UKCCSRC Knowledge Exchange Conference 2024 – Parallel 2c: CO2 Capture – Looping (ECR Meeting Fund)

Alexander Harrison (University of Oxford) and Muhammad Shahbaz (Teesside University) share their takeaways from “Parallel 2c: CO2 Capture – Looping” at the UKCCSRC Knowledge Exchange Conference 2024.

As researchers in carbon capture and related technologies, one of the purposes of Knowledge Exchange conferences, as organised by the UKCCSRC on 5-6 Nov 2024 at the University of Sheffield, is to understand the requirements of government and industry for new process of carbon capture and removal processes, and link these to current research on novel technologies and process. Hence, the parallel session on the second day of the conference, “CO2 Capture – Looping” chaired by Chenggong Sun (University of Nottingham), provided three instructive talks on novel methods for carbon capture, heat integration and ‘blue’ H₂ production, with the key findings providing insights on how ambitious targets over the next 5-10 years might be met.

Dr Wei Li – Nottingham University – Functionalised silica with alkoxylated amines

The first talk in the session was from Dr Wei Li, of Nottingham University, regarding her research on producing silica functionalised with alkoxylated polyethyleneimine (APEI). This study was part of the ABSALT project involving seven partners from four universities from four countries and three industries including BASF (Germany) and PQ (UK). By fixing amine groups to the surface of silica, the looping process eliminates some of the problems of nitrogen leakage with conventional amine looping systems, as highlighted in the opening session by representatives from the Environment Agency. The process has been previously investigated in a 100kg pilot plant and has been shown to be technically feasible (Kim et al., 2021), but with further development. Dr Li’s talk discussed the preparation of the APEI sorbents in a novel method eschewing the use of organic solvents, and thus adhering to green chemistry principles. The degree of alkoxylation of the surface functional groups was also shown to be highly influential on the material properties, with an inherent trade-off between CO₂ capacity and sorbent stability over repeated cycles. At the end of her talk, Dr Li thanked the project funders, specially mentioning the UKCCSRC 2024 Flexible Fund for funding this study.

Summary of the ABSALT project, taken from Dr Li’s presentation

Dr Song He – Cranfield University – Heat recovery in Ca-Cu chemical looping cycles

However, in order to achieve truly cost-effective carbon capture, looping cycles that eschew the need for amines altogether are highly desirable. Therefore, the work of Dr Song He, of Cranfield University, in investigating how to improve the thermal efficiency of the calcium looping process was of considerable interest. He described the calcium looping process in which flue gas from a CO₂ point source (e.g. a power station, cement works or steel plant) is passed over calcium oxide, which reacts to form calcium carbonate. The carbonate is then calcined in a separate reactor to generate a pure stream of CO₂, closing the chemical loop. However, as in all carbon-capture processes, the calcination process to regenerate the sorbent requires a significant heat input, limiting the overall energy efficiency of the process. Therefore, in the scheme described by Dr He, the calcium looping cycle is coupled with chemical looping combustion using copper-based oxygen carriers, and steam methane reforming to generate syngas. The overall process taking flue gas, natural gas and air as inputs at different points in the process, and producing purified CO₂ and electricity as products, with an overall thermal energy efficiency of around 2 MJ/kg_CO2. In a robust and fruitful Q&A section, the importance of translating computational results into experiments was discussed, highlighting the influence of thermally-coupled reactor design, and preparation of hybrid Ca-Cu materials for carbon capture and chemical looping combustion.

Process flow diagram of the heat-integrated Ca-Cu chemical looping system (taken from He et al., 2024)

Economic analysis of the Ca-Cu chemical looping scheme, taken from Dr He’s presentation

Dr Christopher de Leeuwe – University of Manchester– Update on the H₂-RECYCLE project

Lastly, Dr Christopher de Leeuwe, of the University of Manchester, gave us an update on their ongoing H₂-RECYCLE project for chemical looping reforming of methane to produce blue H₂ in a packed-bed reactor with the collaboration of the Department for Energy Security & Net Zero.  He explained that the fundamentals of the CL-reforming process are similar to the chemical looping cycles described by Dr He, however, rather than using two separate reactors for oxyfuel combustion and catalytic reforming, the same material (here, proprietary nickel-based catalysts supplied by Johnson Matthey) acts as both the catalyst and the chemical looping material, and the syngas produced is exported as a product rather than used as a fuel to drive the process. Over the course of a cycle, the material is sequentially oxidised in air to generate heat, and reduced in CO-rich off-gas from elsewhere in the system to generate a solid with high reducing potential, which then reacts with methane to produce syngas. Therefore, by operating three reactors in parallel at different stages of the process, the entire system can be operated pseudo-continuously, generating nearly pure streams of H₂, and CO₂ for storage.

Schematic diagram of the H2-RECYCLE process (taken from Alexandros Argyris et al., 2022)

The project has been ongoing for some time, and has been most exciting to watch for many members of the chemical looping community (ourselves included), as it constitutes one of the first practical demonstrations of the CL-reforming process at near pilot-pilot scale including every unit operation in the overall process, using the largest packed-bed chemical looping reactor built to date in the UK. Chris’ talk reminded us of some of the challenges that come with trying to scale up from the lab-scale, including difficulties with purchasing alloy tubes of the correct size to fit in the reactor, the challenges of working with mains natural gas as opposed to a certified 5.0 purity cylinder, and industrial partners being perplexed that they would call a ‘mere’ 10 kg scale reactor a pilot plant (while all the academics during the talk shuddered at the thought of having to produce that much catalyst by hand!). We look forward to hearing further updates from the project at the next UKCCSRC meeting, where we are sure the Manchester team will have developed a world-first in blue hydrogen production using chemical looping.

Targets for the H2-RECYCLE project, from Dr de Leeuwe’s presentation

References

Alexandros Argyris, P., de Leeuwe, C., Abbas, S. Z., Amieiro, A., Poultson, S., Wails, D., & Spallina, V. (2022). Chemical looping reforming for syngas generation at real process conditions in packed bed reactors: An experimental demonstration. Chemical Engineering Journal, 435, 134883. https://doi.org/10.1016/j.cej.2022.134883

He, S., Zheng, Y., Zeng, X., Wang, J., Gao, L., & Yang, D. (2024). Thermodynamic evaluation of a Ca-Cu looping post-combustion CO2 capture system integrated with thermochemical recuperation based on steam methane reforming. Case Studies in Thermal Engineering, 63, 105327. https://doi.org/10.1016/j.csite.2024.105327

Kim, J.-Y., Woo, J.-M., Jo, S.-H., Kim, H., Lee, S.-Y., Yi, C.-K., Moon, J.-H., Nam, H., Won, Y., Stevens, L. A., Sun, C., Liu, H., Liu, J., Snape, C. E., & Park, Y. C. (2021). Performance of a silica-polyethyleneimine adsorbent for post-combustion CO2 capture on a 100 kg scale in a fluidized bed continuous unit. Chemical Engineering Journal, 407, 127209. https://doi.org/10.1016/j.cej.2020.127209