Thermochemical Conversion of Biomass in the Presence of Molten Alkali-Metal Carbonates under Reducing Environments of N₂ and CO₂

• Main Authors: Tahereh Jalalabadi, Behdad Moghtaderi, Jessica Allen
• Format: Article
• Language: English
• Published: MDPI AG 2020-10-01
• Series: Energies
• Subjects: slow pyrolysis; Boudouard reaction; carbonate gasification; ternary eutectic; biomass
• Online Access: https://www.mdpi.com/1996-1073/13/20/5395

The impact of N₂ and CO₂ atmospheres on the interaction between Eucalyptus pilularis biomass and a ternary molten carbonate eutectic (Li₂CO₃: Na₂CO₃: K₂CO₃) has been investigated at 600 °C and 900 °C. For lower temperature conversion under CO₂, prevention of volatile release in the eutectic treated biomass is slightly higher than under N₂ injection; however, similar bubble-shaped morphology of the remnant char is observed under both carrier gases. By increasing the temperature to 900 °C under CO₂, the reverse Boudouard reaction begins to consume carbon fuel, while molten carbonate gasification also accelerates the reaction to a lower temperature set point (shifted from ~735 °C to ~640 °C). The mass loss of carbonate under CO₂ and N₂ at 900 °C is 0 (negligible) and 18 wt.%, respectively. In the absence of carbon particles, the decomposition of carbonate to M₂O (l) and CO₂ (g), as well as molten salt vaporization, are the sole potential routes of weight loss in an inert gas. Previous observations of biomass and eutectic mixture thermochemical conversion under N₂ have suggested carbon/carbonate gasification is dominant at elevated temperatures, with production of CO expected. However, analysis of gas chromatography (GC) suggests that carbon/carbonate gasification is the weaker pathway by producing only 7 vol.% of CO, compared with molten carbonate decomposition with 27 vol.% CO₂emission for this system.