intermediates, such as gas or bio-oil, which can be upgraded into fuel

and other products.

One type of thermochemical conversion process is pyrolysis, a method that uses

heat to decompose biomass in the absence of oxygen.

Here's one example of a pyrolysis conversion process.

Wood material such as forest residue is a common feedstock for the

pyrolysis process.

For best results, feedstock particles are less than two millimeters in size and

have less than 10% moisture content by weight.

The process of pyrolysis heats the biomass at moderate temperatures in the

absence of oxygen.

This produces vapors that are condensed into liquid bio-oil.

Char is also produced during the pyrolysis process.

Cleanup and stabilization of the bio-oil make it more suitable for storage,

downstream processing, and end use.

Cleanup can consist of filtering out particulates and ash before the

bio-oil is condensed into a liquid.

Stabilization typically involves mild hydrotreating, a process that uses

hydrogen to remove contaminants such as sulfur, nitrogen, or in the case of bio-oils,

oxygen.

Hydrotreating occurs with high hydrogen pressures in the presence of catalysts.

Oxygen is eliminated mostly as water, along with some carbon dioxide.

Other processes to remove oxygen are also being examined.

Eliminating oxygen creates a less reactive bio-oil with lower acidity.

The less reactive bio-oil may be stored longer and is more suitable for use as a

fuel oil.

The less acidic bio-oil may be more readily accepted into current

infrastructure, by achieving chemical compatibility with infrastructure

materials, such as pipes, reactors, and tanks.

Mild hydrotreating is usually followed by more severe hydrotreating, which is

required for the bio-oil to be suitable for use in a conventional

petroleum refinery at several insertion points.

Then, using technologies employed by existing refineries today, the bio-oil

goes through a hydrocracking process, which tailors the molecule

sizes to be in the desired range for gasoline, diesel, or jet fuel.

The Department of Energy is supporting development of innovative technologies

that result in higher quality bio-oil that lowers subsequent upgrading costs,

allows for longer storage, and improves commercial viability.

Advancing these technologies will help bring clean, renewable transportation

fuels to the marketplace

that can be used in place of petroleum.