US2334006A - Motor fuel - Google Patents

Description

Patented Nov. 9, 1943 MOTOR FUEL Melvin M. Holm, San Francisco, Calif., assignor to Standard Oil Company of California, San Francisco, Calif., a corporation of Delaware No Drawing. Original application May 31, 1939, Serial No. 276,623, now Patent No. 2,228,662, dated January 14, 1941. Divided and this application December 16, 1940, Serial No. 370,353

9 Claims.

This application is a division of my copending application Serial No. 276,623, filed May 31, 1939, now United States Patent No. 2,228,662.

This invention relates to the addition of certain esters to motor fuels consisting essentially of branched chain paramn hydrocarbons and having a relatively high antiknock value to increase the antiknock quality thereof.

One object of this invention is to make motor fuels for internal combustion engines, especially for aviation engines, which fuels have antiknock values hitherto unobtainable without theuse of relatively high concentrations of such metalloorganic antiknock agents as lead tetraethyl and iron carbonyl.

Another object is to increase the ant'iknock value of motor fuels consisting essentially of branched chain paraflin hydrocarbons and having initially a relatively high antiknock value and simultaneously to improve the volatility or distillation characteristics of such motor fuels.

Another object is to provide motor fuels consisting essentially of branched chain paramn hydrocarbons having antiknock values higher than any heretofore known for such fuels.

Still another object is to provide motor fuels particularly adapted for use in aviation engines of the liquid-cooled or air-cooled type. e

Other objects will be apparent to those skilled in the art from the disclosure of my invention which follows.

The unusually high antiknock quality of the branched chain parafiin hydrocarbons, such as 2,2,4-trimethyl pentane for example, has been recognized for years, but until very recently pure branched chain paraflln hydrocarbon compounds having such relatively high antiknock values were little more than laboratory curiosities. However, within the past two or three years polymerization processes have been developed which convert gaseous olefins such as propylene, l-butene, and isobutene into branchedchain liquid olefins, which in turn may be converted to the relatively high antiknock paraflln's of corresponding structure by direct hydrogenation. Also, more recently, these relatively high antiknock branched chain paraflln hydrocarbons have been produced by alkylation. Since the 7 development of these processes of polymerization high antiknock relatively pure branched chain liquid paraflins have become commercially available and are sold as iso-octane or hydroctane."

This iso-octane or hydroctane".of commerce, however, even though having a relatively high antiknock value, usually is not alone a satisfactory motor fuel, for it is usually necessary that more volatile constituents, such as natural gasoline for example, be blended with it to make a 10 finished fuel having the desired volatility or distillation curve, so that the fuel will have the desired characteristics relating to starting, acceleration, etc. because the available, more volatile blending stocks themselves, such as natural gasoline, usually have relatively low antiknock values, and

have the effect of lowering the antiknock value of the blend- Even relatively pure isopentane, which is probably the best available volatile blending agent with regard to antiknock value, fails to improve the antiknockyalue of such base fuels to any appreciable extent, if at .all. Thus, in view of the difficulty of increasing the antiknock value of such fuels while at the same time obtaining the desired volatility, it has been necessary to make up the deficiencies in octane number by the use of such organo-metallic antiknock agents as lead tetraethyl. This problem has been especially difilcult in the cases in which, from such commercial iso-octanes, motor fuels have been made which are required to meet the volatility and octane number specifications in the field of aviation and racing, where, for example, octane numbers in the range of 90 to 100 and higher are demanded.

Although the use of small concentrations of such metallo-organic antiknock agents as lead tetraethyl and i'ron carbonyl may not be objectionable, the use of high concentrations has certain recognized disadvantages, such as valve corrosion and spark plug fouling, for example. Moreover, because of such disadvantages, many consumers limit the concentration -of such antiknock agents to certain maximum figures, for example, 3 cc. of lead tetraethyl per gallon. Even if the concentration of such antiknock agent were not limited by specifications, the maximum octane number which can be obtained therewith in the final fuel is limited largely by the octane number of the fuel without the antiknock agent This blending is objectionable present, since it is well known that the first increment of such antiknock agent added gives the major octane number increase and further increments result in progressively smaller increases in octane number. Upon the continued addition of increments of such antiknock agent, eventually a point is reached, around to octane numbers higher than that of the base fuel, at which further addition thereof is either without appreciable effect or is at least entirely uneconomical.

Thus, from the foregoing considerations it may be readily seen that the problem of increasing the antiknock value of such base fuels as those consisting essentially of branched chain paraflln hydrocarbons, such as hydrogenated polymers obtained by polymerization and hydrogenation and alkymers obtained by alkylation, which themselvesinitially have an unusually high antiknock value, and at the same time obtaining a motor fuel having the desired distillation characteristics, is an exceedingly difficult one. This problem is especially acute in the field of aviation gasolines where antiknock values of 100 octane number and well above are now being demanded. As a result of the limitations described above, the fuel manufacturer is forced to maintain high octane number values not only on his commercial iso-octane but also on his more volatile blending stock. However, even with the most careful expensive controls to obtain high antiknock standards both on the base fuel and on the volatile blending stock, the result, especially with regard to the simultaneous attainment of the required antiknock value and distillation curve, is not as satisfactory as is desired.

I have now discovered that certain low-boiling esters are especially suited for blending with high octane motor fuels consisting essentially of branched chain paraffin hydrocarbons to increase the antiknock quality of such fuels. Not only do these esters give an unexpectedly high increase in antiknock value to these motor fuels, which initially have an unusually high'antiknock value, but also at the same time many of them aid in producing a motor fuel having the desired volatility or distillation characteristics and reduce, and in some cases even eliminate, the proportion of volatile constituent which have an adverse effect on or, fail to improve the antiknock value,

.such as natural gasoline or isopentane, which proportion is otherwise required to be blended with the base fuel to produce a fuel having the desired volatility or distillation characteristics.

The esters which may be used according to this invention are the saturated aliphatic esters of monocarboxylic acids, the esters containing from three to seven carbon atoms per molecule and boillng over the range from' 130 to 300 F. Examples are methyl acetate, methyl propionate, methyl normal butyrate, methyl isobutyrate,

, methyl valerate, methyl caproate, ethyl formate,

cule are preferred, the esters containing three carbon atoms per molecule may be used where higher volatility is desired and relatively high water solubility and low heat of combustion are not undesirable, and esters containing six to seven carbon atoms per'molecule may be used where relatively low water solubility and a high heat of combustion are desirable and relatively low volatility oifers no problem.

The branched chain paraflln stocks used as base fuels, according to this invention, comprise those branched chain parafiins containing from five to twelve carbon atoms per molecule. amples are 3-m'ethyl pentane, 2,3-dirnethyl pentane, 2,4-dimethyl pentane, 2,2,3-trimethyl butane, 2,2-dimethyl hexane, 2,5-dimethyl hexane, 2,2,4-trimethyl pentane, 2,2,3-trimethyl pentane, 2,3,4-trimethyl hexane, 2,2,4-trimethyl hexane, 2,3,5-trimethyl heptane, neohexane, and 2,2-dimethyl butane. These compounds are at present made by hydrogenation of the polymers usually obtained by the polymerization of normally gaseous olefinic hydrocarbons or made by the alkylation of isoparafflns with normally gaseous oleiinic hydrocarbons. However, the invention embraces the branched chain paraifin hydrocarbon compoundsv themselves and is not restricted to any specific method of their manufacture. Thus, al-.

though these stocks are frequently referred to as hydrogenated stocks for convenience, the base fuels may be made by reactions involving no hydrogenation step. For example, a suggested above, theproducts obtained by alkylation of isobutane and isopentane with propylene, normal butenes, and isobutene in thepresence of sulfuric acid or aluminum chloride catalysts, are included within the scope of this invention. Furthcrmore, this invention embraces the addition of the esters to any one, or a mixture of any two or more, of these branched chain paraffin hydrocarbon compounds containing from five to twelve carbon atoms per molecule. It is especially signiflcant that the best results are obtained when the branched chain base fuel has an octane number of at least about 85 and may have an, octane number much higher, as high as 100 in the case of 2,2,4-trimethyl pentane, for example, or above 100 in the case of some of the other pure branched chain paraflin hydrocarbons. T

Furthermore, although I have found that branched chain parafiln hydrocarbons as a class give good results when in admixture with esters in accordance with this invention, thebest recontaining four-and five carbon atoms per molesuits are found to be obtained when the base fuel contains substantial proportions of branched by hydrogenation or the processes of .alkylation mentioned above, the distinguishing characteristics of which branched chain parafl'ln hydrocarbons are that the .degree of branching is high, as indicated by the relatively high antiknock value of the base fuel. 'Such hydrocarbons as 2,4-dimethyl pentane, 2,2,3-trimethyl butane, 2,2,4-trimethyl pentane, 2,2-dimethyl hexane, 2,2,4-trimethyl hexane, and 2,3,5-trimethyl heptane illustrate what is meant by hydrocarbons having a relatively high degree of branching. Such branched chain parafllns have at least two or three or more side branches, and the greater the number of carbon atoms in general the greater the number of side chains from the main straight chain. Such branched chain parainns having a high degreeof branching in the mole- Specii'lc exor in mixtures thereof if desired, to obtain a compound havinga high antiknock value when' blended with esters in accordance with this invention.

The proportion of esters added to the base fuel consisting essentially of branched chain paramn hydrocarbons will depend on the octane number and volatility or distillation characteristics desired and should be such that the ester comprises 10 to 50 per cent by volume of the finished fuel. Proportions lower than 10 per cent may, of course, be used but I find that the blending octane numbers increase, in general, with increasing concentration, and the preferred improvement is not reached until about 10 per cent of the ester has been added. Blends containing proportions higher than 50 per cent may be used to obtain a high antiknock value, but are undesirable for some purposes because of the resulting relatively low heats of combustion of such final blends.

The hydrocarbon component comprising 50 to 90 per cent of the finished fuel may be made.

up entirely of branched chain paraffln hydrocarbon stocks as described above, or entirely of one or more of the branched chain paraffin hydrocarbons also described above, or it may also contain substantial proportions, for example 10 to 50 per cent, of volatile blending stocks such as natural gasoline. blending stock for this purpose is isopentane. Moreover, the high antiknock fuel of my invention may, of course, be blended with other motor fuels in the usual manner. v

In order toillustrate the invention, examples of motor fuels made up in accordance therewith and data obtained from tests made thereon are given in Table I below: I

TABLE I Base fuel-commercial iso-octane Oct. No. Vol. Blending Ester of base ester in oct. No

fuel blend of ester Methyl acetate 4 90.0 93.8 25 105.2 D 90.0 99. 7 50 109. 4 Ethyl l'ormate 90.0 92.9 25 101.0 Ethgl acetate.-- 90.0 94. 9 25 109.6 90. 0 100+ 50 110+ Isopropyl l'ormate. 90. 0 93. 9 25 105. 6 0 90.0 100 50 110.0 Isopropyl acetate 90. 0 94. 8 25 109. 2 0 90. 0 100+ 50 110+ Ethyl propionate. 90. 0 94. 8 25 109. 2 o 90.0 100+ 50 110+ Secondary butyl acetate. 90. 0 93. 6 25 104. 4 Do 90. 0 97. 9 60 105. 8 Tertiary butyl acetate-.- 90. 0 90. 2 .25 102. 8 Do 90.0 97.8 50 105.8

In Table I are given the octane number of the base fuel, the octane number of the blend, the volume per cent of ester in the blend, and the "blending octane number of the ester. The "blending octane number of the ester" is obtained by multiplying the difierence between the octane number of the blend and the octane number of A particularly suitable volatilemended by the Cooperative Fuel Research Committee of the American Society for Testing Materials.

It'is apparent from the results set forth in Table I that by means of a mixture of branched chain paraffln hydrocarbons and saturated aliphatic esters of monocarboxylic acids as disclosed herein, motor fuels may be obtained having antiknock values higher than any heretofore known for such base fuels. In each case in Table I the blending value is above 100 for 25 volume per cent of the ester and, in each case where a test was made with per cent, the blending value for 50 per cent was greater than for 25 per cent, showing that the susceptibility of the branched chain paraffin hydrocarbons to increase in anti-knock value by the ester added increases with the proportion of ester added. In other words, the blending octane numbers of these esters increase with increasing concentration. Thus, from the data here given it is seen that such a. fuel containing a large proportion of such ester has a very high anti-knock value, and its anti-knock value is higher than any known for such a base motor fuel. This is especially true of ethyl acetate and ethyl propionate. Moreover, blending such esters with branched chain paraffln hydrocarbons having anti-knock value well above 90.0 octane number, as high as 100 as for 2,2,4-trimethyl pentane, for example, or even above 100, will give still higher antiknock value. No figures can be given to indicate the octane number of these fuels having an anti-knock value above 100 octane number, be-

cause no test has been devised for compounds v creased by the addition of a small concentration of such a metallo-organic anti-knock agent as lead tetraethyl.

The examples in Table I are cited to illustrate the effect of the'esters on anti-knock value.

Although the compounds blended as indicated in Table I may be used as motor fuels, usually the addition of some isopentane,- natural gasoline, or the equivalent, is required in order to meetthe usual gasoline boiling point specifications, the

although each of the specific examples given in Table I above indicates the use of a single ester, two or more esters may be added to the base fuel, and such compositionsare included in this invention. Furthermore, as indicatedabove, one branched chain paraffin hydrocarbon component of the base fuel may be used alone or a mixture of these components thereof may be used.

Results obtained from tests on representative esters indicate that, although 'an increase in.

Tests II Oct. No. Vol. B Ester Base fuel of base gfi' m ester a cot. No fuel V blend of actor Ethyl acetate Commercial lac-octane 90.0 94. 9 25 109. 6 Do Stanavo base 76.3 80.8 25 94.3

Commercial 1mm 90.0 1 100+ so 1 110+ Unhydrogenated polymers 80. 3 89. 5 50 98. 7 Stanavo base I 76.8 91. 7 60 106.6

Secondary butyl acetate Commercial iso-octane 90. 0 93. 6 25 104. 4

Do Stanavo base 76. 3 82 4 25 100. 7

1 These values are indefinitely higher than the values given because of the impossibility of measuring octane number of the blend where the value is above 100.

In Table II above the gasoline designated Table II when the esters of this invention are added to gasolines having an anti-knock 'value' above about 85 and consisting essentially of branched chain paraflln hydrocarbons, the antiknock value increase is surprisingly high as compared with the increase found for other gasolines having a relatively high anti-knock value of 75 to about 85 and not consisting essentially of branched chain paramn hydrocarbons- Table II above'also indicates that the esters as disclosed are effective in base fuels other than those in which they give such unusualresults, and this invention therefore comprehends the novel-blends of such esters with other base fuels to increase the anti-knock value thereof.

Although one of the objects of the invention 40 is to provide high octane fuels containing little or no metallo-organic anti-knock agent, I have found that the blends herein described are readily The 20 susceptible to further improvement in octane number by addition of such an agent as lead tetraethyl. Thus, with the addition of a relatively small quantity of such metallo-organic anti-knock agents as lead tetraethyl extremely high anti-knock values can be obtained. It will therefore be understood that motor fuels with or.

without such metallo-organic anti-knock agents are embraced by .this invention.

The term metallo-organic anti-knock agen 'f. is used herein with the intention that it include those organic compounds of metals, especially 5 the metallo-alkyl compounds such as the well It is to be understood specific m branched chain paraffin hydrocarbons,

esters, and certain prcportionsof the comm.

ents of my new motor fuel have been disclosed fo the purpose of illustration, my invention is not to be limitedthereby but includes' all modifications.

therenf the scope of the appended claims high antiknock motor fuel comprising a motor mel-hy'drocarbons of the type produced by the alkylation of isoparafflns with normally. gaseousjoi'e'flns and a-sufllcient proportion of isoapropyl formate effective to increase substantially Intiknock value of. said base fuel.

/ consisting essentially of isoparafllnic. 7

2. A high antiknock motor fuel comprising a base fuel consisting essentially of isoparafllnic motor fuel hydrocarbons of the type produced by the alkylation of isoparamns with normally gaseous oleflns and from about 10 to about by volume of isopropyl formats to increase substantially .the antlknock value of said base fuel.

3. A high antlknock motor fuel as defined in claim 1 in which said base fuel consisting essentially of isoparamnic motor fuel hydrocarbons has an antilmock value of at least about octanenumber without said isopropyl formate.

4. A high antiknock motor fuel having an antiknock value above octane number comprising a base fuel consisting essentially of isoparafllnic motor fuel hydrocarbons of the type produced .by the alkylation of isoparaflins with normally gaseous olefins and a sufficient proportion of isopropyl formate effective to increase the antiknock value of said base fuel to above 100.

6. A high antiknock motor fuel comprising a base fuel consisting essentially of isoparafllnic motor fuel hydrocarbons of the type produced by the alkylation of isoparafllns with normally gaseous ole'flns and a suflicient proportion of methyl acetate effective to increase substantially the anti-knock value of said base fuel.

7. A high antiknock motor fuel comprising a base fuel consisting essentially of 'isoparafflnic motor fuel hydrocarbons of the type produced by the alkylation of isoparafl'lns with normally gaseous olefins and a sufficient proportion of secondary butyl acetate effective to increasesubstantially the antiknock value of said base fuel.

8. A high antiknock motor fuel comprising a base fuel-consisting essentially of isopa'rafllnic motor fuel hydrocarbons of the type produced by the alkylation of isoparamns with normally ester selected from the group consisting of satufrated aliphatic esters of formic acid and acetic gaseous oleflns and a sufficient proportion of an acid containing three to seven carbon atoms and boiling within the range of to 300 F. effective to increase substantially the antlknock value of said base fuel.

a 9. A high antiknock aviation motor fuel com-' normally gaseous oleflns and having an antiknock value above about 85 and a sufficient pro-' portion of an ester selectedfrom the group consisting of saturated aliphatic esters of formic acid and acetic acid containing three to seven carbon atoms and boiling within the range of 130 to 300? F. effective to increase substantially the antiknocl: valuecf, said ln'tse fuel.

" 'MELVINLLHOLM.