Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – Including alkylation to produce branched-chain paraffin
Reexamination Certificate
1999-02-24
2001-12-25
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
Including alkylation to produce branched-chain paraffin
C585S331000, C585S300000, C585S304000
Reexamination Certificate
active
06333442
ABSTRACT:
SUMMARY OF THE INVENTION
The invention relates to an improved process for the preparation of an aliphatic alkylate with a high octane number from a C4 catalytic cracking or steam-cracking fraction. The isooctane mixture that is obtained can be used as a gasoline component with high octane numbers.
Catalytic cracking, which produces automobile gasoline, also produces a large amount of light hydrocarbons, in particular with 4 carbon atoms. The C
4
hydrocarbon fraction mainly contains butene-1 and butenes-2, isobutene, isobutane, n-butane, as well as a small amount of butadiene-1,3. This fraction is the so-called olefinic fraction because the proportion of olefins (isobutene, butene-1 and butenes-2) that it contains is larger than its proportion of paraffins (isobutane, n-butane). It is most often sent into an alkylation installation that adds the mixture of butenes (isobutene, butene-1 and butenes-2) to the isobutane. As the stoichiometry of the alkylation requires one mol of isobutane per mol of butene, the isobutane content of the fraction that comes from cracking is most generally inadequate for alkylating all of the olefins of this fraction; an outside supply of isobutane is necessary. This importation can be difficult and at the very least expensive.
It is known that it is possible to increase selectively the isobutane concentration of the olefinic hydrocarbon fraction of 4 carbon atoms sent to an alkylation unit. The applicant thus has already described, in French Patent 2,436,176 (to which U.S. Pat. No. 4,268,701 corresponds), a process that comprises:
1. The hydro-isomerization of butene-1 of a C4 olefinic fraction to obtain a C4 fraction that is enriched with butenes-2 and that is low in butene-1, whereby the isomerization of butene-1 accompanies the selective hydrogenation of the butadiene-1,3 that is present;
2. the fractionation of the C4 fraction that is thus obtained to obtain separately an isobutane- and isobutene-enriched fraction and a butenes-2-enriched fraction;
3. the hydrogenation of the isobutane- and isobutene-enriched fraction to convert at least a portion of the isobutene into isobutane and thus to increase the content of the latter; and
4. the alkylation of the butenes-2-enriched fraction with the fraction with an increased isobutane content.
The alkylation product is sent into a stabilization zone, where the final alkylate is separated at the bottom, and the non-transformed C4 hydrocarbons (mainly isobutane) are separated at the top.
The sequence of these operations offers many advantages. The most reactive compound, namely butadiene-1,3, is hydrogenated and will not produce parasitic reactions in the alkylation operation, namely the formation of muds or oils that, in addition to the elimination problem that it poses, brings about excessive acid consumption (sulfuric acid or hydrofluoric acid).
Furthermore, the hydro-isomerization of butene-1 into butenes-2 makes it possible to separate the isobutene (boiling point: −6.9° C.) from butenes-2 (boiling point of butene-2 trans: +9° C.; of butene-2 cis: +3.7° C.) and therefore makes it possible to hydrogenate mainly isobutene into isobutane, while retaining the butenes-2. A mixture (almost stoichiometric or with excess isobutane) that makes it possible to maximize production of the alkylation unit thus is prepared.
Moreover, the characteristics of the alkylate that is produced, namely the “research” and “motor” octane numbers, are considerably improved, regardless of the alkylation process, when the butenes-2 are used as olefins. Thus, in the case of alkylation with sulfuric acid or with hydrofluoric acid, the octane numbers are considerably improved, as Table 1 shows below:
TABLE 1
Butene-1
Butenes-2
Isobutene
HF
H
2
SO
4
HF
H
2
SO
4
HF
H
2
SO
4
IOR*
90-91
97-98
96-97
97-98
94-95
90-91
IOM*
88-89
93-94
92-93
93-94
91-92
88-89
*IOR designates the “research” octane number, and IOM designates the “motor” octane number.
Actually, it is seen that the octane numbers of the “sulfuric” alkylate of isobutene are very considerably lower than those of the “sulfuric” alkylate of the n-butenes, while the octane numbers of the “hydrofluoric” alkylate of butene-1 are very considerably lower than those of the “hydrofluoric” alkylate of butenes-2. The almost-exclusive presence of butenes-2 in the alkylation feedstock therefore makes it possible, both in the case of “sulfuric” alkylation and in that of the “hydrofluoric” alkylation, to obtain maximum octane number values.
It has now been discovered that it was possible also to improve the production of aliphatic alkylate from a C4 catalytic cracking or steam-cracking fraction.
The process of the invention calls for diluting the feedstock of the hydrogenation zone by the top effluent (that mainly contains isobutane) from the separation zone (stabilization) that is located downstream from the alkylation unit. Actually, the hydrogenation reaction is exothermic, and it is necessary to control the rise in temperature in the hydrogenation reactor if maintaining control is desired. Generally, the isobutane that is thus recycled corresponds to 5 to 10 times the amount of isobutene. The isobutene that is thus diluted can thus be hydrogenated almost completely with an acceptable temperature increase (&Dgr;T) that is generally less than 50° C. This way of proceeding is very advantageous, because it makes it possible to simplify the installation of hydrogenation by avoiding the necessity to increase the recycling capacity of the hydrogenated product to the hydrogenation reactor, which would involve providing a larger reservoir and one (or more) additional pump(s).
Generally, the invention proposes an improved process for preparing an aliphatic alkylate with a high octane number from a C4 catalytic cracking or steam-cracking fraction that contains mainly butene-1, butenes-2, isobutene, isobutane, n-butane, as well as a small amount of butadiene-1,3, whereby this process comprises:
(a) The hydro-isomerization of said C4 fraction that has the result of obtaining a mixture that contains for the most part butenes-2, isobutene and isobutane;
(b) the separation, by distillation of the hydro-isomerized fraction, of a butene-2-rich effluent that is collected at the bottom and an isobutane- and isobutene-rich effluent that is collected at the top;
(c) the sending of said isobutene- and isobutane-rich effluent into a hydrogenation zone that produces an effluent that for the most part contains isobutane;
(d) the sending of said butenes-2-rich effluent that is derived from stage (b) and of said effluent that for the most part contains the isobutane that is derived from stage (c) into an alkylation zone that produces, by the addition of isobutane to butenes-2, an isooctane mixture that contains excess isobutane; and
(e) the separation by distillation of excess isobutane, which comes out at the top, and alkylate with an improved octane number, which comes out at the bottom; whereby this process is characterized by the fact that it also comprises
(f) the recycling of the excess isobutane that is recovered in stage (e) upstream from hydrogenation stage (c) of the top effluent from the distillation of stage (b) (whereby said effluent comprises isobutane, isobutene and residual butene-1) so as to dilute the latter.
The process of the invention as defined above is depicted diagrammatically by the accompanying figure, where the different stages can be described as follows.
The C
4
hydrocarbon fraction is introduced via pipe 1 into hydro-isomerization unit R1, in which hydrogen is also introduced. This unit carries out the hydrogenation of the butadiene-1,3 that is present in a small amount and the isomerization of butene-1 into butenes-2. The product of this unit is then introduced via pipe 2 into distillation column C1, which separates, at the bottom, the butenes-2-rich effluent that is sent via pipe 3 to alkylation unit R3, and, at the top, the isobutene and isobutane-rich effluent that is sent via pipe 4 to hydrogenation unit R2 that also receives hydrogen. This unit produces an isob
Cosyns Jean
Didillon Blaise
Quicke Lionel
Griffin Walter D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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