2.3. Conventional pyrolysis of samples
Conventional pyrolysis was performed at two different temperatures
(400 and 800 ◦C) in the electric furnace (EF) shown in Fig. 2a.
Approximately 4 g of sample was introduced into a quartz reactor.
First, the reactor was placed outside the EF and was purged
with N2 for 30 min at a flow rate of 50mLSTP min−1 to ensure an
oxygen-free atmosphere. Meanwhile, the EF was heated up to the
pyrolysis temperature. Once the reactor had been purged and the
EF had reached the desired temperature, the N2 flow was reduced
to 10mLSTP min−1 and the reactor was introduced into the EF for
pyrolysis, the duration of which was 1 h. The gases evolved during
pyrolysis were forced to pass through a condensing system (cooled
by a cryogenic solution of water and NaCl) where the condensable
compounds were removed from the gaseous fraction. Both
the reactor and the condensing system were weighed before and
after the pyrolysis experiment to determine the solid and liquid
yields (respectively). The gas yield was determined by difference.
Then, the gaseous fraction was collected in a Tedlar® bag and analysed
by means of a Varian-CP3800 gas-chromatograph equipped
with a TCD detector and two columns connected in series. The first
column was 80/100 Hayesep Q (2m×1/8 in.×2mm) and the second
column was a 80/100 Molesieve 13X (1.5m×1/8 in.×2mm).
The second column was bypassed by a six-port valve for the analysis
of the CO2 and hydrocarbons. The carrier gas flow (He) was
30 mL/min. The initial oven temperature was set at 40 ◦C, which
was maintained for 1.2 min. It was then programmed to rise from
40 to 65 ◦C at 50◦C/min with an isothermic step of 3.3 min. The
temperature was then lowered from 65 to 55 ◦C at 20◦C/min and
held for 2.6 min. The injector and detector temperatures were fixed
at 150 ◦C. The TCD was calibrated using a standard gas mixture.