Method of producing high octane alkylate gasoline

A stream comprising isobutylene and n-butenes is processed to effect dimerization of the isobutylene, and the resulting isobutylene dimer is fed to an alkylation step.

FIELD OF THE INVENTION 
This invention relates to a method of producing a high octane gasoline 
mixture, utilizing an initial feed stream comprising isobutylene and 
normal butenes. 
In one aspect, the invention relates to a method of producing the 
combination of a high octane gasoline mixture and 1,3-butadiene from an 
initial feed stream comprising isobutylene and normal butenes. In another 
aspect it relates to producing the combination of a high octane gasoline 
mixture and high purity butene-1 from such an initial feed stream which 
also contains butene-1. 
In another aspect, it relates to producing the combination of 
1,3-butadiene, a high octane gasoline, and high purity butene-1 from an 
initial feed stream comprising isobutylene, butene-1, and butenes-2. 
BACKGROUND OF THE INVENTION 
Olefin-containing streams from refineries often contain butenes-2 and 
isobutylene in the presence of other four carbon compounds such as 
butene-1 and n-butane. It is desirable to use parts of such a stream to 
produce a high octane alkylate gasoline. It is also desirable to separate 
isobutylene from this mixture, so that the n-butenes can be used to 
produce valuable 1,3-butadiene. Alternatively, it may be desirable to use 
a portion of the n-butenes to produce some valuable high purity butene-1. 
The presence of isobutylene in a stream to be sent to a butadiene 
manufacturing process is undesirable since the isobutylene is not useful 
in the formation of butadiene. Also, to obtain high purity butene-1, the 
isobutylene must be separated. Isobutylene and butene-1 have very close 
boiling points, however; and their separation by fractional distillation 
is very difficult. 
The present invention addresses all of these needs and problems and 
provides a good solution. 
It is an object of the present invention to provide a method for producing 
1,3-butadiene and a high octane alkylate gasoline from a four carbon 
olefin-containing stream from refineries. It is also an object to produce 
high purity butene-1 from such a stream. 
STATEMENT OF THE INVENTION 
According to the invention, an initial feed stream comprising isobutylene 
and certain n-butenes is subjected to a dimerization process, and the 
resulting dimers of isobutylene are separated from the 4-carbon 
hydrocarbons and used in an alkylation process to produce a high octane 
gasoline. At least a portion of the mixture remaining after removal of the 
dimers is used for production of butadiene and/or high purity butene-1.

PREFERRED EMBODIMENTS OF THE INVENTION 
Referring to the drawing, a four carbon olefin-containing stream 10 from a 
refinery often comprises isobutylene, 1-butene, trans-2-butene, 
cis-2-butene, and normal butane. This stream is fed into a dimerization 
operation 11 which converts the isobutylene to two dimers, whereas the 
butene-1, butenes-2, and the normal butane do not substantially enter into 
the dimerization reaction. The resulting mixture after dimerization is 
labeled 12 in FIG. 1. Fractional distillation of that mixture is labeled 
15. The butenes and normal butane distill overhead in a "second stream" 
40, leaving behind the dimers, which are all charged to alkylation via 19. 
The "second stream" 40 can be charged to a butadiene manufacturing process 
via 16 to produce 1,3-butadiene, or (optionally) a part of that stream 17 
can be further fractionally distilled 28 to separate high purity butene-1 
18 for sale. The higher boiling portion of the f ractionation mixture in 
28 can all be sent to alkylation via 20, or alternately, a protion thereof 
can be sent to a butadiene manufacturing process via 20' to produce 
1,3-butadiene. 
The alkylation feed stream 21 can be fed by a number of streams: optional 
stream 10' (which contains a portion of the original feed olefin stream), 
optional stream 13 which contains a portion of the mixture after 
dimerization, stream 19 containing the distilled dimers, and stream 20 
containing at least a portion of the butenes-2 and normal butane. Also, 
stream 21 can be optionally fed by outside propylene 21'. The alkylation 
stream is subjected to alkylation shown at 26 and is then fractionally 
distilled in 27 to remove overhead propane 23, an upper side stream of 
isobutane 22, alower side stream of normal butane vapor 30, and alkylate 
via 31. Recycled isobutane 22 can be fed (together with a feed isobutane 
and/or isopentane 24) back into the stream 21, via 25, to be alkylated. 
The dimerization operation 11 serves three functions in converting 
isobutylene to dimers. One function is to permit the separation of the 
isobutylene from the close boiling butene-1. The dimerization reaction (as 
specified herein) quickly converts essentially all of the isobutylene to 
the dimers, wheras the 4-carbon normal olefins and normal butane do not 
appreciably enter into the reaction. And the produced dimers have a much 
higher boiling point than the remaining, unreacted 4-carbon hydrocarbons. 
Therefore, fractional distillation after dimerization permits an excellent 
separation of isobutylene, as the dimer, from the remainder of the 
4-carbon hydrocarbons. 
The second function of dimerization also involves the separation which is 
possible after the dimerization operation. Normal butenes to be used in 
the production of 1.3-butadiene should not contain isobutylene since it is 
not useful in the formation of butadiene. The third function of the 
dimerization reaction is in providing the dimers to be used in the 
alkylation step. It is known in the art that by adding isobutylene dimers 
to a given ratio of isoparaffin/olefin one can raise the octane number of 
the mixture. Alternatively, by adding isobutylene dimers, one can produce 
a given octane number with a lower ratio of isoparaffin/olefin than one 
could produce without the addition of the dimers. 
The amounts that are charged to various steps in the operation depend upon 
what types of products are required and upon what amounts of reactants are 
available in the inital feed stream. For example, if more dimer is 
required in the alkylation process, more of stream 10 will be charged to 
dimerization and less (or none) of stream 10 will be sent directly into 
the alkylation stream 21 by way of 10'. Also, for example, "second stream" 
40 will be split, depending on the requirements for 1,3-butadiene and/or 
high purity butene-1. Therefore, streams 10', 13, and 20' represent 
optional steps in FIG. 1. 
In the practice of the invention, the isobutylene dimerization can be any 
isobutylene dimerization known in the art which dimerizes isobutylene but 
which does not significantly affect the butenes that are present. 
The isobutylene dimerization step can employ any suitable catalyst which is 
capable of dimerizing isobutylene. The preferred dimerization catalyst is 
one which will produce relatively high quantities of diisobutylene 
(2,4,4-trimethylpentene-1 and 2,4,4-trimethylpentene-2) with relatively 
small amounts of other C.sub.8 isomers or higher isobutylene oligomers. 
Some examples of suitable dimerization catalysts are cold sulfuric acid; 
nickel-containing and rhodium-containing compounds activated with an 
aluminum alkyl; phosphoric acid on Kieselguhr; silica/alumina sometimes 
promoted with Ni, Co, Fe, Pt or Pd; activated natural clays plus 
activating substances such as ZnO; metallic phosphates such as those of 
iron (III)and cerium optionally supported on carriers such as activated 
carbon; bauxite; activated carbon alone and with metal halides such as 
TiCl.sub.3 ; heteropolyacids such as silicotungstic acid on silica gel and 
phosphomolybdic acid; BF.sub.3.H.sub.3 PO.sub.4 and BF.sub.3.HPO.sub.3 ; 
dihydroxyfluoboric acid; HF and fluorides or oxyfluorides of S, Se, N, P, 
Mo, Te, W, V and Si boiling below 300.degree. C.; BF.sub.3 -diethyl ether 
complexes; BF.sub.3 -hydrocarbon complexes; BF.sub.3 --SO.sub.2 ; and 
AlCl.sub.3 with cocatalysts such as diethyl ether, HCl and nitromethane. 
These catalysts and dimerization processes, including operaton conditions, 
are known in the art. The presently preferred catalyst is cold sulfuric 
acid or a soluble nickel compound activated with an aluminum alkyl, such 
as for example bis(tri-n-butylphosphine) nickel dichloride-ethylaluminum 
dichloride. 
Depending upon the specific catalyst used, the dimerization is generally 
carried out at a temperature of 0.degree.-230.degree. F., at a pressure of 
25-75 psig and with a contact time of 0.1 minute to 1 hour. Because 
isobutylene dimerizes much more readily than the normal butenes, the least 
severe conditions which will substantially completely convert the 
isobutylenes are preferred. 
The alkylation step can be any suitable alkylation process, such as HF 
alkylation or H.sub.2 SO.sub.4 alkylation. The preferred method is the 
conventional HF catalytic alkylation of isobutane with olefins (usually 
C.sub.3 and C.sub.4 olefins) and the isobutylene dimers. This method is 
preferred because with HF alkylation cooling water temperatures can be 
used and refrigeration, as needed in H.sub.2 SO.sub.4 alkylation, is not 
required. 
The HF alkylation should be carried out at a pressure sufficient to mainta 
in the liquid phase. A pressure within the range of above about 135 psig 
is preferred for this reason. A pressure of about 150 psig is more 
preferably used. There is no advantage to exceed to a great amount that 
pressure needed to maintain liquid phases at the alkylation temperature 
selected. 
The temerature used in the alkylation step can be within the range of about 
-10 to about 150.degree. F. because lower temperatures allow production of 
higher octane alkylate using the same isobutane/olefin ratio used at 
higher temperatures, or allow producction of the same octane alkylate at a 
lower isobutane/olefin mol ratio, as is known in the art of alkylation. 
For butylenes alkylate, each 10.degree. F. rise in temperature decreases 
octane by about 0.5 numbers. A temperature of 150.degree. F. can be used, 
but higher pressure is needed to maintain liquid phases; and octane value 
can fall off if the isobutane/olefin ratio is not increased. The excess 
isobutane which does not react with olefins to produce alkylate is 
fractionated from the alkylate and recycled. This fractionation is also 
very expensive. Plant economics will dictate the temperature and 
isobutane/olefin mol ratio used to produce the desired octane akylate. A 
temperature of about 85.degree. F. is most preferred, because plant 
cooling water can be economically used to maintain 85.degree. F. reaction 
temperature. 
The contact time in the HF alkylation should preferably be from about 10 to 
200 seconds, depending upon the type of conventional alkylation reactor 
used; and about 20 seconds is most preferred when using a riser-type 
reactor as described in U.S. Pat. No. 3,213,157, issued Oct. 19, 1965, to 
Phillips Petroleum Company. 
In the HF alkylation, the isobutane/olefin mole ratio (including the 
isobutylene dimers) should preferably be within the range of about 4:1 to 
about 25:1 and more preferably about 10:1 because high isobutane/olefin 
ratios prevent olefin polymerization and allow production of high octane 
alkylate. 
The ratio of HF to total hydrocarbon volume should be within the range of 
about 0.25:1 to about 8:1 and preferably about 4:1 because within these 
ratios the highest octane alkylate is produced. 
The butadiene manufacturing process can be any butadiene manufacturing 
process. 
The fractional distillations can be carried out by any method known in the 
art. The fractional distillation to separate the dimers in 15 will, for 
example, be carried out at a pressure of about 70 psig with a top 
temperature of about 120.degree. F. and a bottom temperature of about 
340.degree. F. Likewise, the fractional distillation for separating high 
purity butene-1 in 28 can, for example, be at about 80 psig with a top 
temperature of about 120.degree. F. and a bottom temperature of about 
140.degree. F. Further, the fractional distillation 27 to separate the 
alkylate gasoline can for example be at about 275 psig with a top 
temperature of about 125.degree. F. and a bottom temperature of about 
430.degree. F. 
CALCULATED EMBODIMENT 
An illustrative calculated embodiment is given in Table I, showing possible 
uses of parts of a typical initial feed stream from a refinery. The 
numbers identifying the streams correspond to the numbers in FIG. 1. 
The flow scheme and material balance are provided to illustrate the 
invention. The operation was "idealized" to simplify the "calculated" 
material balance. The material balance is based on operating dimerization 
unit 11 utilizing sulfuric acid and operating the unit at 500 psig and 
with a residence time within the reactor of about one minute and operating 
the HF alkylation unit 27 at a pressure of 150 psig; at a temperature of 
90.degree. F.; at a contact time of 40 seconds; at an isobutane to total 
olefin (including the isobutylene dimer) mol ratio of about 10:1, and an 
HF catalyst to total hydrocarbon volume ratio of about 4:1. 
TABLE I 
__________________________________________________________________________ 
Calculated Embodiment 
(Pounds Per Hour) 
Stream (10) 
(12) 
(13) 
(14) 
(16) 
(17) 
(18) 
(19) 
(20) 
(21) 
(22) 
(24) 
(25) 
(23) 
(30) 
(31) 
__________________________________________________________________________ 
Component 
Propane 0 0 0 0 0 0 0 0 0 0 0 0 0 200 
0 0 
Isobutene 
600 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
n-Butane 600 600 200 
400 300 
100 
0 0 100 
300 
0 0 0 0 300 
0 
Butene-1 6000 
6000 
2000 
4000 
3000 
1000 
1000 
0 0 2000 
0 0 0 0 0 0 
Butenes-2 
7800 
7800 
2600 
5200 
3900 
1300 
0 0 1300 
3900 
0 0 0 0 0 0 
Isobutane 
0 0 0 0 0 0 0 0 0 0 59,000 
5900 
64,900 
0 0 0 
Diisobutylene 
0 600 200 
400 0 0 0 400 
0 600 
0 0 0 0 0 0 
Akylate 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 12,200 
TOTAL 15,000 
15,000 
5,000 
10,000 
7,200 
2,400 
1,000 
400 
1,400 
6,800 
59,000 
5,900 
64,900 
200 
300 
12,200 
__________________________________________________________________________ 
This invention has been described in detail for purposes of illustration, 
but it is not to be construed as limited thereby. Rather, it is intended 
to cover reasonable changes and modifications which will be apparent to 
one skilled in the art. 
One such modification is to combine the processes of the production of high 
octane alkylate gasoline plus the production of butadiene, and this is 
accomplished by closing the valve in path 17 and leaving the valve in path 
16 open. Another modification is to combine the processes of the 
production of high octane gasoline plus the production of high purity 
butene-1, and this is accomplished by closing the valve in path 16 and 
leaving the valve in path 17 open. A third possibility is to leave the 
valves in both paths 16 and 17 open, thereby accomplishing the production 
of all three products. Further, when outside propylene is used, the valve 
in path 21' is open; otherwise, it is closed. When a portion of the 
original feed olefin stream is fed to the alkylation feed stream 21, the 
valve in path 10' is open; and otherwise, it is closed. Also, when a 
portion of the mixture after dimerization 12 is fed to the alkylation 
stream 21, the valve in path 13 is open; and otherwise, it is closed. And 
when a portion of the higher boiling portion of the fractionation mixture 
in 28 is fed to the butadiene manufacturing process, the valve in path 20' 
is open; and, otherwise, it is closed.