Production of methane from waste biomass using catalytic conversion in supercritical water: nutrient salt recovery

Wet biomass, such as manure or wood waste, can be converted into methane via catalytic conversion in supercritical water. Biologically-derived methane is a more versatile fuel than most traditional biofuels and can be used within the existing infrastructure for natural gas. This supercritical-water conversion method can process wet streams which normally must be dried before conventional gasification, and produces substantially higher methane yields with shorter processing times compared to biological methods.

However, under supercritical conditions salts which are soluble in the aqueous feed stream may precipitate out and lead to catalyst deactivation by core plugging. A salt separation vessel is thus necessary to remove precipitated salts from the supercritical water reaction solution.

We are designing a means of separating salts from biomass feedstocks. The neutron radiography facilities at PSI are able to guide the design of an efficient salt separator, by providing an opportunity to visualize the precipitation and deposition processes occurring inside a continuously operated salt separator in-situ. This method will enable the optimization of the vessel design with respect to separating the salts while maintaining as much biomass in the aqueous feed solution as possible, and will allow real-time visualization of precipitation build-up zones. Preliminary experiments have been carried out to determine materials of construction requirements. The tests will be conducted with borax salts and deuterium oxide in a zircaloy vessel in order to allow maximum image contrast. Supporting information on flow fields inside the vessel are being obtained by computational fluid dynamics simulations.

• Project home page at PSI
• Catalytic Process Engineering group at PSI
• Life-Cycle Assessment of this process at MIT

• Peterson, A., Waldner, M., Fröling, M, Vogel, F., Tester, J. "Methane and Nutrient Salts from Waste Biomass: Development of a Catalytic Conversion Process in Supercritical Water," Alliance for Global Sustainability 2005 Annual Meeting, Cambridge, MA (March 2005). [Poster, PDF]