The dependence of char yield on the amounts of components in precursors for pyrolysed tropical fruit stones and seeds

Thermogravimetric results on the thermal degradation of isolated components extracted from shells of tropical fruit stones and seeds allowed us to establish the dependence of the yield of char obtained by high-temperature pyrolysis (600-900 degreesC) of lignocellulosic raw materials on the content of components in precursors. For char with narrow microporosity development, the following equation. for the char yield (Y) is proposed: [GRAPHICS] where L, C, A and E are, respectively, the percentage (wt.%) of lignin, cellulose, ash and extractives in the precursor. The above equation has been validated by considering the experimental results obtained for the carbonization of guava (Psidium guajava) seeds, dende (Acrocomia karukerana) and tropical almond (Terminalia catappa) shells (from 600 to 700 degreesC), leading to chars for which the porosity is not accessible by N-2 (77 K) because the microporous volume v(N2) is close to zero. When the access of N-2 to the micropores becomes possible (v(N2) > 0), which is the case for tropical almond shells char prepared between 750 and 900 degreesC, the equation proposed is not adequate and must be adjusted by introducing a multiplying coefficient a(c) defined as the char activity, with a(c) = 1 and v(N2) approximate to 0 for an ideal char developing only very narrow microporosity as reference, and a(c) < 1 when v(N2) > 0. (C) 2003 Elsevier Science Inc. All rights reserved.