US3016344A - Upgrading natural gasoline - Google Patents

Description

Sates Unite The present invention relates to the upgrading of natural gasoline and is particularly concerned with improvements in process for the production from such liquid condensates of natural gas, of desirably high -yields of liquid products having octane ratings of 90 or more (F-l clear), for use as a component of motor ga'soline,'particularly ingasoline pools for present-day superfuels having octane ratings of 100 or more (F-l clear).

Of the numerous grades of natural gasoline known and marketed, the accepted grades have the common characteristic of being highly paraflinic and composed principally of hydrocarbon components in the lower boiling end of the gasoline range such that not less than 90% of the natural gasoline evaporates at 275 F. and the end point of the total gasoline is no higher than about 375 With increasing demands for gasolines of higher and higher anti-knock ratings for use as motor fuel in the newer high compression internal combustion engines, the position of natural gasoline in the motor fuel market has weakened considerably. The usual methods for upgrading of virgin naphthas, such as by hydrogenative reforming over noble metal catalyst, have not been found desirable for the needed upgrading of natural gasoline. Numerous processing schemes have been studied with the view of improving or preserving the position ofthe natural gasoline producer in themotor fuel market. Of these, the processes most widely advocated involve isomerization of the C and C fractions of the natural gasoline employing either noble metal catalyst or aluminum chloride type catalysts. These advocated processes have not been successful, however, in achieving desired high octane levels at acceptable yields, since the octane ceilings obtained at equilibrium isomerization fall short of the values demanded to permit blending of these products in the present higher octane motor fuels, and separation of the obtained isomers of desirably high octane quality is difiicult to achieve and uneconomic.

In accordance with the present-invention products of desirably high octane quality are obtained from natural gasoline by a combination of process steps involving fractionation of such gasoline to provide'a lower boiling cut composed chiefly of C and C hydrocarbons (boiling in the range of up to about 160-185, F.) and a residual cut comprising the higher boiling portion of the natural gasoline composed of 90-95% or more or C7 and C hydrocarbons with a small amount of higher boiling hydrocarbons. The lower boiling fraction is subjected to catalytic dehydrogenation and the higher boiling fraction to hydrogenative catalytic reforming; the products of these steps being blended to provide an improved natural gasoline product having an octane clear rating of at least 90 (F-l).

A debutanized natural gasoline having a 67 F-l clear octane rating is upgraded by the process of the invention to a 93 F-l clear product at a liquid yield level of 83 volume percent, The yields and the octanes obtained by this combination of steps are superior to that obtainable by:

A. Dehydrogenation of the total natural gasoline, which is limited to F-l clear octane values not in excess of about 88; B. Hydrogenative reforming of the total natural gasoline ammo Patented Jan. 9, 1962 ice which produced only a 72 volume percent yield at the '88 F-l clear octane level; or

C. Dehydrogenation of the 0;, fraction only, with catalyt-ic reforming of the C -C fraction, by which a 93 F-l gasoline product could be obtained but with significantly lower yields of liquid than that obtainable at the combination under A above.

On the other hand, while at lower octane levels desirably high yields of C and C fractions can be obtained by isomerization, this route is limited in that the octane ceiling obtainable by vapor phase isomerization of pentanesv (at SOD-950 F.) lies at about 84 F-l clear and that obtained from vapor phase isomerization of hexanes is not in excess of 76 F-l clean Isomerization of all or part of a debutanized natural gasoline, accordingly, cannot be employed to obtain upgraded products in excess of 90 F-l clear at the required high yields comprising 85% or more by volume of the charge. The problem is further complicated in that possible or suggested procedures involving fractionation of the equilibrium isomerizate and recycling of the normal pentanes and/or hexanes to further isomerization sufier from the drawback that such separation is difficult and expensive.

In the accompanying drawing there is shown a schematic flow diagram illustrating the practice of the invention.

In the practice of the present invention dehydrogenation of the C -C fraction is carried out preferably over chromia-alumina catalyst at temperatures in the range of 900-l050 F. at about atmospheric pressure and at a liquid hourly space velocity of about 1-4. If desired,

hydrogen or hydrogen-rich gas may be added or recycled to the reactor charge; it has been found beneficial, particularly when the dehydrogenation is effected at high conversion levels.

The reforming of the 07+ hydrocarbon fraction of natural gasoline is preferably carried out over supported platinum catalyst, typically over catalyst preparedv by impregnation of porous alumina with chloroplatinic acid, wherein such reforming is effected at temperatures in the range of about 800-1000 F., at pressures of about 200- 600 p.s.i.g., and at liquid hourly space velocities of about 1-5, hydrogen-rich gas being recycled to the reactor in amounts providing a hydrogen to oil ratio of about 3 or more. The activity of the catalyst can be maintained, where necessary, at desired high levels for longer operating periods by the inclusion of a small amount of halide compound in the feed corresponding to about 50 ppm. of t-butyl chloride by weight of liquid charge, I

Example I Out Cr .Cu C -C Total 1 to 260 Boiling Range, F--." 75115 -185 -btms. (95% pt.)

- 310 dry point Vol. percent of Gasoline 42. 8 28. 6 28. 6 Octane No. (F-l Clear) 75. 9 67. 5 66. 4 67. 1

Paraffins, vol. percent 98. 3 71. 5 42. 6 74. 7 Olefins, vol. percent 1. 7 0 O. 9 1.0 Naphthenes, vol.

percent 0 26. 7 50. 7 22. 1 Aromatics, vol.

percent 0 1. 8 5.8 2. 2

(a) By separate dehydrogenation of the C cut over catalyst containing 20% Cr O on activated alumina, at 1000 F. (outlet temperature) atmospheric pressure and at a liquid hourly space velocity of 1 volume hydrocarbon per volume of catalyst, one mol hydrogen being added with the charge, there is obtained a product having an average octane (F-l clear) of 93 at yields of 89-90 volume percent of charge.

(b) The C cut was separately dehydrogenated over the same chrome-alumina catalyst above described .at 1000 F. (average), 1 atmosphere, and at. a liquid hourly space rate of 1 with the addition of 1 mol of hydrogen per mol of hydrocarbon charged. The dehydrogenated product obtained at 92 volume percent C yield had an F-.1 clear) octane rating of 82..

(c) In a typical operation, dehydrogenation of the above-combined C C fractions as found in the described natural gasoline, operating at 1000 F., 1 space rate (v./hr./v.) and atmospheric pressure with 1 mol Example [I The 0,-1- cut of the natural gasoline described in the previous example was reformed over catalyst composed of 0.5% Pt on activated alumina (prepared by impregnation of the alumina with cliloroplatinic, acid and subsequent hydrogen reduction) at 950 F.,' 300 p.s.i.g., and at a volume space rate of 3 .(v./hr./v.). There was obtained 74% by volume of C;,-{ gasoline having an octane rating of 103 F-l (clear).

By combining the reformate With the C -C dehydrogenation efiluent obtained according to Example Ic above, there was provided an upgraded gasoline of 92 F-1 clear octane rating at a yield of 86% by volume of the original C natural gasoline.

Compared with the results obtained above, by reforming the total natural gasoline (C to bottoms) there is obtained at the 80% yield level an 83 octane product, or with increased severity of operation a 72% yield of liquid product at the 88 octane level.

The C to bottoms fraction can be reformed to 103 F'-l clearoctane level over platinum catalyst without necessitating frequent regeneration. The octane value of the blend of this reformate with the dehydrogenated C5-C fraction will depend upon severity of the dehydrogenation which determines the octane value to which the latter fraction is brought. Thus, by bringing the C -C fraction to 72 (F-l clear) octane and blending with the reformate, the blend will have 79 octane; for a 90F-1 clear blended gasoline the C -C fraction must be brought to 85.9 octane level. In most instances no significant advantage is obtained for separate dehydrogenation of the C and C cuts, respectively; separate dehydrogenation of the'C and C cuts may be practiced, if desired, with some benefit, by choice of optimum conditions for each of these cuts, particularly in those instances in which each of the cuts is high in normal parafiin content. For separate dehydrogenation the C cut is processed at 950-1050 F.'while the 0, out can be treated at lower temperature and/or higher space rate.

gen'ated product with the reformed C cut, the operator can select the severity of the dehydrogenation operation for optimum yield-octane values.

The advantages of the process of the invention are not limited to treatment of natural gasoline, but can be beneficially applied with C -C hydrocarbon fractions from other sources. With any type of charge stock, such as that employed in the illustrative example, wherein the C cut is high in paratfins, the inclusion of the C cut in the charge to reforming is not desirable. As a criterion in the choice of the manner of handling the several cuts contained in a C -C gasoline fraction, it is suggested that for those cuts wherein the paraiiin/naphthene weight ratio is equal to 2 or more, dehydrogenation is the best route; for those cuts in which the paraffin/naphthene weight ratio is 1 or less, reforming is indicated. Where the paraflin/naphthene ratio lies between 1 and 2, the operator has the choice of reforming if high octane number is preferred F-l clear) or dehydrogenation if highest yields 90%) at moderate octane are desired.

Obviously, many modifications and variations of the invention as. hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. I

What is claimed is:.

1. The method of upgrading natural gasoline which comprises fractionating such, gasoline at a cut point in the range of l 6018 5 F. to provide (1) a major fraction of lower boiling hydrocarbons composed chiefly of C and C hydrocarbons and (2) a minor fraction of higher boiling hydrocarbons of which at least 90% by volume is composed of C and C hydrocarbons, passing said lower boiling fraction at catalytic dehydrogenation conditions including substantially atmospheric pressure over chromium oxide-alumina dehydrogenation catalyst and at a processing severity level to obtain therefrom a liquid condensate of at least 85.9 octane level (F clear), collecting the condensable eflluent from said dehydrogenation; subjecting the higher boiling fraction to hydrogenative reforming over supported platinum catalyst at a temperature in the range of 800-1000" F. and at a pressure of 200 to 600 p.s .i.g., and blending the liquid condensate from said hydrogenative reforming with the condensable effiuent from said dehydrogenation to provide an upgraded gasoline material having an octane number of at least 90 (E clear).

2. The method in accordance with claim 1 wherein said fractionation of the natural gasoline charge is made at a cut point within the defined range such that the higher boiling fraction predominates in naphthenes.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,183 Laynglet al. Dec. 8, 1942 2, 24,16 Layne e a1. July 13, 1943 2,348,599 Brown May 9, 1944 2,689,208 Murray et al. Sept. 14, 1954 2,767,124 Myers Oct. 16,1956 ,3 14 R d l1j 1 2,905,619 Sutherland Sept. 22, 1959 2,918,422 Evering et al. Dec. 22', 1959,

Claims (1)

1. THE METHOD OF UPGRADING NATURAL GASOLINE WHICH COMPRISES FRACTIONATING SUCH GASOLINE AT A CUT POINT IN THE RANGE OF 60-185*F. TO PROVIDE (1) A MAJOR FRACTION OF A LOWER BOILING HYDROCARBONS COMPOSED CHIEFLY OF C5 AND C5 HYDROCARBONS AND (2) A MINOR FRACTION OF HIGHER BOILING HYDROCARBONS OF WHICH AT LEAST 90% BY VOLUME IS COMPOSED OF C7 AND C5 HYDROCARBONS PASSING SAID LOWER BOILING FRACTION AT CATALYTIC DEHYDROGENATION CONDITIONS INCLUDING SUBSTANTIALLY ATMOSPHERIC PRESSURE OVER CHROMIUM OXIDE-ALUMINA DEHYDROGENATION CATALYST AND AT A PROCESSING SEVERITY LEVEL TO OBTAIN THEREFROM A LIQUID CONDENSATE OF AT LEAST 85.9 OCTANE LEVEL (F1 CLEAR), COLLECTING THE CONDENSABLE EFFLUENT FROM SAID DEHYDROGENATION; SUBJECTING THE HIGHER BOILING FRACTION TO HYDROGENATIVE REFORMING OVER SUPPORTED PLATINUM CATALYST AT A TEMPERATUARE IN THE RANGE OF 800-1000*F. AND AT A PRESSURE OF 200 TO 600 P.S.I.G., AND BLENDING THE LIQUID CONDENSATE FROM SAID HYDROGENATIVE REFORMING WITH THE CONDENSABLE EFFLUENT FROM SAID DEHYDROGENATION TO PROVIDE AN UNGRADED GASOLINE MATERIAL HAVING AN OCTANE NUMBER OF AT LEAST 90 (F1 CLEAR).

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