Improving carbon product yields in biocarbon production by combining pyrolysis and anaerobic digestion

Solid carbon is an important raw material in industrial processes. Most of the charcoal produced today is via conventional carbonization, which suffers from huge carbon losses due to system inefficiency. Intermediate pyrolysis is principally similar to conventional carbonization and produces biocarbon while capturing the off gasses; among these off gasses is aqueous condensate, which is difficult to utilize due to the high water content and low energy content. This fraction can contain up to 25% of the carbon from feedstock, so utilization of this fraction is important for good overall carbon balance. Anaerobic digestion can be a promising tool for utilizing the carbon in the aqueous condensate by converting it into biomethane. Here, birch and spruce wood were pyrolyzed and the biomethane potential for the aqueous condensates was tested. The mass and carbon balances of the pyrolysis products of birch and spruce at two pyrolysis temperatures were performed, and biocarbon carbon yields ranging from 42% to 54% were obtained. Anaerobic digestion of the aqueous phases collected from the pyrolysis process was performed, with carbon recovery yields between 44% and 59%. A total carbon recovery of 77.8% to 85.7% was obtained, and the primary carbon losses were identified.