Process For The Production Of Mono- And Diolefin Hydrocarbons

Abstract

A process for the production of mono- and diolefin hydrocarbons by the catalytic oxidative dehydrogenation of paraffin hydrocarbons at 400.degree.-700.degree.C in the presence of catalysts comprising mixed oxide systems and consisting of oxides of molybdenum and/or tungsten and oxides of at least one of the following metals: chromium, manganese, iron, nickel and cadmium.

Description

This invention relates to processes for the production of mono- and diolefin hydrocarbons. Said hydrocarbons are used for synthesizing various organic compounds but mainly for the production of synthetic rubbers.

Now it is known to produce mono- and diolefin hydrocarbons by the catalytic oxidative dehydrogenation of paraffin hydrocarbons at a temperature of 400.degree. - 700.degree.C.

Thus, a process is known for the production of n-butenes and butadiene by the oxidative dehydrogenation of n-butane at a temperature of 550.degree. - 700.degree.C in the presence of a calcium-nickel-phosphate catalyst (cf. French Pat. No. 1,319,181). The overall yield of final products on the basis of the initial n-butane is 17.7 wt. percent, the overall selectivity being 35.9 wt. percent.

A process is likewise known for the production of n-butenes and butadiene by the oxidative dehydrogenation of n-butane at a temperature of 400.degree. - 650.degree.C in the presence of a sodium phosphomolybdate or lithium molybdate catalyst (cf. U.S. Pat. No. 3,119,111). The yield of n-butenes is 4.8 wt. percent, and the yield of butadiene, 17.2 wt. percent on the basis of the initial n-butane, the selectivity being 11.3 and 41 wt. percent respectively.

Deficiencies of the known processes are the low yield of final products as well as the necessity of periodically regenerating the catalysts.

It is an object of the present invention to eliminate the above deficiencies.

It is a further and more specific object of the invention to provide a process for the production of mono- and diolefin hydrocarbons making it possible to increase the yield of final products and also to carry out the reaction continuously without regenerating the catalysts.

The foregoing and other objects have been accomplished by the provision of a process for the production of mono- and diolefin hydrocarbons wherein the catalytic dehydrogenation of paraffin hydrocarbons at a temperature of 400.degree. - 700.degree.C is carried out in the presence of catalysts which are mixed oxide systems consisting of oxides of molybdenum and/or tungsten and of oxides of at least one of the following metals: chromium, manganese, iron, nickel and cadmium.

It is preferable to use as catalyst a mixed oxide system consisting of oxides of molybdenum and nickel with an atomic ratio of molybdenum to nickel of 1:0.23 to 1:25.

To increase the mechanical strength of catalysts and enable carrying out the reaction over moving-bed catalysts, said catalysts are preferably employed on carriers of aluminosilicates, silica gel, alumina or mixtures of the same.

To lower the partial pressure of hydrocarbons, improve heat rejection conditions and increase selectivity, the process is preferably carried out in the presence of an inert diluent such as steam, nitrogen, argon, helium or mixtures of the same.

The inert diluent is preferably taken in a molar ratio of diluent to paraffin hydrocarbons of 1:1 to 40:1.

In the present process the oxidative dehydrogenation of paraffin hydrocarbons is carried out in a wide temperature range (400.degree. - 700.degree.C with a molar ratio of oxygen to initial hydrocarbons of 0.1:1 to 3:1 and space velocity of paraffin hydrocarbons of 20- 1,000 hr.sup.-.sup.1.

A preferred embodiment of the invention contemplates the following conditions in carrying out the process: temperature 400.degree. - 650.degree.C, molar ratio of oxygen to initial hydrocarbons of 0.1:1- 2:1, space velocity of paraffin hydrocarbons of 15- 400 hr.sup.-.sup.1.

The catalysts employed in the present process may be prepared by any of the known methods, e.g. by precipitation or evaporation of a mixture of the corresponding solutions of salts with subsequent heat treatment of the precipitate formed. The proportions of the active components in the catalysts may vary over wide ranges.

The monoolefin hydrocarbons produced as final products can be recycled in order to convert them into diolefin hydrocarbons in the conditions of the process.

For a better understanding of the present invention the following Examples of its concrete embodiment are given by way of illustration.

EXAMPLE 1

The oxidative dehydrogenation of n-butane was carried out in a reactor with a stationary bed of nickel-molybdenum catalyst which was prepared as follows.

A solution of 28.5 g of (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.sup.. 4H.sub.2 O in 70 ml of water was mixed with a solution of 94.4 g of Ni(NO.sub.3).sub.3 in 1,100 ml of water, whereupon a grey-green precipitate formed. The mixture was evaporated at 100.degree.C until a pasty light green mass was left. After drying at 120.degree.C this was ignited in a stream of air at 400.degree. - 500.degree.C for 4 hr and pelleted.

The atomic ratio of molybdenum to nickel in the finished catalyst was 1:2.

Oxidative dehydrogenation was carried out at a temperature of 590.degree.C, a molar ratio of n-butane to oxygen to steam of 1:0.25:10 and space velocity of n-butane of 100 hr.sup.-.sup.1. The charge of catalyst was 15 cm.sup.3.

The yield of n-butenes on the basis of the n-butane passed was 4.5 wt. percent and that of butadiene, 21.6 wt. percent, the selectivity being 11.2 and 53.6 wt. percent, respectively.

EXAMPLE 2

The oxidative dehydrogenation of n-butane was carried out in a reactor with a stationary bed of nickel-molybdenum catalyst which was prepared as follows.

198 g of Ni(NO.sub.3).sub.3 was dissolved in 300 ml of distilled water. Simultaneously 60 g of (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.sup.. 4H.sub.2 O was dissolved in 300 ml of boiling distilled water, after which 56.5 ml of 25 percent ammonium hydroxide was added to the cooled solution of ammonium paramolybdate.

The solutions were then poured together with vigorous stirring, the pH during precipitation being 7.8, after which the mixture was stirred for another 2 hr. The precipitate which formed was filtered out, washed with water, press-filtered and dried for 8 hr at 110.degree.C, ground and ignited for 4- 5 hr at 400.degree. - 500.degree.C in a stream of air.

The atomic ratio of molybdenum to nickel in the finished catalyst was 1:0.68.

The process was carried out at a temperature of 597.degree.C, a molar ratio of n-butane to air and argon of 1:7.2:20 and space velocity of n-butane of 100 hr.sup.-.sup.1. The charge of catalyst was 15 cm.sup.3.

The yield of n-butenes on the basis of the n-butane passed was 4.8 wt. percent and that of butadiene, 12 wt. percent, the selectivity being 19.4 and 45.3 wt. percent, respectively.

EXAMPLE 3

The oxidative dehydrogenation of n-butane was carried out in a reactor with a stationary bed of nickel-molybdenum catalyst which was prepared as follows.

28.9 g of Ni(NO.sub.3).sub.3 was dissolved in 10 ml of distilled water with heating, Simultaneously 8.77 g of (NH.sub.4).sub.6 Mo.sub.7 O.sub.24.sup.. 4H.sub.2 O was dissolved in 15 ml of a 30 percent hydrogen peroxide solution (water can also be used as solvent). The two solutions were combined and a carrier (silica gel) was impregnated with the mixture for 2 hr in the air at room temperature. The unabsorbed solution was decanted and the catalyst dried in the air for 24 hr and then at 110.degree. - 120.degree.C for 6- 8 hr, after which it was ignited in a stream of air at 400.degree. - 500.degree.C for 4 hr. The content of active mass in the catalyst was 15 wt. percent, The atomic ratio of molybdenum to nickel in the finished catalyst was 1:4.5.

The process was carried out at a temperature of 610.degree.C, molar ratio of n-butane to oxygen and steam of 1:2:20, and space velocity of n-butane of 25 hr.sup.-.sup.1. The charge of catalyst was 15 cm.sup.3.

The yield of n-butenes on the basis of the n-butane passed was 4.7 wt. percent, and that of butadiene, 10.5 wt. percent, the selectivity being 13 and 29 wt. percent, respectively.

EXAMPLE 4

The oxidative dehydrogenation of n-butane was carried out in a reactor with a stationary bed of nickel-tungsten-molybdenum catalyst which was prepared in a way similar to that described in example 1. The atomic ratio of nickel to tungsten and molybdenum in the finished catalyst was 2:0.1:0.9.

The process was carried out at 580.degree.C, the molar ratio of n-butane to oxygen and steam being 1:0.25:1, and the space velocity of n-butane, 100 hr.sup.-.sup.1.

The yield of n-butenes on the basis of the n-butane passed was 4.7 wt. percent, and that of butadiene, 13.5 wt. percent, the selectivity being 21.8 and 62.7 wt. percent, respectively.

EXAMPLE 5

The oxidative dehydrogenation of n-butane was carried out in a reactor with a stationary bed of molybdenum-cadmium-nickel catalyst which was prepared by a method similar to that described in example 1. The atomic ratio of molybdenum to cadmium and nickel in the finished catalyst was 1:0.1:2.

The process was carried out at 650.degree.C, the molar ratio of n-butane to air and steam being 1:8.4:20, and the space velocity of n-butane, 200 hr.sup.-.sup.1. The charge of catalyst was 15 cm.sup.3.

The yield of n-butenes was 5.7 wt. percent, on the basis of the n-butane passed, and that of butadiene, 15.1 wt. percent, the selectivity being 12.6 and 33.4 wt. percent, respectively.

EXAMPLE 6

The oxidative dehydrogenation of n-butane was carried out in reactors with a stationary bed of chromium-molybdenum, manganese-molybdenum, iron-molybdenum, cadmium-molybdenum and nickel-tungsten catalysts. The catalysts were prepared by methods similar to those described in examples 1, 2 and 3. The charge of catalyst was 15 cm.sup.3. The conditions under which the process was carried out and the results are given in the table.

While the present invention has been described in a preferred embodiment it will be understood that there may be changes and variations without departing from the spirit and scope thereof, as those skilled in the art will be able to perceive. These changes and variations are to be considered as falling within the spirit and scope of the invention as defined in the appended claims. ##SPC1##

Claims

What is claimed is:

1. A process for the production of mono- and diolefin hydrocarbons which comprises subjecting paraffin hydrocarbons to oxidative dehydrogenation at 400.degree. - 700.degree.C in the presence of catalysts comprising mixed oxide systems consisting of oxides of at least one metal selected from the group consisting of molybdenum and tungsten and oxides of at least one metal selected from the group consisting of chromium, manganese, iron, nickel and cadmium, and when the combination is molybdenum plus nickel the atomic ratio of Ni/Mo is between 211 and 25/1.

2. A process as claimed in claim 1, wherein the catalysts are employed on a carrier selected from the group consisting of aluminosilicates, silica gel, alumina and mixtures of the same.

3. A process as claimed in claim 1, wherein oxidative dehydrogenation is carried out in the presence of an inert diluent selected from the group consisting of steam, nitrogen, argon, helium and mixtures of the same.

4. A process as claimed in claim 2, wherein oxidative dehydrogenation is carried out in the presence of an inert diluent selected from the group consisting of steam, nitrogen, argon, helium and mixtures of the same.

5. A process as claimed in claim 3, wherein the molar ratio of inert diluent to paraffin hydrocarbons is 1:1 - 40:1.

6. A process as claimed in claim 4, wherein the molar ratio of inert diluent to paraffin hydrocarbons is 1:1 - 40:1.