Catalyst and process for the selective hydrogenation of...

Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide

Reexamination Certificate

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C502S327000, C502S331000, C502S332000, C502S333000, C502S334000, C502S335000, C502S337000, C502S339000, C502S344000, C502S345000, C502S346000, C502S347000, C502S348000

Reexamination Certificate

active

06350717

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to catalysts comprising noble metals on an aluminum oxide support and a process for the selective hydrogenation of unsaturated compounds in hydrocarbon streams using these catalysts. In particular, the present invention relates to catalysts comprising noble metals on an aluminum oxide support and a process for the selective hydrogenation of alkynes and/or alkadienes in C2 or C3 hydrocarbon streams in which they are present.
In refineries and petrochemical plants, large quantities of hydrocarbon streams are produced, stored and processed. Unsaturated compounds are frequently present in these hydrocarbon streams and their presence is known to lead to problems, particularly in processing and/or storage, or they are not the desired product and are therefore undesirable components of the respective hydrocarbon streams. General overviews of such problems in steam crackers and customary solutions have been given, for example, by H.-M. Allmann, Ch. Herion and P. Polanek in their paper “Selective Hydrogenations and Purifications in the Steamcracker Downstream Treatment” at the DGMK conference “Selective Hydrogenation and Dehydrogenation” on Nov. 11 and 12, 1993, in Kassel, Germany, the manuscript of which has also appeared in Conference Report 9305 of the DGMK Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e. V., Hamburg, pp. 1-30 (ISSN 0938-068X, ISBN 3-928164-61-9), and M. L. Derrien in: L. Cerveny (Editor), Stud. Surf. Sci. Catal., Volume 27, pp. 613-666, Elsevier, Amsterdam 1986.
In C2 streams from steam crackers, the secondary component acetylene is usually undesirable, and in C3 streams the secondary components propyne and allene are usually undesirable.
Analogous problems occur in the case of hydrocarbon streams which come from an FCC cracker or a reformer instead of a steam cracker. A general overview of such problems has been given, for example, by J. P. Boitiaux, C. J. Cameron, J. Cosyns, F. Eschard and P. Sarrazin in their paper “Selective Hydrogenation Catalysts and Processes: Bench to Industrial Scale” at the DGMK conference “Selective Hydrogenation and Dehydrogenation” on November 11 and 12, 1993 in Kassel, Germany, the manuscript of which has also appeared in Conference Report 9305 of the DGMK Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas and Kohle e. V., Hamburg, pp. 49-57 (ISSN 0938-068x, ISBN 3-928164-61-9).
In general, therefore, unsaturated compounds having triple bonds (alkynes, especially acetylene and propyne, the latter also known as “methylacetylene”) usually have to be removed from C2 and C3 hydrocarbon streams and/or, in the case of C3 streams, unsaturated compounds having more than one double bond (alkadienes, especially propadiene, also known as “allene”) have to be removed, in order to obtain the desired products such as ethylene and/or propylene in the quality required.
The removal of undesired unsaturated compounds from hydrocarbon streams in which they are present is frequently carried out by selective hydrogenation of some or all of the undesired unsaturated compounds in the hydrocarbon stream in question, preferably by selective hydrogenation to form more saturated compounds which do not cause problems and particularly preferably to form the components of the hydrocarbon stream which represent the desired products. For example, acetylene is hydrogenated to ethylene in C2 streams and propyne and propadiene are hydrogenated to propylene in C3 streams.
Such compounds typically need to be removed completely or at least to residual contents of a few ppm by weight. The (“over”) hydrogenation to form compounds which are more saturated than the desired product and/or the parallel hydrogenation of a desired product containing one or more multiple bonds to give the corresponding more highly or completely saturated compound should, however, be avoided if possible because of the loss of valuable product associated therewith. The selectivity of the hydrogenation of the undesired unsaturated compounds therefore has to be as high as possible. In addition, a sufficiently high activity of the catalyst and a long operating life are generally desired. At the same time, the catalyst should not promote any other undesirable secondary reactions. Use is customarily made of supported noble metal catalysts in which noble metal is deposited on a catalyst support. Palladium is frequently used as noble metal and the support is generally a porous inorganic oxide, for example silica, aluminosilicate, titanium dioxide, zirconium dioxide zinc aluminate, zinc titanate, spinels and/or mixtures of such supports, but aluminum oxide or silicon dioxide are usually used. In addition, promoters or other additives may also be present. Processes for the selective hydrogenation of unsaturated compounds in hydrocarbon streams in which they are present are known both as a liquid-phase hydrogenation or mixed gas/liquid-phase hydrogenation, in the downflow or upflow mode, and as a pure gas-phase hydrogenation. Various process engineering measures for improving the selectivity have been disclosed for these processes.
DESCRIPTION OF THE PRIOR ART
For example, EP-A 87 980 teaches such a process in a fixed-bed reactor in which the hydrogen for hydrogenation is fed in at least two points along the reactor, thereby achieving a higher selectivity. EP-A 81 041 teaches that the addition of carbon monoxide reduces the hydrogenation and isomerization activity of the palladium used as catalyst metal and thus increases the selectivity. JP-A 01-110 594 teaches the addition of further electron donor compounds, either in the form of a dopant in the catalyst, for example alkali metals, or in the form of an addition to the reaction mixture, for instance of alcohols, ethers or nitrogen-containing compounds.
The use of promoters or dopants in addition to the actual hydrogenation-active catalyst metal is also known.
Thus, J. P. Boitiaux, J. Cosyns, M. Derrien and G. Leger in Hydrocarbon Processing, 1985 (3), pp. 51-59, teach the use of bimetallic catalysts, in particular ones comprising the metals of group VIII (current IUPAC nomenclature: groups 8, 9 and 10), especially palladium, and metals of group IB (current IUPAC nomenclature: group 11) of the Periodic Table of the Elements. EP-A 564 328 and EP-A 564 329 teach the use of catalysts comprising metals of group VIII, especially palladium, and metals of group IIIA (current IUPAC nomenclature: group 3), especially indium or gallium. EP-A 89 252 discloses a process for producing a palladium- and gold-containing supported catalyst and its use. DE-A 21 56 544 teaches a catalyst comprising palladium and zinc on a silica support. EP-A 722 776 discloses a catalyst which is particularly resistant to sulfur impurities and comprises palladium, at least one alkali metal fluoride and optionally silver on an inorganic support such as TiO
2
, ZrO
2
or preferably Al
2
O
3
. EP-A 738 540 teaches a catalyst comprising palladium, silver, alkali metal and fluoride on an aluminum oxide support, with the ratio of fluoride to alkali metal being from 1.3:1 to 4:1.
It is also possible to influence the properties of the catalyst used not only by process engineering measures or the use of certain additives, but also by the type of support and the way in which the active composition is distributed on the internal and external surface area of the support.
Thus, DE-A 20 59 978 teaches palladium catalysts on an alumina (aluminum oxide) support. The support has a BET surface area of about 120 m
2
/g and, before deposition of the palladium, is first subjected to a treatment with steam at 110-300° C. and is subsequently calcined at 500-1200° C.
DE-A 31 19 850 discloses the use of a catalyst comprising palladium and silver on an SiO
2
support having a BET surface area in the range from 10 to 200 m
2
/g or on an Al
2
O
3
support having a BET surface area of less than 100 m
2
/g. The weight ratio of silver to palladium is generally in the range from 0.1 to 20 and, in specific embodiments, in the range from 0.7 to

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