Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
2000-08-04
2002-08-13
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S511000
Reexamination Certificate
active
06433238
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the production of hydrocarbons with a high octane number, obtained by the selective dimerization reaction of isobutene contained in hydrocarbon cuts and to a lesser degree of possible linear butenes, in the presence of moderate quantities of tertiary alcohols and alkyl ethers, which favour the production of higher selectivities on the part of the catalyst. The mixture obtained can then be hydrogenated with the conventional methods to obtain a product with further improved octane characteristics.
2. Discussion of the Background
For reasons of an environmental nature, the composition of gasolines is being reformulated to obtain fuels which burn better and have fewer evaporative emissions.
In order to be able to reach this objective, it is necessary to reduce the content of aromatic compounds (mainly benzene), light olefins (photo-chemically reactive and precursors responsible for the formation of atmospheric ozone), sulfur and also the volatility (to minimize losses) and end boiling point of the gasolines.
All these measurements cause a contraction in the volume and a lack in the octane number of the new gasolines, making it necessary, on the basis of the present uncertainty regarding the use of alkyl ethers in fuels (Europ. Chem. News, May 10-16, 1999), to make more and more use of purely hydrocarbon compounds such as, for example, the alkylate.
These products are capable of positively contributing to the above demands as they have a high octane number (both the Research Octane Number (RON) and the Motor Octane Number (MON) are high), excellent boiling point properties (limited volatility but low end point) and they are practically without olefins and aromatics.
At present the alkylate is obtained by the reaction, in liquid phase, between isoparaffinic hydrocarbons, such as for example isobutane, and olefins, for example propylene, butenes, pentenes and relative mixtures, in the presence of an acid catalyst for the production of C
7
-C
9
hydrocarbons with a high octane number to be used in gasolines (see for example: A. Corma, A. Martinez, Catal. Rev.—Sci. Eng., 35, (1993), 483 and references contained therein).
The main problem of the alkylation process is due to the fact that with an increase in regulations of an environmental nature, both traditional processes (with hydrofluoric acid and with sulfuric acid) are coming up against great difficulties, making the future uncertain: the process with hydrofluoric acid owing to the toxicity of this acid, especially in populated areas, and the process with sulfuric acid owing to the large production of acid mud as well as the extremely corrosive power of the catalyst.
Alternative processes with solid acid catalysts are being developed, but their commercial applicability has yet to be demonstrated.
An alternative process in refining for obtaining products with characteristics similar to the alkylate, can be offered by the hydrogenation of the so-called “polymer” gasoline.
The oligomerization process (often erroneously called polymerization in the field of refining) was widely used in the years 1930-1940 to convert low-boiling C
3
-C
4
olefins into gasolines. The process produces a gasoline with a high octane number (RON about 97) but with a high sensitivity owing to the purely olefinic nature of the product (for more specific details on the process see: J. H. Gary, G. E. Handwerk, “Petroleum Refining: Technology and Economics”, 3
rd
Ed., M. Dekker, New York, (1994), 250).
Typical olefins which are oligomerized are mainly propylene, which gives slightly higher diners or oligomers depending on the process used, and isobutene which mainly gives dimers but always accompanied by considerable quantities of higher oligomers.
If we limit our attention to the oligomerization of isobutene, it is known that this reaction can be carried out either in batch, semi-continuous or in continuous, in both gas-solid phase and in liquid phase, generally at temperatures ranging from 50 to 300° C. and at atmospheric pressure or at such pressures as to keep the reagents in liquid phase, if considered necessary.
Typical catalysts for the industrial oligomerization process of isobutene are phosphoric acid, generally supported on a solid (for example kieselguhr), or cationic exchange acid resins. The latter enable the use of blander temperature and pressure conditions, with respect to supported phosphoric acid (100° C. and 1-2 Mpa vs 200-220° C. and 3-10 Mpa).
Other catalysts have also been claimed in literature, both liquid acids such as H
2
SO
4
or sulfonic acid derivatives, or solid acids such as, for example, silico-aluminas, mixed oxides, zeolites, fluorinated or chlorinated aluminas, etc.; none of these catalysts however have as yet allowed the set up of an industrial process such as that of supported phosphoric acid (F. Asinger, “Mono-olefins: Chemistry and Technology”, Pergamon Press, Oxford, pages 435-456) and that of cationic resins (G. Scharfe, Hydrocarbon Proc., April 1973, 171).
From the product point of view, the main problem of this process lies in the fact that, in the oligomerization phase, heavy oligomers of isobutene such as trimers (selectivity of 15-30%) and tetramers (selectivity of 1-2%), are produced in excessive percentages. Tetramers are not at all within the gasoline fraction as they are too high-boiling and consequently represent a net loss in yield to gasoline; as far as trimers are concerned (or their hydrogenated derivatives), their concentration should be greatly reduced as their boiling point (170-180° C.) is at the limit of future specifications on the end point of reformulated gasolines.
The problem, on the other hand, of minimizing the formation of higher oligomers to dimers with percentages lower than 10-15% is a typical problem of the oligomerization of isobutene as is also specified in literature (C. T. O'Connor, M. Kojima, K. W. Schumann, Appl. Catal., 16, (1985), 193).
This level of heavy compounds is analogous to that of an alkylate and is still tolerable in the gasoline pool.
From what is described above, it is evident that there is great interest in obtaining a new dimerization process of isobutene which allows the synthesis of a higher quality product, by reaching greater selectivities.
This result can be obtained by carrying out the dimerization reaction of isobutene in the presence of primary alcohols (U.S. Pat. No. 5,723,687 of M. Marchionna, F. Ancilotti and M. Di Girolamo) or mixtures of alkyl ethers and primary alcohols (Italian patent application MI97A001129 of M. Di Girolamo and L. Tagliabue) which, if suitably dosed, make it possible to operate with a catalytic species have the correct activity.
Water can also be used (U.S. Pat. No. 4,100,220 of W. G. Bowton and W. P. Stadig) for regulating the activity of the catalyst, but in this case, in addition to dimerization, there is also the hydration of isobutene with the formation of terbutyl alcohol (TBA) and the consequent decrease in the yield to oligomers.
SUMMARY OF THE INVENTION
It has now been surprisingly found that it is possible to selectively obtain the production of a hydrocarbon fraction, particularly rich in dimers (>85%) and practically without tetramers and higher oligomers (<0.5%), by carrying out the selective dimerization of isobutene in the presence of suitable quantities of tertiary alcohols, alkyl ethers and primary alcohols.
DETAILED DESCRIPTION OF THE INVENTION
The reaction product can then be preferably hydrogenated to give a completely saturated end product with a high octane number and low sensitivity. The hydrogenation can be carried out with conventional methods as described for example in F. Asinger, “Mono-olefins: Chemistry and Technology”, Pergamon Press, Oxford, page 455.
As an example, Table I indicates the octane number and relative boiling points of some of the products obtained, using the process of the present invention.
TABLE I
Product
RON
MON
B.T.(° C.)
disobutenes
100
89
100-105
iso-octane
100
100
99
tr
Di Girolamo Marco
Marchionna Mario
Tagliabue Lorenzo
Dang Thuan D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Snamprogetti S.p.A.
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