Preparation Of Li₄SiO₄-based CO₂ Sorbents And Their Structure-property Relationship

The flue gas derived from fossil fuel combustion is characteristic of low CO2 concentration and high temperature,which makes Li4SiO4 an appropriate sorbent for CO2 capture from the flue gas.In this thesis,we prepared Li4SiO4 and Na-and K-doped Li4SiO4 sorbents,whose structure-property relationship was investigated.First,the effects of preparation method on the structure of Li4SiO4 and the CO2 capture performance were studied.The results showed that,the Li4SiO4 sorbent prepared by a sol-gel technique aided with PEG300(polyethylene glycol with a molecular weight of 300),had good CO2 capture performance but suffered from slow adsorption rate at low CO2 concentration,which restricted its practical application.Next,a series of Na-and K-doped Li4SiO4 sorbents were prepared by the PEG300-aided sol-gel method.It was found that the introduction of either Na or K into Li4SiO4 was able to increase the adsorption rate of Li4SiO4 at low CO2 concentration.The Na-doped Li4SiO4 sorbents had high initial rate but with poor anti-sintering property,thus leading to poor cyclic stability,while K-doped sorbents,although with normal initial adsorption rate,exhibited high rate,high capacity and good stability during multiple adsorption/regeneration cycles,mainly due to the self-activation phenomenon and the unique plate-like structure of-sorbent.Among all the K-dope-d Li4SiO4 sorbents developed in this study,the sorbent with a K content of 5 mol%displayed the best CO2 capture performance,with a stable CO2 uptake(in 30 min of adsorption)of 0.31 gco2/gsorbent after 20 adsorption/regeneration cycles at 15%of CO2.The excellent CO2 capture performance of K-doped Li4SiO4 sorbent promises broad applications in post-combustion CO2 capture and sorption-enhanced steam methane reforming.