Fuel and related compositions – Liquid fuels – Heterocyclic carbon compound containing a hetero ring having...
Reexamination Certificate
2001-08-15
2003-04-01
Toomer, Cephia D. (Department: 1714)
Fuel and related compositions
Liquid fuels
Heterocyclic carbon compound containing a hetero ring having...
C044S436000, C044S437000
Reexamination Certificate
active
06540796
ABSTRACT:
The invention relates to fuels with improved ignition characteristics comprising one or more peroxides.
The use of peroxides in fuels has long been common knowledge. Back in the 1940s U.S. Pat. No. 2,378,341 disclosed the use of a peroxide of a hydrocarbon having at least one aliphatic tertiary carbon atom, the peroxy radical in said peroxide connecting two tertiary carbon atoms, while
Ind. Eng. Chem.,
Vol. 41, No. 8, pp. 1679-1682 disclosed the use of di-tert-butyl peroxide and 2,2-bis(tert-butylperoxy)butane for the purpose of improving the ignition of diesel fuels.
In 1961, U.S. Pat. No. 3,003,000 disclosed ketone peroxides and oligomeric ketone peroxides, a process to make them, and their generic use in, inter alia, diesel fuels.
Ignition improvers are desired for use in hydrocarbon distillates and residue-containing oils that are useful as fuels for combustion engines except for their ignition characteristics. Usually, such fuels suffer from a too long ignition lag, i.e., the time between the injection of the fuel into the zone of combustion, as in directly injected engines such as diesel engines, and the moment the fuel ignites, or the time between the activation of external ignition sources, such as spark plugs, and the moment the fuel ignites. As a result, poor combustion efficiency and rough engine operation are observed, with all attendant adverse consequences. The term improved ignition, therefore, means that in combustion engines fuel is burned with improved efficiency, which relates to a higher cetane number of the fuel and a reduced emission of pollutants upon combustion of the fuel in said engine. As is well-known, the use of diesel fuel with improved ignition can result in reductions of the hydrocarbon, carbon monoxide, NOx, and particulate matter (soot) emissions. Depending on the type of fuel and the type and quantity of ignition improver used, reductions of 40% of said emissions are quite feasible.
Presently used commercial products to improve the ignition of (diesel) fuels are di-tert-butyl peroxide and 2-ethylhexyl nitrate, as taught by
Chemtech,
8-97, pp. 38-41. However, these products suffer from various disadvantages. Nitrates may lead to NOx formation upon combustion, while di-tert-butyl peroxide has a low flash-point and high volatility, which can lead to various safety hazards. Nor do most peroxides possess long-term (thermal) stability in diesel fuels. Especially at higher temperatures such as can be encountered in fuel systems, decreased thermal stability can lead to gum formation or other degradation of the fuel. Also, the decomposition products of peroxides generally are (partly) alcoholic in nature, which tends to increase the undesired water uptake by the fuel. Furthermore, most of the peroxides used thus far suffer from a relatively low active matter content and a relatively poor efficiency in improving the cetane number of the fuel. In consequence, there still is a need for fuels with improved characteristics.
Surprisingly, we have found that a specific class of peroxides is very suitable for improving the ignition characteristics of fuels. Accordingly, we claim the use of such peroxides to make ignition improved fuels, as well as the fuel so obtained and the use of said improved fuel.
The fuel according to the invention is characterized in that it comprises from 0.001 to 10 percent by weight of one or more trioxepan compounds, or substituted 1,2,4-trioxacycloheptanes, selected from the group of peroxides represented by formula I
with R
1-3
being independently selected from hydrogen and substituted or unsubstituted hydrocarbyl groups. Preferably, R
1-3
are independently selected from the group consisting of hydrogen and substituted or unsubstituted C
1
-C
20
alkyl, C
3
-C
20
cycloalkyl, C
6
-C
20
aryl, C
7
-C
20
aralkyl, and C
7
-C
20
alkaryl, which groups may include linear or branched alkyl moieties; the optional one or more substituents on each of R
1
-R
3
being selected from the group consisting of hydroxy, alkoxy, linear or branched alkyl, aryloxy, halogen, ester, carboxy, nitrile, and amido. Preferably, R
1
and R
3
are selected from lower alkyl groups, such as methyl, ethyl, and isopropyl, methyl and ethyl being most preferred. R
2
is preferably selected from hydrogen, methyl, ethyl, isopropyl, isobutyl, tertbutyl, amyl, isoamyl, cyclohexyl, phenyl, CH
3
C(O)CH
2
—, C
2
H
5
OC(O)CH
2
—, HOC(CH
3
)
2
CH
2
—, and
The use of the trioxepans according to the invention was found to increase the cetane number of the fuel to an unexpectedly high level, and to reduce the ignition time, proving the products to be very efficient. Therefore, they are considered to be very good candidates for replacing conventional peroxides in said process.
The amount of trioxepans used to improve the ignition time of the fuel is preferably such that the cetane number of treated fuel is at least 2 higher than the cetane number of untreated fuel, when analyzed in accordance with ASTM D613. More preferably, an increase in cetane number of more than 4 is observed in said test. Since the method in accordance with ASTM D613 is not very reproducible and not very suitable for evaluating liquefied gases, the fuels are preferably evaluated in a closed volume combuster (CVC), which relates to the Ignition Quality Tester as described, for instance, by L. N. Allard, G. D. Webster, T. W. Ryan III, A. Beregszazy, C. W. Fairbridge, G. Baker, A. Ecker and Josef Rath, in “Analysis of the Ignition Behaviour of the ASTM D-613 Primary Reference Fuels and Full Boiling Range diesel Fuels in the Ignition Quality Tester (IQM)—Part III”, SAE 1999-01-3591, 1-8, 1999. In the CVC test as described below the ignition time is preferably such that it is at least 5 millisecond shorter, more preferably 10 millisecond shorter, than the ignition time of untreated fuel.
Preferably, one or more of the trioxepans according to formula I are present in the final fuel formulation in an amount of between 0.025 and 5 percent by weight (% w/w). Most preferred is a concentration of trioxepans of formula I in the fuel of between 0.05 and 2.5% w/w. Less peroxide will not result in any noticeable improvement of the ignition characteristics of the fuel, whereas a higher amount may prove to be unsafe or uneconomical.
The fuel according to the invention may contain just the peroxides of formula I as the ignition improver. However, they may also be combined with other ignition improvers, such as conventional di-tert-butyl peroxide and/or 2-ethylhexyl nitrate. If the peroxides of formula I are used together with other ignition improvers, then it is preferred that they make up at least 25% w/w, more preferably at least 50% w/w, most preferably at least 75% w/w, based on the weight of all ignition improvers in the fuel, because the ignition properties of such fuels are most efficiently improved.
The term fuels, as used throughout this document, is meant to encompass all hydrocarbon distillates and residue-containing oils for use in combustion engines and which distil between the kerosene fraction and the lubricating oil fraction of petroleum, as well as liquefied or compressed natural gas, liquid propane gas, liquid butane gas, and mixtures of the liquefied gases. The fuel may comprise the usual additives, such as anti-foam agents, injector cleaning agents, drying agents, cloud point depressants, also known as anti-gel agents, algae control agents, lubricants, dyes, and oxidation inhibitors, but may also comprise further ignition improving or combustion improving additives, provided that such additives do not adversely affect the storage stability of the final fuel composition according to the invention. Preferred fuels are diesel fuel and liquefied gases. In a most preferred embodiment, the fuel is a liquefied gas for use in a diesel engine.
When the trioxepans are used to improve liquefied gases, it can be advantageous to add one or more (aliphatic) hydrocarbon or other conventional co-additives. In a preferred embodiment a liquefied fuel, a trioxepan and one or more aliphatic hydrocarbons with a mo
De Groot Johannes J.
Meijer John
Akzo Nobel N.V.
Fennelly Richard P.
Toomer Cephia D.
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