Thermal treatment and foaming of chars obtained from almond shells: kinetic study

The influence of a combined thermal treatment on the density of chars obtained from almond shells has been investigated. The thermal treatment involves two steps at different heating rates: the first one up to temperatures of 225–400°C; and the second one up to 850°C. Thermogravimetric experiments have been carried out with the intermediate chars obtained after treatment revealing the evolution of the different fractions of the almond shells (i.e. hemicellulose, cellulose and lignin), and their influence on the final density of the chars. An intermediate treatment, where the gases evolved from the last remaining fractions of the cellulose coincide with the char in a fluid or soft state, is required to foam the particles. A kinetic model has been applied to quantify, with excellent results, the evolution of the different fractions.