2.3. Analysis of duckweed pyrolysis products
Duckweed pyrolysis gases were analyzed by Varian 450 GC
(Varian Inc., Palo Alto, CA, USA) with a thermal conductivity detector Effect of sweep gas flow rate. Fig. 1 shows the yield of the duckweed
pyrolysis products (gas, bio-oil, char) (A) and the composition
of pyrolysis gas (B) as a function of the sweep gas (Ar) flow
rate varied in the range of 36–150 mL/min at pyrolysis temperature
of 500 C (Note that Ar flow rate is inversely proportional to
residence time: higher flow rate – lower residence time; for the
sake of simplicity, we will use Ar flow rate as an independent variable).
The results presented in Fig. 1A show a trend towards
increasing the bio-oil yield and decreasing pyrolysis gas yield at
the lower range of Ar flow rates. This effect can be explained by relatively
fast removal of pyrolysis products from the reaction zone
that results in shorter residence time in the heated zone and over
char as the char and oils are being formed. One should note the
higher values for the error bars, especially for bio-oil, at the high
flow rates, which can be attributed to the fact that at these conditions
a small fraction of the oil product in the form aerosols passes
through the condenser without being captured, and, thus, remains
unaccounted for. The experimental data were subjected to statistical
analysis (see Section 2.2), which indicated that the probability
(P) values were well above 0.05 – implying that the observed variations
in the measured values of gas, bio-oil and bio-char yields
due to changes in the flow rate of the sweep gas in the range of
60–150 mL/min are not statistically significant.