What are Renewable Hydrocarbon Biofuels?

From the Alternative Fuels Data Center of the US Department of Energy (2021):

Renewable hydrocarbon biofuels (also called green or drop-in biofuels) are fuels produced from biomass sources through a variety of biological, thermal, and chemical processes. These products are chemically identical to petroleum gasoline, diesel, or jet fuel. Since they meet the same ASTM fuel quality standards as the petroleum fuels they replace, these biofuels can be used in existing engines and infrastructure.

Types of renewable hydrocarbon biofuels include:

• Renewable diesel—Renewable diesel is a biomass-derived transportation fuel suitable for use in diesel engines. It meets the ASTM D975 specification for petroleum in the United States and EN 590 in Europe. It is a commercial fuel produced in the United States and imported from Asia. Five plants produce renewable diesel in the United States, with a combined capacity of over 590 million gallons per year. Production is expected to grow in the near-term with 2 billion gallons of capacity at six plants currently under construction and expansion at three existing plants. The U.S. Energy Information Administration (EIA) does not report renewable diesel production; however, the U.S. Environmental Protection Agency (EPA) reports RFS RIN data, which indicates that the United States consumed over 960 milion gallons in 2020. Nearly all domestically produced and imported renewable diesel is used in California due to economic benefits under the Low Carbon Fuel Standard.
  
  Renewable diesel and biodiesel are not the same fuel. Renewable diesel, previously known as green diesel, is a hydrocarbon produced most often by hydrotreating and also via gasification, pyrolysis, and other biochemical and thermochemical technologies. It meets ASTM D975 specification for petroleum diesel. Biodiesel is a mono-alkyl ester produced via transesterification. Biodiesel meets ASTM D6751 and is approved for blending with petroleum diesel.
  
  
  
• Sustainable aviation fuel (SAF)—SAF is a fuel derived from renewable resources that enables a reduction in net life cycle carbon dioxide emissions compared to conventional fuels. SAF is the preferred, now commonly used term for non-petroleum synthesized jet fuel components produced to the definitions in ASTM D7566. When SAF is blended with conventional jet fuel, it meets ASTM D1655, which allows it to be used in existing aircraft and infrastructure. SAF is commercially available in limited quantities and has been in use at Los Angeles International Airport since 2016 and in late 2020 at San Francisco International Airport. One domestic SAF production facility operates in Los Angeles and several are under construction or planned and imports from an international producer began in late 2020. EIA does not report SAF production; however, EPA reports RFS RIN data, which indicate that the United States consumed 4.6 million gallons in 2020. Currently, seven SAF “pathways” or fuel categories have been approved under the ASTM D7566 standard. All of the neat SAF volumes have to be blended with conventional aviation turbine fuel before they can be certified as ASTM D1655 equivalent and subsequently used in an aircraft. The seven approved pathways (found in the D7566 Annexes) are:
  • Fischer-Tropsch (FT) hydroprocessed synthesized paraffinic kerosene (SPK) fuel using solid biomass resources (e.g., wood residues) (FT-SPK); maximum blend level 50%
  • Synthesized paraffinic kerosene from hydroprocessed esters and fatty acids (HEFA) fuel derived from used cooking oil, animal fats, algae, and vegetable oils (e.g., camelina) (HEFA-SPK); maximum blend level 50%
  • Synthesized isoparaffin fuel from hydroprocessed fermented sugars (SIP), formerly known as direct-sugar-to-hydrocarbon fuel (HFS-SIP); maximum blend level 10%
  • FT-SPK with aromatics fuel using solid biomass resources (e.g., wood residues) (FT-SPK/A); maximum blend level 50%
  • Alcohol-to-jet SPK fuel produced from isobutanol or ethanol (ATJ-SPK); maximum blend level 50%
  • Catalytic hydrothermolysis (or hydrothermal liquefaction) jet fuel derived from fats, oils, and greases (CHJ); maximum blend level 50%.
  • HEFA with hydrocarbons (HC-HEFA) produced from esters and fatty acids at 10% maximum blend concentration.
• Renewable gasoline—Also known as biogasoline or “green” gasoline, renewable gasoline is a biomass-derived transportation fuel suitable for use in spark-ignition engines. It meets the ASTM D4814 specification in the United States and EN 228 in Europe.

Production

Renewable hydrocarbon biofuels can be produced from various biomass sources. These include lipids (such as vegetable oils, animal fats, greases, and algae) and cellulosic material (such as crop residues, woody biomass, and dedicated energy crops). Where production is occurring, the commercial facilities largely focus on renewable diesel production though increased SAF production is expected with several plants under construction. It is common for the same facility to produce both renewable diesel and SAF. As of 2020, there were five commercial renewable diesel plants with a combined capacity of 550 million gallons and one facility producing both renewable diesel and SAF with a capacity of 42 million gallons. Three plants are under expansion and eight are under construction, which are expected to add another 2 billion gallons of capacity. The majority of the new plants and expansion of existing plants are for renewable diesel production—at least three of the facilities will also produce SAF. The United States continues to import renewable diesel, largely from production facilities in Singapore. All SAF and nearly all renewable diesel is used in California due to the state’s Low Carbon Fuel Standard.

Researchers are exploring a variety of methods to produce renewable hydrocarbon biofuels. Production plants may be stand-alone or co-located at petroleum refineries.

Technology pathways being explored for the production of renewable hydrocarbon biofuels include:

• Traditional hydrotreating—Used in petroleum refineries, hydrotreating involves reacting the feedstock (lipids) with hydrogen under elevated temperatures and pressures in the presence of a catalyst. Commercial plants currently use this technology.
• Biological sugar upgrading—This pathway uses a biochemical deconstruction process, similar to that used with cellulosic ethanol with the addition of organisms that convert sugars to hydrocarbons.
• Catalytic conversion of sugars—This pathway involves a series of catalytic reactions to convert a carbohydrate stream into hydrocarbon fuels.
• Gasification—During this process, biomass is thermally converted to syngas and catalytically converted to hydrocarbon fuels.
• Pyrolysis—This pathway involves the chemical decomposition of organic materials at elevated temperatures in the absence of oxygen. The process produces a liquid pyrolysis oil that can be upgraded to hydrocarbon fuels, either in a standalone process or as a feedstock for co-feeding with crude oil into a standard petroleum refinery.
• Hydrothermal processing—This process uses high pressure and moderate temperature to initiate chemical decomposition of biomass or wet waste materials to produce an oil that may be catalytically upgraded to hydrocarbon fuels.

Benefits

Renewable hydrocarbon biofuels offer many benefits, including:

• Engine and infrastructure compatibility—Renewable hydrocarbon biofuels are chemically identical to their petroleum counterparts and therefore minimize compatibility issues with existing infrastructure and engines.
• Increased energy security—Renewable hydrocarbon biofuels can be produced domestically from a variety of feedstocks and contribute to U.S. job creation.
• Fewer emissions—Carbon dioxide captured by growing feedstocks reduces overall greenhouse gas emissions by balancing carbon dioxide released from burning renewable hydrocarbon biofuels compared with conventional fuels.
• More flexibility—Renewable hydrocarbon biofuels are replacements for conventional diesel, jet fuel, and gasoline, allowing for multiple products from various feedstocks and production technologies.

Research and Development

The U.S. Department of Energy’s (DOE) Bioenergy Technologies Office supports research, development, and analysis, as well as design cases (see the following) for renewable hydrocarbon fuels.

• Biochemical Hydrocarbon Pathways (PDF)
• Biological Conversion of Sugars (PDF)
• Thermochemical Hydrocarbon Pathways (PDF)
• In Situ and Ex Situ Pyrolysis (PDF)
• Updated Fast Pyrolysis Design (PDF)
• Algae Hydrocarbon Pathways (PDF)
• Whole Algal Hydrothermal Liquefaction and Upgrading (PDF)
• Biojet Fuel Conversion (PDF)

More Information

Learn more about renewable hydrocarbon biofuels from the links below. The Alternative Fuels Data Center (AFDC) and DOE do not necessarily recommend or endorse these companies (see disclaimer).

• Advanced Biofuels Association
• Commercial Aviation Alternative Fuels Initiative
• U.S. Airport Infrastructure and Sustainable Aviation Fuel (PDF)
• The Feasibility of Producing and Using Biomass-Based Diesel and Jet Fuel in the United States (PDF)
• Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, Hydrotreating, and Hydrocracking: A Design Case (PDF)

The AFDC also provides a publications search for more information.