Optimization of the structural characteristics of CaO and its effective stabilization yield high-capacity CO2 sorbents

Muhammad Awais Naeem,Robin Schäublin,Christoph R Müller,Qasim Imtiaz,Felix Donat,Agnieszka Kierzkowska,Andac Armutlulu

doi:10.1038/s41467-018-04794-5

Abstract

Calcium looping, a CO2 capture technique, may offer a mid-term if not near-term solution to mitigate climate change, triggered by the yet increasing anthropogenic CO2 emissions. A key requirement for the economic operation of calcium looping is the availability of highly effective CaO-based CO2 sorbents. Here we report a facile synthesis route that yields hollow, MgO-stabilized, CaO microspheres featuring highly porous multishelled morphologies. As a thermal stabilizer, MgO minimized the sintering-induced decay of the sorbents’ CO2 capacity and ensured a stable CO2 uptake over multiple operation cycles. Detailed electron microscopy-based analyses confirm a compositional homogeneity which is identified, together with the characteristics of its porous structure, as an essential feature to yield a high-performance sorbent. After 30 cycles of repeated CO2 capture and sorbent regeneration, the best performing material requires as little as 11 wt.% MgO for structural stabilization and exceeds the CO2 uptake of the limestone-derived reference material by ~500%.

Highlights

Calcium looping, a CO2 capture technique, may offer a mid-term if not near-term solution to mitigate climate change, triggered by the yet increasing anthropogenic CO2 emissions
One of the approaches that have been attempted to reduce the sintering-induced capacity decay of CaO-based CO2 sorbents is the incorporation of high-TT stabilizers such as Al2O3, MgO, TiO2, or ZrO2 which are typically inactive for CO2 capture
Considering that the peak associated with carbon disappeared and the oxygen count dropped substantially in the EDX spectra at 1100 °C (Fig. 6d), the limited shrinkage cannot be related to an incomplete conversion of CaCO3 to CaO, but rather to the favorable morphology of the sorbent, which provides sufficient void to accompany substantial volumetric changes during cyclic operations

Summary

Introduction

A CO2 capture technique, may offer a mid-term if not near-term solution to mitigate climate change, triggered by the yet increasing anthropogenic CO2 emissions. The quantity of CO2 captured by the MgO-stabilized sorbents in the initial reaction stage was maintained throughout the ten carbonation/calcination cycles (~0.35 gCO2/gsorbent), whereas unstabilized CaO (Ca100Mg0) experienced an earlier transition to the diffusion-controlled CO2 capture regime, decreasing the overall CO2 uptake with increasing cycle number (from ~0.34 to 0.22 gCO2/gsorbent).

Results

Conclusion