EP1611224A1

EP1611224A1 - Novel fuel with a high octane number and a low aromatic content

Info

Publication number: EP1611224A1
Application number: EP03816671A
Authority: EP
Inventors: Luc Seyfried; Claude Marty
Original assignee: Total France SA
Current assignee: TotalEnergies Marketing Services SA
Priority date: 2003-03-27
Filing date: 2003-03-27
Publication date: 2006-01-04
Anticipated expiration: 2023-03-27
Also published as: US20060288635A1; ES2346207T3; US7918990B2; AU2003251025A1; CA2520077C; CA2520077A1; EP1611224B1; DE60332658D1; WO2004094571A1; ATE468381T1

Abstract

The invention relates to a fuel containing at least 5 vol. %, and preferably at least 10 vol. %, of a hydrocarbon base (B3) consisting essentially of cycloparaffins comprising between 6 and 8 carbon atoms. The ratio R of the quantities by volume (B1+B2)/B3 is higher than 2 and preferably between 2.3 and 19.

Description

New fuel with high octane rating and lower aromatic contents.

The present invention relates to new fuel formulations having a high octane number and lowered contents of aromatic compounds, in particular benzene, capable of being used to supply internal combustion and spark-ignition engines and, in particular, piston engines fitted to aircraft.

We know . that, prior to their placing on the market, the fuels intended to supply internal combustion and spark-ignition engines must meet precise physicochemical characteristics, to guarantee the consumer a high level of mechanical performance and, at the same time, minimize sources of pollution, whether these are generated by exhaust gases or by the product itself during handling or storage. These characteristics, which can vary significantly from one fuel to another, must nevertheless remain in an area defined by official specifications grouped together and published by qualified organizations, such as AFNOR in France or ASTM in the United States. Among these specifications, the octane number or, more precisely, the index measuring the anti-detonating value of a fuel in comparison with a so-called reference gasoline, is an essential characteristic, since it reflects the combustion performance of the fuel in the engine cylinders and, in particular, its knock resistance, that is to say its resistance to self-ignition in uncontrolled mass of the fuel. This phenomenon, well known to those skilled in the art, can have, if it is not controlled, harmful consequences on the service life of the engine, such as premature fatigue and wear of the essential parts of the mechanical power unit assembly.

Thus, for motor vehicles, a distinction is made in the art between two types of octane indices for the fuels intended for the supply of the engines fitted to them, namely the RON (Research Octane Number; in French, number octane research) and the MON (Motor Octane Number; in French, number of motor octane), respectively called, in the profession, FI and F2. In the field of aviation and, more specifically, for aircraft fitted with spark-ignition engines, the fuels offered on the market must be developed with care and must, in particular, very good knock resistance, taking into account the severe and specific conditions of use of these engines, in particular at takeoff, and also for obvious reasons of reliability and operational safety at altitude. Here again, two specific octane numbers have therefore been defined and incorporated into the specifications of aircraft gasoline, namely:

- an index again called MON or engine octane index, which replaces the old directly correlated index, formerly called F3 in the profession, aiming to assess correct operation of the engine assembly in normal operation; say at altitude at steady speed;

- and the so-called supercharge octane index, also called F4 or performance index, reflecting the combustion performance needs of the engine on take-off. A fuel, the commercial name of which is commonly used is “AVGAS 100 LL”, corresponds to a gasoline for an airplane piston engine with positive ignition, the MON of which must be, according to ASTM D910-00, equal to 99.5 and the F4 greater than or equal to 130. The abbreviation “LL” means “Low Lead” (in French: low lead), that is to say that the lead content of the fuel, generally coming of alkyl lead compounds, must be, according to this standard, which is in force today, less than or equal to 0.56 grams per liter of gasoline.

It is this type of aircraft fuel that will be referred to more particularly in the remainder of this description, but the fuels according to the invention can be used in fields other than aviation, for example for engines for competition or similar vehicles, ie for engines requiring fuels with a very high octane number. The fuel that is the subject of the present invention can also be used to supply very diverse systems, for example, a fuel processing unit, such as a reformer, coupled to a fuel cell.

It is known that gasolines produced directly by distillation of crude oil do not have the required characteristics and, in particular, the octane numbers sufficient for their direct placing on the aviation market. The refiner must therefore, at the stage of their manufacture, mix several bases, preferably hydrocarbon, in order to obtain products which, with the possible addition of additives, are adjusted to the various specifications required. These bases and additives can consist, for example and without limitation: of hydrocarbons mainly containing aromatic compounds having, by nature, high octane numbers;

- hydrocarbons resulting from the alkylation of gases containing 1 to 4 carbon atoms, free of aromatic or olefinic molecules;

- light gasolines originating from the direct distillation of crude oil, whether these are isomerized or non-isomerized; - light distillation fractions such as butanes or isopentanes;

- oxygenated or organometallic compounds, the chemical composition of which is specifically chosen to obtain particular properties during the combustion cycle of the fuel in the engine.

The aromatic hydrocarbons used in the composition of a gasoline generally come from a manufacturing process, called "reforming" of gasolines, available in particular, in an oil refinery. This process, sometimes used by the operator in very severe conditions, in direct relation to the quality requirement of the products produced, in particular for gasolines intended for aircraft engines, allows, thanks to a set of chemical reactions s '' performing at high temperature and under high pressure, necessarily in the presence of an appropriate catalyst, to transform molecules with straight or cyclic chains contained in the heaviest gasolines, produced by direct distillation of crude oil, into branched and cyclic aromatic hydrocarbons more stable. These aromatic hydrocarbons are generally called "reformates" in the profession and have a high octane number. However, the presence of such reformates in significant quantities in fuels, which can reach several tens of% by volume, poses a real problem, because of the aromatic molecules which it contains. It is known that the presence of aromatic hydrocarbons and, in particular, of benzene in a fuel goes against the trend of the legislation in force and most certainly to come, as regards the environment. Indeed, faced with the problems linked to the health of consumers, in particular those posed by the emissions of different sources of fossil fuels in places of life, and more specifically by fuels, most of these legislations recommend a reduction in their content of aromatic compounds and in particular in benzene, since this last molecule is considered carcinogenic for humans. Fuels formulations having both a sufficiently high octane number, in accordance with ASTM D910-00, are not found in the art to be used, for example, in spark ignition aircraft engines. , and a lower aromatic content, without the addition of specific octane donor additives.

For example, JP 05179264 offers a fuel formulated with bases conventionally available in an oil refinery, in which substantial quantities of naphthenes and MTBE have been added. Different, more or less complex, processes have then been proposed for reducing the benzene content of fuels, such as, for example, in FR A-2 686 094 or FR-A-2 686 095, which use conventional hydrogenation of the benzene contained in a hydrocarbon base used in the constitution of the fuel, followed by an isomerization operation of the molecules thus formed. All the processes currently proposed for reducing the content of aromatic hydrocarbons and, more particularly, of benzene in gasolines, pose technical difficulties for refiners, while generating additional costs by the necessary use of new and numerous process steps in the gasoline production chain.

The refiner is therefore confronted with a double problem to manufacture economically, from hydrocarbon cuts available in an oil refinery, fuels for aircraft engines with low rates of aromatic compounds and, in particular, of benzene, but having octane numbers high enough to comply with current standards:

- Either formulate fuels with small quantities of aromatic hydrocarbons, but to the detriment of the octane number, this octane deficit must then be compensated for by the addition of additives, resulting in an additional cost for the refiner; moreover, it becomes more and more difficult to use specific additives, because the current tendency being to minimize, even eliminate, the additives not compatible with the environment, such as organic lead derivatives, good suppliers of octane, but also significant sources of pollution for humans, i.e. subjecting various cuts of hydrocarbons used in the composition of this fuel, so to comply with the specifications of petrol for aircraft; these different treatments, however, involve complex processes, therefore generate a significant additional cost for the refiner and can cause production restrictions, linked to the various constraints inherent in each of the processes used.

US-A-2 411 582 discloses the use in a fuel for aviation of a mixture of hydrocarbons comprising spiropentane, that is to say a hydrocarbon of the cycloparaffinic type with 5 carbon atoms , of formula Cs Hs. The research carried out by the Applicant in the field of fuel formulation has now enabled it to establish that the replacement in gasolines for internal combustion and spark-ignition engines and, in particular, for aircraft engines, c that is to say in fuels specifically requiring a very high octane number, a substantial amount of the reformate by hydrocarbons having saturated rings containing 6 to 8 carbon atoms, also called cycloparaffins, cycloalkanes or naphthenes, allows , while respecting the specifications in force, to give them a high octane number of the F4 type, at least equal to 130, and consequently to reduce considerably the content of aromatic hydrocarbons, and in particular benzene, of these fuels.

The invention therefore aims to provide new formulations of fuels for internal combustion engines and spark ignition, which contain a significantly reduced amount of aromatic hydrocarbons compared to the formulations of the prior art, and in which are present cycloparaffins containing 6 to 8 carbon atoms, which give this fuel, used in particular in spark ignition aircraft engines, an octane number and characteristics in accordance with the standard in force. To this end, the subject of the invention is a new fuel for supplying spark-ignition engines and in particular those equipping aircraft, having an octane number F4 at least equal to 130 and a lower content of aromatic compounds, containing substantial amounts of a first hydrocarbon base (B1), consisting essentially of isoparaffins comprising 6 to 9 carbon atoms, and of a second hydrocarbon base (B2) also consisting isoparaffins comprising 4 or 5 carbon atoms and, possibly, other usual hydrocarbons and additives for this type of fuel, in a quantity and a quality sufficient for the fuel to comply with the specifications in force, characterized in that it contains at least 5.0% by volume and preferably at least 10.0% by volume of a hydrocarbon base (B3) composed essentially of cycloparaffins comprising 6 to 8 carbon atoms, and in that the ratio R of the quantities by volume (B1 + B2) / B3 is greater than 2.0 and preferably between 2.3 and 19.0.

The aromatic hydrocarbon content of the fuel according to the invention is less than 10% by volume and, preferably, less than

5% by volume, measured by the FIA method according to standard ASTM D1319, and the benzene content is less than 0.2% by volume and, preferably, less than 0.1% by volume, measured by the spectrometric method infrared according to standard NF EN 238. The determination of the contents of the fuel in any other usual hydrocarbons and additives, in order to make it conform to the regulations in force in the technique or to particular characteristics, is the responsibility of the skilled in the art and poses no particular technical problem. The use in the fuel according to the invention of cycloparaffinic hydrocarbons containing 6 to 8 carbon atoms proves to be particularly advantageous from an economic point of view, for the following reasons:

- it offers a useful outlet for compounds which currently do not have significant practical application, without an expensive conversion treatment;

- it makes it possible to avoid having to proceed with a decyclization of these compounds, carried out for the sole reason that they are precursors of aromatic compounds and in particular of benzene, which can present well known risks, both for human beings than animals;

- it leads to a fuel that complies with existing specifications and does not have the disadvantages of conventional fuels, intended to the same applications, for a generally lower cost than these.

Other characteristics and advantages of the invention will appear in the detailed example which follows, which is not limiting. EXAMPLE

Six series of four fuels and a series of three fuels, intended for supplying aircraft spark ignition engines, of the Avgas 100LL type, were formulated by the Applicant, in accordance with the invention. These fuels are respectively identified

Cl to 04 and 05 to 08 in Table 1, 09 to 012 and 013 to 016 in Table 2, 017 to C20 and 021 to 024 in Table 3, 025 to 027 in Table 4.

Table 1; Fuel formulations according to the invention and characteristics thereof (Fuels 1 to 8).

PCI: Lower Calorific Power, in English “Net Heat of Combustion” TV: Tension de Vapeur, in English “Vapor Pressure” Table 2: Fuel formulations according to the invention and characteristics thereof (Fuels 9 to 16).

PCI: Lower Calorific Power, in English “Net Heat of Combustion” TV: Tension de Vapeur, in English “Vapor Pressure” Table 3: Fuels formulations according to the invention and characteristics thereof (Fuels 17 to 24).

PCI: Lower Calorific Power, in English “Net Heat of Combustion” TV: Tension de Vapeur, in English “Vapor Pressure” Table 4: Fuels formulations according to the invention and characteristics thereof (Fuels 25 to 27).

PCI: Lower Calorific Power, in English “Net Heat of Combustion” TV: Tension de Vapeur, in English “Vapor Pressure” The bases, or cuts of hydrocarbons of petroleum origin, used for the manufacture of fuels in accordance with the invention (Cl to C27), are those commonly used for the manufacture of this type of fuel, with the exception of cutting of cycloparaffinic hydrocarbons, containing 6 to 8 carbon atoms.

The first base used (marked "Base B 1" in Tables 1 to 4), consists essentially of isoparaffins containing 6 to 9 carbon atoms. These isoparaffinic hydrocarbons are preferably isooctanes, the preferred amount of which is present in said cut is greater than 70% by mass and, even more preferably, greater than 75% by mass.

Such a hydrocarbon base can come from different crude oil treatment processes, generally present in an oil refinery. In particular, this cut of isooctane-rich hydrocarbons, also called “alkylate” in the profession, can be produced, for example, by the process of alkylation of isobutane by light olefins.

An alternative is to replace part of this isoparaffinic cut, and at the same time reduce the proportion of alkylate, which is a petroleum base whose manufacturing cost is relatively high, with a cut of hydrocarbons from a isomerization unit for light gasolines, the latter coming from the distillation of crude oil.

The second hydrocarbon base used for the manufacture of fuels in accordance with the invention (marked “Base B2” in the

Tables 1 to 4) also belongs to the family of paraffinic hydrocarbons and can be, for example, a light base consisting essentially of isoparaffinic molecules comprising between 4 or 5 carbon atoms and, preferably, 5 carbon atoms. Such an industrial base contains more than 85% by mass of isopentane and, preferably, more than 90% by mass.

This light paraffinic base can come, for example, from a fractionation of the lighter fraction of the distillate produced by the atmospheric distillation of crude oil. Advantageously, this cut of hydrocarbons can be replaced by a cut with a high concentration of a mixture of normal-butane and isobutane. The third base used (marked "Base B3" in Tables 1 to 4), is a hydrocarbon fraction consisting essentially of cycloparaffins containing 6 to 8 carbon atoms. Advantageously, this base consists of cyclohexanes, the content of which is greater than 80% by mass and, preferably, greater than 90% by mass. It can come from different processes used in a refinery for the treatment of crude oils and, in particular, can be taken at the outlet of the fractionation unit located downstream from an isomerization process for light gasolines. In accordance with the invention, the Applicant has introduced for some of these formulations a fourth base (designated "Base B4" in Tables 1 to 4), essentially consisting of aromatic hydrocarbons, usually used in the formulation of this type of fuel. This cut of hydrocarbons containing 6 to 8 carbon atoms, the content of aromatic compounds of which is greater than

75% by mass, and preferably greater than 80% by mass, comes, for example, from a process for reforming gasolines. The benzene content of this cut of aromatic hydrocarbons, which can usually vary between 0.1% and 10% by volume is, in the present example, equal to 2.6% by volume.

For each of the seven series of fuel formulations, formulated in such a way that the fuel thus produced complies with the specifications in force, the Applicant has introduced a determined quantity of the cycloparaffmic base B3. This is how the contents of this latter base vary in fuels from 0% to

5% by volume (Table 1), 10% to 15% by volume (Table 2), 20% to 25% by volume (Table 3), being equal to 30% by volume in Table 4.

Within each series of formulations, that is to say for a defined content of cycloparaffmic base B3, the Applicant has determined the field of formulations in which the fuels thus formulated comply with the specifications in force for the Avgas 100LL or approach them very closely. In addition, the Applicant has calculated for each fuel thus manufactured (Cl to C27), the ratio R = (B1 + B2) / B3 corresponding to the ratio of the sum of the quantities by volume of the isoparaffinic hydrocarbon fractions (Bl + B2) , on the quantity in volume of the cycloparaffmic section (B3), and it has also calculated for these same formulations C1 to C27, the ratio K = B1 / B2, that is to say the ratio of the quantity by volume of the cut of hydrocarbons containing 6 to 9 carbon atoms (Bl), over the quantity by volume of the cut of hydrocarbons containing 4 or 5 carbon atoms (B2), these two cuts of hydrocarbons being introduced into the fuels manufactured in accordance with the invention.

The main characteristics of the fuels thus formulated are indicated in Tables 1 to 4, the other specifications being in accordance with standard D910-00. The quantities of lead introduced into each fuel manufactured comply with said standard, that is to say 0.56 g / 1, measured according to standard ASTM D3341 or ASTM D5059.

We see, in Tables 1 to 4, that fuels C5 to C27 make it possible to comply with the Avgas 100 LL specifications in force when the contents of cycloparaffinic base B3 vary from 5% to

30% by volume. It can also be seen, for these same fuels, that these specifications are also met when the content of the aromatic base varies from 0% to about 25% by volume. This makes it possible to offer fuels C5, C6, C9, C13, C17, C21, C25, C26 and C27, with very low contents of aromatic compounds (less than 5% by volume) and in particular of benzene (less than 0.1% volume), or with lowered contents of these said molecules for C7, C10, C14, C18, C22, C23 and C24, since the contents of aromatic compounds and of benzene are respectively less than 10% by volume and less than 0.2% in volume.

For these fuel formulations with very low contents, or with lower contents of aromatics and benzene, the content of isoparaffinic base Bl introduced is greater than 40% by volume and, preferably, greater than 43% by volume. On the other hand, when there is no cycloparaffinic cut (B3) in the fuels (Table 1: fuels Cl to C4), the contents of aromatic compounds and benzene are respectively 21.7% and 0.7% by volume for a formulation usually used in the art for this type of fuel. The absence in the Cl fuel of cycloparaffinic (B3) and aromatic (B4) bases does not allow it to comply with the specifications of the Avgas 100LL, the characteristics F4 and 10% distilled being out of specification. It is necessary also note that, in the case of Cl fuel, the high proportion of the isoparaffinic base (B1), which is greater than 90% by volume, makes this fuel economically penalizing, this latter base generally being of cost relatively high workmanship.

Tables 1 to 4 teach that the fuels formulated with a cycloparaffinic base comply with the specifications of the Avgas 100 LL currently in force, when at least 5.0% by volume is introduced into them and, preferably, at least 10.0% by volume of a hydrocarbon fraction consisting essentially of

90% by mass of cyclohexanes, when the R ratio is greater than 2.0 and preferably between 2.3 and 19.0 and when the K ratio is greater than 2.0, and preferably between 2.3 and 10.6.

The fuels thus produced, in accordance with the invention, have various advantages:

- They have a high octane number, thus meeting the specification in octane numbers F4 and MON of Avgas 100LL aircraft gasoline, without requiring additional additions of additives, for example oxygenated, other than those usually used and authorized;

- They are respectful of the environment, because they contain less than 10% by volume of aromatic compounds and in particular less than 0.2% by volume of benzene, and preferably, less than 5% by volume of aromatic compounds and in particular less 0.1% by volume of benzene, thus making fuels more favorable to their current use by the consumer;

- They are cheaper to manufacture, because they do not require additional treatment steps, for example to reduce benzene or increase the octane number; - they make it possible to reduce the specific operating severity of the catalytic reforming units;

- finally, they are compatible with other equivalent hydrocarbons.

Claims

1.- Fuel for the supply of spark-ignition engines and in particular those equipping aircraft, having an octane number F4 at least equal to 130 and a reduced content of aromatic compounds, containing substantial quantities of a first hydrocarbon base (Bl) consisting essentially of isoparaffins comprising 6 to 9 carbon atoms, and a second hydrocarbon base (B2) also consisting of isoparaffins comprising 4 or 5 carbon atoms and, optionally, other hydrocarbons and additives usual for this type of fuel, in a quantity and a quality sufficient for the fuel to meet the specifications in force, characterized in that it contains at least 5.0% by volume and, preferably, at least 10.0% by volume, of a hydrocarbon base (B3) composed essentially of cycloparaffins comprising 6 to 8 carbon atoms, and in that the ratio R of the quantities by volume (B1 + B2) / B3 is greater than 2, 0 and preferably between 2.3 and 19.0.

2. Fuel according to claim 1, characterized in that the ratio K of the quantities by volume B1 / B2 is greater than 2.0 and preferably, between 2.3 and 10.6.

3.- Fuel according to claims 1 and 2, characterized in that the cut of cycloparaffinic hydrocarbons (B3) consists essentially of cyclohexanes.

4. Fuel according to claim 3, characterized in that the content of cyclohexanes in the cut of cycloparaffinic hydrocarbons

(B3) is greater than 80% and, preferably, greater than 90% by mass.

5. Fuel according to any one of the preceding claims, characterized in that the first cut of isoparaffinic hydrocarbons (B1) consists essentially of isoparaffins with eight carbon atoms.

6.- Fuel according to claim 5, characterized in that its content in the cut of isoparaffinic hydrocarbons (B1) with eight carbon atoms is greater than 40% and, preferably, greater than 43% by volume.

7. Fuel according to claims 5 or 6, characterized in that the isoparaffinic hydrocarbons containing eight carbon atoms are isooctanes.

8.- Fuel according to one of claims 5, 6 and 7, characterized in that the isooctane content in the cut of isoparaffinic hydrocarbons (B1) with eight carbon atoms is greater than 70% by mass and, preferably , greater than 75% by mass.

9. Fuel according to any one of the preceding claims, characterized in that the second cut of isoparaffinic hydrocarbons (B2) consists essentially of isoparaffins with five carbon atoms.

10.- Fuel according to claim 9, characterized in that the isoparaffinic hydrocarbons containing five carbon atoms are isopentanes.

11.- Fuel according to one of claims 9 and 10, characterized in that the content of isopentanes in the cut of isoparaffinic hydrocarbons (B2) with five carbon atoms is greater than 85% by mass and, preferably, greater 90% by mass.

12.- Fuel according to claim 9, characterized in that the cut of isoparaffinic hydrocarbons containing 5 carbon atoms is replaced by a cut consisting of hydrocarbons containing 4 carbon atoms.

13.- Fuel according to any one of the preceding claims, characterized in that its content of aromatic compounds is less than 10% by volume and, preferably, less than 5% by volume.

14.- Fuel according to any one of the preceding claims, characterized in that its benzene content is less than 0.2% by volume and, preferably, less than 0.1% by volume.

15. Use of the fuel according to any one of the preceding claims for supplying, alone or as a mixture, spark-ignition engines of aircraft.

16.- Use of the fuel according to any one of the preceding claims for supplying, alone or as a mixture, positive-ignition engines of competition or similar vehicles.

17. Use of the fuel according to any one of the preceding claims for supplying, alone or as a mixture, a fuel treatment unit, such as a reformer, coupled to a fuel cell.