Experimental Study On CO₂ Sorption Properties By Li₂O-Containing Solid Sorbents At High Temperature

The combustion of fossil fuel can brings enough energy for human beings, but also produces a series of great pollutions including greenhouse gas CO₂. The greenhouse effect can induce tremendous climate change and environmental damage, CO₂ capture and storage technology (CCS) has been attracted more and more attention. The study of CO₂ separation at high temperature using solid sorbents can avoid cooling and compressing in the traditional methods and decrease energy consumption, which plays an important role in flue gas from coal-combustion plant.After analyzing and summarizing the research work on solid sorbents for CCS in and abroad, CO₂ soprtion performances using Li₂O-containing sorbents were studied systematically,some innovative research of modification using doping different compounds in the preparation and cyclic CO₂ absorption/desorption has been made in this paper.Lithium orthosilicate (Li₄SiO₄) samples were prepared respectively by solid-state reaction method and sol-gel method. The samples were characterized by X-ray diffraction (XRD), specific surface area (BET), grain size analysis and scanning electron microscope (SEM) methods. The experimental study of CO₂ sorption by Li₂O-containing sorbents was performed by thermogravimetric analysis (TG) and fixed-bed reactor. The effect of different factors which influence the CO₂ sorption at high temperture such as preparation method, reaction temperature, particle size, holding time, CO₂ partial pressure and cyclic times have been analyzed. Different mole metal oxides (Fe₂O₃, TiO₂) were doped in the samples for getting a better CO₂ sorption results. The experimental results showed that the solid solution (Li₄SiO₄(Ti 0.02)) can result in an obvious weight change of CO₂ up to 28.68%(g/g), and after 20 absorption/desorption cycles, CO₂ absorption was reduced by only 19.39%. The sample shows strong capabilities in CO₂ absorption and self-generation.Lithium zirconate (Li₂ZrO₃) and different solid solutions (Li_2-xNa_xZrO₃, Li_2-xK_xZrO₃) were synthesized by solid state reactions. The experimental results showed that the appropriate sodium/potassium carbonate can enhance CO₂ absorption. Especially, where the doping scale (K₂CO₃) x was 0.1, the maximum absorption was equal to 20.22%(g/g). In the CO₂ absorption/desorption experiments, CO₂ sorption of the solid solution Li1.8K0.2ZrO₃ was reduced from 19.01%(g/g) at first cycle to 16.35%(g/g) at 15th cycle, and only by 13.99%, which indicated excellent regeneration.In this paper we calculated systemic thermodynamics with the reactions of Li₂O-containing solid sorbents and CO₂, considered the change of free energy and equilibrium constant with increasing temperature, proposed unique double shell model to describe CO₂ sorption on Li₂O-containing sorbents. Moreover, the four isotherms of the CO₂ sorption by Li₄SiO₄ at different temperature fitted to a double exponential model (ExpDec2), and gained the exponential constants, k1(chemisorption) values are 10 times higher than those of k2(diffusion), which means that the chemisorption process is more dependent on the temperature, and the limiting step of the total process is the lithium diffusion. Furthermore, the activation energy of the chemisorption Ea1 is 105454.9J/mol.