Py-GC-MS of hydrochars produced from brewer’s spent grains

The aim of the study was to understand pyrolysis behavior and analyze the influence of hydrothermal carbonization (HTC) pretreatment on the volatile matter released during pyrolysis of hydrochars, produced from brewer’s spent grains (BSG). The Py-GC–MS was used to analyze the pyrolysis products. The measurements were conducted for three hydrochars produced from BSG at different HTC conditions: (i) 180 °C, 4 h; (ii) 220 °C, 2 h; and (iii) 220 °C, 4 h, and the precursor BSG. The sample was pyrolyzed in the sequence at 300, 400, 500, and 600 °C with a heating rate of 500 °C min −1 and residence time 15 s. Pyrolysis of BSG resulted in more phenolic compounds than hydrochars produced at mild conditions (HTC-180-4 and HTC-220-2). Pyrolysis of high-temperature hydrochar (HTC-220-4) showed the highest share of phenols due to the conversion of furan rings into benzene rings during HTC. Hydrochars (HTC-180-4 and HTC-220-2) produced more furans, and other cyclic oxygen compounds compared to the initial biomass. A significant amount of N-compounds was detected at low pyrolysis temperature for spent grains due to weakly bonded proteins into the biomass structure. However, hydrochars were characterized by fewer N-compounds compared to BSG because of the Maillard reaction occurred during hydrothermal pretreatment leading to more stable N-heterocycles structures. Increased severity during the HTC resulted in a higher share of N-compounds found during Py-GC–MS.