Chemical Looping Hydrogen Generation Using Synthesized Hematite-Based Oxygen Carrier Comodified by Potassium and Copper

Abstract

Hematite has become a promising oxygen carrier (OC) due to its abundance and low cost for chemical looping hydrogen generation (CLHG). However, the poor redox reactivity, low yield, and purity of hydrogen are the main issues using hematite as an OC. In order to solve the problems, a synthesized OC based on iron ore comodified by copper and potassium was first proposed for CLHG to increase the reduction reactivity and hydrogen yield. Experiments were conducted in a batched fluidized bed reactor to evaluate the performance of the synthesized OC. The results demonstrated that the adding of potassium and copper elevated the reduction reactivity. The reduction reactivity was in the sequence of 5Fe1.67Cu10K > 5Fe1Cu10K > 5Fe0.625Cu10K > 5Fe1Cu5K > 5Fe1Cu0K > hematite. As compared with hematite, the oxygen transport conversion increased 70.11% using 5Fe1.67Cu10K. The reduction reactivity enhancement was attributed to the self-diffusion and pores formation via adding potassium as well as the high reactivity and oxygen transport conversion of copper loading. K2Fe4O7 and CuFe2O4 were detected in the synthesized OCs by XRD analysis, which were active phases for reduction. Moreover, the high oxygen transport conversion and reactivity revealed the deep reduction of iron oxides. The hydrogen yield increased 2.1 times on account of the existence of potassium and copper. Meanwhile, the hydrogen production rate was improved. Additionally, 850 °C was suitable for CLHG in consideration of the reaction rate and the low melting point of the additive. The hydrogen purity was up to 99.9%, indicating that copper and potassium play significantly synergistic roles on suppressing carbon deposition. Therefore, the synthesized oxygen carrier based on iron ore comodified by potassium and copper was suitable for CLHG.