Campus Units

Mechanical Engineering, Chemical and Biological Engineering, Agricultural and Biosystems Engineering, Bioeconomy Institute (BEI), NSF Engineering Research Center for Biorenewable Chemicals

Document Type


Publication Version

Accepted Manuscript

Publication Date


Journal or Book Title

Applied Energy



First Page





This study investigates whether the rate of cooling of pyrolysis vapors affects the composition of the resulting bio-oil. Pure cellulose was pyrolyzed in a laboratory-scale fluidized bed reactor at 500 °C and the bio-oil collected in either an indirect contact heat exchange (conventional water-cooled condenser system) or a direct contact heat exchange (liquid quench) system developed in our laboratory. The liquid quench system was estimated to achieve a seven-fold increase in cooling rate compared to the water-cooled condensers. Direct contact cooling in the quench system also eliminated temperature gradients experienced by films of bio-oil running down the walls of the water-cooled condensers. The combination of these two factors helped reduce secondary decomposition of primary pyrolysis products, especially anhydrosugars such as levoglucosan. The quench system increased the yield of levoglucosan by over 20% while minimally effecting yield of other compounds.

The concept of direct contact cooling was applied to a pilot-scale, lignocellulosic biomass pyrolysis plant using water as a more practical quench media than liquid nitrogen. As with the liquid nitrogen quench, the water flashed to gas while the heavy ends of the bio-oil condensed to liquid. The quench vessel was operated above the dew point of the water to assure that it left the vessel as gas along with produced water and light ends of bio-oil, which were recovered in a condenser as an aqueous phase. In pyrolysis experiments with red oak, the quench vessel increased the yield of heavy ends by 15% compared to conventional condensers. These results encourage the design of bio-oil recovery systems that can rapidly quench products to achieve high yields and improve the quality of bio-oil.


This is a manuscript of an article published as Dalluge, Dustin L., Lysle E. Whitmer, Joseph P. Polin, Yong S. Choi, Brent H. Shanks, and Robert C. Brown. "Comparison of direct and indirect contact heat exchange to improve recovery of bio-oil." Applied Energy 251 (2019): 113346. DOI: 10.1016/j.apenergy.2019.113346. Posted with permission.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Copyright Owner

Elsevier Ltd.



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Available for download on Friday, May 28, 2021

Published Version