Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By dehydrogenation
Reexamination Certificate
1998-10-30
2001-02-13
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By dehydrogenation
C585S442000, C585S443000, C585S444000, C585S660000, C585S629000, C585S627000
Reexamination Certificate
active
06187985
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel process for dehydrogenating C
5
-C
22
aliphatic hydrocarbons to the corresponding olefinic hydrocarbons in the presence of a catalyst comprising at least one support, at least one metal from group VIII of the periodic table, and at least one additional element M selected from germanium, tin, lead, rhenium, gallium, indium and thallium. The catalyst can also contain a further metal selected from the group formed by alkali or alkaline-earth metals and/or a metalloid such as sulphur and/or any other chemical element such as a halogen or a halogen-containing compound.
BACKGROUND OF THE INVENTION
Catalyst formulations used in hydrocarbon conversion processes have been the subject of a very large number of studies. Patents and publications demonstrating that the addition of promoters to a base metal improves the quality of catalysts exist in large numbers. For paraffin dehydrogenation catalysts, catalysts comprising, in addition to a support, a noble metal from the platinum family and at least one additional metal M (United States patents U.S. Pat. No. 3,998,900 and U.S. Pat. No. 3,531,543) have been known for a long period. The acidity of the refractory inorganic support can lead to undesirable secondary reactions such as cracking and isomerisation. For this reason the oxide support is generally neutralised by adding at least one alkali or alkaline-earth element.
The metal phase is the hydro-dehydrogenating function which dehydrogenates the paraffins and hydrogenates coke precursors. However, platinum has a hydrogenolysing activity which deleteriously affects the yields of the desired olefins in the paraffin dehydrogenation process. This hydrogenolysing activity can be substantially reduced, and thus the selectivity of the catalyst can be increased, by adding an additional metal M. Further, adding this element M can also increase the hydrogenating properties of the platinum, encouraging hydrogenation of the coke precursors and thus increasing the stability of the catalyst.
Such elements are added in different forms such as mineral salts or organometallic compounds. The manner in which such modifying agents are introduced is not unimportant as it dictates the properties of the catalyst to a great extent. Thus a metal M is advantageously introduced using an organometallic compound of that metal M. Such a technique for introducing a metal M has been described in U.S. Pat. No. 3,531,543. Metal M is introduced in the form of at least one organometallic compound selected from the group formed by complexes, in particular carbonyl or polyketone complexes of metals M, and metal hydrocarbyls of metal M such as alkyls, cycloalkyls, aryls, metal alkylaryls and metal arylalkyls.
Introducing the additional element M in the form of an organometallic compound leads to more effective catalysts but necessitates the use of an organic solvent. The impregnating solvent described in United States patent U.S. Pat. No. 4,548,918 is selected from the group formed by oxygen-containing organic solvents containing 2 to 8 carbon atoms per molecule, paraffin, naphthene or aromatic hydrocarbons essentially containing 6 to 15 carbon atoms per molecule, and halogen-containing oxygen-containing organic compounds containing I to 15 carbon atoms per molecule. Such solvents can be used alone or mixed together.
SUMMARY OF THE INVENTION
In the present invention we have discovered that particularly effective catalysts can be prepared by introducing metal M in the form of an organometallic complex which is soluble in an aqueous solvent. This represents a considerable advance as regards ease of use during production of the catalyst. Using industrial quantities of organic solvents has many disadvantages as regards safety (flammability, toxicity) and as regards costs.
The support for the catalyst of the invention comprises at least one refractory oxide which is generally selected from oxides of metals from groups IIA, IIIA, IIIB, IVA or IVB of the periodic table such as oxides of magnesium, aluminium, silicon, titanium, zirconium or thorium, used alone or mixed together or mixed with oxides of other elements from the periodic table. Charcoal can also be used. X, Y, mordenite, faujasite, ZSM-5, ZSM-4 or ZSM-8 type zeolites or molecular sieves can also be used, as well as mixtures of oxides of group IIA, IIIA, IIIB, IVA or IVB metals with a zeolitic material.
Alumina constitutes the preferred support, the specific surface area of which is advantageously in the range 5 to 400 m
2
per gram, preferably in the range 50 to 350 m
2
per gram.
In addition to a support, the catalyst of the invention includes:
a) at least one group VIII metal selected from iridium, nickel, palladium, platinum, rhodium and ruthenium. Platinum and palladium are preferred metals. The percentage by weight is in the range 0.1% to 10%, preferably in the range 0.1% to 5%.
b) at least one additional element M selected from the group formed by germanium, tin, lead, rhenium, gallium, indium and thallium. Tin and germanium are preferred elements. The percentage by weight is in the range 0.01% to 10%, preferably in the range 0.02% to 5%. In some cases, at least two of the metals from this group can advantageously be used at once.
c) preferably, 0.1% to 3% by weight of at least one alkali or alkaline-earth metal.
Depending on the application, the catalyst can also contain 0.01% to 3% by weight of a halogen or halogen-containing compound. It can also contain 0.01% to 2% by weight of an element such as sulphur.
The catalyst can be prepared using different procedures for impregnating the support and the invention is not limited to any specific impregnation procedure. When several solutions are used, intermediate drying and/or calcining steps can be carried out.
The additional element M can be introduced during production of the support. One method, for example, consists of blending the moist powdered support with catalyst precursors and then forming and drying.
The group VIII metal, additional metal M, alkali or alkaline-earth metal, optional halogen or halogen-containing compound, and optional metalloid, can be introduced simultaneously or successively, in any order. In accordance with the invention, the characteristic feature of contact with the organometallic element M is that it is introduced in an aqueous solvent.
In a further method, the additional metal M can be introduced during synthesis of the support using a sol-gel type technique. As an example, for a support containing alumina, a mixed metal M—alumina gel can be obtained by hydrolysing an organic solution of Al(OR′)
3
in a solvent such as ROH or R′OH with an aqueous solution of an organometallic compound of metal M. R and R′ represent a methyl, ethyl, isopropyl, n-propyl or butyl type alkyl group or a heavier group such as n-hexyl. The alcoholic solvent must be highly dehydrated before introducing the aluminium alcoholate. After hydrolysis, heat treatment of the gel obtained carried out at a temperature in the range 200° C. to 800° C., preferably in the range 300° C. to 700° C., and more preferably in the range 400° C. to 500° C., ensures complete reaction of the hydrosoluble organometallic compound of metal M with the gel, which involves the formation of the mixed oxide Al
2
O
3
—MO
x
.
In a still further method, metal M can be added to an alumina sol. U.S. Pat. No. 3,929,683 describes introducing tin in the form of a salt, for example SnCl
2
into an alumina sol. In the present invention, it is possible to add a hydrosoluble organometallic compound of metal M to an alumina hydrosol, obtained, for example, by precipitating an acid solution of AlCl
3
at pH 4-5, then encouraging the compound of metal M to react with the alumina hydrosol for example using heat or a base.
The precursor of element M can be selected from the group formed by halogen-containing compounds, hydroxides, oxides, carbonates and carboxylates of organometallic compounds of element M. These compounds comprise at least one carbon-M bond. The precursor
Clause Olivier
Didillon Blaise
Le Peltier Fabienne
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
Nguyen Tam M.
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