Carbon dioxide absorption behavior of surface-modified lithium orthosilicate/potassium carbonate prepared by ball milling

Lithium orthosilicate (Li4SiO4) is a ceramic CO2 absorbent with a large absorptive capacity (36.7 wt.%) and heat resistance properties. Li4SiO4 has applications as a separator in molten carbonate fuel cells, and as a direct CO2 absorbent in large-scale emission sources such as thermal power stations. The absorption and desorption reaction equilibrium temperature of Li4SiO4 is around 993 K. This study investigates the CO2 absorption behavior of Li4SiO4 at lower temperatures. Samples whose surfaces were modified with ball milling under an Ar atmosphere exhibited increased Brunauer-Emmett-Teller surface areas. Electron spin resonance (ESR) spectroscopy indicated an increase in the content of Si dangling bonds upon ball milling. Thermogravimetric-differential thermal analysis indicated two different CO2 absorption processes: chemisorption at the Li4SiO4 surface at temperatures below 773 K; bulk diffusion at temperatures above 773 K. Isothermal analysis indicated that ball milling and adding K2CO3 decreased the activation free energy. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.