DE19616736A1 - Selective aromatization catalyst - Google Patents

Abstract

This invention concerns a catalyst, particularly for selective production of aromatics from a hydrocarbon stream with straight-chained, branched or cyclic alkyl or alkylene chains, of 6 to 12 carbon atoms. On an oxide of a transition metal of group IVB of the periodic table, such as TiO2 or ZrO2, this catalyst contains at least one element from the VIIIth secondary group, such as palladium, platinum, rhodium, rhenium or tin, and, optionally, a compound of alkali or earth alkali metals, a compound from the third major or secondary group, or zinc, or at least one compound from the sulphur, tellurium, arsenic, antimony or selenium group. The invention also concerns the use of this catalyst for producing aromatics, such as ethyl benzene or xylolene from C6 to C12-hydrocarbons.

Description

The invention relates to a noble metal-containing catalyst a ceramic carrier for the selective production of aromatics from paraffinic / naphthenic hydrocarbon streams with straight-chain, branched and / or cyclic alkyl or Al kylene chains of 6 to 8 carbon atoms. The invention relates especially the production of C₈ aromatics.

The most important source for technically important C₆ to C₈ aromatics the catalytic refor is like benzene, xylenes or ethylbenzene mieren (so-called reforming). When reforming, straight-chain Pa raffinate hydrocarbons into branched paraffin hydrocarbons and aliphatic-aromatic and aromatic hydrocarbons transferred. This procedure is used to increase the one hand Knock resistance of Otto fuels used, d. H. the obtained reaction mixtures are usually used as such; on the other hand, the resulting aromatic compounds e.g. B. separated by distillation and serve as intermediates and synthesis building blocks e.g. B. for the production of synthetic rubber and synthetic fibers. The ge from components of the C₈ fraction Ethylbenzene is used, for example, to obtain styrene or polystyrene used.

When reforming, different implementations take place such as Isomerization, aromatization (dehydrogenation) and cyclization. The one at temperatures from 450 to 550 ° C and pressures from 15 to Process running at 70 bar is mostly based on platinum catalysts Controlled carriers.

Catalysts that contain metals other than platinum, such as Pt-Re / Al₂O₃ · SiO₂ or Pt / Sn / Al₂O₃ · SiO₂ (so-called. Bimetallic Catalysts) are also known; e.g. B. is a catalyst based on Pt / Sn / Al₂O₃ in J. Mol. Catal. 88 (1994) 359-376 wrote. The carrier materials are mostly Aluminosilicates or zeolites. Pt catalysts on L-zeolites (see Energy Progress 7, (1987), 215-222) achieve a high Aromatic selectivity, which increases the shape selectivity of the carrier is written, but with a low space-time yield. More component catalysts such as Pt / Co / Nd (US Pat. No. 4,136,130) or Pt / Co / Re / Ge (U.S. Patent 4,136,017) on chlorinated (non-zeolitic) Al₂O₃ carriers, however, develop higher activity, but tend to Formation of crack products and thus lower aromatics  selectivity, especially as regards the formation of C₈ aromatics (ethyl benzene; Styrene; Xylenes).

The object of the invention is to provide a catalyst create of the disadvantages mentioned or not in ge has less degree and C₆ to C₈ hydrocarbon streams in high yield to aromatics. A special task is a catalyst with special selectivity for Finding ethylbenzene among the C₈ aromatics with the highest Value creation counts.

The object was achieved by a catalyst based on one or more ceramic oxides of metals from the fourth subgroup (group 4B) of the elements, in particular ZrO₂ and TiO _2, a noble metal selected from the elements of the eighth group of the periodic table of the periodic table of the elements , especially palladium, platinum or rhodium and / or rhenium and / or tin contains.

In addition to the elements mentioned, other elements can are used, in particular rhenium and / or tin as Zu to understand sentences about the elements of the eighth group. A wich tiger part of the invention is the addition of or doping with either compounds of the third main or Subgroup (3A or 3B) or basic compounds such as alkali, Alkaline earth or rare earths or their compounds, which are at Convert temperatures above 400 ° C into the corresponding oxides let The simultaneous doping with several of the named elements or their connections is possible. Well suited are, for example, potassium and lanthanum compounds. Furthermore can the catalyst with sulfur, tellurium, arsenic, antimony or se oil-containing compounds, which often increase selectivity, presumably by a partial "Poisoning", (moderators).

Compared to catalysts known from the prior art the catalysts of the invention have the advantage of higher overall Selectivity for aromatics, especially C₈ aromatics. The Catalysts according to the invention also allow height sales and the associated higher aromatics yield than State of the art catalysts.

So-called. amphoteric ceramic oxides, d. H. especially zircon oxides and titanium or mixtures thereof are used; suitable are also corresponding compounds that can be obtained by calcining let convert into these oxides. According to known ver  drive, for example according to the sol-gel process, precipitation of Salts, dewatering of the corresponding acids, dry mixing, on slurrying or spray drying.

All modifications of zirconium and titanium oxide are used as supports is suitable. However, it has been used for the production of catalysts on the basis of ZrO₂ proven to be advantageous if the Percentage of monoclinic ZrO₂ detectable by X-ray diffraction than 90%. Monocline ZrO₂ is in the X-ray diffraction pattern by two strong signals in the two-theta range of about 28.2 and 31.5 marked.

The doping with a basic compound can be carried out during the Production, for example by joint precipitation or after sluggish, for example by soaking the ceramic oxide an alkali or alkaline earth metal compound or a ver Binding of an element of the third subgroup or a rare one earth metal connection.

The content of alkali or alkaline earth metal, metal of the third Main or sub-group, rare earth metal or zinc is in the generally up to 20% by weight, preferably between 1 and 15 % By weight, particularly preferably between 1 and 10% by weight. As an alkali and alkaline earth metal suppliers are generally used Compounds that are obtained by calcining into the corresponding Let oxides convert. For example, hydroxides are suitable, Carbonates, oxalates, acetates, nitrates or mixed hydroxy carbonates of alkali and alkaline earth metals.

If the ceramic carrier is used additionally or exclusively doped a metal of the third main or subgroup, so in this case, too, you should start from connections that convert to the corresponding oxides by calcining to let. If lanthanum is used, for example, lanthanum Oxide carbonate, La (OH) ₃, La₂ (CO₃) ₃, La (NO₃) ₃ or lanthanum compound gene containing organic anions, such as La acetate, La formate, or La oxalate.

The precious metal component can be used in different ways be applied. For example, the wearer can use a Solution of a corresponding connection of the precious metal or Rheniums or tin can be soaked or sprayed. Suitable Metal salts for the preparation of such solutions are, for example the nitrates, halides, formates, oxalates, acetates of the noble metal connections. Even complex anions or acids complex anions such as H₂PtCl₆ can be used. As be particularly suitable for the production of the invention  The compounds PdCl₂, Pd (OAc) ₂ and Pd (NO₃) 2 proved.

The use of Precious metal sols with one or more components in which the Active component already in whole or in part in the reduced Condition is present.

If precious metal brines are used, they are previously in übli cher way, for example by reduction of a metal salt or a mixture of several metal salts in the presence of a Stabilizers such as polyvinylpyrrolidone produced and then entwe which is impregnated onto the carrier by impregnation or spraying be brought. The manufacturing technology is not pre-ver public German patent application 195 00 366.7 in detail treated.

The content of the catalyst in elements of the eighth group or Rhenium or tin can e.g. B. 0.005 to 5, preferably 0.01 to 2, are particularly preferably from 0.1 to 1.5% by weight. Will be additional Lich rhenium or tin used, their ratio to Precious metal component z. B. 0.5: 1 to 20: 1, preferably 1: 1 to 10: 1 be.

As moderating additives (according to the common idea of par tial poisoning of the catalyst) can if necessary Compounds of sulfur, tellurium, arsenic or selenium are incorporated be set. The addition of carbon monoxide during loading drive of the catalyst is possible. Has been particularly suitable the use of sulfur proved to be useful in the form of ammonium sulfide, (NH₄) ₂S is applied. The molar Ratio of precious metal component to poisoning compound can vary from 1: 0 to 1:10, preferably from 1: 1 to 1: 0.05.

The catalyst can be fixed in the reactor or z. B. in the form a fluidized bed and an appropriate shape to have. Are suitable for. B. Forms such as grit, tablets, monoli the, balls or extrudates (strands, wagon wheels, stars, rings).

The catalyst preparations have a BET surface area of up to 500 m² / g, usually from 10 to 300 m² / g, particularly preferably from 20 up to 100 m² / g. The pore volume is usually between 0.1 and 1 ml / g, preferably from 0.15 to 0.6 ml / g, particularly preferred 0.2 to 0.4 ml / g. The middle one, by Hg penetration analysis tunable pore diameter of the mesopores is generally between 8 and 60 nm, preferably between 10 and 40 nm. The proportion of pores with a width of more than 20 nm generally varies  between 0 and 60%, the use of Carriers with a proportion of macropores (i.e. pores of more than 20 nm) of more than 10%.

The special reaction is carried out at temperatures from 300 to 800 ° C, preferably 400 to 600 and in particular 400 to 550 ° C, and at pressures from 100 mbar to 100 bar, preferably 1 to 40 bar with an LHSV of 0.01 to 100 h ^-1 , preferably 0.1 to 20 h ^{-1 performed} . In addition to the hydrocarbon mixture to be dehydrogenated, diluents such as CO₂, N₂, noble gases or steam can be present. Hydrogen can also be added if required, the volume ratio of hydrogen to hydrocarbon (gases) being from 0.1 to 100, preferably from 1 to 20. The added hydrogen can be used to remove carbon that accumulates on the surface of the catalyst as the reaction time progresses.

In addition to the continuous addition of a gas that the coke prevents deposition during the implementation, there is the possibility the catalyst by passing hydrogen or Regenerate air from time to time. The regeneration is ongoing at temperatures in the range 300 to 900 ° C, preferably 400 to 800 ° C with a free oxidizing agent, preferably with air or in reducing atmosphere, preferably with hydrogen. The Regeneration can be at atmospheric, reduced or above operated at atmospheric pressure. Are suitable for. B. Pressures in the range of 500 mbar to 100 bar.

Catalyst production Examples 1, 2

6.38 g of Pd (OAc) ₂ were dissolved in 500 ml of water with the addition of 5 g of polyvinylpyrrolidone. 500 ml of a 0.34 M sodium citrate solution were added to this solution and the mixture was heated under reflux for 4 h. A clear Pd-Sol was created.
Analysis: 0.3% Pd.

The palladium sol was removed using a heated turntable a two-component nozzle on 200 g ZrO₂ tablets (5 × 3 mm tablets) sprayed on. The mixture was then dried at 120 ° C. for 72 h. The tablets were with their water intake (23.5 ml / 100 g) a solution of 2.96 g of K₂CO₃ soaked in 47 ml of water for 1 h. During the impregnation, it was shaken several times. After that was Dried at 120 ° C for 18 h.  

1.1 g of 40% by weight ammonium sulfide - ((NH₄) ₂S-) solution were diluted with water to 47 ml of solution, the pretreated tablets were soaked and dried at 120 ° C. for 16 h.
Analysis: 1.3% Pd, 0.96% K, 0.17% S.

Examples 3, 4, 5

5.6 g of oxalic acid were dissolved in 55 ml of water. About this solution 4.27 g of Pd (OAc) ₂ were added and heated gently 50 ° C and vigorous stirring.

The zirconia used was in the form of strands and pointed a BET surface area of 92 m 2 / g, a pore volume of 0.25 ml / g (Hg porosimetry) and about 30% of pores with more than 0.02 atm. Each 200 g of ZrO₂ were with one of their water intake (27.2 g water / 100 g) correspondingly concentrated Palla dium solution soaked until the liquid was absorbed (about 30 min). The strands were then rotated at 80 ° C in a rotary evaporator dried. The strands were then ge for 16 h at 120 ° C. dries.

After the palladium was applied, the strands were placed in one Slurried solution of 3.61 g K₂CO₃ in 55 ml water and after again dried in a rotary evaporator at 80 ° C. for about 30 min. The Strands were then dried at 120 ° C for 28 h.

1.1 g of 40% by weight ammonium sulfide solution was diluted with 55 ml of water, the pretreated strands were soaked and dried in a rotary evaporator at 80 ° C. and then at 120 ° C. for 65 h.
Analysis: 0.97% Pd; 0.98% K; 0.13% S; Rest ZrO₂.

Examples 6, 7, 8

5.6 g of oxalic acid were dissolved in 60 ml of water. About this solution 4.27 g of Pd (OAc) ₂ were added and with vigorous stirring and light ter heating to 50 ° C solved. 200 g ZrO₂ strands with one BET surface area of 70 m² / g, a pore volume of 0.28 ml / g and a Pores <20 nm share of about 30% according to their water absorption (30.6 g water / 100 g) soaked with the palladium solution. After about 30 minutes, the strands were rotary evaporated at 80 ° C fer dried. The strands were then ge for 24 h at 120 ° C. dries.  

After the palladium was applied, the strands were placed in one Slurried solution of 3.61 g of K₂CO₃ in 60 ml of water and after again dried in a rotary evaporator at 80 ° C. for about 30 min. The Strands were then dried at 120 ° C for 28 h.

1.1 g of 40% by weight ammonium sulfide solution was diluted with 55 ml of water. The pretreated strands were soaked in the diluted solution and dried in a rotary evaporator at 80 ° C. The strands were then dried at 120 ° C. for 70 h.
Analysis: 0.98% Pd; 0.94% K; 0.11% S.

Examples 9, 10

5.6 g of oxalic acid were dissolved in 52 ml of water. About this solution 4.27 g of Pd (OAc) ₂ were added and heated gently 50 ° C and vigorous stirring.

The zirconia used was in the form of strands and pointed a BET surface area of 46 m² / g, a pore volume of 0.23 ml / g (Hg porosimetry) and about 15% of pores with more than 0.02 µm. 200 g strands were made according to their water absorption (26 g water / 100 g) soaked with the palladium solution. After about 30 min the strands were rotated at 80 ° C steamer dried. The strands were then at 120 ° C. for 14 h dried.

After the palladium was applied, the strands were placed in one Slurried solution of 3.61 g of K₂CO₃ in 52 ml of water and after again dried in a rotary evaporator at 80 ° C. for about 30 min. The Strands were then dried at 120 ° C for 20 h.

1.1 g of 40% by weight ammonium sulfide solution was diluted with 52 ml of water, the pretreated strands were soaked in it and dried in a rotary evaporator first at 80 and then 65 h at 120 ° C.
Analysis: 0.92% Pd; 0.89% K; 0.11% S.

Trials in the pulse reactor

The aromatization of a C₆-C₈ hydrocarbon stream was in a micro-fixed bed pulse reactor. It was about 0.6 g of catalyst weighed in and pulsating (more atmospheric Pressure; without the addition of hydrogen) with pure n-octane strikes. Between two successive n-octane pulses (approx. 1.5 min) helium carrier gas flows through the reactor. The  Flow rate of the carrier gas is approximately 21.5 ml / min. A single pulse contains approx. 100 µg n-octane. The Reak tion products were quantified for each pulse using on-line GC-MS tativ captured.

The results obtained are shown in Table 1. The ange selectivity given relate to the period of each maximum sales achieved. For comparison, a trade was made usual reforming catalyst of known composition selected.

Table 1

The catalysts according to the invention perform at the same temperature higher selectivity with regard to the overall yield on aromatics as the comparative catalyst. The is remarkable high proportion of ethylbenzene, the product with the highest value creation.

Claims (12)

1. Catalyst, in particular for the selective production of Aromatics from hydrocarbon streams with straight-chain, ver branched and / or cyclic alkyl or alkylene chains from 6 up to 8 carbon atoms, containing one on an oxide Transition metal of group 4B of the periodic table of the Elements at least one element selected from the elements the eighth group and / or rhenium and / or tin. 2. Catalyst according to claim 1, containing TiO₂ and / or ZrO₂ as Transition metal oxide. 3. Catalyst according to claim 1, containing 0.005 to 5 wt .-% Palladium, platinum, rhodium and / or rhenium. 4. A catalyst according to claim 1, further comprising a ver Binding an alkali or alkaline earth metal, a compound the third main or sub-group and / or zinc. 5. Catalyst according to claim 4, containing as alkali metal Sodium or potassium. 6. Catalyst according to claim 4, containing as a compound of third main or subgroup a lanthanum, yttrium, Gallium, indium or thallium compound. 7. A catalyst according to claim 1, containing at least one ver bond from the group sulfur, tellurium, arsenic, antimony and / or selenium. 8. A catalyst according to claim 1, characterized by a BET surface area between 10 and 500 m² / g. 9. Catalyst according to claim 1, characterized by pores Width from 8 to 60 nm, with at least 10% of the pores Have a width of more than 20 nm and the specific pores volume is 0.1 to 1 ml / g. 10. A process for the preparation of the catalyst according to claim 1, characterized in that palladium, platinum, rhodium and / or rhenium is applied as a sol to the support.   11. Use of the catalyst according to claim 1 for the preparation of aromatics from hydrocarbons with straight-chain, ver branched and / or cyclic alkyl or alkylene chains from 6 up to 8 carbon atoms. 12. Use of the catalyst according to claim 1 for the preparation of ethylbenzene and / or xylenes.