Enhancement in CO2 adsorption by zeolite synthesized from co-combustion ash of coal and rice husk modified with lithium ion

Abstract

In order to reduce CO2 emissions, new raw materials have been developed for the production of low-cost CO2 adsorbents. A novel adsorbent, NaX zeolite synthesized from co-combustion ash of coal and rice husk was prepared by alkali fusion-hydrothermal synthesis and its optimal preparation condition, modification, physical-chemical characteristics and adsorption capacity of CO2 were investigated. The results showed that the synthesized NaX zeolite could get the highest crystal purity and the largest surface area reached to 583.0 m2/g under the condition that the (SiO2)x·(Al2O3)y/NaOH weight ratio was 1:1.4 and the hydrothermal crystallization time was 12 h. The adsorption capacities of CO2 for NaX zeolite reached 5.03 mmol/g at 298.15 K. The heat of adsorption decreased with increasing adsorption capacity. The modification of NaX zeolite by Li+ exchange could significantly contribute to the CO2 adsorption capacity. Although the LiX zeolite showed little change in morphology and crystal structure, while the specific surface area increased from 583.0 m2/g to 614.0 m2/g, and the adsorption of CO2 at 298.15 K increased to 5.57 mmol/g, which was about 10% higher compared with that of NaX zeolite. Adsorption isotherms of CO2 and N2 for NaX and LiX zeolites were well fitted with the Sip model, confirming the inhomogeneous surface properties of the adsorbents and the exothermic reaction of the adsorption process. The LiX zeolite had higher α value of Henry selectivity for CO2/N2 and better gas separating capacity than that of NaX zeolite. The study disclosed co-combustion ash is a potential raw material for the synthesis of CO2 adsorbents.