PROCESS FOR A CONTINUOUS SYNTHESIS OF ZEOLITIC MATERIALS

Abstract

The present invention relates to a continuous process for preparing a zeolitic material comprising (i) preparing a mixture comprising a source of YO.sub.2, optionally a source of X.sub.2O.sub.3, and a liquid solvent system; (ii) continuously feeding the mixture prepared in (i) into a continuous flow reactor at a liquid hourly space velocity in the range of from 0.3 to 20 h.sup.1 for a duration of at least 1 h; and (iii) crystallizing the zeolitic material from the mixture in the continuous flow reactor, wherein the mixture is heated to a temperature in the range of from 100 to 300 C.; wherein the volume of the continuous flow reactor is in the range of from 150 cm.sup.3 to 75 m.sup.3, as well as to zeolitic materials which may be obtained according to the inventive process and to their use.

Claims

1. A continuous process for preparing a zeolitic material, comprising: preparing a mixture comprising a source of YO.sub.2, optionally a source of X.sub.2O.sub.3, and a liquid solvent system; (ii) continuously feeding the mixture prepared in (i) into a continuous flow reactor at a liquid hourly space velocity in the range of from 0.3 to 20 h.sup.1 for a duration of at least 1 h; and (iii) crystallizing the zeolitic material from the mixture in the continuous flow reactor, wherein the mixture is heated to a temperature in the range of from 100 to 300 C.; wherein the volume of the continuous flow reactor is in the range of from 150 cm.sup.3 to 75 m.sup.3.

2. The process of claim 1, wherein the continuous flow reactor is selected from the group consisting of a tubular reactor, a ring reactor, and a continuously oscillating reactor.

3. The process of claim 1, wherein the wall of the continuous flow reactor comprises a metallic material.

4. The process of claim 1, wherein the surface of the inner wall of the continuous flow reactor is lined with an organic polymer material.

5. The process of claim 1, wherein in (iii) the mixture is heated under autogenous pressure.

6. The process of claim 1, wherein the continuous flow reactor consists of a single stage.

7. The process of claim 1, wherein no matter is added and/or removed from the reaction mixture during its passage through the continuous flow reactor in (iii).

8. The process of claim 1, wherein the mixture prepared in (i) is directly fed to the continuous flow reactor in (ii), wherein while being fed to the continuous flow reactor in (ii), the mixture prepared in (i) is pre-heated.

9. The process of claim 1, wherein the process further comprises (iv) quenching the reaction product effluent continuously exiting the reactor in (iii) with a liquid comprising one or more solvents and/or via expansion of the reaction product effluent; and/or, (v) isolating the zeolitic material obtained in (iii) or (iv); and/or, (vi) washing the zeolitic material obtained in (iii), (iv) or (v); and/or, (vii) drying the zeolitic material obtained in (iii), (iv), (v), or (vi); and/or, (viii) calcining the zeolitic material obtained in (iii), (iv), (v), (vi), or (vii).

10. The process of claim 9, wherein the supernatant obtained from the isolation of the zeolitic material in (v), and/or a feed having the same composition as said supernatant, is not at any point recycled to the reaction mixture during its passage through the continuous flow reactor.

11. The process of claim 1, wherein Y is at least one selected from the group consisting of Si, Sn, Ti, Zr, and Ge.

12. The process of claim 1, wherein X is at least one selected from the group consisting of Al, B, In, and Ga.

13. The process of claim 1, wherein the mixture prepared in (i) contains substantially no phosphorous and/or phosphorous-containing compounds.

14. A zeolitic material obtained according to the process of claim 1.

15. A process, comprising employing a zeolitic material according to claim 14 as a molecular sieve, as an adsorbent, for ion-exchange, as a catalyst and/or as a catalyst support.

Description

DESCRIPTION OF THE FIGURES

[0164] FIGS. 1, 3, and 5 respectively show the X-ray diffraction pattern (measured using Cu K alpha-1 radiation) of the crystalline materials obtained according to Reference Example 1, Comparative Example 1, and Example 1, respectively, wherein the line pattern of the CHA-type framework has been further included in the respective figures for comparison. In the figures, the angle 2 theta in is shown along the abscissa and the intensities are plotted along the ordinate.

[0165] FIG. 2 shows the X-ray diffraction pattern (measured using Cu K alpha-1 radiation) of the intermediate aged seeded synthesis gel obtained according to Comparative Example 1, wherein the line pattern of the CHA-type framework has been further included in the figure for comparison. In the figure, the angle 2 theta in is shown along the abscissa and the intensities are plotted along the ordinate.

[0166] FIG. 4 displays the setup of the tubular flow reactor employed in Example 1.

[0167] FIG. 6 displays the results from selective catalytic reduction testing of Example 2 performed on the fresh samples, wherein the values obtained for the inventive sample is indicated by the symbols , and the values for the comparative sample by the symbols . In the figure, the NOx conversion level in % is plotted along the ordinate, and the temperature is shown along the abscissa.

[0168] FIG. 7 displays the results from selective catalytic reduction testing of Example 2 performed on the samples after aging at 750 C. for 5 h, wherein the values obtained for the inventive sample is indicated by the symbols , and the values for the comparative sample by the symbols . In the figure, the NOx conversion level in % is plotted along the ordinate, and the temperature is shown along the abscissa.

[0169] FIG. 8 displays the results from selective catalytic reduction testing of Example 2 performed on the samples after aging at 850 C. for 6 h, wherein the values obtained for the inventive sample is indicated by the symbols , and the values for the comparative sample by the symbols . In the figure, the NOx conversion level in % is plotted along the ordinate, and the temperature is shown along the abscissa.

EXPERIMENTAL SECTION

[0170] X-ray diffraction experiments on the powdered materials were performed using a Bragg-Brentano diffractometer with a Cu X-ray source and an energy dispersive point detector. The angular range of 2 to 70 (2 theta) was scanned with a step size of 0.02, using a fixed divergence slit.

[0171] For determining the lattice parameters and crystallinity of the samples, the X-ray diffraction data was analysed using the TOPAS V4 software, wherein the sharp diffraction peaks were modeled using the Pawley model containing the pertinent unit cell parameters and space group. These were refined to fit the data. Independent broad peaks were inserted to describe the amorphous content. The crystalline content describes the intensity of the crystalline signal to the total scattered intensity. Included in the model are a linear background, Lorentz and polarization corrections, lattice parameters, space group and crystallite size. The crystallinity value K was calculated as the following ratio:

[00001]$K=\frac{I_{\mathrm{crystalline}}}{I_{\mathrm{crystalline}}+I_{\mathrm{amorphous}}}$

wherein crystalline stands for the total scattered intensity form the sharp crystalline reflections, and amorphous stands for the total intensity of the broad reflections associated to the amorphous content.

[0172] Reference Example 1: Synthesis of chabazite seed crystals

[0173] A mixture containing sodium hydroxide (50 wt % solution), colloidal silica (Ludox LS, 30 wt % aqueous solution), non-crystalline aluminum hydroxide, trimethyl-adamantyl-ammoniumhydroxide (TMAdAOH), and demineralized water was prepared having a 20 H.sub.2O: 0.04 Al.sub.2O.sub.3: 1 SiO.sub.2: 0.12 Na.sub.2O: 0.2 TMAdAOH molar ratio. The synthesis gel was then filled in an autoclave and stirred for 5 days at 160 C. The resulting material was filtered off for separation from the mother liquor, washed with water and dried at 80 C. for obtaining a white powder.

[0174] The XRD-pattern of the product is displayed in FIG. 1 and reveals chabazite as the single crystalline phase.

[0175] Comparative Example 1: Continuous synthesis of chabazite in a 12.5 cm.sup.3 tubular flow reactor

[0176] A mixture containing sodium hydroxide (50 wt % solution), colloidal silica (Ludox LS, 30 wt % aqueous solution), non-crystalline aluminum hydroxide, trimethyl-adamantyl-ammoniumhydroxide (TMAdAOH), and demineralized water was prepared having a 20 H.sub.2O: 0.04 Al.sub.2O.sub.3: 1 SiO.sub.2: 0.12 Na.sub.2O: 0.2 TMAdAOH molar ratio, wherein 10 wt.-% of chabazite from Reference Example 1 based on the amount of SiO.sub.2 was added for obtaining a synthesis gel including the seeds, which was then aged at 85 C. for 48 hours. The XRD-pattern of the aged synthesis gel is displayed in FIG. 2 and shows, in addition to the reflections stemming from the chabazite seed crystals, amorphous parts coming from the silica and alumina sources.

[0177] The resulting material was used for continuous synthesis without further purification. In addition, the XRD patterns of chabazite is visible, which comes from the seeds added to the gel.

[0178] For the continuous synthesis, a tubular flow reactor of 1 meter in length and 4 mm inner diameter, having two inlets and one outlet was employed. The tube reactor was immersed in oil, which was heated to 210-230 C. To keep the water liquid and to prevent evaporation, the reactor was operated under autogenous pressure.

[0179] Prior to being continuously fed into the reactor, the aged synthesis gel was diluted with 100 vol.-% of water based on the volume of the synthesis gel and subsequently fed into the reactor by one to the inlets. In parallel, mother liquor as obtained from Reference Example 1 after separation of the chabazite product was fed into the second inlet at a vol.-% ratio of diluted synthesis gel: mother liquor=1:3, wherein the feeds meet prior to or at the entrance of the tubular reactor. The rate at which the respective feeds in diluted synthesis gel and mother liquor where fed into the reactor were adjusted such, that a flow rate of 1.3 ml/min was achieved, as a result of which the residence time in the reactor was around 12 min.

[0180] The reaction mixture exiting the reactor was continuously quenched with a feed of distilled water at a fate of 10 ml/min for interrupting the reaction and subsequently the pressure was allowed to drop to atmospheric pressure with the aid of a valve without, however, leading to a reduction of the pressure in the reactor. During the reaction, the temperature of the reaction mixture within the tubular flow reactor is adjusted to 210 C., and the autogenous pressure measured in the reactor was in the range of from 2.2-2.5 MPa.

[0181] The crystalline product obtained from the tubular flow reactor was separated from the reaction mixture, washed with water, and dried to afford a white powder. The XRD-pattern of the product is displayed in FIG. 3 and reveals chabazite as the single crystalline phase, wherein the crystallinity of the product was measured to be 64%.

[0182] Example 1: Continuous synthesis of chabazite in a 250 cm.sup.3 tubular flow reactor

[0183] The synthesis of Comparative Example 1 was repeated using a tubular flow reactor of 20 meters in length and 4 mm inner diameter, having two inlets and one outlet. The tube reactor was immersed in oil, which was heated to 210-230 C. To keep the water liquid and to prevent evaporation, the reactor was again operated under autogenous pressure. The reactor setup is depicted in FIG. 4 including the dimensions of the oil bath provided around the tubular reactor.

[0184] The seeded synthesis gel was prepared and aged, diluted and fed together with mother liquor as obtained from Reference Example 1 into the tubular reactor, wherein the feed rate was adjusted to 26 ml/min for achieving the same residence time of around 12 min for the reaction mixture as in Comparative Example 1.

[0185] The reaction mixture exiting the reactor was continuously quenched with a feed of distilled water at a fate of 10 ml/min for interrupting the reaction and the pressure was allowed to drop to atmospheric pressure with the aid of a valve without, however, leading to a reduction of the pressure in the reactor. During the reaction, the temperature of the reaction mixture within the tubular flow reactor is adjusted to 210 C., and the autogenous pressure measured in the reactor was in the range of from 2.2-2.5 MPa.

[0186] The crystalline product obtained from the tubular flow reactor was separated from the reaction mixture, washed with water, and dried to afford a white powder. The XRD-pattern of the product is displayed in FIG. 5 and reveals chabazite as the single crystalline phase, wherein the crystallinity of the product was measured to be 100%. No amorphous phase or other zeolite phases were detected.

[0187] Example 2: Selective catalytic reduction testing

[0188] For catalyst testing, the chabazite obtained from Example 1 was ion-exchange with copper and subsequently calcined, the final material showing a specific BET surface area of 563 m.sup.2/g, and a Langmuir surface area of 740 m.sup.2/g Langmuir. The elemental analysis of the calcined and copper loaded sample gave: Al 4.1 wt %, Cu 3.1 wt %, Na 0.05 wt %, and Si 36 wt %. The Cu content obtained upon ion-exchange is thus slightly higher compared to batch wise prepared chabzite samples.

[0189] The copper-exchange chabazite sample was tested in SCR catalysis and its performance compared to a copper-exchanged sample obtained from a batch synthetic procedure based on Comparative Example 1 (CE 1) of US 2011/0076229 A1. To this effect, the samples were contacted at various temperatures with a gas stream containing nitrogen oxide. The samples were tested in the fresh state, as well as after separate aging regimens in air containing 10 wt.-% water at 750 C. for 5 h, and subsequently at 850 C. for 6 h, respectively.

[0190] More specifically, the samples to be tested were mixed with a slurry of premilled alumina (approx. 30wt % solid content) in a weight ratio zeolite: Al2O3=70:30. After drying and calcination (1 h, 550 C. in air), the resulting cake was crushed and sieved to a particle size of 250-500m which was used for testing. For aging, a fraction of the shaped powders was placed as shallow bed in a high temperature resistant ceramic crucible. In a muffle oven the temperature was ramped up under a flow of air and 10% steam. After reaching the desired value of 750 C. or 850 C. the temperature was kept constant for 5 h, or 6 h respectively, then the heating was switched off.

[0191] Catalytic performance tests on fresh and aged powders were performed in a screening reactor system. 170 mg of shaped powder (fresh or aged) was diluted with corundum of the same particle size to represent 1mL of a coated catalyst with a typical washcoat loading and placed in the reactor. The samples were exposed to a feed gas mixture containing 500 ppm NO, 500 ppm NH.sub.3, 10% O.sub.2, 5% H.sub.2O, and balance N.sub.2 at a gas hourly space velocity of (GHSV) of 70,000 h.sup.1. The samples were tested under stationary conditions at different discrete temperature levels (T=200, 300, 450, and 575 C.). After a sufficient equilibration time, the signal of the online gas analyzers (ABB LIMAS) was averaged for 30s and the resulting value used to calculate conversions.

[0192] The results from the comparative testing experiments prior to and after aging are displayed in FIGS. 6 to 8. Thus, as may be taken from the results from comparative testing, it has quite unexpectedly been found that the catalyst sample prepared using chabazite from the continuous process according to the present invention display substantially higher conversion levels for NOx both in the fresh state (see FIG. 6) as well as after respective aging regimens (see FIGS. 7 and 8, respectively) at low temperatures around 200 C. as well as at high temperatures around 550-600 C. As may be taken from the results in FIG. 6, this surprising technical effect is particularly surprising for the inventive samples at low temperatures after aging at 750 C. (see FIG. 7) and in particular in the fresh state at low SCR temperatures of around 200 C. (see FIG. 6).

[0193] Therefore, it has not only unexpectedly been found that a highly efficient process for the continuous production of zeolitic materials may be provided according to the present invention, but that even more, the present invention provides surprisingly improved zeolitic materials not only with respect to their purity and crystallinity, but furthermore with respect to their chemical characteristics which quite unexpectedly surpass conventional materials to a substantial extent.