In general, the carbon content of biochar is inversely related to biochar yield. Increasing
pyrolysis temperature from 300 to 800°C decreased the yield of biochar from 67 to 26% and
increased the carbon content from 56 to 93% (Tanaka, 1963). Beyond a certain threshold,
the mass of biochar may decrease without any affect on the amount of carbon retained within
it; but as mass is lost, the ash content of biochar increases. In one study, the proportion of
biochar comprised of ash increased from 0.67 to 1.26% between 300°C and 800°C
(Kuwagaki and Tamura, 1990).
For a particular feedstock, the elemental composition of the pyrolysis products can still be
greatly affected by the processing temperature and pyrolysis residence time. The effect of
temperature on the composition of biochar from sugarcane bagasse is listed in Table 3.