NO171674B - PROCEDURE FOR REFORMING HYDROCARBONES, HOW THE HYDROCARBONS ARE CONTACTED WITH A CATALYST CONVERTER CONCERNING THE GREAT ZEOLITE CONTAINING A METAL OF GROUP VIII AND AN EARTHAL METAL METAL - Google Patents

Description

The invention relates to a method for reforming hydrocarbons, where the hydrocarbons are brought into contact with a catalyst comprising a large-pore zeolite containing a metal from group VIII and an alkaline earth metal. The method is particularly applicable for dehydrocyclization of acyclic compounds, especially dehydrocyclization of alkanes containing at least 6 carbon atoms while forming the corresponding aromatic hydrocarbons.

Catalytic reforming is well known within the petroleum industry and refers to the treatment of naphtha fractions to improve the octane number. Among the more important hydrocarbon reactions that take place during conversion operations are dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics and dehydrocyclization of paraffins to aromatic compounds. Hydrocracking reactions that give high yields of light, gaseous hydrocarbons, e.g. methane, ethane, propane and butane must in particular be minimized during conversion, as these reduce the yield of products that boil in the petrol's boiling range.

Dehydrocyclization is one of the main reactions in the conversion process. The conventional methods for carrying out these dehydrocyclization reactions are based on the use of catalysts consisting of a precious metal on a support. Known catalysts of this kind are based on aluminum oxide with from 0.2 to 0.8

wt% platinum and preferably also with another auxiliary metal.

The possibility of using carriers other than aluminum oxide

have also been investigated, and it has been proposed to use certain molecular sieves such as X and Y zeolites. These have proven to be suitable as long as the reactant and product molecules are so small that they can pass through the zeolite's pores. However, catalysts based on these molecular sieves have not been commercially successful.

According to the conventional methods for carrying out the aforementioned dehydrocyclization, the paraffins to be converted are passed over the catalyst, in the presence of hydrogen, at temperatures of the order of 500°C and pressures of from 5 to 30 bar. The paraffins are partially converted into aromatic hydrocarbons, and the reaction is accompanied by isomerisation and cracking reactions which also convert the paraffins into isoparaffins and lighter hydrocarbons.

The reaction rate for the conversion of the hydrocarbons into aromatic hydrocarbons depends on the reaction conditions and the type of catalyst.

The catalysts used so far have given moderately satisfactory results with heavy paraffins, but less satisfactory results with Cg-Cg paraffins, in particular Cg paraffins. Catalysts based on a type L zeolite

are more selective with respect to dehydrocyclization. These can be used to improve the reaction rate by conversion to aromatic hydrocarbons without the need for a higher temperature, since higher temperature usually reduces the stability of the catalyst and gives excellent results with Cg-Cg paraffins. However, there are problems with the length of the service life and with the regeneration ability, and satisfactory regeneration procedures are not known.

In a method for the dehydrocyclization of aliphatic hydrocarbons which is described in US Patent No. 4,104,320, the hydrocarbons are brought in the presence of hydrogen into contact with a catalyst which essentially consists of an L-type zeolite with exchangeable cations, of which at least 90 % are alkali metals selected from ions of sodium, lithium, potassium, rubidium and cesium, and containing at least one metal selected from metals from group VIII in the periodic table, tin and germanium, said metal or metals including at least one metal from group VIII in the periodic system with a dehydrogenating effect, to convert at least part of the raw material into aromatic hydrocarbons.

A particularly advantageous embodiment of this method involves the use of an L-type platinum/alkali metal zeolite catalyst, due to its high activity and selectivity when converting hexanes and heptanes to aromatics, but the lifetime of the catalyst remains a problem.

With the help of the present invention, the shortcomings of the known technique are overcome by using a catalyst consisting of a large-pore zeolite, an alkaline earth metal and a metal from group VIII for the transformation of hydrocarbons with very high selectivity with regard to the transformation of alkanes into aromatics.

The invention thus provides a method for reforming hydrocarbons, which method is characterized in that the hydrocarbons are brought into contact with a catalyst comprising a large-pore zeolite with an effective pore diameter of from 6 to 15 Å containing:

a) at least one metal from group VIII and

b) an alkaline earth metal selected from barium, strontium and

calcium, the selectivity index for the catalyst being

higher than 60%, or the manufacturing conditions are adapted so that the selectivity for N-hexane dehydrocyclization is higher than 60%, and the hydrocarbons are first, simultaneously or finally possibly brought into contact, under reforming conditions and in the presence of hydrogen, with a catalyst comprising a metal oxide carrier in which platinum and rhenium are deposited in an intimate mixture.

The catalyst used in the process has a satisfactory service life.

The large-pore zeolite is preferably an L-type zeolite containing from 0.1 to 5 wt% platinum and from 0.1 to 35 wt% barium. The hydrocarbons are contacted with the barium-exchanged type of zeolite at a preferred temperature of from 400°C to 600°C (preferably from 430°C to 550°C), a liquid space velocity of from 0.3 to 10, a pressure of from 1 atm to 35.2 kg/cm<2> (preferably from 3.5 kg/cm<2> to 31.1 kg/cm<2>) and an H2/HC ratio from 1:1 to 10:1 (preferably from 2:1 to

6:1).

The term "selectivity", as used in connection with the present invention, is defined as the amount of paraffin converted to aromatics as a percentage of the number of moles converted to aromatics and cracking products.

Isomerization reactions and alkylcyclopentane formation are not taken into account when determining the selectivity.

The term "selectivity for n-hexane" is defined here as the amount of n-hexane converted to aromatics, expressed as a percentage of the number of moles of n-hexane converted to aromatics and cracking products.

The selectivity for the conversion of paraffins to aromatics is a measure of the efficiency of the process with regard to the conversion of paraffins to the desired and valuable products, aromatics and hydrogen, as opposed to the less desirable products from hydrocracking.

The selectivity index is a characteristic property of any dehydrocyclization catalyst. The selectivity index is defined as the "selectivity for n-hexane" using n-hexane as feed and by working at 400°C,

0.70 kg/cm 2 , a liquid space velocity of 3 and 3 f^/HC after 20 hours.

Catalysts with high selectivity produce more hydrogen than less selective catalysts, because hydrogen is formed when paraffins are converted to aromatics, and hydrogen is consumed when paraffins are converted to cracked products. An increase in the selectivity of the process increases the amount of hydrogen formed (more aromatization), and decreases the amount of hydrogen consumed (less cracking).

Another advantage of using catalysts with high selectivity is that the hydrogen that is formed is cleaner than that formed by less selective catalysts. This higher degree of purity is due to the fact that more hydrogen is formed while less low-boiling hydrocarbons (cracking products) are formed. The purity of the hydrogen that is formed during reforming is critical if - which is usually the case in an integrated refinery - the formed hydrogen is used in such processes as hydrotreatment and hydrocracking, which require at least a certain minimum partial pressure for the hydrogen. If the purity becomes too low, the hydrogen can no longer be used for this purpose and must be used in a less valuable way, e.g. as fuel gas.

In the method according to the present invention, the hydrocarbons in the feed preferably consist of non-aromatic hydrocarbons containing at least 6 carbon atoms. It is preferable that the feed is essentially free of sulphur, nitrogen, metals and other known poisons for reforming catalysts.

The dehydrocyclization is carried out in the presence of hydrogen at such a pressure that the reaction is favored thermodynamically and unwanted hydrocracking reactions are limited kinetically. The pressures used preferably vary from 1 to 35.2 kg/cm<2>, preferably from 3.5 kg/cm<2> to 21.1 kg/cm<2>, while the molar ratio of hydrogen to hydrocarbons preferably varies from 1: 1 to 10:1, and preferably from 2:1 to 6:1.

In the temperature range from 400°C to 600°C, the dehydrc-cyclization reaction takes place with acceptable speed and selectivity.

If the working temperature is below 400°C, the reaction rate is insufficient and the yield consequently too low for industrial purposes. Likewise, the dehydrocyclization equilibria are unfavorable at low temperatures. When the working temperature is above 600°C, interfering, secondary reactions such as hydrocracking and charring occur which significantly reduce the yield and increase the catalyst's deactivation rate. It is therefore not advisable for the temperature to rise above 600°C.

In the preferred temperature range (430 o C to 550 o C)

for dehydrocyclization, the process is optimal with regard to the catalyst's activity, selectivity and stability.

The fluid space velocity per hour for the hydrocarbons is preferably between 0.3 and 10.

Among the crystalline large-pore zeolites which have been found to be useful for the purposes of the invention, L-type zeolites and synthetic zeolites with faujasite structure, such as zeolites X and Y, are the most important. They have visible pore sizes of the order of 7 to 9 Angstroms.

The composition of L-type zeolites, expressed as the molar ratio between the oxides, can be stated as follows: (0.9 - 1.3)M2/nO:Al2O3(5.2 - 6.9)Si02:yH20

where M denotes a cation, n denotes the valence of M and y can have any value from 0 to 9. Zeolite L, its X-ray diffraction pattern, properties and method of preparation are

described in detail in US Patent No. 3,216,789. US Patent No. 3,216,789 shows the zeolite which is preferred according to the present invention. The formula can vary without changing the crystal structure, e.g. the molar ratio of silicon to aluminum (Si/Al) can vary from 1.0 to 3.5.

The chemical formula for zeolite Y, expressed as the molar ratio between the oxides, can be stated as:

where x has a value greater than 3 and up to approx. 6, and y can have a value up to 9. Zeolite Y in powder form has a characteristic X-ray diffraction pattern which, together with the above formula, can be used for identification. Zeolite Y is described in more detail in US Patent No. 3 130 007.

Zeolite X is a synthetic, crystalline, zeolitic molecular sieve which can be given the formula:

where M represents a metal, especially alkali and alkaline earth metals, n is the valence of M and y can have any value up to 8 depending on M and the degree of hydration of the crystalline zeolite. Zeolite X, its X-ray diffraction pattern, properties and method of preparation are described in detail in US Patent No. 2,882,244.

The preferred catalyst according to the invention is an L-type zeolite inserted with one or more dehydrogenating components.

An essential feature of the catalyst used in the method according to the invention is the presence of an alkaline alkaline earth metal in the large-pore zeolite. The alkaline earth metal must be either barium, strontium or calcium, preferably barium. The alkaline earth metal can be incorporated into the zeolite by synthesis, impregnation or ion exchange. Barium is preferred over the other alkaline earth

in metals because it results in a somewhat less acidic catalyst. A high acidity is undesirable for the catalyst, because it promotes cracking, resulting in lower selectivity.

In one embodiment, at least part of the alkali metal is replaced with barium using known techniques for ion-. exchange in zeolites. This means that the zeolite is brought into contact with a solution containing an excess of Ba<++> ions. The amount of barium should be from 0.1% to 35% of the zeolite.

The dehydrocyclization catalyst used in the method according to the invention contains one or more metals from group VIII, e.g. nickel, ruthenium, rhodium, palladium, iridium or platinum.

The preferred metals from group VIII are iridium and especially platinum, which are more selective with regard to dehydrocyclization and are also more stable under the reaction conditions for dehydrocyclization than the other metals in group VIII.

The preferred percentage of platinum in the catalyst

lies between 0.1% and 5%.

The metals in group VIII are introduced into the large-pore zeolite by synthesis, impregnation or exchange in an aqueous solution of a suitable salt. When it is desired to introduce two metals from group VIII into the zeolite, the operation can be carried out simultaneously or in sequence.

Platinum can e.g. is introduced by impregnating the zeolite with an aqueous solution of tetraminoplatinum(II) nitrate, tetraminoplatinum(II) hydroxide, dinitrodiaminoplatinum or tetraminoplatinum(II) chloride. Platinum can be introduced by an ion-exchange process using cationic platinum complexes, such as tetramineplatinum(II) nitrate.

An inorganic oxide can be used as a carrier to bind the large-pore zeolite containing the metal from group VIII

and the alkaline earth metal. The carrier can be a natural or synthetically produced inorganic oxide or a combination of inorganic oxides. Typical inorganic supports that can be used include clays, aluminum oxide and silica, in which the acidic centers are preferably exchanged with cations that do not give a high degree of acidity (such as Na, K, Rb, Cs, Sr or Ba).

The catalyst can be used in any of the conventional types of apparatus used in the field. It can be used in the form of pills, pellets, granules, fragmented

.bits or in other special forms, placed as a

solid layer within a reaction zone, and the feed material can be sent through this in liquid phase, vapor phase or mixed through the layer. Alternatively, it can be produced in a form suitable for use in a moving bed, or in solid phase/liquid processes, in which the added material is sent upwards through a turbulent bed of finely divided catalyst.

After the desired metal or metals have been introduced, the catalyst is treated in air at approx. 260°C and then reduced in hydrogen gas at temperatures from 200°C to 700°C, preferably from 400°C to 620°C.

At this stage it is ready for use in the dehydrocyclization process. However, in some cases, e.g. when the metal or metals have been introduced by an ion exchange process, it is preferred to eliminate any residual acidity in the zeolite by treating the catalyst with an aqueous solution of a salt or hydroxide of a suitable alkali or alkaline earth metal to neutralize any hydrogen ions that may be formed during the reduction of metal ions with hydrogen.

In order to achieve optimal selectivity, the temperature should be adjusted so that the reaction rate is of a certain magnitude, but since too high a temperature and a reaction that has gone too far can reduce the selectivity, the conversion is kept below 98%. The pressure should also be adjusted within a suitable range. Too high a pressure will set a thermodynamic (equilibrium) limit for the desired reaction, while too low a pressure can result in coking and deactivation.

Although the main advantage of the invention consists in an improvement of the selectivity when converting paraffins (especially Cg-Cg paraffins) to aromatics, it has surprisingly been determined that the selectivity when converting methylcyclopentane to benzene is excellent. This reaction, which involves an acid-catalyzed isomerization step when carried out with conventional conversion catalysts based on chlorinated aluminum oxide, proceeds using the catalyst proposed here with a selectivity that is as good or better than for the known catalyst based on chlorinated aluminum oxide. Thus, the present invention can also be used to catalyze the conversion to aromatics of raw materials with a high content of 5-membered ring alkylnaphthenes.

Another advantage of this invention is that the catalyst used in the present method is more stable than previously known zeolite catalysts. Catalyst stability, or resistance to deactivation, determines its effective service life. Longer service life results in fewer interruptions in the process and less expenditure on regeneration or replacement of the catalyst.

In one embodiment of the method according to the invention, the hydrocarbons in the feed are first brought into contact with a first catalyst, which is a conventional conversion catalyst, and then into contact with a second catalyst, which is a dehydrocyclization catalyst consisting of a large-pore zeolite, an alkaline earth metal and a metal from group VIII.

Use of an advantageous conventional reforming catalyst consisting of an alumina support, platinum and rhenium is discussed in US Patent No. 3,415,737. Other advantageous bimetallic catalysts include platinum-tin, platinum-germanium, platinum-lead and platinum-iridium.

The hydrocarbons can be brought into contact with the two catalysts in sequence (series), with the hydrocarbons first being brought into contact with the first, conventional reforming catalyst and then with the second (dehydrocyclization) catalyst, or, so that the hydrocarbons are first brought into contact with the second catalyst and then with the first catalyst. The hydrocarbons can be brought into contact in parallel, so that a fraction of the hydrocarbons is brought into contact with the first catalyst, and another fraction of the hydrocarbons is brought into contact with the second catalyst. The hydrocarbons can also be brought into contact with both catalysts simultaneously in the same reactor.

The invention is further illustrated by the following examples, which show particularly advantageous embodiments of the method.

Example I

An "Arabian Light" distillate, which had been hydrorefined to remove sulphur, oxygen and nitrogen, was reformed at 7.0 kg/cm 2 , a headspace velocity of 2 and H 2 /HC = 6 with 3 different catalysts. The feed contained 80.2 vol% paraffins, 16.7 vol% naphthenes and 3.1 vol% aromatics, and it contained 21.8 vol% C5, 5 2.9 vol% Cg, 21.3 vol% C^ and 3 .2 volume% Cg.

In the first attempt, the "Arabian Light" distillate was reformed at 499°C using a commercial sulfided platinum-rhenium-alumina catalyst disclosed in US Patent No. 3,415,737.

In the second experiment, the "Arabian Light" distillate was reformed at 493°C using a platinum-potassium L-type zeolite catalyst prepared by: (1) impregnating a potassium L-type zeolite with 0 .8% platinum using tetraamine platinum (II) nitrate, (2) drying the catalyst, (3) calcining the catalyst at 260°C and (4) reducing the catalyst at 480°C to 500°C for 1 hour.

In the third experiment, carried out according to the present invention, the "Arabian Light" distillate was reformed at 4 93 QC using a platinum-barium-type L-zeolite catalyst prepared by: (1) ion exchange of a potassium-type L-zeolite with a volume of 0.17 molar barium nitrate solution large enough to provide an excess of barium compared to the ion exchange capacity of the zeolite, (2) drying the resulting barium-exchanged L-type zeolite catalyst, (3) calcining the catalyst at 590°C, (4) impregnation of the catalyst with 98% platinum using tetramine platinum(II) nitrate, (5)

drying the catalyst, (6) calcining the catalyst at 260°C and (7) reducing the catalyst in hydrogen at 480°C to 500°C for 1 hour.

The results of these three experiments are shown in Table I.

This series of experiments shows that the use of a platinum-barium-type-L-zeolite catalyst in reforming processes gives a selectivity when converting hexanes to benzene markedly better than what was the case for the state of the art.

It should be noted that along with this superior selectivity there is an increase in the formation of hydrogen gas which can be used for other processes. Note also that the purity of the hydrogen gas is higher for the Pt/Ba/L experiment since more hydrogen is formed, while less of plus C2 is formed.

Example II

Another series of experiments was carried out to show that the present method is also effective with other large pore zeolites in addition to the L type of zeolites. The selectivity index was measured for four catalysts.

This second series of experiments was carried out with n-hexane as feed. All experiments in this series were performed at 490°C, 7.0 kg/cm<2> and a space velocity of 3 and H2/HC = 3.

In the first experiment, a platinum-potassium L-type zeolite was used. This was produced by the methods shown in the second process in example I.

In the second experiment, a platinum-barium-L-type-zeo-

slightly applied. This was prepared according to the methods shown in the third process in example I, with the exception that the barium nitrate solution was 0.3 molar instead of 0.7 molar.

In the third experiment, platinum sodium zeolite Y was used, which was prepared by impregnating a sodium zeolite Y with Pt(NHg) 4 (NO 3 ) 2 . This gives a content of 0.8% platinum. The catalyst was then dried, calcined at 260°C and reduced in hydrogen at 480°C - 500°C.

In the fourth experiment, a platinum barium zeolite Y was used which had been prepared by ion exchange of a sodium zeolite Y with 0.3 molar barium nitrate at 80°C, with subsequent drying and calcination at 590°C, after which the zeolite was impregnated with Pt(NH 3 ) 4 (NO 3 ) 2 , yielding 0.8% platinum. The catalyst was then dried, calcined at 260°C and reduced in hydrogen at 480-500°C. The results of these experiments are shown in Table II.

Thus, incorporation of barium into a large-pore zeolite, such as a Y-type zeolite, leads to a dramatic improvement in selectivity for n-hexane. Note that the stability of the platinum-barium L-type zeolite is excellent. There was no reduction in conversion after 20 hours of use when the platinum barium L-type zeolite was used as catalyst.

Example III

A third series of experiments was conducted to show the effect of adding additional ingredients to the catalyst.

This third series of experiments was carried out using a feed that had been hydrorefined to remove sulphur, oxygen and nitrogen; the feed contained 80.9 vol.% paraffins, 16.8 vol.% naphthenes and 1.7 vol.% aromatics. The feed also contained 2.6 vol.%, 47.6 vol.% Cg,

43.4 vol% C^ and 6.3 vol% Cg. All experiments in this series were performed at 490°C, 7.0 kg/cm<2>, a space velocity of 2.0 and 6.0 H2/HC.

In the first experiment, a platinum-sodium zeolite Y was prepared by the methods shown in the third process in Example II.

In the second experiment, a platinum-barium zeolite Y was prepared by the method shown in the fourth process in Example II.

In the third experiment, a platinum-rare-earth zeolite Y was prepared by impregnating a commercial rare-earth zeolite Y from Strem Chemicals Inc. with platinum to a content of 0.8% Pt using Pt(NH3)4 (N03)2; then the zeolite was dried, calcined at 260°C and reduced at 480 - 500°C.

In the fourth experiment, a platinum rare earth barium zeolite Y was prepared by ion exchange, treating a commercial Strem Chemicals Inc. rare earth zeolite Y with a 0.3 molar Ba(NO 3 ) 2 solution at 80° C, dried and calcined at 590°C. Impregnation of the zeolite with Pt(NH3) 4 (N03).-2 gave a platinum content of 0.8%; then the zeolite was dried, calcined at 260°C and then reduced at 480 - 500°C. The results of these tests are given in the table

III.

This series of experiments shows that the addition of rare earth species to the catalyst has a lowering effect on the selectivity.

Example IV

An Arabian Naphtha, hydrorefined to remove sulphur, oxygen and nitrogen was subjected to reforming at 7.0 kg/cm 2 , a headspace velocity of 3 and 3 H„/HC to form a Cg product with an aromatics content of 82 wt% by two different processes. The feed was Arabian Naphtha treated with hydrogen as mentioned above, containing 67.9% paraffins, 23.7% naphthenes and 8.4% aromatics. Distillation results by the D86 method were: start - 95°C, 5% - 103.9°C, 10% - 106.7°C, 30% - 120°C, 50% - 129°C, 70% - 144° C, 90% - 160.5°C, 95% - 168.5°C, final boiling point - 187.8°C.

In the first trial, Arabian Naphtha was reformed at 516°C in a reactor using a conventional reforming catalyst consisting of 0.3 Pt, 0.6 Re, 1.0 Cl (wt%) on aluminum oxide. It was desulfurized separately.

In the second experiment, Arabian Naphtha was subjected to reforming at 4 93 Ci in the same reactor, in which the upper half of the reactor contained the same type of catalyst as in the first experiment and the lower half of the reactor contained - a platinum-barium-L-type zeolite - catalyst prepared according to the methods indicated in example 1.

The results of these two experiments are shown in Table IV.

Claims (9)

1. Process for reforming hydrocarbons, characterized in that the hydrocarbons are brought into contact with a catalyst comprising a large-pore zeolite with an effective pore diameter of from 6 to 15 Å containing: a) at least one metal from group VIII and b) an alkaline earth metal selected from barium, strontium and calcium, the selectivity index for the catalyst being higher than 60%, or the production conditions are adapted so that the selectivity for N-hexane dehydrocyclization is higher than 60%, and the hydrocarbons are first, simultaneously or finally possibly brought into contact, under reforming conditions and in the presence of hydrogen, with a catalyst comprising a metal oxide support in which platinum and rhenium are deposited in intimate mixture. 2. Method according to claim 1, characterized in that a catalyst is used where the alkaline earth metal is barium and the metal from group VIII is platinum. 3. Method according to claim 2, characterized in that a catalyst containing from 0.1 to 35% by weight of barium and from 0.1 to 5% by weight of platinum is used. 4. Method according to claims 1-3, characterized in that a catalyst is used where the zeolite has an apparent pore size of from 7 to 9 Å. 5. Method according to claims 1-4, characterized in that a catalyst is used where the zeolite is selected from zeolite X, zeolite Y and zeolite of type L. 6. Method according to claim 5, characterized in that a catalyst is used where the zeolite is zeolite Y. 7. Method according to claim 5, characterized in that a catalyst is used where the zeolite is a type L zeolite. 8. Method according to claims 1-7, characterized in that the reforming is carried out at a temperature from 400°C to 600°C, a liquid space velocity per hour of 0.3-5, a pressure of from 1 to 35.2 kg/cm<2> and a ratio H2/HC of from 1:1 to 10:1. 9. Method according to claim 8, characterized in that the reforming is carried out at a temperature from 430°C to 550°C, a pressure of from 3.5 to 21.1 kg/cm<2> and a ratio H2/HC of from 2 :1 to 6:1.