Understanding of the oxygen uncoupling characteristics of Cu-Fe composite oxygen carriers for chemical-looping gasification

A Cu-Fe oxygen carrier (OC) with oxygen uncoupling capability is proposed to be applied in chemical-looping gasification with oxygen uncoupling (CLGOU) technology to increase the gasification rate. Density functional theory analysis shows that a chemical reaction occurs after Cu4O4 cluster adsorption onto alpha - Fe2O3 (001) surface. Extension of bond length and transfer of charge indicate the composite oxide has been activated. An optimal molar ratio of 2:1 of CuO to Fe2O3 is determined for the preparation the OC and the oxygen transport capacity is determined at 3.65 wt% with a starting oxygen uncoupling temperature is 749.5 degrees C. The composite OC exhibits good low-temperature oxygen uncoupling characteristics. This OC exhibits stable behaviour and satisfactory oxygen recyclability over 15 consecutive redox cycles at 900 degrees C / 700 degrees C oxygen uncoupling and absorbing temperatures. The high stability is corresponding to the calculation result (high adsorption energy of CuO onto Fe2O3). And oxygen uncoupling rates are much higher than the lower limit (0.4 wt%/min) for cracking. The chemical phases and surface micromorphology all retain stable after cycles. Using combined Coats-Redfern and Malek method, the oxygen uncoupling kinetic model of Cu-Fe OC is determined as a shrinking core model (m = 3).

Automated summary

A Cu-Fe oxygen carrier with oxygen uncoupling capability was proposed for chemical-looping gasification to enhance gasification rate. The optimal molar ratio, oxygen transport capacity, and stability of the composite oxide were determined through experiments. The Cu-Fe OC exhibited good low-temperature oxygen uncoupling characteristics and stable behavior over multiple redox cycles.