Thermochemical Conversion of Biomass in the Presence of Molten Alkali-Metal Carbonates under Reducing Environments of N 2 and CO 2

The impact of N 2 and CO 2 atmospheres on the interaction between Eucalyptus pilularis biomass and a ternary molten carbonate eutectic (Li 2 CO 3 : Na 2 CO 3 : K 2 CO 3 ) has been investigated at 600 °C and 900 °C. For lower temperature conversion under CO 2 , prevention of volatile release in the eutectic treated biomass is slightly higher than under N 2 injection; however, similar bubble-shaped morphology of the remnant char is observed under both carrier gases. By increasing the temperature to 900 °C under CO 2 , 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 CO 2 and N 2 at 900 °C is 0 (negligible) and 18 wt.%, respectively. In the absence of carbon particles, the decomposition of carbonate to M 2 O (l) and CO 2 (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 N 2 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.% CO 2 emission for this system.