KARAS LAWRENCE J
RAMESWARAN RAMESH
ARCO CHEM TECH NL BV (NL)
| US4100220A | 1978-07-11 |
| 1. | In a process for the oligomerization of isobutylene, the improvement which comprises oligomerizing the isobutylene in the presence of tertiary butanol in amount sufficient to promote oligomerization selectivity to the dimer. |
| 2. | In a process for the oligomerization of isobutylene, the improvement which comprises oligomerizing the isobutylene in the presence of isoalkane diluent primarily comprise of isoctane in amount sufficient to enhance oligomerization selectivity to the dimer and to absorb the rection exotherm. |
| 3. | A process for the production of a highoctane gasoline blending mixture mainly comprise of isooctane which comprises oligomerizing isobutylene to the dimer in at least 90% selectivity, the oligomerization being carried out with a sulfonic acid resin catalyst, tertiary butanol selectivity enhancing modifier and isoalkane diluent, hydrogenating oligomerization products to form mainly isooctane, a portion of which comprises a product of the process and a portion of which is recycle to the oligomerization. |
| 4. | The process of claim 1 wherein the isobutylene is formed by dehydration of tertiary butanol. |
Description of the Prior Art The oligomerization of olefins such as isobutylene using acidic catalysts is a known rection.
As described in U. S. 3,760,026, a number of catalysts are known for this rection including cold sulfuric acid, 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 (ICI) and cerium optionally supporte on carriers such as activated carbon, bauxite, activated carbon alone and with metal haliders such as TiC'2 heteropolyacids such as silicotungstic acid on silica gel and phosphomolybdic acid; BF3H3PO4 and BF3HPO3; dihydroxyfluroboric acid HF and fluorides or oxyfluorides of S, Se, N, P, Mo, Te, W, V and Si boiling below 300°C; BF3 dimethyl ether complexes; BF3 hydrocarbon complexes; BF3 S02; and AICI3 with cocatalysts such as dimethyl ether, HCI, and nitromethane. These catalysts and dimerization processes, including operating conditions, are known in the art.
An especially preferred catalyst is a sulfonic acid-type ion exchange resin such as Amberlyst A-15. U. S. Patent 4,447,668 describes isobutylene dimerization using A-15 with methyl t-butyl ether as solvent.
Considerations associated with the isobutylene dimerization involve removal of the substantial heat of rection and the requirement that high selectivity to the dimer product be maintained. The instant invention provides a process wherein these objectives are achieved.
Summary of the Invention In accordance with the present invention, a process is provided for the dimerization of isobutylene in the presence of both a selectivity enhancing amount of tertiary butanol and in the presence of isoalkane diluent. In an especially preferred practice, tertiary butanol such as that derived from the Oxirane propylene oxide/tertiary butanol process is used as starting material and isooctane is the ultimate product.
Brief Description of the Drawina The accompanying drawing is a schematic representation of an especially preferred practice of the invention.
Detailed Description With reference to the drawing and the process represented therein, the tertiary butanol product from the Oxirane process forms the process starting material. The tertiary butanol is fed via line 1 to dehydration zone 2 wherein the tertiary butanol is dehydrated in accordance with known procedures to form isobutylene, water being removed from zone 2 via line 3.
A portion of the tertiary butanol is directe via line 4 for use as a selectivity enhancing modifier in the dimerization of isobutylene which takes place in zone 5 as will be hereinafter described.
Product isobutylene is removed from zone 2 via line 6 and passes to dimerization zone 5 wherein the isobutylene is dimerized in high selectivity to diisobutylene. In order to achieve high dimerization selectivity in zone 5, the provision both of tertiary butanol via lines 4 and 10 in selectivity
enhancing amount and of isooctane via line 7 as dimerization diluent are important in carrying out the process.
The feed composition to zone 5 is adjusted to provide a selectivity enhancing amount of tertiary butanol, generally 1 to 30 wt % and an amount of isoalkane diluent effective both for heat removal and to reduce isobutylene concentration to a level at which optimum selectivity eg. 97% can be achieved, generally 30 to 80 wt % isoalkane based on total feed to zone 5.
The isoalkane diluent used in the dimerzation is comprise of at least 50 wt % isooctane, usually at least 90 wt % isooctane together with minor amonts, eg. 1 to 10 wt % isododecane (2,2,4,4,6 pentamethyl heptane).
In zone 5, the isobutylene containing feed is contacte with a solid dimerization catalyst, preferably a sulfonic acid resin catalyst such as Amberlyst A-15 of Rohm & Haas, at dimerization rection conditions whereby exceedingly high rection selectivity to the dimer is achieved.
Generally small amounts of trimer are also formed in zone 5, eg. less than 10% of the converted isobutylene.
The rection mixture from zone 5 which comprises tertiary butyl alcool, isoalkane, unreacted isobutylene as well as isobutylene dimer and trimer, passes via line 8 to separation zone 9 wherein by conventional procedures a stream comprise of unreacted isobutylene and tertiary butyl alcohol and small amounts of C8'S iS separated and recycle via line 10 to dimerization zone 5. A small purge of this recycle stream may be necessary to maintain tertiary butyl alcohol levels and is provided via line 15. This purge can be recycle to zone 2 to recover the tertiary butyl alcohol and isobutylene values. A higher boiling stream comprise of isoalkane together with isobutylene dimer and trimer passes via line 11 to hydrogenation zone 12 wherein the isobutylene polymer products are hydrogenated to polymer gasoline components. Hydrogen is introduced via line 13.
The product stream from zone 12 mainly comprise of isooctane with some isododecane is removed via line 14, a portion being recycle via line 7 to zone 5 to act as diluent and heat removal agent during the dimerization and the remaining portion as product suitable as a high octane gasoline pool blending component.
The production of tertiary butyl alcohol by means of the Oxirane process is well known and widely practiced on an industrial scale. See, for example, U. S. Patent 3,351,635.
Likewise, the dehydration of tertiary butanol to form isobutylene is well known. See, for example, U. S. Patents 5,625,109,3,510,538, 4,165,343, and 4,155,945.
The dimerization of isobutylene in accordance with the present invention involves various novel features. In the first instance, tertiary butanol is employed as a selectivity enhancing modifier and this results in a substantial improvement in rection selectivity to the dimer as compare to operation without this modifier.
Secondly, isoalkane mainly comprise of isooctane is employed as a diluent to further enhance rection selectivity by reducing isobutylene feed concentration, and to aid in removal of the rection exotherm.
Of course, the integrated system where tertiary butanol is used as overall feedstock and where isoalkane from hydrogenation of product isobutylene dimer and trimer is recycle to the dimerization represents the preferred practice of the invention. However, the above features are believed to be separately novel and patentable.
In general, known oligomerization catalysts and conditions can be employed in the oligomerization step. Suitable conditions include temperatures broadly in the range 0 to 200°C, preferably 10 to 100° C, and the use of pressures sufficient to maintain the liquid phase, illustratively above 50 psig, e. g. 50-500 psig.
Known dimerization catalysts can be used including those described in prior art such as U. S. 3,760,026. The use of sulfonic acid type ion exchange resins such as Amberlyst A-15, Dowex 50 and the like is especially preferred.
A feature of the present invention is the use of tertiary butanol as a selectivity enhancing modifier in the olefin dimerization.
The amount of modifying agent which is used is at least 1 wt %, preferably 5 to 15 wt % based on the weight of olefin plus modifying agent plus diluent in the rection mixture.
By carrying out the oligomerization using both tertiary butyl alcohol and isoalkane, rection selectivity to diisobutylene of at least 90% based on isobutylene converted is achieved. The remaining rection product is essentially the trimer, little or no higher polymers are formed.
From oligomerization zone 5, the rection mixture passes to zone 9 which is appropriately a distillation zone. Unreacted isobutylene and such tertiary buts ! alcohol modifier as remains in the mixture are separated and recycle via line 10 to zone 5. It should be noted that there may be some dehydration of tertiary butyl alcohol in zone 5 and loss of tertiary butyl alcohol in zone 9 which requises the provision of tertiary butyl alcohol via line 4 to the system.
Tertiary butyl alcohol is either consume or produced in zone 5 according to its equilibrium with isobutylene and water. It is advantageous to operate with the feeds at near-equilibrium conditions such that net tertiary butyl alcohol change is near zero.
The mixture of isoalkane and isobutylene polymer products passes via line 11 to hydrogenation zone 12 wherein the unsaturated polymers are hydrogenated in accordance with known procedures to saturated product, mainly isooctane. Hydrogen is introduced via line 13.
Product from zone 12 is removed via line 14 and can be sent directly
to a gasoline blending pool as this stream is essentially comprise of high octane gasoline blending hydrocarbons. A portion is recycle via line 7 to zone 5 to provide the necessary diluentduring oligomerization.
The following example illustrates the invention.
Referring to the accompanying drawing, tertiary butanol from an Oxirane propylene oxide/tertiary butanol process forms the feed to the system. This feed comprises about 94 wt % tertiary butanol with the remainder primarily water and acetone.
About 150,000 Ibs/hr of the tertiary butanol is fed to dehydration zone 2 via line 1 wherein it is dehydrated at about 371 OC and 200 psig using an alumina dehydration catalyst. Water formed by dehydration and introduced with the feed is removed via line 3 at the rate of 60,000 Ibs/hr. A product isobutylene stream comprise by weight of 96.5% isobutylene, 1.0% tertiary butanol, 0.02% water, 1.3% acetone and 1.18% others passes from dehydration zone 2 via line 6 to dimerization zone 5 at the rate of 190,000 Ibs/hr. A portion of the Oxirane process tertiary butanol also passes to zone 5 via line 4 at the rate of 20 Ibs/hr, (this flow is intermittent as needed), a recycle isobutylene and tertiary butyl alcohol stream from zone 9 comprise by weight of 78% isobutylene, 15% tertiary butyl alcohol and 7% C8 and C12 isoalkanes passes at the rate of 221,000 Ibs/hr via line 10 to zone 5 and an iso-octane stream from zone 12 having a composition by weight of 95% isooctane and 5% higher alkanes (mainly isododecane) passes at the rate of 327,000 Ibs/hr via line 7 to zone 5.
The combine feed streams to zone 5 have a composition by weight of 48% isobutylene, 4.5% tertiary butanol, 44% iso-octane, 0.3% water, 2% higher alkanes and 1.2% others. Zone 5 is a reactor packed with A-15 sulfonic acid resin catalyst and the liquid feed is contacte with the catalyst at 190°C and 300 psig at a liquid hourly space velocity of 6hr'.
The rection mixture is removed from zone 5 via line 8 and passes
to separation zone 9 wherein lighter materials are distille overhead at 60°C and 50 psig and pass via line 10 to zone 5 as above described. A purge stream in amount of 1800 Ibs/hr is removed via line 15.
The bottoms isobutylene dimer mixture comprising by weight 34% diisobutylene, 2% higher isobutylene oligomers, 63% iso-alkane diluent and 1 % others passes at the rate of 510,000 Ibs/hr via line 11 to hydrogenation zone 12 wherein the isobutylene polymers are hydrogenated to isoalkanes.
Hydrogen is introduced via line 13 at the rate of 11,500 Ibs/hr, a Pd hydrogenation catalyst supporte on carbon is used and hydrogenation conditions of 150°C, 200 psig and weight hourly space velocity of 5 hr-'are employed.
The hydrogenation can be carried out in accordance with known procedures using a variety of catalysts and rection conditions. To accommodate the hydrogenation rection exotherm a cooled recycle is advisable with the rate of recycle to feed about 3: 1 by weight.
The isoalkane rection product mixture is removed from zone 12 with a portion recycle via line 7 as above described to zone 5 and the net product recovered at the rate of 186,000 Ibs/hr via line 14.
Overall selectivity to isooctane based on tertiary butanol converted in the above system is about 94%. In comparison, where neither the tertiary butanol modifier nor isoctane diluent is employed, overall selectivity is only about 30%.