1. A process of producing a high octane gasoline by the steps of
2. separating from a feed gasoline stream having at least 10 weight percent olefin hydrocarbons a stream comprising C5 hydrocarbons and a stream comprising C6 + hydrocarbons,
3. passing the stream comprising C5 hydrocarbons in admixture with ethylene over an olefin disproportionation catalyst to provide an effluent containing ethylene, propylene, isobutene, and a C5 + heavier gasoline,
4. separating the effluent stream of step (2) to provide a stream comprising ethylene, a stream comprising propylene, a stream comprising isobutene, and a stream comprising the C5 + gasoline,
5. passing a part of the stream comprising ethylene to step (2),
6. passing the stream comprising propylene over an olefin disproportionation catalyst to provide an effluent comprising ethylene and butenes,
7. passing the stream comprising isobutene over a dimerization catalyst to provide an effluent stream comprising diisobutylene,
8. passing the stream comprising ethylene and butenes from step (5) to a separation zone to provide a second ethylene stream and a butenes stream,
9. passing the butenes stream of step (7) to an alkylation zone to an admixture with isobutane to provide a high octane alkylate,
10. passing the stream comprising diisobutylene from step (6) in admixture with at least part of the second ethylene stream from step (7) over an olefin disproportionation catalyst to provide an effluent stream comprising isohexene, and
11. returning the effluent stream comprising isohexenes to step (3).
12. The process of claim 1 including the step of combining the C5 + heavier gasoline stream containing the produced isohexenes of step (3), the high octane alkylate of step (8) and the C6 + gasoline stream of step (1) to provide a gasoline having an increased Motor Octane Value when compared to the feed gasoline having at least 20 weight percent olefins.
13. The process of claim 2 wherein the feed gasoline contains from about 30 to about 70 percent olefin hydrocarbons.
14. The process of claim 2 wherein the olefin disproportionation catalyst of steps (2), (5) and (9) comprises tungsten oxide on silica, alumina, or aluminum phosphate, molybdenum oxide on silica, alumina, or aluminum phosphate, or rhenium oxide on alumina or aluminum phosphate.
15. The process of claim 2 wherein the olefin disproportionation catalyst of steps (2) and (9) comprises an admixture of a solid olefin double bond isomerization catalyst and a solid olefin disproportionation catalyst.
16. The process of claim 5 wherein the olefin disproportionation catalyst is tungsten oxide on silica and the double bond isomerization is MgO.
17. The process of claim 2 wherein the dimerization catalyst of step (6) is silica alumina.
18. The process of claim 2 wherein the volume of gasoline of step (11) is at least 20 percent greater than the volume of the feed gasoline.
19. The process of claim 2 wherein the alkylation zone of step (8) uses an alkylation catalyst which is hydrogen fluoride.
20. The process of claim 2 wherein the feed gasoline is a full range cat-cracked gasoline having an end boiling point which does not exceed 450°F.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to olefin disproportionation. In a further aspect, this invention relates to a method of increasing the octane value of olefinic containing gasoline streams using olefin disproportionation, dimerization, and alkylation steps.
2. Description of the Prior Art comprising
The reaction of olefinic materials to produce other olefinic materials wherein the reaction can be visualized as the breaking of two existing double bonds between first and second carbon atoms, and between third and fourth carbon atoms, respectively, and the formation of two new double bonds, such as between the first and third carbon atoms and the second and fourth carbon atoms, respectively, and wherein the two new double bonds can be on the same or different molecules, has been called "the olefin reaction." The breaking and formation of these bonds can be visualized by using a mechanistic scheme involving a cyclobutane transition state. Thus, two unsaturated pairs of carbon atoms combine to form a 4-center (cyclobutane) transition state which then disassociates by breaking either set of opposing bonds. This reaction can be illustrated by the following formulas: ##SPC1##
Other terms have been utilized to describe the reactions of olefinic materials which are within the scope of the olefin reaction as defined above. These include such terms as "olefin disproportionation," "olefin dismutation," "transalkylidenation," and "olefin metathesis." Throughout the specification and claims the term "olefin disproportionation" is used as a matter of choice and is deemed to be equivalent to the above-mentioned terms, including "the olefin reaction" terminology. Numerous catalyst systems have been reported which effect this reaction, including the catalysts of U.S. Pat. No. 3,261,879, Banks (1966), and U.S. Pat. No. 3,365,513, Heckelsberg (1968).
One important embodiment of the olefin disproportionation reaction is the process wherein propylene is smoothly and efficiently converted to approximately equimolar amounts of ethylene and n-butenes.
Still another important aspect of the olefin disproportionation reaction is the embodiment wherein a mixture of ethylene and a suitable higher olefin is disproportionated. The presence of ethylene in the reaction mixture changes the nature of the olefinic products such that the higher olefin is converted to a lower olefin. Such a result has been termed "ethylene cleavage" or "etheneolysis." Thus, olefins such as normal- or isoamylenes can be converted to lower olefins such as propylene and isobutene. This result is often promoted by the presence of some double bond isomerization activity within the reaction zone.
Today, the oil industry faces the problem of increasing the octane values of gasolines produced in refinery operations. This problem had its genesis in the heavily industrialized countries because of pollution of the atmosphere by automobile exhaust emissions. Technological development to abate such pollution has resulted in the use of catalytic exhaust gas treaters. These catalytic mufflers employ conversion catalysts which are sensitive to lead compounds in the exhaust. Thus it has been proposed that the use of lead in gasolines be greatly curtailed. Therefore, producers of gasolines for the automobile engine have been required to increase the octane value of their refinery gasolines to meet the high performance requirements of the modern internal combustion engine without the assistance of added alkyllead compounds.
OBJECTS OF THE INVENTION
It is an object of this invention to upgrade olefinic gasolines to gasolines having higher octane values. It is a further object of this invention to increase the volume of high octane gasoline from currently available refinery feedstreams. Other objects and advantages of the present invention will be apparent to those skilled in the art from the following summary of the invention, detailed description of the invention and the claims.
SUMMARY OF THE IVENTION
In my process, a cat-cracked gasoline stream containing at least 20 weight percent olefin hydrocarbons is first subjected to a separation step to provide a C5 cut containing both linear and branched C5 olefins. The C5 cut is then passed to an olefin disproportionation zone in the presence of added ethylene wherein it is cleaved to propylene and isobutene. The effluent from this disproportionation zone is passed to a separation zone wherein the lighter olefins are separated from the the C5 + heavier materials. The lighter olefins include ethylene, propylene, and isobutene. The propylene is then passed to a second olefin disproportionation zone wherein the propylene is converted to ethylene and n-butenes. The n-butenes then available are conducted to an alkylation zone wherein they are alkylated with isobutane to provide a high octane alkylate. The isobutenes available are passed to a dimerization zone wherein they are dimerized to diisobutylene. The produced diisobutylene is then passed to a third olefin disproportionation zone wherein it is mixed with ethylene and cleaved to provide isohexenes such as neohexene. The unconverted hydrocarbons (mostly paraffins) from the first disproportionation zone, the high octane alkylate, the isohexenes, and the remaining olefinic gasoline can be combined to provide a gasoline having increased octane value and an increased volume when compared to the octane value and volume of the initial gasoline feed to my process.
In a further aspect of my invention, instead of cleaving the produced diisobutylene with ethylene, the diisobutylene can be disproportionated in the absence of ethylene to provide a stream comprising branched olefins up to C10. The mixture of isoolefins can be combined with the unconverted hydrocarbons from the first disproportionation zone, the high alkylate, and the remaining cat-cracked gasoline to provide the improved gasoline of my process.
BRIEF DESCRIPTION OF THE DRAWING
The sole FIGURE of the drawing schematically illustrates the process of my invention by means of a simplified flow diagram.
DETAILED DESCRIPTION OF THE INVENTION
The starting material for the process of my invention is an olefinic gasoline containing at least about 10 weight percent of olefin hydrocarbons. The gasoline will preferably have an end point which does not exceed about 450°F. The olefin content is advantageously from about 20 to about 70 weight percent. Such streams are readily available in refinery operations and are generally available as a product from a catalytic cracker unit. Preferably, the feed is a full range cat-cracked gasoline. However, a full range material can be fractionated to provide suitable gasoline fractions which are high in olefin content and low in aromatics.
My process has the unique advantage of providing generally increased octane values and decreased light olefins while substantially increasing the volume of gasoline which is available for motor fuel compared to the volume and octane value of the cat-cracked gasoline starting material. This advantage is realized by the unique combination of olefin disproportionation, alkylation and dimerization steps which are employed in my process.
My invention can best be understood by reference to the sole FIGURE of the drawing. A full range cat-cracked gasoline is subjected to separation to provide a C5 cut. The C5 cut is passed through line 1 into olefin disproportionation zone 66 wherein it is mixed with ethylene from line 2 in the presence of a suitable olefin disproportionation catalyst. Within zone 66, the disproportionation (cleavage) of the olefins in the C5 cut provides a lighter material such as ethylene, propylene, n-butenes and isobutenes. The effluent from zone 66 is removed via line 3 and passed to fractionation zone 67 which can comprise one or more fractionators. Therein, ethylene is removed overhead in line 4, and split, a portion thereof being returned to disproportionation zone 66 and another portion thereof being passed to disproportionation zone 70. If desired, any unconverted higher olefins can be recycled from fractionation zone 67 to disproportionation zone 66. However, it is preferred that the conditions in zone 66 be sufficiently severe (low space rate, high ethylene ratio, etc.) to convert substantially all of the cleavable olefins in one pass.
From fractionation zone 67, propylene is removed via line 5 and passed to disproportionation zone 68. The butenes and isobutene, of which the isobutene predominates, are removed from line 10 and fed to dimerization zone 71.
Within disproportionation zone 68, the propylene from line 5 is converted to ethylene and butenes, the effluent containing butenes being passed to fractionation zone 69 which can comprise one or more fractionators. In dimerization zone 71, the isobutenes are converted to diisobutylenes and the effluent from this zone is removed via line 11 and passed to disproportionation zone 70. Within disproportionation zone 70, the diisobutylene feed from line 11 is contacted with ethylene from line 12. In the presence of the olefin disproportionation catalyst this reaction mixture provides large quantities of isohexenes and isobutene and the effluent is removed from disproportionation zone 70 via line 13 and returned to line 3 as feed to fractionation zone 67. Thus, the isohexenes in line 13 are removed within the C5 + gasoline fraction leaving fractionation zone 67 via line 14. As in disproportionation zone 66, the conditions in disproportionation zone 70 are such that high conversions of cleavable olefins are obtained in one pass.
Within fractionation zone 69, ethylene is taken overhead in line 7 and passed to disproportionation zone 70. Unconverted propylene is removed via line 8 and returned to disproportionation zone 68. The butenes produced in disproportionation zone 68 are removed from fractionation zone 69 by line 9. These butenes are then passed to an alkylation zone (not shown) wherein the butenes are alkylated with isobutane to produce a high octane alkylate.
The high octane alkylate produced in the alkylation zone using the feed butenes from line 9 is then combined with the C5 + gasoline fraction in line 14 and this mixture can be combined with the remaing cat-cracked gasoline (not shown) from which the C5 cut was originally taken as feed for line 1. This blend of streams provides a high octane gasoline having an increased motor octane value over the original cat-cracked gasoline and having a significant volume increase.
Those skilled in the art will understand that the simplified flow diagram of my process has omitted many items which are actually needed to operate the process. Thus, the use of pumps, controls, heat exchangers and the like have been omitted to simplify the discussion of my invention. Use of these apparatus and other steps is well within those skilled in the art.
The particular catalysts which are employed in the various catalytic reaction zones of my process are not critical to my invention. As a matter of fact, any catalyst which has the ability to disproportionate propylene to ethylene and butenes can be employed in the disproportionation zones. However, it is preferred, because of ease of operation, to employ solid type catalysts which exhibit disproportionation activity at a temperature in excess of 400°F. as they are characteristically more resistant to catalyst poisons sometimes associated with the feeds. Accordingly, I prefer to use catalysts such as molybdenum oxide on alumina, on silica or on aluminum phosphates; tungsten oxide on silica, on alumina, or on aluminum phosphate, or rhenium oxide on alumina, or on aluminum phosphate in my disproportionation reactors. Preparation, activation, maintenance and use of these catalysts have been reported in the prior art. Of course, these catalysts can also be modified by various treatments also reported in prior art. For example, treatment with compounds of alkali metals or alkaline earth metals, or admixtures with suitable double bond isomerization catalysts, or treatments with reducing gases such as H2 or other gases including CO all have been previously reported to modify olefin disproportionation catalysts.
The conditions in each of the olefin disproportionation zones include reaction pressures in the range 0-2000 psig, preferably 25-500 psig; space rates of 0.1-1000 WHSV, preferably 1-500 WHSV; and reaction temperatures broadly in the range of -60 to about 1200°F but generally dependent upon the specific olefin disproportionation catalyst chosen. The following table illustrates some reaction tremperatures for some specific catalysts.
Disproportionation Temperature, °F Catalyst Broad Preferred WO3 /SiO2 400-1100 600-900 MoO3 /SiO2 400-1100 800-1000 MoO 3 /Al 2 O3 158-500 250-400 WO3 /Al 2 O3 100-750 550-650 Re2 O7 /Al 2 O3 - 60- 1000 100-500 WO3 AlPO 4 600-1200 500-1000 Re2 O7 /AlPO 4 - 60-1000 50-250 MoO 3 /AlPO 4 600-1200 800-1000
because of its high level of activity and durability, the WO3 /Si02 catalyst is presently the preferred olefin disproportionation catalyst.
In the olefin disproportionation (cleavage) zones 66 and 70, the molar ratio of ethylene to higher olefins can be in the range of 1-20, preferably 2-10.
Of particular importance to my process is the admixture of a disproportionation catalyst with a solid double bond isomerization catalyst because these combination catalysts provide increased conversions particularly when the feed olefins comprise ethylene. Some suitable double bond isomerization catalysts are Mg0, Zn0, and alumina. Thus, my most preferred catalyst for use in the disproportionation zones featuring ethylene cleavage is a combination of magnesium oxide and tungsten oxide on silica wherein the amount of double bond isomerization catalyst is about 2:1 to 10:1 parts per part of the olefin disproportionation catalyst. This catalyst is particularly effective in disproportionation zones 66 and 70 wherein the feed comprises substantial amounts of ethylene.
The dimerization zone 71 can employ any suitable dimerization catalyst capable of converting isobutene to diisobutylene. Preferred dimerization catalysts are those capable of producing relatively high proportions of the dimers 2,4,4-trimethylpentene-1 and 2,4,4-trimethylpentene-2 with relatively small amounts of other C8 isomers or higher isobutene oligomers. Some examples of suitable catalysts are silica-alumina, phosphoric acid on kieselguhr, cold sulfuric acid, and the like. Such catalysts and dimerization processes, including operating conditions, are known in the art. A particularly suitable solid catalyst is silica-alumina.
The alkylation step employed in my process is equally well known in the prior art. Thus, the butene alkylation step can employ any suitable catalyst to convert isobutane and butenes to high octane alkylate. Suitable catalysts include sulfuric acid, HF acid and the like. The particular reaction temperature, pressures, and contact times used in the various catalytic reaction zones are also within the skill of those in the art. For example, in an HF-catalyzed alkylation process a typical temperature range is 80°-100°F with a contact time of about 1-10 minutes and with an isobutane to olefin ratio of about 6-15.
In my work I have noted that not all cat-cracked gasolines can be converted in an olefin disproportionation zone with equal effectiveness. The reason for this phenomenon is not completely understood; however, it is believed that the presence of trace amounts of sulfur and/or oxygen components within the cat-cracked gasoline may exhibit a poisoning effect on the activity of the olefin disproportionation catalyst. Accordingly, it may sometimes be desirable to subject the cat-cracked gasoline to a mild hydrotreatment prior to introduction into the first olefin disproportionation zone. Suitable catalysts for such a mild hydrotreatment can be sulfided nickel-alumina catalyst at an operating temperature of 500°-550° F. with a pressure of about 150 psig. However, other suitable hydrotreating catalysts and conditions can be employed. Similarly, it may be advisable to treat the feed by percolation through activated beds of materials such as alumina, mole sieves, magnesium oxide, and the like, at a low temperature to purify contaiminants of the feed to the first or subsequent disproportionation zones.
My invention can further be understood by the following example which is presented to illustrate the process of my invention. It should not be construed to limit the disclosure of my invention as provided above.
A full-range cat-cracked gasoline having an end point of about 385°F and containing about 35 percent olefin hydrocarbons is used as the feed to my process. The Research Octant Number (RON) of the feed is 88.7 and the Motor Octane Number (MON) is 78.2. The processing steps are those as depicted in the FIGURE of the drawing.
Olefin disproportionation reactor 66 contains a mixed bed catalyst comprising 1500 pounds of 8 percent tungsten oxide on silica olefin disproportionation catalyst and 10,500 pounds of magnesium oxide activated in flowing air at a temperature in the range of 1000°-1100° F. The operating conditions in this reactor include a temperature of 750° F. and a pressure of 300 psig.
Olefin disproportionation reactor 68 contains 600 pounds of the 8 percent tungsten oxide on silica activated in the same manner as reactor 66. Reactor 68 is operated at conditions which include a temperature of 725° F. and 325 psig. Olefin disproportionation reactor 70 contains 2,000 pounds of a mixed catalyst of which 200 pounds are the 8 percent tungsten oxide an silica and 1800 pounds of magnesium oxide activated in the same manner as reactor 66. The conditions in reactor 70 include a temperature of 700° F. and a pressure of 400 psig.
Dimerization zone 71 is a dimerization reactor containing 2000 pounds of silica-alumina dimerization catalyst activated in flowing air at 1000°F. Operating conditions in this zone include a temperature of 400° F. and 800 psig.
The material balance set forth below in the table illustrates how my process operates to increase the octane value and volume of gasoline. The feed in line 1 is obtained by fractionating the full range gasoline to provide the C5 cut. ##SPC2##
The butenes in stream 9 are conducted to an HF alkylation unit (not shown) wherein the reaction with isobutane produces high octane alkylate. The alkylate produced by this step is produced in the following yield and has the following properties:
Yield, Barrels/Barrel of Butenes -- 1.75
Research Octane Number (RON) -- Clear -- 96.8
Motor Octane Number (MON) -- Clear -- 94.0
The butenes alkylate is then combined with C5 + gasoline in stream 14 and with the depentenized full range cat-cracked gasoline feed to my process. The process thus treats 3600 barrels per day of cat-cracked gasoline and produces 5570 barrels per day of improved gasoline product. The MON of the product gasoline is 87.5 and the RON of the gasoline is 92.0 which is a substantial increase over the values of the feed cat-cracked gasoline.
Reasonable variations and modifications of my process will be obvious to those skilled in the art without departing from the spirit and scope of the invention as described above.