AU2005238539B2 - Crude oil derived and gas-to-liquids diesel fuel blends - Google Patents

Description

WO 2005/105961 PCT/ZA2005/000060 Crude Oil Derived and Gas-To-Liquids Diesel Fuel Blends 10 Field of the Invention The invention relates to crude oil derived and Gas-To-Liquids (GTL) diesel fuel blends. 15 Background of the Invention Synthetic fuels such as GTL (Gas To Liquids) diesel fuel have seen a significant rise in interest in recent years. They are considered to be extremely clean fuels, with negligible sulfur and aromatics, and are odor-free and have a cetane number of > 70. 20 The GTL diesel fuel used in the examples in this patent specification was manufactured by means of the Sasol Slurry Phase Distillate (Sasol SPDTM) process, which consists of three process steps, as depicted schematically in Fig. 1. 25 In the first step an auto-thermal reforming process is used to convert the natural gas into the synthesis gas, a mixture of CO and H 2 . In a second step the synthesis gas is converted into a so-called syncrude containing predominantly paraffinic hydrocarbons, by a Fischer-Tropsch process. This syncrude is primarily in the form of waxes and distillates, which are further refined in a third, product upgrading step by 30 means of mild hydro-processing, in order to produce products that meet commercial fuel specifications, such as diesel fuel and kerosene. 1 WO 2005/105961 PCT/ZA2005/000060 Summary of the Invention The invention provides a diesel fuel composition comprising both crude oil derived diesel fuel, which crude oil derived diesel fuel has a density at 15 deg C below 0.85 5 kg/I, a sulphur content of less than 10 mg/kg, a polyaromatics content of below 5 mass%, and a cetane number from 51 to 60, and Gas-to-Liquids (GTL) diesel fuel, which GTL diesel has a density at 15 deg C of below 0.78 kg/, a sulphur content of less than 1 mg/kg, polyaromatics below 0.1 mass%, and a cetane number above 65, in a volumetric ratio range of from 1:99 to 99:1 and with a molar H:C ratio of between 10 1.8:1 and 2.1:1. The diesel fuel composition may have less than 10 mg/kg sulphur. The diesel fuel composition may have less than 5 mass% polycyclic aromatics. 15 The crude oil derived diesel fuel may be a fuel meeting the EN590 specification. The volumetric ratio range may be from 1:9 to 9:1. 20 The volumetric ratio range may be from 1:5 to 5:1. The molar H:C ratio may be from 1.85:1 and 2.05:1. The molar H:C ratio may be from 1.9:1 and 2.00:1. 25 The diesel fuel composition may have an ASTM D86 10% distillation temperature of from 180 0 C to 2200C. The ASTM D86 10% distillation temperature may be from 2000C to 2150C. 30 The diesel fuel composition may have a flash point of between 600C and 800C, typically from 650C to 780C. The diesel fuel composition may have a density at 150C of from 0.77 kg/l to 0.84 kg/. 35 2 WO 2005/105961 PCT/ZA2005/000060 The diesel fuel composition may have a density at 150C of from about 0.8 kg/I to about 0.82 kg/I. The diesel fuel composition may have a lower heating value of from 42 500 kJ/kg to 5 43 800kJ/kg, usually from 43 100 kJ/kg to 43 600 kJ/kg, typically from 43 200 kJ/kg to 43 500 kJ/kg. Use of Gas-to-Liquid diesel fuel as a blend component for a diesel fuel composition, which, when combusted in an engine, has reduced NOx and soot emissions, which 10 composition comprises both crude oil derived diesel fuel meeting the European EN590 specification for sulphur-free diesel fuel (designated EU diesel), and the Gas to-Liquids (GTL) diesel fuel, wherein the crude oil derived diesel fuel to Gas-to-Liquid diesel volumetric blend ratio ranges from 1:99 to 99:1 and the composition has a molar H:C ratio of between 1.8:1 and 2.1:1. 15 Reductions in both NOx and soot emissions may be obtained which are greater than indicated by the blending ratio of the GTL diesel in the crude oil derived diesel fuel. Thus, more than 70% of the reduction in both NOx and soot emissions which may be 20 be obtained with neat GTL diesel fuel, may be obtained with a 1:1 GTL:Crude derived diesel ratio. More than 40% of the reduction in both NOx and soot emissions which may be obtained with neat GTL diesel, may be obtained with a 1:4 GTL:Crude derived diesel 25 ratio. However, in some embodiments the reduction in NOx emissions may be less than the reduction in soot emissions, and vice versa. 30 In some embodiments, the reduction in NOx may be minimal, however, the NOx will be reduced by the use of GTL diesel in accordance with the invention. The properties of the composition and the blending ratios of the components are as described above for the composition. 3 WO 2005/105961 PCT/ZA2005/000060 Examples Involving the Invention The effect of GTL diesel fuel blends on exhaust emissions and engine performance 5 has been studied. EU diesel fuel was used as a reference fuel, in addition to being the base stock for the blends. The properties of test fuels used in the investigation are shown in Table 1. Table 1 Properties of the fuels investigated in this study. 10 GTL EU50 EU80 EU Proprty nits2005 Property Units 100% GTL 50:50 Blend 80:20 Blend European diesel fuel EU:GTL EU:GTL sulphur-free diesel fuel Density @ 150C kg/I 0.768 0.802 0.821 0.836 Density @ 200C kg/l 0.765 0.798 0.817 0.832 Cetane Number 71 62 58 54 Total Sulphur mg/kg < 1 4 6 7 D86 Distillation IBP 0C 169 157 174 193 5% 0C 180 193 204 214 10% 0C 187 201 212 221 20% 0C 200 215 225 233 30% 0C 219 231 240 248 40% 0C 235 248 256 264 50% 0C 251 264 270 277 60% 0C 267 277 282 287 70% 0C 283 291 294 299 80% 0C 297 305 307 313 90% 0C 312 322 324 332 95% 0C 321 337 339 354 FBP 0C 329 346 350 360 Flash Point 0C 59 66 76 82 Kinematic Viscosity @ 400C m 1.97 2.54 2.79 2.95 CFPP 0C -19 -18 -17 -17 Cloud Point 0C -18 -17 -15 -14 Total Aromatics* % m/m 0.1 13.5 21.5 26.8 Bi- and Polycyclic aromatics* % m/m 0.0 2.3 3.7 4.6 Hydrogen Content* % m/m 15.0 14.3 13.8 13.5 H/C ratio (molar)* - 2.10 1.98 1.91 1.86 Lower Heating Value* MJ/kg 43.8 43.5 43.2 43.1 HFRR Wear Scar Diameter pm 370 < 400 <400 394 8Values for blends calculated according to blending ratio 4 WO 2005/105961 PCT/ZA2005/000060 Dynamometer tests were conducted with a Mercedes BenzTM E220 CDI vehicle, using the New European Driving Cycle (NEDC) emission test, and without any changes to the basic EU3 emission level engine calibration or engine hardware. The vehicle was tested with its standard calibration without any adaptation, with EU 5 diesel, the 1:1 blend and for the neat GTL fuel. The relevant test vehicle data are shown in Table 2. Table 2 Test vehicle and engine data Vehicle designation Mercedes E 220 CDI Limousine Model year 2003 Transmission 6-speed manual gearbox Gross vehicle mass 2 145 kg Engine designation MB OM646, EU3 emission level Displacement, configuration 2,2 L, in-line 4 cylinder, 4 valves per cylinder Compression ratio 18: 1 Fuel management Common rail fuel injection (peak pressure 1 600 bar) Air management Turbocharged (VNT), intercooled Emission control Cooled EGR, inlet swirl control, close coupled and underfloor oxidation catalysts Rated torque 340 Nm at 2 000 rev/min Rated power 110 kW at 4 200 rev/min 10 The results of the unadapted vehicle emission tests are depicted in Fig. 2 for the EU diesel, EU50, and GTL diesel fuel. The averaged results for the test runs are presented as the percentages relative to the EU diesel reference fuel. FC indicates the volumetric fuel consumption. 15 For neat GTL diesel fuel, an unexpectedly high reduction of >90% for HC and CO emissions was observed. The CO and HC reductions for the 50% blend scale roughly with the blending ratio. The NOx emissions were reduced marginally, with the 50% blend again showing about half the reduction of the neat GTL diesel fuel. 20 The same applies for the HC+NOx data. PM emissions were reduced by up to 30% with the GTL diesel. Surprisingly, a strong non-linear characteristic was evident with the 50% blend (EU50), which showed a reduction of approximately 22%. 25 5 WO 2005/105961 PCT/ZA2005/000060 The potential for further emission reductions with the test fuels, and including the optimisation of a limited number of software parameters in the Engine Control Unit (ECU) of the engine was then investigated. For this purpose, an engine mounted on a test bench was used. Steady state test runs were carried out at five operating 5 points characteristic for NEDC emission test cycle. The software parameters investigated were the Exhaust Gas Recirculation (EGR) rate, the start of pilot injection (SOPI) and the start of main injection (SOMI). The five operating points are shown in Table 3 10 Table 3 Steady state engine test points chosen to reflect NEDC characteristics. Engine Test Engine Speed bmep Power Description Point (rev/min) (bar) (kW) 1 1 000 0 0 Pseudo Idle 2 1 600 3.3 9 3 2 000 2 7 Characteristic operating 4 2000 5 18 pointsfortheNEDC 5 2800 4 20 emission test Fig. 3 shows two examples of results obtained from the steady state test bench work. 15 The figure depicts representative data for the effect of GTL diesel fuel and its blends on the soot - NOx trade-off characterisitc at two operating points, namely 1 600 rev/min and 3,3 bar bmep (brake mean effective pressure), and 2 000 rev/min and 5 bar bmep. In this case, the EGR rate was varied, while the SOPI and SOMI were kept constant and equal to the reference values. Soot emission levels were 20 calculated from exhaust smoke levels determined by FSN (Filter Smoke Number) measurements. It is evident that GTL diesel offers a significant reduction in terms of both soot emissions and NOx for all the EGR rates tested. The soot emission increase for 25 decreasing NOx values follows the expected pattern, and enables a wide range of possible alternative software calibrations. Surprisingly, the strong non-linear behavior of the EU50 blend is again evident - this fuel exhibits almost the same benefits as neat GTL diesel fuel. 6 WO 2005/105961 PCT/ZA2005/000060 A design of experiments (DOE) method was used to numerically optimize the three software parameters simultaneously. The DOE predictions were verified by actual experiments, and an example of the results of the simultaneous optimisation of all three calibration parameters at each of the engine operating points is shown in Fig. 4. 5 In this case the optimisation has been performed to minimise NOx emissions with the GTL diesel fuel. Reductions of between 30% and 75% were obtained, without compromising the other emissions, when compared to the EU diesel. The measured data at the five steady-state test points was used to predict the 10 emissions over the NEDC test cycle. Empirical factors were used to account for the differences between the steady-state and transient engine operation. All results from the selected operating points have been normalized and combined into one universal plot, shown in Fig. 5, to mimic the behavior in a NEDC test with an optimized calibration for each fuel. A surprisingly large reduction in soot and NOx appears to 15 be possible for the GTL diesel fuel and the EU50 and EU80 blends. These reductions are possible without hardware changes to the engine. The neat GTL would allow for a simultaneous soot and NOx reduction of at least 35% compared to the EU diesel calibration. For constant engine-out soot emission, a 20 NOx reduction of 45% seems possible. Due to the non-linear response with the GTL blends, reductions in soot and NOx that are greater than expected when considering the blending ratio, could be obtained with the EU80 and EU50 fuels. This non-linear response is depicted graphically in Fig. 6. 25 A 50% GTL blend would recover approximately 85% of the soot/NOx benefits of neat GTL, while a 20% GTL blend would recover approximately 48% of the benefit. It should be noted that the results shown so far have been facilitated by a simple and cost-efficient software adaptation only. It is to be expected that further improvements will be possible if additionally hardware changes, e.g. in the injection system and/or 30 the combustion chamber design are taken into account. 7

Claims (5)

1. Use of Gas-to-Liquid (GTL) diesel fuel which has a density at 15 deg C of below 0.78 kg/, a sulphur content of less than 1 mg/kg, polyaromatics below 0.1 5 mass%, and a cetane number above 65, as a blend component together with at least a crude oil derived diesel fuel, which crude oil derived diesel fuel has a density at 15 deg C below 0.85 kg/, a sulphur content of less than 10 mg/kg, a polyaromatics content of below 5 mass%, and a cetane number from 51 to 60, for the production of a diesel fuel composition, which diesel fuel composition, when combusted in an 10 engine, has reduced NOx and soot emissions.

2. Use as claimed in claim 1, wherein the reduction of the NOx and soot emissions are reduced in comparison to the crude derived diesel non-linearly to the blending ratio of the GTL diesel in the crude oil derived diesel fuel. 15

3. Use as claimed in claim 1, wherein the reductions in both NOx and soot emissions for a 1:1 GTL:Crude derived diesel ratio are greater than 70% of the reduction obtained with a 100% GTL diesel fuel. 20 4. Use as claimed in claim 1, wherein the reductions in both NOx and soot emissions for a 1:4 GTL:Crude derived diesel ratio are greater than 40% of the reduction obtained with a 100% GTL diesel fuel.

5. Use as claimed in claim 1, wherein the GTL to crude oil derived diesel ratio is

25- from 99:1 to 1:99 and the diesel fuel composition produced has a molar H:C ratio of between 1.8:1 and 2.1:1. 6. Use as claimed in claim 5, wherein the molar H:C ratio is from 1.85:1 and 2.05:1. 30 7. Use as claimed in claim 6, wherein the molar H:C ratio is from 1.9:1 and 2.00:1. 8 WO 2005/105961 PCT/ZA2005/000060 8. A diesel fuel composition comprising both crude oil derived diesel fuel, which crude oil derived diesel fuel has a density at 15 deg C below 0.85 kg/I, a sulphur 5 content of less than 10 mg/kg, a polyaromatics content of below 5 mass%, and a cetane number from 51 to 60, and Gas-to-Liquids (GTL) diesel fuel, which GTL diesel has a density at 15 deg C of below 0.78 kg/l, a sulphur content of less than 1 mg/kg, polyaromatics below 0.1 mass%, and a cetane number above 65, in a volumetric ratio range of from 1:99 to 99:1 and with a molar H:C ratio of between 1.8:1 and 10 2.1:1. 9. A diesel fuel composition as claimed in claim 8, which diesel fuel composition has a density at 150C of from 0.77 kg/I to 0.84 kg/. 15 10. A diesel fuel composition as claimed in claim 9, which diesel fuel composition has a density at 15 C of from about 0.8 kg/l to about 0.82 kg/Il. 11. A diesel fuel composition as claimed in claim 8, which diesel fuel composition has a lower heating value of from 42 500 kJ/kg to 43 800kJ/kg. 20 12. A diesel fuel composition as claimed in claim 11, which diesel fuel composition has a lower heating value of from 43 100 kJ/kg to 43 600 kJ/kg. 13. A diesel fuel composition as claimed in claim 12, which diesel fuel composition 25 has a lower heating value of from 43 200 kJ/kg to 43 500 kJ/k. 14. A diesel fuel composition as claimed in claim 8, having less than 10 mg/kg sulphur. 30 15. A diesel fuel composition as claimed in claim 8, having less than 5 mass% polycyclic aromatics. 16. A blend stock for diesel fuel, said blend stock including the diesel fuel composition as claimed in claim 8. 9 WO 2005/105961 PCT/ZA2005/000060 17. A method of operating a Cl engine to reduce NOx and soot emissions when compared to use of said engine with crude derived diesel fuel, said method including combusting a diesel fuel composition as claimed in claim 8 in the engine under said engine's operating conditions, wherein the reductions in both NOx and soot 5 emissions for a 1:1 GTL:Crude derived diesel ratio being combusted in the engine are greater than 70% of the reduction obtained when a 100% GTL diesel fuel is combusted in the engine. 18. A method as claimed in claim 17, wherein the reductions in both NOx and soot 10 emissions for a 4:1 GTL:Crude derived diesel ratio being combusted in the engine are greater than 40% of the reduction obtained when a 100% GTL diesel fuel is combusted in the engine. 19. Use of Gas-to-Liquid diesel fuel as claimed in claim 1, substantially as herein 15 described and illustrated. 20. A diesel fuel composition as claimed in claim 8, substantially as herein described and illustrated. 20 21. A blend stock for diesel fuel as claimed in claim 16, substantially as herein described and illustrated. 22. A method of operating a Cl engine to reduce NOx and soot emissions as claimed in claim 17, substantially as herein described and illustrated. 25 23. A new use of a Gas-to-Liquid diesel fuel, a new diesel fuel composition, a new blend stock for diesel fuel, or a new method of operating a CI engine, substantially as herein described. 10