Geopolymer oxygen carrier for improved gasification of biomass

Biomass gasification is a route for producing a sustainable synthetic gas (syngas) to be used for chemicals production or energy. Chemical looping gasification (CLG) is an improved technology that can inherently avoid the N2 dilution of the syngas with enrichment in H2, CO, and CH4, an oxygen carrier delivering O2 for gasification through reduction/oxidation steps. CLG is carried out in two distinct reactors, one for gasification and one for carrier regeneration. Natural oxygen carriers include ilmenite, hematite, cuprite and other minerals; these represent the easiest way to accomplish the CLG. In alternative, modified natural carriers or completely synthetic materials may be purposely developed and used. In the present research, a composite geopolymer oxygen carrier was developed with a one-step and green protocol starting from metakaolin, alkaline activator and copper oxide, labelled as GpCu. Particular attention was given to the conversion of the solid carbon residue (char), since is the least reactive but most energetic constituent of biomass. Together with GpCu, a CO2-enriched atmosphere was used in a laboratory fluidized bed, operated at 900 and 945 °C. The yield of CO per gram of char at changing temperature and CO2 molar fraction YCO2 is shown in the figure below, achieving a value very close to the theoretical threshold of 78 mmol/gram at 100vol% of CO2 and 945 °C. The results show that higher temperature is preferable for thermodynamic and kinetic reasons, although the related energy balance reduces the range of auto-thermal operability at lower range of YCO2. The research was funded under the National Recovery and Resilience Plan (NRRP), Mission 04 Component 2 Investment 1.5—NextGenerationEU, Call for tender no.3277 30/12/2021 and award no. 0001052 23/06/2022