Hydrogen Production from Pyrolysis of Biomass Components

Hydrogen energy is key for the global green energy transition, and biomass thermochemical has become an important option for green hydrogen production due to its carbon neutrality advantage. Pyrolysis is the initial step of thermochemical technologies. A systematic analysis of the mechanism of H2 production from biomass pyrolysis is significant for the subsequent optimal design of efficient biomass thermochemical H2 production technologies. Biomass is mainly composed of cellulose, hemicellulose, and lignin, and differences in their physicochemical properties and structures directly affect the pyrolysis hydrogen production process. In this study, thermogravimetry-mass spectrometry-Fourier transform infrared spectroscopy (TG-MS-FTIR) was employed and fixed-bed pyrolysis experiments were conducted to systematically investigate the pyrolysis of biomass component with focusing on hydrogen production. According to the results of TG-MS-FTIR experiments, hemicellulose produced hydrogen through the breaking of C-H bonds in short chains and acetyl groups, as well as secondary cracking of volatiles and condensation of aromatic rings at high temperatures. Cellulose produced hydrogen through the breaking of C-H bonds in volatiles generated from sugar ring cleavage, along with char gasification and condensation of aromatic rings at high temperatures. Lignin produced hydrogen through ether bond cleavage, breaking of methoxy groups, as well as cleavage of phenylpropane side chains and condensation of aromatic rings at high temperatures. Results from fixed-bed pyrolysis experiments further showed that hemicellulose exhibited the strongest hydrogen production capacity, with the maximum H2 production efficiency of 6.09 mmol/g, the maximum H2 selectivity of 17.79%, and the maximum H2 effectiveness of 59% at 800°C.