Corrosion Study of an Austenitic Stainless Steel and a Ni-Cr-Fe Alloy in Hydrothermal Liquefaction Biorefining Conditions

Abstract Catalytic hydrothermal liquefaction (HTL) offers an effective pathway for converting wet biomass into bio-crude with high carbon conversion efficiency. This study examines the impact of key environmental factors-catalyst, inorganic corrodants, and particularly organic acid-on the corrosion behavior of two candidate reactor materials, UNS S30400 and UNS N08811. Autoclave experiments were conducted under HTL conditions, revealing that acetic acid degraded oxide layers, accelerating corrosion rates in both materials. While inorganic corrodants, such as chloride and sulfide ions, had limited impact, acetic acid significantly altered corrosion mechanisms by increasing oxide dissolution and facilitating localized corrosion. UNS N08811 exhibited better corrosion resistance than UNS S30400, making it a more suitable option for reactor construction. These findings highlight the importance of understanding organic acid effects to improve material selection and ensure long-term operational safety in HTL reactors.