WO2018087505A1 - Method for decontaminating a catalyst contaminated with carbon - Google Patents

Abstract

The invention concerns a method for decontaminating a catalyst contaminated with carbon, characterised in that it is implemented at ambient temperature and in that it comprises the following steps: a) providing a reactor comprising at least two electrodes separated from each other, between which a dielectric material is positioned; b) positioning said contaminated catalyst at the surface of said dielectric material; c) circulating an oxidising gas between said electrodes, said gas comprising oxygen; and d) applying an electric field between said electrodes so as to ionise said oxidising gas and form radicals and/or ionised molecules and/or metastable molecules capable of reacting with the carbon of said catalyst, said electric field inducing the deposition of a minimum power of 8 W on said dielectric material.

Description

 METHOD FOR DECONTAMINATING A CONTAMINATED CATALYST

 BY CARBON

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the field of decontamination of carbon-contaminated catalysts. This carbon, during a catalysis reaction, was then deposited inside these catalysts, especially in interstices, damaging or even deactivating the catalysts. STATE OF THE PRIOR ART

 The implementation of heterogeneous catalysis occupies an important place in the industrial processes of hydrocarbon processing. The use of catalysts of zeolite or silica-alumina alumina types, natural or synthetic clays, doped with noble and non-noble metals, makes it possible, in particular, to produce gasoline by cracking hydrocarbons with low added values or isomerization. and aromatization of paraffins. Heterogeneous catalysis makes it possible, by modifying the reaction path, to accelerate the rate of chemical reaction. In the case of the competing reactions, it makes it possible to favor one reaction with respect to another and thus to increase the selectivity of one chemical product rather than another. This heterogeneous catalysis generally used in refineries allows in particular the transformation of heavy loads into gasoline. During these catalysts, it is necessary to regenerate the catalysts in industrial units such as refining units, or petrochemicals which are among the most consumer sectors of catalytic materials.

The catalyst is used in much smaller amounts than the reagents. During the reactions, it is not consumed and appears neither in the balance of the reaction nor in its equation. So, in the case frequently encountered in the industry where the reaction takes place by contact catalysis, the catalytic cycle should be perpetual if and only if the catalyst does not deactivate. The rate at which the solid catalysts lose their activities depends largely on the characteristics of the process: nature and purity of the reagent (s), operating conditions such as the temperature, or the pressure, the reactor used and the catalyst chosen. Thus, catalytic cracking catalysts are deactivated in only a few seconds.

This deactivation is mainly related to the fact that the active sites are essentially located in the pores such as cages, intersecting channels, and channels, with perfectly defined characteristics and especially size close to that of organic molecules. These pores are real nanoreactors in which both the desired reaction and carbon deposition occur, the growth of which is limited by the pore size. These molecules can either poison the acid sites by adsorption or block their access.

Currently, to avoid rapid deactivation of a catalyst, simple regeneration procedures are implemented. For example, catalyst decontamination processes involve the continuous or periodic renewal of the catalyst (s) in a reactor, by withdrawing spent catalysts and adding regenerated catalysts. The implementation of such practices implies that the catalyst regeneration procedures are simple and effective, the choice of a technology for regeneration essentially dependent on the life of the catalyst. Thus, generally, when the catalyst lifetime is greater than one year, or ten thousand hours, as is particularly the case for hydrotreating and hydrocracking catalysts, the ex-situ regeneration is preferred because it allows a simplification of the shutdown procedures and ensures a better control of the regeneration by combustion. However, when the life of the catalyst is about six months, or five thousand hours, dedicated facilities for regeneration / reactivation are to be considered on site, especially if the catalyst is expensive. The operation of the unit is generally called "semi-regenerative mode": the catalyst is not discharged, it is regenerated in the reactor to the detriment of a temporary loss of production. The facilities necessary for performing the regeneration, such as compressors for the circulation of inert gas and oxygen may be permanent elements of the unit or be temporarily installed. However, when the life of the catalyst is shorter, or less than a few weeks, for example less than two hundred hours, the regeneration / reactivation frequency leads to permanent specialized facilities for the regeneration / reactivation of the catalyst. are considered an integral part of the process. The catalyst can either remain in the same reactor that alternates between operation and regeneration / reactivation, or cyclic process, or be transported batchwise or continuously in another reactor dedicated to regeneration / reactivation, continuous regeneration process in a moving bed. The principle of the latter, used for the dehydrogenation of paraffins, skeletal isomerization and catalytic reforming, is to circulate the catalyst in the form of bead / extruded in the same direction as the hydrocarbon feedstock through several reactors in series and then the catalyst of the catalyst. The last reactor is withdrawn continuously at low flow and sent to the regeneration zone. In cyclic mode, the number of fixed bed reactors is selected to ensure almost uninterrupted production. Compared to cyclic mode operation, continuous regeneration technology in a moving bed allows both constant efficiency and selectivity to be maintained. In addition, this technology can be applied under conditions, at low pressures, favoring yields and selectivity, but leads to a rapid deactivation and consequently a shorter cycle time. Despite these advantages, bed reactors operating in cyclic mode are most often preferred to moving bed reactors for reasons including economic. It should be noted that, nowadays, bedreactors operating in cyclic mode can implement processes for decontaminating catalysts contaminated by carbon by combustion in the air, the air being a gas oxidant commonly used in such processes. However, the high exothermicity of the combustion and the thermal properties of the catalysts make it difficult to control the temperature of the process. Hot spots may appear, particularly in places where the carbon has been deposited in or on the catalysts, leading to irreversible catalyst damage, in particular due to metal sintering or else dealumination of the catalyst for example. Therefore, catalysts that have suffered such irreversible damage, and therefore deactivated, must be replaced so as not to disrupt catalysis. However, it should be noted that the regeneration or the replacement of a catalyst are expensive from a strictly pecuniary and environmental point of view. Furthermore, it should be noted that the carbonaceous deposits formed during the catalytic reaction responsible for the deactivation largely depend on the reactor and the catalysts chosen, the nature and purity of the catalysts and / or the reagent (s). (s), the regeneration / reactivation frequency, and the operating or operating conditions of the catalysis, in particular the temperature and / or pressure applied, as well as the oxidizing gas used in the reactor in which catalysis takes place.

It is thus appropriate, rather than replacing damaged catalysts, or deactivated, to regenerate these directly in the same reactor where the catalysis takes place, by implementing mild decontamination processes to avoid, in particular, the creation of hot spots.

Thus, the main drawbacks of the currently used processes are related to the deterioration of catalytic materials requiring replacement after several cycles of operation-regeneration, the high inertia of the treatment since it requires heating to over 550 ° C a large volume of gas in industrial units, at the cost of stopping the industrial process during the catalyst regeneration step (batch processes).

It should be noted that, among the alternative techniques to overcome the difficulties associated with the appearance of hot spots due in particular to thermal regeneration, non-thermal plasma can be considered a promising technology because of its characteristics of no -balanced. In such a plasma, high energy electrons are generated at atmospheric pressure and at low temperatures, it leads to the formation of highly active species such as radicals, excited atoms or molecules, as well as positive ions such as 0 ₂ ⁺ or negative: O, 0 ₂ ^~ and 0 ₃ ^~ . OBJECTIVE OF THE INVENTION

The decontamination process of the invention aims to remedy all or part of the disadvantages of the state of the art and aims in particular to provide a process capable of completely regenerating a contaminated catalyst, in other words deactivated by a carbonaceous deposit, using a minimum of energy via the use of a non-thermal plasma implemented at room temperature. In particular, the method according to the invention implemented at ambient temperature without external heat input, aims to, under a plasma discharge, oxidize the carbon deposit trapped in the catalyst by combining the use of a non-thermal plasma and a flow of an oxidizing gas. The invention therefore aims to efficiently generate, under a plasma discharge and without heat energy input, active species able to oxidize the carbon (especially in the form of coke) trapped in the deactivated catalyst including when the coke is located in the microporosity of the material.

Furthermore, the invention solves the problem associated with the use of heat treatments both expensive, of high inertia and often responsible for the irreversible deterioration of physico-chemical properties of the catalysts. The advantages of the process compared to existing systems are: ease of implementation, no start-up (on / off system), no heating, reduced consumption of catalysts (process consumables), efficiency in terms of operating time treatment, a few minutes.

SUMMARY OF THE INVENTION

 This objective is achieved by a first method of decontaminating a catalyst contaminated with carbon, characterized in that it is implemented at ambient temperature and in that it comprises the following steps:

 a) providing a reactor comprising at least two electrodes spaced apart from each other between which is placed a dielectric material; b) placing said contaminated catalyst on the surface of said dielectric material, the electrodes being asymmetrical so as to have a tip-plane configuration;

 c) circulating an oxidizing gas between said electrodes, said gas comprising dioxygen; and

d) applying an electric field between said electrodes so as to ionize said oxidizing gas and to form radicals and / or ionized molecules and / or metastable molecules adapted to react with the carbon of said catalyst, said electric field inducing the deposition of a minimum power of 8 W on said dielectric material.

Thus, this solution achieves the aforementioned objective. In particular, there is a reactor configured to have a dielectric barrier discharge configuration (commonly referred to as DBD). Such a discharge is obtained by means of the dielectric material placed between the two electrodes. The discharge is initiated by a strong potential difference between the electrodes inducing the formation of an intense electric field. The accumulation of charges on the surface of the dielectric barrier causes a potential drop between the two electrodes and does not allow passage to the arc. The accelerated electrons will then collide with the molecules of the oxidizing gas comprising oxygen and lead to the formation of radicals, ionized and metastable molecules adapted to react with the carbon contaminating the catalyst. It should be noted that the discharge is obtained by applying an intense electric field inducing the deposition of a minimum power of 8 W on said dielectric material and causing the acceleration of electrons, they collide with the species present in the gaseous medium. Thus while the temperature of the electrons is very high (> 1000K), the gaseous medium undergoes a significant increase in temperature after ionization of the gas, in other words after application of the discharge. The temperature of the electrons is then very high, especially higher than that of the heavy particles such as neutrons and ions. Thus, after discharge, a non-equilibrium plasma is produced. The energy of the electrons is thus not transmitted to the molecules in the form of kinetic energy, but only generates radicals and / or ionized molecules and / or metastable molecules adapted to react with the carbon of said catalyst. It should be noted that the non-thermal plasma is defined by a low electron density, generally less than 10 ¹⁹ nrr ³ , and a gas temperature. equivalent to the temperature of the heavy particles which is of the order of the ambient temperature.

For the purposes of the present invention, by non-thermal plasma is meant an ionized oxidizing gas without heat energy input, the ionization of the gas being effected by means of the intense electric field.

Then, the radicals, ionized and metastable molecules will interact with the carbon trapped in the catalysts and regenerate them. Thus, the removal of carbon in the catalyst is accomplished by oxidation reactions initiated by oxygen activation of the oxidizing gas under the discharge.

Advantageously, in this first method, one of the electrodes has a very small diameter which results in the appearance of a more intense electric field.

Advantageously, in this first method, the electrodes may have a diameter of between 0.5 mm and 1.5 mm.

Preferably, in this first method, the voltage applied between the electrodes may be between 10 and 20 kV, preferably between 10 and 18 kV. Below 10 kV, the plasma is not sufficiently stable for the geometry of the reactor used. Preferably, in this first method, the dielectric material may be glass, or quartz, or ceramic.

Advantageously, in this first method, the oxidizing gas may be a mixture of gases comprising oxygen and helium. Such a gas mixture has the advantage of increasing the efficiency of the oxidation of the carbon trapped in the catalysts with respect to the oxidizing impact of a gas consisting solely of oxygen and nitrous oxide, for example. This increase in efficiency is explained by the fact that helium is a gas monoatomic defined by a better energy vector than that defining a diatomic gas. It should be noted that for effective oxidation, it is necessary that the gas comprises at least oxygen.

Advantageously, in this first method, the gas mixture may comprise at least 1% oxygen and 10% helium by volume relative to the total volume of said gas mixture.

Advantageously, in this first method, the oxidizing gas can circulate between said electrodes with a volume flow greater than or equal to 200 ml / min. The above-mentioned objective is also achieved by a second method of decontaminating a catalyst contaminated with carbon, characterized in that it is implemented at ambient temperature and in that it comprises the following steps: a) providing a reactor comprising at least two electrodes spaced apart from each other between which is placed a dielectric material, said electrodes having a cylindrical configuration; b) placing said contaminated catalyst on the surface of said dielectric material;

 c) circulating an oxidizing gas between said electrodes, said gas comprising dioxygen; and

 d) applying an electric field between said electrodes so as to ionize said oxidizing gas and to form radicals and / or ionized molecules and / or metastable molecules adapted to react with the carbon of said catalyst, said electric field inducing the deposition of a minimum power of 8 W on said dielectric material.

By cylindrical configuration, within the meaning of the present application, is meant an external metal electrode connected to a high voltage and of cylindrical shape covering a dielectric material also cylindrical and an internal metal electrode connected to the high voltage.

Advantageously, in this second method, the electrodes may have a diameter of between 0.1 mm and 10 mm.

[0031] Advantageously, in this second method, the voltage applied between the electrodes may be between 9 and 20 kV, preferably between 9 and 18 kV.

Advantageously, in this second method, the dielectric material may be glass, quartz, or ceramic.

Advantageously, the oxidizing gas flowing between the electrodes may have a volume flow greater than or equal to 10 ml / min.

Advantageously, in this second method, the catalyst may be a zeolite in the form of grain or extruded.

Advantageously, in these two processes, the catalyst may be a zeolite.

Advantageously, in these two processes, the carbon may be in the form of coke.

For the purposes of the present invention, coke means a set of heavy compounds, or polyaromatic, retained on or in the catalyst and often responsible for the deactivation of the latter.

Moreover, for these two processes, it should be noted that the oxidizing gas comprises dioxygen (1 -100% by volume relative to the total volume of the mixture) and may further comprise one or more gases among the helium (0-99% by volume relative to the total volume of the mixture), argon (0-99% by volume relative to the total volume of the mixture), or else the dinitrogen (0-99% by volume with respect to the volume total of the mixture). The gas oxidant may also include traces of other compounds such as water (from a few ppm to 2.5%), nitrogen oxide (a few ppm), carbon dioxide (a few ppm) and / or ozone (a few ppm).

BRIEF DESCRIPTION OF THE FIGURES

Other features and innovative advantages of the invention will become apparent on reading the following description, provided for information only and by no means limitative, with reference to FIGS. 1 and 2 illustrating barrier-type plasma reactors. dielectric.

EXAMPLES [0040] Equipment

• Dielectric barrier discharge (DBD) type plasma reactor with a plate axis geometry, or plate pin (Figure 1). This reactor used for the oxidation of coke is of the dielectric barrier discharge type (DBD) with a tip-plane configuration.

 · Dielectric barrier discharge (DBD) type plasma reactor with cylindrical geometry (Figure 2). This reactor used for the oxidation of coke is of the dielectric barrier discharge type (DBD) with a cylindrical configuration.

 • Fast pyrolysis reactor (or "flash pyrolysis") type fluid bed for obtaining a zeolite coked from wood, which causes after a few seconds a deposit of material.

 • Thermogravimetric analyzer (ATD, ATG).

 • MALDI-TOF mass spectrometer.

 • Bipolar pulsed plasma generator (A2E technology).

Products

The zeolite used in Examples 1 to 5 is that marketed under the designation H-ZSM5 of MFI type with a molar ratio. If / AI of 40. This zeolite (hereinafter denoted by the letter P) has optionally been modified by post-synthesis desilication treatments in order to create hierarchical zeolites (hereinafter denoted by the letter H) consisting of a mesoporous system connected to the microporous system of the parent zeolite (P).

 The zeolites used in Examples 7, 8 and 9 are, for their part, of the FAU and MOR types with a Si / Al ratio of 10 and 17. The FAU (whose Si / Al ratio is 17) is marketed under the designation of CBV720.

 MFI-type P and H zeolites were coked in a fluidized bed during the pyrolysis of the wood at 773 K. This gives a zeolite comprising coke in a proportion of about 6.5% by weight of the product. total weight of the coked zeolite. Two types of coke are present in each of the coked zeolites, one is soluble in dichloromethane, mainly composed of alkylbenzenes and alkylnaphthalenes, and highly polyaromatic compounds, defined by a molar mass of between 400 and 1000 g / mol. . The other type of coke is insoluble coke and is partially oxygenated and its molar weight may be greater than 1000 g / mol. An average molar mass of coke can be given: Mcoke = 315 g / mol. The coke is located in the micropores of the zeolite, poisoning the acidic Bransted sites.

The zeolites FAU and MOR were coked during the conversion of propene at 450 ° C. The coke of the FAU type CBV720 zeolite is composed of families of pyrene and coronene type molecules.

Thus, in the examples below, the FAU, MOR and MFI type zeolites are in the form of 2 cm ² surface pellets (Example 1 to 6), with a grain diameter of between 0.2 and 0. , 4 mm (Example 7), grain diameter between 0.63 and 0.8 mm (Example 8) and extruded diameter 1 mm and length between 3 and 6 mm (Example 9). It should be noted that the extrudates were synthesized in the following manner. Obtaining a compact paste following the production of the following mixture:

 9 g of CBV720 13.84 ml of distilled water,

 - 6.75 g NaPMA (NaPMA being poly (methacrylic acid, sodium knows),

- 22.5 g Glycerol, and

 104.1 g of Bohemite Disperal 14/2 SASOL.

 The paste is then extruded as spaghetti son, then dried in a vacuum oven at 70 ° C, and calcined in a muffle furnace at 550 ° C for 12 hours with a step of 1 hour to 100 ° C.

[0047] Measures

• The percentage of coke was determined by combustion using a thermogravimetric analyzer: this technique makes it possible to simulate a regeneration of coked zeolite by combustion. It should be noted that regardless of the zeolite, the mass losses and the combustion temperatures are identical ie = 6.5% wt and 550 ° C. These similarities indicate that the combustion mechanisms are the same despite the presence of intracrystalline mesopores in the zeolite H. Better accessibility of oxygen to the coke molecules via the mesopores does not lead to an improvement in the combustion of the coke.

• The measurement of the porous volumes and the residual acidities show that a part of the coke is localized in the microporosity, poisoning a part of the Bransted acid sites; the other part of the coke is strongly retained on the external surface. Hierarchization, the presence of mesopores by various treatments of the zeolite strongly impacts the nature of the coke.

Indeed, the dissolution of the zeolite (MFI, FAU and MOR) with concentrated hydrofluoric acid (51% vol) allows to release the coke. trapped in micropores like the one strongly adsorbed on the outer surface. The coke molecules in the micropores are sterically blocked, in any case (even at high temperature) they can not leave the microporosity. Part of the coke is soluble in dichloromethane, the other insoluble part forms particles that can be recovered by filtration. It is then possible to classify the coke according to its solubility in CH2Cl2. On the non-hierarchical zeolite, purely microporous, the coke is totally insoluble whereas on a hierarchized zeolite (H) 40% of the coke is soluble. Chromatographic analyzes show that this coke is mainly composed of alkylbenzenes, alkylnaphthalenes. These coke molecules are characteristic of the structure of the MFI zeolite; it is important to remember that the formation of coke is done according to a process of shape selectivity.

The insoluble coke can be characterized qualitatively by mass spectrometry with a MALDI-TOF SM type instrument. The value of the molar masses indicates that the insoluble coke is highly oxygenated and relatively "heavy" up to more than 1000 g / mol. Insoluble coke consists of oxygenated and non-oxygenated molecules. From the mass distribution of the insoluble coke and the composition of the soluble coke, it is possible to estimate the average molar mass of the coke, they are respectively 346 and 315 g / mol on the zeolites P and on H.

Generation of non-thermal plasma

Using a reactor having a tip-plane configuration (Figure 1 and Examples 1 to 6): For the embodiment of Examples 1 to 6 which follow, the plasma discharge takes place in a plasma reactor type Dielectric barrier discharge (DBD) with a plate-axis geometry, or plate pin (Figure 1). This reactor used for the oxidation of coke is of the dielectric barrier discharge type (DBD) with a tip-plane configuration. In particular, use is made of a dielectric barrier discharge reactor (DBD) capable of completely oxidizing to CO2 a carbonaceous deposit composed of aromatic molecules, or other molecules, of high molecular mass present on the surface or in the microporosity of a catalytic material. The reactor comprises, as indicated in FIG. 1, two electrodes spaced apart from each other between which is placed a dielectric material, the two electrodes being asymmetrical, ie they are positioned perpendicularly one by report to the other. One of these electrodes may be copper, for example, and the other may be platinum. Also, a potential generator between the two electrodes is used and adapted to perform a discharge and thus form a non-thermal plasma.

The coked zeolite is in the form of a pellet in Examples 1 to 6 and is deposited directly in the discharge in the space between the needle electrode and the dielectric material, in particular on this one which is preferably glass. With this configuration of highly dissymmetrical electrodes, the discharge is particularly intense in the center of the pellet and then spreads on its surface.

Thus, this reactor is a reactor generating a specific non-thermal plasma that can test the used catalyst in the form of pellet. With this tip-plane geometry, it is possible to evaluate the local impact of a non-thermal plasma on the coke removal by measuring on different locations of the pellet for example the remaining coke content or the recovered acidity.

The high voltage is applied using a bipolar pulsed plasma generator (A2E technology). Thus, the power deposited in the reactor was measured for different voltages applied between the two terminals of the reactor, under an air flow rate of 100 ml / min. Up to 1 1 kV, the power increases linearly with the voltage, beyond it becomes more important, the electric discharges are stabilized. Unstable plasma It is not capable of destroying formed ozone, whereas for a non-thermal cold plasma the ozone formation and destruction rates are equivalent, therefore the ozone content is zero.

Use of a reactor having a cylindrical configuration (FIG. 2 and examples 7 to 9):

The coked zeolite is in the form of grains or extruded in Examples 7 to 9 and is deposited directly into the discharge volume located in the space between the needle electrode and the dielectric material, which is preferably glass. In particular, for Examples 7 to 9, a dielectric barrier discharge (DBD) reactor such as that illustrated in FIG. 2 is used. This reactor is a DBD plasma reactor of cylindrical type and makes it possible to treat catalysts. in the form of grains or extrusions. This reactor makes it possible to regenerate several grams or even tens of grams of zeolite coked catalysts.

Data concerning the use of the two reactors according to FIGS. 1 and 2:

As certain coke molecules trapped inside the zeolite can lead by spontaneous ionization to the formation of radicals, especially ionized and / or metastable molecules, it is possible to use 3D spectroscopy by electron paramagnetic resonance (commonly designated by EPR spectroscopy) to map their concentrations and thus quantify the spatial efficiency of the non-thermal plasma, generated by one of the two reactors, on the elimination of coke. The heating of the pellet, extruded or powder, caused by the electronic avalanche was measured using a laser pyrometer in several places; the temperature rise does not exceed 100 ° C, much lower temperature than the burning of coke (550 ° C). The maximum temperature measured in these insulated DBD reactors in a planar or cylindrical tip configuration is only 200 ° C.

It should be noted that according to currently used methods, the combustion of coke can be obtained at a temperature above 550 ° C.

However, according to the invention, the coke is partially removed, about 40% of the coke initially present, at room temperature after 30 minutes of treatment with a non-thermal plasma under a flow of oxidizing gas comprising dioxygen, such as air, with a power output of only 8 W. The temperature measured inside the reactor generating a non-thermal plasma is less than 373 K, which excludes a removal of coke by a thermal effect.

Quantification of decontamination

From mass losses measured by gravimetric analysis, it is possible to calculate an efficiency in coke removal:

_ (% Coke ₀ -% Coke _t )

^ ~% Coke ₀ with 0 and t percentages of initial coke and after a treatment time t. The influence of the treatment time was carried out on the coked zeolite H under an air flow rate of 100 ml / min. η increases linearly with time to reach a plateau at 0.3 after 30 minutes of treatment. The removal of coke by a cold plasma is a rather local phenomenon. The removal of the center of the pellet, for example, carried out using a 9 mm diameter punch (ie 0.64 cm 2) indicates that the loss of mass in this zone is greater than that obtained on the entire pellet (2 cm ² ). The elimination of coke is therefore a local phenomenon: the yield (η) is more efficient and faster in the center than on the whole, but remains limited to 50%.

Taking into account the relative areas of the two zones: center and periphery and yields (η) obtained on the whole and in the center of the pellet, it is then possible to deduce the efficiency of the elimination of coke located on its periphery (equation 1):

The estimates show that the coke located at the periphery begins to be eliminated from 30 minutes. It would appear that the plasma is able to eliminate a portion of the coke located in the center and that this elimination tends to propagate from the center to the outside of the pellet.

In particular, it should be emphasized that under an oxidizing gas comprising, for example, a mixture of helium and oxygen, the zeolite is completely regenerated, that is to say that all the acidic sites of Br0nsted and the microporous volume are recovered. Cool plasma treatment at room temperature with only 8 W of power for 30 minutes (maximum) of a zeolite deactivated by a heavy coke is as effective as a conventional thermal combustion process requiring a temperature above 550 ° C and for more than 30 min. The fact of being able to completely regenerate the zeolite shows that the non-thermal plasma or rather the metastable species are able to diffuse into the micropores. The zeolite can be considered, like the cold plasma, as an ionic medium in which the radicals can be stabilized. Indeed, it is known that aromatic molecules, such as coke, trapped in the micropores can spontaneously ionize, and the radicals that result have a relatively long life of several days or months. A complete regeneration of the zeolite is therefore performed at room temperature with low energy consumption. Moreover, based on the EPR analysis, it can be said that the active species generated by the non-thermal plasma are able to diffuse inside the micropores of the zeolite.

Example 1

 Characterization of coke trapped in a microporous and hierarchized MFI-type zeolite in the form of a pellet according to a first method of decontamination using a thermal plasma (comparative example):

The amount of coke formed during flash wood pyrolysis, and determined by thermogravimetric analysis, is 6.5% by weight of the total weight of the zeolite. This coke is almost completely removed under a flow of oxidizing gas comprising oxygen, for example air, at a temperature above 550 ° C, which corresponds to a typical temperature for the regeneration of this type of spent catalyst.

The residual pore volumes and the remaining acid sites are shown in Table 1, they show that a portion of the coke is located in the micropores, poisoning the Br0nsted acid sites. Only the volume of the micropores is affected by the coke deposition.

Table 1: Characterization of microporous and hierarchical MFI zeolites P and H

measured by ATD / ATG,

b soluble and insoluble coke determined by digestion of the zeolite in HF- ^c micropore volume and external surface obtained by using the method of tracing in t, ^d volume mesopore = Vtotal-Vmicro (Vtotal determined from the adsorbed volume at p / pO = 0.99),

e Specific surface area measured by BET;

f ^{, g} measured by the pyridine adsorbed on the acid sites of Br0nsted and Lewis after evacuation at 150 ^° C.

Example 2

 Treatment, according to the invention, in a flow of air, by non-thermal plasma microporous and hierarchized MFI type zeolites contaminated with coke in the form of pellet: observation of the influence of the treatment time.

The treatment was carried out in the reactor shown in Figure 1 while the oxidizing gas was air. The coked zeolite in pellet form is placed under the discharge zone. The deposited power was maintained at 8 W, the air flow was 100 ml. min ^-1 . The efficiency (η) is calculated from the quantity of coke removed, it corresponds to: η = (% of coke before treatment -% of coke after treatment) ^* 100% of coke before treatment The maximum efficiency is then equal to 30%. Example 3

 Treatment according to the invention by non-thermal plasma of microporous and hierarchized MFI type zeolites coked in the form of an air pellet: influence of flow rates and deposited power.

The effectiveness of the removal of coke depends on the deposited power (P) and the air flow used. When the non-thermal plasma is unstable (P <8 W), the percentage of coke removed is low, it decreases very slightly with the flow rate. While with stabilized non-thermal plasma (P> 8 W), the elimination of coke is favored and increases with the power deposited. Increasing the airflow improves efficiency. This assumes that high throughput promotes the propagation of the active species generated by the plasma both on the platelet surface and in the micropores of the zeolite.

It should also be noted that an increase in the deposited power improves the efficiency but may remain incomplete. The oxidation of the coke begins with the formation of carboxylic acids (quantified by IR) which are decomposed into carbon oxides with a CO 2 / CO ratio of 2. [0074] The mapping of the radicals carried out by 3D EPR spectroscopy shows that the Coke removal occurs first at the center of the wafer, then a propagation of energetic species continues leading to the elimination of coke at its periphery.

The removal of coke in the zeolite is carried out through oxidation reactions initiated by activation of oxygen dioxygen in the plasma discharge. Also the influence of the air flow on the efficiency of the treatment has been studied and shows that an increase of the flow results in the elimination of a larger quantity of coke: of 38% for a flow of 50 ml / min to more than 60% for 300 ml / min with a power of 16 W. It is then found that the best efficiencies are obtained at high flow and high powers. For example, for a 12 W power, at a low flow rate, the coke is mainly removed in the center of the pellet, near the tip, whereas when the flow is greater than or equal to 200 ml / min, the coke located at the periphery is also oxidized the periphery. These results unambiguously show that the velocity of the gas flow considerably influences the propagation of the discharge on the surface of the pellet. When the airflow is large the discharge becomes more efficient at its periphery, presumably because the active species generated near the tip are quickly transferred there.

Example 4

 Treatment according to the invention by non-thermal plasma of the MFI zeolite coked in pellet form and in different gas mixtures

The treatment was carried out in the reactor shown in FIG. 1. The coked zeolite in pellet form is placed under the discharge zone. The deposited power was maintained at 8 W for 30 minutes, the gas flow was 100 mL.min ¹ . The removal of the coke in the zeolite is particularly effective using a mixture of helium and O 2, as can be seen in Table 2 below. In particular, 90% of the coke is removed. Moreover, it can also be noted that in this configuration, and with a mixture of oxygen and dinitrogen, partial decontamination is obtained. However, by inducing a power greater than 8 W, one also obtains a complete decontamination. This table 2 also highlights the results of the impact of the composition of the gas after 30 minutes.

Table 2: Impact of gas composition after 30 minutes Gas composition 20% 0 ₂ 20% O ₂ - 10% O ₂

80% N ₂ 100% He 80% He 90% He

 Power (W) 8 8 8 8

 Coke removal (%) 34 24 90 87

Example 5

 Evidence of the efficiency of non-thermal plasma treatment and comparison with processes using ozone.

Under the plasma discharge, it is known that ozone, a high oxidizing agent, is formed by reaction between free-radical oxygen species and dioxygen. In some applications, ozone is used as an oxidizer to effect complete oxidation of organic compounds. However, it should be noted that it is possible to remove a portion of the coke from a zeolite using ozone at a temperature of 250 ° C. According to the invention, no external heat is used, but it is important to verify that ozone is not responsible for the removal of coke in the zeolite under plasma discharge. A test was carried out in which the coked zeolite in tablet form was exposed to ozone with a concentration of 200 ppm. The results show that no carbon removal occurs, therefore, it is the plasma discharge and the species generated under discharge that are responsible for the removal of coke and not ozone.

Example 6

 Proof of the complete regeneration of the zeolite in pellet form under non-thermal plasma treatment according to the invention.

According to the processes of the invention, it is possible to use as oxidizing gas a gaseous mixture comprising dinitrogen and oxygen, or else argon and dioxygen. However, the substitution of dinium or argon by helium allows with a maintained power at 8 W, a almost complete regeneration (η ^" 100%). Thus, all coke-poisoned Brnsted acid sites are recovered after only ten minutes of treatment. In addition, the oxidation of coke is almost completely selective in CO2. The active species responsible for the regeneration of the catalyst are the short-lived species (0 ₂ ⁺ 0, 0 ₂ ^~ ), the role of the noble gas (He) being to improve the efficiency of the production of carbon atoms. oxygen (O).

In particular, by using, as an oxidizing gas, a mixture of gases comprising helium and oxygen, and applying a power close to 8 W, it is found that there is almost complete regeneration of the catalyst. Indeed, with 10 or 20% of O2 in He, η reaches 100%, all poisoned Bransted acid sites are recovered after only 10 minutes of treatment, when 8 W of power is applied. In addition, the combustion of coke at room temperature by a non-thermal plasma with a mixture of He-O2 is almost completely selective for CO2 and the carbon balance is almost total (> 95%). It is even noted that the coked zeolitic material, generally characterized by a black color, recovers its original white color after plasma treatment, which proves the effectiveness of plasma treatment at room temperature. The results of the characterization of the coked and regenerated zeolite are presented in Table 3 below.

Table 3: characterization of the initial zeolite, coked and regenerated following the application of non-thermal plasma (He / 02, P = 8 W).

 measured by ATD / ATG,

b soluble and insoluble coke determined by digestion of the zeolite with HF- ^{f, g} measured by the pyridine adsorbed on the acid sites of Br0nsted and Lewis after evacuation at 150 ^° C.

EXAMPLE 7 Decontamination of MOR and FAU type zeolites according to the invention in the form of a grain having a diameter of between 0.2 and 0.4 mm

 In this configuration according to the invention, the type of catalyst that is available in the plasma reactor of the dielectric barrier discharge type of cylindrical geometry (Figure 2) is a FAU or MOR type catalyst. This catalyst is in the form of grain whose diameter is between 0.2 and 0.4 mm. The mass content of coke is greater than 15% on the FAU zeolite and 8% on the MOR zeolite.

The decontamination process is carried out for a period of 1 h20 and the oxidizing gas is a gas mixture comprising at least oxygen and helium. The oxygen is introduced into the reactor with a flow rate of 40 mL / min and the helium is introduced meanwhile with a flow rate of 160 mL / min to thereby create a mixture of oxidizing gas in the reactor.

The voltage applied between the two electrodes is approximately equal to 9.5 kV at a frequency of about 2000 Hz, which induces a reactor power of about 14 W.

In this configuration, there is obtained a fully decontaminated catalyst, that is to say that the percentage of carbon removal initially included in this powder is close to 100% regardless of the type of zeolite. The grains before decontamination were black, and after white decontamination. EXAMPLE 8 Decontamination of an FAU Type Zeolite According to the Invention Presenting in the Form of a Grain Between 0.63 and 0.8 mm

In this configuration according to the invention, the type of catalyst that is available in the plasma reactor of the dielectric barrier discharge type of cylindrical geometry (Figure 2) is a FAU type catalyst. This catalyst is in the form of grain between 0.63 and 0.8mm. The mass content of coke is greater than 15%

The decontamination process is carried out for a period of 2 hours and the oxidizing gas is a gas mixture comprising at least dioxygen and helium. The oxygen is introduced into the reactor with a flow rate of 40 mL / min and the helium is introduced meanwhile with a flow rate of 160 mL / min to thereby create a mixture of oxidizing gas in the reactor.

The voltage applied between the two electrodes is approximately equal to 9.5 kV at a frequency of about 2000 Hz, which induces a power in the reactor of approximately 10 W.

In this configuration, a completely decontaminated catalyst is obtained, that is to say that the carbon removal percentage initially included in the FAU type zeolite is close to 100%. The grains before decontamination were black, and after white decontamination.

EXAMPLE 9 Decontamination of an FAU Type Zeolite According to the Invention in the Form of Extrusions (1 mm Diameter and 3 to 6 mm Length) [0089] In this configuration according to the invention, the FAU type catalyst with 15% coke in extruded form (1 mm diameter and length of 3 to 6 mm) is arranged in the dielectric barrier type plasma reactor of cylindrical geometry (FIG 2).

The decontamination process is carried out for a period of 2 hours and the oxidizing gas is a gas mixture comprising at least oxygen and helium. The oxygen is introduced into the reactor with a flow rate of 40 mL / min and the helium is introduced meanwhile with a flow rate of 160 mL / min to thereby create a mixture of oxidizing gas in the reactor.

The voltage applied between the two electrodes is approximately equal to 9.5 kV at a frequency of about 2000 Hz, which induces a power on the glass (dielectric material) approximately equal to 16.79 W.

In this configuration, a completely decontaminated catalyst is obtained, that is to say that the percentage of carbon removal initially included in these extrudates is close to 100%. The extrudates before decontamination were black, and after decontamination are white.

Claims

1. Process for the decontamination of a catalyst contaminated with carbon, characterized in that it is carried out at ambient temperature and in that it comprises the following steps:

 a) providing a reactor comprising at least two electrodes spaced apart from each other between which is placed a dielectric material, said electrodes being asymmetrical so as to have a tip-plane configuration;

 b) placing said contaminated catalyst on the surface of said dielectric material;

 c) circulating an oxidizing gas between said electrodes, said gas comprising dioxygen; and

 d) applying an electric field between said electrodes so as to ionize said oxidizing gas and to form radicals and / or ionized molecules and / or metastable molecules adapted to react with the carbon of said catalyst, said electric field inducing the deposition of a minimum power of 8 W on said dielectric material.

2. The method of claim 1, wherein said electrodes have a diameter of between 0.5 mm and 1.5 mm.

3. Method according to claims 1 or 2, wherein the voltage applied between said electrodes is between 10 and 20 kV, preferably between 10 and 18 kV.

The method of claim 1, wherein said dielectric material is glass, quartz, or ceramic.

The process of any one of claims 1 to 4, wherein said oxidizing gas is a gas mixture comprising oxygen and helium.

The method of claim 5, wherein said gas mixture comprises at least 1% oxygen and 10% helium volume relative to the total volume of said gas mixture.

7. Process according to any one of claims 1 to 6, wherein said oxidizing gas flows between said electrodes with a flow rate greater than or equal to 200 ml / min.

The process of claim 1, wherein said catalyst is a zeolite.

The process of claim 1, wherein said carbon is in the form of coke.

10. A method for decontaminating a catalyst contaminated with carbon, characterized in that it is carried out at room temperature and in that it comprises the following steps:

 a) providing a reactor comprising at least two electrodes spaced apart from each other between which is placed a dielectric material, said electrodes having a cylindrical configuration;

 b) placing said contaminated catalyst on the surface of said dielectric material;

 c) circulating an oxidizing gas between said electrodes, said gas comprising dioxygen;

d) applying an electric field between said electrodes so as to ionize said oxidizing gas and to form radicals and / or ionized molecules and / or metastable molecules adapted to react with the carbon of said catalyst, said electric field inducing the deposition of a minimum power of 8 W on said dielectric material.

1 1. The method of claim 10, wherein said electrodes have a diameter of between 0.1 mm and 10 mm.

12. The method of claim 10 or 11, wherein the voltage applied between said electrodes is between 9 and 20 kV, preferably between 9 and 18 kV.

The method of claim 10, wherein said dielectric material is glass, quartz, or ceramic.

14. A method according to any one of claims 10 to 13, wherein said oxidizing gas flows between said electrodes with a flow rate greater than or equal to 10 ml / min.

The process of any one of claims 10 to 14, wherein said catalyst is a zeolite in the form of a grain or an extrudate.