INFORM November/December 2025

BIOPRODUCTS

inform November/December 2025, Vol. 36 (10) • 15

Biomass pyrolysis: Liquid properties David C. Dayton

Wood vinegar, pyroligneous acid, liquid smoke, pyrolysis oil, bio-oil, biocrude—these are all names for the hydrocarbon-rich liquid pro duced from biomass pyrolysis. Like petroleum crude and other indus trial oils, it is a chemically complex, multicomponent mixture that is dark and free flowing with a wide molecular weight distribution and boiling range. Beyond that, there are few similarities between bio-oil (the term that will be used here) and other crude oils. Bio-oils already have a range of commercial uses, from energy production to food flavoring. As a renewable fuel, they can substitute for petroleum in boilers that gener ate steam for electricity and heat. In addition, certain chemical components of bio-oils are extracted and incorporated into foods, where they add the distinctive smoky taste found in marinades, barbecue sauces, cheeses, and processed meats such as bacon and sausage. Researchers are also exploring new applications for bio-oils, particularly in advanced biofuels and specialty bioproducts. Efforts are underway to adapt conventional refin ing methods so that bio-oils can be upgraded into drop-in fuels compatible with existing infrastructure. Their rich chemical diversity is opening additional possibilities, including the development of biocides, flame retardants, and even synthetic vanilla. BIOMASS PYROLYSIS Bio-oil results from the thermal decomposition of lignocellulosic material in the absence of oxygen. This process is known as biomass pyrolysis. Typical feedstocks include: wood and wood product residues, agricultural residues—corn stover, cereal straws, and pur pose grown or energy crops—miscanthus, switchgrass, poplar and eucalyptus. Pyrolysis products depend on the feedstock and process conditions, but consist pri marily of solids, liquids, and gases in various ratios. The solid, called char or biochar, is rich in carbon and contains ash material from the starting feedstock. Condensable vapors and aerosols produced during biomass pyrolysis can also be captured as bio-oil. The most abundant component of bio-oil is water, up to 35 weight percent. The water comes from two sources. The first is free water in the feedstock that gets vaporized. The second is referred to as “water of pyrolysis” that originates from the dehydration of cellulose and hemicellulose in biomass during pyrolysis.

• Bio-oil is a product of biomass thermal depolymerization. • Bio-oil is a complex, multicomponent mixture with a wide molecular weight distribution and boiling range. • The elemental composition of bio-oil resembles that of the original biomass. • Bio-oils tend to have high oxygen content, are acidic, and thermally unstable.