ARS Scientists Develop Improved System to lower oxygen levels in pyrolysis-based biofuels, without catalysts

In Pennsylvania, ARS chemist Charles Mullen, lead scientist Akwasi Boateng, and mechanical engineer Neil Goldberg recently filed a patent application for a new system that removes much of the oxygen from bio-oils without introducing catalysts. The three scientists work at the ARS Eastern Regional Research Center in Wyndmoor, Pa.

The team conducted their small pilot-scale study using oak, switchgrass, and pressed pennycress. They modified standard pyrolysis by gradually replacing nitrogen in the processing chamber with recycled noncondensable gases produced during pyrolysis. Unlike the nitrogen, which did not affect oxygen levels at all, the gases derived from biomass were very effective in lowering oxygen levels and acidity. No additional catalysts were needed.

The bio-oils produced from oak and switchgrass using the new process had considerably higher energy content than those produced by conventional fast pyrolysis. The energy content of the oak bio-oil rose 33.3 percent from 23.7 to 31.2 megajoules per kilogram or approximately 2/3 of the energy contained in gasoline. The energy content for switchgrass rose 42 percent, from 23.4 to 33.2 megajoules per kilogram, slightly less than three-fourths of the energy content of gasoline. The energy content in bio-oil produced from pressed pennycress feedstock did not show a similar increase.

Results from this study were published in July in Energy Fuels.