US20050223627A1

US20050223627A1 - Additive for improving the thermal stability of hydrocarbon compositions

Info

Publication number: US20050223627A1
Application number: US10/513,456
Authority: US
Inventors: Frank Eydoux; Christian Bernasconi; Celine Vuillet
Original assignee: Total France SA
Current assignee: Total Marketing Services SA
Priority date: 2002-05-03
Filing date: 2003-05-02
Publication date: 2005-10-13
Also published as: WO2003095593A1; AU2003251031A1; FR2839315B1; FR2839315A1; EP1504078A1

Abstract

The invention relates to the use of at least one additive in order to increase the thermal stability of a hydrocarbon composition, said additive being the product of the condensation reaction between at least one alkenyl succinic or alkyl succinic anhydride I and a primary amine II. The invention also relates to a composition comprising the aforementioned additive, an anti-oxidant and a metal deactivator and to fuels containing same.

Description

A subject of the invention is the use of an additive for improving the thermal stability of hydrocarbon compositions, as well as a particular hydrocarbon composition having an improved thermal stability.
Fuels intended to function in aeroplane engines (for example turbojet engines and ramjet engines), usually called kerosene or jet fuel, are known. They are generally composed of a middle cut from crude oil distillation, generally containing additives.
In an aeroplane, the fuel, in addition to its role of propellant fluid, fulfils other functions. These functions are in particular:

- coolant fluid by means of exchangers: fuel/hydraulic fluid (cooling the hydraulic fluid); fuel/oil (cooling the lubrication oil); fuel/air (cooling the fuel);
- power-transmission fluid: nozzle actuators
- regulation fluid (in particular for the engine).

Until its injection into the combustion chamber or the afterburner, the fuel can be subjected to high temperatures, for example of the order of 200° C., or even higher in contact with the walls.
Subjected to these high temperatures, the fuel is subject to oxidation and thermal decomposition phenomena which cause the formation of varnishes and gums on the one hand, and particles and coke on the other. When deposited on fittings which constitute the fuel system of an aeroplane, these products cause damage and malfunctions (in particular malfunction of the main injectors, damage to the combustion chambers, and to the first turbine stage (excessive temperature), malfunction of the afterburner injectors, vibrations, loss of efficiency of the heat exchangers, etc.) Starting problems (in particular from cold), in-flight reignition, loss of performance can thus occur. These problems also significantly increase the maintenance costs of aeroplanes. Moreover, new generation aeroplanes present still further problems or accentuate the existing problems as they aim to increase the thrust/weight ratio of the engine and to reduce the fuel consumption, which involves: an increase in the speed of rotation of the engine and consequently an increase in the operating temperature of the engine and of the lubrication oil; a reduction in the size of the exchangers (dimensions, weight); an increase in the number of electric and electronic circuits to be cooled and a reduction in the fuel feed rate (consumption). This therefore requires an increase in the thermal capacity of the fuel which must be capable of removing a greater quantity of heat.
It is therefore sought to improve the thermal stability of the fuel by incorporation of an additive or a composition of additives capable of responding to the demands of future aeroplanes and reducing the maintenance costs while responding to the technical problems mentioned above. The increase sought is of at least 100° F., i.e. allowing an increase from 325° F. (163° C.) to 425° F. (218° C.) for the maximum temperatures currently encountered and an increase from 400° F. (204° C.) to 500° F. (259° C.) for the temperatures of the fuel in contact with the walls.
To solve these problems, U.S. Pat. No. 5,468,262 describes an additive for improving the thermal stability of a fuel, this additive being prepared by (i) reaction of a polyamine, an aldehyde and a phenol to form a phenol-aldehyde-amine condensate; and (ii) Mannich's reaction of this condensate with a succinic anhydride carrying a substituent which is a polyolefin with residual unsaturation, in particular polyisobutene. This additive can be schematically represented by the following formula (with PIB for polyisobutene and PA for polyamine/aldehyde):
This additive is used, according to this document, in a proportion comprised between 0.2 and 20% by weight of fuel. Such an additive poses several specific problems. Firstly, the quantities required for the additive to be effective are very large, such that they exceed 2000 ppm, which makes the end fuel very expensive. Moreover, the presence of a heavy PIB group (with residual unsaturation) encourages the initiation of deposits on the walls, which is exactly what one wants to avoid. Finally, such an additive is surface-active by nature (hydrophobic/hydrophilic duality) and significant levels of it encourage contamination of fuel by water, which should be avoided, in particular in fuels for aeroplanes.
EP-A-0678568 describes an additive reducing the deposits in aeroplane jet engines. This additive is a derivative of (thio)-phosphonic acid, used in the example in a quantity of 25 ppm. It is preferably a derivative of polyisobutene thiophosphonic acid, more particularly its ester with pentaerythritol.
However, this additive poses several problems. On the one hand, it is phosphorus-based, which causes atmospheric pollution linked to the discharge of acid compounds (phosphates, phosphoric acids) in the combustion gas. On the other hand, it also comprises a polyisobutene group, and thus poses the same problems as those already outlined above for the additive which is the subject-matter of U.S. Pat. No. 5,468,262.
In order to solve the problems of thermal decomposition and oxidation of the hydrocarbon flow subjected to high temperatures in heat exchangers in refineries, U.S. Pat. No. 3,437,583 proposes the incorporation into the flow of hydrocarbons of an anti-fouling composition comprising a hindered phenol, a succinimide obtained by reaction of an acid or succinic anhydride substituted by a polyamine, and N,N′-disalicylidene-1,2-propane diamine.
The succinimide is obtained from an anhydride or a succinic acid substituted by an R′″ radical comprising 30 to 200 carbon atoms. There again, the presence of such a heavy group encourages the thermal decomposition of the additive, and ultimately proves to be a precursor of deposits and fouling.
U.S. Pat. No. 3,776,835 also describes a method of reducing the rate of fouling on the inside of heat exchangers in which the hydrocarbon flow circulates. This method consists of adding to the hydrocarbon flow (a) hydrogen and (b) an agent for inhibiting deposits, chosen from mono- and poly-amines and -amides comprising 50 carbon atoms. Among the families of chemical compounds capable of being used as agents for inhibiting deposits there are generally mentioned succinimides comprising 20 to 200 carbon atoms.
The use of succinimide-based additives in hydro-carbonated fuels is moreover known to improve other types of properties, in particular cold properties.
Thus Patent Application EP 626.442 deals with problems of degradation of the cold resistance caused by using ester fuels produced from the transesterification of animal or vegetable oils or fats, and recommends the use of such esters combined with a pour point depressant additive and optionally a carboxylic dispersant which can be, among others, a compound obtained by reaction of a substituted succinic anhydride with an amine.
Long-chain succinimides are largely preferred: the succinic acid substituent contains a minimum of 12 and preferably 50 carbon atoms, with a very clear preference for polymers of molecular weight ranging from 700 to 10,000.
The succinimide-based additives are used here as dispersant agents in cold-resistance compositions. In other words their function is to improve still further the cold resistance of the mixture by keeping in suspension the hydrocarbon crystals which form at low temperature to prevent them being deposited. This antisedimentation function relates only to the properties of low-temperature fuels, and makes no contribution to thermal stability at high temperature.
Similarly, U.S. Pat. No. 3,795,495 recommends the use of succinimides combined with an alkyl aminoalkyl phosphate to solve the cold-starting problems of petrol vehicles in the case of the fuel freezing. Succinimide is the product of condensation of a succinic anhydride carrying a substituent R comprising 8 to 50 carbon atoms with a polyamine. There again, the succinimides are used as anti-freezing agents, which implies nothing about their effectiveness as thermal stability additives at high temperature.
A subject of the invention is an additive which allows the thermal stability of the hydrocarbon compositions, in particular fuels for aeroplanes, to be improved with a greater effectiveness than additives already known for this while avoiding the problems encountered with these additives.
The present invention therefore proposes the use, to increase the thermal stability of a hydrocarbon composition, of at least one additive which is the product of the condensation reaction between:

- (i) at least one alkylsuccinic or alkenylsuccinic I anhydride of general formula(I):
  in which:
- R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms; and
- (ii) at least one primary amine II of general formula (II):
  NH₂—[(CH₂)_m—(CHR₁)_n-Z]_x-[(CH₂)_p—(CHR₂)_q]_y—NHR₃
  - in which:
  - R₁and R₂are chosen from hydrogen, alkyl groups comprising 1 to 30 carbon atoms, phenyl groups,
  - R₃is hydrogen or an alkyl group comprising 1 to 30 carbon atoms or a phenyl group or an alkylaromatic group,
  - Z is oxygen or the NH group,
  - x is an integer from 0 to 5 inclusive,
  - y is an integer from 1 to 5 inclusive,
  - m, n, p and q are integers from 0 to 10 inclusive.

The invention also proposes a composition of additives which allows the thermal stability of hydrocarbons to be improved. This composition comprises:

- (a) 1 to 40 parts by weight of at least one antioxidant;
- (b) 0.05 to 10 parts by weight of at least one metal deactivation agent; and
- (c) 1 to 60 parts by weight of at least one thermal stability additive which is the product of the condensation reaction as described above.

It has been noted surprisingly that the combination of the three constituents (a), (b) and (c) above, if these constituents are present in the relative proportions mentioned above, allows the thermal stability of the hydrocarbon compositions to be significantly improved. In particular, the abovementioned composition allows the thermal breakpoint of fuels intended for aviation to be greatly increased, which allows these fuels to be used as coolant fluids at higher temperatures or, at the same temperature, the thermal decomposition of the fuel to be significantly reduced in the heat exchange zones.
The invention also provides a hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition of additives above, in a quantity such that the concentration of said composition as thermal stability additive ranges from 1 to 200 ppm, preferably 1 to 100 ppm, advantageously 1 to 50 ppm.
In the present specification, all concentrations expressed in ppm (parts per million) designate ppm by weight.
The invention also provides a stock solution comprising a solvent and the composition of additives above.
The invention also provides a process for the preparation of the composition of additives above, by mixing different constituents.
The invention finally provides a method for increasing the thermal stability of fuels for aeroplanes, by incorporating an additive or a composition of additives as described above into said fuels.
The invention will now be described in more detail in the description which follows.
The term “alkyl” applies to linear and branched groups.
By the term “alkylaromatic” is meant groups having an alkyl chain which carries an aromatic distal substituent, in particular a phenyl group, the alkyl chain having 1 to 30 carbon atoms.
The term “hydrocarbon mixture” designates any hydrocarbon mixture capable of being used as fuel. The hydrocarbon mixture is advantageously chosen from gasolines, gasoils, kerosenes, DFOs (Domestic Fuel Oil), heavy fuels, synthesis hydrocarbons such as those obtained by oligomerization of olefins or by Fischer-Tropsch synthesis, biofuels such as vegetable oils and the esters of vegetable oils, and mixtures of these products.
The hydrocarbon mixture preferably comprises a middle distillate, i.e. a cut of hydrocarbons the distillation range (determined according to the ASTM D 86 standard) of which is comprised between 60 and 350° C., preferably between 100 and 300° C.
Advantageously, this composition is an aeroplane fuel, for example kerosene, alone or mixed with a gasoline. There may be mentioned for example the fuels known to a person skilled in the art under the following names: JP-4, (MIL-T-5624), JP-5, JP-7, JP-8 (MIL-T-83133), Jet A and JetA-1 (ASTM D 1655). Kerosene can have a distillation range comprised in the range from 60° C. to 360° C., and for example a starting point of 149-221° C., 50% point of 221-231° C., 90% point of 260-343° C. Its API gravity can be 30 to 40. For more details, reference can be made to the publication “Handbook of Aviation Fuel Properties”, Coordinating Research Council Inc., CRC Report No. 530 (SAE, Warrendale, USA, 1983). Particularly advantageous aeroplane fuels are those which conform to the AFQRJOS specification (“Aviation Fuel Quality Requirements for Jointly Operated Systems”) Issue 18 for Jet A-1 of November 1999 (this specification reiterates the most restrictive criteria of the ASTM D 1655 specification and the British DEF STAN 91-91 specification).
The hydrocarbon mixture can have been partly or wholly subject to a desulphuration and/or denitrogenation and/or dearomatization treatment. For example, fuels that have been hydrotreated can be used under more or less severe conditions (comprising a hydrodesulphuration, a saturation of the aromatic and olefinic compounds, even a hydro-denitrogenation).
The hydrocarbon composition advantageously has a sulphur content less than or equal to 0.5% by weight, preferably less than or equal to 0.3% by weight. Its content of aromatic compounds is preferably less than or equal to 25% by volume. It can optionally contain a substantial quantity of oxygenated compounds such as ethers, and/or biofuels such as alcohols, or esters of fatty acids such as for example the methyl ester of rape seed.
Other hydrocarbon compositions are also suitable; the fuel can be intended for applications not related to engines, for example a fuel for ovens, boilers or fuel cells.
The additive according to the invention, as well as the composition of additives, allows the thermal stabilization of the hydrocarbon composition, and therefore responds to the technical problems outlined above. The additive according to the invention is generally used in a quantity of 1 to 200 ppm, preferably 1 to 100 ppm, advantageously 1 to 50 ppm.
The additive according to the invention is prepared by reacting an anhydride I with an amine II. This reaction is carried out at a temperature for example of between 120 to 200° C., and for a period for example between 1 and 36 hours and preferably between 5 and 30 hours.
Condensation of the amines II with the anhydrides I can be carried out without solvent, but a hydrocarbon solvent with a boiling point between 70 and 250° C. is preferably used. The solvent preferably comprises an aromatic or naphthenoaromatic hydrocarbon, for example: toluene, xylenes, diisopropylbenzene or also a petroleum cut with a suitable distillation range.
The additives considered in the invention can in practice be prepared in the following manner: amine II is gradually introduced into a reactor containing anhydride I, maintaining the temperature between 30° C. and 80°. The temperature is then increased to a value of 120 to 200° C., the volatile products formed (in particular water) being eliminated either by entrainment with a stream of inert gas or by azeotropic distillation with the chosen solvent; the final concentration of dry material is for example 40 to 70%.
The preparation methods disclosed for example in the application WO-A-9413758, to which reference is made and the content of which is incorporated into the present application, can be generally applied.
For the preparation of the additive according to the invention, an anhydride I in which the side chain R comprises 4 to 24 carbon atoms, even more preferably 12 to 24 carbon atoms, is preferably used. The side chain R is preferably an alkenyl group.
Examples of alkylsuccinic and alkenylsuccinic anhydride are dodecylsuccinic, dodecenylsuccinic, hexadecylsuccinic, hexadecenylsuccinic, octadecylsuccinic, octadecenylsuccinic, eicosylsuccinic and eicosenylsuccinic anhydrides.
In the additive according to the invention, the amine corresponds to formula II. The R₁and R₂groups are preferably either hydrogen or alkyl groups comprising 1 to 10 carbon atoms, and/or R₃is hydrogen or an alkyl group comprising 1 to 20 carbon atoms, and/or Z is the NH group, and/or m, n, p and q are comprised between 1 and 3 inclusive. The indices x and y are preferably comprised between 0 and 2 inclusive.
Advantageously, amine II corresponds to the following formula IIa: NH₂—[(CH₂)_m—NH]_x—[(CH₂)_p+1]_y—NH₂.
Non-limitative examples of such amines are: for non-alkylated amines:

- diethylenetriamine, dipropylenetriamine,
- triethylenetetramine, tetraethylenepentamine and
- tetrapropylenepentamine;
  and for alkylated amines:
- N-alkylethylenediamines, N-alkylpropylenediamines,
- N-alkylbutylenediamines, N-alkyldiethylenetriamines,
- N-alkyldipropylenetriamines, N-alkyldibutylenetriamines,
- N-alkyltriethylenetetramines, N-alkyltributylenetetramines
- and N-alkyltripropylenetetramines
  having an alkyl radical comprising 1 to 10 carbon atoms.

For the preparation of the additive, the anhydride I and the amine II are used in a preferential molar ratio of anhydride:amine comprised between 1:0.2 and 1:1.
The molecular mass by weight of the additive can vary between 300 and 10000 g/mol.
It is particularly advantageous to use the additive described above in combination with an antioxidant, in a quantity relative to the hydrocarbon composition for example comprised between 1 and 1000 ppm, preferably between 1 and 100 ppm. Sterically hindered phenols can be used as antioxidants such as:

- 2,6-di-t-butyl-4-methylphenol (BHT),
- 2,6-di-t-butylphenol,
- 4,4′-methylene bis(2,6-di-t-butyl-phenol),
- 2,6-di-t-butyl-4-dimethylaminomethylphenol,
- 2,4,6-tri-t-butylphenol and
- 2,4-di-methyl-6-t-butylphenol.

It is likewise advantageous to use a metal deactivation agent in a quantity relative to the hydrocarbon composition for example comprised between 0.1 and 500 ppm, preferably between 0.1 and 20 ppm. Metal chelating compounds can be used as deactivation agents such as for example N,N′-disalicylidene-1,2-propane diamine of formula:
Thus, the hydrocarbon composition according to the invention advantageously comprises:

- (a) 1 to 1000 ppm, and preferably 1 to 100 ppm of at least one antioxidant;
- (b) 0.1 to 500 ppm, preferably 0.1 to 20 ppm of at least one metal deactivation agent;
- (c) 1 to 200 ppm, preferably 1 to 100 ppm, advantageously 1 to 50 ppm of the thermal stability additive according to the invention.

It can also advantageously comprise other additives chosen from the additives usually used for the applications considered, namely for example corrosion-inhibiting additives, anti-freeze additives, antistatic additives, additives improving the cold properties, tracer additives, detergent additives, and their mixtures. The hydrocarbon composition preferably contains at least one detergent additive chosen from the polyisobuteneamines.
In particularly advantageous manner, the composition of additives according to the invention comprises:

- (a) 2 to 40 parts by weight and preferably 4 to 15 parts by weight of at least one antioxidant;
- (b) 0.1 to 3 parts by weight and preferably 0.5 to 2 parts by weight of at least one metal deactivation agent; and
- (c) 2 to 20 parts by weight and preferably 3 to 15 parts by weight of at least one thermal stability additive as described above.

With these ranges of proportions relative to the three constituents (a), (b) and (c), the effectiveness of the composition of additives is particularly significant, and the increase in thermal stability is considerably improved.
In general the additive is supplied in the form of a concentrated solution (“stock solution”) either of thermal stability additive alone or of the composition of additives (a), (b) and (c), or the thermal stability additive mixed with any other standard additive. These “stock solutions” are prepared by dissolving additives in a solvent which can be chosen from the aromatic solvents mentioned above, petroleum cuts (in particular kerosenes), mineral and/or synthesis oils. The “stock solutions” can contain for example 20 to 60% by weight additives and agents. According to its concentration, the stock solution is introduced into the hydrocarbon composition in quantities which can range for example from 150 ppm weight to 1000 ppm weight.
The following examples illustrate the invention without limiting the scope.
Two additives A and B according to the invention are prepared, each by condensation of an anhydride I of formula (I) with a primary amine II of formula (II). Table 1 below details the formula of each of the reagents I and II:

TABLE 1

Addi- Formula

tive R Z R₃ x y m n and q p

A C₂₄ NH H 1 1 2 0 1

alkenyl

group

B C₁₈ NH Mixture of C₁₄to 2 0 3 0 1

alkenyl C₁₈alkyl groups

group
These additives were prepared in the following manner:
Additive A:
a) Synthesis of the Anhydride I:
246.8 g of linear C₂₄alpha-olefin are heated in a reactor to 185° C. under nitrogen and under stirring. 91.1 g of maleic anhydride are then added at a rate such the temperature of the reaction medium remains at 185° C.±2.5° C. The reaction mixture is stirred for 24 hours at 185° C., then cooled down to 60° C. by adding 500 g of xylene (solvent).
b) Synthesis of the Additive:
161.5 g of diethylenetriamine (DETA) are added to the mixture from stage (a), maintaining the temperature at approximately 60° C. Then the water which forms during the condensation reaction is eliminated together with part of the solvent, by azeotropic distillation, with a starting distillation temperature of at least 90° C., and a final distillation temperature of approximately 150° C.
The mixture is then cooled down and filtered, and the condensation product is thus recovered in solution in xylene.
Additive B:
a) Synthesis of the Anhydride I:
234.3 g of linear C₁₈alpha-olefin (n-octadecene) are heated to 185° C. in a reactor under nitrogen and under stirring. 91.1 g of maleic anhydride are then added at a rate such that the temperature of the reaction medium remains at 185° C.±2.5° C. The reaction mixture is stirred for 24 hours at 185° C., then cooled down to 60° C. by adding 500 g of xylene (solvent).
b) Synthesis of the Additive:
190.6 g of tallow triamine are added to the mixture from stage (a), maintaining the temperature at approximately 60° C. Then the water which forms during the condensation reaction is eliminated together with part of the solvent, by azeotropic distillation, with a starting distillation temperature of at least 90° C., and a final distillation temperature of approximately 150° C.
The mixture is then cooled down and filtered, and the condensation product is thus recovered in solution in xylene.

These additives were tested in two JetA-1-type aviation fuels, the properties of which are given in Table 2 below:

TABLE 2


	Jet no. 1	Jet no. 2
		Kerosene cut treated
	Hydrotreated	in a non-extractive
Type	kerosene cut	Kerox unit

Sulphur content	0.0003% by weight	0.0166% by weight
Initial distillation point	145.4° C.	152.9° C.
10% distillation point	161.4° C.	176.1° C.
50% distillation point	189.7° C.	202.0° C.
90% distillation point	238.4° C.	235.5° C.
Final distillation point	257.5° C.	249.8° C.
Density at 15° C.	816.7 kg/m³	808.0 kg/m³

The sulphur content was determined in accordance with the ASTM D 1266 standard, the distillation points in accordance with the ASTM D 86 standard and the density in accordance with the ASTM D 1298 standard.
The non-extractive Kerox process converts the mercaptans contained in a petroleum cut to disulphides.
These two fuels comply with the AFQRJOS specification (“Aviation Fuel Quality Requirements for Jointly Operated Systems”) Issue 18 for Jet A-1 of November 1999. This specification reiterates the most restrictive criteria of the ASTM D 1655 specification and the British DEF STAN 91-91 specification.
The additives were incorporated into the two fuels mixed with an antioxidant (2,6-di-t-butylphenol) and a metal deactivation agent (N,N′-disalicylidene-1,2-propane diamine) The thermal stability breakpoint (here called “breakpoint”) of each of the fuels before and after the addition of additives was determined in accordance with paragraph X2 of the ASTM D 3241 standard.
The breakpoints of the fuels to which additives have not been added are as follows:

- Jet no. 1 295° C.
- Jet no. 2 305° C.

Tables 3 and 4 below detail the composition of the fuels to which additives have been added and the results obtained, with additives A and B respectively.

TABLE 3


(ADDITIVE A)

Fuel	Jet no. 1	Jet no. 2

Content of A	25 ppm	25 ppm
Content of antioxidant	20 ppm	20 ppm
Content of metal deactivator	2.5 ppm	2.5 ppm
Breakpoint	335° C.	335° C.

TABLE 4


(ADDITIVE B)

Fuel	Jet no. 1	Jet no. 2	Jet no. 2

Content of B	25 ppm	8 ppm	25 ppm
Content of antioxidant	20 ppm	20 ppm	20 ppm
Content of metal deactivator	2.5 ppm	2.5 ppm	2.5 ppm
Breakpoint	>400° C.	345° C.	345° C.

Tables 3 and 4 above illustrate the excellent performances of additives according to the invention in terms of improving the thermal stability of aviation fuels. In fact, additives A and B generally allow an increase of at least 30° C. in the thermal stability breakpoint. The increase is often greater, and in the case of additive B it can even be of the order of 100° C.
This increase has been confirmed on very different jet fuels, which demonstrates the effectiveness of the additives regardless of the fuel.

Claims

1-29. (canceled)

30. Use to increase the thermal stability of a hydrocarbon composition, of at least one additive which is the product of the condensation reaction between:

(i) at least one alkylsuccinic or alkenylsuccinic anhydride I of general formula(I):

in which:

R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms; and

(ii) at least one primary amine II of general formula

NH₂—[(CH₂)_m—(CHR₁)_n-Z]_x-[(CH₂)_p—(CHR₂)_q]_y—NHR₃ (II)

in which:

R₁and R₂are chosen from hydrogen, alkyl groups comprising 1 to 30 carbon atoms, phenyl groups,

R₃is hydrogen or an alkyl group comprising 1 to 30 carbon atoms or a phenyl group or an alkylaromatic group,

Z is oxygen or the NH group,

x is an integer from 0 to 5 inclusive,

y is an integer from 1 to 5 inclusive,

m, n, p and q are integers from 0 to 10 inclusive.

31. Use according to claim 30, in which, in the additive, the formula of the amine of formula II is

NH₂—[(CH₂)_m—NH]_x—[(CH₂)_p+1]_y—NH₂.

32. Use according to claim 30, in which the additive is the product of the condensation reaction between compounds I and II, used according to molar ratio I:II comprised between 1:0.2 and 1:1.

33. Use according to claim 30, in which in the additive, the side chain R is an alkyl or alkenyl group comprising 4 to 24 carbon atoms.

34. Use according to claim 33, in which the side chain R comprises 12 to 24 carbon atoms.

35. Use according to claims 30, in which in the additive, the side chain R is an alkenyl group.

36. Use according to claim 30, in which in the additive, the R₁and R₂groups are either hydrogen or alkyl groups comprising 1 to 10 carbon atoms.

37. Use according to claim 30, in which in the additive, R₃is hydrogen or an alkyl group comprising 1 to 20 carbon atoms.

38. Use according to claim 30, in which in the additive, Z is the NH group.

39. Use according to claims 30, in which in the additive, m, n, p and q are comprised between 1 and 3 inclusive.

40. Use according to claim 30, in which the additive is used at the rate of 1 to 200 ppm.

41. Use according to claim 30, in which the additive is used at the rate of 1 to 100 ppm.

42. Use according to claim 30, in which the additive is used at the rate of 1 to 50 ppm.

43. Use according to claims 30, in which the additive is used in combination with an antioxidant and a metal deactivation agent.

44. Method of increasing the thermal stability of aviation fuels comprising the incorporation into said fuels of an additives as describe in claim 30.

45. Composition comprising:

(a) 1 to 40 parts by weight of at least one antioxidant;

(b) 0.05 to 10 parts by weight of at least one metal deactivation agent; and

(c) 1 to 60 parts by weight of at least one thermal stability additive which is the product of the condensation reaction between:

(i) at least one alkylsuccinic or alkenylsuccinic anhydride I of

general formula(I):

in which:

R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms; and

(ii) at least one primary II amine of general formula (II):

NH₂—[(CH₂)_m—(CHR₁)_n-Z]_x-[(CH₂)_p—(CHR₂)_q]_y—NHR₃

in which:

Z is oxygen or the NH group,

x is an integer from 0 to 5 inclusive,

y is an integer from 1 to 5 inclusive,

m, n, p and q are integers from 0 to 10 inclusive.

46. Composition according to claim 45, comprising

(a) 2 to 40 parts by weight of antioxidant;

(b) 0.1 to 3 parts by weight of metal deactivation agent; and

(c) 2 to 20 parts by weight of thermal stability additive.

47. Composition according to claim 45, in which the antioxidant is a sterically hindered phenol.

48. Composition according to claims 45, in which the metal deactivation agent is a metal chelating agent.

49. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition according to claim 45, in a quantity such that the concentration in said composition of thermal stability additive is 1 to 200 ppm.

50. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition according to claim 45, in a quantity such that the concentration in said composition of thermal stability additive is 1 to 100 ppm.

51. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition according to claim 45, in a quantity such that the concentration in said composition of thermal stability additive is 1 to 50 ppm.

52. Stock solution comprising a solvent and the composition according to claim 45.

53. Stock solution according to claim 45, in which the solvent is chosen from aromatic solvents, petroleum cuts, in particular kerosenes, mineral and/or synthesis oils.

54. Process for the preparation of a composition according to claim 45, by mixing various constituents.

55. Method of increasing the thermal stability of aviation fuels comprising the incorporation into said fuels of a composition of additives according to claim 45.

56. Composition comprising:

(a) 1 to 40 parts by weight of at least one antioxidant;

(b) 0.05 to 10 parts by weight of at least one metal deactivation agent; and

in which:

R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms; and

(ii) at least one primary II amine of general formula(II):

NH₂—[(CH₂)_m—NH]_x—[(CH₂)_p+1]_y—NH₂.

in which:

x is an integer from 0 to 5 inclusive,

y is an integer from 1 to 5 inclusive,

m, p are integers from 0 to 10 inclusive.

57. Composition according to claim 56, comprising

(a) 2 to 40 parts by weight of antioxidant;

(b) 0.1 to 3 parts by weight of metal deactivation agent; and

(c) 2 to 20 parts by weight of thermal stability additive

58. Composition according to claim 56, in which the antioxidant is a sterically hindered phenol.

59. Composition according to claims 56, in which the metal deactivation agent is a metal chelating agent.

60. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition according to claim 56, in a quantity such that the concentration in said composition of thermal stability additive is 1 to 200 ppm.

61. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition according to claim 56, in a quantity such that the concentration in said composition of thermal stability additive is 1 to 100 ppm.

62. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and the composition according to claim 56, in a quantity such that the concentration in said composition of thermal stability additive is 1 to 50 ppm.

63. Stock solution comprising a solvent and the composition according to claim 56.

64. Stock solution according to claim 63, in which the solvent is chosen from aromatic solvents, petroleum cuts, in particular kerosenes, mineral and/or synthesis oils.

65. Process for the preparation of a composition according to claim 56, by mixing various constituents.

66. Method of increasing the thermal stability of aviation fuels comprising the incorporation into said fuels of a composition of additives according to claim 56.

67. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and:

(a) 1 to 1000 ppm, of at least one antioxidant;

(b) 0.1 to 500 ppm, of at least one metal deactivation agent; and

(c) 1 to 200 ppm, of at least one thermal stability additive which is the product of the condensation reaction between:

in which:

R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms; and

(ii) at least one primary II amine of general formula(II):

NH₂—[(CH₂)_m—(CHR₁)_n-Z]_x-[(CH₂)_p—(CHR₂)_q]_y—NHR₃

in which:

Z is oxygen or the NH group,

x is an integer from 0 to 5 inclusive,

y is an integer from 1 to 5 inclusive,

m, n, p and q are integers from 0 to 10 inclusive.

68. Hydrocarbon composition according to claim 67, comprising a major part of a hydrocarbon mixture and:

(a) 1 to 100 ppm of at least one antioxidant;

(b) 0. 1 to 20 ppm of at least one metal deactivation agent; and

(c) 1 to 100 ppm of at least one thermal stability additive.

69. Hydrocarbon composition according to claim 67 comprising 1 to 50 ppm of at least one thermal stability additive.

70. Hydrocarbon composition according to claim 67, in which the antioxidant is a sterically hindered phenol.

71. Hydrocarbon composition according to claim 67, in which the metal deactivation agent is a metal chelating agent.

72. Hydrocarbon composition according to claim 67, in which the hydrocarbon mixture is chosen from gasolines, gasoils, kerosenes, DFOs (Domestic Fuel Oil), heavy fuels, synthesis hydrocarbons such as those obtained by the oligomerization of olefins or by Fischer-Tropsch synthesis, biofuels such as vegetable oils and the esters of vegetable oils, and mixtures of these products.

73. Hydrocarbon composition according to claim 67, in which the hydrocarbon mixture comprises a middle distillate having a distillation range comprised between 60 and 350° C., preferably between 100 and 300° C.

74. Hydrocarbon composition according to claim 67, which is a fuel, in particular for aeroplanes.

75. Process for the preparation of a composition according to claim 67, by mixing various constituents.

76. Hydrocarbon composition comprising a major part of a hydrocarbon mixture and:

(a) 1 to 1000 ppm, of at least one antioxidant;

(b) 0.1 to 500 ppm, of at least one metal deactivation agent; and

in which:

R is an alkyl or alkenyl group comprising 4 to 29 carbon atoms; and

(ii) at least one primary II amine of general formula(II):

NH₂—[(CH₂)_m—NH]_x—[(CH₂)_p+1]_y—NH₂.

in which:

x is an integer from 0 to 5 inclusive,

y is an integer from 1 to 5 inclusive,

m, p are integers from 0 to 10 inclusive.

77. Hydrocarbon composition according to claim 76, comprising a major part of a hydrocarbon mixture and:

(a) 1 to 100 ppm of at least one antioxidant;

(b) 0.1 to 20 ppm of at least one metal deactivation agent; and

(c) 1 to 100 ppm of at least one thermal stability additive.

78. Hydrocarbon composition according to claim 76 comprising 1 to 50 ppm of at least one thermal stability additive.

79. Hydrocarbon composition according to claim 76, in which the antioxidant is a sterically hindered phenol.

80. Hydrocarbon composition according to claim 76, in which the metal deactivation agent is a metal chelating agent.

81. Hydrocarbon composition according to claim 76, in which the hydrocarbon mixture is chosen from gasolines, gasoils, kerosenes, DFOs (Domestic Fuel Oil), heavy fuels, synthesis hydrocarbons such as those obtained by the oligomerization of olefins or by Fischer-Tropsch synthesis, biofuels such as vegetable oils and the esters of vegetable oils, and mixtures of these products.

82. Hydrocarbon composition according to claims 76, in which the hydrocarbon mixture comprises a middle distillate having a distillation range comprised between 60 and 350° C., preferably between 100 and 300° C.

83. Hydrocarbon composition according to claim 76, which is a fuel, in particular for aeroplanes.

84. Process for the preparation of a composition according to claim 76, by mixing various constituents.