FR2724926A1 - Improved process for conversion of alkane(s) to alkene(s) - Google Patents

Abstract

A procedure for the conversion of alkanes to alkenes, in which the alkane is contacted with a catalyst comprising a crystalline-microporous metallic silicate contg. 0.01-20% (wt.) In and 0.01-10% (wt.) of a gp. VIII metal, at 300-800 deg C and 1 kPa-1 MPa. Pref. the alkane may be used with an inert gas such as N2, Ar, He or similar gases. The reaction mixt. can be mixed with water vapour or H2; the water vapour pressure being 0.01-10 kPa and H2 pressure 1-10 kPa.

Description

 The present invention relates to an improved process for converting alkanes to alkenes.

The invention particularly relates to an improved process for the conversion of C 2 -C 15 alkanes, corresponding olefins and hydrogen.

 The process of converting alkanes to alkenes is well known. It consists in reacting alkanes with a dehydrogenation catalyst. It is also known that the conversion to alkenes is all the more difficult as the carbon chain of the alkane used is shorter. Usually, the catalyst used in these conversion processes is chosen from platinum, vanadium oxides, chromium, gallium, etc. These catalysts are not very selective in the conversion.

As a result, the conversion rate is low. In addition, the catalyst deactivates very rapidly during the reaction, requiring a very frequent addition of fresh catalyst. These disadvantages render this conversion process economically unattractive for commercial applications.

Due to the importance of alkenes, and especially olefins such as olefins: C2 =,
C3 =, C4 =, iC4 =, research work continues throughout the world to develop an improved process for converting alkanes to alkenes. We have supported work for the development of such an improved process for converting alkanes to alkenes, whereby the conversion is greater and the deactivation of the catalyst used is avoided during the conversion reaction.

 According to US Pat. Nos. 4,120,910, 4,302,620, 4,350,835 and 4,590,323, it has been proposed to use a zeolite containing a metal oxide such as platinum or vanadium oxide, as a catalyst, to convert alkanes to alkenes. However, these processes have not proved commercially viable, because these catalysts become very quickly deactivated during the reaction and their regeneration is difficult; as a result, the yield is not satisfactory.

 In European Patent Application No. 0 351 066, a process for converting alkanes to alkenes has been discussed, wherein a zeolite containing tin and a small amount of a Group VIII metal has been used as a catalyst. With this method, the selectivity of the conversion was evaluated at 86% and the found conversion rate was 31%, when the reaction proceeded at 530 OC.

 Accordingly, the main object of the present invention is to provide an improved process for converting alkanes to alkenes.

 Another object of the present invention is to provide an improved process for converting alkane to alkene, wherein the selectivity rate is increased and the activity and life of the catalyst used is increased.

 The main discovery of the present invention resides in the use of a crystalline and microporous metal silicate material, containing from 0.01 to 20% indium and from 0.01 to 10% of a Group VIII metal, with which the selectivity of the conversion is increased and the activity of the catalyst is not affected during the conversion reaction.

 The process for preparing the above-mentioned catalyst is described in US Pat. No. 4,822,942. According to the process of preparation described in that patent, said catalyst comprises a non-acidic crystalline microporous material containing indium and platinum.

 U.S. Patent No. 4,822,942 describes the use of this catalyst to convert an octane to styrene. This patent does not describe the application of this catalyst to convert an alkane to an alkene. Thanks to our intensive research work in the field of conversion of alkanes to alkenes, we have surprisingly found that when such a catalyst is used to convert alkanes to alkenes, the catalyst plays an important role in the conversion, making the selectivity very large, the catalyst does not deactivate and consequently the yield is also improved (35 t).

 Thus, the present invention provides an improved process for converting alkanes to alkenes which comprises the step of contacting the alkane with a catalyst consisting of a crystalline, microporous metal silicate material containing from 0.01 to 20% of indium and from 0.01% to 10% by weight of a Group VIII metal, at a temperature between 300 and 8000C, and at a pressure of between 1 kPa and 1 MPa.

 The alkane may be mixed with an inert gas such as N21 argon, helium and similar gases. The reaction mixture may also be mixed with steam or hydrogen so as to prevent deactivation.

 The value of the water vapor pressure when it is used can range from 0.01 kPa to 10 kPa. The value of the hydrogen pressure when the latter is used may be between 1 and 100 kPa.

 The invention is described in detail in the examples given below, which are provided only to illustrate the invention and not to limit the scope.

 In the examples given below, the catalyst used is one of those prepared by the process described in the examples of US Pat. No. 4,822,452.

 The ZSM-5 type zeolite catalyst containing 1% by weight of indium is calcined under a nitrogen atmosphere, raising the temperature from room temperature to 500 OC at a rate of 10C per minute. The catalyst is maintained at 5000C overnight, and calcined by heating at a temperature of 500 OC for about 6 hours under an oxygen atmosphere.

EXAMPLE 1
1 g of the catalyst sample obtained above was mixed with stirring with a solution of
Pt (NH3) 4 (OH) 2, in 100 ml of water and maintained at room temperature for 12 hours. The sample was dried, the solid had a platinum content of 0.5% by weight. This sample was then calcined under 2, raising the temperature from room temperature to 300 ° C, in a progression of 0.20C / min and the sample was held at 3000C for 1 hour.

Then, after circulating a stream of nitrogen, the sample was reduced under a flow of H2, the temperature having been increased from 300 to 5000C in a progression of 1 "C. The sample was kept at 5000C for 1 hour, then cooled to room temperature before being flushed with N2 and brought into contact with air.

EXAMPLE 2
The catalyst as prepared by the method described in Example 1, was used for the dehydrogenation of isobutane to isobutene in a continuous flow reactor. The prepared catalyst was reduced by passing H2 for 2 hours at a temperature of 5300C. Then, the H2 supply was interrupted and the isobutane was passed through the catalyst at atmospheric pressure. The results are summarized in Table 1.

TABLE 1

<tb> Time <SEP> of <SEP> Temperature <SEP> VSPH <SEP> (*) <SEP> Conversion <SEP> Selectivity
<tb> pass, <SEP> OC <SEP> (hours) -l <SEP> for <SEP>
<tb> in <SEP> hours <SEP> l <SEP> isobutene <SEP>
<tb><SEP> 2 <SEP> 530 <SEP> 9 <SEP> 36 <SEP> 98
<tb><SEP> 50 <SEP> 530 <SEP> 9 <SEP> 36 <SEP> 98
<tb><SEP> 150 <SEP> 530 <SEP> 9 <SEP> 36 <SEP> 98
<tb> (*) space velocity in weight per hour
From Table 1, it can be seen that the conversion to isobutene is good (36%), the selectivity for isobutene is quite high (98%) and the life of the catalyst is excellent.

EXAMPLE 3
The experiment described in Example 2 was repeated using a ZSM-5 catalyst containing 0.5% by weight of platinum; various reaction products were obtained, isomerization products, hydrogenolysis, dehydrogenation, coke formation, the selectivity for isobutene being low (30%) and aging quite fast.

EXAMPLE 4
Example 3 was repeated replacing the ZSM-5 catalyst with an L-zeolite. Once again, the selectivity for isobutene was lower than that obtained in Example 2 (75% instead of 98%) and the deactivation is fast.

The above examples illustrate the unexpected effects of the invention: the presence of the elements Pt and
In at the same time, it induces a high selectivity of the dehydrogenation reaction leading to high dehydrogenation yields, giving high yields of dehydrogenated products, the catalyst having a long life, even in the absence of hydrogen addition. .

 The advantages of the present invention are as follows: 1. Catalyst strongly active in the dehydrogenation of an alkane.

2. Highly selective catalyst for the formation of alkenes.

3. Stable catalyst even in the absence of H2 addition.

Claims (6)

 1. Improved process for the conversion of alkanes to alkenes, characterized in that it comprises the step of contacting the alkane with a catalyst consisting of a metallic, crystalline, microporous silicate material containing 0.01 at 20% by weight of indium and from 0.01 to 10% by weight of a Group VIII metal, at a temperature of between 300 and 8000 ° C. and at a pressure of between 1 kPa and 1 MPa.  2. Improved process according to claim 1, characterized in that the alkane is used with an inert gas such as nitrogen, argon, helium and similar gases.  3. An improved process according to claims 1 and 2, characterized in that the reaction mixture is mixed with steam or hydrogen.  4. An improved process according to claim 3, characterized in that the value of the pressure of the steam is between 0.01 kPa and 10 kPa.  5. An improved process according to claim 3, characterized in that the value of the hydrogen pressure is between 1 and 100 kPa.  6. Improved process for the conversion of isobutane to isobutene, characterized in that it comprises the step of bringing isobutane into contact with a catalyst consisting of a metallic, crystalline, microporous silicate material containing 1% by weight of indium and 0.5% by weight of platinum, at a temperature of 5300C.