Biotemplated synthesis of highly stable calcium-based sorbents for CO2 capture via a precipitation method

Abstract

The alternation between uptake and release of CO2 by CaO sorbents is a promising method for removal of CO2 from a hot gas stream. The main drawback of this method is the deterioration of CO2 capture capacity following multiples cycles. In the present study, CaO sorbents with a high CO2 capture capacity and improved stability were prepared using chitosan as biotemplate via a simple precipitation method. Effects of mass ratio of chitosan to Ca2+ (0.125:1–2.5:1) on physical properties of the CaO sorbents as well as their CO2 capture performance were investigated. The cyclic CO2 capture performance of the CaO sorbents derived from chitosan template has been compared with that of CaO templated on a synthetic polymer (SDS), a hybrid of chitosan and SDS, and a non-templated CaO sorbent. The variation of chitosan to Ca2+ ratios was found to drastically change both the morphology and size of the CaCO3 products. CaCO3 particles homogeneously amalgamated with the chitosan matrix at a ratio of chitosan to Ca2+ of 0.125:1–0.75:1. With a yet higher ratio of 0.75:1, larger amount of chitosan molecule could incorporate into the CaCO3 particles, but a phase separation was also observed. SDS was found to act as a template for the formation of large CaCO3 particles with a spherical shape. CO2 uptake activity and stability were found to depend on both surface area and shape of the synthetic CaO materials. The CaO sorbent derived from chitosan template exhibited a higher CO2 uptake activity and stability than the other CaO sorbents. The CaO prepared in the presence of chitosan to Ca2+ ratio of 0.75:1 achieved the highest CO2 uptake of 83.75% in the first cycle and retained an excellent carbonation conversion of 57.78% after 20 consecutive test cycles. This finding indicates that the CaO derived from chitosan template constitutes a feasible option as a CO2 sorbent due to its potentially low costs, environmentally benign nature, and elevated CO2 capture capacity.