Chemical looping dry reforming/ electrochemical reforming of methane Although chemical looping dry reforming of methane (CL-DRM) builds on the same chemistry as conventional SMR and dry reforming of methane (DRM), it is a potential alternative, which uses a two-step redox concept through recyclable oxygen storage materials (oxygen carriers) as intermediates. CL- DRM utilises a fundamentally different process configuration to produce syngas with an H2 / CO ratio of 2 during the reduction-oxidation step, highlighted in Figure 2 .9 , 10 CO2 electrolysis is performed at the cathode, whereas electrochemical oxidation of CH4 is performed at the anode. Here, the lattice oxygen of a solid metal oxide (for example, iron oxide) is used to partially oxidise the CH4 to H2 and CO. The regeneration of the reduced metal oxide can be performed in a subsequent step by oxidation with CO 2, producing additional CO. The CL-DRM process is highly advantageous from an environmental point of view, since two greenhouse gas molecules (CH4 and CO 2 ) are converted into valuable products (H2 and CO). The main challenge of CL-DRM using iron oxide as an oxygen carrier is to control the product selectivity to avoid both the complete oxidation of CH4 and the deposition of carbon on the carrier. Furthermore, iron oxides undergo significant chemical, thermal, and physical stresses as oxides cycle between fully oxidised and fully reduced conditions, limiting their longevity. In this respect, it is well known that mixing iron oxides with different refractory oxides, such as ceria, alumina, silica, titania, and zirconia, improves their resistance to sintering at high temperatures. Among the different iron-based O 2 carriers, mixed oxides of iron and cerium appear to be attractive for chemical looping reforming processes, owing to their high capacity for storing O 2 and to the unique redox properties of cerium. Whereas minimisation of coke formation can be achieved by limiting the duration of the reduction step of the CL-DRM or its removal in reaction with CO 2 via the reverse Boudouard reaction, producing a high-purity CO stream. An efficient electrochemical reforming of CH4 /CO 2 to produce syngas in a solid
oxide electrolyser is under development, where redox-stable perovskite-type La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) impregnated with a nano catalyst such as nickel, ruthenium or vanadium is used both as cathode and anode. The strong metal/oxide interface interactions deliver enhanced high-temperature stability and coking resistance for dry reforming of CH4 with CO 2 . CL-DRM technology is currently in its initial stages of development, and its successful implementation depends on future research directions for developing high-performance oxygen carriers. Key takeaways This article is not intended to be a compendium of syngas technologies but rather to provide a high-level overview of available technology options for the production of low-CI syngas, including information about leading technology “ The CL-DRM process is highly advantageous from an environmental point of view, since two greenhouse gas molecules (CH 4 and CO) are converted into valuable products (H 2 and CO) ” providers. The reader is afforded the necessary toolkit to objectively evaluate all available technology options and make an informed decision to pursue the pathway most suited to their need based on risk appetite, feedstocks, utilities and resources available, and the desired end product. For emerging technologies, it is critical to rigorously evaluate the pros and cons. Notwithstanding the aforesaid, a comprehensive techno-economic feasibility report (TEFR) and/or front-end engineering design (FEED) by a competent consultant is essential before converging on the most optimum technology pathway to be pursued, preceding final investment decision (FID) on a complex project for the production of low-CI syngas. VIEW REFERENCES
Ajay Misra arsim.yaja@gmail.com
Refining India
15
Powered by FlippingBook