Biodiesel-fischer-tropsch hydrocarbon blend

Abstract

The invention provides a biodiesel and Fischer-Tropsch derived hydrocarbon blend, whereby the characteristics of the Fischer-Tropsch derived hydrocarbon are used to improve the diesel-like characteristics of biodiesel. The invention also provides a blending component for Compression Ignition engine fuel as well as a method of adjusting the density of a hydrocarbon fuel.

Description

FIELD OF INVENTION

[0001] This invention relates to blending Fischer-Tropsch fuel with biodiesel.

BACKGROUND OF THE INVENTION

[0002] Various companies globally are processing various agriculturally based fatty oils to “biodiesel”, which is typically the methyl or ethyl ester of the respective fatty acids of the triglyceride fatty oils.

[0003] This biodiesel can be used “neat” as a diesel substitute, but more typically is used as a blend (between 5-20%) with conventional (crude based) diesel, for example, SAE 962065.

[0004] Advantages of using biodiesel include the attractive low sulphur and low aromatics content, excellent lubricity and as a renewable fuel, the low net impact on the environment (CO2 emissions etc) compared with fossil fuels.

[0005] The oxygen content of biodiesel is generally considered to aid some particulate matter (PM) reduction (ref. SAE 199901-1475).

[0006] Disadvantages for biodiesel when compared to the proposed 2000 World Wide Fuel Charter for diesel (Category IV) include:

[0007] Marginal cetane no. (50 vs. recommended >55)

[0008] a fuel density that exceeds the recommended density

[0009] excessive viscosity at 40° C.

[0010] a measurably lower calorific value

[0011] marginal properties for cloud point and final boiling point

[0012] Some characteristics of biodiesel are thus sub-optimal with respect to the intentions of engine manufacturers.

[0013] Fischer-Tropsch diesel can be produced from preferably natural gas but also other hydrocarbon feedstocks, and shares the characteristics with biodiesel of an environmentally friendly low sulphur, low aromatics content fuel. Whereas biodiesel consists of mainly linear oxygenates (esters), Fischer-Tropsch diesel consists of mainly highly linear paraffins.

SUMMARY OF THE INVENTION

[0014] In this specification, unless the context clearly indicates the contrary, “Biodiesel” is considered to encompass all biologically derived oils such as, but not limited to, rape seed, cotton, sunflower, coconut and palm, animal fats, soya, etc.; which may have been processed to methyl or ethyl esters of the triglyceride fatty oils.

[0015] According to a first aspect of the invention, there is provided a biodiesel and Fischer-Tropsch derived hydrocarbon blend, whereby the characteristics of the Fischer-Tropsch derived hydrocarbon are used to improve the “diesel” characteristics of biodiesel, for example, fatty methyl esters.

[0016] The Fischer-Tropsch derived hydrocarbon may be blended with biodiesel in varying ratios to improve the resultant diesel fuel's characteristics.

[0017] Thus the invention provides a hydrocarbon composition for use in compression ignition engines (CI), said composition comprising a blend of Fischer-Tropsch derived hydrocarbon and biodiesel in a volumetric ratio of from 1:5 to 4:1 and having a density of above 0.8 kg/l @ 15° C.

[0018] The composition may have a viscosity below 4.1 cSt.

[0019] The volumetric blending ratio may be from 1:4 to 4:1.

[0020] The volumetric blending ratio may be from 1:2 to 2:1.

[0021] Typically the volumetric blending ratio is 1:1.

[0022] The hydrocarbon composition may have a cetane number in excess of 50 typically in excess of 55.

[0023] The hydrocarbon composition may have a Cold Filter Plugging Point (CFPP) in accordance with IP 309 of below −12° C., typically below −15° C.

[0024] Typically the biodiesel may comprise of a mixture of linear C10-C20 methyl esters with minor quantities of water, glycerol and methanol.

[0025] The Fischer-Tropsch hydrocarbon which is blended with biodiesel may be derived from a Fischer-Tropsch synthesis process using a catalyst which is based on a metal selected from a group consisting of iron, cobalt or ruthenium or mixtures thereof.

[0026] The composition of the Fischer-Tropsch hydrocarbon may include a varying mixture of paraffins, olefins and oxygenates. Typically the Fischer-Tropsch hydrocarbon comprises a mixture of both linear and branched C8-C20 paraffins, C9-C20 olefins and C7-C20 alcohols.

[0027] The Fischer-Tropsch hydrocarbon may be a Fischer-Tropsch diesel.

[0028] The Fischer-Tropsch hydrocarbon preferably includes hydroprocessed Fischer-Tropsch hydrocarbon.

[0029] The invention extends to a blending component for a hydrocarbon composition useful in Compression Ignition engines (CI engines), said blending component comprising a blend of Fischer-Tropsch derived hydrocarbon and biodiesel in a volumetric ratio of from 1:5 to 4:1.

[0030] The blending component may have a density of at least 0.8 kg/l at 15° C.

[0031] The blending component may have a viscosity below 4.1 cSt.

[0032] The volumetric blending ratio of Fischer-Tropsch derived hydrocarbon and biodiesel in the blending component may be from 1:4 to 4:1.

[0033] The volumetric blending ratio of Fischer-Tropsch derived hydrocarbon and biodiesel in the blending component may be from 1:2 to 2:1.

[0034] Typically the volumetric blending ratio of Fischer-Tropsch derived hydrocarbon and biodiesel in the blending component is 1:1.

[0035] The invention extends to a method of increasing the density of a hydrocarbon fuel composition having a density of below 0.8 kg/l to above 0.8 kg/l, said method including blending of biodiesel into the fuel composition in a volumetric ratio of bio-diesel to hydrocarbon fuel composition of at least 1:3 as calculated before the blending in of the bio-diesel, thereby to obtain a resulting fuel composition having a density of above the 0.8 kg/l threshold.

[0036] The volumetric ratio may be at least 1:2, typically about 1:1.

EXAMPLE OF THE INVENTION

[0037] The invention will now be illustrated, without limiting the scope thereof, by way of the following examples and illustrative values.

Example 1

Blending Rapeseed Methyl Ester with Hydroprocessed Fischer-Tropsch Derived Diesel

[0038] A hydroprocessed Fischer-Tropsch derived diesel, also referred to as a gas-to-liquids or GTL diesel, was blended in various volumetric ratio's with rapeseed methyl ester and the properties thereof were measured.

[0039] Blending Gas-to-Liquid (GTL) Fuel, a hydroprocessed Fischer-Tropsch derived diesel, with biodiesel has synergistic benefits which are obtained from the combined good qualities of both fuels. Neither biodiesel nor GTL Fuel contains aromatics or sulphur, which would normally limit blending ratios with conventional diesel. GTL Fuel improves the cold flow properties and increases the viscosity associated with biodiesel. On the other hand, Biodiesel increases the GTL Fuel density without weakening its low energy density. More biodiesel (50%) can be mixed with GTL Fuel when used as a replacement base fuel than the standard 20% blends with conventional diesel.

[0040] Biodiesel is prone to gel formation in cold weather. GTL Fuel, on the other hand, has good cold flow properties and a high cetane value as a consequence of the predominately methyl branching that occurs in the terminal positions of the paraffinic chains during the isomerisation process. This type of branching prevents wax crystallisation while maintaining a high cetane number. GTL Fuel has excellent thermal stability that exceeds premium diesel requirements. Other good biodiesel properties include its high flash point, which makes it a safe fuel to use. Both GTL Fuel and Biodiesel are readily biodegradable and non-toxic if spilt.

[0041] GTL Fuel—Biodiesel blends were prepared from biodiesel that was produced from rapeseed oil, (also called rapeseed methyl ester). The blend formulations comprised 90%, 80%, 65%, 50% and 20% biodiesel mixtures with GTL Fuel. The fuel properties of GTL Fuel and biodiesel and blends thereof, are shown in Table 1, 2 and Table 3. The digits following the B in the table header indicate the volumetric percentage of the biodiesel in the composition.

[0042] The net, or lower, volumetric heating values of the GTL Fuel—biodiesel blends (see Table 2) were calculated from the gross heating value results obtained through the ASTM D240 test method, by subtracting the heat of condensation of water. 1 TABLE 1 Full specification analysis of GTL Fuel - biodiesel blends Analysis Units Method B100 B90 B80 B65 B50 B20 GTL Colour ASTM 1 1 1 1 1 <1 <1 D1500 Appearance Caltex 1 1 1 1 1 1 1 CMM76 Density @ 20° C. kg/l ASTM 0.880 0.868 0.857 0.839 0.822 0.788 0.764 D4052 Density @ kg/l ASTM 0.883 0.871 0.860 0.843 0.825 0.791 0.768 15° C. D4052 Distillation ASTM D86 IBP ° C. 323 173 166 166 162 153 150  5% ° C. 333 186 228 199 189 176 173 10% ° C. 335 321 285 222 204 185 178 20% ° C. 336 330 320 280 239 203 192 30% ° C. 337 333 330 312 278 225 208 40% ° C. 337 335 334 326 306 249 226 50% ° C. 338 336 336 332 321 271 244 60% ° C. 338 337 338 335 330 294 263 70% ° C. 339 338 339 337 334 310 281 80% ° C. 341 339 340 339 337 323 297 90% ° C. 346 342 343 342 340 333 315 95% ° C. 352 353 355 352 348 338 326 FBP ° C. 354 359 360 357 355 345 334 Recovery vol % 99 99 98 99 99 99 98 Residue vol % 0.5 0.5 1.0 0.5 0.5 0.7 1.0 Flash point ° C. ASTM D93 125 100 84 73 68 61 59 Viscosity cSt ASTM 4.49 4.11 3.72 3.28 2.89 2.27 1.97 @40° C. D445 CFPP ° C. IP 309 −12 −13 −14 <−15 <−15 <−15 −20 Ash content mass % ASTM <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 D482 Sediment mass % ASTM <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 D473 Water vol % ASTM 0.033 0.023 0.022 0.019 0.015 0.008 0.003 D1744 Carbon mass % ASTM 0.19 0.17 0.14 0.11 0.08 0.03 0.02 Residue D524 Sulphur mass % ASTM 0.0004 0.0004 0.0003 0.0003 0.0002 0.0001 0.0001 D5453 Cu corr. rating ASTM 1b 1b 1b 1b 1b 1b 1b D130 Acid number mgKOH/g ASTM 0.101 0.086 0.073 0.056 0.048 0.023 0.001 D664 Cetane ASTM 63 63 63 63 66 69 71 D613 Elec. pS/m 140 130 100 70 40 10 0 Conductivity O2 stability mg/100 ml ASTM 5.7 4.8 4.1 3.1 2.1 0.16 0.21 D2274 Bromine gBr/100 g IP 129 77.1 68.4 59.3 53.2 38.0 15.9 0.8 number Nitrogen mg/l ASTM 2 1 1 1 1 <1 <1 D5291

[0043] 2 TABLE 2 Heat of combustion of GTL Fuel - biodiesel blends Gross Hydrogen Net heating heating value content value Density Net heating (MJ/kg) (mass %) (MJ/kg) (kg/l) value (MJ/l) B(100) 39.973 11.92 37.444 0.880 32.950 B(90) 40.565 12.15 37.987 0.868 32.973 B(80) 41.330 12.81 38.612 0.857 33.090 B(65) 42.124 13.69 39.219 0.839 32.905 B(50) 43.189 13.19 40.390 0.822 33.201 B(20) 45.346 14.42 42.286 0.788 33.321 GTL 47.015 14.98 43.836 0.764 33.491

[0044] The lubricity properties of the GTL Fuel—biodiesel blends were determined according to the ASTM D6078 and ASTM D6079 test methods which define the scuffing load ball-on-cylinder (SL BOCLE) and high-frequency reciprocating rig (HFRR) lubricity evaluation test methods respectively. Results are shown in Table 3. 3 TABLE 3 High-frequency reciprocating rig (HFRR) and scuffing load ball-on-cylinder (SL BOCLE) lubricity evaluation of GTL Fuel - biodiesel blends B100 B90 B80 B65 B50 B20 GTL HFRR 141 156 150 148 152 166 651 (WSD &mgr;m) SL >6000 >6000 >6000 >6000 >6000 6000 2800 BOCLE Load g

[0045] Characterisation and quantification of the neat biodiesel and GTL Fuel was obtained through Gas Chromatograph Mass Spectrometry (GC MS), Gas Chromatograph Flame Ionisabon Detection (GC-FID) and Fluorescent Indicator Adsorption (FIA).

[0046] Diesel density specifications are tending to become tighter. This is due to the conflicting requirements of a lower density fuel to reduce particulate matter emissions, whilst retaining a minimum density to ensure adequate heat content, which relates to fuel economy. The tightening density specification can be seen from the EN 590:1999 Diesel Fuel Specifications which correlates to EURO 3 emission specifications. Since biodiesel has a higher density than GTL diesel, the greater the biodiesel fraction in the biodiesel—GTL Fuel blends the higher its density (see Table 1 and Table 2). A blend including 30% biodiesel exceeded a density of 0.8 kg/l

[0047] In general, the higher the density of a hydrocarbon fuel, the greater is its volumetric heat of combustion and the lower is its volumetric fuel consumption. However, from Table 2 it is obvious that biodiesel, which is not a hydrocarbon fuel but a methyl ester, has a low net volumetric heating value, also called energy density. Biodiesel will therefore not assist in raising GTL Fuel's energy density but will not lower it significantly. In terms of specifications, higher density for GTL Fuel can therefore be realised by biodiesel blending without influencing its energy density negatively.

[0048] Distillation temperature also influences emissions. A high T90 or T95 temperature will increase the quantity of unburned hydrocarbons and the level of particulate matter emitted. All GTL Fuel—biodiesel blend formulations were below the maximum current T95 distillation EN 590 Diesel Specification limit of 360° C.

[0049] GTL Fuel is mostly paraffinic in nature. 98% (volume %) GTL Fuel is comprised of paraffins and 2% comprises olefins in a hydrocarbon range from C8 to C24. Less than 0.001 volume % aromatics are present in GTL Fuel according to FIA analysis.

[0050] In an engine, the viscosity influences the injection fuel spray. Fuel with a very high viscosity can reduce fuel flow rates, resulting in inadequate fuelling. Such a fuel also atomises poorly, resulting in poor combustion, loss of efficiency and an increase in CO and hydrocarbon emissions. On the other hand, if the fuel viscosity is too low, the injection spray is too soft and will not penetrate far enough into the cylinder and loss of power will occur. Blending GTL Fuel with biodiesel improves the CFPP value of biodiesel and it is possible to attain the winter grade specifications of some European countries (see Table 1).

[0051] Like GTL Fuel, neat rapeseed methyl ester (RME), or biodiesel, has a high cetane number relative to conventional diesel. Blends of biodiesel with GTL Fuel exhibit a high cetane number.

[0052] GTL Fuel blends with biodiesel also improves fuel properties that do not affect engine performance directly. These include the high water content, acid number, bromine number, oxygen stability of biodiesel and the tendency of biodiesel to form carbonous residue. The amount of water present in the neat biodiesel and its acid number are within the EU Draft Specification for biodiesel and ASTM PS121 biodiesel specifications, but is much higher than conventional or synthetic diesel fuel and can lead to corrosion problems. Biodiesel blend formulations with GTL Fuel, with its very low water content and acid number, decrease the water content and acid number of biodiesel proportionally.

[0053] The bromine number of GTL Fuel is very low because it contains less than 2% olefins whereas that of biodiesel is high (see Table 1) because of the large percentage unsaturated methyl esters. Blending of GTL Fuel with biodiesel does not only decrease the susceptibility of biodiesel to gum formation by lowering the bromine number, but also increases biodiesel's resistance to degrade in the presence of oxygen. The insolubles formed in neat RME in the presence of oxygen is much higher than specified according to the Biodiesel EU Draft Specification.

[0054] Thus, it is believed, more biodiesel can be mixed with GTL Fuel than the standard 20% blends with conventional diesel. GTL Fuel—biodiesel blend ratios up to 50% biodiesel still comply with present EN 590:1999 Diesel Specifications. This is in part due to the high cetane number, good cold flow properties and stability of GTL Fuel. Neither biodiesel nor GTL Fuel contains aromatics and both are sulphur free. GTL Fuel improves the cold flow characteristics of biodiesel, whereas biodiesel does not negatively effect the energy density of the GTL fuel.

[0055] Biodiesel increases GTL Fuel density without influencing the GTL Fuel energy density negatively.

[0056] The inventors further believe that advantage of the invention include that with progressively increased blending, the biodiesel characteristics are improved with respect to:

[0057] cetane number exceeds recommended 55

[0058] density is reduced to within the desired range

[0059] viscosity is reduced to within the specified range

[0060] the overall calorific value is closer to “standard” ULSD diesel

[0061] the flash point is closer to “standard” ULSD diesel

[0062] the cold flow properties are better

[0063] the T90 distillation is moderated slightly downwards

[0064] It is believed that positive biodiesel characteristics such as the low aromatics and sulfur content and biodegradability are retained.

[0065] The GTL fuel—biodiesel blend may be utilised as a blending component for blending with crude derived diesel without adversely affecting the good GTL properties or on-spec crude derived qualities.

[0066] Thus, blending Fischer-Tropsch hydrocarbons with biodiesel allows a more compatible mixture and high biodiesel content, whereas blending biodiesel with crude based diesel favours predominantly a minor fraction (520%) of diesel.

[0067] The Fischer-Tropsch hydrocarbon-biodiesel blend may be used as a blending component for blending with crude derived diesel in any blend ratio to enhance the crude derived diesel quality without adversely affecting any of the properties typically included in specifications for crude derived diesel.

Claims

1. A hydrocarbon composition for use in compression ignition engines (CI), said composition comprising a blend of Fischer-Tropsch derived hydrocarbon which includes hydroprocessed Fischer-Tropsch hydrocarbon, send blend having a density of below 0.8 kg/l at 15° C. and bio-diesel having a density of above 0.8 kg/l at 15° C. in a volumetric ratio of from 1:4 to 4:1, said composition having a density of above 0.8 kg/l at 15° C. while maintaining the Fischer-Tropsch derived hydrocarbon's net volumetric heating valve.

2. A hydrocarbon composition as claimed in claim 1, having a viscosity of below 4.1 cSt.

3. A hydrocarbon composition as claimed in claim 1, wherein the volumetric ratio is from 1:2 to 2:1.

4. A hydrocarbon composition as claimed in claim 3, wherein the volumetric blending ratio is 1:1.

5. A hydrocarbon composition as claimed in claim 1, having a cetane number in excess of 50.

6. A hydrocarbon composition as claimed in claim 5, having a cetane number in excess of 55.

7. A hydrocarbon composition as claimed in claim 1, having a CFPP in accordance with IP 309 of below −12° C.

8. A hydrocarbon composition as claimed in claim 7, having a CFPP in accordance with IP 309 of below −15° C.

9. A hydrocarbon composition as claimed in claim 8, wherein the biodiesel comprises of a mixture of linear C10-C20 methyl esters with minor quantities of water, glycerol, and methanol.

10. A hydrocarbon composition as claimed in claim 1, wherein the Fischer-Tropsch hydrocarbon which is blended with bio-diesel is derived from a Fischer-Tropsch synthesis process using a catalyst which is based on a metal selected from a group consisting of iron, cobalt, and ruthenium, or mixtures of two or more thereof.

11. A hydrocarbon composition as claimed in claim 1, wherein the composition of the Fischer-Tropsch hydrocarbon includes a mixture of paraffins, olefins, and oxygenates.

12. A hydrocarbon composition as claimed in claim 11, wherein the Fischer-Tropsch hydrocarbon comprises a mixture of both linear and branched C9-C20 paraffins, C9-C20 olefins, and C7-C20 alcohols.

13. A hydrocarbon composition as claimed in claim 1, wherein the Fischer-Tropsch hydrocarbon is a Fischer-Tropsch diesel.

14. (Canceled)

15. A blending component as claimed in claim 14, having a density of at least 0.8 kg/l at 15° C.

16. A blending component as claimed in claim 14, having a viscosity below 4.1 cSt.

17. A blending component as claimed in claim 14, wherein the volumetric blending ratio of Fischer-Tropsch derived hydrocarbon and biodiesel in the blending component is from 1:4 to 4:1.

18. A blending component as claimed in claim 14, wherein the volumetric blending ratio of Fischer-Tropsch derived hydrocarbon and biodiesel in the blending component is from 1:2 to 2:1.

19. A blending component as claimed in claim 14, wherein the volumetric blending ratio of Fischer-Tropsch derived hydrocarbon and biodiesel in the blending component is 1:1.

20. A method of increasing the density of a hydrocarbon fuel composition having a densisty of below 0.8 kg/l to above 0.8 kg/l, said method including blending of bio-diesel into the fuel composition in a volumetric ratio of bio-diesel to hydrocarbon fuel composition of at least 1:3 as calculated before the blending in of the bio-diesel, thereby to obtain a resulting fuel composition having a density of above the 0.8 kg/l threshold and a net volumetric heating value of about 33 000 MJ/m3 wherein said fuel composition includes hydroprocessed Fischer-Tropsch hydrocarbon.

21. A method as claimed in claim 20, wherein the volumetric ratio is at least 1:2.

22. A method as claimed in claim 21, wherein the volumetric ratio is about 1:1.

23. (Canceled)