Abstract
It is urgent to develop excellent solid CO2 sorbents with higher sorption capacity, simpler synthetic process, better thermal stability and lower costs of synthesis in CO2 capture and storage technologies. In this work, a number of Li4SiO4-based sorbents synthesized by lithium carbonate with three different kinds of fly ashes in various molar ratios were developed. The results indicate that the Li2CO3:SiO2 mole ratio used in the sorbents synthesis significantly affects the CO2 absorption properties. The sorption capacity increased with the excess of Li2CO3 first and then decreased when the excessive quantity was beyond a certain amount. The experiments found that FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4, HCl/CFA-Li4SiO4_0.3 presented the best sorption ability among these fly ash derived Li4SiO4 samples, and the corresponding weight gain was 28.2 wt%, 25.1 wt% and 32.5 wt%, respectively. The three sorbents with the optimal molar ratio were characterized using various morphological characterization techniques and evaluated by thermogravimetric analysis for their capacity to chemisorb CO2 at 450°C - 650°C, diluted CO2 (10%, 20%) and in presence of water vapor (12%). The adsorption curve of FA- Li4SiO4_0.6 at different temperatures was simulated with the Jander-Zhang model to explore the influence of carbon dioxide diffusion on adsorption reaction. Further experiments showed that the adsorbent had a good sorption capacity in a lower partial pressure of CO2 and the presence of steam enhanced the mobility of Li+. What’s more, FA-Li4SiO4_0.6, CFA-Li4SiO4_0.4 and HCl/CFA-Li4SiO4_0.3 particles showed satisfactory sorption capacity in fixed-bed reactor and excellent cyclic sorption stability during 10 sorption/ desorption cycles.
Highlights
Carbon dioxide (CO2) is considered to be the main cause of greenhouse effect
It can be seen that the Li2CO3:SiO2 molar ratio had a significant influence on the synthesized sorbents
The overall weight gain of three kinds of sorbents increased with the excess of Li2CO3 first, decreased when the excessive quantity was beyond a certain amount
Summary
Carbon dioxide (CO2) is considered to be the main cause of greenhouse effect. The CO2 atmospheric concentration has reached an unprecedented high level of 410.79 ppm in 2018 due to the massive emission of carbon dioxide derived from the large-scale combustion of fossil fuel [1] [2] [3]. Li4SiO4 is a promising sorbent because of its high CO2 capture capacity, rapid sorption rates and mild regeneration temperature (900 ̊C) [10] [11] [12]. Low cost materials like fly ash, rice husk ash, diatomite as SiO2 precursors used to synthesize the Li4SiO4-based sorbents has attracted considerable attention in recent years due to their high availability and low cost [15] [16] [17]. In our previous work [24], Li4SiO4-based sorbents from fly-ash(FA) subjected to different pretreatments were synthesized for CO2 capture at high temperatures, finding that different preconditioned FA had different components and significantly affected the morphology, the porosity and the adsorption performance of the sorbents. The effects of the mole ratios of Li2CO3:SiO2 (fly ash) on sorption capacity, the sorbents compositions and particle size were investigated. The fixed-bed reactor has been used to analyze the sorption performance of particle sorbents
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