Lithium silicate (Li4SiO4) material can be applied for CO2 capture in energy production processes, such as hydrogen plants, based on sorption-enhanced reforming and fossil fuel-fired power plants, which has attracted research interests of many researchers. However, CO2 absorption performance of Li4SiO4 material prepared by the traditional solid-state reaction method is unsatisfactory during the absorption/regeneration cycles. Improving CO2 absorption capacity and cyclic stability of Li4SiO4 material is a research highlight during the energy production processes. The state-of-the-art kinetic and quantum mechanical studies on the preparation and CO2 absorption process of Li4SiO4 material are summarized, and the recent studies on the effects of preparation methods, dopants, and operating conditions on CO2 absorption performance of Li4SiO4 material are reviewed. Additionally, potential research thoughts and trends are also suggested.
A synthetic sorbent prepared from carbide slag and dolomite by combustion exhibits high CO2 capture capacity, good cyclic stability and a porous microstructure.
Calcium
looping is one of the most promising technologies for large-scale
CO2 capture, while CaO-based materials suffer from the
deactivation in CO2 capture capacity in the multiple carbonation/calcination
cycles as a result of sintering. Ce-promoted CaO is considered as
an effective CO2 sorbent during calcium looping cycles.
In this paper, the CO2 adsorption performance of Ce-promoted
CaO in the presence of steam was investigated using density functional
theory (DFT) calculations. The cyclic CO2 capture performance
of Ce-promoted CaO in the presence of steam was tested to confirm
the feasibility of DFT calculations. Moreover, the structural and
adsorption parameters, including atomic layout, energy, bond length,
and charge transfer of CO2 and H2O molecules
on Ce-promoted CaO, were determined. The DFT calculation results indicate
that the surface O atoms in Ce-promoted CaO are activated by the Ce
atom; therefore, the CO2 adsorption performance is improved
on Ce-promoted CaO. When the H2O molecule is pre-adsorbed
on Ce-promoted CaO and CaO, the adsorption of CO2 is enhanced.
The CO2 adsorption energies on Ce-promoted CaO and CaO
in the presence of H2O are −1.99 and −1.53
eV, respectively, which are larger than those in the absence of H2O. The co-adsorption of CO2 and H2O
molecules appears feasible on Ce-promoted CaO, while CaO exhibits
obvious inhibition on the co-adsorption. The experimental results
indicate that the Ce species in Ce-promoted CaO exist in the form
of CeO2, which leads to higher CO2 capture activity
and sintering resistance than those of CaO. The presence of steam
in carbonation improves the CO2 capture capacity of Ce-promoted
CaO; therefore, the experimental results agree well with DFT calculations.
The cost of makeup flow of Ce-promoted CaO is 20.3% lower than that
of CaO. Therefore, Ce-promoted CaO appears promising in calcium looping.
Due to the inconsistency and intermittence of solar energy, concentrated solar power (CSP) cannot stably transmit energy to the grid. Heat storage can maximize the availability of CSP plants. Especially, thermochemical heat storage (TCHS) based on CaO/CaCO3 cycles has broad application prospects due to many advantages, such as high heat storage density, high exothermic temperature, low energy loss, low material price, and good coupling with CSP plants. This paper provided a comprehensive outlook on the integrated system of CaO/CaCO3 heat storage, advanced reactor design, heat storage conditions, as well as the performance of CaO-based materials. The challenges and opportunities faced by current research were discussed, and suggestions for future research and development directions of CaO/CaCO3 heat storage were briefly put forward.
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