Bio-oil is a synthetic fuel obtained by heating dried biomass without oxygen in a reactor at a temperature of about 500°C, and it is sometimes known as bio-crude or pyrolysis oil

. It is a mixture of organic compounds, principally acids, alcohols, aldehydes, esters, ketones, and phenols, and it is typically dark brown and free-flowing

. Bio-oil has limited industrial application and is under investigation as a substitute for petroleum

. The exact chemical composition of bio-oil depends on the pyrolysis feedstock and the conditions

. Bio-oil is highly oxygenated, acidic, unstable, and corrosive, which presents problems for its transportation, piping, and storage

. Its fuel value (energy content) is only 50-70% of petroleum fuels

. Bio-oil has not been used as crude fuel because it has too much oxygen and water, and it is soluble in water

. The high water and oxygen content prevent bio-oil from dissolving in bio- diesel, an alternative diesel fuel that is produced from animal fats or vegetable oils