EP2285483A1

EP2285483A1 - Method for the preparation of a cationic zeolite by ionic exchange

Info

Publication number: EP2285483A1
Application number: EP09765985A
Authority: EP
Inventors: Karin Barthelet; Patrick Magnoux; Alain Methivier; Vania Santos
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2008-05-28
Filing date: 2009-05-05
Publication date: 2011-02-23
Also published as: FR2931703A1; US20110288359A1; FR2931703B1; WO2009153423A1

Abstract

The invention relates to a method for the preparation of a cationic zeolite exchanged at least partially with one or more mono and/or multivalent cations. The method includes at least the following steps comprising: separate activation of a zeolite to be exchanged and an anhydrous salt under a dry inert gas stream, dissolution of the anhydrous salt in an anhydrous organic solvent, ionic exchange under a dry inert atmosphere, filtration and stripping with an anhydrous organic solvent, and calcination in the presence of oxygen under a dry gas stream. The invention also relates to the use of prepared zeolities for the separation or purification of hydrocarbon feeds.

Description

PROCESS FOR THE PREPARATION OF A CATIONIC ZEOLITE BY ION EXCHANGE

PRIOR ART

Among the separation or purification processes, many use cationic zeolites as adsorbents. Their principle is based on a selectivity of shape or size, or on a particular affinity of one of the constituents of the charge for the cations. Insofar as the process does not involve any chemical reaction, these are to be avoided. Any conversion of feedstock compounds leads to a drop in yield and can also be at the origin of the formation of coke precursors, thus causing premature aging of the adsorbent. These undesirable phenomena are all the more frequent as the zeolite has active surface sites which are most often acidic sites. Thus, unlike the protonated zeolites, cationic zeolites which do not have, a priori, any Bronsted acid sites, should not have a strong activity. Nevertheless, in certain cases, they have non-negligible activities characterized by reactions involving acidic sites.

In order to obtain very little or no reactive zeolites, it is necessary either to neutralize the activity detected or to avoid its presence. Neutralization in particular with basic solutions is not always effective and has the disadvantage of adding a step to the preparation of the zeolite. The second option would be preferable. A solution already proposed in the literature is to activate the solids under a reducing atmosphere such as NH ₃ (Siegel, H., Schellner, R., Staudte, J., Van Dun, J., Mortier, Zeolites, 1987, 7, 372). in order to neutralize the protons as soon as they form. However, the zeolites thus obtained are likely to contain NH ₃ molecules and therefore no longer have all their porosity accessible. To remedy this, it is proposed in the context of the present invention a process for the preparation by ion exchange of a cationic zeolite exchanged at least partially with one or more monovalent and / or multivalent cations which proves effective for limiting or even canceling the reactivity of these zeolites. The zeolites according to the invention are less active with respect to reactions involving acid sites than when they are prepared according to the prior art.

SUMMARY DESCRIPTION OF THE INVENTION

The invention relates to a process for preparing a cationic zeolite exchanged at least partially with one or more mono- and / or multivalent cations. The process comprises at least the steps of separately activating a zeolite to be exchanged and an anhydrous salt under a dry inert gaseous stream, dissolving the anhydrous salt in an anhydrous organic solvent, ion exchange under dry inert atmosphere, filtration and washing with an anhydrous organic solvent and calcination in the presence of oxygen and in a dry gas stream. The invention also relates to the use of zeolites prepared for the separation or purification of hydrocarbon feeds.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a process for the preparation of a cationic zeolite exchanged at least partially with one or more mono- and / or multivalent cations, said exchanged cationic zeolite being preferably of X, Y, A, β or MFI type, said method of preparation comprising at least the following steps:

a) separate activation of a zeolite to be exchanged and an anhydrous salt under dry inert gaseous flow, b) dissolution of the anhydrous salt obtained at the end of step a) in an anhydrous organic solvent, preferably an anhydrous alcohol , very preferably anhydrous ethanol, c) ion exchange by adding the activated zeolite obtained at the end of step a) in the solution obtained at the end of step b), this step being carried out under a dry inert atmosphere, d) filtration and washing of the solid obtained at the end of stage c) with an anhydrous organic solvent, e) calcination of the solid obtained at the end of stage d), in the presence of oxygen and under a dry gas stream.

The multivalent cation (s) are generally divalent or trivalent cations and are generally alkali-earth or lanthanide cations. The monovalent cation (s) are generally alkaline cations.

Steps a), b), c), d) and e) of the preparation process can generally be carried out under the operating conditions described below.

step a)

The separate activation of the zeolite to be exchanged and the anhydrous salt is preferably carried out in two separate columns.

The zeolite is generally activated under dry inert gaseous flow, preferably under a stream of dry nitrogen, of between 3 and 8 h ^-1 . g ^"1 and at a temperature between 200 and 600 ⁰ C, preferably between 350 ⁰ C and 55O ⁰ C, very preferably between 450 and 55O ⁰ C for a period of between 1 and 20 h.

The anhydrous salt is usually activated in dry inert gas stream, preferably under a dry nitrogen flow, between 3 and 8 I. h ^"1. ^{G" 1} and at a temperature between 50 and 35O ⁰ C, for a period between 1 and 20 h.

step b)

Step b) of dissolving the anhydrous salt obtained at the end of step a) in the anhydrous organic solvent in which a dry inert gas is bubbled, preferably dry argon, is generally carried out at a temperature of between 20 and 60 ^° C. with magnetic stirring at a speed of between 500 and 700 rpm. step c)

Step c) ion exchange by adding the activated zeolite obtained at the end of step a) in the solution obtained at the end of step b) is generally carried out with stirring between 500 and 700 tr / min, at a temperature between 20 and 100 ⁰ C, this step being carried out under a dry inert atmosphere, preferably dry argon, the duration of the exchange being between 1 and 20 h.

A refrigerant system is generally adapted to avoid evaporation of the anhydrous organic solvent during the exchange.

step d)

Step d) is that of filtration and washing of the solid obtained at the end of step c) with an anhydrous organic solvent, preferably an anhydrous alcohol, very preferably anhydrous ethanol.

The volume of the anhydrous organic solvent used is generally at least equal to that used during the ion exchange step.

Furthermore, the solid obtained at the end of step d) can be stored without risk of evolution of its acid-base characteristics.

step e) The step e) of calcination of the solid obtained at the end of step d) in the presence of oxygen, is generally carried out at a temperature of between 200 and 600 ^° C., preferably between 300 and 55 ° C. ⁰ C, for a period of between 1 and 20 h, preferably between 10 and 15 h, under a dry gas stream of between 3 and 8 I. h ^'1 . g ^'1 , preferably under a stream of dry compressed air. It is generally verified by nitrogen adsorption at 77 ^° K that the zeolite has retained its pore volume.

The exchange rate obtained in the mono- and / or multivalent cation (s) is generally verified by inductively coupled plasma atomic emission spectrometry (ICP-AES).

The cationic zeolite thus prepared can be used in any process for the separation or purification of hydrocarbon feeds. We can mention among others potential applications, separation of paraxylene from an aromatic C8 cut, separation of linear paraffins from a kerosene cut, separation of linear paraffins / branched paraffins from a gasoline cut, separation of paraffins / olefins, removal of mercaptans from natural gas, desulphurization of FCC gasolines, denitrogenation of C4-C6 feedstocks for oligomerization.

The decline in activity can generally be demonstrated by testing the zeolite using a model reaction involving the isomerization of 1-dodecene.

Its principle, its implementation and its exploitation are explained in the literature (V. Santos, K. Barthelet, I. Gener, C. Canaff, P. Magnoux, Microporous and

Mesoporous Materials, in press).

The implementation of this test which is a batch and liquid phase experiment comprises the following steps: a) suspension of 3 g of zeolite in 75 g of 95% pure 1-dodecene supplied by Aldrich.

This suspension is carried out in a three-necked balloon. b) degassing of the suspension prepared in a) for a few minutes by bubbling argon, then maintaining it under an inert atmosphere of argon but without bubbling c) stirred with magnetic stirring at 500 rpm and under heating in a bath of silicone oil at 150 ^° C. for 24 h. The three-necked flask is surmounted by a reflux refrigerant system to prevent evaporation of solution during the sampling experiment of 0.05 ml at regular time intervals and analysis of these by gas chromatography column PONA (Paraffin, Olefin,

Naphtene, Aromatic) with a diameter of 200 μm, a film thickness of 0.5 μm and a length of 50 μm.

From the chromatograms, the composition of each sample is determined in 1-dodecene and its different isomers (2-dodecene, 3-dodecene,

4-dodecene, 5-dodecene and 6-dodecene) from which the conversion is calculated 1-dodecene according to the following equation:

"(1 - dodecene) _inllin , - n (\ - dodecene) _f ,

ConviX - dodecene) = - - ^ L x 100. n {\ - dodecene) _initial

It is then possible to draw the curve of the conversion to 1-dodecene as a function of the reaction time, the slope of the tangent at the first points of this curve corresponding to the initial speed of the isomerization reaction of 1-dodecene and reflecting the initial activity of the zeolite tested, that is to say its number of active sites vis-à-vis a reaction involving acid sites.

EXAMPLES

Two NaCaY zeolites with an exchange rate of approximately 25% are prepared by ion exchange from a NaY zeolite in the form of a powder. One of the two NaCaY zeolites is prepared in an aqueous medium and the other in an anhydrous alcoholic medium.

For exchange in an aqueous medium, approximately 10 g of the zeolite are directly suspended in 1 l of CaCb solution at 0.7 g / l (solution prepared from CaCl ₂ .2H ₂ O from Aldrich). Then the flask is heated by means of a silicone bath at 60 ^° C. and the suspension kept under magnetic stirring. A refrigerant system is adapted to avoid evaporation of the suspension during exchange. The exchange lasts approximately 7 hours.

After exchanging the zeolite is filtered, washed with water and dried in an oven at 110 ^° C. Then, it is dehydrated under a stream of nitrogen (3 lh ^"1 .g _zeo f ¹ ) in a tube oven at 450 ^° C. C for 12 hours to remove adsorbed water in the zeolite during exchange The zeolite thus prepared is named NaCaY-26% (aqueous medium).

For exchange in an alcoholic medium, the procedure described in the description of the invention is applied. Before the actual exchange, the zeolite and the salt are dehydrated separately. The NaY zeolite is dehydrated under a stream of nitrogen (3 I.rf ¹ .g _zeo f ¹ ) for 12 h at 450 ⁰ C in a tubular furnace and the anhydrous CaCb salt from Aldrich at 150 ⁰ C under a stream of nitrogen for 12 hours in a column in an oven tubular. The two columns containing one dehydrated zeolite, the other the dehydrated salt are isolated before being disconnected from the furnaces to preserve them from any contact with the air.

The dehydrated salt is dissolved, with magnetic stirring at 500 rpm, in anhydrous ethanol in which argon is bubbled in a round bottom flask. The zeolite is then added to this solution (10 g of solid per 1 I of solution). Then the flask is heated by means of a silicone bath at 60 ^° C. and the suspension maintained under magnetic stirring at 500 rpm. A refrigerant system is adapted to avoid evaporation of the alcohol during the exchange. The system is kept under argon to avoid contact of the suspension with air. The exchange lasts approximately 7 hours.

After exchanging the solid is filtered and washed with anhydrous ethanol (same volume as that used during the ion exchange). The recovered solid is calcined in a column in a tubular oven at 55O ⁰ C for 20 h under a stream of dry compressed air. The zeolite thus prepared is named NaCaY-24% (anhydrous ethanol medium).

The residual acidity of these three solids is determined by means of a model transformation reaction of an olefin (1-dodecene) which makes it possible to characterize the weak activities. The differences in the activity of the two NaCaYs with each other and with the starting NaY are presented in FIG. 1 which shows the variation of the 1-dodecene conversion as a function of time for NaY, NaCaY-26% (aqueous medium) and NaCaY-24% (anhydrous ethanol medium).

It can be seen that the activity of the NaCaY solid is greatly reduced when it is prepared in an alcoholic medium and not in an aqueous medium and becomes similar to that of the starting NaY (initial reaction rates, conversion and number of products formed very close) .

Claims

θREVENDICATIONS

A process for preparing a cationic zeolite exchanged at least partially with one or more mono and / or multivalent cations, said preparation process comprising at least the following steps:

a) separate activation of a zeolite to be exchanged and an anhydrous salt under a dry inert gaseous stream, b) dissolution of the anhydrous salt obtained at the end of step a) in an anhydrous organic solvent, c) ion exchange by addition of the activated zeolite obtained at the end of step a) in the solution obtained at the end of step b), this step being carried out under a dry inert atmosphere, d) filtration and washing of the solid obtained in FIG. from step c) with an anhydrous organic solvent, e) calcination of the solid obtained at the end of step d), in the presence of oxygen and under a dry gas stream.

2. Preparation process according to claim 1 wherein the anhydrous organic solvent is an anhydrous alcohol.

3. Preparation process according to claim 1 wherein the anhydrous organic solvent is anhydrous ethanol.

4. Preparation process according to one of claims 1 to 3 wherein the multivalent cation or cations are alkaline earth or lanthanide cations.

5. Preparation process according to one of claims 1 to 4 wherein the monovalent cation or cations are alkaline cations.

6. Preparation process according to one of claims 1 to 5 wherein the cationic zeolite exchanged is of type X, Y, A, β or MFI.

7. Preparation process according to one of claims 1 to 6 wherein steps a), b), c), d) and e) are carried out under the following operating conditions:

a) separate activation of the zeolite to be exchanged and the anhydrous salt, said zeolite being activated under a dry inert gaseous flow of between 3 and 8 I. h ^'1 . g ^"1 and at a temperature between 200 and 600 ⁰ C for a period of between 1 and 20 h, said anhydrous salt being activated in a dry inert gas stream of between 3 and 8 I. h ^-1 . g ^"1 and at a temperature between

50 and 350 ⁰ C, for a duration of between 1 and 20 hours,

b) dissolving the anhydrous salt obtained at the end of step a) in the anhydrous organic solvent in which a dry inert gas is bubbled, this step being carried out at a temperature of between 20 and 60 ^° C. with magnetic stirring at a speed of between 500 and 700 rpm,

c) ion exchange by adding the activated zeolite obtained at the end of step a) in the solution obtained at the end of step b), this step being carried out with stirring between 500 and 700 rpm, at a temperature of between 20 and 100 ^° C., this step being carried out under a dry inert atmosphere, the duration of the exchange being between 1 and 20 hours,

d) filtration and washing of the solid obtained at the end of stage c) with an anhydrous organic solvent,

e) calcination of the solid obtained at the end of step d) in the presence of oxygen, at a temperature of between 200 and 600 ^° C., for a duration of between 1 and 20 hours, under a dry gas flow of between 3 I. and 8 ^{h -1} · g ^-1.

8. Process for using the zeolites prepared according to one of claims 1 to 7 for the separation or purification of hydrocarbon feeds.

9. Implementation method according to claim 8 for the separation of paraxylene from a C8 cut.

10. Method of implementation according to claim 8 for the separation of linear paraffins from a kerosene cut.

11. Method of implementation according to claim 8 for the separation of linear paraffins / branched paraffins.

12. Method of implementation according to claim 8 for paraffins / olefins separation.

13. Method of implementation according to claim 8 for the removal of mercaptans from natural gas.

14. Method of implementation according to claim 8 for the desulfurization of FCC gasolines.

15. The method of implementation according to claim 8 for the denitrogenation of charges for oligomerization.