Isomerization of olefins

Details Isomerization of olefins Isomerization of olefins

2000-02-10

2001-08-28

Wood, Elizabeth D. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S346000, C502S355000

Reexamination Certificate

active

06281162

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for catalytically isomerizing olefins, particularly for isomerizing alkenyl bridged ring compounds to the corresponding alkylidene bridged ring compound.
BACKGROUND OF THE INVENTION
Olefins often are isomerized to produce different olefins, having different double bond positions, different structures, or both, as maybe necessary for a chemical synthesis or for a process for making fuels or fuel additives. For instance, 5-ethylidene-2-norbornene (“ENB”) is used as a monomer in the production of rubbery polymers. ENB is produced most conveniently by catalytically isomerizing 5-vinyl-2-norbornene (“VNB”). VNB is produced by reacting 1,3-butadiene (BD) with cyclopentadiene (CPD) in an addition reaction commonly known as a Diels-Alder reaction.
Olefin isomerization catalysts include liquid bases, such as mixtures of alkali metal hydroxides and aprotic organic solvents, mixtures of alkali metal amides and amines, and mixtures of organic alkali metal compounds and aliphatic amines. Unfortunately, the catalytic activities of the liquid bases are relatively low, and therefore large amounts of these relatively expensive catalysts must be used. In addition, recovery of the catalyst from the olefin isomerization reaction mixture is very difficult—requiring complicated separation and recovery steps, producing a substantial amount of waste that must be disposed of, and consuming a large amount of energy.
Examples of solid olefin isomerization catalysts are alkali metals supported on high surface area anhydrous supports such as activated carbon, silica gel, alumina and the like. These solid catalysts are difficult to handle because they may ignite and lose activity on contact with oxygen. Also, the isomerization performance of these catalysts is generally poor—both conversion of the feed and selectivity to the desired product are low.
Solid catalysts tend to be either pyrophoric or lacking in desirably high activity. Many of the more active solid catalysts must be separately activated or stabilized in the presence of an oxygen containing gas after the catalyst is synthesized. Isomerization catalysts are needed which do not require separate activation and which also are more resistant to reactive poisons in the olefin feed.
SUMMARY OF THE INVENTION
The present invention provides a process for catalytically isomerizing a stream comprising an olefin feedstock, said process comprising: contacting said stream with a catalyst under first conditions effective to isomerize said olefin feedstock to produce a product, wherein said catalyst is prepared by a method comprising: providing a dried support; thermally mixing a metallic alkali metal with said dried support under second conditions effective to produce a mixture comprising a dispersion of said alkali metal on said dried support, wherein said alkali metal has a given melting point and said second conditions comprise a temperature higher than said given melting point and substantially simultaneous exposure to a gas comprising in the range of from about 0.001 vol % to about 10 vol % of oxygen and a remainder of inert gases to provide a cumulative total amount of said oxygen in said gas at a molar ratio to said metallic alkali metal in the range of from about 0.05-to-1.0 (0.05/1.0) to about 1.0-to-1.0 (1.0/1.0); and recovering said product.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a new method of making selective and efficient catalysts for a process of catalytic isomerization of olefins. The catalyst of the present invention does not require a separate activation step with an oxygen containing gas to achieve a high activity. In addition, the catalyst is more resistant to poisons that are present in the olefin feedstock. The catalyst of the present invention is prepared by thermally mixing a substantially dried support with an alkali metal at a temperature higher than the melting point of the selected alkali metal to achieve substantially uniform dispersion of the alkali metal on the dried support, and substantially simultaneously exposing the dried support and the alkali metal being thermally mixed to a gas mixture comprising oxygen or other active oxygen containing compounds. Various aspects of the process are discussed separately below.
A. Catalyst Preparation
The catalyst comprises a metallic alkali metal and a dried support material. An “alkali metal” suitable for preparation of the isomerization catalyst is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and mixtures or alloys thereof Alloys containing elements other than Group IA of the Periodic Table of the Elements also may be used, but additional steps may be required to remove the other elements chemically or physically before the catalysts can be used for isomerizing olefins. Preferably, an alkali metal useful for preparing the catalyst of the present invention consists essentially of the metal in its elemental (metallic) state. For example, if sodium is the desired metal, substantially pure metallic sodium should be used. A sodium source having a substantial amount of sodium hydroxide (about≧15 wt %) would not be suitable. Sodium, potassium, and mixtures thereof are examples of preferred alkali metals. A more preferred alkali metal consists essentially of metallic sodium. While all of the pure alkali metals are solids at room temperature (about 25° C.), some of the intermetallic alloys made of pure alkali metals are liquids at ambient conditions. These alloys or mixtures may be used for preparing the catalysts of the present invention at or below room temperature (about 25° C.).
A number of materials may be used as the support. The terms “support material” and “support” are used interchangeably herein. Some of the preferred characteristics of a support include, but-are not necessarily limited to: a high surface area; inertness to the alkali metal selected; amenability to being dried to a substantially dried state or form; and sufficient physical strength and chemical integrity under catalyst preparation conditions to remain intact and, under olefin isomerization conditions, to remain active and selective. For example, oxides and/or hydroxides of metals of Groups 1A, 2A, 3A, 4A, and 4B of the Periodic Table of the Elements may be used as a support material.
Specific examples of a suitable support material for making the isomerization catalyst of the present invention include, but are not necessarily limited to, carbon, graphite, talc, clays, diatomaceous earths, magnesium oxide, calcium oxide, strontium oxide, barium oxide, aluminum oxide, gallium oxide, silicon oxide, silicoalumino oxide, titanium oxide, zirconium oxide, hafnium oxide, Celite, and rare earth oxides such as yttrium oxide and lanthanum oxide. In addition, molecular sieves such as zeolites also may be suitable supports for the present invention. While crystalline forms of many such materials are generally stable, amorphous forms also may be used. Amorphous silica-aluminas are examples of such amorphous solids which, like their crystalline counterparts, may be used as supports.
Many compounds may have more than one crystalline form or structure. These various crystalline forms, structures, or their mixtures may be used, provided that they possess the desired physical and chemical properties. For instance, if titanium oxide (also called titania) is the support of choice, then anatase, rutile, or mixtures thereof may be used. Similarly, aluminum oxide may take a variety of crystal structures—alpha, gamma, eta, theta, etc. Pure alpha alumina is not a suitable support material because its surface area generally is too low to produce a catalyst with a desirably high activity.
In general, the support should have a surface area of least about 50 m
2
/g, preferably, at least about 100 m
2
/g, more preferably, at least about 140 m
2
/g. Aluminas with surface areas greater than about 140 m
2
/g are most preferred supports. Structurally, the aluminas may be amorphous, gamma, eta, theta, or mixtures the

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