Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By double-bond-shift isomerization
Reexamination Certificate
1999-01-14
2001-06-05
Johnson, Jerry D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By double-bond-shift isomerization
C585S664000
Reexamination Certificate
active
06242662
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of the production of but-1-ene. But-1-ene is an important compound for the synthesis of copolymers, for example, with ethylene for linear low density polyethylenes, or for the synthesis of butene oxide.
BACKGROUND OF THE INVENTION
A study of the prior art has revealed two documents which describe processes wherein at least one of the products isolated is but-1-ene, these being patents FR-B-2 527 201 and EP-B-0 129 900. The patent FR-B-2 527 201 describes a process in several steps starting with a charge of hydrocarbons having 4 carbon atoms. After undergoing several treatments including an etherification reaction with an aliphatic alcohol, then several treatments for the separation of the various constituents of the mixture, but-1-ene is recovered in a top fraction of a distillation column, the bottom fraction being composed of the other compounds and of non recovered but-1-ene. Said bottom fraction is then passed to an isomerization zone where it is partly converted to isobutene. The patent EP-B-0 12 900 describes a process for producing but-1-ene by isomerization starting with a mixture of hydrocarbons containing but-2-enes. This document raises an important problem which is the service life of the isomerization catalyst and hence of the regeneration of said catalyst. The type of catalyst used is an acid catalyst and the operating conditions of the reaction require a reaction temperature of the order of 250° C. to 400° C. Moreover, this process generates isobutene which is difficult to separate from but-1-ene, even if this compound is present only in traces.
SUMMARY OF THE INVENTION
The present invention relates to a process in several steps for obtaining but-1-ene from a charge comprising hydrocarbons having 4 carbon atoms per molecule including at least one of the isomers of but-2-ene (but-2-ene occurs in the cis and trans forms), said process comprising at least one distillation step and at least one hydro-isomerization step, these steps possibly also being merged.
The advantages of the present invention include the possibility of obtaining but-1-ene with yields greater than 100% by mass with respect to the but-1-ene present in the charge. In comparison with the isomerization processes, it will be noted that the use of a hydro-isomerization catalyst makes it possible to operate at significantly lower temperatures. This lower hydro-isomerization temperature means that the cracking rate is not detectable. The formation of coke, which is the main factor responsible for deactivation of the catalyst, is also very low.
The catalyst used is highly selective of the isomerization reaction with respect to the hydrogenation reactions. Moreover, the amount of hydrogen required for the hydro-isomerization reaction is very small. The losses due to the hydrogenation of butenes are therefore very small and it is not vital to add a means of separating hydrogen from the effluent leaving the hydro-isomerization reactor. However, embodiments in which a means of isolating hydrogen if the effluent leaving the hydro-isomerization reactor contains hydrogen are not excluded from the scope of the present invention.
The invention relates to a process for obtaining but-1-ene wherein a charge containing at least one of the isomers of but-2-ene is passed to a distillation zone linked with a hydro-isomerization zone.
The invention also relates to a device for implementing the process according to the invention.
The charge treated by the process according to the invention may be a cut containing hydrocarbons having 4 carbon atoms, including at least one of the isomers of but-2-ene. It may originate, for example, from steam cracking, fluid catalytic cracking (FCC) or skeletal isomerization.
The charge generally contains butadiene, butanes (n-butane and isobutane), butenes (isobutene, but-1-ene and but-2-enes, cis and trans forms). This charge may be introduced into the distillation zone of the process according to the invention without a prior treatment. However, certain uses require high-purity but-1-ene. For these, it is necessary, therefore, to separate but-1-ene from the products whose boiling point is close to or lower than the boiling point of but-1-ene. Said products are generally butadiene, isobutane and isobutene.
In order to remove butadiene from the mixture, it generally undergoes selective hydrogenation in which case the effluent leaving the selective hydrogenation reactor contains only butanes (n-butane and isobutane), butenes (isobutene, but-1-ene and but-2-ene, cis and trans forms), and traces of butadiene.
Isobutene is usually removed by extraction or by using it as a reagent of a reaction. Isobutene may, for example, be oligomerized, for example, according to a process known as “Polynaphta” developed by the Applicant. It may also react with certain alcohols according to etherification reactions in order to give, for example, methyl tert.butylether (MTBE) or ethyl tert.-butylether (ETBE). Isobutane is generally removed by distillation.
The treatments for removing butadiene and isobutene may be carried out on a charge before its introduction into the distillation zone of the process according to the invention, or on the effluent from the top of the column of the process according to the invention. In preference, they will be carried out before the charge is introduced into the distillation zone. Isobutane is generally removed in the top effluent of the process according to the invention.
REFERENCES:
patent: 5087780 (1992-02-01), Arganbright
patent: 0 129 900 (1985-01-01), None
patent: 2 528 033 (1983-09-01), None
patent: 57-131729 (1982-08-01), None
patent: 1595829 (1990-09-01), None
Didillon Blaise
Dorbon Michel
Forestiere Alain
Hugues Francois
Viltard Jean-Charles
Dang Thuan D.
Institut Francais du Pe'trole
Johnson Jerry D.
Millen White Zelano & Branigan
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