Diisopropyl ether reversion and oligomerization in isopropanol production

A process for the production of an oxygenated fuel blending composition which contains isopropanol by the hydration of propylene in which the by-product diisopropyl ether is subjected to a reversion reaction and the resulting propylene is oligomerized to form olefinic gasoline.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the production of oxygenated 
fuel blending compositions by the hydration of olefins. Specifically, the 
invention relates to a process for the hydration of propylene to produce 
isopropanol for blending into gasoline. 
As is well known, alkylation can produce a premium grade gasoline component 
from olefins by reaction with isoparaffins such as isobutane or 
isopentane. Refineries have, however, experienced a shortage of 
isoparaffins, particularly isobutane, and therefore have an excess of 
olefins. So a way to place these olefins into the motor gasoline pool is 
needed. At the same time, gasoline octane requirements have increased and 
the use of traditional lead-containing gasoline additives has been largely 
discontinued. It has, therefore, become necessary to find alternative 
means to produce high octane fuel compositions without the necessity for 
alkylation. This may be accomplished by producing oxygenated compounds, 
e.g., isopropanol from the excess olefins. 
Furthermore, some gasolines have a maldistribution of high octane 
components and when used without fuel injection can knock under driving 
conditions not predicted by model octane testing. Addition of isopropanol 
to such gasolines provides a good way to improve octane component 
distribution. 
Isopropanol may be made with very high propylene conversions per pass using 
even dilute C.sub.3 olefin-containing feedstocks at low space velocities. 
Under these conditions, however, especially at low water to olefin molar 
feed ratios, large amounts of diisopropyl ether (DIPE) may be formed. The 
present process relates particularly to the treatment of the DIPE 
by-product so that the isopropanol production process can be conducted 
more efficiently.

SUMMARY OF THE INVENTION 
The present invention relates to a process for producing isopropanol 
comprising the steps of contacting water and a propylene-containing 
feedstock in a hydration reaction zone with a hydration catalyst to 
produce isopropanol and by-product diisopropyl ether, separating the 
diisopropyl ether and contacting it with a reversion catalyst under 
reversion conditions to produce an effluent from which propylene is 
recovered and oligomerized to produce olefinic gasoline. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The process of the present invention enables one to use excess C.sub.3 
olefins and incorporate them as high octane components into the motor 
gasoline pool without alkylation. In addition, the present process 
provides a method for employing the by-product of the propylene hydration 
reaction whereby this by-product is in effect incorporated into the motor 
gasoline pool. 
The present invention is most advantageously employed in a process for 
producing isopropanol by the hydration of propylene. Although any such 
process may be employed, the preferred method is the one disclosed in my 
co-pending U.S. patent application Ser. No. 277,438, filed June 25, 1981 
which is incorporated by reference herein. In that method, a feedstock 
comprising C.sub.3 hydrocarbons having a propylene content of from about 
60% to about 85% is used. Preferred is a feed such as that which could be 
obtained by distilling off a C.sub.3 cut from a fluid catalytic cracker. 
It is possible by using the combination of reaction conditions described 
below to obtain a high conversion per pass even employing such dilute 
feedstocks. 
The feedstock containing propylene is reacted with water in the presence of 
an ion exchange catalyst. The catalyst is preferably a sulfonated 
macroreticular copolymer of styrene and divinylbenzene in the acid form. 
Catalysts modified by chlorination to withstand higher temperatures, such 
as Amberlyst XN 1011 and Amberlite XE 372, manufactured by Rohm and Haas, 
are particularly preferred. Other catalysts suitable for the hydration of 
propylene and methods for their preparation are described in U.S. Pat. No. 
2,813,908, incorporated by reference herein. 
In propylene hydration, a propylene-containing feedstock is generally mixed 
with water in a ratio of water to propylene from about 5 to 15, preferably 
from about 8 to 12 and most preferably about 8. The mixture is then fed to 
a reactor, preferably in a downflow, trickle bed configuration, to contact 
the catalyst. 
Hydration conditions generally include a pressure of from about 1,000 to 
2,000, preferably 1,400 to 1,500 psig and a temperature of from about 
275.degree. to 375.degree. F., preferably from about 290.degree. to 
355.degree. F. The conditions are selected so that the propylene is in a 
super-critical gas phase and the water is primarily in the liquid phase. 
Finally, the propylene liquid hourly space velocity is from about 0.15 to 
about 1.5 per hour, preferably from about 0.4 to 0.5 per hour. 
In the hydration stage, the percent propylene conversion should be 
maintained at a predetermined level, generally from about 50% to 90%, 
preferably about 67%. To do so, the temperature in the reactor can be 
raised incrementally to compensate for the loss of catalyst activity 
during the course of the reaction. 
The crude product which emerges from the bottom of the reactor generally 
contains water, isopropanol, diisopropyl ether (a by-product), propylene, 
propane, any C.sub.4 hydrocarbons present in the feed, traces of alcohols 
or ethers derived from reactions of C.sub.4 hydrocarbons and traces of 
C.sub.6 hydrocarbons formed by dimerization of propylene. This crude 
product may be passed through one or more conventional gas-liquid 
separators to separate the gases, i.e., propane, unreacted propylene and 
trace C.sub.4 and lower hydrocarbons from the liquids, i.e., isopropanol, 
water and diisopropyl ether. 
The separated gases generally contain at least 30% unreacted C.sub.3 
olefins. Such olefins, of course, may be fed to a conventional alkylation 
plant where they are allowed to react with isoparaffins in the presence of 
a suitable catalyst such as HF or sulfuric acid. The resultant alkylation 
product, presumably a mixture of high-branched C.sub.7 paraffins is a high 
octane product suitable for direct addition to the motor gasoline pool. As 
discussed, the desirability of alkylation is limited by the stortage and 
high expense of the requisite isobutane. 
Propylene obtained from the overhead of the liquid-gas separator may be 
catalytically oligomerized to make olefinic gasoline, a high octane 
gasoline pool component as disclosed in my co-pending U.S. patent 
application Ser. No. 277,437, filed June 25, 1981. Such oligomerization 
obviates the need to alkylate excess olefins, significantly reducing the 
process cost. 
The crude liquid product from hydration which contains water, isopropanol, 
diisopropyl ether and perhaps traces of C.sub.4 olefin-derived ethers 
and/or alcohols and C.sub.6 olefins is generally caustic neutralized or 
acid is removed by ion exchange. This product is passed to a first 
distillation column which is generally operated at near atmospheric 
pressure at a temperature so that the product taken overhead is primarily 
diisopropyl ether (actually the low-boiling azeotrope which also contains 
4% isopropanol and 5% water, b.p. 62.degree. C.). The bottoms from this 
first distillation column, containing primarily isopropanol and water, are 
passed through a second distillation column. The overhead from the first 
column, primarily diisopropyl ether, is treated in accordance with the 
present invention as discussed hereinbelow. 
The second distillation column containing the isopropanol and water, is 
operated generally at or near atmospheric pressure and at a temperature 
such that the isopropanol-water azeotrope (b.p. 80.degree. C.) having the 
composition of 87.8 weight percent isopropanol and 12.2 weight percent 
water is taken overhead. The column bottoms which consist primarily of a 
very dilute aqueous salt solution may be either (a) desalted by treatment 
with an ion exchange resin and the pure water recycled with makeup water 
to the hydration reactor or (b) discarded. 
Isopropanol is typically separated from the isopropanol-water azeotrope so 
it can be blended with a gasoline blending hydrocarbon stream resulting in 
a oxygenated fuel-containing blending stock which can be used directly in 
the motor gasoline pool. Such separation may be accomplished by any of the 
conventional extraction and/or azeotropic distillation techniques. The 
preferred method which provides a simple, economical way to introduce 
isopropanol from an isopropanol-water azeotrope directly into a gasoline 
blending stock, an extractive blending technique, is the subject of my 
co-pending U.S. patent applications Ser. Nos. 277,295, 277,296 and 
277,440, all filed June 25, 1981 and which are incorporated by reference 
herein. 
Briefly, in accordance with those methods, the azeotrope is dehydrated by 
combining it with a gasoline blending hydrocarbon stream. The gasoline 
blending hydrocarbon may be any hydrocarbon that can be added to the motor 
gasoline pool, including straight run, alkylate, FCC gasoline, reformate, 
or their mixtures such as Chevron Unleaded Regular gasoline (ULR). The 
hydrocarbon may also comprise middle distillates such as hydrocarbon 
mixtures boiling in the jet or diesel fuel range. The mixing may be done 
in a mixing tank, but is preferably accomplished by use of inline mixers 
such as the pipe mixers manufactured by Komax Systems, Inc., as opposed to 
the energy intensive extractors. From about 2 to 15 volumes of hydrocarbon 
per volume of azeotrope, preferably at least 10 volumes are employed. A 
milky emulsion forms on mixing. This emulsion is separated rapidly into 
two phases for example by passing it through a commercial water filter 
coalescer. 
For a 10:1 volume ratio, regardless of the rate of separation, the 
hydrocarbon layer composition is about 91.2 weight percent gasoline, 8.3 
weight percent isopropanol and 0.41 weight percent water. The aqueous 
phase consists essentially of about 75% water and 25% isopropanol. This 
layer represents only a small volume of material, however, (less than 0.1) 
and may be recycled to the second distillation column. The 
isopropanol-hydrocarbon phase emerging from the coalescer can be blended 
with additional gasoline or used directly as automotive fuel without 
further treatment. 
In accordance with the invention, the overhead from the first distillation 
column which is primarily diisopropyl ether (and about 4% IPA and 5% 
water), which was divided from the effluent from the hydration zone is 
contacted with a reversion catalyst in a second reaction zone under 
reversion conditions. 
Almost any acid catalyst may be suitably used as the reversion catalyst in 
accordance with the present invention. Nearly quantitative (&gt;95%) 
reversions to propylene and water were obtained at 50 psig and 330.degree. 
F. with Amberlite XE 372, the preferred catalyst from the propylene 
hydration reaction. Silicalite, an essentially alumina free intermediate 
pore size zeolite of the ZSM-5-type as disclosed in U.S. Pat. No. 
4,061,724, incorporated by reference, is also useful as a reversion 
catalyst although use of such catalyst requires a higher temperature. 
Special zeolitic catalysts are not required to achieve high degrees of 
conversion. Nearly quantitative conversion of DIPE to propylene was 
obtained using a silica-alumina cogel catalyst at 515.degree. F., but no 
conversion was obtained at moderate temperatures employing this catalyst 
(343.degree. F.). In fact, alumina itself reverted greater than 99% of 
DIPE to propylene at 520.degree. F. and 50 psig. Thus, in accordance with 
the present invention the reversion catalyst may comprise any acid 
catalyst, preferably an acid ion exchange resin, a silica-alumina cogel, 
alumina, aluminosilicates and zeolites including the ZSM-5 type zeolites. 
Alumina is most preferred. 
The reversion conditions will depend in part on the acidity of the 
reversion catalyst. Generally, a catalyst having low acidity requires a 
higher temperature than one having a higher acidity. For example, with 
Amberlite XE 372, 99% conversion was obtained at a temperature of 
330.degree. F., whereas silicalite converted only 18% of the DIPE to 
propylene at 343.degree. F. and 99% conversion to propylene was obtained 
only at about 525.degree. F. Reversion temperatures will generally be from 
about 250.degree. to 550.degree. F. 
Regardless of the particular catalyst, reversion conditions will include a 
low pressure, generally from atmospheric to about 500 psig and preferably 
from atmospheric to about 200 psig. The liquid hourly space velocity is 
generally from about 0.1 to 10 and preferably from about 0.5 to 5. 
The effluent from the reversion zone will comprise propylene, IPA and 
water. This effluent is then passed to a separation zone, e.g., a 
gas-liquid separator. The separated propylene is oligomerized to form 
olefinic gasoline. The liquid stream comprising IPA and water may be 
passed to an IPA recovery zone. 
The oligomerization of the resulting propylene may be conducted in any of 
the known and conventional manners. For example, in U.S. Pat. No. 
3,431,317, incorporated by reference herein, propylene is polymerized to 
its dimer and higher weight oligomers by using an alkyl aluminum 
dichloride catalyst at temperatures within the range of 30.degree. to 
100.degree. C. and at pressures of 30 psi to the saturation pressure of 
propylene. 
U.S. Pat. No. 3,483,269, incorporated by reference herein, discloses olefin 
oligomerization in the presence of a heterogeneous catalyst composition 
comprising a .pi.-allyl nickel halide on an inorganic oxide catalyst 
support. 
U.S. Pat. No. 3,773,853, incorporated by reference herein, teaches 
oligomerization with a catalyst comprising a tantalum-containing compound 
at temperatures from ambient to 250.degree. C. and at pressures from about 
1 to 160 atmospheres. 
Oligomerization may be conducted using a liquid phosphoric acid catalyst as 
disclosed in commonly assigned U.S. Pat. No. 3,887,634, incorporated by 
reference herein. In addition, propylene may be oligomerized using a solid 
catalyst consisting essentially of a silica carrier and phosphoric acid 
having a molar ratio of P.sub.2 O.sub.5 to SiO.sub.2 of between 0.6 and 
0.95 and a content of crystalline form of silicium phosphate between 75% 
and 95%, as disclosed in U.S. Pat. No. 3,758,627, incorporated by 
reference herein. 
Other suitable oligomerization catalysts and reaction conditions are 
described in U.S. Pat. Nos. 3,642,932; 3,855,341; 3,907,923; 3,932,553; 
4,017,553; 4,024,203; and 4,098,839, all of which are incorporated by 
reference herein. 
As another example, the Dimersol process disclosed in the Oil & Gas Journal 
of Apr. 28, 1980, pages 77-83, incorporated by reference herein, is a 
catalyzed liquid phase dimerization of propylene. In this process, the 
charge stock may also contain propane, so the C.sub.3 gases may be used. 
In the Dimersol process, the reactor is operated at sufficient pressure to 
keep all the C.sub.3 's liquid at near ambient temperatures. The catalyst, 
which is soluble in the feed, is injected into the feed line to the unit. 
The reactor operates liquid-full which provides residence time for the 
catalyst to contact the feed and for the reaction to take place. The 
exothermic heat of 300 BTU/lb of converted propylene is removed by 
circulation through an air-cooled heat exchanger. The recycle rate is many 
times that of the heat rate, but depends only on maintaining isothermal 
conditions. Typical catalysts that may be employed in this process are 
nickel carboxylate-alkyl aluminum halide combinations as disclosed in 
French Pat. No. 2,438,084, incorporated by reference herein. 
The following examples are merely illustrative and are not intended to 
constitute a limitation on the invention which is defined by the appended 
claims. 
EXAMPLES 
The following Table I set forth the results of tests which illustrate the 
concept of the present invention. All the runs were carried out in a 3/8" 
O.D. Teflon-lined 316 SS reactor tube into the midsection of which the 
indicated catalyst charge was loaded. Two beds of 20 to 32 mesh alundum 
particles which were each about 5" long were placed in the reactor tube to 
provide for mixing of the reagents and supporting the catalyst charge, 
respectively. 
The feed, 95.6% DIPE and 4.4% IPA, simulates the organic composition of an 
upper layer of decanted DIPE/IPA/H.sub.2 O azeotrope which would be 
obtained from the overhead of the first distillation column. (Run No. 4 
employed an organic feed composition 96.5% DIPE and 3.5% IPA.) The feed 
was passed into the reactor tube from the top at the indicated space 
velocities. The LHSV for water was zero in all cases except Run No. 4 
where it was 0.01 hr.sup.-1. 
Because of the multicomponent nature of both product and feed, the results 
in Table I are expressed not in terms of conversion and selectivity, but 
rather in terms of the potential propylene content of each component, 
normalized so that the total C.sub.3.sup.= content of the feed and product 
is 100% (e.g., 1 mole of DIPE contains 2 equivalents of C.sub.3.sup.= ; 1 
mole of IPA contains 1 equivalent of C.sub.3.sup.=). 
The catalyst designations are as follows: "Silicalite" signifies Linde 
Silicalite obtained from Union Carbide; "Cogel" signifies a 65% 
alumina-35% silica cogel; "Alumina" signifies alumina; and "XE 372" 
signifies Amberlite XE 372. 
TABLE I 
__________________________________________________________________________ 
Run 1 2 3 4 5 6 7 
__________________________________________________________________________ 
Catalyst XE 372 
XE 372 
Silicalite 
Silicalite 
Cogel 
Cogel 
Alumina 
Temperature, .degree.F. 
330 330 343 525 508-521 
340-347 
520 
Pressure, psig 
50 500 50 50 50 50 50 
Organic LHSV, hr.sup.-1 
0.95 0.95 0.94 0.93 1.2 1.2 0.83 
% C.sub.3.sup.= Equivalents In Product 
DIPE 0.5 &lt;18 77 0.1 0.02 94 0.3 
IPA 0.4 16 5 0.5 0.3 4 0.3 
C.sub.3.sup.= 
99 36 18 96.8 99 2 99 
Mogas -- -- 2.6 1 -- -- 
__________________________________________________________________________ 
Although the present invention has been illustrated by reference to 
specific embodiments, it will be apparent to those skilled in the att that 
various changes and modifications may be made which clearly fall within 
the scope of this invention. It is not the intent of applicant to be bound 
by the specific embodiments described, but rather only by the appended 
claims.