Biodiesel vs. Renewable Diesel: Key Differences and Motor Fuel Applications
- tsr4946
- Apr 10
- 7 min read
Updated: Apr 14
Prepared by Energy & Environmental Advisors www.eeadvisorsinc.com 1
ASTM D975 Standards for Diesel Fuel
ASTM D975 is the American Society for Testing and Materials (ASTM) Standard Specification for Diesel Fuel Oils, which defines the quality and performance requirements for conventional petroleum, based diesel fuels used in compression ignition engines. It covers various grades of diesel, including No. 1D (light diesel), No. 2D (standard diesel for on road and off-road applications), and No. 4D (heavy fuel for industrial engines). The standard specifies critical properties such as cetane number, sulfur content, lubricity, flash point, cloud point, viscosity, and stability, ensuring fuel compatibility with modern diesel engines and emissions control systems. B0B5 biodiesel blends are included in D975 as part of the diesel fuel specification.
Relationship Between ASTM D975, ASTM D6751, ASTM D7467, and EN 14214
ASTM D6751 – Specification for Biodiesel (B100) Blend Stock: ASTM D6751 defines the quality requirements for pure biodiesel (B100) used as a blending component in diesel fuels. It ensures biodiesel meets necessary chemical and physical properties, such as oxidation stability, free glycerin content, and cold flow properties, to prevent engine damage and fuel system issues.
ASTM D7467 – Specification for Biodiesel Blends (B6B20): ASTM D7467 is a use specification for ASTM D6751compliant biodiesel blended into petroleum diesel at the B6B20 level.
EN 14214 – European Biodiesel Standard: EN 14214 is the European Committee for Standardization (EN) specification for biodiesel (FAME Fatty Acid Methyl Ester) used in European markets. It sets strict limits on parameters such as ester content, iodine value, and cold flow properties, ensuring biodiesel compatibility with European diesel engines and emission regulations. Unlike ASTM D6751, which allows a range of feedstocks, EN 14214 has more stringent requirements on biodiesel composition to maintain fuel stability in colder climates.
Summary of Standards Interaction
ASTM D975 governs finished diesel fuel, including blends with up to 5% biodiesel (B5).
ASTM D6751 applies to B100 biodiesel, which must meet this specification before blending into ASTM D975 diesel.
ASTM D7467 covers B6 to B20 biodiesel blends of fuels that meet both D975 and D6751.2
EN 14214 serves as the European equivalent of ASTM D6751, setting biodiesel fuel quality
for blends in European diesel markets.
These standards ensure fuel quality, engine performance, and environmental compliance for both petroleum based and renewable diesel fuels worldwide.
1. Constituents of Biodiesel and Renewable Diesel
Biodiesel and renewable diesel are both derived from biological sources but differ significantly in
their chemical compositions and properties.
Biodiesel: Produced through transesterification, biodiesel consists of fatty acid methyl esters (FAME) derived from plant oils (such as soybean and canola), animal fats, and recycled cooking oil.
Renewable Diesel: Made via hydrotreating, renewable diesel is composed of pure hydrocarbons, similar to petroleum diesel, but from the same renewable sources as biodiesel such as vegetable oils and animal fats.
2. Manufacturing Process
The production processes for biodiesel and renewable diesel differ fundamentally:
Biodiesel Production (Transesterification)
Transesterification is the chemical process used to produce biodiesel by converting fats and oils into fatty acid methyl esters (FAME). In this process, triglycerides (found in vegetable oils, animal fats, or recycled cooking oils) react with an alcohol, typically methanol or ethanol, in the presence of a catalyst such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). This reaction breaks down the triglycerides, replacing the glycerol backbone with the alcohol molecule, yielding biodiesel as the primary product and glycerin as a byproduct. The biodiesel is then purified to remove excess alcohol, catalyst residues, and contaminants, ensuring it meets ASTM D6751 or EN 14214 standards for use in diesel engines.
Renewable Diesel Production (Hydrotreating)
Hydrotreating is the chemical process used to produce renewable diesel by converting triglycerides and free fatty acids from plant oils, animal fats, or waste oils into hydrocarbon based diesel fuel. In this process, the feedstock is subjected to high temperatures (typically 300400°C) and high pressures in the presence of a hydrogen rich environment and a metal based catalyst, such as nickel molybdenum or cobalt molybdenum. The hydrogen removes oxygen from the feedstock through hydrodeoxygenation, breaking down the triglyceride molecules and converting them into straight chain hydrocarbons. This results in a fuel chemically similar to petroleum diesel but with ultralow sulfur content and a high cetane number. Renewable diesel produced via hydrotreating meets ASTM D975 standards and can be used as a direct replacement for conventional diesel without blending or engine modifications.
3. Blending with Diesel Fuel for Motor Fuel Use
Both biodiesel and renewable diesel can be blended with conventional diesel for use in diesel engines:
Biodiesel Blends: Blends up to B5 (5% biodiesel) are generally considered identical to diesel and meet ASTM D975 standards. B20 (20% biodiesel) is commonly used in fleets and provides a balance of cost, emissions benefits, and operability. Blends higher than B20 may require engine modifications.
Renewable Diesel Blends: Renewable diesel is a drop-in replacement for petroleum diesel and can be used in any ratio (RD100 is 100% renewable diesel). Meets ASTM D975 diesel specifications, requiring no engine modifications.
4. Local Blending for Large Diesel Users
Fleet owners, truck stops, and travel centers can blend biodiesel or renewable diesel at their facilities using inline-blending systems:
Biodiesel Blending: Blended using inline injectors at fueling terminals or manually blended (splash blending). Requires heating in cold climates to avoid gelling.
Renewable Diesel Blending: Easier to blend as it does not require heating and has a low temperature performance similar to petroleum diesel. However, the producer can tailor the cold flow properties to meet the climate where the renewable diesel will be used. Thus, a production designed for use in Texas may not meet the low temperature performance needed in Minnesota.
5. Financial Incentives for Installing a Blending Facility
Organizations investing in biodiesel or renewable diesel blending can benefit from several financial incentives.
Federal Incentives:
The Biodiesel Blender’s Tax Credit provides a $1 per gallon incentive for blenders of biodiesel. 3
The Renewable Fuel Standard (RFS) program offers Renewable Identification Numbers (RINs) that can be sold to obligated parties.
The US Department of Agriculture manages the Higher Blends Infrastructure Program, designed to expand infrastructure and availability for marketing higher blends of biodiesel, renewable diesel, and ethanol. 4
State and Local Incentives:
Some states offer grants and tax credits for blending infrastructure installation.
Low carbon fuel programs, such as California’s Low Carbon Fuel Standard (LCFS), provide additional credits.
6. Financial Incentives for Selling Biodiesel or Renewable Diesel
Distributors and retailers selling biodiesel and renewable diesel can take advantage of multiple financial benefits.
Biodiesel Sales Incentives:
Excise tax reductions and blender credits encourage retailers to sell higher biodiesel blends.
Carbon credit programs can further enhance financial returns.
Renewable Diesel Sales Incentives:
Similar tax benefits and credits under the RFS and LCFS programs.
High demand from government fleets and sustainability focused companies.
7. Environmental and Air Quality Benefits
Switching to biodiesel or renewable diesel significantly reduces greenhouse gas (GHG) emissions and improves air quality.
Biodiesel Benefits:
Reduces particulate matter (PM) emissions by up to 50%.
Cuts carbon dioxide (CO₂) emissions by 74% compared to petroleum diesel.
Provides improved lubricity for older diesel engines.
Renewable Diesel Benefits:
Near zero sulfur content, reducing NOx and PM emissions.
Higher cetane rating results in cleaner and more efficient combustion.
Compatible with advanced emission control technologies.
8. Labeling Requirements for Biodiesel and Renewable Diesel
According to the National Institute of Standards and Technology (NIST) Handbook 44 (2019), specifically Section 3.30 on Liquid Measuring Devices, weights and measures regulatory agencies require labeling on fuel dispensers to indicate the type and content of the fuel being sold. For diesel fuel blends, this includes identifying whether the diesel is Biodiesel or Renewable Diesel, along with the blend percentage. These requirements fall under the jurisdiction of local weights and measures officials and align with user requirements such as GUR.1.1 (Suitability of Equipment) and GUR.3.1 (Method of Operation), which emphasize the need for accurate and clear identification of product type and concentration at the point of sale. Dispensers selling blends exceeding 5% biodiesel (B5) or nonconventional diesel types like Renewable Diesel must clearly label the fuel type to ensure proper consumer information and compliance with ASTM standards.
9. Cold Weather Performance and Gelling Temperatures
The gelling point of diesel fuels varies depending on the composition and blend ratios.
Petroleum Diesel (No. 2D): Begins to gel around 15°F to 5°F (9°C to 15°C).
Biodiesel (B100): Gels at much higher temperatures, around 30°F to 40°F (1°C to 4°C), depending on feedstock.
Renewable Diesel (RD100): Exhibits cold flow properties comparable to or better than petroleum diesel, with gelling at temperatures below 0°F (18°C).
Blending biodiesel for cold climates requires care:
B5 (5% biodiesel): Typically safe down to 10°F to 15°F (9°C to 12°C).
B20 (20% biodiesel): May begin gelling around 20°F (6°C) depending on the feedstock. Renewable Diesel blends (RD20 to RD100): Maintain low temperature performance similar to petroleum diesel, making them ideal for winter use.
For temperatures ranging from 0°F to 30°F, Renewable Diesel or Biodiesel blends no higher than B5 are recommended to avoid gelling. Heated storage and blending infrastructure are often required for higher biodiesel concentrations during winter months.
Conclusion
Both biodiesel and renewable diesel are viable alternatives to petroleum diesel, offering significant environmental benefits and financial incentives. While biodiesel requires blending considerations, renewable diesel is a direct substitute with minimal infrastructure changes needed. Businesses investing in these fuels can benefit from government incentives, improved air quality, and reduced dependence on fossil fuels.
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Sources Include:
1 a) Biodiesel Handling and Use Guide (Fifth Edition) U.S. Department of Energy, Energy Efficiency & Renewable Energy, b)Biodiesel Blending Practices, NATSO 2021, c) NIST HB 442019
4 https://www.rd.usda.gov/HBIIP This is the first year of a transition away from the Blender’s Tax Credit to a clean fuel producer tax credit (45Z). It is rather complicated compared to the old credit and the industry currently lacks guidance on it. Check the link to the treasury.
