Alkaline thermal treatment of seaweed for high-purity hydrogen production with carbon capture and storage potential

Abstract

Current thermochemical methods to generate H₂ include gasification and steam reforming of coal and natural gas, in which anthropogenic CO₂ emission is inevitable. If biomass is used as a source of H₂, the process can be considered carbon-neutral. Seaweeds are among the less studied types of biomass with great potential because they do not require freshwater. Unfortunately, reaction pathways to thermochemically convert salty and wet biomass into H₂ are limited. In this study, a catalytic alkaline thermal treatment of brown seaweed is investigated to produce high purity H₂ with substantially suppressed CO₂ formation making the overall biomass conversion not only carbon-neutral but also potentially carbon-negative. High-purity 69.69 mmol-H₂/(dry-ash-free)g-brown seaweed is produced with a conversion as high as 71%. The hydroxide is involved in both H₂ production and in situ CO₂ capture, while the Ni/ZrO₂ catalyst enhanced the secondary H₂ formation via steam methane reforming and water-gas shift reactions.

While biomass may serve as a renewable source of carbon-neutral hydrogen, it is challenging both to utilize as-found bio-resources and to suppress CO₂ formation. Here, authors convert wet, salty seaweed using alkaline thermal treatment to produce high-purity hydrogen and suppress carbon emission.