Syngas production from lignite via chemical looping gasification with hematite oxygen carrier enhanced by exogenous metals

Chemical looping gasification (CLG) has revealed advantages in the preparation of high-quality syngas and reduction of carbon dioxide. Hematite oxygen carriers (OCs) enhanced by exogenous active metals were investigated in CLG process of lignite by using TG and fixed bed reactor with various analytical methods. The experimental results indicated that Fe2O3 in hematite reacts with different exogenous metals to generate mixed oxide such as CaFe2O5, NiFe2O4, CeFeO3 and CoFe2O4, increasing oxygen vacancy concentration, strengthening lattice oxygen transfer, and improving the conversion efficiency of lignite. The CaO exhibited the best reaction performance among exogenous metals in promoting lignite CLG process with a reactivity order of CaO > CeO2 > NiO > Co2O3. The CaO enhanced the CLG reaction through two pathways. The synergistic effect in CaFe(2)O(5 )reduce the Fe-O bonds intensities, promoting the migration of lattice oxygen in OCs. Carbonation of CaO sorbents shifts the CLG reaction equilibrium towards syngas, which are conductive to improvement of the syngas yield. Water molecular played an important role in promoting carbon conversion, regulating H-2/CO ratio, and reducing calcium loss. Synthesis gas with H-2 concentration 63.19%, heating value 9.20 MJ/m(3) and H-2/CO ratio 5.77 corresponding to carbon conversion efficiency 66.41% and syngas yield 2.56 m3/kg was achieved in CLG of lignite with water participation. The main reaction path of Fe2O3-*CaFe2O5-*CaFe2O5/Fe2.91O4-*Fe(2)O(3)was revealed for CaO modified hematite OCs in CLG process. The main crystal form and lattice oxygen of OCs were regenerated with the improvement of particle size and pore channels. The experimental results indicate a potential application of modified hematite OCs in the CLG of lignite