A wide range of terms and approaches are used to refer to advanced biofuels. These different approaches arise partly because a great diversity of biofuels feedstocks and processes are currently being developed.

The EIBI (European Industrial Bioenergy Initiative) provides a good definition that fixes three main characteristics. Advanced Biofuels are those: (1) produced from lignocellulosic feedstocks (agricultural and forestry residues and wood-based biomass), non-food crops (grasses, miscanthus, algae,…), or industrial waste and residue streams, (2) having low CO2 emission or high GHG reduction, and (3) reaching zero or low ILUC (Indirect Land Use Change) impact. Many advanced biofuels can be blended with fossil fuels in existing vehicles and current infrastructure (“drop-in” fuels) and others need specific engines and new technologies for the transport and the storage.

Producing these advanced biofuels requires high-tech facilities: biorefineries using the last technologies and processes. The feasibility of such plants is one of the key points to release the whole potential of this new generation of biofuels.

1. Cellulosic alcohols

1.1 Types

1.1.1 Cellulosic ethanol

It is the same as conventional bioethanol. It is typically blended with gasoline (10-25% blend with current vehicles and up to 95% blend in specialized engines).
- Cellulosic ethanol – The basics: Concepts and feedstocks.
Cellulosic ethanol biorefineries at commercial scale.
Corn fiber ethanol – Examining 1.5G technologies.

1.1.1 Cellulosic butanol
It is an alcohol that can be used as a transport fuel. The molecule has an energy content similar to that of gasoline, it can be burned without modifications in an existing gasoline engine and it is said to be less corrosive than ethanol. Up to 85% blend with gasoline and up to 25% with diesel.
- Commercial biorefineries and pilot plants through the world: Biobutanol biorefineries.

1.2 Pathways

1.2.2 Thermochemical
2. Biohydrocarbons
Also called, renewable hydrocarbon fuels, green hydrocarbons, drop-in biofuels, and sustainable or advanced hydrocarbon biofuels. They are fuels produced from biomass sources through a variety of processes. These products are similar to petroleum gasoline, diesel or jet fuel in chemical makeup and are therefore considered infrastructure-compatible fuels. They can be used in vehicles without requiring engine modifications and can be transported in existing petroleum fuel pipelines and retail distribution systems.

2.1 Types

2.1.1 Renewable gasoline (biogasoline, green 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.

2.1.2 Renewable diesel (green 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.

2.1.3 Renewable jet fuel (biojet, aviation biofuel) is a biomass-derived fuel that can be used interchangeably with petroleum-based aviation fuel. It can be blended with conventional commercial and military jet fuel by following requirements in the ASTM D7566 specification.

2.2 Pathways

2.2.1 Hydrotreatment 
Hydrotreated Vegetable Oils (HVO) or Hydroprocessed Esters and Fatty Acids (HEFA)
In the HVO production process, hydrogen is used to remove the oxygen from the triglycerides producing a mix of linear paraffins, CO2 and water. Then, the product of the first stage is isomerized, always in presence of hydrogen, in order to branch the linear chains for improving the cold flow properties of the final products. Thus, HVO are mixtures of paraffinic hydrocarbons, free of sulphur and aromatics and with a very high cetane number.
Hydrotreating (HVO) – Concepts, feedstocksand specifications.
- Posts: HVO.
- Examples of commercial biorefineries: Rotterdam Biorefinery / Venice Biorefinery.

2.2.2 Pyrolysis
A complex mixture of oxygenated hydrocarbon fragments. For the production of drop-in transportation fuels (diesel, kerosene or gasoline), chemical treatment (upgrading processes) is needed. Finally co-refining in traditional crude oil refineries is possible.

2.2.3 Gasification
Gasification followed by Fischer-Tropsch synthesis.
- Summary of the status of the pilot and demonstration plants at 2014 (only in Spanish): BIOMASS TO LIQUID (3ª Parte).

2.2.4 Alcohol-To-Fuel
Alcohol dehydration, oligomerization and hydrogenation.


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Hydrotreated Vegetable Oils (HVO) Biorefineries – The rise of renewable diesel

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