Scalable synthesis of the lithium silicate-based high-temperature CO2 sorbent from inexpensive raw material vermiculite

Abstract

A novel Li4SiO4-based high-temperature CO2 sorbent was prepared directly from the expanded vermiculite (EXVMT) for the first time. Due to the separating effect by the existing impurity phases in EXVMT, this new CO2 sorbent Li4SiO4-(EXVMT)-4 possesses better dispersion of Li4SiO4 nanoparticles and higher porosity, which resulted in a much enhanced CO2 sorption/desorption cycling stability. Elemental mapping revealed the homogeneous dispersion of Li4SiO4 with the other co-existing phases and XRD analyses indicates the crystal size of Li4SiO4 in Li4SiO4-(EXVMT)-4 kept almost unchanged even after 10 cycles. In addition, this sorbent exhibited much higher CO2 sorption capacity and faster sorption rate at relatively lower sorption temperature (550 °C). We also demonstrated that this sorbent possesses lower activation energies for both the chemisorption and the diffusion processes, enabling it to be much less affected by CO2 concentration. By decreasing the CO2 concentration from 100 to 20 vol%, the CO2 sorption capacity of Li4SiO4-(EXVMT)-4 only slightly decreased from 19.4 to 18.6 wt%, but the capacity for Li4SiO4 synthesized from pure SiO2 decreased significantly from 22.0 to 11.3 wt%. Thanks to its high CO2 sorption capacity, excellent cycling stability, fast sorption rate, low cost, and scalable synthesis, the VMT derived Li4SiO4-based high-temperature CO2 sorbent is very promising for practical applications.