CA2185652A1

CA2185652A1 - Cleaner burning and cetane enhancing diesel fuel supplements

Info

Publication number: CA2185652A1
Application number: CA002185652A
Authority: CA
Inventors: George A. Olah
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-03-16
Filing date: 1995-03-14
Publication date: 1995-09-21
Also published as: EP0750658A1; EP0750658A4; AU1997395A; WO1995025153A1; JPH09510483A

Abstract

Symmetrical or unsymmetrical dialkyl and dicycloalkyl ethers, or alkyl-cycloalkyl (polycycloalkyl) ethers containing a total of 2 to 24 carbon atoms in which the oxygen atom is attached to primary or secondary, but not to tertiary carbon atoms are cleaner burning and cetane enhancing supplements for diesel fuels. The ether supplements are added in an amount of about 0.5 to 5 % v/v. Cetane numbers can be further enhanced by adding 0.05 to 0.5 % by weight of an alkyl or dialkyl peroxide compound having one to 12 carbon atoms in the alkyl group.

Description

2 1 8 !~65 2 ~ . 150 CLEANER BTJRNING AND CETANE P~
DI~T~:T~r~ FUFT SUPPT~FMF'~ITS
TFi~l`HNIcAT~ FTT'T,n This invention relates to the use of certain ~y LLical or un~y -tLical dialkyl ethers, dicycloalkyl ethers, or alkyl-cycloalkyl ethers containing a total of 2 to 24 carbon atoms, in combination with alkyl or dialkyl peroxides having one to 12 carbon atoms in each alkyl group, 10 as supplements to diesel fuels to provide a cleaner burning fuel with significantly decreased hydrocarbon, carbon monoxide and particulate matter emissions. These supplements also significantly enhance the cetane number of the fuel and impart other desirable properties to the fuel, such as 15 lowered pour and cloud points.
BACRGROUND ART
Diesel fuel ranks second only to gasoline as a fuel for internal combustion engines. Trucks, buses, tractors, 20 locomotives, ships, power generators, etc. are examples of devices that use diesel fuel. Passenger cars are another area of potential growth f or the use of diesel engines that can provide improved fuel efficiency.
Unlike gasoline engines which operate by spark 25 ignition, diesel engines employ compression ignition. In order to avoid long ignition delays resulting in rough engine operation, as well as to minimize misfiring and uneven or incomplete combustion which results in smoke in the exhaust gases that causes a major environmental problem, it is highly 30 desirable to improve the burning quality of diesel fuels to m;nim; ~e environmental pollutants such as hydrocarbons, carbo r~nn~ le, particulate matters, etc. The cetane number (CN) is used to rate the ignition properties of diesel fuel6. In general the cetane number depends primarily on its 35 hydrocarbon composition. Saturated hydrocarbons, particularly those with straight, open chains, have -2t ~`565~
WO 9~/25153 r~ 50 relatively high cetane numbers, whereas unsaturated hydrocarbons have relatively low cetane numbers.
It is nerPc~-cAry to rP~ AJn; 7e that the relationship between the CN of diesel fuel and its performance cannot be 5 eciuated in any way to the octane number of a gasoline and its performance in a spark-ignition engine. Raising the octane number allows an increase in the ~s~ion ratio and thus provides increased power and fuel economy at a particular fuel load. In contrast, in diesel engines, the desired CN
l0 provides good ignition at high loads and low al A~Aric t~:."~e, cltur.~. High cetane fuels eliminate engine roughne66 and diesel knock, allow engines to be started at lower temperatures, provide f aster engine warm-up without misf iring or producing smoke and reduce formation of harmful deposits.
15 On the other hand, too high cetane fuels can result in incomplete combustion and exhaust smoke due to too brief of an ignition delay which does not allow proper mixing o~ the fuel and air.
Commercial diesel fuels have CN numbers of at least 20 40. The suitable diesel fuel has appropriate volatility, pour and cloud point, viscosity, gravity, flash point and contain only small but tolerable levels of sulfur. It i6 al60 significant that carbon, residue formation and ash content should be kept low.
To enhance the properties of diesel fuels, particularly during ignition, cetane improvers are usually added. These c ' are typically aliphatic nitrates, such as isooctylnitrate. The stability, corrosiveness and toxicity of these or other multi-purpose additives are major 30 issues. During winter in cold areas, ethanol is sometime added to diesel fuels to prevent fuel line and filter freezing. However, ethanol lowers the flash point of the fuel and increases corrosion problQms.
It is known from U. s. patent 2, 221, 839 that 35 straight chain aliphatic ethers such as n-butyl ether, n-amyl ether, mono-butyl ether of diethylene glycol, etc., can be used as ign~tion accelerators for hydrocarbon fuels of the 2t 85652 W0 95/251~3 r~ 'O~ISO
c~ es~-ion ignition type. Generally, these ethers are added in an amount of as high as 50 or even 100% of the amount of the fuel. If desired, these ethers can be used by themselves as the fuel, although they are relatively more expensive.
In recent years, environmental concerns necessitate cleaner burning fuels with decreased detrimental emissions.
Diesel fuels are no exception and there is need to ~l;min;r h hydrocarbon, carbon monoxide, particulate matter, etc.
emissions. Gasoline has been formulated with additives to lo help with this problem, but nothing useful has yet been developed for diesel fuel. Despite the need for similar additives for diesel fuel, no truly efficient diesel fuel L~Jv~:Lr~ or Pnh~n--Prs have been discovered so far (See Gasoline and Motor Fuel, Kirk-Othmer Encyclopedia of Chemical 15 Technology, 3rd ed., Wiley-Interscience, New York, Vol. 11, p. 682-689, 1980) .
SUM~qARY OF TIT~ INVENTION
The invention relates to a diesel fuel which 20 contains a supplement for imparting cleaner burning characteristics to the fuel and also for Pnh~ncin-J the cetane number. This supplement comprises a dialkyl, dicycloalkyl or alkyl-cycloalkyl ether compound and an alkyl or dialkyl peroxide - _ 1 The supplement is advantageously present 25 in an amount sufficient to increase the cetane number of the diesel fuel by at least about 2 to 20 points.
Useful ethers contain 2 to 24 carbon atoms and may be symmetrical or unsymmetrical. Also, the oxygen atom is preferably attached to a primary or ~Pr~onrl~ry carbon atom.
30 R-~L ~st~ ative examples of preferred ethers include dihexyl ether, dioctyl ether, di (2-ethyl-1-hexyl) ether, ethyl hexyl ether, methyl octyl ether, ethyl octyl ether and methyl dodecyl ether. The ether compound is present in an amount of about O . 5-10% v/v, and preferably about 1-5% v/v.
The alkyl or dialkyl peroxide compound is present in an amount sufficient to further enhance the cetane number and burning properties of the diesel fuel. The alkyl or : 2 1 85652 Wo 95125153 F~l/~ ~ l50 dialkyl peroxide ollnA would generally be in present in an amount of between about 0.05 to 0.596 v/v, preferably in a ratio of between about 1/10 and 1/100 the amount of the ether ,ou.,d. Advantageously, a dialkyl peroxide which has the 5 same alkyl groups as the ether ,_ o--nA can be used.
Another ~--~QA;- I L of the invention relates to a method for improving the burning efficiency of a diesel fuel which comprises adding to the fuel an ether ~ _-lnA and a peroxide compound in an amount suf f icient to raise the cetane 10 number and impart clean burning characteristics. Any of the ether, 'R described above can be used in this method.
Although an oxygen containing gas such as air can be passed through or added to the fuel in an amount suf f icient to promote the f ormation of peroxides therein, one 15 of the alkyl or dialkyl peroxidQ _ _ ~ described above c~n conveniently be added to the fuel as a ~ of the supplement in an amount sufficient to further enhance the cetane number and burning properties of the fuel.

I have now discovered a class of cleaner burning and cetane ~nhl~nr~i n~ diesel fuel supplements. These additives are symmetrical or ul,~y Lr ical dialkyl, dicycloalkyl, or alkyl-cycloalkyl ethers which contain a 25 total of 2 to 24 carbon atoms, with the ether oxygen atom being attached to primary or secondary but not to tertiary carbon atoms. These ether compositions are thus fllnA;Ir ~ally diffsrent from the octane enhancing tertiary alkyl ethers such as MTBE. Although the carbon atoms of each 30 alkyl group can be between 1 and 12, the higher alkyl ethers, i . e., those having 4 or more carbon atoms in each alkyl group, are preferred~
Effective diesel improving higher alkyl ethers include dibutyl ether, dipentyl ether, dihexyl ether, 35 diheptyl ether, dioctyl ether, dinonyl ether, didecyl ether, methyl hexyl ether, ethyl hexyl ether, methyl heptyl ether, ethyl heptyl ether, methyl octyl ether, ethyl octyl ether, 2 1 8~652 3 ~ 0 methyl decyl ether, ethyl decyl ether, methyl dodecyl ether, ethyl dodecyl ether, hexyl heptyl ether, hexyl octyl ether, hexyl nobornyl ether, hexyl decyl ether, heptyl pentyl ether, heptyl decyl ether, octyl butyl ether, octyl pentyl ether, 5 octyl hexyl ether, octyl heptyl ether, nonyl propyl ether, nonyl octyl ether, nonyl decyl ether, decyl ethyl ether, decyl propyl ether, decyl butyl ether, decyl pentyl ether, decyl hexyl ether, decyl heptyl ether, decyl octyl ether, di (cyclopentylmethyl) ether, di (cyclopentyl-,~-ethyl~ ether, 10 di(cyclohexyl-methyl) ether, di(cyclohexyl-B-ethyl) ether and the like.
Also effective are alkyl-cycloalkyl, dicycloalkyl, alkyl bi(tri, tetra)cycloalkyl and dibicycloalkyl ethers, such as hexyl cyclohexyl ether, hexyl cycloheptyl ether, 15 hexyl cyclooctyl ether, dicyclohexyl ether, heptyl cyclopentyl ether, heptyl cyclohexyl ether, heptyl cycloheptyl ether, heptyl cyclooctyl ether, di-cycloheptyl ether, octyl cyclopentyl ether, octyl cyclohexyl ether, octyl cycloheptyl ether, octyl cyclooctyl ether, dioctyl ether, 20 di-2-norbornyl ether, di-adamantyl ether, diperhydrodicyclopentadienyl ether and the like.
Also ef f ective are the alkyl di- or polycycloalkyl ethers, as are bis (di- and poly)cycloalkyl ethers. These examples are representative but in no way limiting of the 25 types of alkyl (cycloalkyl) ethers which are effective as a - ~ ^nt of the diesel fuel supplements disclosed herein.
As noted above, the ether compound is present to the composition in an amount of about 0 . 5 to 10% and preferably l to 5% v/v/ and results in decreased particulate 30 matter emission when the fuel is combusted.
For the preparation of these ethers, the original Williamson method of ether synthesis using an alkoxide and an alkyl halide works well for acyclic 11nPnr11rnh~red open chain primary halides (see March, J. "Advanced Organic Chemistry, 35 Reactions, Merh:~n;c7nc and Structures", 3d ed., Wiley-Interscience, New York, NY, 1985.

~2 wossnsls3 21 8~ P~ 150 RO M+ + R~-X '~
M-Li+, Na, K
Dialkyl ethers are readily prepared by a variety of methods, including dehydration of the C~lLL-_`IJ~-n~;n~ alcohols with acids, incl~ inq solid acids such as NAFION(D-H or sulfonated polystyrene resins.

2ROH :~ R20 These methods are not applicable to cyclic and polycyclic systems. Bimolecular dehydration of alcohols gives the lower acyclic ethers, but generally results in complex product mixtures due to intramolecular dehydration products with higher homologs or cycloalkyl systems. In 20 spite of many diverse approaches in the literature for the synthesis of 6pecific ethers, no cogent general synthetic method6 exi6t.
Olah et al. have developed a general methyl ether synthe6i6 which employs reductive alkylation of carbonyl _ c (G.A. Olah et al., ;r.Org.Chem 1986, 51 2826). The reaction involves treatment of the carbonyl _ _--d with trimethylorthoformate or other trialkylorthoformates catalyzed by superacidic perfluorinated resin 6ulfonic acids such as NAFION~D-H, followed by reaction with triethylsilane.
30 The general reaction is C~ CH(OR)3 c~OMe Et 8 SiH ~<O~Ie - Nifion-H OMe Nafion-H H

~ WO9S/25153 2 1 ~5~2 I~~
Using the above ~ o~:e~uL ~ polycycloalkyl methyl (alkyl) ether6 are synthesized from the corr~cpr~n~;n~
carbonyl Alkyl-cycloalkyl ethers are also readily prepared 5 by acid catalyzed methanolysis (alcoholysis) of easily available olefins, such as bicyclo[2.2.2]heptene (norbornene) or cyclopropane derivatives such as Binor-S (a 4 + 4 dimer of bicyclot2.2.1~heptadiene (norbornadiene)) using for example the convenient solid superacid, Nafion~-~ (G.A. Olah et al., 10 Synthesis, 1986, 513). Many of these ethers are readily obtainable from refinery byproduct streams containing cyclopentadiene .
15 G~ ROH 3 G~OR
SACS;~r~n et al. .T.org.Chem. 1987, 5~, 4314;
20 Tetrahedron, 1988, 44, 3771 have also developed a more general ether synthesis method by direct reductive coupling of carbonyl _.-d~. Carbonyl ~ c are reductively coupled to symmetrical ethers in the presence of triethylsilane and a catalytic amount of trimethylsilyl 25 triflate or trimethylsilyl iodide.
2 ~-- M ~ < >' ~ =
Me 9Sil Using this general methodology symmetrical bicyclic and polycyclic ethers can be SYn~hPC; 7~
Ull_Y ~L ical ethers can also be prepared by 35 adopting the reductive con~ncation of carbonyl _ u--ds with alkoxysilanes WO95/2SlS3 2 ~ 856~2 E~l~ ISO
R--OTMS + Et3SiH O~R
C~ Me3Sil C=Y
R=~L~se,.l.(ltive u" i~ L, ical ethers suitable as diesel 1 _ ~V~l~ include the following:
10 G~7'~O ~'`0:, G~'`O
, ~k.
It is part of my invention that ether oxygenates 20 enhance cleaner burning properties and elevate cetane number by their ability to initiate radical proce6ses essential for ef~icient combustion. This is affected in part by their ability to form peroxides which then act as radical sources.
This effect can be ~nh:~nrecl by storing the diesel fuel ether 25 supplement blends in contact with oxygen or air or by passing oxygen or air through them.
air or lCH3(CH2)5120 ~ ~CH3(CH2)5]2 To uniformly and in a controlled way improve CNs, particularly when using smaller amounts of the ether ds, 0.05 to 0.5% by weight of an alkyl or dialkyl peroxide ~,, ,_ ' are added as part of the supplement. As 35 noted above, these peroxide . _ '~ are added in a ratio of between about 1/lO and l/100 of the amount of the ether ,_ ` . These peroxide _Il.ds preferably have alkyl ~ WO95/25153 2 1 8~652 r~ ?150 substituents of between one and 20 carbon atoms which are straight chain or branched. For the dialkyl _ -n~, the alkyl substituents can be the same or different and can be symmetric or asymmeric. Preferably, the symmetric dialkyl s peroxide .; _u~lds are preferred. The dialkyl peroxide ~ c which have the same or similar alkyl groups as the ether ~_ _-,l are advantageously used, because they are highly compatible with the ether ~ _ '~. The dialkyl peroxides, and in particular butyl, pentyl, hexyl, or octyl 10 peroxides, are stable by themselves as well as in the presence of the ether ( ~ _ u-lds . The combination results in the formation of only a very limited amount o~ insoluble gum to thus provide convenient stable diesel fuel supplements.
The new ether-peroxide diesel supplements are able 15 to significantly improve the performance of diesel fuels.
Environmental cleanness is ~nh~n~-e-l by cleaner burning and decreased generation of pollutants, i.e., smoke, particulate, incomplete burning products. At the same time, these supplements are also very efficient cetane ~nh;-nc~rs, thus 20 eliminating the need for toxic additives such as octyl nitrate .
To show that the aforementioned ether-peroxide 25 supplements provide significantly improved and cleaner burning characteristics, an emission screening test was perf ormed according to the ERA Federal Test PL u.:e.luL e specified in CFR 40, Part 86, subpart N on a prototype 1991 Detroit Diesel Corporation (DDC) Series 60 heavy duty diesel 30 engine with a typical Diesel No. 2 Fuel to which 5% (v/v) of an ether compound was added. Results are shown below in the table .
_ g _ WO95/25153 2185652 ~ . 150 --Fuel Cetane No .
A: Neat Diesel fuel No. 2 42 . 8 5A + 2% (wt) dihexyl ether 44 . 8 A + 59~ (wt) dihexyl ether 46.3 A + 2% (wt) dioctyl ether 47 . 8 A + 5% (wt) dioctyl ether 49. l A + 5% dihexyl ether +
lO0 . 5% t-butyl peroxide 59 . 6 Dihexyl ether is a highly useful ether - lt. Its boiling point is 228-229C, which makes it compatible for blending into diesel fuels. The 15 ~ddition of 2% dihexyl ether alone increases the CN of the fuel by 2 points, whereas the addition of 5%
increases the CN by 3 . 5 points .
Dioctyl ether is an even better supplement: its boiling point is 286-287C. When blended into No. 2 diesel fuel (CN 42.8), the measured engine CN increases according to the amount blended to above 49 when 5% is used, an increase of over 6 points.
The CN number is further increased in an unexpected manner by the addition of z~n alkyl or dialkyl 25 peroxide compound. As shown in the table, the addition of 0.5% of butyl peroxide to 59~ dioctyl ether increases the CN of the fuel to about 60 while maintaining good stability and f lash point .
Moreover, the hydrocarbon, carbon monoxide and soluble oil fraction of particulate matter emisGions for the last sample was reduced by 32, 14 and 38 per cent, respectively. As little as 0. 2% of the alkyl or dialkyl peroxide ~ _= ' provides an increase in cetane number without forming any appreciable amount of insoluble gum in the fuel, thus reducing particulate emissions.

Claims

THE CLAIMS

What is claimed is:

1. A clean burning diesel fuel composition comprising diesel fuel and a diesel fuel supplement comprising a dialkyl, alkyl-cycloalkyl or dicycloalkyl ether compound that contains a total of 2 to 24 carbon atoms and an alkyl or dialkyl peroxide that contains 1 to 12 carbon atoms in each alkyl group, said supplement being present in an amount sufficient to raise the cetane number and impart clean burning characteristics to the diesel fuel by reducing the amount of emission hydrocarbons.

2. The composition of claim 1 wherein the ether compound is symmetrical and the oxygen atom is attached to a primary or secondary carbon atom.

3. The composition of claim 1 wherein the ether compound is dibutyl ether, dihexyl ether, dioctyl ether, di(2 ethyl 1-hexyl) ether, or methyl dodecyl ether.

4. The composition of claim 1 wherein the ether compound is an alkyl bi(tri, tetra)cycloalkyl, dibicycloalkyl, alkyl polycyclo, or bis (di- and poly) cycloalkyl ether compound.

5. The composition of claim 1 wherein the ether compound is present in the composition in an amount of about 0.5 to 5% v/v.

6. The composition of claim 1 wherein the ether compound is present in an amount sufficient to increase the cetane number of the diesel fuel by at least about 2 points.

7. The composition of claim 1 wherein the peroxide compound is present in an amount of between about 0.05 and 0.5% v/v.

8. The composition of claim 1 wherein the peroxide compound is present in an amount of between about 1/10 and 1/100 the amount of the ether compound.

9. The composition of claim 1 wherein the peroxide, compound is a dialkyl peroxide wherein each alkyl group has at least four carbon atoms.

10. The composition of claim 1 wherein the peroxide compound is dibutyl, dipentyl, dihexyl, or dioctyl peroxide.

11. A method for improving the burning efficiency of a diesel fuel which comprises adding to the fuel a supplement comprising a dialkyl, alkyl-cycloalkyl or dicycloalkyl ether compound that contains a total of 2 to 24 carbons atoms in an amount sufficient to raise the cetane number and an oxygen containing compound in order to impart clean burning characteristics to the fuel by reducing the amount of emission hydrocarbons when the fuel is burned.

12. The method of claim 11 which further comprises selecting the ether compound to be a symmetrical or unsymmetrical dialkyl, alkylcycloalkyl or dicycloalkyl ether compound.

13. The method of claim 11 which further comprises selecting the ether compound to have the oxygen atom attached to a primary or secondary carbon atom.

14. The method of claim 11 which further comprises selecting dihexyl ether, dioctyl ether, di (2-ethyl 1-hexyl) ether, or methyl dodecyl ether as the supplement.

15. The method of claim 11 which further comprises adding the ether compound in an amount sufficient to increase the cetane number of the fuel by at least 2 to 20 points.

16. The method of claim 11 which further comprises adding the ether compound to the fuel in an amount of about 0.5 to 10% v/v.

17. The method of claim 11 wherein the oxygen containing compound comprises air or oxygen gas and which further comprises passing the air or oxygen gas through the fuel in an amount sufficient to promote the formation of alkyl or dialkyl peroxides therein.

18. The method of claim 11 wherein the oxygen containing compound is an alkyl or dialkyl peroxide compound that contains 1 to 12 carbon atoms in each alkyl group and which is added with the supplement in an amount sufficient to further enhance the cetane number and burning properties of the fuel.

19. The method of claim 18 wherein the alkyl peroxide or dialkyl compound is a dialkyl peroxide wherein each alkyl group has at least four carbon atoms and which is added in an amount of between 0.05 to 0.5%.

20. The method of claim 19 wherein the ether compound is added to the fuel in an amount of about 0.5%
to 5% v/v and the alkyl or dialkyl peroxide compound is added in an amount of between about 1/10 and 1/100 the amount of the ether compound.