FUEL COMPOSITION

Abstract: Use of a composition comprising an ester of a monocarboxylic acid and a polyhydric alcohol as a diesel fuel oil lubricity improver, wherein the monocarboxylic acid comprises a C8-C24 linear or branched chain unsaturated acid or a mixture thereof, and the polyhydric alcohol comprises an alcohol of the general formula: CR<1>R<2>R<3>R<4>, or a dimer, trimer or tetramer of the alcohol which is obtainable by condensation thereof, wherein R<1>, R<2> and R<3> are each independtly a C1-C12 linear or branched chain alkylol and R<4> is a linear or branched chain C1-C12 alkyl or a linear or branched chain C1-C12 alkylol wherein the ester comprises at least two free hydroxyl groups.

Description: FUEL COMPOSITION FIELD OF THE INVENTION The present invention relates to a fuel oil composition comprising a diesel fuel oil, and a fuel oil lubricity improver having improved cold storability. The invention further relates to the use of a composition having improved cold storability as a diesel fuel oil lubricity improver. BACKGROUND TO THE INVENTION AND PRIOR ART DISCUSSION Various ester additives are known for addition to hydrocarbon compositions for various purposes. For example, US 2993773 describes esters of alkenyl succinic acid with a large variety of different alcohols. These esters are used to inhibit or prevent deposit-forming in hydrocarbon fuels. GB 1065398 describes how the lubricity of aviation turbojet fuels might be improved using partial esters of a number of different polyhydric alcohols, especially an ester of a C36 dimer acid and sorbitan monooleate. GB 1047493 is concerned with the addition of a lubricity additive to a lubricating oil in which the lubricity additive is a partial or mono ester of a dicarboxylic acid and an oil insoluble glycol such as the monoester of the C36 linoleic dimer acid and glycol. WO 98/11178 discloses a polyol ester distillate fuel additive which exhibits improved lubricity, wear and frictional performance. The polyol ester has unconverted hydroxyl groups. Pentaerythritol is mentioned as one of the alcohol that can be used. DE 196 14 722 A relates to additives for fuels and lubricants essentially consisting of a fatty acid mono-ester, or a mixture of mono- and di-esters of unsaturated fatty acids having 16-22 C atoms with at least two different polyols. These additives are said to exhibit better low temperature behaviour than corresponding monoesters or mono and diester of uniform polyols. EP 0 826 765 A relates to fuel additives for improving lubricity. The additives comprise at least one partial ester of at least one monocarboxylic acid and at least one polyol. The monocarboxylic acid comprises a C4-C24 linear or branched, saturated or unsaturated acid that may be hydroxylated. FR 2 772 783 relates to a lubricious additive for fuels having a low sulphur content (less than 500 ppm) . The additive comprises a mixture of a glycerol monoester (5-95 wt . % ) with another ester or an amine. WO 98/21293 relates to low sulphur diesel fuels containing additives which increase lubricity and reduce smoke in the exhaust. The additive comprises a mixture of two different esters. A preferred ester is one which has no free hydroxyl groups . WO 97/04044 relates to additives for improving the lubricity of fuel oils such as diesel fuel oil. This additive is a mixture of esters of unsaturated monocarboxylic acids. Preferred polyols for forming the esters are saturated aliphatic straight chain polyols . US 3 672 854 relates to a middle distillate having an improved pour point, containing a pour point depressant. The depressant comprises an ester of a saturated C14-C26 carboxylic acid and a polyhydric alcohol having from 4 to 8 hydroxyl groups. US 5 378 249 relates to a biodegradable two cycle engine oil composition comprising a heavy ester a light ester and additives. The oil is mixed with gasoline for the purpose of lubrication. Diesel fuel oils generally comprise petroleum middle distillate fuel oils which boil within the range of about 100°C to about 400°C. There has recently been a drive to reduce the sulphur content of such diesel fuels so as to reduce sulphur dioxide emissions for environmental reasons. As of October 1996, the EU imposed a maximum sulphur content for diesel fuel oil of 0.05% by weight. As a result of this, a problem has arisen in that preparation of low sulphur content fuel oils also reduces the content in the fuels of other components such as polyaromatics . The problem is that the lubricity of the fuel is reduced and this can lead to engine failure. In order to overcome this problem, it has been proposed in WO 94/17160 to provide diesel fuel oil compositions with a lubricity improver additive. Particular examples of such an additive disclosed in WO 94/17160 are glycerol monooleate esters and di-isodecyl adipate esters. Glycerol monooleate esters are in commercial use as diesel fuel oil additives to enhance the lubricity of the diesel fuel oils. EP-A-0773278 also addresses this problem, providing as a lubricity improver additive a hydroxy-substituted carboxylic acid or acid derivative such as ricinoleic acid or glycerol monoricinoleate . SUMMARY OF THE INVENTION The present invention is concerned with a new problem which arises with diesel fuel oil lubricity improvers such as glycerol monooleate. When lubricity improvers of this type are sold, manufacturers recommend that the product be stored above 10°C. This is necessary because, at lower temperatures, the known diesel fuel oil lubricity improvers become unstable with a tendency to cloud or even freeze. The requirement to store at above 10°C to prevent these drawbacks is inconvenient and costly for customers who have to provide specialised storage facilities. Thus, a further aim of the present invention is to provide a lubricity improver which also has improved cold storability. The present invention aims to overcome the drawbacks of the prior art . In a first aspect, the present invention provides use of a composition comprising an ester of a monocarboxylic acid and a polyhydric alcohol as a diesel fuel oil lubricity improver, wherein the monocarboxylic acid comprises a C 8 -C 24 linear or branched chain unsaturated acid or a mixture thereof, and the polyhydric alcohol comprises an alcohol of the general formula: CR 1 R 2 R 3 R 4 , or a dimer, trimer or tetramer of the alcohol which is obtainable by condensation thereof, wherein R 1 , R 2 and R 3 are each independently a Cχ-Cι 2 linear or branched chain alkylol and R 4 is a linear or branched chain Cι-Cχ 2 alkyl or a linear or branched chain Cι~Cι 2 alkylol, wherein the ester comprises at least two free hydroxyl groups. In a second aspect, the present invention provides a fuel oil composition comprising a diesel fuel oil having a sulphur content of no more than 0.05% by weight and a fuel oil lubricity improver comprising an ester of a monocarboxylic acid and a polyhydric alcohol, wherein the monocarboxylic acid comprises a C 8 -C 24 linear or branched chain unsaturated acid or a mixture thereof, and the polyhydric alcohol comprises an alcohol of the general formula: CR 1 R 2 R 3 R 4 , or a dimer, trimer or tetramer of the alcohol which is obtainable by condensation thereof wherein R 1 , R 2 and R 3 are each independently a Cι-Cι 2 linear or branched chain alkylol and R 4 is a linear or branched chain Cχ-Cι 2 alkyl or a linear or branched chain Cι~Cι 2 alkylol, wherein the ester comprises at least two free hydroxyl groups. DETAILED DESCRIPTION OF THE INVENTION It is surprisingly found that, using the esters of the present invention as a diesel fuel oil lubricity improver enables the product to be storable as a liquid at a temperature below 20°C, even at a temperature below -10°C. In addition to these cold stability properties, the esters of the present invention possess ability comparable to the products currently on the market to improve the lubricity of diesel fuel oils. Accordingly, the need to use specialist storage facilities for the lubricity improvers is obviated. The ester of the present invention preferably comprises a diester, which may be part of a mixture comprising a monoester and a diester, and optionally including higher esters such as a triester and a tetraester. R 1 , R 2 and R 3 are preferably each independently a Cι~C linear or branched chain alkylol, more preferably CH 2 OH. R 4 is preferably a Cχ-C linear or branched chain alkyl or alkylol, such as CH 3 , CH 2 0H or CH 2 CH 3 . More preferably R 4 is an alkylol so as to increase the number of free -OH groups in the ester. A particularly preferred alcohol component of the ester is pentaerythritol, although other alcohols such as trimethylolpropane (TMP) and trimethylolethane (TME) may be used. In any event, the final ester should have at least two free -OH groups. The lubricity improver used in the present invention may comprise a single pure ester, or may comprise a mixture containing two or more esters. The carboxylic acid component of the ester may be a linear or branched chain carboxylic acid which is unsaturated and is preferably a Cι 2 -C 22 monocarboxylic acid. Typically, the carboxylic acid has an iodine value of 40 to 180, preferably an iodine value above 60, more preferably above 70, as measured in accordance with the AOCS (American Oil Chemists Society) Official Method cd-1-25. It is preferred to use an unsaturated carboxylic acid, since these are readily available and are often naturally- occurring. Particularly useful unsaturated carboxylic acids include oleic acid, linoleic acid, linolenic acid, palmoleic acid, gadoleic acid, erucic acid and other unsaturated acids with 22 carbon atoms and mixtures thereof. The unsaturated carboxylic acid component may be selected from tall oil fatty acids, soybean fatty acids, rape seed fatty acids, sunflower seed fatty acids, fish oil and fatty acids, and cold fractionated tallow and palm oil fatty acids. The monocarboxylic acid may be substituted, for example, by at least one hydroxyl group. A suitable substituted monocarboxylic acid is ricinoleic acid. In contrast with monoglycerides, the esters of the present invention such as the pentaerythritol esters, have a cold stability which is independent of the molar ratio of fatty acid to alcohol. Thus, lubricity efficiency increases with a decrease in ratio of fatty acid to alcohol in both pentaerythritol and monoglycerides; in the monoglycerides the cold stability decreases whereas in the pentaerythritol esters it does not. Typically, in accordance with the present invention, the amount of fuel oil lubricity improver used in the fuel oil is in the range 1 to lOOOppm, preferably in the range 10 to 500ppm, most preferably in the range 10 to 200ppm. The ester of the present invention may be used as the diesel fuel oil lubricity improver in pure form or in mixture with other components such as the conventional diesel fuel oil lubricity improvers, such as glycerol monooleate. Typically, the amount of ester of the present invention in such a mixture is in the range 60 to 100%wt, preferably in the range 80 to 100%wt, most preferably in the range 90 to 95%wt, especially around 92%. The properties of these mixtures are also improved over known lubricity improvers. The present invention will now be described in further detail, by way of example only, with reference to the following Examples. EXAMPLES Example 1 - lubrici ty performance All tests were done with the unadditized reference diesel fuel RF73-T-93, with a sulphur content of 0.05%. The fuel oil incorporated an amount of lubricity improver as set out in Table 1 below so as to compare the effectiveness of lubricity improvers according to the present invention with those of the prior art. A High Frequency Reciprocating Rig (HFRR) test was carried out as described in D. Wei and H. Spikes, Wear, Vol. Ill, No. 2, p. 217, 1986; and R. Caprotti, C. Bovington, W. Fowler and M. Taylor SAE paper 922183; SAE fuels and lubes. Meeting Oct. 1992; San Francisco, USA. The present applicants are aiming for a wear scar diameter of less than 400 microns at a dosage level of lOOppm. Table 1 wear scar diameter in mi cron for addi ti zed RF73-T-93 Lubricity improver A is a mixture of pentaerytritolmonooleate, pentaerytritoldioleate and pentaerytritoltrioleate including 39% diester. The olefin fraction used for the synthesis of this pentaerythritol ester and for the glycerolmonooleate was obtained by a cold fractionation of tallow fatty acids and has cloud point between 0°C and 6°C. Lubricity improver B is a mixture of 92% of A and 8% of the glycerolmonooleate. Example 2 - cold stabili ty The cold stability of both esters of example 1 was compared by measuring the cloud point according to ASTM method D5950 and the pour point according to ASTM method D5771. In addition, the cold stability of the best performing additive described in WO 97/04044 (additive A) was measured in the same way. Additive A from WO 97/04044 was prepared by esterification of a commercial mixture of oleic and linoleic acids with glycerol to produce a mixed ester product comprising glycerol monooleate and glycerol monolinoleate in approximately equal proportions by weight, and containing minor amounts of glycerol di- and trioleate and linoleate. The results are presented in Table 2. Table 2 cloud poin t and pour point of glycerolmonoolea te and l ubri ci ty improvers A and B The results show that both cloud point and pour point values are significantly lower in the pentaerythritol esters than in the prior art glycerolmonooleate and additive A. Example 3 - l ubrici ty performance As example 1, but the monoglyceride and the lubricity improver A were synthesized with tall oil fatty acids. Tall oil fatty acids as such are also included as comparative example. The results are shown in Table 3. Table 3 Example 4 - cold stabili ty The pour points of the different compounds mentioned in example 3 are compared. In addition to these compounds, the pour points of two additives described in WO 97/38965 are also compared. These additives are mixtures of trimethylolpropane monotalloate (TMP) (ester B of WO 97/38965) and glycerol monotalloate (ester A of WO 97/38965) . In the context of this prior art disclosure, talloate means formed with tall oil fatty acids. The results are shown in Table 4. Table 4 Taken together, these results confirm that the esters of the present invention have good lubricity improvement properties for diesel fuel oils and superior cold storage properties as compared with the lubricity improvers of the prior art.

Claims: CLAIMS 1. Use of a composition comprising an ester of a monocarboxylic acid and a polyhydric alcohol as a diesel fuel oil lubricity improver, wherein the monocarboxylic acid comprises a C 8 -C 24 linear or branched chain unsaturated acid or a mixture thereof, and the polyhydric alcohol comprises an alcohol of the general formula : CR 1 R 2 R 3 R 4 , or a dimer, tri er or tetramer of the alcohol which is obtainable by condensation thereof, wherein R 1 , R 2 and R 3 are each independently a Cι-Cι 2 linear or branched chain alkylol and R 4 is a linear or branched chain Cχ-Cι 2 alkyl or a linear or branched chain Cι-C 12 alkylol wherein the ester comprises at least two free hydroxyl groups. 2. Use according to claim 1, wherein the ester comprises a diester . 3. Use according to claim 1 or claim 2, wherein the ester comprises a mixture comprising a monoester and a diester. 4. Use according to any one of claims 1 to 3, wherein R 1 , R 2 aanndd RR 33 aare each independently a Cι-C 4 linear or branched chain alkylol . 5. Use according to claim 4, wherein R 1 and R 2 and R 3 are each CH 2 0H. 6. Use according to any one of the preceding claims, wherein R 4 is a C 1 -C linear or branched chain alkyl or alkylol. 7. Use according to any one of the preceding claims, wherein R 4 is CH 3 , CH 2 OH or CH 2 CH 3 . Use according to any one of the preceding claims, wherein R 4 is an alkylol. 9. Use according to any one of the preceding claims, wherein the alcohol comprises pentaerythritol. 10. Use according to any one of the preceding claims, wherein the monocarboxylic acid is substituted with at least one hydroxyl group. 11. Use according to any one of the preceding claims, wherein the monocarboxylic acid is a C12-C22 monocarboxylic acid. 12. Use according to any one of the preceding claims, wherein the carboxylic acid has an iodine value of 40-180, as measured in accordance with AOCS Official Method Cd-1-25. 13. Use according to any preceding claim, wherein the unsaturated carboxylic acid comprises a natural fatty acid. 14. Use according to claim 13, wherein the unsaturated carboxylic acid comprises oleic acid, linoleic acid, linolenic acid, palmiloleic acid, arachidic acid or mixtures thereof. 15. A fuel oil composition comprising a diesel fuel oil having a sulphur content of no more than 0.05% by weight and a fuel oil lubricity improver comprising an ester of a monocarboxylic acid and a polyhydric alcohol, wherein the monocarboxylic acid comprises a C 8 -C 24 linear or branched chain unsaturated acid or a mixture thereof, and the polyhydric alcohol comprises an alcohol of the general formula: CR 1 R 2 R 3 R 4 , or a dimer, trimer or tetramer of the alcohol which is obtainable by condensation thereof wherein R 1 , R 2 and R 3 are each independently a Cι-Cι 2 linear or branched chain alkylol and R 4 is a linear or branched chain Cχ-Cι 2 alkyl or a linear or branched chain Cι-Cι 2 alkylol. wherein the ester comprises at least two free hydroxyl groups. 16. A fuel oil composition according to claim 15, wherein the ester is as defined in any one of claims 2 to 14. 17. A fuel oil composition according to claim 16, wherein the amount of the fuel oil lubricity and cold storability improver in the fuel oil is in the range 10 to 500 ppm. 18. Use of an ester of a monocarboxylic acid and a polyhydric alcohol in a diesel fuel oil lubricity improver composition for improving the cold storability of the lubricity improver composition, wherein the monocarboxylic acid comprises a C 8 -C 24 linear or branched chain unsaturated acid or a mixture thereof, and the polyhydric alcohol comprises an alcohol of the general formula: CR 1 R 2 R 3 R 4 , or a dimer, trimer or tetramer of the alcohol which is obtainable by condensation thereof, wherein R 1 , R 2 and R 3 are each independently a Cι~Cι 2 linear or branched chain alkylol and R 4 is a linear or branched chain Cι~Cι 2 alkyl or a linear or branched chain C1-C12 alkylol wherein the ester comprises at least two free hydroxyl groups.

Inventors: PACKET DIRK, PACKET, DIRK
Applicants: FINA RESEARCH, PACKET DIRK, FINA RESEARCH S.A., PACKET, DIRK
Application year: 2000
Main classification: C10L1
IPC codes: C10L1, C10L10