Effects of porous carbon additives on the CO 2 absorption performance of lithium orthosilicate
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Thermochimica Acta, ISSN: 0040-6031, Vol: 637, Page: 31-37
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- Physics and Astronomy; Chemistry; CO2 absorption; Gas pathway; Lithium orthosilicate; Porous carbon
Lithium orthosilicate (Li 4 SiO 4 ) is an attractive high-temperature CO 2 sorbent (>650 °C) because of its large theoretical absorption capacity of up to 36.7 wt%. However, slow kinetics and partial reactions with CO 2 hinder its proper operation as a sorbent under practical conditions. To allow the use of this sorbent at lower operation temperatures, the present studies explored the way to improve the CO 2 absorption kinetics and increase the degree of reaction of Li 4 SiO 4. Porous carbon materials such as CMK-3 were introduced into the sorbent to provide an internal gas pathway. Upon calcination conditions, the carbon amount was controlled in the composites (Li 4 SiO 4 @CMK-X%, where X represents the amounts of CMK-3). In Li 4 SiO 4 @CMK-1.8%, CMK-3 is distributed over the whole solid; in contrast, the additive in Li 4 SiO 4 @CMK-0.5% is mainly observed near the surface of the solid. CO 2 gas sorption study of the composites showed that pores of CMK-3 in Li 4 SiO 4 aid the diffusion of CO 2. In addition, we found that the incorporation of porous carbon provides more active sites for interactions with CO 2 through the formation of cavities between Li 4 SiO 4 and CMK-3. Li 4 SiO 4 @CMK-1.8% had an increased CO 2 absorption capacity (35.4 wt%) and rate (15.2 wt% for the first 5 min) at 600 °C, compared to the CO 2 absorption capacity (16.3 wt%) and rate (5.1 wt% for the first 5 min) of pristine Li 4 SiO 4 ( p -Li 4 SiO 4 ). To confirm the influence of porous carbon on the CO 2 absorption properties, multi-walled carbon nanotube (MWCNT) was also examined as an additive instead of CMK-3. Li 4 SiO 4 @CNT showed similar trends with Li 4 SiO 4 @CMK sorbents.