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.

Inhibition of carbon deposition using iron ore modified by K and Cu in chemical looping hydrogen generation

“…It had been confirmed that the amount of copper adding deepened the reduction of Fe 2 O 3 , and the highest oxygen transport conversion and hydrogen yield of Fe10Cu8K1 also indicated the highest amount of metallic Fe and FeO in the oxygen carriers after reduction in our previous work. 21 Thus, it was more likely to deposit carbon on the oxygen carrier particles because of the large amount of Fe and FeO which were considered as catalysts for carbon deposition. 19,35,38 Fe10Cu5K1 is the suitable oxygen carrier with the highest resistance to carbon deposition among the prepared samples.…”

“…Carbon formation possibly happens when the conversion of fuel and the reactivity of oxygen carrier are low . Much work has focused on developing the methods to enhance the redox rate of iron oxides . The common attempt to increase the reactivity of iron oxides is to introduce foreign additives.…”

“…Potassium and copper appear to be attractive foreign additives. In our previous work, we first proposed to co‐modify the iron ore with potassium and copper, and found that the reactivity of oxygen carrier and hydrogen yield elevated with the increasing amount of potassium and copper because the reduction extent of iron oxides was enhanced on account of the presence of modified additives . Interestingly, it should be noted that the hydrogen purity was improved when Fe/Cu (molar ratio) was 3 and KNO 3 /hematite (mass ratio) was 10% in the modified oxygen carrier.…”

“…15 Much work has focused on developing the methods to enhance the redox rate of iron oxides. 12,[16][17][18][19][20][21] The common attempt to increase the reactivity of iron oxides is to introduce foreign additives. The addition of copper based on the iron oxygen carriers had been proven to be capable to accelerate the rate and reactivity of reduction in the CLC process.…”

Chemical looping hydrogen production with modified iron ore as oxygen carriers using biomass pyrolysis gas as fuel

“…[25][26][27][28] Similarly, few studies have been reported in which the metals, Na, K, Cu and Ca etc., were implemented to enhance the reactivity of natural iron ores. Wang et al 29 reported that adding K and Cu had signicant effects on enhancing the reduction reactivity of hematite, as well as elevating the hydrogen production in the CLH production process. Liu et al 30 reported that the presence of K decreased the carbon deposition, and increased the reduction rate of iron ore and hydrogen yield in CLH production.…”