Hydrogen production and CO2 capture from Linz-Donawitz converter gas via a chemical looping concept

Abstract

Linz-Donawitz converter gas (LDG), an important by-product in the steel industry with CO (55–60 vol%) and CO2 (15–20 vol%) as the main components, is usually used as fuel for heating or power generation, releasing massive of diluted CO2 with the concentration lower than 15 % that is difficult to capture. Herein, we propose a method to produce pure H2 via chemical looping water splitting by using LDG as reducing agent, which can easily concentrate CO2 for capture. Fe2O3, one of the most environmentally friendly and low-cost oxides, was chosen as the oxygen carrier to perform this concept. It was found that the addition of small amounts of Ce0.75Zr0.25O2 solid solution could strongly improve the activity of Fe2O3 for CO conversion, especially at relatively low temperatures. Compared with pure Fe2O3, the CO conversion and H2 yield were increased from 39.5 % and 0.34 mmol·g−1 to 100 % and 2.32 mmol·g−1 at 650 °C, respectively, after adding 5 wt% of Ce0.75Zr0.25O2. The strong interaction between the two oxides contributed to the enhanced performance via promoting CO adsorption and lattice oxygen releasing. Water splitting assisted by air oxidation could fully regenerate the reduced oxygen carrier, and the oxygen carrier was stable during the long-term chemical looping process, with the CO2 capture rate at ca. 95.8 %. In situ DRIFTS results showed that CO2 was producedthrough a direct reaction of lattice oxygen with CO, and the decomposition of carbonate species intermediate by adsorption of CO on the surface of oxygen carriers. This study gave full evidence that it was feasible for achieving H2 generation and CO2 capture in one step via chemical looping reforming of reducing exhaust gases (e.g., LDG) from industrial emissions.