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USDA researchers develop new pyrolysis processes for bio-oil production

Researchers at the US Department of Agriculture (USDA) Agricultural Research Service (ARS) have developed and have filed a patent on a new fast pyrolysis process called Tail Gas Reactive Pyrolysis (TGRP), which removes much of the oxygen from bio-oils without the need for added catalysts.

Fast pyrolysis is the process of rapidly heating biomass from wood, plants and other carbon-based materials at high temperatures without oxygen. Using pyrolysis to break down tough feedstocks produces three things: biochar, a gas, and bio-oils that can be refined to end-products such as green gasoline.

The bio-oils are high in oxygen, making them acidic and unstable, but the oxygen can be removed by adding catalysts during pyrolysis. Although this adds to production costs and complicates the process, the resulting bio-oil is more suitable for use in existing energy infrastructure systems as a “drop-in” transportation fuel that can be used as a substitute for conventional fuels.

The ARS researchers modified the standard pyrolysis process by gradually replacing nitrogen gas in the processing chamber with the gases produced during pyrolysis. The TGRP process was very effective in lowering oxygen levels and acidity, and no additional catalysts were needed.

The team conducted a pilot-scale study using three types of biofeedstock with different characteristics: oak, switchgrass, and pressed pennycress seeds.

Bio-oils produced from oak and switchgrass by the new process had considerably higher energy content than those produced by conventional fast pyrolysis. The energy content of the oak bio-oil was 33.3% higher and contained about two-thirds of the energy contained in gasoline. The energy content for switchgrass was 42% higher, slightly less than three-fourths of the energy content of gasoline.


  • Ghasideh Pourhashem, Sabrina Spatari, Akwasi A. Boateng, Andrew J. McAloon, and Charles A. Mullen (2013) “Life Cycle Environmental and Economic Tradeoffs of Using Fast Pyrolysis Products for Power Generation,” Energy & Fuels 27 (5), 2578-2587 doi: 10.1021/ef3016206





The abstract of the paper cited does not mention anything about a new pyrolysis process.

Recycling the pyrolysis gas as the atmosphere for pyrolysis is all well and good, but how does this affect the cost of the system and its efficiency?  If it does not make the pyrolysis oil directly usable as other than boiler fuel, does it reduce the downstream processing cost enough to be worth the expense?

Biomass is primarily carbohydrate; its products will have oxygen.  Avoiding the introduction of extraneous oxygen is sensible, but at what cost?  Perhaps some process can recycle the products while removing water and CO2, stripping the oxygen out of the system to yield a more energy-dense product.

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