Kinetic and thermodynamic analysis of iron oxide reduction by graphite for CO₂mitigation in chemical‐looping combustion

Abstract

Summary Chemical‐looping combustion (CLC) provides a platform to generate energy streams while mitigating CO2 using iron oxide as a carrier of oxygen. Through the reduction process, iron oxide experiences phase transformation to ultimately produce metallic iron. To understand iron oxide reduction characteristics and optimally design the fuel reactor, kinetic and thermodynamic analyses were proposed, utilizing graphite. This study aims to evaluate the reduction behavior under the non‐isothermal process of various mixture ratios of hematite and graphite via thermogravimetric analysis with simultaneously evaluating evolved gases using a Fourier transform infrared spectrometer. The Coats‐Redfern model was employed to approximate the kinetic and thermodynamic parameters which assessed the different reaction mechanisms together with the distributed activation energy model (DAEM). The results revealed that the hematite‐to‐graphite ratio of 4:1 had the highest reduction degree and had three distinct peaks representing three iron oxide reduction phases. The zero‐order reaction mechanism agreed with the experimental results compared with other reaction models. The thermodynamic analysis showed an overall endothermic spontaneous reaction for the three phases which signified the direct reduction of the iron oxides. The DAEM result validated a stepwise reduction of iron oxides to metallic iron. The study aids the optimal design of the CLC fuel reactor for enhanced system performance.

Some Aspects of the Thermochemical Route for the Valorization of Plastic Wastes, Part I: Reduction of Iron Oxides by Polyvinyl Chloride (PVC)

“…The values of standard entropy (∆rH • ) and free energy (∆rG • ) changes at 1000 • C computed using the HSC thermochemical database [36] are provided below (Table 5) for a set of reactions (Equations ( 4)-( 20)) likely to take place during the thermal treatment and considering simple reducing agents such as C (s) , CO (g) , and H 2(g) . Several scientific findings devoted to the thermodynamic and kinetics aspects as well as the modeling of iron oxide reductions with various reducing agents were summarized recently [44][45][46][47][48]; most of their developed approaches were based on selected reactions being analogous to those described by Equations ( 4)- (20). Reactions of the direct reduction of iron oxides by solid carbon are of endothermic nature (Equations ( 4)-( 6)), hence they should be favored at high temperatures.…”

Synthesis of a new magnetic adsorbent using green tea leaf extract and its application in phenol removal by RSM method

“…The aqueous extract of green tea contains gallocatechin gallate (GCG,> 45%), epigallocatechin gallate (EGCG, 36 to 40%), epigallocatechin (EGC 0.7-2.3%) and epicatechin (EC 0.5-2.2%) [18], which have antibacterial and antioxidant activity. These phenolic compounds have been reported to aid in the process of reducing the metal ions of Au, Ag and Fe [21]. Green tea extract is unquestionably a safe, green and environmentally friendly material, especially for herbals and medicines.…”

Co‐use of organic herbal residue and red mud waste for syngas production by chemical looping gasification

“…15 From a series of OCs that were screened, iron-based OCs have shown the most promise for application in chemical looping technologies. 16 However, further reducing the cost of OCs and increasing their reactivity are important tasks that remain under investigation and, to this end, inert additives such as Al 2 O 3 , TiO 2 , and SiO 2 have shown promise to greatly enhance an OC's performance. 17 In addition, the presence of alkali metals such as Na, Ca, and K are known to contribute to reactivity and gasification rates.…”

“…To date, researchers have conducted a large number of experimental tests on more than 700 kinds of OCs (mainly based on active components such as Fe 2 O 3 , CaSO 4 , NiO, and CuO) 15 . From a series of OCs that were screened, iron‐based OCs have shown the most promise for application in chemical looping technologies 16 . However, further reducing the cost of OCs and increasing their reactivity are important tasks that remain under investigation and, to this end, inert additives such as Al 2 O 3 , TiO 2 , and SiO 2 have shown promise to greatly enhance an OC’s performance 17 .…”