Pyrolysis kinetics of hydrochars produced from brewer's spent grains

The aim of the study was to understand pyrolysis behavior and estimate the kinetic parameters (activation energy and pre-exponential factor A) of the pyrolysis of different hydrochars produced from brewer’s spent grains (BSG). To achieve this, non-isothermal thermogravimetric analysis at different heating rates (5, 10, 20, 40 °C min^-1) in the temperature range 40-900 °C and with constant nitrogen flow (70 mL min^-1) was carried out. The measurements were conducted for the BSG and three hydrochars produced from BSG at different HTC conditions: (i) 180 °C, 4 h; (ii) 220 °C, 2 h; and (iii) 220 °C, 4h. The kinetic parameters were estimated using the Kissinger-Akahira-Sunose (KAS) method. The average activation energy was 285 kJ mol^-1 for BSG and 147, 170, 188 kJ mol^-1 for the hydrochars. Also, BSG and three hydrochars were pyrolyzed at 300, 500, 700, and 900 °C. The yields of the pyrolyzed materials and the elemental analysis were measured and compared with the raw biomass and hydrochars to evaluate changes in composition induced by the pyrolysis process. Moreover, pyro GC-MS analysis was applied to characterize volatile matter released during BSG and its hydrochars decomposition.