Fixed-bed pyrolysis of Cynara cardunculus L. Product yields and compositions

The pyrolysis of Cynara cardunculus L. was studied with the aim of determining the main characteristics of the charcoal formed and the nature and quantity of gases produced. Variables investigated were temperatures between 300°C and 800°C, particle sizes between 0.4 and 2 mm diameter, initial sample weights between 2.5 and 10 g, and nitrogen flow rates between 100 and 300 cm3/min. Experiments were carried out isothermally. Under the conditions of this study, particle size, nitrogen flow rate, and initial sample weight generally did not exert any influence, whereas temperature was very significant. An increase in this variable led to an increase in the fixed carbon content, gases produced and, to a lesser extent, ash percentage. On the other hand, volatile matter and solid yields decreased with increasing temperature. The principal gases generated were H2, CH4, CO and CO2. Heating values of both gas and solid phases were determined from gas composition and elemental analysis. The quality of charcoals and heating value allow the conclusion that the optimal temperature for pyrolysis should be between 600°C and 700°C. Finally, a kinetic study of the pyrolysis, based on gas generation from thermal decomposition of the residue, was carried out. From this model, rate constants for the formation of each gas and their corresponding activation energies were determined.