Biomass SCWG is seen as one of the most promising thermochemical pathways to produce green hydrogen. However, there is a serious concern about corrosion of biomass SCWG reactor alloys for long-term operation due to the presence of high-pressure and high-temperature supercritical water, aggressive catalyst and reducing gaseous products (such as H2 and CO). In this study, the corrosion performance of UNS N06625, a commonly applied Ni-based alloy for high temperature systems, was investigated in the conditions associated with the SCWG of three representative biomass model compounds (including cellulose, lignin, and xylan) at 500 °C and 30 MPa for total 12 cycles of batch-mode operations. The produced gaseous mixtures were collected and analyzed using Micro-GC to explore the environmental chemistry. Except for weight change measurements, the corrosion products formed on the alloys were also characterized using ’EM, EDS and XRD techniques to advance fundamental understanding of how the alloy corrodes under the SCWG conditions. Additional investigations, including cross-sectional SEM/EDS analysis and weight loss measurement following scale removal will be pursed in subsequent research to gain quantitative understanding of corrosion mechanisms.
There is an increasing interest in substituting nonrenewable fossil fuels with clean and renewable energy resources due to the concerns on the greenhouse gas emissions and the depleting fossil resources. Biomass is a renewable resource derived from living organism and/or their byproducts. For example, some agriculture or forestry wastes (like cornstalk or wood sawdust), industrial wastes (such as black liquor), cattle manure from animal husbandry, and even sewage from our daily life usage can be used for bioenergy production. There are many different sources and method for producing hydrogen as a clean fuel. Among them, steam reforming, electrolysis of water and biomass conversion have attracted intensive interesting.1 As of today, the most commercialized hydrogen production method is the steam reforming of fossil fuels; the feedback is not renewable, and a significant quantity of CO2 is produced from the reforming process. The electrolysis of water suffers from similar challenges where a large amount of electricity, more than 50% of which is generated from the combustion of fossil fuels at thermal power plant, is required. Compared with the current state of these processes, production of green hydrogen production from biomass is likely to be a more sustainable way as biomass is widely available and renewable for achieving the target of net-zero carbon emission.
