High yield of carbonaceous material from biomass via pyrolysis-condensation

Biochar is a carbonaceous material produced from pyrolysis of biomass in oxygen-deficient atmosphere, which is the feedstock for production of numerous functional carbon materials. Yield of biochar from biomass in the upstream determines cost in manufacturing downstream biochar-derived materials. In pyrolysis, dominance of cracking reactions removes not only oxygen, hydrogen but also carbon, diminishing biochar production. Therefore, retainment as many carbon-containing organics as possible in pyrolysis is the key for improving yield of biochar. In this study, pyrolysis coupled with in situ condensation (pyro-condensation) method is developed, in which the volatiles are cycled back to surface of biochar constantly. This leads to the re-polymerization of the volatiles after the cracking, which increases molecular sizes of the volatiles and eventually transforms them into part of the biochar, maximizing biochar production while minimizing bio-oil formation. The typical biochar yield reaches 60% for the pyro-condensation of poplar sawdust at 450 °C, doubled that from traditional pyrolysis. Additionally, universality of pyrolysis-condensation method for enhancing biochar yield was confirmed by the use of 25 different types of biomasses as research substrates. The biochar is highly aliphatic, rendering it versatile applications as a reductant, solid fuel, adsorbent for pollutants, or a soil conditioner with a high water retention rate. The configuration of the reactor for pyro-condensation is very simple, and the process shows lower environmental impacts than traditional pyrolysis.