Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce unsaturate
Reexamination Certificate
2001-08-16
2003-10-14
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce unsaturate
C585S326000, C585S327000
Reexamination Certificate
active
06632972
ABSTRACT:
The present invention relates to a process for the selective dimerization of i-butene present in a C
4
raffinate I and comprises the steps of a first hydroisomerization of the raffinate I, a subsequent removal of 2-butene and n-butane by distillation in a column and the selective dimerization of part of the i-butene-containing product from the top of the column.
BACKGROUND OF THE INVENTION
The dimers of i-butene are 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene. They still each contain a double bond and can be passed to the oxo process or to esterification, for example to produce isononyl alcohol from diisobutylene (DIB) and then dinonyl phthalate or, in the case of direct esterification of the DIB, dioctyl phthalate which are used as plasticizers for thermoplastics. Triisobutene can also be processed to produce dodecyl mercaptan, a rubber auxiliary. Finally, mention may be made of the addition of DIB or octanes derived therefrom by hydrogenation to motor fuel.
It is already known that i-butene can be oligomerized over many electrophilic catalysts (Olah, Molaur, Hydrocarbon Chemistry, Wiley, 1995). For example, processes using acidic ion exchangers or pentasil zeolites have been described. A disadvantage of these methods is the low selectivity to DIB, since the processes always form not only the main product but also higher oligomers of i-butene, namely triisobutene (C
12
), tetraisobutene (C
16
), pentaisobutene (C
20
) and so forth, whose proportions decrease further with ever increasing degree of oligomerization. Such a process has to be followed by a separation of the components formed.
If the feed stream contains not only i-butene but also 1-butene or 2-butene, the selectivity to DIB decreases further, since C
8
products are simultaneously formed from i-butene and 1-butene or 2-butene (known as codimers) at high conversions.
Owing to the close proximity of their boiling points to that of DIB, these cannot be separated off at justifiable cost and thus represent a loss source in the process.
For this reason, processes which have a very high selectivity to DIB are sought. One way of increasing the selectivity is high dilution of the i-butene by octanes and oxygen compounds as disclosed in U.S. Pat. No. 5,877,372. However, unreacted i-butene and inert substances have to be separated off and circulated in this process.
Another route is described by EP 0 008 860 A1, where the catalyst is installed in wire mesh pockets in a distillation column. In this process, raffinate I having an i-butene content of about 50% and a 1-butene content of 25% is processed at low pressures. Despite this, the codimers which are virtually impossible to separate off are the major by-products. In addition, low i-butene conversions and thus i-butene losses have to be accepted in this process.
EP 0 850 904 A1 describes the separation of 1-butene and 2-butene from i-butene in C
4
raffinate I by appropriately linking hydroisomerization reactors with various distillation columns. However, the object here is to isolate a very pure i-butene stream.
DE 196 46 405 A1 describes the selective oligomerization of i-butene from a 1-/2-butene-containing C
4
stream, with the particularly troublesome 1-butene being converted into 2-butene by hydroisomerization and the 2-butene being separated from the i-butene by distillation. The resulting i-butane/i-butene stream is oligomerized over a heterogeneous acid catalyst in a reactor. Virtually no codimers which are difficult to remove are formed, but C
12
-oligomers constitute the main product.
SUMMARY OF THE INVENTION
In view of this background, it is an object of the present invention to improve the known processes so that DIB can be prepared in high conversions and with high selectivity from a stream comprising i-butene, 1-/2-butene and butanes.
This object is achieved by a process having the features specified in claim
1
.
The process for preparing diisobutylene (DIB) from an i-butene-containing C
4
raffinate I comprises the steps
a) subjecting the C
4
raffinate I to a first hydroisomerization over a noble metal catalyst, with this being carried out at 30-90° C., preferably 50-60° C., at 5-30 bar, preferably 10-20 bar, at an LHSV of 1-30 h
−1
, preferably 5-30 h
−1
, and using 3-20 standard liters of gaseous hydrogen per liter of liquid C
4
raffinate I, which is above the amount of hydrogen required for the hydrogenation of highly unsaturated compounds in the C
4
raffinate I;
b) fractionally distilling the hydroisomerization product from a) in a fractionation column, with this being carried out at 5-25 bar, preferably 8-12 bar, and the temperature established under this pressure and 2-butene and n-butane being taken off as bottoms and i-butene and i-butane being taken off at the top;
c) optionally taking off a side stream from this fractionation column above the inlet, preferably at the level of the middle of the column, and subjecting it to a second hydroisomerization over a noble metal catalyst, with this hydroisomerization being carried out at 30-90° C., preferably 50-60° C., at 5-30 bar, preferably 10-20 bar, at an LHSV of 1-30 h
−1
and using 3-20 standard liters of gaseous hydrogen per liter of C
4
raffinate I and the hydroisomerization conditions in a) and c) being identical or different; with the hydroisomerization product being recirculated to the fractionation column used under b), preferably above the offtake point;
d) condensing the product from the top of the column in b), dividing it into two parts and subjecting the first part to a third hydroisomerization over a noble metal catalyst, with this hydroisomerization being carried out at 30-90° C., preferably 50-60° C., at 5-30 bar, preferably 10-20 bar, at an LHSV of 1-30 h
−1
, preferably 5-30 h
−1
, and using 0.3-20 standard liters of gaseous hydrogen per liter of condensate and the hydroisomerization conditions in a) and d) being identical or different and the hydroisomerization product from d) being recirculated to the fractionation column of b), preferably into its upper third;
e) introducing the second part of the condensed product from the top of the column in b) into a reactive column in which the C
4
-hydrocarbons are vaporized preferably at 50-100° C. and are passed over an acidic heterogeneous catalyst over which the i-butene is dimerized, with the dimerization being carried out at 40-100° C., at 3-30 bar, preferably 5-20 bar, and an LHSV of 5-50 h
−1
. The catalyst can be present in a special column packing, e.g. in a commercially available packing of the type MONTZ Multipak I which allows separation of the DIB from the feed stream. Thus, inert C
4
-hydrocarbons can be condensed at the top of the reactive column, with part of this condensate being able to be recirculated to the column to remove the heat of reaction and the other part being able to be taken off, and dimerization products, i.e. C
8
-hydrocarbons, being able to be taken off at the bottom of the reactive column.
In the process of the invention, the C
4
stream is thus largely freed of 1-butene and 2-butene and subsequently dimerized over an acidic catalyst installed in a reactive column. The feed stream to this reactive column contains butanes in addition to i-butene, which make the reaction temperature in the fixed bed controllable by removal of the heat of reaction. The process of the invention differs from the process known from DE 196 46 405 A1 in, in particular, the steps c) (optional) and e).
As i-butene-containing C
4
mixture, it is possible to use a C
4
raffinate I which is obtained from the crude C
4
distillation fraction of a cracker product by removing the 1,3-butadiene present therein by extraction and making economic use of it. This extraction also removes other highly unsaturated hydrocarbons, e.g. vinylacetylene, 1,2-butadiene and other acetylene compounds, from the crude C
4
distillation fraction. The C
4
raffinate I obtained after the extraction still contains minor amounts of highly unsaturated compounds. The predominant components of C
4
raffinate I are
Gammersbach Alexander
Gohrt Axel
Grub Joachim
Kaminsky Stefan
Kramer Hans-Joachim
BP Koln GmbH
Dang Thuan D.
Nixon & Vanderhye
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