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Sterol Glucosides in Biodiesel

Haiying Tang, Steven O. Salley, and K. Y. Simon Ng

National Biofuels Energy LaboratoryNextEnergy/Wayne State University

Detroit, MI 48202

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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

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Plants Sterols

Free sterols Sterol esters Sterol glucosides Acylated sterol

glucosides

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Sterol composition in seed oil (mg/kg)Composition 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 204 720 42 702 313 313

Δ5-avenasterol

51 108 122 85 468 35 156

Δ7-stigmastenol

25 108 306 - 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

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Chemical Structure of Sterols Phytosterols mainly include campesterol, β-sitosterol,

stigmasterol, Δ5-avenasterol, Δ7-stigmastenol, and brassicasterol.

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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

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Biodiesel Reaction- Base Transesterification

100 lbs of oil +10 lbs methanol 100 lbs of biodiesel +10 lbs of glycerol

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Physical Properties of Free Sterol Glucosides

Powdery solid, melting point 283-287°C Limited solubility in most organic solvents

except pyridine, chloroform/methanol (2:1)

Soluble in fresh biodiesel.

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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 18

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.

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Precipitates Formation above Cloud Point in Soy-, Cottonseed-, and

Poultry Fat-based Biodiesel Blends

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• 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.

Cold Flow Properties: a current issue with biodiesel

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• 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).

ASTM Test Methods

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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 m glass fiber filter Filtration system from ASTM D4625-04

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Physical Appearance (at 23 ºC for 24 hours )SBO-based Biodiesel

ULSD B5 B10

B20 B50 B70 B100

B2

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Physical Appearance (at 4 ºC for 24 hours)

ULSDULSD

B2 ULSD B5 B10

B20 B50 B70 B100

SBO-based Biodiesel

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Physical Appearance (at -15ºC for 24 hours)

ULSD B5 B10

B20 B50 B70 B100

B2

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Optical Images of Precipitates

50X 200X

Taken from B20 SBO-based biodiesel

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Time to Filter Vs. Temperature

0

5

10

15

20

25

30

35

40

45

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Biodiesel Concentration

Tim

e to filt

er

(min

)

23 ºC

4 ºC

Minus 15 ºC

SBO-based biodiesel

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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.

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Insolubles Mass Vs. Time

0

5

10

15

20

25

30

35

Control 1 hr 2 hr 4 hr 6 hr 8 hr 12 hr 24 hr 72 hr 1 week 2 weeks

Storage Time

Pre

cip

itat

es (

pp

m)

• 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.

0

10

20

30

40

50

0 0.5 hr 1 hr 2 hr 4 hr 8 hr 20 hr 24 hr 72 hr 1 week 2 weeks

Storage Time

Pre

cip

itat

es (

pp

m)

B100

B20

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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.

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Biodiesel-Soybean

-40

-35

-30

-25

-20

-15

-10

-5

0

5

0% 20% 40% 60% 80% 100%

Biodiesel Concentration

Te

mp

era

ture

(o C

)

Cloud pointPour pointCold fiiter plugging pointPoly. (Pour point)Poly. (Cloud point)

Biodiesel-Cottonseed

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0% 20% 40% 60% 80% 100%

Biodiesel Concentration

Tem

per

atu

re (

o C

)

Cloud pointPour pointCold fiiter plugging pointPoly. (Cloud point)Poly. (Pour point)

z

Biodiesel-Poultry fat

-40

-35

-30

-25

-20

-15

-10

-5

0

5

10

0% 20% 40% 60% 80% 100%

Biodiesel Concentration

Tem

per

atu

re (

o C

)

Cloud pointPour pointCold fiiter plugging pointPoly. (Cloud point)Poly. (Pour point)

Cloud Point, Pour Point, and Cold Filter Plugging Point

• The CFPP may indicate relative extent of the insolubles formation at low temperature.

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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.

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Distilled and Oxidized Biodiesel

Oxidative Biodiesel Blends

Distillated SBO-B20

• 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;

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Nature of Insolubles: FTIR Spectra

Insolubles from SBO-B100

Insolubles from SBO-B20

Insolubles fromCSO-B100

Insolubles from CSO-B50

Standard Sterol Glucosides

-OH-CH2 -CH2

C-O-C

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Nature of Insolubles: GC-FID Chromatograms

Insolubles from CSO-B100

Insolubles from SBO-B100

Standard Sterol GlucosidesInternal Standard

Three kinds of Sterol Glucosides

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GC-FID Chromatogram (Continued)

Standard Glycerides

Precipitates from PF-B100

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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.

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“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.

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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.

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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 m.

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Biodiesel Cold Soak Filtration

0

100

200

300

400

500

600

700

800

900

1000

1 2 3 4 5 6 7

B100 Sample

Filtr

ati

on

Tim

e, sec. Lab A

Lab B

Lab C

Lab D

Lab E

Lab F

Lab G

Lab H

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Different Feedstocks of Biodiesel

Biodiesel 1 2 3 4 5 6 7

Feedstock Canola Soy Animal Fat

ImprSoy

Dist Soy

Palm Soy

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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

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Precipitates from REG

Standard sterol glucosides

Precipitates from Nextdiesel

campesterol glucoside stigmasterol glucoside

sitosterol glucoside

Preliminary results :GC-FID Chromatograms

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Process of Crude Soybean Oil to Food-grade Oil

Refining Water degummingCaustic refining

Bleaching Deodorization

Chemical refining– Water degumming

– Chemical neutralization

– Bleaching

– Deodorization

Physical refining– Acid degumming

– Bleaching

– Deodorization

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CR

UD

E O

IL

WA

TE

R

DE

GU

MM

ING

CH

EM

ICA

L N

EU

TR

AL

IZA

TIO

N

DE

OD

OR

IZA

TIO

N

(Dis

tilla

tion

)

BL

EA

CH

ING

Bleaching clays

Steam vacuum

Phospholipids and

gums

Phosphoric acid

Remove portion of

SG

NaOH

Free fatty acids

Reduce portion of

free sterols

Pigments

Reduce portion of

free sterols

Trace component

RE

FIN

ED

OIL

Conventional RBD Process

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Average Composition for Crude and Refined Soybean oil

Data from Van Gerpen, J.; Biodiesel production technology, 2004

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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

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Preliminary Results: Effect of temperature on

removing particles with filtration ppm 23 ºC 4 ºC -15 ºC

ULSD 0.9 0.9 1.43

B2 1.23 1.67 2.57

B5 1.43 3.9 4.23

B10 1.43 6.67 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

Cold filtration is better to remove particles than room temperature filtration

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Preliminary Results: Effect of storage time on

removing particles with cold filtration (4 ºC ) ppm B100 B20

0 5.67 1.67

1 hr - 3

2 hr 3.33 4.83

4 hr 3.33 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.

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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

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SG content of biodiesel after incubation and filtering through DE

Incubation temperature (ºC)

Incubation time

SG content (ppm)

(FBT)

0 0 54 15.03 (fail)

4 6 hr 22 1.2 (pass)

4 12 hr 25 -

10 6 hr 27 -

21 1 day 19 -

21 2 days 16.29 -

21 3 days 17.29 -

Data from Lee et al. Processes of producing biodiesel and biodiesel produced therefrom; Patent application publication, 2007.

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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

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Distillated SBO-biodiesel

Precipitates from SBO-biodiesel

SBO-biodiesel

Preliminary Result: GC-FID Chromatography

Sterol glucosides

Glycerol

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Conclusions

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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.

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Thanks!

Questions?