US2966536A

US2966536A - Isomerization of paraffinic hydrocarbons

Info

Publication number: US2966536A
Application number: US750158A
Authority: US
Inventors: Bethea Sam Rice; Hill Boyd Nixon
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1958-07-22
Filing date: 1958-07-22
Publication date: 1960-12-27
Anticipated expiration: 1977-12-27
Also published as: DE1418168A1

Description

United States Patent and Engineering Company, Elizabeth, N.J., a corporation of Delaware FiledJuly 22, 1958, Ser. No. 750,158

"7 Claims. (Cl. 260-68365) The present invention is directed to a method for isomerizing parafiinic hydrocarbons. More particularly, the invention is directed'to a method for isomerizing paraflinic hydrocarbons While suppressing hydrocracking and increasing conversion of the parahinic hydrocarbon. In

hydrogen to form an isomerized product. The isomerized product is thenrecovered.

The normal parafiin forming the feed mixture to the present invention may suitably be a paraffin hydrocarbon having to 8 carbon atoms in". the molecule. As exemplary of the paraflinic hydrocarbons which may be employed in the present invention may be mentioned normal pentane, normal hexane, normal heptane, and normal octane. While purified normal paraflinic hydrocarbons may form the feedmixture, it is contemplated that mixtures of the parafiinic hydrocarbons may also be employed.

The aromatic hydrocarbon forming the feed mixture with the normal paraflin' may be an aromatic hydrocarbon in the gasoline boiling range such as an aromatic hydrocarbon having 6 to 9c'arbon atoms in the molecule. As exemplary of the aromatic hydrocarbons. may bementioned benzene; toluene; ortho, meta, and para xylenes; ethyl benzene; and the'sever'al C aromatic hydrocarbons. It will be preferred to employ benzene and toluene as the aromatic hydrocarbon.

The amount of aromatic hydrocarbon added is from about 1% to about 15% byvolume of the paraffinic hydrocarbon. A preferred amount for normal hexane ranges from about 3% to about 6% by volume.

The platinum catalyst is suitably a supported platinumcatalyst such as'an alumina supported platinum catalyst. The support may be gamma alumina or a purified alumina, although other supports such as magnesia and zirconia may be used. The'supported platinum catalyst may contain from about 0.3 to about 0.6 weight percent of platinum on alumina, although larger and smaller amounts of platinum on the support may be used.

Temperatures may suitably range from about 600 to about 900 F. with beneficial results being obtained at about 700 toabout 875 F.

Pressures may range from about 300 to about 900 pounds per square inch gauge with best results being obtained in the upper part of the range.

Space velocities may range from about 0.5 to about 4.0 volumes of feedper volume of catalyst per hour with desirable results being obtained at about 1 v./v./ ho'ur.

The reaction is desirably conducted in the presenceof 2,965,536 Patented Dec. 27, 1960 hydrogen in an amount in a range from about 300 to about 3700 standard cubic feet of hydrogen per barrel of feed.- Good results have been obtained with 500 to 3600 standard cubic feet of hydrogen per barrel of feed.

The invention will be further illustrated by reference to the drawing in which:

Fig. 1 is a flow diagram of a preferred mode;

Fig. 2 is a modification of the preferred mode of Fig. l; and

Fig. 3 is a graph showing the yield octane number relationship for the present invention as compared to the prior art practice.

Referring now to the drawing and particularly to Fig. 1, numeral 11 designates a charge line by way of which a parafiinic hydrocarbon such as normal hexane is introduced into the system from a source not shown. Admixed withthe paraflinic hydrocarbon in line 11 is an aromatic hydrocarbon such as benzene introduced into line 11 by line 12 from a source which will be described further. The mixture of parafiinic and aromatic hydrocarbon is then discharged into an isomerization zone 13 which is indicated'as a block in the drawing but which may include a plurality of adiabatic reaction zones containing beds of platinum on alumina catalyst. Hydrogen is introduced to zone 13 by line 14, and temperatures and pressures are adjusted in zone 13 to cause isomerizationof the parailinic hydrocarbon while suppressing hydrocracking reactions and increasing the conversion of theparaffinic hydrocarbon to the desired isomer or isomers.

The isomerized product containing the added aromatic hydrocarbon is discharged from zone 13 by line 15 and when the added aromatic hydrocarbon is benzene and/ or toluene and the parafiinic hydrocarbon is hexane, the product containin the added aromatic is preferably discharged from line lS'by way of branch line 16 controlled by valve 1'7 for use directly as a motor fuel such as in automotive engines or as an aviation fuel. It may be desirable, however, on some occasions to separate the isomerized paraffinic hydrocarbon from the aromatic hydrocarbon and when this is desired, valve 18 in line 1-5 is opened and valve 17 in line 16 is closed. Under these conditions, the product from zone 13 is introducedinto a separation zone 19 illustrated as a distillation zone which is provided with a'heating means such as illustrated by steam coil 20 and with

lines

21, 22, 23, 24, and 25.

Distillation zone 19 is provided with suitable internal vapor-liquid contacting means such as bell cap trays, packing, and the like for insuring intimate contact between vapors and liquids. Zone 19 is also provided With all auxiliary equipment usually'associated with the modern distillation tower such as means for inducing reflux, condensing and cooling means, and the like.

In any event, conditions of temperature and pressure are adjusted in zone 19 to recover isoparafiins such as may be desired either in one fraction by line 21 or in several fractions by

lines

22 and 23 while unreacted feed may be discharged by line 24 controlled by valve 24a. It will be preferred, however, to recycle unreacted feed such as paraffinic hydrocarbons to line 11 by line 26 controlled by valve 27. The separated aromatic hydrocarbon in line 25 may be recycled to line 11 by

lines

28 and 12 by opening valve 29 in line 12 or the aromatic hydrocarbon may be discharged from the system by allowing valve 29 to be closed and opening valve 30 in line 28.

Alternatively, it may be desirable not to separate the unreacted feed from the aromatic hydrocarbon and under these situations valves 24a and 27 would remain closed and the unreacted feed and aromatic hydrocarbon, would be withdrawn from zone 19 by line 25 and introduced into line 26 by opening valve 31. I

When the added aromatic hydrocarbon is discharged through line 16, it will be necessary to continually add aromatic hydrocarbon to the system and this is suitably accomplished by introducing added aromatic hydrocarbon either to supply all of the needs or as make-up by way of line 32 controlled by valve 33.

In Fig. 2 the separation zone 19 provides for separation by extraction. In other words, in Fig. 2, line 15 leads into an extraction zone such as 35 which may be an extraction zone employing sulphur dioxide as a solvent under suitable conditions to separate the aromatic hydrocarbon from the paraflinic hydrocarbons employing suitable conditions in zone 35 to form an extract phase which is withdrawn by way of line 36, and, after freeing of solvent, is returned to line 11. Other selective solvents for aromatics may also be used. A raffinate phase is withdrawn by way of line 37 which contains the iso parafiins and the normal paraffins and, after freeing of solvent, is introduced into zone 38, which is provided with a heating means illustrated by steam coil 39 and which is similar to zone 19. By adjusting temperatures and pressures, the isomerized product is withdrawn from zone 38 by line 40 while the unreacted feed is withdrawn from zone 38 by line 41 and returned to line 11.

In order to illustrate the invention further, runs were made on a normal hexane feed over a platinum catalyst at temperatures from 700 to 875 F., 750 pounds per square inch gauge pressure, a space velocity of l v./v./hour and with 500 to 3600 standard cubic feet of hydrogen per barrel. During these operations, about 3.5% by volume of benzene was added to the normal hexane which initially was free of benzene as shown by the data.

In Fig. 3, the dashed line represents the conventional operation when no benzene was employed while the solid line represents the present invention where benzene had been added.

It will be clear from the data shown in Fig. 3 that substantially improved octane number-yield relationships are obtained with the present invention as opposed to the prior art.

The invention will be further illustrated by a specific run employing a platinum on alumina catalyst at 750 pounds per square inch gauge, 1 v./v./hour and 3700 standard cubic feet of hydrogen per barrel with the other conditions being set out in the following table.

Reactor Temperature, F. (Average) 875 800 Normal Hexane in Feed, Vol. Percent 95. 4 95. 4 Benzene in Feed, Vol. Percent .2 3.6 0.0 Yields, Vol. Percent of Feed:

and Lighter (Total) 7.1 15.8 3. 2 11.1 8. 2 l. 4 6. 2. 9 24. 4 13. 7 22. 3 l3. 5 61. 4 31. 5 95. 6 86. 4 88. 4 79. 0 Conversion of nI-Iexane, Wt. Percent 68. 8 48.1

It will be clear from these data that substantially improved yields of the several isomers were obtained when employing benzene in the feed while charging normal hexane. Further, it is to be emphasized that the conversion of normal hexane to desirable products has been increased over 20 weight percent as shown by the data. The several operations in accordance with the present invention show that hydrocracking has been reduced more than two-fold as judged by the amount of C and lighter materials formed. The production of C isomers has increased almost two-fold and at a 95.6 volume percent C product, the octane number with 3 cos. of tetraethylene lead per gallon has been improved by 15 units as shown by the data in Fig. 3. It will be clear that the present invention is quite important and advantageous in isomerizing paraflnic hydrocarbons. l 4

When isomerizing hexane, it may be desirable to employ benzene and/0r toluene as the added aromatic hydrocarbon whereas When heptane and octane are isomerized, the added aromatic may be toluene, xylene, or ethyl benzenes. In some cases, it may be desirable to employ the C aromatics, but with the C to C hydrocarbons, benzene, toluene, and xylenes will be preferred. When pentane is isomerized, it will be desirable to employ benzene as the added aromatic hydrocarbon.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and secure by Letters Patent 1. A method for isomerizing parafiinic hydrocarbons while suppressing hydrocracking which consists of forming a mixture of normal hexane and about 1% to about 15% by volume based on said hexane of an aromatic hydrocarbon in the gasoline boiling range, said hexane being initially free of aromatic hydrocarbon, then contacting the mixture with an alumina supported platinum catalyst at a temperature in the range from about 600 to about 900 F. at a pressure in the range from about 300 to about 900 pounds per square inch gauge and at a space velocity in the range from about 0.5 to 4.0 v./v./hour in the presence of about 300 to about 3700 standard cubic feet of hydrogen per barrel of mixture to form an isomerized product, and recovering said isomerized product.

2. A method in accordance with claim 1 in which the aromatic hydrocarbon is benzene.

3. A method in accordance with claim 1 in which the aromatic hydrocarbon is toluene.

4. A method for isomerizing parai'finic hydrocarbons while suppressing hydrocracking which consists of forming a mixture of normal hexane and about 3% to about 6% by volume based on said normal hexane of an aromatic hydrocarbon having 6 to 7 carbon atoms in the molecule, said hexane being initially free of aromatic hydrocarbon, then contacting the mixture with an alumina supported platinum catalyst at a temperature in the range from about 600 to about 900 F. in the presence of hydrogen to form an isomerized product, and recovering said isomerized product in admixture with said aromatic hydrocarbon.

5. A method in accordance with claim 4 in which the aromatic hydrocarbon is benzene.

6. A method in accordance with claim 4 in which the aromatic hydrocarbon is toluene.

7. A method for isomerizing parafiinic hydrocarbons while suppressing hydrocracking which consists of forming a mixture of normal hexane and about 1% to about 15% by volume based on said hexane of an aromatic hydrocarbon in the gasoline boiling range and separable from the isomer of said hexane hydrocarbon, said hexane being initially free of aromatic hydrocarbon, then contacting the mixture with a platinum catalyst at a temperature in the range of from about 600 to about 900 F. in the presence of hydrogen to form an isomerized product, separating said isomerized product from said aromatic hydrocarbon, and forming said mixture with said separated aromatic hydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS 2,396,331 Marschner Mar. 12, 1946 2,415,315 Walter et a1 Feb. 4, 1947 2,504,280 Shoemaker et a1 Apr. 18, 1950 2,762,854 McKinley et a1 Sept. 11, 1956 2,766,302 Elkins Oct. 9, 1956 2,798,105 Heinemann et a1. July 2, 1957 2,834,822 Worthington et al May 13, 1958 2,905,736 Belden Sept. 22, 1959 2,906,798 Statues et al Sept. 29, 1959

Claims

1. A METHOD FOR ISOMERIZING PARAFFINIC HYDROCARBONS WHILE SUPPRESSING HYDROCRACKING WHICH CONSISTS OF FORMING A MIXTURE OF NORMAL HEXANE AND ABOUT 1% TO ABOUT 15% BY VOLUME BASED ON SAID HEXANE OF AN AROMATIC HYDROCARBON IN THE GASOLINE BOILING RANGE, SAID HEXANE BEING INITIALLY FREE OF AROMATIC HYDROCARBON, THEN CONTACTING THE MIXTURE WITH AN ALUMINA SUPPORTED PLATINUM CATALYST AT A TEMPERATURE IN THE RANGE FROM ABOUT 600* TO ABOUT 900*F. AT A PRESSURE IN THE RANGE FROM ABOUT 300 TO ABOUT 900 POUNDS PER SQUARE INCH GUAGE AND AT A SPACE VELOCITY IN THE RANGE FROM ABOUT 0.5 TO 4.0 V./V./HOUR IN THE PRESENCE OF ABOUT 300 TO ABOUT 3700 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF MIXTURE TO FORM AN ISOMERIZED PRODUCT, AND RECOVERING SAID ISOMERIZED PRODUCT.