Pyrolysis has been used to produce chemicals and charcoal for thousands of years. It is the thermal destruction of biomass in the absence of oxygen, resulting in a dark brown product called pyrolysis oil, which is then upgraded to a drop-in biofuel.
Biomass is fed into a pyrolysis reactor and heated to temperatures around 500°C, either instantaneously (fast pyrolysis) or more gradually (slow pyrolysis.) This transforms the cellulose and hemi-cellulose into a gas, which when cooled, condenses into pyrolysis oil. The remaining portion of the biomass is transformed into either vapour or char. The pyrolysis oil yield varies depending on the type of pyrolysis and biomass used2. A yield of 50-75 wt% (weight percentage) is common. The undesired vapours and char are fed back into the system and burned to help heat the reactor.
Pyrolysis oil must be further treated in a process called “upgrading” to remove the excess oxygen and water that make it unstable in long-term storage and prevent it from mixing successfully with other hydrocarbon-based fuels. The final biofuel product has a lower percentage of metals and sulphur, making it a much lower emission fuel compared with others.
1 = http://www.pnl.gov/main/publications/external/technical_reports/pnnl-18284.pdf
2 = http://www.eubia.org/index.php/about-biomass/pyrolysis-and-gasification/pyrolysis
3 = http://bioweb.sungrant.org/NR/rdonlyres/B8FDD6F2-5900-4A9C-9CB8-9DA483FD7523/0/PyrolysisOilAuthorsArticle.pdf