SAPO-34 molecular sieve having both micropores and mesopores and synthesis methods thereof

Abstract

The present invention relates to a SAPO-34 molecular sieve having both micropores and mesopores and synthesis method thereof. The mesopore diameter in the molecular sieve is in a range of 2-10 nm and the mesopore volume thereof is 0.03-0.3 cm.sup.3/g. Triethylamine is used as a template agent and the pore size modifiers are added to the synthesis gel at the same time in the synthesis process, thereby the prepared molecular sieve crystals have mesopore distribution besides micropores. The SAPO-34 molecular sieve synthesized in the present invention can be used as catalysts for conversion of oxygen-containing compounds to lower olefins.

Claims

1. A synthesis method for a SAPO-34 molecular sieve, the method comprising: a) formulating an initial gel mixture for synthesizing SAPO-34 molecular sieve; b) adding a pore size modifier into the initial gel mixture obtained in step a) and stirring; c) sealing the gel mixture obtained in step b) and heating the gel mixture obtained in step b) to crystallization temperature, and performing a crystallization step comprising thermostatic crystallization of the gel mixture obtained in step b) under autogenous pressure, and separating a solid product after the crystallization is completed, and washing the solid product to be neutral, and drying the washed solid product, and thus obtaining as-synthesized SAPO-34 molecular sieve; and d) calcining the as-synthesized SAPO-34 molecular sieve obtained in step c) in air to remove the organics contained in the material, and obtaining a SAPO-34 molecular sieve having both micropores and mesopores; wherein the oxide molar proportions of all components in said initial synthesis gel mixture are: SiO.sub.2/Al.sub.2O.sub.3=0.12.0; P.sub.2O.sub.5/Al.sub.2O.sub.3=0.515; TEA/Al.sub.2O.sub.3=15, wherein TEA is triethylamine; T/TEA=0.012, wherein T is the pore size modifier; said pore size modifier is one or more selected from the group consisting of aqueous ammonia, tetramethylammonium hydroxide, diethylamine, tripropylamine, di-n-propylamine, n-propylamine, n-butylamine, cyclohexylamine and a mixture thereof; and the SAPO-34 molecular sieve includes both micropores and mesopores and characterized in that the mesopore diameter of the molecular sieve is 2-10 nm and the mesopore volume thereof is 0.03-0.3 cm.sup.3/g.

2. The synthesis method according to claim 1, wherein the crystallization temperature in step c) is 100-250 C.

3. The synthesis method according to claim 1, wherein the crystallization temperature in step c) is 160-230 C.

4. The synthesis method according to claim 1, wherein the crystallization step in step c) comprises a crystallization time of 0.5100 h.

5. The synthesis method according to claim 1, wherein the crystallization step in step c) comprises a crystallization time of 2-48 h.

Description

DESCRIPTION OF THE DRAWING

(1) FIG. 1: The XRD spectra of the SAPO-34 synthesized in example 1, 3, 4, 5 added with a pore size modifier and in comparative example 1 without the addition of a pore size modifier.

(2) FIG. 2: In this figure, FIG. 2a, FIG. 2b, FIG. 2c, FIG. 2d and FIG. 2e are the SEM photos of the samples in example 1, 3, 4, 5 and comparative example 1 of the present invention.

(3) FIG. 3: In this figure, FIG. 3a and FIG. 3b are the schematic diagrams of nitrogen adsorption isotherms and mesopore distributions of the samples with the numbers of MSP34-1 and SP34 in example 2 of the present invention (adsorption line branch, BJH method).

(4) FIG. 4: In this figure, FIG. 4a and FIG. 4b are the schematic diagrams of nitrogen adsorption isotherms and mesopore distributions of the samples with the numbers of MSP34-2, -3 and -4 in example 6 of the present invention (adsorption line branch, BJH method).

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention is characterized in that the synthesized SAPO-34 molecular sieve has a mesopore pore diameter of 2-10 nm and a mesopore volume of 0.03-0.3 cm.sup.3/g.

(6) The present invention is characterized in that the surface of cubic crystals of the synthesized SAPO-34 molecular sieve can be rough or broken.

(7) The present invention is characterized in that triethylamine is used as a template agent and a pore size modifier is added into a synthesis gel.

(8) The present invention provides a synthesis method of a SAPO-34 molecular sieve having both micropores and mesopores, and the preparation process is as follows:

(9) a) An initial gel mixture for synthesizing SAPO-34 molecular sieve is formulated and the oxide molar proportions of all components are: SiO.sub.2/Al.sub.2O.sub.3=0.12.0; P.sub.2O.sub.5/Al.sub.2O.sub.3=0.515; H.sub.2O/Al.sub.2O.sub.3=10100; TEA/Al.sub.2O.sub.3=15; T/TEA=0.01-2

(10) The pore size modifier is one or more selected from the group consisted of aqueous ammonia, tetramethylammonium hydroxide, diethylamine, tripropylamine, di-n-propylamine, n-propylamine, n-butylamine, cyclohexylamine and a mixture thereof.

(11) b) The gel mixture obtained in step b) is loaded into a stainless steel autoclave lined with polytetrafluoroethylene inside, sealed and then heated to crystallization temperature, and a thermostatic crystallization is performed under autogenous pressure with a crystallization temperature of 100-250 C. and a crystallization time of 5-100 h. After the crystallization is completed, a solid product is separated by centrifugation, washed to be neutral with deionized water and dried in air at 120 C., and thus as-synthesized SAPO-34 molecular sieve is obtained.

(12) c) The as-synthesized SAPO-34 molecular sieve obtained in step b) is calcined in air to remove the organics and a SAPO-34 molecular sieve with a distribution of micropores and mesopores is obtained.

(13) The present invention was described in detail below by way of examples.

(14) Example 1

(15) Gauged raw materials were mixed in a certain sequence in an initial gel molar proportion of 3.0 TEA:0.4 SiO.sub.2:P.sub.2O.sub.5:Al.sub.2O.sub.3:50 H.sub.2O:1.0 T (T=n-propylamine), and all the raw materials used were TEA (analytical pure), silica sol (SiO.sub.2 content is 30 wt %), pseudobochmite (Al.sub.2O.sub.3 content is 70 wt %) and phosphoric acid (H.sub.3PO.sub.4 content is 85 wt %). A gel was formed by sufficient stirring, loaded into a stainless steel autoclave lined with polytetrafluoroethylene inside, sealed and heated to 200 C., and under autogenous pressure, a thermostatic crystallization was performed for 12 h. Then a solid product was separated by centrifugation, washed to be neutral with deionized water and dried in air at 120 C., and thus a SAPO-34 molecular sieve was obtained. After calcined the as-synthesized sample at 600 C. for 4 h to remove the template agent, a SAPO-34 molecular sieve having micropores and mesopores was obtained (the number was MSP34-1). The XRD pattern of the as-synthesized sample was shown in FIG. 1 and the SEM photo thereof was shown in FIG. 2. It can be seen that the surface of cubic crystals of MSP34-1 sample was rough or broken.

(16) Comparative Example 1

(17) Gauged raw materials were mixed in a certain sequence in an initial gel molar proportion of 3.0 TEA:0.4 SiO.sub.2:P.sub.2O.sub.5:Al.sub.2O.sub.3:50 H.sub.2O, and all the raw materials used were TEA (analytical pure), silica sol (SiO.sub.2 content is 30 wt %), pseudobochmite (Al.sub.2O.sub.3 content is 70 wt %) and phosphoric acid (H.sub.3PO.sub.4 content is 85 wt %). A gel was formed by sufficient stirring, loaded into a stainless steel synthetic kettle lined with polytetrafluoroethylene inside, sealed and heated to 200 C., and under autogenous pressure, a thermostatic crystallization was performed for 12 h. Then a solid product was separated by centrifugation, washed to be neutral with deionized water and dried in air at 120 C., and thus a SAPO-34 molecular sieve was obtained. After calcined the sample at 600 C. for 4 h to remove the template agent, a SAPO-34 molecular sieve was obtained (the number was SP34). The XRD pattern of the sample was shown in FIG. 1 and the SEM photo thereof was shown in FIG. 2. It can be seen that the crystal of MSP34-1 sample presented a cubic type and had a smooth surface.

(18) Example 2

(19) The sample with a number of MSP34-1 obtained in example 1 and the sample with a number of SP34 obtained in comparative example 1 were subjected to a nitrogen physical adsorption characterization to measure the specific surface areas and the pore structures of the molecular sieves. The nitrogen adsorption isotherms and the mesopore distributions were shown in FIG. 3 and the specific surface areas and the pore volumes were shown in Table 1. The results indicated that SP34 sample had very little mesopore structure and the specific surface area and pore volume thereof were substantially produced from the contribution of the micropore parts. MSP34-1 sample had a mesopore distribution with a mesopore pore diameter of 2.3 nm and a mesopore volume of 0.07 cm.sup.3/g.

(20) Example 3

(21) Gauged raw materials were mixed in a certain sequence in an initial gel molar proportion of 3.0 TEA:0.4 SiO.sub.2:P.sub.2O.sub.5:Al.sub.2O.sub.3:50 H.sub.2O:0.3 T (T=aqueous ammonia), and all the raw materials used were TEA (analytical pure), silica sol (SiO.sub.2 content is 30 wt %), pseudobochmite (Al.sub.2O.sub.3 content is 70 wt %) and phosphoric acid (H.sub.3PO.sub.4 content is 85 wt %). A gel was formed by sufficient stirring, loaded into a stainless steel autoclave lined with polytetrafluoroethylene inside, sealed and heated to 200 C., and under autogenous pressure, a thermostatic crystallization was performed for 12 h. Then a solid product was separated by centrifugation, washed to be neutral with deionized water and dried in air at 120 C., and thus a SAPO-34 molecular sieve was obtained. After calcined the sample at 600 C. for 4 h to remove the template agent, a SAPO-34 molecular sieve having micropores and mesopores was obtained (the number was MSP34-2). The XRD pattern of the as-synthesized sample was shown in FIG. 1 and the SEM photo thereof was shown in FIG. 2. It can be seen that the surface of cubic crystals of MSP34-2 sample was rough or broken.

(22) Example 4

(23) Gauged raw materials were mixed in a certain sequence in an initial gel molar proportion of 3.0 TEA:0.4 SiO.sub.2:P.sub.2O.sub.5:Al.sub.2O.sub.3:50 H.sub.2O:1.5 T (T=diethylamine), and all the raw materials used were TEA (analytical pure), silica sol (SiO.sub.2 content is 30 wt %), pseudobochmite (Al.sub.2O.sub.3 content is 70 wt %) and phosphoric acid (H.sub.3PO.sub.4 content is 85 wt %). A gel was formed by sufficient stirring, loaded into a stainless steel autoclave lined with polytetrafluoroethylene inside, sealed and heated to 200 C., and under autogenous pressure, a thermostatic crystallization was performed for 12 h. Then a solid product was separated by centrifugation, washed to be neutral with deionized water and dried in air at 120 C., and therefore a SAPO-34 molecular sieve was obtained. After calcined the raw power at 600 C. for 4 h to remove the template agent, a SAPO-34 molecular sieve having micropores and mesopores was obtained (the number was MSP34-3). The XRD pattern was shown in FIG. 1 and the SEM photo was shown in FIG. 2. It can be seen that the surface of cubic crystals of MSP34-3 sample was rough.

(24) Example 5

(25) Gauged raw materials were mixed in a certain sequence in an initial gel molar proportion of 3.0 TEA:0.6 SiO.sub.2:P.sub.2O.sub.5:Al.sub.2O.sub.3:50 H.sub.2O 1.6 T (T=tripropylamine+n-propylamine, tripropylamine/n-propylamine=1:1), and all the raw materials used were TEA (analytical pure), silica sol (SiO.sub.2 content is 30 wt %), pseudobochmite (Al.sub.2O.sub.3 content is 70 wt %) and phosphoric acid (H.sub.3PO.sub.4 content is 85 wt %). A gel was formed by sufficient stirring, loaded into a stainless steel synthetic kettle lined with polytetrafluoroethylene inside, sealed and heated to 200 C., and under autogenous pressure, a thermostatic crystallization was performed for 12 h. Then a solid product was separated by centrifugation, washed to be neutral with deionized water and dried in air at 120 C., and thus a SAPO-34 molecular sieve was obtained. After calcined the raw power at 600 C. for 4 h to remove the template agent, a SAPO-34 molecular sieve having micropores and mesopores was obtained (the number was MSP34-4). The XRD pattern of the as-synthesized sample was shown in FIG. 1 and the SEM photo thereof was shown in FIG. 2. It can be seen that the surface of cubic crystals of MSP34-4 sample was rough or broken.

(26) Example 6

(27) The samples with numbers of MSP34-2, -3 and -4 obtained in example 3, 4 and 5 were subjected to a nitrogen physical adsorption characterization to measure the specific surface areas and the pore structures of the molecular sieves. The nitrogen adsorption isotherms and the mesopore distributions were shown in FIG. 4 and the specific surface areas and the pore volumes were shown in Table 1. The results indicated that the samples MSP34-2, -3 and -4 had a mesopore distribution wherein MSP34-3 sample had two different pore diameters of 2 nm and 3 nm, respectively. The mesopore volumes of the three samples were 0.09, 0.06 and 0.14 cm.sup.3/g, respectively.

(28) TABLE-US-00001 TABLE 1 The specific surface areas and the pore volumes of the samples specific surface area (m.sup.2/g) micropore volume mesopore volume.sup.b No. S.sub.BET S.sub.micropore.sup.a (cm.sup.3/g) (cm.sup.3/g) SP-34 530 530 0.27 0.02 MSP34-1 584 530 0.26 0.07 MSP34-2 656 546 0.27 0.09 MSP34-3 518 474 0.23 0.06 MSP34-4 603 467 0.23 0.14 .sup.aCalculated using t-plot method .sup.bCalculated using BJH method, the cumulative desorption pore volume in a range of 2-50 nm
Example 7

(29) The sample with a number of MSP34-1 obtained in example 1 and the sample with a number of SP34 obtained in comparative example 1 were calcined at 600 C. for 4 h under air, then pressed and sieved to a mesh of 2040. 1.0 g of a sample was weighed and loaded into a fixed bed reactor to carry out a MTO reaction evaluation. The sample was activated at 550 C. for 1 h under nitrogen gas and then reduced to 450 C. to perform a reaction. Methanol was carried by nitrogen gas with a flow rate of 40 ml/min and the weight space rate of methanol was 4.0 h.sup.1. The reaction products were analyzed by an on-line gas chromatograph and the results were shown in Table 2.

(30) Example 8

(31) The samples with numbers of MSP34-2, -3 and -4 obtained in example 3, 4 and 5 were calcined at 600 C. for 4 h under air, then pressed and sieved to a mesh of 2040. 1.0 g of a sample was weighed and loaded into a fixed bed reactor to carry out a MTO reaction evaluation. The sample was activated at 550 C. for 1 h under introducing nitrogen gas and then reduced to 450 C. to perform a reaction. Methanol was carried by nitrogen gas with a flow rate of 40 ml/min and the weight space rate of methanol was 4.0 h.sup.1. The reaction products were analyzed by an on-line gas chromatograph and the results were shown in Table 2.

(32) TABLE-US-00002 TABLE 2 The reaction results of methanol to olefins over the samples* No. SP34 MSP34-1 MSP34-2 MSP34-3 MSP34-4 CH.sub.4 2.87 2.63 2.53 2.41 2.31 C.sub.2H.sub.4 49.96 51.69 52.28 52.58 53.34 C.sub.2H.sub.6 0.64 0.55 0.72 0.64 0.49 C.sub.3H.sub.6 34.13 34.85 33.98 33.79 34.10 C.sub.3H.sub.8 0.98 0.80 0.65 0.69 0.72 C.sub.4+ 8.57 7.56 7.85 7.76 7.94 C.sub.5+ 2.86 1.93 1.79 2.13 1.09 C.sub.6+ 0 0 0.20 0 0 C.sub.2.sup.= C.sub.3.sup.= 84.13 86.54 86.17 86.37 87.44 Life (min) 180-200 240-260 260-280 240-260 260-280 *The highest (ethylene + propylene) selectivity when methanol conversion was 100%.