Method for preparing the silicoaluminate form of the AEI zeolite structure with high yields, and its application in catalysis

Abstract

A synthesis process for a crystalline material with the AEI zeolite structure, comprising (i) preparation of a mixture containing, at least, water, one zeolite with the FAU crystal structure as the only source of silicon and aluminum, a cyclic ammonium cation with alkyl substituents as the OSDA, and a source of alkaline or alkaline-earth cations (A), wherein the synthesis mixture has the following molar composition: SiO.sub.2:a Al.sub.2O.sub.3:b OSDA:c A:d H.sub.2O where a ranges between 0.001 and 0.2; where b ranges between 0.01 and 2; where c ranges between 0 and 2; where d ranges between 1 and 200; and wherein the mixture is free from phosphorous and fluorinated species, (ii) crystallisation of the mixture and, (iii) recovery of the crystalline material. Also, preparation of catalysts based on the AEI zeolite and application as a catalysts in processes including the selective catalytic reduction of NO.sub.x.

Claims

1. Synthesis process for a crystalline material with the AEI zeolite structure, comprising, at least, the following steps: (i) preparation of a mixture containing, at least, water, one zeolite with the FAU crystal structure as the only source of silicon and aluminum, a cyclic ammonium cation with alkyl substituents as the OSDA, and a source of alkaline or alkaline-earth cations (A), wherein the synthesis mixture has the following molar composition:
SiO.sub.2:a Al.sub.2O.sub.3:b OSDA: c A:d H.sub.2O where a ranges between 0.001 and 0.2; where b ranges between 0.01 and 2; where c ranges between 0 and 2; where d ranges between 1 and 200; and wherein the mixture is free from phosphorous and fluorinated species; (ii) crystallisation of the mixture obtained in (i) in a reactor; and (iii) recovery of the crystalline material obtained in (ii).

2. Process according to claim 1, wherein the cyclic ammonium cation used as the OSDA is a quaternary ammonium selected from N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP), N,N-diethyl-2,6-dimethylpiperidinium (DEDMP), N,N-dimethyl-2,6-dimethylpiperidinium, N-ethyl-N-methyl-2,6-dimethylpiperidinium, and combinations thereof.

3. Process according to claim 2, wherein the OSDA is N,N-dimethyl-3,5-dimethylpiperidinium.

4. Process according to claim 1, further comprising another co-operative OSDA present in step (i), which is any organic molecule.

5. Process according to claim 4, wherein the co-operative OSDA is an ammonium cation.

6. Process according to claim 5, wherein the co-operative OSDA is a cyclic ammonium cation.

7. Process according to claim 4, wherein the co-operative OSDA is an amine.

8. Process according to claim 1, wherein the crystallisation process described in (ii) is performed in autoclaves, under static or dynamic conditions.

9. Process according to claim 1, wherein the crystallisation process described in (ii) is performed at a temperature ranging between 100 C. and 200 C.

10. Process according to claim 1, wherein the crystallisation time of the process described in (ii) ranges between 6 hours and 50 days.

11. Process according to claim 1, further comprising the addition of AEI crystals, designed to act as seeds, to the synthesis mixture in a quantity of up to 25% by weight with respect to the total quantity of oxides.

12. Process according to claim 11, wherein the AEI crystals are added before the crystallisation process or during the crystallisation process.

13. Process according to claim 1, wherein the recovery step (iii) is performed using a separation technique selected from decantation, filtration, ultrafiltration, centrifugation and combinations thereof.

14. Process according to claim 1, further comprising the elimination of the organic content retained inside the material by means of an extraction process.

15. Process according to claim 1, further comprising the elimination of the organic content retained inside the material by means of a heat treatment at temperatures ranging between 100 C. and 1000 C. for a period of time ranging between 2 minutes and 25hours.

16. Process according to claim 1, wherein the material obtained is pelletised.

17. Process according to claim 1, wherein any cation present in the material may be exchanged with other cations by means of ion exchange using conventional techniques.

18. Process according to claim 17, wherein the exchange cation is selected from metals, protons, proton precursors and mixtures thereof.

19. Process according to claim 18, wherein the exchange cation is a metal selected from rare earth elements, metals of groups IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIII, and combinations thereof.

20. Process according to claim 19, wherein the metal is copper.

21. Synthesis process for a crystalline material with the AEI zeolite structure, comprising, at least, the following steps: (i) preparation of a mixture containing, at least: water; one zeolite with the FAU crystal structure as the only source of silicon and aluminum; an OSDA selected from the group consisting of N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP), N,N-diethyl-2,6-dimethylpiperidinium (DEDMP), N,N-dimethyl-2,6-dimethylpiperidinium, N-ethyl-N-methyl-2,6-dimethylpiperidinium, and combinations thereof; and a source of alkaline or alkaline-earth cations (A), wherein the synthesis mixture has the following molar composition:
SiO.sub.2:a Al.sub.2O.sub.3:b OSDA:c A:d H.sub.2O where a ranges between 0.001 and 0.2; where b ranges between 0.01 and 2; where c ranges between 0 and 2; where d ranges between 1 and 200; and wherein the mixture is free from phosphorous and fluorinated species; (ii) crystallisation of the mixture obtained in (i) in a reactor; and (iii) recovery of the crystalline material obtained in (ii).

22. The synthesis process according to claim 21, wherein the zeolite with the FAU crystal structure has a SiO.sub.2:Al.sub.2O.sub.3 molar ratio of 21.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1: X-ray diffraction patterns of the materials obtained in the present invention.

EXAMPLES

(2) Below we will describe non-limiting examples of the present invention.

Example 1

Synthesis of N,N-dimethyl-3,5-dimethylpiperidinium (DMDMP)

(3) 10 g of 3,5-dimethylpiperidine (Sigma-Aldrich, 96% by weight) is mixed with 19.51 g of potassium bicarbonate (KHCO.sub.3, Sigma-Aldrich; 99.7% by weight), and dissolved in 140 ml of methanol. Subsequently, 54 ml of methyl iodide (CH.sub.3I, Sigma-Aldrich, 99% by weight) is added, and the resulting mixture is kept under stirring for 5 days at room temperature. Once this time has elapsed, the reaction mixture is filtered in order to eliminate the potassium bicarbonate. The filtrated solution is partially concentrated by means of a rotary evaporator. Once the methanol has been partially evaporated, the solution is washed with chloroform several times and magnesium sulfate is added (MgSO.sub.4, Sigma-Aldrich, 99.5% by weight). Subsequently, the mixture is filtered in order to eliminate the magnesium sulfate. The ammonium salt is obtained by precipitation with diethyl ether and subsequent filtration. The final yield of N,N-dimethyl-3,5-dimethylpiperidinium iodide is 85%.

(4) In order to prepare the hydroxide form of the preceding organic salt: 10.13 g of the organic salt is dissolved in 75.3 g of water. Subsequently, 37.6 g of an anion-exchange resin (Dower SBR) is added, and the resulting mixture is kept under stirring for 24 hours. Finally, the solution is filtered, to obtain N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (with a 94% exchange).

Example 2

Synthesis of the Silicoaluminate Form of the AEI Zeolite Structure Using a Zeolite with the FAU Structure as the Only Source of Silicon and Aluminum

(5) 21.62 g of a 6.9% by weight aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide is mixed with 1.89 g of a 20% by weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%). The mixture is homogenised by being kept under stirring for 10 minutes. Finally, 3.01 g of zeolite with the FAU structure (CBV-720, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=21) is added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.047 Al.sub.2O.sub.3/0.2 DMDMP/0.2 NaOH/15 H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 135 C. for 7 days under static conditions. Once this time has elapsed, the product obtained is recovered by means of filtration, washing it abundantly with water and, finally, is dried at 100 C. The material is calcined at 550 C. for 4 h in an air atmosphere in order to eliminate the organic matter retained inside. The yield of the solid obtained is greater than 80%.

(6) X-ray diffraction shows that the solid obtained presents the characteristic peaks of the AEI structure (see FIG. 1). The chemical composition of the sample indicates a Si/Al ratio of 8.2.

Example 3

Synthesis of the Silicoaluminate Form of the AEI Zeolite Structure Using a Zeolite with the FAU Structure as the Only Source of Silicon and Aluminum

(7) 2.24 g of a 7.4% by weight aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide is mixed with 0.173 g of a 20% by weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%). The mixture is homogenised by being kept under stirring for 10 minutes. Finally, 0.193 g of zeolite with the FAU structure (CBV-720, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=21) is added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.047 Al.sub.2O.sub.3/0.4 DMDMP/0.2 NaOH/15 H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 135 C. for 7 days under static conditions. Once this time has elapsed, the product obtained is recovered by means of filtration, washing it abundantly with water and, finally, is dried at 100 C. The material is calcined at 550 C. for 4 h in an air atmosphere in order to eliminate the organic matter retained inside. The yield of the solid obtained is practically 90%.

(8) X-ray diffraction shows that the solid obtained presents the characteristic peaks of the AEI structure (see FIG. 1). The chemical composition of the sample indicates a Si/Al ratio of 9.0.

Example 4

Preparation of the Cu-exchanged Silicoaluminate Form of Zeolite AEI

(9) The sample synthesised and calcined according to the method presented in Example 2 of the present invention is washed with 150 g of a 0.04 M aqueous solution of sodium nitrate (NaNO.sub.3, Fluka, 99% by weight) per gram of zeolite.

(10) 0.053 g of copper acetate [(CH.sub.3COO).sub.2Cu.H.sub.2O, Probus, 99%) is dissolved in 48 ml of water, and 0.48 g of the previously-washed zeolite is added. The suspension is kept under stirring for 20 h at room temperature. Once this time has elapsed, the product obtained is recovered by means of filtration and washed abundantly with water. Finally, the material is calcined in air at 550 C. for 4 h. The final copper content in the sample is 4.7% by weight.

Example 5

Heat Teatments in the Presence of Water Vapour

(11) The sample prepared according to Example 4 of the present invention is treated with steam in a muffle furnace with 100% H.sub.2O (2.2 ml/min) at 750 C. for 13 hours. The solid obtained is characterised by means of X-ray diffraction, and the characteristic peaks of the AEI zeolite structure are observed (see FIG. 1).

Example 6

Catalytic Assay for the SCR of NOx

(12) The activity for the selective catalytic reduction of NOx is studied using a quartz fixed-bed tubular reactor 1.2 cm in diameter and 20 cm in length. In a typical experiment, the catalyst synthesised according to the present invention is compacted into particles with a size ranging between 0.25-0.42 mm, which are introduced into the reactor, and the temperature is increased to 550 C. (see the reaction conditions in Table 2); subsequently, this temperature is maintained for one hour under a flow of nitrogen. Once the desired temperature has been reached, the reaction mixture is fed. The SCR of NOx is studied using NH.sub.3 as the reducing agent. The NOx present at the reactor gas outlet is continuously analysed by means of a chemiluminescence detector (Thermo 62C). The catalytic results are summarised in Table 3.

(13) TABLE-US-00002 TABLE 2 Reaction conditions for the SCR of NOx. Total gas flow (ml/min) 300 Catalyst loading (mg) 40 NO concentration (ppm) 500 NH.sub.3 concentration (ppm) 530 O.sub.2 concentration (%) 7 H.sub.2O concentration 5 Temperature interval tested ( C.) 170-550

(14) TABLE-US-00003 TABLE 3 Conversion (%) of NOx at different temperatures (200 C., 250 C., 300 C., 350 C., 400 C., 450 C., 500 C.) using the Cu-AEI catalysts prepared according to Examples 4 and 5 of the present invention Conversion (%) of NOx at different temperatures 200 250 300 350 400 450 500 C. C. C. C. C. C. C. Exam- 73.6 94.3 99.6 99.7 98.6 97.5 89.1 ple 4 Exam- 55.3 89.0 97.1 97.9 95.0 89.2 78.0 ple 5

Example 7

Synthesis Using a Zeolite with the FAU Structure and Sodium Silicate as Sources of Aluminum and Silicon, Respectively

(15) 1.982 g of a 6.4% by weight aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide is mixed with 0.167 g of a 20% by weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%). The mixture is homogenised by being kept under stirring for 10 minutes. Subsequently, 0.084 g of zeolite with the FAU structure (CBV-500, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=5.2) and 0.69 g of sodium silicate (NaSiO.sub.3, Sigma Aldrich, Na.sub.2O 10.6% by weight and SiO.sub.2 26.5% by weight) are added, and the mixture is kept under stirring until the desired concentration is reached. The composition of the final gel is SiO.sub.2/0.047 Al.sub.2O.sub.3/0.2 DMDMP/0.2 NaOH/15 H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 135 C. for 7 days under static conditions. Once this time has elapsed, the product obtained is recovered by means of filtration, washing it abundantly with water, and, finally, is dried at 100 C.

(16) X-ray diffraction shows that the solid obtained presents the characteristic peaks of the AEI structure. The yield of the solid obtained is less than 40%.

Example 8

Synthesis Using a Zeolite with the FAU Structure and LUDOX as Sources of Aluminum and Silicon, Respectively

(17) 2.001 g of a 6.4% by weight aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide is mixed with 0.164 g of a 20% by weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%). The mixture is homogenised by being kept under stirring for 10 minutes. Subsequently, 0.080 g of zeolite with the FAU structure (CBV-500, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=5.2) and 0.454 g of Ludox (SiO.sub.2, Sigma Aldrich, 40% by weight) are added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.047 Al.sub.2O.sub.3/0.2 DMDMP/0.2 NaOH/15 H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 135 C. for 7 days under static conditions. Once this time has elapsed, the product obtained is recovered by means of filtration, washing it abundantly with water, and, finally, is dried at 100 C.

(18) X-ray diffraction shows that the solid obtained is amorphous.

Example 9

Synthesis Using Zeolite with the FAU Structure and Aerosil as Sources of Aluminum and Silicon, Respectively

(19) 1.996 g of a 6.4% by weight aqueous solution of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide is mixed with 0.158 g of a 20% by weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%). The mixture is homogenised by being kept under stirring for 10 minutes. Subsequently, 0.078 g of zeolite with the FAU structure (CBV-500, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=5.2) and 0.181 g of Aerosil are added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.047 Al.sub.2O.sub.3/0.2 DMDMP/0.2 NaOH/15 H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 135 C. for 7 days under static conditions. Once this time has elapsed, the product obtained is recovered by means of filtration, washing it abundantly with water, and, finally, is dried at 100 C.

(20) X-ray diffraction shows that the solid obtained is amorphous.