Mineral oils: processes and products – Chemical conversion of hydrocarbons – Hydrogenation
Reexamination Certificate
1999-09-17
2001-06-12
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Hydrogenation
C208S143000
Reexamination Certificate
active
06245220
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns the selective catalytic hydrogenation of diolefinic compounds to &agr;-olefinic compounds at rates of at least 1.5 times higher, normally at least 3 times higher or even 5 times higher than the rate of hydrogenation of &agr;-olefinic compounds to saturated compounds. The catalyst contains palladium and at least one element selected from tin and lead.
BACKGROUND OF THE INVENTION
Hydrocarbon conversion processes, for example steam cracking, visbreaking, catalytic cracking and coking, are carried out at high temperatures to produce a wide variety of olefinic compounds such as ethylene, propylene, n-butene-1, n-butene-2 compounds, isobutene or pentenes, and diolefinic compounds such as 1,2-propadiene, 1,3-butadiene and other compounds with boiling points in the “gasoline” cut range and which can be olefinic or diolefinic. Such processes inevitably lead, however, to the formation of highly unsaturated compounds such as diolefins (for example 1,2-propadiene), also alkynes (for example acetylene, propyne, 1-butyne, etc.). Such compounds have to be eliminated to allow the different cuts from those processes to be used in the chemical industry or for polymerisation processes. As an example, the C
4
cut from steam cracking contains a high proportion of 1,3-butadiene, butene-1, butene-2 compounds and isobutene.
Conventionally, butadiene is separated from the olefinic cut, for example by extractive distillation in the presence of dimethylformamide or N-methylpyrrolidone. The olefinic cut thus obtained contains isobutane, isobutene, butene-1, butene-2 compounds, n-butane and 1,3-butadiene, the latter being in an amount which can be between 0.1% to 2% by weight.
If butadiene is not an upgraded product, the cut can be directly treated using catalyst in the presence of hydrogen to transform the butadiene into n-butenes.
If the butene-1 and isobutane are desired products, processes must be used which produce a large quantity of butene-1 and separate different compounds, such as selective hydrogenation of butadiene to butenes with a small amount of isomerisation of butene-1 to butene-2, or separation of the isobutene by etherification with methanol to produce methyl-tertiobutyl ether.
There is currently a large demand for butene-1. This compound is used as a monomer in the polymer industry. Such use necessitates almost complete hydrogenation of butadiene, the presence of which is only tolerated in amounts of less than 10 ppm by weight.
Attaining these low butadiene contents with conventional catalysts based on nickel or palladium means a reduction in the butene-1 content due to butane formation and isomerisation of butene-1 to butene-2. In order to inhibit isomerisation of butene-1 to butene-2 compounds, some bimetallic formulae comprising palladium and a different metal have been proposed. In particular, palladium-silver systems can be cited, such as those described in U.S. Pat. No. 4,409,410, or palladium-gold, palladium-zinc, palladium-copper, palladium-cadmium, or palladium-tin systems, such as those described in Japanese patent application JP-A-87/05 4540. Proposed solutions for limiting consecutive hydrogenation, and thus butane formation, are more limited. As described in the literature (see, for example, “Selective Hydrogenation Catalysts and Processes: Bench to Industrial Scale”, J. P. Boitiaux et al., in “Proceedings of the DGMK Conference”. Nov. 11-13, 1993, Kassel, Germany), the hydrogenation selectivity for converting highly unsaturated compounds (diolefins and acetylenic compounds) to olefins originates from considerable complexation of the unsaturated compound on the palladium, preventing the olefins from accessing the catalyst and thus preventing their transformation to paraffins. This is clearly illustrated in the publication cited above were 1-butyne is selectively transformed to butene-1 on a palladium based catalyst. However, it should be noted that the rate of hydrogenation is relatively low. When all of the acetylenic compound has been converted, butene-1 hydrogenation is carried out at a much higher rate than the hydrogenation of the acetylenic compound. This phenomenon is also encountered with selective hydrogenation of butadiene.
This phenomenon poses several problems in industrial units. Firstly, in order to meet specifications regarding butadiene in the olefinic cut, a large quantity of butene-1 is transformed to butane since when the residual concentration of butadiene is low, the hydrogenation rates of butadiene and butene-1 are close to each other. Developing a catalyst which can allow butadiene hydrogenation at a rate which is much higher than the rate of butene-1 hydrogenation, whether these compounds are alone or mixed, is thus very important. This corresponds to catalyst properties which allow hydrogenation with high rate constant ratios for the hydrogenation of butadiene over that of butenes.
The importance of such a catalyst is not limited to an increase in butene-1 selectively but it can also allow better control of the hydrogenation process. In the event of minor local hydrogen distribution problems, using such a catalyst would not lead to high conversion of butenes to butane and would thus minimise the problems of high exothermicity linked to these poorly controlled hydrogenation reactions which would aggravate distribution problems.
To solve this problem, it was important to develop a hydrogenation catalyst which could hydrogenate 1,3-butadiene to butenes while inhibiting the isomerisation of butene-1 to butene-2 and which was less active for consecutive hydrogenation of butene-1 to butane.
SUMMARY OF THE INVENTION
We have now discovered that catalysts constituted by palladium and at least one element M selected from tin and lead, have a 1,3-butadiene to butene-1 hydrogenation rate which is at least one and a half times higher, usually 3 times higher or even 5 times higher than the rate of hydrogenation of butene-1 to butane, whether these compounds are hydrogenated mixed together or separately. Further, these catalysts can inhibit isomerisation of butene-1 to butene-2 compounds.
The aim of the invention is thus to provide a composition of matter which can hydrogenate diolefinic compounds to &agr;-olefinic compounds.
A further aim of the present invention is to provide a composition of matter which can produce a diolefins/&agr;-olefins hydrogenation rate ratio of at least 1.5:1.
A third aim of the present invention is to provide a composition of matter with good selectively towards butene-1 with respect to all n-butenes during hydrogenation of 1,3-butadiene.
The invention thus provides a hydrogenation catalyst characterized in that it comprises particles of a porous support and, as active elements, palladium distributed at the periphery of the particles and at least one element M selected from tin and lead.
Preferably, a proportion of at least 80% of the palladium is comprised in the volume of the particles (for example spherules or extrudates) constituting the catalyst which is defined between the periphery of the particles and a depth of 500 &mgr;m, as shown in the following cross sectional diagram:
The palladium content in the catalyst is in the range 0.025% to 1.0% by weight, preferably in the range of 0.03% to 0.5% by weight. The element M (tin and/or lead) content in the catalyst is generally in the range of 0.05% to 4% by weight, preferably 0.2% to 4% for tin and 1% to 4% by weight for lead. The element M/palladium atomic ratio is advantageously in the range 0.1 to 3.
The support in the hydrogenation catalyst of the invention can be selected from the group of compounds including aluminas, silicas, silico-aluminates and clays. Low acidity supports are preferred, such as silicas, aluminas with low specific surface areas, or aluminosilicates exchanged with alkalis.
The support can, for example be an alumina in a particulate form, for example in the form of spherules, extrudates, or in pellets. It can, for example, be in the form of spherules with an average diameter which is generally in the ran
Cameron Charles
Didillon Blaise
Gautreau Christophe
Institut Francais du Pe'trole
Millen White Zelano & Branigan
Myers Helane E.
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