FUEL COMPOSITION

Abstract: This invention relates to a diesel fuel composition having enhanced lubricity, said composition comprising a major amount of a diesel fuel as base fuel blended with a minor amount of a nitrogen rich fraction characterised in that the nitrogen rich fraction is derived from a source material selected from (i) a solvent extract of a solid or semi-solid natural fossil, or, (ii) a refinery process stream or blend, the sulphur to nitrogen atom ratio in the nitrogen rich fraction being less than 4. The nitrogen rich fraction has an absolute nitrogen content of at least 1000 ppm by weight and this fraction is (re)blended with the base fuel is no more than 1% by weight of the total fuel composition. Methods of separating, recovering and reblending such naturally occurring nitrogen compounds can be installed or retro-fitted at existing refinery and crude oil processing facilities without any substantial increase in production costs.

Description: FUEL COMPOSITION This invention relates to fuel compositions of low sulphur content which contain at least one component capable of enhancing the lubricity of such low sulphur fuels Fuels such as diesel are widely used in automotive transport due to their low cost However, one of the problems with such fuels is the presence of relatively high concentrations of sulphur compounds Excessive sulphur contπbutes to exhaust particulate emissions and can also degrade the effectiveness of some exhaust after- treatment technology which is being introduced in response to regulated limits on exhaust emissions As a result, the permitted level of sulphur in diesel fuel has been progressively reduced over the years and further reductions are planned for the future Whilst a reduction in sulphur content can be readily achieved by well known processes such as hydrodesulphuπsation which is generally earned out m the presence of a catalyst, such process also adversely affect the lubricity of the resultant desulphuπsed product Consequently, it is necessary to formulate compositions which are low in sulphur content but are also of the desired lubricity in order to minimise wear and fπction when used m automotive engines and to minimise the damage to the injection system of a diesel engine It has hitherto been the practice to add anti-wear agents to such formulations including fatty acid, fatty acid esters, lactones, polyoxyalkylene ethers, ammo compounds and the like for this purpose However, compositions containing compounds such as esters are expensive m terms of both mateπal costs and the cost of additive storage facilities A publication by Wei and Spikes entitled 'The lubricity of diesel fuels' (published in Wear, 11 1 (1986) 217) discloses that heterocychc nitrogen compounds, like quinohne and indole, also have a beneficial effect on the antiwear performance of base fuels Although these compounds do not have a surfactant like structure they are of the same general structure as the natural compounds that are destroyed duπng hydrotreatment A further article by D Wei et al in Lubπcation Science, 1989, 2(1), pp 63-67 entitled "The Influence of Chemical Structure of Certain Nitrogen-Containing Organic Compounds on Their Antiwear Effectiveness The Cπtical Role of Hydroxy Group" shows that the presence of hydroxy groups m some nitrogen-containing compounds improve their antiwear performance significantly The article concludes that hydroxy substituted benzothiazoles are most effective in wear reduction and anti-scuffing With this in view the author reports the results of the tests earned out on films formed on rubbing surfaces by the benzo-deπvatives of pyπdme and thiazole. with or without hydroxy groups on the πngs The article concludes that protective films formed on rubbing surfaces by the above heterocychc compounds beaπng a hydroxy group are significantly different from those produced by their analogues with similar chemical composition and physical properties It has also been found that some polycychc aromatic compounds such as eg carbazoles have limited solubility m the fuel to function efficiently (Wei et al, Journal of Petroleum (Petroleum Processing) Vol 4, No 1 , p90, March 1988) Work conducted by Tonen (Japanese patent application No 7-194502) included alkyl carbazoles, e g methyl and ethyl carbazole, where the alkyl group was attached to the hetero-atom itself JP-A-100176175 relates to a method of imparting excellent lubricating and water- separating properties to a low sulphur (< 0 2 wt%) diesel fuel by adding thereto a specific nitrogen compound (eg n-hexylamine) alone or together with a lubricity improving fatty acid ester In each of these instances, the lubricity enhancing component generally has to be synthesised separately and introduced into the fuel from an external additive This is not only wasteful of resources but also causes proliferation of chemicals into this industry Moreover, extensive testing is needed to ensure that such externally sourced additives do not have any undesirable side-effects Other references such as JP-A- 100008070 relate to a base mateπal for improving the lubπcity of gas oils (<0 05 wt% S) suitable for use in diesel engines, the base material being a catalytic or thermally cracked light oil containing > 4 wt% of a tπ- or poly-cychc aromatic hydrocarbon and > 15 ppm by mass of basic nitrogen The base matenal is used in an amount of 2-15 wt% of the gas oil There is no mention of the sulphur to nitrogen atom ratio in the base mateπal used in the gas oil Similarly, JP-A-080259966 relates to a diesel oil composition which is prepared by (a) subjecting a mixture of 80-97 5 vol% of a direct distillation light oil (LGO) and 2.5-20 vol% of a light oil (LGO 9 ) to a deep desulphuπsation step to form a desulphuπsed oil mateπal (FDGO) and (b) blending the FDGO with up to 8 vol% of a light cracking oil (LCO) The resultant composition is said to have a sulphur content of up to 500 ppm. a nitrogen content of up to 60 ppm and a polycyclic aromatic content of 3.5-6.0 vol%. The source of nitrogen in these compositions is not clear. There is no mention of the sulphur to nitrogen atom ratio in the fractions blended. It has now been found that the lubricity of fuels can be enhanced without excessive recourse to additives from an external source but by using components already present in specific fractions of oils and fossil fuels from a natural source which have a relatively low sulphur to nitrogen atom ratio. Accordingly, the present invention provides a diesel fuel composition having enhanced lubricity, said composition comprising a major amount of a diesel fuel as base fuel blended with a minor amount of a nitrogen rich fraction characterised in that the nitrogen rich fraction is derived from a source material selected from (i) a solvent extract of a solid or semi-solid natural fossil, or, (ii) a refinery process stream or blend, such that the sulphur to nitrogen atom ratio in said nitrogen rich fraction is less than 4. The diesel fuel composition suitably has a sulphur content of less than 500 ppm by weight, preferably less than 150 ppm and more preferably less than 50 ppm by weight which is the so called ultra-low sulphur automotive diesel oil (hereafter "ULSADO"). The relatively low sulphur levels can be achieved in a number of ways. For instance, this may be achieved by well known methods such as catalytic hydrodesulphurisation. The lubricity properties of ultra-low sulphur (50 ppm or less) base fuels with a T 5 of suitably < 370°C, preferably < 360°C, particularly benefit from the presence of the nitrogen compounds referred to above. Especially, the lubricity properties are more of an issue with diesel fuels because diesel fuel injection pumps are more sensitive to wear problems. In particular, the rotary distribution diesel fuel injection pumps are solely lubricated by the fuel itself. These pumps contain precisely engineered components to maintain the consistency and precision of the injected fuel volume and to ensure a long service life. If the pump components become worn, irregular fuel injection may occur thereby leading to poor drivability, and increased emissions and may eventually lead to pump seizure. The base fuels of the present invention may comprise mixtures of saturated and aromatic hydrocarbons and these can be derived from straight run streams, themially or catalytically cracked hydrocarbon feedstocks, hydrocracked petroleum fractions, catalytically reformed hydrocarbons, or synthetically produced hydrocarbon mixtures. The present invention is particularly applicable to the automotive diesel oils, especially the so called ULSADO that have recently been introduced into the UK market (which may be sampled from Esso's Fawley Refinery) The mtrogen-πch fraction can be deπved from a source hich is either a solid or a semi-solid fossil fuel by solvent extraction or a refinery process stream or fuel blend These sources of mtrogen-πch fraction will hereafter be termed as "source materials" for convenience The source compπsing refinery process streams or fuel blends suitabh distil within the diesel oil boiling range 150-450°C, preferably 150-400°C and will jointK be referred to hereafter as "DOBR" for convenience The DOBR in turn can oπgmate directly from the pipestill or from secondary processing such as catalytic cracking of a heavy gas oil from the atmospheπc or vacuum pipestill Methods of processing petroleum crude to obtain \ aπous process streams are w ell known in the art and are descπbed in detail for instance by Keith Owen and Trevor Collev in "Automotive Fuels Reference Book", Second Edition, published by the Society of Automotι\ e Engineers Inc, Warrendale, PA, USA (1995) Specifically, Chapter 3 of this text-book at pages 29- 49, Chapter 15 on Diesel Fuel Characteπstic Influencing Combustion at pages 385-418, Chapter 18 at pages 519-522 relating to lubπcity additives for diesel fuels, and Appendix 12 at pp 865-890 which is a 'Glossary of Terms' give all the information that is necessary to make and charactense such streams The mtrogen-πch fraction can be extracted from the source mateπals by a number of methods depending upon the nature of the source mateπal For instance where the source mateπal is a natural solid or semi-solid fossil fuel such as eg coal, bitumen or oil shale, the nitrogen πch fraction is suitably recovered therefrom b\ a solvent extraction method such as eg using tetrahydrofuran or the like which preferentially extracts the nitrogen πch polar compounds therefrom The solvent extraction may ha\ e to be repeated several times and the extracts concentrated to enπch the extract in nitrogen containing compounds Where the source mateπal is a DOBR, it preferably with a final boiling point at the upper end of this boiling range, le 300-420°C. more preferably 350- 400°C, where such nitrogen compounds tend to be concentrated nitrogen-rich fraction may be separated and reco\ ered from DOBR by a method compπsing a using a stationary/liquid phase separation method in which the stationary phase is suitably selected from an absorbent like alumina, silica, silicic acid, clay and/or a zeolite. or b. a liquid/liquid phase separation based on the preferential partition of the components of the appropriate fractions between mutually immiscible solvents, or c. osmosis through a membrane. Of these, the stationary/liquid phase separation method is preferable and the stationary phase is most preferably siliceous eg Biosil® (silicic acid). This method is readily implemented using column chromatography techniques. In some instances, it may be necessary to conduct a two- or multi-stage separation process in order to achieve the desired concentration of nitrogen in the fraction to render it to be suitable for blending with the diesel fuel. When the nitrogen-rich fraction has been separated and recovered from DOBR. it is preferable to determine the sulphur to nitrogen ratio in such a nitrogen-rich fraction. It is necessary to do so in order to ensure that introduction of sulphur values into the diesel fuel are minimized thereby avoiding contravention of any environmental legislation. Thus, it is valuable to determine the suitability of the nitrogen-rich fraction for blending with diesel fuels and also to enable he most efficient use of the nitrogen values in the fraction. Thus, the desired fraction suitably has an absolute nitrogen content of at least 1000 ppm, preferably 2,000ppm; a basic nitrogen content suitably of at least 200 ppm, preferably more than 400 ppm, eg 500 ppm; and a sulphur to nitrogen atom ratio of less than 4, preferably less than 1. Such a specification enables the nitrogen-rich fraction to be re-blended into the diesel fuel while still keeping the sulphur content within the desired specification. Thus, the nitrogen-rich fraction so separated and recovered is suitably such that it contains at least 0.6% by weight (6,000 ppm) of nitrogen and is then re-blended into the diesel fuel. The amount of the nitrogen-rich fraction re -blended with the diesel fuel is suitably no more than about 1%, preferably 0.5% and most preferably 0.1% by weight of the total fuel composition. By re-blending existing and naturally occurring nitrogen compounds in such fossil fuels, no extensive manufacturing or synthetic facilities need be set up to generate such lubricity enhancing compounds. Moreover, methods of separating, recovering and reblending such naturally occurring nitrogen compounds can be installed or retro-fitted at existing refinery and crude oil processing facilities without any substantial increase in production costs. The antiwear and lubricity performance of the fuel compositions of the present invention were measured according to the so-called high frequency reciprocating rig test (hereafter referred to as "HFRR"). The HFRR test consists of a loaded upper ball 6mm in diameter, which oscillates against a static lower plate. Both friction and contact resistance are monitored throughout the test. The tests are conducted according to the standard procedure published as CEC F-06-A-96 in which a load of 2N (200g) was applied, the stroke length was 1mm, the reciprocating frequency was 50 Hz and sample temperature of 60°C. The ambient temperature and humidity were controlled within the specified limits and the calculated value of wear scar diameter was corrected to the standardized water vapour pressure of 1.4 kPa. The specimen ball was a grade 28 (ANSIB3.12), AISI E-52100 steel with a Rockwell harness "C" scale (HRC) number of 58-66 (ISO 6508), and a surface finish of less than 0.05μm R a , and the lower plate was AISI E-52000 steel machined from anealed rod, with a Vickers hardness "HV30" scale number of 190-210 (ISO 6507/1). It is turned, lapped and polished to a surface finish of 0.02μm R a . TABLE 1 Summary of HFRR test conditions The present invention is further illustrated with reference to the following Examples. The source materials covered include a heavy catalytically cracked gas oil (CCGO) and a typical refinery fuel blend (Fawley blend). Isopar® M and a blend (67:33by volume) of Isopar® M and mixed xylenes, available from most fine chemical suppliers, were used as base fuels to demonstrate the good lubricity performance of the nitrogen-rich fractions. Full details are shown in Table 2 below. TABLE 2 * GCD (Gas chromatography Distillation) conducted according to ASTM D The source materials were separated into fractions of increasing polarity by column chromatography. The majority of this was done using silica and Biosil® (silicic acid) stationary phases; however, a few others such as alumina and clay were also investigated. Details of the solvent elution systems used are given below: 1. Fractionation of catalytically cracked gas oil The CCGO was fractionated by a two stage operation. In the first stage silica was employed as the stationary phase. The most polar fraction from this process was then fractionated further using silicic acid. A. CCGO fractionated on silica 300gms of the CCGO were blended with 200gms of pentane and the resulting blend was run onto the column. The eluents were then added sequentially and the separate fractions collected as shown in Table 3 belo . TABLE 3 Silica fractionation of catal ticall cracked as oil iPA = isopropyl alcohol B. Silica fraction 5 (THF fraction) further fractionated on Biosil In this stage 20gms of the Silica fraction 5 (Silica F5), from above, was added to 180gms of silicic acid (Biosil) that had been treated 20gms of water overnight. The solvent eluents were then added in sequence and the fractions collected separately as shown in Table 4 below. TABLE 4 Fractionation of Silica fraction 5 on Biosil iPA = isopropyl alcohol It was found that non-polar compounds do not interact with the stationary phase and thus pass through the column quicker than polar compounds. Solvent eluents with increasing polarity were sequentially passed through the column to assist the removal of compounds with increasing the polarity. The more polar fractions were used to investigate boundary lubrication effects using the HFRR technique outlined above. Compositional analysis data for the resultant fractions are shown in Table 5 and treat rates used and the HFRR results achieved are shown in Table 6 below: TABLE 5 Composition and erformance of fractions from catal ticall cracked stream 10,000 ppm = 1% - = data not available There was an insufficient amount of biosil fraction 1 to conduct any compositional analysis or HFRR evaluation. TABLE 6 Fractions blended into a mixture of Isopar®M and mixed xylenes (67:33 by volume) at concentrations shown in above Table. BF = Biosil® fraction - = data not available The silica polar fraction (fraction 5) and the latter Biosil fractions 3 to 5 boosted the lubricity performance to an improved level (smaller wear scar diameter). These fractions have high N content (> 0.6%>, 6,000 ppm), a basic nitrogen content of 500 ppm or more and have an improved S/N ratio (0.1 vs 10) when compared with the original sample prior to fractionation. Thus, the improved lubricity performance is achieved with a smaller amount of added fraction and with a smaller increase in S content. 2. Fractionation of Fawley fuel blend This fuel blend was fractionated using silica and clay as the stationary phase. A. Fawley fuel blend fractionated on Silica 300gms of the fuel blend was run onto the column, and following this the eluents were added sequentially and the separate fractions collected as shown in Table 7 below. TABLE 7 B. Fawley fuel blend fractionated on Clay 300gms of the fuel blend was run onto the column, and following this the eluents were added sequentially and the separate fractions collected as shown in Table 8 below. TABLE 8 Clav fractionation of Fawlev fuel blend Compositional analysis data for the starting blend and key fractions are shown in Table 9 and treat rates used and the HFRR results achieved for the silica and clay polar fractions are shown in Table 10 below: TABLE 9 BF = Biosil Fraction, 10,000 ppm = 1% TABLE 10 Fractions blended into a Isopar® at concentrations shown in above Table. These data show that both fractions had a beneficial effect on the lubricity performance of Isopar M, with the clay fraction being more potent than the Silica fraction.

Claims: Claims: 1. A diesel fuel composition having enhanced lubricity, said composition comprising a major amount of a diesel fuel as base fuel blended with a minor amount of a nitrogen rich fraction characterised in that the nitrogen rich fraction is derived from a source material selected from (i) a solvent extract of a solid or semi-solid natural fossil, or, (ii) a refinery process stream or blend such that the sulphur to nitrogen atom ratio in said nitrogen rich fraction is less than 4. 2. A diesel fuel composition according to Claim 1 wherein said base fuel has a sulphur content of less than 500 ppm by weight. 3. A diesel fuel composition according to Claim 1 or 2 wherein said base fuel has a sulphur content of less than 50 ppm by weight and a T 95 of < 370°C. 4. A diesel fuel composition according to any one of the preceding Claims wherein the nitrogen-rich fraction is derived from a refinery process stream or fuel blend which distil within the diesel oil boiling range 150-450°C. 5. A diesel fuel composition according to any one of the preceding Claims wherein the nitrogen-rich fraction is derived from a refinery process stream or fuel blend which distil within a diesel oil boiling range of 150-400°C. 6. A diesel fuel composition according to any one of the preceding Claims wherein the refinery process stream or fuel blend is sourced from a pipestill or from a secondary processing of a stream comprising catalytic cracking of a heavy gas oil in turn derived from the atmospheric or vacuum pipestill. 7. A diesel fuel composition according to any one of the preceding Claims wherein the nitrogen rich fraction is derived from refinery process stream or blend by a method comprising: a. using a stationary/liquid phase separation method in which the stationary phase is an absorbent, or b. a liquid/liquid phase separation based on the preferential partition of the components of the appropriate fractions between mutually immiscible solvents, or c. osmosis through a membrane. 8. A diesel fuel composition according to Claim 7 wherein the absorbant in the stationary phase is selected from alumina, silica, silicic acid, clay and/or a zeolite. 9. A diesel fuel composition according to any one of the preceding Claims 1-3 wherein the nitrogen-rich fraction is extracted from a natural solid or semi-solid fossil fuel selected from coal, bitumen and oil shale using a solvent extraction method. 10. A diesel fuel composition according to Claim 7 wherein the solvent used for solvent extraction is tetrahydrofuran. 11. A diesel fuel composition according to any one of the preceding Claims wherein the nitrogen rich fraction has an absolute nitrogen content of at least 1000 ppm by weight. 12. A diesel fuel composition according to any one of the preceding Claims wherein the nitrogen rich fraction has an absolute nitrogen content of at least 1000 ppm by weight, a basic nitrogen content of at least 200 ppm by weight. 13. A diesel fuel composition according to any one of the preceding Claims wherein said nitrogen rich fraction has an absolute nitrogen content of at least 6000 ppm by weight. 14. A diesel fuel composition according to Claim 12 wherein the nitrogen rich fraction has a sulphur to nitrogen atom ratio of less than 1. 15. A diesel fuel composition according to any one of the preceding Claims wherein the amount of the nitrogen-rich fraction (re)blended with the base fuel is no more than 1%) by weight of the total fuel composition.

Inventors: ABBOTT DOUGLAS J, BARBOUR ROBERT HOWIE, RICKEARD DAVID J, ABBOTT, DOUGLAS, J., BARBOUR, ROBERT, HOWIE, RICKEARD, DAVID, J.
Applicants: ABBOTT DOUGLAS J, BARBOUR ROBERT HOWIE, EXXONMOBIL RES & ENG CO, RICKEARD DAVID J, ABBOTT, DOUGLAS, J., BARBOUR, ROBERT, HOWIE, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY, RICKEARD, DAVID, J.
Application year: 2000
Main classification: C10L1
IPC codes: C10L1, C10L10