(570g) Methane Looping Reforming to Syngas: Optimal Process Conditions and Carrier Lifetime Assessment

Globally, synthesis gas (H₂ and CO) and its market has been estimated to expand at a compounded average growth rate (CAGR) of 9.1%, from 2021 to 2031, due to the versatility associated with syngas downstream processing ^[1].

To date, the mixture of H₂ and CO mainly comes from natural gas, residual oils, petroleum, and coal, as these are the only sources able to cover the world's demand for energy and chemicals.

However, among fossil alternatives, methane is the most investigated reactant, since it is the earth’s cleanest burning hydrocarbon, recognized to be a less impacting source for air pollution respect bioenergy or common fuels. Also, natural gas recoverable resources have been estimated to being able to sustain today’s production for over 250 years ^[2].

Currently, the only fully commercialized process based on methane utilization is the steam methane reforming (SMR). However, the critical issues associated with this process, such as the high production costs needed to provide huge amounts of steam at high temperature (650-1000 °C) and pressure (5-40 bar), as well as the severe CO₂ release (about 9 to 12 tons of CO₂ per ton of hydrogen) ^[3], motivate the study of alternative processes for synthesis gas and hydrogen production.

In this work, a looping process, from methane to syngas, was studied with thermogravimetric analysis characterization (TGA) and experiments in a fixed bed reactor. The process was studied cyclically exploiting the redox properties of a Ce-based oxide oxygen carrier synthetized with a simple forming procedure.

TGA experiments were focused on the identification of the optimal temperatures ranges for methane partial oxidation (900-1000 °C) and carrier regeneration (400-900 °C), while fixed bed testing was performed isothermally (at 900 or 950 °C), with a 10% CH₄ feed stream in N₂ for the stage of reforming and with 3% O₂ in N₂ for the regeneration.

The effect of the process times on carbon deposition, specific syngas yields, and selectivity, was inspected, together with the investigation of best conditions to fully regenerate the carrier, adjust the syngas final ratio, and ensure stable performances.

The obtained results confirmed the possibility to work in fully isothermal operations, with specific yields of syngas per mass of O₂ carrier around 6.8 mmol g^-1, preserved even along several cycles, paving thus the path to the development of alternative and effective processes for syngas production.

Reference:

(1) Global Industry. Syngas and Derivatives Market (Feedstock: Coal, Petroleum, Biomass Waste, and Others; Production Technology: Partial Oxidation, Steam Reforming, Biomass Gasification, and Others; and End-User: Chemicals, Power Generation, Liquid Fuels, and Gaseous Fuels)- Global Industry Analysis, Size, Share, Growth, Trends, and Forecast, 2021-2031. https://www.transparencymarketresearch.com/syngas-derivatives-market.html.

(2) WEO Special Report: Are We Entering a Golden Age?; 2011. https://www.iea.org/reports/weo-special-report-are-we-entering-a-golden-age.

(3) Lunsford, J. H. Catalytic Conversion of Methane to More Useful Chemicals and Fuels: A Challenge for the 21st Century. Catalysis Today 2000, 63 (2–4), 165–174. https://doi.org/10.1016/S0920- 5861(00)00456-9.

Figure: Syngas specific yields and ratio for eight consecutive redox cycles.