Renewable Hydrocarbon Biofuels
Renewable hydrocarbon biofuels (also called "green" hydrocarbons, biohydrocarbons, drop-in biofuels, and sustainable or advanced hydrocarbon biofuels) are fuels produced from biomass sources through a variety of biological, thermal, and chemical processes. These products are similar to petroleum gasoline, diesel, or jet fuel in chemical makeup and are therefore considered infrastructure-compatible fuels. It is expected that these fuels can be used in vehicles without requiring engine modifications and can use existing petroleum fuel pipelines and retail distribution systems.
Types of renewable hydrocarbon biofuels include:
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.
Renewable diesel—Also called "green" diesel, renewable diesel is a biomass-derived transportation fuel suitable for use in diesel engines. It meets the ASTM D975 specification in the United States and EN 590 in Europe.
Renewable diesel is distinct from biodiesel. While renewable diesel is chemically similar to petroleum diesel, biodiesel is a mono-alkyl ester, which has different physical properties and hence different fuel specifications (ASTM D6751 and EN 14214). The two fuels are also produced through very different processes. While biodiesel is produced via transesterification, renewable diesel is produced through various processes such as hydrotreating (isomerization), gasification, pyrolysis, and other thermochemical and biochemical means. Moreover, biodiesel is produced exclusively from lipids (such as vegetable oils, animal fats, grease, and algae), whereas renewable diesel is produced from lipids and cellulosic biomass (such as crop residues, woody biomass, and dedicated energy crops).
Renewable jet fuel—Also called "biojet" or aviation biofuel, renewable jet fuel is a biomass-derived fuel that can be used interchangeably with petroleum-based aviation fuel. Certain biojet fuel can be blended up to 50% with conventional commercial and military jet (or aviation turbine) fuel by following requirements in the ASTM D7566 specification.
Synthetic paraffin kerosene (SPK) fuels can be blended in variable amounts between 10% and 50% depending on the fuel type with conventional commercial and military jet (or aviation turbine) fuel while synthetic kerosene with aromatics (SKA) fuels can be used interchangeably with fossil fuels. Blending is required with SPK fuels because they lack sufficient aromatic hydrocarbons, which are present in conventional jet fuel. While aromatic hydrocarbons are limited in jet fuel to prevent smoke formation during combustion, a minimum aromatic content is needed to cause elastomer swell in aircraft fuel systems and increase fuel density.
The following fuel categories are approved by the ASTM D7566 standard:
- Hydrogenated esters and fatty acids (HEFA) fuels derived from used cooking oil, animal fats, algae, and vegetable oils (e.g., camelina) (HEFA-SPK)
- Fischer-Tropsch (FT) fuels using solid biomass resources (e.g., wood residues) (FT-SKA)
- FT fuels with aromatics using solid biomass resources (e.g., wood residues) (FT-SKA)
- Synthetic iso-paraffin (SIP) from fermented hydroprocessed sugar, formerly known as direct-sugar-to-hydrocarbon fuels. Blends of up to 10% are permitted for this fuel (SIP-SPK)
- Alcohol-to-jet (ATJ) fuels produced from isobutanol and blended to a maximum level of 30% (ATJ-SPK).
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). Researchers are exploring a variety of methods to produce renewable hydrocarbon biofuels. Production plants may be standalone or co-located at petroleum refineries.
Technology pathways 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.
- Biological sugar upgrading—This pathway uses a biochemical deconstruction process similar to what is 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.
Currently, commercial-scale production of renewable hydrocarbon biofuels in the United States is limited. At the end of 2016, there were four commercial facilities with a combined capacity of 280 million gallons (Cetane Energy, Diamond Green Diesel, and Renewable Energy Group in Louisiana producing diesel and AltAir Fuels in California producing jet fuel).
Renewable hydrocarbon biofuels offer many benefits, including:
Engine and infrastructure compatibility—Renewable hydrocarbon biofuels are similar 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.
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
- Biological Conversion of Sugars
- Thermochemical Hydrocarbon Pathways
- In Situ and Ex Situ Pyrolysis
- Updated Fast Pyrolysis Design
- Algae Hydrocarbon Pathways
- Whole Algal Hydrothermal Liquefaction and Upgrading
- Biojet Fuel Conversion
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
- The Feasibility of Producing and Using Biomass-Based Diesel and Jet Fuel in the United States
- Fungible and Compatible Biofuels: Literature Search, Summary, and Recommendations
- Production of Gasoline and Diesel from Biomass via Fast Pyrolysis, Hydrotreating, and Hydrocracking: A Design Case
The AFDC also provides a publications search for more information.