US2407716A - Superfuel - Google Patents

Description

Sept. 17, 1946. R. F. MARscHNER Y SUPER FUEL 2' Sheets-Sheet l `Filed June 29, 1940 NAKRWNNW QA IQ@ Sept. 17, 1946. R. F. MARSCHNER SUPER FUEL Filed June 29, 1940 Z'Sheetsf-Sheet 2 WS NEQQ W35@ Sx NNN.

Patented Sept. 17, 1946 SUPERFUEL Robert F. Marschner, Chicago, Ill., assignor to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application June 29, 1940, Serial No. 343,179

4 Claims. l

This invention relates to a new and improved super fuel particularly for aviation purposes and it pertains more particularly to improved methcds and means for obtaining cyclopentane and cyclopentane-neohexane blends. The invention also relates to motor fuels comprising isooctanecyclopentane and isooctane-cyclopentane-neohexane blends either with or without the addition of tetra alkyl lead.

An object of my invention is to provide an aviation fuel superior to any heretofore known and particularly with respect to octane number and ritical compression ratio, coupled with an optimum volatility range and response to tetra alkyl lead.

Cyclopentane is superior in its blending octane value to any other hydrocarbon fraction of motor fuel. Thus the blending value of cyclopentane may range from about 115 to 160 octane numbers by the research method depending upon the fuel into which it is blended and the concentration. The rating of aviation fuels should be under the supercharged conditions of actual flight. Since the C. F. R.R. method is a fair indication of supercharged performance, research octane numbers are more significant in connection with aviation fuels than are the motor octane numbers. The C. F. R.-R. octane number of cyclopentane is above 100.

Cyclopentane is inert to cold concentrated sulfurie acid,` does not respond to the usual tests for unsaturaticn, is stable to atmospheric oxidation and produces no gum on standing in contact with various metals. In short, it exhibits all the stability characteristics demanded by aviation gasolines. Cyclopentane has a boiling point of 121 F. and a Reid vapor pressure of about pounds. These properties are highly desirable in an aviation fuel for starting and acceleration purposes. Cyclopentane has an additional advantage of a high sensitivity, a property which is rare among chemically inert and stable hydrocarbons. Sensitive hydrocarbons have the general property of permitting high engine power outputs when a deficiency of air with respect to fuel is supplied to the engine, i. e., under rich mixture conditions. A highly sensitive hydrocarbon fuel is particularly advantageous for military aviation purposes for taking off, climbing, etc. Cyclopen- 'taneis the most sensitive o f all tested naph-r thenes, it has a higher heat Value than aromatics (due to its higher hydrogen-to-carbon ratio) and it is more stable and more responsive to lead tetra ethyl than olen hydrocarbons. This c-ombination of the desirable properties of extremely high octane number, volatility of the proper magnitude and extreme chemical stability, together with sensitivity and heating value, make cyclopentane of unique value as an aviation fuel constituent. An object of my invention is to utilize the high blending octane number, the stability, the sensitivity and the volatility qualities of cyclopentane together with commercial isooctane to make a motor fuel having an octane number about or higher even in the absence of tetra alkyl lead and having much greater octane numbers when small amounts of tetra alkyl lead are employed.

Cyclopentane as heretofore recovered by the close fractionation of naphthas has not been entirely free from normal pentane and has con: tained relatively large amounts of methylpentanes. For example, an A. S. T. M 5% to 95% range of 104 to 140 F. may usually indicate the presence of as much as 20% n-pentane and 40% Z-methylpentane. It is entirely possible to secure such a bo-iling range from a mixture of npentane and 2-methylpentane, only, without any cyclopentane whatsoever. Furthermore, there has been no appreciation of the fact that neohexane boils Within 1 F. of the cyclopentane so that when the narrow boiling range of the fraction is the sole criterion, a product which is assumed to be cyclopentane may, in fact, be chief- 1y neohexane. I have discovered that a cyclopentane-neohexane composition which is substantially free from normal pentane and methylpentanes is' a remarkably superior blending agent for isooctane aviation fuels, particularly when the proportion of cyclopentane to neohexane ranges from about 1:3 to 9:1. This mixture of from about 30% to 90% of cyclopentane With about 70% to 10% of heohexane is so distinctly new as a commercial product and it offers such remarkable advantages in an isooctane aviation super fuel that I have given it the name ultrane Ultrane has a Reid vapor pressure of about 8 to 10 pounds. It boils within the narrow limits of to 124 F. It has a refractive index above 1.38, an A. P. I. gravity be1ow'75", an

3 octane number above 95 C. F. R.R. and a blend ing octane number which may be as high as 160 C. F. R.-R.

Commercial isooctane may have an initial boiling point of about 165 F. but between the 10 and 90 points the boiling temperature is within the range of about 200 to 240 F. and it has a Reid vapor pressure of only about 2 pounds. By blending about 30 to 70% of ultrane with 30 to 70% isooctane, preferably equal parts of ultrane and isooctane, the resulting motor fuel has an ideal volatility *for-Y aviation purposes, itis remarkably-stable against gum formation and deterioration of all kinds, it offers exceptionally valuable starting and acceleration characteristics and it is characterized by a clear octane number of at least about 100 C. F. R.R.

It has been proposed to substitute a dilute cyclopentane fraction for the normal pentane content of an ordinary gasoline and even of aviation gasoline but my invention distinguishes from such proposals in several respects. In the first place, my ultrane has a boiling range of only 4 or 5 degrees F. and althoughk a slightly wider lboiling range may be permissible, it is essential that the ultrane should be substantially free from normal pentane. In the next place, ultrane is prepared from such charging stocks that it has a certain proportion of cyclopentane to neohex-vv ane, the cyclopentane preferably predominating to the extent of about 2:1 and the over-all limits being about 30 to 90% cyclopentane and 70 to neohexane. Finally, the lultrane is not blended with ordinary gasolines such as are produced by thermal or catalytic cracking or reforming or such as are produced by hydrogenation of oils or the polymerization of refinery gases. The ,isooctane with which my ultrane is blended is a synthetic hydrocarbon which may be obtained `'byithe alkylation of clef-ins by means ofisovparaiins to produce isoheptane, isooctane, isononane or isodecane, or it maybe produced by the selective polymerization of oleiins (such as butylenes or pentenes to produce isooctene or isononene or isodecene) followed by hydrogenationof isooctene to isooctane, isononene to iso- `nonane or isodecene to isodecane. The isooctaneA to which this invention relates is the commercial rather than chemically pure product but it is characterized by the absence of appreciable 'amounts of' low boiling hydrocarbons, its 10% point being about 200 F, and its 90% point being about 240 to 270 F. When such isooctane is blended with about 30 to 70 parts by volume of ultrane, the resulting motor fuel is superior in performance to any motor fuel which has heretofore been known.

From extended laboratory research and the study of all available literature, I have found that ultrane is present in almost all light naphthas 'from all types of crude petroleum. The amount *of ultrane in various light naphthas containing the C5,` Cs and Cv hydrocarbons in the crude are as follows:

4 Russian and South American light naphthas contain similar amounts of ultrane.

In practicing my invention I fractionate light virgin naphthas from any crude, or any otherwise derived light naphthas which contain appreciable amounts of ultrane, under carefully controlled conditions to obtain a hydrocarbon fraction boiling from about 80 to 150 or 160 F. and preferably boiling within the range of 100 to 140 F. as determined by ordinary distillation. This fraction which mayV be termed ultrane concentrate will be contaminated with normal. pentane and even with normal hexane, both of which have extremely low octane numbers. It is essential, therefore, to separate the `ultrane fraction from Vthese contaminants. Study of the boiling points of hydrocarbons shows that within the boiling range of about 100 to 160 F. the only hydrocarbons present are: Y y

Traces of benzene will be `found in fractions boiling as low as 140 F. It Will be notedA from the above table that cyclopentane and neohexane boil within 1 of each other and commercial separation of these two by fractionation -is practically impossible. In practicing my invention I effect close fractionation of my ultrane concentrate in order to remove therefrom the n-pentane, which is characterized by a high A. P. I. gravity and a very low octane number, together with substantially all the normal hexane which is characterized by a relatively high gravity and an even lower octane number. `The 23.7 boiling point differential between n-pentane and cyclopentane makes commercial fractionation between these two hydrocarbons commercially feasible. It is a little more diicult only 14.7.

to obtain a sharp fractionation commercially between neohexane and 2,3-dimethyl butane because in this case the boiling pointV differential is However, sharp fractionation at this point is not as important as in the lower range since the 2,3-climet/hylV butane is more valuable than the neohexane as a blending agent. It is only necessary to prevent any substantial amount of the methylpentanes or n-hexane from contaminating the ultrane and this I have found can be easily done in .commercial operations. 1 prefer to retain as little as conveniently possible of the 2,3-dimethyl butane in theultrane since contammation with much 2,3-dimethy1 butane also includes. some methylpentanes.

` My invention also contemplates means for fractionating ultrane from other components of light naphthas and means for fractionating -the ultrane itself into its component parts, the .latter being-.preferably accomplished Y ,by means of azeotropic distillation of the ultrane with methanol. The inventionr will be more clearly' understood from the following detailed description and from vthe accompanying drawings Figure'2 is a chart showing which form a part `of this specification which l Y 1 Figure 1 is a vdiagrammatic flow sheetV of my improved process and and in the remarkable and improved v unexpected octane number and gravity characteristics of the `ultrane as distilled from virgin light naphtha.

The light naphtha may be from any of the crude sources above indicated, preferably from .a crude which is high in light naphtha components. Instead of employing a virgin naphtha, I may employ a hydrogenated cracked naphtha. Cyclopentene and cyclopentadiene as Well as cyclopentane are formed in catalytic cracking and in thermal cracking. On hydrogenation both of these cycloolefns are converted into cyclopentane. Cyclopentadiene boils at 105.8 and cyclopentene boils at 111.4 but pentadiene-1,3 which has an octane number after hydrogenation of only 64 C. F. R.-lVl., boils between them at 108.5 so that it is desirable to hydrogenate the cracked `products before fractionation rather than afterwards. When cracked naphthas are employed it is thus possible to separate cyclopentane from normal pentane by hydrogenating the cracked naphtha before effecting the'distillation.

Catalytically dehydrogenated light naphtha may leave cyclopentane unchanged or may partially convert it into normal pentane. Catalytically dehydrogenated heavy naphthas may give appreciable amounts of cyclopentane resulting from the simultaneous destructive hydrogenation of alkylcyclopentanes. Therefore, my light naphtha charge may be obtained from a catalytic reforming process.

My preferred charging stock is a virgin light naphtha from crudes containing to 50% of gasoline such `as Mid Continent, East and West Texas, Pennsylvania, California, Coastal or certain foreign crudes. This charging stock is introduced from line l0 by pump Ii through coils i2 of furnace I3 and thence through transfer line I4 to crude still or fraotionating column l5 which is provided with suitablereflux means I0 at its top and reboiler means l 'i at its base. The temperature at the base of this crude still column is preferably about 400 to 600 F. and topped crude is removed from the base of this still through line i0. The temperature at the top of `crude still column i5 is preferably about 250 to ,350 F. at atmospheric pressure or about 35,0 to 450 F. under pressure of about 80 pounds gauge. The light naphtha overhead products are `with- -drawn through line i 9, through cooler into dea ing coils but which is preferably introduced reflux liquid, the temperature at the top of debutanizer tower 2| is held at about 40 to 80 F. at atmospheric pressure or 150 to 200 F. at 80 pounds gauge. Butanes and lighter are taken overhead in line 23. Reboiler coil 24' at the base of debutanizer column 2| maintains a temperature of about 200 to 400 F. at which temperature debutanized light naphtha is Withdrawn through line 25 to isopentane column 26.

The top of isopentane column 26 is maintained at about 80 to 100 F. at atmospheric pressure or 210 to 280 F. at 80 pounds gauge by suitable reflux means 27, which may be a cooling coil but Which is preferably introduced reflux liquid. The reflux ratio in this case should be relatively high, preferably about 20:1 to 60:1. Isopentane is removed overhead through line 2B.

The bottom of isopentane column 26 is provided with a reboiler 29 which maintains temperature of about 250 to 450 F. at which temperature the remaining light naphtha is Withdrawn through line 30 to dehexanizer column 3 I.. A reboiler 32 at the bottom of this column maintains a temperatureof about 300 to 350 F. and anintermediate naphtha is withdrawn from this column through line 33.

The top of the dehexanizer column 3i is maintained at a temperature of about 150 to 180 F. at atmospheric pressure or about 280 to 300 F. at 80 pounds gauge by suitable reflux mieans 34 which, as hereinabove described, may be cooling coils or added reflux liquid. The overhead pentane-hexane fraction is the material previously called ultrane concentrate. It is introduced by line 35 into depentanizer column 36. The top of this column, is cooled by suitable reflux means 3l to temperatures of 100 to 120 at atmospheric pressure or about 230 to 270 F. at 80 pounds gauge. Normal pentane is drawn overhead through line 38.

The base of depentanizer column 36 is provided with reboiling means 39 for maintaining a temperature about 150 to 350 F., depending upon the pressure, which temperature must be sufficiently high to insure the removal of substantially all of the normal pentane from the hydrocarbons which leave the base of depentanizer column 30 through line 40 to the Aultrane column 4i.

Reboiler e2 in the base of the ultrane column maintains a temperature of 150 to 350 F. Vand branched hexanes are Withdrawn from the base of this column through line 3. Suitable reflux means 44 at the top of the ultrane column maintain a temperature of about 130 to 140 F. at atmospheric pressure or about 250 to 280 F. at 80 pounds gauge. Here the use of a high reflux ratio is particularly important and We have found lthat in. 10-20 plate columns, the reflux `ratio should range from about :1 to about 10021. The ultrane overhead from column Mis withdrawn through line l5 and cooler 55 to ultrane storage tank G7.

With proper control of ilovvrates, temperatures, pressures, etc. in the fractionation system as hereinabove described, the ultrane should be substantially free from normal pentane and from rnethylpentanes and normal hexane. If the fractionation has not been sufficiently close,y l may rerun the ultrane in either a batch still provided with an eificient fractionating column and employing a high reflux ratio, and by this means obtain necessary sharpness of fractionation and freedom from normal pentane and other undesirable hydrocarbons which distinguishes ultrane from the .so-called close cut-fractions heretofore obtained. Such rerunning is necessary in the case of the rare crudes which contain unusually small amounts of ultrane.

The boiling point of the ultrane as above stated should be about 120 to 124 F., its refractive index (ND20) should be above 1.3800, preferably above 1.3900, its A. P. I. gravity below '75 and preferably below and its octane number above C. F. R.-R.

The isooctane referred to herein is the commercial product which may for instance be prepared by polymerizing isobutylene to isooctene, then hydrogenating the isooctene to isooctane. Alternatively, it may be prepared bv` the alkylation of isobutane with butenes or by the dehydroalkylation of isobutane. It may also be prepared by destructive alkylation of higher branched paraiiins. My invention does not relate specifically to any particular methodV of obtaining the isooctane but by this term I mean to include the aviation motor` fuels prepared by the above or any rother processes which contain substantial amounts of 2,2,4-trimethyl pentane, 2,2,3-trimethyl pentane and 2,3,4-trimethyl pentane and which have an octane rnumber' above 90 C. F.

R..M. or above 9.0 octane number by any of the ordinary test methods.

Theisooctane or equivalent product is withdrawn from storage tank 48 by pump 49 and into blending line 50 While ultrane from tank 41 is withdrawn by pump i, line 52 and line 53 to blending line 50. I prefer to employ about equal parts of isooctane and ultrane but, as above stated, my aviation super fuel may contain from about 30 to 70% ultrane and from 70 to 30% isooctane. The volatility and octane numbers of a While ultrane is my preferred blending fuel for use with isooctane, it should be understood that Y I may further fractionate the ultrane to obtain substantially pure cyclopentane. Ultrane, for example, maybe Withdrawn through line 54 to anazeotropic distillation unit employing methanol or other Water-solubleA azeotropic agent. The neoheXane-methanol azeotrope boils several Ydegrees below cyclopentane-methanol azeotrope When distillation is carried out under the proper pressure. As a rule, such azeotropes can be fractionated more easily than the hydrocarbons alone about 10% ofeach of the following fuels wer blended with a standard reference fuel:

The critical lcompression ratio of pure cyclopentane is 10.8 as compared With only 7.5 for isooctane. With 1 cc. of tetraethyllead rper gallon, the critical compression ratioof cyclopentane is increased from 10.8 to 13.5 while that of isooctane is increased from 7.5 only'to 9.8 with a corresponding amount of added tetraethyllead. Cyclopentane with 1 cc. of tetraethyllead is almost exactly equivalent to isooctane plus three times as much tetraethyllead. The critical compression ratio of cyclopentaneis even superior to that of such anti-knock hydrocarbons as ethylbenzene and, of course, cyclopentane is markedly superior to ethylbenzene as a blending agent for isooctane because of its high volatility, relatively high heating value and stability. Furthermore, the addition of tetraethyllead raises the compression ratio of cyclopentane more than that of ethylbenzene. One of the outstanding characteristics of ultrane is its effect in increasing the critical compression ratio of the isooctane aviation fuel.

While I have described in detail a preferred embodiment of my invention-it shouldbe understood that various modications and alternative procedures will be apparent from the above description to those skilled in the art.

I claim:

1. A composition of matter consisting essentially of cyclopentane and neohexane and containing about 30 to 90% by volume of cyclopentane which composition is substantially free from normal pentane and which is characterized by a boiling range of about 120 to'124 F., a redue, in part, to the fact that the presence of the fractive index above 1.38, A. P. I. gravity below azeotropic agent increases the volume. While azeotropic distillation is a preferred method of Y obtaining the pure cyclopentane, it may be under- I stood that other processes maybe employed.

These processes are not an essential part of the present invention and are therefore not discussed in greater detail. Cyclopentane may be blended with isooctane to form aviation super fuels in 75 and an octane number above 95 C. F. YR.R.

2. An Iaviation super fuel whichY comprises about 30 to 70% Aof the composition defined in claim 1 together with about 70 to 30% of an iso- 0 octane motor fuel having a 10% point of about 200 F. and a 90% point of about 230 to 270 F.

3.' An aviation super fuel which comprises a commercial isooctane motor fuel having a C. F. R.M. octane number of at least about 90 blended with about 30% t0 70% of ultrahe 4. The aviation super fuel or enum 3 which contains from about 1 to about 6 cc. of tetra alkyl Y lead per gallon of aviation super fuel.

ROBERT F. MARSCI-INER.

Images