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Biomass liquefaction is the conversion of solid (cellulosic) biomass materials to oil. During the mid-to-late 1980s, commercial interest of the thermochemical conversion of biomass focused on liquefaction. Unlike the initial gasification studies, the preliminary liquefaction studies utilized woody biomass, or lignocellulose material, as the feedstock. Woody biomass was considered superior to that of corn stover due to its potentially lower cost and greater availability.

Pyrolysis is the process of heating biomass in the lack of oxygen or in the presence of a limited amount of oxygen. The pyrolysis oil can be used directly as a fuel or as an intermediate for production of chemicals.

Fast pyrolysis is a thermal decomposition process operating at moderate temperatures (450 to 600°C, 840 to 1,110°F), with high heat transfer rates to the biomass particles and a short residence time. Under these conditions, organic vapors, gases, and char are produced. A short residence time is required to obtain the maximum yield of the liquid.

The vapors are condensed to produce pyrolysis oil (often referred to as bio-oil). Yields of liquid products as high as 79% of the initial dry weight of the biomass can be achieved. Generally, the process produces little or no waste and either the pyrolysis gas or charcoal is used to heat the reactor and the other can be used to supplement the other in heating, dry the feedstock, the charcoal can be sold as a byproduct, or the pyrolysis gas can be used to fuel a gas engine.

Pyrolysis oil is greenhouse gas neutral, does not produce SOx (sulfur dioxide) emissions and produces approximately half of the NOx (nitrogen oxide) emissions compared to fossil fuels.

See also: Biofuels, Biomass, Biomass – Liquefaction, Biomass To Liquids, Torrefaction.