Biomass hydrothermal liquefaction (HTL) is usually operated in harsh environments due to the presence of hot pressurized water reaction medium, alkaline catalysts, inorganic and organic corrosive constituents released during the conversion. Corrosion knowledge gaps exist on the selection of suitable alloys of construction. Previous studies in high temperature aqueous solutions have indicated that the contents of alloying elements (such as Cr and Mo) are key factors influencing corrosion protection of Fe-Ni-Cr alloys. Increasing the contents of Cr and/or Ni in constructional alloys may alter the corrosion mode and reduce the extent, leading to an acceptable long-term performance of the refining reactor. This study investigates the corrosion performance of three candidate alloys with varying Cr and Ni contents, including P91 UNS K91560 (Fe-9Cr), SS304 UNS S30400 (Fe-18Cr-8Ni), and Alloy 33 UNS R20033 (Fe33Cr-31Ni) in a static autoclave containing a simulated aqueous (inorganic) phase of a biomass conversion product mixture (800 ppm KCl + 1M K2CO3) at 310°C for 10 days. Post exposure examinations on corroded alloys show that the surface scales grown on the lower alloyed steels (P91 and SS304) consists of an (Fe,Cr)3O4 spinel layer. Conversely, the oxide scale on the highly alloyed Alloy 33 consists of a multi-layered outer Ni-rich oxide, middle Ni-Cr-Fe spinel, and inner Cr-rich oxide. The thicknesses of the oxide layers formed on P91, SS304, and Alloy 33 were approximately 7 μm, 1.1 μm, and 500 nm, respectively. Besides the oxide thickness, increasing the Cr and Ni content also reduces the overall weight change of the alloys.

Subject
Materials, Nickel based alloys, Oxide formation, Molybdenum alloys, Oxide layers, Metal oxides, Nodules, Commercial alloys, Film formation, Steel, Corrosion protection, Aluminum alloys, Alloys
Keywords:
Bioenergy, corrosion, steel, chloride
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2021
Association for Materials Protection and Performance (AMPP)
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