(516b) Alkaline Thermal Treatment of Challenging Waste Biomass Feedstocks for in-Situ H2 Production with Tandem Carbon Sequestration

Bioenergy with carbon capture and storage (BECCS) is a method of carbon dioxide removal which will be a critical component of CO₂ removal and storage from the atmosphere. In the IPCC-AR5 report, it was concluded that warming below 2^oC could not be achieved if BECCS deployment is limited (high confidence). This is because BECCS is theoretically carbon-negative as CO₂ is captured by both biomass growth and the coupled downstream CO₂ capture. The thermochemical conversion of biomass (e.g., gasification) are among the most prominent methods for BECCS as they combine proven technologies (e.g., thermal gasifiers) with emerging carbon capture systems. Unfortunately, they are often hampered by high temperatures and pressures, feedstock purity requirements, pure oxidant demand, and low actualized CO₂ capture ability. Alkaline thermal treatment (ATT) is a promising and robust BECCS method which can run at mild temperatures and pressures (<500^oC, 1 bar) and produces carbon-free high-purity H₂ (>90% v/v) in a single reactor. Hydroxide salts are utilized during the ATT reaction (e.g., NaOH, KOH, LiOH, etc.), facilitating the degradation and conversion of organic matter. Tandemly, carbon from the biomass is captured in the form of stable carbonate salts (e.g., Na₂CO₃). In this study, we report on the H₂ production and CO₂ capture potential of a wide variety of difficult-to-process biomass sources using alkaline thermal treatment, including wet and salty seaweeds, construction and demolition organics, and plastics commingled with marine wastes. Characterization of the reaction intermediates and products is performed to better elucidate the underlying reactive mechanisms. Gas-phase reforming catalysts, such as Ni/ZrO₂, are utilized to boost H₂-yields and increase the degree of energy recovery from the biomass. Finally, regeneration methods to recover the spent alkaline material for further conversion are considered, including metathesis with Ca-rich industrial wastes or molten salt electrolysis for carbonate electrosplitting.