Precipitate Formation above the Cloud Point in Soy-, Cottonseed-, and

Poultry Fat-based Biodiesel Blends

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

National Biofuels Energy LaborotoryNextEnergy/Wayne State University

Detroit, MI 48202

Present to International Congress on Biodiesel: The Science and The

TechnologiesNovember 7, 2007

• Precipitates formation in biodiesel blend may have serious implications.– Clog fuel filter for diesel

engine fuel delivery system.– Formed deposits on engine

parts such as injectors and other critical fuel system.

Cold Flow Properties: a current issue with biodiesel

• 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 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

• The effects of biodiesel on cold-flow fuel properties when blended with ULSD have not been fully elucidated;

• Few studies on the effect of biodiesel blends on the amount of precipitate formation under low temperature storage.

Critical Issues

• Investigate the effect of blend levels on the precipitate formation at low temperature storage;

• Understand the mechanism of precipitate formation;

• Correlate the relationship between CP,PP, and CFPP and precipitate formation;

• Investigate the nature of precipitates.

Objectives

• Samples: – Soybean-, Cottonseed-, and Poultry fat- based biodiesel, and

certification #2 ULSD – ULSD, B2, B5, B10, B20, B50, B70, and B100– 300 ml

• Storage Temperature and Time– -15 ºC – 4 ºC – 23 ºC (Control)– 24 hours

• Filter– Vacuum pump: 20 inHg (~68 Kpa)– 0.7 m glass filter medium

Experimental

Experimental

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

ULSD B5 B10

B20 B50 B70 B100

B2

Physical Appearance (at 4 ºC for 24 hours)

ULSDULSD

B2 ULSD B5 B10

B20 B50 B70 B100

SBO-based Biodiesel

Physical Appearance (at -15ºC for 24 hours)

ULSD B5 B10

B20 B50 B70 B100

B2

Optical images of precipitates from B20 SBO-based biodiesel

5X 20X

• Precipitates are observed above cloud point for biodiesel blends– Storage temperature– Storage time– Blending levels – Feedstock

Precipitates above Cloud Point

Time to filter Vs. TemperatureBiodiesel-Soybean oil

0

5

10

15

20

25

30

35

40

45

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

Biodiesel Concentration

Tim

e t

o f

ilte

r (m

in)

23 ºC

4 ºC

Minus 15 ºC

Precipitate Mass Vs. Temperature

• Significant mass of “new” precipitate at 4 ºC;

• Above the cloud point precipitate” is very different in nature as compared to the normal wax-crystal like precipitate formed below cloud point.

Precipitate Mass Vs. Time• Different mechanisms for the precipitate formation;• For B20, the relatively fast appearance of precipitate can be attributed to the solvency effect.

Precipitate Mass Vs. Feedstock• CSO- and PF- based biodiesel had lower precipitate levels than the SBO-based biodiesel;

• The difference may be attributed to the presence of unsaturation FAME and minor components.

FAME CompositionFAME composition (wt) %

FA SBO CSO PF

C14:0 0.00% 0.76% 1.04%

C16:0 14.10% 24.74% 21.82%

C16:1 0.70% 0.37% 3.71%

C18:0 5.15% 2.68% 7.61%

C18:1 25.29% 18.45% 36.59%

C18:2 48.70% 52.99% 27.02%

C18:3 6.08% 0.00% 1.78%

∑SFA (%) 19.2 28.2 30.9

∑UFA (%) 80.8 71.8 69.1

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 CFPP

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

Nature of Precipitates

Possibility

Stetyl glycosides;

Monoglycerides, diglycerides, triglycerides of total glycerin;

Dimers, trimers, tetramers of oxidative products;

Solvency effect when blend with ULSD.

Nature of Precipitates: FTIR Spectrum

SBO-B100

SBO-B20

CSO-B100

CSO-B50

Standard Sterol Glucosides

-OH-CH2 -CH2

C-O-C

-COO

Nature of Precipitates: CG-FID Chromatogram

CSO-B100

SBO-B100

Standard Sterol Glucosides

SBO-B100

Internal Standard

Three kinds of sterol glucosides

Nature of Precipitates: CG-FID Chromatogram

Standard Glycerides

PF-B100

Further Results

Oxidative Biodiesel Blends

Distillated SBO-B20 • After cols soak test, no

precipitates is observed on distilled or oxidized B100, or even on B20;

• Distillated B100 doesn't include sterol glycosides;

• The nature of “the above cloud point precipitate” formation is different from the oxidized insoluble observed from high temperature stability test of biodiesel.

Conclusions

• Storage temperature, storage time, biodiesel blend level, and feedstock affect the mass of precipitate formed;

• Solvency of ULSD has a significant influence on precipitates formation;

• Precipitates from SBO- and CSO-based biodiesel are due to sterol glucosides. However, the precipitates from PF-based biodiesel can be attributed to glycerides.

AcknowledgementFinancial support from the Department of Energy (Grant #

DE FG36-05GO85005) and Michigan’s 21st Century Job Fund

is gratefully acknowledged.