Natural dolomite modified with carbon coating for cyclic high-temperature CO2 capture

An efficient MgO-stabilized CaO sorbent via the citric acid treated dolomite coupled with carbonization process (denoted as carbon coating) was developed for CO2 capture at high temperature. The citric acid was used as a carbon source to produce the coated carbon, which was expected to effectively prevent the crystallites (CaO and MgO) from sintering. The original dolomite and citric-acid-treated dolomite with subsequent calcination in air were also prepared for comparison. Different characterizations (thermal decomposition, phase composition, morphology, and nitrogen adsorption) were performed. The cyclic-CO2-capture performance was tested in a fix-bed reactor. During the carbonization in N2 atmosphere, the acidified dolomite transformed into carbon-coated, Mg-doped calcite, which could control thermal sintering and prevent the de-mixing of CaO and MgO in the secondary calcination step in air. Thus, the sorbent prepared using carbon coating achieved smaller grains, larger specific surface area and pore volume and more uniform distribution of CaO and MgO, which led to its superior activity and stability, compared to two reference sorbents.