The gas fraction is mainly composed of carbon dioxide and carbon
monoxide (Fig. 3). Their yields (masses by mass unit of RH) increase
with temperature due to the enhancement of
decarboxylation and decarbonylation reactions. In addition, this
fraction is also composed of small amounts of H2 and C1–C4
hydrocarbons.
As observed in Fig. 3, CO concentration increases with the temperature,
whereas that of CO2 decreases. This occurs because at
temperatures below 450 C decarboxylation reactions prevail, but
at temperatures above 450 C the main secondary reactions are
those of decarbonylation, and therefore the release of CO is higher.
The yield of light hydrocarbons (C1–C4) and H2 also increases with
temperature due to the severity of cracking reactions.
This non-condensable gas is of low value as a heat source in a
pyrolysis process due to the dilution with the carrier gas (N2).