USDA Researchers Develop Pyrolysis Reactor For Localized Conversion of Biomass to Bio-Oil as an Intermediate Stage in Fuels Processing

6 April 2007

Researchers at the US Department of Agriculture’s Agricultural Research Services (ARS) have built a pilot-scale (2.5 kg of biomass/hour) fluidized-bed fast pyrolysis reactor to convert perennial grasses to bio-oil, and have tested the reactor on switchgrass.

The prototype reactor produces a quantity of bio-oil that is 60% of the weight of the switchgrass fed into the reactor, with energy conversion efficiencies ranging from 52 to 81%. The char produced would provide all the energy required for the endothermic pyrolysis reaction process.

After testing the composition and fuel properties of the produced liquid, the researchers found that the energy content was about the same as the parent switchgrass but the energy density was more than 2.5X greater.

One economic problem for the transport of large quantities of biomass—such as switchgrass—to refineries for further processing is its bulk and light weight. A technical—and economic—problem is breaking down the cellulosic material to release the sugars that can be fermented to produce ethanol.

Both issues potentially could be addressed by the localized conversion of the biomass to bio-oil for subsequent upgrading to fuels and chemicals, according to the researchers.

The study, the results of which will be published in Industrial and Engineering Chemistry Research, can be used to design similar tests for other grasses and for the design and scale-up of reactors for larger operations.

One possible outcome would be the development of small-scale, distributed pyrolysers that could be used by farmers locally to produce the pyrolytic oil. Farmers could then sell the product as a crude product to oil refiners, who in turn, would convert it into transportation or heating fuels.