Wood vinegar, also known as Pyroligneous Acid, is a liquid product generated during the pyrolysis of biomass. Specifically, wood vinegar is a liquid mixture obtained by cooling the condensable gases produced when biomass (such as wood, wood chips, agricultural waste, etc.) is heated and decomposed under anaerobic conditions. Essentially, wood vinegar is a by-product generated during the pyrolysis of biomass.

Wood vinegar typically appears as reddish-brown or dark brown and possesses a distinctive smoky smell. Its color intensity varies depending on the type of raw material and pyrolysis conditions, and the color tends to lighten after refining. The density of wood vinegar generally ranges from 0.99 to 1.018 g/mL, and its pH is acidic, typically falling between 2 and 4. Its acidic nature primarily stems from the presence of organic acids, such as acetic acid.

Wood vinegar is an extremely complex mixture, and its chemical composition varies significantly depending on the raw materials, pyrolysis conditions, and refining methods. According to research, wood vinegar contains more than 200 organic compounds. The main components of wood vinegar can be divided into two major parts:

Moisture: The moisture content in wood vinegar is typically between 80-90%, making it the most abundant component. The moisture originates from free and bound water in biomass materials, as well as water vapor generated during the pyrolysis process.

Organic compounds: The remaining 10-20% are organic compounds, which come in a wide variety of types. These mainly include acids, phenols, alcohols, ketones, aldehydes, esters, furans, and their derivatives. These organic substances endow wood vinegar with unique chemical and biological activities.