PROCESS FOR THE CONTINUOUS PREPARATION OF ZEOLITES USING ULTRASOUND

Abstract

An intensified continuous process for synthesizing zeolite crystals is described, said process comprising a continuous supply of a continuously prepared gel, said gel then being continuously crystallized, said process comprising at least one application of ultrasound.

Claims

1. An intensified, continuous process for the synthesis of zeolite crystals, said process comprising a continuous supply of a gel prepared continuously, said gel then being crystallised continuously, said process comprising at least one application of ultrasound.

2. The process according to claim 1, comprising at least the following steps: a) continuously supplying a composition capable of generating zeolite crystals; b) continuously introducing said composition into at least one crystallisation reaction zone subjected to ultrasound, and c) continuously recovering the crystals formed in step b).

3. The process according to claim 1, wherein the ultrasound is applied at least at one point in the continuous synthesis of zeolite crystals.

4. The process according to claim 1, wherein the ultrasound is applied in a continuous, or sequenced or alternated manner or a combination of these different methods.

5. The process according to claim 1, wherein the frequency of the applied ultrasound is between 10 kHz and 5 MHz.

6. The process according to claim 1, wherein the electric power supplied by the ultrasound generator is between 3 W and 500 W.

7. The process according to claim 1, wherein the fraction of the time of exposure to ultrasound relative to the time of residence of the reaction medium in the continuous reactor is between 0.05% and 50%.

8. The process according to claim 1, wherein the reaction temperature is between 70 C. and 180 C.

9. The process according to claim 1, further comprising one or more steps of adding seed(s) to the reaction medium.

10. The process according to claim 1, further comprising a step of ultrasound irradiation at the end of the synthesis, in a humid medium, before separation of the mother liquors.

11. The process according to claim 1, wherein the zeolite crystals prepared are zeolite crystals selected from MFI type zeolites, MOR type zeolites, OFF type zeolites, MAZ type zeolites, CHA type zeolites, HEU type zeolites, FAU type zeolites, EMT type zeolites, LTA type zeolites, and titanosilicalites.

12. The process according to claim 1, wherein the zeolite crystals prepared are zeolite crystals selected from X zeolite, MSX zeolite and LSX zeolite.

13. The process according to claim 1, wherein the zeolite crystals prepared are zeolite crystals with hierarchical porosity.

14. A use of ultrasound, during the continuous synthesis of zeolite crystals at a reaction temperature between 70 C. and 180 C., said ultrasound being used at a frequency between 10 kHz and 5 MHz.

Description

Example 1: Continuous Process Without Ultrasound at 80 C.

[0099] X zeolite crystals in sodium form (NaX) are prepared from solutions of sodium aluminosilicate and sodium silicate, with a step of adding a seeding agent. Thus, 100 ml of reaction medium are prepared by mixing the solutions of sodium silicate and sodium aluminosilicate at 80 C. in a mixer with a high shear rate.

[0100] The crystallisation takes place at 80 C. for 2 hours, by circulating the reaction medium with a flowrate of 60 ml.min.sup.1 to pass it through a tubular reactor of 0.5 cm in diameter and 22.5 cm in length, said reactor being equipped with a plate transducer located outside the tube, but which remains inactive for this example.

Example 2: Continuous Process with Ultrasound at 80 C.

[0101] Crystals of X zeolite in sodium form (NaX) are prepared from solutions of sodium aluminosilicate and sodium silicate, with a step of adding a seeding agent. As in the previous example, 100 ml of reaction medium are prepared by mixing the solutions of sodium silicate and sodium aluminosilicate at 80 C. in a mixer with high shear rate.

[0102] The crystallisation takes place at 80 C. for 2 hours, by circulating the reaction medium with a flowrate of 60 ml.min.sup.1 to pass it through a tubular reactor of 0.5 cm in diameter and 22.5 cm in length which is, for the purposes of this example, exposed to ultrasound generated using the plate transducer whose frequency is equal to 34.5 kHz. The electrical power of the generator is fixed at 40 W.

[0103] Ultrasound is applied continuously only at the tubular reactor, which corresponds to a continuous circulation of the synthesis gel with an ultrasound point irradiation.

[0104] FIGS. 1 and 2 show that in the absence of ultrasound, the zeolite crystals allowing to reach an adsorption of toluene (T50) of approximately 24% are obtained after 120 minutes (Example 1, FIG. 1). With the application of ultrasound (Example 2, FIG. 2), the zeolite crystals allowing to reach an adsorption of toluene (T50) of about 24% are obtained as early as 80 minutes, which demonstrates the great interest of the use of ultrasound for the intensified process for the continuous preparation of zeolite crystals according to the present invention. It is therefore observed that the synthesis duration can be greatly reduced ( less time in Example 2) by application of ultrasound, without degradation of the adsorption properties of the zeolite obtained. This corresponds to an intensification of the continuous process for preparing zeolites.