1. Sterol Glucosides in Biodiesel
Haiying Tang, Steven O. Salley, and
K. Y. Simon Ng
National Biofuels Energy Laboratory
NextEnergy/Wayne State University
Detroit, MI 48202

2. Outline
Chemical structure and physical properties of sterol glucosides
Precipitates formation above cloud point in Soy-, Cottonseed-, and Poultry Fat-based Biodiesel Blends
“Filter-Blocking Tendency ” test and cold soak filtration
Analysis method
Typical processing technique for oil refining
Possible techniques to remove sterol glucosides
Conclusion

3. Plants Sterols Free sterols Sterol esters Sterol glucosides
Acylated sterol glucosides

4. Sterol composition in seed oil (mg/kg)
Palm
Soy
bean
Rapeseed
Cottonseed
Corn oil
Safflower
Sunflower
β-sitosterol
1894
1908
3549
3961
7722
1809
2352
campesterol
358
720
1530
170
2691
452
313
stigmasterol
204 42
702
Δ5-avenasterol 51
108
122 85
468 35
156
Δ7-stigmastenol 25
306 -
117
696
588
other 26 36
612
173
195
Net % in oil
0.26%
0.36%
0.61%
0.43%
1.18%
0.35%
0.39%
Data From Gunston ed al, The lipid handbook, 1994

5. Chemical Structure of Sterols
Phytosterols mainly include campesterol, β-sitosterol, stigmasterol, Δ5-avenasterol, Δ7-stigmastenol, and brassicasterol.

6. What is Sterol Glucoside in Biodiesel?
Sterol Glycosides occurs naturally in vegetable oils, mainly as soluble fatty acid esters ;
Usually, the acyl sterol glycosides at concentrations are two to ten fold greater than those of the non-acylated forms;
Hydrolyzed during transesterification process and become insoluble.
β-sitosterol glucoside is the most typical sterol glucoside. :
β-sitosterol glucosides

7. Biodiesel Reaction- Base Transesterification
100 lbs of oil +10 lbs methanol lbs of biodiesel +10 lbs of glycerol

9. Physical Properties of Free Sterol Glucosides
Powdery solid, melting point °C
Limited solubility in most organic solvents except pyridine, chloroform/methanol (2:1)
Soluble in fresh biodiesel.

10. Typical Concentration of SG in Biodiesel (ppm)
Feedstock
SG 1
SG 2
β-sitosterol
Total sterol
Soy #1 Crude Grade
272 78
1908
3600
Soy #2 Degummed Grade 54
Soy #3 Refined Grade
190
Soy #4 (processed poorly) 25
Cottonseed oil #1 22 10
3961
4258
Cottonseed oil #2 8
Corn oil
480 45
7722
11700
Palm oil
141
118
1894
2558
Safflower Crude Grade 14
1809
3478
Sunflower 18
2352
3917
Canola
Data from 1 Ringwald SC. Biodiesel characterization in the QC environment;
2 Pfalzgraf et al , Identification of sterol glucosides in biodiesel and their effect on filterability.

11. Precipitates Formation above Cloud Point in Soy-, Cottonseed-, and Poultry Fat-based Biodiesel Blends

12. Cold Flow Properties: a current issue with biodiesel
Precipitates formation in biodiesel blends may have serious implications.
Clogging of fuel filters.
Formation of deposits on engine parts such as injectors and other critical fuel system components.

13. ASTM Test Methods
Cold–flow properties: traditional petroleum wax precipitation
Cloud point (CP, ASTM 2500): at which crystallization begins.
Pour point (PP, ASTM 97): at which the fuel no longer will pour.
Cold filter plugging point (CFPP, ASTM 6371): at which fuel starts to plug a fuel filter.
Total insoluble: high temperature in the presence of oxygen
ASTM D 2274 (Accelerated Method): Oxidation Stability of Distillate Fuel (95 ºC for 16 h).
ASTM D 4625: Storage Stability of Middle Distillate, Petroleum (43 ºC for selected periods up to 24 weeks).

14. Filtration system from ASTM D4625-04
Experimental
Samples:
SBO-, CSO-, and PF- based biodiesel
ULSD, B2, B5, B10, B20, B50, B70, and B100
300 mL volume
Storage Temperature and Time
-15 ºC for 24 hr
4 ºC for 24 hr
23 ºC for 24 hr (Control)
Allow to come to room temperature
without external heating
Filter
Vacuum pump: ~68 kpa
0.7 mm glass fiber filter
Filtration system from ASTM D

15. Physical Appearance (at 23 ºC for 24 hours )
SBO-based Biodiesel
ULSD B2 B5
B10
B20
B50
B70
B100

16. Physical Appearance (at 4 ºC for 24 hours)
SBO-based Biodiesel
ULSD
ULSD
ULSD B2
B10 B5
B20
B50
B70
B100

17. Physical Appearance (at -15ºC for 24 hours)
B10
ULSD B2 B5
B20
B50
B70
B100

18. Optical Images of Precipitates
50X
200X
Taken from B20 SBO-based biodiesel

19. Time to Filter Vs. Temperature
SBO-based biodiesel

20. Insolubles Mass Vs. Temperature
No significant mass of “new” insolubles as result of blending at 23 ºC ;
Significant effect at 4 ºC;
Above the cloud point insolubles are very different in nature as compared to the normal wax-crystal like insolubles formed below cloud point.

21. Insolubles Mass Vs. Time
Different mechanisms for the insolubles formation from B20 and B100;
For B20, the relatively fast appearance of insolubles can be attributed to a solvency effect.
B100
B20

22. Insolubles Mass Vs. Feedstock
CSO- and PF- based biodiesel had lower insolubles levels than the SBO-based biodiesel;
The difference may be attributed to the presence of naturally occurring levels of sterol glucosides in the feedstocks.

23. Cloud Point, Pour Point, and Cold Filter Plugging Point
The CFPP may indicate relative extent of the insolubles formation at low temperature.

24. Nature of Insolubles Possibilities
Sterol glucosides: Soluble within vegetable oil; however, hydrolyzed during transesterification process and become insoluble.
Monoglycerides, diglycerides, triglycerides of total glycerin;
Dimers, trimers, tetramers of oxidative products;
Solvency effect when blended with ULSD.

25. Distilled and Oxidized Biodiesel
After cold soak test, no insoluble was observed in distilled or oxidized B100, or even in B20;
Insolubles formation is due to minor component;
Insolubles formation is not due to oxidized product.
The nature of “the above cloud point insolubles” formation is different from the oxidized insolubles observed in the high temperature stability test of biodiesel;
Distillated SBO-B20
Oxidative Biodiesel Blends

26. Nature of Insolubles: FTIR Spectra
-CH2
-CH2
-OH
C-O-C
Insolubles from SBO-B100
Insolubles from SBO-B20
Insolubles fromCSO-B100
Insolubles from CSO-B50
Standard Sterol Glucosides

27. Nature of Insolubles: GC-FID Chromatograms
Insolubles from CSO-B100
Insolubles from SBO-B100
Internal Standard
Standard Sterol Glucosides
Three kinds of Sterol Glucosides

28. GC-FID Chromatogram (Continued)
Precipitates from PF-B100
Standard Glycerides

29. Summary 1
Storage temperature, storage time, biodiesel blend level, and feedstock affect the mass of insolubles formed;
Solvency of ULSD has a significant influence on insolubles formation;
Insolubles from SBO- and CSO-based biodiesel are due to sterol glucosides. However, the insolubles from PF-based biodiesel can be attributed to glycerides.

30. “Filter-Blocking Tendency ”Test
Tests
300ml of fuel at 20ml/min
Filter
ASTM D2068/IP387
1.6 micron
Result calculated based on pressure and volume measured during the test.

31. Filter-blocking tendency (FBT)
Effect of SG on FBT
SG content (ppm)
Filter-blocking tendency (FBT)
22 (Control)
1.05 (pass) 32
1.47 (fail) 52
2.90 (fail) 72
15.03(fail)
Adding SG to biodiesel caused it to fail to the FBT test;
SG presence at high enough levels could potentially cause filter problems.
Data from Lee et al. The role of sterol glucoside on filter plugging, Biodiesel Magazine 2007.

32. Biodiesel Cold Soak Filtration
Storage temperature and time
4 ºC (refrigerator)
16 hours
Allow sample to come to the room temperature (23 ºC to 24 ºC )
Filter
Vacuum pump: 22.5 inches Hg (~76.2 Kpa)
Whatman 47 mm GF/F, 0.7 mm.

34. Biodiesel Cold Soak Filtration

35. Different Feedstocks of Biodiesel1 2 3 4 5 6 7
Feedstock
Canola
Soy
Animal Fat
ImprSoy
Dist Soy
Palm

36. Analysis of Sterol Glucosides
The presence of sterol glucosides in biodiesel residues has been confirmed using FTIR and GC-FID
Qualification will be evaluated by GC- FID, HPLC, and FTIR with purchased known standards

37. Preliminary results :GC-FID Chromatograms
sitosterol glucoside
stigmasterol glucoside
campesterol glucoside
Precipitates from REG
Precipitates from Nextdiesel
Standard sterol glucosides

38. Process of Crude Soybean Oil to Food-grade Oil
Chemical refining
Water degumming
Chemical neutralization
Bleaching
Deodorization
Physical refining
Acid degumming
Refining
Water degumming
Caustic refining
Bleaching
Deodorization

39. Conventional RBD Process Phospholipids and gums
Phosphoric acid
NaOH
Bleaching clays
Steam vacuum
CRUDE OIL
CHEMICAL NEUTRALIZATION
BLEACHING
DEODORIZATION
(Distillation)
WATER DEGUMMING
REFINED OIL
Phospholipids and gums
Free fatty acids
Pigments
Trace component
Reduce portion of free sterols
Reduce portion of free sterols
Remove portion of SG

40. Average Composition for Crude and Refined Soybean oil
Data from Van Gerpen, J.; Biodiesel production technology, 2004

41. Process techniques to remove SG
Filtering:  removal of particulate from media with a steel screen, cartridge or filter paper
Effect of filter pore sizes
Effect of filter types
Cold filtering: holding the biodiesel at a lower temperature for desired time before the filtering process. 
Effects of cold filter temperature
Effect of storage time
Particle

42. Preliminary Results: Effect of temperature on removing particles with filtration
ppm
23 ºC
4 ºC
-15 ºC
ULSD
0.9
1.43 B2
1.23
1.67
2.57 B5
3.9
4.23
B10
6.67
B20
1.57
7.77
4.57
B50
2.23 14
22.33
B70
3.33
19.23
20.77
B100
5.77
9.1
32.23
1.43
2.57
4.23
6.67
4.57
22.33
20.77
32.23
Cold filtration is better to remove particles than room temperature filtration

43. Preliminary Results: Effect of storage time on removing particles with cold filtration (4 ºC )
ppm
B100
B20
5.67
1.67
1 hr - 3
2 hr
3.33
4.83
4 hr
5.83
8 hr 5
7.33
20 hr
13.67
7.17
24 hr
11.67
8.5
3 days 30
9.33
1 weeks 40
14.33
2 weeks 43
25.17
Longer storage time in cold soak test could more effective to remove particles in biodiesel.
1.67 3
4.83
5.83
6.83
7.33
7.17
8.5
9.33
14.33
25.17

44. Process techniques to remove SG (Con.)
Adsorbent treatment:
Removal of particulate with a porous pad or a “cake” of filter-aid-type materials
Diatomaceous earth (DE)
Magnesol
Carbon
Magnesium silicate
Act as deep filtration
Effect of concentration
Effect of incubation time
Effect of temperature
Mix Tank
Filter
Finished product tank
Untreated Biodiesel
Adsorbent

45. SG content of biodiesel after incubation and filtering through DE
Incubation temperature (ºC)
Incubation time
SG content (ppm)
(FBT) 54
15.03 (fail) 4
6 hr 22
1.2 (pass)
12 hr 25 - 10 27 21
1 day 19
2 days
16.29
3 days
17.29
Data from Lee et al. Processes of producing biodiesel and biodiesel produced therefrom; Patent application publication, 2007.

46. Process techniques to remove SG (Con.)
Water degumming: a basic process to wash biodiesel product to remove contaminants
Effect of water ratio
Effect of mixing temperature
Vacuum distillation: an energy intensive technique for biodiesel processing
Effect of temperature
Effect of pressure

47. Preliminary Result: GC-FID Chromatography
Sterol glucosides
SBO-biodiesel
Glycerol
Precipitates from SBO-biodiesel
Distillated SBO-biodiesel

48. Conclusions

49. Future Work
Evaluate and develop processing strategies to reduce sterol glucosides content in biodiesel;
Develop a robust analytical method to determine the sterol glucosides content in biodiesel.
In the next steps, we will

50. Thanks!
Questions?