FR3137311A1 - Process for treating a catalyst comprising a zeolite - Google Patents

Abstract

The present invention relates to a process for preparing a catalyst comprising at least one aluminosilicate type zeolite of the ZSM-5 family, a binder comprising silicon oxide and/or aluminum oxide, said treatment comprising : - (i) a mixture of the zeolite in powder form, the binder and/or the precursor of the binder, and optionally the additive, then - (ii) shaping said mixture into catalyst particles, characterized in which said treatment also includes - (iii) a steam treatment, said steam treatment operating - either on the catalyst in the form of particles, - or on the zeolite in powder form before mixing (i), said steam treatment comprising bringing said particles into contact of catalyst or said zeolite powder with a flow of steam treatment gas comprising water vapor, at a temperature of at least 400°C and a pressure of at least 106 Pa.

Description

Process for treating a catalyst comprising a zeolite

The present invention relates to a new method for treating a material comprising a ZSM-5 type zeolite. This material advantageously finds applications as a catalyst, as a catalyst support, but also as an adsorbent or separation agent. The invention will focus more particularly on an application of this material as a catalyst.

Crystallized microporous materials, such as zeolites, are solids widely used in the oil industry as catalysts, particularly for heterogeneous catalysis of isomerization, cracking or alkylation of hydrocarbons, or for the conversion of olefins, from ethylene to propylene for example. But this type of material can also be used as a catalyst support: by adding an active element, such as copper for example, an oxidation catalyst is obtained, in particular of ethanol to acetaldehyde, copper can be combined with other elements such as chromium. This type of material can also be used to convert alcohols into gasoline.

For high-temperature catalytic oligomerization-cracking reactions in the absence of hydrogen, ZSM-5 zeolite (MFI structural type) is one of the most studied active phases because it has multiple advantages. The confinement of reactants and products in the medium-pore microporous network of ZSM-5 (10-atom tetrahedral openings) is conducive to the desired reactions while ensuring the diffusion of products to the outside of the pores. The Si/Al ratio that dictates the quantity of acid sites can be modulated by the zeolite synthesis protocol over a wide range (from 15 to 400 mol./mol.). This medium-pore-opening zeolite with a three-dimensional porous network is much less sensitive to coking than more open zeolites (e.g., Y and Beta zeolites of structural type FAU and BEA respectively) or one-dimensional closed zeolites (e.g., ZSM-22 of structural type TON). The synthesis of the zeolite also presents a moderate cost acceptable for industrial application. The refining and petrochemical industry is always looking for zeolite catalysts that have improved properties, particularly with regard to the conversion of hydrocarbon species depending on the application (yield and/or selectivity of the catalyzed reactions), and/or with regard to their stability over time, their mechanical resistance, etc. Patent US-4,663,492 discloses a catalyst based on ZSM-5 zeolite in the context of a process for converting methanol into gasoline, this catalyst being previously treated with steam at atmospheric pressure to increase its activity with regard to this conversion, this treatment being followed or preceded by calcination.

Also known from US patent No. 8,759,598 is a zeolite-based catalyst, in particular of the CHA zeolite type, in the context of a process for converting ethylene into propylene. This document recommends reducing the number of acid sites of the zeolite found specifically on the surface of the material. To do this, it proposes several methods, including surface silylation, steam treatment or treatment with a dicarboxylic acid.

Patent EP-3 428 249 also discloses a process for converting ethylene from a cut originating from the fractionation of an effluent from a catalytic cracking unit into propylene, aromatics and other products of interest: this conversion process is carried out in a conversion unit using a zeolite-based catalyst operating at a temperature of between 500 and 650°C and under a partial olefin pressure of between 1 and 2 bars. This catalyst comprises, for example, a ZSM-5 zeolite in a silica-type matrix. The invention then aims to improve the performance of catalysts comprising a ZSM-5 type zeolite, more particularly targeting the conversion of ethylene or ethanol into propylene, other short olefins and other products of interest, and this without calling into question or overly complicating their method of preparation.

In the context of the present invention, the olefins produced can be used for all applications using short olefins: monomers or polymers (Polyethylene, Polypropylene, Polyesters) for plastics after separation of each, or, alone or in a mixture, charges for processes capable of producing fuel (aviation fuel, known as "jet", gasoline, distillate).

The invention firstly relates to a process for preparing a catalyst comprising at least one aluminosilicate zeolite of the ZSM-5 family, a binder comprising silicon oxide and/or aluminium oxide, and optionally at least one additive, said process comprising: - (i) a mixture of the zeolite in powder form, the binder and/or a precursor of the binder, then - (ii) shaping said mixture into catalyst particles. Said process also comprises (iii) a steam treatment, said steam treatment operating
- either on the catalyst in the form of particles, (after shaping (ii) therefore)
- either on the zeolite in powder form before mixing (i),
said (iii) steam treatment comprising bringing said catalyst particles or said zeolite powder into contact with a steam treatment gas flow comprising water vapor, at a temperature of at least 400°C and a pressure of at least 10 ⁶ Pa.

In the context of the present invention, the term “silica” or “silicon oxide” also means silicon oxide, optionally in hydrated form. This may be the case in particular when the steam treatment is carried out on the solid in the form of particles, for example by kneading-extrusion in the case of extrudates, and just dried after shaping. Similarly, in the context of the present invention, the term “alumina” or “aluminum oxide” also means aluminum oxide, optionally in hydrated form.

Whether they are (shaped) catalyst particles or zeolite powder, they can be arranged in a bed of a given thickness, which the vapor treatment gas will be led to cross.

The catalyst “particles” may be in different forms depending on the chosen shaping: they may be grains, beads, extrudates, of various and more or less regular shapes. The term “particles” in the context of the invention generically encompasses all possible forms conventionally known for this type of catalyst.

The term “powder” relating to zeolite should be understood in its usual sense; this powder has, for example, a particle size between 2 and 100 µm.

The term “precursor” of a binder is well known in the field of catalysts; it designates the compound which, once mixed and treated, in particular thermally, will become the binder. In the context of the invention, the binder is therefore a silicon and/or aluminum oxide, which can be mixed as is with the zeolite, or which can be introduced in the form of a compound, for example organic, which will be transformed into oxide in the final catalyst.

The term "bed" is understood in its conventional sense in the field of catalysts (catalytic bed): it is an arrangement in layer(s) of catalyst particles, supported by conventional mechanical means (metal grids, etc.) allowing the passage of a gaseous or liquid flow through its thickness. We are therefore considering here a fixed bed type bed, where the particles are not in motion, not stirred in the reaction medium defined by the reactor concerned.

It should be noted that the preparation process of the invention may provide for other steps, before the first step (i) or after the last (ii) or (iii) or between two steps. Thus, between the mixing (i) and the shaping (ii), one or more steps may be intercalated, for example a treatment with a basic solution (ammonia solution) and/or a treatment with an acid solution. The mixing may also be carried out with the addition of an acid, such as nitric acid.

It has been shown in the context of this invention that, for this type of catalyst combining a ZSM-5 zeolite and a silicic and/or aluminic binder, steam treatment at both high temperature and high pressure gave very interesting results, whether the steam treatment was carried out on the catalyst or on the zeolite before its incorporation into the catalyst: the treated catalyst makes it possible to achieve higher conversion rates and/or yields of propylene and aromatic compounds in the case of the catalysis of the reaction for converting ethylene into propylene, as well as higher stability of the conversion and/or yields.

In the case of ethanol conversion, the catalyst treated according to the invention makes it possible to achieve higher conversion rates and propylene yields, as well as higher stability of the conversion and/or yields. It was also found that the mechanical properties of the catalyst were not altered by this steam treatment.

Preferably, the temperature at which the steam treatment is carried out is between 400 and 600°C, in particular between 450 and 600°C, for example between 500 and 560°C. (This is the temperature reached by the catalyst particles or the zeolite powder, generally due to contact with the steam treatment gas flow having this temperature.

Preferably, the duration of the vapotreatment is at most 5 hours, in particular at most 3 hours, in particular at most 2 hours, preferably between 45 minutes and 2 hours or between 1 hour and 1 hour 30. It is therefore a duration which can be quite short, and therefore not too costly in terms of catalyst preparation time.

Preferably, the pressure at which the steam treatment is carried out is between 10 ⁶ Pa and 3.10 ⁶ Pa, in particular between 1.5.10 ⁶ Pa and 2.5.10 ⁶ Pa. This pressure is understood as that of the enclosure in which the catalyst particles or the zeolite powder are arranged to carry out this steam treatment. As will be mentioned later, this enclosure may be a chemical reactor, in particular a hydrocarbon conversion reactor which uses the catalyst in question, which may be equipped with a pressure regulator arranged downstream of the particles/powder to be treated in the reactor (downstream and upstream being understood according to the overall direction of the gas flow passing through them).

Preferably, the flow rate of the vapor treatment gas stream at the reactor inlet is between 0.01 and 3 NL per hour and per gram of catalyst, in particular between 0.01 and 2 NL per hour and per gram of catalyst.

Advantageously, the vapor treatment gas flow may contain a mixture of gases comprising water vapor and at least one or more gases, chosen from N ₂ , CO ₂ , Ar, He, CH ₄ , air or any mixture thereof, preferably air or nitrogen. The volume proportion of water vapor in the vapor treatment gas is advantageously between 30 and 100%, in particular between 40 and 90%, preferably between 50 and 80%.

The water vapour content in the vapour treatment gas can be constant or change for at least part of the vapour treatment. Choosing a constant water content is the simplest solution. Changing it, in particular increasing it gradually or in stages, can also be interesting. Similarly, the pressure and temperature during vapour treatment can be constant or vary, with gradual increases or by one or more stages in temperature or pressure in particular.

According to a first variant, the binder is a silicon oxide. It can be introduced during the preparation of the catalyst at least partly in the form of colloidal silica and/or in the form of precipitated silica and/or silica gel, preferably both in the form of colloidal silica and in the form of precipitated silica, or both in the form of colloidal silica and in the form of silica gel. Such a binder is particularly inert with respect to the conversion reactions to be catalyzed, much more so than alumina for example, which is advantageous, because it will increase the durability, and this without interfering with the reactions to be catalyzed: this avoids any disturbance, any risk of promoting a reaction leading to unwanted by-products.

According to another variant, the binder is an aluminum oxide. The alumina precursor, used for the preparation of the catalyst according to the invention, is preferably chosen from the group formed by hydrargillite, bayerite, boehmite, amorphous gels, so-called transition aluminas which comprise at least one phase taken from the group comprising the rho, chi, eta, gamma, kappa, theta and alpha phases. Preferably, the alumina precursor is a boehmite.

Preferably, the catalyst comprises between 20 and 80% by weight of zeolite, in particular between 30 and 70% by weight of zeolite, or between 50 and 70% by weight of zeolite, and between 20 and 80% by weight of binder, for example between 30 and 70% by weight of binder, or between 30 and 50% by weight of binder.

For the mixing and shaping of the catalyst, at least one additive can be added, which may in particular have the function of helping to control the viscosity of the mixture before shaping, particularly when this shaping is an extrusion of the mixture in pasty form. In the final catalyst, particularly when it has been cooked/calcined, the additive disappears, particularly when it is made of organic material. It may be, for example, a cellulose derivative, particularly methylcellulose.

The Si/Al atomic ratio of the zeolite contained in the catalyst of the invention is preferably between 12 and 200, in particular between 15 and 180, preferably between 20 and 150. It is for example 25, 40 or 140.

The catalyst may also comprise at least one doping element, for example part of the group consisting of sodium, potassium, magnesium, calcium, phosphorus, copper, silver, manganese, molybdenum. Preferably the doping element is phosphorus, optionally combined with one or more other elements. The content of doping element is preferably such that the atomic ratio of the element to the aluminum contained in the zeolite is less than or equal to 0.8.

The element is introduced by any type of preparation known to those skilled in the art, for example by dry impregnation, by excess impregnation, by chemical vapor deposition or any other type. Concerning the phosphorus element, it can for example be introduced by using one or more precursors of the phosphoric acid or ammonium dihydrogen phosphate or hypophosphorous acid type.

According to a variant, the catalyst according to the invention comprises at least two ZSM-5 zeolites (which have been mixed, for example, in the aforementioned mixing step, or in a prior mixing step), among which at least two have different Si/Al atomic ratios, for example in a mass ratio of 10/90 to 90/10, in particular 20-80 to 80-20, for example between 40-60 and 60-40. Indeed, it appears that the catalytic properties are linked at least in part to the Al site content of the zeolite: combining two zeolites with different Si/Al ratios can make it possible to adjust the overall acidity of the material and thus more easily improve the catalytic properties of the catalyst and the compromise between activity and selectivity.

The shaping of the catalyst into particles can be carried out by any known method, such as, for example, kneading/extrusion, shaping by draining (known by the Anglo-Saxon term "oil-drop"), granulation, compaction, atomization.

In the case where the steam treatment (iii) is carried out on the catalyst in the form of particles, (once the catalyst has been shaped) said steam treatment (iii) of the catalyst may be preceded by drying (on the shaped catalyst therefore), in particular at a temperature of at least 60°C, and preferably at most 150°C, in particular between 60 and 100°C, preferably in the region of 80°C. It has been found that simple drying before the steam treatment was sufficient, and that calcination was not necessary, either before or after the steam treatment: by implementing the steam treatment step of the invention, it is therefore possible, surprisingly, to dispense with calcination of the catalyst. A calcination step is thus replaced by a steam treatment step in the process for preparing the catalyst, which thus avoids extending the preparation time of the catalyst and complicating this preparation process.

In a first embodiment, the steam treatment of the catalyst can be carried out in the form of a catalytic bed of catalyst particles which is arranged in a hydrocarbon catalytic conversion reactor. This is referred to as “in situ” steam treatment, since the catalytic bed which is steam treated is already in the reactor in its functional position to carry out the catalysis by contacting with a hydrocarbon feedstock flow and/or a flow intended to react with a feedstock flow, such as hydrogen for example: the bed is thus first crossed by the steam treatment gas flow, then by the hydrocarbon feedstock/reagent flow. This is an interesting implementation, since it limits handling and intermediate storage of catalyst, it avoids the use of a dedicated vapor treatment device, and because the hydrocarbon conversion reactor is generally already equipped with all the appropriate means to implement the invention (gas injection and evacuation means, means to heat the enclosure/gas flows, and pressurization means, means to regulate these operating conditions in particular using sensors equipping the reactor, etc.)

In a second embodiment, the steam treatment of the shaped catalyst or the steam treatment of the zeolite powder is carried out in a dedicated enclosure, different from that of the conversion reactor where the catalyst will ultimately be placed. This is called “ex-situ” steam treatment. This enclosure may be installed near the hydrocarbon feedstock conversion reactor, or be located on the catalyst production site. This variant is also interesting in that it allows the catalyst to be treated without using the hydrocarbon conversion reactor.

The invention also relates to a device for implementing the method described above, and which comprises a reactor for the catalytic conversion of hydrocarbons in which is arranged a catalytic bed of catalyst particles comprising at least one aluminosilicate zeolite of the ZSM-5 family, a binder comprising silicon oxide and/or aluminum oxide, the reactor comprising means for injecting and evacuating steam treatment gas comprising water vapor. As mentioned above, this is an “in-situ” implementation of the invention, where the flow of steam treatment gas will pass through the catalytic bed as will the hydrocarbon feedstock and/or a flow of reagent to be subsequently converted.

The invention also relates to the catalyst obtained by the treatment method or the treatment device described above, and in which the majority of the Al sites, in particular at least 60 or 70 or 75% or 80% of the Al sites, of the ZSM-5 zeolite is in the form of Al with oxidation state IV. This type of aluminum is conventionally characterized by MAS NMR of aluminum ²⁷ Al.

Advantageously, at most 30%, in particular at most 20% or at most 15% of the Al sites of the ZSM-5 zeolite are in the form of Al of oxidation state VI.

It is known to those skilled in the art that the Al sites are in state IV when they are integrated into the framework of the zeolite. It has been found that the steam treatment step of the process according to the invention could influence/modify the degree of oxidation of a portion of the aluminum in the zeolite. Said steam treatment would lead to extracting a certain proportion of these Al sites from this framework, which changes their degree of oxidation, and which has proven to be beneficial, unexpectedly, for the properties of the catalyst. One explanation put forward would be that this extraction leads to a reduction in the strongest acidity of the zeolite, leading, in particular, to a lesser tendency for the catalyst to cok and to better stability thereof.

The invention also relates to a process for converting a feedstock comprising ethylene or ethanol into propylene, other short olefins and gasoline or aromatic compounds, which uses a catalyst as treated and/or described above, with contacting of said feedstock with said catalyst.

Please note that it is preferable, before starting the catalytic conversion process, to activate the catalyst in the form of a particle bed, this activation being able to take the form of a heat treatment such as drying at high temperature in air, and/or calcination aimed at burning any traces of oil or grease that may be present.

The operating conditions of the ethylene conversion process are for example described in patent EP-3 428 249, to which reference may be made for more details and which can be summarized as follows: a unit for converting ethylene into propylene and other products of interest is used, which is a catalytic unit using a zeolite-based catalyst operating at a temperature of between 500°C and 650°C, and under a partial pressure of olefins of between 1 and 2 bars, with an hourly weight rate (weight of feedstock per weight of catalyst and per hour) of between 0.1 and 10 h ^-1 , preferably of between 1 and 7 h ^-1 , and advantageously of between 2 and 6 h ^-1 .

In the case where the reaction charge is ethanol, the latter is first dehydrated into ethylene, which is transformed, under the same operating conditions as those of dehydration and on the same catalyst, in the presence of water released by the dehydration reaction, into oligomers, that is to say into light C3-C6 olefins. The operating conditions of the ethanol conversion process are for example described in patent FR-2 948 937, to which reference will be made for more details and which can be summarized as follows: for example a temperature of between 300 and 600°C, preferably of between 450 and 575°C, under a pressure of between 0.1 and 1.5 MPa, preferably of between 0.1 and 0.5 MPa, with an hourly weight rate (weight of charge per weight of catalyst and per hour) of between 0.1 and 10 h ^-1 , preferably of between 1 and 4 h ^-1 .

The invention relates to a catalyst comprising at least one zeolite or aluminosilicate of the ZSM-5 family and a binder comprising silicon oxide and/or aluminum.

It is implemented in the following examples using different catalysts with the following formulations:

Catalyst A
It comes in the form of extrudates (cylinders with a diameter of 1.4 mm, a length of between 2 and 6 mm) containing 60% by weight of ZSM-5 zeolite with an Si/Al atomic ratio of 140 (commercially available from the company Zeolyst, under the commercial reference CBV28014) and 40% of silicon oxide-based binder obtained from precipitated silica powder, available under the commercial name NYASIL ^TM 20 marketed by the company Nyacol Nano Technology) and which is an amorphous silica powder structured on a nanometric scale.
The preparation of the catalyst from the zeolite and the silica source was carried out with a shaping additive, here a cellulose derivative: METHOCEL ^TM , in a proportion of 4% by weight relative to the total dry solid, available from the DuPont company, and which is a polymer derived from cellulose and soluble in water.

The zeolite, silica source, additive and water were mixed and kneaded. When the paste exhibited the appropriate rheology, it was extruded through a die.

After forming into an extrudate, and before the steam treatment according to the invention, the catalyst was dried at 80°C in air in an oven for 24 hours.

Catalyst B
It is identical to catalyst A (and prepared in the same way), except that the ZSM-5 zeolite here has an Si/Al atomic ratio equal to 40 (available from the company Zeolyst under the commercial reference CBV8014).

Catalyst C
It is identical to catalyst A (and prepared in the same way), except that the ZSM-5 zeolite here has an Si/Al atomic ratio equal to 25 (available from the company Zeolyst under the commercial reference CBV5524G).

Catalyst D
It comes in the form of extrudates (cylinders with a diameter of 1.4 mm, length between 2 and 6 mm) containing 30% by weight of ZSM-5 zeolite with an Si/Al atomic ratio of 140 (commercially available from the company Zeolyst, under the commercial reference CBV28014) and 70% of aluminium oxide-based binder obtained from boehmite powder available under the commercial name SB3 marketed by the company Sasol.

The preparation of the catalyst from the zeolite and the alumina source was carried out with a shaping additive, here a cellulose derivative: METHOCEL ^TM , in a proportion of 4% by weight relative to the total dry solid, available from the DuPont company, and which is a polymer derived from cellulose and soluble in water.

Zeolite, alumina source, additive, nitric acid peptizing agent, at a rate of 6% by weight relative to alumina, and water were mixed and kneaded for 30 minutes. Then an ammoniacal solution based on NH ₄ OH, with an atomic ratio of base to acid of 40% was added. When the paste exhibited the appropriate rheology, it was extruded through a die.

After forming into an extrudate, and before the steam treatment according to the invention, the catalyst was dried at 120°C in air in an oven for 24 hours.

Catalyst E
It comes in the form of ZSM-5 zeolite powder with an Si/Al atomic ratio of 140 (commercially available from the company Zeolyst, under the commercial reference CBV28014).

Catalyst F
It comes in the form of ZSM-5 zeolite powder with an Si/Al atomic ratio of 40 (commercially available from the company Zeolyst, under the commercial reference CBV8014.

Catalyst G
It comes in the form of extrudates (cylinders with a diameter of 1.4 mm, length between 2 and 6 mm) containing 60% by weight of catalyst E in the form of powder steam-treated under pressure and 40% of binder based on silicon oxide obtained from precipitated silica powder available under the trade name NYASILTM20 marketed by the company Nyacol Nano Technology). The shaping of the catalyst is carried out according to the protocol described for catalyst A.

Catalyst H
It comes in the form of extrudates (cylinders with a diameter of 1.4 mm, length between 2 and 6 mm) containing 60% by weight of catalyst F in the form of powder steam-treated under pressure and 40% of binder based on silicon oxide obtained from precipitated silica powder available under the trade name NYASILTM20 marketed by the company Nyacol Nano Technology). The shaping of the catalyst is carried out according to the protocol described for catalyst B.

The invention applies steam treatment to catalysts A to F, preferably without prior calcination (or subsequent calcination before use).

This steam treatment is carried out on the catalyst in the form of particles arranged in a catalytic bed, by passing through said catalytic bed a flow of steam treatment gas comprising water vapor, at a temperature of at least 400°C and a pressure of at least 10 ⁶ Pa, for a duration of at most 3 hours.

To do this, in the case of catalysts A to D, 10 g of catalyst are loaded into a steel tubular reactor so that it can be crossed by a steam treatment fluid, in this case a gas flow containing water vapor and possibly other gases such as air or nitrogen, and to withstand high pressures. The unpacked thickness of the catalyst bed is here 7 cm. This reactor is placed in a heating enclosure. The water is vaporized upstream of the reactor in another tubular reactor (called a "vaporizer") filled with silicon carbide, and the vaporizer-steam treatment reactor junction lines are heated to 220°C. The gas injected at the same time as the water vapor also passes through the vaporizer.
In the case of catalysts E and F, the zeolite powder is pelletized and sieved to retain only the fraction with a particle size between 200 and 500 µm. 6 g of this powder are mixed with 6 g of carborundum (silicon carbide, SiC) with a particle size around 500 µm, and loaded into the same type of reactor as that used for catalysts A to D. The unpacked thickness of the catalyst bed diluted in SiC is 4 cm.

For each steam treatment step according to the invention, a temperature T in °C of the catalytic bed, a pressure P in bar/Pa (in the tubular reactor containing the catalyst), a duration D in hours of treatment, which corresponds to the duration during which the temperature T was reached and maintained (duration of the temperature plateau therefore), a flow rate Q of steam treatment gas passing through the catalytic bed expressed in NL/h/g (standardized liter per hour and per gram of catalyst), and a volume percentage of water vapor in the steam treatment gas comprising a mixture of water vapor and air, are defined.

Examples 1 to 10 according to the invention
Catalysts A, B, C, D, E and F were subjected to steam treatment as mentioned above, according to operating conditions indicated in Table 1 below: No. Example Vapor-treated catalyst Yes/Al
at./at. zeolite State T(°C) D (h) % Water Vol P
(bar) P
(Pa) Q
(NL/h/g) 1 HAS 140 Extruded 500 1 80 16 1.6. 10 ⁶ 1 2 HAS 140 Extruded 500 2 80 11 1.1.10 ⁶ 1 3 HAS 140 Extruded 600 1 30 6 0.6. 10 ⁶ 1 4 HAS 140 Extruded 500 1 100 16 1.6. 10 ⁶ 1 5 HAS 140 Extruded 500 1 80 21 2.1. 10 ⁶ 1 6 B 40 Extruded 500 2 80 11 1.1.10 ⁶ 1 7 C 25 Extruded 500 2 80 11 1.1.10 ⁶ 1 8 D
140 Extruded 500 1 80 16 1.6. 10 ⁶ 1 9 E
Tested after shaping - catalyst G 140 Powder 500 1 80 16 1.6. 10 ⁶ 0.6 10 F
Tested after shaping - catalyst H 40 Powder 500 1 80 16 1.6.10 ⁶ 0.6

Examples 11 to 15 (comparative)
The four examples 11 to 14 use catalyst A:
- Example 11 is comparative because it uses the catalyst just calcined without any steam treatment. The calcination was carried out in air with a flow rate of 1 NL/h per gram of catalyst for 2 hours.
- Example 12 is comparative because it operates the vapor treatment at atmospheric pressure.
- Examples 13 and 14 are comparative because they operate at pressures of 5 bars, below the threshold of 10 bars preferred according to the invention.
- Example 15 uses catalyst D. It is comparative because it is the catalyst just calcined without any steam treatment. The calcination was carried out in air with a flow rate of 1 NL/h per gram of catalyst for 2 hours.

The operating conditions are recalled in table 2 below, with the same conventions as in table 1:

No. Example catalyst Yes/Al
at./at. T(°C) D (h) % Water Vol P
(bar) P
(Pa) Q
(NL/h/g) 11 (comp.) HAS 140 - - - - - - 12
(comp.) HAS 140 600 2 50 1 1. 10 ⁵ 1 13
(comp.) HAS 140 500 2 50 5 5. 10 ⁵ 1 14
(comp.) HAS 140 400 2 50 5 5. 10 ⁵ 1 15
(comp.) D 140 - - - - - -

The physicochemical characteristics of these different examples were studied, as well as their performance as a catalyst for the conversion reaction of ethylene to propylene or ethanol to propylene.

Regarding the texture of the examples with catalyst A:
The microporous volume of the zeolite in powder form, before incorporation into the catalyst, is 0.175 cm ³ /g. It corresponds to the microporous volume (pore diameter less than 2 nm) calculated from the nitrogen adsorption isotherm by the t-plot method. The measurement of the nitrogen adsorption isotherm was carried out at 77 K following the ASTM D3663-03 standard, using a Micromeritics 2020 ASAP device. Just before analysis, the sample is placed under secondary vacuum (1 x10-5 mbar) for 1 hour at 100 ° C and then for 4 hours at 450 ° C. We therefore expect approximately 0.105 cm ³ /g of microporous volume in the 60% zeolite extrudates, which is the case for all the examples concerned. The differences observed between the examples are not significant, and identical to those of the catalyst of example 8 which did not undergo steam treatment. Steam treatment would therefore have no impact on the microporous texture of the zeolite, at least when the zeolite contains little aluminum (high Si/Al atomic ratio).

To determine the degree of oxidation of aluminum on the catalysts after steam treatment (Tables 4 and 7), each sample was analyzed by MAS NMR of aluminum 27 in a 4 mm CPMAS probe on an Avance 400 spectrometer (v = 12 kHz). The ²⁷ Al NMR spectrum was obtained using the single-pulse MAS sequence under selective (low radiofrequency field, approximately 25 kHz) and quantitative (low pulse angle equal to π/22 corresponding to a duration of 1 μs) conditions. The recycling time (d1) is 0.5 s. The chemical shifts are referenced relative to Al(NO ₃ ) ₃ , δ = 0 ppm.

Table 3 below indicates for the examples concerned the % of Al sites at oxidation degrees IV and VI. It shows that high pressure steam treatment leads to a percentage of Al at degree VI of at least 5%. We also note the absence of Al at oxidation degree V.

No. Example catalyst Yes/Al
Mol. Al IV (%) Al VI (%) 3 HAS 140 90 10 4 HAS 140 85 15 5 HAS 140 95 5

Textural analyses on the examples using catalyst A by nitrogen adsorption isotherm show that steam treatment does not affect the microporosity of the catalysts.

Measurements were also made to quantify the catalytic performance of some of the examples for converting ethylene predominantly to propylene.

Separate tests are carried out to evaluate the catalytic performance of each catalyst.

For each test, a reaction unit operating in a fixed bed crossed with 1 g of diluted catalyst (reactive bed) is loaded (same bed thickness in the different tests).

Before starting each catalytic test, each of the catalysts concerned is activated at 550°C in air with a flow rate of 6 NL/h for 1 hour. This activation consists of drying the catalyst before use and calcination aimed at burning any traces of oil and grease that may be present. The whole is then inerted under a nitrogen flow with a flow rate of 6 NL/h, then the hydrocarbon feedstock consisting of pure ethylene or pure ethanol is injected.

For each test with ethylene feed, 7 g/h of feed are injected onto the catalyst. For each test with ethanol feed, 2 g/h of feed are injected onto the catalyst. The reaction conditions used are a temperature of 500°C and a pressure of 0.17 MPa. At the reactor outlet, all of the effluent maintained in gaseous form by heating the transfer lines is analyzed by gas chromatography.

The catalytic performances thus obtained for each of the catalysts are given in tables 4 and 5 below:
For tests with ethylene load (Table 4), they are expressed using the following criteria:
- the conversion of ethylene X(ethyl.) and the yield of propylene Y(propyl.) expressed as follows:

X(ethyl) = 1 – (mass fraction of ethylene in the effluent)

Y(propyl.) = mass fraction of propylene in the effluent

- the purity of propylene in the cut consisting of propane and propylene P(propyl.), corresponding to 55% conversion of ethylene, expressed as follows:

P(propyl.) = mass fraction of propylene in the effluent / mass fractions of propylene and propane in the effluent

The activity of the catalyst is characterized by the conversion of the initial ethylene X. The selectivity of the catalyst is characterized by the purity of propylene P and the yield of propylene Y.

The stability of catalyst performance is quantified as follows:

Conversion stability = (initial conversion – conversion after 15 hours under load)/initial conversion

Stability of propylene yield = (initial propylene yield – propylene yield after 15 hours under load) / initial propylene yield

For tests with ethanol load (Table 5), the performances are expressed using the following criteria:
The conversion of ethanol X(ethanol), the yield of ethylene Y(ethyl.) and the yield of propylene Y(propyl.) expressed as follows:

X(ethanol) = 1 – (mass fraction of ethanol in the effluent)

Y(ethyl) = mass fraction of ethylene in the effluent

Y(propyl.) = mass fraction of propylene in the effluent

The activity of the catalyst is characterized by the conversion of the initial ethanol. The selectivity of the catalyst is characterized by the yield of propylene Y.

Table 4 below groups together these different performance values for examples 1 to 14 (ethylene charge):

No. Ex. X(ethyl.) initial

(%) X(ethyl.)
after 15 hours under load

(%) Conversion loss after 15 hours

(% relative) Y(propyl.)
Initial

(%) Y(propyl.) after 15 hours under load

(%) Loss of propylene yield after 15 hours

(% relative) P(propyl.) for a 55% X(ethyl.) conversion

(%) 1 70 52 26% 19 16 16% 91 2 60 39 35% 18 13 28% 93 3 58 43 26% 18 14 22% 93 4 49 33 33% 16 12 25% 90 5 68 46 32% 19 14 26% 91 6 79 67 15% 19 18 5% 85 7 77 62 19% 20 18 10% 87 9 70 52 26% 19 16 16% 91 10 79 67 15% 19 18 5% 85 11(comp.) 66 4.8 93% 20 1.4 93% 93 12 (comp.) 61 40 34% 18 13 28% 91 13 (comp.) 66 34 48% 19 11 42% 92 14
(comp.) 63 10 84% 18 3 83% 92

We deduce from the results given in Table 4 that:
- The catalysts with zeolites with Si/Al atomic ratios of 25 and 40 treated according to the invention under pressure exhibit the highest activity and good stability: they correspond to examples 6, 7, for the vapour-treated extrudates 10 for the vapour-treated then shaped powder.
- The catalyst with zeolite of atomic ratio Si/Al 140 is a little less active and selective, but presents a better purity in propylene: considering example 2 with the ratio Si/Al 140 to compare with examples 6 and 7.
Furthermore, the performances are all superior to those obtained with these catalysts after steam treatment at atmospheric pressure or insufficiently high pressure: Compared to the catalyst steam treated at atmospheric pressure (example 11), the catalyst steam treated under pressure is more active and more stable (example 1) or more stable and more selective in propylene (example 3) or has performances equivalent to the catalyst steam treated at atmospheric pressure (example 2), but having been steam treated under pressure for 2 hours compared to 4 hours at atmospheric pressure, which allows a saving of time and energy.

Furthermore, all the vapour-treated catalysts show a significant gain in stability compared to the non-vapour-treated catalyst.

Table 5 groups together the different performance values for examples 8 and 15 (ethanol charge):

It is deduced from the results in Table 5 that the catalyst prepared in accordance with the invention (Example 8) exhibits better stability of ethanol conversion, better propylene yield (to the detriment of ethylene yield) and better stability of propylene yield.

Claims (19)

Process for preparing a catalyst comprising at least one aluminosilicate zeolite of the ZSM-5 family, a binder comprising silicon oxide and/or aluminium oxide, said treatment comprising: - (i) a mixture of the zeolite in powder form, the binder and/or the binder precursor, and optionally the additive, then - (ii) shaping said mixture into catalyst particles, characterized in that said treatment also comprises - (iii) steam treatment, said steam treatment operating
- either on the catalyst in the form of particles,
- either on zeolite in powder form before mixing (i),
said steam treatment comprising bringing said catalyst particles or said zeolite powder into contact with a steam treatment gas flow comprising water vapor, at a temperature of at least 400°C and a pressure of at least 10 ⁶ Pa. Method according to the preceding claim, characterized in that the temperature at which (iii) the steam treatment is carried out is between 400 and 600°C, in particular between 450 and 600°C, preferably between 500 and 560°C. Method according to one of the preceding claims, characterized in that the duration of vapotreatment is at most 5 hours, in particular at most 3 hours, or at most 2 hours, preferably between 45 minutes and 2 hours or between 1 hour and 1 hour 30. Method according to one of the preceding claims, characterized in that the pressure at which the steam treatment is carried out is between 10 ⁶ Pa and 3.10 ⁶ Pa, in particular between 1.5.10 ⁶ Pa and 2.5.10 ⁶ Pa. Method according to one of the preceding claims, characterized in that the flow rate of the vapor treatment gas flow is between 0.01 and 3 NL per hour per gram of catalyst, and in particular between 10.01 and 2 NL per hour and per gram of catalyst. Method according to one of the preceding claims, characterized in that the flow of vapor treatment gas contains a mixture of gases comprising water vapor and at least one other gas, in particular air and/or nitrogen, the water vapor content in the vapor treatment gas being constant or changing during at least part of the vapor treatment. Method according to the preceding claim, characterized in that the volume proportion of water vapor in the vapor treatment gas is between 30 and 100%, in particular between 40 and 90%, preferably between 50 and 80%. Method according to one of the preceding claims, characterized in that the binder comprises, in particular consists of, silicon oxide introduced into the catalyst at least partly in the form of colloidal silica and/or in the form of precipitated silica, preferably both in the form of colloidal silica and in the form of precipitated silica. Method according to one of claims 1 to 7, characterized in that the binder comprises, in particular is constituted by, aluminum oxide introduced at least in part into the catalyst in the form of at least one compound chosen from the group formed by hydrargillite, bayerite, boehmite, amorphous gels, so-called transition aluminas which comprise at least one phase taken from the group comprising the rho, chi, eta, gamma, kappa, theta and alpha phases, and preferably is a boehmite. Method according to one of the preceding claims, characterized in that the Si/Al atomic ratio of the zeolite is between 12 and 200, in particular between 15 and 180, preferably between 20 and 150. Method according to one of the preceding claims, characterized in that the steam treatment (iii) is carried out on the catalyst in the form of particles, and in that said steam treatment of the catalyst is preceded by drying, in particular at a temperature of at least 60°C, and preferably at most 150°C, in particular between 60 and 100°C. Method according to one of the preceding claims, characterized in that the vapor treatment of the catalyst is carried out in the form of a catalytic bed of catalyst particles, said bed being arranged in a catalytic hydrocarbon conversion reactor and crossed by said vapor treatment gas flow. Device for implementing the method according to one of the preceding claims, characterized in that it comprises a reactor for the catalytic conversion of hydrocarbons in which is arranged a catalytic bed of catalyst particles comprising at least one aluminosilicate zeolite of the ZSM-5 family, a binder comprising silicon oxide and/or aluminum oxide, and in that the reactor comprises means for injecting and evacuating vapor treatment gas comprising water vapor. Catalyst obtained by the process according to one of claims 1 to 12, characterized in that the majority of the Al sites, in particular at least 60 or 70 or 75% or 80% of the Al sites, of the ZSM-5 zeolite is in the form of Al with oxidation state IV. Catalyst obtained by the process according to one of claims 1 to 12, characterized in that at most 30%, in particular at most 20% of the Al sites of the ZSM-5 zeolite are in the form of Al with oxidation state VI. Catalyst obtained by the process according to one of claims 1 to 12, characterized in that the catalyst comprises between 20 and 80% by weight of zeolite, in particular between 30 and 70% by weight of zeolite, and between 20 and 80% by weight of binder, in particular between 30 and 70% by weight of binder. Catalyst obtained by the process according to one of claims 1 to 12, characterized in that the catalyst comprises at least one doping element, in particular part of the group consisting of sodium, potassium, magnesium, calcium, phosphorus, copper, silver, manganese, molybdenum. Catalyst obtained by the process according to one of claims 1 to 12, characterized in that the catalyst comprises at least two ZSM-5 zeolites, among which at least two have different Si/Al atomic ratios. A process for converting a feedstock comprising ethylene or ethanol into propylene and gasoline or aromatic compounds, comprising contacting said feedstock with the catalyst according to one of claims 14 to 18 or the catalyst prepared according to one of claims 1 to 12.