Hydrogenation of organic compounds with the use of the NEMCA...

Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is contaminant in desired hydrocarbon

Reexamination Certificate

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C585S250000, C585S260000, C585S263000

Reexamination Certificate

active

06194623

ABSTRACT:

The present invention relates to a novel process for the selective hydrogenation of at least one organic compound which has at least one unsaturated group, use being made of the so-called NEMCA effect, and quite generally to the use of this effect for the selective hydrogenation of compounds of this type.
There are a wide range of processes for the hydrogenation of organic compounds. They are generally carried out with either homogeneous or heterogeneous catalysis which generally comprise metals, in particular metals in subgroup VIH of the Period Table, as active component.
Electrochemical hydrogenation of compounds of this type has in the past been carried out and described only very infrequently, at least one an industrial scale. An overview of reactions of this type and the relevant prior art is given by DE-A 196 20 861. According to that document, organic compounds are hydrogenated under the application of a voltage with a hydrogen-containing gas on a catalyst which is formed by in situ coating of the support material with the active metal.
The processes described in DE-A 196 20 861 use electrical equivalents in stoichiometric form as hydrogenation or reduction equivalents. In contrast to this, the NEMCA effect requires only catalytic quantities of electrical equivalents. It affects the selectivity of the catalytic hydrogenation.
The NEMCA effect per se has to date primarily been examined and described in the scientific literature. An overview of the reactions carried out to date is given in: “The Electrochemical Activation of Catalytic Reactions”, C. G. Vayenas et al., Modern Aspects of Electrochemistry 29, J. Bockris et al., pub., Plenum Press, N.Y. 1996, pp. 57-202.
In consideration of the above prior art, one object of the present invention is to provide a novel process for the selective hydrogenation of organic compounds which have at least one unsaturated group, which in particular can be carried out in a way which is straightforward to implement, without the need for elaborate separation of the catalyst from the product which is obtained, and in which the hydrogenations of interest here can be carried out with high conversion ratio and at the same time high selectivity for the desired product.
This object is achieved by the method according to the invention.
Accordingly, the present invention relates to a process for the selective hydrogenation of at least one organic compound having at least one unsaturated group, by bringing the at least one organic compound into contact with a hydrogen-containing gas in the presence of a catalyst, characterized in that the catalyst comprises an active material which is applied to a solid electrolyte to which, in turn, a metallic substrate is connected in such a way that a current flows through the solid electrolyte, so that the active material can be kept at a constant potential and a voltage is applied to the catalyst during the hydrogenation.
As already indicated in the introduction, the so-called NEMCA effect (Non-Faradaic Electrochemical Modification of Catalytic Activity) is used in the implementation of the process according to the invention. This effect is based on the discovery that by applying an electric voltage between, on the one hand, an active material which is applied, preferably in the form of layers, to a solid electrolyte and, on the other hand, a further metallic substrate, likewise preferably in the form of layers, which is in turn connected to the solid electrolyte, it is possible for the activity or selectivity of a catalyst to be greatly altered.
In the scope of the present process, it is in principle possible to hydrogenate all organic compounds which have at least one selectively hydrogenatable unsaturated group.
Examples which may be mentioned in this regard include, amongst others, organic compounds which have two or more unsaturated groups of the same type, of which only a specific selection are hydrogenated in the scope of the novel process. Also envisagable are organic compounds which have at least two different unsaturated groups, of which one or more are selectively hydrogenated.
Naturally, a mixture of two or more organic compounds is also envisagable, each compound having at least one unsaturated group and each differing from the others in terms of at least one unsaturated group, it being possible for a specific selection of these organic compounds to be selectively hydrogenated in the process according to the invention.
Likewise, of course, mention may be made of mixtures of two or more different organic compounds which have the same unsaturated group, it being possible for a specific selection of these organic compounds to be selectively hydrogenated in the scope of the process according to the invention.
Preferably, unsaturated hydrocarbons, for example alkenes and/or alkynes, are selectively hydrogenated in the process according to the invention.
The present invention therefore relates in particular to a process, as described above, wherein the at least one organic compound having at least one unsaturated group is a hydrocarbon having C—C double bonding or at least one C—C triple bond, or a mixture of at least one hydrocarbon having at least one C—C double bond and at least one hydrocarbon having at least one C—C triple bond.
An example of this is, amongst others, the hydrogenation of dehydrolinalool to form linalool, in which the C—C triple bond is selectively hydrogenated. The product of this selective hydrogenation, linalool, is an important intermediate product for the production of perfumes and vitamins.
The present invention also relates to a process, as described above, wherein the at least one organic compound having at least one unsaturated group is ethyne or a mixture of ethene and ethyne.
In the scope of the present invention, it is thus for example possible, depending on the selected process conditions, when there is a mixture of ethene and ethyne, either to hydrogenate ethene selectively to form ethane, or to hydrogenate ethyne selectively to form ethene.
The catalyst used according to the invention consists of a composite which comprises at least one active material that is applied to a solid electrolyte which is in turn connected to a metallic substrate in such a way that a current flows through the solid electrolyte, so that the active material can be kept at a constant potential.
The active material used is preferably at least one catalytically active metal in subgroup VIE of the Period Table, alone or in combination with at least one further metal in subgroup I and/or VII. Among these, Pd, Pt, Ru, Rh, Au, Ag and Ni are preferably used as active material, and in particular preferably Pd, Pt and Rh. The catalytically active material is preferably applied in the form of a porous layer to a solid electrolyte, the layer generally having a thickness of from 0.001 to 1 mm, preferably from 0.001 to 0.050 mm.
An ion conducting and/or proton conducting solid electrolyte, preferably a ceramic material, is used according to the invention as the solid electrolyte. Examples of materials which can be used according to the invention as a solid electrolyte include: &bgr;″-Al
2
O
3
, &bgr;-Al
2
O
3
, Li
+
, Na
+
, K
+
conducting &bgr;-Al
2
O
3
, Nasicon (in this regard see “J. Electrochem. Soc., Vol. 145 No. 5, May 1998, p. 1518) and Nafion®, &bgr;″-Al
2
O
3
being preferably used.
Suitable metallic substrates are likewise, in principle, all materials which can be used as a complementary electrode for the active material described above, including the metals of which the catalytic layer is made, use being in particular made of metals in subgroup I of the Period Table, and more preferably Au or Ag.
The level of the voltage applied during the hydrogenation (per electrochemical cell) is in the range of from +5 V to −5 V, preferably +2 V to −2 V and in particular +1 V to −1 V. The current produced by application of this voltage is in the range of from 0.1 to 100 &mgr;A/cm
2
, its sign being defined by the direction of the voltage drop.

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