Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By skeletal isomerization
Patent
1996-01-22
1997-08-19
Caldalola, Glenn A.
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By skeletal isomerization
C07C 522, C07C 527
Patent
active
056591047
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The present invention concerns a skeletal isomerisation process for olefins containing at most 20 carbon atoms, more particularly the isomerisation of n-butenes to isobutenes and n-pentenes to isopentenes (isoamylenes), using a particular catalyst.
Reducing the amount of alkyl lead in petrol has meant that for a number of years, the refiner has had to incorporate different compounds into petrols, in particular alcohols and esters, to increase the octane number. In addition to methanol which is one of the most widely known additives, MTBE (methyl tertiobutyl ether) has anti-knock properties which improve the quality of petrols and increase their octane index to a greater extent than that obtained using methanol. MTBE also has other advantages, such as: poorest anti-knock properties;
MTBE is normally obtained from isobutene and methanol in accordance with the following reaction: ##STR1##
The isobutene is generally contained in C.sub.3 -C.sub.4 olefinic cuts from catalytic cracking, steam cracking, thermal cracking and visbreaking effluents. The quantities of isobutene provided by these processes, however, are not sufficient to allow widespread development of the MTBE production process.
For this reason, complete or almost complete isomerisation of the butenes contained in the effluents from the processes described above has been proposed in order to produce larger quantities of isobutenes.
A number of processes have been described in the literature, using a variety of catalysts. The catalysts used are generally alumina based, or more particularly activated or steam treated aluminas (U.S. Pat No. 3,558,733), using eta or gamma alumina, halogenated aluminas (U.S. Pat. No. 2,417,647), bauxite, aluminas treated with boron derivatives (U.S. Pat. No. 3,558,733), silicon (U.S. Pat. No. 4,013,590, U.S. Pat. No. 4,038,337, GB-A 2 129 701 and U.S. Pat. No. 4,434,315), group IIIA elements or zirconium and various aluminosilicates, etc.
The majority of these catalysts exhibit fairly low conversions per pass and low selectivity due to side reactions such as cracking or polymerisation. These latter reactions also cause a rapid decrease in performance and thus poor performance stability over time.
AIM OF THE INVENTION
In our recent patent (FR-92/10.949), we discovered that a catalyst obtained from alumina, preferably eta or gamma alumina, to which a specific quantity of titanium (0.03% to 0.6% by weight) had been added and which was preferably steam treated under precise conditions, surprisingly produced substantially improved selectivities, conversions and cycle times if the catalyst was used in the presence of steam.
The present invention consists in using a modified catalyst compared to that described in FR-92/10.949, which increases the isobutene yield and above all considerably improves stability, and which can be used to carry out the skeletal isomerisation of n-pentenes or n-butenes with a low or zero quantity of water.
The catalyst is obtained from alumina, preferably eta or gamma alumina, to which 0.03% to 0.6% by weight of titanium and 0.05% to 5% by weight of an oxide of an element from group IIIA (boron, aluminium, gallium, indium, thallium) has been added, this element preferably being boron. This catalyst can then preferably be steam treated under specific conditions.
DETAILED DESCRIPTION
In the process of the invention, either a C.sub.4 olefinic cut alone produced from the processes described above can be isomerised after removal of the C.sub.3 cut, or the whole C.sub.3 -C.sub.4 olefinic cut can be isomerised.
In accordance with the invention, linear olefinic hydrocarbons containing 5 to 20 carbon atoms per molecule can also be isomerised.
The feed to be isomerised is brought into contact with the catalyst at a temperature of between 300.degree. C. and 570.degree. C. (preferably between 310.degree. C. and 550.degree. C. when it is constituted by butenes and/or pentenes) at a pressure of between 1 and 10 bars absolute (preferably between 1 and 5 bars absolute when the feed is constituted by b
REFERENCES:
patent: 2301342 (1942-11-01), Sumerford et al.
patent: 2422884 (1947-06-01), Burgin
patent: 5321195 (1994-06-01), Travers et al.
Burzynski Jean-Pierre
Chaillard Albert
Travers Christine
Caldalola Glenn A.
Institut Francais du Pe'trole
Wood Elizabeth D.
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