1. Field of the Invention
The present invention relates to a process for the metathesis of olefins. More particularly the invention relates to a process wherein the catalyst is part of a distillation structure and the products are simultaneously separated from the reactants and each other by fractional distillation during the reaction.
2. Related Art
Broadly metathesis has been defined as a chemical reaction in which an element or radical in one compound changes places with another element or radical in another compound. See The Van Nostrand Chemist""s Dictionary, D. Van Nostrand Company, Inc., 1953, page 463. More specifically olefin metathesis can be defined as the redistribution of alkylidene moieties to give a mixture of olefins. In effect, this reaction takes place via cleavage of the olefin double bond. Generally the reactions of olefinic molecules in the presence of metal-containing catalysts to produce other olefinic molecules are known in the art as xe2x80x9cdisproportionationxe2x80x9d, xe2x80x9cdismutationxe2x80x9d or xe2x80x9cmetathesisxe2x80x9d reactions.
The metathesis reactions are of considerable interest because of the versatility of the reaction and the numerous olefinic hydrocarbons available from petrochemical sources which are suitable for use in the reaction to yield useful products. One such reaction is the metathesis of propylene with itself to produce n-butene and ethylene. See, for example, U.S. Pat. No. 4,046,832. The reverse reaction is the metathesis of ethylene with n-butene to produce propylene and is disclosed in U.S. Pat. No. 5,026,936. Another use of the metathesis reaction is to produce 2-methyl-2-butene from the reaction of 2-methyl-1-propene and 2-butene. See U.S. Pat. No. 3,702,827.
Finally, the simultaneous disproportionation of olefins and fractional distillation is reported in U.S. Pat. No. 4,709,115. Therein the disproportionation of butene with itself to produce ethylene or propylene and hexene or pentenes is disclosed.
Catalysts that are known to catalyze the metathesis include the oxides of tungsten, rhenium and cobalt/molybdenum.
Briefly the present invention relates to metathesis reaction carried out a in distillation column reactor, that is, reaction and fractional distillation of the reactants and products are carried out concurrently in the distillation column reactor wherein the catalyst may be in the form to act as a distillation structure or part of a distillation structure or alternatively the catalyst may be located in beds or zones preferably located within the distillation column reactor.
One embodiment of the present invention comprises the production of propylene from the reaction of 2-butene with ethylene in a distillation column reactor. Preferably the catalyst is supplied in the form to act as a distillation structure or part of a distillation structure and loaded into the upper portion of a distillation column reactor. The 2-butene is fed above the bed and the ethylene is fed below the bed. Product propylene is taken as overhead and any heavies produced are removed as bottoms.
In a second embodiment the present invention relates to a process for the production of higher molecular weight olefins useful in the manufacture of detergents. More particularly the invention relates to the metathesis of olefins having higher molecular weight than that desired with lower molecular olefins to produce the desired molecular weight olefins.
In another embodiment the present invention comprises the metathesis of isobutylene with 2-butene to produce 2-methyl-2-butene and propylene. The catalyst is loaded into the upper portion of a distillation column reactor. The isobutylene is fed below the bed. Product 2-methyl-2-butene is taken as bottoms while propylene is removed as overheads.
Another embodiment of the present invention comprises the metathesis of isobutylene with itself to produce 2,3-dimethyl-2-butene (tetramethylethylene or TME) and ethylene. The catalyst is loaded into the upper portion of a distillation column reactor. The isobutylene is fed below the bed. Product TME is taken as bottoms along with any C8= or C12=oligomerization product. Ethylene is removed as overheads. The TME is separated from the heavy oligomers by fractional distillation. The C8=oligomers are then separated from the C12=oligomers by fractional distillation and fed to a single pass down flow reactor with ethylene for metathesis to 3,3-dimethyl-1-butene (neohexene).