Development of CaO-based adsorbents loaded on charcoal for CO2 capture at high temperature

Carbon dioxide is undoubtedly one of the major contributors to global warming and climate change. Despite being the main source of carbon dioxide, fossil fuels remain the main source of energy and its usage is likely to continue pending development of efficient alternative energy sources. Therefore, development of effective strategies for controlling the emission and concentration of carbon dioxide is highly desirable. Among the available methods for carbon dioxide reduction, carbon dioxide capture and storage technologies have attracted significant attention due to their cost-effective performance. Recently, CaO has been employed to create novel sorbent and enhance CO₂ capture. However, CaO-based adsorbents require support materials to improve their performance. Charcoal has been identified as promising support material especially at high temperatures due to its relatively low-cost and availability even though it has not been fully explored in literature.

To this note, Professor Ningbo Gao, Kailun Chen (Master student), and Professor Cui Quan from Xi’an Jiaotong University developed a charcoal supported CaO-based adsorbents. Three different methods: physical mixing, sol-gel, and wet impregnation were used to investigate the role of charcoal in enhancing the capture and stability of CaO-based adsorbents. X-ray diffraction among other methods were used to investigate the morphology and structural properties of the adsorbent. Additionally, the influence of the preparation methods, carbonation temperature, and CaO loading on the capture performance was assessed. The work is currently published in the Fuel journal.

Among the investigated methods, adsorbent prepared by the sol-gel method exhibited excellent carbon dioxide capture and stability. For instance, adsorbent with a mass ratio of CaO to charcoal of 4:1 recorded initial capacity of 15.1mmolg^-1 and maintained a 60% higher capacity after 15 cycles of carbonation as compared to sol-gel CaO without charcoal support. High CO₂ diffusion rate was attributed to good pore volume of 0.166 cm³.g^-1 and high surface area. Based on the observation from X-ray diffraction and other methods, parent charcoal successfully prevented the growth of CaO agglomeration particles and porous structure developed by the sol-gel method. This enhanced the resistance to CaO sintering and overall performance of the adsorbent. Charcoal, despite being partially consumed during CO₂ absorption, remains a good and cost-effective CaO carrier. It was worth noting that the presented adsorbents may not be suitable for CO₂ capture under some conditions due to the chemical properties of charcoal.

In summary, the research team investigated CO₂ capture performance of charcoal supported CaO-based adsorbents using three methods. Sol-gel preparation method is proved to be more effective for adsorbent preparation as compared to wet impregnation, physical mixing, and other CaO loading methods. Charcoal has the advantage of inhibiting the growth of CaO crystalline. Furthermore, it was noted that charcoal derived from pyrolysis of biomass has great potential of improving the economic viability and utilization of biomass resources in CO₂ capturing processes. Altogether, the study by Professor Ningbo Gao and his colleagues will pave way for further development of high-performance charcoal supported CaO-based adsorbents for CO₂ capture.