Attainment of the theoretical yield of carbon from biomass

Previous work has shown that very high yields of charcoal are obtained when pyrolysis of the biomass feedstock is conducted at elevated pressure in a closed vessel, wherein the pyrolytic vapors are held captive and in contact with the solid products of pyrolysis. In this paper, we show that, for som e biomass species, the yield of carbon produced by this process effectively attains the theoretical value predicted to exist when thermochemical equil ibrium is realized. Various agricultural wastes (e.g., kukui nut, macadamia nut, and pecan shells) and tropical species (e.g., eucalyptus, leucaena, a nd bamboo) offer higher yields of carbon than the hardwoods traditionally e mployed by industry in the U.S. and Europe. Moreover, the yields of carbon from oat and rice hulls and from sunflower seed hulls are nearly as high as the yields of carbon from hardwoods. There is a correlation between the yi eld of carbon and the acid-insoluble lignin content of the feed. Charcoal b riquettes made from agricultural wastes and lump charcoal from tropical spe cies are promising sources of renewable carbon for use in the smelting of m etal ores.