Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – Diolefin product
Reexamination Certificate
1999-09-09
2003-12-23
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
Diolefin product
C585S601000, C585S606000, C585S607000, C585S608000, C585S609000, C585S616000, C585S617000
Reexamination Certificate
active
06667423
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for the production of a diene that comprises a stage a) for decomposition of at least one tertiary alkyl ether into at least one tertiary olefin of high purity, a stage b) for purification of the tertiary olefin and a stage c) for oxidizing dehydrogenation of this tertiary olefin into a diene.
It relates in particular to a process for the production of isoprene from the decomposition of tert-amyl-methyl-ether (TAME) or ethyl-tert-amyl-ether (ETAE) into isoamylenes of high purity that contain 2-methyl-but-1-ene and 2-methyl-but-2-ene, the separation of isoamylenes from methanol or respectively ethanol, and the oxidizing dehydrogenation of these isoamylenes into isoprene (2-methyl-buta-1,3-diene).
The first stage of the process according to the invention is a method for the production of high-purity isoamylenes from an ether, TAME or ETAE whose production makes it possible, for example, to upgrade an olefinic fraction with five carbon atoms that contains at least one 2-methylbutene, such as the one that is produced by the catalytic cracking on the moving bed (called F.C.C, whose initials come from the English “Fluid Catalytic Cracking”), steam cracking, the dehydrogenation of isopentane or isomerization of olefins with five carbon atoms. Their synthesis results from the selective addition of methanol, or ethanol on isoamylenes (2-methyl-but-1-ene and 2-methyl-but-2-ene). It involves balanced reactions that can be enhanced within the framework of synthesis of TAME and ETAE as within the framework of their decomposition.
In the latter case, it is possible to obtain, in a selective manner, the isoamylenes with a high purity. This process then makes it possible to prevent the distillation of the isoamylenes of a fraction with five carbon atoms, a difficult process taking into account small differences between the boiling points of the different olefins with five carbon atoms.
By contrast, it is generally easy to separate the TAME or the ETAE from the hydrocarbon fraction from which it is obtained. Once isolated, the ether can be decomposed again to form the initial tertiary olefin and the alcohol that is used. This takes place by an endothermic process in the presence of a generally acid catalyst and at a higher temperature than for the synthesis. The tertiary olefin that is produced can then have high purity based on operating conditions. In a second stage of the process, the tertiary olefin is dehydrogenated to form a diene, preferably isoprene.
The polymerization of the isoprene results in cis-1,4-polyisoprene, an equivalent of natural rubber, which exhibits excellent purity and a homogeneity that is greater than that of natural rubber.
BACKGROUND OF THE INVENTION
It has been shown that isoprene can be produced from a process of three successive stages. U.S. Pat. No. 3,391,214 describes the production of isoprene from isopentane that undergoes a scheme of three reactions (a hydroperoxidation and two epoxidations) in the presence of catalysts that are specific to each stage of the process. The feedstock that is used, however, is isopentane.
The process for decomposition of the tertiary alkyl ethers into tertiary olefins has been known for a long time, as, for example, Patent Application EP-A-0 068 785 shows, and various acidic solids have been described as catalysts of these reactions. Patent Application FR-A-2 291 958 relates to a process for decomposition of TAME or ETAE respectively into isoamylenes and methanol or isoamylenes and ethanol, with use of catalysts that are selected from among the salts, oxides or complexes of tetravalent uranium and can be supported on an alumina-a, for example, that has a Lewis acidity.
International Application WO-A-91/01 804 describes the production of isoamylenes from TAME with a clay catalyst that is treated with an acid that is selected from among hydrofluoric acid, hydrochloric acid and a mixture of hydrofluoric and hydrochloric acids.
U.S. Pat. No. 5,227,564 describes the decomposition of TAME in a vapor phase and in the presence of a catalyst that contains a silica-alumina zeolite, and Patent Application EP-A-0 589 557 and U.S. Pat. No. 4,536,605 describe the use of a catalyst with a calcined silica-alumina base. U.S. Pat. No. 5,171,920 describes the process for obtaining at least one tertiary olefin by decomposition of the corresponding ether, either TAME or ETAE, with a catalyst that consists of silica that is modified by the addition of at least one element, such as Li, Cs, Mg, Ca or La, for example. Such solids are not very active due to the absence of acidity, and they have a mediocre stability over time: the data of Table 1 of Example 13 of said patent indicate that in 800 hours, it is necessary to increase the temperature of 50° C. to keep the ether conversion level constant.
These catalysts that are based on alumina, silica or silica-alumina require the addition of water to improve the recovery of the alcohol and to prevent the secondary reaction of formation of the corresponding dialkyl ether, which is, for example, dimethyl ether (or DME) in the case of the methanol:
2MeOH
Me—O—Me+H
2
O
This is described in particular in Patent Applications GB-A-1 165 479 and EP-A-0 589 557. The presence of water, however, lowers the activity of the catalyst by lowering its acidity (see in particular Patent Application GB-A-1 165 479) and can then make it necessary to operate at a higher temperature, which can interfere with the service life of the catalyst. In addition, the presence of water induces an additional secondary reaction: the water reacts with the tertiary olefins to form an alcohol, such as, for example, in the case of isoamylene to form 2-methyl-butan-2-ol. According to this process, therefore, a loss of the tertiary olefin yield is recorded.
Finally, U.S. Pat. No. 5,095,164 describes a process for decomposition of tertiary alkyl ethers such as TAME or ETAE that use ion exchange resins, for example the sulfonated styrene-divinylbenzene resins. It is thus possible to cite the resin Amberlyst 15
(R)
of RHOM & HAAS or the resin M-31
(R)
that is marketed by DOW CHEMICAL. U.S. Pat. No. 4,447,668 also uses an ion exchange resin for producing isoamylenes and diisoamylenes from the separation of TAME.
One of the major drawbacks of the resins that are cited above is the impossibility of using them at high temperature, more specifically above 120° C. Actually, at high temperature, these resins lose sulfonic groups and therefore lose at least in part their activity and/or their acidity. The decomposition reactions of the ethers are endothermic, however; the thermodynamic equilibrium of the reaction is therefore shifted toward olefin production the higher the temperature. An operating temperature that is limited to 120° C. is reflected by weak ether conversion and limited by the laws of thermodynamics.
U.S. Pat. No. 5,095,164 that is cited above uses distillation equipment with a catalyst that is placed at the bottom of a column and that operates between 50 and 100° C., preferably between 60 and 80° C. The thermodynamic equilibrium of the decomposition reaction, which is poorly placed due to the fairly low operating temperature, is shifted by the elimination of the reaction products (tertiary olefin and corresponding alcohol) by distillation. Such a process, however, presents difficulties for the purification of the products. In particular, it uses large amounts of water for the extraction and/or the recovery of the alcohol. In addition, the unconverted ether is recovered at the bottom of the column with significant amounts of alcohol. It should then be purified before being recycled in the process.
The oxidative dehydrogenation of the olefins to form dienes is a process that has been known for a very long time by ones skilled in the art. It is carried out in the presence of catalysts of any type, but that usually contain iron, oxygen and another metallic element. The reaction for oxidizing dehydrogenation of isoamylenes into isoprene is described in, for example, the Encyclope
Dumonteil Claire
Forestiere Alain
Marion Marie-Claire
Dang Thuan D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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