«Milestone Report Empirical Study of the Stability of NREL/TP-540-41619 Biodiesel and Biodiesel Blends May 2007 Milestone Report R.L. McCormick ...»
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National Renewable Energy Laboratory
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Empirical Study of the Stability of NREL/TP-540-41619
Biodiesel and Biodiesel Blends May 2007
National Renewable Energy Laboratory
Golden, Colorado S.R. Westbrook Southwest Research Institute San Antonio, Texas NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 Milestone Report Empirical Study of the Stability of NREL/TP-540-41619 Biodiesel and Biodiesel Blends May 2007 Milestone Report R.L. McCormick National Renewable Energy Laboratory Golden, Colorado S.R. Westbrook Southwest Research Institute San Antonio, Texas Prepared under Task No. FC079400 National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337
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Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste Acknowledgments This study is the result of a collaborative program between the National Renewable Energy Laboratory (NREL) and the National Biodiesel Board (NBB), with technical direction from the ASTM Biodiesel Stability Task Force. The authors acknowledge financial support from NBB and technical assistance from NBB technical director Steve Howell. Additionally the authors thank Teresa Alleman, Stu Porter, and Melissa Williams for their assistance in completing this project.
i Executive Summary In support of the U.S. Department of Energy Fuels Technologies Program Multiyear Program Plan goal of identifying fuels that can displace 5% of petroleum diesel by 2010, the National Renewable Energy Laboratory (NREL), in collaboration with the National Biodiesel Board (NBB) and with subcontractor Southwest Research Institute, performed a study of biodiesel oxidation stability. The objective of this work was to develop a database that supports specific proposals for a stability test and specification for biodiesel and biodiesel blends. B100 samples from 19 biodiesel producers were obtained in December of 2005 and January of 2006 and tested for stability. Eight of these samples were then selected for additional study, including long-term storage tests and blending at 5% and 20% with a number of ultra-low sulfur diesel (ULSD) fuels. These blends were also tested for stability. The study used accelerated tests as well as tests that were intended to simulate three real-world aging scenarios: (1) storage and handling, (2) vehicle fuel tank, and (3) high-temperature engine fuel system.
Several tests were also performed with two commercial antioxidant additives to determine whether these additives improve stability. This report documents completion of NREL’s Fiscal Year 2007 Annual Operating Plan Milestone 10.1.
The B100 samples examined show a broad distribution of stability on accelerated tests, with oil stability index (OSI) or Rancimat induction time results ranging from less than 1 hour to more than 9 hours and ASTM D2274 total insolubles ranging from less than 2 mg/100 ml to nearly 18 mg/100 ml.
The accelerated test data indicate that if the B100 stability is above roughly a 3-hour induction time, blends prepared from that B100 appear to be stable on the OSI and D2274 tests.
The D4625 long-term storage results for B100 indicate that most biodiesel samples, regardless of initial induction time, will begin to oxidize immediately during storage. If induction time is near or below the 3-hour limit, the B100 will most likely go out of specification for either stability or acid value within 4 months. Even B100 with induction times longer than 7 hours will be out of specification for oxidation stability at only 4 months, although these samples may not have shown a significant increase in acidity or in deposit formation. The 3-hour B100 induction time limit appears to be adequate to prevent oxidative degradation for both B5 and B20 blends in storage for up to 12 months.
For tests that simulated fuel tank aging and high temperature stability, we conclude that stable B100 (longer than 3 hours induction time) leads to stable B5 blends. For B20, the results are less definitive, but provide considerable evidence that B100 with induction time of at least 3 hours produces stable B20 blends, but the test cannot differentiate between intermediate and highly stable samples for acid number increase or sediment formation under these worst-case test conditions. Additional work is required to confirm this finding and to determine whether an additional stability test for the B20 blend is required.
These results indicate that B100 stability is the main factor that affects the stability of B5 and B20 blends, independent of diesel fuel aromatic content, sulfur level, or stability. An antagonism between unstable B100 and diesel fuel was observed. For B100 with an induction time lower than 3-hours, the level of deposits formed on the D2274 stability test was well above what would be expected based on the B100 deposit level and the percentage of biodiesel in the fuel. This antagonistic effect was significantly greater for B20 than for B5. The hindered phenolic antioxidants tested here prevented oxidative degradation of B100 in the storage simulation, and prevented degradation of biodiesel blends in the storage, fuel tank, and high-temperature simulations.
We recommend that additional tests be performed with real equipment to validate these conclusions.
ASTM ASTM International, a standards setting organization Bxx designation of biodiesel or biodiesel blend (B100 is pure biodiesel, B20 is a 20% blend, for example) EN European Normalisation ISO International Standards Organization KOH potassium hydroxide NBB National Biodiesel Board NREL National Renewable Energy Laboratory OSI oil stability index (also called Rancimat induction time) PV peroxide value RME rapeseed methyl ester T90 90% boiling temperature ULSD ultra-low sulfur diesel
Acronyms and Abbreviations
B100 and Diesel Fuel Properties
Accelerated Stability Tests
Simulation of Real-World Aging Scenarios
Results: Stability of B100
Accelerated Testing and Characterization
Storage Stability of B100
B100 Antioxidant Testing
Results: Stability of Biodiesel Blends
Diesel Fuel Properties and Stability
Stability of B5 Blends
Simulated Vehicle Fuel Tank Aging
Simulated Vehicle Tank Aging Followed by High Temperature Testing
Stability of B20 Blends
Simulated Vehicle Fuel Tank Aging
Simulated Vehicle Tank Aging Followed by High-Temperature Testing
Do Accelerated Tests Predict B100 Storage Stability?
Is B100 Stability a Predictor of Blend Stability?
Aging and In-Use Scenario Tests (Storage, Vehicle Tanks, High-Temperature Environment)
How Do Diesel Fuel Properties Effect Stability?
How Do Antioxidant Additives Affect Stability?
Is a 3-Hour B100 Induction Time Adequate?
Stability in Simulated Vehicle Fuel Tank and High-Temperature Environments........... 59 Conclusions and Recommendations
iv Appendix A: B100 Characterization and Stability Test Data
Appendix B: D4625 Results for B100 Samples
Appendix C: D4625 Results for Petroleum-Derived Diesel Fuels
Appendix D: Accelerated Test Results for B5 Blends
Appendix E: B5 Blend Storage, Fuel Tank, and High-Temperature Stability Results............ 75 Appendix F: Accelerated Test Results for B20 Blends
Appendix G: B20 Blend Storage, Fuel Tank, and High-Temperature Stability Results......... 83 v Tables Table 1. Results of D6468 Ullage Purge Scoping Tests
Table 2. Results of D4625 (6-Day, 80ºC Modification) Ullage Purge Scoping Tests.
.............. 8 Table 3. Biodiesel Samples Obtained and Preliminary Characterization
Table 4. Results of ASTM D6468 Performed on B100 Samples at 150°C/180 Minutes and Modified for Gravimetric Determination of Deposits
Table 5. B100 Samples Selected for Long-Term Storage and Blending Studies
Table 6. Characterization Results for B100 Samples Downselected for Further Study and Blending*
Table 7. Results of Accelerated Stability Tests for Biodiesel Treated with Antioxidant Additives
Table 8. Characterization Results for Petroleum Diesel Samples To Be Used in Preparation of B5 and B20 Blends
Table 9. B5 Samples Downselected for More Detailed Study
Table 10. Accelerated Test Results for B5 Samples Treated with Antioxidant
Table 11. B20 Samples Downselected for More Detailed Study
Table 12. Accelerated Test Results for B20 Samples Treated with Antioxidant
Figure 1. Glass vessel used for D4625 stability test
Figure 2. Histogram for B100 OSI or Rancimat induction time
Figure 3. Relationship between B100 OSI or Rancimat induction time and ASTM D525 results.
Circled data points indicate that no oxidation was observed after 780 minutes and the results are simply plotted as 780 minutes
Figure 4. Histogram for B100 ASTM D2274 total insolubles
Figure 5. Relationship between B100 OSI or Rancimat induction time and D2274 total insolubles
Figure 6. Relationship between B100 D2274 total insoluble and iso-octane insoluble.
.......... 13 Figure 7. Change in total acid number on D2274 versus D2274 total insolubles for B100 samples
Figure 8. Change in total acid number on D2274 versus OSI or Rancimat induction time for B100 samples
Figure 9. Change in OSI or Rancimat for B100 samples over 4 weeks in D4625 test.
........... 18 Figure 10. Peroxide value measured for B100 samples over the D4625 test
Figure 11. Change in acid value for B100 samples on the D4625 test
Figure 12. Total insoluble measured for B100 samples over the D4625 test
Figure 13. Total acid number results for D4625 long-term storage testing of antioxidanttreated B100 samples
Figure 14. Total insoluble results of ASTM D4625 long-term storage test for antioxidanttreated B100 samples
Figure 15. Total insolubles for petroleum diesel fuels on the D4625 test
Figure 16. Histogram of OSI or Rancimat induction times for B5 samples
Figure 17. Histogram of D2274 (biodiesel modification) total insolubles results for B5 samples
Figure 18. Histogram of D6468 percent reflectance results for B5 samples
Figure 19. Histogram of D6468 gravimetric insoluble results for B5 samples
Figure 20. Peroxide value over the D4625 test for B5 samples
Figure 21. Acid value for B5 blends over the D4625 test
Figure 22. Total insolubles formation for B5 blends in the D4625 test
Figure 23. Total insolubles formation for B5 samples treated with antioxidant additives on the D4625 test
Figure 24. Peroxide value for B5 blends after 1 week aging at 80ºC, as a function of B100 OSI or Rancimat induction time
Figure 25. Acid value for B5 blends after 1 week aging at 80ºC, as a function of B100 OSI or Rancimat induction time
Figure 26. Total insoluble for B5 blends after 1 week aging at 80ºC, as a function of B100 OSI or Rancimat induction time
Figure 27. Filter reflectance and gravimetric insolubles formation for B5 samples aged for 1 week at 80ºC and tested with the D6468 thermal stability test as a function of B100 OSI or Rancimat induction time
Figure 28. Histogram of OSI or Rancimat induction times for B20 samples
vii Figure 29. Histogram of D2274 (biodiesel modification) total insolubles results for B20 samples
Figure 30. Histogram of D6468 percent reflectance results for B20 samples
Figure 31. Histogram of D6468 gravimetric insoluble results for B20 samples
Figure 32. Peroxide value for B20 samples tested on D4625 test
Figure 33. Acid value for B20 samples tested on the D4625 test
Figure 34. Total insolubles formed from B20 samples tested on the D4625 test
Figure 35. Total insolubles formation for B20 samples treated with antioxidant additives on the D4625 test.
Figure 36. Peroxide value for B20 blends after 1 week aging at 80ºC, as a function of B100 OSI or Rancimat induction time
Figure 37. Acid value for B20 blends after 1 week aging at 80ºC, as a function of B100 OSI or Rancimat induction time
Figure 38. Acid value for B20 blends after 1 week aging at 80ºC, as a function of B20 OSI induction time
Figure 39. Total insolubles for B20 blends after 1 week aging at 80ºC, as a function of B100 OSI induction time