Advanced Chemical Looping Concept for Energy and Fuels Applications

The increasing energy consumption creates the need to investigate new routes for utilization of the available resources, like natural gas and biogas, to produce fuels and chemicals. CH₄ is considered as one of the most affordable carbon feedstocks in the world. However, direct conversion of CH₄ into chemicals results in low yields due to the high C-H bond dissociation energy (436 kJ·mol^-1). As a result, CH₄ is mainly converted indirectly, by reforming it to syngas, a mixture of H₂ and CO, as an intermediate step. Syngas is a key building block with many downstream applications, as it is used in several synthesis processes for a wide range of chemicals and fuels. Most of the produced syngas is used for the synthesis of ammonia for fertilizers and for hydrogen production, which is exploited in refining processes, while the “gas to liquid” routes for fuels production account for ~8 % consumption.

Currently, different methane reforming processes exist and the most widely studied for syngas production are steam reforming (SRM), dry reforming (DRM), partial oxidation (POM) and autothermal reforming of methane (ARM). During reforming, several side reactions may occur. The water-gas-shift (WGS) reaction leads to a decrease or increase of the H₂/CO ratio. In addition to WGS, CH₄ decomposition (MD) and the Boudouard reaction (BR) may occur. These are responsible for carbon deposition on the active metal sites, leading to catalyst deactivation.

Chemical looping is an emerging technology, capable of low-emission, with application in production of heat, fuels, chemicals, and electricity. The power of the chemical looping concept will be demonstrated in Super-Dry Reforming [1]. Super-dry reforming of methane (SDRM) was developed for enhanced CO production from CH₄ and CO₂. The process uses a CO₂ sorbent (CaO/ZrO₂), an oxygen carrier (Fe₂O₃/MgAl₂O₄), and a CH₄ reforming catalyst (Ni-Fe/MgAl₂O₄), as well as CH₄ and CO₂ in a 1:3 feed ratio. SDRM combines an exothermic process, CaCO₃ formation, with two endothermic processes, CH₄ reforming and Fe₃O₄ reduction, thereby looping the energy utilization. The isothermal coupling of these three different processes results in a higher CO production and free of carbon deposition as compared to conventional DRM. Herein, details of the individual steps and the full process of SDMR, as well as perspectives and economic aspects will be presented [2-5].

References

[1] L.C. Buelens, V.V. Galvita, H. Poelman, C. Detavernier, G.B. Marin, Super-dry reforming of methane intensifies CO₂ utilization via Le Chatelier’s principle, Science 354(6311) (2016) 449-452.

[2] J. Hu, L. Buelens, S.-A. Theofanidis, V.V. Galvita, H. Poelman, G.B. Marin, CO2 conversion to CO by auto-thermal catalyst-assisted chemical looping, Journal of CO₂ Utilization 16 (2016) 8-16.

[3] K. Verbeeck, L.C. Buelens, V.V. Galvita, G.B. Marin, K.M. Van Geem, K. Rabaey, Upgrading the value of anaerobic digestion via chemical production from grid injected biomethane, Energy & Environmental Science 11(7) (2018) 1788-1802.

[4] J. Hu, V.V. Galvita, H. Poelman, C. Detavernier, G.B. Marin, A core-shell structured Fe₂O₃/ZrO₂@ZrO₂ nanomaterial with enhanced redox activity and stability for CO₂ conversion, Journal of CO₂ Utilization 17 (2017) 20-31.

[5] J. Hu, V.V. Galvita, H. Poelman, C. Detavernier, G.B. Marin, Catalyst-assisted chemical looping auto-thermal dry reforming: Spatial structuring effects on process efficiency, Applied Catalysis B: Environmental 231 (2018) 123-136.