NREL-Biodiesel-Handling-and-Use-Guide-6th-Edition.pdf

Biodiesel Handling and Use Guide Sixth Edition iii This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

Acknowledgments Funding provided by Clean Fuels Alliance America under agreement CRD-15-00593. The authors thank Richard Nelson of Enersol Resources, Steve Howell of Marc-IV Consulting, and Scott Fenwick of Clean Fuels Alliance America for guidance and input.

Lead Authors Robert McCormick, National Renewable Energy Laboratory (NREL)

Kristi Moriarty, NREL iv This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

List of Acronyms AST aboveground storage tank Bxx biodiesel blend containing xx vol % biodiesel CFPP cold filter plugging point EPA U.S. Environmental Protection Agency LM low metals grade of biodiesel LTFT low-temperature flow test OEM original equipment manufacturer UST underground storage tank v This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

Table of Contents Introduction Biodiesel Basics

What Is Biodiesel?

Biodiesel vs. Renewable Diesel Straight Vegetable Oil Benefits of Biodiesel Use

Properties and Handling of Biodiesel (B100) B100 Specification Energy Content Low-Temperature Properties Oxidation Stability Microbial Contamination Transport Biodiesel Quality

Biodiesel Blends Specifications

B5 and Lower Blends B6 to B20 Blends

Materials Compatibility Low-Temperature Properties Lubricity Stability of Biodiesel Blends Bulk Blending, Storage, and Transport Vehicle Refueling Infrastructure

Codes and Regulations Retail and Fleet Station Equipment Checklist for Installing B20 Dispensing Equipment or Converting Underground Storage Tanks

Use of Biodiesel Blends in Other Markets

On-Road Off-Road Rail Marine Home Heating Power Generation Use of High Blends and B100

Safety, Health, and Environmental Issues Signs, Labels, and Stickers Fire Safety Considerations

Frequently Asked Questions Information Resources Glossary Appendix A. Sample Biodiesel Safety Data Sheet Appendix B. Biodiesel Materials Compatibility Summary Tables Appendix C. Pump Labeling Appendix D. Refueling Equipment Compatibility Appendix E. Engine and Vehicle Manufacturer Approvals vi This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

List of Figures Figure 1. Basic transesterification process Figure 2. Biofuels life cycle Figure 3. ASTM D4625 long-term storage stability for B100 samples having a range of initial Rancimat induction periods. (a) Rancimat induction period (dashed line is 3-h minimum requirement),

(b) peroxide content, and (c) acid number (dashed line is 0.5-mg KOH/g maximum requirement)

Figure 4. Rancimat induction period for ASTM D4625 storage for B20 blends collected in the United States in 2016. Upper dashed line is 6-hour minimum stability required by ASTM D7647.

Lower dashed line is 3-hour stability level below which the formation of acids and peroxides is observed

Figure 5. Re-additization during storage of a biodiesel blend. (a) Induction period (dashed line is 6-h minimum requirement for B20 blends). (b) Peroxide content. (c) Acid number (dashed line is 0.3-mg KOH/g maximum allowable value) measured throughout storage

Figure 6. Typical station fuel dispenser and underground storage piping Figure 7. Placards for transport of combustible and flammable liquids Figure C-1. Federal Trade Commission-compliant B20 and B100 pump labels

List of Tables Table 1. Requirements for Biodiesel (B100) Blendstock as Listed in ASTM D6751-23a Table 2. Typical Energy Density and Specific Energy of Diesel, Heating Oil, and Biodiesel Table 3. ASTM D7467-20a Specification for Diesel Blends B6 to B20 (reprinted with permission of

ASTM)

Table 4. ASTM D396-21 Specification for Heating Oil Blends B6 to B20 Table 5. Fuel Dispenser and Underground Storage Piping Components Table B-1. Elastomer Compatibility With Biodiesel Table D-1. UL Biodiesel Testing Standards for Refueling Equipment Table D-2. Tank Manufacturer Combability With Biodiesel Blends Table D-3. Dispensers, Hanging Hardware, Shear Valves, Submersible Turbine Pumps

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Introduction This document serves as a background and guide for those who blend, distribute, and/or use biodiesel and biodiesel blends. It provides basic information on the proper and safe use of biodiesel in compression-ignition engines, home heating oil systems, boilers, and other applications. This guide is intended to help users, fleets, blenders, distributors, and others understand the handling and use of biodiesel and biodiesel blends. Information on the environmental benefits of biodiesel is also provided.

Biodiesel is produced from plant oils, animal fats, recycled cooking oils, and/or greases and has several advantages:

• Renewable, with a much lower carbon intensity/life cycle greenhouse gas emissions profile than petroleum diesel fuel, such that it reduces global warming emissions.

• Can be used at up to at least 20% blend level in most diesel equipment with zero or minor modifications.

• Compatible with all new on- and off-road diesel engines—often called “new technology diesel engines” (NTDEs)—and burners and backward-compatible with most equipment.

• Demonstrated to reduce tailpipe soot emissions and other criteria pollutants from older (e.g., legacy) engines without modern emission controls, as well as from industrial boiler and home heating systems.

• Nontoxic, biodegradable, and suitable for sensitive environments.

In this report, biodiesel refers to the fuel (commonly called an ester, or fatty acid methyl esters [FAME]) produced from renewable fats, oils, and/or greases that meets the most current ASTM International Standard D6751 (D6751-23a at the time of this writing).1 Biodiesel is most commonly used as a blend with petroleum diesel fuels, including ASTM International Standard D975 grades No. 1 and No. 2 diesel fuel or ASTM International Standard D396 heating oil, as well as other distillate and residual fuel oils. The number following the letter “B” in a biodiesel blend indicates the percent by volume (vol %) of biodiesel in 1 gallon of fuel (e.g., B20 is 20% biodiesel by volume); the remainder of the fuel can be No. 1 or No. 2 diesel, heating oil, or any other distillate or residual fuel. Pure (or neat) biodiesel is called B100. Appendix A shows a sample safety data sheet for biodiesel (B100).

1 ASTM International. 2023. Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels. West Conshohocken, PA. https://www.astm.org/d6751-20a.html.

NTDEs refers to on- and off-road diesel engines manufactured beginning in about 2010 in the United States that include state-of-the-art emissions control systems. The exact configurations of the systems may vary, but often include components like diesel oxidation catalysts, particulate filters, and selective catalytic NOx reduction systems.

https://www.astm.org/d6751-20a.html

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At concentrations of up to 5 vol % (B5) in conventional diesel fuel or heating oil, the mixture falls under the ASTM D975 diesel fuel or ASTM D396 heating oil specifications, respectively, is considered diesel fuel or heating oil, and can be used in any application that uses diesel fuel or No. 1 or No. 2 grade heating oil.2 At concentrations of 6–20 vol % (B6 to B20), the ASTM D7467 specification applies, and these biodiesel blends can be used in many applications that use diesel fuel or heating oil with minor or no modifications to the equipment.3

Higher blend levels between B20 and B100 may require special handling and equipment modifications. These issues can potentially be managed with heaters and/or changing engine seal and gasket materials. Consult your engine manufacturer and/or dealer for further information about procedures and/or precautions before using biodiesel blends higher than B20.

2 The properties of fit-for-purpose diesel fuel is defined in ASTM D975 and for heating oils in ASTM D396.

3 ASTM International. 2023. Standard Specification for Diesel Fuel Oil, Biodiesel Blend (B6 to B20). West Conshohocken, PA. https://www.astm.org/d7467-20a.html

ASTM International (astm.org) is a consensus-based volunteer standards group that comprises experts across numerous industries. Committee D02—Petroleum Products, Liquid Fuels, and Lubricants—covers biodiesel, diesel, and heating oil specifications (in addition to many other products). Membership in D02 includes engine and fuel injection equipment companies, fuel producers, and fuel users (as well as other interested parties).

ASTM standards are recognized in the United States by most government entities. Specifications are living documents and may be updated frequently to reflect the most current needs of the industry. Any ASTM method or specification will include a number and a year at the end, such as D6751-23a. This means the most current version of the method was published in 2023; a letter after the year indicates that more than one modification has been published in a given year. Users need to ensure they are using the most up-to-date version of a test method or specification.

https://www.astm.org/d7467-20a.html http://astm.org/

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Biodiesel Basics What Is Biodiesel?

Biodiesel is a commercially available, lower-carbon-intensity fuel for use in diesel engines, boilers, and home heating oil systems. It can directly replace or be blended with distillate and residual fuel oils, like diesel fuel or heating oil. Biodiesel is manufactured from plant oils (e.g., soybean oil, cottonseed oil, canola oil, corn oil), recycled/used cooking greases (e.g., yellow grease), animal fats (e.g., beef tallow, pork lard, poultry fat), or various combinations of these feedstocks. In addition, other oilseed crops are being commercialized such as camelina, Brassica carinata, and CoverCress™.

The biodiesel production process is known as transesterification, which converts these oils, fats, and/or greases into long-chain mono-alkyl esters, or biodiesel. The esters are commonly referred to as fatty acid methyl esters (FAME) when methanol is used in the transesterification reaction.

Virtually all biodiesel production today uses methanol. Roughly speaking, 100 pounds of oil, fat, and/or grease is reacted with 10 pounds of alcohol, usually methanol (although production from other alcohols is possible), in the presence of a catalyst (usually sodium methoxide)4 to form 100 pounds of biodiesel and 10 pounds of glycerin (or glycerol). Crude glycerin is a coproduct of the biodiesel process and has economic value. Biodiesel is a legally registered fuel and fuel additive with the U.S. Environmental Protection Agency (EPA). The EPA registration is feedstock- and process-agnostic and includes all biodiesel that meets the most current ASTM biodiesel specification, D6751. Figure 1 provides a simplified diagram of the transesterification process.

Figure 1. Basic transesterification process

4 Most biodiesel producers use sodium or potassium methoxide, rather than methanol + sodium hydroxide or potassium hydroxide

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Biodiesel vs. Renewable Diesel Renewable diesel is another alternate fuel used in compression-ignition engines and is produced from some of the same renewable feedstocks as biodiesel. However, the way that these feedstocks are processed into renewable diesel is considerably different than biodiesel.

As discussed above, biodiesel is primarily made through transesterification to produce fatty acid methyl esters. Renewable diesel is produced by a process called hydroprocessing or hydrotreating—indicating a reaction with hydrogen. Hydroprocessing produces chemicals identical to some of the compounds found in conventional diesel fuel. Like biodiesel, renewable diesel has very low sulfur content, which is advantageous environmentally. Renewable diesel typically has a very high cetane number and can be made to meet a range of cloud point requirements.

Straight Vegetable Oil Raw or refined plant oils, fats, or recycled greases that have not been processed into biodiesel or renewable diesel should be avoided for use in compression-ignition engines. Research shows oils, fats, and/or greases, even at concentrations as low as 1%, can cause long-term engine deposits, ring sticking, lube oil gelling, and other maintenance problems and can reduce engine life.5

These problems are caused mostly by the much higher viscosity, or thickness, of the raw fats and/or oils compared to diesel fuel for which the engines and injectors were designed. The process of converting oils, fats, and greases to biodiesel by transesterification ensures the viscosity is reduced to values more similar to conventional diesel fuel.

Benefits of Biodiesel Use

Biodiesel Is a Low-Carbon-Intensity Fuel and Reduces Greenhouse Gas Emissions Carbon intensity refers to the amount of greenhouse gases emitted per unit of energy consumed, usually stated in grams of CO2 equivalent per megajoule (CO2eq/MJ). The carbon intensity of petroleum-based diesel fuels is typically around 95 g CO2eq/MJ. Biodiesel carbon intensity depends on feedstock used, but ranges from around 18 g CO2eq/MJ for waste cooking oil to 21 g CO2eq/MJ for soybean oil (or 30 g CO2eq/MJ when including indirect land use change effects).6 Because of biodiesel’s lower carbon intensity, when biodiesel displaces petroleum in any application, it significantly reduces life cycle greenhouse gas emissions. These life cycle analysis results show greenhouse gas emissions for soy B100 are 67% to 77% lower than those from petroleum diesel. Figure 2 presents a basic overview of the life cycle of CO2 emissions produced and recycled when biodiesel is generated from agricultural feedstocks and utilized in a vehicle.

5 U.S. Department of Energy. 2021. “Straight Vegetable Oil as a Diesel Fuel?”

https://afdc.energy.gov/files/u/publication/straight_vegetable_oil_as_diesel_fuel.pdf.

6 H. Xu, L. Ou, Y. Li, T.R. Hawkins, and M. Wang. 2022. “Life Cycle Greenhouse Gas Emissions of Biodiesel and Renewable Diesel Production in the United States.” Environ. Sci. Technol. 56: 7512–7521.

https://afdc.energy.gov/files/u/publication/straight_vegetable_oil_as_diesel_fuel.pdf

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

Figure 2. Biofuels life cycle.

Image copyright Clean Fuels Alliance America, used with permission.

Biodiesel Reduces Soot Emissions Because biodiesel contains approximately 11 wt% oxygen (i.e., an oxygenate), when it is blended into petroleum fuels it will dilute certain compounds that have a high soot (e.g., particulate matter) formation tendency and enhance combustion, thereby reducing particulate emissions. This is a major benefit for pre-2010 model year on-road engines and for many off-road engines not equipped with diesel particle filters. These reductions are greater for higher biodiesel blend levels, but also depend on engine design, calibration, and operating conditions.

Biodiesel use in home heating oil systems and boilers can reduce soot by as much as 60% for B100 and roughly 10% for B20.7,8

7 A. Macor and P. Pavanello. 2009. “Performance and emissions of biodiesel in a boiler for residential heating.”

Energy 34: 2025–2032.

8 S. Win Lee, T. Herage, and B. Young. 2004. “Emission reduction potential from the combustion of soy methyl ester fuel blended with petroleum distillate fuel.” Fuel 83: 1607–1613.

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Properties and Handling of Biodiesel (B100) This section describes the basic properties of B100 and considerations for its handling and blending. The storage and handling procedures for B100 are different than for B20 and lower biodiesel blends and vary from those for diesel fuel, especially in cold weather. Using B20 and lower blends significantly reduces or eliminates the effects of these property differences.

However, because many distributors store and handle B100 before blending, a good understanding of B100 properties is valuable.

Several significant attributes specific to B100 should be considered when handling, storing, and using B100:

• B100 is a good solvent. It may loosen or dissolve varnish and sediments in fuel tanks and fueling systems left by conventional diesel or other fuels over time. This may be especially true in systems that have never used biodiesel. If a system contains sediments, the tanks and fuel system should be cleaned before B100 is handled or used. A good indication that B100 is cleaning the tank is an initial increase in filter plugging. Over time, filter change intervals should return to normal. This should not be an issue for B20 or lower blends. Spills should be cleaned up immediately, as B100 may not be compatible with some types of paint.

• B100 gels at higher temperatures than most diesel fuel and heating oil. This must be considered if handling or using B100, especially in aboveground storage tanks (ASTs).

The temperature where B100 starts to gel will vary with the feedstock and can range from −3°C to 15°C (27°F to 60°F) or higher,9 so heated fuel lines and tanks may be needed in colder months, even in moderate climates. As B100 begins to gel, the viscosity increases quickly, which can increase stress on fuel pumps. The high cloud point of B100 may make its use challenging in colder climates.

• B100 is not compatible with some hoses and gaskets. B100 may degrade, soften, or seep through some hoses, gaskets, seals, elastomers, glues, and plastics with prolonged exposure. Polypropylene, polyvinyl, and Tygon materials are particularly vulnerable to B100, as are some nitrile rubber compounds. Before handling or using B100, ask the

9 T. Alleman. 2020. Assessment of BQ-9000 Biodiesel Properties for 2017. Golden, CO: National Renewable Energy Laboratory. NREL/TP-5400-75795. https://www.nrel.gov/docs/fy20osti/75795.pdf; T. Alleman. 2020.

Assessment of BQ-9000 Biodiesel Properties for 2018. Golden, CO: National Renewable Energy Laboratory.

NREL/TP-5400-75796. https://www.nrel.gov/docs/fy20osti/75796.pdf; T. Alleman. 2020. Assessment of BQ-9000 Biodiesel Properties for 2019. Golden, CO: National Renewable Energy Laboratory. NREL/TP-5400-76840.

https://www.nrel.gov/docs/fy20osti/76840.pdf; T. Alleman. 2021. Assessment of BQ-9000 Biodiesel Properties for 2020. Golden, CO: National Renewable Energy Laboratory. NREL/TP-5400-79815.

https://www.nrel.gov/docs/fy21osti/79815.pdf; T. Alleman. 2022. Assessment of BQ-9000 Biodiesel Properties for 2021. Golden, CO: National Renewable Energy Laboratory. NREL/TP-5400-83108.

https://www.nrel.gov/docs/fy22osti/83108.pdf.

In the United States, it is equally common to handle B99 and B99.9 blends. The considerations in this section also apply to B99 and B99.9, as these fuel blends may qualify for a tax credit for biodiesel blending.

https://www.nrel.gov/docs/fy20osti/75795.pdf https://www.nrel.gov/docs/fy20osti/75796.pdf https://www.nrel.gov/docs/fy20osti/76840.pdf https://www.nrel.gov/docs/fy21osti/79815.pdf https://www.nrel.gov/docs/fy22osti/83108.pdf

This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

equipment vendor or original equipment manufacturer (OEM) if the equipment is suitable for B100 or biodiesel. If your equipment is not compatible with B100, the materials should be replaced with materials that are, such as Teflon, Viton, fluorinated plastics, or nylon. For bulk handling of B100, seals, gaskets, and hoses must be compatible with B100. (See Appendix B for information about material compatibility.) Using B100 in an engine or burner constructed with incompatible materials can cause a fuel spill on a hot engine, ruin a fuel pump, or clog a filter as the hose material gradually erodes. Use extreme care to ensure any part of the fuel system that touches the fuel is compatible with B100.

• B100 is not compatible with some metals and plastics. Biodiesel will degrade and form high sediment levels if contacted for long periods with lead, tin, or zinc (galvanized surfaces). Testing with biodiesel meeting today’s ASTM D6751 specification with copper or copper-containing metals (e.g., brass, bronze) also shows the potential for long-term degradation or sediment formation, although values were similar to that of conventional petroleum-based fuel.10 These high sediment levels may clog filters. B100 may also permeate some common plastics (e.g., polyethylene, polypropylene) over time, so these should not be used for storing B100.

• B100 is compatible with most lubricants and filters. No modifications are required in most cases for biodiesel.

B100 Specification The specification for B100 is frequently updated at ASTM, and as of this writing the most current version is D6751-23a, summarized in Table 1. Anyone buying or using B100 must be aware of the most current version of the specification—it is the user’s responsibility to stay current. Specification updates may be significant (e.g., the addition of a new testing requirement) or may be more subtle, such as updated information in an appendix or a new test method. At the end of the specification, users can find a summary of changes that includes updates from the previous version. For the most up-to-date version of the specification, check the ASTM website (astm.org). Countries outside the United States may use other specifications, such as

EN14214:2012+ A2:2019.11

10 R. Kerr, T. Butcher, N. Islam, and M. Haverly. 2022. “Monitoring Biodiesel Blends in Heating Applications – Effects of Exposure Conditions.” IASH 2022 Proceedings of the 17th International Conference on Stability, Handling, and Use of Liquid Fuels, Dresden, Germany, 11–15 Sept. 2022.

11 DIN EN 14214 Liquid petroleum products - Fatty acid methyl esters (FAME) for use in diesel engines and heating applications - Requirements and test methods (includes Amendment :2019), https://www.en-standard.eu http://www.astm.org/ https://www.en-standard.eu/

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Table 1. Requirements for Biodiesel (B100) Blendstock as Listed in ASTM D6751-23a

Property Test Method

Grade No. 1-B

S15, S15 LM

Grade No. 1-B S500

Grade No. 2-B

S15, S15 LM

Grade No. 2-B S500

Sulfur,a % mass (ppm), max D5453 0.0015 (15) 0.05 (500) 0.0015 (15) 0.05 (500)

Cold soak filterability, seconds, max D7501 200 200 360 360

Monoglyceride content, % mass, max D6584 0.40 0.40

Metals, ppm (μg/g), max, Grades:

No. 1-B S15, S500; No 2-B S15, S500

Calcium and magnesium, combined EN 14538 5 5 5 5

Sodium and potassium, combined EN 14538 5 5 5 5

No. 1-B S15 LM, No. 2-B S15 LM

Sodium, potassium, calcium, and magnesium, combined

EN 14538 4 4

Requirements for All Grades

Flash point (closed cup), °C, min D93 93 93 93 93

Alcohol control; one of the following shall be met:

1. Methanol content, mass %, max EN 14110 0.2 0.2 0.2 0.2

2. Flash point, °C, min D93 130 130 130 130

Water and sediment, % volume, max D2709 0.050 0.050 0.050 0.050

Kinematic viscosity,b mm2/s, 40 °C D445 1.9-6.0 1.9-6.0 1.9-6.0 1.9-6.0

Sulfated ash, % mass, max D874 0.020 0.020 0.020 0.020

Copper strip corrosion, max D130 No. 3 No. 3 No. 3 No. 3

Cetane number, min D613 45 45 45 45

Cloud point,c °C D2500 Report Report Report Report

Carbon residue,d % mass, max D4530 0.050 0.050 0.050 0.050

Acid number, mg KOH/g, max D664 0.50 0.50 0.50 0.50

Free glycerin, % mass, max D6584 0.020 0.020 0.020 0.020

Total glycerin, % mass, max D6584 0.240 0.240 0.240 0.240

Phosphorus content, % mass, max D4951 0.001 0.001 0.001 0.001

Distillation temperature, atmospheric equivalent temperature, 90% recovered, °C, max

D1160 360 360 360 360

Oxidation stability, hours, min EN 15751 3 3 3 3 a Other sulfur limits may apply in selected areas in the United States and in other countries.

b The 6.0-mm2/s upper viscosity limit is higher than petroleum-based diesel fuel and should be taken into consideration when blending.

c The cloud point of biodiesel is generally higher than petroleum-based diesel fuel and should be taken into consideration when blending.

d Carbon residue shall be run on the 100% sample.

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ASTM D6751 was originally developed to ensure the quality of biodiesel blended with diesel fuel and heating oil. Any biodiesel used in the United States should meet ASTM D6751 before blending. ASTM D6751 is based on the physical and chemical properties needed for safe and satisfactory diesel engine and boiler operations. It is not based on the specific feedstock or the manufacturing process used to produce the biodiesel. The finished blendstock must meet the properties specified in Table 1, as well as the following definition from ASTM D6751 and the workmanship clauses:

ASTM definition: “Biodiesel, n, a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B100.”

ASTM workmanship clauses:

“The biodiesel fuel shall be visually free of undissolved water, sediment, and suspended matter.”

“The diesel fuel shall also be free of any adulterant or contaminant that can render the fuel unacceptable for its commonly used applications.”

The No. 1-B grades meets more stringent purity requirements intended to provide better low-temperature performance for engines. Most biodiesel produced at the time of this publication is No. 1-B grade.9 The 1-B grade is recommended if ambient temperatures for the end use application are below 0°C (32°F). The low metals (LM) grades are limited to 4 ppm total for sodium, potassium, magnesium, and calcium and are for applications using diesel engines with modern diesel particulate filters and selective catalytic reduction exhaust aftertreatment.

This specification was not originally intended to be applied to B100 used as a neat fuel for on-road applications, but ASTM D6751 does allow its use as a B100 neat fuel specification if desired. Buyers and sellers are encouraged to use ASTM D6751 for the commercial trading of biodiesel (B100). Other arrangements or specifications can be legally used if the buyer and seller agree, as long as they meet pertinent local, state, and federal regulations (e.g., EPA sulfur limits, Occupational Safety and Health Administration safety limits on flash point).

Moreover, the B100 used in making biodiesel blends must meet the requirements of ASTM D6751 for blends to be legal on- and off-road fuels under the Clean Air Act fuel registration requirements and to be a legal blending component under many state regulations.12

The intent of each quality requirement in Table 1 is described here:

• Group I and II metals. Higher levels of sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) can cause deposits to form, catalyze undesired side reactions, and adversely affect emissions control equipment. The Group I and II metals are limited as the combination of metals in each category, Na+K and Ca+Mg. The specification upper limit is 5 ppm, combined, for each pair of metals. The LM grade is intended for diesel engine applications using advanced emission controls, especially diesel particle filters

12 Depending on point of blending, biodiesel may meet the EN14214 specification for quality in lieu of ASTM D6751.

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and selective catalytic reduction systems, and limits the total of all four of these metals combined to 4 ppm. These metals can accumulate on the filter, increasing filter pressure drop and reducing filter maintenance interval. Almost all biodiesel in the United States is routinely well below LM grade limit.9

• Flash point. A minimum flash point for diesel fuel is required for fire safety. The flash point of B100 is required to be at least 93°C (200°F) to ensure all the alcohol from production is removed; it is classified as nonhazardous under the National Fire Protection Association code.

• Alcohol. It is critical to ensure the manufacturer has removed excess alcohol (typically methanol) used in the production process. Residual methanol in the fuel is a safety issue, because even very small amounts dramatically reduce the flash point. Methanol can also negatively affect fuel pumps, seals, and elastomers, and can result in poor engine combustion properties. The intent of the alcohol control requirement is to limit volatile alcohols to less than 0.2 wt %. This can be accomplished by meeting a higher flash point requirement of 130°C (266°F) or by measuring methanol content by gas chromatography.

• Water and sediment. This refers to free water droplets and sediment particles suspended in the B100. The allowable level for B100 is set at the same level as for conventional diesel fuel. Poor manufacturing or contact with excessive water during transport or storage can cause B100 to be out of specification for water content. Excess water can lead to corrosion and provides an environment for microorganisms. Fuel oxidation can also raise sediment levels, so this test can be used in conjunction with acid number, oxidation stability, and viscosity to determine if fuels have oxidized too much during storage.

• Kinematic viscosity. A minimum viscosity is required for some applications because of the potential for power loss caused by injection pump and injector leakage. This is not an issue for B100, and the minimum is set at the same level as for No. 2 diesel fuel and No.

2 heating oil. The maximum viscosity is limited by the design of engine fuel injection systems. Higher-viscosity fuels can cause poor fuel combustion that leads to deposit formation as well as higher in-cylinder penetration of the fuel spray, which can result in elevated engine oil dilution with fuel. The maximum allowable viscosity in ASTM D975 for No. 2 diesel is 4.1 mm2/s at 40°C (104°F). ASTM D6751 allows for slightly higher viscosity than ASTM D975 (up to 6.0 mm2/s), primarily because the normal viscosity of B100 is slightly higher than that of diesel fuel and because this standard is for B100 to be used as a blendstock. Biodiesel blends of 20 vol % or lower with No. 2 diesel fuel should have viscosities between the 1.9 and 4.1 mm2/s, within the range allowed by ASTM D975. Biodiesel blended with No. 1 diesel fuel can have viscosities as low as the 1.3-mm2/s lower limit for No. 1 in ASTM D975.

• Sulfated ash. This test measures the amount of residual alkali catalyst in the biodiesel, as well as any other ash-forming compounds that could contribute to injector deposits or fuel system fouling.

• Sulfur. This limit is by EPA regulations at 15 ppm to reduce sulfate and sulfuric acid pollutant emissions and to protect exhaust catalyst systems on newer diesel engines.

Biodiesel generally contains less than 15 ppm sulfur. The ASTM D5453 test for sulfur in fuel should be used for accurate results for B100. Other test methods, like ASTM D1266, This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

ASTM D2622, ASTM D3120, and ASTM D4294 may provide falsely high results caused by test interference with the oxygen in B100.

• Copper strip corrosion. This test is used to indicate potential difficulties with copper and bronze fuel system components. The requirements for B100 and conventional diesel are identical, and biodiesel meeting other ASTM D6751 specifications always passes this test. Copper and bronze may not corrode in the presence of biodiesel, but prolonged contact with these catalysts can degrade the fuel and cause sediment to form with petroleum diesel or with biodiesel.

• Cetane number. An adequate cetane number is required for good engine performance.

Cetane number is a measure of the ignition quality of the fuel and influences white smoke, cold starting, and combustion roughness. The cetane number requirements depend on engine design, size, and nature of speed and load variations, as well as starting and atmospheric conditions. The ASTM minimum limit for B100 cetane number is set at

45. There is no minimum cetane number for heating oil or marine fuels. The cetane index (ASTM D976 or ASTM D4737) is not an accurate predictor of cetane number for biodiesel or biodiesel blends because it is based on a calculation that uses specific gravity and distillation curve for petroleum diesel. The specific gravity and distillation curve for biodiesel are different and may provide falsely low cetane values using the cetane index calculation methods.

• Cloud point. This is the most used measure of low-temperature operability. There is no specification for cloud point for biodiesel, though reporting the value is required in the ASTM D6751 specification. Fuels are generally expected to operate at temperatures down to their cloud point. The cloud point of B100 is typically higher than the cloud point of conventional diesel fuel. Low-temperature properties and strategies for ensuring good low-temperature performance of biodiesel blends are discussed in more detail in later sections.

• Carbon residue. This is a measure of the carbon-depositing tendency of a fuel and approximates the tendency for carbon deposits to form in an engine or boiler. For conventional diesel fuel, the carbon residue is measured on the 10% distillation residue.

Because B100 boils entirely at the high end of the diesel fuel range and in a very narrow temperature range, it is difficult to leave only a 10% residue when distilling biodiesel.

Therefore, biodiesel carbon residue specifies that the entire biodiesel sample be used rather than the 10% distilled residue.

• Acid number. For biodiesel, acid number is primarily an indicator of free fatty acids (natural degradation products of fats and oils or a component of some biodiesel feedstocks) and can be elevated if a fuel is not properly manufactured or has undergone oxidative degradation. Acid numbers higher than 0.50 mg KOH/g have been associated with fuel system deposits and reduced life of fuel pumps and filters.

• Free and total glycerin. A measure of the amount of unconverted or partially converted fats/oils and byproduct glycerin in B100. Incomplete conversion of the fats and oils into biodiesel can lead to high total glycerin from elevated mono-, di-, and triglycerides.

Incomplete removal of glycerin can lead to high free and total glycerin. If the glycerides are too high, the storage tank, fuel system, and engine can be contaminated. Fuels that

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exceed these limits are highly likely to plug fuel filters and cause other problems.

Controls for glycerides should be implemented at the B100 level before blending, as this test method (D6584) is highly sensitive to the presence of diesel fuel (some of which will be falsely counted as biodiesel in the method) and should not be used for biodiesel blends.

• Phosphorus content. Phosphorus is limited to 10 ppm maximum in biodiesel because high levels can adversely affect emissions control systems. Phosphorus above 10 ppm can be present in some plant oils and recycled greases before making it into biodiesel, but the biodiesel reaction and cleanup steps (i.e., water washing) essentially remove all phosphorous compounds in the finished biodiesel. At this time, biodiesel produced in the United States generally has phosphorus levels less 1 ppm.9

• T90 distillation. T90 is defined as the temperature at which 90% of the fuel has distilled.

The specification was incorporated to ensure that fuels have not been contaminated with high-boiling materials such as used motor oil or raw fats and oils. B100 exhibits more of a single boiling point rather than a distillation curve. The fatty acids from which biodiesel are produced are mainly straight chains with 16 to 18 carbons that have similar boiling point temperatures. The atmospheric boiling point range of biodiesel is generally 330°C to 357°C (626°F to 675°F).

• Oxidation stability. Biodiesel can oxidize during storage and handling, leading to the formation of peroxides, acids, gums, and deposits. The minimum oxidation stability requirement is intended to ensure the storage stability of B100 and biodiesel blends in clean tanks.

• Cold soak filterability. This specification was added in 2008 in response to data indicating that some B100 could, in blends up to B20, form precipitates at temperatures above the cloud point of the blend. B100 meeting the cold soak filterability requirements does not form these precipitates. This, along with cloud point, is needed to predict low-temperature operability.

• No. 1-B grade. The No. 1-B grade has year-round limits on cold soak filterability and monoglycerides. These limits ensure that trace components in biodiesel are minimized.

Energy Content With conventional diesel fuels, the inherent energy content of the fuel is the largest factor affecting the fuel economy, torque, and horsepower delivered by the fuel. The energy content of petroleum diesel fuel can vary up to 15% from supplier to supplier and from summer to winter.

No. 2 diesel fuel usually has higher energy content than No. 1 diesel fuel. Neat biodiesel (B100) contains about 7.5% less energy per gallon than typical No. 2 diesel fuel. Due to the similar carbon chain length number of the fatty acid chains in the oils and fats used to produce biodiesel, the energy content of biodiesel is similar, regardless of the feedstock and the particular biodiesel process. The energy content of biodiesel and diesel fuel blend linearly, so the energy content of B50 would be midway between the energy content of the starting biodiesel and diesel fuel.

However, these differences in energy content do not inherently translate into lower biodiesel fuel economy, especially with engines that employ modern diesel particulate filter/selective catalytic reduction technology that can be positively impacted by lower particulate emissions of biodiesel.

Typical reference values for various fuels and biodiesel are shown in Table 2.

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Table 2. Typical Energy Density and Specific Energy of Diesel, Heating Oil, and Biodiesel

Specific Energy Btu/lb (MJ/kg)

Energy Density Btu/gal (MJ/L)

Typical diesel No. 2 a 18,320 (42.6) 128,488 (3881)

Typical heating oil b 18,545 (43.2) 139,000 (38.7)

Typical biodiesel (B100) c 16,270 (37.8) 119,550 (33.3) a https://afdc.energy.gov/fuels/properties b https://noraweb.org/wp-content/uploads/2016/10/NORA-Silver-Chapter-2.pdf c https://afdc.energy.gov/fuels/biodiesel_basics.html

Low-Temperature Properties Understanding the low-temperature properties of fuels and how they impact utilization is extremely important to ensure a good user experience. Unlike gasoline, diesel fuels and biodiesel can freeze or gel as the temperature drops. If the fuel begins to gel, it can clog filters on dispensing equipment and may eventually become too thick to pump. B100 is commonly stored in heated aboveground tanks for blending. Important low-temperature performance metrics for handling and blending of B100 are:

• Cloud point, defined as the temperature at which small solid crystals are first visually observed as the fuel is systematically cooled.13 Below a fuel’s cloud point, these crystals might plug filters or could drop to the bottom of a storage tank. This phenomenon may occur with diesel fuels or with B100.

• Pour point, defined as the temperature at which the fuel contains so many agglomerated crystals it is essentially a gel and will no longer flow.14 Distributors and blenders use pour point as an indicator of whether the fuel can be pumped, even if it would not be suitable for use at this temperature for most diesel engine applications.

13 Cloud point methods: ASTM D2500, D5771, D5772, or D5773.

14 Pour point methods: ASTM D97, D5949, or D5950.

The difference in energy content between diesel fuel and biodiesel can be noticeable when comparing diesel fuel with B100. For B20, historical field studies indicate the differences in power, torque, and fuel economy are less than 2%, depending on the diesel fuel (for an on-road vehicle that gets 5.5 miles per gallon, this is a difference of about 0.1 miles per gallon). Most users report little or no difference in fuel economy between B20 and diesel fuel. Any differences between B20 and diesel fuel are about the same as would be expected between summer and winter diesel fuel. As the amount of biodiesel in the blend is lowered, differences in energy content become proportionally less significant: Blends of B5 or lower cause no noticeable differences in performance compared to diesel fuel.

https://afdc.energy.gov/fuels/properties https://noraweb.org/wp-content/uploads/2016/10/NORA-Silver-Chapter-2.pdf https://afdc.energy.gov/fuels/biodiesel_basics.html

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These guidelines should be followed for storing biodiesel (B100) in cold temperatures:

• The cloud point of B100 starts around −3°C (27°F) and may be up to 16°C, though in some rare cases can have a cloud point as high as 20°C (68°F). The pour point of B100 is usually only a few degrees lower than the cloud point, so once biodiesel begins to freeze, gelling can occur rapidly if the temperature drops only a few degrees further.

• B100 should be stored at temperatures at least 2.5°C to 5°C (5°F to 10°F) higher than the cloud point. Because the cloud point of the B100 varies, the storage temperature for trouble-free use will not be the same for all biodiesels.

• Aboveground B100 tanks and fuel lines should be designed for the cold flow properties of biodiesel and the local climate. Fuel pumps, lines, and dispensers must be protected from cold and wind chill with properly approved heating and insulating equipment.

• Most B100 can be stored underground in most cold climates without additional considerations because underground storage temperatures are normally above 7°C (45°F).

Most of the time, once crystals form in fuels, they will generally go back into solution as the fuel warms.15 However, that process can be slow if the fuel is heated only slightly above the cloud point. Crystals formed in biodiesel or diesel fuel can drop to the bottom of the tank and begin to build up. Slow agitation can prevent crystals from building up on the tank bottom or, once present in the fuel, can help convert the crystals back into liquid.

The low-temperature performance of B100 cannot be effectively managed with current cold flow additives, as can diesel fuel and biodiesel blends. The level of saturated compounds in B100 is too high for most additives to be effective. Cold flow additives have been used much more successfully with biodiesel blends. Users should work directly with the additive manufacturers on this issue.

Oxidation Stability Biodiesel is thermally very stable but can be susceptible to oxidation in storage. Oxidation stability of fuels depends on initial fuel quality and additives but is also driven by storage conditions such as exposure to contaminants, heat, air, and light—oxidizing conditions that can accelerate degradation/aging. A high resistance to aging is necessary to ensure fuel retains quality throughout the supply chain. A fuel’s resistance to oxidation, referred to as its oxidation reserve, is determined using accelerated aging tests, which can indicate if a fuel will be stable during typical storage and handling.

Fuel aging and oxidation can lead to the production of acids, increased viscosity, and the formation of gums and sediments that clog filters. Biodiesel with high oxidation stability will generally take longer than biodiesel with low oxidation stability to reach a condition that would

15 G.M. Chupka, J. Yanowitz, G. Chiu, T.L. Alleman, and R.L. McCormick. 2011. “Effect of Saturated Monoglyceride Polymorphism on Low-Temperature Performance of Biodiesel.” Energy and Fuels 25 (1): 398–405.

doi: 10.1021/ef1013743.

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be problematic. Monitoring stability—measured as Rancimat induction period and the acid number of B100 over time—is recommended if it will be stored for longer time periods.

For B100, an oxidation stability measurement is carried out using the test method EN15751 (also referred to as the Rancimat test and listed in ASTM D6751, ASTM D7467, and ASTM D396 as oxidation stability). This analysis involves heating a small fuel sample to 110°C (230°F) while air is bubbled through the fuel at a controlled flow rate and recording the amount of time the fuel takes to degrade under these conditions (its induction period). These conditions are referred to as being accelerated because the temperature of the test is much higher than will occur in real-world storage and because the fuel is saturated with oxygen from the flowing air. This extreme aging does not mimic any condition the fuel might encounter in use, but is designed to force rapid oxidation, which differentiates stable and unstable fuels. Results from this test provide a relative stability index; longer times mean more stable fuel.

In some cases, deposits from the cleaning or solvent effect of B100 have been confused with gums and sediments that could form in storage as the B100 ages. Although sediment can clog a filter in either case, care should be taken to make sure the reason for the clogging is properly identified. For example, if oxidation stability and acid number are within specification, sediments are most likely due to the cleaning effect and not to aging or oxidation.

Guidelines to help identify biodiesel and storage conditions that will provide the highest levels of stability follow:

• Certain metals such as rust, copper, brass, bronze, lead, tin, and zinc will accelerate the degradation process and may form even higher levels of sediment. If possible, B100 (as well as petroleum diesel) should not be stored in systems that contain these metals.

Copper fuel lines are common in home heating oil systems, however, and storage results indicate similar or lower sediment levels with B100 than with petroleum home heating oil.

• Antioxidants, whether natural or incorporated as additives, can significantly increase the storage life or stability of B100. The use of antioxidant additives is highly recommended with B100, especially with longer-term storage. Actual results and improvements may vary depending upon the chemistry of each additive.

• Limiting or preventing biodiesel contact with air reduces or eliminates fuel oxidation and increases storage life. Commercially, this is done by using a nitrogen blanket on storage tanks or storing biodiesel in sealed drums or totes with minimal headspace.

Accelerated stability tests like EN15751 will show if a fuel has high or low stability, but this cannot exactly predict the amount of time a fuel can be stored. The stability requirement in D6751 is that B100 have a minimum three-hour oxidative reserve prior to being blended, so most biodiesel producers make B100 with higher oxidation reserve values. If the biodiesel will be stored for some time prior to blending, biodiesel with antioxidants or higher oxidation reserve should be considered or the induction time and acid number can be monitored at regular intervals to ensure the biodiesel meets D6751 prior to blending.

A very useful evaluation of diesel fuel stability during storage for research purposes is the ASTM D4625 storage stability test. This is used to simulate storage at ambient temperature, This report is available at no cost from the National Renewable Energy Laboratory at www.nrel.gov/publications.

roughly 21°C (70°F), to gain a sense of how a fuel may behave over long periods of time. The test conditions are meant to accelerate aging by a factor of 4 for S500 diesel fuels—i.e., 1 week of storage at D4625 conditions (43°C or 110°F, slightly open to air) simulates 1 month of storage at 21°C (70°F). This acceleration factor has not been validated for B100 or other low-sulfur distillate fuels, but it is still a useful guide. ASTM D4625 data (see Figure 3)16 indicate that B100 will lose oxidation stability gradually over time, eventually dropping below the specification minimum of 3 hours. Higher initial induction period values can provide longer storage time before biodiesel goes out of specification. Figure 3 also shows that as the oxidation stability is reduced to near zero, the material can oxidize due to complete loss of “oxidation reserve.” This is evident in the increase in peroxide values, peroxides being the initial primary product of fuel oxidation. Acid numbers remain relatively constant until peroxide values become very high (>1,500 ppm), as acids are secondary products. Once sufficient peroxides have formed, the acid number increases rapidly via peroxide degradation.

Measurement of insoluble material in the B100 samples in Figure 3 was not statistically significant during ASTM D4625 storage for 13 weeks (simulating 1 year of storage); however, highly oxidized biodiesels—having acid numbers well above the ASTM D6751 limit of 0.5 mg KOH/g—have historically been shown to form insoluble materials.17 Studies such as this show that B100 can lose its oxidation reserve to fall below the specification limit before the fuel forms acids and insoluble materials, which could become problematic.