FR2653764A1 - Use of a catalyst of aluminosilicate type containing gallium in aromatisation of light fractions largely containing hydrocarbons containing two carbon atoms per molecule - Google Patents

Abstract

The invention relates to the use of a zeolite catalyst in the aromatisation of a fraction containing C2 light gases in the presence of olefins. The catalyst used has the following composition expressed by weight: … …  a) 0.01 to 10% by weight of gallium …  b) 0.1 to 99.49% of a matrix …  c) 0.5 to 99.99% of a zeolite with the following approximate chemical formula: M2/nO.Al2O3.xSiO2 where … …  M represents a proton and/or a metal cation, …  n is the valency of the said cation, …  x is a number between 12 and 1000, … the said zeolite having an MFI structure and additionally being synthesised in fluoride medium and having a fluorine content of between 0.01 and 1.5% by weight incorporated during the synthesis. …

Description

The present invention relates to the use of a type catalyst

  aluminosilicate comprising a zeolite with an MFI structure, synthesized in a fluoride medium, containing silicon, aluminum, and gallium, in the reactions of aromatization of light cuts containing mainly 2 carbon atoms per molecule in the presence of olefins , and inert gases such as methane, nitrogen,

  - carbon monoxide and hydrogen.

  The synthesis in fluoride media of this type of zeolite with an MFI structure has already been described in the European patent.

CFR EP-A-172068.

  When the catalyst used in the present invention is described in the French patent application of the applicant n

88/09632 of July 12, 1988.

  The zeolites obtained by the synthesis procedure described is in EP-A172068 are zeolites of MFI structure whose X-ray diffraction diagrams have characteristics corresponding to the specifications in Table 1. These zeolites of MFI structure have as approximate chemical formula after calcination expressed in oxide form: M2 / nO, A1203, xSiO2 ox can vary from 12 to 1000 and o M represents the valence compensation cation (s) n. The important point is that these solids contain, after the synthesis step and also after the step of removing organic compounds, the fluorine element. The fluorine content in the zeolite determined by elemental analysis is between 0.01 and 1.5% by weight for calcined solids, advantageously between 0.1 and 1.0% and preferably between 0.2

and 0.8%.

  TABLE I: Characteristics of the X-diffraction spectrum of the zeolites of MFI structure used in the invention I (Id (A) tI / o dhkl (À) I / Io (OM) (10 0 m) (10- m) d ( 10- /) 0 I_ _ _ _ _ I_ _ I_ _ _ _ _ I_ _ t _ _ _ I 11.08-11.26 FF 4.06-4.10 ff 2.722-2.793 ff 9.94-10, 20 mf 3.99-4.05 f 2, 725-2.749 ff 9.68- 9.90 f 3.83-3.89 F 2.677-2.697 ff 8.98- 9.08 ff 3.80-3, 86 m 2.648-2.670 ff 8.00- 8.09 ff 3.74-3.78 mf 2.605-2.619 ff 7.40- 7.52 ff 3.70-3.74 mf 2.581-2.597 ff 7.03- 7.22 ff 3.63-3.67 mf 2.545-2.557 ff 6.64- 6.84 f 3.58-3.62 ff 2.508-2.526 ff 6.30- 6.42 f 3.46-3, 50 ff 2.4792.50 ff, 95- 6.07 f 3.42-3.46 f 2.407-2.419 ff 5.67- 5.79 f 3.38-3.42 ff 2.393-2.401 ff, 54- 5.61 f 3.33-3.37 f 2.326-2.340 ff, 32- 5.42 ff 3.29-3, 33 ff 2.314-2.332 ff t, 10- 5.23 ff 3.23-3.27 ff 2.195-2.209 ff, 01- 5.08 f 3.16-3.20 I ff 2.104-2.120 t ff 4.95- 5.03 f 3.12-3.16 ff 2.077-2.095 ff 4.84- 4.93 ff 3.08-3.12 ff 2.070-2.084 ff t4.59- 4.64 ff 3.03-3.07 f 2.004-2.022 f 4.44- 4.50 ff 2.976-3.020 tf 1, 985-2.005 I f 4.34- 4.40 f 2, 953-2.962 f 1.944-1.964 I ff 4.23- 4.29 f 2.855-2.881 ff 1.907-1.922 t ff I _ _ _ _ _ _ _ _ I _ _ _ t _ _ _ _ _ _ _ _ I _ _ _ I _ _ _ _ I _ FF = very strong; F = strong; mF = medium to strong; m = medium mF = medium to low; f = weak; ff = very low The presence of fluorine in zeolites with MFI structure gives these solids properties, in particular acid and ion exchange properties, quite different from those of zeolites with MFI structure synthesized in a conventional manner, it is -adire in an alkaline medium (US 3,702,886 for example). After synthesis and elimination of the organic compounds by calcination, the solids are characterized by an infrared vibration spectrum which exhibits bands conventionally assigned to the Si-OH groups (area 3730-3750 cm) and to the structural AI-OH groups (region 3580-3640 cm 1) very weak compared to those of an MFI structure zeolite

classic, with the same Si / Al ratio.

  The absence or almost absence of structural Al-OH groups in the zeolites according to the invention is confirmed by the ion exchange capacities of these solids. Indeed the ion exchange capacities for cations such as for example Na +, K +, Ga3 +, Pt (NH3) 42+ etc are much lower than the total theoretical exchange capacities 3 4 which can be calculated from the content

  aluminum of the crystal structure.

  These solids, which have little or no structural hydroxyls and whose exchange capacity is very reduced, surprisingly have remarkable acidic properties. Thus the thermoresorption of ammonia which makes it possible to account for the overall acidity of a solid (number and strength of the different types of acid sites) shows that the solids comprising fluorine incorporated into the structure are very acidic. The ammonia thermoresorption spectra are comparable to those which would be obtained with zeolites of conventional MFI structure, however the acidity of the solids according to the invention is of a different nature. These improved acid properties of solids synthesized in fluoride medium is confirmed

  by microcalorimetry of ammonia adsorption.

  The introduction of fluorine into zeolites is a method which has already been proposed for increasing the acidity of these solids (J. MIALE and C. CHANG US 4,540,841). However, in the prior art, fluorine is introduced into the zeolite by modifications carried out after the synthesis. In other words, a conventional synthesis is carried out, that is to say in an alkaline medium, then the solid is treated by a technique which in principle makes it possible to fix fluorine. These previously proposed techniques generally suffer from major flaws. They are, for example, as is the case when the solid is treated with gaseous fluorine, capable of leading to a degradation of the crystalline order (US 4,297,335). In the preparation of the catalyst used in the present invention, fluorine is introduced into the zeolite at the level of the synthesis and, on the contrary, allows solids to be obtained.

very well crystallized.

  -By specific treatments, it is possible to partially or completely eliminate the fluorine contained in the solids used in the composition of the catalysts used without altering their crystallinity. One technique that can be used to defluorinate solids consists in carrying out a treatment in an ammonia solution at temperatures comprised for example between ambient

  and 200 C (autoclave treatment under autogenous pressure).

  The partial or complete elimination of fluorine leads: - on the one hand as indicated above to the appearance in the IR spectrum of two bands located around 3740 and 3608 cm-1 corresponding, according to the attributions admitted in the literature scientific, to the terminal silanol groups and to the structural AI-OH groups respectively and, - on the other hand to the restoration of the ion exchange capacity as can be calculated from the aluminum content of

solid structure.

  Thus, depending on the defluorination treatment, solids containing a quantity of Al-OH and Si-OH groups and a variable ion exchange capacity can be obtained for the same Si / Al framework ratio. A partially defluorinated solid therefore contains, in addition to conventional acid sites of the Al-OH type which can play the role of exchange sites, particular acid sites whose exact nature is not yet fully understood but which undeniably result from the introduction into fluorine solids during synthesis. It is this peculiarity of the solids synthesized in a fluoride medium that we have taken advantage of to prepare catalysts containing gallium and which can be sucked for example by flavoring - cuts with a high olefin content with 2 carbon atoms per molecule, accompanied C2 to C4 light gases containing paraffins as well as inert gases such as methane, hydrogen, nitrogen and carbon monoxide. Such constituents can for example be contained

  in gases from catalytic cracking units.

  The present invention therefore relates to the use in aromatization of cuts with a high C2 content (ethane and ethylene) of a catalyst of the aluminosilicate type of the following composition expressed by weight: a) 0.01 to 10% by weight of gallium, of preferably 0.3 to 7%, b) 0.1 to 99.49% of a matrix chosen from the group formed by alumina, silica, magnesia, clay and any combination of at least two of the compounds aforementioned and c) 0.50 to 99.99% of a zeolite synthesized in a fluoride medium with a chemical formula generally approximated as follows: M2 / n0, Al203 xSiO2, where M represents a proton and / or a metal cation n is the valence of the cation x is a number between 12 and 1000 (SiO2 / A1203 molar ratio), the zeolite having a fluorine content of between 0.01 and 1.5% by weight, preferably 0.1 to 1% by weight, fluorine being incorporated during synthesis, said zeolite being also characterized by an X-ray diffraction diagram born in the

table 1.

  After synthesis in a fluoride medium, the solid can be subjected if necessary to a defluorination treatment making it possible to adjust its ion exchange capacity, to the gallium content which it is desired to introduce. The lower the fluorine content, the lower the

gallium may be high.

  The defluorination treatment is more or less severe depending on the level of defluorination desired. It consists of one or more successive treatments of the solid, at reflux in an ammonia solution of normality of between approximately 0.05 and 5N and preferably between 0.1 and 3N, for a duration of between approximately 0.5 and 5 hours and preferably between 1 and 4 hours with a V / P ratio defined as the volume of solution relative to the weight of dry solid of between approximately 5 and 50 cm3g1 and preferably between 10 and cm3g. The solid, after each washing is then abundantly washed with distilled water and dried in an oven. After these treatments and according to their severity, the fluorine content of the solid is between 0.9 and 0.01% by weight. If one eliminates, by repeated treatments, substantially all of the fluorine, one still ends up with solids which are distinguished in particular by their IR spectrum in the region 3800-3500 cm1l of the zeolites of conventional MFI structure with the same Si / Al ratio of frame: the solids contained in the catalyst according to the invention have a higher proportion of groups

Si-OH.

  The partially or totally defluorinated solid can be subjected as it is to the deposition of gallium or shaped by any technique known to those skilled in the art. It can in particular be mixed with a generally amorphous matrix, for example with a wet powder of alumina gel. The mixture is then shaped, for example by extrusion through a die. The zeolite content of the support thus obtained is generally between approximately 0.5 and

  99.99% and advantageously between around 40 and 90% by weight.

  The matrix content of the catalyst is between 0.1 and 99.49% and advantageously between about 10 and 60%. The shaping can be carried out with matrices other than alumina, such as, for example magnesia, silica alumina, natural clays (kaolin, bentonite), and by techniques such as extrusion, pastillage , the coating or the coagulation in drops ("oil drap"). The gallium is then deposited on the support by any process known to those skilled in the art and allowing the metal to be deposited in the zeolite. One can use the cation exchange technique with competition oQ the competing agent is preferably ammonium nitrate, or the technique of deposition of gallium on the catalyst by impregnation. Gallium exchange or impregnation solutions can be prepared from gallium compounds such as, for example, gallium oxide, gallium nitrate, l0 gallium sulfate, gallium halides or hydroxide. gallium. These ion exchange or impregnation techniques can also be used to deposit the metal directly on the zeolite powder, before its possible mixing with a matrix. The gallium content deposited on the catalyst at the end of the ion exchange step or steps depends on the fluorine content of the solid; it is between 0.01 and% by weight relative to the whole of the catalyst and preferably between 0.3 and 7.0% by weight. The gallium content of the catalysts can be adjusted in the same range independently of the fluorine content

  using an impregnation type technique.

  The catalyst thus defined is used for the aromatization reaction of light gases, based on ethylene and ethane, in the presence or absence of inert gases for the reaction, such as nitrogen, hydrogen, methane or carbon monoxide. This reaction is of particular interest because it makes it possible to recover residues from refining operations, for example gases from catalytic cracking units, into products with higher added value (benzene, toluene, xylenes) while contributing to the production of large quantities of hydrogen essential for the processes

hydrotreatment for example.

  The feed containing the light gases C2 and optionally inert gases for the aromatization reaction is brought into contact with the catalyst used in the present invention at a temperature between 400 and 700 C, and more particularly between 480

and 580 C.

  The following examples illustrate the invention without, however,

limit its scope.

  All the catalysts used in the following examples

  contain 20% of a matrix and 80% of zeolite.

  EXAMPLE 1 Preparation of a zeolite A entering into the composition

of the catalyst according to the invention.

  A zeolite with an MFI structure with an Si / Al atomic ratio close to 25 is prepared from a source of aluminum and silicon, at

  namely partially dealuminated Tixolex 28.

  Tixolex 28 is a sodium aluminosilicate marketed by Rhône Poulenc and characterized by the atomic ratios Si / Al = 7.3 and Na / Al = 1, 1. The partially dealuminated form is prepared as follows: 60 g of Tixolex 28 are stirred for 3 hours at room temperature with 600 ml of HNO3 M / 2. The product obtained is filtered and washed with water until pH 7. After drying at 80 ° C., it is stored in a relative humidity of 80%. The weight composition is as follows 76.10% SiO2; 5.46% A1203; 0.24% Na20; 17.63%

Total H2O.

  A reaction mixture A is prepared, the molar and weight compositions of which are indicated in Table 2. For this, the mixture of NH4F, N (C3H7) 4+ Br and water is added with stirring to partially dealuminated Tixolex. The crystallization of reaction mixture A is carried out in an autoclave, the internal coatings of which consist of polytetrafluoroethane, at 190 ° C. for

3.5 days.

TABLE 2

  I {ITixolex partiallyi I I I dealuminated NH4F N (C3H7) 4Br H20 I lI t SiO2 A1203 i I

- I I

moles 0.2 0.0084 0.04 0.1 d 1.6 [

| HAVE

  g 9 15.8 1.48 26.6 28.8 I - I I l l I After crystallization the solid is filtered and washed with a

  10% diethylamine solution then with hot water solution.

  The solid is then dried at 80 C. The crystallographic analysis shows that the product A is a zeolite with an MFI structure, the X-ray diffraction diagram of which corresponds to the specifications in table 1. The chemical analysis of the product A after calcination in air at 550 C is as follows: Atomic Si / Al products: 28

F (% by weight): 0.8.

  EXAMPLE 2 Catalyst Al used in accordance with the invention.

  The zeolite A of Example 1 is subjected to a first treatment lasting 4 hours with an ammonia solution of 0.2N concentration at the temperature of 10 ° C., the product is then

  filtered and washed with distilled water, then dried in an oven at 150 C.

  After treatment, a solid is obtained whose crystallinity and Si / Al ratio are not altered but whose fluorine content

is 0.05% by weight.

  The solid A of Example 1 thus treated is shaped by extrusion with a binder or matrix of aluminum type in an amount of 80%.

  by weight of zeolite and 20% by weight of binder.

  Catalyst A1 is prepared in the following manner: a pseudo-boehmite alumina supplied by the company CONDEA is peptized by

  addition of nitric acid then kneaded.

  Catalyst A1 is obtained by mixing this pseudo boehmite with the zeolite having undergone the defluorination procedure

partial described above.

  This zeolite is introduced at the rate of 80 g of zeolite per 20 g of binder and then kneaded; the dough obtained, after adjusting its consistency by adding small amounts of water, is forced through a 1.4 mm diameter die, then dried under air flow

  at 120 C and calcined at 550 C for one hour.

  Gallium is deposited on the extrudates by ion exchange. The exchange solution is prepared from gallium nitrate Ga (N03) 3 0.15N. The pH of the gallium solution is adjusted to 2.1 with

ammonia.

  The gallium content reached after three exchanges was

  3.10% by weight relative to the extrudates.

EXAMPLE 3

  By way of comparison, a catalyst B1 is prepared using an MFI zeolite conventionally synthesized in the medium

  alkaline, namely CBV 5020 sold by the company CONTEKA.

  The Si / Al atomic ratio of this zeolite is equal to 28, its Na 2 O content of 200 ppm and its specific surface of 410 m2 / g. Content

fluorine: 0.05%.

  This zeolite is then shaped by extrusion with an aluminum binder in an amount of 80% by weight of zeolite and 20% by weight of binder, according to the operating technique described in Example 2. Gallium is then introduced (3.10 % by weight) according to the procedure described in this same example 2.

EXAMPLE 4

  The catalysts AI and B1 were tested in the aromatization of a C2 fraction of the following weight composition: - methane: 6.1% - ethane: 48.4% ethylene: 44.7% - propane: 0.8%%. The operating conditions were as follows: - temperature: 550 C - atmospheric pressure - hourly weighted flow rate in section C2 equal to 5 times the weight of the catalyst.

  The results obtained are presented in Table 3.

TABLE 3

AI B1 CATALYST

WEIGHTED PRODUCT ICOMPOSITION

  Hydrogen I 1.67 1.53 I Methane I 7.57 - 9.18 Ethane 42.55 42.45 Ethylene 8.52 8.39 Propane 3.57 4.33 Propene 2.27 2.75 t10 Butanes 3, 18 3.86 Butenes 1.42 1.72 Pentanes 1.41 1.71 Hexanes 0.44 0.53 Heptanes 0.35 0.42 Benzene 4.39 3.69 Toluene 11.68 9.8 2 C8 aromatics 8.92 27.051 750 23.1 I Aromatics C9 + 2.06 2.12 We can see the superiority of the catalysts prepared according to the invention, based on zeolite type MFI synthesized in fluoride medium. Indeed, if the activity of the two catalysts A1 and B1 is practically identical, the production of aromatic hydrocarbons from

  AI catalyst is significantly better.

EXAMPLE 5

  The catalyst Al of Example 2 is used for the aromatization reaction of a gas from a catalytic cracking unit, of the following composition by weight: - hydrogen: 1.36% - methane: 27.75% ethane: 21.87% - ethylene: 20.19% - propane: 3.71% - propene: 18.58% nitrogen: 5.75% - Co: 0.61%

- C02: 0.18%

100%.

  The operating conditions were as follows: - temperature 530 ° C. atmospheric pressure - hourly weight flow in catalytic cracking gas equal to

3 times the weight of the catalyst.

  On leaving the reactor, the product had the following composition by weight: - hydrogen: 2.68 - methane: 28.55 - ethane: 19.86 - ethylene: 4.81 - propane: 3.79 - propene: 3.96 - butanes: 2.40 - butenes: 1.85 pentanes: 1.32 - hexanes: 0.39 - heptanes: 0.31 - nitrogen: 5.75

- CO: 0.61

- C02: 0.18

  - benzene: 6.78 - toluene: 9.59 - C8 aromatics: 5.46 23.54 - C9 aromatics: 1.71 100. It can therefore be seen that by operating according to the invention, it is possible to recover in aromatic hydrocarbons, part

  significant gas from a catalytic cracking unit.

Claims (4)

  1) Use in the flavoring of a cut consisting mainly of hydrocarbons with 2 carbon atoms per molecule of a catalyst containing by weight: a) 0.01 to 10% of gallium, b) 0.1 to 99.49% of a matrix chosen from the group consisting of alumina, silica, magnesia, clay and any combination of at least two of the above-mentioned compounds, c) 0.50 to 99.99% of a zeolite synthesized in fluoride medium, of SiO2 / A1203 molar ratio of between 12 and 1000, said zeolite further having a fluorine content of between 0.01 and 1.5% by weight, the fluorine being incorporated during the synthesis of the so-called zeolite, which has a diagram of   X-ray diffraction in accordance with Table 1.   2) Use according to claim 1 of a catalyst containing 0.3 at 7% gallium by weight.   3) Use according to one of claims 1 and 2 of a catalyst   in which the said zeolite presents in its IR spectrum two bands located around 3730-3750 and 3580-3640 cm 1 corresponding to the terminal silanol groups and to the structural A1-OH groups respectively.   4) Use according to one of claims 1 to 3 of a catalyst   wherein said matrix is an alumina.