DE10023279A1 - Catalyst, for the aromatization of aliphatic and alicyclic hydrocarbons, comprises a porous oxide or oxide mixture of Ti, Zr and/or Hf modified at least on the surface. - Google Patents

Abstract

A catalyst, for the aromatization of aliphatic and alicyclic hydrocarbons, comprises a porous oxide or oxide mixture of Ti, Zr and/or Hf containing at least on the surface, 0.01-10 wt.% of a Group 5, 6 and/or 7 element in oxidized form and having 0.005-6 wt.%, at least on the surface; Ga, In, Cu, Ag, Zn, Mn, Fe, Co, Ni, Pd and/or Pt in oxidized and/or metallic form. A catalyst (I), for the aromatization of aliphatic and alicyclic hydrocarbons, comprises a porous oxide or oxide mixture of Ti, Zr and/or Hf containing at least on the surface, 0.01-10 wt.% of a Group 5, 6 and/or 7 element in oxidized form; and having a specific surface area of 30-300 m<2>/g; the capacity to repeatedly absorb and desorb hydrogen at 400-700 deg C; no strongly acid and/or basic centers; and having 0.005-6 wt.%, at least on the surface; Ga, In, Cu, Ag, Zn, Mn, Fe, Co, Ni, Pd and/or Pt in oxidized and/or metallic form. An Independent claim is included for a process for the production of the catalyst (I) by preparing a hydroxide and/or oxide mixture of Ti, Zr and/or Hf; modifying the surface of the mixture with a Group 5, 6 and/or 7 element; and modifying the resulting intermediate on the surface and/or within the bulk with Ga, In, Cu, Ag, Zn, Mn, Fe, Co, Ni, Pd and/or Pt; followed by calcining at 300-750 deg C in air, oxygen or inert gas to obtain all named elements in oxide form.

Description

The invention relates to selective catalysts for the aromatization of aliphatic or alicyclic hydrocarbons with at least 7 carbon atoms in the chain, process for their manufacture and their use.

Aromatics such as toluene, ethylbenzene, p-xylene and o-xylene are important aromatic hydrocarbons, which are the main components of high-octane fuels and are used as starting materials for diverse synthesis reactions in the chemical industry. The ethylbenzene formed from the C ₈ fraction is used, for example, to obtain styrene or polystyrene. Flavoring is therefore one of the most important petrochemical processes for upgrading paraffinic hydrocarbons. Because catalysts are indispensable for the technical implementation of aromatization processes, the development of effective catalysts is a constant requirement for catalysis research.

Aromatics have been obtained from hydrocarbon fractions mainly containing C ₆ -C ₈ paraffins for decades using the known reforming process and its modifications. The successfully used Pt / Al ₂ O ₃ reforming catalysts, which have since been modified and improved in many ways, e.g. B. by the use of bimetallic or multimetallic additives and by various types of carrier are described, for example, by BC Gates, JR Kratzer and GC Schuit, Chemistry of Catalytic Processes, McGraw-Hill, NY 1979. In general, a yield of 25 -40% C ₆ -C ₈ aromatics at 450-550 ° C under 1-2 MPa with a molar hydrogen / carbon ratio of 10/1 to 100/1 on catalysts containing 0.5-1.0% by weight of platinum reached.

Despite widespread use, the above catalyst systems have had significant ones Disadvantage. On the one hand, catalysts containing precious metals are expensive. On the other hand, at Reforming process on such catalysts in addition to aromatization also various Conversion reactions of hydrocarbons take place, such as. B. isomerization, Dehydrogenation, cyclization and cracking reactions, the products of which the yield Reduce valuable products, especially of alkyl aromatics. The valuable carbon carrier Oil is therefore underused. In addition, the temporal stability of the Catalysts in need of improvement in the necessary working conditions, whereby additional effort and / or environmental problems in the regeneration or refurbishment of the Catalysts are created.

With the catalysts described in DE-OS 196 12 000 A1, which contain, for example, Cr, La and Zr oxide, highly selective, noble metal-free aromatization catalysts have been proposed which avoid the disadvantages listed above. In comparison with classic Pt / Al ₂ O ₃ catalysts, this new class of aromatization catalysts, for example (with a catalyst containing Cr-La / Zr oxide), is used in the conversion of n-octane to alkyl aromatics, see examples of DE OS 196 12 000 A1, an increase in C ₆ -C ₈ aromatics selectivity from 61 to 85-90% was achieved. The resulting aromatic fraction in this catalyst consisted of about 70-90% o-xylene and ethylbenzene and only 1% of the physiologically questionable benzene.

The catalysts according to DE-OS 196 12 000 A1 had with all previously known reforming Common catalysts that they deactivate significantly over time. The However, the rate of catalyst deactivation affects its life and thus the economy of its application or its applicability in general crucial.

The invention has therefore set itself the task of the temporal stability of the known Ti, Zr and / or Hf-containing highly selective aromatization catalysts according to DE-A-196 12 000 to improve.

According to the invention, this object has been achieved by catalysts which are based on an oxide or Oxide mixture of the elements titanium, zirconium and hafnium based, and that on the Surface, optionally at the same time in bulk, is additionally modified by an or several oxides of the elements of the 5th, 6th and 7th subgroup of the PSE and the addition characterized in that they additionally include one or more elements selected from the elements Ga and In III. Main group, Cu and Ag of subgroup I, Zn of II. Subgroup, Mn of subgroup VII and Fe, Co, Ni, Pd and Pt of subgroup VIII of the PSE in oxidic and / or metallic form in an amount of 0.005 to 6% by weight, based on the total mass of the catalyst.

The oxide or oxide mixture of the elements Ti, Zr and Hf can additionally one or more Oxides of the elements of main group II and / or subgroup III including the Contain lanthanides of the Periodic Table of the Elements (PSE) and / or of aluminum. The elements Mg, Ca, Ba and Y, La, Ce or mixtures thereof are preferred.

Preferred additives according to the invention are those of the elements Ga, Cu, Zn, Mn, Fe, Co, Ni, of which Fe, Co and Ni are particularly preferred.

Another feature of the catalysts of the invention is that they are quantitative reversibility of their conversion from treatment by treatment to hydrogen Atmosphere in the temperature range from 250 to 900 ° C in the reduced form  by treatment in an oxygen-containing atmosphere in the temperature range 300 to 700 ° C resulting oxidized form (and vice versa).

The aromatization catalysts according to the invention are preferably prepared in such a way that in a known manner

• a) first a hydroxide, oxide, oxide mixture or hydroxide / oxide mixture of the elements Titanium, zirconium and hafnium is produced as a basic body, which additionally one or more oxides of the elements of main group II and / or subgroup III including the periodic table of elements (PSE) and / or of lanthanides Can contain aluminum, and that, again using known methods,
• b) this hydroxide, oxide, oxide mixture or hydroxide / oxide mixture thereafter at the Surface or in bulk with one or more connections of the elements of the 5th, 6th and 7th Subgroup of the PSE is modified and that according to the invention
• c) this product produced according to i) and ii) on the surface or in bulk with one or several compound (s) of the elements Ga and In III. Main group, Cu and Ag the I. subgroup, Zn of the II. Subgroup, Mn of the VII. Subgroup and Fe, Co, Ni, Pd and Pt of subgroup VIII of the PSE modified and then at temperatures between 300 and 750 ° C is calcined in air, oxygen or inert gas, so that all in i), ii) and iii) as a result, the elements mentioned are present in oxidized form.

Then the oxidized product with hydrogen or a hydrogen-containing gas in the Temperature range from 400 to 700 ° C over a period of at least 5 minutes up to treated for several hours, reducing reducible components.

The hydroxide, oxide, oxide mixture or hydroxide / oxide mixture prepared according to ii) can if necessary at temperatures of 300-750 ° C in air, oxygen or inert gas be annealed.

The base body is prepared using known preparation techniques, preferably through the steps of precipitation, filtering, drying and calcining,  Suitable compounds in stages i), ii) and iii) are the water-soluble salts of mentioned elements, for example the nitrates or chlorides, the nitrates being preferred are.

The modification on the surface or in bulk can be carried out in stages ii) and iii) for example by impregnation techniques such as watering, mixed precipitation or others suitable procedures are carried out.

Particularly suitable elements of the 5th, 6th and 7th subgroup of the PSE are chromium, molybdenum and tungsten.

The compounds of iron, nickel and cobalt are particularly preferred as additives in the Stage iii).

Thermal treatment in air, oxygen or inert gas in the temperature range of 300-750 ° C creates a porous solid with a surface area of 30 to 300 m ² / g. After cooling, if appropriate immediately before the catalytic reaction, the catalyst, as stated above, is treated with hydrogen or a hydrogen-containing gas in the temperature range from 400 to 800 ° C. over a period of at least 5 minutes to several hours and thereby reduced.

The catalysts have the special property of repeating the same amount of Consume hydrogen if it is previously treated with oxygen Atmosphere in the temperature range of 300-700 ° C were converted into an oxidized form. The measurement of this property, recognized as important for the purpose according to the invention takes place through the so-called temperature-programmed reduction, which is carried out with the catalysts is carried out in its oxidized form.

The catalysts of the invention are suitable for the selective catalytic production of Aromatics from aliphatic and / or alicyclic hydrocarbons. Opposite the in DE-OS 196 12 000 A1 catalysts described have the inventive Catalysts have the advantage of a higher temporal stability of the catalytic activity.  

The invention therefore also relates to the use of those described above Catalysts for the selective catalytic conversion of aliphatic or alicyclic Hydrocarbons with at least 6 carbon atoms in the longest chain in benzene or alkyl substituted benzenes. The catalyst is particularly suitable for catalytic Conversion of saturated or unsaturated hydrocarbons with 7 to 12 Hydrocarbons in the chain. The saturated hydrocarbons are included at least 7 to 12, preferably 7 to 10, in particular at least 7 to 8 Carbon atoms in the longest chain, preferred.

The new catalysts show high aromatization selectivities, as already described in DE-OS 196 12 000 A1, a higher temporal stability of the catalytic activity in the conversion of n-alkanes into aromatic compounds. she are special because of their ease of manufacture and the relatively inexpensive components economically.

The invention will be explained in more detail below by examples.

example 1 Production of a Cr / La / Zr oxide catalyst not according to the invention in accordance with DE OS 196 12 000 A1 as a comparative catalyst

A solution of 49.7 g of ZrOCl ₂ × 8H ₂ O and 2.66 g of La (NO ₃ ) ₃ × 6H ₂ O is prepared by slowly adding the salts to 100 ml of bidistilled water with stirring at room temperature. The solution is added dropwise simultaneously with a 25% NH ₃ solution into the distilled water, the pH of which has been adjusted to 10 with NH ₃ . The hydroxide mixture obtained in this way is, after filtering off, washed with distilled water until the Cl ^- ions can no longer be detected using an AgNO ₃ test. The (Zr, La) hydroxide mixture is then dried in air at 120 ° C for 24 hours.

19.6 g of the dried (Zr, La) hydroxide mixture are slowly added to 50 ml of a 2.34 g (NH ₄ ) ₂ CrO ₄ solution at room temperature with stirring. With constant stirring, the water in the mixture obtained is evaporated at 50 ° C. for 1 hour. The product is dried for 24 hours at 120 ° C and used as a catalyst precursor for the following preparations.

13 g of the precursor are treated for 4 hours at 600 ° C in air. The product obtained is the CrO _x / La ₂ O ₃ / ZrO ₂ catalyst in accordance with DE-OS 196 12 000. The catalyst contains 4% by weight of Cr and has a BET specific surface area of 145 m ² / g. and is used as a comparative catalyst (see Example 5).

Example 2 Production of an Ni / Cr / La / Zr oxide catalyst according to the invention

9.78 g of the precursor according to Example 1 are added to 50 ml of a solution containing 1.0987 g of Ni (NO ₃ ) ₂ × 6H ₂ O with stirring at room temperature. With constant stirring, the water in the mixture obtained is evaporated to near dryness at 60 ° C. for 1-2 hours. The product is dried at 120 ° C. for 8 hours and then calcined in air at 600 ° C. for 4 hours.

The Ni / Cr / La / Zr oxide catalyst obtained contains 4.46 mol% Ni, 8.95 mol% Cr, 2.5 mol% La and 84.09 mol% ZrO ₂ and has a specific BET surface area of 164.8 m ² / g.

Example 3 Production of an Fe / Cr / La / Zr oxide catalyst according to the invention

9.79 g of the precursor according to Example I are added at room temperature with stirring to 50 ml of a solution containing 1.5191 g of Fe (NO ₃ ) ₃ × 9H ₂ O. With constant stirring, the water in the mixture obtained is evaporated to near dryness at 60 ° C. for 1-2 hours. The product is dried at 120 ° C. for 8 hours and then treated in air at 600 ° C. for 4 hours.

The Fe / Cr / La / Zr oxide catalyst obtained contains 4.47 mol% Fe, 8.95 mol% Cr, 2.5 mol% La and 84.08 mol% ZrO ₂ and has a specific BET surface area of 145.7 m ² / g.

Example 4 Characterization of a Ni / Cr / La / Zr oxide catalyst according to the invention by measurement the hydrogen consumption of its oxidized form using the TPR method

TPR measurements were carried out in an apparatus according to the method described by NW Hurst et al [Catal. Rew. 24 (1982) 149]. 100 mg of the catalyst prepared in accordance with Example 2 were thermally treated in an argon stream at 300 ° C. for 1 h. After cooling to 50 ° C, the sample was heated in a 5% H ₂ -in-Ar flow of 15 ml / min with a linear heating rate of 10 K / min to a final temperature of 750 ° C. This is the first TPR run, called TPR1. The hydrogen consumption that occurred was detected catatometrically and is the TPR1 result, characterized by the TPR1 hydrogen consumption given in Table 1. The sample was then cooled to 50 ° C. in an Ar stream. Ar was then replaced by 20% O _{2 in} He current and the sample was heated to 600 ° C. and treated at this temperature for 1 h in order to reoxidize the sample. The catalyst in the oxidized form was cooled to 50 ° C. in an Ar stream. The Ar stream was then replaced by the 5% H ₂ -in-Ar stream at the flow rate of 15 ml / min and the sample was linearly reheated at 10 K / min up to 750 ° C. This is the second TPR run, called TPR2, and the hydrogen consumption detected by catatometry is the TPR2 result, characterized by the TPR2 hydrogen consumption given in Table 1.

Table 1

TPR1 and TPR2 characteristics of Ni / Cr / La / Zr oxide catalyst

Example 5 Catalytic testing of a Cr / La / Zr oxide catalyst not according to the invention according to DE OS 196 12 000 A1

The aromatization of n-octane as a test reaction was carried out at normal pressure in a temperature-controlled quartz flow reactor with a diameter of 8 mm, which was heated by means of a radiation furnace. A sample of 0.25 g of the Cr / La / Zr oxide catalyst produced according to Example 1 with a grain size of 0.3 mm to 0.8 mm was treated in the reactor for 2 h at 550 ° C. in flowing hydrogen . A stream of hydrogen saturated with n-octane was then passed over the catalyst at the same temperature. The molar ratio n-octane / H ₂ was 1 / 12.5 and the flow rate 1.5 l / h. The quantitative analysis of the reaction products was carried out using online GC.

The calculation of the degree of n-octane conversion U (%) and the product yield A (%) was carried out accordingly

U = (E _a - E _out) x 100 / E;

With
E _model: number of moles employed hydrocarbon, and
E _from : number of moles of unreacted hydrocarbon

A = P _i × 100 / E _off ;

With
P _i : number of moles of product i.

Table 2

Results of the n-octane DHC on the Cr / La / Zr oxide catalyst as a comparative catalyst

Example 6 Catalytic testing of a Ni / Cr / La / Zr oxide catalyst produced according to Example 2

The test was carried out analogously to Example 5.  

Table 3

Results of the n-octane DHC on the Ni / Cr / La / Zr oxide catalyst

The example demonstrates the improved temporal stability of the catalytic activity of the catalyst according to the invention

Example 7 Catalytic testing of an Fe / Cr / La / Zr oxide catalyst prepared according to Example 3

The test was carried out analogously to Example 5.

Table 4

Results of the n-octane DHC on the Fe / Cr La / Zr oxide catalyst

The example demonstrates the improved temporal stability of the catalytic activity of the catalyst according to the invention

Claims (14)

1. Catalyst for the aromatization of aliphatic and alicyclic hydrocarbons, consisting of a porous oxide or oxide mixture of one or more elements Ti, Zr and Hf, which at least on the surface one or more elements of the 5, 6 and 7 subgroup of the PSE in contains oxidized form in an amount of 0.01 to 10 wt .-%, based on the total mass of the catalyst;
has a specific surface area in the range of 30 to 300 m ² / g;
has the ability to repeatedly take up and release hydrogen in the temperature range of 400 to 700 ° C;
has no strongly acidic and / or strongly basic centers, characterized in that the catalyst additionally has at least one or more elements on the surface, selected from the elements Ga and In III. Main group, Cu and Ag of subgroup I, Zn of subgroup II, subgroup Mn of VII and subgroup Fe, Co, Ni, Pd and Pt of subgroup VIII of PSE in oxidized and / or metallic form in an amount of 0.005 to 6 wt .-%, based on the total mass of the catalyst contains. 2. Catalyst according to claim 1, characterized in that it additionally contains an oxide or several oxides, selected from the elements of the 2nd main group, the elements of the 3rd Subgroup including the lanthanides, the element aluminum and their mixtures, in an amount of 0.01 to 20% based on the total mass of the catalyst. 3. Catalyst according to claim 2, characterized in that it additionally, one or more Contains elements selected from magnesium, calcium, barium, yttrium, lanthanum, cerium and Mixtures of these 4. Catalyst according to claim 1, characterized in that it additionally contains iron, cobalt, Contains nickel or mixtures thereof.   5. Catalyst according to claim 1, characterized in that the elements Ga and In III. Main group, Cu and Ag of subgroup I, Zn of subgroup II, Mn of VII. Subgroup as well as Fe, Co, Ni, Pd and Pt of subgroup VIII of PSE on the surface and are contained in the bulk of the catalyst. 6. A method for producing the catalyst according to claim 1 by

• a) first a hydroxide, oxide, oxide mixture or hydroxide / oxide mixture of the elements titanium, zirconium and hafnium is produced, and
• b) this hydroxide, oxide, oxide mixture or hydroxide / oxide mixture is then modified on the surface with one or more compounds of the elements of the 5th, 6th and 7th subgroup of the PSE,

characterized in that

• a) this product produced according to i) and ii) on the surface or in bulk with one or more compounds the elements Ga and In III. Main group, Cu and Ag of subgroup I, Zn of subgroup II, subgroup Mn of VII and subgroup Fe, Co, Ni, Pd and Pt of subgroup VIII of PSE is modified and then at temperatures between 300 and 750 ° C in Air, oxygen or inert gas is calcined, so that all the elements mentioned in i), ii) and iii) are in the result in oxidized form.

7. The method according to claim 6, characterized in that in addition one or more Oxides of the elements of main group II and / or subgroup III including the Lanthanides of the Periodic Table of the Elements (PSE) through their compounds Impregnation techniques are introduced. 8. The method according to claim 6, characterized in that the elements Ga and In III. Main group, Cu and Ag of subgroup I, Zn of subgroup II, Mn of VII. Subgroup as well as Fe, Co, Ni, Pd and Pt of subgroup VIII of the PSE by Impregnation techniques applied to the surface and / or in the bulk of the catalyst are, preferably the elements iron, cobalt, nickel and mixtures thereof. 9. The method according to claim 6, characterized in that after the calcination or immediately before the catalytic reaction, a reduction with hydrogen or a  hydrogen-containing gas in the temperature range from 400 to 800 ° C over a period of is carried out for at least 5 minutes up to several hours, 10. The method according to claim 9, characterized in that the reduction at 600 to 800 ° C is carried out .. 11. The method according to claim 6, characterized in that the product of step ii) Temperatures of 300-750 ° C in air, oxygen or inert gas is annealed. 12. Use of a catalyst with the features of claim 1 for catalytic Conversion of aliphatic and alicyclic hydrocarbons with 7-12 Longest chain carbon atoms or mixtures thereof in alkyl substituted benzenes. 13. Use according to claim 10 for converting n-heptane into toluene. 14. Use according to claim 10 for converting n-octane into a mixture of o-xylene and ethylbenzene.