NO176475B - Process for catalytic dehydrogenation of paraffins - Google Patents

Description

The invention relates to a method for catalytic dehydrogenation of paraffinic hydrocarbons and propane, as stated in the introductory part of patent claims 1 and 8 respectively.

Background.

Catalytic dehydrogenation of hydrocarbons has been carried out for many years and constitutes an important catalytic process in light of the increasing demand for dehydrogenated products that can be refined into various forms, such as high octane petrol, plastics and synthetic rubbers.

Furthermore, in light of increasing production of LPG (liquefied natural gas), it seems particularly interesting to convert a part of these paraffinic hydrocarbons into dehydrogenated products, such as propylene, which is particularly interesting for the production of plastic materials.

Catalytic dehydrogenation of hydrocarbons is carried out in the presence of catalytic compositions containing platinum deposited on a support material. The catalytic compositions may also contain other catalytically active metals such as tin or indium and other activators based on alkali or alkaline earth metals.

Such processes and catalytic compositions are described e.g. in US patents 2,479,209, 2,602,772, 2,930,763, 3,531,543, 3,745,112, 3,892,657, 3,909,451, and further in US patents 4,329,258, 4,363,721 and 4,430,517.

Furthermore, most of these patents also describe the use of a halogen to improve the yield of the dehydrogenation reaction.

However, despite all these already proposed procedures, when used to dehydrogenate propane, the yield of the reaction at 600°C will not exceed approximately 30-35%, i.e. 70-81% in relation to the theoretical conversion, taking into account the thermodynamic limitations.

There is therefore a need to produce a process for the dehydrogenation of paraffinic hydrocarbons which enables significant improvements in yield.

US patent 4,880,764 describes a catalyst comprising platinum, alkali or alkaline earth metal, but also containing elements from group IVA in the periodic table. Both the catalyst and its production method are different from that used in the present method.

US patent 3,649,565 also describes a catalyst containing a platinum group component, a lead component and alkali or alkaline earth metals, the preparation of which is different from the present one.

In connection with the present invention, however, the method of manufacture and preparation of the catalyst is critical.

Purpose.

The purpose of the present invention is to produce an improved process for the dehydrogenation of paraffinic hydrocarbons with from 3 to 6 carbon atoms in the presence of a catalyst containing at least one metal selected from the platinum group, a metal selected from the turn group and an activating metal.

Another object of the invention is to produce an improved process for the dehydrogenation of propane to propylene in the presence of a catalyst containing one or more metals selected from the platinum group, a metal selected from the turn group and an activator of the alkali or alkaline earth metal type, where the deposition of the one or more metals from the platinum group on the catalyst is carried out in two steps.

The invention.

These objects are achieved with a procedure for the hydrogenation of paraffinic hydrocarbons and propane, as stated in the characterizing part of patent claims 1 and 8, respectively. Further advantageous features appear from the associated independent claims.

The method of the present invention for the catalytic dehydrogenation of paraffinic hydrocarbons having from 3 to 6 carbon atoms in the presence of a catalyst consisting of an aluminum oxide support material containing at least one metal from the platinum group together with a co-catalyst and an activator is carried out by passing the raw material to is dehydrogenated over a catalyst containing from 0.1 to 2 weight percent of at least one metal from the platinum group, from 0.1 to 2 weight percent of at least one metal from the turn group as co-catalyst and from 0.5 to 5 weight percent of at least one alkali - or alkaline earth metal as activator, where said catalyst is obtained by subjecting the aluminum oxide support material, containing the co-catalyst, to calcination at a temperature between 450 and 550°C,

- for a first treatment with a compound of metal from the platinum group, said first treatment being followed by calcination in air and reduction in the presence of hydrogen at a temperature between 450 and 550°C; - then an intermediate treatment to deposit the activator, where said intermediate treatment is followed by calcination at a temperature between 380 and 550°C; and - a second treatment with a compound of metal from the platinum group, where said second treatment is followed by calcination at a temperature not exceeding 525°C,

where the dehydrogenation is carried out in the presence of said catalyst at a temperature between 400 and 800°C, at a pressure from 0.001 to 10 atmospheres and a weight space velocity (WHSV) between 0.1 and 21.

The method of the present invention can be used for the dehydrogenation of paraffinic hydrocarbons with from 3 to 6 carbon atoms, and in particular for the dehydrogenation of propane and butanes.

The applicant has unexpectedly found that by using the method of the invention it was possible to increase the yield of the dehydrogenation reaction significantly compared to the thermodynamic equilibrium, where said yield was close to exceeding 90% when propane was dehydrogenated at a temperature of approximately 600°C.

The catalyst used under the present invention comprises an aluminum oxide support material where at least one metal from the platinum group (herein defined and referred to as the metal from the platinum group), one metal from the turn group (herein defined and referred to as the metal from the turn group) has been introduced. and an alkali or alkaline earth metal type activator (as herein defined and referred to as the activator). The platinum group metal, as defined herein, may be selected from the group consisting of platinum, palladium, rhenium, iridium, rhodium, osmium, ruthenium or mixtures thereof, platinum being preferred. The metal of the turn group, as defined herein, may be selected from the group consisting of tin, germanium, lead or mixtures thereof, tin being preferred, which may be present as a compound such as the oxide. The activator can be an alkali metal selected from the group consisting of cesium, rubidium, potassium, sodium, lithium or mixtures thereof, or an alkaline earth metal selected from the group consisting of barium, strontium, calcium, magnesium or mixtures thereof, or also mixtures of alkali and alkaline earth metals , where potassium is preferred; other activators known to be effective may also be considered.

The aluminum oxide used as a support material usually has a specific area between 150 and 350m<2>/g and a pore volume between 0.2 and 1.2 ml/g.

It is recommended to use an aluminum oxide with a purity higher than 98.5%, and where the sodium content does not exceed 1% and the iron content does not exceed 0.1%.

The applicant has unexpectedly found that the manner and the specific sequence of deposition of the catalytic metal compounds on the support material, together with the conditions of intermediate calcination have an important influence on the activity of the catalyst within the framework of a dehydrogenation reaction.

The applicant has found that by using the following sequence for treating the aluminum oxide support material, a suitable catalyst is obtained for use in the method of the present invention.

The aluminum oxide support material is first impregnated with a compound of the metal from the turn group, in order to achieve a concentration of said metal in the finished catalyst between 0.1 and 2 weight percent, and preferably between 0.15 and 1.0 weight percent. Tin is preferred as a metal from the tin group. According to one embodiment of the invention, a slurry of aluminum oxide and an aqueous solution of stannous chloride is formed. The curd is dried at a temperature of 80 to 100°C. The aluminum oxide cake containing the stannous chloride is then pulverized and finally formed into pellets which are calcined at a temperature between 450 and 550°C for 12 to 20 hours.

The support material thus formed is then treated to add to it a compound of the metal from the platinum group. According to the present invention, the support material is treated in order to deposit on it, in a first step, a small part of the total quantity of the metal from the platinum group that will be present in the end. The amount of platinum group metal typically deposited at this step is between 10% and 40% of the total amount of platinum group metal. The deposition of said metal can be carried out using any suitable technique such as impregnation. When platinum is to be deposited, the support material is usually impregnated with an aqueous solution of chloroplatinic acid. After this impregnation, the newly impregnated carrier material is subjected to a calcination at a temperature between 450 and 550°C for 15 to 20 hours.

The calcined carrier material is then subjected to reduction in a hydrogen atmosphere at a temperature between 450 and 550°C for 1 to 4 hours.

The applicant has found that this reduction step is very important and has a beneficial effect on yield in the dehydrogenation of paraffinic hydrocarbons in the presence of this catalyst.

Before carrying out a second treatment with the metal from the platinum group, the support material is subjected to an intermediate treatment with an activator.

The alkali or alkaline earth metal is preferably well distributed on the support material. Generally, the amount of alkali or alkaline earth metal compound present on the support material is between 0.5 and 5 percent by weight and in particular between 0.8 and 2.5 percent by weight expressed as metal. Most often, potassium is deposited on the support material in an amount corresponding to 0.8 to 2 percent by weight expressed as metal. It is believed that the activator will usually be in the form of an oxide on the support material rather than in its metallic form.

The activator can be deposited on the support material in accordance with any suitable method such as impregnation. However, it is preferred to deposit the activator, preferably potassium, by impregnating the support material with an aqueous solution of its nitrate.

The carrier material thus impregnated is subjected to calcination at a temperature between 380 and 550°C to decompose the nitrate and fix the oxide of the alkali or alkaline earth metal on the carrier material. Usually the calcination is carried out in air for 3 to 7 hours.

According to the present invention, the metal from the platinum group is finally deposited on the carrier material thus formed in an amount sufficient to give a total content of said metal on the carrier material between 0.1 and 2 percent by weight, and preferably between 0.2 and 1 percent by weight. The deposition of this metal can be carried out using any suitable technique such as impregnation. However, at this stage of processing the carrier material, removal of the compounds already deposited on it must be avoided. For this purpose, the applicant has found that for this second impregnation with the metal from the platinum group it is advantageous to use an aqueous solution of a complex of platinum with the general formula (Pt L£X2, (Pt LOX4 or (Pt L4)X2, where L denotes a ligand selected from NH3, R-NH2 or NH2-R-NH2, where R is a hydrocarbon radical having from 2 to 6 carbon atoms, preferably from 2 to 4 carbon atoms, and where X denotes NO3 or a halogen An aqueous solution of the the aminated complex with the formula (Pt(NH3)4)Cl2 is particularly preferred. After this impregnation, the newly impregnated support material is dried and then subjected to calcination in air at a temperature between 450° and 525°C for 10 to 20 hours.

According to the present invention, the thus produced catalyst can be used in the dehydrogenation process without the need for the use of other activators to increase stability or selectivity, but it is understood that the usual activators can be added without deviating from the scope of the present invention.

According to the method of the invention, a raw material of a paraffinic hydrocarbon with from 3 to 6 carbon atoms, preferably a raw material of propane, is brought into contact with the catalyst as described above, under the operating conditions for dehydrogenation. This process can be carried out in a fixed catalyst bed reactor or a mobile catalyst bed reactor or even in a fluidized catalyst bed reactor; the procedure is most often carried out under continuous conditions, although it can also be carried out in batches. The hydrocarbon raw materials can be processed in liquid form, or in a mixed liquid-vapor phase, or also in vapor phase.

The dehydrogenation process is usually carried out in the vapor phase, at a temperature between 400 and 800°C at a pressure between 0.01 and 10 atmospheres and at a weight space velocity (WHSV) between 0.1 and 21 h'<1>.

When propane is used as raw material, the temperature is generally 530 to 650°C, the pressure is between 0.5 and 3 atmospheres and the weight space velocity is between 1 and 10.

The raw material can be diluted with usual gaseous diluents, in a molar ratio usually between 1 and 10 mol of diluent per mol of raw material. N2, CO2 and H20 are most often used as diluents.

The applicant has also found that it is more interesting to add hydrogen together with the raw material in a molar ratio generally between 0.05 and 0.5 mol of hydrogen per mol of raw material, whether the raw material is also diluted with gaseous diluents or not.

The flowing medium from the dehydrogenation zone contains some unreacted raw material, hydrogen and dehydrogenation products. This flowing medium is first cooled and sent to a separator to separate hydrogen and recover a liquid phase rich in dehydrogenated hydrocarones. This latter phase is then subjected to a series of separations to recover the desired product, i.e. propylene when propane is dehydrogenated, and recycle the unreacted phase to the reactor.

Example 1.

Preparation of the catalyst.

Alumina of 99.8% purity with a specific surface area of 189 m<2>/g and a pore volume of 0.94 ml/g was used.

This aluminum oxide was first impregnated with an aqueous solution of SnCl2. The impregnation was carried out to achieve a final tin content of 0.49% by weight. After this impregnation, the support material was calcined at 500°C for 18 hours. The tin-containing support was then impregnated with a solution of I^PtCl* to deposit about 0.15% platinum on the support. The support material was then subjected to a further calcination at 500°C for 18 hours. The support material was kept in the oven at 500°C and flooded with hydrogen for 1 hour to effect a reduction.

The carrier material thus impregnated was then treated with a solution of potassium nitrate to deposit on it 1.00 weight percent potassium, expressed as metal.

After this impregnation, the support material was subjected to calcination to fix the oxide of alkali metal on the support material; where said calcination was carried out in air at 400°C for 5 hours.

Finally, the second impregnation of the support material with a platinum compound was carried out to achieve a final platinum content of 0.40% by weight. To carry out this impregnation, the carrier material was brought into contact with an aqueous solution of a platinum-aminated complex with the formula (Pt(NH3)4)Cl2. After the impregnation, the carrier material was calcined in air at 500°C.

A propane feedstock was dehydrogenated by passing it through a reactor in the presence of the catalyst prepared as described above, and under the following operating conditions:

Temperature: 600°C

Pressure: 1.1 atmosphere.

WHSV: 3

Hydrogen was added together with the raw material in a molar ratio of 0.1 mol/mol raw material.

Propylene was still recovered from the flowing medium with a yield of 91.1% of the thermodynamic equilibrium under these conditions.

For comparison, different catalysts were prepared (Table 1).

Catalyst A

only an impregnation with platinum was carried out.

Catalyst B

only one impregnation with all the catalytic metals and the activator was carried out. Catalyst C

a calcination and a reduction were performed after impregnation with platinum, but the second impregnation with platinum was not performed.

Catalyst D

platinum was deposited by two impregnations, but without performing calcination or reduction after the first impregnation.

Catalyst E

platinum was deposited on an Al203/Sn support material in a single impregnation, without the addition of activator.

These catalysts were tested as described above for the dehydrogenation of propane feedstock under operating conditions identical to those described above. The results are reproduced in table n.

Example 2

Various catalysts were prepared in accordance with the method of the invention (see table HI above) with an aluminum oxide identical to that in example I.

These catalysts were used for the dehydrogenation of a propane feedstock according to the following operating conditions.

Temperature: 600°C

Pressure: 1.1 atmospheres (0.11 MPa)

WHSV: 3

H2/HC: 0.1 mol/mol (HC = hydrocarbons)

The results obtained with these catalysts are reproduced in the following table.

Example 6

The catalysts prepared in example 4 were used for the dehydrogenation of n-butane raw material under the following operating conditions.

Temperature: 630°C

Pressure: 2 atmospheres (0.2 MPa)

WHSV: 5

H2/HC: 0.4

A yield of 72% of theoretical and a selectivity of 94.5% was achieved.

When a catalyst prepared as in Comparative Example IA was used, a yield of only 48% was obtained with a selectivity of only 93.6%.

Claims (8)

1. Process for the catalytic dehydrogenation of paraffinic hydrocarbons with from 3 to 6 carbon atoms, in the presence of a catalyst comprising an aluminum oxide support material containing at least one metal from the platinum group together with a co-catalyst and an activator characterized in that the raw material to be dehydrogenated is passed over a catalyst containing from 0.1 to 2 weight percent of at least one metal from the platinum group, from 0.1 to 2 weight percent of at least one metal from the turn group as co-catalyst and from 0.5 to 5 weight percent of i at least one alkali or alkaline earth metal as activator, where said catalyst is obtained by subjecting the aluminum oxide support material, containing the co-catalyst and calcined at a temperature between 450 and 550°C, - to a first treatment with a compound of metal from the platinum group, where said first treatment is followed by calcination in air and reduction in the presence of hydrogen at a temperature between 450 and 550°C ; - an intermediate treatment to deposit the activator, said intermediate treatment being followed by calcination at a temperature between 380 and 550°C; and - a second treatment with a compound of metal from the platinum group, where said second treatment is followed by calcination at a temperature not exceeding 525 °C, where the dehydrogenation is carried out in the presence of said catalyst at a temperature between 400 and 800°C, at a pressure between 0.01 and 10 atmospheres and with a space velocity between 0.1 and 21 h"<1>. 2. Method according to claim 1, characterized in that the raw material to be dehydrogenated is introduced into a catalyst containing from 0.15 to 1 weight percent of a metal from the turn group, from 0.2 to 1 weight percent of a metal from the platinum group, and from 0.8 to 2.5 weight percent of an alkali or alkaline earth metal. 3. Procedure according to claim 1, characterized in that platinum is used as a metal from the platinum group. 4. Method according to claim 1, characterized in that the second impregnation with a metal from the platinum group is carried out with a compound of general formula (Pt 1^) X2, (Pt 1^ X4 or (Pt L4)X2, where L denotes a ligand selected from the group comprising NH3, R- NH 2 or NH 2 -R-NH 2 , where R is a hydrocarbon radical of 2 to 4 carbon atoms and where X is NO 3 or a halogen. 5. Method according to claim 4, characterized in that (Pt(NH3)4)Cl2 is used as platinum compound for the second impregnation step. 6. Method according to claim 1, characterized in that potassium is used as an activator. 7. Method according to claim 1, characterized in that 0.05 to 0.5 mol of hydrogen is added together with each mol of paraffinic hydrocarbon. 8. Process for the catalytic dehydrogenation of propane, in the presence of hydrogen in a molar ratio of from 0.05 to 0.5 mol of hydrogen per mol of propane over a catalyst comprising an aluminum oxide support material containing at least one metal from the platinum group together with a co catalyst and an activator, characterized in that the raw material to be dehydrogenated is passed over a catalyst containing 0.2 to 1 weight percent platinum, 0.15 to 1 weight percent tin as co-catalyst and 0.8 to 2 weight percent potassium as activator, where catalyst is obtained by subjecting the aluminum oxide support material containing the co-catalyst and calcined at a temperature between 450 and 550°C, - a first treatment with a platinum compound, said first treatment being followed by calcination in air and reduction in the presence of hydrogen at a temperature between 450 and 550°C; - an intermediate treatment to deposit potassium, where said intermediate treatment is followed by calcination at a temperature between 380 and 550°C, and - a second treatment with a platinum compound, where said second treatment is followed by calcination at a temperature of a maximum of 525°C , where the dehydrogenation is carried out in the presence of said catalyst at a temperature between 530°C and 650°C, a pressure between 0.5 and 3 atmospheres and a space velocity between 1 and 10 h"<1>.