US2321280A - Safety fuel - Google Patents

Description

Patented June 8, 1943 SAFETY FUEL Cecil Brown, Baton Rouge, La), assignor to Standard Oil Development Company, a corporation of Delaware Claims.

The present invention is directed to fuels for aircraft, known as safety fuels. V

Safety fuels are characterized bya high flash point, a high octane number, good volatility and gum stability. For example, a good safety fuel should have a Tag closed cup flash point of 100 F. or more, an octane number of about 100, and a boiling range of about 300-400 F. It should have also the other characteristics of good aviation gasoline, such as a good gum stability and a good breakdown test. I

The desirability of using a safety fuel has long been apparent in the aviation industry. Thus far, however, the industry has, not universally adopted any standard safety fuel, primarily because there has been no available source of supply of such fuels ata suitable price. v

It has hitherto been proposed to produce safety fuels by several methods such as the destructive hydrogenation of selected dlstillates or crudes, the extraction with sulfur dioxide of certain distillates or crudes, and thecatalytic cracking under selected conditions of such extracts The fuels produced by the first method are rather high priced due to the limited quantity of suitable raw materialsl The fuels produced by the latter two methods have so low' an initial octane number and so low a lead susceptibility that the amount of lead required to convert them into100 octane fuels makes their cost well-nigh prohibitive.

I have now found that fuels having satisfactory characteristics for safety fuels such as high initial octane number, high lead susceptibility and suitable boiling range can be produced from C4 iso-hydrocarbons. For example, the copolymerization of normal and isobutylene yields a heavy hydrocarbon fraction which, when hydrogenated,

boils between about 300 and 385 F., has ahigh flash point and a high octane number.

I have found that by cutting themixture of hydrocarbons produced by the reaction between an isoparafiln and an olefin, such as isobutane and normal or isobutylene, at about 300 F., it is possible to produce a heavy fraction having a boiling range of from about 300 to 400 F. which has .a Tag closed cup flash in excess of 100 F., a high initial octane number, and a high lead susceptibflity. A particularly desirable safety fuel, according to the present invention, is a blend of the last mentioned heavy fraction of alkylation product with hydrogenated tri-isobutylenes boil-, ing between about 330 and 380 F., with the latter constituting from 10 to 50% of the blend. These types of fuels are disclosed and claimed in No Drawing. Application December 7, 1938",

. SerialNo. 244,357

copending application Serial No." 457,947, filed July 22, 1942.

The basic materials for the safety fuels of the present invention are available in large quantities and the methods by which they are converted into the desired safety fuels are not costly. -For example, practically all refinery gases resulting fromcracking processes of various types contain substantial percentages of isobutylene and normal butylenes which can be caused to co-polymerize by being'contacted with sulfuric acid of a strength ranging from -60 to 75% at a temperature between about 175 and 250 F. This process is usually conducted with a view of producing dimer, and to this end it is customary to recycle trimer to thereaction chamber. As the result of the present inventiomthis process can be car- 'ried out with a view of producing, the highest yield per pass of high boiling hydrocarbons,

whereby 'the efficiency of the method is increased. If desired, the process can be so controlled as to produce mainly trimer by allowing the concentration of dimer to buildup in the reaction chamber.

There are large reservoirs of isobutane which can be utliized as sources of raw material for the second embodiment of the present invention. The reaction between isobutane and the olefins of refinery gases proceeds with ease at normal room temperatures in the" presence of concentrated sulfuric acid. This reaction, which yields a product containing C5+ hydrocarbons, can be made to yield a product boiling mainly within the ,safety fuel range by recycling C5 Cshydrocarbons to the reaction zone.

The fuels of the present invention do not'per se have an octane number of 100. The co-p'olymer of isobutylene and normal butylenes, Whenhydrogenated, has an octane number of about90 which can be brought to 99.5 with 3 cc. of tetraethyl lead per gallon.- Likewise, the high boiling alkylation fraction, especially when'blended with about 40% of hydrogenated triisobutylenefhas a clear octane number of abopt 90 whichtcan be raised to 100 with 3 'cc. of tetraethyl lead.

per gallon. v

The safety-fuel ofthe present invention is preferably composed entirely of the reaction product of an iSO-C4 hydrocarbon with a different C4 hydrocarbon. It may be mentioned, however, that, when the fuel is an alkylation product, it may be produced from isopentane or isohexane as well as from isobutane. Likewise, olefins other than .thebutylenes may be employed. In any 'case, the fuel, as-previously men tioned, may contain substantial quantities of hydrogenated triisobutylene. Other suitable blending agents are alkylated aromatics boiling between.300 and 400 F. Typical examples of such alkylated aromatics are ethyl benzene, propyl benzene,- isopropyl benzene, methyl ethyl benzene, o, m, p, trimethyl benzene, 1, 2, 3, trimethyl benzene 1, 2, 4, trimethyl benzene 1, 3 5, secondary butyl benzene, isobutyl benzene, tertiary butyl benzene, and methyl isopropyl hen-- zene, p.

Alternatively, a fraction boiling between 300 and 400 F. of the product resulting from the alkylation of aromatics with olefins may, be employed.

The characteristics of' typical examples of aviation safety fuel according to the present invention are given in the following table. Fuel A of this table was prepared by reacting isobutylene and normal butylene in the presence of sulfuric acid of a strength of about 70% at a temperature of 170 F., recovering from the product a fraction boiling above 300 F. and hydrogenating this fraction by contacting it with a catalyst composed of M003, ZnO and MgO at a temperature of SOD-600 F. and under a pressure of 3000 pounds per square inch in the presence of a large excess of hydrogen.

Fuel B was prepared by reacting isobutane and the isoand normal butylene in C4 reflnery cut in the presence of sulfuric acid having a strength of 98% at a temperature of 70 F. and under a pressure sufficient to maintain the reactants in the liquid state and recovering from the product a fraction having the boiling range shown in the table.

.Fuel C was prepared by blending with fuel B hydrogenated triisobutylene boiling between 330 and 358 F., the latter constituting 40% of the blend,

Fuel A Fuel B Fuel A. P. I. gravi 52 7 55.8 55. 8 Color Saybolt +19 +26 +27 Aniline point. F 182 189 Sulfur .percen t.. 0. 01 0. 02 0. 008 Doctor.-. Passes Passes Passes Corrosion cu. dish.. Passes Passes Passes ish, m s 3.6 3. 8 Acid heat... 2 1 2 Bromine No.- 3 1 2 Flash .Tag closed cup.. 112 1 Reid vapor pressure Below is! Below 1! Below 1;! Army octane number 89. 4 77. 0 85. 3 DtO. +3.0 cc. TEL 99. 5 96. 4 100 Initial F 304 323 328 319 336 336 324 341 340 336 351 347 345 357 352 352 363 355 362 373 361 Final F 384 393 385 Recovery .pcrcent. 98. 0 98. 0 98. 0 Residue .do 1.0 l. 0 l. 0

.The nature and objects of the present invention having thus been described, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. A safety fuel boiling substantially completely between about 300 and 400 F., having a flash point of at least 100 F. by'the closed cup method, composed predominantly of the parafiinic compounds formed by the reaction between isobutane and a C4 olefin and contain- 2. A safety fuel boiling substantially completely between about 300 and 400 F.,having a flash point of at least 100 F. by the closed cup method, composed predominantly of the paraflinic compounds formed by the reaction between isobutane and isobutylene, and containing sufficient antiknock agent to bring its octane number to about 100.

the closed cup method composed predominantly of saturated branched chain hydrocarbons of a the above stated boiling range which are separated from the products produced by reacting isopentane and at least one mono-olefin under alflkylating. conditions in the presence of an alkylation catalyst.

5. A safety fuel according to claim 4 in which sufficient: anti-knock agent is added to raise the octane number to about 100.

6. A safety fuel boiling substantially com-' pletely between about 300 and about 400 F. having a flash point of at least 100 F. by the closed cup method composed predominantly of saturated branched chain hydrocarbons of the herein stated boiling range and which'are separated from the product produced by reacting isopentane and at least one C4 olefin under alkylating conditions in the presence of an alkylation catalyst.

7. A safety fuel boiling substantially completely between about 300 and about 400 F. having a flash point of at least 100 F. by the closed our: method composed predominantly of sat- -urated branched chain hydrocarbons of the herein specified boiling range and which are separated from the product produced by reacting isopentane and isobutylene under alkylatlng conditions in the presence of an alkylation catalyst.

8. A safety fuel according to claim 7 in which sumcient anti-knock agent is added to raise the ing suflicient antiknock agent to bring its octane number to about 100,

octane number to about 100.

9. A safety fuel boiling substantially completely between about 300 F. and about 400 F., having a flash point'of at least F. by

the closed cup method, composed predominantlyof paraflinic reaction products of an isoparaffln taken from the groupconsisting of isobutane and isopentane and an olefin and containing sufllcient antiknock agent to bring the octane number to about 100.

10. A safety fuel boiling substantially completely between about 300 F. and about 400 F.. having a flash point of at least 100 F. by the closed cup method, composed predominantly of parafllnic reaction products of an isoparamn taken from the group consisting of isobutane and isopentane and at least one butene and containing suflicient antiknock agent to bring the octane number to about 100.

L. BROWN.