WO2010003913A2

WO2010003913A2 - Method for manufacturing zeolite-based catalysts, zeolite-based catalysts and use thereof for aromatization of hydrocarbons

Info

Publication number: WO2010003913A2
Application number: PCT/EP2009/058489
Authority: WO
Inventors: Anna Omegna; Martin Claus
Original assignee: Süd-Chemie AG
Priority date: 2008-07-11
Filing date: 2009-07-06
Publication date: 2010-01-14
Also published as: WO2010003913A3; DE102008032712A1

Abstract

A method for manufacturing a gallium aluminosilicate catalyst comprising the steps of (a) preparing a zeolite-analogous gallium aluminosilicate, (b) hydrothermally treating the zeolites from step (a) with steam and (c) treating the product from step (b) with acid. A catalyst so manufactured is used for the aromatization of alkanes.

Description

Process for the preparation of zeolite-based catalysts, zeolite-based catalysts and their use for the aromatization of

hydrocarbons

The invention relates to a process for the preparation of catalysts based on crystalline galloaluminosilicate, as well as their use for the aromatization of light hydrocarbons.

Zeolites, ie crystalline aluminosilicates, can be represented by the general formula

M _2ZnO Al ₂ O ₃ XSiO ₂ YH ₂ O

where M is a metal cation of valence n, x is equal to or greater than two, and y takes on a value that varies with the pore volume of the zeolite crystal.

In crystalline zeolite-analogous galloaluminosilicates, trivalent gallium atoms are incorporated into the lattice in addition to silicon and aluminum atoms. Tetrahedra of oxygen atoms form a defined cavity system with channels and pores, whereby the characteristic properties of the zeolite are defined by the size and number of these pores. If, for example, after the synthesis of the zeolite, the cations M are replaced by protons, acidic compounds are obtained.

Catalysts based on crystalline zeolite-analogous galloaluminosilicates are mainly used in the petrochemical industry for the production of valuable organic intermediates. Due to their dehydrogenation and cyclization properties, they are suitable for the conversion of lower hydrocarbons such as alkanes from liquefied petroleum gas (LPG) to aromatic hydrocarbons such as benzene, toluene or xylenes (BTX). These are important starting materials for syntheses for the production of synthetic fibers, polyesters, and other plastics.

In the aromatization of short-chain alkanes, use is primarily made of crystalline galloaluminosilicate catalysts having a high SiO ₂ content, in which x in the above mentioned general formula is greater than 12. These catalysts have a desired high degree of stability.

The introduction of gallium atoms into zeolites to produce active catalysts suitable for the aromatization of C _Σ -Cs alkanes can be accomplished by various methods.

US 4,636,483 discloses a process for preparing a gallium-modified zeolite-based catalyst wherein the gallium component is formed by impregnating calcined droplets containing crystalline aluminosilicate and phosphorus-containing alumina binder with an aqueous solution of a gallium metal salt.

EP 0 252 705 describes the incorporation of gallium into catalytically active zeolites by treating a zeolite with an aqueous medium containing gallium under alkaline conditions or by means of ion exchange.

US 4,861, 933 discloses the preparation of a galliummodifizierten Aluminiumsilikatzeo- Lithen by impregnation or ion exchange, and subsequent calcination at at least 700 ⁰ C.

No. 6,593,503 discloses a process for producing a zeolite, wherein the zeolite is treated with acid in a first step in order to reduce its aluminum content, and in a second step with a metal compound from the group nickel, palladium, molybdenum, gallium, platinum or a combination thereof is impregnated to obtain a metal-promoted zeolite.

EP 0 351 312 discloses the preparation of a catalytic zeolite in a fluoride medium, wherein the fluoride is introduced into the zeolite in the synthesis, so that it has a fluorine content of 0.02 to 1, 5 wt .-%.

EP 0 443 539 discloses the hydrothermal crystallization of a zeolite wherein the hydrothermal treatment takes place at a plurality of successive temperature levels and the resulting products are subjected to ion exchange. US 4,761, 51 1 discloses the treatment of galloaluminosilicates with steam (so-called steaming).

The hydrothermal crystallization shows some advantages compared to the ion exchange or impregnation, for example the more homogeneous distribution of the gallium atoms. In active catalysts, the gallium atoms are positioned in the zeolite pores in the vicinity of lattice aluminum atoms.

Steaming is a well-known method for the preparation of active and stable zeolite catalysts. During this treatment, aluminum atoms are removed from the framework. By removing a portion of the aluminum atoms from the lattice, the acidic sites can be reduced.

For gallo (alumino) silicates, it is desirable that Si-O-Ga bonds are hydrolyzed in the steaming. However, in addition to Si-O-Ga bonds, hydration in the steaming also hydrolyzes Si-O-Al bonds, releasing aluminum atoms. Hydrothermal treatment thereby leads to inactive, outside the lattice localized aluminum. This leads to reduced activity and selectivity, for example in the context of the aromatization of aliphatic hydrocarbons.

The object of the present invention is therefore to provide a process for the preparation of galloaluminosilicate catalysts having improved activity and selectivity in the aromatization of aliphatic hydrocarbons.

Surprisingly, it has now been possible in the present invention to obtain an improved BTX yield in the aromatization of aliphatic hydrocarbons by a subsequent acid treatment of a steam-treated zeolite.

During this treatment, the off-grid aluminum inactive species are removed by the acid treatment. In this respect, the catalyst of the invention has a relation to the catalysts of the prior art reduced proportion of lying outside the crystal lattice aluminum. Acid-treated, crystalline galloaluminosilicate catalysts prepared according to the invention have better properties in activity and selectivity than non-acid-treated, crystalline galloaluminosilicate catalysts. They are particularly suitable for use in the conversion of alkanes to aromatics.

The method according to the invention comprises the following steps:

(a) providing a crystalline galloaluminosilicate,

(b) hydrotreating the zeolite from step (a) with steam; and (c) treating the product from step (b) with acid.

The zeolite is provided by methods known in the art (step (a)). For the further process steps according to the present invention, the zeolites can be used in their hydrogen or ammonium form. Preference is given to using zeolites with a pentasil structure, for example ZSM-5.

The hydrothermal treatment (b) of the zeolite is carried out at temperatures of about 400 ⁰ C to about 800 ⁰ C, preferably from about 500 ⁰ C to about 700 ⁰ C with water vapor, for example from about 0.5 to about 12 hours, with shorter or longer treatment times are possible.

For the acid treatment (c) both organic and inorganic acids are suitable. Examples of these are hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic acid, citric acid, oxalic acid and mixtures thereof. Preferably, hydrochloric acid is used.

The concentration of the acid may range from about 0.01 to about 1 mol / l, preferably from about 0.05 to about 0.7 mol / l, and more preferably from about 0.1 to about 0, 5 mol / l.

For example, the zeolite is suspended in an acid solution by stirring, the concentration of zeolite being from about 1 to about 1000 g / L, preferably from about 100 to about 500 g / L, and more preferably from about 100 to about 300 g / L. The acid treatment may be preferred over a period of about 1 to about 48 hours from about 5 to about 30 hours, and more preferably from about 20 to about 30 hours.

After step (c) according to the invention, optional washing, drying and calcination steps may follow. The conditions for this are well known to the skilled person.

The catalyst according to the invention is particularly suitable for the preparation of aromatics such as benzene, toluene and xylenes from aliphatic hydrocarbons, for example having 2 to 5 C atoms.

In the aromatization using the catalyst according to the invention, the reaction gas is brought into contact with the catalyst. Typical reaction conditions are:

Temperature: from about 350 ⁰ C to about 650 ⁰ C, preferably from about 400 ° C to about 570 ⁰ C;

Pressure: from about 1,000 hPa (about atmospheric pressure) to about 20,000 hPa, preferably from about 2,000 hPa to about 10,000 hPa; LHSV: from about 0.2 hr ^-1 to about 5 hr ^-1, preferably from about 0.5 hr ^-1 to about 2 hr ^-1 .

A "moving-bed" system or a "fixed-bed" system are particularly suitable for this application.

In general, therefore, the present invention also relates to an apparatus comprising the catalyst prepared by the process according to the invention.

The invention is explained in more detail by the following examples without it being intended to be limited by them.

Example 1: Preparation of a zeolite-analogous galloaluminosilicate (step (a))

7.1 g NaOH are homogenized with 7.3 g NaAIO ₂ and 7.4 g Ga (NO ₃ ) ₃ in 200 g water with stirring. 208.5 g of colloidal silica is diluted with 49.1 g of H ₂ O and added slowly to the first mixture with stirring. This reaction approach is filled in a stainless steel autoclave with a nominal content of 0.5 I and reacted at 17O ⁰ C for 60 hours with stirring and under autogenous pressure. After filtration, washing with water and drying, 80 g of a crystalline Galloaluminosili- kates with a molar SiCV (Al ₂ Os + Ga 2θ3) ratio of 30: 1.

Example 2: hydrothermal treatment (step (b))

The galloaluminosilicate prepared in Example 1 is converted by two-time ion exchange with einmolarer ammonium nitrate solution at 80 ⁰ C for 2 hours each in the ammonium form, wherein in each case after the ion exchange process is washed with water. For conversion into the acidic H-form, the galloaluminosilicate is after calcination at 12O ⁰ C for 16 h then calcined at 600 ⁰ C for 5 h in a tubular reactor in a humid air flow.

Example 3: Acid treatment (step (c))

10 g of the acidic Galloaluminosilikats prepared in Example 2 are suspended in 50 ml of a 0.1 molar hydrochloric acid solution and stirred for 24 h. After filtration, washing and drying at 120 ⁰ C for 3 h, the resulting zeolite powder is calcined at 540 ⁰ C for 2 h. The SiO ₂ ZAl ₂ O ₃ mol / mol ratio is increased from 39.7: 1 by washing out the aluminum during the acid treatment from 35.7: 1.

Example 4: Carrying out an aromatization; Comparative example with zeolite not according to the invention

The catalytic properties of the catalyst prepared in Example 2 were investigated in the reaction of n-butane to BTX aromatics. The catalytic studies were carried out in a tubular reactor. The catalyst bed is flowed through by the reaction gas. The gas flow is regulated via MFC (Mass Flow Controller). The liquid products accumulate in a product container attached to the reactor while the gas is passed to the outside via a gas meter. The reaction mixture is analyzed by chromatography. First, the catalyst is activated at 55O ⁰ C for 12 h in a nitrogen stream in the reactor. The catalyst shows at the reaction temperature of 54O ⁰ C and a GHSV of 220 h ^"1 an n-butane conversion of 78% at a selectivity to BTX of 43%. Example 5: Carrying out an aromatization; Example with zeolite according to the invention

The catalytic properties of the catalyst prepared in Example 3 were investigated in the reaction of n-butane to BTX aromatics. The catalytic studies were carried out in a tubular reactor. The catalyst bed is flowed through by the reaction gas. The gas flow is regulated via MFC. The liquid products accumulate in a product container attached to the reactor while the gas is directed to the outside via a gas meter. The reaction mixture is analyzed by chromatography. First, the catalyst is activated at 55O ⁰ C for 12 h in a nitrogen stream in the reactor. The catalyst shows an n-butane conversion of 92% with a selectivity to BTX of 55% at the reaction temperature of 540 ° C. and a GHSV of 220 h ^-1 . Thus, the yield of BTX with the catalyst according to the invention of 33.5 % to 50.6%.

Claims

claims

A process for producing a galloaluminosilicate catalyst, comprising the following steps:

(a) providing a zeolite analogous galloaluminosilicate,

2. The method according to claim 1, characterized in that the hydrothermal treatment (b) is carried out at temperatures of 400 ⁰ C to 800 ⁰ C.

A process according to any one of the preceding claims, characterized in that the acid in step (c) is hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic acid, citric acid, oxalic acid or a mixture thereof.

4. The method according to any one of the preceding claims, characterized in that the concentration of the acid from 0.01 to 1 mol / l.

A process according to any one of the preceding claims wherein the gallium modified aluminosilicate zeolite is suspended in the acid.

6. Method according to the preceding claim, characterized in that the concentration of gallium-modified aluminosilicate zeolite in the acid is from 1 to 1000 g / l.

7. The method according to any one of the preceding claims, characterized in that the duration of the acid treatment (c) of 1 to 48 hours.

8. The method according to any one of the preceding claims, characterized in that following step (c) following further steps: washing, drying and / or calcination.

9. Catalyst, obtainable according to one of the preceding claims.

10. Use of a catalyst according to the preceding claim for the aromatization of aliphatic hydrocarbons.

Use according to the preceding claim, characterized in that hydrocarbons having 2 to 5 carbon atoms are converted into aromatic hydrocarbons, preferably benzene, toluene and xylene.

12. Apparatus comprising the catalyst according to claim 9.