Geopolymer-composites with thermomechanical stability as oxygen carriers for fluidized bed chemical looping combustion with oxygen uncoupling

Oxygen carriers based on geopolymer composites with enhanced thermal and mechanical stability have been synthesized and been proposed for chemical looping combustion with oxygen uncoupling. Geopolymer synthesis belongs to green chemistry and ensures chemical and mechanical properties similar to those of high temperature sintering. Suitable metal oxides, such as combinations of Cu, Mn and Fe oxides, have been used as active fillers in geopolymer matrices. Thermogravimetric analysis conducted at 900 °C pointed out the excellent performance of the CuO-based oxygen carrier, and the overall performance trend of CuO > CuMn-oxides > MnFe-oxides. The performance of the CuO based material (around 1.0% wt. of transferred O) was confirmed in tests carried out in a fluidized bed at 900 °C, where a slightly lower carrying capacity, and a remarkable oxidation rate index (37.1 ± 1.4%) were obtained. Tests of wood-char combustion confirmed the ability of the CuO-based oxygen carrier to operate in a real chemical looping combustion process. Moreover, attrition and crushing tests demonstrated that the mechanical resistance of geopolymer-based oxygen carriers was comparable to that of materials currently used for fluidized bed application.