Hydrothermal liquefaction (HTL) of wet and waste biomass feedstocks into crude bio-oils and other chemicals has attracted particular attention in Canadian and international clean energy sectors. Until today, very little effort has been employed to address corrosion problems of HTL core components under operation, leading to a significant delay in the construction of industrial-scale HTL plants. In fact, a range of oxygenated, aggressive sulfur and/or chlorinated compounds, as well as organic acids, can be introduced during the conversion at the operating temperature range of 200–400℃, consequently creating highly corrosive environments to the reactor alloys. It is thus important to investigate the performance of alloys exposed to conversion processes to determine the cost-effective construction and long-term safe operation of the HTL plants. In this study, the corrosion resistance of two candidate austenitic stainless steels, including UNS S31000 and UNS S31603, was assessed in a batch reactor containing bamboo feedstock. The corrosion behaviors of the austenitic stainless steels were evaluated using weight change measurement methods and advanced microscopy techniques. To advance corrosion mechanistic understanding, the chemistry of conversion products was also analyzed. This paper is a summary of our most recent results obtained.  

Hot dilute acidic pre-hydrolysis biorefining is a pre-treatment technology recently developed for converting raw biomass materials into sugar streams and other valuable intermediate chemicals at elevated temperatures. However, corrosion database of steels and alloys in hot dilute acidic solutions are very limited, resulting in the cost-effective selection of materials of construction difficult. Corrosion studies were thus performed to identify suitable alloys of construction and advance the understanding of how alloying elements (e.g., Cr and Mo) present in steels and alloys affect the formation and properties of surface oxides. In this paper, the corrosion performance of three alloys (UNS S31603, UNS S32101 and UNS N06625) in hot dilute sulfuric acids are introduced. The alloys exhibited active general corrosion and even pitting in the hot acidic solutions. Alloy 625 has better resistance to the hot dilute acid compared to SS 316L and duplex 2101. This may be attributed to the higher contents of Mo in the alloy. Long-term tests indicate that their corrosion rates are gradually increased with time. The introduction of 100 ppm Cl- from raw biomass feedstocks into the acid solution only has marginal effect on corrosion. 

Stabilized austenitic stainless steel (SS) grade 347 is used extensively in high-temperature processes in the petroleum refining industry, while duplex SS (DSS) grade 2205 is a relatively newer material in the industry. Though these grades of SSs perform well in refinery process streams, there are incidents of failure of process equipment attributable to stress corrosion cracking (SCC).  The paper deals with a study on the cracking susceptibility of SS grade 347 and DSS grade 2205 in refinery simulated process environments containing hydrogen sulfide and chloride.  The paper also reports the electrochemical behavior of these SSs in the medium containing hydrogen sulfide and chloride.  The electrochemical behavior of the alloys was assessed by cyclic polarization experiments.  Slow strain rate test (SSRT) was used to evaluate the susceptibility of the alloys to SCC. The cyclic polarization studies indicate that the H2S – chloride synergism had a pronounced effect on the localized corrosion susceptibility of 347 SS, while the effect was marginal on the alloy DSS 2205. The SCC susceptibility of 347 SS and DSS 2205 is strongly influenced by hydrogen sulfide-chloride synergism.  Initiation of corrosion pits and the sulfidation of active pits due to the synergism were the important steps in the initiation of SCC.