Technical Report

NREL/TP-540-46592

March 2010

Analysis of Biodiesel Blend 

Samples Collected in the 

United States in 2008

T.A. Alleman, L. Fouts, and R.L. McCormick
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy

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Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-540-46592

March 2010

Analysis of Biodiesel Blend 

Samples Collected in the 

United States in 2008

T.A. Alleman, L. Fouts, and R.L. McCormick

Prepared under Task No. FC08.9400
NOTICE

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iii

Acknowledgments

The authors thank the U.S. Department of Energy Vehicle Technologies Program and the 

National Biodiesel Board for funding and support of this project. 
iv

Executive Summary

In the summer of 2008, NREL conducted a nationwide survey of the quality of B20, a blended 

fuel consisting of about 20 volume percent (vol%) biodiesel and 80 vol% petroleum diesel. 

Thirty-three samples were collected prior to the announcement of a new ASTM specification, 

D7467, for B6−B20. The B20 samples were tested against multiple properties—those included in 

the eventual D7467 specification and other properties of interest. Because this study preceded the 

announcement of the specification, the samples could not be termed “on” or “off” specification.

Previous NREL surveys have shown that biodiesel blending has been problematic, because the 

samples have been almost evenly distributed above and below B20. In this survey, only 60% of 

the samples were nominally B20 (i.e., B18−B22), and the majority of the rest of the samples 

contained less biodiesel, typically B2, B5, and B10. Two samples contained over 20 vol% 

biodiesel, likely the result of poor blending. 

The induction period (IP) stability and acid value (AV) are key parameters in the quality of a 

Bxx blend. Although the D7467 specification was not applicable at the time of sample collection, 

25% of the samples were below the 6-hour proposed limit. It is noteworthy that the average IP, 

8.4 hours, was well above the 6-hour limit. Every sample but one met the proposed AV 

specification of 0.3 mgKOH/g, a low failure rate similar to that of previous NREL surveys. 

The minimum flash point of Bxx blends is allowed to vary depending on the type of diesel fuel 

used and the cloud point of the blend. The average cloud point was -12.6°C, and the samples all 

readily met the flash point minimum of 38°C. The B20 samples all met the sulfur limit of 15 

ppm, except for one sample that was likely contaminated. The range of cetane number for the 

blends was 46 to 52. 

The current specification contains a combined water and sediment value, although there is 

interest in separating these parameters into Karl Fisher water and particulate contamination. As 

expected by its polar nature, biodiesel will have a higher water saturation point than that of diesel 

fuel. The average Karl Fisher water content of the B20 samples was 130 ppm, about 30% higher 

than that of conventional diesel fuel. Almost all the samples showed very low particulate 

contamination except one, which was likely contaminated during collection. The metal content 

of the blends was also low, although the amount of sodium in one sample would not have 

allowed the B100 to meet the D6751 specification.

Typically, little or no information is known about the parent fuels to provide complete 

information about the source of the biodiesel used in Bxx blends. However, advanced analytical 

techniques have helped to overcome this hurdle. The B100 feedstock can be determined by using 

multi-dimensional gas chromatography. The blends in this study were produced mainly from 

soybean-derived B100, although a significant number of animal-fat-derived B100 samples were 

also found. 

Another critical B100 parameter is the glycerin content, which is impossible to reliably 

determine for Bxx because of method limitations. A novel ion chromatography technique was 

used to extract and analyze the glycerin in the biodiesel portion of the blend. Overall, the 

biodiesel was typically on-specification for glycerin.
v

Table of Contents

Introduction ................................................................................................................................................. 1

Materials and Methods ............................................................................................................................... 1

Results and Discussion.............................................................................................................................. 4

Standard Tests............................................................................................................................4

Biodiesel Content of Blends ................................................................................................4

Induction Period Stability ....................................................................................................5

Acid Value ...........................................................................................................................6

Flash Point ...........................................................................................................................8

Cloud Point ..........................................................................................................................8

Other Properties from D7467...............................................................................................9

Nonstandard Tests......................................................................................................................9

Karl Fisher Moisture ............................................................................................................9

Particulate Contamination..................................................................................................10

Interfacial Tension .............................................................................................................11

Free and Total Glycerin .....................................................................................................11

Group I and II Metals.........................................................................................................12

Feedstock Analysis............................................................................................................13

Conclusions............................................................................................................................................... 14

References................................................................................................................................................. 16
vi

List of Figures

Figure 1. The 2008 B20 sample collection sites .......................................................................... 2

Figure 2. Typical MDGC/FID chromatograms for B20; top: diesel component, bottom: 

biodiesel component ..................................................................................................... 4

Figure 3. Blend percentage results for B20 samples collected in 2008 ....................................... 5

Figure 4. Induction period stability for the 2008 B20 survey ...................................................... 6

Figure 5. Acid value results for the 2008 B20 survey................................................................. 7

Figure 6. B20 samples analyzed by modified D664 method ....................................................... 7

Figure 7. Flash point results for the 2008 B20 survey ................................................................. 8

Figure 8. Cloud point results for the 2008 B20 survey ................................................................ 9

Figure 9. Karl Fisher moisture results for the 2008 B20 survey ................................................ 10

Figure 10. Particulate contamination results for the 2008 B20 survey, using D6217 or D7321 . 11

Figure 11. Water interfacial tension results for the 2008 B20 survey.......................................... 12

Figure 12. Free and total glycerin by ion chromatography for 2008 B20 survey samples; 

results extrapolated to B100 properties....................................................................... 13

Figure 13. Feedstocks used in the blends collected in the 2008 B20 survey ............................... 14

List of Tables 

Table 1. ASTM D7467-08 Specifications and Methods for the 2008 B20 Quality Survey ....... 2

Table 2. Nonspecification Test Performed on 2008 B20 Survey Samples................................. 3

Table 3. Chromatographic Conditions for MDGC/FID Method ................................................ 3

Table 4. Average and Minimum and Maximum Group I and II Metal Content of B20 Samples 

(ppb)............................................................................................................................ 13
1

Introduction

Biodiesel has considerable potential to displace traditional petroleum in the transportation sector. 

Biodiesel production in the United States grew from 25 million gallons in 2003 to 683 million 

gallons in 2008 [1]. The vast majority of biodiesel used as a blendstock in the United States is 

blended with petroleum diesel fuel and signified “Bxx” (e.g., B20), where xx is the volume 

percent of the biodiesel content in the fuel. 

Minnesota has mandated B2, and Illinois encourages the use of B11 by waiving a sales tax [2]. 

Although these and other mandates exist, no Bxx fuel specifications existed until October 2008. 

At that time, ASTM International adopted specifications for up to 5 volume percent (vol%) 

biodiesel in diesel fuel (D975) and a stand-alone specification for 6 vol% to 20 vol% biodiesel 

(B6-B20, D7467). These specifications allow regulatory agencies to ensure the quality of 

biodiesel blends.

Surveys of B100 and B20 to determine quality have been conducted since 2004, providing part 

of the data necessary for ASTM to establish blend specifications. The first National Renewable 

Energy Laboratory (NREL) quality survey was conducted in 2004 on B100 and B20 [3]. A 

significant issue with blend percentage was noted; in fact, 18 of 33 presumably samples that 

were presumably of B20 were outside the accepted B18 to B22 window for biodiesel content. In 

addition, results for induction period stability showed that a majority of the blends were below 

2.5 hours. In a spring 2007 survey of retail stations selling B20 at unspecified locations, 

researchers at Wayne State University also found very low stability for biodiesel blends [4]. 

Subsequent NREL surveys focused on B100 rather than the finished blends [5, 6].

Here we report the results of a B20 survey conducted in summer 2008. The B20 samples were 

purchased from retail stations or obtained from fleets throughout the United States. Analyses 

included properties in the D7467 specification, which had not yet taken effect when samples

were collected, and other properties of interest. The feedstock used in each blend was also 

determined from the fatty acid methyl ester (FAME) profile measured by multidimensional gas 

chromatography (MDGC), and the free and total glycerin content of the parent biodiesel was 

determined through ion chromatography (IC). 

Materials and Methods

The B20 samples were collected at retail stations and from fleets throughout the United States

(Figure 1). Samples were collected only from pumps that were either labeled as dispensing B20

or stated to be dispensing B20 by on-site staff. These locations were identified by selecting 

pumps with voluntary B20 labeling or by polling station staff. One gallon of each fuel was 

collected and stored in metal fuel cans in cold storage until sampled for analysis. Aliquots were 

taken from these cans into 1-L glass jars for additional analysis. The bulk samples were tested 

for properties thought to immediately impact engine operability and proposed specification 

properties for future versions of D7467 (Table 1). The D7467 specification limits presented in 

Table 1 were not in effect at the time of sample collection, so samples cannot be judged as “onspecification” or “off-specification.” All testing was performed per the methods without 

deviation.
2 

Figure 1. The 2008 B20 sample collection sites 

Table 1. ASTM D7467-08 Specifications and Methods for the 2008 B20 Quality Surveya

Property 

Test Method,

ASTM unless 

otherwise noted 

D7467-08 

Specification Notes 

Acid number 

 (mgKOH/g), max 

D664, D02.06 

modifications 0.3 Tested on all samples 

Viscosity 

 (mm2

/s at 40°C) D445 1.9-4.1b

 Not tested 

Flash point (°C), min D93 52c Tested on all samples 

Cloud point (°C) D2500, D4539, D6371 Reportd Tested on all samples 

Sulfur (ppm), max D5453 15e Tested on all samples 

Distillation temperature 

 (°C), 90% recovered, max D86 343 Not tested 

Ramsbottom carbon 

 residue, 10% bottoms 

 (mass%), max 

D524 0.35 Not tested 

Cetane number, min D613 40 Tested using ASTM 

D6890, all samples 

One of the following: 

 Cetane index, min 

 Aromatics (vol%), max 

D976 

D1319 

40 

35 

Not tested 

Not tested 

Ash content (mass%), max D483 0.01 Not tested 

Water and sediment 

 (vol%), max D2709 0.05 Not tested 

Biodiesel content (vol%) D7371 6.-20. Tested on all samples 

Copper corrosion 

 (3 h at 50°C), max D130 No. 3 Not tested 

Oxidation stability (h), min EN14112 6 Tested on all samples 

Lubricity (HFRR at 60°C, 

m), max D6079 520f Not tested 

a

D7467 limits are given for reference but were not in effect at the time of the survey. 

b

 If No.1 diesel fuel is used in the blend, minimum viscosity shall be 1.3 mm2/s. c

 If No.1 diesel fuel is used in the blend or a cloud point of less than -12°C is specified, the flash point minimum is 38°C. 

d

 Cloud point is based on operability limits and time of year where the blend will be used. e

 All samples were on-road and must meet the 15-ppm maximum sulfur limit. 

f

 If diesel fuel meets D975 lubricity requirements, it is not necessary to test the lubricity of the blend. 
3

Several tests that are not part of the D7467 specification were also performed (Table 2). ASTM 

tests were performed without deviation from the method. Free and total glycerin was measured 

by ion chromatography (IC). In this method, samples were separated by a high-efficiency anion 

exchange separator column (Metrohm CARB1 150 mm x 4.0 mm, part number 6.1013.010) with 

an electrochemical detector. The mobile phase was 0.10 M sodium hydroxide solution at 1.0

mL/min. The sample loop was 10 μL. The IC method required two separate injections, one for 

free glycerin and one for total glycerin. Five grams of the sample were extracted with 

approximately 35 g of water in the free glycerin determination. The glycerin was quantitatively 

extracted into the aqueous layer, which was removed and injected directly on the IC. The total 

glycerin is composed of free glycerin plus glycerin in mono-, di-, and tri-glycerides. To measure 

total glycerin, the glycerides must first be reduced to free glycerin and soap before aqueous 

extraction and analysis. To accomplish this, 2.5 g of Bxx was mixed with ca. 6 mL 1.0 M 

potassium hydroxide and heated to 95°C for 1 hour while stirred at 400 rpm. The samplewas

allowed to cool to room temperature, and glycerin was water-extracted with three 20-g water 

washes. The aqueous solution from these extractions was composited and injected into the IC. 

Table 2. Nonspecification Test Performed on 2008 B20 Survey Samples

Property

ASTM Test Method

(unless

otherwise noted)

Notes

Group I and II metals (ppm) D7111 Tested on all samples

Karl Fisher (ppm) D6304 Tested on all samples

Particulate contamination (mg/L) D6217 or D7321 Tested on all samples

Interfacial tension (mN/m) D971 Tested on all samples

Free and total glycerin

 (mass%) In-house method Tested on all samples

The B20 samples were analyzed for biodiesel feedstock using MDGC with flame ionization 

detection (FID). The MDGC/FID method uses a Deans switch to separate the B100 blendstock

from the diesel fuel in the mixture. The B100 blendstock is quantified on a highly polar column 

that separates individual FAMEs in a method developed by Agilent [7]. Chromatographic 

conditions are listed in Table 3. Each Bxx sample was accurately weighed to 0.25 g and mixed 

with 1 mL high-performance liquid chromatography-grade hexane before injection. Figure 2

illustrates a typical chromatogram of a B20 using this method. 

Table 3. Chromatographic Conditions for MDGC/FID Method 

Primary column HP-5ms, 15 m x 0.25 mm x 0.1 μm

Secondary column HP-INNOWAX, 30 m x 0.25 mm x 0.5 μm

Deans restrictor Deactivated fused silica, 0.77 m x 0.1 mm

Injection Split, 200:1

Injector temperature 250°C

EPC pressure 33.86 psi, He, constant pressure

Injection volume 0.5 μL

HP-5 ms column flow 1.5 mL/min

PCM 30.7 psi He, constant pressure

HP-INNOWAX column flow 3.5 mL/min

FID temperatures 275°C

Oven program

 Initial temperature 50°C for 0 min

 Ramp 1 20°C/min to 210°C for 18 min

 Ramp 2 20°C/min to 230°C for 13 min

Cut times Depend on specific chromatographic system
4

5 10 15 20 25 min

pA

0

50

100

150

200

250

300

350

 FID1 A, Front Signal (2009\MARCH\031909EVENING 2009-03-19 16-12-09\031909_53659.D)

5 10 15 20 25 min

pA

0

50

100

150

200

250

300

350

 FID2 B, Back Signal (2009\MARCH\031909EVENING 2009-03-19 16-12-09\031909_53659.D)

 16:0

 16:1

 18:0

 18:1

 18:2

 18:3

Figure 2. Typical MDGC/FID chromatograms for B20; top: diesel component, bottom: biodiesel 

component 

Results and Discussion

Standard Tests

Biodiesel Content of Blends

Twenty-six samples came from public pumps and seven came from fleets with on-site fueling. 

Figure 3 shows the biodiesel content measured in each sample. Each sample was considered to 

be nominally B20 if the measured biodiesel content was between 18 and 22 vol%, and 57% of 

samples were in this range. The majority of non-B20 samples contained lower percentages of 

biodiesel—typically, B2, B5, and B11. Six of the seven fleet samples were nominally B20, the 

seventh had slightly low biodiesel content (17 vol%). Only two samples had extremely high 

biodiesel content (B55 and B90), suggesting that the blend had been prepared without adequate 

mixing so that when the sample was pumped from the tank bottom it contained a higher level of 

the more dense biodiesel. 

In 2004, half the non-B20 samples were high in biodiesel content and half were low. This was 

attributed to poor blending practices. In the 2008 survey, however, it is likely that the lowbiodiesel-content samples were blended accurately to lower levels but then mistakenly sold from 

a pump labeled B20.
5

Sample ID

0 5 10 15 20 25 30 35

Biodiesel Content, D7371, %

0

20

40

60

80

100

Nominally B20

Less than B20

Greater than B20

Fleet Samples

Figure 3. Blend percentage results for B20 samples collected in 2008

Induction Period Stability

The induction period (IP) stability, sometimes called the Rancimat or Oil Stability Index (OSI), 

is an indicator of the oxidative stability of fuels. The IP for neat diesel fuel is well over 24 hours

[8, 9]. Previous work has shown the IP of biodiesel and biodiesel blends to be significantly less 

than that of diesel fuel unless treated with a synthetic antioxidant [10]. ASTM D6751, the 

specification for B100 as a blendstock, sets the IP at a minimum of 3 hours. This is intended to 

ensure an IP of 6 hours, minimum, for B6 to B20 as required by D7467. 

The IP results are presented in Figure 4. The IP testing was stopped after 12 hours. These 

samples were artificially assigned a value of 12 hours. No information was collected on the 

amount of time these fuels spent in storage before sample collection. 

The average B20 IP was 8.4 hours, well above the limit set in D7467. Three fleet samples were 

at or just below the 6-hour limit for D7467. For all samples with an IP of less than 6 hours, it was 

impossible to determine if the samples were “fresh” or “aged.” In “aged” Bxx blends, the IP 

begins to drop as the fuel ages [11]. Using the current specification, 75% of the B20 samples 

would be on-specification. 
6

Sample ID

0 5 10 15 20 25 30 35

Induction Period,

EN14112, hrs

0

5

10

15

20

25

Nominally B20

Less than B20

Greater than B20

Specification is 6 hrs, min

Testing was stopped

after 12 hours

Average B20 Induction Period = 8.4 hrs

Fleet Samples

Figure 4. Induction period stability for the 2008 B20 survey

Acid Value

The acid value (AV) measures the amount of acids present in the fuel. These acids can be formed 

as the fuel begins to age and degrade. As with the IP, it is not possible to determine if aging had 

begun prior to sampling and impacted the AV. However, a majority of the sample AVs were 

below the detection limit of 0.05 mgKOH/g (Figure 5). Only one of the 33 samples was higher 

than the proposed D7467 AV specification level of 0.5 mgKOH/g. The 2007 B100 survey 

showed almost all the B100 to be on-specification for AV with very low failure rates [6], which 

was also seen in the 2008 B20 survey.

Several modifications to the AV method have been proposed through ASTM to improve 

detection limits. These modifications, including a smaller sample size and more dilute reagents,

are included in the newest version of the AV test method, D664, which will decrease the 

detection limit from 0.05 mgKOH/g to 0.01 mgKOH/g. To illustrate the impact of these changes, 

the samples were tested with the current D664 method and with the proposed modifications. 

Figure 6 compares results for both methods. Samples that were below the detection limit using 

the traditional method were assigned a value of 0.05 mgKOH/g. A slight bias was observed 

between the current and modified method—the result of a delay between initial testing 

conducted using D664 and subsequent testing conducted using the modified method. Efforts

were made to minimize the delay, but in some cases, several weeks elapsed between testing;

thus, the fuel continued to age and the AV increased. The improvements in the D664 acid value 

test method allow greater precision at very low acid values, providing a better understanding of 

the critical fuel property.
7

Sample ID

0 5 10 15 20 25 30 35

Acid Value, D664, mgKOH/g

0.0

0.1

0.2

0.3

0.4

Nominally B20

Less than B20

Greater than B20 Specification Limit = 0.3, max

Fleet Samples

Samples at 0.05 mgKOH/g are 

below detection limit

Figure 5. Acid value results for the 2008 B20 survey

Acid Value, D664, mgKOH/g

0.0 0.1 0.2 0.3 0.4 0.5

ASTM SC06 proposed

modifications to D664, mgKOH/g

0.0

0.1

0.2

0.3

0.4

0.5

Note samples that are below detection

limit on D664 have been assigned a 

value at that limit of 0.05

The samples were analyzed using the

current method upon collection. There

was a delay of several weeks before

they were analyzed using the 

modified method.

Figure 6. B20 samples analyzed by modified D664 method 
8

Flash Point

The flash point is an important measure for ensuring the safe handling of fuels. A minimum flash 

point for fuels typically is set to avoid a flammable fuel/air mixture in normal use. The flash 

point of a mixture is dominated by the lowest flash component in that mixture. Thus, for Bxx 

blends, the flash point temperature is dominated by the diesel fuel, which has a significantly 

lower flash point than that of B100. For this reason, the flash point specification for Bxx blends 

is identical to that for diesel fuels set in D975. The minimum allowable flash point for Bxx 

blends composed of No. 2 diesel fuel is 52°C, while any blend containing No. 1 diesel fuel or 

any blend with a cloud point below -12°C can have a flash point as low as 38°C. For this survey, 

all samples had a flash point above 38°C. No information was available about the diesel fuel 

used in the Bxx blends. Of the four samples with flash point below 52°C, only one had a cloud 

point (CP in Figure 7) below -12°C.

Sample ID

0 5 10 15 20 25 30 35

Flash Point, D93, o

C

35

40

45

50

55

60

65

70

75 Nominally B20

Less than B20

Greater than B20

52oC minimum flash point if

CP is >-12o

C

38o

C flash point if

CP is <-12o

C

Figure 7. Flash point results for the 2008 B20 survey

Cloud Point

The cloud point is an important parameter for cold weather operability and is the temperature at 

which the first crystals appear in a fuel upon cooling under specified conditions. Cloud point is 

not specified but rather given as a report value. The cloud point needed to ensure appropriate 

cold weather operability depends on several factors, including geography and time of year. 

Figure 8 reports the cloud point for the fuels collected in this survey. The cloud point ranged 

from -7°C to -25°C. The average B20 cloud point was -12.6°C, and the median was -11.3°C. 
9

Sample ID

0 5 10 15 20 25 30 35

Cloud Point,

D2500 o

C

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

Nominally B20

Less than B20

Greater than B20

Average B20 CP = -12.6oC Fleet Samples

Figure 8. Cloud point results for the 2008 B20 survey

Other Properties from D7467

Three additional properties from the D7467 specification were tested. These properties were 

sulfur, cetane number, and ash. The sulfur content of the blends was tested with D5453. For 

samples that were nominally B20, the average sulfur content was 7.3 ppm, with a minimum of 

3.7 ppm and a maximum of 16.2 ppm. Previous survey work has never found samples that do not 

meet the on-highway sulfur specification of 15 ppm, so the 16.2 ppm sample was unusual. This 

sample also had high particulate contamination (as discussed later in the report) and may have 

been contaminated during collection at the fleet. Samples that contained less than 20 vol% 

biodiesel had a slightly lower average sulfur content of 5.7 ppm and ranged from 3.5 ppm to 8.2 

ppm. The two samples with greater than 20 vol% biodiesel had less than 4.5 ppm sulfur. The 

derived cetane number (a measure of ignition delay) of the Bxx blends was tested using D6890. 

The cetane numbers of the samples ranged from 45 to 56. All Bxx blends were below detection 

limits on the D482 ash content test. 

Nonstandard Tests

Additional testing was performed on the Bxx blends to further characterize the fuels in the 

marketplace.

Karl Fisher Moisture

Currently, biodiesel blends are required to meet a combined free water and sediment limit of 

0.050 vol% by D2709, a centrifuge test. Previous survey work has shown that biodiesel and 
10

biodiesel blends rarely fail the water and sediment requirement. Free water is present once fuels 

become water-saturated. Any water in fuels below the saturation level is soluble. At room 

temperature, the water saturation level of B100 is between 1,200 and 1,500 ppm and may be a 

function of impurity levels and degree of oxidation [12]. Typical ultra-low-sulfur No. 2 diesel 

(ULSD) fuel will be saturated between 50 and 100 ppm water [13]. The soluble water was 

measured by coulometric Karl Fisher (KF, ASTM D6304). Figure 9 shows soluble water levels 

for the Bxx survey samples. The average KF titration (KF, ASTM D6304, Procedure B) for the 

B20 samples was 130 ppm, about 30% higher than expected for ULSD based on limited data 

from Stanfel [13]. 

Sample ID

0 5 10 15 20 25 30 35

Karl Fisher Water, D6304, ppm

0

50

100

150

200

250

300

350

Nominally B20

Less than B20

More than B20 B20 average KF water = 130 ppm

Fleet Samples

Figure 9. Karl Fisher moisture results for the 2008 B20 survey 

Particulate Contamination

Particulate contamination is a concern for any diesel fuel because fine particles may damage 

modern, very high pressure fuel injection systems. A majority of the samples collected in this 

study were tested using the diesel method, D6217, which at the time of the survey was the only 

particulate contamination method for distillate fuels. That method does not cover biodiesel or 

biodiesel blends. A new method specific to biodiesel and biodiesel blends (D7321) was adopted 

in the middle of the survey, and the final seven samples were tested using the new method. Only

small differences can be noted between these two highly similar methods. 

Each method determines the particulate contamination as the mass collected on a standard filter 

after a set volume of fuel is filtered. To compare the methods, five samples were tested using 

both D6217 and D7321. Results showed some variation between methods, but overall trends 

were similar and there was no consistent bias for this small sample set (Figure 10). Except for
11

one sample, the particulate contamination results are typically below 10 mg/L, a level cited as 

acceptable by engine manufacturers [14].

Sample ID

0 5 10 15 20 25 30 35

Particulate Contamination, mg/L

D6217 or D7321

0

20

40

60

80

Nominally B20

Less than B20

Greater than B20

Filled symbols are D6217

Hollow symbols are D7321

Fleet Samples

Figure 10. Particulate contamination results for the 2008 B20 survey, using D6217 or D7321 

Interfacial Tension

Water interfacial tension (IFT) can indicate how effective coalescing water separator filters will 

be at removing free water from fuels that will be introduced into an engine. One measure of 

interfacial tension is the DuNuoy ring method, ASTM D971. Figure 11 shows the interfacial 

tension of the Bxx survey samples. The average IFT is 12.3 mN/m, slightly lower than that 

observed in the 2004 survey; however, the range of IFT values was significantly less in this 

survey. The IFT of diesel fuel has dropped since ULSD fuel was introduced to 9−25 mN/m, 

likely as a result of increased surfactancy from lubricity and other additives [13]. The IFT values 

of Bxx blends collected in this survey were similar to those of U.S. ULSD samples, but at the 

lower end of the range. 

Free and Total Glycerin

One assumption for Bxx blends is that if the B100 and diesel fuel are on-specification, the Bxx 

blend will be on-specification. At the time of this survey, before the B6-B20 specification was 

adopted, this was the only metric used to assess Bxx quality. An important parameter for B100 is 

the free and total glycerin content measured by ASTM D6584. One of the significant drawbacks 

to this method is the extreme sensitivity to even trace amounts of diesel fuel. Therefore, for Bxx 

blends, it is not possible to use D6584 to extract the glycerin information about the B100 used 

for blending unless the parent B100 is available. Excess free and total glycerin can impact engine 

operability by causing injector deposits and plugging fuel filters; it could also impact cold 

weather operability.
12

Sample ID

0 5 10 15 20 25 30 35

Interfacial Tension, D971, mN/m

0

5

10

15

20

25

Nominally B20

Less than B20

Greater than B20

Average B20 IFT = 12.3 mN/m

Fleet Samples

Figure 11. Water interfacial tension results for the 2008 B20 survey

A new IC-based method has been developed that can determine the free and total glycerin 

content of Bxx blends and, by inference, that of the parent B100. The samples in this survey 

were tested using the IC method to determine the B100 free and total glycerin content. Figure 12

shows the free and total glycerin results calculated using the exact biodiesel concentration of the 

B100 used in these blends. Thus, for a B20 sample, the free and total glycerin was multiplied by 

5 to allow comparison with the ASTM D6751 specification for B100. All of the samples 

collected met the B100 specifications for free and total glycerin. 

Group I and II Metals

The Bxx blend samples were also tested for Group I and II metal content: Na, K, Mg, and Ca. 

Biodiesel might contain Group I and II metals if contaminated during the production process. 

These metals can cause oxidation and soaps to form or might negatively impact the durability of 

emission control catalysts and filters. The samples were tested using ASTM D7111. Table 4 lists 

the minimum, maximum, and average metal content for the samples. For Mg and K, all samples 

were below the detection limit. Low levels of Ca were observed in a few samples. Only one 

sample showed elevated Na content in the blend; it was so high (2,000 ppb) that the B100 would 

likely be off-specification. 
13

Sample ID

0 5 10 15 20 25 30 35

Free Glycerin, Extrapolated to B100

IC Method, mass%

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

Total Glycerin, Extrapolated to B100

IC Method, mass%

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Nominally B20

Less than B20

Greater than B20

Hollow symbols are free glycerin

Filled symbols are total glycerin

Fleet Samples

Figure 12. Free and total glycerin by ion chromatography for 2008 B20 survey samples; results 

extrapolated to B100 properties

Table 4. Average and Minimum and Maximum Group I and II Metal Content of B20 Samples (ppb)

Metal Minimum a Maximum Average

Mg BDL(100) BDL(100) b BDL(100)

K BDL(100) BDL(100) BDL(100)

Ca BDL(100) 652 219

Na BDL(500) 2,000 c 606 d

a All samples were measured using ASTM D7111. b BDL(100) is below the detection limit of 100 ppb. c BDL(500) is below the detection limit of 500 ppb. d Sample would be off-specification for Na+K in B100.

Feedstock Analysis

The FAME profile of biodiesel can be used to determine the parent fat or oil used in production. 

For example, the FAME profile of soy-derived biodiesel is approximately 10% methyl palmitate, 

up to 5% methyl stearate, about 25% methyl oleate, 50% methyl linolenate, and less than 10% 

methyl linoleate [15]. Although the profile changes slightly with changes in such factors as 

ambient growing temperature and rainfall, this typical FAME profile can be compared with 

measured FAME profiles to identify the parent fat or oil. 

Each Bxx sample was analyzed using MDGC/FID to determine the source of the B100. 

Soybean-derived biodiesel was the most common source in these blends and accounted for 78% 

of the samples (Figure 13). Of the remaining samples, 21% of the Bxx blends were made from 
14

biodiesel produced from mixed feedstock sources such as soybean oil and animal fat. Only two 

samples were made from neat animal-fat-derived biodiesel. The B100 feedstock could not be 

identified for one sample, a B2. The MDGC/FID method readily identifies the feedstock for B5 

and greater samples. FAME recovery from these samples was in excess of 90%. For blend 

samples lower than B5, FAME recovery dropped significantly as biodiesel content dropped, 

although the FAME profile appeared to be intact.

Feedstock

Frequency

0

5

10

15

20

25

30

Soy/Animal 

Animal

Soy

Unknown

Figure 13. Feedstocks used in the blends collected in the 2008 B20 survey

To further validate this technique, hand blends were produced from a B100 with a known FAME 

content and a certification diesel fuel. The B2 blend was mixed volumetrically and analyzed with 

the MDGC/FID. The FAME recovery was better than that for the real-world samples, but still 

less than the recovery from higher blends. Although the recovery was low, the FAME profile 

was intact and the source could be positively identified, confirming the results from the realworld samples. 

Conclusions

Biodiesel blend samples were collected from around the United States in the summer of 2008. 

These samples were tested against the D7467 specification for B6-B20, which was adopted in 

October 2008. Sixty percent of the samples collected were nominally B20. The rest of the 

samples had lower biodiesel content, such as ~B10, B5, and B2. This is in contrast to NREL’s 

previous B20 survey, in which the biodiesel samples were evenly distributed above and below 

B20. Twenty-five percent of the samples failed to meet the proposed induction period stability 

specification of 6 hours, although on average the induction period was well above this level. The 
15

samples readily met the other proposed specification properties, with one sample with high AV 

and one sample having high sulfur, likely the result of contamination. No failures on flash point 

were noted. Although part of the specification, cloud point is a report value. For the 2008 B20 

survey, the average cloud point was -12.6°C, with a range from -7°C to -25°C. 

Although not in the specification, several other properties of interest were measured. The water 

content of fuels, an important parameter for handling, was measured by Karl Fisher. The B20 

blends had an average water content of 130 ppm, about 30% higher than that of conventional 

diesel fuel. One method of quantifying the particles in fuel is to measure the particulate 

contamination. For these fuels, particulate levels were low, and only one fuel had levels above 20 

mg/L. 

Interfacial tension, a measure of the efficacy of water separator filters to remove water from 

fuels, was similar to ULSD for the B20 samples. Industry-wide, the IFT for diesel fuels has been 

decreasing and this survey showed the same trend. IFT for the B20 blends was slightly below 

2004 levels, but within the range of ULSD samples. 

Analysis of the Group I and II metals revealed very low levels, as expected in biodiesel blends. 

One sample had Na content sufficiently high that the B100 used in the blend was offspecification for this parameter. 

Researchers characterized the B100 used in the blend using novel chromatographic techniques. 

Typically, information about the parent B100 in a Bxx blend is lost when diesel fuel is added. 

Ion chromatography is insensitive to diesel fuel, however, allowing the free and total glycerin to 

be analyzed in the blend. Results show that the parent B100s met the D6751 specification for 

glycerin. A multidimensional GC technique allowed the feedstock of the parent B100 to be 

determined. The biodiesel used to blend these samples was produced predominantly from 

soybean oil, and animal fat was the second most common feedstock. 

Although the B6-B20 specification was not applicable in mid-2008 when the B20 samples were 

collected, a majority of the samples would be meet that specification, with the exception of 

oxidation stability. The adoption of the specification expands the market for future studies to 

include all blends between B6 and B20 and another survey is recommended to assess compliance 

with the specification in the near future. 
16

References

1. Energy Information Administration. August 2009 Monthly Energy Review: Renewable 

Energy; http://www.eia.doe.gov/emeu/mer/renew.html.

2. Alternative & Advanced Fuels–Biodiesel Incentives and Laws;

http://www.afdc.energy.gov/afdc/fuels/biodiesel_laws.html.

3. McCormick, R.L.; Alleman, T.L.; Ratcliff, M.; Moens, L.; Lawrence, R. Survey of the 

Quality and Stability of Biodiesel and Biodiesel Blends in the United States in 2004; 

NREL/TP-540-38836; National Renewable Energy Laboratory: Golden, CO, October 

2005; http://www.nrel.gov/docs/fy06osti/38836.pdf.

4. Tang, H.; Abunasser, N.; Wang, A.; Clark, B.R.; Wadumesthrige, K.; Zeng, S.; Kim, M.; 

Salley, S.O.; Hirschlieb, G.; Wilson, J.; Ng, K.Y.S. Quality survey of biodiesel blends 

sold at retail stations. Fuel 2008, 87, 2951-2955; DOI: 10.1016/j.fuel.2008.04.029. 

5. Alleman, T.L.; McCormick, R.L.; Deutch, S. 2006 B100 Quality Survey Results; 

NREL/TP-540-41549; National Renewable Energy Laboratory: Golden, CO, May 2007; 

http://www.nrel.gov/docs/fy07osti/41549.pdf. 

6. Alleman, T.L.; McCormick, R.L. Results of the 2007 B100 Quality Survey; NREL/TP540-42787; National Renewable Energy Laboratory; Golden, CO, March 2008; 

http://www.nrel.gov/docs/fy08osti/42787.pdf. 

7. McCurry, J.D.; Wang, C. Analysis of Fatty Acid Methyl Ester (FAME) Content and 

Distribution in Biodiesel Blends Using Heat-cutting 2D Gas Chromatography; Agilent 

Technologies publication 5989-8107EN; Agilent Technologies: Santa Clara, CA, March 

2008; http://www.chem.agilent.com/enUS/Search/Library/_layouts/Agilent/PublicationSummary.aspx?whid=55043&liid=1873

8. Shiotani, H.; Goto, S. Studies of Fuel Properties and Oxidation Stability of Biodiesel 

Fuel; SAE Technical Paper No. 2007-01-0073; SAE International: Warrendale, PA, 

January 2007; http://www.sae.org/technical/papers/2007-01-0073.

9. Miyata, I.; Takei, Y.; Tsurutani, K.; Okada, M. Effects of Bio-Fuels on Vehicle 

Performance: Degradation Mechanism Analysis of Bio-Fuels; SAE Technical Paper No. 

2004-01-3031; SAE International: Warrendale, PA, October 2004; 

http://www.sae.org/technical/papers/2004-01-3031.

10. McCormick, R.L.; Westbrook, S.R. Empirical Study of the Stability of Biodiesel and 

Biodiesel Blends; NREL/TP-540-41619; National Renewable Energy Laboratory: 

Golden, CO, May 2007; http://www.nrel.gov/docs/fy07osti/41619.pdf.

11. McCormick, R.L.; Alleman, T.L.; Waynick, J.A.; Westbrook, S.R.; Porter, S. Stability of 

Biodiesel and Biodiesel Blends: Interim Report; NREL/TP-540-39721; National 

Renewable Energy Laboratory: Golden, CO, April 2006;

http://www.nrel.gov/docs/fy06osti/39721.pdf.
17

12. Routt, D. “Testing Biodiesels’ Saturation Properties under the Influence of Variable 

Temperature, Biodiesel Type and #2 Diesel Concentration”; ASAE Section Meeting 

Presentation Paper Number PNW05-1014; 2005 Pacific Northwest ASAE Section 

Meeting, Lethbridge, Alberta, Canada, September 22-24, 2005; 

http://asae.frymulti.com/section_meeting.asp?confid=smppnr. 

13. Stanfel, C. Fuel filtration: Protecting the diesel engine. Filtration & Separation 2009, 46

(3), 22-25; http://www.filtsep.com/view/1727/fuel-filtration-protecting-the-dieselengine/.

14. World Wide Fuel Charter, 4th Edition; European Automobile Manufacturers Association, 

Alliance of Automobile Manufacturers, Engine Manufacturers Association, and Japan 

Automobile Manufacturers Association, September 2006; 

http://www.autoalliance.org/index.cfm?objectid=96B9A0F5-1D09-317FBB2D56C35C3A5F04).

15. Physical and Chemical Characteristics of Oils, Fats, and Waxes, 2nd Edition, American 

Oil Chemists Society, 2006.
F1147-E(10/2008)

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Analysis of Biodiesel Blend Samples Collected in the United States 

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14. ABSTRACT (Maximum 200 Words)

The quality of B20 (20 vol% biodiesel, 80 vol% petroleum diesel fuel) in the United States was sampled in 2008. 

Thirty-two samples from retail locations and fleets using B20 were tested against the proposed D7467 B6-B20 

specification, which took effect later in 2008. Sixty percent were ±2% (nominally) B20. Twenty-five percent failed the 

proposed minimum induction period stability of 6 hours; the overall average was 8.4 hours. All B20 samples met 

proposed specifications for acid value, cetane, and ash. Ion chromatography was used to determine free and total 

glycerin in B20 blends. Results showed that all the B100 used for blending met D6751 glycerin specifications. 

Samples were analyzed by multidimensional gas chromatography to determine the B100 feedstock; most was soyderived; some was animal-derived. The average dissolved water in B20 samples was 130 ppm, 30% higher than the 

typical saturation level of diesel fuel. Particulate contamination in the B20 was below 20 mg/L in every case but one. 

15. SUBJECT TERMS

biodiesel; biodiesel blends; biodiesel quality; biodiesel quality survey; National Renewable Energy Laboratory

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