Supercritical Water Gasification (SCWG) of Lignocellulosic Biomass for Hydrogen Production: Reaction Kinetics and Corrosion Performance of Candidate Constructional Alloy
Abstract
Supercritical water gasification (SCWG) holds immense promise as a sustainable and efficient method for green hydrogen production from lignocellulosic biomass, contributing to the transition from a petroleum-based economy towards bioeconomy.
Understanding the kinetics of SCWG processes is critically important for future development and scale-up applications of the SCWG technology. In this thesis work, we developed a general kinetic model to predict the yields of gases from SCWG of various lignocellulosic feedstocks with varying contents of cellulose, hemicellulose, and lignin. Subsequently, a comparison study was conducted between the SCWG of biomass in a batch and a self-built continuous-flow reactor. We discussed the application of both batch and continuous reactors in terms of feedstock type, system control, challenges, and future perspectives to maximize the efficiency of biomass SCWG.
The harsh operating conditions of SCWG, characterized by high temperature, high pressure, and a corrosive environment, pose challenges in selecting suitable construction materials for reactor design. Thus, we investigated the corrosion behavior of a widely used constructional alloy: Inconel 625. As the major component apart from biomass model compounds, the presence of ash content in biomass feedstocks may influence the SCWG process, affecting both its catalytic potential and corrosive tendencies. We have validated that ash content exhibits certain catalytic effects on SCWG of biomass, and a small amount of ash does not significantly impact corrosion. On the contrary, a small amount of ash can help neutralize the acidity of reaction products, thereby inhibiting corrosion. Furthermore, we evaluated the corrosive impacts of lignocellulosic biomass model compounds (cellulose, hemicellulose, and lignin) with or without NaOH (as a catalyst) addition during SCWG. This work demonstrated the distinct corrosion behaviors of Inconel 625 during SCWG of different model compounds and sulfur content in lignin contributed to the highest corrosion rate.