Direct conversion of rice husk into hydrogen and sodium silicate via alkaline thermal treatment with low-CO₂ emission

This study presents a novel single-step method for producing sodium silicate and high-purity hydrogen from rice husk biomass with reduced CO₂ emission using alkaline thermal treatment (ATT). Conventional methods extract amorphous silica from rice husk through an energy-intensive, CO₂-emitting process, followed by a separate reaction with sodium carbonate to synthesize sodium silicate. In contrast, the proposed method eliminates this additional step by directly generating sodium silicate while simultaneously producing hydrogen, ensuring a reduced carbon-emission process. ATT enables interconnected reactions, including in-situ CO₂ capture, enabling decarbonized hydrogen production as an energy carrier and sodium silicate for high-value applications. The use of NaOH promotes hydrogen generation at lower temperatures while capturing CO₂ as solid carbonates, distinguishing this process from conventional gasification. Additionally, sodium carbonates formed in situ react with SiO₂ in rice husk ash, enabling direct sodium silicate synthesis. Experimental results demonstrate that ATT at 950°C, with a rice husk-to-NaOH ratio of 1:3 and 1.9 g of SiO₂, yields up to 5.1 g of sodium silicate and 51 mmol of hydrogen per gram of rice husk, with reduced CO₂ emission. Optimizing reaction conditions through elemental analysis enhances hydrogen yield and improves sodium silicate synthesis, highlighting the sustainability of this approach.