DE19516318A1 - Selective aromatization catalyst, process for its manufacture and use - Google Patents

Abstract

The invention relates to a selective catalyst for the aromatisation of aliphatic or alicyclic hydrocarbons with at least 6 carbon atoms in the longest chain and for dehydrating alkanes in alkenes. The novel catalyst is a porous composite consisting of an oxide of a transition metal from the IV, V or VI sub-group of the periodic system of elements and carbon, in which the catalyst has an area of 10 to 1000 m<2>/g. In the process, a mixture of oxides, hydroxides, alkoxides or compounds of a transition metal convertible into oxides and carbon are heat-treated in the temperature range from 800 to 1400 DEG C until a porous composite is formed and then treated with hydrogen or a hydrogen-containing gas. Production using a sol-gel process is also described. The preferred field of application of the catalysts is the production of toluene, o-xylene and ethyl benzene with excellent selectivity.

Description

The invention relates to a selective catalyst for Flavoring of aliphatic or alicyclic carbons hydrogens with at least 6 carbon atoms in the chain, Process for its production and its use.

C₆-C₈ aromatics such as toluene, ethylbenzene, p-xylene and o- Xylenes are important aromatic hydrocarbons that The main components of high-octane fuels are and also as Starting materials for diverse synthetic reactions in the chemical industry. The flavoring is therefore one of the most important processes in petrochemicals Refining paraffinic hydrocarbons. Because of the Indispensability of catalysts for technical reali The development of the flavoring processes is ef fective catalysts a constant demand on the Kataly se research.

Obtaining C₆-C₈ aromatics from mainly C₆-C₈- Hydrocarbon fractions containing paraffins for decades after the well-known reforming process modifications. The successful Pt / Al₂O₃ reforming catalysts, which are now diverse have been modified and improved, e.g. B. by using bi- or multimetallic additives and various  Variations of the carrier are described for example by Gates, B.C., Katzer, J.R. and Schuit, G.C. in Chemistry of Catalytic Processes, McGraw-Hill, N.Y. 1979. Thereby in generally a yield of 25 to 40% C₆-C₈ aromatics 450-550 ° C under 1-2 MPa with a molar hydrogen / Koh ratio of 10/1 to 100/1 an (0.5-1% by weight) - Pt- containing catalysts reached. By-products of reforming process are those formed by dehydrogenation reactions Hydrogen and formed by hydrogenolysis (hydrocracking) light n-paraffins, which the yield of valuable products Reduce.

Despite the progress made, the above have Disadvantages of catalyst systems. Precious metal catalysts expensive. The temporal stability of the catalysts in the necessary working conditions are in need of improvement, which causes additional effort and / or environmental problems in the Regeneration or workup of the catalysts arise. The selectivity for the target product is determined by the above. No ben reactions reduced; the valuable carbon carrier Oil is underused.

The invention has for its object new catalysts gates with high selectivity for aromatization reactions to provide and a process for their preparation and their use in a catalytic aromatization process.

According to the invention this object is achieved with a se selective aromatization catalyst that is featured through a porous composite consisting of (i) an oxide a transition metal of groups IVb, Vb or VIb or a mixture thereof and (ii) carbon, the catalyst tor a surface according to the BET method of 30 to 300 m² / g and the ability to reversibly absorb hydrogen in the Has a temperature range of 400 to 700 ° C.

An oxide of the elements Ti, Zr, V, Nb, Ta, Cr, W or Mo can be used, in particular of zirconium, titanium, tantalum or niobium.

The surface, determined by the BET method (J.Amer.Chem.Soc. 60 (1938) 309), lies in particular in Be  ranging from 50 to 200 m² / g.

It was also found that the catalyst was on surfaces are predominantly not strongly acidic or strong has basic centers. This resulted in a. Acidity measurement by means of the temperature-programmed desorption Ammonia (TPDA) or carbon dioxide.

It has also been found that the most common pore radio us of the pores in the composite formed as a framework structure is in the range from 1.5 to 5 nm, preferably 1.5 to 3 nm, d. H. on the border between mesopores and micropores.

The ability of the catalyst to absorb water fabric - and with subsequent flushing with inert gas - again for the complete release of this absorbed hydrogen is an essential feature of the invention. Here means "full constant charge "that a catalyst that after a first saturation with hydrogen and subsequent inert gas purge the amount of hydrogen that is then fed to him again releases essentially completely again. This attribute of the catalyst is in its context with the catalytic activity is not yet clear, but it is one for the Efficacy according to the invention is an important requirement. The production of the selective aromatization catalyst tors takes place in such a way that a composite consisting of

• (a) one or more oxides or mixed oxides of transition metals of group IVb, Vb or VIb of the periodic table or Mixtures thereof; or
• (b) one or more thermally convertible to an oxide Group IVb, Vb or VIb transition metal compounds the periodic table or mixtures thereof; and
• (c) carbon or one or more thermally in coals Transferable compounds

in the temperature range from 800 to 1400 ° C until the formation of a porous composites from oxides of transition metals and carbons fabric with a surface of 30 to 300 m² / g and capable thermal reversible absorption of hydrogen delt and after cooling, if necessary immediately  before the catalytic reaction, with hydrogen or a hydrogen-containing gas in the temperature range from 400 to 700 ° C over a period of at least 5 minutes to several Hours.

It is preferably an unsupported compo sit, in which the above-mentioned oxygen compounds of Transition metals either into a carbon framework built in or in front of it in a fine distribution lie or with the carbon in a transition metallic Scaffold structure is installed or on this in fine Ver division exists.

The transition metal compounds are preferably the Oxides, hydroxides or oxygen acids of the elements Ti, Zr, V, Nb, Ta, Cr, W or Mo are used, especially those from Zirkoni um, titanium, tantalum or niobium.

The production of the composite can be done in different ways respectively. A preferred method is that after a sol-gel process is used in which

• (1) from an aqueous and / or alcoholic solution or a corresponding sol of a pyrolyzable carbon ver binding,
• (2) an aqueous and / or alcoholic sol with oxides, Hydroxides or oxygen acids of transition metals Group IVb, Vb or VIb of the Periodic Table of the Elements or Mixtures of these compounds and
• (3) from stabilizing complexing agents a mixed sol is formed and after removing the solution is shaped and thermally treated up to about 800 ° C, to put together by pyrolyzing the carbon compounds with the transition metal oxides to composite moldings with porö to get its carbon skeleton.

In this process, from a hydrosol, the after drying is present as a hydrogel, and through the subsequent Eating pyrolysis is a coked product (composite) in which the Transition metal compound (s) in fine distribution, preferred wise even distribution, in a carbon skeleton  is (are) installed.

As a pyrolyzable carbon compound for example "Pechic Acid" [e.g. B. prepared according to Fuel, 73 (1994) - 243] or a carbohydrate such as sucrose. It can a low-viscosity polyacrylic acid can also be used.

Hydrogen per oxide, acetylacetone or polyalcohols used. The complex formers serve to precipitate poorly soluble over to avoid gang metal compounds from the gel. The addition the complexing agent is therefore expediently already at Hydrolysis of a hydrolyzable compound of these elements, preferably an alkoxy compound, or in peptization a transition metal oxide or hydroxide.

Advantageous transition metal compounds are exemplary wise those that can form solutions or brine. This includes ren for example oxo acids, alkoxides, inorganic salts of organic acids, brine of peroxyacids, e.g. B. Zirconium (IV) propoxide, niobium (V) ethoxide, tetrabutyl orthotitanate, Te traisopropyl orthotitanate, niobium oxide hydrate, tan talum (V) ethoxide, molybdenum (VI) oxide, vanadium (V) oxide, tungsten acid etc.

Another way of making the composite consists of a high carbon substance like for example activated carbon or certain polymers, with a aqueous and / or alcoholic solution of oxides, hydroxides or oxygen acids of transition metals of group IVb, Vb or VIb of the Periodic Table of the Elements or Mixtures impregnate these connections.

Carbon is both a high carbon content substance as well as pure carbon up to graphitic Understand carbon, as in further heat treatment development.

It is essential to the invention that the thermal treatment development of the porous moldings in the range from 800 to 1400 ° C, preferably 850 to 1300 ° C depending on the chosen transition measurement tall connection only goes to the oxide and if possible no X-ray  genetically detectable carbide formation is caused, to ensure catalytic effectiveness.

The oxides formed are often crystalline and can X-ray can be detected by gene diffraction.

Following the thermal treatment and preferably immediately before use as a catalyst, the invented molded composite of hydrogen treatment according to the invention either with hydrogen gas alone or with a gas that Contains hydrogen. This hydrogen treatment over a period of 5 minutes to several hours carried out. This treatment is preferably carried out 30 to 90 Minutes. Without this procedural measure or with a ge wrestling hydrogen saturation is the catalytic activity not sufficient d. H. the yield of target products is too low.

"Hydrogen-containing gas" means a gas where the part that is not hydrogen is among the conditions essentially no reaction with the water incoming fabric.

The catalyst has the property of being absorbed To release hydrogen completely again, for example an inert gas is passed through it. The measurement the water important property for the purpose of the invention takes place through the so-called temperature-programmed reduction (TPR) and the temperature-programmed desorption of water fabric (TPDH).

The catalyst of the invention is suitable for selective ven catalytic production of aromatics from aliphatic and / or alicyclic hydrocarbons.

The invention therefore also relates to the use of the selective catalytic catalysts described above conversion of aliphatic or alicyclic carbons Hydrogens with at least 6 carbon atoms in the length most chain in benzene or alkyl-substituted benzenes.

The catalyst is particularly suitable for catalytic Conversion of saturated or unsaturated hydro  substances with 6 to 12 carbon atoms in the chain. Here are the saturated hydrocarbons with at least 6 to 12, preferably at least 6 to 10, in particular at least 6 to 8 carbon atoms in the longest chain are preferred.

For example, n-hexane in benzene, n-heptane in Toluene and n-octane in xylene and ethylbenzene with great selek activity converted.

In comparison to the known Pt / Al₂O₃ catalyst ren with this new class of aromatization catalysts gates, for example, in the conversion of n-octane to alkyl aromatics with a zirconium oxide / C-containing Catalyst an increase in the C₆-C₈ aromatic selectivity of 61 to 64% achieved. The resulting aromatic fraction existed about 85% of o-xylene in the catalyst according to the invention and ethylbenzene and only 4.4% from the physiological point of view benzen. On the other hand, only 33.4% C₈- on Pt / Al₂O₃ Aromatics, but about 30% benzene. In the n-hexane conversion with a Zro₂ / C catalyst, the aromatic fraction is too 100% benzene, while a platinum catalyst is a mixture of C₆, C₇ and C₈ aromatics.

The new catalysts show outstanding selectivity vity and increased yield in the conversion of n-alkanes into aromatic compounds. They are also easy because of their Manufacturability and the relatively inexpensive components be particularly economical.

Another advantage is that the emergence of physiologically questionable benzene with input products 7 carbon atoms in the chain almost completely below can be pressed. Furthermore, the yield of valuable material products to the disadvantage of otherwise occurring by-products elevated.

The invention is illustrated below by examples are explained. The catalysts of the invention are marked as follows:  

"Transition metal oxide / C source / thermal temperature Treatment in Ar "

C sources: P (pitchic acid), (B) sucrose, AK (activated carbon); Example: TiO₂ / Z / 1100.

example 1 Production of a catalyst according to the invention by Sol-gel process with pitchic acid as an organic component

Dissolved by hydrolysis of 0.01 mol of zirconium (IV) propylate in 12.5ml methanol and 1.5g acetylacetone, with 25ml distillate A "zirconium oxide sol" was produced in water under ice cooling posed. A solution of. Was added to this sol under ice cooling 0.32g "Pechic Acid", 0.32g Glycerin and 2.5ml distilled Water in 10 ml of methanol is added dropwise and with stirring adds. The methanol was expanded by heating to about 60 ° C evaporated. The binary gel formed can be partial Drying can be deformed by extrusion or tableting. It was transferred to a xerogel by drying at 110 ° C. The xerogel can become more substantial at fragments at will Strength are crushed. The xerogel was in at 900 ° C Argon atmosphere thermally treated for 1h. Form and firm remain intact.

The catalyst ZrO₂ / P / 900 obtained has a specific surface area according to BET of 143m² and one of the most common Pore radius of 1.9nm. According to the X-ray structure analysis zirconium is predominantly present as a crystalline oxide tetragonal structure. The average crystallite size be carries 6.8nm.

Example 2 Production of a catalyst according to the invention by Sol-gel process with sucrose as an organic component

0.01 mol of zirconium (IV) propylate and 0.78 g of acetylacetone were dissolved in 5 ml of methanol. To this solution was  Room temperature a solution of 0.78 g acetylacetone in 2.5 ml distilled water added with stirring. By heating The methanol was largely evaporated to about 60 ° C. Here a yellow translucent binary gel formed, the was converted into a xerogel by drying at 110 ° C. The Xerogel was as in Example 1 for 1 h at 900 ° C in Argonatmo sphere thermally treated.

The catalyst ZrO₂ / S / 900 obtained has a specific surface area according to BET of 126m² and a most common Pore radius of 2.4 nm. According to the X-ray structure analysis zirconium is predominantly present as a crystalline oxide tetragonal structure. The average crystallite size be carries 4.5nm.

Example 3 Production of a catalyst according to the invention by Impregnation process

4.5 g of activated carbon (from Fluka) were mixed with an aqueous Solution of 1.44g ZrO (NO₃) ₃ · 7H₂O impregnated at pH = 1. To Drying at 120 ° C for 4h, the catalyst was 4h in one Ar current thermally treated at 1000 ° C. The ZrO₂ content was 10% by weight.

The catalyst has a specific surface from 840m² / g.

Example 4 Characterization of a catalyst according to the invention Measurement of the hydrogen absorption capacity by means of temperature programmed reduction (TPR) and temperature programmed Desorption of hydrogen (TPDH)

TPR and TPDH measurements were carried out in one apparatus speaking that of Robertson et al. [J. Catal. 37 (1975) 424] specified. 500mg of the catalyst ZrO₂ / P / 900 were thermally treated in an argon stream at 300 ° C. for 1 hour. To The sample was cooled to room temperature for one first hydrogen uptake in a 5% H₂-in-Ar stream with a Heating rate of 10K / min up to a final temperature of 750 ° C heated. The sample was then cooled to room temperature  door in the H₂ / Ar stream. Then the H₂ / Ar current was again replaced by Ar and the sample in the Ar current linear at 10K / min heated to 800 ° C to desor beers.

After this pretreatment procedure there was another linear heating of the sample in a 5% H₂-in-Ar flow up to 750 ° C. The resulting hydrogen consumption was ka tharometrically detected and gave the TPR result, known characterized by the hydrogen consumption given in Table 1 and the peak maximum temperature. After cooling, Electricity linearly heated to 800 ° C. The amount of desorb the hydrogen was again recorded continuously and gave the TPDH result in Table 1. The TPR and TPDH Results are a measure of the reversible hydrogen uptake Measuring or dispensing capacity of the catalyst in the area of the reak tion temperatures of the catalytic reactions.

Table 1

TPR and TPDH characteristics of ZrO₂ / P / 900

Example 5 Catalytic testing of a catalyst according to the invention

The catalytic reaction was carried out in a heated, temperature-controlled quartz flow freak gate with a diameter of 8mm. A sample of 500 mg of the catalyst prepared in accordance with Example 1 ZrO₂ / P / 900 and a grain size of 0.3mm to 0.8mm was in Reactor treated for 1 h at 550 ° C in flowing hydrogen. Thereafter, at the same temperature, one with hydro  saturated hydrogen flow, see Tables 2 and 3, given over the catalyst. The reaction reached after 1 h a steady state. Analysis of the reaction products was carried out on-line gas chromatography; gas chromatography cal separation of the aromatics and the other C₅-C₉ coal water Hydrogen was carried out on a Benton 34 column, which was the lowest boiling C₁-C₄ reaction products on an alumina column.

The calculation of the degree of conversion U and the selectivity S took place accordingly

U = (E - A) x 100 / E;

With
E: number of moles of hydrocarbon used, and
U: number of moles of unreacted hydrocarbon

S = Pi x n x 100 / (E - A) x m;

With
Pi: number of moles of product i,
n: carbon number in i, and
m: carbon number in the educt.

Table 2

Results of the n-hexane conversion on the catalyst ZrO₂ / P / 900 at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 550 ° C, molar ratio n-hexane / H₂ = 1/6, hydrogen flow 3 l / h

Table 3

Results of the n-octane conversion on the catalyst ZrO₂ / P / 900 at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 550 ° C, molar ratio n-hexane / H₂ = 1/15, hydrogen flow 3 l / h

Example 6 Catalyst TiO₂ / P / 900

This catalyst was prepared analogously to Example 1 characterized analogously to Example 4 and analogously to Example 5 examined catalytically. The catalyst has a BET Surface of 308m², a most common pore radius of 5.0nm and a TiO₂ particle size of 4.7 nm.  

Table 4

TPR and TPDH characteristics of TiO₂ / P / 900

Table 5

Results of the n-hexane conversion on the catalyst TiO₂ / P / 900 at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 550 ° C, molar ratio n-hexane / H₂ = 1/6, hydrogen flow 3 l / h

Table 6

Results of the n-octane conversion on the catalyst TiO₂ / P / 900 at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 550 ° C, molar ratio n-octane / H₂ = 1/15, hydrogen flow 3 l / h

Example 7 Catalyst ZrO₂ / S / 900

This catalyst was prepared analogously to Example 2 characterized analogously to Example 4 and analogously to Example 5 examined catalytically. The catalyst has a BET Surface of 126sqm, a common pore radius of 2.4nm and a Zro₂ particle size of 4.5 nm.

Table 7

TPR and TPDH characteristics of ZrO₂ / S / 900

Table 8

Results of the n-octane conversion on the catalyst ZrO₂ / S / 900 at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 550 ° C, molar ratio n-octane / H₂ = 1/15, hydrogen flow 3 l / h

Example 8 Catalyst ZrO₂ / Ak / 900

This catalyst was described as in Example 3 prepared, characterized analogously to Example 4 and analogously to Example 5 examined catalytically. The catalyst has over a BET surface area of 840m².  

Table 9

TPR and TPDH characteristics of ZrO₂ / Ak / 900

Table 10

Results of the n-octane conversion on the catalyst ZrO₂ / Ak / 900 at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 550 ° C, molar ratio n-octane / H₂ = 1/15, hydrogen flow 3 l / h

Example 9 Niobium oxide / P / 900 catalyst

This catalyst was prepared analogously to Example 1 characterized analogously to Example 4 and analogously to Example 5 examined catalytically. The catalyst has a BET Surface of 185m.

Table 11

TPR and TPDH characteristics of niobium oxide / P / 900

Table 12

Results of the n-octane conversion on the catalyst niobium oxide / P / 900 at normal pressure after a reaction time of 1 hour, catalyst weight 500 mg, reaction temperature 550 ° C., molar ratio n-octane / H₂ = 1/15, hydrogen flow 3 l / h

Example 10 (Comparative Example 1) Comparative catalyst Pt / Al₂O₃

This comparative catalyst was a classic reforming catalyst that is made by impregnation a γ-Al₂O₃ with a specific surface area of 300 m² / g was made with hexachloroplatinic (IV) acid. The platinum Content was 0.5%. After the impregnation, the catalyzer Calculated in air for 1 hour at 500 ° C and then in water for 1 hour fabric reduced. The catalytic testing was carried out analogously to Example 5.

Table 13

Results of the n-hexane conversion on the catalyst Pt / Al₂O₃ at normal pressure after 1h reaction time, catalyst weight 500mg, reaction temperature 500 ° C, molar ratio n-hexane / H₂ = 1/6, hydrogen flow 3 l / h

Table 14

Results of the n-octane conversion on the Pt / Al₂O₃ catalyst at normal pressure after 1 hour reaction time, catalyst weight 500 mg, reaction temperature 450 ° C, molar ratio n-octane / H₂ = 1/15, hydrogen flow 3 l / h

Example 11 (Comparative Example 2) Comparative catalyst Ga / HZSM-5

This catalyst is a classic catalyst for aromatizing light hydrocarbons fabrics. The catalyst was made by using HZSM-5 a 0.05 molar aqueous solution of Ga (NO₃) ₃ was soaked. It was then gradually heated up to 500 ° C in air Leave at 500 ° C for 1 hour. In this form it became a catalyst used. The catalytic testing was carried out analogously to Bei game 5.

Table 15

Results of the n-hexane conversion on the catalyst Ga / HZSM-5 at normal pressure after 1 h reaction time, catalyst weight 500 mg, reaction temperature 500 ° C, molar ratio n-hexane / H₂ = 1/6, hydrogen flow 3 l / h

Claims (18)

1. Selective aromatization catalyst, characterized by a porous composite consisting of an oxide of a transition metal of group IVb, Vb or VIb and carbon, the catalyst having a surface area by the BET method of 30 to 300 m² / g and the ability to be reversible Has uptake of hydrogen in the temperature range 400 to 700 ° C. 2. Catalyst according to claim 1, characterized in that the transition metal oxide is an oxide of zirconium, titanium, Is tantalum or niobium. 3. Catalyst according to claim 1, characterized in that the surface according to the BET method in the range from 50 to 200 m² / g, preferably 100 to 180 m² / g. 4. Catalyst according to claim 1, characterized in that the surface of the catalyst is essentially none has strongly acidic or strongly basic centers. 5. A catalyst according to claim 1, characterized in that the most common pore radius of the pores in the range of 1.5 to 5 nm, preferably 1.5 to 3 nm. 6. Catalyst according to claim 1, characterized in that the oxides of the transition metals are essentially crystalline are. 7. A process for the preparation of a selective aromatization catalyst, characterized in that a composite consisting of

• (a) one or more oxides or mixed oxides of transition metals of group IVb, Vb or VIb of the periodic table or mixtures thereof; or
• (b) one or more compounds of transition metals of group IVb, Vb or VIb of the periodic table or mixtures thereof which can be thermally converted into an oxide; and
• (c) carbon or one or more compounds which can be thermally converted into carbon

in the temperature range from 800 to 1400 ° C until the formation of a porous composites from oxides of transition metals and carbons fabric with a surface of 30 to 300 m² / g and capable thermal reversible absorption of hydrogen delt and after cooling, if necessary immediately before the catalytic reaction, with hydrogen or a hydrogen-containing gas in the temperature range from 400 to 700 ° C over a period of at least 5 minutes to several Hours. 8. The method according to claim 7, characterized in that the thermal treatment up to the formation of the composite in the tempe temperature range from 850 to 1300 ° C. 9. The method according to any one of claims 7 or 8, characterized records that the oxides of the transition metals until formation crystalline phases are treated thermally. 10. The method according to claim 7, characterized in that the composite is produced by a sol-gel process in which

• (1) an aqueous solution or an aqueous-alcoholic solution or a sol of a pyrolyzable carbon compound,
• (2) an aqueous or aqueous-alcoholic sol with oxides, hydroxides or oxygen acids of transition metals of group IVb, Vb or VIb of the PSE or their mixtures and
• (3) complexing agents

a mixed sol formed after removal of the solvent molded and pyrolytically treated to 800 ° C to  Composite molded articles with a porous carbon structure. 11. The method according to claim 10, characterized in that the pyrolyzable carbon compound pechic acid or a Is sucrose derivative. 12. Use of a selective aromatization catalyst having the features of claim 1 for catalytic conversion of aliphatic or alicyclic hydrocarbons or Mixtures of these with at least 6 carbon atoms in the longest chain in benzene or alkyl substituted benzenes. 13. Use according to claim 12 for catalytic conversion of saturated or unsaturated hydrocarbons with 6 up to 12 carbon atoms in the longest chain. 14. Use according to claim 13 for catalytic conversion of n-heptane in toluene. 15. Use according to claim 13 for catalytic conversion of n-octane in a mixture of o-xylene and ethylbenzene. 16. Use according to claim 13 for catalytic conversion of n-hexane in Benzen.