Optimizing hydrogen gas production from genetically modified rice straw by steam co-gasification

Future sustainability visions include clean, renewable energy from hydrogen, which can be produced, among other ways, by biomass steam gasification. This study explores strategies addressing the limitations in steam co-gasification of herbaceous biomass, using Monster-TUAT1 rice straw, a genetically modified rice plant with a taller and bigger stalk developed by Tokyo University of Agriculture and Technology (TUAT), and Giant Miscanthus, a promising energy crop, as the feedstock. Firstly, compared with the typical rice straw, the Monster TUAT1 demonstrated superior steam gasification performance with a 1.75 times higher hydrogen gas yield and 27.0 % less tar generation. With a focus on overcoming the challenges posed by high silica content in the Monster TUAT1, co-gasification of it with an energy crop of Giant Miscanthus was performed. However, even under the optimum operation condition (750 °C, steam flowrate: 0.15 g/min), the hydrogen gas yield was only 29.3 mmol/g-C with a tar yield of 27.6 %wt. and a carbon conversion efficiency of 45.9 %, which is deemed unsatisfactory for hydrogen production. Thus, strategies for enhancement were proposed, including the incorporation seaweed biochar with high alkali and alkaline earth species, calcined scallop shell powder, and alkali metal salt into the gasifier. Consequently, the introduction of 10 %wt. of calcined scallop shell resulted in an increase in H₂ yield to 37.0 mmol/g-C and 24.3 % CO₂ reduction. The addition of alkali metal salt led to 43.9 % increase of H₂ product with a 15 %wt. tar yield. The most significant improvement occurred with the introduction of seaweed biochar at 50 %wt., increasing of the hydrogen gas yield to 62.0 mmol/g-C with 86 % of carbon conversion efficiency and tar reduction to 5.5 %. These findings demonstrate the viability of utilizing herbaceous biomass such as rice straw in conjunction with the strategic solutions of co-gasification to overcome constraints in improving hydrogen production.