Chemistry of hydrocarbon compounds – Purification – separation – or recovery
Reexamination Certificate
2000-02-17
2002-08-13
Manoharan, Virginia (Department: 1764)
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
C203S099000, C203S091000, C203S100000, C208S144000, C585S250000
Reexamination Certificate
active
06433242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for fractionating a dibutene mixture and to the use of the dibutene fractions.
2. Discussion of the Background
Dibutene is the term used for mixtures of isomeric C
8
olefins obtained by dimerizing n-butenes or C
4
streams containing n-butene. For this purpose it is particularly advantageous to employ the so-called raffinate II or raffinate III, which are inexpensively obtained from the processing of crude C
4
cuts.
In order to obtain raffinate II or III, butadiene is removed from crude C
4
cuts in a first step. This is done either by extracting the butadiene or selectively hydrogenating it to the linear butenes. Both cases produce a virtually butadiene-free C
4
cut, which is raffinate
1
. In the second step, isobutene is removed from the C
4
stream by, for example, reacting it with methanol to prepare methyl tert-butyl ether (MTBE). MTBE is a sought-after motor fuel component. Other options are to react the isobutene from the raffinate I with water to give TBA (tertiary butanol) or to subject the isobutene to acid-catalyzed oligomerization to form diisobutene. The now isobutene-free C
4
cut, raffinate II, desirably contains the linear butenes and possibly butanes. As an option, it is also possible to separate off the 1-butene by distillation; if this is done, the cut that is free from 1-butene is referred to as raffinate III.
For the preparation of di-n-butene, either raffinate II or raffinate III can be employed. The use of other industrial C
4
streams, such as those from Fischer-Tropsch olefins, for example, is possible. The critical feature is that essentially only linear butenes are present in the feedstock.
The oligomerization of such n-butene-containing C
4
streams to mixtures that contain essentially C
8
olefins is known in principle; there are three process variants, which are described below.
The oligomerization over acidic catalysts (process A) has been known for a long time, and, in industry, for example, zeolites or phosphoric acid on supports are employed. This process produces isomer mixtures of branched olefins which constitute primarily dimethylhexenes (WO 92/13818). A process which is likewise carried out worldwide is the oligomerization with soluble Ni complexes, known as the DIMERSOL process (process B) (B. Cornils, W. A. Herrmann, Applied Homogenous Catalysis with Organometallic Compounds, page 261-263, Verlag Chemie 1996). Finally, mention should also be made of the oligomerization over nickel fixed-bed catalysts, such as, for example, the process of OXENO-GmbH. The process has entered the literature as the OCTOL process (process C) (Hydrocarbon Process., Int. Ed. (1986) 65 (2. Sect. 1), page 31-33).
The dibutenes obtained by the above-noted processes are prized starting materials in the chemical industry. For example, it is possible by hydroformylation to obtain aldehydes which are longer by one carbon atom—in the case of dibutene, C
9
aldehydes—which in turn are further employed for important industrial products. Examples include the hydrogenation of the aldehydes to give alcohols and their reaction with carboxylic acids to give esters. For instance, the acidification of the alcohols with phthalic anhydride leads to diisononyl phthalates, which are highly prized plasticizers in the plastics processing industry. Also important and carried out industrially is the oxidation of the aldehydes to the corresponding carboxylic acids, which are reacted inter alia to give oil-soluble metal salts. These salts are employed, for example, as drying accelerators for coatings (siccatives), or as stabilizers for PVC.
Another exemplary industrial application is the strong-acid-catalyzed reaction of olefins (dibutenes) with carbon monoxide and water to give the carboxylic acids that are longer by one carbon atom, which has entered the literature under the name KOCH reaction. In this case, tertiary branched carboxylic acid mixtures are obtained which, because of their branched nature, are in turn highly suitable for producing the abovementioned metal salts. A particularly important use of the tertiary carboxylic acids is the reaction with acetylene to give vinyl esters, which are used as comonomers for the internal plasticization of polymers. Copolymers of vinyl esters of tertiary carboxylic acids with vinyl acetate, for example, are the basis for environmentally friendly water-dispersible paints and coating materials, and energy-saving thermal insulation renders in buildings.
Dibutene is not a uniform substance but rather is a mixture of many structural isomers which in turn are composed of virtually all the double-bond isomers in different proportions, with many of the double-bond isomers also exhibiting a cis/trans isomerism. Depending on the production process, these constitutional and configurational isomers can be present in different proportions.
When dibutene is prepared from raffinate II or III, the product contains olefin mixtures of essentially unbranched, singly branched and doubly branched substructures. The information given below in the table is only a guide, since varying proportions of the individual structural groups are obtained depending on the process conditions.
One measure of the degree of branching is the iso index, which is easily determined by those skilled in the art. It is defined by the number of branchings per molecule. Accordingly, linear octenes (n-octenes) have an iso index of 0, methylheptenes an iso index of 1 and dimethylhexenes an iso index of 2. The calculation of the iso index of mixtures must take account of the mass fractions of the individual groups of compounds.
TABLE 1
Typical structure distribution in dibutenes, each from
different preparation processes, starting from raffinate III.
A Zeolite catalysis
B Dimersol
C Octol
n-Octene
~0%
~6%
~13%
3-Methylheptenes
~5%
~59%
~62%
3,4-Dimethylhexenes
~70%
~34%
~24%
Other C
8
olefins
~25%
~1%
~1%
Iso index
>1.9
≅1.29
≅1.12
If instead of raffinate II or raffinate III other isobutene-containing C
4
cuts are used, such as raffinate I, there is also formation of a host of further, even more highly branched structures, essentially trimethylhexenes such as 2,2,4-trimethylpentenes, 2,2,3-trimethylpentenes, 2,3,4-trimethylpentenes, 2,3,3-trimethylpentenes, etc. Such dibutenes, with an iso index of more than 2, are also known by the name “codibutylene”.
The performance properties of the products produced from dibutene are often dependent on the composition and, especially, on the degree of branching of the olefin employed. This may take on very extreme forms, as is evident from the examples below.
An important field of use of dibutenes is the preparation of C
9
alcohols which in turn are esterified with carboxylic acids. For instance, dibutene produces isononanol mixtures, which are esterified with phthalic anhydride to give isononyl phthalates: these are employed as plasticizers in plastics.
The degree of branching of the isononyl chains of the phthalates is closely related to the degree of branching of the olefin employed, so that the properties of the phthalates are significantly co-determined by the structure of the olefin mixture that is employed.
TABLE 2
Comparison of typical dynamic viscosities of nonyl
phthalates employed industrially.
Hydro-
Viscosities of the
Oligomerization
formylation
isononyl phthalates
Crude material
process
process
(20° C.)
Raffinate
A
Co-HP
≅165
mPa s
Raffinate II or III
A
Co-HP
116-120
mPa s
Raffinate II or III
B or C
Co-HP
70-85
mPa s
Raffinate II or III
B or C
Rh-HP
90-100
mPa s
Wherein:
Co-HP: Classic cobalt high-pressure process, 200-300 bar, 140-180° C.; and
Rh-HP: Rhodium high-pressure process, 150-300 bar, 120-130° C., is unmodified or triphenylphosphine oxide-modified rhodium catalyst.
Other performance properties of the plasticizers are similarly heavily dependent on their degree of branching. Wadey et al. in J. Vinyl Tech. (1990) 208-211 show the marked dependency of the plasticizer properties of d
Manoharan Virginia
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
OXENO Olefinchemie GmbH
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