char. According to the simulation, this rapid mass loss basically af-
fects the cellulose-derived char. This situation is shown in
Fig. 5
.
The behaviour observed for EFB pulp can be extended to all
investigated pulps. When the heating rate increases the curvature
of DTG curves increases as well. For any pulp, according to raw
material and pulping process, there is a heating rate that produces
the ignition of char. In order to fit this complex process with a sta-
ble set of kinetic parameters we can not use a nth-order kinetic
model. For a rapid char oxidation this model leads to a reaction or-
der close to zero and unusually high pre-exponential factor and
activation energy. However, applying autocatalytic kinetic it is pos-
sible to fit sharp peaks by modifying (basically) the nucleation or-
der. As shown in
Fig. 5
, usually an increase of the heating rate
modifies slightly the curvature of the char peak (from 5
°
C/min
to 10
°
C/min). In this case the nucleation order slightly increases
as well. However, when ignition occurs (from 10
°
C/min to 20
°
C/
min), the nucleation order increases dramatically without signifi-
cant consequences for the other kinetic parameters. The main ef-
fect is observed for the activation energy: when the nucleation
order increases the activation energy decreases. This is expected
because both changes are consequences of an increasing reaction
rate (
Table
5 shows that standard deviations of activation energy
and nucleation order are related). For all chars, the activation en-
ergy has a comparable value as obtained for charcoal or mineral