Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By skeletal isomerization
Patent
1996-05-03
1999-02-23
Yildirim, Bekir L.
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By skeletal isomerization
C07C 527
Patent
active
058746617
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 filing based on international application PCT/EP94/01937, filed Jun. 14, 1994, which in turn is based on GB application 9312245.5 filed Jun. 14, 1993.
This invention relates to the treatment of hydrocarbons, especially branched aliphatic hydrocarbons, and more especially olefinic hydrocarbons, to effect isomerization of the hydrocarbon skeleton.
Olefinic hydrocarbons are employed as starting materials in the hydroformylation, or oxo, process, for the eventual manufacture of numerous valuable products, e.g., alcohols, esters and ethers derived therefrom, aldehydes, and acids. In many of those end uses, linear or lightly branched hydrocarbon chains have advantages compared with more heavily branched chains.
In the oxo process itself, moreover, olefins with heavily branched chains are less reactive than those with linear or lightly branched structures and, for a given degree of branching, certain isomers are less reactive than others.
Olefinic feedstocks, especially in the C.sub.4 to C.sub.20, and more particularly in the C.sub.6 to C.sub.15 range, are frequently produced by oligomerization of lower molecular weight original starting materials, a process that, because of rearrangements that take place during the reaction, may produce an undesirably high proportion of multiply branched olefins, even if the original materials are linear. Also, the locations of the branches, at sites close to each other on the hydrocarbon chain, or in the central region of the chain, or both, resulting from the oligomerization further reduce the reactivity of the molecules in the oxo reaction.
There are other areas in which a less highly branched hydrocarbon has advantages; these include the alkylation of aromatic hydrocarbons by reaction with olefins in the manufacture of surfactants and polyolefin stabilizers.
There is accordingly a need to provide a method to reduce the degree of branching of a hydrocarbon material.
It has now been found that contacting a branched olefinic hydrocarbon material with a catalyst in the form of a molecular sieve having a 10-membered ring pore structure reduces the degree of branching of the material.
This finding is surprising since more highly branched isomers are thermodynamically more stable than less highly branched isomers. The finding is also surprising in view of the teachings of EP-B-247802 that a linear olefin may be isomerized to a branched olefin by contacting it with a zeolite having such a structure, for example ZSM-23, examples being given of isomerization of n-butene to isobutene.
U.S. Pat. No. 5,157,194 obtains similar results when employing microcrystalline ZSM-22, another 10-numbered ring zeolite, reporting high yields of isobutene from an n-butene feed.
In WO 91/18851, there is disclosed a process for interconversion, including isomerization, of unsaturated compounds, e.g., n-olefins containing 3 to 9 carbon atoms, using a catalyst comprising a molecular sieve ion-exchanged with a cation to provide a Lewis acid site. Suitable molecular sieves include silica/alunina phosphates (SAPO) and zeolites. Favored conditions for isomerization include a temperature in the range 250.degree. to 500.degree. C., especially 375.degree. to 475.degree. C., and a pressure of 0.08 to 0.12 MPa, especially about atmospheric, n-butene readily isomerizing to iso-butene.
EP-A-523838 describes a similar process of isomerizing linear alkenes to branched alkenes, while WO 93/03118 describes a process in which an alkene feed is contacted with two catalysts sequentially for increasing the branched alkene content.
The present invention provides a method of reducing the degree of branching of a branched olefinic feedstock, which comprises contacting it under conditions facilitating skeletal isomerization with a molecular sieve having a 10-membered ring pore structure.
The invention is applicable to all branched olefinic species, but is especially applicable to olefins having from 4 to 20 carbon atoms, more especially to olefins having from 7 to 16 carbon atoms, and particularly alken
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Martens Luc Roger Marc
Mathys Georges Marie Karel
Verrelst Wim Herman
Bell Catherine L.
Exxon Chemical Patents Inc.
Hunt John F.
Yildirim Bekir L.
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