US2204215A - Manufacture of motor fuel - Google Patents

Description

June 11, 1940.

B. s. GREENSFELDER Er AL MANUFACTURE OF MOTOR FUEL Filed June 15, 1936 4 MSQRSY dan. \m. JQ N\ Patented- June 11, V1940` UNITED STATES 'MANUFACTUBE oF Moron FUEL Bernard Sntro Greensfelder, Martinez, and

Russell Norman Shiras, Long Beach, Calif., assignors to Shell Development Company, San

, Francisco, Calif., a' corporation of Delaware Application June 15, 1936, serial No. 85,196

7 Claims.

This invention relates to improvements in motor fuels and process for manufacturing such fuels from mineral hydrocarbon oils.

'Ihree of the qualities which characterize good 5 gasolines are high antik'nock rating, vapor pressure below a certain maximum, and a properly balanced distillation range. The influence of these qualities on the performance of motor fuels in gasoline engines has been the subject of intensive studies during preceding years. Summariz-l ing the results of these studies, it may be stated. that, in general, high octane number permits the use of high engine compression ratios which, according to statistics, have risen from an average of 4.5 a few years ago to over 6 to date with a corresponding increase in engine efficiency. Effective volatility, as expressed in terms of vapor pressure and A.' S. T. M. distillation, should be such as to combine the lowest possible vapor pressure with a distillation curve which indicates highest volatility index, volatility index being indicative of the percent evaporated at 167 and 284 F. when distilling in accordance with A. S.

T. M. method D 86-35. Motor fuels having the -u above effective volatility requirements insure ease of starting, quick acceleration and freedom from vapor lock. Improvements in the effective volatility of `motor fuels can be achieved by lowering the vapor pressure, or the temperatureV of the 50% evaporated, or both.

The term octane number as hereinafter used refers to A. S. T. M. octane number, A. S. T. M. method D 357-34T, provided the number is 100 or below. Octane numbers above 100, are blending octane numbers, as defined by Sprake et al. in Proceedings of World Petroleum Congress, London 1933, page 170.

The studies of the problem of engine knock have revealed that octane number is afunction of the fuel composition, as well as of engine conditions. It was found that octane numbers of an homologous series of hydrocarbons depend upon the number of carbon atoms in their molecules and upon the compactness of their molecular structure, octane numbers rising with numerical decrease and centralization of carbon atoms. Thus theoctane number of normal heptane is zero, as compared with -19 for normaloctane, while 2-2-3-3 tetramethyl butane, which is one of 130. Double bonds generally contribute to a speeds, depreciate in octane number at higher,

engine temperatures and speeds. Moreover, numerous aromatic compounds have comparatively high melting points, which greatly limit of the isomeric octanes, has an octane number their use at low atmospheric temperatures. Even in summer time, airplane engines have been known to have difculties when flying at high altitudes, due to obstruction of the fuel lines traceable to frozen aromatic compounds, and oleiines are excluded from many aviation gasolines by specications'because of their tendency -to form gums. l

'Ihe eect of tetraethyl lead on the octane number of fuels has also been studied and a factor called the lead susceptibility has been introduced. It has been established that some gasolines show more improvement in octane number for a given addition of tetraethyl lead than do others. Thisvariation in susceptibility' was found to be a function ofthe composition of the fuel, those components which depreciate in octane number at elevated temperatures, in general, being less susceptible to lead. In other words, paranic and naphthenic hydrocarbons were found to be much more susceptible to octane number improvement by the addition of tetraethyl lead than olenes and particularly aromatic compounds. Some aromatica are known to possess negative lead susceptibilities.

We have discovered that by close fractionation of suitable low boiling petroleum products, such as naphthas, particularly those obtained from naphthenic base crudes, such as California crudes, natural gasoline, recovery gasoline, etc., two valuable fractions of a boiling range suitable for motor fuels can be isolated, in which nonaromatic hydrocarbons of centralized and/or cyclic structures possessing high octane numbers and lead susceptibilities are concentrated. By blending these fractions with gasolines, blended motor fuels may be produced having antiknock ratings which are not only improvements over those of the unblended gasolines, but which do not depreciate even when these blended fuels are used in engines operating under most severe conditions. y

The low boiling fraction of our invention has a boiling range as measured by the and 95% points of the A. S. T. M. distillation method D 86-35, within 40 to 60 C., while the higher boiling fraction has a boiling range as determined in the samemanner of within 75 to 95 C., and preferably within 75 to 90 C. These fractions consist of naphthenic and branched parainic and/or oleflnic hydrocarbons. For convenience and for the reasons hereinafter explained, we

shall refer to these two fractions as cyclopentane 3 fraction and cyclo-hexane fraction, respectively. As mentioned hereinbefore, we obtain these fractions by fractional distillation of petroleum -or petroleum products, particularly of the type of natural gasoline or similar hydrocarbon mixtures, which may or may not contain aromatic hydrocarbons, and which are preferably derived,

in order to assure proper compositions of these valuable fractions and their substantial yields, from naphthenic base crudes, such as California, Gulf, and some of the West 'Texas crudes or natural gases accompanying these crudes.

Analyses'of many samples of different origins have shown the fraction boiling from iO-60 C. to be characterized by the presence of a considerable amount of cyclopentane, boiling at 50 C.

and having an octane number of approximatelyl 130, and relatively small quantities of 292 dimethyl butane, 101 octane number, and 2-3 dimethyl butane, 124 octane number. `If the original material contains products from a cracking process, this fraction may also contain isomers ofv hexene which possess relatively high octane numbers. Although, naturally, the concentration of cyclopentane in this fraction varies depending upon its source, we have found that in most cases the concentration of this cyclic hydrocarbon in the properly produced fraction is not below 5% and, frequently, is found to be in excess of about 20%. Whereas these concentrations of cyclopentane are preferred limits, we have found that fractions boiling between about 40-160 C. may still be valuable for blending in gasolines, even though such fractions are deficient in cyclopentane since the branched hexanes contained in the fraction have high antiknock values as afore pointed out. For example, when the fraction is obtained from a cracked distillate, it may contain predominating amounts of branched olefines. such as methyl pentenes, and very small amounts only of cyclopentane.

'I'he octane rating of the cyclopentane fraction varies somewhat with its composition within a fairly definite range, that of the preferred type of -this fraction being in excess of 80.

'I'he cyclohexane fraction, as the name indicates, includes cyclohexane and also substantial proportions of other hydrocarbons of branched paraillnic and/or oleiinic and/or naphthenic types. 'Ihe concentration of cyclohexane may vary within wide limits, but we prefer to use fractions containing at least 5% cyclohexane, a1- though lower concentrations are permissible, provided the concentration of branched hydrocarbons is such as to assure that the fraction has an octane number of at least '70, the fractions boiling within the range of r15--95 C. having octane ratings below '70 being considered unsuitable for use in blended gasolines in accordance with this invention; an excessive depression of the octane rating of fractions of our preferred boiling range may sometimes be due to relatively high concentrations of some objectionable hydrocarbons, such as Z-methylhexane which has an octane rating of 55. By limiting the upper limit of the boiling range of this fraction to 90" instead of 95 C. certain of these branched heptanes having low antiknock qualities may be eliminated while those boiling below 90 C., all of which possess high antiknock values, are retained in the fraction.

A characteristic of our cyclopentane and cyclohexane fractions is that they are substantially free from aromatic and normal paraiiinic hydrocarbons. Although the boiling temperature of benzene (80.2 C.) is within the boiling range of our cyclohexane fraction, this aromatic hydrocarbon is excluded therefrom in the course of fractional distillation due to the known fact, that the vapor pressure relations of benzene and nhexane cause their nearly complete removal from fractions boiling at temperatures above C. The mixture of these two hydrocarbons is distilled with other hydrocarbons in the boiling range from 60 C. to 75 C. and, therefore, is excluded from both our fractions.

While in the foregoing we have described the cyclopentane and cyclohexane fractions as boiling within the range of 40 to 60 C. and '75 to 95 C., respectively, we do not wish to include in these compounds, unstable unsaturated compounds of the type of diolefines, etc., they may be treated with chemicals or other refining agents such as alkali, doctor solution, sulfuric acid, clay, etc.

In the attached drawing, a iiow diagram illustrates a method, by which the two desired fractions may be separated from a mixture containing them, and by which the remaining fractions are utilized to produce either further quantities of the desired fractions, or antiknock gasoline with which the desired fractions may be blended, thus further improving its antiknock rating and/or volatility. Vapors of natural gasoline or other suitable mineral oil, are introduced from a source not shown through line I into fractionating column 2, from which an overhead vapor boiling below C. is removed through vapor line 3, and a bottom stream, boiling above 90 C., through line 4. 'Ihe vapors from line 3 are discharged into fractionator 5 in which they are separated into a bottom fraction boiling between 75 and 90 C., and an overhead vapor fraction boiling below 75 C. 'I'he 75/90 C. fraction passes through conduit 6 to tank 1. tion boiling below 75 C. is conducted through line I to fractionator 9 in which it is separated into a bottom fraction boiling between 60 C. and 15 C. which is withdrawn through line I0, and a vapor fraction boiling below 60 C. 'I'he latter fraction passes through vapor line I I' to fractionator-I2, in which it is separated into a bottom fraction boiling between 40 C. and 60 C., which is conducted through line I3 to tank Il, and an overhead product boiling below 40 C. which passes through lines I5 and I6 into manifold I1 where it joins the bottom streams from lines I and I0 from the fractionators 2 and B, respectively. The combined streams are now forced by pump I8 in line I9 through coil 20 in furnace 2|, in which they are heated under superatmospheric pressure,

'I'he vapor fracif desired, to a cracking or reforming temperature. 'Ihe cracked or reformed product now enters through line 22 into fractionator 23, which may consist of a system of fractionating columns, in which they are separatedinto at least 3 fractions: a normally gaseous fraction which escapes through overhead line 24 and goes to an absorption plant not shown; a gasoline type fraction, which is withdrawn through side line 25; and a tarry bottom fraction which is removed through bottom line 26. A tar-free fraction heavier than gasoline may be produced which flows through side conduit 21 and is recirculated through the heating coil 20 by pumpl in line I9 to be recracked.

Ihe gasoline fraction in line 25 may be conducted through line 28 into fractionator 2 to be recirculated through the fractionating system comprising the fractionators 2, l, l, I2, for the production of additional cyclopentane and cyclohexane fractions. Or it may be taken through line 29 to gasoline tank 30. On its way to tank 30 this gasoline may be chemically treated, in a treating plant not shown, in order to desulfurize and/or render it storage stable.

The cyclohexane and cyclopentane fractions in tanks 1 and Il, respectively, may be conducted through lines 3|, 29, and 22, 29, respectively, to blending tank 30 for the production of blended gasoline of desired specifications.

The overhead fraction boiling below 40 C. from fractionator I2 and'line I5, instead of being passed through line I6 as described, may be conducted through line 3l into fractionator Il, in which normal pentane is withdrawn as the bottom product through line Il and manifold I7 to go to the reforming unit; and an.overhead vapor boiling below 35 C. consisting of isopentane and lighter hydrocarbons which is transferred through line 35 to stabilizer 3E in which isopentane is separated from the lighter hydrocarbons. The latter pass through lines 31 and 24 to the absorption plant not shown, and the isopentane is transferred through line 3l to tank 3Q. If desired, isopentane may be introduced into the blended gasoline in tank 30 by conducting it through lines 40 and 29. Portions of overhead products from the columns 23 and/or 36 may be recirculated through the cracking coil 20 together with normally liquid hydrocarbons from line 21 and be caused to polymerize or condense therewith.

While the described cyclopentane and cyclohexane fractions have proven to be excellently suited for blending with motor gasolinas, their use is not restricted to this. The fractions alone or in combination with each other have the p'ropcrtes of motor fuels for general as well as special purposes. Mixtures of the two fractions may produce aviation gasolines which meet the most exacting demands with regard to volatility,knock rating, and freezing point.

The cyclopentane fraction nds a further application in the manufacture of low vapor pressure gasolines by replacing aliphatic pentanes and lighter hydrocarbons. Thus, by substantially removing aliphatic pentanes and lighter hydrocarbons from a motor gasoline, whereby the vapor pressure of the gasoline is lowered substantially below normal, and then replacing the removed fractions with cyclopentane fraction, a gasoline can be produced having a higher effective volatility and volatility index and a lower vapor pressure and vapor lock tendency than the original motor gasoline. Instead of depentanized gasoline base, a debutanized gasoline having a subnormal volatility can be markedly improved by being blended with a'suicient quantity of the cyclopentane fraction to result in a blend having volatility of normal gasoline. The antknock rating may be considerably raised by this substitution, and may further be improved by incorporating an effective quantity of the cyclohexane fraction, the improvement being particularly noticeable where the octane number of the orginal gasoline is below 70.

The proportions of the two fractions required for blending with existing motor gasolines cannot be specified with any degree of accuracy. However, in studying a large number of gasolines, that is, hydrocarbon mixtures boiling between about 30 C. and 200 C. and produced by fractional distillation of petroleum crudes or their fractions, as well as of cracked or reformed distillates, or obtained by blending of straight run and cracked petroleum fractions, alone, or with hydrogenated or synthetic hydrocarbon products, we have found that the concentrations of the cyclopentane and cyclohexane fractions in such gasolines rarely exceed about 8% and about 15% respectively. By adding our cyclopentane and/or cyclohexane fractions to such gasolines, we increase their content of these fractions substantially beyond normal concentrations, which enables us to produce gasolines of markedly superior quality.

Aviation gasolines of very good quality are produced by blending our cyclopentane and cyclohexane fractions, alone, without the addition of a third hydrocarbon component, 1 to 5 parts of the lighter fraction in 10 parts-of the blend being required to meet specifications for this type of motor fuel. If the vapor pressure specifications permit, isopentane may be added to the blended gasoline, isopentane having ablending octane number of above 90. The presence of isopentane is not only beneficial to the'antiknock rating, but it improves the starting qualities of gasolines, a property which is of great importance in gasolines used in cold weather.

The following examples illustrate our invention:

Example 1 A blend is prepared of 10% by volume of a debutanized gasoline base of the properties shown below, with of a cyclopentane fraction and 10% of a cyclohexane fraction. To 80 volume percent of the resulting blend' 20% of an isopentane fraction is subsequently added.

Bla'ndeigogiyis- 80,7,

o me, o Gasbase, 20% Regular oline cyclopentane 20,7 ism gasbase frac., 10 am oline cyclobexane prac trac.

77 4S 40 42 58 50 59 65 58 70 123 l2() 130 189 189 189 l 201 all mi 200 F. 207 207 206 206 Reid V. P. at 100 F 2. l 4. 2 8. 5 8.6 Octane No 50 6l `68 56 Example 2.f

An aviation gasoline consisting of 3 parts of a cyclopentane fraction and 7 parts of a cyclohexane fraction has the following properties:

An aviation gasoline is prepared by blending 4 parts of a depentanized aviation gasoline base with 3 parts of a cyclopentane fraction and 3 parts of a cyclohexane fraction.

We claim as our invention:

1. A gasoline-type motor fuel of normal vapor pressure consisting essentially of a blend of a depentanized portion of a gasoline distillate havmg a subnormal vapor pressure and a quantity of a cyclopentane fraction obtained by distillation of petroleum oil containing said fraction consisting essentially of naphthenic and [branched chain aliphatic hydrocarbons and being substantially free from aromatic and normal paraflinic hydrocarbons.

2. A gasoline-type motor fuel of normal vapor pressure consisting essentially of a blend of a depentanized portion of a gasoline distillate having a subnormal vapor pressure and a quantity of a mineral oil fraction having a boiling range not exceeding 40 C. to 60 C. consisting essentially of naphthenic and branched chain aliphatic hydrocarbons and being substantially free from aromatic and normal parailinic hydrocarbons.

3. A gasoline-type motor fuel of normal vapor pressure consisting essentially of a blend of a depentanized portion of a gasoline distillate having a subnormal vapor pressure and a quantity of a cyclopentane fraction obtained by distillation oi petroleum oil containing said fraction consisting essentially of naphthenic and branched chain aliphatic hydrocarbons and being substantially free from aromatic and normal paramnic hydrocarbons, said quantity being from 1 to 5 parts in 10 parts of the blend.

4. A gasoline-type hydrocarbon mixture of normal vapor pressure and volatility index consisting essentially of a blend of a depentanized portion of a gasoline distillate having a subnormal vapor pressure and volatility index, and a quantity of a mixture of cyclopentane and cyclohexane fractions, said fractions obtained by distillation of petroleum oil containing said fractions consisting essentially of naphthenic and branched chain aliphatic hydrocarbons and being substantially free from aromatic and normal paraiiinic hydrocarbons.

5. A gasoline-type hydrocarbon mixture of normal vapor pressure and volatility index oonmal vapor pressure and volatility index consisting yessentially of a blend of a depentanized portion of a gasoline distillate having a subnormal vapor pressure and volatility index and a quantity of a mixture of two mineral oil fractions having boiling ranges not exceeding 40 C. to 60 Cpand 75 C. to 90 C. respectively, said fractions consisting essentially of a naphthenic and branched chain aliphatic hydrocarbons and being substantially free from aromatic and normal paramnic hydrocarbons.

7. A gasoline-type motor fuel of normal vapor pressure consisting essentially of a blend of a gasoline distillate substantially free from C5 and lighter hydrocarbons having a subnormal vapor pressure and a quantity of a cyclopentane fraction obtained by distillation of petroleum oil containing said fraction consisting essentially oi naphthenic and branched chain aliphatic hydrocarbons and being substantially free from aromatic and normal paraflinic hydrocarbons.

BERNARD SUTRO GREENSFEIDER. RUSSELL NORMAN SHIRAS.

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