chabazite-like structure, the main channel is composed of eight rings, and the orifice is 0.38nmx0.38nmo. The SAPO-34 molecular sieve is in the MTO (methanol to produce low-carbon olefin) reaction due to its suitable acidity and pore structure. It has attracted much attention due to its excellent catalytic performance.

SAPO-34 molecular sieves are generally carried out by hydrothermal synthesis 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 tetraethyl hydroxide hinge (TEAOH), morpholine (MOR), piperidine, isopropylamine (i-Pi'NH ₂ ), triethylamine (TEA), diethylamine (DEA). ), dipropylamine (Pr ₂ NH), and the like, and mixtures thereof. The synthesis steps are generally as follows:

(1) Preparation of crystallization mixture: according to the ratio relationship

(0.5-10) R: (0.05-10) SiO ₂ : (0.2-3) Al ₂ O ₃ : (0.2-3) P ₂ O ₅ : (20- 200) H ₂ O, wherein R represents a templating agent, a metering material And mixed in a certain order, in which 85% of orthophosphoric acid and 1/4 of deionized water are generally added to the pseudoboehmite, and 1/4 of deionized water is added during the full stirring process. The mixture is labeled A; the mixture prepared from silica sol, templating agent and another 1/4 deionized water is labeled B, then B is slowly added to A while vigorously stirring for a while, then the last 1/4 deionization Add water and stir well into a gel;

(2) Aging: The crystallization mixture is sealed in a stainless steel autoclave lined with polytetrafluoroethylene and aged at room temperature for a certain period of time;

(3) Crystallization: The autoclave is heated to 150-250 Torr, and the crystallization reaction is carried out under autogenous pressure. After the crystallization is completed, the solid product is filtered or centrifuged, and washed with deionized water to neutrality. That is, the original powder of SAPO-34 molecular sieve is obtained.

In addition to hydrothermal synthesis, SAPO-34 can also be synthesized by gas phase transfer (VPT) or microwave heating. The gas phase transfer method is to prepare a zeolite molecular sieve synthetic liquid containing no templating agent into a dry glue, and then place the dry glue on the surface. In a stainless steel reactor lined with polytetrafluoroethylene, water and an organic amine are used as a liquid phase portion, and the dry gel is converted into a zeolite molecular sieve under the action of mixed steam at a certain temperature. It can synthesize SAPO-34 in a larger composition range using hydrothermal methods using different organic amine templating agents, but water is still an indispensable component for gas phase synthesis of silicoaluminophosphate molecular sieves.

The 1998 literature (Angewandte Chemie-International Edition, 1998, 37(5): 609-611) first reported the synthesis of molecular sieves by combinatorial chemistry. In 2003, Zhang et al. (Chemial Communications, 2003, (17): 2232-2233) will combine The chemistry was successfully applied to the synthesis of SAPO-34 molecular sieves, and the influencing factors of the synthesis were systematically and quickly studied. South Korea's Jhmig et al. (Mici'oporous and Mesoporous Materials, 2003, 64(1-3): 33-39) studied the synthesis of SAPO-34 by microwave heating, and found that microwave heating facilitates the crystal formation of SAPO-34. SAPO-5 with AFI structure.

Small-grained molecular sieves have their own advantages in terms of diffusion and mass transfer, so the synthesis of small-sized SAPO-34 is directly concerned by researchers.

Patent WO 00/06493 describes the obtaining of a phosphorus-containing molecular sieve having a smaller particle size and a narrower particle size distribution by agitation such as stirring or tumbling.

EPA 541915 reports the conversion of methanol to an olefin (phosphine) using an aluminophosphate crystalline molecular sieve catalyst. This specification describes the advantages of a small particle size catalyst in the ruthenium process and provides a means to promote the production of small particle size materials by agitating the synthesis mixture to produce SAPO-34 having a median particle size in the range of about 0.6-1.4 microns.

WO 01/36328 describes a process in which a 0.5-30 micron diameter SAPO is produced from an aqueous synthesis mixture comprising a templating agent, a source of essential elements of molecular sieve structure and a water-miscible organic solvent, and a surfactant as a morphological modifier. 34 spherical particles. The use of the solvent is the dissolution of a source of silicon into the aqueous synthesis mixture.

WO 2003/048042 reports a process for obtaining a small particle size SAPO-34 molecular sieve by using tetraethyl orthosilicate as a silicon source, using a structure directing agent of TEAOH or a mixture of TEAOH and DPA.

WO 2003/048043 reports the obtaining of small particle size silicoaluminophosphate molecular sieves by providing a silicon source in the form of an alkaline organic solution using a structure directing agent of TEAOH or a mixture of TEAOH and DPA. Summary of the invention

The present invention provides a novel method for synthesizing small-grain SAPO-34 molecular sieves.

In a first aspect, the present invention provides a method of synthesizing a SAPO-34 molecular sieve, wherein the SAPO-34 molecular sieve has a volume median diameter of less than 800 nm, and the method comprises the steps of:

a) Treat the mixture of aluminum source, silicon source, organic amine and deionized water at 170~220 °C under autogenous pressure 0.1 to 48 hours, to obtain a mixture a);

b) Adding a mixture of cerium source and deionized water in situ to the mixture a) to obtain a mixture b), and maintaining the mixture b) at a temperature of 150 to 220 ° C for a period of 0.1 to 48 hours.

In a second aspect, the present invention provides a method of synthesizing a small-grain SAPO-34 molecular sieve, wherein the volume intermediate diameter of the SAPO-34 molecular sieve is less than 800 nm, the method comprising the following steps: a) aluminum source, organic Mixing the amine and deionized water at 170~220 ° C under autogenous pressure for 0.1 to 48 hours to obtain a mixture a);

b) Adding a mixture of cerium source, silicon source and deionized water in situ to the mixture a) to obtain a mixture b), and maintaining the mixture b) at a temperature of 150 to 220 ° C for a period of 0.1 to 48 hours.

In a preferred aspect of the first and / or second aspects, the treatment temperature in step a) is from 180 to 210 °C. In another preferred aspect of the first and / or second aspects, the processing time in step a) is 5 to 30 hours. In another preferred aspect of the first and / or second aspects, the temperature in step b) is from 150 to 220 ° C and the time is from 0.1 to 48 hours.

In another preferred aspect of the first and / or second aspects, the temperature in step b) is from 170 to 200 ° C and the time is from 5 to 30 hours.

In another preferred aspect of the first and / or second aspects, both steps a) and c) are carried out with continuous agitation or rotation.

In another preferred aspect of the first and / or second aspect, the molar ratio of the mixture b) is -Si0 ₂ /Al ₂ 0 ₃ = 0.05~1;

Ρ ₂ Ο ₅ /Α1 ₂ Ο ₃ = 0.5 ~ 1.5 ;

Η ₂ Ο / Α _{1 2} Ο ₃ = 20 ~ 150;

R/Al ₂ O ₃ = 0.5 to 10, wherein R is an organic amine.

In another preferred aspect of the first and / or second aspect, the silicon source is any one or a mixture of any one of a silica sol, an active silica, a orthosilicate; the aluminum source And a mixture of any one or any one of an aluminum salt, an activated alumina, an alkoxy aluminum, an aluminum sol, and a pseudoboehmite; the phosphorus source is orthophosphoric acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, Any one or a mixture of any of several organic compounds or phosphorus oxides.

In another preferred aspect of the first and / or second aspect, the organic amine is any one of diethylamine, triethylamine, tetraethylammonium hydroxide, morpholine or a mixture of any of several .

In another preferred aspect of the first and/or second aspect, the SAPO-34 molecular sieve has a volume median diameter of less than 600 nm. In another preferred aspect of the first and/or second aspect, the SAP0-34 molecular sieve has a volume median diameter of less than 500 nm.

In a third aspect, the present invention provides a SAP0-34 molecular sieve synthesized according to the above method.

In a fourth aspect, the present invention provides a catalyst for the acid-catalyzed reaction or a catalyst for the conversion of an oxygen-containing compound to an olefin, which is obtained by calcining the above-mentioned SAPO-34 molecular sieve in an air of 400 to 700 Torr.

The mixture after step c) is cooled, and the solid product is obtained by centrifugation, washed with deionized water to neutrality, and dried in 12 CTC air to obtain a small-grain SAPO-34 molecular sieve, wherein the small-grain SAPO- The volume median diameter of the 34 molecular sieve is less than 800 nm. DRAWINGS

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing a 2L kettle apparatus having an in-situ feeding function employed in Examples 1-5. among them:

1 gas cylinder

2 pressure regulator

3 check valve

4 ball valve

5 sampling tube

6 electric mixer

7 thermocouple

8 stainless steel synthetic kettle

9 shut-off valve

10 pressure gauge

11 heating jacket

The key to determining the grain size during the crystallization of molecular sieves is to control the rate of nucleation and the growth rate of the crystal. If the rate of formation of the nucleus is greater than the growth rate of the crystal, it is advantageous to obtain a small-grain molecular sieve. The present invention is based on the theory that a source of aluminum, a source of silicon (added or added in the next stage), an organic amine and a portion of water are premixed and treated at elevated temperatures for a period of time. High temperature treatment can effectively activate the surface of the aluminum source, especially when using alumina such as pseudoboehmite as the aluminum source, the effect of high temperature treatment is particularly important. Subsequently, using a corrosion-resistant liquid pump In the high temperature state in situ, the mixed solution of the phosphorus source, the silicon source (or added in the previous stage) and the remaining water is directly driven into the solution subjected to the high temperature activation treatment. After mixing the two, the temperature of the solution may be slightly lowered, but the suitable temperature required for crystallization can be quickly reached, and a large number of crystal nuclei are rapidly formed under the action of organic amines, and finally a small crystal grain is obtained: .

It should be noted that the silicon source and the organic amine are separately mixed and subjected to high temperature treatment, and then a mixed solution of a phosphorus source, an aluminum source and a residual water is added in situ at a high temperature, and a small-grain SAPO-34 molecular sieve cannot be obtained, and the product is in the middle. Squamous quartz with a dense phase. In addition, since the gel formed after the mixing of the aragonite is very viscous, this method also causes great difficulty in feeding. Similarly, a phosphorus source, an aluminum source, a silicon source (added or added in the next stage) and a portion of the water are first mixed for high temperature pretreatment, then the high temperature is added in situ to the silicon source (added or added in the previous stage), organic amine and residual water. , can not get SAPO-34, can only get dense phase quartz. Further, if the mixed solution after the high-temperature activation treatment is cooled, and then an aqueous phosphoric acid solution is added, it is also disadvantageous to obtain a small-grain molecular sieve, which may be caused by a certain change in the state of the alumina activated surface during the cooling.

The invention has the advantages that in the synthesis process, a part of the material is directly added in situ at a high temperature, which omits the cumbersome cooling and temperature increase.

This synthesis method is not limited to the synthesis of SAPO-34 small-grain molecular sieves. If the organic amine is replaced by a templating agent suitable for guiding a molecular sieve of a certain structure, a small-grain molecular sieve of the corresponding structure can be synthesized.

The invention is characterized in that an aluminum source, a silicon source, an organic amine and a part of water are first mixed, the mixed solution is preactivated at a high temperature for a certain period of time, and then a mixed solution of a phosphorus source and a residual water is added to crystallize and synthesize SAPO-34.

The present invention is characterized in that an aluminum source, an organic amine and a part of water are first mixed, and the mixed solution is preactivated at a high temperature for a certain period of time, and then a mixed solution of a phosphorus source, a silicon source and a residual water is added to crystallize and synthesize SAPO-34.

The specific preparation process is as follows - a) mixing an aluminum source, a silicon source, an organic amine and a part of water at room temperature, charging into a synthesis kettle, sealing, and heating at a self-generated pressure for a certain period of time;

b) after the phosphorus source and the remaining water are uniformly mixed, the mixed solution is added to the a) system in situ by a liquid pump, and maintained at a certain temperature for crystallization;

c) After the crystallization is completed, the solid product is centrifuged, washed with deionized water to neutrality, and dried in 12 CTC air to obtain a small-grain SAPO-34 molecular sieve raw powder.

The specific preparation process can also be as follows:

a) mixing aluminum source, organic amine and part of water at room temperature, charging into a synthesis kettle, sealing, and heating at a self-generated pressure for a certain period of time; b) after the phosphorus source, the silicon source and the remaining water are uniformly mixed, the mixed solution is added to the a) system in situ by a liquid pump, and maintained at a certain temperature for crystallization;

c) After the crystallization is completed, the solid product is centrifuged, washed with deionized water to neutrality, and dried in 120 Torr air to obtain a small-grain SAPO-34 molecular sieve raw powder.

The processing temperature in the above step a) is 170-220 °C, and the processing time is 0.1-48h. Optimized processing temperature is

180- 210 ° C, processing time is 5- 30h. The crystallization temperature in step b) is 150-220 ° C, and the crystallization time is 0.1-48 h. The crystallization temperature was optimized to 170-20 CTC and the crystallization time was 5 30 h. In order to homogenize the synthetic gel system, both the processing and the crystallization process are dynamic.

The ratio of each raw material used is, in terms of molar ratio:

Si0 ₂ /Al ₂ 0.3 = 0.05 - 1;

Ρ ₂ Ο ₅ /Α1 ₂ Ο ₃ = 0.5 ~ 1.5;

3⁄4Ο/Α1 ₂ Ο ₃ = 20~ 150;

R/Al ₂ O. ₃ = 0.5 to 10, wherein R is an organic amine.

The silicon source used is one of silicon sol, active silica, orthosilicate or a mixture of any of the following; aluminum source is aluminum salt, activated alumina, aluminum alkoxide, aluminum sol, thin One or a mixture of any one of diaspores; the phosphorus source is one or a mixture of any one of orthophosphoric acid, ammonium hydrogencarbonate, ammonium dihydrogen phosphate, organic phosphide or phosphorus oxide. The organic amine used is one or a mixture of any of diethylamine, triethylamine, tetraethylammonium hydroxide, and morpholine.

The orthosilicate is an alkyl orthosilicate wherein the alkyl group is a C1-C3 alkyl group.

The decyloxy group in the aluminum alkoxide is a C1-C5 decyloxy group.

The synthesized SAPO-34 molecular sieve sample has a volume median diameter of less than 800 nm, preferably a volume median diameter of less than 600 nm, more preferably a volume median diameter of less than 500 nm.

In this patent, the molecular sieve particle size is determined by laser particle size method (Malvern's Mastersizer 2000 laser particle size analyzer). The volume median diameter (particles are considered equivalent spheres) can also be expressed as D _5Q or D _a5 , which means the particle size value that divides the entire volume distribution into two halves.

The synthesized SAPO-34 molecular sieve is calcined in 400-700 Torr air, and can be used as a catalyst for acid-catalyzed reaction and an oxygen-containing compound to be converted into a catalyst for the reaction of the olefin.

The invention is described in detail below by way of examples, but the invention is not limited to the examples.

In the examples, the molecular sieve particle size was determined by laser particle size (Malvern's Mastersizer 2000 laser particle size analyzer). The volume median diameter (particles are considered equivalent spheres) can also be expressed as D _5Q or D _{Q 5} , which means The entire volume distribution is exactly equal to the particle size of the two halves. Example 1

Add 132 g of pseudoboehmite (72% by weight) and 540 g of water to a 2 L synthesis kettle, stir well, then add 87 g of silica sol (28% by weight;), stir well, add 290 g of triethylamine, seal, and heat up with stirring. Treat to 210 ° C for 20 h. After 218.5 g of phosphoric acid (85% by weight) was mixed with 200 g of water, the aqueous solution was pumped into a 2 L autoclave with a pump for 3 minutes, and kept at 20 CTC for 15 hours. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in 12 CTC of air to obtain a small-grain SAPO-34 molecular sieve raw powder. The particle size of the sample was measured by a laser particle size analyzer. The results showed a single peak with a Gaussian distribution and a median diameter of 480 nm. Example 2

To a 2 L synthesis kettle, 380 g of aluminum isopropoxide and 540 g of water were added, and the mixture was stirred. Then, 120 g of tetraethyl orthosilicate and 140 g of diethylamine were added, sealed, and the mixture was heated to 180 ° C with stirring for 5 hours. After 218.5 g of phosphoric acid (85% by weight) was mixed with 200 _{§ of} water, the aqueous solution was pumped into a 2 L autoclave with a pump for 3 minutes, and kept at 200 ° C for 10 h. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C to obtain a small-grain SAPO-34 molecular sieve original powder. The particle size of the sample was measured by a laser particle size analyzer. The results showed a single peak with a Gaussian distribution and a median diameter of 300 nm. Example 3

To a 2 L synthesis kettle, 380 g of an aluminum sol (25%) and 540 g of water were added, and the mixture was stirred, and then 140 g of diethylamine was added thereto, sealed, and heated to 200 ° C under stirring for 5 hours. After 218.5 g of phosphoric acid (85 wt%), 50 g of silica sol (28 wt%) and 200 g of water were mixed, the aqueous solution was pumped into a 2 L autoclave with a pump for 3 minutes, and kept at 200 ° C for 15 h. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in 120 Torr of air to obtain a small-grain SAPO-34 molecular sieve raw powder. The particle size of the sample was measured by a laser particle size analyzer. The results showed a single peak with a Gaussian distribution and a median diameter of 390 nm. Example 4

Add 132 g of pseudoboehmite (72%) and 727 g of tetraethylammonium hydroxide (35 wt%) to a 2 L synthesis kettle, stir well, seal, and warm to 200 °C with stirring, and treat 25 ho 218.5 g of phosphoric acid (85 After the weight of /.), 50g silica sol (28% by weight) and 240 _§ water were mixed, pump the aqueous solution into the 2L kettle with phosphoric acid for 3 minutes, and keep it at 180 °C. Crystallization for 25h. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C to obtain a small-grain SAPO-34 molecular sieve original powder. The particle size of the sample was measured by a laser particle size analyzer. The results showed a single peak with a Gaussian distribution and a median diameter of 600 nm. Comparative example 1-4

The SAPO-34 molecular sieves were synthesized according to the compounding ratio and crystallization conditions of the above Examples 1-4, respectively. The difference was that instead of the two-twisting method, all the materials were uniformly mixed at room temperature, sealed, and raised to the crystallization temperature for crystallizing. After synthesis, the solid product was centrifuged, washed with deionized water to neutrality, and dried in 120 Torr air. The solid samples were sequentially recorded as DBL-1 to DBL-4, and XRD analysis showed that several samples were pure. Phase SAPO-34. The particle size measurement results of the laser particle size analyzer showed that the particle size distribution of several samples was a single peak with a Gaussian distribution, and the median diameters were 5 micrometers (DBL-1), 7 micrometers (DBL-1), and 4 micrometers (DBL-, respectively). 1) and 2 microns (DBL-1). Comparative example 5

Add 132 g of pseudoboehmite (72% by weight) and 540 g of water to a 2 L synthesis kettle, stir well, then add 87 g of silica sol (28% by weight), stir well, add 290 g of triethylamine, seal, and heat up to stirring. At 140 ° C, treatment for 20 h. After 218.5 g of phosphoric acid (85% by weight) was mixed with 200 g of water, the aqueous solution was pumped into a 2 L autoclave with a pump for 3 minutes, and kept at 200 ° C for 15 hours. Then, the solid product was centrifuged, washed with deionized water to neutrality, and dried in air at 120 ° C, and the product obtained by XRD detection was SAPO-34. The results of the laser particle size analyzer showed a single peak with a Gaussian distribution, and the sample had a median diameter of 3 μm. Comparative example 6

To the 2L synthesis kettle, 132 g of pseudoboehmite (72% by weight), 218.5 g of phosphoric acid (85% by weight;), 87 g of silica sol (28% by weight) and 74 (water), stirred, sealed, and heated under stirring were added. It was treated for 10 h at 210 ° C. Then 290 g of triethylamine was added in a pump over 3 minutes and kept at 200 10 for 10 h. Then, the solid product was centrifuged, washed with deionized water to neutral, and dried in 120 Torr air. After drying, the product obtained by XRD detection is a squamous quartz crystal phase. Comparative Example 7

290 g of triethylamine and 50 g of silica sol (28% by weight:) were placed in a 2 L synthesis kettle, and the mixture was stirred, sealed, and heated to 210 ° C under stirring for 20 hours. Mix 132g of pseudoboehmite (72% by weight), 218.5g of phosphoric acid (85% by weight) with 840g of water, stir well and pump into 2L of the kettle within 10 minutes (the gel formed by phosphorus aluminum is thicker, viscosity Big, Transport is difficult) and kept crystallized at 200 ° C for 15 h. Then, the solid product was centrifuged, washed with deionized water until neutral, and after drying in air at 120 ° C, the product obtained by XRD detection was a mixed crystal phase of SAPO 34 and tridymite.

The SEM showed that the particle size of the SAPO-34 crystal was about 2-5 microns. Comparative example 8

Adding 518.6 g of tetraethylammonium hydroxide (35 wt%) and 50 g of silica sol (28 wt%;) to a 2 L synthesis kettle, stirring, sealing, heating to 21 CTC with stirring, and treating 10 h of 105.6 g of pseudoboehmite After mixing (72%), 174.8 g of phosphoric acid (85% by weight) and 550 g of water, the aqueous solution was pumped into a 2 L autoclave with a pump for 10 minutes, and kept at 180 ° C for 25 h. Then, the solid product was centrifuged, washed with deionized water until neutral, and after drying at 120 ° C in air, the product obtained by XRD detection was a mixed crystal phase of SAPO-34 and tridymite. The results of the laser particle size analyzer showed a single peak with a Gaussian distribution, and the sample had a median diameter of 2 μm. Example 5

The samples obtained in Examples 1 and 2 were calcined at 600 ° C for 4 hours, then tableted and crushed to 20 40 mesh. The l.Og sample was weighed into a fixed bed reactor for MTO reaction evaluation. The reaction was carried out by activating nitrogen gas at 550 ° C for 1 hour and then cooling to 45 CTC. Methanol was carried by nitrogen with a nitrogen flow rate of 40 ml/min and a methanol weight space velocity of 2.01^. The reaction product was analyzed by on-line gas chromatography. The results are shown in Table 1.

Table 1 Results of methanol conversion to olefins in samples

* 100% methanol conversion highest (ethylene + propylene) selectivity

Claims

Rights request

A method of synthesizing SAPO-34 molecular sieve, wherein the volume intermediate value of the SAPO-34 molecular sieve is less than 800 nm, and the method comprises the following steps:

a) Treat the mixture of aluminum source, silicon source, organic amine and deionized water at 170~220 °C under autogenous pressure

0.1 to 48 hours, to obtain a mixture a);

b) Adding a mixture of phosphorus source and deionized water in situ to the mixture a) to obtain a mixture b), and maintaining the mixture b) at a temperature of 150 to 220 ° C for a period of 0.1 to 48 hours.

2. A method of synthesizing a small-grain SAPO-34 molecular sieve, wherein the volume intermediate diameter of the SAPO-34 molecular sieve is less than 800 nm, the method comprising the steps of:

a) a mixture of aluminum source, organic amine and deionized water is treated at 170 to 220 ° C under autogenous pressure for a period of 0.148 hours to obtain a mixture a);

b) adding a mixture of a phosphorus source, a silicon source and deionized water in situ to the mixture a) to obtain a mixture b), and maintaining the mixture b) at a temperature of from 150 to 220 ° C for a period of from 0.1 to 48 hours.

3. A method according to claim 1 or 2, wherein the processing temperature in step a) is from 180 to 210 °C.

4. A method according to claim 1 or 2, wherein the processing time in step a) is 5 to 30 hours.

5. A method according to claim 1 or 2, wherein the temperature in step b) is from 150 to 22 (TC, and the time is from 0.1 to 48 hours.

6. A method according to claim 1 or 2, wherein the temperature in step b) is 170 to 20 (TC, and the time is 5 to 30 hours.

7. A method according to claim 1 or 2, wherein both steps a) and c) are carried out under continuous agitation or rotation.

8. Process according to claim 1 or 2, wherein the molar ratio in the mixture b) is:

Si0 ₂ /Al ₂ 0 ₃ = 0.05-1

P ₂ 0 ₅ /A1 ₂ 0 ₃ = 0.5 ~ 1.5 ;

Η ₂ Ο/Α1 ₂ Ο ₃ = 20~ 150;

R/AI2O3 = 0.5 to 10, wherein R is an organic amine.

9. The method according to claim 1 or 2, wherein the silicon source is any one or a mixture of any one of a silica sol, an active silica, a orthosilicate; the aluminum source is an aluminum salt a mixture of any one or any combination of activated alumina, aluminum oxyaluminate, aluminum sol, pseudoboehmite; the phosphorus source is orthophosphoric acid Any one or a mixture of any of ammonium, ammonium dihydrogen phosphate, organic phosphide or phosphorus oxide.

10. The method according to claim 1 or 2, wherein the organic amine is any one of diethylamine, triethylamine, tetraethylammonium hydroxide, morpholine or a mixture of any of several.

11. The method according to claim 1 or 1, wherein the volume median diameter of the SAPO-34 molecular sieve is less than '600iim.

12. The method according to claim 1 or 2, wherein the SAPO-34 molecular sieve has a volume median diameter of less than 500 nm.

13. A SAPO-34 molecular sieve synthesized according to the method of claim 1 or 2.

An acid-catalyzed catalyst or a catalyst for the conversion of an oxygen-containing compound to an olefin, which is obtained by calcining an SAPO-34 molecular sieve according to claim 13 in an air of 400 to 700 Torr.