Preparation And Modification Studies Of Novel Li₄SiO₄ Sorbent With Superior Performance At Low CO₂ Concentration

Li₄SiO₄ sorbent,which is recognized as one of the most promising high-temperature solid CO₂ sorbents owing to its low regeneration temperature?i.e.,low energy consumption?,has drawn extensive attention in CO₂ capture field.However,the performance of Li₄SiO₄ is poor under low CO₂ concentration?<20 vol.%?,which is not feasible for its industrial application.Hence,it is necessary and important to enhance the performance of Li₄SiO₄ at low CO₂concentration.One kind of Si source and several organic precursors of Li were selected as raw materials in this research,and the novel Li₄SiO₄ with superior performance at low CO₂ concentration was successfully prepared.In addition,to further improve the performance of Li₄SiO₄ and accelerate its industrial application,the modification with doping Na₂CO₃ and K₂CO₃ into novel Li₄SiO₄ was also studied.In terms of the preparation of novel and highly efficient Li₄SiO₄ sorbent,silica sol was selected as Si source and lithium acetate dehydrate and lithium lactate were selected as precursors of Li respectively.The silica sol was mixed with the solution of lithium precursors,and then they were stirred and vapored.Finally,the sorbent was attained after4h-calcination at 900^oC in air in a muffle oven.While the surface of the traditional Li₄SiO₄prepared by solid state reaction is dense and smooth,the novel Li₄SiO₄ has many embossment on its surface,which provide lager contact surface area between CO₂ and sorbent to improve absorption.Under low CO₂ concentration of 15 vol.%,the absorption capacity of novel Li₄SiO₄ was enhanced to be 8 times of that of the traditional Li₄SiO₄.Moreover,lots of micro-sized pores were formed in the novel Li₄SiO₄ after multiple cycles,which facilitates its performance to be improved with the increasing number of cycles.The novel Li₄SiO₄ prepared using lithium acetate dehydrate and silica sol performs better with conversion increasing from about 39%to around 70%over 40 cycles.With respect to the research of doping,Na₂CO₃ and K₂CO₃ were doped into the novel Li₄SiO₄ fabricated with lithium acetate dehydrate and silica sol to further improve its performance.The doped Li₄SiO₄ was prepared through adding the Li₄SiO₄ powers into the solution of dopants,and then they were mixed,vapored,ground and sieved to be the final samples.The doped samples with different portions of 5 wt.%,10 wt.%,20 wt.%Na₂CO₃and 1 wt.%,5 wt.%,10 wt.%K₂CO₃ were obtained.The experimental results indicate that the doped Li₄SiO₄ largely outperforms the original Li₄SiO₄ on absorption rates.The sorbents doped with 10 wt.%Na₂CO₃ and 5 wt.%K₂CO₃ acquire the best conversion of about 90%,which is higher than the reported 80%and there is only 5%loss during the 40 cycles.The improvement mechanism of doping alkali carbonate proposed in literatures was firstly verified in this research,through a series of experiments combined with characteristics of TG-DSC and in situ XRD,which will promote the theoretical research for Li₄SiO₄ sorbents.All the studies mentioned above indicate that the superior Li₄SiO₄ sorbent with high absorption capacity and excellent durability can be successfully synthesized.And its performance can be further improved by doping Na₂CO₃ or K₂CO₃,which is more suitable to be used into industrial application.