US2228662A - Motor fuel - Google Patents

Description

Patented Jan. 14,1941

PATENT OFFICE 2,228,662 MOTOR. FUEL Melvin M. Holm, San Francisco, Cali1'., assignor to Standard Oil Company of California, San Francisco; Calif., a corporation of Delaware No Drawing. Application May 31, 1939, Serial No. 276,623

9 Claims.

This invention relates to the addition of cer-'- tain esters to motor fuels consisting essentially of branched chain parafiin hydrocarbons and having a relatively high anti-knock value to increase the anti-knock quality thereof.

One object of this invention is to make motor fuels for internal combustion engines, especially for aviation engines, which fuels have anti-knock values hitherto unobtainable without the use of relatively high concentrations of such met-alloorganic anti-knock agents as lead tetraethyl and iron carbonyl.

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

Another object is to provide motor fuels consisting essentially of branched drocarbons having anti-knock 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.

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

The unusually high anti-knock quality of the branched chain paraffin hydrocarbons, such as 2,2,4-trimethyl pent-ane for example, has'been' recognized for years, but until very recently pure branched chain paraifin hydrocarbon compounds having such relatively high anti-knock 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, '1- butene, andiso-butene into branched chain liquidolefins, which in turn may be converted to the relatively high anti-knock parafiins of corresponding structure by direct hydrogenation.

Also, more recently, these relatively high anti-' knock branched chain paraflin hydrocarbons have been produced by alkylation. Since the development of theseprocesses of polymerization.

followed by hydrogenation and of alkylatiomthe high'anti-knock relatively pure branched chain liquid paramns have become commercially available and are sold'as iso-octane or hydroctane.

.factory motor fuel,

chain parafiin hy- This iso-octane or "hydroctane" of commerce, however, even though having a relatively high anti-knock value, usually is not alone a satis-. for it is usually necessary that more volatile constituents, such as natural gasoline for example, be blended with it to make a finished fuel having the desired volatility or distillation curve, so that the fuel will have the desired characteristics relating to starting, acceleration, etc. This blending is objectionable because the avail-able, more volatile blending stocks themselves, such as natural gasoline, usually have relatively low anti-knock values, and have the effect of lowering the anti-knock value of the blend. Even relatively pure isopentane, which is probably the best available volatile blending agent fails to improve the anti-knock value of such base fuels to any appreciable extent, if at all. Thus, in view of the difilculty of increasing the anti-knock value-of such fuels while at the same time obtaining the desired volatility, it has been with regard to anti-knock value,

necessary to make up the deficiencies in octane Although the use of small concentrations of such metallo-organic anti-knock agents as lead tetraethyl an iron carbonyl may not be objectionable, the use of high concentrationshas cerdisadvantages, suchas valve corrosion and spark plug fouling, for example.

tain recognized 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 anti-knock agent were not limited by specifications, the maximum octane number which can, be obtained therewith in the final fuel is limited largely by theoctane' number of-the fuel without the anti-knockagent the first in-- present, since it is well known that crement of such anti knock agent added gives the majoroctane number increase and further 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 problemof increasing the anti-knock 'value'of such base fuels as those consisting essentially of branched chain parafiln hydrocarbons, such as hydrogenated polymers obtained by polymerization and hydrogenation and alkymers obtained by alkylation, which themselves initially have an unusually high anti-knock value, and at the same time obtaining a motor fuel having the desired distillation characteristics, is an exceedingly difilcult one. This problem is especially acute in the field of aviation gasolines where anti-knock values of 100 octane number and well above are 'now being demanded. As a result of the limitations described above, the fuel manufactureris forced to maintain high octane number values not only on his commercial isooctane but also on his more volatile blendin stock. However, even with the most careful expensive controls to obtain high anti-knock standards both on the base fuel and on the volatile blending stock, the result, especially with regard to the simultaneous attainment of the required anti-knock 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 paraflin hydrocarbons to increase the anti-knock quality of such fuels. Not only do these esters give an unexpectedly high increase in anti-knock value to these motor fuels. which initially have an unusually high anti-knock value, but also at the same time many anthem. aid in producing a motor fuel having the desired voiatib.

ity or distillation characteristics and reduce; and in some cases even eliminate, the proportion of volatile constituents which have an adverse efl'ect on or fail to improve the anti-knock 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 boiling over the range from 130 to 300 F. Ex-

amples are methyl acetate, methyl propionate, methyl normal butyrate, methyl isobutyrate, methyl valerate, methyl 'caproate, ethyl formate, ethyl acetate, ethyl valerate, normal propyl formate, isopropyl acetate, isopropyl normal butyrate, normal butyl formate, normal butyl acetate, tertiary butyl propionate, normal amyl acetate, and isohexyl formate. 4

From the point of view of the number of carbon atoms per molecule the esters containing four and five carbon atoms per molecule, such as ethyl acetate, and isopropyl acetate, are preferred since they have'a relatively low water solubility and at the same time a relatively high volatility and high heat of combustion. Although the esters containing four andfive carbon atoms per molecule are preferred, the esters containing three carbon atoms per molecule may be used-where higher The branched chain paraihn stocks used as base base fuels, according to this invention, comprise those branched chain paramns containing from five to twelve carbon atoms per molecule.

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, and 2,3,5-trimethyl heptane.

' 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 isoparailins withnormally gaseous olefinic hydrocarbons. However, the invention embraces the branched chain parafiin hydrocarbon compounds themselves and is not restricted to-miy specific method of their manufacture. Thus, although these stocks are frequently referred to as hydrogenated stocks forconvenience, the base fuels may be made by reactions involving no hydrogenation step. For example, as suggested above, the products obtained by alkylation of isobutane and isopentane with propylene, normal butenes, and isobutene in the presence of sulfuric acid or aluminum chloride catalysts, are included within the scope of this invention. Furthermore, this invention embraces the addition of the esters to any one, or a mixture of any two or more, of these branched chain paraflin hydrocarbon compounds containing from five to twelve carbon atoms per molecule. It is especially significant 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 ase of some of the other pure branched chain rafiln hydrocarbons.

Furthermore, although I have found that branched chain paramn hydrocarbons as a class in accordance with this invention, the best results are found to be obtained when the base fuel contains substantial proportions of branched chain parafiin hydrocarbons obtained asthe result of the processes of polymerization followed by hydrogenation or the processes of alkylation mentioned above, the distinguishing characterisa relatively high degree of branching. Such branched chain paraflins 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 paraillns having a high degree of branching in the molecule as indicated by the high'initial anti-knock value can be used alone as single compounds, or in mixtures Specific examples are 3-methyl pentane, 2,3-" dimethyl'pentane, 2,4-diniethyl pentane, 2,2,3-

give good results when in admixture with esters m i thereof if desired, to obtain a compound having a high anti-knock value when blended with esters in accordance with this invention.

The proportion of esters added to the base fuel consisting essentially of branched chain paraifin hydrocarbons will, depend on the actane number and volatility or distillation characteristics desired and should be such that the ester comprises 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 anti-knock value, but are undesirable for some purpose 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 paraffin hydrocarbon stocks as described above, or entirely of one or more of the branched chain parafiin 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. A particularly suitable volatile blending stock for this purpose is isopentane. Moreover, the high anti-knock fuel of my invention may, of course, be blended with other motor .fuels in the usual manner.

In order to illustrate the invention, examples of motor fuels made up in accordance therewith and dataobtained fromtests made thereon are given in Table I below:

TABLE I Base fuel-commercial iso-octane Oct.

Oct. Vol. per- Blendin Ester ig g Not of cent ester Oct. No.

fuel blend 111 blend of ester Methyl acetate. 90. 0 93.8 25 105. 2 Do 90. 0 99. 7 109. 4 50 Ethyl formate. 90. 0 92. 9 25 101. 6.

Ethyl acetate 90. 0 94. 9 25 109. 6

Do 90. 0 100+ 50 110+ Isopropyl formate 90. 0 93. 9 25 105. 6 Do 90.0 100 50 110.0 Isopropyl acetate 90. 0 94. 8 25 109. 2 Do .I 90.0 100+ 50 110+ Ethyl propionate 90. 0 94. 8 25 3095 Do 90. 0 100+ .50 110+ Secondary butyl acetate. 90. 0 93. 6 25 104. 4 Do 90. o 97. 9 50 105.8 Tertiary butyl acetate. 90. O 93. 2 25 102. 8 Do 90.0= 97.8 50 105.8

number of the anti-knock value, and its a measure of the effectiveness of the particular ester in the particular stock with which such ester is blended. The octane numbers given in Table I were obtained by the A. S. T. M.C. F. R. D357-37T method, commonly referred to as the motor method. This test is recommended 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 parafiin 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 50 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 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 paraffin hydrocarbons havinganti-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 anti-knock value. 'No figures can be given to indicate the octane number of these fuels having an anti-knock value above 100 actane number, because no test has been devised for compounds having such a high octane number; however, an indication of what the anti-knock value is can be obtained from the blending value shown in Table I above. Moreover, the anti-knock value of these blends can be still further increased by the addition of a small concentration of such a metalloorganic anti-knock agent as lead tetraethyl.

The examples in Table I are cited to illustrate the effect of the esters on anti-knock value. 41 though 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 meet the usual gasoline boiling point specifications, the amount of isopentane or natural gasoline required, however, usually being substantially less than if no ester had been added. Moreover, although each of the specific examples givenin 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 indicated above, one branched chain parafiin hydrocarbon component of the base fuel maybe used alone or a mixture of these components thereof may be used.

Resultsobtained from tests on representative tane number is obtained when-such organic compounds are added to base fuels other than those consisting essentially of branched chain araffin hydrocarbons described above, an unexpectedly and unpredictably high increase in anti-knock value is obtained with the branched chain parafesters indicate that, although an increase in ocfin hydrocarbons, as indicated by the relatively high blending values obtained therefor, which obtained for the other gasolines tested.

TABLE II for the purpose of illustration, my invention is notto be limited thereby but includes all modifications thereof within the scope of the appended claims.

Oct.

Oct. Vol. per- Blending Ester Base fuel g' y No. of cent ester Oct. No. me] blend in blend of ester Commercial iso-octane 90.0 94.9 25 109. 6 lgn lfl Stanavo ase 76. 3 80.8 25 94. 3 Commercial iso-octane 90.0 100+ 50 l fiffi Unhydrogenated polymers... 80. 8 89. 5 50 98. 7 D -3.-- Stanavo base .76. 8 91. 7 50 10 e 1 t t Commercial iso-octane 90. 0 93. c 25 104, 4 132 buty see a e Stanavo base 76.3 82.4 25 100. 7

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 commercial iso-octane is a motor fuel consisting essentially of branched chain paraffln hydrocarbons, the degree of branching of which is high, obtained as the result of polymerization and hydrogenation as mentioned above. The gasoline designated unhydrogenated polymers" consists essentially of olefin hydrocarbons and the gasoline designated "Stanavo base is a straight run gasoline. It will be clear from 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 paraflin hydrocarbons, the anti-knock valno increase is surprisingly high as compared with the increase found for other gasolines having a relatively high anti-knock value of to about 85 and not consisting essentially of branched chain paraffin hydrocarbons.

Table II above also indicates that the esters as disclosed are effective in base fuels other than those in which they give such unusual results, 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 is to provide high octane fuels containing-little or no metallo-organicanti-knock agent, I have found that the blends herein described are readily susceptible to further improvement in octane number by addition of such an agent as lead tetraethyl. Thus, with the addition ofa relatively small quantity of such metallo-organic 1 effective to increase the anti-knock value of motor fuel.

It is to be understood that, although specific branched chain paraffin hydrocarbons, specific esters, and certain proportions of the constituents of my, new motor fuel have been disclosed 2. A high anti-knock motor fuel comprising,

a base fuel consisting essentially of isopar'afiinic.

motor fuel hydrocarbons of relatively high antiknock value and a suflicient proportion of a saturated aliphatic. ester of a monocarboxylic acid having more than two and less than'eight carbon atoms per molecule and boiling within the range of 130 to 300 F. effective to increase substantially the anti-knock value of said base fuel. 3. A high anti-knock motor fuel as defined in claim 2 in which said base fuel consisting essentially of isoparafiinic motor fuel hydrocarbons has an anti-knock value of at least about octane number without said ester. Y I 4. A highanti-knock motor fuel having an anti-knock value above octane number comprising a base fuel consisting essentially of isoparafiinic motor fuel hydrocarbons having a relatively high anti-knock value anda sufficient proportion of a saturated aliphatic ester of a monocarboxylic acid having more than two and less than eight carbon atoms per molecule and boiling within therange of to 300 F. effective to increase substantially the anti-knock'value of said base fuel to above 100.

5. A high anti-knock motor fuel as defined in claim 2 containing a minor proportion of a metallo-organic anti-knock agent.

MELVIN M. HOLM.