Technical challenges and corrosion research progress in bio-crude co-processing

Bio-oil (BO), produced from fast pyrolysis (FPBO) and hydrothermal liquefaction (HTL-BO) methods, is a promising renewable energy source derived from biomass. However, its undesirable properties such as high oxygen and moisture content resulting in high corrosivity and poor thermal stability, have hindered its widespread adoption as a drop-in fuel and necessitate its upgrading. Co-processing BO with petroleum intermediates in existing fluid catalytic cracking (FCC) units presents a promising approach for converting low-quality bio-crudes into valuable fuels. Nonetheless, three primary challenges - BO's low thermal stability, high corrosivity, and immiscibility with petroleum fractions - complicate its co-processing. This review summarizes these critical challenges related to BO storage and co-processing, with a particular emphasis on corrosion issues. Recent progress in corrosion research related to BO handling, including both FPBO and HTL-BO, is thoroughly examined. This includes studies on corrosion in pure BO, BO with additives, mixtures of BO and petroleum fractions, and model BO. The effect of different process parameters—such as alloying elements, testing temperature, exposure time, BO sources, catalysts, and inorganic corrodents—on the corrosion susceptibility of candidate steels was investigated. Chromium-enriched alloys demonstrated superior corrosion resistance compared to low chromium alloys, particularly at elevated temperatures. Blending BO with petroleum fractions and additives was found to improve the resistance to corrosivity and thermal stability. Beyond weight loss immersion experiments, electrochemical techniques, such as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP), are effective in obtaining in-depth corrosion mechanisms in BO environments, though challenges remain. Finally, research challenges and knowledge gaps are discussed to direct future efforts, including understanding BO phase behavior, corrosion mechanisms in BO environments, improvements in experimental methods and standards, and potential research paths. © 2024 The Author(s)