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Experimental Section

Materials

Dry yerba mate twigs (YMT) (0.35 cm average diameter and 1.25 cm length) were supplied by a local manufacture (Mate Larangeira S.A., Argentina). They were milled and sieved. Fractions of average particle size less than 2 mm were reserved for pyrolysis experiments. Proximate and ultimate analyses of the YMT are reported in Table 1. They were carried out by conventional ASTM standards and using a Carlo Erba EA 1108 instrument, respectively. Higher heating value (HHV) was measured using a Parr 1341 oxygen bomb calorimeter.

Table 1. Proximate and elemental analyses of the yerba mate twigs used in pyrolysis experiments

Proximate analysis (wt%, dry basis)

Volatiles

72.1

Ash

3.1

Fixed Carbona

24.8

Elemental analysis (wt%, dry, ash free-basis)

C

46.4

H

5.9

N

1.2

Oa

46.5

HHV (MJ kg-1)

17.8

a Estimated by difference.

Kinetic Measurements of the Pyrolysis of Yerba Mate Twigs

Kinetic measurements for the pyrolysis of samples of yerba mate twigs were carried out by non-isothermal thermogravimetry (TG-DTG) from ambient temperature up to 900 °C, operating under flowing nitrogen. A Netzsch STA 409 thermogravimetric balance equipped with a N2 flow device and a data acquisition system was used to perform the measurements. Preliminary experiments were first conducted in order to assess operating conditions for which diffusional effects were negligible. Accordingly, masses of 10 mg, N2 flow rates of 400 cm3 min-1, and a heating rate of 100 °C min-1 were employed. Further details of the experimental procedures employed have been depicted in previous own works (Bonelli et al., 2007; Gonzalez et al., 2008).

 
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