This invention relates to unleaded aviation gasoli compositions. More particularly, this invention provid unleaded high octane aviation gasoline compositions which c achieve performance levels comparable to, if not better tha present-day aviation gasolines. Additionally, this inventi accomplishes this important advantage on an economical basi while at the same time conserving worldwide petrole resources.

While leaded aviation gasolines have perform wonderfully well in actual service for many years, pressur are being applied to eliminate use of leaded aviati gasoline. If these efforts succeed, the refining indust will be faced with the problem of trying to provide unlead aviation gasoline that performs as well as leaded aviati gasoline and that does not exceed the economic constraints the marketplace. In fact, a scientific debate exists whether it is even possible to produce an unleaded aviati gasoline comparable to the so-called 100/130 low-lead aviati gasoline now in widespread use in the United States. Whi petroleum refiners generally believe this to be possible, th also believe that the fuel will be very expensive.

When attempting to eliminate use of alkyllead antikno compounds in aviation gasoline base fuels, it is essential

provide aviation fuel compositions which not only have t requisite octane quality but additionally have the requisi heat of combustion, as this is a measure of the distance aircraft can fly before refueling. Accordingly, th invention has as its principal object the provision particular aviation fuel compositions that possess both t necessary octane quality for aviation service and the nece sary heat of combustion for aviation service. Another obje is to keep the metal content of the fuel composition as low is consistent with achieving the foregoing objectives.

This invention involves, inter alia, the discovery th it is possible to provide aviation fuels having the necessa heat content (normally expressed in terms of BTU per pound fuel) and octane quality, by use in forming the fuel appropriate proportions of aviation alkylate, a gasolin soluble dialkyl ether octane-blending agent and cyclopentadienyl manganese tricarbonyl compound. In so cases, it is desirable to also include other suitable gasoli hydrocarbon components in the finished aviation fu composition, such as isopentane, suitable aromatic gasoli hydrocarbons, light hydrocracked gasoline fractions, and/or ₆ gasoline isomerate in order to ensure that the compositi possesses the requisite combination of properties. It will appreciated therefore that the present invention is economical way of providing unleaded aviation gasolines havi the requisite octane quality and heat of combustion to satis aviation engine requirements.

In accordance with this invention, there is provided unleaded aviation gasoline composition which comprises:

(a) from 85 to 92 volume percent of aviation alkylate;

(b) from 4 to 10 volume percent (preferably about 4 to abo 8 volume percent) , of at least one ether selected fr methyl tertiary-butyl ether, ethyl tertiary-butyl ethe methyl tertiary-amyl ether, and mixtures of any two all three of the foregoing ethers;

(c) from zero to 10 volume percent of one or more oth hydrocarbons falling in the aviation gasoline boili range; and

(d) from 0.25 to 0.6 gram, more preferably, in the range about 0.4 to about 0.6 gram, and most preferably in t range of about 0.4 to about 0.5 gram, of manganese p gallon as one or more cyclopentadienyl mangane tricarbonyl compounds; wherein the sum of the amounts of (a) and (b) , and also of ( if present, is 100 volume percent; with the proviso that a that (a) , (b) and (d) , and also (c) if present, a proportioned such that said composition has (i) an ASTM D 23 heat of combustion of at least 18,000 BTU per pound (a preferably is at least 18,700 BTU per pound), and (ii) minimum knock value lean rating octane number of 100 determined by ASTM Test Method D 2700 and wherein motor meth octane ratings are converted to aviation ratings in the mann described in ASTM Specification D 910-90. An ASTM D 2382 he of combustion value of at least 18,000 BTU per pound is deem sufficient to provide the range of flight required in actu aircraft service. The preferred minimum value of 18,700 B

per pound corresponds to the requirement of the present AS Specification D 910-90.

A preferred embodiment of this invention is an aviati gasoline composition as above described further characteriz by having a minimum supercharged knock value octane number 130. In other words, the gasoline composition additionall has a minimum performance number reported to the nearest whol number and as determined by ASTM Test Method D 909 of 130. I this connection, a minimum performance number of 130 equivalent to a knock value determined using isooctane pl 1.28 milliliters of tetraethyllead per gallon.

In particularly preferred embodiments, the aviati alkylate is formed by acid-catalyzed isoparaffin-olefi alkylation wherein the butene fraction of a mixed olef feedstock is isobutene depleted — i.e., the butene fracti contains, if any, less than 30 percent of isobuten especially when a hydrofluoric acid alkylation catalyst syst is used. Preferably, less than 20% of the butene fraction o the mixed olefin feedstock to the hydrofluoric acid-catalyz alkylation process is isobutene. Another suitable approach i to use substantially pure isobutene as the olefin feedstock i the hydrofluoric acid-catalyzed alkylation process. Alterna tively, the aviation alkylate can be produced by sulfuri acid-catalyzed isoparaffin-olefin alkylation. The aviati alkylates produced in these processes typically are highl branched paraffin hydrocarbons (chiefly in the C ₇ to C ₉ rang that distill at temperatures in the range of up to 200°C a have clear octane ratings in the range of 92-96. Alkylati

processes for producing aviation alkylate are known in the a of gasoline manufacture and are referred to for example in L. Lafferty and R. W. Stokeld, Adv. Chem. Ser.. 103, 1 (1971) ; D. Putney, Advances in Petroleum Chemistry and Refi ing. Vol. 2., Interscience Publishers, a division of Jo Wiley & Sons, Inc., New York, 1959, Chapter 5; R. Dixon and Allen, Ibid, Volume 3, Chapter 6; and R. H. Rosenwal Encyclopedia of Chemical Technology, Wiley-Interscience, Thi Edition, Volume 2, 1978, pages 52-58. Each of the references is incorporated herein by reference.

In general there are two ways of producing for use aviation alkylate manufacture, a mixed olefin feedsto depleted in isobutene. One is to remove isobutene from t feedstock by physical separation procedures, such distillation. The other involves recourse to chemic separation such as by charging the feedstock to a reactor which the isobutene is selectively reacted with a low alcohol such as methanol or ethanol to produce methyl tert ary-butyl ether or ethyl tertiary-butyl ether. The remaind of the feedstock from which isobutene has been removed is r covered for use in producing the aviation alkylate. F further details concerning the processing useful selectively reacting isobutene with a lower alcohol to fo the ether, reference may be had, for example, to U. 4,528,411; 5,243,090; 5,024,679 and E.P. 390,596 A2, each which is incorporated herein by reference.

As noted above one or more other hydrocarbons falling the aviation gasoline boiling range can be (but need not b

present in the aviation fuel compositions, provided that t finished fuel blend has the combination of lean value octa quality and heat of combustion content required by th invention. Thus, for example, the fuel blend may contain to about 10 volume % of aromatic gasoline hydrocarbons, least a major proportion of which are mononuclear aromatic h drocarbons such as toluene, xylenes, the mesitylenes, eth benzene, etc. Other suitable optional gasoline hydrocarb components that can be used in formulating the aviation fue of this invention include isopentane, light hydrocrack gasoline fractions, and/or C ₅ . ₆ gasoline isomerate.

Preferred aviation fuel compositions of .this inventi are further characterized by having: a) a copper strip corrosion as determined by ASTM Te Method D 130 of number 1, maximum; b) a potential gum (5-hour aging gum) as determined by AS Test Method D 873 of 6 mg per 100 mL maximum, or potential gum (16-hour aging gum as determined by AS Test Method D 873) of 10 mg per 100 mL; c) a sulfur content as determined by ASTM Test Method D 12 or D 2622 of 0.05% by weight maximum; d) a freezing point as determined by ASTM Test Method D 23 of -72°F maximum; and e) a water reaction as determined by ASTM Test Method D 10 wherein the volume change, if any, does not exceed ± mL.

Another embodiment of this invention provides the meth of operating a four stroke cycle, reciprocating pist

aircraft engine which comprises providing or using as the fu for said engine a gasoline composition of this invention.

Still another embodiment of this invention provides, combination, at least one four stroke cycle, reciprocati piston aircraft engine and at least one fuel storage ta operatively connected with said at least one engine so as deliver fuel required to operate said engine, said at lea one fuel storage tank containing a gasoline composition this invention as the fuel for said engine.

Cyclopentadienyl manganese tricarbonyl compounds whi can be used in the practice of this invention inclu cyclopentadienyl manganese tricarbonyl, methylcyclopentadien manganese tricarbonyl, dimethylcyclopentadienyl mangane tricarbonyl, trimethylcyclopentadienyl manganese tricarbony tetra ethylcyclopentadienyl manganese tricarbony pentamethylcyclopentadienyl manganese tricarbonyl, ethylcycl pentadienyl manganese tricarbonyl, diethylcyclopentadien manganese tricarbonyl, propylcyclopentadienyl mangane tricarbonyl, isopropylcyclopentadienyl manganese tricarbony tert- butylcyclopentadienyl manganese tricarbonyl, octylcycl pentadienyl manganese tricarbonyl, dodecylcyclopentadien manganese tricarbonyl, ethylmethylcyclopentadienyl mangane tricarbonyl, indenyl manganese tricarbonyl, and the lik including mixtures of two or more such compounds. Preferr are the cyclopentadienyl manganese tricarbonyls which a liquid at room temperature such as methylcyclopentadien manganese tricarbonyl, ethylcyclopentadienyl mangane tricarbonyl, liquid mixtures of cyclopentadienyl mangane

tricarbonyl and methylcyclopentadienyl manganese tricarbonyl mixtures of methylcyclopentadienyl manganese tricarbonyl a ethylcyclopentadienyl manganese tricarbonyl, etc. Preparatio of such compounds is described in the literature, for example U.S. 2,818,417, disclosure of which is incorporated herein i toto. The aviation fuels of this invention will contain amount of one or more of the foregoing cyclopentadien manganese tricarbonyl compounds sufficient to provide t requisite octane number and valve seat wear performan characteristics.

In another preferred embodiment the unleaded gasoli composition additionally contains at least one antioxidant i an amount not in excess of 8.4 pounds per 1000 barrels, sai antioxidant being selected from the group N,N'-diisopropyl-p phenylenediamine, N,N'-di-sec-butyl-p-phenylenediamine, 2,4 dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol 2, 6-di-tert-butylphenol, a mixture of 75% minimum 2,6-di-tert butylphenol plus 25% maximum di- and tri-tert-butylphenol; an a mixture of 75% minimum di- and triisopropyl phenols plus 25 maximum di- and tri-tert-butylphenol. Most preferably th amount of such antioxidant does not exceed 4.2 pounds per 100 barrels.

It is to be understood that the fuels of this inventio are unleaded in the sense that a lead-containing antiknoc agent is not deliberately added to the gasoline. Trac amounts of lead due to contamination of equipment or li circumstances are permissible and are not to be deeme excluded from the practice of this invention.

Other components which can be employed, and under certa circumstances are preferably employed, include dyes which not contribute to excessive induction system deposit Typical dyes which can be employed are 1, dialkylaminoanthraquinone, p-diethylaminoazobenzene (Col Index No. 11020) or Color Index Solvent Yellow No. 107, meth derivatives of azobenzene-4-azo-2-naphthol (methyl derivativ of Color Index No. 26105) , alkyl derivatives of azobenzene- azo-2-naphthol, or equivalent materials. The amounts us should, wherever possible, conform to the limits specified ASTM Specification D 910-90.

Fuel system icing inhibitors may also be included in t fuels of this invention. Preferred are ethylene glyc monomethyl ether and isopropyl alcohol, although materia giving equivalent performance may be considered acceptable f use. Amounts used should, wherever possible, conform to t limits referred to in ASTM Specification D 910-90.

In accordance with other preferred embodiments th invention further provides: A) The method of operating a four stroke cycle, r ciprocating piston aircraft engine which compris operating said engine on, providing to said engin and/or using in said engine, a gasoline composition this invention; and

B) Apparatus which comprises in combination (i) at least o four stroke cycle, reciprocating piston aircraft engin and (ii) at least one fuel storage tank operative

connected with said at least one engine so as to delive fuel required to operate said engine, said at least on fuel storage tank containing a gasoline composition o this invention as the fuel for said engine.

Aviation engine lubricating oils meeting the requirement necessary for such usage are available as articles of commerc from a number of well known suppliers of formulate lubricating oil compositions. A few commercially availabl aviation lubricating oils suitable for use in accordance wit various manufacturers' specifications include Mobil AV 1 20W 50 aviation oil available from Mobil Oil Company; Phillips 6 X/C 20W-50 aviation oil available from Phillips Petroleu Company; and a line of aviation oils sold under the Aeroshel trademark of Shell Oil Company such as Aeroshell 15W-5 multigrade aviation oil, Aeroshell W100 SAE 50 aviation oi and Aeroshell W80 aviation oil.

Alkyl ethers, such as methyl tertiary butyl ether (MTBE) , ethyl tertiary butyl ether (ETBE) , tertiary amyl methyl ethe (TAME) , etc. , which can be used as blending agents in moto gasolines in order to improve octane quality possess substantial drawback when used in conventional unleade aviation base fuel. This results from the fact that if use in amounts such as 15 volume % in an aviation base fuel (th amount required to achieve a substantial increase in octan quality in the absence of an antiknock agent) , the heat con tent of the resultant fuel is reduced to such an extent tha it is not only below the ASTM standards for 100/130 grad aviation gasoline, but less than 18,000 BTU/lb as well. Thi

in turn means that the use of the ether at these levels su stantially reduces the range of the aircraft, which obvious is a most undesirable result.

Despite the foregoing shortcoming of the ether blendi components, a feature of this invention is the excelle cooperation which exists among the ether, the aviati alkylate and the cyclopentadienyl manganese tricarbon compound used as essential ingredients in producing t aviation fuel. Pursuant to this invention, amounts of su alkyl ethers of up to about 10 volume % are used in t aviation fuel composition without fear of diminishing t range of the resultant aviation fuel, this result being due the copresence in the fuel composition of the cyclopentadien manganese tricarbonyl compound and the aviation alkylate. other words, the alkyl ether, the aviation alkylate and t cyclopentadienyl manganese tricarbonyl work together concentrations of 5-10 volume % of the ether in the aviati fuel to provide a finished aviation fuel which possesses t heat content necessary to satisfy the 18,000 BTU/lb lev required pursuant to this invention (and preferably t current ASTM specification level of 18,700 BTU/lb as well and at the same time possesses the octane quality necessary satisfy the performance requirements of the aircraft engin

Presented in Table I are the heat contents and octa qualities of typical individual blending components such are utilized in forming the finished fuels of this inventio In each case, the properties shown for the individual blendi component are those possessed by the component when utiliz in the absence of any other component or additive.

Table I

In particular, the data in Table I show that the onl component thereof having the requisite heat content to satisf requirements of ASTM D 910 is the aviation alkylate. On th other hand, its octane quality is insufficient. The thre ether blending agents have good octane qualities, but poo heat contents. The toluene, which exemplifies aromati gasoline components, has a poorer heat content than th aviation alkylate, although it is still better than the hea contents of the ethers, and the octane quality of the toluen is not substantially better than that of the aviatio alkylate.

When preparing the multicomponent blends of thi invention, it is important to employ the components in th proper proportions in order to achieve the requisit properties such as described above. This is illustrated b the data in Table II which show the octane qualities and hea contents of three different fuel blends not of this invention Fuel X is a blend of 50 volume % of a commercially-availabl aviation alkylate gasoline, 30 volume % of MTBE, and 20 volum % of toluene. Fuel Y is composed of the same components i

the respective volume % proportions of 60, 30, and 10 %. Fuel Z, the same three components are in the proportions 75, 15, and 10 volume %, respectively. Table II also presen the specification values set forth in the latest version ASTM D 910. Each fuel blend contains 0.3 grams of mangane per gallon as methyl cyclopentadienyl manganese tricarbony

Table II

It will be seen from Table II that none of the fuels achieve the desired combination of properties at the level of methy cyclopentadienyl manganese tricarbonyl used.

The following Comparative Examples set forth laborator test data which further illustrate the difficulties that wer encountered in seeking to achieve the objectives of thi invention using combinations of the aviation alkylate, th ether, and the cyclopentadienyl manganese tricarbonyl, with o without auxiliary gasoline hydrocarbons. In these Comparativ Examples all percentages are by volume.

COMPARATIVE EXAMPLE A

Blends are formed from 85% Chevron aviation alkylate fro the Pascagoula, Mississippi refinery having a heat content o approximately 19,100 btu/lb, 5% of MTBE, 10% toluene, an methylcyclopentadienyl manganese tricarbonyl (MCMT) in amount equivalent to 0.3 , 0.4, and 0.5 grams of manganese per gallon

The actual heat content of the fuels (ASTM D 2382) was foun to be 18,700 BTU/lb. The lean rating octane numbers wer 96.3, 97.1 and 97.9 at the three respective manganese levels

COMPARATIVE EXAMPLE B Blend are formed from 92% of the same Chevron aviatio alkylate as used in Comparative Example A, 8% of MTBE an methylcyclopentadienyl manganese tricarbonyl (MCMT) in amount equivalent to 0.3, 0.4, and 0.5 grams of manganese per gallon The actual heat content of the fuels (ASTM D 2382) was foun to be 18,763 BTU/lb. The lean rating octane numbers wer 96.7, 97.8 and 99.2 at the three respective manganese levels

COMPARATIVE EXAMPLE C Blends are formed from 90% of the same Chevron aviatio alkylate as in Comparative Example A, 5% of MTBE, 5% toluene and methylcyclopentadienyl manganese tricarbonyl (MCMT) i amounts equivalent to 0.3, 0.4, and 0.5 grams of manganese pe gallon. The actual heat content of the fuels (ASTM D 2382 was found to be 18,781 BTU/lb. The lean rating octane numbe were 96.2, 97.7 and 98.6 at the three respective manganes levels.

COMPARATIVE EXAMPLE D Blends are formed from 90% of the same Chevron aviatio alkylate as in Comparative Example A, 10% of MTBE, and MCMT i amounts equivalent to 0.3, 0.4, and 0.5 grams of manganese pe gallon. The actual heat content of the fuels (ASTM D 2382 was found to be 18,702 BTU/lb. The lean rating octane numbe were 97.3, 98.2 and 99.1 at the three respective manganes levels.

The test results of Comparative Examples A-D abo indicate that although the heats of combustion were sa

isfactory, more than 0.6 gram of manganese per gallon as MCM would be necessary to achieve the 100 lean rating octan number in the fuel blends therein described.

COMPARATIVE EXAMPLE E

A blend is formed from 90% of Chevron aviation alkylat from the Pascagoula, Mississippi refinery produced from a isobutene-depleted butene feedstock to the alkylation unit 10% of MTBE, and MCMT in amount equivalent to 0.3 gram o manganese per gallon. The actual heat content of the fue (ASTM D 2382) was found to be 18,671 BTU/lb. The lean ratin octane number of this fuel was 99.6.

The heat of combustion of the fuel of Comparative Exampl E was satisfactory, albeit slightly below the AST Specification 910-90 minimum value of 18,700 BTU/ lb. I fact, on the basis of the test work reported herein, sligh adjustment in the makeup of the base fuel of used in that fue composition (e.g., use of a slightly higher amount of th alkylate and slightly less MTBE, or alternatively, replacemen of the MTBE by ETBE) would enable its heat of combustion to b raised to reach this specification level. Likewise the lea rating octane number of the fuel of Comparative Example E wa close to the target value of 100. As will be seen fro Example 1 hereinafter, the presence of slightly more than 0. gram of manganese per gallon as MCMT enables this particula fuel to reach the target 100 octane value.

COMPARATIVE EXAMPLE F

Blends are formed from 85% of the same Chevron aviati alkylate as used in Comparative Example E, 5% of MTBE, a MCMT in amounts equivalent to 0.3, 0.4 and 0.5 grams manganese per gallon. The actual heat content of the fue (ASTM D 2382) was found to be 18,724 BTU/lb. The lean rati octane numbers were 98.1, 99.1 and 99.7 at the thr respective manganese levels.

From Comparative Example F it is seen that the heat combustion achieved the target value, and that the inclusi in this fuel of suitable amounts of MCMT in the range of abo

0.5 and up to 0.6 gram manganese per gallon would provide t target 100 lean rating octane number.

EXAMPLE 1 Blends are formed from 90% of the same Chevron aviati alkylate as used in Comparative Example E, 10% of MTBE, a MCMT in amounts equivalent to 0.4 and 0.5 grams of mangane per gallon. The actual heat content of the fuels (ASTM 2382) was found to be 18,671 BTU/ lb. The lean rating octa numbers were 99.8 and 101.6 at the respective mangane levels. The base fuel blend without the MCMT had a le rating octane number of 95.9.

EXAMPLE 2

Blends are formed from 92% of the same Chevron aviati alkylate as used in Comparative Example E, 8% of MTBE, a

MCMT in amounts equivalent to 0.4 and 0.5 grams of mangane per gallon. The actual heat content of the fuels (ASTM

2382) was found to be 18,767 BTU/ lb. The lean rating octa

numbers were 100.9 and 104.0 at the respective manganes levels. The base fuel blend without the MCMT had a lea rating octane number of 95.0.

EXAMPLE 3 Blends are formed from 90% of the same Chevron aviatio alkylate as used in Comparative Example E, 5% of MTBE, 5% o toluene, and MCMT in amounts equivalent to 0.4 and 0.5 gram of manganese per gallon. The actual heat content of the fuel (ASTM D 2382) was found to be 18,823 BTU/lb. The lean ratin octane numbers were 99.9 and 101.6 at the respective manganes levels. The base fuel blend without the MCMT had a lea rating octane number of 94.3.

EXAMPLE 4

The gasoline compositions of Examples 1-3 wer additionally subjected to supercharge ratings in accordanc with ASTM Test Method D 909. The supercharge performanc numbers (SPN) of these fuels reported to the nearest whol number are set forth in Table III.

Table III

It can be ^' seen from the foregoing that in one of i preferred forms this invention provides an unleaded aviati gasoline composition which comprises a blend of from 85 to 92 by volume of aviation alkylate gasoline, from 4 to about 1 by volume of a gasoline-soluble dialkyl ether gasoli blending agent, from about 0.25 to about 0.6 grams manganese per gallon as at least one cyclopentadien manganese tricarbonyl compound, and optionally up to about 1 by volume of other gasoline hydrocarbons with the proviso th said gasoline composition possesses at least the octane qual ties and heat contents called for by ASTM Specification D 91 90.

Other suitable fuel compositions of this invention wi now be readily apparent to those skilled in the art from consideration of the foregoing disclosure.

This invention is susceptible to considerable variatio

Thus it is not intended that this invention be limited by t

specific exemplifications set forth hereinabove. Rather wh is intended to be covered is the subject matter within t spirit and scope of the ensuing claims.