FR2953153A1 - HYDROPHOBIC ZEOLITHE EXCHANGED WITH A TRANSITION METAL AS ALDEHYDESE ADSORBENT - Google Patents

Abstract

The present invention relates to the use of a zeolite having an Si / Al ratio of between 20 and 100, exchanged, partially or totally, with a transition metal, such as iron, as an aldehyde adsorbent, in particular acetaldehyde, and an air filter containing such a zeolite.

Description

The present invention relates to the use of a hydrophobic zeolite exchanged with a transition metal for adsorbing aldehydes such as acetaldehyde, especially in an air filter.

Zeolites are tetrahedral silicoaluminates of the family of crystallized microporous tectosilicates with high specific surface area, with pore sizes varying according to the structure of the zeolite from 3 to 13 Å. There are zeolites in the natural state that have been known for a long time, the main ones being clinoptilolite, chabazite and mordenite, and synthetic zeolites known since the 1950s with numerous industrial applications using their adsorption properties, exchange of ions or catalysis. Synthetic zeolites, unlike natural zeolites, are pure products. To date, more than 200 different structures are known, the main ones being A, faujasite (X and Y), mordenite, ferrierite, pentasil and beta. These zeolites are obtained by hydrothermal synthesis. The structure of zeolites is described as a sequence of SiO4 and A104- (carrying a negative charge) tetrahedra, with pooling of oxygen in the three directions of space. These are the sequences that generate channels and cavities specific to each structure. The general formula of a zeolite is written as follows: M A102 xSiO2. wH2O where x represents the atomic ratio Si / Al, w represents the amount of water present and M represents the compensation cation which is most often Na + (sodium form) and / or optionally K +, 1 M + compensating the negative charge related to aluminum (lNa + / lAl) through the tetrahedral structure (A104-) and pooling of oxygen.

These zeolites are also commercially available in acid form, that is to say in a form where the compensation cations have been exchanged with H + ions. In the normal state, there is water (capillary condensation) in the pores of a zeolite (wH2O). However, this water can be removed by raising the temperature. Synthetic zeolites, that is to say more than 99% pure, are crystallized microporous silicates whose channel and cavity sizes vary according to the structure between 3 and 13 Å. They are in the form of powdery powder, the size of the crystals being on average a few microns, advantageously between 1 and 2 microns. Finally, for a defined structure, it is possible, by known technologies, namely dealumination (treatment under steam at high temperature followed by acid treatment), or replacement of Al by Si (for example by treatment with with SiC14), increase the Si / Al ratio while maintaining the same structure. With a low Si / Al ratio (minimum value 1 for zeolite A, 1.3 for X and 2.6 for Y), there are many compensating cations (1 M + / l Al). Such zeolites are therefore hydrophilic with a high affinity for polar molecules such as water. When the Si / Al ratio is, on the contrary, high, for example Si / Al = 100 for a Y zeolite, there are very few compensation cations and therefore very little affinity for the polar molecules. Such hydrophobic zeolites, generally having a Si / Al ratio of between 5 and 100, are known for their use in the adsorption at ambient temperature of VOCs (Volatile Organic Compounds), most often for their concentration after regeneration. air, at air temperatures of the order of 200 ° C. The effluents to be treated have a relatively variable humidity (50 to 100%) and the water vapor content is between 1 and 2% of the volume, whereas that in VOC is most often of the order of a few ppm to a few tens of ppm. These zeolites have adsorption capacities and efficiencies which depend on the type of zeolite and on its Si / Al ratio for a given VOC.

Thus, a Y zeolite of Si / Al ratio of 100 has a high efficiency for the adsorption of aromatic compounds such as toluene, with an adsorption capacity of the order of 25% by weight. It should be noted, however, that hydrophobic zeolites, indispensable for the adsorption of VOCs in the presence of water, have a very low efficiency for aldehydes and in particular acetaldehyde. However, the toxicity of these aldehydes is currently recognized as a carcinogen. It therefore appears essential to develop filters that are effective for the trapping of these compounds by adsorption. The inventors have thus discovered that hydrophobic zeolites exchanged, partially or totally, with a transition metal were capable of adsorbing aldehydes, and in particular acetaldehyde. Such zeolites are obtained by partial or total exchange of the compensation cation with a metal cation, for example Fe2 + (2Na + ù> 1 Fe2 +). The compensation cation, most often Na +, can indeed be partially or totally replaced by the ion exchange mechanism with other cations, with different degrees of valence (m), for example Fe2 + (m = 2), the degree of valence representing the number of positive charges carried by the exchange cation.

After exchange, the formula of the exchanged zeolite is then written as follows: ## EQU1 ## where x is always greater than 1 and represents the Si / Al atomic ratio, Mn + represents the compensation cation, Cm + represents the ion exchanged with Mn + (ex: Fe2 + with m = 2), m representing the valence degree of Cm +, n represents the degree of valence of the compensation cation Mn + and y represents the exchange rate.

The subject of the present invention is therefore the use of a hydrophobic zeolite exchanged, partially or totally, with a transition metal such as iron, cobalt or manganese, and preferably iron, as an adsorbent. aldehydes.

By "aldehyde" is meant, in the context of the present invention, a volatile chemical molecule having a CHO aldehyde function. It may be in particular acetaldehyde and formaldehyde, and more particularly acetaldehyde. A zeolite according to the invention may especially adsorb at least 2% by weight of acetaldehyde.

For the purposes of the present invention, the term "hydrophobic zeolite" means a zeolite having an Si / Al ratio more particularly comprised between 20 and 100.

Advantageously, the zeolites according to the invention will have an Si / Al ratio of between 30 and 50, and in particular of approximately 40.

Advantageously, the degree of exchange with the transition metal will be between 0.001 and 1, advantageously between 0.01 and 0.8, more advantageously between 0.1 and 0.8, and even more advantageously between 0.1 and 0. , 7, and preferably between 0.1 and 0.5.

The zeolite used to carry out the partial or total exchange with a transition metal may be in sodium form (i.e., the compensation cation that compensates for the negative charge of A104- is Na +) or an acid form (when the compensation cation is H), both forms being commercially available. In particular, the zeolite may be in acid form. Under these conditions, the zeolite exchanged with a transition metal according to the invention may correspond to the following formula: ## EQU1 ## where: - Cm + represents a metal cation of a transition metal, advantageously chosen from Fe2 +, Fei +, Col +, Cl0 +, Mn2 + and Mn3 +, even more advantageously chosen from Fe2 + and Fei +, and preferably being Fe2 +, - m represents the valence of the metal cation Cm + (that is to say the number of charges positive that carries this metal cation) and may more particularly represent 1, 2 or 3, and preferably 2 or 3, - Mn + (compensation cation) represents an alkaline or alkaline earth ion, such as Na +, K +, Li + or Cal + and advantageously Na +, an H + ion or a mixture thereof (i.e., the groups A104- are compensated by different compensation cations), n represents the valence of the compensation cation Mn + and may be more especially be between 1 and 2, - there shows the exchange rate of the compensation cation Mn + by the Cm + cation and is advantageously between 0.001 and 1, advantageously between 0.01 and 0.8, more advantageously between 0.1 and 0.75, more advantageously between 0 and , 1 and 0.7, and preferably between 0.1 and 0.5, and - x represents the Si / Al ratio and is advantageously between 20 and 100, more preferably between 30 and 50, and preferably from about 40.

The zeolites according to the invention will be in particular more than 99% pure (synthetic zeolites), in particular with a size of the channels and cavities varying according to the structure between 3 and 13 Å. They are in the form of powdery powder, the size of the crystals being on average a few microns, advantageously between 1 and 3 microns, especially between 1 and 2 microns.

Preferably, the zeolite is exchanged with iron, and preferably iron (II) (Fe2 +). The zeolite used may be chosen from zeolite beta, pentasil, mordenite and ferrierite, more particularly from zeolite beta and pentasil, and preferably will be pentasil such as ZSM-5. It may be more particularly in an acid form.

The zeolite may then be used in admixture with a binder, chosen in particular from a sol of silica and an alumina, in particular of the pseudobohemite type and advantageously peptized with nitric acid. The binder content, expressed as SiO 2 or Al 2 O 3, will especially be between 10 and 50%, preferably between 15 and 20%. The average particle size of this zeolite mixed with a binder may be in particular between 0.5 and 1 mm.

Such a zeolite may moreover be used in combination (for example in intimate mixture) with at least one other adsorbent which may be another adsorbent of aldehydes and / or an adsorbent of other molecules which may also be desirable. remove from a gaseous effluent such as aromatics (eg toluene), hydrocarbons (eg butane), NO2 or H2S, or even solid particles suspended in the gaseous effluent.

Moreover, in view of its use for adsorbing aldehydes, and especially acetaldehyde, contained in a gaseous effluent, the zeolite may be deposited on any suitable support.

Such a zeolite may especially be used in an air filter. Thus, the zeolites according to the invention may be used to purify any gaseous effluent containing an aldehyde such as acetaldehyde, and especially the air of a passenger compartment or a building interior such as a house, building, warehouse, factory, etc.

The zeolites according to the invention may also be used in the form of granules such as extrudates, or in the form of a honeycomb for reducing pressure losses, in a ducted effluent, for example, in the air-conditioning, ventilation or heating a building such as a house, a building, a warehouse, a factory, etc. The preparation of an exchanged zeolite according to the present invention is well known to those skilled in the art.

In general, to carry out this exchange with a transition metal, the zeolite (commercially available) is suspended, with stirring, in an aqueous solution of a metal salt which it is desired to introduce the Cm + cation (Fe2 + for example). as sulphate (m = 2)).

The parameters that will influence the exchange, and therefore the final content of cation Cm + after exchange, will include the temperature, the concentration of metal salt in the solution, the volume ratio of solution / weight of zeolite (V / P), and the reaction time.

The present invention also relates to an air filter comprising a hydrophobic zeolite exchanged, partially or totally, with a transition metal such as iron, cobalt or manganese, as described above.

This zeolite may especially be mixed with a binder as described above, to form particles having for example a mean particle diameter of between 0.5 and 1 mm.

Such a zeolite may moreover be used in combination (for example in intimate mixture) with at least one other adsorbent which may be another adsorbent of aldehydes and / or an adsorbent of other molecules which may also be desirable. to remove from a gaseous effluent such as aromatics (eg toluene), hydrocarbons (eg butane), NO2 or H2S, or even solid particles suspended in the gaseous effluent. 30 This filter can be used in particular in a passenger compartment (in the ventilation system, air conditioning or heating) or inside a building such as a house, a building, a warehouse, a factory, etc. (eg in ventilation, air conditioning, heating, etc.).

This filter may comprise a piece of felt (in dimensions adapted to the location in which it will be positioned, for example in a ventilation system, heating or air conditioning) on which will have deposited the zeolite exchanged as described above by techniques well known to those skilled in the art. This piece of felt can then be folded according to a technique well known to those skilled in the art in order to minimize the pressure drops during its use.

The object of the present invention will be better understood in the light of the non-limiting examples and the figures which follow.

FIGURES

FIGS. 1a to 1d and 2 show, as a function of time, the aldehyde concentration at the outlet of the adsorbent bed expressed in total carbon and measured by FID, also called the leakage curve (solid line curve), as well as the adsorption capacity (% by weight) (dashed curve), for an iron-exchanged pentasil zeolite with an Si / Al ratio of 40 (FIG. 1a), 18 (FIG. 1b) or 150 (FIG. 1c), an iron-exchanged zeolite with an Si / Al ratio of 40 (Fig. 1d), or a non-exchanged pentasil zeolite with an Si / Al ratio of 40 (Fig. 2). 30 EXAMPLES

1. Preparation of a Zeolite According to the Invention For this example, a zeolite of pentasil type (ZSM-5) acid form of Si / Al (atomic) ratio of 40 originating from ZEOLYST (United States) is used. It is in the form of a fine white powder whose grain size is of the order of 1 to 3 microns.

This zeolite is shaped with an alumina binder by extrusion. Alumina is first peptized with nitric acid to form a gel.

These operations are carried out with an in-line extrusion device comprising two kneader-extruders (the first for the formation of the alumina gel which then mixes with the zeolite in the second kneader). The unit comprises 4 feeders: 2 for powders (zeolite and alumina) and 2 for liquids (nitric acid and water) to adjust the rheology of the powder before passing through a die).

In this case, the die is composed of holes 1.8 mm in diameter. The extrudates leaving the die are dried at 120 ° C. for a few hours and then undergo a heat treatment at 450 ° C. to give them good mechanical strength. Their length is between 4 and 12 mm.

These extrusions are then iron exchanged by dipping (with supernatant solution) in a solution of iron (II) sulphate (FeSO4.7H2O), the purity of the crystalline salt of which is greater than 99.5%. The demineralised water used has a conductivity of less than 15 μs. The operating conditions are as follows: FeSO4.7H2O: 0.5 molar, ie 138 g / L of FeSO4 7H2O V / P: 3 (volume of solution in liters / weight of dry extrudates per kg) Temperature: 60 ° C Time exchange: 4 hours.

The extrudates are recovered by separating them from the iron sulphate solution and washing is carried out by three successive soaks with deionized water in order to remove the unchanged iron and the salt present. These pentasil / Fe extrudates are dried in an oven at 120 ° C and then heat treated in air at 400 ° C.

The extrudates are then crushed - screened for the experiments described below, the average particle size of which is between 0.5 and 1 mm. However, in order to obtain particles having an average size of 0.5 to 1 mm, it is also possible to replace the die previously used by a die having smaller holes, in particular between 1 mm and 0.5 mm. Such extrudates have, moreover, been produced under the conditions of Example 1 by replacing the die composed of holes 1.8 mm in diameter with a die comprising holes 1 mm in diameter or 0.5 mm in diameter. diameter.

Under these conditions, the iron content of the zeolite is 0.58%, which corresponds to an exchange rate of 50%, the zeolite then meets the formula 0.25Fe 0.5H A102 40SiO2.

The other zeolites used in the following examples were prepared according to the same protocol using other types of zeolites initially. It should be noted, however, that the iron exchange could have been carried out on the zeolite itself before being shaped with the binder. Acetaldehyde adsorption test

Comparative Test 1: The adsorption tests are conducted in a 19 mm diameter fixed bed reactor surrounded by heating shells.

The gaseous mixture passing through the zeolite bed according to the invention consists of air, acetaldehyde and water vapor at controlled concentrations. The acetaldehyde is fed from a standard 1% acetaldehyde bottle in N 2 (p = 26 bars), and the water vapor content is regulated by a controlled temperature saturator (air bubbling). ). The flow rates of air and N2 / acetaldehyde are controlled by mass flow meters.

The zeolite according to the invention used is in the form of granules of 0.5 - 1 mm. The height of the bed is 2.54 cm, a volume of 7.2 cm3.

Before starting the adsorption phase, the zeolite of the invention is treated in dry air at 200 ° C. for a minimum of two hours, with a flow rate of 100 Nl / h, and then returned to ambient temperature before introduction of the water and acetaldehyde.

During the adsorption phase, the concentration of acetaldehyde by FID (flame ionization) is monitored at the reactor outlet, this analyzer having previously been calibrated from air-acetaldehyde mixtures at different concentrations of acetaldehyde.

The experiments are conducted until the concentration of aldehyde at the outlet is equal to the input.

The operating parameters are as follows: ambient temperature, ie 20 ° C., acetaldehyde concentration: 30 ppm, water vapor content: between 1 and 2% by volume, volumetric hourly speed: 20,000 hours -1.

From the leakage curves, for given operating conditions, the amount of acetaldehyde retained by the zeolite, and therefore its adsorption capacity, is deduced by integration.

It is also possible to note the time before rupture, that is to say the time during which the acetaldehyde leakage is zero, as well as the amount of accumulated acetaldehyde retained at each instant.

The results obtained with 4 different zeolites (iron-exchanged pentasil with a Si / Al ratio of 40, of 18, or of 150, or beta exchanged with iron with a Si / Al ratio of 40) are presented in FIGS. d and in the following table: Structure Si / Al% Fe Adsorption Capacity Weight (%) Pentasil Iron 40 0.58 2.7 (131) * Pentasil Iron 18 1.6 0.47 (22) * Pentasil Iron 150 0.3 0.8 (32) * Beta Iron 40 0.76 2.3 (104) * * (): Acetaldehyde mass adsorbed in mg.

It will be noted that with iron pentasil zeolite with a Si / Al ratio of 150 or 18, the experiment is stopped after about 5 hours because the concentration of acetaldehyde at the outlet is very close to the entry showing that the saturation is reached (see FIGS. 1b and 1c), whereas with the other two products the saturation is not reached after more than 20 hours of operation (see FIGS. 1a and 1d). In addition, it is clear from the above table that the acetaldehyde adsorption capacity of zeolites having an Si / Al ratio of 40 is much higher than that of zeolites having an Si / Al ratio of 18 or 150. .

These results clearly show that the Si / Al ratio of the zeolite is very important for good adsorption of acetaldehyde, it should not be too low or too high.

Comparative test 2:

The results obtained with a non-exchanged ZSM-5 pentasil zeolite are presented in FIG. 2 and in the following table in comparison with the results obtained with the same zeolite exchanged with iron: Si / Al structure Adsorption capacity Weight (%) Pentasil not exchanged 40 0.13 (6) Pentasil Iron 40 2.7 (131) * * (): Mass acetaldehyde adsorbed in mg.

These results clearly show that the exchange of the zeolite with a metal is necessary since the saturation is reached after only one hour with the non-exchanged zeolites (see FIG. 2) and that the adsorption capacity obtained is much higher. low. Comparative Test 3: The same adsorption test of acetaldehyde was carried out with the following two adsorbents: activated carbon with a particle size of 0.3 to 0.5 mm (adsorbent used in the prior art) , and an iron-exchanged zeolite according to the invention having the following characteristics: pentasil structure H with a Si / Al ratio of 40 (ZSM-5), o iron content of 0.5%, o content by bonding Al 2 O 3 by 20%, and particle size of 0.5 to 1 mm.

The operating conditions were as follows: Fixed bed reactor with a diameter of 19 mm Adsorber volume: 7.2 cm3, ie a height of 25.4 mm Concentrations: acetaldehyde: 30 ppm, ie 59 mg / Nm3 water: 1, Remaining 5%: N2 Volumetric Hourly Speed: 20,000 hours - a rate of 144 NI / h.

The results obtained are presented in the following table: Adsorbent Mass acetaldehyde Adsorbed adsorption capacity (mg) (% by weight) Activated carbon 17.2 0.52 Iron-exchanged zeolite 306 4.6 It is therefore clear, in view of these results, that the zeolite exchanged with iron according to the invention has an adsorption capacity of acetaldehyde much higher than that of activated carbon.

Claims (12)

REVENDICATIONS1. Use of a zeolite having an Si / Al ratio of from 20 to 100, exchanged, partially or totally, with a transition metal such as iron, cobalt or manganese, and preferably iron, as an adsorbent aldehydes. 2. Use according to claim 1, characterized in that the Si / Al ratio of the zeolite is between 30 and 50, and preferably is about 40. 3. Use according to any one of claims 1 and 2, characterized in that the exchange rate by the transition metal is between 0.001 and 1, preferably between 0.01 and 0.8, more preferably between 0, 1 and 0.75, still more preferably between 0.1 and 0.7, and preferably between 0.1 and 0.5. 4. The use as claimed in claim 1, wherein the zeolite exchanged with a transition metal has the following formula: metal of a transition metal, advantageously chosen from Fe 2+, Fei +, Col +, Co +, Mn 2+ and Mn 3 +, even more advantageously chosen from Fe 2+ and Fei +, and preferably being FeZ +, m represents the valence of the Cm + metal cation, in particular 1 , 2 or 3, and preferably 2 or 3, - Mn + represents an alkaline or alkaline-earth ion, such as Na +, K +, Li + or Cal +, and advantageously Na +, an H + ion or a mixture thereof, - n represents the valence of the Mn + cation, in particular between 1 and 2, y is between 0.001 and 1, advantageously between 0.01 and 0.8, more advantageously between 0.1 and 0.75, still more advantageously between 0.1. and 0.7, and preferably between 0.1 and 0.5, and - x is between 20 and 100, advantageously between e 30 and 50, preferably about 40. 5. Use according to any one of claims 1 to 4, characterized in that the zeolite is exchanged with iron, and preferably iron (II). 6. Use according to any one of claims 1 to 5, characterized in that the zeolite is in a sodium or acid form, and in particular acid. 7. Use according to any one of claims 1 to 6, characterized in that the zeolite is selected from zeolite beta, pentasil, mordenite and ferrierite, and is preferably pentasil, such as ZSM-5. 8. Use according to any one of claims 1 to 7, characterized in that the zeolite is used in a mixture with a binder, chosen in particular from a silica sol and an alumina including pseudobohemite type and preferably peptized with acid nitric. 9. Use according to claim 8, characterized in that the binder content expressed as SiO2 or Al203 is between 10 and 50%, preferably between 15 and 20%. 20 10. Use according to any one of claims 1 to 9, characterized in that the zeolite is used in an air filter. 11. Use according to any one of claims 1 to 10 for purifying any gaseous effluent containing an aldehyde such as acetaldehyde, especially the air of a passenger compartment or a building interior. . An air filter comprising a zeolite having an Si / Al ratio of from 20 to 100, partially or totally exchanged with a transition metal such as iron, cobalt or manganese according to any one of claims 1 to 9. 15 30