Chemistry of hydrocarbon compounds – Saturated compound synthesis – By isomerization
Reexamination Certificate
2003-09-16
2004-09-28
Dang, Thuan Dinh (Department: 1764)
Chemistry of hydrocarbon compounds
Saturated compound synthesis
By isomerization
C585S745000, C585S748000
Reexamination Certificate
active
06797853
ABSTRACT:
BACKGROUND OF THE INVENTION AND PRIOR ART
The present invention relates to a process for the isomerisation of paraffin hydrocarbons catalysed by an acidic ionic liquid catalyst in the presence of a cyclic hydrocarbon additive containing a structural entity with a tertiary carbon atom, which improves the selectivity towards the formation of multibranched paraffin hydrocarbons.
Paraffin hydrocarbons with high degree of branching are known to be useful blending components for motor gasoline due to their high octane numbers. Such paraffin hydrocarbon fraction can be produced in an isomerisation process increasing the octane number of the C
4
-C
9
cuts. Isomerisation of C
4
, C
5
and C
6
paraffins are common refinery processes based on use of e.g. an acidic Friedel-Crafts catalyst such as AlCl
3
. Processes including higher fractions (C
7
to C
9
hydrocarbons) meet with significant difficulties due to low selectivity and low octane number of the once-through products.
Several different concepts based on the use of liquid catalysts, solid catalysts as well as supported catalysts have been reported in connection with paraffin isomerisation. Some references also describe the use of specific hydrocarbon additives to the paraffin feed resulting in a positive effect on the isomerisation reaction, such as reduced catalyst deactivation or higher selectivity towards branched products by limiting the cracking reactions. In the following some applications of such hydrocarbon additives are described.
U.S. Pat. No. 4,035,286 describes the isomerisation of methylpentane in the presence of catalyst systems comprised of a mixture of fluorinated alkane sulphonic acids and antimony pentafluoride, e.g. CF
3
SO
3
H and SbF
5
. In this example a mixture of methylcyclopentane and cyclohexane is used as additives to the hydrocarbon feed in order to reduce cracking. The amount of methylcyclopetane/cyclohexane mentioned in the patent is in the range 2 wt % to 30 wt % and preferably from 5 wt % to 15 wt %.
In two articles, (1) “M. Bassir, B. Torck, M. Hellin, Bull. Soc. Chim. Fr., 1987, V.4, pages 554-562”, and (2) “M. Bassir, B. Torck, M. Hellin, Bull. Soc. Chim. Fr., 1987, V.5, pages 760-766, respectively, the influence of isobutane as additive on the isomerisation of n-heptane catalysed by a mixture of HF and SbF
5
is reported. Both articles mention the use of a feed-mixture of isobutane (40-50 wt %), n-pentane (20-25 wt %), n-hexane (20-25 wt %) and n-heptane (10-20 wt %) concluding that n-heptane is isomerised without any cracking. In the case where the feed is composed of isobutane (40 wt %) and n-heptane (60 wt %), the amount of cracking is limited (in the order of 5 wt %).
U.S. Pat. No. 3,903,196 discloses the use of isobutane as additive in the isomerisation of n-hexane catalysed by a mixture of HF and SbF
5
on a solid support like fluorinated alumina. The isobutane concentrations in the hydrocarbon feed are above 25 wt % and preferably above 40 wt %. The presence of the hydrocarbon additive results in a reduced catalyst deactivation.
A different example on the use of hydrocarbon additives to the hydrocarbon feed in the paraffin isomerisation is described in U.S. Pat. No. 3,201,494. In this reference, isomerisation of pentane, hexane and heptane compounds is carried out using hexafluoroantimonic acid as catalyst. Use of isobutane (preferably 5 wt %-25 wt %) has shown increase of the rate of the isomerisation reaction. Furthermore, the deactivation rate of the catalyst can be decreased by adding certain cycloalkane compounds chosen from methylcyclopentane, cyclohexane, methylcyclohexane and ethylcyclohexane (preferably 5 wt %-50 wt %) to the feed.
In U.S. Pat. No. 3,394,202 the same catalyst system, hexafluoroantimonic acid, is described as a supported catalyst concept and used for paraffin hydrocarbon isomerisation. This system has the same advantageous characteristics, when isobutane and cycloalkanes are used as additives to the feed.
A relatively new class of acidic catalysts based on ionic liquids, amongst produced from AlCl
3
, has recently been described in the literature (P. Wasserscheid, W. Keim, Angew. Chem., Int. Ed., 2000, V. 39, pages 3772-3789; T. Welton, Chem. Rev., 1999, V. 99, pages 2071-2083). This group of compounds also referred to as molten salts are constituted of:
(1) an inorganic anion, typically formed from metal halides, such as AlCl
4
−
, Al
2
Cl
7
−
or other inorganic anions (SO
4
2−
, NO
3
−
, PF
6
−
, CF
3
SO
3
−
, BF
4
−
etc.), and
(2) an organic cation, typically derived from N-heterocyclic or alkylammonium entities.
The melting point of ionic liquids is relatively low and an increasing number of ionic liquids are described with melting points below room temperature. Below some characteristics of ionic liquids are listed:
(1) They have a liquid range of about 300° C.
(2) They are good solvents for a wide range of inorganic, organic and polymeric materials.
(3) They exhibit Brønsted and Lewis acidity as well as superacidity.
(4) They have low or no vapour pressure.
(5) Most ionic liquids are thermally stable up to near 200° C., some ionic liquids are stable at much higher temperature (about 400-450° C.).
(6) They are relatively cheap and easy to prepare and upscale.
(7) They are non-flammable and easy in operation.
(8) They are highly polar but non-coordinating materials.
Ionic liquids most frequently demonstrate Lewis acidic properties once they are formed by metal halides. In many cases, however, the ionic liquids also show strong Brønsted (proton) acidity. The proton acidity may originate both from the cation if it contains a proton at the quarternised N atom or from the anion if it contains protons, for instance in HSO
4
−
, H
2
PO
4
−
.
Also HCl produced via partial hydrolysis for example of the chloroaluminate anion can explain strong proton acidity of the ionic liquids. Addition of a Brønsted Acid, e.g. H
2
SO
4
, to an ionic liquid containing chloroaluminate anions will also increase the amount of protons in the medium and in the case when the Brønsted Acid reacts with the ionic liquid, HCl is liberated to the medium.
Lewis-acidic properties of ionic liquids are governed by two major factors: (1) the nature of the anion, and (2) the molar ratio of the organic part to the inorganic part (for instance in the case of ionic liquids based on metal halides Me (Hal)
n
by the molar fraction of Me (Hal)
n
). If X
Me(Hal)n
<0.5, the ionic liquid is called basic; if X
Me(Hal)n
=0.5, this is the case of neutral ionic liquid, and finally if X
Me(Hal)n
>0.5, the ionic liquid can be classified as acidic or in some cases superacidic.
The effect of superacidity of ionic liquids is quite frequently observed for AlCl
3
-based compositions. Sometimes this effect is related to the presence of dry HCl in the system, which is dissolved in the ionic liquid. The Hammett function H
0
for such systems (H
0
=−18) indicates superacidic properties of the ionic liquids comparable with those of HF—TaF
5
(H
0
=−16) and “magic acid” HF—SbF
5
or FSO
3
H—SbF
5
(H
0
=−25). All these systems are much stronger acids as compared to the conventional 100% H
2
SO
4
(H
0
=−12), which marks the border of superacidity. Such ionic liquids are also stronger than the solid superacids like SO
4
/ZrO
2
(H
0
=−16), H
3
PW
12
O
40
(H
0
=−13.5) or H-Nafion (H
0
=−12).
Room-temperature ionic liquids are promising media for a wide range of catalytic reactions including downstream oil processing, basic organic synthesis and fine chemicals production. Among these processes of potential commercial interest are various alkylation, oligomerisation and isomerisation reactions (D. Zhao, M. Wu, Y. Kou, E. Min, Catalysis Today, V. 74, 2002, pages 157-189).
DETAILED DESCRIPTION OF THE INVENTION
The object of the present invention is a process for the conversion of linear and/or branched paraffin hydrocarbons, into hydrocarbons with a higher degree of bran
Herbst Konrad
Houzvicka Jindrich
Zavilla John
Dang Thuan Dinh
Dickstein , Shapiro, Morin & Oshinsky, LLP
Haldor Topsoe A/S
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