Co-processing of pyrolysis vapors with bio-chars for ex-situ upgrading

Co-processing of woody biomass with two bio-chars (bio-chars made from switchgrass and red oak bark) was studied as a way of upgrading the pyrolysis vapors. The clean woodchips were pyrolyzed with and without bio-chars under atmospheric pressure at the target temperature of 500 °C. The co-processing with both bio-chars showed a significant influence on the bio-oil yields, moisture content and pH value of bio-oils. However, the vapor-upgrading process significantly decreased the carbon yield in the bio-oil when using switchgrass bio-char was used for co-processing. The bio-oil yield decreased from 49.31% (non-bio-char) to 44.81% with the switchgrass bio-char and to 48.68% with the bio-char from the red oak bark. The lost mass of bio-oil ended-up in the gaseous phase as reflected in an increased content of carbon dioxide and carbon monoxide. The gaseous-phase composition of hydrogen increased from 0.82% to 3.74%, of carbon dioxide from 21.16% to 32.33%, and of carbon monoxide from 16.49% to 23.19% with the addition of the switchgrass bio-char compared to non-bio-char pyrolysis.