Insight into carbon structural variation from steam gasification of rice straw on enhancing hydrogen generation

Converting biomass waste into hydrogen energy through gasification is a crucial pathway for producing "green hydrogen". In a fixed bed reactor, a representative biomass waste, rice straw (RS), was pyrolyzed at N₂, H₂O, CO₂, and O₂ atmospheres to generate hydrogen. Solid C-13 Nuclear Magnetic Resonance Spectroscopy (¹³C-NMR) and Fourier Transform infrared spectroscopy (FTIR) were employed to elucidate the carbon structure and functional groups of the samples. The hydrogen ratio in pyrolysis gas is monitored by gas chromatography (GC). The results show that hydrogen release from RS increases after 400 °C because of thermal polymerization occurrence shown in thermogravimetric(TG) analysis. Pyrolysis of RS at N₂, H₂O, CO₂ and O₂ atmosphere for H₂ formation with the order is H₂O > CO₂>N₂>O₂. H₂O is acted as catalyst, impregnant, and reactant for char forming reaction and gas rearrangement to facilitate H₂ production which increases to 205.84 mL/g at 900 °C. The phenolic groups increase for forming the active intermediates to combines with H radical from H₂O to form H₂. Meanwhile, the H₂O facilitates the rearrangement, condensation, and polymerization reaction of aromatic rings to form H₂. The bridged aromatic carbon increases. H₂ is also formed by gas rearrangement reaction from CH₄ to H₂ during steam gasification. These results are the guide for equipment development and industrialization for biomass waste to hydrogen energy.